Bi-based electrocatalysts for acidic CO₂-to-formate electrolysis: Dynamic interfacial microenvironment regulation and industrial perspectives

Electrochemical CO₂ reduction reaction (CO₂RR) to formic acid/formate in acidic media offers a promising route to suppress bulk carbonate formation, reduce carbonate crossover, and improve carbon utilization relative to conventional alkaline systems. However, acidic CO₂RR remains challenged by severe hydrogen evolution reaction (HER) competition, catalyst instability, and carbonate regeneration induced by local interfacial alkalization, particularly at industrially relevant current densities and in membrane electrode assembly (MEA) electrolyzers. Owing to their relatively weak hydrogen adsorption and preferential stabilization of the *OCHO intermediate, Bi-based catalysts are particularly attractive for selective CO₂-to-formate conversion under acidic conditions. This review establishes a multiscale framework linking intrinsic active-site regulation with extrinsic interfacial microenvironment engineering, including electronic-structure modulation, heterointerface construction, electrolyte and cation effects, spatial confinement, and electrode/reactor integration. Particular emphasis is placed on distinguishing acidic bulk operating conditions from the actual local interfacial environment and on understanding the trade-off between HER suppression and carbonate regeneration. At the device level, industrially relevant performance metrics and reporting parameters-including full-cell voltage, energy efficiency, single-pass carbon efficiency, carbon balance, product concentration, CO₂ flow rate, product crossover, electrode area, and durability-are critically evaluated across flow cells, MEA electrolyzers, and solid-state-electrolyte configurations. Finally, device-dependent degradation mechanisms and a staged roadmap toward scalable acidic CO₂-to-formate electrolysis are discussed.