CO Residence Time Modulates Multi-Carbon Formation Rates in a Copper Based Zero Gap CO2 Electrolyzer

Abstract

Carbon dioxide (CO2) electrolysis on copper (Cu) catalysts has attracted interest for its direct production of C2+ feedstocks. Using the knowledge that CO2 reduction on copper is primarily a tandem reaction of CO2 to CO and CO to C2+ products, we show that modulating CO concentrations within the liquid catalyst layer allows for C2+ selectivity of > 80 % at 200 mA cm-2 in a membrane electrode assembly over broad conversion conditions. The importance of CO pooling is demonstrated through residence time distribution curves, varying flow fields (serpentine/parallel/interdigitated), and flow rate. While serpentine flow fields require high conversions to limit CO selectivity and maximize C2+ selectivity, the longer CO residence times of parallel flow fields reach similar selectivity over broad flow rates. Critically, we show that parts of the catalyst area are predominantly reducing CO instead of CO2 as supported by CO reduction experiments and transport modelling of the reactor. In addition, higher cation crossover from the anolyte is shown to maximize C2 + selectivity providing further evidence of cation effect on C-C coupling rates.