By altering the flow rate of CO2, we showed that although higher single-pass carbon efficiency (SPCE) values could be obtained, the highest HCOO -selectivity was observed with a minimum flow rate of 15 mL min -1 (SPCE = 14%) (Fig. ). We paired the Cu-SPy GDE with a Ni foam anode for water oxidation to drive full-cell CO2R over the course of 6 h. At -300 mA cm -2 , a low and stable full-cell potential (Ecell) of -2.7 V was obtained with a steady average FEHCOO-value of approximately 67%, giving a full-cell energy efficiency for HCOO -of 31% and a SPCE of 14% (Fig. ). No additional SPy was found in solution throughout electrolysis showing that the molecule was stable on the surface (Table ), and replacement of the electrolyte solution after 6 h showed that the high FEHCOO-was retained (Fig. ), thereby ruling out contributions from solution-dissolved species.