Breaking the Linear Scaling Relationship by Compositional and Structural Crafting of Ternary Cu–Au/Ag Nanoframes for Electrocatalytic Ethylene Production

Fundamentals and Challenges of Ligand Modification in Heterogeneous Electrocatalysis

The development of efficient catalytic materials in the energy field could promote the structural transformation from traditional fossil fuels to sustainable energy. In heterogeneous catalytic reactions, ligand modification is an effective way to regulate both electronic and steric structures of catalytic sites, thus paving a prospective avenue to design the interfacial structures of heterogeneous catalysts for energy conversion. Although great achievements have been obtained for the study and applications of heterogeneous ligand-modified catalysts, the systematical refinements of ligand modification strategies are still lacking. Here, we reviewed the ligand modification strategy from both the mechanistic and applicable scenarios by focusing on heterogeneous electrocatalysis. We elucidated the ligand-modified catalysts in detail from the perspectives of basic concepts, preparation, regulation of physicochemical properties of catalytic sites, and applications in different electrocatalysis. Notably, we bridged the electrocatalytic performance with the electronic/steric effects induced by ligand modification to gain intrinsic structure-performance relations. We also discussed the challenges and future perspectives of ligand modification strategies in heterogeneous catalysis.

Ag-Mediated Growth of Au/Ag-Cu Ternary Heterostructures for Selective Electrochemical CO2 Reduction

Copper (Cu)-based nanocatalysts play crucial roles in the electrochemical CO2 reduction reaction (ECO2RR) for sustainable energy resources. Particularly, Cu-based nanostructures incorporating Au and Ag are promising, offering enhanced activity, selectivity, and stability. However, precise control over the structure and composition of heterostructures remains challenging, hindering the development of highly efficient catalysts. Herein, we present a silver (Ag) transition-layer-mediated approach to synthesize ternary heterostructures with two specific morphologies, namely, Au/Ag-Cu-side and Au/Ag-Cu-tip, which exhibit different Ag-Cu interface epitaxial patterns. The two heterostructures achieve high C2 product selectivity in ECO2RR. Especially, the Au/Ag-Cu-side structure achieves 50.3% C2 selectivity with 35.5% ethanol, while the tip structure shows higher ethylene selectivity. Our study reveals the impact of the Ag layer in directing deposition sites on heterostructure growth and further facilitating the design of multicomponent Cu-based catalysts with enhanced structural integrity and ECO2RR performance.

Locally Varying Surface Binding Affinity on Pd-Au Nanocrystals Enhances Electrochemical Ethanol Oxidation Activity

Noble metal nanocrystals face challenges in effectively catalyzing electrochemical ethanol oxidation reaction (EOR)-represented multistep, multielectron transfer processes due to the linear scaling relationship among binding energies of intermediates, impeding independent optimization of individual elemental steps. Herein, we develop noble metal nanocrystals with a range of local surface binding affinities in close proximity to overcome this challenge. Experimentally, this is demonstrated by applying tensile strain to a Pd surface and decorating it with discrete Au atoms, forming a diversity of binding sites with varying affinities in close proximity for guest molecules, as evidenced by CO probing and density functional theory calculations. Such a surface enables reaction intermediates to migrate between different binding sites as needed for each elemental step, thereby reducing the energy barrier for the overall EOR when compared to reactions at a single site. On these tailored surfaces, we attain specific and mass activities of 32.7 mA cm-2 and 47.8 A mgPd-1 in EOR, surpassing commercial Pd/C by 10.9 and 43.8 times, respectively, and outperforming state-of-the-art Pd-based catalysts. These results highlight the promise of this approach in improving a variety of multistep, multielectron transfer reactions, which are crucial for energy conversion applications.

Engineering highly selective CO2 electroreduction in Cu-based perovskites through A-site cation manipulation

Perovskites exhibit considerable potential as catalysts for various applications, yet their performance modulation in the carbon dioxide reduction reaction (CO2RR) remains underexplored. In this study, we report a strategy to enhance the electrocatalytic carbon dioxide (CO2) reduction activity via Ce-doped La2CuO4 (LCCO) and Sr-doped La2CuO4 (LSCO) perovskite oxides. Specifically, compared to pure phase La2CuO4 (LCO), the Faraday efficiency (FE) for CH4 of LCCO at -1.4 V vs. RHE (reversible hydrogen electrode) is improved from 38.9% to 59.4%, and the FECO2RR of LSCO increased from 68.8% to 85.4%. In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy spectra results indicate that the doping of A-site ions promotes the formation of *CHO and *HCOO, which are key intermediates in the production of CH4, compared to the pristine La2CuO4. X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and double-layer capacitance (Cdl) outcomes reveal that heteroatom-doped perovskites exhibit more oxygen vacancies and higher electrochemical active surface areas, leading to a significant improvement in the CO2RR performance of the catalysts. This study systematically investigates the effect of A-site ion doping on the catalytic activity center Cu and proposes a strategy to improve the catalytic performance of perovskite oxides.

