Full atomistic reaction mechanism with kinetics for CO reduction on Cu(100) from ab initio molecular dynamics free-energy calculations at 298 K

Tailoring the Surface and Interface Structures of Copper-Based Catalysts for Electrochemical Reduction of CO2 to Ethylene and Ethanol

Electrochemical CO₂ reduction to valuable ethylene and ethanol offers a promising strategy to lower CO₂ emissions while storing renewable electricity. Cu-based catalysts have shown the potential for CO₂ -to-ethylene/ethanol conversion, but still suffer from low activity and selectivity. Herein, the effects of surface and interface structures in Cu-based catalysts for CO₂ -to-ethylene/ethanol production are systematically discussed. Both reactions involve three crucial steps: formation of CO intermediate, CC coupling, and hydrodeoxygenation of C₂ intermediates. For ethylene, the key step is CC coupling, which can be enhanced by tailoring the surface structures of catalyst such as step sites on facets, Cu⁰ /Cu^δ+ species and nanopores, as well as the optimized molecule-catalyst and electrolyte-catalyst interfaces further promoting the higher ethylene production. While the controllable hydrodeoxygenation of C₂ intermediate is important for ethanol, which can be achieved by tuning the stability of oxygenate intermediates through the metallic cluster induced special atomic configuration and bimetallic synergy induced the double active sites on catalyst surface. Additionally, constraining CO coverage by the complex-catalyst interface and stabilizing CO bond by N-doped carbon/Cu interface can also enhance the ethanol selectivity. The structure-performance relationships will provide the guidance for the design of Cu-based catalysts for highly efficient reduction of CO₂ .

Electrochemical CO2 reduction toward multicarbon alcohols - The microscopic world of catalysts & process conditions

Tackling climate change is one of the undoubtedly most important challenges at the present time. This review deals mainly with the chemical aspects of the current status for converting the greenhouse gas CO2 via electrochemical CO2 reduction reaction (CO2RR) to multicarbon alcohols as valuable products. Feasible reaction routes are presented, as well as catalyst synthesis methods such as electrodeposition, precipitation, or sputtering. In addition, a comprehensive overview of the currently achievable selectivities for multicarbon alcohols in CO2RR is given. It is also outlined to what extent, for example, modifications of the catalyst surfaces or the use of bifunctional compounds the product distribution is shifted. In addition, the influence of varying electrolyte, temperature, and pressure is described and discussed.

Electrochemical CO2 reduction to ethylene by ultrathin CuO nanoplate arrays

Electrochemical reduction of CO₂ to multi-carbon fuels and chemical feedstocks is an appealing approach to mitigate excessive CO₂ emissions. However, the reported catalysts always show either a low Faradaic efficiency of the C₂₊ product or poor long-term stability. Herein, we report a facile and scalable anodic corrosion method to synthesize oxygen-rich ultrathin CuO nanoplate arrays, which form Cu/Cu₂O heterogeneous interfaces through self-evolution during electrocatalysis. The catalyst exhibits a high C₂H₄ Faradaic efficiency of 84.5%, stable electrolysis for ~55 h in a flow cell using a neutral KCl electrolyte, and a full-cell ethylene energy efficiency of 27.6% at 200 mA cm⁻² in a membrane electrode assembly electrolyzer. Mechanism analyses reveal that the stable nanostructures, stable Cu/Cu₂O interfaces, and enhanced adsorption of the *OCCOH intermediate preserve selective and prolonged C₂H₄ production. The robust and scalable produced catalyst coupled with mild electrolytic conditions facilitates the practical application of electrochemical CO₂ reduction.

Oxide-derived copper has been extensively studied as catalysts for CO₂ electroreduction but its catalytic stability and selectivity still need to be improved. Here, the authors report ultrathin CuO nanoplate arrays for CO₂ reduction with high ethylene selectivity and enhanced long-term stability.

Trends in oxygenate/hydrocarbon selectivity for electrochemical CO(2) reduction to C2 products

The electrochemical conversion of carbon di-/monoxide into commodity chemicals paves a way towards a sustainable society but it also presents one of the great challenges in catalysis. Herein, we present the trends in selectivity towards specific dicarbon oxygenate/hydrocarbon products from carbon monoxide reduction on transition metal catalysts, with special focus on copper. We unveil the distinctive role of electrolyte pH in tuning the dicarbon oxygenate/hydrocarbon selectivity. The understanding is based on density functional theory calculated energetics and microkinetic modeling. We identify the critical reaction steps determining selectivity and relate their transition state energies to two simple descriptors, the carbon and hydroxide binding strengths. The atomistic insight gained enables us to rationalize a number of experimental observations and provides avenues towards the design of selective electrocatalysts for liquid fuel production from carbon di-/monoxide.

