Regulating competing reaction pathways for efficient CO₂ electroreduction in acidic conditions

Electrochemical carbon dioxide reduction reaction (CO₂RR) converts CO₂ into valuable chemicals by consuming renewable electricity at mild conditions, making it a promising approach to achieving carbon neutrality. However, the reaction of CO₂ with hydroxide ions to form carbonates leads to low carbon utilization and energy efficiency in near-neutral or alkaline CO₂RR. The high concentration of protons in acidic media can effectively mitigate carbonate formation and deposition, thereby significantly minimizing carbon loss and energy consumption. Unfortunately, hydrogen evolution reaction (HER) is more kinetically favorable than CO₂RR in acidic media. Herein, we comprehensively overview recent progress in acidic CO₂RR and propose two strategies derived from the competing reaction pathways of HER and CO₂RR: one focuses on regulating the H⁺ mass transport, while the other aims to modulate the intrinsic kinetic activity of CO₂RR. The two strategies are designed to compete for the limited active sites on the catalyst surface, inhibit side reactions, and enhance the activity and selectivity of CO₂RR. The representative approaches include modulating the interface electric field, constructing a local alkaline environment, and regulating competing adsorption sites. Finally, we also review the technical challenges and future perspectives of acidic CO₂RR coupled with membrane electrode assemblies (MEAs).