Addressing electrolyte composition effects in CO2 electroreduction

Graphs showing CO bound to the Cu(100( hollow site (Download Image)

Restructuring and concentration of K+ ions over a model Cu(100) catalyst surface as the applied voltage is shifted from (a) –0.2 V/RHE to (b) –1.0 V/RHE. CO is shown bound to the Cu(100) hollow site.

The electrochemical conversion of CO2 into chemical fuels and other commodity products is an attractive strategy for mitigating carbon emissions while offsetting the use of fossil resources. Nevertheless, the adoption of such approaches in industrial settings has been limited by the poor efficiency and selectivity of the electrochemical cells that are used to drive CO2 electroreduction. One way that researchers have found to improve these crucial performance metrics is to alter the composition of the electrolytes that are used in these electrochemical cells. However, progress in this area is often slowly made by following an Edisonian-style search, where new electrolytes are tested in benchtop experiments on a trial-and-error basis following empirical trends and the chemical intuition of researchers.

In a recent study, scientists from LLNL have laid the groundwork for developing accurate theory-based assays that can accelerate electrolyte screening for electrochemical CO2 conversion applications. The team employed hybrid quantum–classical simulations that are capable of describing the delicate interplay between applied electrical potentials and the composition and structure of the reaction microenvironment. They show that CO, a key selectivity-determining reaction intermediate, is induced by solvent and electrolyte restructuring effects to bind to active sites on copper catalyst terraces known to promote the formation of desirable C2 products such as ethylene and ethanol. The study also revealed that the relative driving force to bind to these particular active sites is enhanced with increasing cathodic potentials and more alkaline environments, underscoring the strong interplay between applied potential and microenvironment effects on the electroreduction of CO2.

This work was supported through the Laboratory Directed Research and Development Program (19-SI-005 and 18-FS-019).

[S.E. Weitzner, S.A. Akhade, J.B. Varley, B.C. Wood, M. Otani, S.E. Baker, and E.B. DuossToward Engineering of Solution Microenvironments for the CO2 Reduction Reaction: Unraveling pH and Voltage Effects from a Combined Density-Functional–Continuum TheoryJ. Phys. Chem. Lett. 11(10), 4113–4118 (2020), doi: 10.1021/acs.jpclett.0c00957.]