Reduction-tolerant SnO2assisted by surface hydroxyls for selective CO2electroreduction to formate over wide potential range

Tin oxide based materials have been identified as active catalysts for electrochemical CO2-to-formate conversion. However, the oxide is unstable and can easily reconstruct via self-reduction under CO2reduction reaction (CO2RR) condition, resulting in undesired elevated hydrogen evolution reactivity. In this work, a stable tin dioxide (SnO2-1) electrocatalyst with abundant surface hydroxyls was synthesized via sodium cation assisted calcination method. The resulting electrocatalyst exhibits higher selectivity toward formate in a wide potential window compared with the one with very little hydroxyl groups. In addition, we demonstrate that SnO2-1 can operate at high current density of 200 mA·cm−2for at least 6 h while maintaining FEformateover 80%. Assisted with density functional theory (DFT) calculations, we propose that the presence of surface hydroxyls factors significantly into the overall performance of CO2RR, including optimization of the formation energy of key intermediate *OCHO and help SnO2to preserve partially reduced active surface.