Catalytic activity and controllable deposition of platinum nanoparticles on ionic polymer-functionalized graphene as catalysts for direct methanol fuel cells

Direct methanol fuel cells (DMFCs) are considered promising candidates for mobile and -erating temperature [1]. Moreover, platinum (Pt) is an excellent catalyst and one of the best electrode materials for DMFCs [2-4]. However, the high cost, low electrocatalytic activity and stability of common Pt catalyst inhibit their broad application for DMFCs [3]. It is well known that the electrocatalytic performance of a fuel cell greatly depends on the composi-tion, shape, size, and dispersion of the catalyst nanoparticles (NPs). The materials supporting catalyst play an important role in controlling these properties [5]. However, during fuel-cell operation, a gradual oxidation of the carbon support leads to detachment of Pt NPs from the carbon support, allowing their agglomeration, which can reach an unacceptable level [6]. In the past few years, graphene has emerged as the ideal material for a variety of dif-ferent energy applications including fuel cells, Li-ion batteries, supercapacitors, and solar cells. This is because of its large thermal conductivity, high surface area, high mechanical stability, and excellent electrical conductivity [7]. Chemical modification of the inert surface of graphene sheets is necessary for the uniform dispersion of Pt NPs. Currently, chemical modification is achieved by methods including acid oxidation, ionic liquid [8], and conduc-tive polymer [9]. Recently, we developed a facile and efficient route to decorate Pt NPs onto reduced gra-phene oxide (RGO) functionalized with poly(diallyldimethyl ammonium chloride) ( PDDA), as acationic polymer. In this work, we investigated the synergistic effect of a poly(sodium 4-styrenesulfonate) (PSS)-functionalized graphene support and PDDA polymer for obtain-ing better electrocatalytic performance for DMFCs. These results demonstrated that, with high electronic conductivity and easier charge transfer, Pt/PDDA- PSS-functionalized RGO (PRGO) exhibited higher activity and stability than did Pt-decorated PDDA-RGO (Pt/PDDA-RGO), and Pt-decorated RGO (Pt/RGO).PSS (MW = 70,000) and PDDA (20 wt% in water) was purchased from Sigma-Aldrich (St. Louis, MO, USA). Graphite (99.9%) was purchased from Bay Carbon Inc. (Bay City, MI, USA) and H2PtCl66H2O was purchased from Sigma-Aldrich. Ethanol (99.8%), methanol (99.8%), and ethylene glycol (EG, 99.0%) were purchased from DAE JUNG Company and used without further purification. Distilled water was used in all preparation experiments.Graphene oxide (GO) was synthesized from graphite powders using a modified Hummer’s method [10]. Briefly, graphite powders were first oxidized by sulfuric acid (H