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Electrochemical CO2 reduction targets the electrolytic conversion of carbon dioxide to more useful fuels and chemicals. Most metal electrocatalysts produce two-electron reduced products from CO2 reduction (CO, COOH-) with some selectivity over the reduction of protons to H2 in water. Cu is a unique electrocatalyst in that it can produce a range of multi-electron products, including C2 (ethylene, ethanol, acetaldehyde) and C3 (ethylene glycol, propanol) molecules. The broad range of products formed on Cu present a different challenge, namely in tailoring the selectivity of products by modifying the reaction conditions or electrode structure. Sonoelectrochemical electrolysis offers opportunities for improving the selectivity of CO2 reduction. Ultrasonic agitation of the electrolyte can improve mass transport to the electrode interface compared to stagnant solutions and generate radicals that contribute to the electrochemical transformations. Here, we describe experiments to understand the effects of sonoelectrochemical reactors for the selectivity of carbon dioxide reduction on polycrystalline Cu electrodes. We explore the multiple effects that sonication can have on the reaction, including improved mass transport and thermal effects on the electrolyte. In temperature-controlled sonoelectrochemical experiments we observe a change in the electrolytic CO2 branching ratios, with a particular shift towards the formation of liquid-phase products. Finally, we detail the potential for combining sonoelectrochemical CO2 reduction to other strategies for targeted selectivity on Cu in new reaction schemes.

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