Introduction of the SiO ₂ Buffer Layer Enables High CO Selectivity in Bicarbonate Electrolyzer

Liquid-phase bicarbonate electrolyzers offer an energy-efficient alternative to conventional gas-fed systems but suffer from intense hydrogen evolution that severely competes with CO 2 reduction. Here, we demonstrate that introducing a thin SiO 2 buffer layer onto the catalyst surface effectively suppresses the hydrogen evolution reaction (HER) by restricting H + transport in a cation exchange membrane bicarbonate electrolyzer. Together with an optimized KHCO 3 concentration and a hydrophilic carbon paper substrate that promotes HCO 3 – diffusion and in situ CO 2 generation, the modified electrode achieves a CO Faradaic efficiency of 89% at 50 mA cm –2 . The CO partial current density reaches 125 mA cm –2 at 250 mA cm –2, representing a 2.8-fold enhancement compared to the unoptimized system. This interfacial modulation strategy shows broad applicability to Ag nanoparticle and CoPc@CNT catalysts, highlighting its potential to advance integrated CO 2 capture and electroreduction technologies.