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

BiO_x shows promising selectivity in catalyzing the electrochemical reduction of CO₂ 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 Bi₂O₃ and elaborate on active sites through in situ Raman and density functional theory (DFT) analyses. The Mn-doped Bi₂O₃ transforms to Mn-doped Bi₂(CO₃)O₂ in KHCO₃ and subsequently reduces to Mn-modified metallic Bi under cathodic potentials. The undoped Bi₂O₃ 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 CO₂ reduction.