Nowadays, ever-growing demand for fuel cells has inspired great effort to seek alternative cathode materials to replace current commercial Pt/C catalyst. Spinel catalysts with low cost and adjustable properties revealed fascinating prospects. Unique nanostructures were designed to increase active sites, facilitate kinetics, and decrease mass transport resistance. Meanwhile, both direct and mediate coupling between Ag and MFe₂O₄ were proposed to enhance their catalytic activities. Furthermore, different conductive matrixes such as graphene, carbon nanotube and fiber have been utilized as support for these materials to improve conductivity. Heteroatoms such as N and S introduced into graphene lattice were proposed to transfer neighboring carbon atoms to “active regions” with enhanced catalytic activity. The integration of metal oxide nanoparticles with heteroatom-doped graphene demonstrated superior oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities. However, as to the deposition of dumbbell nanocomposites on N or S doped graphene, binding to different components might introduce different electron transfer and active sites.

Herein, Ag-MnFe₂O₄ nanoparticles were synthesized and deposited on N-doped graphene (N-rGO) and S-doped graphene (S-rGO), respectively. According to their reduction peaks, N-rGO demonstrated higher catalytic activity than S-rGO. Moreover, Ag-MnFe₂O₄ nanoparticles on N-rGO (Ag-MnFe₂O₄/N-rGO) showed more enhanced effects than those particles on S-rGO (Ag-MnFe₂O₄/S-rGO). Thus, Ag-MnFe₂O₄/N-rGO can be developed to replace Pt for ORR.