Catalyst design for electrochemical selective oxidation of aldehydes to carboxylic acids

Abstract

In the global carbon neutrality context, green hydrogen, a key carrier of clean energy, requires urgent breakthroughs in production technology. In water electrolysis, the high energy consumption and low efficiency of the oxygen evolution reaction (OER) at the anode severely limit overall energy conversion efficiency. The electrocatalytic selective oxidation of aldehydes shows potential to replace the OER due to its low thermodynamic potential and fast kinetics, and it can transform aldehydes into high-value carboxylic acids through precise catalyst control. This paper reviews catalyst design strategies for this process, focusing on reaction mechanisms, design principles, and structure–performance relationships. By analyzing the activation of C=O bonds and C–H bond cleavage kinetics, core design principles based on electronic structure regulation and synergistic effects are proposed, and a catalyst performance model is established using in situ characterization and theoretical calculations. This provides theoretical guidance for designing efficient catalysts and prospects for future research directions, such as non-precious metal catalyst development and complex reaction network regulation, offering new ideas for the industrial application of “green hydrogen–high-value chemicals” co-production technology.

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1. Introduction

Against the backdrop of global carbon neutrality strategies, green hydrogen, one of the most promising clean energy carriers, has become a research focus for the energy transition due to the urgent need for its efficient production technology.^1–6 Currently, water electrolysis based on proton exchange membranes (PEMs) and anion exchange membranes (AEMs) is the main way to produce green hydrogen.^7–12 However, both suffer from the high overpotential and slow kinetics of the oxygen evolution reaction (OER) at the anode; this limits the overall energy conversion efficiency.^13–18 Also, the OER's reliance on precious metal catalysts and its production of low-value oxygen further restrict the technology's economic viability.^19–24 Thus, developing efficient, low-energy-consumption anode replacement reactions has become a key research direction in hydrogen production via water electrolysis.^25–29

In electrocatalytic hybrid water electrolysis systems, utilizing biomass-derived aldehydes to replace the OER with selective oxidation demonstrates significant technical advantages.^30–34 This reaction exhibits a far lower thermodynamic potential and faster reaction kinetics compared to the OER.^35–39 Its core value lies in replacing the 4-electron process of the OER with a 2-electron transfer pathway (aldehyde → carboxylic acid), substantially reducing the theoretical electrolysis voltage.⁴⁰ The choice of electrocatalytic oxidation pathway has a decisive impact on the system voltage: the direct oxidation pathway (aldehyde → carboxylic acid), characterized by fewer electron transfers and a more controllable energy barrier, operates at a significantly lower voltage than both the indirect oxidation pathway (aldehyde → CO₂) and conventional OER.^41–47 This strategy not only significantly enhances energy utilization efficiency but also, through deep integration with the electrolyzer system, enables the simultaneous production of hydrogen at the cathode and high-value carboxylic acid products at the anode.^48,49 This synergy constructs an integrated “low-energy hydrogen production–biomass upgrading” system, opening a new pathway for the high-value valorization of biomass resources.^50–53

The key to achieving this technological approach lies in the design and optimization of catalysts.^54–56 The electro-catalytic oxidation of aldehyde molecules involves complex multi-electron transfer and proton-coupled reaction pathways, and selective control faces many challenges.^57–64 An ideal catalytic system needs to meet several key requirements at the same time: lowering the activation energy barriers of key steps thermodynamically; precisely controlling the selectivity of reaction pathways kinetically; and being able to adapt to long-term electrochemical operating conditions in terms of stability.^65–75 This necessitates a fundamental understanding of key scientific aspects, such as the electronic structure of active sites, their surface coordination environments, and the adsorption behavior of reaction intermediates, at the atomic scale.^76–78 Such insights are essential for guiding the development of catalysts that simultaneously meet the requirements of high efficiency, high selectivity, and high stability, thereby advancing the practical application of this integrated system.^79–82

This review systematically elaborates on the strategies for designing catalysts for the selective electrocatalytic oxidation of aldehydes to carboxylic acids, focusing on three key aspects: reaction mechanisms, catalyst design principles, and structure–activity relationships. In terms of reaction mechanisms, the multiple-electron transfer process in the electrocatalytic oxidation of aldehydes is thoroughly analyzed, revealing the crucial impact of C=O bond activation mechanisms and C–H bond cleavage kinetics on reaction selectivity. Regarding catalyst design, key technical strategies for electronic structure regulation and synergistic effects are proposed from the atomic scale to the macroscopic structure, as shown in Fig. 1. By integrating advanced in situ characterization techniques and theoretical computation methods, a quantitative correlation model between the electronic structure of catalysts, surface properties, and catalytic performance is established, providing significant theoretical guidance for the rational design of catalysts. Addressing the key challenges in current research, this paper further explores future research directions such as the development of non-precious metal catalysts and the regulation of complex reaction networks, offering innovative ideas for the industrial application of the “green hydrogen–high-value chemicals” co-production technology. This review, as shown in Fig. 2, not only constructs a systematic theoretical framework for the selective oxidation of aldehydes but also indicates the development direction for the practical application of electrocatalytic technology in energy conversion and the high-value utilization of biomass.

Fig. 1 A schematic diagram of catalyst design for the electrocatalytic selective oxidation of aldehydes to carboxylic acids, covering the two core design principles of electronic structure regulation and synergistic effects.

Fig. 2 Historical development of catalyst design for the electrocatalytic oxidation of aldehydes to carboxylic acids. Reproduced from refs. 126 and 89 with permission from John Wiley and Sons, copyright 2017, 2023. Reproduced from refs. 125, 115 and 123 with permission from the American Chemical Society, copyright 2016, 2021, 2025. Reproduced from ref. 120 with permission from Elsevier, copyright 2019. Reproduced from refs. 131 and 90 with permission from the Royal Society of Chemistry, copyright 2022, 2024.

2. Mechanism of electrocatalytic oxidation of aldehydes to carboxylic acids

The electrocatalytic selective oxidation of aldehydes to carboxylic acids follows a universal competing pathway regulation mechanism. The key lies in the precise design of the catalyst's surface/interface microenvironment to dynamically regulate competition between the direct oxidation pathway (generating carboxylic acid) and the indirect oxidation pathway (deep oxidation to CO₂).⁸³ In hybrid water electrolyzers, this reaction replaces the traditional OER at the anode, synergistically coupling with the cathodic hydrogen evolution reaction (HER) to enable a low-voltage-driven “aldehyde oxidation–hydrogen cogeneration” system. The ion transport properties of the electrolyzer (such as OH⁻ migration rate and proton transmembrane flux) directly influence the dynamic equilibrium of the reaction microenvironment by regulating the interfacial double-layer structure. As illustrated in Fig. 3, the competition between these two pathways is fundamentally determined by the adsorption strength of key intermediates, the distribution of reaction energy barriers, and the pH-modulated interfacial microenvironment. In alkaline media, OH⁻ promotes the deprotonation of *R–COOH to form easily desorbed R–COO⁻, while acidic conditions require the tendency for over-oxidation of the *R–CH(OH)₂ intermediate to be overcome. The membrane–electrode assembly (MEA) within the electrolyzer can directionally amplify the promotional role of OH⁻ or H⁺ for specific elementary steps—e.g., an AEM accelerates OH⁻ diffusion toward the anode to stabilize carboxylate, whereas a PEM efficiently scavenges H⁺ to suppress acid-catalyzed side reactions. The direct channel achieves high-yield synthesis by the fast desorption of the carboxylic acid precursor (*R–COOH) within an optimized adsorption-energy window, whereas the indirect channel is triggered by strongly bound *R–CO intermediates that undergo deep oxidation.

Fig. 3 Direct and indirect oxidation reaction pathways in the electrocatalytic selective oxidation of aldehydes to carboxylic acids.

The crux of their rivalry resides in the dynamic tuning of the adsorption–desorption balance: the pH environment reshapes the “volcano-type” optimum by altering the intermediate evolution trajectory. Alkaline conditions widen the optimal window, while acidic media must mitigate C–C cleavage risks during *R–CH(OH)₂ dehydration. During cell operation, the potential field distribution and current density across the anode and cathode jointly modulate the catalyst's d-band center in real time, dynamically sustaining an optimal adsorption energy via continual adjustment of metal–intermediate orbital hybridization—a prerequisite for retaining high selectivity at industrial current densities (>500 mA cm⁻²). C=O bond activation is the decisive mechanistic step. Surface active sites polarize the C=O bond through d–π hybridization, anchoring the O atom while suppressing C–C scission. The kinetics of adjacent C–H bond cleavage, governed by proton-coupled electron transfer (PCET), steer the reaction direction: alkaline media lower the barrier via OH⁻-assisted dehydrogenation, whereas acidic media rely on d-band-tuned suppression of radical side reactions. Flow-field engineering in the cell minimizes concentration polarization, ensuring that the local concentration of reactants at active sites satisfies the kinetic demands for ordered C–H bond scission and prevents pathway deviation at high current densities. This spatiotemporal synergy of bond-activation sequences and pH-dependent intermediate stability dictates the selective trajectory of the reaction. Over-strong adsorption drives *R–COOH toward deep oxidation, while overly weak adsorption cripples kinetics. The electrolyte environment further modulates the critical threshold of this balance by reconfiguring the EDL and interfacial electric-field strength. In hybrid cells, this threshold can be decoupled via a bipolar membrane (BPM): the anode compartment is kept acidic to optimize aldehyde adsorption, the cathode compartment alkaline to accelerate the HER, and the ionic interlayer delivers site-specific H⁺/OH⁻ via water dissociation, lifting the single-pH restriction on the adsorption window.

The electronic structure of the catalyst—particularly the d-band center—tunes the adsorption energy by modulating the hybridization between surface atomic orbitals and intermediate molecular orbitals, thereby suppressing poisoning species formation.⁸⁴ During cell operation, the potential-field distribution across the anode and cathode compartments, in concert with the local current density, jointly perturb the catalyst's d-band center. By continuously modulating the degree of metal–intermediate orbital hybridization, the system dynamically maintains the adsorption energy within an optimal window; this is the decisive factor for sustaining high selectivity at industrial current densities. Within this framework, C=O bond activation operates as the governing mechanism. Surface active sites polarize the C=O bond through d–π hybridization, anchoring the oxygen terminus while simultaneously suppressing C–C scission. The kinetics of adjacent C–H bond cleavage, steered by PCET, dictate the reaction trajectory: alkaline media lower the barrier via OH⁻-assisted dehydrogenation, whereas acidic regimes rely on d-band-center tuning to quench radical side reactions. Flow-field engineering in the electrolyzer enhances mass-transfer efficiency (e.g., by mitigating concentration polarization), ensuring that the local reactant concentration at active sites satisfies the kinetic requirements for ordered C–H bond scission and thereby preventing pathway deviation at elevated current densities. This spatiotemporal synergy of bond-activation sequences, integrated with pH-dependent control of intermediate stability, ultimately determines the selective pathway. Over-strong adsorption drives *R–COOH toward deep oxidation, whereas overly weak adsorption cripples kinetics. The electrolyte environment further modulates the critical threshold of this adsorption balance by reconfiguring the electric double-layer structure and interfacial electric-field strength. In a hybrid cell, this threshold is decoupled through a bipolar membrane (BPM): the anodic chamber is maintained under acidic conditions to optimize aldehyde adsorption, the cathodic chamber is rendered alkaline to accelerate HER, and the ionic interlayer supplies H⁺/OH⁻ via water dissociation. Thus, system-level constraints imposed by a single pH window on the adsorption-energy optimum are transcended.

3. Design principles for electrocatalysts in selective oxidation of aldehydes to carboxylic acids

Based on in-depth analysis of the reaction mechanism for the electrocatalytic oxidation of aldehydes to carboxylic acids, this section summarizes catalytic performance data from representative studies (including faradaic efficiency, product selectivity, and key reaction parameters). The results demonstrate that the selectivity of aldehyde oxidation reactions is synergistically regulated by multiple critical factors. Through analysis of typical catalyst systems, the following discussion elaborates on core design principles for selectivity regulation, focusing on optimization strategies for electronic structures of active sites and key parameters of synergistic effects.

3.1 Electronic structure modulation

3.1.1 Chemical states. Chemical valence modulation, as a core strategy for precisely designing electrocatalytic active interfaces, provides an atomic-level reaction pathway modulation paradigm for the selective oxidation of aldehydes to carboxylic acids by constructing a dynamic electronic synergy network among multivalent metal sites, as illustrated in Fig. 4. This strategy achieves a breakthrough in overcoming the activity–selectivity–stability trade-off limitations of conventional catalysts under industrial-grade current densities. It accomplishes this by precisely decoupling key elementary steps in multi-step reactions (e.g., adsorption activation, C–H bond cleavage, intermediate desorption) and directionally matching the electronic microenvironment requirements of each step.

Fig. 4 Schematic diagram of valence regulation for the electrocatalytic selective oxidation of aldehydes to carboxylic acids.

The chemical valence modulation strategy achieves dynamic optimization of reaction pathways and efficient regulation of product selectivity by precisely constructing electronic synergistic effects among multivalent active sites. As concluded from a comparison of catalyst performances for the selective oxidation of aldehydes to carboxylic acids via valence-state modulation listed in Table 1, copper-based bimetallic catalytic systems exhibit unique electronic synergies, as exemplified by representative systems such as formaldehyde, glucose, and furfural. In the cuprous oxide/copper foam heterostructure (Cu_xO@CF) developed by Pan et al. (Fig. 5a), the dual-valence Cu⁰ and Cu⁺ sites exhibit distinct roles: electron-rich Cu⁰ sites facilitate formaldehyde adsorption and activation by reducing the binding energy between the formaldehyde hydration intermediate (HOCH₂O*) and hydroxyl groups (OH) by 0.25 eV, while electron-deficient Cu⁺ sites directionally cleave C–H bonds via σ-bond orbital hybridization. This enables an industrial-grade current density of 165 mA cm⁻² at 0.35 V vs. RHE and nearly 100% faradaic efficiency for formic acid production (Fig. 5b and c).⁸⁵ This synergistic mechanism is further extended to the CuFe bimetallic system. The electron-donating properties of Fe dynamically suppress irreversible Cu²⁺ accumulation, and its p–d orbital hybridization reconstructs the interfacial electron cloud distribution, reducing the C–H bond dissociation energy barrier by 40%. This enables stable operation at 100 mA cm⁻² under an ultralow potential of 0.10 V vs. RHE, resolving the activity–stability trade-off.⁸⁶ Based on this electronic structure optimization strategy, an integrated anode aldehyde oxidation–cathode hydrogen evolution device achieves an industrial-grade current density of 500 mA cm⁻² at a cell voltage of 0.6 V while maintaining nearly 100% formic acid selectivity for 50 h.⁸⁷ Nitrogen doping expands the modulation dimensions through local electronic reconstruction. In the nitrogen-doped copper/cupric oxide/copper foam (N–Cu/Cu₂₊₁O/CF) system (Fig. 5e), nitrogen atoms occupy oxygen vacancies to form strong N–Cu interactions, enhancing charge transfer efficiency between Cu⁰ and Cu⁺ by 2.3-fold. This results in a 96.6% formaldehyde conversion rate at 0.125 V (Fig. 5d) and stabilizes the faradaic efficiency for formic acid above 99% by simultaneously promoting O–H bond dissociation in water molecules and C–H bond activation in formaldehyde (Fig. 5f).⁸⁸ These studies reveal the core role of chemical valence modulation: by designing dynamic electron transfer channels between multivalent sites, the electronic microenvironment on the catalyst surface is directionally regulated to achieve gradient matching of key intermediate adsorption barriers and synergistic optimization of reaction kinetics. This provides a universal paradigm for designing industrial-grade catalysts for directional aldehyde oxidation.

