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As an effective approach to converting carbon oxide (CO2) into value‐added carbonaceous products, the electrochemical CO2 reduction reaction (ECO2RR) has shown considerable potential for carbon neutrality, addressing global pollution and climate issues. Copper (Cu)‐based electrocatalysts (CuECs) are acknowledged as important candidates for the ECO2RR of multi‐carbon products. Nevertheless, the complicated electron transfer and multiple competitive pathways in the multi‐carbon production process raise challenges of product selectivity. While achieving high current density and structural stability, improving the product selectivity of CuECs has become crucial to their practical applications. Herein, an overview of the fundamental thermodynamic and kinetic principles of ECO2RR are presented. Then, the typical strategies are summarized for increasing CuEC selectivity for the formation of multi‐carbon products from CO2, including morphological control, component design, defect design, and interface design. The catalyst design, catalytic performance, and reaction mechanisms involved in these strategies are reviewed. Finally, the major challenges and future prospects for high‐performance electrocatalysts in ECO2RR are discussed. [ABSTRACT FROM AUTHOR]

The photocatalytic CO2 reduction reaction (CO2RR) represents a promising solution to alleviate environmental and energy issues stemming from CO2 emissions while simultaneously enabling the production of high-value multi-carbon fuels. However, the efficient generation of multi-carbon products remains challenging due to high kinetic barriers, sluggish C–C coupling processes, and intricate reaction pathways. This review provides a comprehensive overview of the latest advancements in synthesizing C2+ products through CO2 photoreduction, highlighting the crucial role of active site design and the C–C coupling mechanism. Specifically, we emphasize the correlation between the structure of active sites and the key intermediates of C–C coupling, which is fundamental for achieving deep photoconversion of CO2. Finally, we offer a glimpse into future challenges and prospects, outlining potential directions for the development of CO2-to-multicarbon photoconversion, aiming to contribute novel insights to this exciting field. [ABSTRACT FROM AUTHOR]

Strain engineering on metal‐based catalysts has been utilized as an efficacious strategy to regulate the mechanism and pathways in various electrocatalytic reactions. However, controlling strain and establishing the strain‐activity relationship still remain significant challenges. Herein, three different and continuous tensile strains (CuPd‐1.90%, CuAu‐3.37%, and CuAg‐4.33%) are successfully induced by introducing heteroatoms with different atomic radius. The catalytic performances of CuPd‐1.90%, CuAu‐3.37%, and CuAg‐4.33% display a positive correlation against tensile strains in electrochemical CO2 reduction reaction (CO2RR). Specifically, CuAg‐4.33% exhibits superior catalytic performance with a 77.9% Faradaic efficiency of multi‐carbon products at −300 mA cm−2 current density, significantly higher than those of pristine Cu (Cu‐0%). Theoretical calculations and in situ spectroscopies verify that tensile strain can affect the d‐band center of Cu, thereby altering the binding energy of *CO intermediates and Gibbs free energies of the C–C coupling procedure. This work might highlight a new method for precisely regulating the lattice strain of metallic catalysts in different electrocatalytic reactions. [ABSTRACT FROM AUTHOR]

The stable operation of the CO2 reduction reaction (CO2RR) in membrane electrode assembly (MEA) electrolyzers is known to be hindered by the accumulation of bicarbonate salt, which are derived from alkali metal cations in anolytes, on the cathode side. In this study, we conducted a quantitative evaluation of the correlation between the CO2RR activity and the transported alkali metal cations in MEA electrolyzers. As a result, although the presence of transported alkali metal cations on the cathode surface significantly contributes to the generation of C2+ compounds, the rate of K+ ion transport did not match the selectivity of C2+, suggesting that a continuous supply of high amount of K+ to the cathode surface is not required for C2+ formation. Based on these findings, we achieved a faradaic efficiency (FE) and a partial current density for C2+ of 77 % and 230 mA cm−2, respectively, even after switching the anode solution from 0.1 M KHCO3 to a dilute K+ solution (<7 mM). These values were almost identical to those when 0.1 M KHCO3 was continuously supplied. Based on this insight, we successfully improved the durability of the system against salt precipitation by intermittently supplying concentrated KHCO3, compared with the continuous supply. [ABSTRACT FROM AUTHOR]

Porous carbon confined Cu-Ag heterostructure derived from MOF enables optimizing the electronic state of the reaction site and lowering the formation energy of the key intermediate *OCCHO to facilitate the generation of C 2 H 4. [Display omitted] • Novel MOF-derived CuO/Ag@C catalyst enhances CO 2 RR efficiency, achieving 48.6% FE for C 2 H 4. • Porous carbon confinement optimizes Cu-Ag active sites, boosting C C coupling and catalytic performance. • DFT calculations reveal CO spillover from Ag to Cu, enhancing *CO coverage and electron density optimization. • Low overpotential (−0.7 V vs. RHE) results in high C 2 product yield and long-term catalyst stability. Electrochemical reduction of CO 2 into valuable multi-carbon (C 2) chemicals holds promise for mitigating CO 2 emissions and enabling artificial carbon cycling. However, achieving high selectivity remains challenging due to the limited activity and active sites of C C coupling catalysts. Herein, we report an Ag-modified Cu-oxide catalyst (CuO/Ag@C) derived from metal-organic frameworks (MOF), capable of efficiently converting CO 2 to C 2 H 4. The MOF-derived porous carbon confines the size of metal nanoparticles, ensuring sufficient exposure of active sites. Remarkably, the CuO/Ag@C catalyst achieves an impressive Faradaic efficiency of 48.6% for C 2 H 4 at −0.7 V vs. RHE, demonstrating excellent stability. Both experimental results and theoretical calculations indicate that Ag sites promote the production of CO, enhancing the coverage of *CO on Cu sites. Furthermore, the reconfiguration of charge density at the Cu-Ag interface optimizes the electronic states of the reaction sites, reducing the formation energy of the key intermediate *OCCHO, thereby favoring C 2 H 4 production effectively. This work provides insight into structurally rational catalyst design for highly active and selective multiphase catalysts. [ABSTRACT FROM AUTHOR]

To improve the electrocatalytic transformation of carbon dioxide (CO2) to multi-carbon (C2+) products is of great importance. Here we developed a nitrogen-doped Cu catalyst, by which the maximum C2+ Faradaic efficiency can reach 72.7% in flow-cell system, with the partial current density reaching 0.62 A cm−2. The in situ Raman spectra demonstrate that the ∗CO adsorption can be strengthened on such a N-doped Cu catalyst, thus promoting the ∗CO utilization in the subsequent C–C coupling step. Simultaneously, the water activation can be well enhanced by N doping on Cu catalyst. Owing to the synergistic effects, the selectivity and activity for C2+ products over the N-deoped Cu catalyst are much improved.

