Lignocellulosic biomass in electrochemical energy conversion and value-added chemicals production

Abstract

Lignocellulosic biomass, as an abundant and renewable carbon resource, holds great promise for reducing dependence on fossil fuels and advancing the transition toward sustainable energy systems. However, its highly cross-linked architecture and complex chemical composition present significant challenges to efficient energy conversion and value-added utilization. In recent years, the rapid progress of electrochemical technologies has opened new pathways for the conversion and valorization of lignocellulose. For example, fuel cells enable the direct conversion of lignocellulosic biomass into high-quality energy carriers, such as electricity and hydrogen; nevertheless, issues such as CO₂ emissions, limited conversion efficiency, and low overall energy utilization remain. In contrast, electrocatalytic technology offers precise control over reaction kinetics and product selectivity, enabling the efficient conversion of lignocellulose-derived compounds into value-added chemicals and overcoming the inherent limitations of conventional thermochemical and biochemical routes. Within this context, this review provides a comprehensive overview of recent advances in the electrochemical conversion of lignocellulosic biomass, highlights the key challenges impeding its practical application, and discusses future perspectives for achieving efficient and sustainable biomass conversion.

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Green foundation

1. This review provides an overview of electrochemical strategies for lignocellulosic biomass conversion. Key advances include the efficient transformation of lignocellulose into high-quality energy carriers, such as electricity and hydrogen, and the production of value-added chemicals under electrocatalytic conditions, all aligned with green chemistry principles.

2. As one of the most abundant renewable carbon sources, lignocellulose has long been underutilized due to its structural complexity. Electrochemical approaches offer pathways to convert lignocellulose into electricity, hydrogen, fuels, and value-added chemicals, improving resource efficiency and reducing dependence on fossil resources.

3. Future research should focus on industrial-scale reactors, systematic elucidation of conversion mechanisms, and integration with green economy frameworks. This review summarizes key advances and outlines prospective strategies, providing guidance for designing scalable, efficient, and sustainable lignocellulosic electrochemical platforms.

1. Introduction

Carbon neutrality has emerged as a primary goal in the global energy transition, with the overconsumption of fossil fuels remaining the principal contributor to rising carbon emissions.^1,2 Among the various renewable energy strategies, lignocellulosic biomass, owing to its abundance, renewability, and near carbon-neutral cycle, represents a critical carbon resource for advancing a low-carbon energy transition.^3,4 Through photosynthesis, lignocellulose captures atmospheric CO₂ and stores it in chemical bonds, facilitating energy use with minimal net carbon emissions relative to fossil fuels.

Lignocellulose is composed of three natural polymers—cellulose, hemicellulose, and lignin—organized into a complex hierarchical structure. While this architecture confers exceptional mechanical strength, it also renders lignocellulose highly recalcitrant, a long-standing barrier to its efficient conversion and valorization.^5–7 Conventional biochemical and thermochemical methods have enabled partial utilization of lignocellulose, but both suffer from intrinsic limitations, including poor selectivity, high energy consumption, low yields, and limited economic viability.⁸ These challenges underscore the urgent need for transformative conversion strategies.

In recent years, lignocellulose has emerged as a promising feedstock for various fuel cell technologies, including solid oxide fuel cells (SOFCs), direct carbon fuel cells (DCFCs), and microbial fuel cells (MFCs). Nevertheless, these systems face technical challenges such as low efficiency, ash-related issues, and high operational costs, which necessitate the development of advanced catalysts and optimized processing conditions. Recently, low-temperature biomass-based flow fuel cells have been proposed as a viable solution, employing lignocellulose as the primary fuel to achieve efficient power generation under mild conditions and demonstrating considerable potential for future applications.^9,10 Moreover, electrochemical conversion has attracted increasing attention due to its mild reaction conditions and environmental compatibility. This approach utilizes electrons in place of chemical oxidants or reductants, enabling precise control over product selectivity and allowing operation under renewable electricity.^11,12 Recently, Yan et al. utilized single-atom Ru anchored on Co(OH)₂ (Ru SAs/Co(OH)₂) to facilitate the efficient simultaneous electrocatalytic oxidation and hydrogenation of HMF. This symmetrical system achieved a record-breaking combined yield of 177.7% in a flow cell and maintained long-term stable operation for over 240 hours, demonstrating the immense industrial potential of electrocatalytic biomass conversion.¹³ Electrochemical strategies not only reduce the carbon footprint but also facilitate the sustainable and selective production of fuels, hydrogen, electricity, and value-added chemicals.

Overall, lignocellulosic biomass combines abundant availability with significant functional potential; however, its structural complexity and inherent recalcitrance pose major challenges to efficient utilization. Overcoming these challenges requires integrated advances in fractionation and electrocatalysis. This review highlights recent developments in the electrochemical transformation of lignocellulosic biomass into renewable energy and value-added chemical products, focusing on three key aspects: (i) the structural features and composition of lignocellulosic biomass (Fig. 1a); (ii) electrochemical pathways for electricity and hydrogen generation (Fig. 1b); and (iii) electrocatalytic strategies for the production of fuels and high-value chemicals (Fig. 1c). Finally, the review highlights the key challenges and outlines prospective research directions to fully exploit the potential of lignocellulosic biomass within sustainable energy systems (Fig. 1d).

Fig. 1 Schematic overview of the electrochemical utilization of lignocellulosic biomass. (a) The structural units of lignocellulosic biomass. (b) Conversion of lignocellulosic biomass into energy. (c) Electrocatalytic conversion of lignocellulosic biomass into chemicals. (d) Future perspectives of lignocellulosic biomass in electrochemistry.

2. Composition of lignocellulosic biomass

Lignocellulosic biomass is a carbon-neutral and renewable feedstock that originates from a wide range of sources, including agricultural residues, forestry biomass, herbaceous plants, and various biomass wastes.^14,15 It is primarily composed of three biopolymers—cellulose, hemicellulose, and lignin—which together form a complex three-dimensional heterogeneous network. Cellulose, the main structural carbohydrate of plant cell walls, is a linear polysaccharide composed of D-anhydroglucopyranose units linked by β-(1 → 4) glycosidic bonds, with cellobiose as the repeating structural unit.^16,17 Extensive intra- and intermolecular hydrogen bonding among cellulose chains generates densely packed crystalline regions that confer remarkable mechanical strength and structural stability, while the amorphous domains are more susceptible to chemical and enzymatic degradation, facilitating subsequent transformation and utilization.¹⁸ Hemicellulose, an amorphous and branched heteropolysaccharide, consists of various monosaccharides, including pentoses (e.g., D-xylose, L-arabinose), hexoses (e.g., D-glucose, D-galactose, D-mannose), and uronic acids (e.g., D-galacturonic acid, 4-O-methyl-D-glucuronic acid),^14,15 with a typical degree of polymerization ranging from 100 to 200.^19,20 It associates with cellulose microfibrils through hydrogen bonding and may form covalent linkages with lignin, thereby imparting rigidity and flexibility to the plant cell wall.²¹ Lignin, the most abundant renewable aromatic polymer, is composed of three primary monolignol units—syringyl (S), guaiacyl (G) and p-hydroxyphenyl (H).²² These structural units are interconnected via ether linkages (e.g., α-O-4, β-O-4) and carbon–carbon bonds (e.g., β–β, β-5, 5–5, β-1) to form an amorphous, cross-linked three-dimensional polymer network.^22,23 Among these linkages, β-O-4 ether bonds account for approximately 50% of the total and are the most reactive sites during lignin depolymerization, playing a critical role in lignin valorization toward fuels and value-added chemicals.²⁴ Cellulose and hemicellulose typically constitute about 70% of lignocellulosic biomass and are intricately cross-linked with lignin through hydrogen bonding and covalent interactions,^14,15 forming a dense and robust structural framework. This highly cross-linked, multicomponent architecture endows lignocellulosic biomass with outstanding mechanical strength and resistance to degradation, yet simultaneously represents the major bottleneck hindering its efficient energy conversion and high-value utilization.

3. Conversion of biomass into energy

Lignocellulosic biomass has emerged as a critical renewable energy resource due to its abundance, renewable nature, and inherent carbon neutrality. Consequently, the efficient conversion of lignocellulosic biomass into electricity and hydrogen has become a key research frontier for sustainable energy systems. Among the available strategies, fuel cells have garnered increasing attention, as they can directly utilize lignocellulosic biomass and its derivatives as fuels, offering high energy conversion efficiency, low emissions, and strong alignment with carbon-neutral pathways. In parallel, advances in low-temperature electrolysis have demonstrated that lignocellulosic biomass and its derivatives can act as hydrogen and electron donors, thereby lowering both the energy demand and economic cost of electrolysis, while creating opportunities for hydrogen production and storage. This section provides a critical overview of recent advances in the electrochemical conversion of lignocellulosic biomass into electricity and hydrogen.

3.1 Biomass-based fuel cells

3.1.1 High-temperature biomass fuel cells. The solid oxide fuel cell (SOFC), as a typical high-temperature fuel cell that typically operates above 600 °C, represents a promising solid-state energy conversion technology, offering high efficiency and low environmental impact for power generation. Compared to conventional fuel cells using liquid electrolytes, SOFCs exhibit several inherent advantages, including high structural stability, corrosion resistance, and the elimination of electrolyte leakage.^25,26 The basic structure of an SOFC consists of a porous anode and cathode, separated by a dense solid electrolyte. Fuel is electrochemically oxidized at the triple-phase boundary (TPB) on the anode side, while oxygen ions (O²⁻) generated at the cathode migrate through the electrolyte to react with the fuel, enabling continuous electrical energy generation.^27,28

SOFCs are compatible with a wide range of fuels, such as natural gas, biogas, syngas derived from biomass or coal gasification, and hydrogen.^29,30 In recent years, lignocellulosic biomass, a renewable and abundant resource, has gained attention as a feedstock for SOFC applications. Fig. 2a illustrates the conversion pathway of lignocellulosic biomass from gasification to its utilization in solid oxide fuel cells. Lignocellulosic can first be gasified into syngas, which can then be used as fuel for SOFCs.^31,32 The similar temperature ranges of lignocellulosic gasification and SOFC operation support effective thermal integration, which contributes to efficient and low-emission energy conversion.³⁰ For instance, Perna et al. reported that the SOFC achieved a peak power density of 1391 mW cm⁻² when fueled with pine-derived biogas at 750 °C,³³ while Hibino et al. obtained approximately 0.41 W cm⁻² using raw biomass such as silvergrass and goldenrod.³⁴ However, impurities produced during biomass gasification, such as tar, siloxanes, and hydrogen sulfide (H₂S), can significantly impact the anode performance. Accordingly, recent research has focused on optimizing biomass gasification conditions to improve fuel purity and system stability. Common anode materials include Ni/GDC (gadolinia-doped ceria), Ni/YSZ (yttria-stabilized zirconia), and Ni/SDC (samaria-doped ceria) composites.^35,36 Incorporating perovskite oxides and metallic nanoparticles into Ni/YSZ anodes has been shown to mitigate carbon and sulfur accumulation, while ceria-based anodes doped with transition metals have also exhibited strong anti-sulfur and anti-carbon capabilities.^36–38 For instance, Hou et al. decorated the SOFC anode with A-site deficient perovskite oxide ((La_0.8Sr_0.2)_0.95CoO_3−x) and combined it with a strategy of distributing highly active catalysts on the carbon fuel, effectively enhancing the number of three-phase reaction sites and reaction kinetics.³⁸ This dual-catalyst modification significantly improved the performance of the biochar-powered SOFC, increasing the maximum power output from 279.6 mW cm⁻² to 371.5 mW cm⁻² at 850 °C, while simultaneously extending discharge life and enhancing fuel utilization. Moreover, integrating biomass gasification with SOFCs in a continuous system can further improve overall energy efficiency. Mojaver et al. developed an integrated system combining SOFCs, steam biomass gasification, and high-temperature sodium heat pipes, achieving an output power of 208 kW with an electrical efficiency of 43.71% and an overall efficiency of 74.31%.³⁹ Kalina proposed a hybrid system integrating SOFCs, wood gasification, internal combustion engines, and an organic Rankine cycle (ORC), demonstrating a biomass-to-electricity conversion efficiency of 37%–40%.⁴⁰ Similarly, Zhang et al. integrate coal-biomass co-gasification with SOFC, a supercritical CO₂ cycle, and ORC cycles to achieve energy cascade utilization, yielding 59.18% thermal efficiency and 55.02% exergy efficiency while reducing emissions and costs.⁴¹ Recently, Hou et al. developed a novel power–heating–freshwater trigeneration system by integrating a biomass gasifier-SOFC with geothermal waste heat recovery, coupled with desalination and domestic heating units, achieving a maximum exergetic efficiency of 64.49% and an optimal unit product cost of 4.94 $ per GJ.⁴² Integrating biomass SOFC technology offers a promising route to high-efficiency, low-emission power generation. However, challenges remain, including limited thermodynamic efficiency, high costs, and environmental concerns. Future research should prioritize advanced materials, system optimization, and effective integration strategies to enable scalable and sustainable deployment.

Fig. 2 Schematic illustration of a (a) SOFC, (b) DCFC, (c) MFC and (d) redox medium-mediated fuel cell fueled by lignocellulosic biomass.

Compared with SOFCs, the direct carbon fuel cell (DCFC) represents another promising high-temperature fuel cell technology that directly converts the chemical energy of solid carbon fuels into electricity with high efficiency. Operating at approximately 500 °C, DCFCs can theoretically achieve thermal efficiencies exceeding 100% with efficiencies approaching 90%.^6,43 Additionally, they offer the advantage of low CO₂ emissions, making them highly attractive for clean energy applications. A typical DCFC consists of a cathode, an anode, and a solid electrolyte, and it shows considerable potential for integration into sustainable energy systems.^6,44 Biomass-derived carbon is considered an ideal fuel for DCFCs due to its abundance, renewability, and high carbon content. It is typically produced from lignocellulosic biomass via high-temperature, oxygen-limited pyrolysis.⁴⁵ Lignocellulosic biomass can first be carbonized and subsequently employed as the fuel in DCFCs for electricity generation (Fig. 2b). Li et al. demonstrated that carbon derived from pyrolyzed sawdust can achieve relatively high peak power densities in DCFCs.⁴⁶ Furthermore, syngas by-products such as H₂ and CH₄ generated during the pyrolysis process contribute to enhanced electrochemical performance. In a comparative study, Palniandy et al. evaluated the cell performance of wood-based and non-wood-based carbon.⁴⁷ Their results indicated that carbon from rubberwood outperformed rice husk, owing to its higher fixed carbon content, lower ash content, and richer surface oxygen-containing functional groups. Notably, carbon from rubberwood subjected to alkaline pretreatment achieved a peak power density of 2.94 mW cm⁻², whereas acid treatment resulted in a decline in performance due to the loss of catalytic mineral components. Similarly, Kawase and Ido investigated molten carbonate direct biomass fuel cells (DBFCs) for converting the chemical energy of various biomass fuels—including coconut shell-activated carbon, cedar chips, cedar charcoal, and coffee grounds—into electricity.⁴⁸ Among these, cedar charcoal demonstrated the best long-term stability (over 800 h) and efficient power generation, attributed to its favorable carbon content and resistance to tar and H₂S. These findings underscore the importance of optimizing biomass pretreatment strategies to improve electrochemical conversion efficiency. Biomass feedstocks also vary significantly in their physicochemical properties, such as ash content, moisture, fixed carbon, and volatile matter, which influence carbon reactivity and cell performance. Qiu et al. reported that carbon from sugarcane bagasse, with its low crystallinity and high surface area, achieved a higher peak power output in DCFCs compared to carbon derived from wheat straw and corn cobs.⁴⁹ Lower crystallinity provides a greater number of active sites for electrochemical reactions, while a porous structure facilitates mass transport and reduces diffusion resistance, thereby enhancing the overall reaction kinetics. In addition, Kacprzak et al. found that biomass-derived carbon with a larger pore size distribution could significantly improve DCFC performance, further emphasizing the critical role of carbon structural optimization.⁵⁰ Mehrpooya and Hosseini integrate municipal solid waste (MSW) conversion via plasma gasification-melting (PGM) with a DCFC to produce high-quality syngas and electricity.⁵¹ By optimizing char separation fraction and fuel cell operating temperature, the system achieves a maximum overall efficiency of 79.5%.

