Mechanistic reaction pathways of enhanced ethylene yields during electroreduction of CO-CO co-feeds on Cu and Cu-tandem electrocatalysts.

Unlike energy efficiency and selectivity challenges, the kinetic effects of impure or intentionally mixed CO feeds on the catalytic reactivity of the direct electrochemical CO reduction reaction (CO2RR) have been poorly studied. Given that industrial CO feeds are often contaminated with CO, a closer investigation of the CO2RR under CO/CO co-feed conditions is warranted. Here, we report mechanistic insights into the CO2RR reactivity of CO/CO co-feeds on Cu-based nanocatalysts. Kinetic isotope-labelling experiments-performed in an operando differential electrochemical mass spectrometry capillary flow cell with millisecond time resolution-showed an unexpected enhanced production of CH, with a yield increase of almost 50%, from a cross-coupled CO-CO reactive pathway. The results suggest the absence of site competition between CO and CO molecules on the reactive surface at the reactant-specific sites. The practical significance of sustained local interfacial CO partial pressures under CO depletion is demonstrated by metallic/non-metallic Cu/Ni-N-doped carbon tandem catalysts. Our findings show the mechanistic origin of improved C product formation under co-feeding, but also highlight technological opportunities of impure CO/CO process feeds for HO/CO co-electrolysers.