Zhang, Z.Trần-Phú, T.Yuwono, J.Ma, Z.Yang, Y.Leverett, J.Hocking, R.K.Johannessen, B.Kumar, P.Amal, R.Daiyan, R.2025-10-142025-10-142025Applied Catalysis B: Environmental, 2025; 371:125203-1-125203-90926-33731873-3883https://hdl.handle.net/2440/147758The 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 ± 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.en© 2025 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).CO₂ reduction; electrocatalysis; acid stable; In situ XASJournal article10.1016/j.apcatb.2025.125203732630Yuwono, J. [0000-0002-0915-0756]