Nanoreactor Confined and Enriched Intermediates for Electroreduction of CO2 to C2+ Products

In the process of electroreduction of carbon dioxide (eCO2RR) to multi-carbon (C2+) products, it is imperative to enhance the concentration of key intermediate species on the catalyst surface. The utilization of micro-nano reactors to achieve confinement effects has been widely observed in various catalytic reactions, yet it has seldom been employed in eCO2RR. Here, we present a novel nanoreactor composed of stacked CuS nanosheets for eCO2RR to C2+ products. In comparison to catalyst comprising of nanosheet with open space, the C-C coupling within this confined nanospace is significantly enhanced, resulting in the increase of Faraday efficiency (FE) of C2+ products to 53 %. In situ infrared (IR) spectroscopy reveals the confinement and enrichment of key intermediate by the nanoreactor. Our research findings demonstrate that a meticulously designed nanoreactor can elevate the selectivity of C2+ products, thereby aiding in the design of eCO2RR catalysts.

Sulfidation-Induced Surface Local Electronic and Atomic Structures in a Silver Catalyst Enables Silicon Photocathode for Selective and Efficient Photoelectrochemical CO2 Reduction

Converting CO2 to value-added chemicals through a photoelectrochemical (PEC) system is a creative approach toward renewable energy utilization and storage. However, the rational design of appropriate catalysts while being effectively integrated with semiconductor photoelectrodes remains a considerable challenge for achieving single-carbon products with high efficiency. Herein, we demonstrate a novel sulfidation-induced strategy for in situ grown sulfide-derived Ag nanowires on a Si photocathode (denoted as SD-Ag/Si) based on the standard crystalline Si solar cells. Such an exquisite design of the SD-Ag/Si photocathode not only provides a large electrochemically active surface area but also endows abundant active sites of Ag2S/Ag interfaces and high-index Ag facets for PEC CO production. The optimized SD-Ag/Si photocathode displays an ideal CO Faradic efficiency of 95.2% and an onset potential of +0.26 V versus the reversible hydrogen electrode, ascribed to the sulfidation-induced synergistic effect of the surface atomic arrangement and electronic structure in Ag catalysts that promote charge transfer, facilitate CO2 adsorption and activation, and suppress hydrogen evolution reaction. This sulfidation-induced strategy represents a scalable approach for designing high-performance catalysts for electrochemical and PEC devices with efficient CO2 utilization.

Selectivities of Stepped Cu-M (M = Pt, Ni, Pd, Zn, Ag, Au) Bimetallic Surface Environment for C1 and C2 Pathways

Copper (Cu) emerges as a highly efficient and cheap catalytic agent for the electrochemical reduction of carbon dioxide (CO2RR), promising a sustainable route toward carbon neutrality. Despite its utility, the Cu catalyst exhibits limitations in terms of product selectivity, highlighting the need for the development of a superior catalyst design. Herein, we present a density functional theory (DFT) investigation into the selectivities of Cu-M (M = Pt, Ni, Pd, Zn, Ag, Au) bimetallic catalysts (BMCs) for the carbon dioxide reduction reaction (CO2RR). The interaction between the metals of Cu-M makes the surface electrons reconstruct so that the d-band center shifts to the Fermi level. In terms of CO2 activation, the Cu-Ni catalyst exhibits superior performance. Additionally, the Cu-Pd catalyst favors the formation of *COH along the reaction pathway, favoring the generation of CH4. Conversely, the Cu-Ni catalyst preferentially produces *CHO, thereby favoring the production of CH3OH. For the Cu-Ag catalyst, the reaction intermediates along the C2 pathway are *CO-*CHO and *COH-*CHO. The Cu-Ni catalyst follows a reaction path that proceeds via *CO-*CO → *CO-*COH → *COH-CHO. On the other hand, the Cu-Pt catalyst exhibits a reaction sequence of *CO-*CO → *CO-*CHO → *OCH-*OCH. This study provides guiding significance for the design of Cu-based bimetallic catalysts aimed at improving the selectivities and efficiency of the CO2RR process.

