Nonprecious Bimetallic (Fe,Mo)–N/C Catalyst for Efficient Oxygen Reduction Reaction

Abstract

Developing highly efficient catalysts for cathodes remains an important matter of the research of fuel cells. Here, we report a bimetallic iron- and molybdenum-based nitrogen-doped carbon catalyst ((Fe,Mo)–N/C), acting as an efficient catalyst for oxygen reduction reaction (ORR) at the cathode. The catalyst was synthesized by pyrolysis of a complex precursor obtained through a facile ion-exchange process based on the hard–soft-acid–base (HSAB) principle. The dilution effect of Mo prevents Fe species from aggregation, leading to a high content of Fe. Besides, the synergistic catalysis effect of Fe and Mo enhances the graphitization degree of carbon, resulting in a high electrical conductivity of carbon at a relative low pyrolysis temperature (700 °C). Different initial Fe/Mo mole ratios were tested to determine the optimal catalyst. The (Fe,Mo)–N/C catalyst with Fe/Mo = 0.75 affords an excellent ORR activity, comparable to commercial Pt/C catalysts, and follows a four-electron mechanism under acidic conditions. Our present work demonstrates that both Fe–Nx and Mo–Nx can act as the active sites simultaneously. Notably, we have developed a versatile, new route toward the preparation of efficient catalysts with hierarchical porous structures for fuel cells.