Identification of Sn₅ Active Site on SnO₂(110) for CO₂ Electroreduction via Constant-Potential Method and...

Although tin oxide catalysts have been extensively used in electrocatalytic CO₂ reduction (CO₂ER) to HCOOH (including both HCOO^- and HCOOH), the identification of the active site and the underlying reaction mechanism remain subjects of debate. Through constant-potential density functional theory (DFT) calculations and microkinetic simulations, we have pinpointed the Sn₅ site on SnO₂(110) surfaces as the active site, where CO₂ER proceeds via a CO₂_n (binding through O atoms)-mediated mechanism, noticeably distinct from the mechanisms identified via the constant-charge method. The significant stabilization of CO₂_n species at the Sn₅ site can be explained by the hard and soft acids and bases (HSAB) principle. Furthermore, the synergetic interaction between Sn₅ and Sn₄ sites offers an additional pathway for the formation of adsorbed hydrogen species at potentials more negative than -1.2 V, thereby enhancing the current density and Faradaic efficiency of HCOOH on SnO₂(110). The simulated Faradaic efficiencies and current densities of products align well with experimental observations on tin oxide catalysts. This study highlights the essential role of the constant-potential method in elucidating the active site and CO₂ER mechanism on SnO₂(110), providing insights that can enrich the design principles for CO₂ER and other technologically relevant reactions.