High Durability of a 14-Membered Hexaaza Macrocyclic Fe Complex for an Acidic Oxygen Reduction Reaction Revealed by In Situ XAS Analysis

Junya Ohyama; Makoto Moriya; Ryo Takahama; Kazuki Kamoi; Shin Kawashima; Ryoichi Kojima; Teruaki Hayakawa; Yuta Nabae

doi:10.1021/jacsau.1c00309

High Durability of a 14-Membered Hexaaza Macrocyclic Fe Complex for an Acidic Oxygen Reduction Reaction Revealed by In Situ XAS Analysis

JACS Au. 2021 Sep 20;1(10):1798-1804. doi: 10.1021/jacsau.1c00309. eCollection 2021 Oct 25.

Authors

Junya Ohyama¹, Makoto Moriya^{2

3}, Ryo Takahama³, Kazuki Kamoi³, Shin Kawashima⁴, Ryoichi Kojima⁴, Teruaki Hayakawa⁵, Yuta Nabae⁵

Affiliations

¹ Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan.
² College of Science, Academic Institute, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan.
³ Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan.
⁴ Corporate Research & Development, Asahi Kasei Corporation, 2767-11 Niihama, Shionasu, Kojima, Kurashiki, Okayama 711-8510, Japan.
⁵ Department of Materials Science and Engineering, Tokyo Institute of Technology, 2-12-1 S8-26, Ookayama, Meguro-ku, Tokyo 152-8552, Japan.

Abstract

Nonplatinum metal (NPM) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) have been developed; however, NPM catalysts still need to be improved in terms of both their catalytic activity and durability. To overcome these problems, an Fe active site contained within a more compact ligand than conventional, porphyrinic, 16-membered ring ligands, or more specifically, a hexaaza macrocyclic ligand with a 14-membered ring (14MR), was developed. In this study, the durability of the Fe-14MR complex was compared to that of Fe phthalocyanine (FePc), which has a 16-membered ring ligand, using in situ X-ray absorption spectroscopy; demetalation of the Fe complexes was directly observed during electrochemical experiments performed under acidic ORR conditions. It was found that Fe-14MR is significantly more resistant to demetalation than FePc during the ORR.