Plasmon-Enhanced Electrochemical Reduction of Carbon Dioxide at a Copper-Silver Cathode

Carbon dioxide (CO₂) reduction can prevent emission of CO₂ into the atmosphere while simultaneously generating valuable products such as renewable fuels and chemical precursors. The fundamental challenge in CO₂ reduction is selectively producing multiple-carbon-containing compounds that have higher energy density or higher value than single carbon products. To address this challenge, we study plasmonically active cathodes that can both alter the selectivity and decrease the onset potential of electrochemical reactions upon illumination. Our research aims to understand the mechanism of plasmon-enhanced electrocatalysis and how it can be used to direct the selectivity of CO₂ reduction at voltage-biased cathodes.

We electrochemically deposited copper nanostructures on a silver foil and coated them with 10 nm of silver to create a plasmonically active cathode. The catalyst was stable for multiple days of electrochemical experiments. Illumination with 365 nm light, close to the plasmon resonance of silver, selectively enhanced some CO₂ reduction products while simultaneously suppressing undesired hydrogen evolution. At -1.0 V_RHE, ethylene, methane, formate, and products containing three carbons were enhanced upon illumination while the selectivity of carbon monoxide decreased. We investigated the product distribution trends with temperature and found that local heating, a potential plasmonic mechanism, cannot account for the selectivity changes observed in the light. This enhancement of select CO₂ reduction products is a promising demonstration of the potential for plasmon-enhanced electrochemical conversion.

This work was largely supported by the National Science Foundation, Grant No. CBET-1653430. Work was primarily performed at the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy, Award No. DE-SC0004993. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy, Contract No. DE-AC02-05CH11231.