Electric-field-driven CO2 polarization and bioinspired proton blocking unlock CO2 reduction in strong acid without metal cations

Metal-cation-free CO2 electroreduction (CO2R) in strong acidic media mitigates CO2 reactant losses, eliminates the risk of metal salt precipitation, and broadens device tolerance compared to acidic, neutral, or alkaline system using metal cations. However, such an acidic environment still poses challenges due to the inert and nonpolar nature of CO2 and intensely competitive hydrogen evolution reaction. Inspired by aquaporins in acidophiles, we engineer sharp-triangle Au nanostructures capped with a hexadecyltrimethylammonium chloride (CTAC) layer enriched with cationic sites. The intense local electric fields generated by the high-curvature tips of Au nanocatalyst polarize CO2 molecules, increasing their dipole moment to facilitate adsorption and activation. Meanwhile, the CTAC layer acts as a proton barrier, suppressing HER by mimicking the proton-blocking mechanism of aquaporins. This dual-function design enables continuous CO2R for 100 hours in a flow electrolyzer at pH 1.0, achieving an energy efficiency of 60% and near-unity Faradaic efficiency for CO production. This bioinspired strategy represents a significant advancement in CO2R technology by integrating rational catalyst design principles. Metal-cation-free CO2 electroreduction in strong acid minimizes reactant loss and salt precipitation yet struggles with CO2 activation and hydrogen evolution competition. Here, the authors report bioinspired sharp gold triangles with a proton-blocking layer that polarize CO2 and suppress hydrogen evolution.