Reviewing the impact of halides on electrochemical CO₂ reduction

Electrochemical CO₂ reduction reaction (CO₂RR) is a promising technology for mitigating global warming and storing renewable energy. Designing low-cost and efficient electrocatalysts with high selectivity is a priority to facilitate CO₂ conversion. Halide ion (F^–, Cl^–, Br^–, I^–) modified electrocatalysts is a potential strategy to promote CO₂ reduction and suppress the competitive hydrogen evolution reaction (HER). Therefore, a comprehensive review of the role and mechanism of halide ions in the CO₂RR process can help better guide the future design of efficient electrocatalysts. In this review, we first discuss the role of halide ions on the structure and morphology of electrocatalysts. Secondly, the relationship between the halide ions and the valence states of the active sites on the catalyst surface is further elaborated on. Thirdly, the mechanisms of halide in enhancing CO₂ conversion efficiency are also summarized, including the involvement of halide ions in electron transfer and their influence on the reaction pathway. Finally, we conclude with a summary and future outlook.