Advances in catalyst and reactor design for CO₂ electroreduction to methanol

Abstract

The electroreduction of CO₂ to methanol constitutes an attractive strategy for sustainable energy storage and carbon recycling. Methanol is not only a versatile chemical feedstock but also a liquid energy carrier compatible with existing infrastructure. However, the multi-step proton–electron transfer process and competing reaction pathways significantly limit methanol selectivity and production rates. This review provides a critical overview of recent progress in CO₂-to-methanol electro-conversion, including both direct CO₂ reduction reactions and indirect CO reduction reactions. We focus on mechanistic insights, emphasizing key intermediates such as CO*, CHO*, and CH₃O*, and identify structure–activity relationships through operando characterization and density functional theory calculations. The discussion spans a wide range of catalyst platforms, from molecular complexes, single-atom catalysts, and nanoclusters to alloy materials, and explores strategies such as tandem catalysis and interface engineering to increase selectivity and efficiency. We further explore developments in gas-fed flow cells and membrane–electrode assemblies that enable high-rate, stable operation. Finally, we highlight current limitations in catalyst design and system integration and outline emerging strategies to enable scalable and carbon-neutral methanol electrosynthesis.

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Chuan Xia

Chuan Xia is a Professor of Materials and Energy at the University of Electronic Science and Technology of China (UESTC). His group focuses on developing novel catalysts and device architectures that can be applied in electrocatalysis. He has won the J. Evans Attwell Welch postdoctoral fellowship (2019), Best Applied Paper Award of AIChE (2020), and Falling Walls Science Breakthroughs of the Year Award (2022), Top 10 News Stories of Scientific and Technological Progress in China (2022), Sichuan Youth May Fourth Medal (2023), and the Chinese Chemical Society Young Chemist Award (2023). More information about his research can be found at: https://www.chuan-lab.com.

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1. Introduction

The industrial revolution triggered rampant fossil fuel consumption, resulting in the continuous accumulation of greenhouse gases, particularly CO₂, causing severe climate crises. This unsustainable trajectory has triggered widespread environmental consequences, ranging from rising sea levels to intensified extreme weather events.^1–3 In parallel, the global shift to clean energy technologies such as solar, wind, and hydropower offers a significant opportunity to decarbonize energy systems.^4,5 However, the intermittent and location-dependent nature of these renewables imposes critical demands for robust, large-scale energy storage and carbon capture-conversion strategies. The electrochemical CO₂ reduction reaction (CO₂RR) offers a compelling solution that simultaneously addresses energy storage and carbon neutrality. By directly converting captured CO₂ into energy-rich chemicals and fuels using renewable electricity, the CO₂RR offers a sustainable means to close the anthropogenic carbon cycle. This technology not only enables temporal storage of excess renewable electricity in chemical bonds but also transforms CO₂ from a liability into a feedstock for high-value carbon-based products.^6–8 In recent decades, tremendous progress has been made in converting CO₂ to low-carbon molecules, particularly C₁ products, which require fewer electrons and offer well-defined reaction pathways. Among these, carbon monoxide (CO)^9,10 and formate (HCOO⁻)^11,12 have been extensively studied because of their relatively simple two-electron transfer mechanisms, high selectivity on metal catalysts and potential as intermediates in tandem or hybrid systems. In contrast, methanol is a particularly attractive target due to its favorable energy density, liquid-phase stability, and broad industrial utility.

Methanol is a globally traded platform molecule with an annual production exceeding 98 million metric tons and projected demand growth in the energy, materials, and hydrogen storage sectors.^13–15 It plays a central role in the manufacturing of formaldehyde, acetic acid, methyl tert-butyl ether (MTBE), dimethyl ether (DME), and a wide range of solvents and plastics.^16–19 As a liquid fuel, methanol can be used in internal combustion engines, direct methanol fuel cells (DMFCs), or reformed to generate hydrogen.^20,21 Furthermore, methanol is gaining traction in synthetic biology and biomanufacturing: methylotrophic microbes can use it as a carbon feedstock to produce single-cell proteins²² and pharmaceutical intermediates,²³ advancing the development of “electro-bio” hybrid systems for high-value chemical synthesis.

Currently, nearly all industrial methanol is synthesized via syngas (CO + H₂) hydrogenation at high temperatures and elevated pressures using fossil-derived natural gas or coal.^24,25 This thermocatalytic process is energy-intensive, centralized, and associated with high CO₂ emissions. In contrast, the electroreduction of CO₂ to methanol offers a decentralized, low-temperature, and carbon-neutral alternative that can be enabled by renewable electricity. In principle, this process enables direct integration with carbon capture systems and distributed green power infrastructure, forming a closed-loop carbon cycle.^26–28 Despite this conceptual appeal, electrocatalytic methanol synthesis remains at an early stage, facing numerous technical bottlenecks that hinder its industrial translation.^29,30 While copper-based catalysts dominate CO₂RR research for multi-carbon products (e.g., ethylene and ethanol),^31–33 methanol—a critical C₁ platform molecule—has received limited attention, often emerging as a minor byproduct in C₂₊ synthesis. Current catalytic systems struggle to balance high methanol selectivity (>50%) with industrially relevant current densities (>200 mA cm⁻²), necessitating innovative strategies to reconfigure reaction networks.

The electrochemical conversion of CO₂ to methanol is a complex transfer process involving the formation and transformation of several key intermediates. It requires six electrons and six protons, progressing through a series of adsorbed species such as *CO₂, *COOH, *CO, *CHO, *CH₂O, and *CH₃O. Among these, *CO is a critical branching point that can lead to a variety of C₁ or C₂₊ products, depending on the surface coverage, electronic properties of the catalyst, and local microenvironment. Achieving selective methanol production necessitates precise control over the binding energy and protonation kinetics of these intermediates, while minimizing competing pathways such as the hydrogen evolution reaction (HER), CO desorption, and further reduction to methane.^34–37 To date, two general electrocatalytic strategies have been pursued for CO₂-to-methanol conversion: the direct CO₂ reduction route and the indirect CO reduction reaction (CORR) route. In the direct pathway, CO₂ is converted to methanol in a single reactor over a multifunctional catalyst. This approach is conceptually simple but suffers from sluggish CO₂ activation and poor selectivity due to multiple competitive reactions. In the indirect route, CO₂ is first selectively reduced to CO using high-performance CO₂-to-CO catalysts such as Ag, Zn, or molecular complexes,^38–40 followed by a second electrochemical step in which CO is further reduced to methanol. This tandem strategy, while more complex in terms of system integration, benefits from decoupling the reaction kinetics and independently optimizing each step. In both routes, the ability to stabilize intermediate species, such as *CO, *CHO, and *CH₃O, is essential for achieving high selectivity and energy efficiency. For the direct CO₂RR, we analyze critical bottlenecks in CO₂ activation and C–H/C–O bond formation, highlighting strategies to stabilize key intermediates through alloy engineering,^41,42 microenvironment modulation^43,44 and surface molecular tuning.^45,46 For indirect pathways, we evaluate tandem catalytic systems that spatially or temporally separate CO generation and methanol synthesis, emphasizing the role of *CO coverage and oxidation state dynamics in steering CO reduction selectivity. In addition to catalyst development, several non-catalytic factors profoundly influence the methanol yield, including the electrolyte composition, pH, ion transport, gas–liquid–solid interface engineering, and reactor architecture. For example, gas diffusion electrodes (GDEs) and membrane–electrode assemblies (MEAs) are crucial for scaling up to commercially viable current densities while maintaining product selectivity (Fig. 1). Emerging in situ and operando characterization tools, such as attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray absorption spectroscopy (XAS), and Raman, offer unprecedented insights into reaction intermediates, dynamic surface states, and degradation pathways.^47–50 Moreover, integrated machine learning approaches accelerate rational catalyst design with tailored electronic/geometric properties.

Fig. 1 Summary of material synthesis, in situ characterization and device fabrication for electrochemical CO₂-to-methanol.

