Unexpected catalytic performance of Fe-M-C (M = N, P, and S) electrocatalysts towards oxygen reduction reaction: surface heteroatoms boost the activity of Fe2M/graphene nanocomposites

The rational design of non-noble materials as low-cost, highly efficient, and durable catalysts to improve the oxygen reduction reaction is extremely urgent and challenging. The oxygen reduction reaction is a kinetically sluggish process that greatly affects the energy conversion efficiency. In this paper, novel hierarchical heteroatoms-co-doped Fe2M/graphene (M = P, N) nanocomposites were developed by a facile strategy, including hydrothermal and subsequent calcination methods. The thermal treatment of an ionic liquid and thiourea not only supplied heteroatom sources but also promoted the formation of iron phosphide and iron nitride and enhanced their catalytic performances. The electrochemical results indicated that the as-obtained hybrid catalysts manifested enhanced electrocatalytic activity toward the oxygen reduction reaction owing to the strong synergistic effects. The high content of heteroatoms distributed on the surface and interface of the hybrids and the density functional theory calculations suggested that Fe-N-C, Fe-P-C, and Fe-S-C multiple active surface sites were formed at the hybrids interfaces. Moreover, these results demonstrated that heteroatom-doped catalysts could effectively form a charge-transfer channel and thus modify the charge distribution in the hybrids interfaces. The as-prepared heteroatoms-doped Fe2M/graphene hybrids would be developed into highly efficient catalysts as ideal alternatives for noble metal catalysts in practical applications.