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

The acidic electrochemical CO 2 reduction reaction (CO 2 RR) holds promise for achieving a carbon-neutral future and can promote efficient CO 2 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 (CuO x ) catalysts for acidic CO 2 reduction (CO 2 RR) by incorporating bismuth oxide (BiO x ) and achieved a maximum formic acid Faradaic efficiency (FE HCOOH ) of 97 ± 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 CO 2 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 CO 2 RR and highlights the potential of electrolyte modification to tailor product selectivity. • Stabilized Cu + in acidic CO 2 RR using dual CuO x /BiO x metal oxide matrix. • Extended catalyst stability using facile and scalable FSP synthesis. • Achieved remarkable formic acid selectivity (FE = 97 %) under acidic conditions. • Tuned C 2+ product distributions via distinct anion adsorption in electrolytes.