Complementary Operando Spectroscopy identification of in-situ generated metastable charge-asymmetry Cu2-CuN3 clusters for CO2 reduction to ethanol

Copper-based materials can reliably convert carbon dioxide into multi-carbon products but they suffer from poor activity and product selectivity. The atomic structure-activity relationship of electrocatalysts for the selectivity is controversial due to the lacking of systemic multiple dimensions for operando condition study. Herein, we synthesized high-performance CO₂RR catalyst comprising of CuO clusters supported on N-doped carbon nanosheets, which exhibited high C₂₊ products Faradaic efficiency of 73% including decent ethanol selectivity of 51% with a partial current density of 14.4 mA/cm⁻² at −1.1 V vs. RHE. We evidenced catalyst restructuring and tracked the variation of the active states under reaction conditions, presenting the atomic structure-activity relationship of this catalyst. Operando XAS, XANES simulations and Quasi-in-situ XPS analyses identified a reversible potential-dependent transformation from dispersed CuO clusters to Cu₂-CuN₃ clusters which are the optimal sites. This cluster can’t exist without the applied potential. The N-doping dispersed the reduced Cu_n clusters uniformly and maintained excellent stability and high activity with adjusting the charge distribution between the Cu atoms and N-doped carbon interface. By combining Operando FTIR and DFT calculations, it was recognized that the Cu₂-CuN₃ clusters displayed charge-asymmetric sites which were intensified by CH₃^* adsorbing, beneficial to the formation of the high-efficiency asymmetric ethanol.

Copper-based materials can convert carbon dioxide into multi-carbon products but suffer from poor activity and selectivity. Here, the authors report CuO clusters supported on nitrogen-doped carbon nanosheets for the reduction CO₂-to-ethanol, and investigate the change in the catalytic sites while in operation.

Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites

The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity. Dilute alloy catalysts─in which isolated atoms or small ensembles of the minority metal on the host metal lead to enhanced reactivity while retaining selectivity─are particularly promising as selective catalysts. Several dilute alloy materials using Au, Ag, and Cu as the majority host element, including more recently introduced support-free nanoporous metals and oxide-supported nanoparticle "raspberry colloid templated (RCT)" materials, are reviewed for selective oxidation and hydrogenation reactions. Progress in understanding how such dilute alloy catalysts can be used to enhance selectivity of key synthetic reactions is reviewed, including quantitative scaling from model studies to catalytic conditions. The dynamic evolution of catalyst structure and composition studied in surface science and catalytic conditions and their relationship to catalytic function are also discussed, followed by advanced characterization and theoretical modeling that have been developed to determine the distribution of minority metal atoms at or near the surface. The integrated approach demonstrates the success of bridging the divide between fundamental knowledge and design of catalytic processes in complex catalytic systems, which can accelerate the development of new and efficient catalytic processes.

Promoting Electrocatalytic Reduction of CO2 to C2 H4 Production by Inhibiting C2 H5 OH Desorption from Cu2 O/C Composite

The electrochemical CO₂ reduction reaction (CO₂ RR) has great potential in realizing carbon recycling while storing sustainable electricity as hydrocarbon fuels. However, it is still a challenge to enhance the selectivity of the CO₂ RR to single multi-carbon (C₂₊ ) product, such as C₂ H₄ . Here, an effective method is proposed to improve C₂ H₄ selectivity by inhibiting the production of the other competitive C₂ products, namely C₂ H₅ OH, from Cu₂ O/C composite. Density functional theory indicates that the heterogeneous structure between Cu₂ O and carbon is expected to inhibit C₂ H₅ OH production and promote CC coupling, which facilitates C₂ H₄ production. To prove this, a composite electrode containing octahedral Cu₂ O nanoparticles (NPs) (o-Cu₂ O) with {111} facets and carbon NPs is constructed, which experimentally inhibits C₂ H₅ OH production while strongly enhancing C₂ H₄ selectivity compared with o-Cu₂ O electrode. Furthermore, the surface hydroxylation of carbon can further improve the C₂ H₄ production of o-Cu₂ O/C electrode, exhibiting a high C₂ H₄ Faradaic efficiency of 67% and a high C₂ H₄ current density of 45 mA cm^-2 at -1.1 V in a near-neutral electrolyte. This work provides a new idea to improve C₂₊ selectivity by controlling products desorption.

