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 (V_O-rich N-SnO₂ NS) for promoting CO₂ conversion to HCOO⁻ is reported. Due to the likely synergistic effect of N dopant and V_O, the V_O-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 V_O and N dopants. Theoretical calculations elucidate that the reaction free energy of HCOO* protonation is decreased on the V_O-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.