Ligand-engineering Cu-based catalysts to accelerate the electrochemical reduction of CO2

Two typical Cu-based complex catalysts with piperazine (PR) and p-phenylenediamine (pPDA) ligands were designed to elucidate whether the ligands can tailor the reduction behavior of the Cu species and thus modulate their electrochemical CO2 reduction reaction (eCO2RR) activity. Specifically, Cu-PR underwent a significant in situ transformation into Cu nanoparticles enriched with a Cuδ+/Cu0 interface for high eCO2RR activity, compared to Cu-pPDA. This finding reveals the importance of ligand engineering in modulating the eCO2RR performance of Cu-based complexes.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Modulation of active center distance of hybrid perovskite for boosting photocatalytic reduction of carbon dioxide to ethylene

Solar-driven photocatalytic CO2 reduction is an energy-efficient and sustainable strategy to mitigate CO2 levels in the atmosphere. However, efficient and selective conversion of CO2 into multi-carbon products, like C2H4, remains a great challenge due to slow multi-electron-proton transfer and sluggish C-C coupling. Herein, a two-dimensional thin-layered hybrid perovskite is fabricated through filling of oxygen into iodine vacancy in pristine DMASnI3 (DMA = dimethylammonium). The rational-designed DMASnI3(O) induces shrinkage of active sites distance and facilitates dimerization of C-C coupling of intermediates. Upon simulated solar irradiation, the DMASnI3(O) photocatalyst achieves a high selectivity of 74.5%, corresponding to an impressive electron selectivity of 94.6%, for CO2 to C2H4 conversion and an effective C2H4 yield of 11.2 μmol g-1 h-1. In addition, the DMASnI3(O) inherits excellent water stability and implements long-term photocatalytic CO2 reduction to C2H4 in a water medium. This work establishes a unique paradigm to convert CO2 to C2+ hydrocarbons in a perovskite-based photocatalytic system.

Atomic Dispersed Hetero-Pairs for Enhanced Electrocatalytic CO2 Reduction

Electrochemical carbon dioxide reduction reaction (CO2RR) involves a variety of intermediates with highly correlated reaction and ad-desorption energies, hindering optimization of the catalytic activity. For example, increasing the binding of the *COOH to the active site will generally increase the *CO desorption energy. Breaking this relationship may be expected to dramatically improve the intrinsic activity of CO2RR, but remains an unsolved challenge. Herein, we addressed this conundrum by constructing a unique atomic dispersed hetero-pair consisting of Mo-Fe di-atoms anchored on N-doped carbon carrier. This system shows an unprecedented CO2RR intrinsic activity with TOF of 3336 h-1, high selectivity toward CO production, Faradaic efficiency of 95.96% at - 0.60 V and excellent stability. Theoretical calculations show that the Mo-Fe diatomic sites increased the *COOH intermediate adsorption energy by bridging adsorption of *COOH intermediates. At the same time, d-d orbital coupling in the Mo-Fe di-atom results in electron delocalization and facilitates desorption of *CO intermediates. Thus, the undesirable correlation between these steps is broken. This work provides a promising approach, specifically the use of di-atoms, for breaking unfavorable relationships based on understanding of the catalytic mechanisms at the atomic scale.

Alloy Catalysts for Electrocatalytic CO2 Reduction

CO2 conversion is an anticipated route to resolve the energy crisis and environmental pollution, in which electrocatalysis is one of the technologies closest to industrialization. Alloy catalysts are promising candidates for electrocatalysis, and the high tenability in electronic structures and surface physical and chemical properties allows alloy catalysts high catalytic activity and selectivity for electrocatalytic CO2 reduction. Herein, the recent advances in alloy catalysts for electrocatalytic CO2 reduction have been systematically summarized, with insight into the structure of the active center, catalytic performance, and mechanism, to uncover the key to their high catalytic performance. The alloy catalysts are mainly classified as binary and multi-metallic alloys (medium entropy and high entropy alloy) based on components and mixed configuration entropy, on which the relationship among the active center, catalytic performance, and mechanism has been fully discussed to inspire the rational design of alloy catalysts. Finally, the current challenges and future perspectives are presented to propose the dilemma and development direction for alloy catalysts. This review provides an overview of about the recent progress and future development of alloy catalysts to present a guideline for future research work on relevant catalysts.

Multilayer-Cavity Tandem Catalyst for Profiling Sequentially Coupling of Intermediate CO in Electrocatalytic Reduction Reaction of CO2 to Multi-Carbon Products

Electrochemical CO2  reduction reaction (CO2 RR) is an effective approach to address CO2  emission, promote recycling, and synthesize high-value multi-carbon (C2+ ) chemicals for storing renewable electricity in the long-term. The construction of multilayer-bound nanoreactors to achieve management of intermediate CO is a promising strategy for tandem to C2+ products. In this study, a series of Ag@Cu2 O nanoreactors consisting of an Ag-yolk and a multilayer confined Cu shell is designed to profile electrocatalytic CO2 RR reactions. The optimized Ag@Cu2 O-2 nanoreactor exhibits a 74% Faradaic efficiency during the C2+ pathway and remains stable for over 10 h at a bias current density of 100 mA cm-2 . Using the finite element method, this model determines that the certain volume of cavity in the Ag@Cu2 O nanoreactors facilitates on-site CO retention and that multilayers of Cu species favor CO capture. Density functional theory calculations illustrate that the biased generation of ethanol products may arise from the (100)/(111) interface of the Cu layer. In-depth explorations in multilayer-bound nanoreactors provide structural and interfacial guidance for sequential coupling of CO2 RR intermediates for efficient C2+ generation.

