Fourteen-Membered Macrocyclic Fe Complexes Inspired by FeN <sub>4</sub> -Center-Embedded Graphene for Oxygen Reduction Catalysis
Makoto Moriya, Ryo Takahama, Kazuki Kamoi, Junya Ohyama, Shin Kawashima, Ryoichi Kojima, Mariko Okada, Teruaki Hayakawa, Yuta Nabae
Abstract
For the broad application of polymer electrolyte fuel cells (PEFCs), the development of nonprecious-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; however, they suffer from low density and uncertain chemical structure of their active sites. This study reports a novel 14-membered macrocyclic Fe complex, which was inspired by FeN4 centers in pyrolyzed catalysts, unlike typical macrocyclic MN4 complexes that have 16-membered rings. This 14-membered macrocycle possesses strong Fe–N bonds with an average bond distance of 1.90 Å, as evidenced by single-crystal X-ray diffraction (XRD), which are markedly shorter than those in porphyrin (2.0 Å). This complex demonstrates high electrocatalytic activity for oxygen reduction in both acidic and basic media.