Theoretical Modeling of Electrochemical Proton-Coupled Electron Transfer

Proton-coupled electron transfer (PCET) plays an essential role in a wide range of electrocatalytic processes. A vast array of theoretical and computational methods have been developed to study electrochemical PCET. These methods can be used to calculate redox potentials and pK_a values for molecular electrocatalysts, proton-coupled redox potentials and bond dissociation free energies for PCET at metal and semiconductor interfaces, and reorganization energies associated with electrochemical PCET. Periodic density functional theory can also be used to compute PCET activation energies and perform molecular dynamics simulations of electrochemical interfaces. Various approaches for maintaining a constant electrode potential in electronic structure calculations and modeling complex interactions in the electric double layer (EDL) have been developed. Theoretical formulations for both homogeneous and heterogeneous electrochemical PCET spanning the adiabatic, nonadiabatic, and solvent-controlled regimes have been developed and provide analytical expressions for the rate constants and current densities as functions of applied potential. The quantum mechanical treatment of the proton and inclusion of excited vibronic states have been shown to be critical for describing experimental data, such as Tafel slopes and potential-dependent kinetic isotope effects. The calculated rate constants can be used as input to microkinetic models and voltammogram simulations to elucidate complex electrocatalytic processes.

Stabilizing Cu2+ Ions by Solid Solutions to Promote CO2 Electroreduction to Methane

Copper is the only metal catalyst that can perform the electrocatalytic CO₂ reduction reaction (CRR) to produce hydrocarbons and oxygenates. Its surface oxidation state determines the reaction pathway to various products. However, under the cathodic potential of CRR conditions, the chemical composition of most Cu-based catalysts inevitably undergoes electroreduction from Cu²⁺ to Cu⁰ or Cu¹⁺ species, which is generally coupled with phase reconstruction and the formation of new active sites. Since the initial Cu²⁺ active sites are hard to retain, there have been few studies about Cu²⁺ catalysts for CRR. Herein we propose a solid-solution strategy to stabilize Cu²⁺ ions by incorporating them into a CeO₂ matrix, which works as a self-sacrificing ingredient to protect Cu²⁺ active species. In situ spectroscopic characterization and density functional theory calculations reveal that compared with the conventionally derived Cu catalysts with Cu⁰ or Cu¹⁺ active sites, the Cu²⁺ species in the solid solution (Cu-Ce-O_x) can significantly strengthen adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH₄ instead of dimerization to give C₂ products. As a result, different from most of the other Cu-based catalysts, Cu-Ce-O_x delivered a high Faradaic efficiency of 67.8% for CH₄ and a low value of 3.6% for C₂H₄.

Au-activated N motifs in non-coherent cupric porphyrin metal organic frameworks for promoting and stabilizing ethylene production

Direct implementation of metal-organic frameworks as the catalyst for CO₂ electroreduction has been challenging due to issues such as poor conductivity, stability, and limited > 2e⁻ products. In this study, Au nanoneedles are impregnated into a cupric porphyrin-based metal-organic framework by exploiting ligand carboxylates as the Au³⁺ -reducing agent, simultaneously cleaving the ligand-node linkage. Surprisingly, despite the lack of a coherent structure, the Au-inserted framework affords a superb ethylene selectivity up to 52.5% in Faradaic efficiency, ranking among the best for metal-organic frameworks reported in the literature. Through operando X-ray, infrared spectroscopies and density functional theory calculations, the enhanced ethylene selectivity is attributed to Au-activated nitrogen motifs in coordination with the Cu centers for C-C coupling at the metalloporphyrin sites. Furthermore, the Au-inserted catalyst demonstrates both improved structural and catalytic stability, ascribed to the altered charge conduction path that bypasses the incoherent framework. This study underlines the modulation of reticular metalloporphyrin structure by metal impregnation for steering the CO₂ reduction reaction pathway.

Metal-organic frameworks are promising catalysts for CO₂ electroreduction, yet limited by their poor conductivity and stability. Here, Au nanoneedles are inserted into the metalloporphyrin framework to activate C-C coupling and stabilize the structure for much enhanced ethylene production.

Mechanistic routes toward C3 products in copper-catalysed CO2 electroreduction

The mechanistic insights of CO2 electrochemical reduction on Cu materials up to C3 fragments are investigated by combining experiments and theory.

