High specific surface area Fe–N–C electrocatalysts for the oxygen reduction reaction synthesized by a hard-template-assisted ball milling strategy

Abstract

Non-noble metal iron-based catalysts, featuring an abundant atomically dispersed Fe–nitrogen–carbon (Fe–N–C) structure, have been identified as highly promising alternatives to platinum group metal (PGM) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, there are still huge challenges in synthesizing high-performance Fe–N–C catalysts via the traditional mechanochemical method assisted only by the assisted liquid. In this study, we utilized a hard-template-assisted mechanochemical strategy followed by high-temperature pyrolysis to synthesize Fe–N–C catalysts with high specific surface area (1444.4 m² g⁻¹), due to the improved ZIF-8 precursor and the uniform distribution of the Fe–N–C motif. The introduction of NaCl as an unaltered hard template during the mechanochemical reaction not only improved the conversion efficiency and porous carbon framework of the precursor, but also optimized the distribution of the metal element, providing greater possibilities for the traditional ball milling method. Benefitting from the precise doping control and porous carbon framework, the optimized 2%Fe-ZIF@NaCl electrocatalyst demonstrated a high half wave potential (E_1/2 = 0.831 V) in acidic media and a promising maximum power density (504 mW cm⁻²) in H₂–O₂ PEMFCs. The hard template expands the application scenarios of mechanochemical methods on the basis of the assisted liquid method.