MXene-Regulated Metal-Oxide Interfaces with Modified Intermediate Configurations Realizing Nearly 100% CO2 Electrocatalytic Conversion

Electrocatalytic CO2 reduction via renewable electricity provides a sustainable way to produce valued chemicals, while it suffers from low activity and selectivity. Herein, we constructed a novel catalyst with unique Ti3 C2 Tx MXene-regulated Ag-ZnO interfaces, undercoordinated surface sites, as well as mesoporous nanostructures. The designed Ag-ZnO/Ti3 C2 Tx catalyst achieves an outstanding CO2 conversion performance of a nearly 100% CO Faraday efficiency with high partial current density of 22.59 mA cm-2 at -0.87 V versus reversible hydrogen electrode. The electronic donation of Ag and up-shifted d-band center relative to Fermi level within MXene-regulated Ag-ZnO interfaces contributes the high selectivity of CO. The CO2 conversion is highly correlated with the dominated linear-bonded CO intermediate confirmed by in situ infrared spectroscopy. This work enlightens the rational design of unique metal-oxide interfaces with the regulation of MXene for high-performance electrocatalysis beyond CO2 reduction.

Electrochemical Carbon Dioxide Reduction to Ethylene: From Mechanistic Understanding to Catalyst Surface Engineering

Electrochemical carbon dioxide reduction reaction (CO2RR) provides a promising way to convert CO2 to chemicals. The multicarbon (C2+) products, especially ethylene, are of great interest due to their versatile industrial applications. However, selectively reducing CO2 to ethylene is still challenging as the additional energy required for the C-C coupling step results in large overpotential and many competing products. Nonetheless, mechanistic understanding of the key steps and preferred reaction pathways/conditions, as well as rational design of novel catalysts for ethylene production have been regarded as promising approaches to achieving the highly efficient and selective CO2RR. In this review, we first illustrate the key steps for CO2RR to ethylene (e.g., CO2 adsorption/activation, formation of *CO intermediate, C-C coupling step), offering mechanistic understanding of CO2RR conversion to ethylene. Then the alternative reaction pathways and conditions for the formation of ethylene and competitive products (C1 and other C2+ products) are investigated, guiding the further design and development of preferred conditions for ethylene generation. Engineering strategies of Cu-based catalysts for CO2RR-ethylene are further summarized, and the correlations of reaction mechanism/pathways, engineering strategies and selectivity are elaborated. Finally, major challenges and perspectives in the research area of CO2RR are proposed for future development and practical applications.

Achieving Tunable Selectivity and Activity of CO2 Electroreduction to CO via Bimetallic Silver-Copper Electronic Engineering

Limited comprehension of the reaction mechanism has hindered the development of catalysts for CO₂ reduction reactions (CO₂ RR). Here, the bimetallic AgCu nanocatalyst platform is employed to understand the effect of the electronic structure of catalysts on the selectivity and activity for CO₂ electroreduction to CO. The atomic arrangement and electronic state structure vary with the atomic ratio of Ag and Cu, enabling tunable d-band centers to optimize the binding strength of key intermediates. Density functional theory calculations confirm that the variation of Cu content greatly affects the free energy of *COOH, *CO (intermediate of CO), and *H (intermediates of H₂ ), which leads to the change of the rate-determining step. Specifically, Ag₉₆ Cu₄ reduces the free energy of the formation of *COOH while maintaining a relatively high theoretical overpotential for hydrogen evolution reaction(HER), thus achieving the best CO selectivity. While Ag₇₀ Cu₃₀ shows relatively low formation energy of both *COOH and *H, the compromised thermodynamic barrier and product selectivity allows Ag₇₀ Cu₃₀ the best CO partial current density. This study realizes the regulation of the selectivity and activity of electrocatalytic CO₂ to CO, which provides a promising way to improve the intrinsic performance of CO₂ RR on bimetallic AgCu.

Scalable synthesis of coordinatively unsaturated metal-nitrogen sites for large-scale CO2 electrolysis

Practical electrochemical CO₂-to-CO conversion requires a non-precious catalyst to react at high selectivity and high rate. Atomically dispersed, coordinatively unsaturated metal-nitrogen sites have shown great performance in CO₂ electroreduction; however, their controllable and large-scale fabrication still remains a challenge. Herein, we report a general method to fabricate coordinatively unsaturated metal-nitrogen sites doped within carbon nanotubes, among which cobalt single-atom catalysts can mediate efficient CO₂-to-CO formation in a membrane flow configuration, achieving a current density of 200 mA cm^-2 with CO selectivity of 95.4% and high full-cell energy efficiency of 54.1%, outperforming most of CO₂-to-CO conversion electrolyzers. By expanding the cell area to 100 cm², this catalyst sustains a high-current electrolysis at 10 A with 86.8% CO selectivity and the single-pass conversion can reach 40.4% at a high CO₂ flow rate of 150 sccm. This fabrication method can be scaled up with negligible decay in CO₂-to-CO activity. In situ spectroscopy and theoretical results reveal the crucial role of coordinatively unsaturated metal-nitrogen sites, which facilitate CO₂ adsorption and key *COOH intermediate formation.