Discovering surface reaction pathways using accelerated molecular dynamics and network analysis tools

We present an automated method that maps surface reaction pathways with no experimental data and with minimal human interventions. In this method, bias potentials promoting surface reactions are applied to enable statistical samplings of the surface reaction within the timescale of ab initio molecular dynamics (MD) simulations, and elementary reactions are extracted automatically using an extension of the method constructed for gas- or liquid-phase reactions. By converting the extracted elementary reaction data to directed graph data, MD trajectories can be efficiently mapped onto reaction pathways using a network analysis tool. To demonstrate the power of the method, it was applied to the steam reforming of methane on the Rh(111) surface and to propane reforming on the Pt(111) and Pt₃Sn(111) surfaces. We discover new energetically favorable pathways for both reactions and reproduce the experimentally-observed materials-dependence of the surface reaction activity and the selectivity for the propane reforming reactions.

We present an automated method that maps surface reaction pathways with no experimental data and with minimal human interventions.

Dynamics of Heterogeneous Catalytic Processes at Operando Conditions

The rational design of high-performance catalysts is hindered by the lack of knowledge of the structures of active sites and the reaction pathways under reaction conditions, which can be ideally addressed by an in situ/operando characterization. Besides the experimental insights, a theoretical investigation that simulates reaction conditions-so-called operando modeling-is necessary for a plausible understanding of a working catalyst system at the atomic scale. However, there is still a huge gap between the current widely used computational model and the concept of operando modeling, which should be achieved through multiscale computational modeling. This Perspective describes various modeling approaches and machine learning techniques that step toward operando modeling, followed by selected experimental examples that present an operando understanding in the thermo- and electrocatalytic processes. At last, the remaining challenges in this area are outlined.

Comprehensive Mechanism of CO2 Electroreduction on Non-Noble Metal Single-Atom Catalysts of Mo2 CS2 -MXene

In this work, a series of non-noble metal single-atom catalysts of Mo₂ CS₂ -MXene for CO₂ reduction were systematically investigated by well-defined density-functional-theory (DFT) calculations. It is found that nine types of transitional metal (TM) supported Mo₂ CS₂ (TM-Mo₂ CS₂ ) are very stable, while eight can effectively inhibit the competitive hydrogen evolution reaction (HER). After comprehensively comparing the changes of free energy for each pathway in CO₂ reduction reaction (CO₂ RR), it is found that the products of TM-Mo₂ CS₂ are not completely CH₄ . Furthermore, Cr-, Fe-, Co- and Ni-Mo₂ CS₂ are found to render excellent CO₂ RR catalytic activity, and their limiting potentials are in the range of 0.245-0.304 V. In particular, Fe-Mo₂ CS₂ with a nitrogenase-like structure has the lowest limiting potential and the highest electrocatalytic activity. Ab initio molecular dynamics (AIMD) simulations have also proven that these kinds of single-atom catalysts with robust performance could exist stably at room temperature. Therefore, these single TM atoms anchored on the surface of MXenes can be profiled as a promising catalyst for the electrochemical reduction of CO₂ .

Potential-dependent C-C coupling mechanism and activity of C2 formation in the electrocatalytic reduction of CO2 on defective Cu(100) surfaces

The potential-dependent C-C coupling mechanism for C₂ formation in the electrocatalytic reduction of CO₂ is studied on several defective Cu(100) surfaces, and a nonmonotonic trend is observed between the effective free energy barriers and the average coordination numbers. Further structural analysis reveals that Cu surface strain along the parallel and vertical directions with respect to the C-C bond would have distinct impacts on the modulation of the barriers.

Improved electrochemical conversion of CO2 to multicarbon products by using molecular doping

The conversion of CO₂ into desirable multicarbon products via the electrochemical reduction reaction holds promise to achieve a circular carbon economy. Here, we report a strategy in which we modify the surface of bimetallic silver-copper catalyst with aromatic heterocycles such as thiadiazole and triazole derivatives to increase the conversion of CO₂ into hydrocarbon molecules. By combining operando Raman and X-ray absorption spectroscopy with electrocatalytic measurements and analysis of the reaction products, we identified that the electron withdrawing nature of functional groups orients the reaction pathway towards the production of C₂₊ species (ethanol and ethylene) and enhances the reaction rate on the surface of the catalyst by adjusting the electronic state of surface copper atoms. As a result, we achieve a high Faradaic efficiency for the C₂₊ formation of ≈80% and full-cell energy efficiency of 20.3% with a specific current density of 261.4 mA cm^-2 for C₂₊ products.

