Co-electroreduction of CO and glyoxal promotes C3 products.

The conversion of CO2 and CO using electricity offers a promising, sustainable approach to achieve valuable products. Although CO electroreduction to C1 and C2 products has seen rapid progress in efficiency and production rate, C3 synthesis remains a major challenge. Here we show that C3 products lie along the ethylene pathway by using a probe reactant and isotope-labelled CO. We find that glyoxal addition promotes C3 formation while suppressing acetate/ethanol production, while itself scarcely being consumed. Spectroscopy reveals lower CO* coverage in the presence of glyoxal. Reaction-order experiments show higher coverages of CO* and of OH- species linked to suppressing ethylene in favour of C3. By combining both strategies to suppress ethylene formation with an abundance of OH- and blocking acetate/ethanol formation with glyoxal, we report a high selectivity for C3 products, including a 53% Faradaic efficiency. These insights aid the design of future catalysts for C3 production.