The Role of Protons in CO2 Reduction on Gold under Acidic Conditions

Carbonate formation constitutes a major obstacle in the electrochemical CO2 reduction reaction (CO2RR), restricting the industrial implementation of this reaction. Even when adopting mild acidic electrolytes, carbonate formation is still observed. The fundamental reason lies in the inevitable OH– generation when H2O is the proton donor, leading to subsequent carbonate formation. Thus, exploring the reaction pathway of the CO2RR in the acid, especially if a proton can directly participate in the reaction, is critical. Herein, we employed a rotating ring-disk electrode and surface interrogation scanning electrochemical microscopy to investigate the electrode process of the CO2RR in acid. A pH-dependent behavior of CO2RR is observed, indicating proton acting as the reactant in the RDS, originating from the early onset of CO2 adsorption under locally acidic conditions.