Preparation Of Carbon Nanofiber Supported Fe Co Ni Materials And Their Catalytic Performance For Oxygen Reduction

Platinum is widely used as catalyst for oxygen reduction in the fuel cell cathode but due to its global reserve is limited and it easily gets deactivated in practical application because of poisoning, which seriously hindered the development of fuel cell. A lot of researches show that many nitrogen-doped carbon materials and transition metal compounds have comparable activity and stability in alkaline medium, but it is not ideal in acidic medium. In this paper, PAN carbon nanofibers supported transition metal were prepared using the method of electrostatic spinning, impregnation and heat treatment in NH3. TEM, SEM, XPS, Raman and XRD characterization method were used to characterize the morphology, structure and composition of carbon nanofibers. Besides, cyclic voltammetry, current- time curve and rotating disk electrode method were used to test the catalytic activity of carbon nanofibers for ORR in acid medium.With the Fe/Co ratio of 1:1, the carbon nanofibers loading different quantity of metal were studied. The carbon nanotubes grew on the surfaces of the carbon nanofibers loading 1% and 2% of metal, and the carbon nanotubes on the surface of samples loading 1% of metal looked like bamboo, those on the surface of the samples loading 2% of metal were more smooth and smaller in diameter. The carbon nanotube structures enhanced the stability of the catalyst. When changing heat treatment atmosphere with nitrogen or the heat treatment temperature, there were no obvious carbon nanotubes on the surface of carbon nanofibers, by changing the Fe/Co ratio of 1:3 or 3:1, the carbon fiber surface only existed short metal rod coated carbon. According to the electrochemical test, the carbon nanofibers loading metal had better catalytic activity for oxygen reduction reaction than the pure carbon nanofibers. The oxygen reduction peak potential of the carbon nanofibers loading Fe and Co was at 0.50 V when the load was 2%, and its stability in acid medium was far better than the carbon nanofibers loading single metal. The Fe/Co ratio had little influence on the catalytic activity for oxygen reduction reaction but the heat treatment does. After heat treatment in 900?, the carbon nanofibers loading 2% of metal with Fe/Co ratio of 1:1 had the best catalytic activity for oxygen reduction reaction, its oxygen reduction peak potential was at 0.62 V, which was better than the commercial Pt/C catalyst.Finally we checked the influence of transition metal(Ni) on carbon nanofibers. The study found that there were no carbon nanotubes on the surface of the carbon nanofibers loading Fe/Co/Ni. The increasing of loading promoted the etching effect on carbon nanofibers, and the carbon nanofibers surface appeared more holes defects and fracture phenomenon, and when the load exceeds 0.5%, the catalyst activity for oxygen reduction began to decline.When the load was 0.5%, the Fe/Co/Ni ratio had little influence on the surface morphology of carbon fibers. According to the electrochemical test, the carbon nanofibers loading different Fe/Co/Ni ratios all showed good catalytic activity for oxygen reduction reaction in acid medium. Among them, the carbon nanofibers loading Fe/Co/Ni ratio of 4:2:1 had the best catalyst activity for oxygen reduction reaction. Its oxygen reduction peak potential was at 0.61 V.