Silver/Copper Interface for Relay Electroreduction of Carbon Dioxide to Ethylene

Tuning the CO2 Reduction Selectivity of an Immobilized Molecular Ag Complex beyond CO

The electrochemical reduction of carbon dioxide (CO2) to produce fuels and chemicals has garnered significant attention. However, achieving control over the selectivity of the resulting products remains a challenging task, particularly within molecular systems. In this study, we employed a molecular silver complex immobilized on graphitized mesoporous carbon (GMC) as a catalyst for converting CO2 into CO, achieving an impressive selectivity of over 90% at -1.05 V vs RHE. Notably, the newly formed silver nanoparticles emerged as the active sites responsible for this high CO selectivity rather than the molecular system. Intriguingly, the introduction of copper ions into the restructured Ag-nanoparticle-decorated carbon altered the product selectivity. At -1.1 V vs RHE in 0.1 M KCl, we achieved a high C2 selectivity of 75%. Furthermore, not only the Ag-Cu bimetallic nanoparticle but also the small-sized Ag-Cu nanocluster decorated over GMC was proposed as active sites during catalytic reactions. Our straightforward approach offers valuable insights for fine-tuning the product selectivity of immobilized molecular systems, extending beyond C1 products.

Pulsed Electrolysis Promotes CO2 Reduction to Ethanol on Heterostructured Cu2O/Ag Catalysts

The electrochemical conversion of carbon dioxide (CO2) into ethanol with high added value has attracted increasing attention. Here, an efficient catalyst with abundant Cu2O/Ag interfaces for ethanol production under pulsed CO2 electrolysis is reported, which is composed of Cu2O hollow nanospheres loaded with Ag nanoparticles (named as se-Cu2O/Ag). The CO2-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-Cu2O/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 Cu2O/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 Cu2O/Ag and regenerated Cu+ species under pulsed electrolysis steers the reaction pathway toward ethanol. This work provides some insights into selective ethanol production from CO2 electroreduction via combined catalyst design and non-steady state electrolysis.

Unraveling the synergistic effects of Cu-Ag tandem catalysts during electrochemical CO2 reduction using nanofocused X-ray probes

Controlling the selectivity of the electrocatalytic reduction of carbon dioxide into value-added chemicals continues to be a major challenge. Bulk and surface lattice strain in nanostructured electrocatalysts affect catalytic activity and selectivity. Here, we unravel the complex dynamics of synergistic lattice strain and stability effects of Cu-Ag tandem catalysts through a previously unexplored combination of in situ nanofocused X-ray absorption spectroscopy and Bragg coherent diffraction imaging. Three-dimensional strain maps reveal the lattice dynamics inside individual nanoparticles as a function of applied potential and product yields. Dynamic relations between strain, redox state, catalytic activity and selectivity are derived. Moderate Ag contents effectively reduce the competing evolution of H2 and, concomitantly, lead to an enhanced corrosion stability. Findings from this study evidence the power of advanced nanofocused spectroscopy techniques to provide new insights into the chemistry and structure of nanostructured catalysts.

Elaborate tree-like Cu-Ag clusters from green electrodeposition for efficiently electrocatalyzing CO2 conversion into syngas

The electrocatalytic carbon dioxide reduction (CO2RR) is one of the emerging technologies that can effectively transform carbon dioxide (CO2) into valuable products. Electrocatalysts deriving from green synthesis methods will significantly help to establish a new green carbon cycle. Herein, a green electrodeposition method without additional reducing agents was used to synthesize Cu-Ag bimetallic catalysts, and it is shown that the combination of Cu and Ag obviously affects the morphology of the Cu-Ag catalysts, resulting in the formation of elaborate tree-like Cu-Ag clusters. An as-deposited Cu-Ag/carbon fiber (Cu-Ag/CF) catalyst exhibits high activity, selectivity and stability toward the CO2RR; in particular, the elaborate dendritic Cu-Ag/CF can efficiently reduce CO2 to syngas with high selectivity (Faradaic efficiency (FE) > 95%) at a low onset potential (-0.5 V). This work provides a rational strategy to overcome the significantly different reaction capacities during the reduction of Ag+ and Cu2+, leading to the formation of a controlled morphology of Cu-Ag, which is favourable for the design and development of highly efficient Cu or Ag catalysts via green methods for electrocatalyzing the CO2RR.

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.