Biomass-derived carbon is a sustainable and efficient fuel for DCFCs, facilitating renewable energy conversion with reduced environmental impact. However, cell performance is highly dependent on the carbon's microstructure, impurities, and surface functionalities. Moreover, widespread reliance on batch-mode fuel feeding constrains long-term operational stability and scalability. Future research should focus on system optimization and the development of continuous fuel feeding strategies to ensure reliable and scalable DCFC operation. Although SOFCs and DCFCs can convert raw biomass into electricity, their high operating temperatures (typically above 500 °C) present challenges in thermal management and system complexity. Hence, the development of low-temperature fuel cell technologies is of considerable practical significance for enhancing efficiency and scalability.

3.1.2 Low-temperature biomass fuel cells. Microbial fuel cells (MFCs) are an emerging bioelectrochemical technology that converts the chemical energy of biomass into electricity via microbial metabolism at temperatures below 50 °C.^52,53 Compared with SOFCs and DCFCs, MFCs operate under mild conditions, eliminating the risk for high-temperature environments and making them particularly suitable for the conversion of wet biomass.⁵⁴ In an MFC system, microorganisms metabolize fuel into CO₂ while releasing electrons, which are transferred to the anode via redox mediators and then flow through an external circuit to the cathode, where they combine with protons and oxygen to form water, thereby generating electricity.⁵⁵ However, the dense and recalcitrant structure of lignocellulosic biomass limits direct microbial utilization, and it requires pretreatment to produce small molecules, which can subsequently serve as fuel for MFCs to generate electricity (Fig. 2c). Takeuchi et al. investigated the relationship between the degree of cellulose degradation and electricity output, finding that higher degrees of cellulose degradation significantly increased the current density of MFC.⁵⁶ In MFC systems using rice bran as a substrate, pretreated rice bran via hydrodynamic cavitation resulted in approximately 26% higher electron transfer compared to untreated biomass. Therefore, pretreating lignocellulosic biomass to produce fermentable intermediates, such as soluble sugars, phenolic compounds, acetic acid, furfural, and 5-hydroxymethylfurfural (HMF), is essential for improving MFC performance, as these compounds serve as accessible carbon sources for microbial metabolism. The type of intermediate product significantly influences the performance of MFCs. Catal et al. evaluated the power generation performance of various monosaccharides in MFCs, showing that D-mannose produced the lowest peak power density, whereas D-glucuronic acid resulted in the highest.⁵⁷ In addition, glucose, one of the most commonly used MFC fuels, can enter multiple non-electrogenic metabolic pathways due to its high fermentability, leading to low coulombic efficiency.⁵⁸ In contrast, phenolic compounds derived from lignin depolymerization, although potentially inhibitory to microbes, can act as electron shuttles and enhance electron transfer. For instance, the addition of humic acids has been shown to significantly increase the peak power density of glucose-substrate MFCs.⁵⁹ Moreover, optimizing operational conditions is critical for promoting the growth and activity of electrogenic microbes in the anode chamber. The use of buffering solutions can further support microbial metabolism and mitigate proton transport limitations, thereby improving overall system efficiency.⁶⁰ In addition, Lachquer et al. utilized transition metal-modified Keggin-type lacunar polyoxometalate salts (Cs₅Pmo₁₁M(H₂O)O₃₉, M = Co, Fe) as cathode catalysts in microbial fuel cells (MFCs) to achieve efficient wastewater-driven electricity generation and COD removal, while enhancing oxygen reduction performance, demonstrating their potential for integrated wastewater treatment and renewable power production.⁶¹ Although MFCs can convert pretreated biomass into electricity under mild conditions, their practical performance is hindered by issues such as microbial contamination, catalyst deactivation, and excessive biofilm growth. Effective biomass pretreatment is critical for improving fuel availability, but its high cost and complexity remain significant barriers to large-scale implementation. Future research should prioritize the development of cost-effective pretreatment methods and the identification of robust microbial strains and catalysts to promote the broader application of MFCs in real-world settings.

MFCs have made notable progress, but their low efficiency and limited power density hinder large-scale application. To overcome these barriers, Larsson et al. proposed a novel flow fuel cell system based on vanadium redox couples, where V³⁺/VO₂⁺ and VO²⁺/VO₂⁺ serve as the anodic and cathodic redox pairs, respectively.⁶² As shown in Fig. 2d, this system enables the conversion of biomass into electricity under mild conditions while avoiding the thermal losses associated with traditional Carnot-cycle heat engines. Due to its low cost and favorable electrochemical properties, the Fe³⁺/Fe²⁺ redox couple is another promising candidate for electron mediation. Gong et al. demonstrated that wheat straw could be directly oxidized by Fe³⁺ at the anode, and the resulting Fe²⁺ was subsequently reoxidized at the cathode through reaction with VO₂⁺ and oxygen, achieving a maximum power density of 100 mW cm⁻² at 80–90 °C.⁶³ Similarly, Zhao et al. constructed an electron transport chain composed of [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻, VO²⁺/VO₂⁺, and NO₃⁻/NO redox couples, enabling efficient electron transfer from corn stover alkaline lignin to oxygen.⁶⁴ Under optimized conditions, the system achieved a peak power density of 200.3 mW cm⁻² and an overall electron conversion efficiency of approximately 90%. In an acid–base asymmetric configuration, [Fe(CN)₆]³⁻ effectively extracted electrons from lignin, and the resulting [Fe(CN)₆]⁴⁻ was reoxidized in a liquid flow fuel cell with the assistance of (VO₂)₂SO₄ and HNO₃ catalysis, thereby sustaining continuous electricity generation. In addition, Zu et al. employed a similar approach using glucose as the substrate and achieved a power density of 125.7 mW cm⁻² and a discharge current density of 314.2 mW cm⁻², which is 755 times higher than that of conventional MFCs.⁶⁵ In addition, Li and Song designed a straw-based fuel cell using methyl violet as the redox mediator, nickel foam as the anode, and Pt/C as the cathode. With 65 wt% ZnCl₂ as the solvent, the system achieved a maximum power output of 0.3 mW cm⁻².⁶⁶

Polyoxometalates (POMs), composed of multiple transition metal oxyanions interconnected through shared oxygen atoms, exhibit exceptional physicochemical properties. Their reversible redox characteristics, combined with high catalytic efficiency in organic hydrolysis and oxidation reactions, position POMs as effective redox mediators and catalysts in low-temperature biomass fuel cells.^9,10,67 Liu et al. introduced a high-efficiency fuel cell utilizing POMs as catalysts for the conversion of biomass into electricity.⁹ This solar-assisted hybrid fuel cell system, which integrates features of solar cells, fuel cells, and redox flow batteries, uses natural biomass such as starch, cellulose, lignin, switchgrass, and wood powder as fuel. In this design, H₃PMo₁₂O₄₀ acts as both photocatalyst and electron mediator to oxidize biomass at the anode, while oxygen is reduced at the Pt/C cathode. When cellulose was used as the substrate, the fuel cell reached a power density of 0.72 mW cm⁻², approximately 100 times greater than that of traditional MFCs. The catalytic activity of POMs replaces that of precious metal electrodes, and their robust self-regeneration properties enable the oxidation of organic impurities in raw biomass without requiring purification, significantly lowering operational costs and expanding the range of usable biomass feedstocks. To further enhance efficiency, Liu et al. later developed a noble-metal-free fuel cell system using H₃PW₁₁MoO₄₀ as the anodic catalyst and H₁₂P₃Mo₁₈V₇O₈₅ as the cathodic redox couple.¹⁰ This system demonstrated electricity generation from raw biomass materials, including cellulose, starch, and lignocellulosic powder, achieving a power density nearly 3000 times higher than that of conventional MFCs. Unlike noble-metal catalysts, POMs exhibit high tolerance to both organic and inorganic contaminants, eliminating the need for biomass pretreatment. Subsequently, Wu et al. found that the number of hydroxyl groups in fuel molecules was positively correlated with the POM photochemical reaction rate.⁶⁸ Fuels rich in hydroxyl groups, such as starch, hemicellulose, and cellulose, exhibited high reduction potential and delivered superior power output, making them ideal candidates for liquid catalyst-based fuel cells. The excellent catalytic properties of POMs in both hydrolysis and oxidation reactions position them as promising catalysts for liquid biomass fuel cells. Similarly, Zhao et al. employed H₃PMo₁₂O₄₀ as an electron and proton carrier at the anode, with oxygen reduction at the Pt-based cathode, converting lignin into electricity and achieving a peak power density of 0.96 mW cm⁻², 560 times higher than phenol-fed MFCs.⁶⁹ They later developed a novel process that couples biomass pretreatment with energy storage and generation, utilizing POMs and Fe³⁺ as redox mediators and proton carriers.⁷⁰ In this system, POMs are reduced during the “charging” phase via biomass oxidation and reoxidized in a flow reactor during the “discharging” phase, while Fe³⁺ acts as the terminal electron acceptor for oxygen reduction. This approach improved the power density by 5000–6000 times compared to phenol-fed MFCs and tenfold over traditional biomass fuel cells. It offers a promising strategy for integrating biomass conversion with flexible energy storage and introduces the novel concept of hybrid biomass fuel cell-flow battery systems.

Low-temperature biomass fuel cells are primarily classified into microbial fuel cells (MFCs) and flow fuel cells. Despite significant progress, the practical performance of MFCs remains constrained by challenges such as microbial contamination, catalyst deactivation, and excessive biofilm growth, along with the necessity of biomass pretreatment, which substantially increases operational costs. In contrast, flow biomass fuel cells employing POMs as redox mediators and catalysts combine low cost with high efficiency, enable the conversion of raw biomass into electricity, and thus hold considerable promise for scalable industrial applications.

3.2 Biomass-based electrochemical hydrogen production

Hydrogen (H₂) is a clean energy carrier with a high energy density of 143 MJ kg⁻¹, and global demand is expected to reach 400 million tons by 2050 due to its wide applications in industry, power, and transportation.^71,72 However, about 96% of current hydrogen production still depends on fossil fuels, highlighting the need for sustainable alternatives.⁷³ Biomass is considered a promising renewable hydrogen source due to its abundance, availability, and carbon neutrality. Traditional hydrogen production methods from biomass include thermochemical reforming and microbial processes. While thermochemical routes offer high efficiency, they require high temperatures and yield hydrogen with limited purity.⁷⁴ Microbial methods operate under mild conditions but suffer from low reaction rates, limiting scalability.⁷⁵ Water electrolysis produces high-purity hydrogen but is energy-intensive and costly.⁷⁶ To improve efficiency, recent studies have explored replacing the anodic oxygen evolution reaction (OER) with the electrooxidation of biomass-derived molecules, which offers more favorable thermodynamics and kinetics, enabling lower cell voltages and higher efficiency.⁷⁷ However, direct electrochemical conversion of raw biomass remains challenging due to its complex structure. Lignocellulosic biomass often requires depolymerization into smaller intermediates before oxidation. Additionally, conventional metal-based catalysts are vulnerable to deactivation by impurities like sulfur compounds and CO. In proton exchange membrane electrolyzer cells (PEMECs), organic acids produced during oxidation may neutralize alkaline electrolytes, affecting system stability and scalability. To address these limitations, recent efforts have focused on developing alternative catalytic systems and innovative electrolyzer configurations. Liu et al. proposed a chemical-electrochemical conversion (CEC) strategy that employs POMs as both redox mediators and proton carriers for the direct electrooxidation of untreated biomass (Fig. 3a).⁷⁸ POMs exhibit several notable advantages, including strong oxidative potential, tunable redox properties, excellent chemical stability under acidic and oxidative conditions, and outstanding resistance to deactivation by both organic and inorganic contaminants. Unlike noble-metal-based catalysts, POMs enable the direct electrooxidation of raw lignocellulosic feedstocks without requiring extensive pretreatment. Moreover, their reversible redox characteristics support sustained catalytic activity over prolonged operation. This CEC system achieved hydrogen production with an energy input as low as ∼16.7% of that required for conventional water electrolysis, by partially substituting water with biomass as both the hydrogen and electron donor. Importantly, this approach eliminates the need for precious metal catalysts and complex biomass preprocessing, thereby significantly reducing overall costs and enhancing system scalability. They introduced transition metal salts (particularly FeCl₃) into the POM system, which coordinate with the oxygen-donor groups in carbohydrates, thereby promoting cellulose hydrolysis and facilitating the reoxidation of reduced POM species to sustain the high oxidative capacity of the system. This synergistic effect enables the efficient electrooxidation of raw biomass coupled with hydrogen evolution.⁷⁹ Moreover, Liu et al. demonstrated that tuning the pH conditions allows the synthesis of lacunary POMs with significantly enhanced oxidative activity toward biomass.⁸⁰ Notably, the POM catalytic system is also applicable to the electrochemical upgrading and hydrogen production from plastic wastes.^81,82

Fig. 3 (a) Schematic illustration of POM-catalyzed direct biomass oxidation coupled with hydrogen evolution at the cathode. (b) Schematic illustration of the integration of reactors: stored glucose-POM solution and H₃PO₄ solution at the far left and right, respectively; a ‘shared cell’ (tank storing Fe²⁺/Fe³⁺ solution) in the center; and the inclusion of LFFCs (a biomass fuel cell stack) and PEMEC (the hydrogen electrolyzer), reproduced from ref. 83 with permission from Springer Nature,⁸³ copyright 2019. (c) Schematic illustration of a multipurpose electrocatalytic system integrating anodic low-potential R-COH oxidation with cathodic hydrogen evolution.

In a parallel development, Li et al. designed a flow-based electrochemical system that integrates a fuel cell with an electrolyzer, wherein internal redox cycling between Fe³⁺ and Fe²⁺ enables the continuous regeneration of redox mediators (Fig. 3b).⁸³ This configuration facilitated efficient hydrogen production from glucose under ambient conditions without the need for an external electrical input, highlighting its potential for decentralized and off-grid hydrogen generation. Similarly, Hibino et al. employed an 85% phosphoric acid solution to directly convert raw biomass materials—such as bread crumbs, cedar sawdust, and rice bran—into hydrogen at 150 °C.⁸⁴ Their study demonstrated that functionalized mesoporous carbon electrodes exhibited electrocatalytic performance comparable to that of commercial Pt/C catalysts, achieving nearly 100% hydrogen yield in both batch and continuous-flow modes. Compared with conventional water electrolysis and ethanol-based hydrogen production, this approach markedly reduced overall energy consumption. In a subsequent study, they further demonstrated the efficient electrolysis of cellulose extracted from waste newspaper using carbonyl-functionalized carbon electrodes in a phosphoric acid medium, achieving an impressively low energy input of only 1.27 kWh Nm⁻³ for hydrogen generation.⁸⁵

Wang et al. reported a bipolar hydrogen generation system that simultaneously produces H₂ at both the anode and cathode under an ultralow cell voltage of approximately 0.1 V (Fig. 3c).^86,87 Unlike conventional water splitting, this system operates via the coupling of low-potential anodic oxidation of biomass-derived aldehydes with the cathodic hydrogen evolution reaction (HER). At the anode, aldehydes are electrocatalytically converted into the corresponding carboxylates and H₂ on a copper catalyst at a low onset potential of 0.05 V vs. RHE. Due to the low applied potential, the hydrogen atoms from the aldehyde groups are released as H₂ through Tafel recombination rather than being oxidized to H₂O via the traditional Volmer step. Notably, the aldehydes used—such as HMF and furfural—are abundant and readily accessible biomass-derived compounds, obtainable from various sustainable feedstocks including starch, cellulose, and hemicellulose. The oxidation products (corresponding carboxylic acids) are value-added chemicals and serve as key precursors for a wide range of products, including pharmaceuticals, fragrances, and sustainable polymers. However, this approach remains limited by the low operating voltage and its applicability only to small-molecule aldehydes.

