Microenvironment Tuning through Bi Morphology for Efficient Bicarbonate Electroreduction

Bicarbonate electroreduction in cation exchange membrane-based assemblies provides a complementary route for CO 2 conversion but is limited by coupled CO 2 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 CO 2 diffusion. Electrochemical open-circuit potential measurements quantify interfacial pH, revealing that elevated pH promotes in situ CO 2 generation, boosting selectivity and lowering cell voltage. Incorporating a hydrophilic filter membrane further extends OH – and CO 2 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.