(Bi)carbonate reduction as a new pathway beyond conventional CO2 reduction.

Electroreduction of carbonate and bicarbonate is emerging as a chemically distinct route beyond conventional gas-fed CO2 electrolysis. Yet the nominal ionic-carbon feed does not uniquely identify the immediate electroactive species. This review examines both indirect conversion, in which HCO3 - or CO3 2- is locally protonated to regenerate molecular CO2 before conventional CO2RR, and direct conversion, in which solvated (bi)carbonate-derived species are activated at the cathode. We further discuss a surface- or lattice-mediated regime involving catalyst-bound carbonate reservoirs. Although these pathways may coexist, they differ fundamentally in carbon-species transport, interfacial reaction steps, catalyst-design requirements and reactor architectures. Using this pathway-resolved framework, we analyze the roles of acid-base speciation, proton-coupled electron transfer, cation-carbonate structuring, membrane-regulated carbon flux and catalytic microenvironments. We further evaluate catalyst and electrolyzer design, mechanistic evidence, carbon accounting and integration with carbon capture, including emerging direct-air-to-chemicals concepts. Finally, we identify the mechanistic and system-level requirements for advancing (bi)carbonate electrolysis towards energy-efficient, closed-loop capture-conversion processes.