Solvent Effect on Electrochemical CO2 Reduction Reaction on Nanostructured Copper Electrodes

Connor Deacon-Price; Alisson H M da Silva; Cássia S Santana; Marc T M Koper; Amanda C Garcia

doi:10.1021/acs.jpcc.3c03257

Solvent Effect on Electrochemical CO₂ Reduction Reaction on Nanostructured Copper Electrodes

J Phys Chem C Nanomater Interfaces. 2023 Jul 12;127(29):14518-14527. doi: 10.1021/acs.jpcc.3c03257. eCollection 2023 Jul 27.

Authors

Connor Deacon-Price¹, Alisson H M da Silva², Cássia S Santana¹, Marc T M Koper², Amanda C Garcia¹

Affiliations

¹ Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands.
² Leiden Institute of Chemistry, Leiden University, Gorlaeus Laboratories, P.O. Box 9502, 2300 RA, Leiden, The Netherlands.

Abstract

The electrochemical reduction of CO₂ (CO₂RR) is a sustainable alternative for producing fuels and chemicals, although the production of highly desired hydrocarbons is still a challenge due to the higher overpotential requirement in combination with the competitive hydrogen evolution reaction (HER). Tailoring the electrolyte composition is a possible strategy to favor the CO₂RR over the HER. In this work we studied the solvent effect on the CO₂RR on a nanostructured Cu electrode in acetonitrile solvent with different amounts of water. Similar to what has been observed for aqueous media, our online gas chromatography results showed that CO₂RR in acetonitrile solvent is also structure-dependent, since nanocube-covered copper (CuNC) was the only surface (in comparison to polycrystalline Cu) capable of producing a detectable amount of ethylene (10% FE), provided there is enough water present in the electrolyte (>500 mM). In situ Fourier Transform Infrared (FTIR) spectroscopy showed that in acetonitrile solvent the presence of CO₂ strongly inhibits HER by driving away water from the interface. CO is by far the main product of CO₂RR in acetonitrile (>85% Faradaic efficiency), but adsorbed CO is not detected. This suggests that in acetonitrile media CO adsorption is inhibited compared to aqueous media. Remarkably, the addition of water to acetonitrile has little quantitative and almost no qualitative effect on the activity and selectivity of the CO₂RR. This indicates that water is not strongly involved in the rate-determining step of the CO₂RR in acetonitrile. Only at the highest water concentrations and at the CuNC surface, the CO coverage becomes high enough that a small amount of C₂₊ product is formed.