Electrochemical CO2 reduction has garnered significant interest in the conversion of sustainable energy to valuable fuels and chemicals. Cu‐based bimetallic catalysts play a crucial role in enhancing *CO concentration on Cu sites for efficient C─C coupling reactions, particularly for C2 product generation. To enhance Cu's electronic structure and direct its selectivity toward C2 products, a novel strategy is proposed involving the in situ electropolymerization of a nano‐thickness cobalt porphyrin polymeric network (EP‐CoP) onto a copper electrode, resulting in the creation of a highly effective EP‐CoP/Cu tandem catalyst. The even distribution of EP‐CoP facilitates the initial reduction of CO2 to *CO intermediates, which then transition to Cu sites for efficient C─C coupling. DFT calculations confirm that the *CO enrichment from Co sites boosts *CO coverage on Cu sites, promoting C─C coupling for C2+ product formation. The EP‐CoP/Cu gas diffusion electrode achieves an impressive current density of 726 mA cm−2 at −0.9 V versus reversible hydrogen electrode (RHE), with a 76.8% Faraday efficiency for total C2+ conversion and 43% for ethylene, demonstrating exceptional long‐term stability in flow cells. These findings mark a significant step forward in developing a tandem catalyst system for the effective electrochemical production of ethylene. [ABSTRACT FROM AUTHOR]

To improve the electrocatalytic transformation of carbon dioxide (CO2) to multi-carbon (C2þ) products is of great importance. Here we developed a nitrogen-doped Cu catalyst, by which the maximum C2þ Faradaic efficiency can reach 72.7% in flow-cell system, with the partial current density reaching 0.62 A cm-2. The in situ Raman spectra demonstrate that the *CO adsorption can be strengthened on such a N-doped Cu catalyst, thus promoting the *CO utilization in the subsequent C--C coupling step. Simultaneously, the water activation can be well enhanced by N doping on Cu catalyst. Owing to the synergistic effects, the selectivity and activity for C2þ products over the N-deoped Cu catalyst are much improved. [ABSTRACT FROM AUTHOR]

The electrochemical carbon dioxide reduction reaction (CO2RR) holds substantial promise for producing high‐value chemicals and fuels, drawing significant attention from both academia and industry. This work proposes an in‐situ electrodeposition method to prepare indium‐doped copper (Cu)‐based catalysts on carbon paper (Cu100Inx−CP, x=3.9, 4.5, 4.8, 5.1, and 7.6, denoting the molar ratio of In to Cu in the catalyst.). The catalysts Cu100Inx−CP were used for CO2RR to produce multi‐carbon (C2+) products. Characterization results showed that In was highly dispersed in the Cu particles at x<5.1. The Cu100In5.1−CP (containing 0.95 wt % In based on Cu) was very efficient for electrocatalytic CO2RR. The in‐situ Raman spectroscopy showed that Cu100In5.1−CP enhanced *CO intermediate adsorption and promoted the production of C2+ products due to the synergistic effect between In and Cu. In doping could suppress HER, enhanced *CO intermediate adsorption, and C−C coupling for the production of C2+ products in CO2RR. [ABSTRACT FROM AUTHOR]

Abstract Strain engineering on metal‐based catalysts has been utilized as an efficacious strategy to regulate the mechanism and pathways in various electrocatalytic reactions. However, controlling strain and establishing the strain‐activity relationship still remain significant challenges. Herein, three different and continuous tensile strains (CuPd‐1.90%, CuAu‐3.37%, and CuAg‐4.33%) are successfully induced by introducing heteroatoms with different atomic radius. The catalytic performances of CuPd‐1.90%, CuAu‐3.37%, and CuAg‐4.33% display a positive correlation against tensile strains in electrochemical CO2 reduction reaction (CO2RR). Specifically, CuAg‐4.33% exhibits superior catalytic performance with a 77.9% Faradaic efficiency of multi‐carbon products at −300 mA cm−2 current density, significantly higher than those of pristine Cu (Cu‐0%). Theoretical calculations and in situ spectroscopies verify that tensile strain can affect the d‐band center of Cu, thereby altering the binding energy of *CO intermediates and Gibbs free energies of the C–C coupling procedure. This work might highlight a new method for precisely regulating the lattice strain of metallic catalysts in different electrocatalytic reactions.

The electroreduction of carbon dioxide (CO2) to multi‐carbon (C2+) compounds offers a viable approach for the up‐conversion of greenhouse gases into valuable fuels and feedstocks. Nevertheless, current industrial applications face limitations due to unsatisfactory conversion efficiency and high overpotential. Herein, a facile and scalable plasma fluorination method is reported. Concurrently, self‐evolution during CO2 electroreduction is employed to control the active sites of Cu catalysts. The copper catalyst modified with fluorine exhibits an impressive C2+ Faradaic efficiency (FE) of 81.8% at a low potential of −0.56 V (vs a reversible hydrogen electrode) in an alkaline flow cell. The presence of modified fluorine leads to the exposure and stabilization of high‐activity Cu+ species, enhancing the adsorption of *CO intermediates and the generation of *CHO, facilitating the subsequent dimerization. This results in a notably improved conversion efficiency of 13.1% and a significant reduction in the overpotential (≈100 mV) for the C2+ products. Furthermore, a superior C2+ FE of 81.6% at 250 mA cm−2, coupled with an energy efficiency of 31.0%, can be achieved in a two‐electrode membrane electrode assembly electrolyzer utilizing the fluorine‐modified copper catalyst. The strategy provides novel insights into the controllable electronic modification and surface reconstruction of electrocatalysts with practical potential. [ABSTRACT FROM AUTHOR]

