Promotional effect of surface hydroxyls on electrochemical reduction of CO2 over SnO x /Sn electrode

Display Omitted * The presence of SnO x on tin electrode enhances the catalytic activity for CO2 electrochemical reduction. * Formation of surface hydroxyls plays an important role for CO2 reduction. * Bicarbonate is the common intermediate to produce both formate and CO. * From bicarbonate to COOH [low * ] opens the channel for CO formation. Tin oxide (SnO x ) formation on tin-based electrode surfaces during CO2 electrochemical reduction can have a significant impact on the activity and selectivity of the reaction. In the present study, density functional theory (DFT) calculations have been performed to understand the role of SnO x in CO2 reduction using a SnO monolayer on the Sn(112) surface as a model for SnO x . Water molecules have been treated explicitly and considered actively participating in the reaction. The results showed that H2O dissociates on the perfect SnO monolayer into two hydroxyl groups symmetrically on the surface. CO2 energetically prefers to react with the hydroxyl, forming a bicarbonate (HCO3(t)[low * ] ) intermediate, which can then be reduced to either formate (HCOO[low * ] ) by hydrogenating the carbon atom or carboxyl (COOH[low * ] ) by protonating the oxygen atom. Both steps involve a simultaneous C[single bond]O bond breaking. Further reduction of HCOO[low * ] species leads to the formation of formic acid in the acidic solution at pH