Recent Advances in Catalyst Structure and Composition Engineering Strategies for Regulating CO2 Electrochemical Reduction

Electrochemical CO₂ reduction has been recognized as a promising solution in tackling energy- and environment-related challenges of human society. In the past few years, the rapid development of advanced electrocatalysts has significantly improved the efficiency of this reaction and accelerated the practical applications of this technology. Herein, representative catalyst structures and composition engineering strategies in regulating the CO₂ reduction selectivity and activity toward various products including carbon monoxide, formate, methane, methanol, ethylene, and ethanol are summarized. An overview of in situ/operando characterizations and advanced computational modeling in deepening the understanding of the reaction mechanisms and accelerating catalyst design are also provided. To conclude, future challenges and opportunities in this research field are discussed.

The role of hydrophobic hydration in the free energy of chemical reactions at the gold/water interface: Size and position effects

Metal/water interfaces catalyze a large variety of chemical reactions, which often involve small hydrophobic molecules. In the present theoretical study, we show that hydrophobic hydration at the Au(100)/water interface actively contributes to the reaction free energy by up to several hundreds of meV. This occurs either in adsorption/desorption reaction steps, where the vertical distance from the surface changes in going from reactants to products, or in addition and elimination reaction steps, where two small reactants merge into a larger product and vice versa. We find that size and position effects cannot be captured by treating them as independent variables. Instead, their simultaneous evaluation allows us to map the important contributions, and we provide examples of their combinations for which interfacial reactions can be either favored or disfavored. By taking a N₂ and a CO₂ reduction pathway as test cases, we show that explicitly considering hydrophobic effects is important for the selectivity and rate of these relevant interfacial processes.

Promoting ethylene production over a wide potential window on Cu crystallites induced and stabilized via current shock and charge delocalization

Electrochemical CO₂ reduction (CO₂RR) in a product-orientated and energy-efficient manner relies on rational catalyst design guided by mechanistic understandings. In this study, the effect of conducting support on the CO₂RR behaviors of semi-conductive metal-organic framework (MOF) - Cu₃(HITP)₂ are carefully investigated. Compared to the stand-alone MOF, adding Ketjen Black greatly promotes C₂H₄ production with a stabilized Faradaic efficiency between 60-70% in a wide potential range and prolonged period. Multicrystalline Cu nano-crystallites in the reconstructed MOF are induced and stabilized by the conducting support via current shock and charge delocalization, which is analogous to the mechanism of dendrite prevention through conductive scaffolds in metal ion batteries. Density functional theory calculations elucidate that the contained multi-facets and rich grain boundaries promote C-C coupling while suppressing HER. This study underlines the key role of substrate-catalyst interaction, and the regulation of Cu crystalline states via conditioning the charge transport, in steering the CO₂RR pathway.

Hydrogen Coupling on Platinum Using Artificial Neural Network Potentials and DFT

To date, the understanding of reactions at solid-liquid interfaces has proven challenging, mainly because of the inaccessible nature of such systems to current experimental techniques with atomic resolution. This has meant that many important features, including free energy barriers and the atomistic structure of intermediates, remain unknown. To tackle these issues, we construct and utilize a high-dimensional neural network (HDNN) potential for the simulation of hydrogen evolution at the HCl(aq)/Pt(111) interface, taking into consideration the influence of adsorbate-adsorbate, adsorbate-solvent interactions, and ion solvation explicitly. Long time scale MD simulations reveal coadsorbed H_ad/H₂O_ad on the surface. The free energy profiles for the Tafel and Heyrovsky type hydrogen coupling are extracted using umbrella sampling. It is found that the preferential mechanism can change depending on the surface coverage, highlighting the dual mechanistic nature for HER on Pt(111). Our work demonstrates the importance of controlling the solvent-substrate interactions in developing catalysts beyond Pt.

Designing Copper-Based Catalysts for Efficient Carbon Dioxide Electroreduction

The electroreduction of carbon dioxide (CO₂ ) has been emerging as a high- potential approach for CO₂ utilization using renewables. When copper (Cu) based catalysts are used, this platform can produce multi-carbon (C₂₊ ) fuels and chemicals with almost net-zero emission, contributing to the closure of the anthropogenic carbon cycle. Nonetheless, the rational design and development of Cu-based catalysts are critical toward the realization of highly selective and efficient CO₂ electroreduction. In this review, first the latest advances in Cu-catalyzed CO₂ electroreduction in the product selectivity and electrocatalytic activity are briefly summarized. Then, recent theoretical and mechanistic studies of CO₂ electroreduction on Cu-based catalysts are investigated, which serve as programs to design catalysts. Strategies for devising Cu catalysts that aim at promoting different key elementary steps for hydrocarbon and C₂₊ oxygenates production are further summarized. Moreover, challenges in understanding the mechanism, operando investigation of Cu catalysts and reactions, and systems' influences are also presented. Finally, the future prospects of CO₂ electroreduction are discussed.

