Advances in local pH modulation for selective acidic CO₂ electroreduction

Acidic CO₂ electroreduction offers a strategy for high carbon efficiency via in situ utilization of regenerated CO₂, but acidic conditions kinetically favor the hydrogen evolution reaction, which leads to diminished selectivity toward CO₂ reduction products. To suppress the hydrogen evolution reaction and improve CO₂ reduction selectivity, it is essential to have a locally alkaline or near-neutral microenvironment near the catalyst surface during acidic CO₂ electrolysis. Herein, we review recent advances in local pH regulation strategies, including bulk pH regulation, current-induced OH^- effects, catalyst morphology effects, alkali cation effects, and surface polymer coatings, followed by the mechanistic understanding of local pH modulation in acidic media. Additionally, to circumvent salt precipitation caused by a locally alkaline environment and highly concentrated cations during acidic CO₂ electrolysis, alkali cation-free electrolyte design is discussed. Eventually, perspectives on future research efforts in local pH regulation and understanding during acidic CO₂ reduction are also provided in this minireview.