Research Progress of Copper-Based Bimetallic Electrocatalytic Reduction of CO2

Fossil fuels are still the main source of energy in today’s society, so emissions of CO2 are inevitable, but when the CO2 level in the atmosphere is too high, many environmental problems will arise, such as the greenhouse effect, among others. Electrocatalytic reduction of CO2 is one of the most important methods that one can use to reduce the amount of CO2 in the atmosphere. This paper reviews bimetallic catalysts prepared on the basis of copper materials, such as Ag, Au, Zn and Ni. The effects of different ratios of metal atoms in the bimetallic catalysts on the selectivity of CO2RR were investigated and the effects of bimetallic catalysts on the CO2RR of different ligands were also analysed. Finally, this paper points out that the real reaction of CO2RR still needs to be studied and analysed, and the effect of the specific reaction environment on selectivity has not been thoroughly studied. This article also describes some of the problems encountered so far.

Design strategy of a Cu-based catalyst for optimizing the performance in the electrochemical CO2 reduction reaction to multicarbon alcohols

The electrochemical CO₂ reduction reaction (ECRR) is a promising method to reduce excessive CO₂ emissions and achieve a sustainable carbon cycle. Due to the high reaction kinetics and efficiency, copper-based catalysts have shown great application potential for preparing multicarbon (C₂₊) products. C₂₊ alcohols have high economic value and use-value, playing an essential role in modern industry. Therefore, we summarize the latest research progress of the ECRR to synthesize C₂₊ alcohols on Cu-based catalysts and discuss the state-of-the-art catalyst design strategies to improve CO₂ reduction performance. Moreover, we analyzed in detail the specific reaction pathways for the conversion of CO₂ to C₂₊ alcohols based on DFT calculations. Finally, we propose the problems and possible solutions for synthesizing C₂₊ alcohols with copper-based catalysts. We hope that this review can provide ideas for devising ECRR catalysts for C₂₊ alcohols.

Photocatalytic CO2-to-Ethylene Conversion over Bi2S3/CdS Heterostructures Constructed via Facile Cation Exchange

Solar-driven CO2 conversion to multicarbon (C2+) products has emerged as a key challenge, yet this calls for a systematic investigation on the overall reaction process and mechanism at an atomic level based on the rational design of highly selective photocatalysts. Herein, we report the synthesis of compact Bi2S3/CdS heterostructures via facile cation exchange, by which a unique pathway of CO2-to-C2H4 photoconversion is achieved. Specifically, the BCS-30 shows an optimal C2H4 production rate of 3.49 μmol h-1 g-1 based on the regulation of band structures and energy levels of photocatalysts by controlled growth of Bi2S3 at CdS surface. Both experimental and theoretical results (DFT calculations) identify Bi atoms as new catalytic sites for the adsorption of CO* and formation of *CO-*CO dimers that further hydrogenate to produce ethylene. Overall, this work demonstrates vast potentials of delicately designed heterostructures for CO2 conversion towards C2+ products under mild photocatalytic conditions.

Current state of copper-based bimetallic materials for electrochemical CO2 reduction: a review

The increasing CO2 concentration in the atmosphere has caused profound environmental issues such as global warming. The use of CO2 as a feedstock to replace traditional fossil sources holds great promise to reduce CO2 emissions. The electrochemical conversion of CO2 has attracted much attention because it can be powered by renewable sources such as solar energy. In this review article, we provide insight into the important parameters when studying CO2RR and give a comprehensive review on the description of synthesis methods with electrocatalytic CO2 reduction over bimetallic copper-based materials. Due to the important bibliographic data on Cu bimetallic materials, we have limited this review to Sn, In, Pd, Zn and Ag. At the end of this review, challenges and perspectives for further upgrading have been included to briefly highlight the important future considerations of this rapidly growing technology.

CO2 Electrolysis via Surface-Engineering Electrografted Pyridines on Silver Catalysts

The electrochemical reduction of carbon dioxide (CO₂) to value-added materials has received considerable attention. Both bulk transition-metal catalysts and molecular catalysts affixed to conductive noncatalytic solid supports represent a promising approach toward the electroreduction of CO₂. Here, we report a combined silver (Ag) and pyridine catalyst through a one-pot and irreversible electrografting process, which demonstrates the enhanced CO₂ conversion versus individual counterparts. We find that by tailoring the pyridine carbon chain length, a 200 mV shift in the onset potential is obtainable compared to the bare silver electrode. A 10-fold activity enhancement at −0.7 V vs reversible hydrogen electrode (RHE) is then observed with demonstratable higher partial current densities for CO, indicating that a cocatalytic effect is attainable through the integration of the two different catalytic structures. We extended the performance to a flow cell operating at 150 mA/cm², demonstrating the approach’s potential for substantial adaptation with various transition metals as supports and electrografted molecular cocatalysts.