Breaking Scaling Relationships in CO2 Reduction on Copper Alloys with Organic Additives

Boundary conditions for catalyst performance in the conversion of common precursors such as N₂, O₂, H₂O, and CO₂ are governed by linear free energy and scaling relationships. Knowledge of these limits offers an impetus for designing strategies to alter reaction mechanisms to improve performance. Typically, experimental demonstrations of linear trends and deviations from them are composed of a small number of data points constrained by inherent experimental limitations. Herein, high-throughput experimentation on 14 bulk copper bimetallic alloys allowed for data-driven identification of a scaling relationship between the partial current densities of methane and C₂₊ products. This strict dependence represents an intrinsic limit to the Faradaic efficiency for C-C coupling. We have furthermore demonstrated that coating the electrodes with a molecular film breaks the scaling relationship to promote C₂₊ product formation.

Electrocatalytic reduction of CO2 and CO to multi-carbon compounds over Cu-based catalysts

The electrocatalytic reduction of CO₂ with H₂O to multi-carbon (C₂₊) compounds, in particular, C₂₊ olefins and oxygenates, which have versatile applications in the chemical and energy industries, holds great potential to mitigate the depletion of fossil resources and abate carbon emissions. There are two major routes for the electrocatalytic CO₂ reduction to C₂₊ compounds, i.e., the direct route and the indirect route via CO. The electrocatalytic CO₂ reduction to CO has been commercialised with solid oxide electrolysers, making the indirect route via CO to C₂₊ compounds also a promising alternative. This tutorial review focuses on the similarities and differences in the electrocatalytic CO₂ and CO reduction reactions (CO₂RR and CORR) into C₂₊ compounds, including C₂H₄, C₂H₅OH, CH₃COO^- and n-C₃H₇OH, over Cu-based catalysts. First, we introduce the fundamental aspects of the two electrocatalytic reactions, including the cathode and anode reactions, electrocatalytic reactors and crucial performance parameters. Next, the reaction mechanisms, in particular, the C-C coupling mechanism, are discussed. Then, efficient catalysts and systems for these two reactions are critically reviewed. We analyse the key factors that determine the selectivity, activity and stability for the electrocatalytic CO₂RR and CORR. Finally, the opportunities, challenges and future trends in the electrocatalytic CO₂RR and CORR are proposed. These insights will offer guidance for the design of industrial-relevant catalysts and systems for the synthesis of C₂₊ olefins and oxygenates.

Theoretically probing the possible degradation mechanisms of an FeNC catalyst during the oxygen reduction reaction

For the FeNC catalyst widely used in the oxygen reduction reaction (ORR), its instability under fuel cell (FC) operating conditions has become the biggest obstacle during its practical application. The complexity of the degradation process of the FeNC catalyst in FCs poses a huge challenge when it comes to revealing the underlying degradation mechanism that directly leads to the decay in ORR activity. Herein, using density functional theory (DFT) and ab initio molecular dynamics (AIMD) approaches and the FeN₄ moiety as an active site, we find that during catalyzing the ORR, Fe site oxidation in the form of *Fe(OH)₂, in which 2OH* species are adsorbed on Fe on the same side of the FeN₄ plane, results in the successive protonation of N and then permanent damage to the FeN₄ moiety, which causes the leaching of the Fe site in the form of Fe(OH)₂ species and a sharp irreversible decline in the ORR activity. However, other types of OH* adsorption on Fe in the form of HO*FeOH and *FeOH intermediates cannot cause the protonation of N or any breaking of Fe-N bonds in the FeN₄ moiety, only inducing the blocking of the Fe site. Meanwhile, based on the competitive relationship between catalyzing the ORR and Fe site oxidation, we propose a trade-off potential (U ^RHE _TMOR) to describe the anti-oxidation abilities of the TM site in the TMN _X moiety during the ORR.

Key to C2 production: selective C-C coupling for electrochemical CO2 reduction on copper alloy surfaces

The C-C coupling kinetic variations are observed on Cu alloys with Pt, Pd, or Au surface sites. The OC-COH coupling is kinetically more favorable than OC-CHO coupling, which originates from increased reactivity of adsorbed *CO species. Linear energy relations for C-C association/dissociation could simplify the energetic evaluation for C₂ production.

