Theoretical and Experimental Studies on the Relationship between the Structures of Molybdenum Nitrides and Their Catalytic Activities toward the Oxygen Reduction Reaction

Two carbon-supported molybdenum nitrides, MoN/C and Mo2N/C, were prepared by varying the experimental conditions in NH3 atmosphere. The physical properties of the catalysts were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The catalytic activities of the catalysts toward the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) were characterized by potentiodynamic measurements. The results show that the MoN/C exhibits higher catalytic activity toward the ORR than the Mo2N/C. Both catalysts are inert to methanol. The results from the density functional theory calculation indicate that both the MoN and the Mo2N facilitate dissociation of oxygen molecules. The suitable geometric structure of the MoN and the preferred oxygen adsorption type on it contribute to the higher activity of the MoN/C toward the ORR. The calculation results agree well with the results from the experiments.