In this review, we aim to provide a comprehensive and critical evaluation of recent progress in electrochemical CO₂ reduction to methanol. We begin by outlining the fundamental mechanistic principles of the CO₂RR and CORR to methanol, emphasizing key intermediate species and rate-determining steps. We then categorize and assess state-of-the-art catalysts across multiple material classes, highlighting their structural features, performance metrics, and mechanistic insights. Particular attention is given to molecular-level design strategies, interface engineering, and tandem reaction systems. We further explore how gas-fed flow-cells, MEAs and local electrolyte engineering are reshaping the operational landscape, enabling high-rate, stable methanol production. Finally, we discuss the remaining challenges in selectivity control, catalyst durability, and large-scale deployment, while identifying emerging opportunities in tandem electrocatalysis, operando-guided design, system integration, and technoeconomic optimization. Through this analysis, we aim to provide a forward-looking perspective that supports the development of scalable, carbon-neutral methanol electrosynthesis.

2. Direct CO₂ electroreduction toward methanol

The electrochemical CO₂-to-methanol process constitutes a complex multi-step cascade involving selective multi-electron/proton transfers. The core mechanistic challenge resides in controlling the trajectory of adsorbed intermediates, steering them through sequential hydrogenation steps while effectively suppressing competing pathways, including *CO desorption, over-reduction to methane (CH₄), C–C coupling toward C₂₊ products and the HER.^51,52 A comprehensive understanding of the kinetics and thermodynamics governing each elementary step, particularly the kinetically bottlenecked CO hydrogenation to *CHO, is essential for designing catalysts with high methanol production activity.⁵³ Recent advances in catalyst design and mechanistic understanding have propelled progress in steering CO₂RR pathways toward methanol. This section analyzes advanced catalytic strategies for direct CO₂-to-methanol conversion, focusing on catalyst design, including phthalocyanine molecular catalysts, Cu-based catalysts and non-Cu compound systems. We also thoroughly analyze the key reaction mechanisms involving dependent active sites, guiding rational catalyst optimization. Challenges in balancing methanol selectivity, current density, and long-term stability are critically discussed. This comprehensive overview aims to accelerate efficient direct CO₂-to-methanol systems for a circular carbon economy. To provide an intuitive overview of the historical development in this research domain, Fig. 2 presents a chronological timeline highlighting key advancements in methanol synthesis.

Fig. 2 Timeline of the major development of CO₂-to-methanol electrocatalysts in the CO₂ reduction reaction.

2.1. Electrochemical CO₂-to-methanol mechanism analysis

The current mechanistic understanding of electrochemical CO₂-to-CH₃OH conversion primarily encompasses two distinct pathways: the CO-mediated route and the HCOO⁻-involving pathway^19,34,54 (Fig. 3). The CO-mediated pathway proceeds through electrochemical CO₂ reduction to adsorbed CO*, followed by sequential hydrogenation. CO₂ initially undergoes two-electron reduction to form surface-bound CO*, with subsequent proton-coupled electron transfer (PCET) generating CHO* and CH₂O* intermediates. The reaction cascade culminates in CH₃O* formation, which undergoes final protonation to yield CH₃OH (CO₂ → CO* → CHO* → CH₂O* → CH₃O* → CH₃OH). This route is dominated by molecular catalysts or Cu-based catalysts, where the CO adsorption geometry facilitates C–H bond formation.^35,55 The HCOO⁻-involving pathway initiates through proton-assisted CO₂ reduction to surface-adsorbed formate (*OCHO). This intermediate undergoes C–O bond cleavage and protonation reactions to generate HCO* and H₂O, followed by hydrogenation to form CH₂O* and subsequent PCET to form CH₃OH (CO₂ → *OCHO → HCO* → CH₂O* → CH₃O* → CH₃OH). With respect to the HCOO⁻-involving pathway, Du et al. proposed that this mechanism becomes kinetically constrained above pH > 4.9, where formic acid tends to dissociate strongly.⁵⁶ In addition, CO* and CHO* have been identified as critical intermediates by experimental observations of the electrochemical CO₂-to-methanol conversion.³⁶

Fig. 3 Proposed reaction mechanism for CO₂-to-methanol conversion. Reproduced from ref. 54 with permission from Elsevier, copyright 2020.

2.2. Phthalocyanine molecular catalyst in CO₂-to-methanol

Molecular catalysts have emerged as a powerful class of materials for electrochemical CO₂ reduction because of their well-defined active sites, tunable ligand environments, and capacity for rational structure–function design. Their square-planar geometry enables precise control over catalytic properties for targeting products through axial ligands and peripheral substituents.^57–60 Among various phthalocyanine molecules, cobalt phthalocyanine (CoPc) has attracted particular attention because of its moderate CO binding energy, high catalytic stability, and capacity to mediate multi-electron transfer processes. The central Co–N₄ unit provides a favorable platform for stabilizing *CO intermediates, which are essential for steering the reduction pathway toward methanol. However, the challenge lies in suppressing CO desorption and promoting its sequential protonation to methanol via *CHO and *CH₃O intermediates—a transformation that requires delicate control over the electronic structure and local reaction microenvironment. For example, Wang et al. demonstrated that immobilizing metal phthalocyanine complexes (FePc, CoPc, and NiPc) onto CNTs can significantly enhance the catalytic performance by improving the electron transfer kinetics for CO₂ reduction.⁶¹ Among these, CoPc/CNT exhibited exceptional activity, converting CO₂ to methanol via a domino process (Fig. 4A). The catalyst achieved an FE over 40% for methanol, with a partial current density exceeding 10 mA cm⁻² at −0.94 V versus the reversible hydrogen electrode (vs. RHE) (Fig. 4B). Notably, functionalizing the phthalocyanine ligand with electron-donating groups, such as amino substituents (e.g., CoPc-NH₂), further improved the durability, likely by stabilizing key intermediates and modifying the electronic configuration around the metal center. During 12 h of continuous electrolysis, the system maintained a stable FE for methanol (FE_methanol) of 28% (Fig. 4C). This study advances the field of CO₂ electroreduction by demonstrating a highly active and selective molecular catalyst for methanol production. The CoPc/CNT catalyst and its optimized version CoPc-NH₂/CNT offers new insights into the design of molecular catalysts for the multi-electron CO₂RR. These findings underscore how molecular-level dispersion and ligand engineering enhance catalytic performance and stability. In another intriguing study, Ye et al. revealed how strain engineering substantially enhances the catalytic activity of CoPc for electrochemical CO₂-to-methanol conversion.⁶² By systematically modulating the diameter of single-walled CNT (SWCNT) supports, they introduced controlled lattice strain into CoPc molecular structures. This strain-induced modification strategically altered both the local coordination geometry and electronic configuration of CoPc, resulting in optimized *CO intermediate adsorption and subsequent protonation toward methanol formation (Fig. 4D). In flow-cell electrolyzers, CoPc/SWCNT catalysts achieved methanol partial current densities as high as 66.8 mA cm⁻², with more than 30% methanol FE, substantially outperforming their counterparts supported on multi-walled CNTs (Fig. 4E). Mechanistic insights from DFT calculations revealed that the curvature-imposed strain in SWCNT-supported CoPc strengthens *CO adsorption through d-orbital rehybridization, thereby facilitating deeper reduction to methanol. In contrast, planar CoPc configurations on larger-diameter MWCNTs favor competitive *CO desorption pathways. Overall, this work provides fundamental insights into strain-activity relationships, and curvature engineering is proposed as a generic design strategy for molecular electrocatalyst optimization. Another notable development involves the design of dual-site cascade catalysts. By co-depositing two distinct phthalocyanine molecules, nickel tetramethoxyphthalocyanine (NiPc-OCH₃) and CoPc-NH₂, onto a shared carbon support, researchers have created molecular heterojunctions that enable intermediate spillover (Fig. 4F).⁶³ In this configuration, NiPc-OCH₃ sites efficiently reduce CO₂ to CO, which then diffuses to adjacent CoPc-NH₂ sites for further hydrogenation to methanol. This synergistic approach mimics the function of tandem catalytic systems at the molecular scale, achieving methanol partial current densities of 150 mA cm⁻² relative to CoPc-NH₂/CNT (∼125 mA cm⁻²) (Fig. 4G). Mechanistic analysis attributed the performance improvement to molecular-scale CO spillover from the NiPc-OCH₃ sites to the methanol-active CoPc-NH₂ sites. This work offers valuable insights into the design of efficient electrocatalysts for CO₂ reduction and highlights the importance of molecular-scale CO spillover in enhancing catalytic performance. Overall, phthalocyanine-based molecular catalysts offer a model platform for studying and improving CO₂-to-methanol conversion due to their atomic precision, synthetic flexibility, and accessible electronic tunability. Their performance underscores the importance of coordinated strategies involving ligand design, site isolation, electronic modulation, and nanostructured supports. Nonetheless, challenges remain in extending their stability under industrially relevant conditions, maintaining catalyst dispersion during extended operation, and scaling up the synthesis of high-loading molecular systems. Continued advances in operando spectroscopy and computational modeling will be critical in guiding next-generation molecular catalyst design for selective and durable methanol electrosynthesis.

