Selective Enhancement of Methane Formation in Electrochemical CO₂ Reduction Enabled by a Raman-Inactive Oxygen-Containing Species on Cu

The role of oxygen-containing species on Cu catalysts in the electrochemical CO₂ reduction reaction (CO₂RR) remains unclear due to the difficulty in its stabilization under reaction conditions. Co-electrolysis of CO₂ with an oxidant is an effective strategy to introduce oxygen-containing species on Cu during the CO₂RR. In this work, we present concrete evidence demonstrating that an oxygen-containing species is able to not only enhance the rate of the CO₂RR but also tune selectivities for certain products. Co-electrolysis of CO₂ with H₂O₂ on Cu selectively accelerates the CH₄ production rate by up to a factor of 200, but with only a slight enhancement of C₂₊ products. Combined investigations using in situ Raman spectroscopy with density functional theory calculations reveal that a Raman-inactive Cu oxide species is responsible for the improved CH₄ production. Results reported in this work highlight the possibility of enhancing Cu-based CO₂RR catalysts by introducing stable oxygen-containing catalytic structures.