Electrocatalytic CO ₂ Reduction in Acidic Media: From Fundamental Challenges to Sustainable Solutions

Abstract Electrocatalytic CO 2 reduction reaction (CO 2 RR) in acidic media attracts significant attention due to its ability to circumvent the low carbon utilization efficiency and system instability associated with carbonate formation in traditional alkaline/neutral systems. However, although high proton concentrations in acidic environments inhibit carbonate generation, they simultaneously intensify hydrogen evolution reaction (HER) competition and compromise the adsorption stability of key intermediates, thereby severely restricting CO 2 reduction selectivity and efficiency. Thus, it is a great challenge to effectively suppress HER and accelerate acidic CO 2 RR. This review commences with an overview of recent progress in acidic CO 2 electrolysis, addressing the fundamental limitations hindering the use of acidic electrolytes. It subsequently systematically examines advanced strategies to overcome these challenges, encompassing the regulation of the electrolyte microenvironment, the role of alkali cations, surface and interface functionalization, nanoconfinement structural design, and the exploitation of novel electrolyzers. The conclusion proffers insights into emerging challenges and future research directions. It is anticipated that this timely endeavor could galvanize research efforts to mitigate CO 2 crossover, catalyze novel insights for resolving the “alkalinity problem”, and propel CO 2 RR into a more sustainable and viable technology.