Preparation And Electrochemical Study Of Adode Catalysts Used In Direct Methanol Fuel Cell

Carbon support is one of important component of catalyst of polymer membrane fuel cell (PMFCs). Carbon black and carbon nanotube, as the most common support of catalyst, have many amorphous carbon particles existing in the crude carbon, which are easy to be oxidized and affect the stability of catalyst. They have to be removed by mixed acid. While mixed acid with strong oxidizing ability will destroy the surface of carbon and produce some of functional group, such as–COOH, which cause the metal particles grow on these defect sites and agglomerate seriously. Moreover, there are large amount of micropores (<2.5 nm) existing in carbon black, metal particles codeposited in these micropores will not play any electrocatalysis and cause the low utilization of catalysts. As a good electrode material of super capacitor, PPy can change the distribution of carbon pore diameter, cover the defects of carbon, and thereby improve the inert surface of carbon,the ultilization of catalyst and the capacity of catalyst layer.In this paper, in situ chemical polymerization method was used to synthesize PPy-C composites. The morphology, particle size, specific surface and pore distribution, electron and proton conductivity and capacity were researched.Using the prepared PPy-C as supports, high electroactivity anode catalysts (Pt/PPy-XC72, PtM/PPy-C (M=Co, Fe)) of methanol oxidation were prepared. Moreover, by means of the replacement method, a novel core-shell structured Co@PtRu/MWCNT composite was obtained.Scanning electron microscope (SEM), transmission clectron mircroscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy - dispersive spectrometry (EDS), cyclic voltammetry (CV) and linear sweep scan technology (LSS) were used to evaluate morphology, electrochemical activity and stability of catalysts. Over-oxidation treantment technology was used to search the effect of high vlotage to the performance of catalysts. The dynamic mechanism of methanol oxidation was discussed. The main innovative achievements include:Naphthalene sulfuric acid (NSA) was used as the proton acid of pyrrole polymerization. The NSA anions were encapsulated into the net structured PPy, improving the conductivity of PPy-C and metal dispersion on carbon.By one-step route, a novel PtFe/PPy-XC72 catalyst was synthesized with Fe3+ ions as oxidant agent and one component of the PtFe alloy. Besides high methanol oxidation activity by this synthesis route, the trivial processes, such as washing and filtering of PPy-C, were omitted.With sodium borohydride/hydrate hydrazine as reducing agent to prepare cobalt core, and by the synthesis route: Co + PtCl6²⁺ + Ru³⁺→Co²⁺ + PtRu, a novel core-shell structured Co@PtRu/MWCNT composite was obtained. With sodium nitrate as buffering agent, the reduction potentials of Pt and Ru were controlled to the near same value, thus Pt and Ru were reduced together and PtRu alloy was formed. Electrochemical test shows that this novel catalyst has large electrochemical specific surface and high methanol oxidation activity.