Effective electrochemical conversion of CO2 to value-added liquid multi-carbon products driven by renewable energy is a promising approach to alleviate excessive CO2 emission and achieve large-scale renewable energy storage. However, the selectivity and catalytic activity towards liquid multi-carbon products of CO2 electroreduction reaction are still unsatisfactory due to the sluggish C–C coupling process and the formation of complex oxygen-containing intermediates. Hence, designing and fabricating highly effective electrocatalysts is crucial for practical applications in this field. Here, we developed Cl-modified Cu catalyst (Cu-Cl) for efficient electrochemical reduction of CO2 to ethanol. The optimal Faradaic efficiency and partial current density of ethanol on the Cu-Cl sample reached 26.2% and 343.2 mA·cm−2 at −0.74 V (vs. reversible hydrogen electrode (RHE)), which were 1.66 and 1.76 times higher than those of the catalyst without Cl decoration, outperforming those in most previously reported works. Density functional theory (DFT) calculations revealed that the Cl-modified Cu surface suppressed the parasitic hydrogen evolution reaction (HER) and reduced the energy barrier for the C–C coupling process, making the formation of key intermediates favorable for ethanol production. Thus, the decoration of Cl on the Cu surface facilitated ethanol formation. [ABSTRACT FROM AUTHOR]

Electrocatalytic carbon dioxide reduction reaction (CO2RR) holds the promise of both overcoming the greenhouse effect and synthesizing a wealth of chemicals. Electrocatalytic CO2 reduction toward carbon-containing products, including C1 products (carbon monoxide, formic acid, etc), C2 products (ethylene, ethanol, etc.) and multi-carbon products (e.g., n-propanol), provides beneficial fuel and chemicals for industrial production. The complexity of the multi-proton transfer processes and difficulties of C-C coupling in electrochemical CO2 reduction toward multi-carbon(C2+) products have attracted increasing concerns on the design of catalysts in comparison with those of C1 products. In this paper, we review the main advances in the syntheses of multi-carbon products through electrocatalytic carbon dioxide reduction in recent years, introduce the basic principles of electrocatalytic CO2RR, and detailly elucidate two widely accepted mechanisms of C-C coupling reactions. Among abundant nanomaterials, copper-based catalysts are outstanding catalysts for the preparation of multi-carbon chemicals in electrochemical CO2RR attributing to effective C-C coupling reactions. Regarding the different selectivity of multi-carbon chemicals but extensively applied copper-based catalysts, we classify and summarize various Cu-based catalysts through separating diverse multi-carbon products, where the modification of spatial and electronic structures is beneficial to increase the coverage of CO or lower the activation energy barrier for forming C-C bond to form the key intermediates and increase the production of multi-carbon products. Challenges and prospects involving the fundamental and development of copper-based catalysts in electrochemical CO2 reduction reaction are also proposed.

Abstract Electrochemical CO2 reduction has garnered significant interest in the conversion of sustainable energy to valuable fuels and chemicals. Cu‐based bimetallic catalysts play a crucial role in enhancing *CO concentration on Cu sites for efficient C─C coupling reactions, particularly for C2 product generation. To enhance Cu's electronic structure and direct its selectivity toward C2 products, a novel strategy is proposed involving the in situ electropolymerization of a nano‐thickness cobalt porphyrin polymeric network (EP‐CoP) onto a copper electrode, resulting in the creation of a highly effective EP‐CoP/Cu tandem catalyst. The even distribution of EP‐CoP facilitates the initial reduction of CO2 to *CO intermediates, which then transition to Cu sites for efficient C─C coupling. DFT calculations confirm that the *CO enrichment from Co sites boosts *CO coverage on Cu sites, promoting C─C coupling for C2+ product formation. The EP‐CoP/Cu gas diffusion electrode achieves an impressive current density of 726 mA cm−2 at −0.9 V versus reversible hydrogen electrode (RHE), with a 76.8% Faraday efficiency for total C2+ conversion and 43% for ethylene, demonstrating exceptional long‐term stability in flow cells. These findings mark a significant step forward in developing a tandem catalyst system for the effective electrochemical production of ethylene.

Carbon utilization efficiency is of vital importance for electrochemical CO2 reduction systems. Proton exchange membrane (PEM) electrolyzers using nonalkaline electrolytes can prevent CO2 crossover and increase carbon utilization efficiency, yet they suffer from unfavored C─C coupling and severe hydrogen evolution. Herein, an iodine‐mediated approach to facilitate C─C coupling on Cu‐based catalysts toward multi‐carbon products in a neutral PEM electrolyzer is reported. By in situ constructing an I‐modified Cu surface, the hydrogenation of *CO is promoted and the C─C coupling process progresses through the *CO−*COH pathway with a low energy barrier. A high Faradaic efficiency of ≈72% and a high partial current density of 575 mA cm−2 are achieved for multi‐carbon products. The present study demonstrates an efficient approach to developing advanced CO2 electrolyzers for high‐value products with high efficiency. [ABSTRACT FROM AUTHOR]

Abstract The electroreduction of carbon dioxide (CO2) to multi‐carbon (C2+) compounds offers a viable approach for the up‐conversion of greenhouse gases into valuable fuels and feedstocks. Nevertheless, current industrial applications face limitations due to unsatisfactory conversion efficiency and high overpotential. Herein, a facile and scalable plasma fluorination method is reported. Concurrently, self‐evolution during CO2 electroreduction is employed to control the active sites of Cu catalysts. The copper catalyst modified with fluorine exhibits an impressive C2+ Faradaic efficiency (FE) of 81.8% at a low potential of −0.56 V (vs a reversible hydrogen electrode) in an alkaline flow cell. The presence of modified fluorine leads to the exposure and stabilization of high‐activity Cu+ species, enhancing the adsorption of *CO intermediates and the generation of *CHO, facilitating the subsequent dimerization. This results in a notably improved conversion efficiency of 13.1% and a significant reduction in the overpotential (≈100 mV) for the C2+ products. Furthermore, a superior C2+ FE of 81.6% at 250 mA cm−2, coupled with an energy efficiency of 31.0%, can be achieved in a two‐electrode membrane electrode assembly electrolyzer utilizing the fluorine‐modified copper catalyst. The strategy provides novel insights into the controllable electronic modification and surface reconstruction of electrocatalysts with practical potential.

