(726f) Directing Selectivity of Electrochemical CO2 Reduction at Plasmonic Cathodes

Electrochemical carbon dioxide (CO₂) reduction can be part of the solution to reducing greenhouse gas emissions by converting CO₂ into valuable fuels or chemicals. The greatest challenge in CO₂ reduction is selectively making a single product at a low applied overpotential. To address this challenge, we study plasmonic cathodes which, upon illumination, can both alter the selectivity and lower the onset potential of electrochemical reactions. This can occur when hot electrons, formed by the decay of the plasmon oscillation, interact with adsorbed species at the surface of the electrode. Our research aims to understand the role plasmonically generated hot electrons play in directing the selectivity of CO₂ reduction at voltage-biased cathodes.

We study this reaction in a custom temperature-controlled gas flow cell. CO₂ flowing through the cell can be pre-mixed in precise ratios with argon for CO₂ partial pressure experiments. The cell temperature can be held at a constant 22 C during both dark and illuminated experiments and permits temperature variation studies. Precise product quantification is achieved by an in-line gas chromatograph for gaseous products and by ex situ NMR for liquid products. We explore variations in product distribution with changes in electrochemical potential, illumination intensity, light wavelength, and the plasmonic catalyst. We demonstrate that illumination of a voltage-biased plasmonic silver cathode selectively enhances CO₂ reduction products while simultaneously suppressing undesired hydrogen evolution. Strikingly, methanol is produced only upon illumination, representing an improvement in both selectivity and efficiency. These results indicate that by tuning the cathode structure and composition we can achieve greater plasmonic enhancements in selectivity and activity towards hydrocarbon products from CO₂ reduction.

This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.

The work is supported by the National Science Foundation under Grant No. 1106400 (Graduate Research Fellowship) and CBET-1653430 (CAREER, Electrochemical Systems Program).

Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.