Atom vacancies induced electron-rich surface of ultrathin Bi nanosheet for efficient electrochemical CO2 reduction

The overpotential and selectivity of electrochemical CO2 reduction over metal electrodes are closely related to the adsorption strength of key intermediate. Defect engineering of the materials can modulate the energetic difference between the antibonding states and the Fermi level, thus strengthening the surface-adsorbate chemical bonds and boosting the steady progress of the electrochemical reaction. Here, we proposed an efficient strategy to electrochemically reduced layered Bi2O2CO3 to Bi nanosheet with (001) dominant facet and atom vacancies. The Bi nanosheet exhibits 90 % CO2-to-formate Faradaic efficiency at a low overpotential of 420 mV and excellent stability over 100 h in 0.1 M KHCO3 electrolyte. Spectroscopic and computational studies confirm that the Bi atom vacancies induced the electron-rich surface, leading the movement of p states towards the Fermi level, hence decreasing the activation energy of CO2 to CO2-* radical and promoting the stability of OCHO* intermediate via p orbitals hybridization between the O in carbon-containing intermediates and the Bi electrode.