Fourteen-Membered Macrocyclic Fe Complexes for Oxygen Reduction Catalysis Inspired by FeN4 Centers Hosted by Graphene

For the globalization of polymer electrolyte fuel cells, the development of non-precious-metal (NPM) catalysts for oxygen reduction is extremely important. To date, many NPM catalysts have been synthesized by pyrolyzing Fe-, N-, and C-containing precursors, but they suffer from the density and uncertain chemical structure of their active sites. This study reports a 14-membered macrocyclic Fe complex, which was inspired by FeN₄ centers in the pyrolyzed catalysts, whereas typical macrocyclic MN₄ complexes have 16-membered rings. This 14-membered macrocycle has strong Fe-N bonding with an average bond distance of 1.90 Å, which has been evidenced by single-crystal X-ray diffraction, and is markedly shorter than that in porphyrin, 2.0 Å. Promising electrocatalytic activities for oxygen reduction have been demonstrated in both of acidic and basic media.