In summary, replacing water with biomass as the anodic oxidation substrate constitutes a promising strategy to reduce the energy consumption of electrolysis while enabling sustainable hydrogen production. The incorporation of advanced catalytic systems, such as POMs, not only diminishes reliance on noble metals and intensive biomass pretreatment but also expands the range of applicable biomass feedstocks and operational conditions. Future research efforts should be directed toward the advancement of catalyst design, system engineering, and process integration, with the aim of enabling the scalable and sustainable deployment of electrochemical hydrogen production technologies from biomass. This section primarily focuses on the conversion of native biomass to hydrogen, which holds practical significance for industrial implementation. The anodic oxidation of selected biomass-derived small molecules, coupled with cathodic hydrogen evolution, has been extensively reviewed in prior studies; therefore, a detailed discussion of these systems falls outside the scope of the present study.

3.3 Technical assessment of biomass conversion to hydrogen and electricity

Fig. 4a–d presents a systematic comparison of four representative biomass fuel cell technologies with respect to energy efficiency, economic viability, environmental sustainability, operational stability, and operational safety. SOFCs and DCFCs demonstrate superior energy conversion efficiency. Notably, DCFCs achieve theoretical thermodynamic efficiencies approaching 90%—representing the theoretical limit for converting biomass chemical energy into electricity—owing to the negligible entropy change associated with the direct electrochemical oxidation of biomass-derived carbon (C + O₂ = CO₂).^6,43 However, the high operating temperatures of DCFCs lead to the accumulation of biomass ash, which blocks electrode pores and corrodes the electrolyte. This results in a drastic increase in internal resistance and irreversible performance degradation, thereby compromising operational stability.⁸⁸ In comparison, the stability of SOFCs is primarily constrained by carbon deposition (coking) from tars in biomass syngas and poisoning by impurities.^34,89 Furthermore, the rigorous high-temperature and high-pressure operating conditions required for these technologies pose significant safety risks, severely limiting their applicability in non-industrial settings. The relatively short lifespan of high-temperature fuel cell components necessitates frequent maintenance and replacement, leading to high cumulative energy consumption and carbon emissions during manufacturing.⁹⁰ This severely undermines their competitiveness in terms of techno-economic analysis (TEA) and life cycle assessment (LCA).

Fig. 4 Evaluation of (a) SOFC, (b) DCFC, (c) MFC, and (d) redox medium-mediated fuel cells powered by lignocellulosic biomass across five metrics: efficiency, economic viability (or TEA), environmental sustainability (or LCA), operational stability, and operational safety. Evaluation of (e) hydrogen production via water electrolysis and (f) hydrogen production via biomass electrolysis powered by lignocellulosic biomass across five metrics: efficiency, economic viability (or TEA), environmental sustainability (or LCA), operational stability, and operational safety.

Compared with high-temperature fuel cells, MFCs exhibit distinct characteristics. Benefiting from mild operating conditions (ambient temperature and pressure in an aqueous phase), MFCs demonstrate significant advantages in LCA, characterized by low energy consumption and minimal carbon emissions.^52,53 Their exceptional environmental sustainability and operational safety highlight their unique value in environmental remediation. However, limited by the slow extracellular electron transfer (EET) rates of biofilms, MFCs suffer from inherent deficiencies in energy efficiency, particularly power density.^55,91 Consequently, TEA indicates high capital costs per unit of installed capacity, where revenue from electricity sales alone is insufficient to offset the high material costs, making them unsuitable for large-scale baseload power generation. Alternatively, redox medium-mediated fuel cells offer the most balanced comprehensive performance. By employing liquid-phase redox mediators (e.g., POMs or VO²⁺/VO₂⁺),^9,10,64,67 this approach fundamentally circumvents carbon deposition issues on solid electrode surfaces, yielding operational stability significantly superior to that of high-temperature systems (SOFCs and DCFCs). Nevertheless, this system faces critical challenges regarding electrolyte crossover and component degradation. Specifically, the corrosion of bipolar plates and current collectors, along with the degradation of electrocatalysts under strongly acidic or oxidative conditions, remain key technical bottlenecks.⁹² Despite these challenges, the liquid-mediated design paradigm provides a highly promising pathway to overcome the durability limitations of biomass conversion.

Therefore, each biomass fuel cell technology possesses distinct trade-offs: high-temperature fuel cells offer exceptional efficiency suitable for industrial-scale generation but are hindered by stability issues and safety concerns; conversely, low-temperature technologies are safer and more environmentally friendly but are constrained by slow reaction kinetics or material corrosion. Therefore, future development should prioritize differentiated selection and optimization tailored to specific application requirements.

As illustrated in Fig. 4e and f, biomass electrochemical hydrogen production offers significant advantages in environmental sustainability and operational safety by avoiding the kinetically sluggish oxygen evolution reaction (OER) and instead coupling hydrogen evolution with thermodynamically favorable biomass oxidation reactions. This strategy not only fundamentally eliminates the safety hazards associated with H₂/O₂ crossover but also substantially reduces system energy consumption.^93,94 TEA and LCA evaluation indicate that this route offers superior environmental and economic benefits: the hydrogen production cost is controlled at 2.0–3.0 USD per kg H₂, and the lifecycle carbon footprint is merely 1.0–2.5 kg CO₂ per kg H₂, exhibiting significant competitiveness over traditional thermochemical pathways in decentralized application scenarios.⁹⁵ However, the long-term operational stability of catalysts remains a critical bottleneck constraining its commercial prospects. Complex organic reaction systems are highly susceptible to active site masking, catalyst poisoning, and component corrosion, which limits the scalability of this technology as a standalone route. To address the stability challenges of single-source biomass hydrogen production and the intermittency of renewable energy, Zhu et al. proposed an Integrated Hydrogen Production System (IHPS) that deeply integrates photovoltaic water electrolysis (WE), biomass gasification (BG), and natural gas reforming (NGR).⁹⁶ This system innovatively utilizes the electrolytic byproduct oxygen as a gasifying agent and reforming oxidant, while recovering the high-temperature sensible heat from gasification (1100 K) to preheat the reforming feed (750 K), thereby achieving a system-level leap in efficiency. This coupling strategy demonstrates breakthrough advantages across multi-dimensional performance metrics. (1) Energy efficiency breakthrough: the overall system energy efficiency reaches 64.19%, an increase of 9.87% compared to the single-energy path (54.32%). (2) Deep decarbonization: lifecycle carbon emissions are reduced to 4.45 kg CO₂ per kg H₂, a reduction of approximately 67% compared to traditional processes (13.5 kg CO₂ per kg H₂), with 76% of the hydrogen derived from renewable sources. (3) Cost-effectiveness: while ensuring a stable daily supply of 24 960 Nm³, the capital expenditure (CAPEX) is approximately 23.68 million USD, representing a 69.26% reduction compared to a standalone photovoltaic electrolysis scheme requiring large-scale energy storage (77.04 million USD).

Therefore, future research on biomass hydrogen production technology should focus on the design and development of highly stable, poison-resistant catalysts and stable electrolyzer component materials, thereby enhancing the long-term operational stability of the biomass hydrogen production reaction system.

4. Electrocatalytic conversion of biomass

Lignocellulosic biomass, owing to its high density of oxygenated functional groups and aromatic frameworks, represents a promising renewable feedstock for the sustainable production of value-added chemicals.^97,98 Through electrocatalytic conversion, lignocellulosic biomass can be selectively transformed into a wide range of value-added chemicals, including gluconic acid, xylonic acid, methylfurans, furan dicarboxylic acids, aromatic derivatives, and alkanes.⁹⁹ A central goal of biomass valorization is to selectively exploit its inherent oxygen-containing groups and aromatic frameworks for targeted chemical transformations. Accordingly, developing efficient electrocatalytic strategies to harness the structural complexity of lignocellulosic biomass holds significant promise for sustainable chemical manufacturing.

4.1 Conversion of lignin and its derivatives

4.1.1 Electrocatalytic depolymerization of lignin. Electrocatalytic technologies have long been recognized as promising strategies for lignin depolymerization due to their high efficiency, cost-effectiveness, and environmentally friendly characteristics. In electrocatalytic lignin depolymerization, electron transfer between the electrode and lignin derivatives initiates molecular rearrangements and the cleavage of chemical bonds. For example, selective cleavage of O–H or C–C bonds can lead to the formation of quinone derivatives, while the oxidation of lignin side chains and aromatic ring-opening reactions may yield phenolic aldehydes, ketones, aliphatic carboxylic acids, and their corresponding salts. However, C–C bond cleavage remains a significant challenge, partly due to the relatively high bond dissociation energy and inherent stability of C–C bonds compared to C–O bonds.^100,101 Yan et al. developed an electrochemical method using low-cost nickel foam as the working electrode to depolymerize ethanol-pretreated lignin (Fig. 5a).¹⁰² In lignin from sweetgum and poplar, vanillin and syringaldehyde were the main products, with a total yield of up to 17.5%. Additionally, Li et al. designed an electrochemical system based on the synergistic interaction between a Pb/PbO₂ anode and a Cu/Ni–Mo–Co cathode (Fig. 5b).¹⁰³ Under alkaline conditions, this system efficiently degraded lignin from corn stalks, producing a variety of high-value aromatic compounds, including ferulic acid, vanillin, and syringaldehyde, via coupled electrochemical oxidation and reduction processes. Similarly, Qin et al. developed a bifunctional electrocatalyst by doping CoMoO₄ with phosphorus, achieving nearly complete lignin derivative conversion at the anode with a benzoic acid selectivity of 56%, while the cathode converted furfural with an 84% conversion rate and 78% selectivity toward 2-methylfuran.¹⁰⁴ To further improve raw lignin degradation efficiency, reduce side reactions, and lower processing costs, optimizing the reaction pathway is crucial. Lignin dissolution and monomer repolymerization are significantly affected by pH. Under alkaline conditions, monomers are more prone to condensation, oligomerization, or oxidative degradation.¹⁰⁵ Therefore, Stahl et al. developed an electrochemical system employing TEMPO and 4-acetamido-TEMPO (ACT) as catalytic mediators to achieve the chemoselective oxidation of primary alcohol groups in lignin to carboxylic acids under mild alkaline conditions (Fig. 5c).¹⁰⁵ Applicable to both lignin model compounds and ethanol organosolv-extracted poplar lignin, this method increased acidic functional groups and water solubility without significantly changing the molecular weight distribution. Subsequent acidolysis efficiently depolymerized the oxidized lignin, yielding up to 30 wt% aromatic monomers. This two-step “pre-oxidation–acidolysis” strategy offers a promising route to enhance monomer yields and advance lignin valorization. Recently, Karanwal et al. achieved efficient electrocatalytic hydrogenolysis of birch biomass under mild conditions using 5 wt% Pd/C, affording 19.6 wt% lignin-derived phenolic monomers with a high selectivity of 41.6% toward 4-n-propanol syringol.¹⁰⁶ Cleavage of the benzene–oxygen (C_aryl–O(C)) bond in the lignin β-O-4 linkage is a promising strategy to suppress the condensation of degradation products and thereby enhance product value. However, its electrochemical activation remains challenging due to the high bond dissociation energy (∼409 kJ mol⁻¹) of the C_aryl–O(C) linkage and the susceptibility of aromatic compounds to over-reduction.¹⁰⁷ Zou et al. developed an aqueous electrochemical reduction strategy regulated by molecular adsorption using a CuO nanorod catalyst with residual Cu(I) species, as shown Fig. 5d, enabling the efficient cleavage of lignin β-O-4 C_aryl–O(C) bonds by lowering the proton attack energy barrier, and yielding 10.9 wt% of guaiacylglycerol, with an outstanding selectivity of >63.0% from poplar lignin.¹⁰⁷ Recently, Zou et al. engineered a vacancy-rich nickel hydroxide catalyst (Ni(OH)₂–V) to realize the highly efficient electrocatalytic depolymerization of lignin.¹⁰⁸ This strategy enabled selective C_α–C_β bond cleavage of β-O-4 linkages while suppressing phenol overoxidation, achieving the conversion of poplar and corn stover lignin into 14.24 and 19.54 wt% aromatic monomers, respectively.

Fig. 5 (a) Electrocatalytic depolymerization of raw lignin pretreated with ethanol on nickel foam under alkaline conditions, reproduced from ref. 102 with permission from the American Chemical Society,¹⁰² copyright 2020. (b) Electrocatalytic degradation of corn stalk lignin using a Pb/PbO₂ anode and a Cu/Ni–Mo–Co cathode under alkaline conditions, reproduced from ref. 103 with permission from Elsevier,¹⁰³ copyright 2018. (c) Electrocatalytic depolymerization of lignin via TEMPO/ACT-mediated oxidation and subsequent acidolysis to yield aromatic monomers, reproduced from ref. 105 with permission from the American Chemical Society,¹⁰⁵ copyright 2019. (d) Electrocatalytic depolymerization of lignin using CuO nanorods, reproduced from ref. 107 with permission from the American Chemical Society,¹⁰⁷ copyright 2024.

Electrocatalytic lignin conversion can also be achieved using liquid-flow fuel cell (LFFC) systems, which are highly suitable for industrial-scale applications. Zhao et al. developed an LFFC system driven by lignin oxidation, where the depolymerization process was largely governed by the cleavage of β-O-4 ether bonds.¹⁰⁹ Under electrocatalytic conditions, aromatic ring-opening reactions led to the formation of aliphatic acids, accompanied by minor CO₂ generation. However, the system exhibited poor product selectivity and faced challenges in product separation. To address the issue of product overoxidation in electrocatalytic lignin conversion, Wessling et al. developed an electrochemical membrane reactor integrated with in situ nanofiltration.¹¹⁰ This configuration enables the continuous depolymerization of lignin while concurrently separating aromatic monomers through the nanofiltration membrane, thereby preventing their overoxidation to carboxylic acids or CO₂ and thus markedly enhancing both product selectivity and retention. Moreover, the incorporation of electrode rods into a 3D-printed turbulent flow mixer effectively reduces membrane fouling and electrode polarization, further enhancing the overall process efficiency.¹¹¹ Similarly, Wang et al. employed a three-dimensional electrode (TDE) reactor featuring a Pb/PbO₂ anode for efficient electrocatalytic degradation of poplar lignin.¹¹² In this system, hydroxyl radicals (˙OH) generated at the anode facilitated bond cleavage within the lignin matrix, while hydrogen species participated in subsequent hydrogenation steps, leading to the formation of value-added aromatic products, predominantly 4-methylanisole.

