(79g) Photoelectrochemical CO2 Reduction at Plasmonic Nanostructured Silver Electrodes

Electrochemical CO₂ reduction could help mitigate carbon emissions while producing valuable fuels or chemical feedstocks. However, inefficiency and low selectivity toward a hydrocarbon product have limited the commercial viability of this process. Plasmonic hot-carriers and the strong local electric fields produced by plasmon excitation may open new pathways for CO₂ reduction, resulting in increased product selectivity and lower overpotential. Our research aims to understand the fundamentals underlying plasmon-generated excited charge transfer from voltage-biased cathodes to CO₂ reduction intermediates to selectively and efficiently form desirable hydrocarbon products.

We have designed a custom gas flow cell to probe the mechanism of plasmon-enhanced CO₂ reduction on nanostructured noble metal electrodes fabricated by nanosphere lithography. This temperature-controlled photoelectrochemical cell is specifically designed to allow quantitative analysis of gaseous and liquid products formed at an illuminated working electrode. The geometry of the cell enables front-illumination of the photoelectrode and maximizes the electrode surface area to electrolyte volume ratio to increase liquid product concentration and hence enhance ex situ spectroscopic sensitivity towards them. Gas is bubbled through the electrolyte in the working electrode chamber during operation to maintain a saturated reactant concentration and to continuously mix the electrolyte. Gaseous products are detected by an in-line gas chromatograph, and liquid products are analyzed ex situ by NMR. Product distribution and photocurrent are measured while varying electrochemical potential, illumination intensity, light wavelength, temperature, and the plasmonic catalyst. We demonstrate that plasmonic photocurrent on voltage-biased silver (Ag) nanopyramid cathodes is selective for CO₂ reduction over the competing hydrogen evolution reaction. Our results suggest that further plasmonic enhancements in selectivity and activity towards specific CO₂ reduction reactions are possible by tuning the electrode structure and composition.

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 Graduate Research Fellowship under Grant No. 1106400.

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.