Fig. 5 (a) HRTEM image of Cu_xO@CF. (b) LSV curves of CF, Cu@CF, and Cu_xO@CF in 1 M KOH with 100 mM HCHO at a scan rate of 5 mV s⁻¹. (c) The faradaic efficiency of the FOR at different potentials. Reproduced from ref. 85 with permission from Elsevier, copyright 2023. (d) Comparison of the conversion and faradaic efficiency at various applied potentials. (e) TEM image of N–Cu/Cu₂₊₁O/CF. (f) Stability test of N–Cu/Cu₂₊₁O/CF. Reproduced from ref. 88 with permission from Elsevier, copyright 2023.

Table 1 Comparison of the performances of aldehyde electro-oxidation catalysts tuned by chemical valence modulation for selective carboxylic acid production

Electrocatalyst	Reactant	Product	Cell voltage	Faradaic efficiency	Yield	Ref.
CuxO@CF	Formaldehyde	Formic acid	0.35 VRHE	≈100%	≈100%	85
CuFe	Formaldehyde	Formic acid	0.6 V	≈100%	≈100%	86
N–Cu/Cu2+1O/CF	Formaldehyde	Formic acid	0.42 V	>99%	≈100%	88
Pt–PtOx	Glucose	Gluconic acid	1.2 VRHE	105%	91%	89
Cu3Ag7/CF	Formaldehyde	Formate	0.5 V	100%	100%	90
Cu3Ag7	Formaldehyde	Formate	0.6 V	100%	≈100%	91
H-PdCu Ans	Furfural	Furoic acid	0.1 VRHE	93.3%	—	92
Cu–Pt/Cu	Furfural	2-Furoic acid	0.6 V	>80%	≈100%	93
M-CATs	HMF	FDCA	1.42 V	>85%	>95%	94

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Electronic structure optimization of noble metals and bimetallic systems further validates the universality of multivalent division of labor in selective control. The dynamic valence reconstruction mechanism of Pt⁰–PtO_x revealed by van der Ham et al. for Pt-based catalysts (Fig. 6a) achieves spatiotemporal decoupling of reaction pathways through atomic-level oxidation state partitioning: metallic Pt⁰ selectively activates the lone pair electrons of the C₆–OH group in glucose via its high electron density, inducing dehydrogenation to form glucaric dialdehyde (23% yield at 0.64 V vs. RHE), while oxidized PtO_x drives terminal carboxylation through strong coordination of surface-adsorbed oxygen species (O*/OH*) with the C₁=O group, boosting the glucaric acid yield to 91% at 1.2 V vs. RHE (Fig. 6b and c).⁸⁹ This valence-dependent activation strategy is further refined in copper–silver bimetallic interfacial systems. Our team designed a Cu₃Ag₇/CF catalyst (Fig. 6d) by precisely tuning the Cu/Ag atomic ratio (3 : 7), creating a unique interfacial electronic structure in alkaline media. During the reaction, formaldehyde undergoes hydrated deprotonation to form the H₂C(OH)O* intermediate, which is anchored at synergistic adsorption sites formed by hybridization of Ag 4d and Cu 3d orbitals. The electron-deficient nature of Cu dominates C–H bond cleavage, while the electron-rich Ag surface promotes the hydrogen evolution reaction. This precise electronic division enables the system to drive an industrial-grade current density of 500 mA cm⁻² at a cell voltage of 0.5 V while achieving 100% formic acid selectivity and synergistic enhancement of hydrogen evolution (Fig. 6e and f), significantly outperforming conventional Ag catalysts.⁹⁰ Building on this, Jiang's team further optimized the intermediate adsorption strength through Cu–Ag interfacial engineering (Fig. 6g). Theoretical calculations demonstrate that interfacial charge redistribution reduces the binding energy between key intermediates and the catalyst surface, significantly lowering the energy barrier of the rate-determining step. This strategy achieves a breakthrough in maintaining 100% formate selectivity under a high current density of 500 mA cm⁻² at a working voltage of 0.60 V (Fig. 6h and i).⁹¹ These studies collectively confirm, through multidimensional electronic structure modulation, the synergistic advantages of bimetallic interfaces in promoting C–H bond activation and product selectivity control.

Fig. 6 (a) The role of Pt oxidation state on the activity and selectivity was elucidated for the electrocatalytic oxidation of glucose. (b) Blank LSV and LSV of 0.1 M glucose, 0.1 M gluconate, and 0.1 M glucuronate in 0.2 M PBS (pH = 7) on a polycrystalline Pt electrode recorded at a scan rate of 1 mV s⁻¹. The potential windows 0–0.85 V and >0.85 V vs. RHE correspond to Pt⁰ and PtO_x, respectively. (c) Cyclic voltammograms of polycrystalline Pt mesh electrode obtained under neutral conditions (0.2 M phosphate buffer) in an H-cell at 50 mV s⁻¹. Reproduced from ref. 89 with permission from Wiley, copyright 2023. (d) HRTEM image of the Cu₃Ag₇/CF electrocatalysts. (e) Yield of furfuryl alcohol and formate at different voltages. (f) Yield of furfuryl alcohol and formate at different current densities. Reproduced from ref. 90 with permission from the Royal Society of Chemistry, copyright 2024. (g) Electrocatalytic water reduction coupled with HCHO oxidation under alkaline conditions. (h) Faradaic efficiencies of H₂ and formate production for five consecutive 1 h controlled-current (150 mA) electrolysis cycles. (i) Chronopotentiometric curves for five consecutive controlled-current electrolysis cycles conducted at 100 and 500 mA cm⁻². Reproduced from ref. 91 with permission from Springer Nature, copyright 2023.

Structural confinement effects and d-band center modulation provide new dimensions for valence state partitioning. In the three-dimensional hollow palladium–copper alloy network (H-PdCu Ans) constructed via the Kirkendall effect, Cu doping induces electron transfer from Pd 4d orbitals to Cu 3d orbitals, resulting in a downshift of the Pd d-band center and a significant enhancement in electron transfer kinetics. This valence reconstruction accelerates the polarized activation of the C=O bond in furfural molecules, achieving simultaneous hydrogen production (5 mmol g⁻¹ h⁻¹ H₂ yield), 93.3% faradaic efficiency for furanoic acid (FA) synthesis, and 16.2 mW cm⁻² power output at an ultralow potential of 0.1 V vs. RHE.⁹² In CuPt nanodendrites prepared by galvanic replacement, the 2 nm Pt surface layer induces a downshift of the Pt d-band center through Cu–Pt interfacial electronic effects, significantly weakening the adsorption strength of intermediates such as HOCH₂O*. This enables a bipolar hydrogen production current density of 498 mA cm⁻² at 0.6 V with 80% faradaic efficiency, demonstrating the optimization capability of interfacial valence engineering on intermediate desorption kinetics.⁹³ In the conductive metal–organic framework (M-CAT) catalytic system, the reversible valence transition of the M–O₄ site (M = Co/Ni) (M(II)/M(III)) is the core mechanism for regulating reaction selectivity. The formation of the high-valence M(III) state induces a downward shift in the metal d-orbital energy level, significantly enhancing electronic coupling between the metal and π* orbital of the HMF aldehyde group (in situ infrared spectroscopy confirms a redshift in the C=O bond vibration frequency, Δν ≈ 82–88 cm⁻¹), thereby efficiently activating the C=O bond through enhanced Lewis acidity. Meanwhile, the spatial confinement effect of the MOF channels precisely guides the directional adsorption of the reactant onto the active center. This synergistic effect of valence-driven electronic structure optimization and geometric microenvironment regulation ultimately achieves the efficient conversion of HMF to FDCA (yield > 95%), providing a clear structural paradigm for the design of highly selective biomass electro-oxidation catalysts.⁹⁴ Future research should focus on in situ dynamic characterization techniques for atomic-level valence partitioning, combined with cross-scale theoretical simulations to elucidate the structure–activity relationships between multivalent synergy and reaction pathways. Additionally, reversible valence cycling strategies must be developed to overcome the activity–stability trade-off under industrial-grade current densities, providing universal electronic engineering paradigms for efficient conversion of complex aldehyde molecules.

3.1.2 Dynamic reconstruction. Dynamic reconstruction, through the self-adaptive structural changes to catalysts during the reaction process to regulate their electronic structures in real time, has become one of the key mechanisms for optimizing the selective electro-oxidation of aldehydes to carboxylic acids. Specifically, the active sites on the surface of the catalyst will undergo reversible structural transformations (such as changes in valence, surface reconstruction, or phase transformation) under reaction conditions. As shown in Fig. 7, this dynamic change can not only repair the deactivated sites due to deep oxidation or poisoning, but also precisely adjust the surface electronic structure according to the specific needs of the aldehyde oxidation reaction environment. As shown by the data in Table 2, the real-time optimization of the electronic structure directly affects the adsorption energy of key intermediates and the reaction pathways, thereby continuously maintaining the catalyst's high selectivity and high activity for the target carboxylic acid products. Therefore, dynamic reconstruction is not only self-adaptive behavior of the catalyst surface, but essentially a key way to achieve efficient electronic structure regulation. It provides an essential theoretical basis and design strategy for designing aldehyde electro-oxidation catalysts for carboxylic acids with high selectivity, high activity, and long-term stability.

Fig. 7 Schematic diagram of dynamic reconstruction regulating the selective electrocatalytic oxidation of aldehydes to carboxylic acids.

Table 2 Comparison of the performances of aldehyde electro-oxidation catalysts tuned by dynamic reconstruction modulation for selective carboxylic acid production

Electrocatalyst	Reactant	Product	Cell voltage	Faradaic efficiency	Yield	Ref.
PdCu	Formaldehyde	Formic acid	0.42 V	≈100%	≈100%	95
Cu2O	Formaldehyde	Formic acid	0.9 VRHE	>100%	9698 μmol cm^−2 h^−1	96
Ni(OH)2/NF	HMF	FDCA	1.39 VRHE	>94%	100%	97
NiNPs/GO–Ni-foam	HMF	FDCA	0.4 V	94.8 ± 4.8%	86.9 ± 4.1%	98
CoNiP-NIE	HMF	FDCA	1.46 VRHE	>82%	85.5 g h^−1 m^−2	100

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The core of the dynamic surface reconstruction mechanism lies in establishing a reversible redox cycling system, as exemplified by the palladium–copper (PdCu) bimetallic catalyst developed by Zou's team. Traditional Cu-based catalysts in low-potential aldehyde oxidation reactions (LP-AORs) exhibit a dynamic deactivation–reactivation cycle: Cu⁰ active sites oxidize to Cu⁺ oxides under high oxidative potentials, leading to deactivation, but can reversibly recover via non-electrochemical reduction. By introducing Pd, a unique self-reactivation cycle is constructed (Fig. 8a). In situ characterization reveals that at a low working potential of 0.42 V, Pd's d-band center modulation not only protects Cu sites from deep oxidation (maintaining a high current density of 400 mA cm⁻²) but also accelerates the non-electrochemical reduction of intermediates such as hydroperoxyl (*OOH) species. This enables the catalyst to remain stable during 120 h of continuous operation (Fig. 8b and c).⁹⁵ Such intermetallic electronic coupling achieves dynamic protection and regeneration of active sites, surpassing the stability limits of conventional Cu-based catalysts.

Fig. 8 (a) Catalyst evolution of the Cu catalyst and relationship between activity and valence in LP-AOR. (b) Energy barrier of the transition state of the non-electrochemical reaction on Cu and PdCu. (c) A comparison of the LSV of the bipolar H₂ production device and traditional water splitting device. The anodic electrolyte is 1 M KOH with 200 mM HCHO and the scan rate is 5 mV s⁻¹. Reproduced from ref. 95 with permission from Springer Nature, copyright 2024. (d) HRTEM image of Cu₂O. (e) The proportion of HCOOH from the EOD pathway and tandem reaction. (f) The faradaic efficiency of FOR/Cu₂O at various potentials for 1 h in the electrolyte containing 1 M KOH/HCHO, matched with the HER. Reproduced from ref. 96 with permission from the Royal Society of Chemistry, copyright 2023.

Particularly noteworthy is the Cu₂O system (Fig. 8d), which demonstrates a more sophisticated self-renewal mechanism through the reversible valence state transition between Cu₂O and Cu(OH)₂. In alkaline media, the Cu₂O active center forms an intrinsic tandem reaction with formaldehyde molecules: Cu(OH)₂ generated under high potentials is spontaneously reduced and regenerated by formaldehyde molecules (Fig. 8e). This dynamic equilibrium maintains a formic acid production rate of 9.64 mmol cm⁻² h⁻¹ over a wide potential window of 0.9 V vs. RHE, achieving faradaic efficiencies exceeding 100% (Fig. 8f).⁹⁶ The dual role of surface-adsorbed OH⁻ species—serving as active sites for electrochemical oxidative dehydrogenation (EOD) while participating in the Cannizzaro reaction—further highlights the precise regulation of reaction pathways by dynamic reconstruction.