β-O-4 dimers are frequently used as model compounds to investigate the depolymerization mechanisms of lignin. For example, Cui et al. developed an electrocatalytic system based on atomically dispersed platinum catalysts (Pt₁/N-carbon nanotubes, Pt₁/N-CNTs) to induce selective cleavage of the C_α–C_β bond in β-O-4 dimers (Fig. 6a).¹¹³ In this system, tert-butyl hydroperoxide (^tBuOOH) was introduced as a radical initiator, generating ^tBuO˙ or ^tBuOO˙ radicals, which undergo C–O coupling with the C_β radical to form unstable adducts that readily facilitate subsequent C_α–C_β bond cleavage. This strategy achieved a high dimer conversion of 99%, with benzaldehyde obtained in a yield of 81%, demonstrating excellent reactivity and selectivity. Qin et al. employed β-O-4 dimers as model compounds to elucidate the reaction pathways in lignin depolymerization with a phosphorus-doped CoMoO₄ bifunctional electrocatalyst.¹⁰⁴ Mechanistic studies revealed that P-doping upshifted the d-band center, enhanced C_α–C_β bond adsorption and cleavage, and facilitated the selective formation of benzoic acid. The cleavage of the benzene–oxygen (C_aryl–O(C)) bond in the β-O-4 linkage remains challenging due to its high bond dissociation energy and the susceptibility of aromatic compounds to over-reduction. Zou et al. employed 2-phenoxy-1-phenylethanol (PPE) as a model compound and developed an aqueous electroreduction strategy using CuO nanorods enriched with residual Cu(I) as the cathode (Fig. 6b). In an undivided cell with a PbO₂ anode at −0.4 V vs. RHE, this system achieved high yields of hydroquinone and benzyl alcohol, 95.3% and 88.6%, respectively.¹⁰⁷ Moreover, Fang et al. proposed an alternative cleavage mechanism based on the formation of C_α–oxygen radical (C_α–O˙) intermediates, employing CoS as the catalyst to enable electrochemical bond scission under mild and solvent-free conditions.¹¹⁴ Under oxidative potentials, Co³⁺ sites generated hydroxyl radicals (˙OH) in situ, which abstracted hydrogen atoms from the C_α-OH moiety to form C_α–O˙ radicals, thereby initiating C_α–C_β bond cleavage (Fig. 6c). This system operated efficiently at a relatively low potential (1.05 V vs. RHE), affording high yields of vanillin (V-aldehyde) and 2,2-methoxyphenoxyacetaldehyde (M-aldehyde), at 83% and 90%, respectively. Recently, Wang et al. constructed an electrochemical–chemical tandem catalysis system to achieve efficient electrocatalytic cleavage of lignin β-O-4 linkages (Fig. 6d).¹¹⁵ Using the β-O-4 dimer 2-phenoxy-1-phenylethanol as a model compound and Au-nanoparticle-decorated CuO nanoflakes (Au/CuO) as the electrocatalyst, they systematically investigated the depolymerization mechanism of lignin. The reaction proceeds through two key steps: (i) electrochemical dehydrogenation of the C_α–OH group, followed by (ii) non-electrochemical cleavage of the C_α–C_β bond, with the accelerated dehydrogenation step markedly enhancing the cleavage efficiency. Specifically, Au nanoparticles serve as active sites for C_α–OH oxidation, while the CuO substrate facilitates substrate adsorption. Under 0.95 V_RHE, the Au/CuO electrode delivered product yields of 99.2% phenol and 80.2% benzoic acid, along with a record-high faradaic efficiency (FE) of 74.7%. These studies further underscore the utility and representativeness of β-O-4 dimers as model substrates in mechanistic investigations, and highlight the potential of non-precious metal electrocatalysts in sustainable lignin valorization.

Fig. 6 (a) Electrocatalytic cleavage of β-O-4 dimers using atomically dispersed Pt₁/N-CNTs with ^tBuOOH as a radical initiator, reproduced from ref. 113 with permission from the American Chemical Society,¹¹³ copyright 2021. (b) Electrocatalytic depolymerization of β-O-4 dimer (PPE) using CuO nanorods with residual Cu(I) via sequential proton–electron transfer and C_aryl–O(C) bond cleavage, reproduced from ref. 107 with permission from the American Chemical Society,¹⁰⁷ copyright 2024. (c) Electrocatalytic cleavage of β-O-4 dimers via C_α–O˙ radical formation using CoS in 1 M KOH, reproduced from ref. 114 with permission from Elsevier,¹¹⁴ copyright 2023. (d) Electrocatalytic cleavage of β-O-4 dimers using Au-nanoparticle-decorated CuO nanoflakes (Au/CuO) via electrochemical C_α–OH dehydrogenation and subsequent C_α–C_β bond cleavage, reproduced from ref. 115 with permission from Wiley-VCH,¹¹⁵ copyright 2025.

4.1.2 Electrocatalytic oxidation of lignin monomers. Depolymerization of lignin generates a series of small-molecule platform compounds, typically featuring aromatic-ring structures such as phenol, catechol, phenylethanol, and cyclohexanone. These compounds possess well-defined molecular structures and reactive sites, facilitating mechanistic studies of electrocatalytic transformations as well as their valorization into high-value chemicals, including aldehydes and carboxylic acids, with potential applications in fragrances, plastics, and pharmaceuticals. Phenylethanol and its derivatives represent a representative class of lignin-derived monomers that can undergo selective C–C bond cleavage under electrocatalytic conditions, yielding valuable aromatic aldehydes and carboxylic acids. Duan et al. developed a Mn-doped CoOOH (MnCoOOH) electrocatalyst that efficiently cleaves phenylethanol-type substrates in 1 M KOH, achieving aromatic acid salt yields of up to 80–99%. Mechanistic studies revealed that the high-pH environment promotes H_α deprotonation of the substrate to form an alkoxide anion (Fig. 7a).¹¹⁶ Simultaneously, surface-adsorbed OH species facilitate β-hydride elimination and carbonyl formation. Subsequent keto–enol tautomerization generates a carbanion, which undergoes nucleophilic attack by OH, followed by dehydrogenation, gem-diol formation, and C–C bond cleavage, ultimately producing benzoate products. Beyond phenylethanol, KA oil, a hydrogenation mixture of cyclohexanol and cyclohexanone derived from phenol, is another important lignin-based platform compound that can be electrochemically oxidized into adipic acid (AA), a key precursor of Nylon-66. Nickel-based electrocatalysts are widely recognized as the most promising systems for KA oil oxidation.^117,118 For instance, Duan et al. intercalated sodium dodecyl sulfate (SDS) into layered Ni(OH)₂, enhancing the aqueous enrichment of cyclohexanone and achieving a 3.6-fold increase in product yield with faradaic efficiency improving from 56% to 93%, and the reaction pathway was also elucidated (Fig. 7b).¹¹⁷ Molecular dynamics simulations indicated that SDS facilitated the accumulation of cyclohexanone in the interlayer or edge interface of the catalyst (inset in Fig. 7b), thereby accelerating the reaction kinetics. This strategy showed broad compatibility with other hydrophobic aldehydes and ketones. Similarly, Chen et al. employed a synergistic substrate enrichment and adsorption activation strategy by constructing a Co₃O₄/graphdiyne (GDY) interfacial system.¹¹⁹ They utilized the hydrophobic π domain of GDY to enrich cyclohexanone and simultaneously adjusted the d-band center of Co sites to enhance adsorption activation, achieving efficient adipic acid production. Additionally, doping strategies have proved effective in improving Ni-based catalytic performance. Wang et al. demonstrated that substituting Cu²⁺ into the octahedral sites of Ni(OH)₂ significantly enhanced its activity for the oxidation of cyclohexanol to AA, with a yield of 84% and selectivity of 87%.¹¹⁸ Mechanistically, Cu²⁺ weakened the Ni–O bonds in NiOOH, promoting the generation of surface O˙ radicals that selectively attacked the C_β position to form epoxide intermediates, lowering the C–C bond cleavage barrier and improving efficiency.

Fig. 7 (a) Electrocatalytic oxidation of phenylethanol-type lignin monomers using Mn-doped CoOOH (MnCoOOH) in 1 M KOH via selective C–C bond cleavage, reproduced from ref. 116 with permission from Wiley-VCH,¹¹⁶ copyright 2021. (b) Electrocatalytic oxidation of KA oil to adipic acid using SDS-intercalated Ni(OH)₂, reproduced from ref. 117 with permission from Springer Nature,¹¹⁷ copyright 2022. (c) Electrocatalytic oxidation of phenol to p-benzoquinone (BQ) using a homogeneous Co³⁺/Cu²⁺ redox system, reproduced from ref. 120 with permission from Wiley-VCH,¹²⁰ copyright 2023. (d) Electrocatalytic oxidation of catechol to maleic acid (MA) using a CuO foam electrode with Zn²⁺ as a coordinating agent, reproduced from ref. 121 with permission from the American Chemical Society,¹²¹ copyright 2023.

Phenol and catechol are among the most common aromatic intermediates obtained from thermal or catalytic lignin depolymerization. Their electrocatalytic oxidation typically yields benzoquinones (BQ) or carboxylic acids, offering considerable potential for value-added chemical production. However, these reactions are prone to overoxidation, leading to poor selectivity and limiting their practical application. Zhang et al. developed a homogeneous redox system composed of Co³⁺/Cu²⁺ that improved the selectivity of phenol-to-BQ conversion, though yields remained below 70% (Fig. 7c).¹²⁰ Waldvogel et al. achieved near-quantitative conversion using an IrO₂ electrode in a mixed electrolyte of acetonitrile, methanol, and water, but the current density was limited to just 2 mA cm⁻².¹²² Han et al. designed a bimetallic FeRu@NHPC catalyst, achieving >99.9% BQ selectivity and substantially enhanced current density.¹²³ The superior performance was attributed to weak substrate adsorption on NiPt nanoparticles, which suppressed side reactions, and to Ru nanoparticles modified with atomically dispersed Fe, which promoted rapid product desorption. Catechol, due to its two hydroxyl groups, readily forms stable complexes with metal ions under alkaline conditions, making it an ideal precursor for the electrocatalytic synthesis of cis,cis-maleic acid (MA). Gong and co-workers employed a CuO foam electrode and introduced Zn²⁺ as a coordinating agent to inhibit catechol polymerization side reactions, achieving an MA yield of 90% with 87% selectivity (Fig. 7d).¹²¹ This coordination strategy showed excellent compatibility with various metal electrodes; however, precise control of cation concentration was required to prevent precipitation or suppression of the primary reaction.

4.1.3 Electrocatalytic hydrogenation of lignin monomers. Phenol, a representative lignin-derived monomer, is widely employed as a model compound for investigating electrochemical hydrogenation (ECH) behavior. The primary products include cyclohexanone, cyclohexanol, and cyclohexane. Cyclohexanone and cyclohexanol, collectively known as KA oil, are important organic solvents and chemical intermediates in diverse industrial processes, while cyclohexane serves as both a valuable fuel and a key intermediate for synthesizing various organic chemicals. Noble metal catalysts such as Pt, Pd, Ru, and Rh demonstrate high activity for phenol ECH but suffer from limitations including low current densities and restricted product selectivity. Furthermore, the HER constitutes the major competing side reaction during phenol ECH, highlighting the urgent need for more efficient catalytic systems. Zhou et al. developed carbon-supported Ni–MoO₂ heterostructured catalysts for the ECH of phenol in H₂SO₄ aqueous (Fig. 8a).¹²⁴ By tuning the density of oxygen vacancy (O_v) sites, they achieved high yields of cyclohexanol (up to 95%) and cyclohexanone (up to 86%). In situ characterization and density functional theory (DFT) calculations revealed that the enhanced phenol adsorption strength accounted for the improved catalytic performance. In addition, 1-cyclohexene-1-ol was identified as a key intermediate, whose hydrogenation pathway, and thus product selectivity, was strongly influenced by the O_v density. To enhance the utilization efficiency of phenol, Wu et al. developed an integrated electrochemical system that couples cathodic phenol reduction with anodic phenol oxidation, achieving the simultaneous production of cyclohexanone and benzoquinone from phenol and water.¹²³ By employing nitrogen-doped hierarchically porous carbon (NHPC)-supported NiPt and FeRu catalysts as the cathode and anode, respectively, the system achieved exceptional selectivities exceeding 99.9% for both target products. The outstanding electrocatalytic performance was attributed to the tailored surface properties of the NiPt alloy nanoparticles and Fe single-atom-decorated Ru nanoparticles, which exhibited weak adsorption toward cyclohexanone and benzoquinone, respectively, thereby preventing over-reduction or over-oxidation. In addition, Liu et al. developed an innovative dual-catalyst electrochemical strategy for the efficient electrocatalytic hydrogenation and deoxygenation of model bio-oil compounds in aqueous media (Fig. 8b).¹²⁵ This system, comprising suspended Pt/C and soluble POMs, enabled deep hydrogenation of phenol and delivered a remarkable working current density of up to 800 mA cm⁻² along with faradaic efficiencies exceeding 99%, significantly surpassing the performance limitations of conventional ECH systems (typically <60 mA cm⁻², FE ∼20–60%). More importantly, this approach proved applicable to a broad range of lignin-derived monomers, including guaiacol, demonstrating its versatility and potential for practical biomass upgrading. Building on Liu's study, Yang et al. employed a similar system using various lignin-derived compounds as substrates and demonstrated that the cleavage mechanisms are closely dependent on the type of substrate.¹²⁶

Fig. 8 (a) Electrocatalytic hydrogenation of phenol using carbon-supported Ni-MoO₂ heterostructured catalysts with an oxygen vacancy (O_v) in H₂SO₄, reproduced from ref. 124 with permission from Wiley-VCH,¹²⁴ copyright 2023. (b) Electrocatalytic hydrogenation and deoxygenation of lignin-derived monomers using a dual-catalyst system of suspended Pt/C and soluble POMs in aqueous media, reproduced from ref. 125 with permission from the Royal Society of Chemistry,¹²⁵ copyright 2020. (c) Electrocatalytic hydrogenation of guaiacol using a Pt/C catalyst in a stirred slurry electrochemical reactor (SSER), reproduced from ref. 127 with permission from Wiley-VCH,¹²⁷ copyright 2020. (d) Electrocatalytic hydrogenation of guaiacol to 2-methoxycyclohexanol using a ternary PtRhAu catalyst, reproduced from ref. 128 with permission from the American Chemical Society,¹²⁸ copyright 2021. (e) Electrocatalytic hydrogenation of lignin-derived monomers and furans in a flow-cell system using a highly electrolyte-permeable Rh diffusion electrode, reproduced from ref. 129 with permission from Springer Nature,¹²⁹ copyright 2023.

Guaiacol, an important lignin-derived monomer, exhibits electrochemical behavior distinct from phenol, often limited by adsorption site-blocking effects, with the initial adsorption step acting as the rate-determining step.¹³⁰ By tuning catalyst composition and reaction conditions, selective control over different reaction pathways can be achieved. Wijaya et al. conducted an ECH study of guaiacol using a stirred slurry electrochemical reactor (SSER) with a Pt/C catalyst (Fig. 8c).¹²⁷ By comparing different catholyte–anolyte combinations, including acidic, neutral, and alkaline electrolytes, they found that the acid–acid and neutral–acid systems exhibited superior conversion performance. Notably, at temperatures above 60 °C, the reaction favored cleavage of the methoxy group. Wang et al. developed a carbon felt-supported ternary RhPtRu catalyst for the selective ECH of guaiacol, achieving a faradaic efficiency (FE) of up to 62.8% and 91.2% selectivity toward methoxy-cyclohexane derivatives.¹³¹ This excellent performance is attributed to the strong inhibition of C–OCH₃ bond cleavage. Similarly, Peng et al. developed a ternary PtRhAu electrocatalyst that enables highly efficient and selective conversion of guaiacol to 2-methoxycyclohexanol (Fig. 8d).¹²⁸ The incorporation of Rh and Au modulates the electronic structure of Pt, optimizing the energetic pathway of the reaction intermediates, and thereby facilitating hydrogenation while effectively suppressing C–OCH₃ bond cleavage. This catalyst achieved a faradaic efficiency of 58% at a current density of 200 mA cm⁻². Moreover, Peng et al. developed a flow-cell system with a highly electrolyte-permeable rhodium (Rh) diffusion electrode, enabling the efficient electrocatalytic hydrogenation of lignin monomers and furans (Fig. 8e).¹²⁹ The system achieved a faradaic efficiency of up to 64% at an industrially relevant current density of 500 mA cm⁻². In situ infrared reflection-absorption spectroscopy revealed electrode potential-dependent reaction pathways and intermediates, indicating a broad potential window for the hydrogenation of lignin-derived aromatic compounds.

