Stable dual metal oxide matrix for tuning selectivity in acidic electrochemical carbon dioxide reduction

The acidic electrochemical CO2 reduction reaction (CO2RR) holds promise for achieving a carbon-neutral future and can promote efficient CO2 utilization by attenuating the carbonate/bicarbonate formation reaction. However, catalyst degradation in strong acids and the competing hydrogen evolution reaction (HER) often result in short catalyst lifetime and poor product selectivity. Herein, this study introduces a strategy to stabilize copper oxide (CuOx) catalysts for acidic CO2 reduction (CO2RR) by incorporating bismuth oxide (BiOx) and achieved a maximum formic acid Faradaic efficiency (FEHCOOH) of 97 f 1 % at-2.7 V vs. RHE and maintaining over 90 % FE for more than 20 h. In situ XAS, SR-FTIR and density functional theory (DFT) calculations show that the catalyst can inhibit *H adsorption and promote selective CO2 conversion to HCOOH via the HCOO* pathway. Further electrolyte anion modulation achieves ethanol and acetone production at Faradaic efficiencies of 17 % and 16 % in phosphoric and perchloric acid, respectively. In situ analyses reveal that distinct anion adsorption influence key intermediates, such as *CO, leading to shifts in C2+ product distributions. This work offers insights into designing acid-stable electrocatalysts for CO2RR and highlights the potential of electrolyte modification to tailor product selectivity.