This self-healing capability enables catalysts to adapt to potential and temperature fluctuations under industrial-scale reaction conditions, as further validated for nickel-based catalysts. Ultrathin Ni(OH)₂ nanosheets grown on nickel foam (Ni(OH)₂/NF) (Fig. 9a) are transformed in situ into the highly active nickel oxyhydroxide (NiOOH) phase during reactions, achieving complete HMF conversion within 90 min at 1.39 V vs. RHE, with both FDCA yield and faradaic efficiency reaching 100% (Fig. 9b and c).⁹⁷ Klinyod et al. precisely regulated the NiOOH content on the surface of nickel nanoparticles/graphene oxide–nickel foam (NiNPs/GO–Ni foam) through electrochemical treatment, elevating the faradaic efficiency to 94.8%. Density functional theory (DFT) calculations confirmed that this dynamically generated NiOOH phase selectively drove HMF conversion to FDCA via the 5-hydroxymethylfuroic acid (HMFCA) pathway.⁹⁸ Notably, even after multiple catalytic cycles, the catalytic activity remains at its initial level as long as the NiOOH component on the electrocatalyst surface remains stable or retains its regenerative capacity.⁹⁹

Fig. 9 (a) SEM image of Ni(OH)₂/NF. (b) Plot of HMF conversion and product yields of Ni(OH)₂/NF against reaction time in 1.0 m KOH solution containing 10 mm HMF at 1.39 V vs. RHE. (c) FDCA yield and FE of Ni(OH)₂/NF during five successive reuse cycles. Reproduced from ref. 97 with permission from John Wiley and Sons, copyright 2021. (d) TEM and high-resolution TEM (HRTEM, inset) images of the CoNiP nanoarray. (e) Eight successive cycles at 1.50 V vs. RHE of CoNiP-NIE during HMFOR. (f) FE_FDCA and yields of CoNiP-NIE and CoNi-LDHNIE at different potentials. Reproduced from ref. 100 with permission from Elsevier, copyright 2022.

To address stability challenges in industrial applications, the cobalt–nickel phosphide (CoNiP) nanosheet-integrated electrode (CoNiP-NIE) designed by Shao's team elevates the dynamic reconstruction mechanism to new heights through the reversible transition between Co/Ni–OH and CoOOH/NiOOH oxidation states (Fig. 9d). This dynamic transition, supported by a three-dimensional conductive network, not only stabilizes the faradaic efficiency above 82% over a broad potential window of 1.40–1.70 V vs. RHE (reaching a peak of 87.2% at 1.50 V) but also limits efficiency decay to within 0.5% after eight cycles (Fig. 9e and f).¹⁰⁰ This exceptional stability not only resolves practical bottlenecks but also creates favorable conditions for achieving atomically precise relay catalysis. Future research could employ in situ characterization techniques to further unravel the critical conditions of dynamic reconstruction, establish quantitative structure–activity relationships between self-healing capacity and reaction selectivity, and ultimately realize the autonomous regulation of catalytic systems at the molecular scale.

3.1.3 Defect engineering. Defect engineering has emerged as a pivotal strategy for enhancing electrocatalytic aldehyde oxidation performance by modulating the electronic structure of catalysts, optimizing reaction pathways, and amplifying synergistic effects. As illustrated in Fig. 10, atomic-scale defect engineering enables the reshaping of coordination environments and charge distributions at active sites. Through precisely introducing specific types of crystalline defects and controlled oxygen vacancies, this approach creates distinctive active microenvironments that effectively regulate both the intensity and mode of interactions between reactant molecules and catalyst surfaces. Such a tailored design not only significantly reduces activation energy barriers for critical reaction steps but also achieves precise control over reaction pathways by optimizing the adsorption configurations of intermediates. A comparative overview of catalyst data for selective aldehyde-to-acid oxidation achieved via defect modulation is presented in Table 3. This strategy ultimately overcomes the selectivity limitations inherent to conventional catalysts with pristine crystalline structures.

Fig. 10 Schematic diagram of defect design regulating the selective oxidation of aldehydes to prepare carboxylic acids.

Table 3 Comparison of the performances of aldehyde electro-oxidation catalysts tuned by defect engineering modulation for selective carboxylic acid production

Electrocatalyst	Reactant	Product	Cell voltage	Faradaic efficiency	Yield	Ref.
CoOxHγ-MA	HMF	FDCA	1.52 V	83%	98%	101
NiFeOx/NiFeNx	Glucose	Gluconic acid	1.39 V	87%	83%	102

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The directional construction of oxygen vacancies introduces a localized electronic imbalance on the catalyst surface, and this unique electronic structure can effectively modulate the charge distribution of metal active centers. Oxygen vacancies can be introduced through reduction treatment, chemical etching, or topotactic transformation, all of which essentially alter the coordination state of metal centers by local atomic loss, inducing electronic redistribution. For example, CoO_xH_γ-MA nanosheets, through the synergistic reduction treatment of methylamine (MA) and sodium borohydride (NaBH₄, BH), form a high concentration of oxygen vacancies in the meso–microporous composite structure. X-ray photoelectron spectroscopy (XPS) characterization shows that after reduction treatment, the Co 2p binding energy shifts negatively by 0.1–0.2 eV, indicating that oxygen vacancies significantly increase the proportion of Co²⁺ and shift the electronic density towards the metal center (Fig. 11a); the enhanced electron paramagnetic resonance (EPR) signal further confirms the increased concentration of oxygen vacancies (Fig. 11b). This electronic state modification significantly reduces the adsorption energy of the HMF aldehyde group. Density functional theory (DFT) calculations confirm that oxygen vacancies preferentially stabilize the aldehyde oxidation intermediate, driving the reaction along the carboxylic acid formation pathway, ultimately achieving an FDCA yield of 98% and a faradaic efficiency of 83% at 1.52 V (Fig. 11c).¹⁰¹

Fig. 11 (a) XPS Co 2p spectra and (b) EPR signals against the g values of CoO_xH_y, CoO_xH_y-MA, CoO_xH_y BH, and CoO_xH_y-MA/BH. (c) The conversion of HMF and yields of oxidation products. Reproduced from ref. 101 with permission from the Royal Society of Chemistry, copyright 2023. (d) SEM images of the NiFeO_x-NF catalyst. (e) Concentration of glucose and oxidation products as a function of time for chronoamperometric tests at 1.30 V vs. RHE. (f) In situ ATR-FTIR spectra collected at potentials ranging from 1.0 to 1.6 V vs. RHE with steps of 100 mV. Reproduced from ref. 102 with permission from Springer Nature, copyright 2020.

In more complex multi-component systems, the combination of synergistic effects of defects and directional regulation of reaction pathways further highlights the universality of the design framework. The three-dimensional nickel foam-supported nickel iron oxide/nickel iron nitride (NiFeO_x/NiFeN_x) dual-catalyst system (Fig. 11d), through a topotactic transformation strategy, integrates oxygen-vacancy-rich NiFeO_x with nitrogen-doped NiFeN_x nanosheet arrays. Here, the oxygen vacancies in NiFeO_x enhance the adsorption and activation of C–H bonds in glucose molecules, while doping NiFeN_x with nitrogen induces charge redistribution, accelerating the interfacial electron transfer rate. The synergy between the two not only enables the electrolysis system to drive a stable current of 100 mA cm⁻² at a low voltage of 1.39 V but also increases the faradaic efficiency and gluconic acid yield to 87% and 83%, respectively, through the guluronic acid reaction pathway (Fig. 11e).¹⁰² More importantly, in situ infrared spectroscopy and theoretical simulations confirm that oxygen vacancies dominate path selectivity by reducing the aldehyde oxidation energy barrier, while nitrogen doping suppresses side reactions (Fig. 11f). This closed-loop design logic of “defect-path-economy” shows significant advantages at the industrial level: compared with traditional chemical oxidation processes, the electrocatalytic strategy reduces the production cost of gluconic acid and achieves the co-production of high-purity hydrogen, reflecting the multi-level optimization concept from atomic-level active site design to macroscopic reactor integration.

3.1.4 Coordination microenvironment regulation. By precisely engineering the coordination environment of active sites (e.g., ligand species, coordination number, electronic structure) and constructing spatially confined architectures (e.g., porous frameworks, layered structures, or confined nanocavities), as illustrated in Fig. 12, dynamic regulation of reactant adsorption, intermediate stabilization, and electron transfer pathways can be achieved. As detailed in Table 4, which compares the performance of various catalysts for the selective oxidation of aldehydes to carboxylic acids through microenvironment modulation, this strategy significantly enhances catalytic efficiency and selectivity.

Fig. 12 Coordination microenvironment regulates aldehyde electrocatalytic oxidation to prepare acids.

Table 4 Comparison of the performances of aldehyde electro-oxidation catalysts tuned by coordination microenvironment regulation modulation for selective carboxylic acid production

Electrocatalyst	Reactant	Product	Cell voltage	Faradaic efficiency	Yield	Ref.
BZ-NiCo(OH)x	HMF	FDCA	1.4 V	95.39%	95.24%	103
Ni-HHTP/Ni-HITP	HMF	FDCA	1.5 VRHE	>85%	>83%	104
NiFeCo wrinkled nanosheet	HMF	FDCA	1.26 VRHE	98%	98.7%	106
Co3O4@PNC	HMF	FDCA	1.45 VRHE	>90%	95%	107
Co3O4@NC	HMF	FDCA	1.47 VRHE	95%	>91.5%	108
NiCoBDC	HMF	FDCA	1.55 VRHE	78.8%	99%	109

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Taking coordination microenvironment regulation as an example, benzoic acid (BZ)–modified BZ-NiCo(OH)_x nanowires (Fig. 13a) significantly change the electronic density of the nickel/cobalt (Ni/Co) active centers through a strong electron-withdrawing effect, accelerating the dehydrogenation process of lattice hydroxyl groups (–OH) and forming electron-deficient Ni/Co sites. This reconstruction of the coordination microenvironment increases the current density to 111.20 mA cm⁻² (four times higher than that of the unmodified system) (Fig. 13b), and drives 5-hydroxymethylfurfural (HMF) oxidation along an efficient pathway to 2,5-furandicarboxylic acid (FDCA), with the yield and faradaic efficiency (FE) reaching 95.24% and 95.39%, respectively (Fig. 13c).¹⁰³ Additional studies found that in the two-dimensional conductive metal–organic frameworks nickel-based hexahydroxytriphenylene (Ni-HHTP)/nickel-based hexaaminotriphenylene (Ni-HITP) (Fig. 13d), the difference in electronegativity of the coordination atoms (O or NH₂) of Ni directly affected the catalytic activity.¹⁰⁴ The single Ni–O₄ tetrahedral site in Ni-HHTP, due to its high electronegativity, significantly enhances the dehydrogenation ability of hydroxymethyl and aldehyde groups, with a turnover frequency (TOF) of 0.219 s⁻¹ (Fig. 13e and f), and remains stable after five cycles, fully demonstrating the key role of coordination atom selection in microenvironment optimization.¹⁰⁵

Fig. 13 (a) TEM image of BZ-NiCo(OH)_x. (b) Comparison of HMFOR current densities at 1.4 V. (c) Percentage changes of HMF, HMFCA, DFF, FFCA, and FDCA for BZ-Ni(OH)_x at 1.40 V. Reproduced from ref. 103 with permission from John Wiley and Sons, copyright 2024. (d) HRTEM image of Ni-HHTP. (e) TOF comparison between Ni-HHTP and Ni-HITP at 1.5 V vs. RHE. (f) The reaction process of HMF directly oxidized by Ni-O₄. Reproduced from ref. 105 with permission from the American Chemical Society, copyright 2024.

In terms of spatial confinement and dynamic regulation of active phases, Fe/Co-modified wrinkled β-nickel hydroxide (β-Ni(OH)₂) nanosheets (Fig. 14a) induce the formation of the β-nickel oxyhydroxide (β-NiOOH) active phase, achieving 98.7% FDCA yield and 98% faradaic efficiency (FE) at a low potential of 1.26 V (Fig. 14b).¹⁰⁶ Density functional theory (DFT) calculations indicate that Fe/Co co-doping not only reduces the adsorption energy of HMF but also optimizes the synergistic oxidation pathway of hydroxyl and aldehyde groups, avoiding competing adsorption issues (Fig. 14c). Similarly, the phosphorus/nitrogen (P/N) co-doped cobalt tetraoxide@porous nitrogen-doped carbon (Co₃O₄@PNC) catalyst (Fig. 14d) constructs dual-functional sites of tri-coordinated phosphorus oxide (C₃P=O) and pyrrolic nitrogen, achieving differentiated adsorption of HMF and OH⁻, completing efficient transformation within 2 h, and demonstrating excellent cycling stability (FDCA yield and FE both remain >90% after four cycles) (Fig. 14e and f).¹⁰⁷ The confinement effect of its porous carbon shell (PNC) not only increases the density of active sites but also establishes efficient mass transfer channels, highlighting the synergistic advantages of spatial confinement and electronic regulation.¹⁰⁸

Fig. 14 (a) SEM image of NiFeCo-LDHs. (b) HMF conversion, FDCA yields and FE of NiFeCo-LDHs. (c) Dehydrogenation energy profiles of the Ni–OH bond on the Ni(OH)₂, Fe, Co-doped and FeCo co-doped electrodes. Reproduced from ref. 106 with permission from the Royal Society of Chemistry, copyright 2025. (d) SEM images of Co₃O₄@PNC (inset: the corresponding SAED pattern). (e) Time–current curve and transfer charge number of Co₃O₄@PNC catalyzing HMFOR at a constant voltage of 1.45 V. (f) Four-cycle electrocatalytic HMFOR yields and faradaic efficiency of Co₃O₄@PNC. Reproduced from ref. 107 with permission from John Wiley and Sons, copyright 2024. (g) Concentrations of HMF and the oxidation products at different electrolysis times. (h) FDCA yield rates and FE of NiBDC, NiCoBDC, NiFeBDC and NiMnBDC for 4 h electrolysis. (i) FE, selectivity and yield rate of FDCA using NiCoBDC-NF during four successive electrolysis processes. Reproduced from ref. 109 with permission from the Royal Society of Chemistry, copyright 2020.