4.2 Conversion of cellulose and its derivatives

4.2.1 Electrocatalytic oxidation of glucose. Glucose, a six-carbon polyhydroxy aldehyde derived from cellulose hydrolysis, is rich in functional groups and features an extended carbon backbone, enabling diverse reaction pathways and the formation of complex oxidation products. Under electrocatalytic oxidation conditions, it can be selectively converted into value-added compounds such as gluconic acid (GNA), glucaric acid (GRA), and formic acid through C–C bond cleavage. GNA and GRA are important products formed via non-C–C bond cleavage reactions during the electrocatalytic oxidation of glucose, and they are widely used in metal complexation agents and healthcare applications. Liu et al. reported that NiFe oxide (NiFeOx) catalysts supported on nickel foam enable the selective electrooxidation of glucose at terminal hydroxyl and aldehyde groups, affording GRA (Fig. 9a).¹³² By coupling glucose oxidation with the HER, the assembled electrolyzer achieved a current density of 100 mA cm⁻² at 1.39 V, with a faradaic efficiency of 87% and a GRA yield of 83%. To reduce energy input, Zhang et al. developed a mediated electrooxidation strategy using the Cu(I)/Cu(II) redox couple as an intermediate (Fig. 9b).¹³³ In this system, Cu(OH)₂ is chemically regenerated via the reduction of Cu(II) by glucose, exploiting the reducing nature of its aldehyde group. Cu(I) is electrochemically oxidized to Cu(II) at a low onset potential of 0.7 V_RHE, and the resulting Cu(II) species selectively oxidizes glucose to GNA, completing the redox cycle with a faradaic efficiency up to 98.7%. Recently, Bitter et al. investigated the effect of Pt oxidation states on the product selectivity of glucose electrooxidation (Fig. 9c).¹³⁴ They found that metallic Pt⁰, dominant at low potentials (<0.8 V_RHE), promotes the dehydrogenation of primary hydroxyl groups to form glucose dialdehyde, whereas oxidized Pt (PtO_x), formed at higher potentials (>1 V_RHE), favors aldehyde group oxidation, yielding GNA.

Fig. 9 (a) Selective electrocatalytic oxidation of glucose to GRA using NiFeOx catalysts, reproduced from ref. 132 with permission from Springer Nature,¹³² copyright 2020. (b) Electrocatalytic oxidation of glucose to GNA using the Cu(I)/Cu(II) redox couple, with chemical regeneration of Cu(OH)₂ and low onset potential, reproduced from ref. 133 with permission from Wiley-VCH,¹³³ copyright 2021. (c) Electrocatalytic oxidation of glucose over Pt, where metallic Pt⁰ dominant at low potentials favors glucose dialdehyde formation, while oxidized Pt (PtO_x) formed at higher potentials promotes aldehyde oxidation to GNA, reproduced from ref. 134 with permission from Wiley-VCH,¹³⁴ copyright 2023.

In addition, glucose can undergo electrochemical oxidation accompanied by C–C bond cleavage to produce formic acid (FA), as shown in Fig. 10a, during which arabinose, erythrose, glyceraldehyde, and glycolaldehyde are generated as intermediates in sequence. Ni- and Co-based catalysts have garnered significant attention due to their excellent activity in facilitating this transformation. Wang's group developed a NiCoP catalyst supported on Ni foam, which undergoes in situ reconstruction to form a NiCoOOH/NiCoP heterointerface during electrolysis (Fig. 10b).¹³⁵ In this structure, NiCoOOH provides the active sites for glucose oxidation into FA, while NiCoP ensures efficient electron transport. This system achieved an 85% yield of formic acid at a current density of 200 mA cm⁻² under an applied potential of 1.47 V_RHE. To further reduce the operating potential, Chen et al. synthesized a NiCuO catalyst derived from a NiCu alloy, which exhibited a faradaic efficiency of 94.6% and a selectivity of 93.3% at a lower potential of 1.29 V (Fig. 10c).¹³⁶ DFT calculations revealed that Cu incorporation increases the electron density around Ni and optimizes the d-band center, thereby enhancing intermediate adsorption and catalytic conversion. Heterostructure engineering has also proved effective in improving catalytic performance. Zhang's team constructed a porous NiO/NiCo₂O₄ nanowire array, which benefits from a high surface area, rapid mass transport, and interfacial synergism between the two components (Fig. 10d).¹³⁷ These features significantly promoted both glucose oxidation and the HER. Duan et al. employed CoOOH as the catalyst and used DFT to elucidate the mechanism of C–C bond cleavage (Fig. 10e).¹³⁸ The results indicated that μ₁-OH-Co³⁺ species are responsible for oxidizing aldehyde groups to form formic acid, while μ₂-O-Co³⁺ species facilitate dehydrogenation at the α-hydroxyl site. Ma's group synthesized ultrathin Ni–O–Co nanosheets via a Cl⁻-corrosion and calcination method. The material exhibits a high density of exposed active sites, Co²⁺-mediated electron transfer through μ-O bridges, and rapid formation of NiOOH species (Fig. 10f).¹³⁹ As a result, this catalyst achieved a current density exceeding 220 mA cm⁻² and a faradaic efficiency greater than 90% at 1.4 V_RHE. Recently, we developed a highly efficient POM-based system for glucose oxidation to formic acid coupled with hydrogen production.¹⁴⁰ Glucose is selectively oxidized at the POM anode to formic acid, while hydrogen is continuously evolved at the cathode. The system operates at low energy input, enabling both POM regeneration and efficient hydrogen evolution at the cathode. Furthermore, the system maintains high performance under illumination and is applicable to a variety of biomass substrates, including fructose, maltose, starch, and cellulose.¹⁴¹

Fig. 10 (a) Electrocatalytic oxidation of glucose to FA via sequential intermediates including arabinose, erythrose, glyceraldehyde, and glycolaldehyde. Electrocatalytic C–C bond cleavage of glucose to FA using (b) NiCoOOH/NiCoP, reproduced from ref. 135 with permission from the American Chemical Society,¹³⁵ copyright 2024. (c) NiCuO, reproduced from ref. 136 with permission from Elsevier,¹³⁶ copyright 2024. (d) Porous NiO/NiCo₂O₄, reproduced from ref. 137 with permission from the Royal Society of Chemistry,¹³⁷ copyright 2024. (e) CoOOH, reproduced from ref. 138 with permission from Wiley-VCH,¹³⁸ copyright 2023. (f) Ni–O–Co nanosheets, reproduced from ref. 139 with permission from Elsevier,¹³⁹ copyright 2025.

4.2.2 Electrocatalytic oxidation of HMF. 5-Hydroxymethylfurfural (HMF), derived from the hydrolysis of cellulose, is an important platform molecule for the synthesis of value-added compounds in bioplastics, pharmaceuticals, and aviation fuels. Notably, the aldehyde and hydroxyl groups in HMF can be fully oxidized via electrocatalysis to yield 2,5-furandicarboxylic acid (FDCA), a crucial precursor for the production of biodegradable polyethylene furanoate (PEF) plastics. The electrocatalytic oxidation of HMF to FDCA generally proceeds through two possible pathways (Fig. 11a).^142–144 Under alkaline conditions, the reaction typically follows pathway II, where HMF is first oxidized to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), then further converted to 5-formyl-2-furancarboxylic acid (FFCA), and finally oxidized to FDCA. During the electrocatalytic oxidation of HMF, the competing OER significantly reduces the efficiency of HMF-to-FDCA conversion, especially under high current density conditions, thus representing a major bottleneck for industrial application. To address this challenge, Sun and colleagues employed a Ni–Cu bimetallic catalyst that effectively suppresses the OER, maintaining nearly 100% faradaic efficiency for FDCA at 1.5 V.¹⁴² Mechanistic studies revealed that the introduction of Cu inhibits the key dehydrogenation steps in the OER and lowers the energy barrier for the conversion of HMF to FDCA (Fig. 11b). To overcome the competitive adsorption between OH⁻ and HMF under alkaline conditions, Wang et al. designed an oxygen-vacancy-rich Co₃O₄ catalyst (Fig. 11c), enabling selective adsorption of HMF on Co sites while OH⁻ occupies the oxygen vacancies, thereby markedly enhancing the catalytic efficiency.¹⁴⁴ In addition, Shi et al. fabricated Cu foam decorated with Cu(OH)₂ as an efficient electrocatalyst for the selective oxidation of HMF to FDCA over a wide potential window, achieving nearly 100% faradaic efficiency and a 98.7% FDCA yield.¹⁴⁵ Electrochemical analyses revealed that in situ-generated CuOOH species serve as the primary active sites for HMF oxidation. Furthermore, the incorporation of sulfate ions (SO₄²⁻) into CuO can lower the onset potential for HMF oxidation and enhance the catalytic activity of CuOOH (Fig. 11d), thereby improving the performance of HMF conversion to FDCA.¹⁴³ The structure and properties of catalyst play a crucial role in enhancing HMF electrooxidation. Poerwoprajitno et al. significantly improved HMF oxidation activity by tuning the facet ratio of Ni dendrites.¹⁴⁶ Similarly, Wang's group increased the number of active sites and adsorption capacity by incorporating Cu to form a CuCo₂O₄ spinel structure, which effectively increased the Co³⁺ active sites and boosted FDCA yield by fourfold compared to pure Co₃O₄.¹⁴⁷ Yan et al. constructed a symmetric HMF electrolysis system utilizing single-atom Ru anchored on Co(OH)₂ (Ru SAs/Co(OH)₂). Driven by Ru-N₄ sites that promote d–p orbital hybridization and lower the activation energy of the C=O bond, this system attained a remarkable combined yield of 177.7% (FDCA 92.3% + DHMF 85.4%) in a flow cell. Notably, it demonstrated industrial-grade stability exceeding 240 hours, far surpassing conventional systems (<50 h). TEA estimates a revenue of 5812.4 USD per ton of FDCA, highlighting the system's exceptional durability and economic potential.¹³ Duan et al. developed a single-pass continuous-flow reactor (SPCFR) that combines short residence time with segregated substrate feeding (Fig. 11e), achieving a high HMF conversion of 95.8% and FDCA selectivity of 96.9%, along with successful kilogram-scale electrochemical synthesis of FDCA.¹⁴⁸

Fig. 11 (a) The two predominant pathways for the electrocatalytic oxidation of HMF. Electrocatalytic oxidation of HMF using (b) Ni–Cu bimetallic catalyst, reproduced from ref. 142 with permission from Wiley-VCH,¹⁴² copyright 2023. (c) LSV curves of Co₃O₄ and V₀-Co₃O₄ in 1 M KOH, with the inset showing the schematic illustration of V₀-Co₃O₄ catalyzing the conversion of HMF to FDCA, reproduced from ref. 144 with permission from Wiley-VCH,¹⁴⁴ copyright 2021. (d) Schematic diagram of HMF conversion to FDCA under a CuOOH-SO₄²⁻ catalytic system, reproduced from ref. 143 with permission from the American Chemical Society,¹⁴³ copyright 2023. (e) The SPCFR system developed, showing three key features that suppress non-faradaic degradation, enabling high selectivity towards target product and scalable synthesis at high concentrations, reproduced from ref. 148 with permission from Springer Nature,¹⁴⁸ copyright 2023. (f) Schematic of adsorption behaviors of –OH and –CHO groups during Cu³⁺-mediated indirect oxidation process and direct oxidation process, reproduced from ref. 149 with permission from Wiley-VCH,¹⁴⁹ copyright 2021.

Moreover, the aldehyde group in HMF can be oxidized to form HMFCA, which holds potential applications in pharmaceutical chemistry. However, the yield of HMFCA is typically low due to its tendency to undergo overoxidation to form FDCA. For example, Tong et al. employed copper oxide/hydroxide (CuO_xH_y) grown on copper foam as a model electrocatalyst to investigate potential-dependent product selectivity in the electro-oxidation of HMF (Fig. 11f).¹⁴⁹ At low potentials, the catalyst predominantly exists as CuO and catalyzes HMF electro-oxidation through a Cu²⁺-mediated direct surface electron-transfer pathway, which exhibits relatively low activity. Around 1.4 V, CuO is electrochemically converted to a Cu³⁺–OOH species, which acts as a chemical oxidant and mediates an indirect oxidation pathway that preferentially oxidizes aldehyde (–CHO) moieties over hydroxyl (–OH) groups. At approximately 1.5 V, a Cu³⁺-mediated direct electron-transfer mechanism becomes dominant, in which the high surface coverage of the catalyst predominantly hinders –CHO adsorption, whereas the increased potential mainly promotes –OH adsorption and subsequent oxidation, thereby reversing the selectivity. These findings demonstrate that varying the applied potential tunes the catalyst's active phase, reaction pathway, and adsorption properties, enabling selective oxidation for HMF to HMFCA. In order to enhance the selectivity of HMFCA, Wang and co-workers employed a Cu catalyst to achieve highly selective electrooxidation of HMF at a low potential (−0.4 V_RHE), with HMFCA as the sole liquid product and a current density exceeding 100 mA cm⁻².⁸⁶ In this system, –CHO in HMF undergoes selective oxidation via a single-electron transfer pathway. The key to this strategy lies in the fact that under alkaline and bias-free conditions, the C–H bond in the –CHO group can be effectively cleaved, a process significantly facilitated by metal catalysts such as Cu and Au. Based on this research, Fu et al. systematically elucidated the reaction mechanism of non-classical anodic hydrogen production during the low-potential electrooxidation of HMF to HMFDC by combining in situ spectroscopic techniques with DFT calculations.¹⁵⁰ The mechanistic study revealed that in alkaline media, HMF forms two interconvertible gem-diol intermediates: 5-(dihydroxymethyl)furan-2-methanol anion (DHMFM⁻) and its dianion (DHMFM²⁻) (Fig. 12a). DHMFM²⁻ undergoes oxidation via hydride (H⁻) transfer, producing hydrogen gas (H₂), whereas DHMFM⁻ is oxidized through proton (H⁺) transfer to generate water (H₂O). With increasing applied potential, the oxidation rate of DHMFM⁻ markedly increases, shifting the equilibrium toward DHMFM⁻ and consequently suppressing or terminating anodic hydrogen evolution. Despite these advances, achieving high catalytic efficiency at elevated potentials in the electrochemical synthesis of HMFDC from HMF remains a critical challenge. Thus, developing robust and efficient catalytic systems is essential for advancing industrial-scale applications.

Fig. 12 (a) Two pathways of the HMF oxidation reaction in alkaline medium via (i) DHMFM⁻ intermediate oxidation to produce HMFCA and H₂O, and (ii) DHMFM²⁻ intermediate oxidation to produce HMFCA and H₂, reproduced from ref. 150 with permission from Springer Nature,¹⁵⁰ copyright 2023. (b) Electrocatalytic oxidation of HMF to DFF using single-atom Ru-doped NiO catalyst, reproduced from ref. 151 with permission from Wiley-VCH,¹⁵¹ copyright 2022.

