Insights into electrochemical CO2 reduction on tin oxides from first-principles calculations

Density functional theory calculations were used to unravel the mechanism of CO2 electroreduction on SnOx surfaces. Under highly reducing conditions (< −0.6 V vs. RHE), the SnO(101) surface with oxygen vacancies is likely the active phase for CO2 reduction. We showed that the proton-electron transfer to adsorbed *CO2 forming *OCHO, a key intermediate for producing HCOOH, is energetically more favorable than the formation of *COOH, justifying the selectivity trends observed on Sn-based electrocatalysts. With linear scaling relations, we propose the free formation energy of *CO2 at the oxygen vacancy as the reactivity descriptor. By engineering the strain of the SnO(101) surface, the selectivity towards HCOOH can be further optimized at reduced overpotentials.