Fig. 4 (A) CO₂-to-methanol domino process of CoPc/CNT. (B) Partial current densities for different products. (C) Product selectivity and current density during the 12 h CO₂RR. Reproduced from ref. 61 with permission from Springer Nature, copyright 2019. (D) Diameter-dependent structural deformation of CoPc on CNTs. (E) Methanol partial current densities for CoPc/SWCNT and the comparative sample. Reproduced from ref. 62 with permission from Springer Nature, copyright 2023. (F) Dual-site (CoPc-NH₂ + NiPc-OCH₃)/CNT vs. simple mixture in CO₂-to-methanol. (G) j_methanol in the flow cell. Reproduced from ref. 63 with permission from Springer Nature, copyright 2025.

2.3. Copper-based single atoms and clusters catalysts in CO₂-to-methanol

Cu occupies a unique position in the electrocatalytic CO₂ reduction landscape because of its unmatched ability to facilitate the formation of both C₁ and C₂₊ products. However, bulk Cu surfaces often suffer from poor selectivity and complex product distributions due to the concurrent formation of CH₄, C₂H₄, and other hydrocarbons. To overcome these limitations, recent efforts have focused on tailoring the atomic environment of Cu through the design of single-atom catalysts (SACs)^64,65 and sub-nanometer clusters.^66,67 These advancements not only deepen the atomic-level understanding of catalytic mechanisms but also lay a material foundation for high-value-added carbon cycle technologies. Through atomically dispersed structural design, Cu-based single-atom catalysts enable the precise modulation of active sites and expose a high proportion of coordinatively unsaturated sites. For example, He et al. presented a scalable production method for efficient Cu single-atom decorated carbon membranes (CuSAs/TCNFs) used in the electroreduction of CO₂-to-methanol (Fig. 5A).⁶⁸ The CuSAs/TCNFs catalyst achieves an FE of 44% for methanol production, with a partial current density of −93 mA cm⁻². Remarkably, at −0.9 V vs. RHE, methanol and CO were exclusively partitioned into the liquid (44% FE) and gas phases (56% FE), respectively, demonstrating unparalleled product selectivity (Fig. 5B). Mechanistic studies indicated that the reduction of *COH to *CHOH (leading to methanol) has a lower free energy barrier than the reduction of *COH to *C (leading to methane) at the Cu–N₄ sites does, explaining the higher selectivity for methanol over methane. Overall, the distinct configuration of the CuSAs/TCNFs, with isolated Cu atoms and a through-hole carbon framework, creates an efficient catalyst for CO₂-to-methanol by promoting key reaction steps and favoring the desired product formation. In another example, Yang et al. demonstrated an interfacial engineering strategy for synthesizing atomically dispersed Cu sites immobilized onto MXene nanosheets (denoted as Ti₃C₂Cl_x), enabling high electrocatalytic CO₂-to-methanol activity (Fig. 5C).⁶⁹ The prepared single-atom SA-Cu-MXene catalyst exhibited a characteristic volcano-shaped trend of methanol production over the applied potential, reaching a peak FE of 59.1% at −1.4 V vs. RHE (Fig. 5D). This value markedly surpasses that of the MXene-supported Cu nanoparticles (14.6% FE under identical conditions). DFT calculations revealed that a single Cu atom possessing an electronically unsaturated structure facilitates the rate-determining step (transformation of HCOOH* to the adsorbed CHO*). In addition to single-atom Cu catalysts, Cu clusters also exhibit significant potential in the CO₂RR. Inspired by the hard–soft acid–base (HSAB) theory, Huang's group introduced strategic manipulation of electronic delocalization in Cu-based catalytic motifs to switch CO₂ electroreduction pathways toward methanol.⁷⁰ The authors fabricated microflower-like Cu₂NCN with a hierarchical architecture (Fig. 5E). The anomalously low first-shell Cu coordination number (1.8) in Cu₂NCN toward CuO (5.6) confirmed pronounced undercoordination and electron delocalization at the Cu sites (Fig. 5F). The catalyst of Cu₂NCN demonstrates one of the highest CO₂-to-methanol conversion selectivities reported to date (70%), coupled with an exceptional partial current density of −92.3 mA cm⁻² (Fig. 5G). The delocalization state-induced selective bond breaking in Cu₂NCN critically enhances the selectivity and efficiency of CO₂-to-methanol. The mechanism analysis revealed that the improved catalytic efficacy stems from dual-factor synergy: electron delocalization within Cu active sites, which facilitates charge transfer during CO₂ activation, and diminished Cu–O interfacial interactions, which effectively suppress undesired byproduct formation. In summary, Cu SACs and nanoclusters offer highly tunable platforms for selective CO₂-to-methanol conversion. By controlling the Cu site's coordination environment and electronic structure, researchers can tune critical reaction steps (*CO binding, *CHO formation, *CH₃O protonation). Combined with scalable fabrication and stable supports, these insights provide practical catalysts for distributed methanol production. This concept could also be broadly applied to develop improved catalysts, such as tuning charge delocalization in high-entropy alloys or single-atom catalysts via support engineering and constructing charge-transfer heterojunctions to increase activity.

Fig. 5 (A) The synthesis process of CuSAs/THCF. (B) Product FE at CuSAs/TCNFs. Reproduced from ref. 68 with permission from American Chemical Society, copyright 2019. (C) Selective etching of the Ti₃(Al_1−xCu_x)C₂ MAX phase to form SA-Cu-MXene. (D) FE for SA-Cu-MXene. Reproduced from ref. 69 with permission from American Chemical Society, copyright 2021. (E) SEM and TEM (inset) images of Cu₂NCN. (F) FT-EXAFS spectrum (first-shell fitting) of Cu₂NCN. (G) CO₂RR product distribution of Cu₂NCN in the MEA electrolyzer. Reproduced from ref. 70 with permission from Springer Nature, copyright 2022.

