Aligned InS Nanorods for Efficient Electrocatalytic Carbon Dioxide Reduction

Advanced systems for enhanced CO2 electroreduction

Carbon dioxide (CO2) electroreduction has extraordinary significance in curbing CO2 emissions while simultaneously producing value-added chemicals with economic and environmental benefits. In recent years, breakthroughs in designing catalysts, optimizing intrinsic activity, developing reactors, and elucidating reaction mechanisms have continuously driven the advancement of CO2 electroreduction. However, the industrialization of CO2 electroreduction remains a challenging task, with high energy consumption, high costs, limited reaction products, and restricted application scenarios being the issues that urgently need to be addressed. To accelerate the progress of CO2 electroreduction towards practical application, this review shifts the research focus from catalysts to aspects such as reactions and systems, aiming to improve reaction efficiency, reduce technical costs, expand the range of products, and enhance selectivity, offering readers a new perspective. In particular, innovative and specific design strategies such as CO2 reduction coupled with alternative oxidation, co-reduction reaction of CO2 and C/N/O/S-containing species, cascade systems, and integrated CO2 capture and reduction systems are discussed in detail. Additionally, personal views on the opportunities and future challenges of the aforementioned innovative strategies are provided, offering new insights for the future research and development of CO2 electroreduction.

High-Entropy Metal Sulfide Promises High-Performance Carbon Dioxide Reduction

The efficient conversion of carbon dioxide (CO2) requires the development of stable catalysts with high selectivity and reactivity within a wide potential range. Here, the high-entropy metal sulfide CuAgZnSnS4 is designed for CO2 reduction with excellent performance (FEcarbon products ≥ 90%) in whole test potential windows (600 mV) based on the synergistic effect of the high-entropy metal sulfide. In particular, CuAgZnSnS4 exhibits better single-product selectivity with the highest FEHCOOH/FECO value (29.03) at -1.28 versus reversible hydrogen electrode (RHE). In combination with in situ measurements and theoretical calculations, it is further revealed that the synergistic effect of CuAgZnSnS4 realizes the controllable regulation of the surface electronic structure at Sn active sites, strengthening orbital interactions between *OCHO and Sn active sites. As a result, the effective adsorption and activation of *OCHO instead of *H are obtained, improving the single-product selectivity of electrocatalytic CO2 reduction and inhibiting the competitive hydrogen evolution reaction significantly. Our findings may complete the understanding of the synergistic effect for high-entropy materials in catalysis and offer new insight into the design of efficient electrocatalysts with high catalytic activity.

Modulating the Active Sites of VS2 by Mn Doping for Highly Selective CO2 Electroreduction to Methanol in a Flow Cell

Methanol is a valuable liquid C1 product in CO2 electroreduction (CO2ER); however, it is hard to achieve high selectivity and a large current density simultaneously. In this work, we construct Mn2+-doped VS2 multilayer nanowafers applied in a flow cell to yield methanol as a single liquid product to tackle this challenge. Mn doping adjusts the electronic structure of VS2 and concurrently introduces sulfur vacancies, forming a critical *COB intermediate and facilitating its sequential hydrogenation to methanol. The optimal Mn4.8%-VS2 exhibits methanol Faradic efficiencies of more than 60% over a wide potential range of -0.4 to -0.8 V in a flow cell, of which the maximal value is 72.5 ± 1.1% at -0.6 V along with a partial current density of 74.3 ± 1.1 mA cm-2. This work opens an avenue to rationally design catalysts for engineering C1 intermediates toward CO2ER to a single liquid methanol in a flow cell.

Mo4+-Doped CuS Nanosheet-Assembled Hollow Spheres for CO2 Electroreduction to Ethanol in a Flow Cell

Electrocatalytic CO2 reduction reaction (CO2RR) to ethanol has been widely researched for potential commercial application. However, it still faces limited selectivity at a large current density. Herein, Mo4+-doped CuS nanosheet-assembled hollow spheres are constructed to address this issue. Mo4+ ion doping modifies the local electronic environments and diversifies the binding sites of CuS, which increases the coverage of linear *COL and produces bridge *COB for subsequent *COL-*COH coupling toward ethanol production. The optimal Mo9.0%-CuS can electrocatalyze CO2 to ethanol with a faradaic efficiency of 67.5% and a partial current density of 186.5 mA cm-2 at -0.6 V in a flow cell. This work clarifies that doping high valence transition metal ions into Cu-based sulfides can regulate the coverage and configuration of related intermediates for ethanol production during the CO2RR in a flow cell.

Regulation Strategy of Nanostructured Engineering on Indium-Based Materials for Electrocatalytic Conversion of CO2

Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.

