Direct Observation of Surface-Bound Intermediates in CO/CO<sub>2</sub> Reduction on a Polycrystalline Cu Electrode Using Broad-Band SFG Spectroscopy
XiaoLin Liu, YinYi Ma, Qian‐Tong Song, Hao Huang, Yuhan He, Shi‐Gang Sun, Zhaohui Wang
Abstract
Interface-specific detection of adsorbed key intermediates and product species on the Cu electrode is critical for unraveling the electrocatalytic mechanism of CO 2 reduction. In this study, Cu-catalyzed electrocatalysis of CO and CO 2 reduction (COR and CO 2 R, respectively) is investigated using in situ broad-band sum-frequency generation (BB-SFG) spectroscopy. By analysis of the potential-dependent SFG spectra of surface-bound CO (*CO) and possible intermediates in the C–H stretching vibrational range, valuable insights into the electrocatalysis of CO 2 R are obtained. The SFG spectra of the C–H vibrations reveal two distinct adsorption configurations of surface-bound ethoxy (“standing” and “lying”) on Cu, which provides new molecular evidence to support the presence of C 2 intermediates with the atoms of O and C at both ends attached to the Cu surface in the pathway leading to ethanol formation. Moreover, we observed distinct potential-dependent SFG features of *CO in COR and CO 2 R, while the ethoxy intermediates and product distributions are nearly identical, suggesting that the dimerization of *CO might not be the rate-determining step for the C–C coupling to form ethanol. With these findings, we present a mechanistic scheme for the formation of C 1 and C 2 products with surface-bound CO and ethoxy intermediates for the formation of ethanol.