Converting CO2 into valuable chemicals has been intensively explored in recent years. Benefited from the substantial cost reduction of renewable electricity, the electrochemical methods have been emerging as a potential means for CO2 capture and conversion. Recently, molecular tuning has been recognized as a powerful technique to modify catalyst's surface and verified effective in improving CO2RR performance. However, there are few comprehensive and insightful reviews on molecularly modified Cu‐based catalysts to precisely modulate the activity and selectivity of C2+ products in CO2 reduction. Herein, the development of CO2RR plausible reaction mechanisms is first introduced. The process and reaction pathways of the carbon‐carbon coupling are briefly discussed. Four main aspects of the molecular tuning strategy of the CO2RR are described as the first coordination layer, second coordination layer, outer layer, and confined effects. The understanding of the improved C2+ performance is demonstrated for molecularly modified Cu‐based catalysts. The challenges and perspectives in this field are addressed to further inspire the disclosure of the fundamental understanding in CO2RR, the system optimization, advanced in situ and operando techniques, and integration of CO2 capture and conversion technology with high activity and selectivity for durable applications. [ABSTRACT FROM AUTHOR]

Electroreduction of CO2 to multi‐carbon (C2+) products is a promising approach for utilization of renewable energy, in which the interfacial water quantity is critical for both the C2+ product selectivity and the stability of Cu‐based electrocatalytic sites. Functionalization of long‐chain alkyl molecules on a catalyst surface can help to increase its stability, while it also tends to block the transport of water, thus inhibiting the C2+ product formation. Herein, we demonstrate the fine tuning of interfacial water by surface assembly of toluene on Cu nanosheets, allowing for sustained and enriched CO2 supply but retarded water transfer to catalytic surface. Compared to bare Cu with fast cathodic corrosion and long‐chain alkyl‐modified Cu with main CO product, the toluene assembly on Cu nanosheet surface enabled a high Faradaic efficiency of 78 % for C2+ and a partial current density of 1.81 A cm−2. The toluene‐modified Cu catalyst further exhibited highly stable CO2‐to‐C2H4 conversion of 400 h in a membrane‐electrode‐assembly electrolyzer, suggesting the attractive feature for both efficient C2+ selectivity and excellent stability. [ABSTRACT FROM AUTHOR]

Cu-based catalysts for efficient C2+ production from CO2 electrocatalytic reduction reaction (CO2ERR) exhibit significant promise, but still suffer from ambiguous mechanisms due to the intrinsic structure instability during electroreduction. Herein, we report an oxide-derived copper nanowire bundle (OD-Cu NWB) for efficient CO2ERR to C2+ products. OD-Cu NWBs with a well-preserved nanowire bundle morphology lead to promoted multi-carbon production compared to commercial copper powders. The formation of OD-Cu NWBs shows a great dependence on the precipitation/calcination temperatures and per-reduction potentials, which further influence the ultimate CO2ERR performance correspondingly. The optimized preparation parameters for the formation of a well-ordered nanowire bundle morphology are found, leading to a preferred C2+ production ability. Besides the nanowire bundle morphology, the oxide-derived Cu essence of OD-Cu NWBs with stabilized Cu+ species from per-reduction also promotes the CO2ERR activity and facilitates the C-C coupling of key intermediates for C2+ production. This work provides a facile strategy and inspiration for CO2ERR catalyst developments targeting high-valued multi-carbon products. [ABSTRACT FROM AUTHOR]

This review makes a comprehensive summary of improving the selectivity of electrocatalytic CO 2 reduction to C 2 products, including the optimisation of catalysts, electrolytes and electrolytic cells. [Display omitted] Reducing the consumption of fossil fuels and improving the utilization of carbon dioxide (CO 2) are urgently needed to mitigate the effect of increasing CO 2 concentration in the atmosphere, which has led to global temperature rising and climate change. Electrochemical CO 2 reduction (ECR) is a promising strategy for converting CO 2 into high-value-added multi-carbon compounds (such as ethylene:C 2 H 4 and ethanol: C 2 H 5 OH) through proton coupled electron transfer (PCET) steps, in which copper (Cu) is to date the only metal that can promote C–C coupling to produce C 2 products in aqueous solutions. However, due to the inherent moderate adsorption capacity of Cu on carbon-containing small molecule groups and the variety of C 2 products intermediates, low product selectivity remains the dominant drawback of metal Cu-based catalysts. A large number of strategies have been investigated to optimize the distribution of electrolysis products, including alloying, anion and cation species regulation, facet design, and tandem catalysis. In this review, we first elaborate the reaction mechanism of C 2 products generation on Cu-based catalysts, aiming to provide guidance for designing more selective catalysts. Then, with the intention of providing new insights into improving C 2 olefins and oxides, we summarize the aspects, including catalysts, electrolytes microenvironment, electrolyzer design, and other factors that affect the selectivity of C 2 products in catalytic systems. Finally, the main challenges and prospects for the future of Cu-based catalytic systems are outlined. The review is expected to stimulate more extensive studies on highly selective electrocatalysts of C 2 products by ECR. [ABSTRACT FROM AUTHOR]

