Mechanism of halide ions in regulating product selectivity in electrocatalytic CO₂ reduction

Electrocatalytic CO₂ reduction (ECO₂RR) is a promising route to sustainable fuel and chemical production, yet its practical application is hindered by the formidable challenge of precisely controlling product selectivity. In recent years, electrolyte engineering, particularly the regulatory role of halide ions, has attracted considerable interest due to their significant influence on the catalyst's surface/interfacial microenvironment and reaction pathways. This review focuses on halide ions as a key tool, systematically elaborating on how they induce dynamic surface reconstruction and specific crystal facet exposure in catalysts through specific adsorption, tune surface roughness to increase active site density, modulate the catalyst's electronic structure via their unique electronegativity to stabilize key active valence states, optimize the adsorption behavior of critical reaction intermediates, and thereby steer reaction pathways. The synergistic mechanism of dynamic surface reconstruction-valence stabilization-electronic structure tuning-pathway guidance is summarized to provide insights for the rational design of efficient and highly selective ECO₂RR catalysts.