2,5-Diformylfuran (DFF) is also one of the key products derived from the electrochemical oxidation of HMF. However, under low-alkalinity conditions, DFF is more readily formed, which may be attributed to the preferential adsorption of the hydroxymethyl group in HMF on the catalyst surface. Nevertheless, the inherently low catalytic activity in such environments significantly limits the efficient production of DFF. Recently, Duan et al. conducted the electrooxidation of HMF in a neutral electrolyte using a single-atom Ru-doped NiO catalyst (Ru₁-NiO) (Fig. 12b). The results demonstrated that at a relatively low potential of 1.283 V and a current density of 10 mA cm⁻², a high selectivity of 90% toward DFF was achieved.¹⁵¹

4.2.3 Electrocatalytic hydrogenation of HMF. The electrocatalytic hydrogenation of HMF primarily involves three reaction pathways: reduction of the hydroxymethyl group, reduction of the aldehyde group, and transformations of the furan ring. Selective hydrogenation of the aldehyde group leads to the formation of 2,5-bis(hydroxymethyl)furan (DHMF), while simultaneous reduction of both functional groups can yield products such as 5-methylfurfuryl alcohol (MFA), 2,5-dimethylfuran (DMF), and hexane-1,2-diol (HD). Additionally, ring-opening reactions of the furan moiety may produce 2,5-hexanedione-1,6-diol (HHD).^152,153 The complexity and diversity of these reaction pathways significantly increase the challenge of controlling product selectivity. Moreover, the electroreduction kinetics of HMF are relatively slow and often accompanied by the formation of low-value byproducts, highlighting the urgent need to develop electrocatalysts that combine high activity with excellent selectivity for efficient and controllable conversion. During electroreduction, surface-adsorbed hydrogen atoms (H_ads) serve as the key active species in HMF electrocatalytic hydrogenation (ECH). The reaction mechanism and product distribution are strongly influenced by the solution pH, applied potential, and catalyst properties.^154,155 Yuan et al. systematically investigated the effect of pH on HMF electroreduction using Cu electrodes in conjunction with density functional theory (DFT) calculations, revealing fundamental mechanistic differences between hydrogenation and hydrogenolysis pathways (Fig. 13a).¹⁵⁶ Under neutral to mildly alkaline conditions (pH 7–9), the aldehyde group undergoes preferential hydrogenation, resulting in BHMF as the major product. In contrast, under acidic conditions, hydrogenolysis becomes dominant, favoring the formation of MF and subsequent conversion to DMF. Mechanistically, the transformation of HMF to MF and subsequently to DMF predominantly proceeds via a proton-coupled electron transfer (PCET) pathway, which is kinetically favored at high proton concentrations (low pH). Conversely, the hydrogenation of the aldehyde group to BHMF or MFA can occur via either PCET or hydrogen atom transfer (HAT). As HAT depends mainly on the surface coverage of H_ads, which is relatively insensitive to pH at a fixed potential versus the reversible hydrogen electrode (RHE), HAT-driven hydrogenation reactions remain efficient at elevated pH and thus dominate under such conditions.

Fig. 13 (a) Electrocatalytic reduction pathways and mechanisms of HMF on Cu electrodes, reproduced from ref. 156 with permission from Wiley-VCH,¹⁵⁶ copyright 2022. (b) Electrocatalytic reduction mechanism of HMF to DHMF on Ru₁Cu and Cu catalysts, reproduced from ref. 157 with permission from Wiley-VCH,¹⁵⁷ copyright 2022. Electrocatalytic (c) oxidation and (d) reduction mechanisms of HMF on Co₃O₄ catalysts, reproduced from ref. 158 with permission from Elsevier,¹⁵⁸ copyright 2023. (e) Electrocatalytic hydrogenation (ECH) pathways of HMF on Co₃O₄ nanocatalyst via a combined Langmuir–Hinshelwood (L–H) and proton-coupled electron transfer (PCET) mechanism, reproduced from ref. 159 with permission from Elsevier,¹⁵⁹ copyright 2023.

In addition, Li and co-workers developed a bimetallic AgCu nanoalloy catalyst supported on pyrolyzed alginic acid sodium (PA) for the efficient ECH of HMF to DHMF under mild conditions.¹⁶⁰ The Ag₁Cu₁/PA catalyst achieved a remarkable DHMF selectivity of 94%, with a conversion of 93.2% and a faradaic efficiency of 61.8%, significantly outperforming the monometallic Ag/PA catalyst. Mechanistically, H_ads were identified as the key reactive intermediates for proton-coupled electron transfer during HMF hydrogenation. The introduction of Cu into the Ag lattice enhanced electron conductivity and reduced the onset potential for ECH. Similarly, Ji et al. designed a Ru₁Cu single-atom alloy electrocatalyst for the efficient electrochemical reduction of HMF to DHMF.¹⁵⁷ This catalyst demonstrated significantly enhanced performance compared to pure Cu, achieving a high productivity of 0.47 mmol cm⁻² h⁻¹ and a faradaic efficiency of 85.6%. Mechanistic studies indicated that the introduction of isolated Ru atoms effectively promotes water dissociation, generating a higher coverage of H_ads, which in turn accelerates the selective hydrogenation of HMF (Fig. 13b). In order to increase the utilization rate of HMF, Liu et al. developed an oxide-derived silver (OD-Ag) electrode that enables highly selective (up to 98.2%) electrocatalytic hydrogenation of HMF to BHMF in a three-electrode flow cell, exhibiting excellent operational stability. When paired with the anodic electrooxidation of HMF to FDCA, the system achieved a combined faradaic efficiency of up to 163%.¹⁶¹ Cu-based and Ag-based catalysts have demonstrated excellent performance in the ECH of HMF. Numerous studies on similar catalytic systems have been reported.

Ni-based and Co-based catalysts also demonstrate excellent catalytic performance in the ECH of HMF. For example, Pan et al. developed a paired electrolysis system using a self-supported ultrathin Co₃O₄ nanowire catalyst for the efficient conversion of HMF.¹⁵⁸ The system simultaneously produces FDCA at the anode and DHMF at the cathode with high selectivity and yields (95.7% FDCA, 78.8% DHMF) without external hydrogen or oxygen. The coupled anodic oxidation and cathodic reduction enable efficient electron use, achieving a total faradaic efficiency of 127%. The mechanism results indicate that a Co³⁺/Co⁴⁺ valence cycle occurs during the catalytic oxidation of HMF over Co₃O₄ (Fig. 13c). Co³⁺ is first oxidized to Co⁴⁺ under a positive potential, and the high-valence Co⁴⁺ abstracts protons and electrons from the hydrated aldehyde group to form HMFCA, subsequently oxidizing the hydroxyl group to an aldehyde to generate FFCA, and ultimately producing FDCA. OH⁻ facilitates both the oxidation of Co₃O₄ and the hydration of HMF, thereby accelerating the reaction kinetics. During the cathodic reduction (Fig. 13d), Co₃O₄ is first reduced to low-valence Co(OH)₂, generating H_ads on its surface. Adsorbed HMF undergoes PCET to form a ketyl radical, which is further reduced by H* or another PCET step to yield DHMF. PBS serves as the proton donor, and the concurrent HER indicates the involvement of adsorbed hydrogen in the reduction process. Furthermore, they focused on exploring the hydrogenation mechanism of HMF on the Co₃O₄ nanocatalyst,¹⁵⁹ proposing that the buffer-promoted electrocatalytic hydrogenation (ECH) of HMF likely follows a combined Langmuir–Hinshelwood (L–H) and PCET mechanism (Fig. 13e). Under a negative potential, Co₃O₄ is reduced to Co(OH)₂, generating H_ads on the electrode surface, accompanied by H₂ evolution (steps 1–2). HMF then undergoes carbonyl protonation or forms a stable donor–acceptor complex (step 3), after which an electron attacks the carbonyl carbon and H_ads is added to complete the hydrogenation (step 4). Due to differences in proton-donating abilities among buffer salts, the rate-determining steps are step 4 for phosphate, step 2 for borate, and step 3 for carbonate systems.

4.3 Conversion of furfural

4.3.1 Electrooxidation of furfural. Furfural (FF), a key platform molecule obtained from the acid-catalyzed dehydration of pentoses (C₅ sugars) derived from hemicellulose hydrolysis, can be electrochemically transformed into a range of valuable products, including furfuryl alcohol (FFA), 2-methylfuran (2-MF), 2-furoic acid (2-FA), and tetrahydrofurfuryl alcohol (THFA). These derivatives serve important functions as biofuels, chemical intermediates, solvents, and other high-value chemicals.

2-FA is a key oxidation product of FF and serves as a valuable precursor for organic synthesis, pharmaceuticals, and fragrances.¹⁶² Although the traditional Cannizzaro reaction can produce 2-FA, it is limited by low yields and harsh reaction conditions.¹⁶³ By contrast, electrochemical oxidation provides a green and sustainable alternative, allowing selective two-electron oxidation at ambient temperature using water as the oxidant. Notably, catalysts based on Au, Ni, and Cu have demonstrated excellent selectivity toward 2-FA.^163,164 Holewinski et al. systematically investigated FF oxidation on Pt/C electrodes and found that product selectivity strongly depends on the applied potential (Fig. 14a): at 0.9–1.0 V, 2-FA predominates; at 1.1 V, 5-hydroxyfuroic acid (5-HFA) becomes dominant; and at potentials above 1.2 V, 5-hydroxy-2(5H)-furanone and maleic acid (MA) are the main products.¹⁶⁵ To reduce the dependence on electrode potential, Lin et al. introduced 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as a redox mediator, as shown in Fig. 14b, achieving simultaneous anodic and cathodic conversion of FF to 2-FA with an overall faradaic efficiency of 127.1%, effectively suppressing side reactions such as hydrogen and oxygen evolution.¹⁶⁶ Similarly, Banat et al. developed Ru/reduced graphene oxide (Ru/RGO) nanocatalysts that enabled concurrent anodic and cathodic conversion of FF, generating FFA and 2-MF at the cathode and 2-FA and 5-hydroxyfuroic acid at the anode.¹⁶⁷ Despite the excellent performance of noble metal catalysts in FF electrooxidation, their high cost and limited availability constrain large-scale application. To address this, Wang et al. developed a low-potential anodic aldehyde oxidation system coupled with cathodic H₂ evolution, operating at merely 0.1 V.¹⁶⁸ In this system, the low-potential oxidation of aldehydes to acids allows hydrogen atoms to recombine into H₂ rather than forming H₂O, with an energy consumption of only 0.35 kWh m⁻³, substantially lower than conventional water electrolysis. Subsequently, a Cu/Cu foam anode system was developed to simultaneously upgrade FF, generate H₂, and harvest electric energy, efficiently producing 2-FA and rapidly releasing H₂ near 0 V, where the low potential and Cu metal serve as critical factors (Fig. 14c).¹⁶⁹

Fig. 14 (a) Proposed reaction mechanism for the electro-oxidation of FF on Pt under different applied potentials, reproduced from ref. 165 with permission from the American Chemical Society,¹⁶⁵ copyright 2019. (b) Schematic diagram of FF to 2-FA mediated by TEMPO⁺/TEMPO, reproduced from ref. 166 with permission from Springer Nature,¹⁶⁶ copyright 2022. (c) The electricity output mode developed in Wang's study. Left: configuration of a single cell; right: polarization curves of the corresponding half-reactions, reproduced from ref. 169 with permission from Wiley-VCH,¹⁶⁹ copyright 2021.

Maleic acid (MA) is an important chemical intermediate used in resins, lubricating additives, plasticizers, coatings, and pharmaceuticals,¹⁷⁰ and its efficient production is highly desirable for the chemical industry. Recently, electrochemical oxidation of FF has emerged as a green route for MA synthesis. Kyoung-Shin Choi et al. proposed a novel electrochemical strategy employing PbO₂ as the anode material.¹⁷¹ This system efficiently oxidizes FF while suppressing competing water oxidation, achieving a high MA yield of 65.1%.

4.3.2 Electrocatalytic hydrogenation of furfural. Furfuryl alcohol (FFA) is the most common reduction product of FF and finds broad applications in dispersants, thermosetting resins, acid-resistant bricks, lubricants, and plasticizers. Therefore, efficient conversion of FF to FFA is of significant importance for biomass valorization.^172,173 Traditional hydrogenation methods rely on metal catalysts such as Cu, Ni and Pt under high temperature and pressure (2–8 MPa H₂, 150–200 °C), which involve potential safety risks.^174,175 In contrast, electrochemical hydrogenation enables the upgrading of FF to FFA under ambient conditions without the need for external H₂.¹⁷⁶ In the electrocatalytic reduction of FF to FFA, copper-based catalysts—including nanocrystalline and nanoporous structures—exhibit excellent performance, achieving high selectivity and faradaic efficiency.^177,178 In particular, CuO nanowires containing metallic Cu (Cu⁰) facilitate FFA desorption (Fig. 15a), synergistically enhancing electrochemical hydrogenation and achieving 91.5% FF conversion with 100% selectivity toward FFA.¹⁷⁹ The performance of copper-based catalysts can be further enhanced via surface engineering. For example, O₂ plasma treatment of Cu to produce OP-Cu introduces CuO_x sites, which improve reaction kinetics and increase defect density, leading to a faradaic efficiency of 91% for FFA at −0.56 V.¹⁸⁰ The catalytic performance of Cu can also be enhanced through heteroatom or active atom doping. Wang et al. demonstrated that P-doped Cu₃P increases hydrogen coverage while suppressing H₂ desorption, as shown in Fig. 15b, achieving 100% selectivity toward FFA and a faradaic efficiency of 98%.¹⁸¹ Similarly, Ag-modified Cu nanowire arrays (Ag@Cu NWAs/CF) leverage Cu–Ag synergistic effects to attain high FF conversion (99.6%), FFA selectivity (96.6%), and faradaic efficiency (96.1%) (Fig. 15c).¹⁸² Anions have a significant impact on the electrochemical hydrogenation of furfural. Zou and co-workers investigated the effect of KHCO₃ and phosphate-buffered saline (PBS) on FF electrochemical hydrogenation over a Cu catalyst.¹⁸³In situ spectroscopy and molecular dynamics (MD) simulations revealed that bicarbonate ions reside in the first solvation shell of furfural and form strong hydrogen bonds (Fig. 15d), whereas phosphate ions are located only in the second solvation shell, resulting in weaker hydrogen-bond interactions. Consequently, FF adopts a parallel adsorption configuration on the electrode surface in KHCO₃, leading to carbonyl activation and accelerated ECH kinetics toward FFA. In contrast, in PBS, carbonyl activation is suppressed, resulting in slower ECH and a severe competing hydrogen evolution reaction. Recently, Wan and co-workers effectively regulated the electrochemical reduction (ECR) mechanism of furfural by introducing cerium oxide components into copper-based catalysts.¹⁸⁴ The resulting Cu/CeO₂ system exhibited excellent electrocatalytic performance in a flow-cell reactor, achieving a faradaic efficiency of 97 ± 1% and a conversion rate of 19.1 ± 0.4 mol h⁻¹ m⁻² at a partial current density of 0.1 A cm⁻². Mechanistic investigations revealed that the Cu/CeO₂ interface alters the ECR pathway of furfural from the conventional proton-coupled electron transfer (PCET) mechanism observed on pure Cu catalysts to an electrochemical hydrogen atom transfer (HAT) mechanism, thereby enabling the highly efficient and selective conversion of furfural to a single product, furfuryl alcohol (Fig. 15e). In addition, non-noble catalysts such as MoS₂ can accelerate the Langmuir–Hinshelwood surface reaction by enhancing H_ads and FF adsorption at edge sites, achieving FF conversion to FFA with high faradaic efficiencies of 73.3–86.3% and outstanding selectivity above 95%.¹⁸⁵ Moreover, different MoS₂ phases (2H and 1T) exhibit distinct pathway preferences: the 1T phase favors FFA formation (selectivity 94.4%), while the 2H phase tends to promote furan radical dimerization to HFN (selectivity 42.7%) (Fig. 15f).¹⁸⁶ Noble-metal catalysts also exhibit outstanding performance in the electrochemical hydrogenation of FF. Li et al. investigated the hydrogenation mechanism of FF on Pb electrodes by modulating the local environment, including H₃O⁺, H₂O and H/D ratio.¹⁸⁷ They found that the proton source critically controls the pathway selectivity: FFA is formed via hydrogenation following a Langmuir–Hinshelwood mechanism, involving the coupling of adsorbed FF and surface H atoms, whereas 2-MF is produced via hydrogenolysis following an Eley–Rideal mechanism, in which adsorbed FF reacts directly with solution-phase protons.

