Carbide/carbon Composites With Enhanced Effect As Supports Forplatinium Electrocatalysis In Methanol Oxidation

Direct methanol fuel cells(DMFC) have received high attention because of the high energy conversion efficiency, low operating temperature, and less pollution. Catalysts(including noble metals and materials) are the most important material in direct methanol fuel cell. Among them, the support materials can directly affect the dispersion, catalytic efficiency and stability of noble metals. Therefore, the research and exploration of low cost, large surface area, high performance and stable support materials are urgently required. Based on the understanding of “support and catalytic performance” relationship, we designed and synthesized a series of new carbide/carbon composites support materials in order to provide an idea for exploring new high-performance catalyst support materials in future.Tungsten carbide/porous carbon(WC/PC) composites have been successfully synthesized through a soft-template method with phenolic resin as carbon source, and the formation mechanism of composite materials are also studied. After loading Pt nanoparticle, the Pt/WC/PC catalysts were prepared and the electrical interaction between Pt and support were analyzed. Meanwhile, the influences of the tungsten content and calcination temperature on the structure and electrochemical properties of the materials were investigated. The obtained Pt/WC/PC catalyst exhibits the high unit mass electroactivity towards methanol electrooxidation, which is about 2.6 times as that of the commercial Pt/C(JM) catalyst. Furthermore, the Pt/WC/PC catalyst displays much stronger resistance to CO poisoning and better durability towards methanol electrooxidation compared with the commercial Pt/C(JM) catalyst. The high electrocatalytic performaces of Pt/WC/PC catalyst are mainly attributed to the co-catalyst effect of WC for Pt, and high specific surface area of support materials.Based on the above experiments, tungsten carbide and graphitic carbon composites(WC/GC) have been synthesized by introducing nickel salt as graphitic catalysts, and formation mechanism of composite materials are also analyzed. The obtained Pt/WC/GC catalyst exhibits the high unit mass electroactivity towards methanol electrooxidation, which is about 2.0 times as that of the commercial Pt/C(JM) catalyst, and larger electrochemical active surface area of Pt compared with the Pt/C(JM) catalyst. Furthermore, the Pt/WC/GC catalyst displays lower onset potential, much stronger resistance to CO poisoning and better durability towards methanol electrooxidation. Compared with Pt/WC/PC catalyst, Pt/WC/GC catalyst has better electrochemical active surface area of Pt, which suggests the utilization of Pt for catalyst can be improved by enhancing the degree of graphitization of carbon support.With phenolic resin and TEOS as raw materials, a novel simultaneous hard-template method was adopted to synthesize silicon carbide/porous carbon composites(Si C/PC), and regulate the specific surface area, crystallinity as well as amount of silicon carbide by changing the amount of TEOS and calcination temperature. The formation mechanism of composite materials was analyzed as well. The synthetic Si C/PC hybrid exhibited a large specific surface area of 1163.3 m2/g, and the Si C nanoparticles(NPs) with about 10 nm are well dispersed on the carbon materials. After loading Pt NPs, the Pt/Si C/PC catalysts were prepared and the electrical interaction between Pt and support were analyzed.The Pt/Si C/PC catalyst exhibits the better electrochemical active surface area of Pt towards methanol electrooxidation, which is about 1.6 and 1.2 times of those of the commercial Pt Ru/C(JM) and Pt/C(JM) catalysts. Meanwhile, the Pt/Si C/PC catalyst exhibits the highest unit mass electroactivity, which is about 3.1 and 3.6 times of those of the commercial Pt Ru/C(JM) and Pt/C(JM) catalysts. Moreover, the Pt/Si C/PC catalyst displays the best stability. The enhanced electrocatalytic activity of Pt/Si C/PC catalyst is attributed not only to the strong electrical interaction beween Pt and Si C supports, but also to its large surface area and proper porous structure.With ion-excharge resion as carbon, silicon carbide and graphitic carbon composites(Si C/GC) have been synthesized by in-situ method. Meanwhile, the influence of molar ratios of Na2 Si O3 to K4[Fe(CN)6 and calcination temperature on the structure, crystallinity and degree of graphitization of carbon were investigated. The formation mechanism of composite materials are also analyzed. The obtained Pt/Si C/GC catalyst exhibits the high unit mass electroactivity towards methanol electrooxidation, which is about 2.0 times as that of the commercial Pt/C(JM) catalyst. Furthermore, the Pt/Si C/GC catalyst displays similar electrochemical active surface area of Pt, and better durability compared with the commercial Pt/C(JM) catalyst. The four kinds of carbide/carbon composites for use as catalyst support in methanol electrooxidation have been comparatively analysized. The results showed that WC/C support was better than that of Si C/C support for anti-CO poisoning of catalyst, however, Si C/C support was better than that of WC/C support for the catalytic activity and stability of catalyst.