Single-Site Metal-Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2 H4

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO₂ reduction reaction (CO₂ RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal-organic framework (MOF), named as Cu-MOF-CF, to realize improved electrochemical CO₂ RR performance, is reported. The Cu-MOF-CF shows suppression of CH₄ , great increase in C₂ H₄ selectivity (48.6%), and partial current density of C₂ H₄ at -1.11 V versus reversible hydrogen electrode. The outstanding performance of Cu-MOF-CF for CO₂ RR results from the improved microenvironment of the Cu active sites that inhibits CH₄ production, more CO intermediate produced by single-site Cu-MOF in situ for CF, and the enlarged active surface area by porous Cu-MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO₂ RR.

Recent Advances of Core-Shell Cu-Based Catalysts for the Reduction of CO2 to C2+ Products

Copper is a key metal for carbon dioxide (CO₂ ) reduction reaction, which can reduce CO₂ to value-added products. The core-shell structure can effectively promote the C-C coupling process due to its strong synergistic effect originated from its unique electronic structure and interface environment. Therefore, the combination of copper and core-shell structure to design an efficient Cu-based core-shell structure catalyst is of great significance for electrocatalytic CO₂ reduction (CO₂ RR). In this review, we first briefly summarize the basic principle of CO₂ RR. In addition, we outline the advantages of core-shell structure for catalysis. Then, we review the recent research progresses of Cu-based core-shell structures for the selective reduction of multi-carbon (C₂₊ ) products. In the end, the challenges of using core-shell catalyst for CO₂ RR are described, and the future development of this field is prospected.

Highly Selective CO2 Electroreduction to C2+ Products over Cu2O-Decorated 2D Metal-Organic Frameworks with Rich Heterogeneous Interfaces

The electroreduction of carbon dioxide into high-value-added products is an effective approach to alleviating the energy crisis and pollution issues. However, there are still significant challenges for multicarbon (C₂₊) product production due to the lack of efficient catalysts with high selectivity. Herein, a Cu-rich electrocatalyst, where Cu₂O nanoparticles are decorated on two-dimensional (2D) Cu-BDC metal-organic frameworks (MOFs) with abundant heterogeneous interfaces, is synthesized for highly selective CO₂ electroreduction into C₂₊ products. A high C₂₊ Faradaic efficiency of 72.1% in an H-type cell and 58.2% in a flow cell are obtained, respectively. The heterogeneous interfaces of Cu₂O/Cu-BDC can optimize the adsorption energy of reaction intermediates during CO₂ electroreduction. An in situ infrared spectroscopy study indicates that the constructed interfaces can maintain the particular distribution of Cu valence states, where the C-C coupling is promoted to efficiently produce C₂₊ products owing to the stabilization of *CHO and *COH intermediates.

Back-illuminated photoelectrochemical flow cell for efficient CO2 reduction

Photoelectrochemical CO2 reduction reaction flow cells are promising devices to meet the requirements to produce solar fuels at the industrial scale. Photoelectrodes with wide bandgaps do not allow for efficient CO2 reduction at high current densities, while the integration of opaque photoelectrodes with narrow bandgaps in flow cell configurations still remains a challenge. This paper describes the design and fabrication of a back-illuminated Si photoanode promoted PEC flow cell for CO2 reduction reaction. The illumination area and catalytic sites of the Si photoelectrode are decoupled, owing to the effective passivation of defect states that allows for the long minority carrier diffusion length, that surpasses the thickness of the Si substrate. Hence, a solar-to-fuel conversion efficiency of CO of 2.42% and a Faradaic efficiency of 90% using Ag catalysts are achieved. For CO2 to C2+ products, the Faradaic efficiency of 53% and solar-to-fuel of 0.29% are achieved using Cu catalyst in flow cell.

Heteroatoms Induce Localization of the Electric Field and Promote a Wide Potential-Window Selectivity Towards CO in the CO2 Electroreduction

Carbon dioxide electroreduction (CO2 RR) is a sustainable way of producing carbon-neutral fuels. Product selectivity in CO2 RR is regulated by the adsorption energy of reaction-intermediates. Here, we employ differential phase contrast-scanning transmission electron microscopy (DPC-STEM) to demonstrate that Sn heteroatoms on a Ag catalyst generate very strong and atomically localized electric fields. In situ attenuated total reflection infrared spectroscopy (ATR-IR) results verified that the localized electric field enhances the adsorption of *COOH, thus favoring the production of CO during CO2 RR. The Ag/Sn catalyst exhibits an approximately 100 % CO selectivity at a very wide range of potentials (from -0.5 to -1.1 V, versus reversible hydrogen electrode), and with a remarkably high energy efficiency (EE) of 76.1 %.

