Sulfur-assisted ammonia treatment of a fibrous carbon matrix to fabricate a high-content pyrrole-type Fe–N–C catalyst for superior oxygen reduction

Abstract

High-content pyrrole-type metal–nitrogen–carbon (M–N–C) catalysts are emerging as promising candidates in the electrocatalytic oxygen reduction reaction (ORR); however, it is still challenging to achieve their effective synthesis. Herein, we successfully prepared a high-content pyrrole-type Fe–N–C catalyst through ammonia treatment assisted with sulfur, starting with the electrospinning of imidazole coordination polymer fibers. The hierarchical porous fiber-derived carbon matrix not only works as an excellent receiver to anchor Fe atoms, but also benefits ammonia diffusion and the replacement of sulfur atoms during secondary sintering. The ammonia treatment with pre-sulfur doping is experimentally and theoretically proved to be favorable for the etching of carbon atoms and creation of pyrrole-type N sites. The optimized pyrrole-type Fe–N–C catalyst shows excellent ORR activity (E_1/2 = 0.89 V; J_L = 5.58 mA cm⁻²). The as-assembled Zn–air battery also shows remarkable power density and rechargeable performance. This work provides a novel method to prepare a high-content pyrrole-type M–N–C catalyst with a fibrous structure, which can be used in designing advanced electrocatalysts for various sustainable energy devices.