Microenvironmental Regulation of Fe─N 4 Catalytic Sites for Oxygen Reduction Reaction in Electrochemical Devices

The non-metallic-Pt materials with high activities for oxygen reduction reaction (ORR) have attracted considerable attentions, but still face challenges related to the mismatched performance in device applications, especially for the atomic site catalysts. In this work, we propose a microenvironment-regulation strategy on introducing amino-fluorinated cyclotriphosphazene as grafting agents to address the critical issue on the mass-transfer limitations for the highly active and well-defined Fe─N₄ sites in phthalocyanine macrocycles. When this functional cyclotriphosphazene was grafted to polyphthalocyanines by the amidate linkage, the large steric hindrance of cyclotriphosphazene and the low surface energy of C─F bonding in fluorinate groups provide the enriched channels with low hygroscopicity, which guarantees the oxygen supply to Fe─N₄ sites and the hydroxyl leave from catalyst molecules. This microenvironment regulation improves the activities of catalyst molecules in electrochemical testing, and an amplified effect are also shown in the corresponding electrode assemblies. As results, the superior peak power densities of 178 mW cm^-2 in aqueous Zn-air batteries (1.4-fold enhancements) and 616 mW cm^-2 in alkaline membrane fuel cells (2.5-fold enhancements) are obtained. These findings offer a deeper understanding of non-Pt catalysts and provide a promising approach to their applications in advanced electrochemical devices.