Mechanistic insights into the effect of halide anions on electroreduction pathways of CO2 to C1 product at Cu/H2O electrochemical interfaces

Abstract

Various elementary reaction steps during CO₂ electroreduction into C₁ product are systematically studied at specifically adsorbed halide anions modified Cu(111)/H₂O interfaces via theoretical calculations with the aim of identifying the effect of halide anions X⁻ (X = F, Cl, Br, I) on CO₂ electroreduction reaction activity, mechanisms and product selectivity in this work. Our present studies show that halogen atoms can be adsorbed on the Cu electrodes during CO₂ electroreduction, thus leading to notable electronic interactions between halogen atoms and Cu(111)/H₂O interface. It is found that halogen atoms can gain electrons in the order of F > Cl > Br > I, showing that the adsorbed halide anions can be formed. The presence of halide anions can notably be favor of CO formations. CO electroreduction pathways towards C₁ product at Br⁻ and I⁻ modified Cu(111)/H₂O interfaces are examined due to poor selectivity of CO electroreduction into CHO at F⁻ and Cl⁻ modified Cu(111)/H₂O interfaces. The calculated results indicate that the presence of Br⁻ and I⁻ facilitate CO₂ electroreduction into C₁ product since notably enhanced CO₂ electroreduction activity can be achieved, which may be ascribed to the formations of chemically adsorbed anion radical ˙CO₂⁻ and more positive onset potentials for CO formations. Notably, it is found that the electroreduction pathways of CO₂ into CH₄ and CH₃OH product may be able to parallelly occur at Br⁻ and I⁻ modified Cu(111)/H₂O interfaces, whereas only CH₄ production pathways can occur at clean Cu(111)/H₂O interface. Thus, it can be concluded that the presence of halogen anions on Cu alter mechanism and product selectivity of CO₂ electroreduction. Our present mechanistic insights into this effect may be able to give a theoretical guideline for control of mechanisms and product selectivity during CO₂ electroreduction.