To further integrate coordination microenvironments with confinement effects, the two-dimensional MOF material nickel–cobalt terephthalate (NiCoBDC, where BDC stands for 1,4-benzenedicarboxylate) achieves a breakthrough in FDCA production. By leveraging layered structural confinement and atomic-level synergy between nickel/cobalt (Ni²⁺/Co) bimetallic sites (Fig. 14g), it elevates the FDCA yield to 99% (rate: 20.1 μmol cm⁻² h⁻¹) with a faradaic efficiency (FE) of 78.8% under alkaline conditions (pH = 13) (Fig. 14h and i), while effectively suppressing HMF degradation.¹⁰⁹ This performance leap originates from the high-density bimetallic active sites, ordered mass transport channels, and stable electronic synergy network provided by the 2D confinement structure, enabling holistic optimization from molecular adsorption to product diffusion. The closed-loop design logic of “microenvironment–confinement–performance” not only offers atomic-level active site optimization strategies for electrocatalytic aldehyde oxidation but also establishes a theoretical foundation for the industrial applications of complex biomass conversion systems. From single-coordination modification to multidimensional confinement synergy, the interplay between coordination microenvironments and spatial confinement effects continues to propel electrocatalytic technology toward high efficiency, stability, and cost-effectiveness.

3.2 Synergistic effect

3.2.1 Interfacial synergistic effect. The synergistic effect at the interface, as shown in Fig. 15, enhances the catalytic performance for the selective oxidation of aldehydes to carboxylic acids by optimizing interfacial electron transfer and mass transport. This is achieved through strong interactions between the carrier and the active components, which improve the adsorption and activation of reactants, and selective desorption of products. Research has identified four key synergistic mechanisms that play crucial roles in enhancing catalytic performance: dynamic regeneration and stabilization of active sites, confinement effects on key intermediates, optimization of charge transfer by the conductive network of the carrier, and coupling effects of the metal-carrier interfacial electric field. These mechanisms, working together across multiple scales, fundamentally determine the performance of the catalyst and provide a theoretical basis for the optimization of specific catalytic systems.

Fig. 15 Schematic diagram of interfacial synergistic effects regulating the electrocatalytic selective oxidation of aldehydes to carboxylic acids.

Regarding dynamic regeneration of active sites, the nickel hydroxide-modified carbon paste electrode (Ni(OH)₂-X/CPE) developed by Kavian's team exemplifies this mechanism. This system achieves efficient Ni²⁺/Ni³⁺ redox cycling through a 3D nanoporous/zeolite X composite structure, demonstrating an electron transfer coefficient of 0.7 and a catalytic rate constant of 6.1 × 10⁴ cm³ mol⁻¹ s⁻¹ in 0.5 M formaldehyde electrolyte.¹¹⁰ The exceptional performance stems from zeolite molecular sieves stabilizing reaction intermediates via confinement effects, while valence state cycling at nickel active centers ensures continuous regeneration of catalytic sites, perfectly illustrating the synergy between dynamic active site regeneration and confinement effects. Meanwhile, the sandwich-structured ruthenium/manganese dioxide catalyst (S-Ru/MnO₂) maintains a current density of 47 mA cm⁻² under neutral conditions through spatial confinement by monolayer MnO₂ nanosheets (Fig. 16a), achieving near-complete HMF conversion with 98.7% FDCA yield (Fig. 16b and c).¹¹¹ This spatial constraint not only optimizes reactant orientation but also alters thermodynamic reaction pathways by modulating local OH⁻ concentration.

Fig. 16 (a) HRTEM image of S-Ru/MnO₂. (b) FE and FDCA yield after six successive pulse electrolysis cycles. (c) LSV curves of H-Ru/MnO₂ and S-Ru/MnO₂. Reproduced from ref. 111 with permission from Elsevier, copyright 2025. (d) SEM images of the Ag₂O@NF anode. (e) 2-FA yield and anodic FE under different operating voltages in a coupled flow cell. (f) Two possible pathways of HMF oxidation to FFCA. Reproduced from ref. 112 with permission from Elsevier, copyright 2024. (g) SEM image of Ni_xSe_y–NiFe LDH@NF at high magnification. (h) Cyclic voltammetry scans over Ni_xSe_y–NiFe LDH@NF with different scan rates in the non-Faraday region. (i) LSV curves with current density normalized by the calculated ECSA of different catalysts for HMF oxidation. Reproduced from ref. 113 with permission from the Royal Society of Chemistry, copyright 2021.

Regarding charge transfer efficiency, the Ag₂O-loaded nickel foam (Ag₂O@NF) with its 3D conductive framework (Fig. 16d) optimizes catalytic performance, achieving complete furfural conversion and 98.9% furanoic acid (2-FA) yield at an optimal voltage of 1.7 V (Fig. 16e and f).¹¹² Similarly, the Ni_xSe_y–NiFe layered double hydroxide (LDH) hierarchical structure (Ni_xSe_y–NiFe@NF) integrates tightly bonded Ni_xSe_y nanowire arrays with NiFe-LDHs (Fig. 16g), enabling synergistic optimization of electron transfer and mass transport. This configuration delivers 99.3% FDCA yield and 98.9% faradaic efficiency (Fig. 16h and i).¹¹³ For the poly(1,5-diaminonaphthalene) (P-1,5-DAN) thin-film modified electrode, embedding Ni(II)/Ni(III) redox-active ions into the polymer matrix reduces the onset oxidation potential to 700 mV while achieving an oxidation current density exceeding 7 mA cm⁻² and a catalytic rate constant of 2 × 10⁶ cm³ mol⁻¹ s⁻¹.¹¹⁴ This enhancement arises from the polymer matrix not only providing a uniform microenvironment for nickel active centers but also optimizing electron transport pathways through its conductive network. Notably, the Ru/RGO nanocomposite electrode developed by Banat's team via microwave irradiation anchored 3.5 nm Ru nanoparticles onto an RGO substrate. The interfacial synergy between the highly conductive graphene network and metallic particles not only facilitates efficient charge transfer but also simultaneously optimizes hydrogenation/oxidation dual pathways in paired electrolysis. This design achieves the co-production of 77% 2-furancarboxylic acid and 61% 5-hydroxy-2-furoic acid (5-HFA) derivatives at the anode, highlighting the decisive role of interfacial microenvironment regulation in complex reaction networks.¹¹⁵

The synergistic effects of nanostructure design and carrier selection are further validated in the nano-nickel phosphate (nano-NiPh)-modified glassy carbon electrode system. This catalyst achieves a formaldehyde oxidation peak potential of 0.7 V in 0.1 M NaOH solution with a catalytic rate constant of 4.1 × 10⁶ cm³ mol⁻¹ s⁻¹, while demonstrating a linear relationship between oxidation peak current and formaldehyde concentration.¹¹⁶ The high conductivity of the glassy carbon substrate efficiently promotes electron transfer, and the unique nanostructure of nickel phosphate optimizes reactant adsorption and product desorption, exemplifying the advantages of multiscale synergistic design. For more complex interfacial electronic effects, the platinum-modified hydroxyapatite (Pt/HAP) system (Fig. 17a) exhibits unique properties.¹¹⁷ The coupling of Pt with hydroxyapatite's piezoelectric field reduces the C=O adsorption energy to −0.96 eV and directs formic acid generation via the ˙OH pathway (reaction energy: −4.83 eV, Fig. 17c). Experimental results confirm 96% HMF conversion with 70% selectivity for 5-formyl-2-furancarboxylic acid (FFCA, Fig. 17b).¹¹⁸ Similarly, in the nickel molybdate–carbon nanotube–carbon fiber composite (NiMoO₄-CNTs-CF, Fig. 17d), strong electronic interactions between CNTs and NiMoO₄ endow the catalyst with cycling stability (no performance decay over 5 cycles), in the electro-synthesis of furanoic acid (FA) from furfural (FUR) (yield: 96.98%, faradaic efficiency: 95.47%) and the electro-synthesis of 2,5-furan dicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF) (yield: 93.78%, faradaic efficiency: 89.42%) (Fig. 17e and f), revealing the key role of the synergy between the metal oxide and carbon support for durability.¹¹⁹

Fig. 17 (a) HRTEM image of Pt/HAP. (b) HMF conversion and HMFCA, FFCA, FDCA yields for different catalysts. (c) DFT calculation for the conversion of formaldehyde to formic acid over Pt/HAP. Reproduced from ref. 118 with permission from Elsevier, copyright 2022. (d) TEM image of NiMoO₄-CNTs-CF. (e) FDCA yield, FE and FDCA selectivity of the electrooxidation of HMF on the NiMoO₄-CNTs-CF electrode. (f) NiMoO₄-CNTs-CF electrode in five successive electrolysis cycles. Reproduced from ref. 119 with permission from Elsevier, copyright 2022.

As evidenced by the data in Table 5, interfacial synergistic effects significantly enhance the performance of aldehyde electrooxidation to carboxylic acids through multiscale regulation. The dynamic regeneration mechanism stabilizes reaction intermediates via porous support structures while maintaining the valence cycling of metal active sites. Interfacial electric field coupling strengthens electron transfer efficiency between the metal and support, and the spatial confinement effect precisely controls the reaction pathways through nanostructures to improve selectivity. More importantly, these mechanisms achieve efficient catalysis throughout the entire process from reactant adsorption to product desorption via multiscale coordination, including atomic-level electronic structure modulation, construction of the nanoscale confinement environment, and optimization of the macroscale conductive network. These synergistic design principles not only provide a theoretical framework for understanding existing catalytic systems, but also point the way for developing novel, highly efficient aldehyde oxidation catalysts.

Table 5 Comparison of the performances of catalysts for the selective oxidation of aldehydes to carboxylic acids via interfacial synergistic effects

Electrocatalyst	Reactant	Product	Cell voltage	Faradaic efficiency	Yield	Ref.
Ni(OH)2-X/CPE	Formaldehyde	Formic acid	0.87 VRHE	—	—	110
S-Ru/MnO2	HMF	FDCA	1.55 VRHE	79%	98.7%	111
Ag2O@NF	HMF	2-FA	1.7 V	93.8%	98.9%	112
NixSey–NiFe@NF	HMF	FDCA	1.47 VRHE	98.9%	99.3%	113
P-1,5-DAN	Formaldehyde	Formic acid	0.65 VRHE	—	—	114
Ru/RGO	Furfural	2-FA/5-HFA	0.8–1.4VAg/AgCl	>81%	77%/61%	115
nano-NiPh	Formaldehyde	formic acid	0.70 VAg/AgCl	—	—	116
Pt/HAP	HMF	FFCA	—	—	70%	118
NiMoO4-CNTs-CF	FUR/HMF	FA/FDCA	1.42 V	96.98%/93.78%	95.47%/89.42%	119

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3.2.2 Atomic synergistic catalysis. In the electrocatalytic selective oxidation of aldehydes to carboxylic acids, the design concept of the synergistic effect, as shown in Fig. 18, realizes the efficient series connection and precise control of complex reaction pathways by constructing a synergistic network of multiple active sites. The key challenge in the transformation of aldehyde molecules lies in the need to activate multiple functional groups across differentiated energy barriers, which is often difficult to balance with adsorption strength and reaction kinetics using a single active site. By constructing bimetallic/multimetallic systems with complementary functions, it is possible to decouple and reorganize reaction steps at the atomic scale. For example, in the palladium–gold alloy catalyst (Pd₃Au₇/C) (Fig. 19a), the Au surface dynamically regulates the reaction pathway, while the Pd sites reduce the oxidation onset potential of glucose by 50% (from 0.2 to 0.1 V vs. RHE), increasing the current density at 0.4 V vs. RHE by 122% through interfacial electron transfer, and achieving a glucose conversion rate of 67% with 87% selectivity after 6 h of electrolysis (Fig. 19b and c).¹²⁰ Similarly, the Pd₁Au₂/C system (Fig. 19d) realizes relay catalysis of the HMF oxidation pathway through the division of labor between Pd and Au sites: Pd specializes in the oxidation of primary alcohol groups to generate 5-hydroxymethyl-2-furoic acid (HMFCA), while Au specifically activates the aldehyde group to generate 2-formyl-5-furoic acid (FFCA), and the deep oxidation to 2,5-furandicarboxylic acid (FDCA) is completed at the Pd–Au interface, achieving 100% HMF conversion and 83% FDCA selectivity within 1 h at 0.9 V vs. RHE (Fig. 19e and f), a significant improvement over monometallic catalysts.¹²¹ This bimetallic synergistic paradigm has been multidimensionally expanded in high-entropy alloys of iron, cobalt, nickel, and copper (FeCoNiCu). Wu et al. synthesized a “novel” defect-rich FeCoNiCu layered double hydroxide (LDH) on nickel foam (D-FeCoNiCu-LDH/NF) (Fig. 19g), where the Cu–Co heterometallic bridge promoted hydroxyl dehydrogenation, the Cu–Cu homologous sites dominated the dehydrogenation of the carbon chain to generate aldehyde intermediates, and the Cu–Ni synergistic interface specifically catalyzed the deep oxidation conversion of the aldehyde group to the carboxyl group (Fig. 19i). This multi-level relay mechanism enables the glucose oxidation system for gluconic acid production to achieve nearly 100% glucose conversion and over 90% gluconic acid selectivity (at 100 mA cm⁻²) at a low potential of 1.22 V (Fig. 19h).¹²²

Fig. 18 Schematic diagram of the synergistic catalytic regulation of aldehydes by atoms for selective carboxylic acid production by electrocatalysis.

Fig. 19 (a) TEM image of the Pd₃Au₇/C sample. (b) Polarization curves of glucose oxidation recorded on different catalysts. (c) Cyclic voltammograms of 0.1 M glucose oxidation recorded on Pd/C (black line) and Pd₃Au₇/C (red line). Scan rate = 5 mV s⁻¹, N₂-purged 0.1 M NaOH electrolyte, T = 293 K. Reproduced from ref. 120 with permission from Elsevier, copyright 2019. (d) TEM (scale bar 20 nm) and high-resolution TEM (HRTEM, scale bar 1 nm, inset) images of the Pd₁Au₂/C sample. (e) Molar yield of FDCA from the oxidation of 0.1 M KOH + 0.02 M HMF. Reaction conditions: 1 h; AEM-electrolysis flow cell; anode potential 0.9 V vs. RHE; 25 °C. (f) Product distribution on Pd₁Au₂/C for the oxidation of 0.02 M HMF in 0.1 M KOH. Reaction conditions: 1 h; AEM-electrolysis flow cell; 25 °C. Reproduced from ref. 121 with permission from the Royal Society of Chemistry, copyright 2014. (g) SEM image of D-FeCoNiCu-LDH/NF. (h) LSVs for D-FeCoNiCu-LDH/NF, FeCoNiCuCr-LDH/NF, FeCoNiCu-LDH/NF, D-FeNiCu-LDH/NF D-FeCoCu-LDH/NF and D-FeCoNi-LDH/NF for glucose electrooxidation in 1.0 M KOH with 0.1 M glucose. (i) Reaction pathway for the conversion of glycolaldehyde (*C₂H₄O₂) to oxalic acid (*C₂H₂O₄). Reproduced from ref. 122 with permission from the Royal Society of Chemistry, copyright 2024.

