Theoretical understanding of the effect of specifically adsorbed halide anions on Cu-catalyzed CO2 electroreduction activity and product selectivity

Abstract

Initial CO₂ electroreduction into CO and its subsequent electroreduction pathways were selected to study the effect of specifically adsorbed halide anions X⁻ (X = F, Cl, Br, I) on CO₂ electroreduction activity and product selectivity at Cu(111)/H₂O interfaces via DFT calculations. The calculated results show that the presence of halide anions can exert a notable effect on the CO₂ adsorption characteristics and that chemically adsorbed CO₂ molecules can be formed. Furthermore, the halide-anion-modified Cu(111)/H₂O interfaces could significantly enhance the initial CO₂ electroreduction into CO activity, which is regarded as the rate-determining step during CO₂ electroreduction at clean Cu(111)/H₂O interfaces. Analysis of the initial CO₂ electroreduction and Volmer reaction pathways showed that the halide-anion-modified Cu(111)/H₂O interfaces could suppress the HER and thus improve the CO₂ electroreduction activity and product selectivity. It is speculated that the enhanced initial CO₂ electroreduction activity at the F⁻-, Cl⁻-, Br⁻-, and I⁻-modified Cu(111)/H₂O interfaces may originate from the decreased work functions and anion radical ^·CO₂⁻ formations. Simultaneously, we concluded that dimer OCCO formations in the presence of halide anions were more favorable than CHO during CO electroreduction according to the order of I⁻ > Br⁻ > Cl⁻ > F⁻ and could result in the production of C₂ product, suggesting an improved CO₂ electroreduction product selectivity. The present analyses of electronic structure may explain the more favorable OCCO formations in the order of I⁻ > Br⁻ > Cl⁻ > F⁻. The present understanding of this effect will provide an improved scientific guideline for the control of CO₂ electroreduction pathways and design of more efficient electrocatalysts.