Probing Cation Effects on *CO Intermediates from Electroreduction of CO<sub>2</sub> through Operando Raman Spectroscopy
Si Young Lee, Jimin Kim, Gwangsu Bak, Eunchong Lee, Dayeon Kim, Suhwan Yoo, Jiwon Kim, Hyewon Yun, Yun Jeong Hwang
Abstract
Cations in an electrolyte modulate microenvironments near the catalyst surface and affect product distribution from an electrochemical CO 2 reduction reaction, and thus, their interaction with intermediate states has been tried to be probed. Herein, we directly observed the cation effect on *CO intermediates on the Cu(OH) 2 -derived catalyst in real time through operando surface-enhanced Raman spectroscopy at high overpotentials (−1.0 V RHE ). Atop *CO peaks are composed of low-frequency binding *CO (*CO LFB ) and high-frequency binding *CO (*CO HFB ) because of their adsorption sites. These two *CO intermediates are found to have different sensitivities to the cation-induced field, and each *CO is proposed to be suitably stabilized for efficient C–C coupling. The proportions between *CO HFB and *CO LFB are dependent on the type of alkali cations, and the increases in the *CO HFB ratio have a high correlation with selective C 2 H 4 production under K + and Cs +, indicating that *CO HFB is the dominant and fast active species. In addition, as the hydrated cation size decreases, *CO LFB is more sensitively red-shifted than *CO HFB, which promotes C–C coupling and suppresses C 1 products. Through time-resolved operando measurements, dynamic changes between the two *CO species are observed, showing the rapid initial adsorption of *CO HFB and subsequently reaching a steady ratio between *CO LFB and *CO HFB .