The atomic synergistic catalysis strategy based on a multi-active-site synergistic network, by precisely allocating functional sites and optimizing synergistic mechanisms, overcomes inherent limitations of single active sites in balancing adsorption strength and reaction kinetics, achieving efficient serial linkage and precise control of complex reaction pathways. This strategy is exemplified in the rhenium–phenanthroline/nickel oxide (Re₁-phen/NiO) single-atom catalyst: the unique “suspended” Re=O double bond forms a dual-active interface with the NiO carrier, realizing efficient catalysis through a triple-synergistic mechanism—electronic synergy (0.96 |e| charge transfer between Re and NiO) enhances interface stability; geometric synergy (hydrogen bond network between the phenanthroline ligand and carrier) optimizes the spatial configuration of the active center; coordination synergy (Re=O double bond synchronously activates hydroxyl/aldehyde groups) enables directional transformation of reactants. This multi-level synergistic effect not only precisely directs the reaction pathway to glucaric acid (with a selectivity of 94%) but also shortens the conversion time for key intermediates, fully demonstrating the universal value of the atomic synergistic design concept.¹²³ This design concept is further deepened in the nickel–cobalt–phosphorus (Ni–Co–P) ternary system (Fig. 20a): phosphorus induces the formation of the highly active Ni₂P phase, and cobalt anchors the intermediate, increasing the oxidation activity of FFCA by 2.8 times and reducing the desorption rate from 32% to 7%, ultimately achieving an FDCA yield of 96.5% (Fig. 20b and c).^124–126 The sulfur-coordinated nickel–cobalt sulfide (Ni–CoS) nanosheets, through the electronic modulation effect of sulfur, activate the aldehyde group at the cobalt site and accelerate FDCA formation at the nickel site, achieving yields and selectivities of 97.1% and 98%, respectively, demonstrating the unique advantages of non-metal elements participating in synergistic catalysis.¹²⁷

Fig. 20 (a) TEM and EDS mapping images of the Ni–Co–P nanoparticles. (b) FDCA yields, FE, and production rate at constant potential oxidation of 5 mM HMF after passing a stoichiometric amount of charge to convert 5 mM HMF into FDCA. (c) J–V curves of 5 mM DFF, HMFCA, and FFCA oxidations. Reproduced from ref. 124 with permission from John Wiley and Sons, copyright 2024. (d) TEM image of the Ni₂Co₁-MOF sample. (e) Ni₂Co₁-MOF during HMF oxidation at 1.35 V vs. RHE. (f) Electrolytic performance of MOFs. Reproduced from ref. 130 with permission from Elsevier, copyright 2024.

The introduction of dynamic regulation and precise mass transfer mechanisms endows the relay catalytic systems with environmental adaptability.¹²⁸ The Fe/Co system, through the electron cycling of the Fe³⁺/Co²⁺ redox pair, achieves 94% FDCA yield in 0.1 M KOH, but fails in 1 M strong alkali due to the suppression of the disproportionation reaction, with the yield dropping to 61%, revealing the dynamic response capability of bimetallic components to the reaction microenvironment.¹²⁹ The nickel–cobalt metal–organic framework (NiCo-MOF) catalyst (Fig. 20d), with 0.24 nm ultra-short site spacing that accelerates intermediate diffusion, constructs a three-stage relay pathway: Co initiates aldehyde oxidation (1.0 V RHE), Ni dominates hydroxyl transformation (1.35 V RHE), and Co completes the final oxidation, achieving a stable output of 97.3% FDCA yield and 90% faradaic efficiency (Fig. 20e and f).¹³⁰ This spatiotemporal synergistic strategy reaches new heights in the nickel–copper alloy nanotube (NiCu NT) bifunctional system: the anode achieves 100% HMF conversion and 99% FDCA selectivity (20 mM), while the cathode efficiently generates hydrogen, reducing the full-cell operating potential by 350 mV (100 mA cm⁻²), and maintaining performance stability under high-concentration (100 mM) conditions, breaking through the traditional catalytic system's sensitivity to substrate concentration.¹³¹

As collectively revealed by the cases and evidenced by the data in Table 6, the core principles for constructing a multi-scale synergistic network include regulating the redox potential of active sites through intermetallic electronic interactions to match the energy barriers of multiple reaction steps, controlling the adsorption strength of intermediates via heterogeneous interfaces or defect engineering to balance activation and desorption processes, designing sub-nanometer spatial arrangements to accelerate mass transfer efficiency, and introducing dynamic regulatory elements to respond to changes in the reaction microenvironment. The systematic application of these principles provides an efficient solution for the conversion of biomass aldehydes to high-value carboxylic acids, which is both atomically precise and engineering feasible.

Table 6 Comparison of the performances of aldehyde electro-oxidation catalysts tuned by atomic synergistic catalysis for selective carboxylic acid production

Electrocatalyst	Reactant	Product	Cell voltage	Faradaic efficiency	Yield	Ref.
Pd3Au7/C	Glucose	Gluconate	0.4 VRHE	63.3%	87%	120
Pd1Au2/C	HMF	FDCA	0.9 VRHE	100%	83%	121
FeCoNiCu	Glucose	Gluconic acid	1.22 V	95%	>90%	122
Re1-phen/NiO	Glucose	Gluconic acid	1.28 VRHE	95%	94%	123
Ni–Co–P	HMF	FDCA	1.5 V	77%	96.5%	124
Ni–CoS	HMF	FDCA	1.45 VRHE	96.4%	97.1%	127
Co2Fe1-1.8@NiF	HMF	FDCA	1.535 VRHE	91.5%	94%	129
Ni2Co1-MOF	HMF	FDCA	1.35 VRHE	90%	97.3%	130
NiCu NTs	HMF	FDCA	1.424 VRHE	96.4%	99%	131

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4. Conclusion

Driven by the global carbon neutrality strategy, the electrocatalytic selective oxidation of aldehydes to carboxylic acids, by replacing the high-energy-consuming and low-value-added oxygen evolution reaction in traditional water electrolysis for hydrogen production, provides an innovative breakthrough to address the economic and efficiency bottlenecks in the large-scale production of green hydrogen. This review systematically expounds the core paradigm of catalyst design: the breakthrough in the reaction mechanism originates from the synergistic regulation of C=O bond polarization activation and orderly dehydrogenation of C–H bonds, achieving the highly selective synthesis of carboxylic acid products by suppressing C–C bond cleavage and deep oxidation side reactions. Catalyst design focuses on two major dimensions—electronic structure and synergistic effects. The former precisely controls the adsorption strength of intermediates and reaction energy barriers through d-band center optimization, dynamic valence balancing, and defect engineering, significantly reducing the activation energy of key steps. The latter combines interfacial synergistic catalysis, atomic relay reactions, and spatial confinement effects to reconstruct the energy distribution of multi-electron transfer pathways, simultaneously enhancing mass transfer efficiency and selectivity control. The quantitative structure–property relationship model at the atomic level, constructed based on in situ characterization and theoretical simulation, reveals the mechanisms of how strategies such as valence regulation, dynamic reconstruction, defect engineering, and coordination microenvironment optimization break through the traditional catalyst's “activity–selectivity–stability” bottleneck. The electronic synergistic effects of multivalent metal sites, self-healing mechanisms of dynamic redox cycles, and optimization of diverse defects in synergistic pathways have shown significant advantages in copper-based, palladium-based, and nickel-based systems: optimized catalysts can achieve high Faraday efficiency and high carboxylic acid selectivity at industrial-level current densities (>500 mA cm⁻²), successfully constructing a prototype of a co-production system for “green hydrogen production and high-value chemical synthesis”. These advances not only provide new insights into the mechanisms of electrocatalytic oxidation reactions but also lay the theoretical and experimental foundations for the technological transformation of energy–chemical coupling systems under the carbon neutrality goal.

However, this technology (particularly the hybrid water electrolyzer configuration) still faces severe challenges when moving towards industrial application: the fundamental issues of long-term corrosion and activity decay of highly active non-precious metal catalysts in acidic or high-concentration aldehyde media remain unresolved; the membrane–electrode interface is prone to mass transfer polarization and mechanical delamination under high current density due to aldehyde permeation and bubble entrapment; furthermore, industrial-grade aldehyde feedstocks have complex compositions, and impurities (such as sulfur and chloride ions) may poison active sites, potentially further amplifying the risk of side reactions. It is precisely these bottlenecks that have driven the emerging trend of utilizing aldehyde oxidation to replace the OER and deeply integrating it within hybrid water electrolyzers: through the synergistic effect of atomic-scale defect engineering and dynamic valence cycling, theparallel production of “low-voltage hydrogen evolution–high-value carboxylic acids” can be achieved within a single reactor, providing a novel strategy for selective oxidation to carboxylic acids that is more energy-efficient and atom-economical than traditional chemical oxidation. To address the aforementioned challenges, subsequent research can focus on leveraging machine learning–high-throughput experimentation coupled platforms to construct a “composition–defect–interface” database for the precise screening of acid-resistant, poison-tolerant, and self-healing-capability catalytic systems; concurrently, developing novel configurations such as gradient pH or dual-membrane electrolyzers to adapt to the conversion requirements of different biomass-derived aldehyde feedstocks.

Aldehyde electrocatalytic oxidation technology is rapidly advancing from fundamental research towards industrial implementation. Current research underscores the critical importance of selection of the system environment: although alkaline systems enhance reaction kinetics via hydroxyl ions (OH⁻), their scalability is severely constrained by equipment corrosion, escalating electrolyte costs, and product separation challenges. In contrast, acidic systems exhibit substantially greater industrial potential, leveraging their high compatibility with PEM environments, rapid proton transport kinetics, and simplified product separation protocols. Nevertheless, the industrialization of acidic systems demands that three core hurdles are overcome: first, achieving uniform active site distribution, robust carrier-active component interfacial stability, and scalable continuous manufacturing processes during catalyst mass production are paramount for cost control and performance reproducibility, necessitating atomic-level precision synthesis strategies (e.g., coupled spray pyrolysis–electrochemical deposition) and establishing cross-scale structure–performance correlation models. Second, reactor design must integrate acid compatibility with process intensification; this entails optimizing modular PEM electrolyzers with 3D flow fields, low-resistance electrode–membrane interfaces, and multi-compartment separation units to synergistically enhance mass transfer and product recovery efficiency. Finally, ensuring long-term operational stability requires dynamic coordination among catalytic materials, reactor architecture, and process parameters, mandating the implementation of a self-repair mechanism based on in situ catalyst state monitoring and intelligent operational parameter control to effectively mitigate time-dependent deactivation phenomena such as *CO poisoning and active site dissolution.

Against this backdrop, the development of acid-resistant, highly active, and low-cost non-noble metal catalytic materials has become the key to breaking the deadlock: for example, atomically dispersed transition metal–nitrogen/carbon materials (Fe–N–C, Co–N–C) can precisely control the adsorption strength of intermediates through coordination microenvironments, while transition metal carbides/nitrides (Mo₂C, VN) utilize chemically inert interfaces combined with dynamic self-protection mechanisms (such as in situ passivation layers) to enhance acid resistance while maintaining high catalytic activity. Furthermore, catalyst design needs to integrate multidimensional innovative strategies: on the one hand, by designing high-entropy alloys, single-atom catalysts, and metal–organic framework materials, combined with defect engineering and dynamic valence cycling, to achieve synergistic optimization of electronic states and corrosion resistance; on the other hand, leveraging machine learning and high-throughput computing to build a “composition–structure–property” database, to accelerate the targeted screening of acid-resistant catalysts, and to develop multi-active-site synergistic networks to efficiently convert complex substrates such as aromatic aldehydes and long-chain aldehydes.

At the same time, the design of reactors and electrolyzers also needs to be improved through a “catalyst–reactor–process” collaborative scaling strategy, to develop high-efficiency PEM electrolyzer clusters suitable for acidic systems: at the material level, use gradient pore carriers to ensure mass transfer uniformity, at the device level, optimize the electrode–membrane interface structure to reduce mass transfer resistance, and at the system level, design modular integrated units to achieve seamless scaling from laboratory gram-scale to industrial ton-scale; exploring multi-reaction coupling devices (such as aldehyde oxidation–hydrogen evolution bifunctional electrolyzers), to achieve the synergistic production of carboxylic acids and green hydrogen through spatiotemporal control, maximizing the efficiency of resource and energy utilization.

Looking to the future, the large-scale implementation of electrocatalytic aldehyde oxidation technology requires the construction of an integrated innovation system across the entire chain of “materials–devices–processes”: developing intelligent self-healing systems to utilize in situ sensing technologies for the real-time monitoring of catalyst conditions and dynamic adjustment of operating parameters; designing gradient pH reactors or dual-membrane electrolyzers to accommodate the conversion needs of different biomass aldehydes; and establishing collaborative platforms among industry, academia, and research to promote the integrated validation of catalyst macro-scale preparation processes, reactor engineering optimization, and system control algorithms. Through interdisciplinary integration and technological convergence, this technology has the potential to become the core link between the green hydrogen economy and biomass refining. It will not only break through the energy-efficiency bottleneck of water electrolysis for hydrogen production but also open up new pathways for the synthesis of “zero-carbon chemicals”, providing a systemic solution for the deep integration of the energy transition and green chemistry under the global carbon neutrality goal.

Author contributions

L. W. and J. L. supervised the review writing process. J. L. conceived the theme and framework of the review. Y. C. designed the review's structural content, collected most of the literature materials, and performed data analysis. H. J. and Y. Y. provided technical expertise in relevant fields and assisted in revising the review. All authors participated in the review discussions, and examined and revised the final manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (52272222), the Taishan Scholar Young Talent Program (tsqn201909114, tsqn201909123), and the University Youth Innovation Team of Shandong Province (202201010318).

