| It is well known that carbon supported platinum is the most efficient catalyst in fuel cells. Carbon is easily oxidated at harsh conditions which leads the catalyst lose its activity. Also platinum is easily poisoned by strong chemisorption of CO at the active sites of the surface, since CO inevitably exists in the anode fuel. Considering their defects above, carbon supported platinum catalysts are seldom used in fuel cells. There are a few reports about the silicon carbide supported platinum based bimetal catalysts because of the low surface area of silicon carbide. But advantages of the silicon carbide, such as the stability, the conductivity and the thermal conductivity, showed its possibility used as substrate of anode fuel. Furthermore, PtRu bimetallic catalysts have high tolerability to CO poisoning and the PtRh bimetallic catalysts have high catalytic activity for ethanol oxidation. Therefore, research on silicon carbide supported platinum based bimetal catalysts has a high theoretical significance and wide application foreground.This thesis firstly presents a systematically study on platinum catalysts deposited on silicon carbide which is etched with different acids and methods. The effects of the amount of platinum on the surface of etched silicon carbide and their catalytic activity in methanol electro-oxidation were investigated by means of cyclic voltammetry(CV). Using SiC with the best etched methods as substrate, the effects of the deposit structure, the amount of platinum, ruthenium alloy catalysts and platinum, rhodium alloy catalysts and calcination atmosphere on the formation of supported PtRu, PtRh alloy catalysts were studied by means of CV. The relationship between the surface structure and composition of the catalysts and their catalytic activity in methanol or ethanol was examined.The whole thesis is divided into five chapters, which are illustrated briefly as follows:In chapter one, progress in research of anodic catalysts in fuel cell, the significance of the research project and the main research work in this thesis are introduced.In chapter two, Using the etched SiC as substrate, the Pt/SiC has been prepared by chemical reduction. The effects of the amount of platinum on the etched silicon carbide and their catalytic activity in methanol electro-oxidation were investigated by means of cyclic voltammetry(CV). After etching by HF+HNO3, the surface area went up from11m2/g to140m2/g without changing the structure of original SiC. HF+HNO3etched SiC used as substrate, the Pt/SiC catalysts showed their best performance in methanol electro-oxidation, and the oxidation current went up to430mA/cm-2.In chapter three, a serious of HF+HNO3etched SiC supported PtRu catalysts have been synthesized by chemical reduction. The effections of the variation of the deposit structures and the amount of platinum and ruthenium on the surface of etched silicon carbide and their catalytic activity in methanol electro-oxidation which were effected by calculation temperature and Pt, Ru contents were investigated by means of cyclic voltammetry(CV). The result showed that catalysts showed the best catalytic activity with the ratio of2:1for Pt and Ru. The onset oxidation potential appears to be0.5V which shifted negatively nearly50mV than that of pure Pt catalyst. And the oxidation current density went up high to64mA/cm2. After calculated at400℃, the PtRu/SiC catalysts showed the best catalytic activities. And the value of [If/Ib] confirmed that PtRu catalyst had the highest CO resistance.In chapter four, a series of etched SiC supported PtRh catalysts have been synthesized by chemical reduction. The effects of the variation of the deposit structures and the amount of platinum and rhodium on the surface of etched silicon carbide and their catalytic activity in ethanol electro-oxidation which were affected by calculate temperature, the ratio of platinum and rhodium and deposit process were investigated by means of cyclic voltammetry(CV). The result showed that The PtRh/SiC showed the best performance in ethanol oxidation after they were calculated at450℃with the first and the second oxidation peak potential at0.62V and1.03V. Moreover, the first and second peak current densities were213mA and417mA, respectively, which were higher than any other PtRh/SiC calculated at different temperatures; after the two steps deposition, Pt/Rh/SiC catalysts showed the best catalytic activity. The first oxidation peak potential appears to be0.58V which nearly shifted40mV than that of pure Pt, the second oxidation peak potential appears to be0.98V which is about80mV lower than Pt catalyst; when ratio of platinum and rhodium was10wt.%and6wt.%, the onset oxidation potential of Pt10Rh6/SiC was0.16V which was much lower than that of Pt/SiC(0.3V). The first and second oxidation peak potential negatively shifted to certain extent, which illustrated that the catalysts could promote ethanol oxidation under low potential.In chapter six, the whole thesis was summarized and the problems to be solved have been put forward. |
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