Mechanistic insight into electrocatalytic glyoxal reduction on copper and its relation to CO(2) reduction

Copper electrodes produce several industrially relevant chemicals and fuels during the electrochemical CO(2) reduction reaction (CO(2)RR). Knowledge about the reaction pathways can help tune the reaction selectivity toward higher-value products. To probe the uncertain role of the C(2) molecule glyoxal, we electrochemically reduced it on polycrystalline Cu and quantified its liquid-phase products, namely, ethanol, ethylene glycol, and acetaldehyde. The gas phase contained hydrogen and traces of ethylene. In contrast with previous hypothesis, a one-to-one comparison with CO(2)RR on Cu indicates that glyoxal is neither a major intermediate in the pathway toward ethylene nor in the pathway toward ethanol. In addition, great possibilities for the selective, low-temperature production of ethylene glycol are open, as computational modelling shows that ethylene glycol and ethanol are produced on different active sites. Thus, apart from the mechanistic insight into CO(2)RR, this study gives new directions to facilitate the electrification of chemical processes at refineries.