Influence of halide ions on the electrochemical reduction of carbon dioxide over a copper surface

The electrochemical reduction of carbon dioxide (ERCO 2 ) to valuable chemicals and fuels is one of the promising approaches for reducing excess CO 2 concentration in the atmosphere. However, it faces the great challenge of high overpotential since CO 2 is a thermodynamically stable molecule. Thus, an efficient catalyst and high energy input are required to drive the transformation. Among many strategies for improving CO 2 reduction, halide ions adsorbed on a Cu surface have been identified to be significantly important through establishing the X ad -C bond (X = F, Cl, Br, I), which weakens the C-O bonds of CO 2 to lower the hydrogenation potential barriers. Therefore, an in-depth understanding of the halide modified copper (Cu) electrocatalyst (Cu-X) can help to design efficient Cu-X electrocatalysts for the ERCO 2 . For this reason, the recent progress in the synthesis of Cu-X is introduced briefly in this review. Then, the impact of halide ions on the activity and selectivity is elaborated, which includes factors influencing the catalytic performance of Cu-X electrocatalysts, such as the morphology, oxidation state, and electrolyte pH/composition. In addition, the mechanism of halide influence on the chemical activation of CO 2 in Cu electrocatalysts is discussed in detail. Finally, a summary and outlook on designing highly selective and stable Cu-X electrocatalysts for the ERCO 2 in the future is provided. Specifically adsorbed X − ions on the Cu surface establish the X-carbon bond with CO 2 attracted to the electrode, which weakens the C-O bonds of CO 2 to lower the hydrogenation potential barriers, leading to CO 2 conversion to hydrocarbon products.