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Abstract Bis‐porphyrin nanocages (M₂BiCage, M = FeCl, Co, Zn) and their host‐guest complexes with C₆₀and C₇₀were used to examine how molecular porosity and interactions with carbon nanomaterials affect the CO₂reduction 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 CO₂to CO. A complex of C₇₀bound inside(FeCl)₂BiCageachieves 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), andCo₂BiCageachieves high turnover frequencies (≈1300 h⁻¹,η= 520 mV) with 90% FE_CO. In general, blocking the pore with C₆₀or C₇₀improves the catalytic performance of(FeCl)₂BiCageand has only small effects onCo₂BiCage, 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 C₆₀/C₇₀to improve the performance of(FeCl)₂BiCage, in contrast to effects often proposed for other carbon nanosupports.