The electrochemical carbon dioxide reduction reaction (CO 2 RR) is a promising solution to the current environmental and energy issues. Cu is the only metal catalyst able to convert CO 2 into high-value-added hydrocarbons. However, Cu catalysts tend to degrade with the decrease in the hydrocarbon selectivity under operation conditions. Herein, we monitored the morphological evolution of Cu nanocatalysts and correlated with changes in the selectivity of hydrocarbon products during electrochemical CO 2 reduction. Initial Cu nanospheres quickly reconstructed into nanocubes within 1 h of CO 2 electrolysis and then gradually turned into even smaller irregular nanoparticles. Interestingly, the above unstable Cu nanocube offered the maximum ethylene selectivity. We successfully stabilized these Cu nanocubes using a 2D graphene surface doped with nitrogen to achieve high ethylene selectivity over 24 h. Our X-ray photoelectron spectroscopy (XPS) and density-functional theory (DFT) investigations show that the strong interaction between Cu and pyridinic nitrogen on the 2D graphene surface plays a key role in stabilizing Cu nanocubes.
Electrocatalytic CO2 reduction is an effective way to close the global carbon cycle. Tin oxides have been demonstrated as promising catalysts to convert CO2 into formate with high selectivity but...
Copper is distinctive in electrocatalyzing reduction of CO 2 into various energy-dense forms, but it often suffers from limited product selectivity including ethanol in competition with ethylene. Here, we describe systematically designed, bimetallic electrocatalysts based on copper/gold heterojunctions with a faradaic efficiency toward ethanol of 60% at currents in excess of 500 mA cm −2 . In the modified catalyst, the ratio of ethanol to ethylene is enhanced by a factor of 200 compared to copper catalysts. Analysis by ATR-IR measurements under operating conditions, and by computational simulations, suggests that reduction of CO 2 at the copper/gold heterojunction is dominated by generation of the intermediate OCCOH*. The latter is a key contributor in the overall, asymmetrical electrohydrogenation of CO 2 giving ethanol rather than ethylene.
Burning of fossil fuels increases CO2 concentration in the atmosphere, resulting in a series of climate-and environment-related concerns such as global warming, sea-level rise, and melting of glaciers. Therefore, utilization of renewable energy to reduce the CO2 concentration, in order to realize a sustainable development, is urgent. Capturing and utilizing CO2, a greenhouse gas, can not only address these concerns but also alleviate the current scenario of energy shortage. Thermal catalytic CO2 hydrogenation offers various pathways with high conversion efficiencies to produce fuels and industrial chemicals including CO, HCOOH, CH3OH, and CH4. However, CO2 is chemically inert due to the highly stable C=O bond. Thus, harsh reaction conditions such as high temperature and pressure are required for CO2 hydrogenation.Electrocatalytic CO2 reduction using renewable electricity and water is a promising alternative to thermocatalysis. This technology can not only store and transport the intermittent solar or wind energy but can also use water as the proton source instead of H2, which is indispensable for thermal CO2 hydrogenation. Electrochemical CO2 reduction under ambient conditions is a proton-coupled electron transfer process. The key to promote the electrochemical reduction of CO2 is to develop highly selective and active catalysts with high stability. Among various CO2 electrocatalysts, copper-based catalysts have attracted significant attention and have been extensively investigated, since they exhibit good selectivity and efficiency for the reduction of CO2 to hydrocarbons and alcohols. A broad range of products, up to 16 different gases and liquids, can be obtained in the CO2 electroconversion on copper. Copper is the only metal that has a negative adsorption energy for *CO and a positive adsorption energy for *H. Thus, it has a unique property of generating > 2e − transfer products. However, selectivity of the target product is still low, especially for high value-added C2+ species (C2H4, C2H5OH, CH3COOH, CH3CHO, n-C3H7OH, etc.).The selectivity of various products on copper-based catalysts could be enhanced by surface engineering techniques such as tuning the morphologies, particle sizes, surface facets, strains levels, and atomic coordination. Electrolyte engineering could also aid in CO2 electroreduction. Therefore, improving the selectivity of C2+ products by modifying copper-based catalysts could be a hot research topic. In addition, C-C coupling is a key step in forming C2+ products, though the C2+ product formation pathway is complex, and the mechanisms are still unclear. Considering these, this paper mainly reviews the research progress in copper-based catalysts producing C2+ species in the last five years. It also discusses the possible reaction mechanisms and the factors that affect the product selectivities. In the end, further research directions are proposed.
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