2.4. Copper-based composite catalysts in CO₂-to-methanol

While single-metal Cu catalysts offer a foundational understanding of the CO₂RR, their performance is often limited by poor product selectivity, structural instability, and susceptibility to side reactions. To overcome these challenges, researchers have increasingly turned to composite catalyst systems in which Cu is integrated with secondary components, such as heteroatoms, metal dopants, or oxide phases, to construct multifunctional catalytic environments. Cu composites outperform monometallic Cu in the CO₂RR, with enhanced performance stemming from synergistic component interactions, interfacial modulation and active site optimization. One effective strategy involves dual doping of Cu-based materials with both cationic and anionic species to introduce synergistic modifications. For instance, the simultaneous incorporation of Ag and S into a Cu₂O/Cu matrix was shown to significantly enhance methanol selectivity by tuning both the bulk electronic structure and the local reaction microenvironment (Fig. 6A).⁷¹ The electrocatalytic performance of the Ag,S–Cu₂O/Cu catalyst under various applied voltages is presented in Fig. 6B. A distinct potential-dependent selectivity trend was observed: increasing cathodic polarization progressively suppressed H₂ and HCOOH generation while enhancing methanol formation. Notably, optimal performance was achieved at −1.18 V vs. RHE, where the catalyst attained a substantial current density of 122.7 mA cm⁻² accompanied by a peak methanol FE of 67.4%. DFT computations reveal a dual-site regulatory mechanism in which anionic S induces charge redistribution in neighboring Cu atoms through electronic structure modulation, significantly lowering the energy barrier for *CO hydrogenation to *CHO intermediates. Concurrently, cationic Ag species preferentially increase the activation energy of the HER pathway. Atomically dispersed secondary metal sites have also been proven effective in enhancing methanol selectivity. In a representative example, single Sn atoms were integrated into an oxygen-deficient CuO framework, creating Sn₁/V_O-CuO catalysts with dual-functional activity (Fig. 6C).⁷² This bifunctional catalyst achieves superior CO₂-to-methanol activity, achieving a remarkable methanol FE of 88.6% with a substantial current density of 67 mA cm⁻² (Fig. 6D). Sn₁/V_O-CuO-90 exhibited stable CO₂RR performance over 36 h at −2.0 V vs. Ag/Ag⁺, as evidenced by its stable current density and sustained FE (Fig. 6E). By bridging advanced operando experiments and DFT calculations, the catalyst facilitates CO₂ activation by lowering the activation energy required for *COOH dissociation into *CO, and then, the *CO intermediate subsequently binds to the Cu species, enabling its further reduction and ultimately resulting in high selectivity toward methanol. The atomic-level engineering of metal-defect interfaces opens new avenues for sustainable fuel synthesis, demonstrating how precise control over catalytic microenvironments can overcome inherent limitations in complex electrochemical transformations. Alloying effectively overcomes linear scaling constraints in catalysis by synergistically modulating electronic structures and intermediate adsorption strengths. The incorporation of Cu into alloy catalysts enables precise control of the catalytic performance through localized electron redistribution, thereby enhancing both the activity and selectivity simultaneously.^73–77 For example, a CuGa₂ alloy synthesized via a high-temperature solid-state reaction exhibited an ordered structure composed of alternating Cu and Ga layers.⁷⁸ The unit cells of the CuGa₂ crystal structures are illustrated in Fig. 6F, featuring alternating Cu (1D sheets) and Ga (square nets). This arrangement maximizes the surface exposure of the metal atoms. The activity trends during the CO₂RR varied with composition: the CuGa₂ catalyst demonstrated a record-high FE of 77.26% for methanol at −0.3 V vs. RHE, outperforming its Cu₉Ga₄ counterpart (37.75%) (Fig. 6G). To gain deeper insights into the CO₂-to-CH₃OH mechanism of CuGa₂, in situ ATR-FTIR spectroscopy was employed. As shown in Fig. 6H, under applied potentials of −0.1 to −1.1 V vs. RHE, two distinct vibrational features emerged at 1519 cm⁻¹ and 1373 cm⁻¹. These characteristic peaks correspond to the asymmetric and symmetric (OCO) stretching vibrations of the carboxylate group in the adsorbed HCOO⁻ intermediate, respectively. Notably, the observed hydrogen spillover phenomenon, where adsorbed hydrogen species migrate from Cu active sites to adjacent Ga sites, facilitates subsequent hydrogenation of the formate intermediate, ultimately leading to methanol formation through a cascade reaction pathway. This potential-dependent product distribution suggests a cathodic shift favoring multi-carbon oxygenate formation over competitive H₂ evolution and formate production pathways. These Cu-based composites demonstrate how multi-component systems can be engineered to circumvent limitations associated with monometallic surfaces. By introducing heteroatoms or fabricating alloys, the local electronic density of Cu can be redistributed, the binding strength of intermediates can be selectively modulated, and undesired side reactions can be suppressed. More importantly, these architectures often create spatially segregated reaction domains or bifunctional interfaces that enable a cascade mechanism. Nevertheless, challenges remain in the rational design and control of composite catalyst structures. The precise spatial distribution and interaction of dopants, the chemical nature of interfacial phases, and long-term stability under operational conditions are all critical factors that require further investigation. Advanced synthesis methods—such as atomic layer deposition, ion-exchange strategies, and controlled solid-state transformations—will be essential for pushing the performance of Cu-based composites to the level required for commercial methanol electrosynthesis.

Fig. 6 (A) Schematic of the x,y-Cu₂O/Cu catalyst preparation. (B) CO₂RR activity on the Ag,S–Cu₂O/Cu electrode. Reproduced from ref. 71 with permission from Springer Nature, copyright 2022. (C) Atomic-scale Sn dispersion (circled) in HAADF-STEM images. (D) FE_methanol of Sn₁/Vo-CuO-90 in the [Bmim]BF₄/H₂O electrolyte. (E) Chronoamperometric stability at −2.0 V vs. Ag/Ag⁺. Reproduced from ref. 72 with permission from Wiley-VCH GmbH, copyright 2021. (F) Crystal structure of CuGa₂. (G) FE of liquid products (MeOH, formate) during the CO₂RR over CuGa₂. (H) In situ ATR-FTIR which was conducted during the CO₂RR of CuGa₂. Reproduced from ref. 78 with permission from Wiley-VCH GmbH, copyright 2022.

2.5. Non-Cu-based materials in CO₂-to-methanol

Despite the widespread exploration of Cu-based systems for catalytic CO₂ reduction to methanol, their inherent tendency to generate multiple liquid products (e.g., ethanol, acetate, and formate) alongside methanol introduces significant challenges in downstream product isolation, thereby escalating energy and economic costs. This limitation stems from the non-selective *CO dimerization and C–C coupling pathways inherent to the electronic structure of Cu under operational conditions. To address this problem, there is a compelling need to develop non-Cu-based catalytic systems that exclusively steer CO₂-to-methanol with high activity, circumventing the thermodynamic and kinetic constraints of their Cu-based counterparts. Palladium (Pd)-based systems have recently emerged as promising alternatives for selective CO₂-to-methanol conversion because of their strong *CO adsorption and moderate hydrogenation activity. For example, Xiong and collaborators successfully fabricated Pd nanoparticles anchored on MnO₂ nanosheets via hydrothermal synthesis followed by solution-phase deposition.⁷⁹Fig. 7A illustrates the methanol synthesis mechanism via the CO₂RR on Pd/MnO₂. TEM images confirmed monodisperse Pd nanoparticles (∼3.0 nm) on the MnO₂ nanosheets (Fig. 7B). CO₂ electrochemical reduction assessment in a flow-cell revealed composition-dependent activity trends: the Pd_1.80%/MnO₂ catalyst accomplished a record-high FE of 80.9 ± 1.5% for methanol at −0.6 V vs. RHE, surpassing its Pd_1.23%/MnO₂ and Pd_2.45%/MnO₂ counterparts (Fig. 7C). To gain deeper insight into the CO₂-to-CH₃OH conversion mechanism catalyzed by Pd/MnO₂, in situ DRIFTS and DFT calculations were performed. The observed maximum wavenumbers for *CO (∼2192 cm⁻¹) and *OH (∼1660 cm⁻¹) intermediates on Pd_1.80%/MnO₂ at −0.6 V vs. RHE indicate their strongest chemisorption at this potential. This enhanced adsorption stabilizes key reactive configurations: the strengthened *CO–Pd interaction lowers the activation barrier for its hydrogenation to transfer during subsequent steps (*CHO* → *CH₂O* → *CH₃O*), synergistically steering the reaction pathway toward methanol with suppressed C–C coupling byproducts (Fig. 7D). Theoretical calculations indicate that *CO hydrogenation to *CHO* serves as the rate-determining step (Fig. 7E). In another instance, Zheng and collaborators successfully fabricated ultrathin Pd nanosheets that partially overlapped with SnO₂ nanoparticles.⁸⁰ As evidenced by CO stripping, the SnO₂ NPs lack CO adsorption capacity, whereas Pd/SnO₂ inherits this property from the Pd nanosheets. This inherent CO-binding capability is crucial for enabling further CO reduction to CH₃OH (Fig. 7F). Electrochemical CO₂RR assessments in a 0.1 M NaHCO₃ solution revealed that the Pd/SnO₂ NS catalyst exhibited superior performance in CO₂ reduction to methanol. Specifically, it achieved a 54.8% FE for methanol at −0.24 V vs. RHE, along with an enhanced current density and impressive stability over 24 hours, outperforming individual Pd NSs and SnO₂ NPs (Fig. 7G). These interfaces played a pivotal role in weakening CO poisoning on Pd and promoting the subsequent reduction process. This work highlights the significant potential of Pd/SnO₂ NSs in the CO₂RR and guides efficient electrocatalyst design for the CO₂RR. The exploration of non-Cu catalysts expands the material design space and introduces new mechanisms for controlling selectivity. These systems point to a broader design philosophy that emphasizes interfacial engineering, tandem site integration, and electron/proton transfer coordination.

