In Situ Surface-Enhanced Raman Spectroscopic Evidence on the Origin of Selectivity in CO₂ Electrocatalytic Reduction

Abstract

The electrocatalytic reduction of CO 2 (CO 2 ER) to liquid fuels is important for solving fossil fuel depletion. However, insufficient insight into the reaction mechanisms renders a lack of effective regulation of liquid product selectivity. Here, in situ surface-enhanced Raman spectroscopy (SERS) empowered by 13 C/ 12 C isotope exchange is applied to probing the CO 2 ER process on nanoporous silver (np-Ag). Direct spectroscopic evidence of the preliminary intermediates, *COOH and *OCO − , indicates that CO 2 is coordinated to the catalyst via diverse adsorption modes. Further, the relative Raman intensities of the above intermediates vary notably on np-Ag modified by Cu or Pd, and the liquid product selectivity also changes accordingly. Combined with density functional theory calculations, this study demonstrates that the CO 2 adsorption configuration is a critical factor governing the reaction selectivity. Meanwhile, *COOH and *OCO − are key targets in the initial stage regulating liquid product selectivity, which could facilitate future selective catalyst design.

The in situ study of surface species and structures of oxide-derived copper catalysts for electrochemical CO2 reduction

“…The CO 2 can be reduced to preliminary intermediates at low potentials, thus we can assume that the CuO x species were from the adsorption of preliminary intermediates (such as *CO 2 or *OCO -) on the Cu, which has been observed on the metal Ag. 43 From the above results, we can deduce that the CuO x existed during CO 2 RR was just the singal of chemisorption of CO 2 on Cu, which was not the main factor for facilitating C2+ products during CO 2 RR. And the CuO x species were not specific for the Cu oxide derived catalysts.…”

B‐Cu‐Zn Gas Diffusion Electrodes for CO2 Electroreduction to C2+ Products at High Current Densities

“…[18,31,32] These Raman signals remain essentially unchanged under operando conditions demonstrating the stability of the active Cu + species even at high reduction potentials.This is expected to contribute to the efficient conversion of CO 2 to C 2+ products at the comparatively high applied current densities. Operando electrochemistry Raman measurements were additionally used to detect possible intermediates of the eCO 2 RR on 0.5 B-Cu and 0.5 B-Cu:0.025 Zn electrodes.T he peak at 1072 cm À1 is assigned to the anti-symmetrical stretching of *OCO, [32,33] which can be observed from apotential of below À0.23 Vvs. RHE and increases in intensity at more cathodic potentials for the 0.5 B-Cu electrode ( Figure 5A).…”

“…This implies that the activation of CO 2 can be achieved at more positive potentials for the 0.5 B-Cu:0.025 Zn electrode additionally supporting the observed higher eCO 2 RR activity for the 0.5 B-Cu:0.025 Zn electrode as compared with the 0.5 B-Cu electrode ( Figure 4C). Raman peaks at 283, 344, and 2095 cm À1 for both 0.5B-Cu and 0.5 B-Cu:0.025 Zn electrodes correspond to adsorbed CO on Cu, [31][32][33][34] which represents the key intermediate for C À Cc oupling and C 2+ products formation. Thepeak at about 2713 cm À1 is associated to the C À H vibration [35] and further confirms the formation of hydrocarbons.…”

B‐Cu‐Zn‐Gasdiffusionselektroden für die elektrokatalytische CO2‐Reduktion zu C2+‐Produkten bei hohen Stromdichten

“…Operando-elektrochemische Raman-Messungen wurden zusätzlich eingesetzt, um mçgliche Zwischenstufen der eCO 2 RR an 0,5 B-Cu-und 0,5 B-Cu:0,025 Zn-Elektroden zu detektieren. Der Peak bei 1072 cm À1 wird der antisymmetrischen Streckung von *OCO zugeordnet, [32,33] der bei der 0,5 B-Cu-Elektrode ab einem Potential von unter À0,23 Vvs. RHE zu beobachten ist und bei kathodischeren Potentialen an Intensitätz unimmt (Abbildung 5A).…”

“…Dies impliziert, dass die Aktivierung von CO 2 bei positiveren Potentialen fürd ie 0,5 B-Cu:0,025 Zn-Elektrode erreicht werden kann, was zusätzlich die beobachtete hçhere eCO 2 RR-Aktivitätf ürd ie 0,5 B-Cu:0,025 Zn-Elektrode im Vergleich zur 0,5 B-Cu-Elektrode unterstützt (Abbildung 4C). Die Raman-Peaks bei 283, 344 und 2095 cm À1 sowohl fürd ie 0,5 B-Cu-als auch fürd ie 0,5 B-Cu:0,025 Zn-Elektroden entsprechen dem adsorbierten CO auf Cu, [31][32][33][34] welches das Schlüsselintermediat fürd ie C-C-Kupplung und die Bildung von C 2+ -Produkten darstellt. Der Peak bei ca.…”