Geometric Modulation of Local CO Flux in Ag@Cu2 O Nanoreactors for Steering the CO2 RR Pathway toward High-Efficacy Methane Production

The electroreduction of carbon dioxide (CO₂ RR) to CH₄ stands as one of the promising paths for resourceful CO₂ utilization in meeting the imminent "carbon-neutral" goal of the near future. Yet, limited success has been witnessed in the development of high-efficiency catalysts imparting satisfactory methane selectivity at a commercially viable current density. Herein, a unique category of CO₂ RR catalysts is fabricated with the yolk-shell nanocell structure, comprising an Ag core and a Cu₂ O shell that resembles the tandem nanoreactor. By fixing the Ag core and tuning the Cu₂ O envelope size, the CO flux arriving at the oxide-derived Cu shell can be regulated, which further modulates the *CO coverage and *H adsorption at the Cu surface, consequently steering the CO₂ RR pathway. Density functional theory simulations show that lower CO coverage favors methane formation via stabilizing the intermediate *CHO. As a result, the best catalyst in the flow cell shows a high CH₄ Faraday efficiency of 74 ± 2% and partial current density of 178 ± 5 mA cm^{- 2} at -1.2 V_RHE , ranking above the state-of-the-art catalysts reported today for methane production. These findings mark the significance of precision synthesis in tailoring the catalyst geometry for achieving desired CO₂ RR performance.

Predictions of Chemical Shifts for Reactive Intermediates in CO2 Reduction under Operando Conditions

The electroreduction of CO₂ into value-added products is a significant step toward closing the global carbon loop, but its performance remains far from meeting the requirement of any practical application. The insufficient understanding of the reaction mechanism is one of the major causes that impede future development. Although several possible reaction pathways have been proposed, significant debates exist due to the lack of experimental support. In this work, we provide opportunities for experiments to validate the reaction mechanism by providing predictions of the core-level shifts (CLS) of reactive intermediates, which can be verified by the X-ray photoelectron spectroscopy (XPS) data in the experiment. We first validated our methods from benchmark calculations of cases with reliable experiments, from which we reach consistent predictions with experimental results. Then, we conduct theoretical calculations under conditions close to the operando experimental ones and predict the C 1s CLS of 20 reactive intermediates in the CO₂ reduction reaction (CO₂RR) to CH₄ and C₂H₄ on a Cu(100) catalyst by carefully including solvation effects and applied voltage (U). The results presented in this work should be guidelines for future experiments to verify and interpret the reaction mechanism of CO₂RR.

Recent advances on enhancing the multicarbon selectivity of nanostructured Cu-based catalysts

The rapid development and affordability of renewable energy sources necessitate innovative energy storage technologies to compensate for their intermittency. The electrochemical reduction of CO2 presents an attractive strategy for renewable energy storage, with considerable advancements in recent years. Copper-based catalysts have spearheaded this progress due to their intrinsic ability to produce valuable multicarbon reaction products. However, Cu is inherently unselective, and considerable efforts are needed to achieve the selective production of multicarbon reaction products on Cu-based catalysts. A multitude of factors affect the selectivity of Cu-catalysts, such as morphology, metal co-catalysts, and incorporation of oxidizing agents. In this review, we have summarized the current progress and the most important strategies for tuning the selectivity towards multicarbon reaction products over nanostructured Cu-based catalysts.

CO2 reduction on pure Cu produces only H2 after subsurface O is depleted: Theory and experiment

We elucidate the role of subsurface oxygen on the production of C₂ products from CO₂ reduction over Cu electrocatalysts using the newly developed grand canonical potential kinetics density functional theory method, which predicts that the rate of C₂ production on pure Cu with no O is ∼500 times slower than H₂ evolution. In contrast, starting with Cu₂O, the rate of C₂ production is >5,000 times faster than pure Cu(111) and comparable to H₂ production. To validate these predictions experimentally, we combined time-dependent product detection with multiple characterization techniques to show that ethylene production decreases substantially with time and that a sufficiently prolonged reaction time (up to 20 h) leads only to H₂ evolution with ethylene production ∼1,000 times slower, in agreement with theory. This result shows that maintaining substantial subsurface oxygen is essential for long-term C₂ production with Cu catalysts.