Fig. 7 (A) Catalytic mechanism for CO₂ electroreduction to methanol over MnO₂ and Pd/MnO₂. (B) TEM image of Pd_1.80%/MnO₂. (C) FE (methanol, CO, H₂) and methanol energy efficiency of Pd_1.80%/MnO₂ over various cell voltages. (D) Pd_1.80%/MnO₂ catalyst monitored by time-dependent in situ DRIFTS. (E) Free energy diagrams during the CO₂RR on MnO₂ and Pd/MnO₂. Reproduced from ref. 79 with permission from American Chemical Society, copyright 2023. (F) CO stripping voltammetry. (G) Potential-dependent FE for methanol, formate, and H₂ with different Pd : Sn ratios. Reproduced from ref. 80 with permission from Wiley-VCH GmbH, copyright 2018.

3. CO reduction reaction toward methanol

Electrocatalytic conversion of CO to methanol requires the orchestration of a selective cascade of 4e⁻ transfer. The pivotal challenge lies in precisely directing the transformation of adsorbed intermediates (such as *CO, *CHO, and *CH₂OH) along the desired hydrogenation pathway. This necessitates the simultaneous suppression of key competing reactions, including C–C coupling and the HER. Designing highly active and selective methanol catalysts demands critical insights into the kinetics and thermodynamics of each elementary step, especially overcoming the rate-limiting hydrogenation of *CO to *CHO.⁸¹ In addition, compared with CO₂-to-methanol, electrochemical CO-to-methanol offers multiple strategic advantages. First, since CO is more reactive than CO₂ and binds more readily to metallic surfaces, it provides a more favorable starting point for C₁ product formation. Second, the absence of CO₂ activation steps leads to lower thermodynamic barriers and typically allows for operation at lower overpotentials. Third, the modular nature of tandem CO₂-to-CO followed by the CORR to methanol enables independent optimization of each catalytic stage, facilitating system integration with spatially or temporally separated reactors. Moreover, the use of pure CO feedstocks, whether from CO₂ electrolysis, biomass reforming, or industrial off-gases, opens the door for flexible deployment across diverse sectors.

Recent breakthroughs in the CORR have demonstrated significant improvements in both methanol selectivity and partial current density. These advances are driven primarily by innovations in catalyst design, especially molecular catalysts and atomically precise alloy systems, and in electrode architecture, such as microporous layers and MEA, which enhance CO transport and suppress competing reactions. In the following subsections, we discuss two major classes of CORR catalysts that have achieved promising performance: (1) molecular phthalocyanine complexes, which offer tunable coordination environments and well-defined mechanistic pathways, and (2) copper-based single-atom alloys, which combine the favorable *CO binding of Cu with the hydrogenation activity of noble metals such as Rh. We also examine how local microenvironments, spin states, and interfacial properties affect CORR performance and highlight strategies for scaling up these systems through improved mass transport and device integration.

3.1. Electrochemical CO-to-methanol mechanism analysis

From a mechanistic perspective, the CORR avoids the high overpotential associated with *CO₂ activation and bypasses intermediates such as *COOH, which dominate the CO₂RR. Instead, the reaction proceeds through direct adsorption and stepwise hydrogenation of *CO on the catalyst surface and proceeds predominantly through sequential hydrogenation steps (*CO → *CHO → *CH₂O → *CH₃O → CH₃OH), which also facilitates catalyst design by modulating *CO binding strength and hydrogenation kinetics rather than the dual challenges of CO₂ activation and C–O bond retention faced in the CO₂RR.^53,82 The critical factors governing this process are the binding energy of *CO, the kinetics of proton–electron transfer at each step, and the suppression of undesirable pathways such as C–C coupling (leading to C₂₊ products) or further hydrogenation to CH₄. An efficient CORR thus requires finely balanced catalytic sites that stabilize *CO just enough to undergo hydrogenation but not so strongly as to promote surface poisoning or inhibit product desorption. These combined advantages position the CORR as a potentially more efficient and selective route.

3.2. Phthalocyanine molecular catalysts in CO-to-methanol

In the context of the CORR toward methanol, transition metal phthalocyanines, particularly CoPc, have shown remarkable promise under ambient conditions. The catalytic activity of CoPc in the CORR arises from the unique interaction between the central metal ion and the conjugated macrocycle. In a previous study, Li et al. demonstrated that in CoPc-NH₂/CNT systems, methanol production consistently co-occurs with CO generation. Notably, the overpotential required for CO reduction to methanol significantly exceeds that for CO₂-to-CO. To address these challenges, Li et al. implemented a mechanism-driven strategy informed by system dynamics studies to investigate CoPc-NH₂/CNT performance in the CORR to methanol.⁸³ To overcome CO mass transfer limitations, they designed a microporous layer (MPL) (Fig. 8A) that enhanced CO transport, increasing the methanol FE from 40% to 66%. Within a specific potential window, methanol and H₂ partial current densities exhibited exponential growth (Fig. 8B), confirming potential-dependent CORR behavior. This simultaneous activity/selectivity enhancement was attributed to catalyst–electrolyte interface microenvironment modulation. Mechanistic studies via pH-dependent Tafel analysis and kinetic isotope effects revealed that methanol formation was pH-independent, with protons originating from solvent water. *CO hydrogenation to *CHO was identified as the rate-determining step (Fig. 8C). CO reaction order studies revealed Henry-type adsorption isotherms, where increased CO pressure elevated surface coverage. Under synergistic MPL application and 10 atm CO, an 84% methanol FE and >20 mA cm⁻² partial current density (−0.98 V vs. RHE) were achieved (Fig. 8D), enabling efficient CO-to-methanol conversion. Compared with mononuclear CoPc, binuclear cobalt phthalocyanine (B-CoPc) features unique spatial configurations and bridging ligands, which are expected to enhance the CORR performance. Ding et al. achieved a significant improvement in the catalytic efficiency of the CORR to methanol by thermally inducing a spin-state transition of the Co active centers in a B-CoPc molecular catalyst.⁸⁴ DFT calculations confirmed that CO²⁺ spins crossover from low spins to high spins, which can facilitate electron transfer to *CO intermediates, weakening C–O bonding and promoting subsequent hydrogenation (Fig. 8E). In MEA tests, the B-CoPc catalyst exhibited excellent catalytic activity and stability, achieving a 53% CH₃OH FE at −0.7 V vs. RHE and continuous operation for 10 h (Fig. 8F). These studies elucidate critical factors for CO-to-methanol conversion-mass transfer optimization, interface engineering, and spin state modulation, providing foundational insights for sustainable CO utilization. Future work should focus on atomic-scale catalyst design and reactor engineering synergies to advance industrial implementation.

Fig. 8 (A) CO electroreduction to methanol on CoPc-NH₂/CNT-coated carbon paper: Bare (left) vs. MPL-modified (right). (B) Product partial current density for methanol and H₂ at different electrode potentials. (C) Proposed methanol reaction pathways from kinetic analysis. (D) Dependence of the methanol FE and partial current density on the electrode potential for CO reduction at 10 atm CO. Reproduced from ref. 83 with permission from Springer Nature, copyright 2022. (E) MEA configuration for the CORR. (F) The stability of M-CoPc-400 was tested at a voltage of −0.7 V (vs. RHE). Reproduced from ref. 84 with permission from Springer Nature, copyright 2023.