References

1. G. S. Cassol, C. Shang, A. K. An, N. K. Khanzada, F. Ciucci, A. Manzotti, P. Westerhoff, Y. H. Song and L. Ling, Ultra-fast green hydrogen production from municipal wastewater by an integrated forward osmosis-alkaline water electrolysis system, Nat. Commun., 2024, 15, 2617.
2. K. de Kleijne, M. A. J. Huijbregts, F. Knobloch, R. van Zelm, J. P. Hilbers, H. de Coninck and S. V. Hanssen, Worldwide greenhouse gas emissions of green hydrogen production and transport, Nat. Energy, 2024, 9, 1139–1152.
3. J. C. Li, Y. Q. Ma, C. Zhang, C. Zhang, H. J. Ma, Z. Q. Guo, N. Liu, M. Xu, H. X. Ma and J. S. Qiu, Green electrosynthesis of 3,3′-diamino-4,4′-azofurazan energetic materials coupled with energy-efficient hydrogen production over Pt-based catalysts, Nat. Commun., 2023, 14, 8146.
4. Q. R. Liang, Y. N. Huang, Y. X. Guo, X. Zhang, X. M. Hu, H. Zeng, K. Liang, D. Y. Zhao, L. Jiang and B. Kong, Efficient osmosis-powered production of green hydrogen, Nat. Sustain., 2024, 7, 628–639.
5. Z. F. Wang, Y. Yang, Z. F. Zhao, P. H. Zhang, Y. S. Zhang, J. J. Liu, S. Q. Ma, P. Cheng, Y. Chen and Z. J. Zhang, Green synthesis of olefin-linked covalent organic frameworks for hydrogen fuel cell applications, Nat. Commun., 2021, 12, 1982.
6. H. Zhao, D. Lu, J. R. Wang, W. G. Tu, D. Wu, S. W. Koh, P. Q. Gao, Z. C. J. Xu, S. L. Deng, Y. Zhou, B. You and H. Li, Raw biomass electroreforming coupled to green hydrogen generation, Nat. Commun., 2021, 12, 2008.
7. L. Chen, X. L. Dong, Y. G. Wang and Y. Y. Xia, Separating hydrogen and oxygen evolution in alkaline water electrolysis using nickel hydroxide, Nat. Commun., 2016, 7, 11741.
8. J. K. Lee, G. Anderson, A. W. Tricker, F. Babbe, A. Madan, D. A. Cullen, J. D. Arregui-Mena, N. Danilovic, R. Mukundan, A. Z. Weber and X. Peng, Ionomer-free and recyclable porous-transport electrode for high-performing proton-exchange-membrane water electrolysis, Nat. Commun., 2023, 14, 4592.
9. B. Z. Lu, C. Wahl, R. dos Reis, J. Edgington, X. K. Lu, R. H. Li, M. E. Sweers, B. Ruggiero, G. Gunasooriya, V. Dravid and L. C. Seitz, Key role of paracrystalline motifs on iridium oxide surfaces for acidic water oxidation, Nat. Catal., 2024, 7, 868–877.
10. M. Retuerto, L. Pascual, J. Torrero, M. A. Salam, A. Tolosana-Moranchel, D. Gianolio, P. Ferrer, P. Kayser, V. Wilke, S. Stiber, V. Celorrio, M. Mokthar, D. G. Sanchez, A. S. Gago, K. A. Friedrich, M. A. Peña, J. A. Alonso and S. Rojas, Highly active and stable OER electrocatalysts derived from Sr₂MIrO₆ for proton exchange membrane water electrolyzers, Nat. Commun., 2022, 13, 7935.
11. H. B. Tao, H. Liu, K. J. Lao, Y. P. Pan, Y. B. Tao, L. R. Wen and N. F. Zheng, The gap between academic research on proton exchange membrane water electrolysers and industrial demands, Nat. Nanotechnol., 2024, 19, 1074–1076.
12. J. Wei, Y. F. Shao, J. B. Xu, F. Yin, Z. J. Li, H. T. Qian, Y. P. Wei, L. Chang, Y. Han, J. Li and L. Gan, Sequential oxygen evolution and decoupled water splitting via electrochemical redox reaction of nickel hydroxides, Nat. Commun., 2024, 15, 9012.
13. E. Fabbri, M. Nachtegaal, T. Binninger, X. Cheng, B. J. Kim, J. Durst, F. Bozza, T. Graule, R. Schäublin, L. Wiles, M. Pertoso, N. Danilovic, K. E. Ayers and T. J. Schmidt, Dynamic surface self-reconstruction is the key of highly active perovskite nano-electrocatalysts for water splitting, Nat. Mater., 2017, 16, 925–931.
14. F. T. Haase, A. Bergmann, T. E. Jones, J. Timoshenko, A. Herzog, H. S. Jeon, C. Rettenmaier and B. Roldan Cuenya, Size effects and active state formation of cobalt oxide nanoparticles during the oxygen evolution reaction, Nat. Energy, 2022, 7, 765–773.
15. W. H. Lee, M. H. Han, Y. J. Ko, B. K. Min, K. H. Chae and H. S. Oh, Electrode reconstruction strategy for oxygen evolution reaction: maintaining Fe-CoOOH phase with intermediate-spin state during electrolysis, Nat. Commun., 2022, 13, 605.
16. W. H. Lee, Y. J. Ko, J. H. Kim, C. H. Choi, K. H. Chae, H. Kim, Y. J. Hwang, B. K. Min, P. Strasser and H. S. Oh, High crystallinity design of Ir-based catalysts drives catalytic reversibility for water electrolysis and fuel cells, Nat. Commun., 2021, 12, 4271.
17. W. L. Li, F. S. Li, H. Yang, X. J. Wu, P. L. Zhang, Y. Shan and L. C. Sun, A bio-inspired coordination polymer as outstanding water oxidation catalyst via second coordination sphere engineering, Nat. Commun., 2019, 10, 5074.
18. L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A. Doyle, C. Kirk, A. Vojvodic, H. Y. Hwang, J. K. Norskov and T. F. Jaramillo, A highly active and stable IrO_x/SrIrO₃ catalyst for the oxygen evolution reaction, Science, 2016, 353, 1011–1014.
19. R. D. L. Smith, M. S. Prévot, R. D. Fagan, Z. P. Zhang, P. A. Sedach, M. K. J. Siu, S. Trudel and C. P. Berlinguette, Photochemical route for accessing amorphous metal oxide materials for water oxidation catalysis, Science, 2013, 340, 60–63.
20. J. Wang, S. J. Kim, J. P. Liu, Y. Gao, S. Choi, J. Han, H. Shin, S. Jo, J. Kim, F. Ciucci, H. Kim, Q. T. Li, W. L. Yang, X. Long, S. H. Yang, S. P. Cho, K. H. Chae, M. G. Kim, H. Kim and J. Lim, Redirecting dynamic surface restructuring of a layered transition metal oxide catalyst for superior water oxidation, Nat. Catal., 2021, 4, 212–222.
21. Q. L. Wang, C. Q. Xu, W. Liu, S. F. Hung, H. B. Yang, J. J. Gao, W. Z. Cai, H. M. Chen, J. Li and B. Liu, Coordination engineering of iridium nanocluster bifunctional electrocatalyst for highly efficient and pH-universal overall water splitting, Nat. Commun., 2020, 11, 4246.
22. Y. Z. Wen, C. Liu, R. Huang, H. Zhang, X. B. Li, F. P. G. de Arquer, Z. Liu, Y. Y. Li and B. Zhang, Introducing bronsted acid sites to accelerate the bridging-oxygen-assisted deprotonation in acidic water oxidation, Nat. Commun., 2022, 13, 4871.
23. L. Yang, G. T. Yu, X. Ai, W. S. Yan, H. L. Duan, W. Chen, X. T. Li, T. Wang, C. H. Zhang, X. R. Huang, J. S. Chen and X. X. Zou, Efficient oxygen evolution electrocatalysis in acid by a perovskite with face-sharing IrO₆ octahedral dimers, Nat. Commun., 2018, 9, 5236.
24. N. Zhang, X. B. Feng, D. W. Rao, X. Deng, L. J. Cai, B. C. Qiu, R. Long, Y. J. Xiong, Y. Lu and Y. Chai, Lattice oxygen activation enabled by high-valence metal sites for enhanced water oxidation, Nat. Commun., 2020, 11, 4066.
25. T. Liu, C. Lan, M. Tang, M. X. Li, Y. T. Xu, H. R. Yang, Q. Y. Deng, W. C. Jiang, Z. Y. Zhao, Y. F. Wu and H. P. Xie, Redox-mediated decoupled seawater direct splitting for H₂ production, Nat. Commun., 2024, 15, 8874.
26. Y. Park, H. Y. Jang, T. K. Lee, T. Kim, D. Kim, D. Kim, H. Baik, J. Choi, T. Kwon, S. J. Yoo, S. Back and K. Y. Lee, Atomic-level Ru-Ir mixing in rutile-type (RuIr)O₂ for efficient and durable oxygen evolution catalysis, Nat. Commun., 2025, 16, 579.
27. J. Qi, Y. D. Du, Q. Yang, N. Jiang, J. C. Li, Y. Ma, Y. J. Ma, X. Zhao and J. S. Qiu, Energy-saving and product-oriented hydrogen peroxide electrosynthesis enabled by electrochemistry pairing and product engineering, Nat. Commun., 2023, 14, 6263.
28. A. Vadakkayil, C. Clever, K. N. Kunzler, S. S. Tan, B. P. Bloom and D. H. Waldeck, Chiral electrocatalysts eclipse water splitting metrics through spin control, Nat. Commun., 2023, 14, 1067.
29. L. Q. Wang, S. F. Hung, S. Zhao, Y. Wang, S. W. Bi, S. X. Li, J. J. Ma, C. C. Zhang, Y. Zhang, L. L. Li, T. Y. Chen, H. Y. Chen, F. Hu, Y. P. Wu and S. J. Peng, Modulating the covalency of Ru-O bonds by dynamic reconstruction for efficient acidic oxygen evolution, Nat. Commun., 2025, 16, 3502.
30. D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu, A. F. Carley, A. A. Herzing, M. Watanabe, C. J. Kiely, D. W. Knight and G. J. Hutchings, Solvent-free oxidation of primary alcohols to aldehydes using Au-Pd/TiO₂ catalysts, Science, 2006, 311, 362–365.
31. G. J. ten Brink, I. Arends and R. A. Sheldon, Green, catalytic oxidation of alcohols in water, Science, 2000, 287, 1636–1639.
32. D. Wang, P. Wang, S. C. Wang, Y. H. Chen, H. Zhang and A. W. Lei, Direct electrochemical oxidation of alcohols with hydrogen evolution in continuous-flow reactor, Nat. Commun., 2019, 10, 2796.
33. T. H. Wang, L. Tao, X. R. Zhu, C. Chen, W. Chen, S. Q. Du, Y. Y. Zhou, B. Zhou, D. D. Wang, C. Xie, P. Long, W. Li, Y. Y. Wang, R. Chen, Y. Q. Zou, X. Z. Fu, Y. F. Li, X. F. Duan and S. Y. Wang, Combined anodic and cathodic hydrogen production from aldehyde oxidation and hydrogen evolution reaction, Nat. Catal., 2022, 5, 66–73.
34. B. J. Xu, X. Y. Liu, J. Haubrich and C. M. Friend, Vapour-phase gold-surface-mediated coupling of aldehydes with methanol, Nat. Chem., 2010, 2, 61–65.
35. F. Y. Cheng, J. A. Shen, B. Peng, Y. D. Pan, Z. L. Tao and J. Chen, Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts, Nat. Chem., 2011, 3, 79–84.
36. D. Galyamin, J. Torrero, I. Rodríguez, M. J. Kolb, P. Ferrer, L. Pascual, M. A. Salam, D. Gianolio, V. Celorrio, M. Mokhtar, D. G. Sanchez, A. S. Gago, K. A. Friedrich, M. A. Peña, J. A. Alonso, F. Calle-Vallejo, M. Retuerto and S. Rojas, Active and durable R₂MnRuO₇ pyrochlores with low Ru content for acidic oxygen evolution, Nat. Commun., 2023, 14, 2010.
37. S. Verma, S. Lu and P. J. A. Kenis, Co-electrolysis of CO₂ and glycerol as a pathway to carbon chemicals with improved technoeconomics due to low electricity consumption, Nat. Energy, 2019, 4, 466–474.
38. Z. Y. Wu, F. Y. Chen, B. Lie, S. W. Yu, Y. Z. Finfrock, D. M. Meira, Q. Q. Yan, P. Zhu, M. X. Chen, T. W. Song, Z. Yin, H. W. Liang, S. Zhang, G. Wang and H. Wang, Non-iridium-based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane water electrolysis, Nat. Mater., 2023, 22, 100–108.
39. J. H. Yu, F. A. Garcés-Pineda, J. González-Cobos, M. Peña-Díaz, C. Rogero, S. Giménez, M. C. Spadaro, J. Arbiol, S. Barja and J. R. Galan-Mascarós, Sustainable oxygen evolution electrocatalysis in aqueous 1 M H₂SO₄ with earth abundant nanostructured Co₃O₄, Nat. Commun., 2022, 13, 4341.
40. S. Aralekallu, L. K. Sannegowda, M. D. Kurkuri, R. K. Pai and H.-Y. Jung, Hybrid water electrolysis as the way forward to sustainable hydrogen production, Sustainable Energy Fuels, 2025, 9, 2928–2940.
41. J. Li, Y. Ma, X. Mu, X. Wang, Y. Li, H. Ma and Z. Guo, Recent advances and perspectives on coupled water electrolysis for energy-saving hydrogen production, Adv. Sci., 2025, 12, 2411964.
42. P. Wang, J. Zheng, X. Xu, Y.-Q. Zhang, Q.-F. Shi, Y. Wan, S. Ramakrishna, J. Zhang, L. Zhu, T. Yokoshima, Y. Yamauchi and Y.-Z. Long, Unlocking efficient hydrogen production: nucleophilic oxidation reactions coupled with water splitting, Adv. Mater., 2024, 36, 2404806.
43. S. Kong, A. L. Li, J. Long, K. Adachi, D. Hashizume, Q. K. Jiang, K. Fushimi, H. Ooka, J. P. Xiao and R. Nakamura, Acid-stable manganese oxides for proton exchange membrane water electrolysis, Nat. Catal., 2024, 7, 252–261.
44. Z. H. Li, X. F. Li, H. Zhou, Y. Xu, S. M. Xu, Y. Ren, Y. F. Yan, J. R. Yang, K. Y. Ji, L. Li, M. Xu, M. F. Shao, X. G. Kong, X. M. Sun and H. H. Duan, Electrocatalytic synthesis of adipic acid coupled with H₂ production enhanced by a ligand modification strategy, Nat. Commun., 2022, 13, 5009.