A simple method was proposed to activate alkaline Cu(OH)2 with an acidic ionomer, Nafion, to regulate its surface microenvironment, including hydrophobicity and local basicity. In particular, the direct complete neutralization reaction between Cu(OH)2 and Nafion in aqueous solution induces the exposing of vast anions which can exclude the in‐situ‐formed hydroxides and raise the local basicity. Remarkably, the optimal Nafion‐activated Cu(OH)2‐derived Cu can efficiently suppress the hydrogen evolution reaction (HER) and improve the selectivity for multi‐carbon products in the CO2 electroreduction reaction (eCO2RR). The H2 Faradaic efficiency (FE) decreased to 11% at a current density of 300 mA/cm2 (−0.76 V vs. RHE) in a flow cell, while the bare one with H2 had an FE of 40%. The total eCO2RR FE reaches as high as 83%, along with an evidently increased C2H4 FE of 44% as compared with the bare one (24%), and good stability (8000 s), surpassing that of most of the reported Cu(OH)2‐derived Cu. The experimental and theoretical results both show that the strong hydrophobicity and high local basicity jointly boosted the eCO2RR as acquired by felicitously introducing ionomer on the Cu(OH)2‐derived Cu surface. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of CO2 to valuable multi-carbon products is an important potential solution to environmental and energy crises caused by fossil fuel burning. As an effective way to address the drawbacks of direct CO2 reduction, the reduction of CO to multi-carbon products remains a challenge, specially lacking high-efficient, selective and low-cost metal-free catalysts. N-heterocyclic carbenes (NHCs) have been shown to be effective metal-free catalysts for converting CO2 to CO or C1-products, but the facile release of CO limits the further reduction to valuable multi-carbon fuels. In this study, using density functional theory calculations, we developed heterogeneous NHCs by incorporating NHCs into the graphene lattice and found that these NHCs could stably adsorb and effectively activate CO molecules, enabling the efficient conversion of CO into CH3OH, C2H4 and C2H5OH with low limiting potentials, i.e., –0.70, –0.45 and –0.36 V, respectively. These limiting potentials for C2-products are lower than those of most known metal-based or metal-free electrocatalysts. Moreover, competitive hydrogen evolution reaction can be effectively inhibited. The excellent catalytic performance is attributed to the charge transfer between NHCs and CO as well as the strong hybridization of C-2p orbitals of carbene carbon atoms in NHCs and carbon atoms in CO molecule. Our findings suggest that these heterogeneous NHCs exhibit high catalytic activity and selectivity for the conversion of CO to valuable C2-products. This study is the first report of NHC-based metal-free electrocatalysts for the conversion of CO to multi-carbon products, which will offer cost-effective opportunities for CO2 reduction.

The electrochemical reduction of CO2 (CO2RR) into valuable chemicals and fuels is a promising approach for sustainable energy storage and compromising greenhouse gas emissions, among which the formation of higher-valued multi-carbon products (C2+) is desired. However, selective CO2RR to C2+ usually suffers from a low reaction rate and low selectivity for the complex and long pathways. More seriously, the catalytic system involving catalyst, interface and microenvironment changes dynamically at realistic working conditions, which regrettably causes misleading results regarding the promoted factor and reaction mechanism of CO2RR. To this regard, it is necessary to develop the advanced in situ techniques to track the dynamic evolution of the catalytic system under operating conditions. Here, we discuss the necessary factors and key challenges in producing C2+ products, including current state-of-the-art copper-based catalyst, as well as the dynamic evolution of the catalyst structure, oxidation state and composition. Then, we present the strategies using advanced in situ and operando characterizations to monitor the deep triggers of dynamic evolution and deeply understand the reaction mechanism. Finally, we highlight how the cross-coupled model and data-driven flow enable the new paradigm of in situ characterization with higher accuracy and efficiency.

Abstract A simple method was proposed to activate alkaline Cu(OH)2 with an acidic ionomer, Nafion, to regulate its surface microenvironment, including hydrophobicity and local basicity. In particular, the direct complete neutralization reaction between Cu(OH)2 and Nafion in aqueous solution induces the exposing of vast anions which can exclude the in‐situ‐formed hydroxides and raise the local basicity. Remarkably, the optimal Nafion‐activated Cu(OH)2‐derived Cu can efficiently suppress the hydrogen evolution reaction (HER) and improve the selectivity for multi‐carbon products in the CO2 electroreduction reaction (eCO2RR). The H2 Faradaic efficiency (FE) decreased to 11% at a current density of 300 mA/cm2 (−0.76 V vs. RHE) in a flow cell, while the bare one with H2 had an FE of 40%. The total eCO2RR FE reaches as high as 83%, along with an evidently increased C2H4 FE of 44% as compared with the bare one (24%), and good stability (8000 s), surpassing that of most of the reported Cu(OH)2‐derived Cu. The experimental and theoretical results both show that the strong hydrophobicity and high local basicity jointly boosted the eCO2RR as acquired by felicitously introducing ionomer on the Cu(OH)2‐derived Cu surface.

Abstract Electrochemical CO2 reduction reaction (CO2RR) to multi-carbon products would simultaneously reduce CO2 emission and produce high-value chemicals. Herein, we report Cu electrodes modified by metal–organic framework (MOF) exhibiting enhanced electrocatalytic performance to convert CO2 into ethylene and ethanol. The Zr-based MOF, UiO-66 would in situ transform into amorphous ZrOx nanoparticles (a-ZrOx), constructing a-ZrOx/Cu hetero-interface as a dual-site catalyst. The Faradaic efficiency of multi-carbon (C2+) products for optimal UiO-66-coated Cu (0.5-UiO/Cu) electrode reaches a high value of 74% at − 1.05 V versus RHE. The intrinsic activity for C2+ products on 0.5-UiO/Cu electrode is about two times higher than that of Cu foil. In situ surface-enhanced Raman spectra demonstrate that UiO-66-derived a-ZrOx coating can promote the stabilization of atop-bound CO* intermediates on Cu surface during CO2 electrolysis, leading to increased CO* coverage and facilitating the C–C coupling process. The present study gives new insights into tailoring the adsorption configurations of CO2RR intermediate by designing dual-site electrocatalysts with hetero-interfaces.

