Electrocatalytic performance of Ni modified MnO_x/C composites toward oxygen reduction reaction and their application in Zn-air battery

摘要

A series of Ni modified MnO_x/C composites were synthesized by introducing NaBH_4 to MnO_2/C aqueous suspension containing Ni(NO_3)_2. The physical properties and the activity of the composites toward the oxygen reduction reaction (ORR) were investigated via transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and the electrochemical techniques. The results show that the higher activity of the composites toward the ORR is correlated with the higher content of MnOOH species transformed from Mn(Ⅱ) on the surface of the composite. The main nickel species in the composites is Ni(OH)_2, while Ni(OH)_2 shows little activity toward the ORR. However, introducing Ni(OH)_2 with proper amount into the MnO_x/C improves the distribution of the active material MnO_x, which contributes to a surface with more MnOOH. The optimal composite is of the Ni/Mn atomic ratio of 1:2 and the MnO_x loading of 28 wt.%. The maximum power density of the zinc-air battery with the optimized Ni modified MnO_x/C as the cathode catalyst reaches up to 122 mW cm~(-2), much higher than the one with the MnO_x/ C as the air cathode catalyst (89 mW cm~(-2)), and slightly higher than those with the Pd/C and Pt/C as the cathode catalysts.