Study On Synthesis Of Heteroatom-doped Carbon Materials And Their Oxygen Reduction Performance

Heteroatom doping as an effective way to improve the electrochemical performance of carbon materials can greatly broaden the application of carbon materials, which opens up the application of carbon materials in fuel cells research field. Fuel cells have been drawn considerable interest for energy, due to their high energy conversion efficiency and environmental friendliness. Up to now, the Pt-based materials are widely used as the catalyst for ORR. The high cost, poor resistance to methanol interference and CO poisoning, and unstability of Pt-based catalyst greatly restricte their application for fuel cells. So, it is important to explore the novel cathode catalysts for fuel cells with low cost, high performance and good stability. Heteroatom doped carbon materials have superior electrocatalytic performances for oxygen reduction in alkaline medium, which can be promising cathode catalysts for next-generation fuel cells. Based on this, this thesis has carried out the following work around the topic of heteroatom doped carbon materials:(1) Study on synthesis of Mn3O4 nanorods coated by a layer of nitrogen-doped carbon and their oxygen reduction reaction electrocatalytic performance.Mn3O4 nanorods coated by a layer of nitrogen-doped carbon(Mn3O4@CNx) are synthesized via hydrothermal and high temperature calcinations reaction, using organic dicyandiamide as carbon and nitrogen source. Scanning electron microscopy, high resolution transmission electron microscope and X-ray photoelectron spectroscopy show that the rod-like morphology of Mn3O4 nanorods are indeed coated by a layer of amorphous CNx with the thickness of about 5 nm and nitrogen element is doped in the carbon materials and exists with different chemical states. Cyclic voltammetry, linear sweep voltammetry and current- time show that Mn3O4@CNx nanorods display an excellent electrocatalytic performances for oxygen reduction reaction in alkaline medium in terms of electrocatalytic activity, excellent tolerance to crossover effect of methanol, CO poisoning and long-term stability.(2) Study on synthesis of biomass-based nitrogen-doped carbon materials and their oxygen reduction reaction electrocatalytic performance.Biomass-based nitrogen-doped carbon materials are synthesized using the natural abundance amaranthus waste(the discarded leaves, the extract remains of natural amaranthus red and stalks of amaranthus) as nitrogen as well as carbon sources via one process of high temperature carbonization. X-ray photoelectron spectroscopy shows that the nitrogen element is successfully doped in carbon materials in pyridine, pyrrole and graphite types. The electrochemical measurents indicate that nitrogen-doped carbon synthesized at 800 oC has superior electrocatalytic activity and proves to be a promising alternative for costly Pt-based electrocatalysts in fuel cells in terms of excellent electrocatalytic performance, long-term stability and tolerance to crossover effect of methanol, CO poisoning.(3) Study on synthesis of biomass-based nitrogen, sulfur, dual-doped carbon materials and their oxygen reduction reaction electrocatalytic performance.High specific surface area porous nitrogen, sulfur, dual-doped carbon materials are synthesized using honeysuckles as carbon, nitrogen and sulfur sources via high temperature carbonization. Characterization results show that the nitrogen and sulfur elements are successfully doped in carbon materials. The nitrogen, sulfur, dual-doped carbon synthesized at 800 oC has high specific surface area(802.7795 m2 g-1), a graphene-like structure and exhibits excellent ORR activity in alkaline medium with superior tolerance to crossover effect of methanol, CO poisoning and stability to those of Johnson Matthey Pt/C catalyst.