Study On Application Of Sulfur Compounds For Electrocatalytic Oxidation Of Methanol And Hydrazine

Direct methanol fuel cell (DMFC) is a promising device due to the free-pollution, the abundant sources, high energy transfer efficiency, the safety for the storage and transportation of the fuel and direct hydrazine fuel cell (DHFC) has the characteristics of high volume energy density and no catalyst poisoning besides some advantages above-mentioned. Both DMFC and DHFC possess the potential application for portable equipment, electric car and field power, which is of great importance for sovling scarcity of energy sources and environmental pollution. However, the low electrochemical activity and high cost of anode electrocatalysts are still one of the key issues hindering the commercial application of DMFC and DHFC. Therefore, to improve the electrocatalytic activity and to decrease the loading mass of noble metals are effective routes to the commercial application of DMFC and DHFC. In this dissertation, sulfur compounds (thionine, L-cystein) modified anode electrocatalysts or catalyst supports in DMFC and DHFC have been evaluated. Their micrographs, structure, properties and applications have been investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), energy dispersive spectroscopy (EDS), cyclic voltammetry (CV) and chronoamperometry method etc.The main points of this dissertation are summarized as follows:(1) Commercial catalysts E-TEK 20 wt.% Pt/C and PtRu/C were supported on graphite and covered with a film of Nafion to adsorbe thionine. The effects of adsorbing thionine on the electrochemical properties of the Pt/C/graphite and PtRu/C/graphite for methanol electrooxidation were investigated by CV. The peak current densities of methanol oxidation on the Th/Pt/C/graphite and Th/PtRu/C/graphite are 3.77 and 2.51 times as high as that on the Pt/C/graphite and PtRu/C/graphite, respectively, which is correlative to the adsorption capacity of thionine. The anti-poisoning ability and long-term cycle stability of the electrode modified with thionine are improved obviously.(2) As the support of Au catalyst for hydrazine electrooxidation, the L-cystein grafted carbon nanotubes (CNTs-SH) were prepared by chemical synthesis method and characterized by FTIR. The morphology and crystal form of the CNTs-S-Au catalyst were characterized by TEM and XRD, respectively. The results demonstrate that CNTs-SH are beneficial to loading Au electrocatalysts with well dispersion and small particle size (2.8 nm) by forming S-Au bond. The good electrocatalytic property of the CNTs-S-Au catalyst for hydrazine oxidation was characterized by CV. The process of hydrazine electrooxidation is determined by diffusion step and its electron transfer number is 4. These results indicate that CNTs-SH are the promising catalyst support for hydrazine electrooxidation.(3) Pt electrocatalysts for catalytic oxidation of hydrazine were supported on the carbon nanotubes modified with thionine and investigated by SEM, TEM, EDS, XRD and electrochemical methods. The results demonstrate that carbon nanotubes were modified with thionine successfully and the CNTs/Th are beneficial to loading Pt electrocatalysts with well dispersion and small particle size (4.5 nm). The electrochemical activity and long-term cycle stability of hydrazine oxidation on Pt/Th/CNTs/GC are better than that on Pt/CNTs/GC. The electrocatalytic properties of Pt for hydrazine electrooxidation are improved obviously by thionine.