LAUSR

Pt nanoparticles on suitable supports are commonly employed as electrocatalysts to improve the slow kinetics of methanol oxidation [1]. However, it is not cost-effective and suffers from two serious limitations. Firstly, in the course of methanol oxidation, the evolution of CO gas poisons the Pt-catalyst leading to its reduced cyclic stability and secondly, Pt nanoparticles (NPs) undergo coarsening at the operative voltage in fuel cell, gradually losing its activity. In this context, alloying Pt with a non-noble element along with achieving a dispersion of the catalyst on a conducting support can solve these problems. We have demonstrated earlier that dispersion of ultrafine Pt NPs on a reduced graphitic oxide (rGO) is achievable through a microwave (MW) assisted synthesis route [2], as shown in Figure 1 (a, e,f). However, achieving an alloy/intermetallic nanoparticle catalyst still remains a challenge owing to the difficulties associated with the co-reduction of two metals with widely different reduction potentials. In this work, we report a MW-based wet chemical approach for alloying Pt NPs with Bi on rGO support that enhances the stability of the catalyst. In the MW-assisted ultrafast route, we were able to synthesize Pt-Bi intermetallic nanoparticles on rGO support upon reaction. X-ray diffraction (XRD) shows the formation of PtBi alloy phases with two distinct intermetallic compositions (Figure 1 (g)), hexagonal PtBi phase, along with rhombohedral PtBi2 phase. Figure 1 (c) shows high resolution transmission electron (HRTEM) image of PtBi intermetallic nanoparticle showing fringes corresponding to (100) planes of the hexagonal structure. Scherrer analysis from the XRD pattern and detailed scanning transmission electron microscopy (STEM) coupled with EDS of the particles reveal that the larger particles have PtBi2 stoichiometry, and the smaller ones have a PtBi stoichiometry (Figure 2).