Bicarbonate Rebalances the *COOH/*OCO^– Dual Pathways in CO₂ Electrocatalytic Reduction: In Situ Surface-Enhanced Raman Spectroscopic Evidence

Abstract

Understanding the reactive site/CO2/electrolyte interfacial behaviors is very crucial for the design of an advantageous CO2 electrocatalytic reduction (CO2ER) system. One important but unrevealed question is how the CO2ER process is influenced by the high concentration of HCO3 –, which is deliberately added as electrolyte or from the inevitable reaction between dissolved CO2 and OH–. Here, we provide unambiguous in situ spectroscopic evidence that on Ag-based catalysts, HCO3 – is apt to facilitate *OCO– generation and therefore rebalances CO2ER pathways. By employing an alternative acid electrolyte to restrict the exchange between CO2 and HCO3 – and eliminating the effect of solution pH, we reveal that HCO3 – can decrease the onset potential of *OCO– and promote further formate production. Theoretical calculations indicate HCO3 – can stabilize the adsorption of *OCO– instead of *COOH. The renewed understanding of the role of HCO3 – could facilitate the judicious selection of electrolytes to regulate the CO2ER pathway and product distribution.

In situ scanning tunneling microscopy studies of carbonate-induced restructuring of Ag-decorated Cu(100) electrodes

“…35 This is also supported by a recent surface-enhanced Raman spectroscopy study of nanoporous CuAg electrodes in 0.1 M KHCO 3 , where CO and COOH adsorbates were only adsorbed at ≤−0.3 V, that is, at considerably more negative potentials. 36…”

The Missing Link for Electrochemical CO2 Reduction: Classification of CO vs HCOOH Selectivity via PCA, Reaction Pathways, and Coverage Analysis

“…We observe that all the metals are nicely grouped according to their main product color. Note especially the separation between the CO- (blue) and HCOOH-producing (yellow) metals, which previous descriptor plots were unable to fully separate. ,,,− All four PCA plots describe 70+% of the variation in the data set (additional PCA plots and discussion can be found in the Supporting Information section “Additional PCA Results”). This is a strong indicator that 2D and 3D representations of metal catalyst product distribution are suitable.…”

“…Several studies have tried to give an explanation regarding CO vs HCOOH selectivity. ,,,− Many hypotheses have been made as to what critical factors need to be considered in theoretical calculations to explain this part of CO 2 R product selectivity, such as pH, cations, surface structure, the amount of water molecules in solution, the binding energy and coverage of protons on the surface, steric constraints, and adsorbate–adsorbate interactions. Here, we provide a comprehensive, data-based explanation, aiming to reproduce the experimental trends with DFT calculations and explaining CO vs HCOOH selectivity, utilizing descriptor analysis, reaction barriers, and catalyst surface coverage.…”

Unveiling the effects of ions in the electric double layer on the carbon dioxide reduction reaction

“…Moreover, Shan et al noted that HCO 3 − could improve the stability of the intermediate *OCO − on the surface, hence facilitating the formation of this intermediate and further formate. 121…”

“…Moreover, Shan et al noted that HCO 3 À could improve the stability of the intermediate *OCO À on the surface, hence facilitating the formation of this intermediate and further formate. 121 In terms of non-buffering anions, the formed higher local pH gave better selectivity to ethylene (C 2 H 4 ) (445%) and total C 2+ products (465%). Especially for halide anions of Cl À , Br À and I À , they could specifically adsorb on the surface of catalysts, changing surface morphologies and surface charges during the CO 2 RR.…”