• Cu-based nanostructures are highly valued in electrochemical carbon dioxide reduction (eCO 2 R) due to their ability to produce various value-added hydrocarbons and oxygenates. • Current research aims to direct eCO2R towards the formation of multi-carbon (C2+) products and to understand the complex mechanisms of carbon-carbon (C-C) coupling. • The study computationally explores the effects of doping Cu nanostructures with trace amounts of Zr atoms, finding that Zr dopants are energetically favourable and enhance charge transfer to adjacent Cu atoms. • The effect of Zr is to reduce the activation barriers for C-C coupling, promoting the formation of C1 and C2 hydrocarbons. • The interaction between Zr and oxygen weakens the C-O bond, facilitating its cleavage. The formation of C 3 products and the selectivity between hydrocarbons and oxygenates are influenced by the hydrogenation sequence on different carbon atoms. Cu-based nanostructures have garnered significant attention in the field of electrochemical carbon dioxide reduction (eCO 2 R), due to their significant activity and ability to produce a variety of value-added hydrocarbons and oxygenates. Current research efforts focus on steering eCO 2 R towards the formation of multi-carbon (C 2+) products and elucidating the complex mechanisms of C-C coupling. One promising approach involves transition metals into Cu nanostructures. This study computationally investigates the impact of trace Zr atom doping on Cu nanostructures, specifically at the interfaces of (100) and (110) surfaces of ultrathin Cu nanowires. Our findings reveal that Zr dopants are energetically favourable and facilitate charge transfer to adjacent Cu atoms, thereby reducing the activation barriers for C-C coupling and enhancing the formation of C 1 and C 2 hydrocarbons. Additionally, the Zr-O interaction weakens the C-O bond, promoting C-O bond cleavage. The formation of C 3 products, and the selectivity between hydrocarbons and oxygenates, are influenced by the hydrogenation sequence on different carbon atoms. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: Dual-site electrocatalysts with in situ formed metal-oxide interfaces are proposed and demonstrated to enhance the formation of multi-carbon products from electrochemical CO2 reduction. The 0.5-UiO/Cu delivers a high C2+ Faradaic efficiency of over 74% with notably boosted formation rate and durability, surpassing most reported electrocatalysts. A unique mechanism of UiO-66 to induce in situ reconstruction of Cu surface and formation of UiO-66-derived amorphous ZrOx/Cu interface is uncovered, which improves the selectivity and productivity toward C2+ products.Electrochemical CO2 reduction reaction (CO2RR) to multi-carbon products would simultaneously reduce CO2 emission and produce high-value chemicals. Herein, we report Cu electrodes modified by metal–organic framework (MOF) exhibiting enhanced electrocatalytic performance to convert CO2 into ethylene and ethanol. The Zr-based MOF, UiO-66 would in situ transform into amorphous ZrOx nanoparticles (a-ZrOx), constructing a-ZrOx/Cu hetero-interface as a dual-site catalyst. The Faradaic efficiency of multi-carbon (C2+) products for optimal UiO-66-coated Cu (0.5-UiO/Cu) electrode reaches a high value of 74% at − 1.05 V versus RHE. The intrinsic activity for C2+ products on 0.5-UiO/Cu electrode is about two times higher than that of Cu foil. In situ surface-enhanced Raman spectra demonstrate that UiO-66-derived a-ZrOx coating can promote the stabilization of atop-bound CO* intermediates on Cu surface during CO2 electrolysis, leading to increased CO* coverage and facilitating the C–C coupling process. The present study gives new insights into tailoring the adsorption configurations of CO2RR intermediate by designing dual-site electrocatalysts with hetero-interfaces. [ABSTRACT FROM AUTHOR]

The stable operation of the CO 2 reduction reaction (CO 2 RR) in membrane electrode assembly (MEA) electrolyzers is known to be hindered by the accumulation of bicarbonate salt, which are derived from alkali metal cations in anolytes, on the cathode side. In this study, we conducted a quantitative evaluation of the correlation between the CO 2 RR activity and the transported alkali metal cations in MEA electrolyzers. As a result, although the presence of transported alkali metal cations on the cathode surface significantly contributes to the generation of C 2+ compounds, the rate of K + ion transport did not match the selectivity of C 2+ , suggesting that a continuous supply of high amount of K + to the cathode surface is not required for C 2+ formation. Based on these findings, we achieved a faradaic efficiency (FE) and a partial current density for C 2+ of 77 % and 230 mA cm -2 , respectively, even after switching the anode solution from 0.1 M KHCO 3 to a dilute K + solution (<7 mM). These values were almost identical to those when 0.1 M KHCO 3 was continuously supplied. Based on this insight, we successfully improved the durability of the system against salt precipitation by intermittently supplying concentrated KHCO 3 , compared with the continuous supply., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

[Display omitted] The increasing CO 2 emissions and accompanying climate challenges have boosted the exploration of candidate pathways for storing and utilizing renewable carbon resources. Electrochemical CO 2 reduction (ECO 2 R) has been proven as a promising technology for artificial carbon fixation. Nevertheless, the unsatisfactory multi-carbon (C 2+) product selectivity hinders its widespread use. Recently, the indirect route via electrochemical CO reduction (ECOR) to C 2+ products has become a potential alternative through the combination with ECO 2 R. In this review, we briefly summarize the most recent and instructive research in the ECOR development process from advanced ECOR catalysts and reaction mechanisms. Furthermore, the challenges and outlooks based on current understanding in this field are expounded. These insights and perspectives offer meaningful guidance for grasping ECOR and designing relevant catalysts with enhanced C 2+ product selectivity. [ABSTRACT FROM AUTHOR]

Electrocatalytic CO 2 reduction reaction (CO 2 RR) to produce multi-carbon products (C 2+) is one of the most sustainable manners to achieve net-zero carbon emissions. Among many approaches, enriching grain boundaries (GBs) in copper (Cu) catalysts has been demonstrated to enable enhancement for C 2+ production. However, it still lacks effective strategies to controllably synthesize abundant GBs, rendering efficient C 2+ production a persistent challenge, especially at ampere-level current density. Herein, we propose a novel strategy, which can achieve unconventional grain fragmentation during thermal annealing and thus create controllable GB densities. The catalyst with the utmost GB density exhibits a peak C 2+ faradaic efficiency of ca. 70.0 % in H-type cell and 68.2 % in flow cell; even more impressively, it delivers an ultra-high C 2+ current density of 0.768 A cm−2, outperforming most recently reported results. A combination of in situ spectroscopies and theoretical calculations reveal that the enrichment of GBs yields more active sites for a higher *CO coverage, leading to promotion of the *CO-*CO coupling process and ultimately high C 2+ production performance. [Display omitted] • An unconventional grain fragmentation strategy is proposed to controllably tune the density of Cu GBs. • The optimal catalyst exhibits a C 2+ current density of 0.768 A cm−2, outperforming most reported counterparts. • The high C 2+ production stems from a higher *CO coverage and more facile *CO-*CO coupling over Cu GBs. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of carbon dioxide (CO2RR) into value‐added chemicals is a promising tactic to mitigate global warming. However, this process resists catalyst preparation, low faradaic efficiency (FE%) towards multi‐carbon products, and insights into mechanistic understanding. Indeed, it is demonstrated that this Fe single‐atom catalyst (Fe SAC) exists in three oxygen coordination of Fe–(O)3 configuration in Nafion coated functionalized multi‐wall carbon nanotubes (Fe‐n‐f‐CNTs), which is obtained via a simple ionic exchange method under ambient conditions. The electrochemical performance reveals that Fe SACs achieve an FE of 45% and a yield rate of 56.42 µmol cm−2 h−1 at −0.8 VRHE for ethanol. In situ X‐ray analysis reveals that the Fe SACs have variable electronic states and keeps close +3 of the oxidation state at the potential range of CO2RR. The catalytic feature reduces the reaction energy and induces the electrons transferred to the adsorbed products intermediates of *COOH and *OCHO, thus promoting CO. The carboxylic functional group on the CNTs stabilizes the Fe active sites via electrostatic interaction, verified by density functional theory calculations. The yield rate of Fe SACs indicates that the Fe single‐atom site can instantly provide a large CO to help conversion of CO2‐to‐C2 product on the CNTs. [ABSTRACT FROM AUTHOR]

