| Titanium oxy nitride has been developed as an attractive material formany electrochemical applications because of its specific properties whichcan be tuned as a function of its N/O ratio. It has been synthesized by variousmethods that the results of each are quite different. Among them, sputtering ismost attractive since the products are under control through this method. Butthe equipment is too expensive for industrialization. On the other hand,sol gel method is simple and cheap, but the products so far contain littlenitrogen. The findings of this thesis suggest that the titanium oxy nitrideprepared by an anhydrous sol gel method is an interesting anode for oxygenelectrodes for water electrolysis and PEMFC.Urea was chosen as nitrogen source and then mixed with titanium sourceunder an anhydrous environment, followed by a calcination under nitrogen toprepare the titanium oxy nitride. The characters, such as components, surfacearea, appearance and conductivity were controlled by adjusting the temperature and period of calcination. It was found that the products calcinedunder relatively lower temperature were equipped with small surface areaaround20m2/g while they appeared conchoidal fracture pieces. The XRDresults showed that they were less crystalline. The products were insulatorthat the impedance of them was more than200while the resistance wasmore than20cm that it suggested a negative result of using as oxygenelectrodes. The crystalline of titanium oxy nitride changed from anatase torutile as the temperature of calcination rising. The surface area of titaniumoxy nitride approached180m2/g and nitrogen content reach7.34%whenrising temperature to800@. The material showed good conductive that theimpedance of which was around20while the resistance decreased to7×104cm. The product maintained conchoidal fracture structure and thesize of pieces was1m. Further raising the temperature to1000@, theproduct appeared the crystalline of titanium nitride instead of titanium dioxideand the surface area increased to352m2/g while nitrogen content increased to18.54%. The impedance of the product was around23while the resistancewas7×104cm. Meanwhile, the period of calcination also affected theproperties of material although it was much slighter compare to that oftemperature. The products calcined under800@for different time showedalmost same crystalline, feature and surface area, but the nitrogen content decreased to5.74%when prolonged the period of calcination to5hours. Theimpedance of this product was around33while the resistance was7.3×104cm. It might be caused by the tendency of forming Ti O band intitanium oxygen nitrogen system which would cause the release of nitrogen,and further cause the decrease of conductivity.Titanium oxy nitride was introduced into water electrolysis as the anodecatalyst for oxygen evolution. The material calcined under lower temperaturewas very stable even the operating potential reached2V, without showing anyoxidation or reduction reaction that no oxygen evolution reaction washappened. Meanwhile, the capacity of the material was5F/g which might becaused by the properties of material itself. When the calcination temperaturerising to700@, the material beared better capacity and obvious oxidationpeak. The capacity reached192F/g at calcination temperature of800@while298F/g at calcination temperature of1000@. It might be caused bythe feature of material that the pore structure formed well as calcinationtemperature increasing. The activity of the material was lower than that ofRuO2according to the polarization curves, which suggested the difference ofkinetics between these two materials. Whereas, the Tafel slope of titaniumoxy nitride suggested better stability than RuO2that it was40mV/dec oftitanium oxy nitride calcined under800@which was smaller than that of RuO2.Besides the water electrolysis, titanium oxy nitride was also introducedinto PEMFC as the catalyst support in this thesis. A better stability of titaniumoxy nitride was found that no obvious oxidation was found even in highpotential region. The platinum distributed uniformly on titanium oxy nitridethat the particle size was around8nm. The oxygen reduction reaction washappened via four electron transfer route. The electrochemical surface areawas31.2m2/g and the degradation of ECSA was only26%after1000cyclesof cyclic voltammetry test, which was much more stable than Pt/C. Moreover,the single cell performance was tested that the initial open voltage was0.971V and the maximum power density of161.67mW/cm2was observed at0.317V where the current density was0.51A/cm2that it was poorer than that ofPt/C. However, the stability in single cell was tested and a better stabilitywhen using Pt/TiOxNywas found that no obvious degradation was found in20hours. It might suggest the great potential of titanium oxy nitride using inPEMFC.
|
PDF Full Text Request