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

• The higher MnOOH content leads to a better ORR activity.
• Proper Ni(OH)2 loading contributes to the uniform distribution of the MnOx.
• The optimal Ni/Mn atomic ratio in the composite is 1:2.
• The optimal MnOx(Ni/Mn = 1:2) content in the composite is 28 wt.%.
• The Pmax for the Zn–air cell with the Ni–MnOx/C cathode is 122 mW cm−2.

A series of Ni modified MnOx/C composites were synthesized by introducing NaBH4 to MnO2/C aqueous suspension containing Ni(NO3)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 MnOx/C improves the distribution of the active material MnOx, which contributes to a surface with more MnOOH. The optimal composite is of the Ni/Mn atomic ratio of 1:2 and the MnOx loading of 28 wt.%. The maximum power density of the zinc–air battery with the optimized Ni modified MnOx/C as the cathode catalyst reaches up to 122 mW cm−2, much higher than the one with the MnOx/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.