Bulk-immiscible CuAg alloy nanorods prepared by phase transition from oxides for electrochemical CO2 reduction

Combining Cu and Ag in an alloy state holds promise to serve as a tandem catalyst for electrocatalytic CO₂ reduction, but is restricted by immiscibility in the bulk. Here, a far-from-equilibrium method is developed to synthesize CuAg alloy by electroreduction of Cu₂Ag₂O₃ under a large cathodic overpotential. The alloy state of CuAg is conducive to the formation of C₂₊ molecules. A high formation rate of C₂H₄ of 159.8 μmol cm^-2 h^-1 is reached on the CuAg alloy nanorods, 2.3 times higher than that on pure Cu.

Electrocatalytic CO2 reduction to alcohols by modulating the molecular geometry and Cu coordination in bicentric copper complexes

Electrocatalytic reduction of CO₂ into alcohols of high economic value offers a promising route to realize resourceful CO₂ utilization. In this study, we choose three model bicentric copper complexes based on the expanded and fluorinated porphyrin structure, but different spatial and coordination geometry, to unravel their structure-property-performance correlation in catalyzing electrochemical CO₂ reduction reactions. We show that the complexes with higher intramolecular tension and coordination asymmetry manifests a lower electrochemical stability and thus more active Cu centers, which can be reduced during electrolysis to form Cu clusters accompanied by partially-reduced or fragmented ligands. We demonstrate the hybrid structure of Cu cluster and partially reduced O-containing hexaphyrin ligand is highly potent in converting CO₂ into alcohols, up to 32.5% ethanol and 18.3% n-propanol in Faradaic efficiencies that have been rarely reported. More importantly, we uncover an interplay between the inorganic and organic phases to synergistically produce alcohols, of which the intermediates are stabilized by a confined space to afford extra O-Cu bonding. This study underlines the exploitation of structure-dependent electrochemical property to steer the CO₂ reduction pathway, as well as a potential generic tactic to target alcohol synthesis by constructing organic/inorganic Cu hybrids.

Electrocatalytic reduction of CO2 into multi-carbon alcohols of high economic merit offers an effective means to close the carbon cycle. Here the authors show the synergy between inorganic and organic phases derived from rationally designed molecular precursors to produce alcohols in high efficiency.

Preparation of trimetallic electrocatalysts by one-step co-electrodeposition and efficient CO2 reduction to ethylene

Use of multi-metallic catalysts to enhance reactions is an interesting research area, which has attracted much attention. In this work, we carried out the first work to prepare trimetallic electrocatalysts by a one-step co-electrodeposition process. A series of Cu-X-Y (X and Y denote different metals) catalysts were fabricated using this method. It was found that Cu10La1Cs1 (the content ratio of Cu2+, La3+, and Cs+ in the electrolyte is 10 : 1 : 1 in the deposition process), which had an elemental composition of Cu10La0.16Cs0.14 in the catalyst, formed a composite structure on three dimensional (3D) carbon paper (CP), which showed outstanding performance for CO2 electroreduction reaction (CO2RR) to produce ethylene (C2H4). The faradaic efficiency (FE) of C2H4 could reach 56.9% with a current density of 37.4 mA cm-2 in an H-type cell, and the partial current density of C2H4 was among the highest ones up to date, including those over the catalysts consisting of Cu and noble metals. Moreover, the FE of C2+ products (C2H4, ethanol, and propanol) over the Cu10La1Cs1 catalyst in a flow cell reached 70.5% with a high current density of 486 mA cm-2. Experimental and theoretical studies suggested that the doping of La and Cs into Cu could efficiently enhance the reaction efficiency via a combination of different effects, such as defects, change of electronic structure, and enhanced charge transfer rate. This work provides a simple method to prepare multi-metallic catalysts and demonstrates a successful example for highly efficient CO2RR using non-noble metals.

