Green synthesis of hierarchical carbon coupled with Fe3O4/Fe2C as an efficient catalyst for the oxygen reduction reaction

Abstract

A green synthesis strategy is reported here for the fabrication of a hierarchical Fe-based carbon electrocatalyst for catalyzing the oxygen reduction reaction. This strategy involves the grinding of the organic ligand (1,4-benzenedicarboxylic acid) and metal salt (iron chloride hexahydrate) with a minute quantity of solvent at room temperature and thermal annealing under a N₂ atmosphere. The metal salt introduced plays dual roles. One is as a hard template for creating a hierarchical porous structure, which is important for controlling the overall mechanism and kinetics of the catalysis process by affecting the mass transport and exposure of active sites. The other one is as a metal source for building the MOF structure that can drive Fe₃O₄ and Fe₂C active sites for catalyzing the oxygen reduction reaction. Combining the merits of porosity and MOFs, the catalyst synthesized by 120 min grinding (BM-Fe@NC-120) possesses good ORR performance in 0.1 M KOH with a half-wave potential of 0.80 V, a limiting current density of −5.08 mA cm⁻², excellent long-term durability and resistance to methanol, indicating the validity of this eco-friendly route for scalable synthesis of catalysts for future practical fuel-cell applications.