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

Abstract

The electrochemical reduction of carbon dioxide (ERCO₂) to valuable chemicals and fuels is one of the promising approaches for reducing excess CO₂ concentration in the atmosphere. However, it faces the great challenge of high overpotential since CO₂ is a thermodynamically stable molecule. Thus, an efficient catalyst and high energy input are required to drive the transformation. Among many strategies for improving CO₂ 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 CO₂ 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 ERCO₂. 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 CO₂ in Cu electrocatalysts is discussed in detail. Finally, a summary and outlook on designing highly selective and stable Cu–X electrocatalysts for the ERCO₂ in the future is provided.