Using Host‐Guest Chemistry to Examine the Effects of Porosity and Catalyst‐Support Interactions on CO 2 Reduction

Abstract Bis‐porphyrin nanocages ( M 2 BiCage , M = FeCl, Co, Zn) and their host‐guest complexes with C 60 and C 70 were used to examine how molecular porosity and interactions with carbon nanomaterials affect the CO 2 reduction activity of metalloporphyrin electrocatalysts. The cages were found to adsorb on carbon black to provide electrocatalytic inks with excellent accessibilities of the metal sites (≈50%) even at high metal loadings (2500 nmol cm −2 ), enabling good activity for reducing CO 2 to CO. A complex of C 70 bound inside (FeCl) 2 BiCage achieves high current densities for CO formation at low overpotentials (| j CO | >7 mA cm −2 , η = 320 mV; >13.5 mA cm −2 , η = 520 mV) with ≥95% Faradaic efficiency (FE CO ), and Co 2 BiCage achieves high turnover frequencies (≈1300 h −1 , η = 520 mV) with 90% FE CO . In general, blocking the pore with C 60 or C 70 improves the catalytic performance of (FeCl) 2 BiCage and has only small effects on Co 2 BiCage , indicating that the good catalytic properties of the cages cannot be attributed to their internal pores. Neither enhanced electron transfer rates nor metal‐fullerene interactions appear to underlie the ability of C 60 /C 70 to improve the performance of (FeCl) 2 BiCage , in contrast to effects often proposed for other carbon nanosupports.