Study On Synthesis Of Nitrogen-doped Carbon Sphere Materials And Its Oxygen Reduction Performance

Durning the last decade, fuel cells have received enormous attention from research institutions andcompanies as novel electrical energy conversion systems, with the advantages of high efficient andenvironment friendly, are promising candidate for application in household power source and electricvehicle transportation and so on. The major limitation of FCs is the performance of oxygen reductionreaction (ORR) at the cathode. Up to now, the platinum-based materials are widely used as the catalyst forORR. However, the largescale commercialization of FCs has been hampered by the low long-termdurablity and high cost of the Pt-based electrocatalysts. Recently, the investigation of electrocatalystsfocuses on reducing or replacing Pt-based catalysts in fuel cells and developping new ORR electrocatalysts.Among the developed catalysts, nitrogen-doped carbons and their composites are already known to act asefficient catalysts for ORR.Here, the simple, friendly and novel methods for the fabrication of nitrogen-doped mesh-like carbonmicrospheres and nitrogen-doped carbon spheres have been developed and the obtained nitrogen-dopedcarbons have been applied for ORR in alkaline media. Additionally, we used as-prepared mesoporousnitrogen-doped carbon spheres as the catalyst supports of Pt nanoparticles (NPs) and studied theelectrocatalytic performances of obtained Pt-m-N-C nanohybrids for ORR in alkaline meadia in detail. Themain contents of this thesis are as follows:(1) Nitrogen-doped mesh-like carbon microspheres were first synthesized via a simple hydrothermalreaction, activation and carbonized process of low-cost, nitrogen-riched biomass gastrodia elata. Theobtained material was characterized by SEM, TEM, Raman, XPS and so on. The results show disorder andmicropore structure, high specific surface area (up to1721m2g-1) and ca.3.07%nitrogen content. Besides,the electrochemical measurents indicate nitrogen-doped mesh-like carbon microspheres catalyst exhibitshigh electrocatalytic activity, dominant direct four-electron transfer pathway, superior long-term durablity,methanol crossover resistance, and selectively activity to a commerical Pt/C catalyst in alkaline solution.(2) The biomass, a sustainable and cheap raw material, was selected as the carbon and nitrogensources to synthesize nitrogen-doped carbon with different methods. And then, we obserive their ORRperformance and optimize the preparation process. At the same time, we also research the relationship between the annealing temperature and ORR performance, showing different reaction mechanism. Theobtained nitrogen-doped carbons were characterized by SEM, TEM, chemisorption analyzer and elementalanalysis and so on. The results showed that nitrogen-doped carbons had the microporous structure, highsurface area as well as2.1%of nitrogen content. The nitrogen-doped carbon was used as a metal freeelectrocatalyst for oxygen reduction in alkaline solution and showed high electrocatalytic activity, excellentlong-term stability, CO poisoning resistance, and tolerance to crossover effect of methanol.(3) Mesoporous nitrogen-doped carbon microspheres and Pt NPs were deposited on m-N-C viaone-pot and heat treatment. XRD, TEM, EDX, and XPS were used to characterize the catalyst. It was foundthat Pt NPs were uniformly deposited on m-N-C. The electrocatalytic properties of the Pt-m-N-C electrodefor ORR have been investigated through CV, I-t and LSV. The Pt-m-N-C electrode not only showedexcellent catalytic activity than m-N-C, but also showed ca.1.6times higher mass activity and excellentlong-term stability, CO poisoning resistance, and methanol crossover resistance than commercial Pt/Ccatalysts towards ORR. This can be attributed to the Pt NPs of uniform size, high dispersion and nitrogendoping, making for active defects edge exposure and more easily adsorbed oxygen molecules. Besides, theresults also due to the nitrogen doping into graphitized carbon structural surface and the electronic overlapor bonding with Pt atoms, which can effectively slow down the Pt NPs oxidation, reunion and migration.The above results not only provide low-cost materials and new methods for the fabrication ofnitrogen-doped carbon sphere materials, but also give the new try to improve the utilization of the nobelmetal particles, solve the problem of CO poisoning, and the crossover effect of methanol.