Mn-doped Bi2O3 grown on PTFE-treated carbon paper for electrochemical CO2-to-formate production

• Mn-doped Bi 2 O 3 electrode was prepared for electrochemical CO 2 reduction (CO 2 RR). • Mn-doping significantly improves the catalytic performance. • The electrode reacts with KHCO 3 and then reduces to Mn-modified Bi under CO 2 RR. • Mn-doping alters the electronic properties, affecting key intermediates’ sorption. BiO x shows promising selectivity in catalyzing the electrochemical reduction of CO 2 to formate, but the process suffers from high overpotential and a low rate. Moreover, the active sites are still ambiguous under electrochemical conditions. Herein, we introduce Mn-doping to enhance the activity of binder-free Bi 2 O 3 and elaborate on active sites through in situ Raman and density functional theory (DFT) analyses. The Mn-doped Bi 2 O 3 transforms to Mn-doped Bi 2 (CO 3 )O 2 in KHCO 3 and subsequently reduces to Mn-modified metallic Bi under cathodic potentials. The undoped Bi 2 O 3 is found to follow the same phase transitions but at a different rate. The DFT analyzes the impact of doping the Bi(012) with Mn and indicates significantly improved selectivity for formate generation. Further, the importance of the substrate’s hydrophobicity for long-term stability is demonstrated. This study offers in-depth insights into the design and understanding of doped BiO x -based electrodes for CO 2 reduction.