Crucial Role of Surface Hydroxyls on the Activity and Stability in Electrochemical CO2 Reduction.

The role of surface hydroxyls is significant for understanding catalytic performance of metallic oxides for CO2 electroreduction reaction (CO2ER). This Communication describes, employing SnO x as a model system, how to moderate coverage of hydroxyl to derive a stable Sn branches catalyst for CO2ER with a 93.1% Faradaic efficiency (FE) of carbonaceous products. With use of in situ attenuated total reflection surface enhanced infrared adsorption spectroscopy (ATR-SEIRAS) and density functional theory (DFT) calculations, we found that a proper amount of surface hydroxyls offered effective sites to boost CO2 adsorption via hydrogen bond. However, a higher surface coverage of hydroxyls leads to self-reduction of Sn-OH. We also explained the competition between self-reduction and CO2 reduction over Sn-based catalysts. The findings revealed the quantitative correlation between surface coverage of hydroxyl and CO2ER activity and suggested a logical extension to other metal oxide catalysts for CO2ER.