Trace level of atomic copper in N-doped graphene quantum dots switching the selectivity from C1 to C2 products in CO electroreduction

To unravel the relationship between trace Cu on the metal-free catalysts toward CO/CO2 reduction reaction (CO/CO2RR), we investigated the effect of trace Cu loading in N-doped graphene quantum dots (NGQDs) on CO/CO2RR. A general trend is that increasing the Cu loading in NGQDs switches the selectivity from C1 (CH4) to C2 products in CORR. When 2.5 μg/cm2 Cu with the atomic size is loaded on NGQDs, the selectivity shifts from 62% Faradaic efficiency (FE) of CH4 to 52% FE of C2 products in CORR. Further increasing the atomic Cu loading to 3.8 μg/cm2 promotes the FE of C2 products to 78%. CO2RR requires one order of magnitude higher Cu loading than CORR to switch the selectivity from C1 to C2 products due to the low partial pressure of CO. This study clarifies the distinct impact of trace (ppm level) Cu on the activity/selectivity between CORR and CO2RR. [Display omitted] •The effect of trace Cu loading in NGQDs on CO/CO2RR was investigated systemically.•The trace Cu can switch products from C1 to C2 with major acetate product in CORR.•A similar trend was observed in CO2RR, while more Cu loading is required.•The highest mass activity reaches 124 A/mg1 Cu in CORR.•A mechanism is proposed for the selectivity shift in CORR.