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To design an efficient electrocatalyst for CO 2 reduction, a comprehensive understanding of the catalytic architecture and the reaction mechanism is required. Herein, we synthesized and analyzed a series of fac-[Re(bpy-X) (CO) 3 Cl] (abbreviated as Re I (bpy-X); bpy-X = 4,4′-disubstituted-2,2′bipyridine; X = t Bu, CH 3 , mesityl, H, phenyl, and methyl ester) catalysts for electrocatalytic CO 2 reduction with and without adding the cocatalyst [Zn(cyclam)] 2+ (cyclam = 1,4,6,11tetraazacyclotetradecane). Both computational and experimental results show that in the experiments bearing the [Zn(cyclam)] 2+ cocatalyst, the Re(I) catalysts require less energy input to reduce the CO 2 , indicating that the CO 2 -to-CO conversion occurs at a lower overpotential. Interestingly, in the Re(I) electrocatalyst bearing a strong electron-withdrawing group (methyl ester), [Zn(cyclam)] 2+ does not improve the CO 2 reduction activity. These results emphasize the importance of how the electronic distribution throughout the molecular architecture can enhance or suppress the nucleophilicity of Re I (bpy-X) electrocatalysts, even in the presence of a cocatalyst.

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