Electroreduction of CO2 into valuable fuels and feedstocks offers a promising way for CO2 utilization. However, the commercialization is limited by the low productivity. Here, we report a strategy to enhance the productivity of CO2 electroreduction by improving diffusion of CO2 to the surface of catalysts using porous organic cages (POCs) as an additive. It was noted that the Faradaic efficiency (FE) of C2+ products could reach 76.1 % with a current density of 1.7 A cm−2 when Cu‐nanorod(nr)/CC3 (one of the POCs) was used, which were much higher than that using Cu‐nr. Detailed studies demonstrated that the hydrophobic pores of CC3 can adsorb a large amount of CO2 for the reaction, and the diffusion of CO2 in the CC3 to the nanocatalyst surface is easier than that in the liquid electrolyte. Thus, more CO2 molecules make contact with the nanocatalysts in the presence of CC3, enhancing CO2 reduction and inhibiting generation of H2. [ABSTRACT FROM AUTHOR]

The electrocatalytic reduction of CO2 presents a promising strategy in addressing environmental and energy crisis. Significant progress has been achieved via CO2 gas diffusion electrolysis, to react at high selectivity and high rate. However, the gas diffusion layer (GDL) of the gas diffusion electrode (GDE) still suffers from low tolerance and limited active sites. Here, the hydrophobic 1-octadecanethiol molecular was functionalized over the Cu catalyst layer of the GDE, which simultaneously stabilizes the GDL and exposes abundant active solid-liquid-gas three-phase interfaces. The resultant GDE exhibits multi-carbon (C2+) product selectivity over faradaic efficiency (FE) of 70.0% in the range of 100 to 800 mA·cm−2, with the peak FEC2+ of 85.2% at 800 mA·cm−2. Notably, the strengthened GDE could continuously drive high-current electrolysis for more than 100 h without flooding. This work opens a new way to improve CO2 gas diffusion electrolysis via surface molecular engineering. [ABSTRACT FROM AUTHOR]

Electrochemical CO 2 reduction has garnered significant interest in the conversion of sustainable energy to valuable fuels and chemicals. Cu-based bimetallic catalysts play a crucial role in enhancing * CO concentration on Cu sites for efficient C─C coupling reactions, particularly for C 2 product generation. To enhance Cu's electronic structure and direct its selectivity toward C 2 products, a novel strategy is proposed involving the in situ electropolymerization of a nano-thickness cobalt porphyrin polymeric network (EP-CoP) onto a copper electrode, resulting in the creation of a highly effective EP-CoP/Cu tandem catalyst. The even distribution of EP-CoP facilitates the initial reduction of CO 2 to * CO intermediates, which then transition to Cu sites for efficient C─C coupling. DFT calculations confirm that the * CO enrichment from Co sites boosts * CO coverage on Cu sites, promoting C─C coupling for C 2+ product formation. The EP-CoP/Cu gas diffusion electrode achieves an impressive current density of 726 mA cm -2 at -0.9 V versus reversible hydrogen electrode (RHE), with a 76.8% Faraday efficiency for total C 2+ conversion and 43% for ethylene, demonstrating exceptional long-term stability in flow cells. These findings mark a significant step forward in developing a tandem catalyst system for the effective electrochemical production of ethylene., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Producing high‐value fuels and chemicals via photo/electrochemical CO2 reduction reaction (CO2RR) remains an attractive goal to mitigate the negative impact of CO2 emissions and provide a sustainable energy source. The large industrial scale is currently discriminated by the relatively low product selectivity (a high cost is expected for separating the products) and the activity. The selective CO2 reduction into higher‐order multi‐carbon products is desirable from the economic point of view. Yet, most of the reported electrocatalysts have produced C1 and C2 products; however, the production of C3 products is less common. Cu‐based catalysts are the most documented systems to produce C3 products because of the exclusive C−C coupling ability of the Cu system. However, creating multi‐carbon products on non‐Cu catalysts is unfairly discussed. Growing the research activity on non‐Cu catalysts will enrich the categories of alternative catalysts and propose more understanding of the CO2RR mechanism. This should guide the development of more creative catalysts with the optimum configuration for high activity and selectivity for high‐value C3 products. The catalysts′ development progress, including metallic Cu, biphase, or bimetallic Cu, non‐Cu‐based catalysts, has been discussed in light of the catalyst activity and selectivity. Some insights on the reaction mechanism for the desired C3 product (most commonly, n‐propanol) and other C3+ products are also discussed. [ABSTRACT FROM AUTHOR]

Electroreduction of CO2 to multi‐carbon products has attracted considerable attention as it provides an avenue to high‐density renewable energy storage. However, the selectivity and stability under high current densities are rarely reported. Herein, B‐doped Cu (B‐Cu) and B‐Cu‐Zn gas diffusion electrodes (GDE) were developed for highly selective and stable CO2 conversion to C2+ products at industrially relevant current densities. The B‐Cu GDE exhibited a high Faradaic efficiency of 79 % for C2+ products formation at a current density of −200 mA cm−2 and a potential of −0.45 V vs. RHE. The long‐term stability for C2+ formation was substantially improved by incorporating an optimal amount of Zn. Operando Raman spectra confirm the retained Cu+ species under CO2 reduction conditions and the lower overpotential for *OCO formation upon incorporation of Zn, which lead to the excellent conversion of CO2 to C2+ products on B‐Cu‐Zn GDEs. [ABSTRACT FROM AUTHOR]