3.3. Copper-based single-atom alloys in CO-to-methanol

Copper-based single-atom alloys (SAAs) offer distinct advantages for selective CO electroreduction, particularly toward valuable oxygenates such as methanol. By incorporating isolated metal atoms into the Cu host, SAAs create spatially separated but cooperative active sites. The Cu matrix provides optimal CO adsorption and facilitates multi-step proton–electron transfer, whereas the single-atom dopants function as efficient hydrogenation centers. Crucially, this architectural design enables a tandem-like mechanism in which CO bound to Cu can migrate to adjacent dopant sites for sequential hydrogenation without over-hydrogenation to methane. This spatial and functional decoupling minimizes undesirable C–C coupling pathways and allows each site to operate near its optimal potential, significantly increasing the selectivity and efficiency for methanol production compared with those of pure Cu or conventional alloys. For example, Zhang et al. demonstrated a novel Rh₁Cu₄ alloy catalyst that achieved significant progress in CO electroreduction to methanol.⁸⁵ Uniform dispersion of isolated Rh sites within the Cu matrix markedly enhanced the catalytic performance. HAADF-STEM imaging and elemental mapping (Fig. 9A) confirmed the homogeneous distribution of Rh in the Rh₁Cu₄ nanoparticles. Theoretical calculations demonstrate that these isolated Rh sites substantially increase surface *H coverage compared with that of pure Cu (which favors C₂₊ products), thereby promoting the hydrogenation of *CH₂OH intermediates (Fig. 9B) and driving efficient CO-to-CH₃OH conversion. Electrocatalytic testing revealed exceptional methanol selectivity (46.2%), with a partial current density of 111.7 mA cm⁻² (Fig. 9C). Notably, the catalyst maintained stable operation for 120 hours at 500 mA cm⁻² (Fig. 9D), outperforming state-of-the-art analogs and demonstrating potential for industrial-scale implementation. To elucidate the C₁-selectivity mechanism of the Rh₁Cu₄ alloy catalyst, comparative kinetic analyses of the reaction pathways on different surfaces were conducted (Fig. 9E). The potential-determining step for the C₂₊ pathway on Cu(111) resulted in a lower energy barrier (0.99 eV) than did the C₁ pathway (1.04 eV), which is consistent with experimental observations of preferential C₂₊ formation on Cu catalysts. Conversely, the Rh₁Cu₄(111) surface inverted this energy landscape, significantly reducing the barrier for the C₁ pathway. Further analysis under high *H coverage conditions (Fig. 9F) revealed that the *CH₂OH dehydroxylation step (methane pathway, ΔG = 0.42 eV) was thermodynamically less favorable than direct *CH₂OH hydrogenation (methanol pathway). This intrinsic thermodynamic preference fundamentally drives selective methanol formation. These findings elucidate how metal surface composition governs reaction pathway selectivity and provide critical guidance for designing highly selective C₁-product catalysts. Precise control over the atomic arrangement and electronic structure enables targeted steering of CO electroreduction selectivity. This mechanistic insight establishes a foundation for developing efficient electrocatalytic methanol synthesis technologies.

Fig. 9 (A) HAADF-STEM image of Rh₁Cu₄. (B) Mechanism of CH₃OH formation on the Rh₁Cu₄ catalyst. (C) Methanol electrosynthesis activity at −0.95 V vs. RHE across RhCu catalysts with different Rh contents. (D) Stability of Rh₁Cu₄ at 500 mA cm⁻² and a voltage of 4.2 V. (E) Free energy landscape of CO-to-methanol conversion on the Cu(111) surface and Rh₁Cu₄(111) surface. (F) Free energy profile along the C₁ pathway on Rh₁Cu₄(111). Reproduced from ref. 85 with permission from American Chemical Society, copyright 2023.

4. Device engineering toward methanol production

While catalyst development has achieved substantial progress in enhancing selectivity and intrinsic activity for electrochemical CO₂/CO reduction to methanol, industrial implementation critically depends on device-level optimization. Electrocatalytic performance is governed by the local reaction environment, which includes the electrode architecture, electrolyte composition, gas transport dynamics and cell configuration.^86–88 Given the multi-step PCET mechanism of methanol synthesis, precise control over the local pH, intermediate stabilization, and product extraction are essential for attaining high current densities, FEs and operational longevity.

Advancing catalyst technologies for practical systems also necessitates resolving stability limitations. Methanol-selective catalysts, particularly molecular complexes and single-atom alloys, often suffer from leaching, restructuring, or aggregation during operation. Concurrently, cell-level durability challenges, including membrane degradation, salt precipitation, and electrode delamination, further constrain operational lifetimes.^89–91 While certain gas-fed configurations demonstrate stable methanol production for 30–50 hours, sustaining performance over thousands of hours remains critical for industrial deployment. Furthermore, scaling methanol electrosynthesis introduces multiple challenges: uniform gas distribution, thermal management, pressure control, and integrated product separation. Addressing these issues requires modular reactor stacks, scalable catalyst deposition methods, and coupled gas–liquid separation units. System viability further depends on integrating upstream processes (CO₂ capture/CO generation) with downstream methanol purification to establish closed-loop carbon cycles.

Consequently, transcending catalyst innovation, the advancement of electrochemical methanol production depends on device engineering, which enables high selectivity, efficiency, and long-term durability under industrially relevant conditions. The following subsections highlight the progress in reactor configurations and electrolyte engineering that underpin these system-level advances.

4.1. Reactor configuration and mass transport control

Conventional H-type cells have served as valuable platforms for fundamental mechanistic studies but are inherently limited by mass transport and gas solubility constraints. CO₂ and CO gases exhibit low solubilities in aqueous electrolytes (∼33 mM for CO₂ at 1 atm, 25 °C), resulting in diffusion-limited current densities and low single-pass conversion efficiencies. To overcome this, gas diffusion electrode (GDE) and flow-cell configurations have emerged as leading architectures for high-rate methanol electrosynthesis. For example, Ye et al. synthesized imine-bridged covalent organic nanosheets (imine-CONs) and demonstrated significantly enhanced methanol activity.⁹²Fig. 10A depicts the electrocatalytic flow-cell design, featuring the catalytic interface of the iminium-CON cathode. Operating in the flow-cell, the iminium-CON cathode delivered a high partial current density (91.7 mA cm⁻²) at −0.78 V vs. RHE (Fig. 10B). In flow-cells, reactant gases are continuously fed to the catalyst layer through a porous GDE, dramatically reducing the diffusion path length and enabling high local reactant concentrations at the triple-phase boundary. This architecture decouples gas transport from electrolyte ion transport, allowing methanol partial current densities to exceed 100 mA cm⁻² with FE > 40% in optimized systems. However, engineering the GDE results in a delicate balance: the hydrophobicity must be tuned to prevent flooding while ensuring sufficient wetting for proton and electrolyte access. Moreover, maintaining structural integrity and minimizing carbonate precipitation over extended operations remain ongoing challenges. Therefore, Rufford et al. presented a novel approach to address the issue of electrolyte flooding in gas diffusion layers (GDLs).⁹³ The performance of the GDLs was enhanced by vacuum-infiltration of localized polytetrafluoroethylene (PTFE) at the microporous layer (Fig. 10C). The interfacial PTFE confinement enabled <10% electrolyte permeation rates toward the original GDLs at 300 mA cm⁻². This strategy enables commercial GDL customization for CO₂ electrolysers, accelerating the industrial deployment of carbon-based GDEs. Another intriguing study was reported by Sargent et al.⁹⁴ They utilized a GDL positioned adjacent to the catalyst layer to facilitate CO₂ diffusion and reaction under alkaline conditions. The use of a polymer-based GDL confined the reaction zone within the layers, resulting in both hydrophobicity and electrical conductivity (Fig. 10D) and increased operational stability, providing constant ethylene selectivity for over 150 hours (Fig. 10E).

Fig. 10 (A) Flow-cell electrochemistry schematic depicting the interfacial ion behavior at catalyst surfaces. (B) Methanol partial current densities for iminium-CONs and their corresponding samples. Reproduced from ref. 92 with permission from Wiley-VCH GmbH, copyright 2023. (C) GDE-embedded PTFE was produced via vacuum-mediated imbibition. Reproduced from ref. 93 with permission from American Chemical Society, copyright 2022. (D) PTFE-embedded GDE fabrication via vacuum-assisted infiltration. (E) Polymer-based electrode stability assessment. Reproduced from ref. 94 with permission from the American Association for the Advancement of Science, copyright 2018.