Recent Advances in Interface Engineering for Electrocatalytic CO2 Reduction Reaction

Electrocatalytic CO₂ reduction reaction (CO₂RR) can store and transform the intermittent renewable energy in the form of chemical energy for industrial production of chemicals and fuels, which can dramatically reduce CO₂ emission and contribute to carbon-neutral cycle. Efficient electrocatalytic reduction of chemically inert CO₂ is challenging from thermodynamic and kinetic points of view. Therefore, low-cost, highly efficient, and readily available electrocatalysts have been the focus for promoting the conversion of CO₂. Very recently, interface engineering has been considered as a highly effective strategy to modulate the electrocatalytic performance through electronic and/or structural modulation, regulations of electron/proton/mass/intermediates, and the control of local reactant concentration, thereby achieving desirable reaction pathway, inhibiting competing hydrogen generation, breaking binding-energy scaling relations of intermediates, and promoting CO₂ mass transfer. In this review, we aim to provide a comprehensive overview of current developments in interface engineering for CO₂RR from both a theoretical and experimental standpoint, involving interfaces between metal and metal, metal and metal oxide, metal and nonmetal, metal oxide and metal oxide, organic molecules and inorganic materials, electrode and electrolyte, molecular catalysts and electrode, etc. Finally, the opportunities and challenges of interface engineering for CO₂RR are proposed.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Ultrasound-boosted selectivity of CO in CO2 electrochemical reduction

Among the possible products of CO₂ electrochemical reduction, CO plays a unique and vital role, which can be an ideal feedstock for further reduction to C₂₊ products, and also the important component of syngas that can be used as feedstock for value-added chemicals and fuels. However, it is still a challenge to tune the CO selectivity on Cu electrode. Here we newly construct an ultrasound-assisted electrochemical method for CO₂ reduction, which can tune the selectivity of CO₂ to CO from less than 10% to >80% at -1.18 V versus (vs.) reversible hydrogen electrode (RHE). The partial current density of CO production is significantly improved by 15 times. By in-situ Raman study, the dominating factor for the improved CO production is attributed to the accelerated desorption of *CO intermediate. This work provides a facile method to tune the product selectivity in CO₂ electrochemical reduction.

Engineering Bismuth-Tin Interface in Bimetallic Aerogel with a 3D Porous Structure for Highly Selective Electrocatalytic CO2 Reduction to HCOOH

Electrochemical reduction of CO₂ (CO₂ RR) into valuable hydrocarbons is appealing in alleviating the excessive CO₂ level. We present the very first utilization of metallic bismuth-tin (Bi-Sn) aerogel for CO₂ RR with selective HCOOH production. A non-precious bimetallic aerogel of Bi-Sn is readily prepared at ambient temperature, which exhibits 3D morphology with interconnected channels, abundant interfaces and a hydrophilic surface. Superior to Bi and Sn, the Bi-Sn aerogel exposes more active sites and it has favorable mass transfer properties, which endow it with a high FE_HCOOH of 93.9 %. Moreover, the Bi-Sn aerogel achieves a FE_HCOOH of ca. 90 % that was maintained for 10 h in a flow battery. In situ ATR-FTIR measurements confirmed that the formation of *HCOO is the rate-determining step toward formic acid generation. DFT demonstrated the coexistence of Bi and Sn optimized the energy barrier for the production of HCOOH, thereby improving the catalytic activity.

Copper decorated with nanoporous gold by galvanic displacement acts as an efficient electrocatalyst for the electrochemical reduction of CO2

The reduction of carbon dioxide (CO2) is recognized as a key component in the synthesis of renewable carbon-containing fuels. Herein, we report on nanoporous gold (NPAu) decorated with copper atoms for the efficient electrochemical reduction of CO2. A facile and green galvanic displacement technique was developed to incorporate Cu onto the surface of the nanoporous gold-zinc (NPAuZn) electrode. The effect of zinc on the morphology and electrochemical performance of the formed NPAuCu electrodes for CO2 reduction was systematically investigated. The NPAuCu electrode exhibited 16.9 and 2.86 times higher current density than those of polycrystalline gold and NPAuZn at -0.60 V (vs. RHE) in a 0.1 M CO2-saturated NaHCO3 solution, respectively. A far higher faradaic efficiency was achieved at the NPAuCu electrode for the electrochemical reduction of CO2 to CO, CH4 and HCOOH. The facile synthesis of the NPAuCu electrode demonstrated in the present study can be employed as a promising strategy in the development of high-performance electrocatalysts for energy and environmental applications.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Copper-alloy catalysts: structural characterization and catalytic synergies

Recent progress in the development of copper-alloy catalysts is highlighted, focusing on the structural and mechanistic characterizations of the catalysts in different catalytic reactions, and challenges and opportunities in future research.

CuAg nanoparticle/carbon aerogel for electrochemical CO2 reduction

A small sized CuAg heterostructure anchored by a silk fibroin-derived carbon aerogel exhibits electrocatalytic CO2-to-CO conversion.

