Active Surface Structure of SnO₂ Catalysts for CO₂ Reduction Revealed by Ab Initio Simulations

Tin oxide (SnO₂) is an efficient catalyst for the CO₂ reduction reaction (CO₂RR) to formic acid; however, the understanding of the SnO₂ surface structure under working electrocatalytic conditions and the nature of catalytically active sites is a current matter of debate. Here, we employ ab initio density functional theory calculations to investigate how the selectivity and reactivity of SnO₂ surfaces toward the CO₂RR change at varying surface stoichiometry (i.e., reduction degree). Our results show that SnO₂(110) surfaces are not catalytically active for the CO₂RR or hydrogen evolution reaction, but rather they reduce under an applied external bias, originating surface structures exposing few metal tin layers, which are responsible for formic acid selectivity.