Fig. 15 (a) Schematic illustration of FFA desorption promoted by the Cu⁰ catalyst, reproduced from ref. 179 with permission from Springer Nature,¹⁷⁹ copyright 2022. (b) The schematics illustrating the electrocatalytic FHR and HER at the catalyst surface, reproduced from ref. 181 with permission from Elsevier,¹⁸¹ copyright 2019. (c) Schematic illustration of FF conversion on Ag@Cu NWAs/CF electrocatalyst, reproduced from ref. 182 with permission from Elsevier,¹⁸² copyright 2022. (d) Schematic of the anionic effect for inducing FF adsorption behaviors and carbonyl electrophilic activity change in KHCO₃ and PBS, reproduced from ref. 183 with permission from the American Chemical Society,¹⁸³ copyright 2024. (e) Proposed mechanism and the role of ceria in the electrocatalytic FF-to-FA valorization, reproduced from ref. 184 with permission from Springer Nature,¹⁸⁴ copyright 2025. (f) Tentative mechanism of structural phase-directed selectivity control on electrocatalytic reduction of FFL to FFA or HDF, reproduced from ref. 186 with permission from the American Chemical Society,¹⁸⁶ copyright 2022.

2-Methylfuran (2-MF) is another major reduction product of FF, typically formed via sequential hydrogenation of FF to FFA followed by C–O bond cleavage. Due to its higher octane number compared to gasoline and its utility as a high-value chemical intermediate, 2-MF has attracted attention as a potential biofuel.^188,189 Electrochemical reduction of FF to 2-MF is a four-electron process, with Cu-based catalysts being particularly promising due to their abundance and moderate competition from the hydrogen evolution reaction. Cu catalysts selectively generate 2-MF while suppressing the formation of pinacol byproducts.^190,191 Li et al. identified two mechanisms on Cu electrodes (Fig. 16a): electrocatalytic hydrogenation and direct electroreduction, producing FFA, 2-MF, and coupling products, with 2-MF formation dependent on H_ads at the electrode/electrolyte interface.¹⁹² Biddinger et al. demonstrated that electrolyte pH significantly affects product distribution: mild acidity favors FFA formation, while strong acidity accelerates side reactions (Fig. 16b). High selectivity can thus be achieved by tuning the FF concentration, electrolyte pH, and electrode potential.¹⁹³ Zhang et al. employed P-doped carbon-supported single-atom Cu catalysts (Cu/PC) to achieve efficient FF to 2-MF conversion under near-neutral conditions, with single-atom Cu suppressing HER and enhancing FFA adsorption, thereby promoting conversion to 2-MF.¹⁹⁴ Furthermore, the incorporation of Pd to form bimetallic CuPdx/C enhanced H_ads, modified the adsorption modes of FF, and lowered the hydrogenation barrier for the conversion of FurCH₂* to FurCH₃*, thereby significantly improving 2-MF selectivity (Fig. 16c). Under 0.1 M acetic acid (pH 2.9, −0.58 V) conditions, the faradaic efficiency and 2-MF yield reached 75% and 78%, respectively.¹⁹⁵

Fig. 16 (a) Schematic illustration of the direct electroreduction and electrocatalytic hydrogenation pathways of FF on a copper electrode, reproduced from ref. 192 with permission from Springer Nature,¹⁹² copyright 2022. (b) Schematic illustration of the reaction pathways of FF catalyzed by Cu electrocatalysts in different acidic electrolytes, reproduced from ref. 193 with permission from the American Chemical Society,¹⁹³ copyright 2016. (c) Gibbs free energy profile derived from DFT calculations for ECH of FF to FA or MF over Cu (111) and Cu₃Pd (111) surfaces, reproduced from ref. 195 with permission from Wiley-VCH,¹⁹⁵ copyright 2022. (d) Schematic illustration of the differences in surface catalytic reactions between Cu and Pb catalysts, reproduced from ref. 196 with permission from the American Chemical Society,¹⁹⁶ copyright 2020. (e) Schematic illustration of the green synthesis route for biomass-derived aviation fuels using FF as the substrate, reproduced from ref. 197 with permission from the Royal Society of Chemistry,¹⁹⁷ copyright 2020.

In electrochemical reductive coupling, FF can be converted into C₁₀–C₁₂ fuels, where ketyl radicals generated from the carbonyl group serve as key intermediates enabling C–C bond formation and molecular weight increase. Xu et al. investigated the electrochemical coupling of FF with benzaldehyde on Pb and Cu electrodes,¹⁹⁶ finding that Cu favors cross-coupling, whereas Pb promotes FF self-coupling to HFN (Fig. 16d). Sun and co-workers developed a catalyst-free aqueous dimerization approach on carbon electrodes (Fig. 16e), achieving 94% HFN yield and 93% faradaic efficiency.¹⁹⁷ High catalytic activity in flow electrolyzers suggests the potential for large-scale FF coupling. Tetrahydrofurfuryl alcohol (THFA), owing to its excellent compatibility and biodegradability, has emerged as a promising green solvent alternative.¹⁹⁸ Berlinguette et al. designed electrocatalytic Pd membrane reactors that enable selective electrocatalytic hydrogenation of FF under H₂-free conditions, producing THFA.¹⁹⁹ Protons generated at the Pt anode migrate to the Pd cathode, are reduced to adsorbed hydrogen, and permeate the Pd membrane to react with FF, achieving a two-step consecutive conversion: carbonyl hydrogenation to FFA, followed by furan-ring hydrogenation to THFA. Similarly, Schröder et al. demonstrated that the composition of Pd- and Pt-based catalysts strongly affects product selectivity: high Pd content favors furan-ring hydrogenation, whereas the addition of Pt facilitates THFA formation.²⁰⁰ Furthermore, compared with HCl electrolyte, the use of H₂SO₄ further enhances THFA selectivity.

In conclusion, the electrocatalytic conversion of lignocellulosic biomass enables selective upgrading into a wide range of valuable products, establishing it as a promising approach for sustainable green chemical manufacturing. However, the inherent structural complexity of biomass poses significant challenges to precise control over reaction pathways and product selectivity. Future research should prioritize unraveling the intricate relationships between biomass structure and electrocatalytic mechanisms, alongside the rational design of advanced catalysts and optimized reactor configurations. Moreover, integrating multiscale characterization techniques with computational modeling will deepen mechanistic insights, thereby accelerating the development of scalable, efficient, and customizable electrocatalytic biomass conversion technologies.

4.4 Techno-economic feasibility and environmental footprint of electrochemical routes

To comprehensively evaluate the state-of-the-art and industrial potential of converting biomass into high-value chemicals, we have summarized key performance indicators—including catalyst types, stability, electrolyzer configurations, and FE—across various substrates in electrocatalytic processes. As shown in Table 1, different catalytic systems exhibit significant variability. Biomass electrochemical conversion demonstrates path-dependent catalytic characteristics: oxidation pathways (e.g., lignin depolymerization, glucose and HMF oxidation) predominantly utilize non-noble metal catalysts (Ni, Co), exhibiting superior activity and FEs (>80%) in alkaline media. Conversely, hydrogenation pathways (e.g., furfural and HMF reduction) rely more heavily on Cu-based or noble metal (Pd, Pt, Ru) catalysts and often require acidic or buffered solutions to modulate product selectivity. Despite achieving high conversion rates in biomass electrocatalytic systems, catalyst stability remains a critical bottleneck restricting industrial application. The primary deactivation mechanisms are attributed to electrode surface coking/fouling caused by the polymerization of organic intermediates (specifically humin formation), oxidative leaching of active metals, and CO poisoning. To overcome mass transport limitations and economic constraints, reactor engineering is accelerating the transition from H-type cells to flow electrolyzers. This shift aims to significantly enhance current density and space–time yield, laying the foundation for reduced operating expenses (OPEX) and environmental footprints. However, commercial assessment necessitates constructing a quantitative mapping from “reactor performance” to “economic and environmental indicators”. TEA and LCA studies reveal the non-linear decisive roles of current density, component lifespan, and energy structure on final costs and carbon footprints. For instance, Ebrahimpourboura et al. comprehensively evaluated the feasibility of integrating a mediator-assisted electrocatalytic lignin valorization process into a corn stover biorefinery. In terms of LCA, this integrated process significantly reduced the environmental footprint; depending on the allocation method (e.g., economic or displacement), the global warming potential (GWP) of ethanol production decreased by 10% to 46% compared to traditional processes.²⁰¹ Regarding TEA, the project achieved a return on investment (ROI) of 12.71%. Notably, although the electrochemical reactor accounted for the majority of the capital expenditure (CAPEX, approx. 216 million USD), the unit was highly efficient, consuming only 3.5% of the total energy input. While the electrocatalytic oxidation of HMF to FDCA demonstrates excellent selectivity at the laboratory scale, its industrial potential has long lacked systematic quantitative assessment. Patel et al. assessed a 100-tonne per day FDCA electrocatalytic plant, finding that economic viability is highly dependent on technical parameters.²⁰² In the base scenario, the project was unprofitable (NPV −15.91 million USD), with production costs (1532 USD per tonne) slightly higher than its petroleum-based competitors. However, in an optimized scenario (current density 40 mA cm⁻², 15% reduction in HMF feedstock cost), costs dropped to 1047 USD per tonne, and NPV surged to 72.3 million. Cost breakdown analysis indicated that HMF feedstock accounts for 77% of the total, far exceeding electricity (14%). Environmentally, the electrocatalytic route reduced climate change indicators by approximately 40% compared to thermochemical processes; the electrolysis and purification steps contributed less than 5% to the footprint, with the main burden stemming from toxic solvents in upstream HMF production.

Table 1 Summary of the performance of representative catalysts for electrochemical conversion of biomass