[Display omitted] Recent progress and challenges of photocatalytic CO 2 conversion into value-added multi-carbon products. • Significance and fundamental principle of photocatalytic CO 2 conversion. • General view of photocatalytic CO 2 conversion to multi-carbon products. • The synthesis, properties, activities and mechanism of photocatalysts for CO 2 conversion were summarized based on different multi-carbon products. • Key strategies to improve activity and selectivity of photocatalytic CO 2 conversion. • Main challenges and prospects of photocatalytic CO 2 conversion to multi-carbon products. In recently years, photocatalytic CO 2 conversion into the value-added chemicals represents a promising approach to relieve the current energy and environmental problems, because it can be powered by renewable solar energy. This review introduces the principles and mechanisms of photocatalytic CO 2 conversion, with a particular focus on the research progress and key strategies involved in the behavioural manipulation of interfacial electron transfer and selectivit of multi-carbon products. Besides, the structure–activity relationship has also been summarized about the currently reported photocatalyst focuing on generation on multi-carbon products. Furthermore, the review also probes the current challenges and future directions, including improved CO 2 conversion efficiency and selectivity, understanded the reaction mechanism and considerated the economic and environmental factors. We sincerely hope that this review will attract more research attention towards photocatalytic CO 2 conversion for the synthesis of value-added multi-carbon products. [ABSTRACT FROM AUTHOR]

The electrochemical CO 2 reduction reaction (CO 2 RR) has been widely recognized as a promising approach to achieve the carbon cycle balance in human society. However, potent electrocatalysts are required to achieve the selective conversion of CO 2 to high value-added chemical products. Here, we reported a Ruddlesden-Popper layered perovskite catalyst, namely La 2- x Ag x CuO 4- δ , which exhibits enhanced activity and selectivity towards CO 2 RR by tuning the A-site cations with Ag doping. Combinatorial characterizations and theoretical calculation reveal the partial replacement of Ag+ on the A-site of La 2 CuO 4 can tune the electronic structure of Cu2+ ions of the B site, improving the adsorption/activation of crucial reaction intermediates. Importantly, Ag doping constructs oxygen vacancies, which shifts the reaction pathways from the two-electron transfer reduction to the multi-electron/proton transfer reduction, thereby promoting the formation of multi-carbon products. Taken together, these findings offer fresh insights for the strategic development of efficient perovskite electrocatalysts for CO 2 RR. [Display omitted] • La 2- x Ag x CuO 4- δ catalyst with abundant oxygen vacancy was prepared by Ag doping. • La 1.8 Ag 0.2 CuO 4- δ remarkably enhanced the electrochemical CO 2 reduction to C 2. • Ag atoms and oxygen vacancies on La 2- x Ag x CuO 4-δ promotes the CHO−CHO coupling. [ABSTRACT FROM AUTHOR]

The electrochemical conversion of carbon dioxide (CO 2 ) into ethanol with high added value has attracted increasing attention. Here, an efficient catalyst with abundant Cu 2 O/Ag interfaces for ethanol production under pulsed CO 2 electrolysis is reported, which is composed of Cu 2 O hollow nanospheres loaded with Ag nanoparticles (named as se-Cu 2 O/Ag). The CO 2 -to-ethanol Faradaic efficiency is prominently improved to 46.3% at a partial current density up to 417 mA cm -2 under pulsed electrolysis conditions in a neutral flow cell, notably outperforming conventional Cu catalysts during static electrolysis. In situ spectroscopy reveals the stabilized Cu + species of se-Cu 2 O/Ag during pulsed electrolysis and the enhanced adsorbed CO intermediate ( * CO)coverage on the heterostructured catalyst. Density functional theory (DFT) calculations further confirm that the Cu 2 O/Ag heterostructure stabilizes the * CO intermediate and promotes the coupling of * CO and adsorbed CH intermediate ( * CH). Meanwhile, the stable Cu + species under pulsed electrolysis favor the hydrogenation of adsorbed HCCOH intermediate ( * HCCOH) to adsorbed HCCHOH intermediate ( * HCCHOH) on the pathway to ethanol. The synergistic effect between the enhanced generation of * CO on Cu 2 O/Ag and regenerated Cu + species under pulsed electrolysis steers the reaction pathway toward ethanol. This work provides some insights into selective ethanol production from CO 2 electroreduction via combined catalyst design and non-steady state electrolysis., (© 2023 Wiley‐VCH GmbH.)

Electrochemical reduction of CO 2 to valuable multi-carbon products is an important potential solution to environmental and energy crises caused by fossil fuel burning. As an effective way to address the drawbacks of direct CO 2 reduction, the reduction of CO to multi-carbon products remains a challenge, specially lacking high-efficient, selective and low-cost metal-free catalysts. N-heterocyclic carbenes (NHCs) have been shown to be effective metal-free catalysts for converting CO 2 to CO or C 1 -products, but the facile release of CO limits the further reduction to valuable multi-carbon fuels. In this study, using density functional theory calculations, we developed heterogeneous NHCs by incorporating NHCs into the graphene lattice and found that these NHCs could stably adsorb and effectively activate CO molecules, enabling the efficient conversion of CO into CH 3 OH, C 2 H 4 and C 2 H 5 OH with low limiting potentials, i.e., –0.70, –0.45 and –0.36 V, respectively. These limiting potentials for C 2 -products are lower than those of most known metal-based or metal-free electrocatalysts. Moreover, competitive hydrogen evolution reaction can be effectively inhibited. The excellent catalytic performance is attributed to the charge transfer between NHCs and CO as well as the strong hybridization of C-2p orbitals of carbene carbon atoms in NHCs and carbon atoms in CO molecule. Our findings suggest that these heterogeneous NHCs exhibit high catalytic activity and selectivity for the conversion of CO to valuable C 2 -products. This study is the first report of NHC-based metal-free electrocatalysts for the conversion of CO to multi-carbon products, which will offer cost-effective opportunities for CO 2 reduction. [Display omitted] • This work presents a metal-free electrocatalyst with heterogeneous N-heterocyclic carbenes as the active centers. • The designed electrocatalyst exhibits high catalytic activity and selectivity for the conversion of CO to valuable C 2 -products. • This work is the first report of NHC-based metal-free electrocatalyst for the reduction of CO to multi-carbon products, opening a new and cost-effective method for CO 2 reduction. [ABSTRACT FROM AUTHOR]