The core advantages of the MEA electrolyzer include achieving high current density operation, low energy consumption, a compact and simplified system architecture, and ease of scale-up.^9,95–97 This makes it one of the most promising pathways for advancing the electrocatalytic CO₂RR from the laboratory to industrial applications. However, hydroxide ions (OH⁻) generated at the cathode react with cations (e.g., K⁺) permeating from the anolyte and with CO₂ to form carbonate/bicarbonate salts. In a low-water environment, these salts readily precipitate, crystallize and deposit within the cathode catalyst layer or gas flow channels.^98,99 This blocks pores and ultimately leads to cell failure. In this section, we systematically discuss the solutions proposed by researchers to address the salt deposition issue in MEAs. In 2025, Lin et al. developed a non-isothermal operating strategy for CO₂ electrolyzers by maintaining a thermal gradient with a cooled cathode and a heated anode.¹⁰⁰ This approach leverages thermal diffusion to expel cations from the cathode vicinity, thereby suppressing salt precipitation while concurrently enhancing the anodic reaction kinetics and cathodic CO₂ solubility (Fig. 11A). The non-isothermal system demonstrated stable operation for more than 200 hours at 100 mA cm⁻², significantly outperforming conventional isothermal configurations. This thermal gradient approach represents a pivotal improvement in the deployment of viable CO₂ conversion systems. This method addresses the critical issue of salt precipitation in CO₂ electrolysis, enabling more sustainable and scalable industrial applications. Addressing salt precipitation in CO₂ electrolysis, Wang et al. enhanced cathode flow channel performance by applying hydrophobic parylene coatings, which improved droplet removal and suppressed salt deposition (Fig. 11B).¹⁰¹ This modification significantly increased the stability within the MEA configuration, increasing the operation duration from 100 hours to over 500 hours at 200 mA cm⁻². By combining in situ Raman spectroscopy and optical microscopy, this study quantified salt precipitation under various anolyte concentrations and current densities, linking these phenomena to performance loss. These findings provide a comprehensive understanding of salt formation mechanisms and validate effective mitigation strategies, advancing the development of stable, high-performance CO₂RR technologies for industrial scalability. In another significant study, the same research team developed an innovative acid-humidification approach.¹⁰² Using HCl-humidified CO₂, they achieved stable operation exceeding 1000 hours at 100 mA cm⁻² with a 4-cm² Ag/GDE, maintaining a CO FE >90% in CO₂RR MEA electrolyzers (Fig. 11C). This system significantly outperformed the water-humidified systems, which failed within 200–500 hours. The method proved scalable, delivering over 2000 hours of stability in a 100-cm² electrolyzer and 4500 hours using HNO₃-humidification. Crucially, acid vapor does not alter the rate of K⁺ crossover from the anolyte but enhances salt removal. This occurs because acids stronger than carbonic acid produce anions that significantly increase the solubility of salts, dissolving or preventing bicarbonate precipitation in the gas flow channels. The acid-humidification strategy shows promise for direct CO₂-to-methanol systems but requires careful verification. Key considerations include catalyst compatibility under acidic conditions, local pH effects on methanol pathways, potential interactions with key intermediates, and acid-type optimization.

Fig. 11 (A) MEA electrolyzer architecture for the CO₂RR featuring titanium bipolar plates with integrated liquid-cooling channels. Reproduced from ref. 100 with permission from Springer Nature, copyright 2025. (B) Parylene deposition process on the cathode flow channels. Reproduced from ref. 101 with permission from Springer Nature, copyright 2025. (C) Acid-humidified CO₂ delivery system configuration. Reproduced from ref. 102 with permission from the American Association for the Advancement of Science, copyright 2025.

4.2. Electrolyte design and microenvironment control

The design of the electrolyte composition and precise control of the electrode–electrolyte interfacial microenvironment are paramount for optimizing the activity, selectivity, and stability of the electrocatalytic CO₂RR. Electrolyte components, including cations (e.g., K⁺, Cs⁺), anions (e.g., HCO₃⁻, Cl⁻), pH, CO₂ gas partial pressure and specific additives (e.g., halides, ionic liquids), profoundly influence reaction pathways.^103–106 Here, we specifically discuss the influence of engineered ionic liquid electrolytes and controlled CO₂ partial pressure on the efficiency of CO₂-to-methanol conversion. Ionic liquids, which serve as multifunctional electrolytes, significantly increase the CO₂RR conversion efficiency due to their exceptional CO₂ solubility and affinity, stabilize critical reaction intermediates via non-covalent interactions and enable precise tuning of the electrode–electrolyte interface through the structural design of cations/anions. For example, Han et al. utilized solvothermal processing to fabricate Cu_2−XSe(y) nanocatalysts.¹⁰⁷ The Cu_1.63Se(1/3) nanocatalyst delivered an FE of 77.6% for methanol at 41.5 mA cm⁻²via [Bmim]PF₆/CH₃CN/H₂O as supporting electrolytes (Fig. 12A). Notably, ionic liquids featuring imidazolium cations and fluorinated anions act as high-performance supporting electrolytes in CO₂-to-CH₃OH, leveraging their synergistic effects on CO₂ solubility and intermediate stabilization. Fig. 12B illustrates the proposed mechanistic pathway for electrocatalytic CO₂-to-methanol conversion over the Cu_2−xSe(y) catalysts. During initial CO₂ reduction, ionic liquid-containing electrolytes increase the CO₂ concentration and are transported to catalytic surfaces, promoting adsorption as CO₂˙⁻ intermediates. These adsorbed species bind to active sites, accelerating the formation of key *CO intermediates critical for methanol synthesis. Subsequent electron/proton transfer at optimized Cu sites then converts *CO into *CHO, ultimately driving methanol formation. Furthermore, elevated CO₂ pressure critically enhances CO₂RR performance through three synergistic mechanisms: modulation of the local microenvironment of the catalyst, restructuring of the electrochemical double layer, thermodynamic facilitation of CO₂ activation and mitigation of mass transport limitations. Our group previously demonstrated a pressure-mediated synthesis protocol that generates heterogeneous electrocatalysts featuring hydride surfaces for enhanced hydrogen transfer kinetics. In 2022, Gong et al. presented an efficient strategy for CO₂-to-methanol electroreduction via enhanced oxygen binding affinity on a molybdenum carbide catalyst.¹⁰⁸ The Mo₂C/N-CNT catalyst comprises molybdenum carbide nanoparticles anchored on nitrogen-doped CNT (N-CNT) with a particle size of approximately 5.0 nm (Fig. 12C). Under 40 atm CO₂ pressure, the selectivity of CH₃OH reached 80% at 4 mA cm⁻², with a turnover number of 238.6 (Fig. 12D and E). Concurrently, the authors note that future work should optimize intermediate adsorption via elemental doping and pressure tuning while validating the proposed formyl pathway with additional experimental and computational evidence. Further investigations should also develop precise electrolyte–electrode interface models and quantify kinetic barriers.

Fig. 12 (A) Comparison of the electrocatalytic performance of the Cu-based catalysts. (B) Proposed reaction mechanism on the Cu_2−xSe(y) electrode. Reproduced from ref. 107 with permission from Springer Nature, copyright 2019. (C) TEM images of Mo₂C/N-CNT. (D) Schematic representation of the high-pressure CO₂RR system. (E) Potential-dependent product distribution during the CO₂RR at 40 bar. Reproduced from ref. 108 with permission from Springer Nature, copyright 2022.

