Proton Flux Engineering for Selective CO 2 Electroreduction

ABSTRACT The carbon dioxide reduction reaction (CO 2 RR) is central to carbon valorization and renewable electricity storage, yet its selectivity, efficiency, and durability depend on coordinating proton availability with electron transfer at dynamic electrochemical interfaces. Despite advances in catalysts, electrolytes, hydrogen evolution suppression, and devices, proton effects are described by isolated descriptors, such as pH, water activity, buffer capacity, cation identity, hydrophobicity, ionomer chemistry, and local alkalinity. This fragmentation obscures how protons regulate initiation, *COOH formation, *CO/formate branching, *CO coverage, C─C coupling, hydrogen evolution, and high‐flux decay. A proton‐centered perspective is needed to link atomic proton‐transfer events with interfacial microenvironments and device operation. This review establishes proton regulation as a mechanistic framework for CO 2 RR by examining proton sources, transport pathways, interfacial accessibility, hydrogen‐bond‐network reorganization, local electric fields, and proton‐coupled electron‐transfer timing. By integrating molecular mechanisms, microenvironment modulation, in situ characterization, and gas‐diffusion or membrane‐electrode architectures, we organize dispersed observations into a source–transport–utilization framework. This framework shows how proton location, dose, and temporal availability define kinetic boundaries between hydrogen evolution, one‐carbon (C 1 ) products, and multicarbon (C 2+ ) pathways, while governing stability under practical fluxes. Proton regulation guides selective, scalable, and durable CO 2 electroconversion.