Controllable Synthesis And Electrocatalysis Performance Investigation Of The Non-platinum Catalysts

As a kind of new energy, fuel cells have become a safe and reliable energy installation graduallybecause of their efficiency and environmentally friendly property. However, the high cost and scarcity of Pthinder the commercial implementation of fuel cells. Therefore, how to improve utilization or find out asuitable substitute for Pt has become the focus of the current study. For the cathode, nitrogen–dopednon–precious metal catalysts are probably the best option based on their efficiency and stability; for theanode, the choice of a suitable support is one of the key factors affecting the performance of the catalyst.The main research contents of this thesis are to develop nitrogen–doped carbon supported non–preciousmetal cathode catalysts and direct ethanol fuel cell (DEFC) anode catalysts, which have the simplepreparation technology, low–cost, high activity for oxygen reduction reaction (ORR) and ethanolelectrooxidation. Study the structure, particle size and chemical speciation of catalysts, by means of variousmaterials measurements and electrochemical methods; the home–made anode catalyst was used to preparemembrane electrode assembly (MEA) and a single DEFC. The effect of support on the performance ofDEFC was investigated and a possible mechanism was also proposed. The main contents of the thesis arefollowing:Firstly, not only the current research of low temperature fuel cell, the progress of catalyst and catalyticmechanism were given, but also the current questions about the fuel cell catalyst, objective and the mainresearch contents of this paper were described in detail.Secondly, controllable synthesis of cobalt, nitrogen–codoped carbon materials with specialmorphology and ORR catalytic performance study. Yolk–shell and peanut–like structured cobalt, nitrogen–codoped carbon (Co–N–C) catalysts have been synthesized controllably without a template.Melamine was used as nitrogen precursor, formaldehyde as carbon precursor and cobalt acetate as metalprecursor. According to XPS, the N atoms partially remain in the resulting carbon structures and mainlyexhibit graphitic and pyridinic configurations after pyrolysis at800oC. In0.1M KOH electrolyte, theoxygen reduction reaction (ORR) onset potential for the yolk–shell and peanut–like structured Co–N–Ccatalysts are high up to–0.07and–0.067V vs. SCE, respectively, which are only ca.40mV less than thatof the Pt/C catalyst (–0.03V). The catalysts show a very slow attenuation (only4%) with a high currentretention even after30000s of chronoamperometry tests. The catalysts also possess a much higherselectivity and a significantly reduced methanol crossover effect.Thirdly, controllable synthesis of nitrogen doping carbon materials with highly active sites and ORRperformance study.4,4′,4″-s-triazine-1,3,5-triyltri-p-aminobenzoic acid (H3TATAB) is a kind ofnitrogenrich triazine carboxylic acid ligand, and the synthesis process is quite simple. We have successfullysynthesized a novel N–doped ORR catalyst using H3TATAB as nitrogen precursor, ferrous chloride asmetal precursor after pyrolysis in N2. The activity of the catalyst depended on metal contents andheat–treated temperatures. The results showed that the Fe–N70%/C–800catalyst (the content of Fe complexwas70%and the catalyst was pyrolyzed at800°C) had good catalytic activity toward ORR with the onsetpotential at0.91V vs. RHE and the kinetic current density of4.3mA cm-2at0.6V vs. RHE in alkalinemedium. According to rotating disk electrode (RDE) measurement, the overall electron transfer number inthe catalyzed ORR was found to be3.7–3.9. Fe–N70%/C–800catalyst had better tolerance to methanolcrossover effect in comparison with commercial Pt/C.Fourthly, based on a new support for synthesis of palladium/hydroxyapatite and ethanolelectrooxidation performance study. Hydroxyapatite (HAP) is a kind of green material with hydroxyl–rich surface. Based on HAP, a facile and low–cost preparation of palladium/hydroxyapatite catalyst isintroduced in this thesis through a solvothermal reaction without additives. According to transmissionelectron microscopy (TEM) and field emission scanning electron microscopy (FESEM), the as–prepared Pdnanoparticles were evenly deposited on the surface of HAP, which suggested HAP was a better support.Cyclic voltammetry and chronoamperometry tests demonstrated that the Pd/HAP catalyst possessed a muchhigher current density (246mA cm2) than the Pd/C catalyst (109mA cm2) towards ethanolelectrooxidation, and better stability as well. In the direct ethanol fuel cell (DEFC) test, Pd/HAP catalystgives better performance than that with Pd/C. The voltage (OCV) and power density of Pd/HAP catalyst are0.73V and50mW cm2, while Pd/C catalyst are0.66V and36mW cm2, respectively. These resultsindicate that the HAP is a better support and the catalyst developed in this study may be a better candidatefor DEFC. A possible mechanism consistent with the experimental is also proposed.