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 CO₂ reduction. Here, we demonstrate that introducing a thin SiO₂ 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 KHCO₃ concentration and a hydrophilic carbon paper substrate that promotes HCO₃^- diffusion and in situ CO₂ 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 CO₂ capture and electroreduction technologies.