Mechanistic insight into electrocatalytic glyoxal reduction on copper and its relation to CO₂ reduction

Copper electrodes produce several industrially relevant chemicals and fuels during the electrochemical CO₂ reduction reaction (CO₂RR). Knowledge about the reaction pathways can help tune the reaction selectivity toward higher-value products. To probe the uncertain role of the C₂ 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 CO₂RR 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 CO₂RR, this study gives new directions to facilitate the electrification of chemical processes at refineries.