Understanding the role of Cu+/Cu0 sites at Cu2O based catalysts in ethanol production from CO2 electroreduction -A DFT study

Cu₂O based electrocatalysts generally exhibit better selectivity for C₂ products (ethylene or ethanol) in electrochemical carbon dioxide reduction. The surface characteristic of the mixed Cu⁺ and Cu⁰ chemical state is believed to play an essential role that is still unclear. In the present study, density functional theory (DFT) calculations have been performed to understand the role of copper chemical states in selective ethanol formation using a partially reduced Cu₂O surface model consisting of adjacent Cu⁺/Cu⁰ sites. We mapped out the free energy diagram of the reaction pathway from CO intermediate to ethanol and discussed the relation between the formation of critical reduction intermediates and the configuration of Cu⁺/Cu⁰ sites. The results showed that Cu⁺ sites facilitate the adsorption and stabilization of *CO, as well as its further hydrogenation to *CHO. More importantly, as compared to the high reaction energy (1.23 eV) of the dimerization of two *CO on Cu⁺/Cu⁰ sites, the preferable formation of *CHO on the Cu⁺ site makes the C-C coupling reaction with *CO on the Cu⁰ site happen under a relatively lower energy barrier of 0.58 eV. Furthermore, the post C-C coupling steps leading to the formation of the key intermediate *OCHCH₂ to C₂ compound are all thermodynamically favoured. Noteworthily, it is found that *OCHCH₂ inclines to the ethanol formation because the coordinatively unsaturated Cu⁺ site could maintain the C-O bond of *OCHCH₂, and the weak binding between *O and Cu⁺/Cu⁰ sites helps inhibit the pathway toward ethylene. These findings may provide guidelines for the design of CO and CO₂ reduction active sites with enhanced ethanol selectivity.

Atomically Dispersed NiN3 Sites on Highly Defective Micro-Mesoporous Carbon for Superior CO2 Electroreduction

Direct electrochemical conversion of CO₂ to CO product powered by renewable electricity is widely advocated as an emerging strategy for alleviating CO₂ emissions while addressing global energy issues. However, the development of low-cost and efficient electrocatalysts with high Faradaic efficiency for CO production (FE_CO ) and high current density remains a grand challenge. Herein, a robust single nickel atomic site electrocatalyst, which features isolated and dense single atomic NiN₃ sites anchored on highly defective hierarchically micro-mesoporous carbon (Ni-SAs/HMMNC-800), to enable enhanced charge transport and more exposed active sites for catalyzing electrochemical CO₂ -to-CO conversion, is reported. The Ni-SAs/HMMNC-800 catalyst achieves excellent activity and selectivity with high FE_CO values of >90% throughout a wide potential range (the FE_CO reaches 99.5% at -0.7 V vs reversible hydrogen electrode) and a CO partial current density as high as 13.0 mA cm^-2 at -0.7 V versus reversible hydrogen electrode, as well as a far outstanding durability during long-term continuous operation, indicating a superior CO₂ electroreduction performance than that of other reference samples and most of previously reported carbon-based single atom electrocatalysts. Experimental and density functional theory calculations reveal that atomic NiN₃ coordination sites coupled adjacent defects are favorable to significantly enhancing the formation of COOH* reaction intermediates while suppressing the competing hydrogen evolution reaction, thereby enhancing the electrocatalytic activity for CO₂ -to-CO reduction. Notably, this work provides a valuable new prospect for designing and synthesizing efficient and cost-effective single atom CO₂ electroreduction catalysts for practical applications.

Confined Growth of Silver-Copper Janus Nanostructures with {100} Facets for Highly Selective Tandem Electrocatalytic Carbon Dioxide Reduction

Electrocatalytic carbon dioxide reduction reaction (CO₂ RR) holds significant potential to promote carbon neutrality. However, the selectivity toward multicarbon products in CO₂ RR is still too low to meet practical applications. Here the authors report the delicate synthesis of three kinds of Ag-Cu Janus nanostructures with {100} facets (JNS-100) for highly selective tandem electrocatalytic reduction of CO₂ to multicarbon products. By controlling the surfactant and reduction kinetics of Cu precursor, the confined growth of Cu with {100} facets on one of the six equal faces of Ag nanocubes is realized. Compared with Cu nanocubes, Ag₆₅ -Cu₃₅ JNS-100 demonstrates much superior selectivity for both ethylene and multicarbon products in CO₂ RR at less negative potentials. Density functional theory calculations reveal that the compensating electronic structure and carbon monoxide spillover in Ag₆₅ -Cu₃₅ JNS-100 contribute to the enhanced CO₂ RR performance. This study provides an effective strategy to design advanced tandem catalysts toward the extensive application of CO₂ RR.

Anchoring Ionic Liquid in Copper Electrocatalyst for Improving CO2 Conversion to Ethylene

Electrochemical conversion of CO₂ to valuable fuels is appealing for CO₂ fixation and energy storage. The Cu-based catalysts feature unique superiorities, but achieving high ethylene selectivity is still restricted. In this study, we propose the anchoring of an ionic liquid (IL) on a Cu electrocatalyst for improving the electrochemical CO₂ reduction to ethylene. In a water-based electrolyte and a commonly used H-type cell, a high ethylene Faradaic efficiency of 77.3 % was achieved at -1.49 V (vs. RHE). Experimental and theoretical studies reveal that an IL can modify the electronic structure of a Cu catalyst through its interaction with Cu, making it more conducive to *CO dimerization for ethylene formation.

