Tailoring CO2 supply microenvironment via a Janus electrode for enhanced CO2 electrochemical reduction to formate

Official URL: http://dx.doi.org/10.1016/j.ces.2026.125284

Electrochemical reduction of CO2 to formic acid offers a sustainable route for carbon utilization. However, achieving simultaneously high selectivity and activity remains challenging due to inherent conflicts between CO2 mass transport and proton supply. Herein, we addressed this conflict through a Janus gas diffusion electrode featuring a hydrophobic side for local CO2 enrichment and a relatively hydrophilic side for promoting proton-coupled CO2 reduction, which was realized by selectively coating relatively hydrophilic tin catalysts on only one side of a hydrophobic carbon paper, leaving the opposite side unmodified. The resulting Janus electrode not only featured a geometrically halved catalyst loading but also delivered a high Faradaic efficiency of 96.4% for HCOOH at −1.29 V vs. RHE. Combined theoretical and experimental analyses reveal that the hydrophobic side accumulated a CO2-rich bubble layer, establishing a pronounced concentration gradient across the electrode. This gradient drove the spontaneous diffusion of enriched CO2 toward the relatively hydrophilic catalytic side for efficient reduction. The tailored CO2 supply microenvironment not only significantly suppressed H2 evolution but also enhanced the calculated electronic coupling between the Sn catalyst and CO2 molecules, which stabilized the key OCHO intermediate and in turn made the free-energy change more favorable This simple yet effective Janus design offers a promising strategy toward efficient CO2 conversion in aqueous media.