Microenvironment Tuning through Bi Morphology for Efficient Bicarbonate Electroreduction

Bicarbonate electroreduction in cation exchange membrane-based assemblies provides a complementary route for CO₂ conversion but is limited by coupled CO₂ concentration and interfacial pH. Here, we design a bismuth nanoflower (Bi-NF) catalyst with interconnected channels that enhance mass transfer, regulate local pH, and facilitate CO₂ diffusion. Electrochemical open-circuit potential measurements quantify interfacial pH, revealing that elevated pH promotes in situ CO₂ generation, boosting selectivity and lowering cell voltage. Incorporating a hydrophilic filter membrane further extends OH^- and CO₂ transport pathways. The optimized Bi-NF electrode achieves nearly 100% Faradaic efficiency for formate at 50 mA cm^-2 and a practical partial current density of 240 mA cm^-2 at 3.5 V. These results demonstrate that combining morphology engineering with controlled mass transport is an effective strategy to enhance performance and elucidate the mechanisms of bicarbonate electrolysis.