Rational-Designed Principles for Electrochemical and Photoelectrochemical Upgrading of CO2 to Value-Added Chemicals

The chemical transformation of carbon dioxide (CO2 ) has been considered as a promising strategy to utilize and further upgrade it to value-added chemicals, aiming at alleviating global warming. In this regard, sustainable driving forces (i.e., electricity and sunlight) have been introduced to convert CO2 into various chemical feedstocks. Electrocatalytic CO2 reduction reaction (CO2 RR) can generate carbonaceous molecules (e.g., formate, CO, hydrocarbons, and alcohols) via multiple-electron transfer. With the assistance of extra light energy, photoelectrocatalysis effectively improve the kinetics of CO2 conversion, which not only decreases the overpotentials for CO2 RR but also enhances the lifespan of photo-induced carriers for the consecutive catalytic process. Recently, rational-designed catalysts and advanced characterization techniques have emerged in these fields, which make CO2 -to-chemicals conversion in a clean and highly-efficient manner. Herein, this review timely and thoroughly discusses the recent advancements in the practical conversion of CO2 through electro- and photoelectrocatalytic technologies in the past 5 years. Furthermore, the recent studies of operando analysis and theoretical calculations are highlighted to gain systematic insights into CO2 RR. Finally, the challenges and perspectives in the fields of CO2 (photo)electrocatalysis are outlined for their further development.

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.

Predesign of Catalytically Active Sites via Stable Coordination Cluster Model System for Electroreduction of CO2 to Ethylene

Purposefully designing the well-defined catalysts for the selective electroreduction of CO₂ to C₂ H₄ is an extremely important but challenging work. In this work, three crystalline trinuclear copper clusters (Cu₃ -X, X=Cl^- , Br^- , NO₃ ^- ) have been designed, containing three active Cu sites with the identical coordination environment and appropriate spatial distance, delivering high selectivity for the electrocatalytic reduction of CO₂ to C₂ H₄ . The highest faradaic efficiency of Cu₃ -X for CO₂ -to-C₂ H₄ conversion can be adjusted from 31.90 % to 55.01 % by simply replacing the counter anions (NO₃ ^- , Cl^- , Br^- ). The DFT calculation results verify that Cu₃ -X can facilitate the C-C coupling of identical *CHO intermediates, subsequently forming molecular symmetrical C₂ H₄ product. This work provides an important molecular model system and a new design perspective for electroreduction of CO₂ to C₂ products with symmetrical molecular structure.

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.

Single-Atom Electrocatalysts for Multi-Electron Reduction of CO2

The multi-electron reduction of CO₂ to hydrocarbons or alcohols is highly attractive in a sustainable energy economy, and the rational design of electrocatalysts is vital to achieve these reactions efficiently. Single-atom electrocatalysts are promising candidates due to their well-defined coordination configurations and unique electronic structures, which are critical for delivering high activity and selectivity and may accelerate the explorations of the activity origin at atomic level as well. Although much effort has been devoted to multi-electron reduction of CO₂ on single-atom electrocatalysts, there are still no reviews focusing on this emerging field and constructive perspectives are also urgent to be addressed. Herein recent advances in how to design efficient single-atom electrocatalysts for multi-electron reduction of CO₂ , with emphasis on strategies in regulating the interactions between active sites and key reaction intermediates, are summarized. Such interactions are crucial in designing active sites for optimizing the multi-electron reduction steps and maximizing the catalytic performance. Different design strategies including regulation of metal centers, single-atom alloys, non-metal single-atom catalysts, and tandem catalysts, are discussed accordingly. Finally, current challenges and future opportunities for deep electroreduction of CO₂ are proposed.

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.

Revisiting the Grain and Valence Effect of Oxide-Derived Copper on Electrocatalytic CO2 Reduction Using Single Crystal Cu(111) Foils

Oxide-derived Cu (OD-Cu) has been viewed as a highly active form for catalyzing the multielectron transfer of electrochemical CO₂ reduction, but the underlying catalytic mechanism is still controversial. In the current study, the crystalline and valency factors that influence the CO₂R activities of OD-Cu are revisited by employing single crystal Cu(111) foils that exclude convolutions from initial morphological and crystallographic heterogeneity. We observe that the overall CO₂R performance, especially the C₂H₄ selectivity, correlates well with the initial oxidation level of the Cu(111) foil, of which the surface oxide layer is reduced into small fragments comprising rich grain boundaries and diversely orientated facets. Nonetheless, we find that the polycrystallinity and grain boundaries of OD-Cu, in this circumstance, are not the major causes of the observed activity enhancement. Instead, a transition state between the initial oxide and the finally reduced copper phases, as well as its longevity, dictates the catalytic property of OD-Cu in electrochemical CO₂ reduction. Consequently, this work furnishes further evidence and in-depth understanding to help clarify the catalytic mechanism of OD-Cu in CO₂R.