A Planar, Conjugated N₄-Macrocyclic Cobalt Complex for Heterogeneous Electrocatalytic CO₂ Reduction with High Activity

Metal complexes have been widely investigated as promising electrocatalysts for CO₂ reduction. Most of the current research efforts focus mainly on ligands based on pyrrole subunits, and the reported activities are still far from satisfactory. A novel planar and conjugated N₄-macrocyclic cobalt complex (Co(II)CPY) derived from phenanthroline subunits is prepared herein, and it delivers high activity for heterogeneous CO₂ electrocatalysis to CO in aqueous media, and outperforms most of the metal complexes reported so far. At a molar loading of 5.93×10⁻⁸ mol cm⁻², it exhibits a Faradaic efficiency of 96 % and a turnover frequency of 9.59 s⁻¹ towards CO at −0.70 V vs. RHE. The unraveling of electronic structural features suggests that a synergistic effect between the ligand and cobalt in Co(II)CPY plays a critical role in boosting its activity. As a result, the free energy difference for the formation of *COOH is lower than that with cobalt porphyrin, thus leading to enhanced CO production. © 2020 Wiley-VCH GmbH