We next explored how FEMeOH varies with CNT diameter at -0.93 V (Supplementary Fig. and). The FEMeOH decreases from 53.2% for CoPc/SWCNT to 13.9 % for CoPc/50. The conversion of CO2 to MeOH involves six electron transfers, so that high charge transfer resistance will negatively affect FEMeOH. Electrochemical impedance spectroscopy (EIS) at -0.93 V shows that CoPc/SWCNT has less charge transfer resistance than CoPc/15 and CoPc/50, indicating more facile substrate reduction with CoPc/SWCNT (Supplementary Fig. ).