		Catalyst	Catalyst stability	Deactivation mechanism	Electrolyzer types	Potential (V vs. RHE)	Electrolyte	Con. or yield (%)	FE (%)	Ref.
Conversion of lignin and its derivatives	Electrocatalytic depolymerization of lignin	Nickel foam	—	—	Undivided cell	1.425	1.0 KOH	17.5 (vanillin and syringaldehyde)	—	102
		Anode: Pb/PbO2	Anode: Pb/PbO2(10 h)	Lignin and its intermediates adsorb onto the electrode surface, occupying active sites	Undivided cell	≈3.34	1.0 NaOH	93.29% (lignin)	—	103
		Cathode: Cu/Ni–Mo–Co	Cathode: Cu/Ni–Mo–Co (15 h)
		P-doped CoMoO4 supported on nickel foam	5 cycles	Oxygen-induced peroxidation of P-doped CoMoO4	H-type cell	1.33	1.0 M KOH	99% (2-phenoxy-1-phenylethanol)	—	104
		4-Acetamido-TEMPO	—	—	Undivided cell	1.49	H2O/CH3CN (70/30) NaHCO3/Na2CO3 (pH 10)	30 wt% (monomeric aromatic compounds from oxidized lignin)	—	105
		5 wt% Pd/C	5 cycles	Decrease in Pd loading	H-type cell	≈−0.45	2.0 M HClO4 (perchloric acid) with 30 wt% isopropanol (IPA) as co-solvent	100	70	106
		CuO nanorods	—	—	Undivided cell	−0.4	NaHCO3 (pH:3–4)	95.3 (phenol)	—	107
								88.6 (benzyl alcohol)
		Ni(OH)2–V	25 cycles	—	Undivided cell	1.4	1.0 M KOH	Aromatic monomer yield: 14.24 wt% (real lignin)	63.8	108
		VO^2+/VO2^+	32 h	Active species disappeared	Liquid flow fuel cell	1.42	Anolyte: 4.0 M KOH (optimized, tested range 1–4 M).	51.9 (COD)	97	109
							Catholyte: 2.0 M H2SO4 containing 0.37 M (VO2)2SO4
		Pyrolytic carbon (glassy carbon)	—	—	Flow cell reactor	−0.39	1 mM potassium ferricyanide + 1 mM ferrocyanide in 1 M potassium chloride (KCl).	—	—	111
	Electrocatalytic oxidation of lignin monomers	MnCoOOH	200 h	—	Undivided cell and flow cell	1.45	1.0 M KOH	>99% yield (1-phenylethanol to benzoic acid)	—	116
		SDS-Ni(OH)2	20 h	—	Undivided cell	1.45	1.0 M KOH	92 (adipic acid)	93	117
		2% Cu-Ni(OH)2	32 h	The amorphization of the catalyst materials	Undivided cell	1.62	1.0 M KOH	86 (adipic acid)	—	118
		Co3O4/GDY	10 cycles	—	Undivided cell	1.5	1.0 M KOH	82 (adipic acid)	92	119
		Anode: Ti/PbO2 plate	10 h	The formation of a polymer film (poly-phenol) on the anode surface, which hinders electron transfer	Undivided cell	—	0.2 M H2SO4	98.5% (phenol conversion)	68.5	120
		Cathode: stainless steel plate (CuSO4 and CoSO4)
		Anode: FeRu/NHPC	90 h	—	H-type cell	0.9	0.5 M H2SO4	>99	98	123
		Cathode: NiPt/NHPC
		CuO	36 h	—	Undivided cell	1.25	1.0 M KOH	90 (cis,cis-muconic acid)	87	121
	Electrocatalytic hydrogenation of lignin	Ni/MoO2-Ov	5 cycles	—	H-type cell	−0.7	0.1 M H2SO4	95 (cyclohexanol)	53	124
		SiW12 + Pt/C	—	—	H-type cell	−0.26	0.1 SiW12	99 (phenol conversion)	>99	125
		PW12 + Pt/C	—	—	H-type cell	0.8	0.25 PW12 and NaBH4	99 (phenol conversion)	94.7	126
		Pt/C	5 h	—	Stirred slurry electrochemical reactor	−0.45 V	0.5 M H2SO4	77	82	127
		RhPtRu/carbon felt	40 h	—	H-type cell	−0.11	0.2 M HClO4	Selectivity: 91.2% (to methoxy-cyclohexanes)	62.8	131
		PtRhAu/carbon felt	60 h	—	H-type cell	−0.12	0.2 M HClO4	Conversion: 95% (guaiacol)	≈58	128
		Rh/CF	60 h	—	Flow cell	−0.16 to −1.36	0.2 M HClO4	Guaiacol conversion: 90%	64	129
								furfuryl alcohol (FA) conversion: 97%
Conversion of cellulose and its derivatives	Monomers electrocatalytic oxidation of glucose	NiFeOx	48 h	—	Two-electrode electrolytic cell (undivided)	1.35	1.0 M KOH	Glucaric acid yield: 83%	87	132
		Cu(OH)2/Cu2O	10 h	—	Flow cell electrolyzer	0.7	1.0 M KOH	Selectivity: ∼100% (to gluconic acid)	98.7	133
		Polycrystalline Pt electrode	6 h	Partial CO poisoning of Pt^0	Undivided cell	0.64 (Pt^0) or 1.2 (PtOx)	0.2 M PBS (phosphate buffer solution)	Pt^0: selectivity to glucose dialdehyde (23%)	100	134
								PtOx: selectivity to gluconate (91%)
		NiCoP/NF	8 cycles	—	Undivided cell	1.47	1.0 M KOH	FA yield: 85% (from glucose)	82	135
								74% (from mixed sugars)
		NiCuO	24 h	The depletion of glucose concentration	H-type cell	1.39	1.0 M KOH	77.2% (FA)	94.6	136
		NiO/NiCo2O4/NF	24 h	The change in substrate (glucose) concentration and pH value	Two-electrode electrolyzer	1.35 (500 mA cm^−2)	1.0 M KOH	72% (FA)	72	137
		CoOOH/CC	—	—	Undivided cell	1.3–1.7	1.0 M KOH	—	60–70	138
		NiCoO–NS/NF	50 h	—	Undivided cell	1.3	1.0 M KOH	95.56 (glucose conversion)	90	139
	Electrocatalytic oxidation of HMF	Ni–Cu/NF	70 cycles	—	Undivided cell	1.45	1.0 M KOH	99.51% (FDCA)	99.67	142
		CuOOH–SO4^2−	15 cycles	—	Undivided cell	1.35	1.0 M KOH	99.9% (FDCA)	99.9	143
		V0-Co3O4	—	—	Undivided cell	1.47	1.0 M KOH	91.9% (FDCA)	88.1	144
		CoOOH/NF	>100 h	—	Single-pass continuous flow reactor	1.5	1.0 M KOH	96.9% (FDCA)	95	148
		CuOxHy/Cu foam	10 cycles	—	Continuous-flow reactor	1.5	1.0 M KOH	Total yield: >98% (FDCA)	98	149
		Ru SAs/Co(OH)2	240 h	—	Symmetrical flow-cell reactor	1.8	Anolyte: 1.0 M KOH	FDCA 92.3%	123.5	13
							Catholyte: neutral PBS	DHMF 85.4%
		Ru SAs/Co(OH)2	7 cycles (56 h)	—	H-type cell	ECO:1.4	Anolyte: 1.0 M KOH	FDCA yield: 95.5%	146	13
						ECH: −0.4	Catholyte: neutral PBS	DHMF yield: 92.4%
		Au–Ni	—	—	Undivided cell	0.13 V–0.43 V	1.0 M KOH	Selectivity to HMFCA: >85%	100	150
		Ru1-NiO	—	—	Undivided cell	1.5	1.0 M PBS	42.5 (DFF)	70 (DFF)	151
								75.8 (FFCA; upon further oxidation)
	Electrocatalytic hydrogenation of HMF	Cu foam	—	—	H-type cell	−0.6	pH 4.5: 0.5 M acetate (CH3COONa-CH3COOH) + 0.5 M Na2SO4	40 (HMF conversion)	—	156
		Ag1Cu1/P	3 cycles	The formation of impurities (dimerization products of HMF) which can affect selectivity	H-type cell	−0.354	Catholyte: 0.05 M borate buffer (Na2B4O7) (pH 9.14)	93.2% (HMF conversion)	61.8	160
							Anolyte: 0.1 M KOH
		Ru1Cu SAA	10 cycles	—	Undivided cell	−0.3	0.5 M PBS	65.9 (HMF conversion)	87.5	157
		OD-Ag	3 h	—	Flow cell	−0.51	0.5 M borate buffer (pH 9.2)	90 (HMF conversion)	80	161
		Co3O4 on Ni foam	2 h	The reconstruction of Co3O4 to Co(OH)2	H-type cell	—	0.1 M phosphate	96 (HMF conversion)	80 (BHMF)	159
Conversion of furfural	Electrocatalytic oxidation of furfural	Pt/C	—	Surface poisoning by CO derived from spontaneous decarbonylation of furfural	Flow cell	0.9	0.25 M HClO4	Furoic acid	—	165
		Pt/C	—	Surface poisoning by CO derived from spontaneous decarbonylation of furfural	Flow cell	1.1	0.25 M HClO4	5-Hydroxyfuroic acid	—	165
		Pt/C	—	Surface poisoning by CO derived from spontaneous decarbonylation of furfural	Flow cell	1.2	0.25 M HClO4	5-Hydroxy-2(5H)-furanone and maleic acid	—	165
		PbO2 and TEMPO	100 cycles	—	Flow cell	3.08	0.1 M KOH + 2 mM TEMPO	99.3 (furoic acid)	98.6	166
		Ru/RGO nanocomposite	—	—	Paired electrolyzer	−1.07	2 M H2SO4	97 (cathode)	95	167
		Ru/RGO nanocomposite	—	—	Paired electrolyzer	1.82	1 M KOH	85 (anode)	81	167
		Cu	6 cycles	—	H-type cell	0	1 M KOH	93	100	169
		PbO2	—	—	Undivided cell	2	0.5 M H2SO4	72.6 (maleic acid)	42.2	171
	Electrocatalytic hydrogenation of furfural	CuO nanowires	7 cycles	—	Undivided cell	−0.2	1.0 M PBS	91.5	100	179
		Cu3P/CFC	3 cycles	—	H-type cell	−0.55	1 M KOH	100	98	181
		Ag@Cu NWAs/CF	6 cycles	—	H-type cell	−0.51	0.5 M borate buffer	99.6	96.1	182
		ED-Cu	7 cycles	—	Undivided cell	−0.4	1.0 M KHCO3	90	98	183
		Cu/a-CeO2−	20 cycles	—	H-type cell	−0.4 V	1 M KOH	97.6	97	184
		Cu/a-CeO2−	20 cycles	—	Continuous-flow electrolyzer	−0.5 V	1 M KOH	—	97	184
		MoS2	4 cycles	Slight surface oxidation	H-type cell	−0.65 V	0.05 M Na2B4O7	60	73.3	185
		1T-MoS2	3 cycles	—	H-type cell	−0.47	0.4 M borate buffer	98	30	186
		Cu	—	—	H-type cell	−0.55	0.5 M H2SO4	10	40 (furfuryl alcohol)	192
		Cu foil	—	The formation of solid degradation products (humins) that deposit on the electrode surface	H-type cell	−0.55	0.5 M H2SO4	20	40 (furfuryl alcohol)	193
		Cu1PC	6 cycles	—	H-type cell	−0.75	0.1 M acetate buffer solution	100	90 (furfuryl alcohol)	194
		Cu1PC	6 cycles	—	H-type cell	−0.9	0.1 M acetate buffer solution	100	60 (2-methylfuran)	194
		CuPd0.021/C	6 cycles	—	H-type cell	−0.58	0.1 M acetic acid	90	75 (2-methylfuran)	195
		Cu	—	—	Undivided cell	−0.5	0.25 M phosphate buffer	—	80	196
		Pd	—	—	Undivided cell	−0.3	0.25 M phosphate buffer	—	100	196
		Carbon paper	—	—	Undivided cell	−0.44	0.1 M KOH	94	93	197
		Carbon Paper	—	—	Flow cell	−2.1	0.1 M KOH	89	82	197
		Pd membrane catalyst	—	—	Electrocatalytic palladium membrane reactor	1	1 M H2SO4	100	—	199
		Pd : Pt on glassy carbon	—	Polymers/oligomers (humins) formed from furfural	H-type c ell	−50 mA cm^−2	0.5 M H2SO4	50	8	200

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Consequently, developing green upstream processes and improving current density are key to realizing industrialization. Currently, despite outstanding laboratory performance, techno-economic and life cycle assessments for actual industrial scenarios remain relatively scarce.

5. Conclusion and perspectives

In summary, this review systematically highlights recent advances in the electrochemical utilization of lignocellulosic biomass, focusing on pathways for electricity and hydrogen production as well as the synthesis of value-added chemicals. As a renewable and abundant resource, lignocellulosic biomass holds significant potential to replace conventional fossil fuels. However, its application in electrochemical systems remains at an early stage. Future research should focus on developing scalable, industrially viable, and integrated technologies, while gaining a deeper understanding of biomass structural characteristics and optimizing catalyst screening strategies, to enable efficient and sustainable electrochemical conversion of biomass. Our perspectives for future studies are outlined as follows:

5.1 Design of scalable reactors for industrial applications

In fundamental studies of biomass electrochemical conversion, small-scale reactors, such as undivided cells and H-type cells, are widely employed due to their operational simplicity and ease of performance evaluation. However, scaling these systems to pilot or industrial levels introduces significant challenges, including prevalent side reactions, increased solution resistance, elevated cell voltages, low current densities, and limited continuous operation. Recent advances in flow electrolyzers and membrane electrode assemblies (MEAs) have demonstrated the potential to achieve industrially relevant current densities at moderate cell voltages, enhance product yields, reduce energy consumption, and partially suppress side reactions. Nonetheless, several critical challenges remain: high flow rates, while beneficial for mass transport, can reduce single-pass conversion efficiency; gas evolution under high-current operation can disrupt substrate adsorption and compromise catalyst and membrane stability; and crossover of substrates and products diminishes yield and accelerates component degradation. To address these issues, future efforts should focus on optimizing electrode architecture and gas–liquid management, as well as developing membranes with high chemical and mechanical stability in organic media. Additionally, integrating process-scale modeling tools such as ASPEN and COMSOL can provide mechanistic insights and predictive guidance for the rational design and scale-up of high-performance, continuous-flow biomass electrochemical systems.

5.2 Development of biomass carbon electrodes for liquid flow fells

The integration of biomass with fuel cells offers promising opportunities for diversified utilization. Biomass can serve as an efficient fuel for power generation, be electrochemically converted into value-added chemicals, and facilitate green hydrogen production, thereby opening new avenues for the sustainable use of biomass resources and the advancement of fuel cell technologies. Currently, flow fells still rely heavily on coal- and petroleum-derived carbon electrodes, whose nonrenewable nature and high cost constrain large-scale applications. In contrast, biomass-derived carbon electrodes exhibit advantages such as renewability, structural tunability, and low environmental impact. They can maintain interconnected transport channels at the macroscopic scale to reduce flow resistance, while developing abundant hierarchical pores and active sites at the microscopic level, thus balancing mass transport and electrochemical reactivity. Although research in this area remains limited, the development of low-cost, high-performance biomass carbon materials and the optimization of structure–property relationships are expected to significantly reduce system costs and accelerate the construction of green, efficient energy systems.

5.3 Catalyst prediction and screening enabled by emerging technologies

Accurate catalyst prediction and efficient screening remain crucial for advancing the performance of biomass electrocatalytic conversion. DFT has been instrumental in elucidating reaction pathways, interfacial electronic structures, and energy barriers, providing fundamental guidance for catalyst design. However, DFT's reliance on idealized models limits its ability to fully capture real electrocatalytic environments, including solvent effects, interfacial electric fields, catalyst dynamics, and operational complexities, resulting in gaps between theory and experiment. Emerging data-driven approaches, such as machine learning (ML) and artificial intelligence (AI), offer effective solutions by enabling rapid property prediction through extensive catalyst databases and can further be applied to predict the cleavage patterns of C–C, C–O, and C–H bonds in biomass molecules. Integrating AI with automated experimentation allows the establishment of closed-loop optimization platforms, shifting catalyst development from empirical trial-and-error to intelligent design. By combining DFT mechanistic insights with AI predictive capabilities, the discovery of efficient, cost-effective catalysts can be accelerated, thereby facilitating the industrial-scale implementation of biomass electrocatalysis.

5.4 In-depth elucidation of reaction mechanisms

A fundamental understanding of biomass electro-conversion mechanisms is vital for rational catalyst design and reactor optimization. The intrinsic structural complexity and functional heterogeneity of biomass feedstocks give rise to multiple parallel and competing reaction pathways, yielding diverse products such as electricity, chemicals, and electrode materials. This complexity complicates the identification of key intermediates, rate-limiting steps, and active sites at the electrode–electrolyte interface. While some studies have investigated specific substrates or catalysts, a comprehensive theoretical framework encompassing diverse biomass types and catalytic conditions is lacking. There is an urgent need for systematic mechanistic investigations that combine representative model compounds with advanced in situ characterization techniques and theoretical simulations. In particular, the integration of data-driven ML approaches can overcome the limitations of conventional trial-and-error strategies, enabling more precise catalyst design and improved control over reaction pathways.

5.5 Separation and purification of electrocatalytic products

In the electrocatalytic upgrading of lignocellulosic biomass, product separation and purification are critical steps that determine the purity, quality, and overall economic efficiency of the process. However, current studies primarily focus on electrocatalytic performance, while the separation and purification of post-reaction mixtures have received limited attention. The major challenges lie in the typically low product concentration, as solubility limitations and side reactions often lead to highly diluted products, resulting in considerable energy and material consumption during downstream processing. In addition, the separation of target products from by-products remains difficult and requires exploiting physicochemical property differences such as boiling point, solubility, or molecular size to achieve efficient purification. Future efforts should focus on improving product concentration and developing highly selective reaction systems while integrating green separation technologies—such as membrane separation, extractive distillation, or in situ electrochemical separation—to reduce energy consumption and simplify purification procedures. Furthermore, establishing energy and techno-economic evaluation models for separation processes will be essential to guide process optimization, scale-up, and the sustainable industrial implementation of electrocatalytic lignocellulose conversion.

5.6 Safety protocols and device durability in industrial scale-up

The electrochemical conversion of biomass offers the notable advantage of mild reaction conditions; however, process safety and the long-term durability of electrochemical devices remain core prerequisites for its industrial implementation. Although lignocellulose itself is chemically inert, its bulk storage is susceptible to microbial fermentation, which can lead to spontaneous heating risks, while mechanical grinding generates fine organic particles, thereby introducing potential hazards of combustible dust. Furthermore, the long-term durability of electrochemical devices constitutes a critical bottleneck limiting the advancement of biomass electrochemical conversion. As comprehensively analyzed by Saji, the degradation of device components—particularly the corrosion of bipolar plates and current collectors, along with the instability of electrocatalysts—significantly shortens the operational lifespan of the systems.⁹² Notably, even in the absence of extreme thermal stress, continuous exposure to corrosive electrolytes and electric field environments markedly accelerates material degradation and failure. Therefore, the comprehensive and systematic assessment of process safety, as well as the development of high-performance, corrosion-resistant electrochemical devices, have become pivotal directions for the industrial progression of biomass electrochemical conversion.

5.7 Assessment and optimization of economic viability

Although lignocellulosic biomass is inherently carbon-neutral and environmentally advantageous, the electrochemical conversion process involves multiple energy-intensive steps, rendering the overall sustainability uncertain. Sole reliance on carbon neutrality is insufficient for comprehensive environmental evaluation. Conducting a rigorous life cycle assessment (LCA) is essential to quantify carbon footprints and environmental impacts throughout different process pathways and to develop a systematic cradle-to-grave evaluation framework. Concurrently, techno-economic analysis (TEA) is critical to assess process feasibility and competitiveness, considering cost-intensive stages such as feedstock pretreatment, catalyst use, and product separation. Sensitivity analyses addressing external factors like electricity pricing, feedstock availability, and market demands will guide optimization and commercialization strategies. Integrating LCA and TEA with robust experimental data and standardized evaluation methodologies will facilitate cross-comparisons and accelerate the deployment of sustainable biomass electrochemical conversion technologies.

Author contributions

Guohao Xu: conceptualization, investigation, methodology, data curation, visualization, writing – original draft, writing – review & editing. Xiaotong Chen: formal analysis, software, visualization, writing – review & editing. Weizhuo Xu: data curation, visualization, writing – review & editing. Qiujin Shi: supervision, validation, visualization, writing – review & editing. Yun Lu: supervision, validation, visualization, writing – review & editing. Wei Liu: project administration, resources, funding acquisition, supervision, validation, visualization, writing – review & editing.

Conflicts of interest

The authors declare no conflict of interest.

Data availability

Data availability is not applicable to this article as no new data were created or analyzed in this study.

Acknowledgements

The authors are grateful for financial support from the National Key Research and Development Program of China (No. 2023YFC3903000), the National Natural Science Foundation of China (No. 22278446 and No. U24A20490) and the Science and Technology Innovation Program of Hunan Province (No. 2024RC1010). The authors are also grateful for technical support from the High-Performance Computing Center of Central South University.

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