Adjusted Preferential Adsorption of Intermediates via Regulation of the Electronic Structure during the Electrocatalytic CO2 Reduction Process

The surface electronic structures of catalysts play a crucial role in CO2 adsorption and activation. Here, sulfur vacancies are introduced into CuInS2 nanosheets (Vs-CuInS2) to evaluate the effect of electronic structures at the surface-active sites on the electrochemical CO2 reduction reaction (CO2RR). Vs-CuInS2 exhibits a significant disparity in the highest FEformate/FECO (6.50) compared to that of CuInS2 (1.86). Specifically, the maximum current density (Jmax) of carbon products on Vs-CuInS2 is 78.78 mA cm-2, and a Faraday efficiency of carbon products (FEcarbon products) of ≥80% is achieved in 600 mV wide potential windows. In situ Raman measurements and density functional theory calculations elucidate the origin of the apparent alterations in the carbon product selectivity. The introduction of sulfur vacancies realizes the controllable regulation of the local electronic density around the metal active sites, inducing the transformation of *COOH and *OCHO from competitive adsorption on CuInS2 to specific adsorption on Vs-CuInS2. In addition, the regulation of electronic structures on Vs-CuInS2 inhibits *H adsorption. This work reveals the transfer of adsorption of CO2RR intermediates via regulation of the electronic structure, complementing the understanding of the mechanism for the enhanced CO2RR.

Ag+ -Doped InSe Nanosheets for Membrane Electrode Assembly Electrolyzer toward Large-Current Electroreduction of CO2 to Ethanol

It is an appealing approach to CO2 utilization through CO2 electroreduction (CO2 ER) to ethanol at high current density; however, the commonly used Cu-based catalysts cannot sustain large current during CO2 ER despite their capability for ethanol production. Herein, we report that Ag+ -doped InSe nanosheets with Se vacancies can address this grand challenge in a membrane electrode assembly (MEA) electrolyzer. As revealed by our experimental characterization and theoretical calculation, the Ag+ doping, which can tailor the electronic structure of InSe while diversifying catalytically active sites, enables the formation of key reaction intermediates and their sequential evolution into ethanol. More importantly, such a material can well work for large-current conditions in MEA electrolyzers with In2+ species stabilized via electron transfer from Ag to Se. Remarkably, in an MEA electrolyzer by coupling cathodic CO2 ER with anodic oxygen evolution reaction (OER), the optimal catalyst exhibits an ethanol Faradaic efficiency of 68.7 % and a partial current density of 186.6 mA cm-2 on the cathode with a full-cell ethanol energy efficiency of 26.1 % at 3.0 V. This work opens an avenue for large-current production of ethanol from CO2 with high selectivity and energy efficiency by rationally designing electrocatalysts.

Coupling Value-Added Anodic Reactions with Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction features a promising approach to realize carbon neutrality. However, its competitiveness is limited by the sluggish oxygen evolution reaction (OER) at anode, which consumes a large portion of energy. Coupling value-added anodic reactions with CO₂ electroreduction has been emerging as a promising strategy in recent years to enhance the full-cell energy efficiency and produce valuable chemicals at both cathode and anode of the electrolyzer. This review briefly summarizes recent progresses on the electrocatalytic CO₂ reduction, and the economic feasibility of different CO₂ electrolysis systems is discussed. Then a comprehensive summary of recent advances in the coupled electrolysis of CO₂ and potential value-added anodic reactions is provided, with special focus on the specific cell designs. Finally, current challenges and future opportunities for the coupled electrolysis systems are proposed, which are targeted to facilitate progress in this field and push the CO₂ electrolyzers to a more practical level.

Electrocatalytic Reduction of CO2 Coupled with Organic Conversion to Selectively Synthesize High-Value Chemicals

The electrochemical process of coupling electrocatalytic CO₂ reduction and organic conversion reaction can effectively reduce the reaction overpotential and obtain value-added chemicals. Moreover, because of the diversity of substrates and the designability of coupling forms, more and more attention has been paid to this field. This review systematically summarizes the research progress of coupling electrolysis in recent years, (1) co-electrolysis of CO₂ and organics at the cathode to obtain specific products with high selectivity, (2) replacing traditional anodic oxygen evolution reaction (OER) with other valuable oxidation reactions to improve energy utilization efficiency and economic benefits of CO₂ conversion, (3) in an electrolytic cell without membrane, the cathode and anode jointly transform CO₂ and organics to redox products. We hope that the examples and insights on coupling electrolysis introduced in this review can inspire researchers to further explore and innovate in this direction.