45. A. Odenweller and F. Ueckerdt, The green hydrogen ambition and implementation gap, Nat. Energy, 2025, 10, 110–123.
46. K. V. Petrov, C. I. Koopman, S. Subramanian, M. T. M. Koper, T. Burdyny and D. A. Vermaas, Bipolar membranes for intrinsically stable and scalable CO₂ electrolysis, Nat. Energy, 2024, 9, 932–938.
47. I. Slobodkin, E. Davydova, M. Sananis, A. Breytus and A. Rothschild, Electrochemical and chemical cycle for high-efficiency decoupled water splitting in a near-neutral electrolyte, Nat. Mater., 2024, 23, 398–405.
48. G. Chen, C. Fu, W. Zhang, W. Gong, J. Ma, X. Ji, L. Qian, X. Feng, C. Hu, R. Long and Y. Xiong, Solar-driven production of renewable chemicals via biomass hydrogenation with green methanol, Nat. Commun., 2025, 16, 665.
49. K. de Kleijne, M. A. J. Huijbregts, F. Knobloch, R. van Zelm, J. P. Hilbers, H. de Coninck and S. V. Hanssen, Worldwide greenhouse gas emissions of green hydrogen production and transport, Nat. Energy, 2024, 9, 1139–1152.
50. S. X. Bai, F. F. Liu, B. L. Huang, F. Li, H. P. Lin, T. Wu, M. Z. Sun, J. B. Wu, Q. Shao, Y. Xu and X. Q. Huang, High-efficiency direct methane conversion to oxygenates on a cerium dioxide nanowires supported rhodium single-atom catalyst, Nat. Commun., 2020, 11, 954.
51. J. Lan, Z. X. Wei, Y. R. Lu, D. C. Chen, S. L. Zhao, T. S. Chan and Y. W. Tan, Efficient electrosynthesis of formamide from carbon monoxide and nitrite on a Ru-dispersed Cu nanocluster catalyst, Nat. Commun., 2023, 14, 2870.
52. B. Li, J. L. Mu, G. F. Long, X. E. Song, E. D. Huang, S. Y. Liu, Y. Wei, F. F. Sun, S. Q. Feng, Q. Yuan, Y. T. Cai, J. Song, W. R. Dong, W. Q. Zhang, X. M. Yang, L. Yan and Y. J. Ding, Water-participated mild oxidation of ethane to acetaldehyde, Nat. Commun., 2024, 15, 2555.
53. W. C. Ma, S. J. Xie, X. G. Zhang, F. F. Sun, J. C. Kang, Z. Jiang, Q. H. Zhang, D. Y. Wu and Y. Wang, Promoting electrocatalytic CO₂ reduction to formate via sulfur-boosting water activation on indium surfaces, Nat. Commun., 2019, 10, 892.
54. M. Bourrez, R. Steinmetz, S. Ott, F. Gloaguen and L. Hammarström, Concerted proton-coupled electron transfer from a metal-hydride complex, Nat. Chem., 2015, 7, 140–145.
55. Y. H. Cao, L. Guo, M. Dan, D. E. Doronkin, C. Q. Han, Z. Q. Rao, Y. Liu, J. Meng, Z. Huang, K. B. Zheng, P. Chen, F. Dong and Y. Zhou, Modulating electron density of vacancy site by single Au atom for effective CO₂ photoreduction, Nat. Commun., 2021, 12, 1675.
56. Y. Kim, J. G. Smith and P. K. Jain, Harvesting multiple electron-hole pairs generated through plasmonic excitation of Au nanoparticles, Nat. Chem., 2018, 10, 763–769.
57. J. Lee, J. Lee and J. Seo, Exchange coupling states of cobalt complexes to control proton-coupled electron transfer, Nat. Commun., 2024, 15, 8688.
58. T. F. Liu, M. Y. Guo, A. Orthaber, R. Lomoth, M. Lundberg, S. Ott and L. Hammarström, Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions, Nat. Chem., 2018, 10, 881–887.
59. T. F. Markle, J. W. Darcy and J. M. Mayer, A new strategy to efficiently cleave and form C-H bonds using proton-coupled electron transfer, Sci. Adv., 2018, 4, eaat5776.
60. X. L. Pan, M. Y. Yan, Q. Liu, X. B. Zhou, X. B. Liao, C. L. Sun, J. X. Zhu, C. McAleese, P. Couture, M. K. Sharpe, R. Smith, N. H. Peng, J. England, S. C. E. Tsang, Y. L. Zhao and L. Q. Mai, Electric-field-assisted proton coupling enhanced oxygen evolution reaction, Nat. Commun., 2024, 15, 3354.
61. A. Yamaguchi, R. Inuzuka, T. Takashima, T. Hayashi, K. Hashimoto and R. Nakamura, Regulating proton-coupled electron transfer for efficient water splitting by manganese oxides at neutral pH, Nat. Commun., 2014, 5, 4256.
62. E. Pastor, F. Le Formal, M. T. Mayer, S. D. Tilley, L. Francàs, C. A. Mesa, M. Grätzel and J. R. Durrant, Spectroelectrochemical analysis of the mechanism of (photo)electrochemical hydrogen evolution at a catalytic interface, Nat. Commun., 2017, 8, 14280.
63. Q. L. Wang, S. F. Hung, K. J. Lao, X. Huang, F. H. Li, H. B. Tao, H. B. Yang, W. Liu, W. J. Wang, Y. Q. Cheng, N. Hiraoka, L. P. Zhang, J. M. Zhang, Y. H. Liu, J. Z. Chen, Y. H. Xu, C. L. Su, J. G. Chen and B. Liu, Breaking the linear scaling limit in multi-electron-transfer electrocatalysis through intermediate spillover, Nat. Catal., 2025, 378–388.
64. W. Zhang, Y. Li, L. J. Wu, Y. D. Duan, K. Kisslinger, C. L. Chen, D. C. Bock, F. Pan, Y. M. Zhu, A. C. Marschilok, E. S. Takeuchi, K. J. Takeuchi and F. Wang, Multi-electron transfer enabled by topotactic reaction in magnetite, Nat. Commun., 2019, 10, 1972.
65. T. X. Huang, X. Cong, S. S. Wu, J. B. Wu, Y. F. Bao, M. F. Cao, L. W. Wu, M. L. Lin, X. Wang, P. H. Tan and B. Ren, Visualizing the structural evolution of individual active sites in MoS₂ during electrocatalytic hydrogen evolution reaction, Nat. Catal., 2024, 7, 646–654.
66. A. Pei, P. Wang, S. Y. Zhang, Q. H. Zhang, X. Y. Jiang, Z. X. Chen, W. W. Zhou, Q. Z. Qin, R. F. Liu, R. Du, Z. J. Li, Y. C. Qiu, K. Y. Yan, L. Gu, J. Y. Ye, G. I. N. Waterhouse, W. H. Huang, C. L. Chen, Y. Zhao and G. X. Chen, Enhanced electrocatalytic biomass oxidation at low voltage by Ni₂+-O-Pd interfaces, Nat. Commun., 2024, 15, 5899.
67. X. P. Qin, H. A. Hansen, K. Honkala and M. M. Melander, Cation-induced changes in the inner- and outer-sphere mechanisms of electrocatalytic CO₂ reduction, Nat. Commun., 2023, 14, 7607.
68. P. C. Ye, K. Q. Fang, H. Y. Wang, Y. H. Wang, H. Huang, C. B. Mo, J. Q. Ning and Y. Hu, Lattice oxygen activation and local electric field enhancement by co-doping Fe and F in CoO nanoneedle arrays for industrial electrocatalytic water oxidation, Nat. Commun., 2024, 15, 1012.
69. Y. L. Zhu, H. A. Tahini, Z. W. Hu, J. Dai, Y. B. Chen, H. N. Sun, W. Zhou, M. L. Liu, S. C. Smith, H. T. Wang and Z. P. Shao, Unusual synergistic effect in layered ruddlesden - popper oxide enables ultrafast hydrogen evolution, Nat. Commun., 2019, 10, 149.
70. H. Li, P. Wen, D. S. Itanze, Z. D. Hood, S. Adhikari, C. Lu, X. Ma, C. C. Dun, L. Jiang, D. L. Carroll, Y. J. Qiu and S. M. Geyer, Scalable neutral H₂O₂ electrosynthesis by platinum diphosphide nanocrystals by regulating oxygen reduction reaction pathways, Nat. Commun., 2020, 11, 3928.
71. J. M. Liang, J. T. Liu, L. S. Guo, W. H. Wang, C. W. Wang, W. Z. Gao, X. Y. Guo, Y. L. He, G. H. Yang, S. Yasuda, B. Liang and N. Tsubaki, CO₂ hydrogenation over Fe-Co bimetallic catalysts with tunable selectivity through a graphene fencing approach, Nat. Commun., 2024, 15, 512.
72. Y. Pan, Y. J. Chen, K. L. Wu, Z. Chen, S. J. Liu, X. Cao, W. O. Cheong, T. Meng, J. Luo, L. R. Zheng, C. G. Liu, D. S. Wang, Q. Peng, J. Li and C. Chen, Regulating the coordination structure of single-atom Fe-N_xC_y catalytic sites for benzene oxidation, Nat. Commun., 2019, 10, 4290.
73. P. Xu, J. J. Xie, D. S. Wang and X. P. Zhang, Metalloradical approach for concurrent control in intermolecular radical allylic C-H amination, Nat. Chem., 2023, 15, 498–507.
74. Y. S. Xu, D. X. Wu, Q. H. Zhang, P. Rao, P. L. Deng, M. G. Tang, J. Li, Y. J. Hua, C. T. Wang, S. K. Zhong, C. M. Jia, Z. X. Liu, Y. J. Shen, L. Gu, X. L. Tian and Q. B. Liu, Regulating Au coverage for the direct oxidation of methane to methanol, Nat. Commun., 2024, 15, 564.
75. W. L. Zhou, H. Su, W. R. Cheng, Y. L. Li, J. J. Jiang, M. H. Liu, F. F. Yu, W. Wang, S. Q. Wei and Q. H. Liu, Regulating the scaling relationship for high catalytic kinetics and selectivity of the oxygen reduction reaction, Nat. Commun., 2022, 13, 6414.
76. J. Baek, M. D. Hossain, P. Mukherjee, J. H. Lee, K. T. Winther, J. Leem, Y. Jiang, W. C. Chueh, M. Bajdich and X. L. Zheng, Synergistic effects of mixing and strain in high entropy spinel oxides for oxygen evolution reaction, Nat. Commun., 2023, 14, 5936.
77. S. S. Chen, Z. L. Zhang, W. Chen, B. E. G. Lucier, M. S. Chen, W. L. Zhang, H. H. Zhu, I. Hung, A. M. Zheng, Z. H. Gan, D. S. Lei and Y. N. Huang, Understanding water reaction pathways to control the hydrolytic reactivity of a Zn metal-organic framework, Nat. Commun., 2024, 15, 10776.
78. J. C. Hao, Z. C. Zhuang, K. C. Cao, G. H. Gao, C. Wang, F. L. Lai, S. L. Lu, P. M. Ma, W. F. Dong, T. X. Liu, M. L. Du and H. Zhu, Unraveling the electronegativity-dominated intermediate adsorption on high-entropy alloy electrocatalysts, Nat. Commun., 2022, 13, 2662.
79. M. G. Li, F. X. Lin, S. P. Zhang, R. Zhao, L. Tao, L. Li, J. Y. Li, L. Y. Zeng, M. C. Luo and S. J. Guo, High-entropy alloy electrocatalysts go to (sub-)nanoscale, Sci. Adv., 2024, 10, eadn2877.
80. X. Z. Li, Y. Y. Fang, J. Wang, H. Y. Fang, S. B. Xi, X. X. Zhao, D. Y. Xu, H. M. Xu, W. Yu, X. Hai, C. Chen, C. A. H. Yao, H. B. Tao, A. G. R. Howe, S. J. Pennycook, B. Liu, J. Lu and C. L. Su, Ordered clustering of single atomic Te vacancies in atomically thin PtTe₂ promotes hydrogen evolution catalysis, Nat. Commun., 2021, 12, 2351.
81. J. Wei, H. Tang, L. Sheng, R. Y. Wang, M. H. Fan, J. L. Wan, Y. H. Wu, Z. R. Zhang, S. M. Zhou and J. Zeng, Site-specific metal-support interaction to switch the activity of Ir single atoms for oxygen evolution reaction, Nat. Commun., 2024, 15, 559.
82. C. Zhan, F. Dattila, C. Rettenmaier, A. Herzog, M. Herran, T. Wagner, F. Scholten, A. Bergmann, N. López and B. R. Cuenya, Key intermediates and Cu active sites for CO₂ electroreduction to ethylene and ethanol, Nat. Energy, 2024, 9, 1485–1496.
83. K. Nakamura, T. Takahashi, T. Hosomi, W. Tanaka, Y. Yamaguchi, J. Liu, M. Kanai, Y. Tsuji and T. Yanagida, van der Waals interactions between nonpolar alkyl chains and polar oxide surfaces prevent catalyst deactivation in aldehyde gas sensing, Nat. Commun., 2024, 15, 9211.
84. X. Chen, L. P. Granda-Marulanda, I. T. McCrum and M. T. M. Koper, How palladium inhibits CO poisoning during electrocatalytic formic acid oxidation and carbon dioxide reduction, Nat. Commun., 2022, 13, 38.
85. Y. Pan, Y. Li, C.-L. Dong, Y.-C. Huang, J. Wu, J. Shi, Y. Lu, M. Yang, S. Wang and Y. Zou, Unveiling the synergistic effect of multi-valence Cu species to promote formaldehyde oxidation for anodic hydrogen production, Chem, 2023, 9, 963–977.
86. M. Zheng, J. Zhang, P. Wang, H. Jin, Y. Zheng and S. Z. Qiao, Recent advances in electrocatalytic hydrogenation reactions on copper–based catalysts, Adv. Mater., 2024, 36, 2307913.
87. X. Gao, Y. Pan, J. Qiu, J. Peng, S. Wang and Y. Zou, Enhancing the stability of Cu-based electrocatalyst via Fe alloy in electrocatalytic formaldehyde oxidation with long durability, Adv. Funct. Mater., 2024, 35, 2417545.
88. H. Yu, S. Jiang, W. Zhan, Y. Liang, K. Deng, Z. Wang, Y. Xu, H. Wang and L. Wang, Formaldehyde oxidation boosts ultra-low cell voltage industrial current density water electrolysis for dual hydrogen production, Chem. Eng. J., 2023, 475, 146210.
