Elucidation of the Synergistic Effect of Dopants and Vacancies on Promoted Selectivity for CO2 Electroreduction to Formate.

Sn-based materials are identified as promising catalysts for the CO2 electroreduction (CO2RR) to formate (HCOO- ). However, their insufficient selectivity and activity remain grand challenges. A new type of SnO2 nanosheet with simultaneous N dopants and oxygen vacancies (VO -rich N-SnO2 NS) for promoting CO2 conversion to HCOO- is reported. Due to the likely synergistic effect of N dopant and VO , the VO -rich N-SnO2 NS exhibits high catalytic selectivity featured by an HCOO- Faradaic efficiency (FE) of 83% at -0.9 V and an FE of > 90% for all C1 products (HCOO- and CO) at a wide potential range from -0.9 to -1.2 V. Low coordination Sn-N moieties are the active sites with optimal electronic and geometric structures regulated by VO and N dopants. Theoretical calculations elucidate that the reaction free energy of HCOO* protonation is decreased on the VO -rich N-SnO2 NS, thus enhancing HCOO- selectivity. The weakened H* adsorption energy also inhibits the hydrogen evolution reaction, a dominant side reaction during the CO2RR. Furthermore, using the catalyst as the cathode, a spontaneous Galvanic Zn-CO2 cell and a solar-powered electrolysis process successfully demonstrated the efficient HCOO- generation through CO2 conversion and storage.