Halide-aided controlled fabrication of Pt–Pd/graphene bimetallic nanocomposites for methanol electrooxidation

Abstract

Fabrication of agglomeration-free Pt-based bimetallic nanoparticles (NPs) supported on carbon structures is extremely important for direct methanol fuel cells (DMFCs) applications. In this study, by introducing halide ions and ascorbic acid (AA) as a reducing agent in the synthesis recipe a controlled co-reduction of graphene oxide sheets, H₂PtCl₆ and Na₂PdCl₄ is achieved. The microstructure and morphological features of fabricated Pt–Pd bimetallic NPs deposited on reduced graphene oxide (RGO) sheets, herein after called as Pt–Pd/RGO bimetallic nanocomposites (NCs), are evaluated by X-ray diffraction and transmission electron microscopy. The results reveal that for the samples prepared in the presence of halide ions (i.e. Pt–Pd/RGO-5KI and Pt–Pd/RGO-15KI) the uniformity and dispersion of Pt–Pd bimetallic NPs are significantly improved on RGO sheets over the sample prepared in the absence of halide ions (i.e. Pt–Pd/RGO-0KI). The electrocatalytic activities of Pt–Pd/RGO bimetallic NCs towards methanol oxidation are investigated by cyclic voltammetric and chronoamperometric measurements. Among the various Pt–Pd/RGO bimetallic NCs prepared, Pt–Pd/RGO-15KI exhibits the best electrocatalytic activity and stability for methanol oxidation. The improved methanol oxidation on Pt–Pd/RGO-15KI is due to the enhanced uniformity, dispersion and lower size of Pt–Pd NPs, and synergistic roles played by Pt, Pd and the RGO support. The present halide-aided fabrication strategy will be significantly helpful to the further design of Pt-based nanocomposites with desired properties relevant to DMFCs applications.