89. M. P. J. M. van der Ham, E. van Keulen, M. T. M. Koper, A. A. Tashvigh and J. H. Bitter, Steering the selectivity of electrocatalytic glucose oxidation by the Pt oxidation state, Angew. Chem., Int. Ed., 2023, 62, e202306701.
90. L. Zhao, Z. Lv, Y. Shi, S. Zhou, Y. Liu, J. Han, Q. Zhang, J. Lai and L. Wang, Simultaneous generation of furfuryl alcohol, formate, and H₂ by co-electrolysis of furfuryl and HCHO over bifunctional CuAg bimetallic electrocatalysts at ultra-low voltage, Energy Environ. Sci., 2024, 17, 770–779.
91. G. Li, G. Han, L. Wang, X. Cui, N. K. Moehring, P. R. Kidambi, D.-e. Jiang and Y. Sun, Dual hydrogen production from electrocatalytic water reduction coupled with formaldehyde oxidation via a copper-silver electrocatalyst, Nat. Commun., 2023, 14, 525.
92. X. Zhang, T. Y. Liu, Y. Zhou, L. Zhang, X. C. Zhou, J. J. Feng and A. J. Wang, A transformative strategy to realize hydrogen production with electricity output through ultra-low potential furfural oxidation on hollow PdCu alloy networks, Appl. Catal., B, 2023, 328, 122530.
93. H. Z. Liu, J. Q. Yu, Y. F. Chen, J. K. Lee, W. Y. Huang and W. Z. Li, Cu-based bimetallic catalysts for electrocatalytic oxidative dehydrogenation of furfural with practical rates, ACS Appl. Mater. Interfaces, 2023, 15, 37477–37485.
94. Y. X. Zhang and N. Kornienko, Conductive metal-organic frameworks bearing M-O₄ active sites as highly active biomass valorization electrocatalysts, ChemSusChem, 2022, 15, e202101587.
95. M. Yang, Y. Jiang, C. L. Dong, L. Xu, Y. Huang, S. Leng, Y. Wu, Y. Luo, W. Chen, T. T. T. Nga, S. Wang and Y. Zou, A self-reactivated PdCu catalyst for aldehyde electro-oxidation with anodic hydrogen production, Nat. Commun., 2024, 15, 9852.
96. L. Xiao, W. Dai, S. Mou, X. Wang, Q. Cheng and F. Dong, Coupling electrocatalytic cathodic nitrate reduction with anodic formaldehyde oxidation at ultra-low potential over Cu₂O, Energy Environ. Sci., 2023, 16, 2696–2704.
97. J. F. Zhang, W. B. Gong, H. J. Yin, D. D. Wang, Y. X. Zhang, H. M. Zhang, G. Z. Wang and H. J. Zhao, In situ growth of ultrathin Ni(OH)₂ nanosheets as catalyst for electrocatalytic oxidation reactions, ChemSusChem, 2021, 14, 2935–2942.
98. S. Klinyod, N. Yodsin, M. T. Nguyen, Z. Pasom, S. Assavapanumat, M. Ketkaew, P. Kidkhunthod, T. Yonezawa, S. Namuangruk and C. Wattanakit, Unraveling the electrocatalytic activity in HMF oxidation to FDCA by fine-tuning the degree of NiOOH phase over Ni nanoparticles supported on graphene oxide, Small, 2024, 20, 2400779.
99. J. N. Hausmann, P. V. Menezes, G. Vijaykumar, K. Laun, T. Diemant, I. Zebger, T. Jacob, M. Driess and P. W. Menezes, In–liquid plasma modified nickel foam: NiOOH/NiFeOOH active site multiplication for electrocatalytic alcohol, aldehyde, and water oxidation, Adv. Energy Mater., 2022, 12, 2202098.
100. Y. Song, W. Xie, Y. Song, H. Li, S. Li, S. Jiang, J. Y. Lee and M. Shao, Bifunctional integrated electrode for high-efficient hydrogen production coupled with 5-hydroxymethylfurfural oxidation, Appl. Catal., B, 2022, 312, 121400.
101. R. Y. Zhong, P. W. Wu, Q. Wang, X. T. Zhang, L. Du, Y. H. Liu, H. K. Yang, M. Gu, Z. C. Zhang, L. M. Huang and S. Y. Ye, Room-temperature fabrication of defective CoO_xH_ynanosheets with abundant oxygen vacancies and high porosity as efficient 5-hydroxymethylfurfural oxidation electrocatalysts, Green Chem., 2023, 25, 4674–4684.
102. W. J. Liu, Z. Xu, D. Zhao, X. Q. Pan, H. C. Li, X. Hu, Z. Y. Fan, W. K. Wang, G. H. Zhao, S. Jin, G. W. Huber and H. Q. Yu, Efficient electrochemical production of glucaric acid and H₂ via glucose electrolysis, Nat. Commun., 2020, 11, 265.
103. X. P. Liu, X. H. Wang, C. X. Mao, J. Y. Qiu, R. Wang, Y. Liu, Y. Chen and D. L. Wang, Ligand-hybridization activates lattice-hydroxyl-groups of NiCo(OH)_x nanowires for efficient electrosynthesis, Angew. Chem., Int. Ed., 2024, 63, e202408109.
104. M. Klingenhof, H. Trzesniowski, S. Koch, J. Zhu, Z. Zeng, L. Metzler, A. Klinger, M. Elshamy, F. Lehmann, P. W. Buchheister, A. Weisser, G. Schmid, S. Vierrath, F. Dionigi and P. Strasser, High-performance anion-exchange membrane water electrolysers using NiX (X = Fe,Co,Mn) catalyst-coated membranes with redox-active Ni-O ligands, Nat. Catal., 2024, 7, 1213–1222.
105. S. Yang, Y. Guo, P. Zhao, H. Jiang, H. Shen, Z. Chen, L. Jiang, X. Xue, Q. Zhang and H. Zhang, Unraveling the electrooxidation mechanism of 5-(hydroxymethyl)furfural at a molecular level via nickel-based two-dimensional metal–organic frameworks catalysts, ACS Catal., 2024, 14, 449–462.
106. B. K. Chen, B. W. Yang, Y. Q. Su, Q. D. Hou, R. L. Smith Jr., X. H. Qi and H. X. Guo, NiFeCo wrinkled nanosheet electrode for selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, Green Chem., 2025, 27, 2117–2129.
107. M. Li, H. Sun, C. Wang, Y. Liu, Q. Xia, J. Meng, H. Yu and S. Dou, Balancing competitive adsorption on Co₃O₄@P, N-doped porous carbon to enhance the electrocatalytic upgrading of biomass derivatives, Small, 2025, 21, 2409765.
108. H. Sun, Y. Gao, M. Chen, M. Li, Q. Xia, Y. Liu, J. Meng, S. Dou and H. Yu, Synergistic boosting the electrooxidation of biomass-based 5-hydroxymethylfurfural on cellulose-derived Co₃O₄/N-doped carbon catalysts, Mater. Today Catal., 2024, 7, 100062.
109. M. Cai, Y. Zhang, Y. Zhao, Q. Liu, Y. Li and G. Li, Two-dimensional metal–organic framework nanosheets for highly efficient electrocatalytic biomass 5-(hydroxymethyl)furfural (HMF) valorization, J. Mater. Chem. A, 2020, 8, 20386–20392.
110. S. Kavian, S. N. Azizi and S. Ghasemi, Preparation of a novel supported electrode comprising a nickel(II) hydroxide-modified carbon paste electrode (Ni(OH)₂-X/CPE) for the electrocatalytic oxidation of formaldehyde, Chin. J. Catal., 2016, 37, 159–168.
111. Y. Q. He, C. Y. Ma, S. H. Mo, C. L. Dong, W. Chen, S. Chen, H. Pang, R. Z. Ma, S. Y. Wang and Y. Q. Zou, Unilamellar MnO₂ nanosheets confined Ru-clusters combined with pulse electrocatalysis for biomass electrooxidation in neutral electrolytes, Sci. Bull., 2025, 70, 193–202.
112. Z. W. Dai, X. Liu, N. Liu, Y. C. Zhang and X. B. Zhao, Upgrading biomass derived furan aldehydes by coupled electrochemical conversion over silver-based electrocatalysts, Chem. Eng. J., 2024, 488, 151001.
113. Y. Zhong, R.-Q. Ren, J.-B. Wang, Y.-Y. Peng, Q. Li and Y.-M. Fan, Grass-like Ni_xSe_y nanowire arrays shelled with NiFe LDH nanosheets as a 3D hierarchical core–shell electrocatalyst for efficient upgrading of biomass-derived 5-hydroxymethylfurfural and furfural, Catal. Sci. Technol., 2022, 12, 201–211.
114. R. Ojani, J. B. Raoof and S. R. H. Zavvarmahalleh, Preparation of Ni/poly(1,5-diaminonaphthalene)-modified carbon paste electrode; application in electrocatalytic oxidation of formaldehyde for fuel cells, J. Solid State Electrochem., 2008, 13, 1605–1611.
115. G. Bharath and F. Banat, High-grade biofuel synthesis from paired electrohydrogenation and electrooxidation of furfural using symmetric Ru/reduced graphene oxide electrodes, ACS Appl. Mater. Interfaces, 2021, 13, 24643–24653.
116. A. H. Touny, R. H. Tammam and M. M. Saleh, Electrocatalytic oxidation of formaldehyde on nanoporous nickel phosphate modified electrode, Appl. Catal., B, 2018, 224, 1017–1026.
117. L. Gong, N. Agrawal, A. Roman, A. Holewinski and M. J. Janik, Density functional theory study of furfural electrochemical oxidation on the Pt (1 1 1) surface, J. Catal., 2019, 373, 322–335.
118. Z. Chen, H. Zhou, F. Kong and M. Wang, Piezocatalytic oxidation of 5-hydroxymethylfurfural to 5-formyl-2-furancarboxylic acid over Pt decorated hydroxyapatite, Appl. Catal., B, 2022, 309, 121281.
119. Y. Wu, Z. L. Guo, C. X. Sun, Y. D. Yang and Q. Li, Integrated experimental and DFT analysis on the efficient and green upgrading of agroforestry biomass derived furan chemicals over NiMoO₄-CNTs-CF electrocatalyst with bi-catalytic sites, Ind. Crops Prod., 2022, 187, 115492.
120. T. Rafaïdeen, S. Baranton and C. Coutanceau, Highly efficient and selective electrooxidation of glucose and xylose in alkaline medium at carbon supported alloyed PdAu nanocatalysts, Appl. Catal., B, 2019, 243, 641–656.
121. D. J. Chadderdon, L. Xin, J. Qi, Y. Qiu, P. Krishna, K. L. More and W. Z. Li, Electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid on supported Au and Pd bimetallic nanoparticles, Green Chem., 2014, 16, 3778–3786.
122. X. H. Wu, Z. J. Zhao, X. C. Shi, L. Q. Kang, P. Das, S. Wang, S. Q. Chu, H. Wang, K. Davey, B. Zhang, S. Z. Qiao, J. L. Gong and Z. S. Wu, Multi-site catalysis of high-entropy hydroxides for sustainable electrooxidation of glucose to glucaric acid, Energy Environ. Sci., 2024, 17, 3042–3051.
123. X. Jiang, X. Wu, M. Lv, X. Pan, H. Wang, C. Li, M. Chen, W. Chen, B. Zhang, G. Yu, Z.-S. Wu, B. Qiao, B. Liu, F. E. Kühn and T. Zhang, “Suspended” single rhenium atoms on nickel oxide for efficient electrochemical oxidation of glucose, J. Am. Chem. Soc., 2025, 147, 4886–4895.
124. J. Woo, J. Choi, J. Choi, M.-Y. Lee, E. Kim, S. Yun, S. Yoo, E. Lee, U. Lee, D. H. Won, J. H. Park, Y. J. Hwang, J. S. Yoo and D. K. Lee, Mechanistic Insights into the role of elements in Ni-Co-P catalysts for electrochemical conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, Adv. Funct. Mater., 2025, 35, 2413951.
125. N. Jiang, B. You, R. Boonstra, I. M. T. Rodriguez and Y. Sun, Integrating electrocatalytic 5-hydroxymethylfurfural oxidation and hydrogen production via Co-P-derived electrocatalysts, ACS Energy Lett., 2016, 1, 386–390.
126. N. Jiang, X. Liu, J. Dong, B. You, X. Liu and Y. Sun, Electrocatalysis of furfural oxidation coupled with H₂ evolution via nickel-based electrocatalysts in water, ChemNanoMat, 2017, 3, 491–495.
127. Z. F. Zhao, T. Y. Guo, X. Y. Luo, X. T. Qin, L. X. Zheng, L. Yu, Z. Q. Lv, D. Ma and H. J. Zheng, Bimetallic sites and coordination effects: electronic structure engineering of NiCo-based sulfide for 5-hydroxymethylfurfural electrooxidation, Catal. Sci. Technol., 2022, 12, 3817–3825.
128. F. Wang, Y. Gu, B. Tian, Y. Sun, L. Zheng, S. Liu, Y. Wang, L. Tang, X. Han, J. Ma and M. Ding, Spinel-derived formation and amorphization of bimetallic oxyhydroxides for efficient electrocatalytic biomass oxidation, J. Phys. Chem. Lett., 2023, 14, 2674–2683.
129. Y. Ramli, V. Chaerusani, Z. Yang, Z. Feng, S. Karnjanakom, Q. Zhao, S. Li, Y. Li, A. Abudula and G. Guan, Degradation effect on oxidation of 5-hydroxymethyl-2-furaldehyde over cobalt-iron electrocatalysts in alkaline condition, J. Environ. Chem. Eng., 2024, 12, 113666.
130. Z. Zhao, M. Zhu, M. Qu, X. Luo, Q. Hu, X. Shen, W. Zheng, Y. Jia, Q. Sun, J. Chen and H. Zheng, Relay electrocatalysis with bimetallic sites for highly efficient oxidation in multiple cascade reaction, Chem. Eng. J., 2024, 484, 149768.
131. L. X. Zheng, Y. J. Zhao, P. H. Xu, Z. Q. Lv, X. W. Shi and H. J. Zheng, Biomass upgrading coupled with H₂ production via a nonprecious and versatile Cu-doped nickel nanotube electrocatalyst, J. Mater. Chem. A, 2022, 10, 10181–10191.

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