Optimization of manganese oxide amount on Vulcan XC-72R carbon black as a promising support of Ni nanoparticles for methanol electro-oxidation reaction

Abstract

Different Ni−MnOx/C electrocatalysts were prepared by chemical reduction of nickel ions at MnOx/C, containing various metal oxide weight percentages, as a support. Sodium borohydride was employed as a reducing agent with the aid of microwave irradiation. Electrocatalyst surface morphology, crystalline structure and chemical composition were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX), respectively. Incorporating manganese oxide in Ni−MnOx/C resulted in the formation of smaller and homogeneously distributed nickel nanoparticles. Electrocatalytic activity of Ni−MnOx/C towards methanol oxidation reaction in KOH solution was investigated using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The oxidation current density was enhanced with increasing MnOx weight percentage to achieve the highest activity at Ni−MnOx/C containing 7.5 wt.% MnOx. The electrocatalyst stability during long-time operation was examined. A lower charge transfer resistance value was measured at Ni−MnOx/C surface when methanol was introduced to the supporting electrolyte. A faster electron transfer rate was observed when MnOx was added in an increased content.