Oxygen coordinated Cu single atom catalysts: a superior catalyst towards electrochemical CO₂ reduction for methane production

Abstract

Single atom catalyst (SAC) show significant promise in electrocatalytic carbon dioxide reduction reaction (eCO₂RR) to produce valuable chemicals, representing one of the most promising ways to achieve a carbon neutral cycle. Methane is one of the many valuable products from eCO₂RR. Rational design of SAC through deliberate coordination regulation and controlled synthesis at low temperatures toward methane production remains very limited. Herein in this paper, Cu SAC with coordination of four oxygen atoms (Cu-O₄) were prepared by soaking Cu nanocrystals on carbon support in acetic acid solution at 60 °C for 12 h. The coordination structure was revealed by extended X-ray absorption fine structure spectrum and X-ray photoelectron spectroscopy. Cu-O₄ SAC demonstrates excellent activity and selectivity towards methane production, with a Faradaic efficiency (FE) of 63.0% and partial current density of 200.5 mA cm^-2. Theoretical calculation indicates less positive charge of Cu center and stronger charge delocalization in Cu-O₄ SAC than Cu-N₄ SAC due to the stronger π bonding interaction in Cu-O₄ SAC, which stabilizes the methane intermediates and lowers the potential determining step on Cu-O₄ SAC. Strong hydrogen adsorption on Cu-O₄ SAC suppresses hydrogen evolution and may favor hydrogenation of reaction intermediates to methane. The limiting potential indicates that methane is more favored on Cu-O₄ SAC than CO, methanol and formate, corroborating the high selectivity of methane production on Cu-O₄ SAC. This work highlights the importance of regulation of the coordination environment in SAC in steering products in eCO₂RR.

Keywords

Single atom catalyst / oxygen coordination / charge delocalization / CO₂ reduction

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