5. Summary and outlook

Electrochemical CO₂ reduction to methanol represents a critical node at the intersection of renewable energy storage, sustainable chemical manufacturing, and carbon circularity. As the demand for low-carbon fuels and platform chemicals intensifies in the context of climate targets and decarbonization mandates, methanol stands out for its energy density, liquid-phase processability, and versatility across fuel, chemical, and biological value chains. However, realizing scalable and economically viable methanol electrosynthesis requires concerted advances at multiple levels, from catalyst design and mechanistic understanding to reactor engineering and system integration. Future breakthroughs necessitate progress in the following three key areas:

5.1. Catalyst design

Cobalt phthalocyanine (CoPc), a prototypical molecular catalyst for methanol production, has unique advantages in the CO₂RR because of its well-defined active site and tunable electronic structure. Current research strategies involve modulating the electron density of the Co center through the introduction of electron-withdrawing/donating substituents (e.g., –NH₂) or axial ligands on the phthalocyanine ring. This enhances *CO intermediate adsorption and facilitates multi-electron transfer, thereby improving methanol selectivity. Despite these advances, CoPc molecules suffer from aggregation, detachment, or degradation of active sites during prolonged electrolysis. Concurrently, the intrinsic reaction mechanisms remain incompletely elucidated. Therefore, we propose the following optimization strategies: (1) developing robust covalent grafting strategies to tether the molecular catalyst to the carbon support via stable bonds (e.g., amide, ether and aryl linkages). This prevents aggregation and desorption but requires careful synthesis to ensure that the tethering group does not block the active site or alter its electronic properties. (2) Anchoring CoPc onto carriers possessing specific properties, such as high-conductivity polymers (e.g., covalent organic frameworks, COFs), materials with high mechanical properties (e.g., polyoxymethylene, POM), and molecular sieve-templated porous materials, facilitates improved electron transfer efficiency and dispersion of the catalyst, thereby increasing its catalytic activity.^109–114 (3) Constructing bimetallic phthalocyanine or binuclear metal phthalocyanine systems,^115–118 which spatially decouple CO₂ activation, accelerate *CO hydrogenation pathways and stabilize oxygen-containing intermediates. (4) Integration of CO-selective Ag or Zn nanoparticles with molecular CoPc/CNT electrocatalysts. This cascade design strategically controls the local CO intermediate concentration at the catalyst–electrolyte interface. (5) DFT and more advanced molecular dynamics were used to predict not only the catalytic activity but also the thermodynamic stability of the proposed catalyst structures and their potential decomposition pathways. These findings can guide synthetic efforts toward the most promising candidates before ever stepping into a lab.

Additionally, copper-based catalysts remain among the most promising materials for driving CO₂ electroreduction to methanol. For example, Cu-based alloys disrupt linear scaling relationships, uniquely enabling reactivity and selectivity control that is unattainable with monometallic systems.^119–122 The incorporation of secondary metals into Cu matrices modifies the local electronic structure, fine-tunes intermediate adsorption energetics, and thereby enhances catalytic activity and product selectivity.^11,123 Nevertheless, the efficiency of the use of Cu-based catalysts for methanol production via the electrocatalytic CO₂RR remains suboptimal. To overcome these challenges, the following strategic optimizations have been formulated: (1) most Cu-based catalysts incorporate one foreign metal atom into the copper host, but single-site catalysts face inherent limitations. Intermediates often block their sparse active sites, causing severe performance degradation. To address this, designing tunable heteronuclear dual-atom sites on copper substrates offers a promising solution.^77,124 (2) Researchers predominantly use monometallic Cu hosts in Cu-based SAA catalysts for the ECR, but bimetallic or polymetallic hosts could provide superior electronic adjustability. (3) Emerging Cu-based high-entropy alloy catalysts exhibit tunable active sites and superconductivity, positioning them as promising candidates for emergent catalytic properties.^125–127

5.2. In situ characterization techniques

The electrocatalytic conversion of CO₂ to methanol involves complex processes such as electron transfer, intermediate species formation, and dynamic catalyst evolution. Deciphering this intricate reaction mechanism necessitates the integration of multiple operando/in-situ characterization techniques. First, in situ ATR-FTIR was employed to elucidate the formation, transformation, and surface migration pathways of key reaction intermediates during methanol generation.^128,129 Complementary in situ electrochemical quartz crystal microbalance (EQCM) measurements simultaneously monitor adsorption–desorption dynamics at the catalyst–electrolyte interface with high temporal resolution, which provides real-time monitoring of adsorption–desorption behaviors at the catalyst surface with high temporal resolution, providing essential mass-change data for catalyst optimization.^130,131 Second, in situ XAS addresses the fundamental question of dynamic structural evolution at catalytically active sites. This technique systematically investigates (1) the dynamic stability and structural integrity of active centers in operational microenvironments and (2) the evolution of the coordination geometries throughout the catalytic cycle and the structural composition of the genuine catalytically active sites. By utilizing experimentally determined geometric/electronic structural parameters, structure–activity relationship models should be created. Through combined DFT calculations and dynamics simulations, key elementary steps in CO₂ reduction pathways can be systematically probed to elucidate the dynamic evolution of active sites and their regulatory role in reaction selectivity.

5.3. Device design and scaling up

Optimizing and scaling up electrode reactors for the production of target products has significant importance for the resource utilization of carbon emissions and the advancement of related technologies and industries.^96,97,132 However, current methanol production methods are typically confined to H-type cells. Therefore, achieving highly selective methanol production within practical device architectures is critically important. To date, challenges in electrolyte management, catalyst flooding, gas crossover, and long-term operational durability must be addressed before commercial viability is achieved. To address this challenge, we propose the following strategies: (1) redesigning gas flow fields to ensure uniform reactant gas distribution and enhance mass transfer efficiency; (2) employing advanced coating techniques and thermo-compression processes to minimize interfacial contact resistance and delamination risks; and (3) optimizing reactor assembly processes by carefully considering the uniformity of mass transfer, heat transfer, and electric field distribution at bipolar plate/diffusion layer interfaces. (4) Compact multi-stage reactors (e.g., stacked MEAs and cascaded flow cells) with optimized inter-stage gas/liquid management should be designed to minimize CO transfer losses and energy penalties between CO generation and CO reduction units, and CO-selective membranes for efficient CO extraction/purification from the first stage (CO₂-to-CO) feed stream should be developed, and CEM/AEM membranes with reduced cation crossover (to minimize carbonate formation or specific permeability to maintain optimal local pH in each stage) should be tailored. In summary, on the basis of prior research achievements, integrated studies spanning chemistry, materials science, and engineering disciplines should be conducted. This multidisciplinary approach focuses on developing highly stable catalysts, gaining fundamental insights into the catalytic reaction mechanisms, and optimizing device fabrication processes. The overarching goal is to achieve the direct electrosynthesis of methanol with high activity. Furthermore, optimizing the local microenvironment at the electrode surface, such as by employing ionic liquid-modified electrodes or designing microporous reactors, enhances the CO₂ concentration and proton delivery pathways, promoting C–O bond dissociation and C–H bond construction to increase the FE for methanol.

5.4. Tandem electro-biosystem

Transforming CO₂ into valuable long-chain compounds via the CO₂RR continues to pose a formidable obstacle. In addition, synthetic biology has several innovative applications in the utilization of carbon resources. For example, in synthetic biology, microorganisms can be engineered to convert simple C₁ or C₂ compounds such as methane, methanol and acetic acid into more complex molecules, which can be used as building blocks for a variety of chemicals and materials. The core significance of integrating CO₂ reduction technology with bio-fermentation technology lies in transforming CO₂ into high-value green products, seamlessly integrating technological innovation, economic benefits, and environmental gains. This approach represents both a pivotal trajectory for future green low-carbon industries and an indispensable stride toward sustainable development for mankind.

Conflicts of interest

The authors declare no conflicts of interest.

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

C. X. acknowledges the “Pioneer” and “Leading Goose” R&D Program of Zhejiang (No. 2023C03017), the National Key Research and Development Program of China (2024YFB4105700), NSFC (52171201), and the Natural Science Foundation of Sichuan Province (2025NSFJQ0017). Z. Chen acknowledges the National Natural Science Foundation of China (No. 22308050), the China Postdoctoral Science Foundation-Funded Project (No. 2023M740503), and the Natural Science Foundation of Sichuan Province (No. 24NSFSC6168).

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Footnote

† These authors contributed equally to this work.

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