Tuning the Product Selectivity of the Cu Hollow Fiber Gas Diffusion Electrode for Efficient CO2 Reduction to Formate by Controlled Surface Sn Electrodeposition

The efficient CO₂ electrochemical reduction reaction (CO₂RR) relies not only on the development of selective/active catalysts but also on the advanced electrode configuration to solve the critical issue of poor CO₂ mass transport and derived sluggish cathodic reaction kinetics. In this work, to achieve a favorable reaction rate and product selectivity, we designed and synthesized an asymmetric porous Cu hollow fiber gas diffusion electrode (HFGDE) with controlled Sn surface electrodeposition. The HFGDE derived from the optimal Sn electrodeposition condition exhibited a formate Faradaic efficiency (FE) of 78% and a current density of 88 mA cm^-2 at -1.2 V versus reversible hydrogen electrode, which are more than 2 times higher than those from the pristine Cu HFGDE. The achieved performance outperformed most of the other Sn-based GDEs, indicating the creation of sufficient contact among CO₂, electrolyte, and electrode catalyst through the design of the hollow fiber pore structure and catalytic active sites. The enhancement of formate production selectivity and the suppression of the hydrogen by-product were attributed to the optimized ratio of SnO_x species on the electrode surface. The best performance was seen in the HFGDE with the highest Sn²⁺/Sn⁴⁺ (120 s deposition), likely due to the modulating effect of the Cu substrate via electron donation with Sn species. The selectivity control strategy developed in the asymmetric HFGDE provides an efficient and facile method to stimulate selective electrochemical reactions in which the gas-phase reactant with low solubility is involved.

Potential Link between Cu Surface and Selective CO2 Electroreduction: Perspective on Future Electrocatalyst Designs

Electrochemical reduction of carbon dioxide (CO₂ RR) product distribution has been identified to be dependent on various surface factors, including the Cu facet, morphology, chemical states, doping, etc., which can alter the binding strength of key intermediates such as *CO and *OCCO during reduction. Therefore, in-depth knowledge of the Cu catalyst surface and identification of the active species under reaction conditions aid in designing efficient Cu-based electrocatalysts. This progress report categorizes various Cu-based electrocatalysts into four main groups, namely metallic Cu, Cu alloys, Cu compounds (Cu + non-metal), and supported Cu-based catalysts (Cu supported by carbon, metal oxides, or polymers). The detailed mechanisms for the selective CO₂ RR are presented, followed by recent relevant developments on the synthetic procedures for preparing Cu and Cu-based nanoparticles. Herein, the potential link between the Cu surface and CO₂ RR performance is highlighted, especially in terms of the chemical states, but other significant factors such as defective sites and roughened morphology of catalysts are equally considered during the discussion of current studies of CO₂ RR with Cu-based electrocatalysts to fully understand the origin of the significant enhancement toward C₂ formation. This report concludes by providing suggestions for future designs of highly selective and stable Cu-based electrocatalysts for CO₂ RR.

Interplay between halides in the electrolyte and the chemical states of Cu in Cu-based electrodes determines the selectivity of the C2product

The interaction between selectivity/activity (CH₄and C₂H₄) and electrode structure (Cu⁰, Cu⁺and Cu²⁺)/electrolyte properties (Cl⁻, Br⁻and I⁻) was investigated.

Bi-Doped SnO Nanosheets Supported on Cu Foam for Electrochemical Reduction of CO2 to HCOOH

Design and fabrication of efficient electrocatalysts is essential for electrochemical reduction of carbon dioxide (CO₂). In this work, bismuth (Bi)-doped SnO nanosheets were grown on copper foam (Bi-SnO/Cu foam) by a one-step hydrothermal reaction method and applied for the electrochemical reduction of CO₂ to formic acid (HCOOH). The experimental results indicated that Bi doping stabilized the divalent tin (Sn²⁺) existing on the surface of the electrocatalyst, making it difficult to be reduced to metallic tin (Sn⁰) during the electrochemical reduction process. In addition, combining with density functional theory (DFT) calculations, it is found that Bi doping and electron transfer from the catalyst to the Cu foam substrate could enhance the adsorption of *OOCH intermediates. As such, the Bi-doped SnO electrocatalyst exhibited a superior faradaic efficiency of 93% at -1.7 V (vs Ag/AgCl) for the reduction of CO₂ to HCOOH, together with a current density of 12 mA cm^-2 and excellent stability in at least 30 h of operation.

Zn-Doped Cu(100) facet with efficient catalytic ability for the CO2 electroreduction to ethylene

Theoretical calculations demonstrate that Zn-doped Cu(100) facet possesses efficient catalytic ability for the CO₂-to-C₂H₄ conversion. This work provides deep insights into the formation mechanism of C₂H₄ on transition metal doped Cu surface.