(191c) Theoretical Insights into the Effects of Anion Identity and Concentration on Electrocatalytic Reduction of CO2 on Au

The electrochemical reduction of carbon dioxide to useful chemical precursors such as CO can enable the sustainable conversion of intermittent energy from renewable sources while lowering atmospheric CO₂ levels. Recent experimental results on Au and Ag in alkaline solutions show that increasing electrolyte concentration improved the current density by several folds to match economic viability criteria in addition to lowering the onset potential to form CO.

Potential dependent ab-initio molecular dynamics (AIMD) and density functional theory (DFT) methods have been used to provide insights into the reduction of CO in alkaline solutions on Au electrodes. We show that the adsorption of CO₂ proceeds together an electron transfer from the metal in the rate determining step. The interaction of the alkaline electrolyte anion (OH^-) with the catalyst increases the electron density at the Au electrode thus lowering the cathodic potential for e^- transfer. The onset potential for CO₂ reduction is calculated to change from -2.3 V to -1.5 V as the KOH concentration is increased which is consistent with experimentally observed improvements in current density. The first protonation of *CO₂ (-) leads to the formation of hydroxy carbonyl intermediate (*COOH) via the transfer of a proton from solvent H₂O molecule is more favorable than the protonation to form the formate anion from a near surface H₂O molecule due to the additional stabilization of the generated solvated OH^- species. The subsequent electron transfer and protonation of *COOH generates carbon monoxide and water as the final products of CO₂ reduction with small energy penalties. Spontaneously formed bicarbonate species are found to subsequently decompose at more cathodic potentials.

In this work, we provide mechanistic insights into the interplay between the electrolyte ions, the interface, and the adsorbed intermediates during CO₂ electroreduction to generate products with high selectivity and current density at acceptable overpotentials.