Gold-in-copper at low *CO coverage enables efficient electromethanation of CO2

The renewable-electricity-powered CO2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels. Renewable methane produced using CO2 electroreduction attracts interest due to the established global distribution network; however, present-day efficiencies and activities remain below those required for practical application. Here we exploit the fact that the suppression of *CO dimerization and hydrogen evolution promotes methane selectivity: we reason that the introduction of Au in Cu favors *CO protonation vs. C-C coupling under low *CO coverage and weakens the *H adsorption energy of the surface, leading to a reduction in hydrogen evolution. We construct experimentally a suite of Au-Cu catalysts and control *CO availability by regulating CO2 concentration and reaction rate. This strategy leads to a 1.6× improvement in the methane:H2 selectivity ratio compared to the best prior reports operating above 100 mA cm-2. We as a result achieve a CO2-to-methane Faradaic efficiency (FE) of (56 ± 2)% at a production rate of (112 ± 4) mA cm-2.

Electrokinetic and in situ spectroscopic investigations of CO electrochemical reduction on copper

Rigorous electrokinetic results are key to understanding the reaction mechanisms in the electrochemical CO reduction reaction (CORR), however, most reported results are compromised by the CO mass transport limitation. In this work, we determined mass transport-free CORR kinetics by employing a gas-diffusion type electrode and identified dependence of catalyst surface speciation on the electrolyte pH using in-situ surface enhanced vibrational spectroscopies. Based on the measured Tafel slopes and reaction orders, we demonstrate that the formation rates of C₂₊ products are most likely limited by the dimerization of CO adsorbate. CH₄ production is limited by the CO hydrogenation step via a proton coupled electron transfer and a chemical hydrogenation step of CO by adsorbed hydrogen atom in weakly (7 < pH < 11) and strongly (pH > 11) alkaline electrolytes, respectively. Further, CH₄ and C₂₊ products are likely formed on distinct types of active sites.

Electrokinetic results are key to understanding the mechanisms in electrochemical CO reduction reaction. Here, the authors determine mass transport free kinetics using a gas-diffusion electrode and identified dependence of copper surface speciation on the electrolyte pH using in situ surface enhanced spectroscopies.

Spatial-confinement induced electroreduction of CO and CO2 to diols on densely-arrayed Cu nanopyramids

The electroreduction of carbon dioxide (CO2) and carbon monoxide (CO) to liquid alcohol is of significant research interest. This is because of a high mass-energy density, readiness for transportation and established utilization infrastructure. Current success is mainly around monohydric alcohols, such as methanol and ethanol. There exist few reports on converting CO2 or CO to higher-valued diols such as ethylene glycol (EG; (CH2OH)2). The challenge to producing diols lies in the requirement to retain two oxygen atoms in the compound. Here for the first time, we demonstrate that densely-arrayed Cu nanopyramids (Cu-DAN) are able to retain two oxygen atoms for hydroxyl formation. This results in selective electroreduction of CO2 or CO to diols. Density Functional Theory (DFT) computations highlight that the unique spatial-confinement induced by Cu-DAN is crucial to selectively generating EG through a new reaction pathway. This structure promotes C-C coupling with a decreased reaction barrier. Following C-C coupling the structure facilitates EG production by (1) retaining oxygen and promoting the *COH-CHO pathway, which is a newly identified pathway toward ethylene glycol production; and, (2) suppressing the carbon-oxygen bond breaking in intermediate *CH2OH-CH2O and boosting hydrogenation to EG. Our findings will be of immediate interest to researchers in the design of highly active and selective CO2 and CO electroreduction to diols.

Direct and continuous generation of pure acetic acid solutions via electrocatalytic carbon monoxide reduction

Electrochemical CO₂ or CO reduction to high-value C₂₊ liquid fuels is desirable, but its practical application is challenged by impurities from cogenerated liquid products and solutes in liquid electrolytes, which necessitates cost- and energy-intensive downstream separation processes. By coupling rational designs in a Cu catalyst and porous solid electrolyte (PSE) reactor, here we demonstrate a direct and continuous generation of pure acetic acid solutions via electrochemical CO reduction. With optimized edge-to-surface ratio, the Cu nanocube catalyst presents an unprecedented acetate performance in neutral pH with other liquid products greatly suppressed, delivering a maximal acetate Faradaic efficiency of 43%, partial current of 200 mA⋅cm^-2, ultrahigh relative purity of up to 98 wt%, and excellent stability of over 150 h continuous operation. Density functional theory simulations reveal the role of stepped sites along the cube edge in promoting the acetate pathway. Additionally, a PSE layer, other than a conventional liquid electrolyte, was designed to separate cathode and anode for efficient ion conductions, while not introducing any impurity ions into generated liquid fuels. Pure acetic acid solutions, with concentrations up to 2 wt% (0.33 M), can be continuously produced by employing the acetate-selective Cu catalyst in our PSE reactor.