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

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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.