Promoting Effect of Ni in PtNi Bimetallic Electrocatalysts for the Methanol Oxidation Reaction in Alkaline Media: Experimental and Density Functional Theory Studies

Carbon-supported bimetallic PtmNin electrocatalysts with different Pt/Ni atomic ratios were synthesized through a modified polyol process. The as-prepared electrocatalysts were characterized by X-ray diffraction, transmission electron microscopy, voltammetry techniques, and single-cell tests. It was revealed that the PtmNin bimetallic nanoparticles were uniformly distributed on carbon supports with average diameters of about 3 nm. Pt and Ni were partially alloyed, indicated by the decreased Pt lattice constants compared with that of pure Pt. The results of the electrochemical measurements showed that the PtmNin/C catalysts, compared with the Pt/C, have superior specific activity toward the methanol electrooxidation reaction (MOR) in alkaline media as well as a higher power density in a direct methanol fuel cell test with the Pt3Ni1/C as the anode catalyst. Density functional theory studies further revealed that the electronic structure of Pt was modified by Ni due to the charge transfer from Ni to Pt atoms in PtmNin clusters, leading to a weakened CO adsorption on PtmNin binary clusters than on Pt itself. This provides an explanation for the enhanced MOR activity of the PtmNin/C catalysts.