Elucidating electrochemical CO2 reduction reaction processes on Cu(hkl) single-crystal surfaces by in situ Raman spectroscopy

Abstract

Cupric materials are known to catalyze the electrochemical CO₂ reduction reaction (CO₂RR) and significantly improve the selectivity of multi-carbon products. Surface facets and structural effects play a critical role in the CO₂RR. However, these surface mechanisms are poorly understood, and identifying trace intermediates on atomically-flat Cu(hkl) single-crystal surfaces, in situ, is a tremendously challenging task requiring sophisticated technical know-how. Here, in situ Raman spectroscopy was used to provide critical evidence of CO₂RR intermediates, especially the selectivity-determining intermediates *OCCO and *CH₂CHO on Cu(hkl) surfaces. Combining the spectroscopic results with theoretical calculations, Cu(111) facilitates the generation of C₁ products through the formation of *COOH and *CO, while Cu(110) further generates C₂ through the pathway of *OCCO and *CH₂CHO. In addition, high KHCO₃ concentrations facilitate the formation of the *OCCO structure, promoting C₂ products. This work provides a significant breakthrough for understanding the CO₂RR mechanism that can guide the design of high-efficiency catalysts.