| Fuel cells have been reconginzed as a kind of energy technologies, due to its high conversion efficiency, high energy density and operation convenient. In the pre-sent of energy shortage and environment pollution serious, it meets the need of new power sources for practical application. The cathodes oxygen reduction reaction(ORR) is one of the important processes. To date, Pt-based catalysts are still consid-ered the best catalyst. However, Pt is scare and expensive. A lot of using Pt-based catalysts has seriously hindered the development of commercialization of fuel cells.Therefore, it is necessary to develop and research of non-Pt-based catalysts. The studies find that nitrogen and transition metal co-doped carbon (M-N-C) material catalyst,exhibited high catalytic ORR activity and stability. Among the active sites plays a key role in catalytic activity in ORR process. However, the research of active site is still controversial and uncertainty. In this thesis,we have synthesized several carbon-based non-noble metal catalysts and studied their catalytic activity and active site for ORR. The concrete content is as follows:The preparation of the Co doped carbon-nitrogen-based catalyst Co-N-C and investigation the active site of ORR of the synthetic catalysts. The Co-N-C catalyst was prepared by high temperature pyrolysis of using the Co(NO3)2·6H2O as Co source and 1-ethyl-3-methyl imidazolium Dioyanamide as C/N source. And the catalyst is characterized by HRTEM, XRD and XPS. The catalyst performance for ORR was tested though the electrochemical method. Compared to other catalyst, we also been established that the active sites of the Co-N-C catalyst for the ORR are the Co-N species (most likely Co2N) and metallic Co particles or N-C species do not serve as active sites and interaction with the Co-N species. The result indicates Co-N-C cata-lyst show a rather good catalytic performance in the basic solution, with the Eonset=0.97 V (vs. RHE), E1/2=0.82 V, mass activity =8.25 mA/mg, which is higher than the commercial Pt/C catalyst. And after accelerated durability tests, It's mass activity decreases by 4%,but commercial Pt/C decreases by 28%,this result exhibits that Co-N-C catalyst has better durability. To study the Co content and pyrolysis temperature affect Co-N-C catalysts ORR activity, the increasing of Co content is helpful to form the Co-N species, and pyrolysis temperature 800 ? is the most beneficial to form the Co-N species. This result indicates that the temperature and content factors affect the structure of the catalyst site, and play a key role in the catalyst ORR performance.The preparation of the Fe doped carbon-nitrogen-based catalyst Fe-N-C and in-vestigation the active site of ORR of the synthetic catalysts. The Fe-N-C catalyst was prepared by high temperature pyrolysis of using the FeCl3·6H2O as Fe source and 2-Aminopyrimidine (C4H5N3) as the C/N source. And the catalyst is characterized by HRTEM, XRD and XPS. The catalyst performance for ORR is tested though the elec-trochemical method. Compared to other catalysts,we also been established that the active sites of the Fe-N-C catalyst for the ORR are Fe-N species. The other Fe-C or N-C species do not serve as active sites and interaction with the Fe-N species. The result indicates Fe-N-C catalyst show a good catalytic performance in the basic solu-tion, with Eonset =0.95 V (vs. RHE), E1/2 =0.78 V, mass activity =8.09 mA/mg, this result show Fe-N-C catalyst have good ORR activity. And after accelerated durabil-ity tests, It's mass activity decreases by 10%, but commercial Pt/C decreases by 28%,this result exhibits Fe-N-C catalyst has better durability. To study the N content af-fect Fe-N-C catalysts ORR activity, the increasing of N content is helpful to increase the content of Fe-N, and improve the ORR performance. The study established a new method for studying the structure and properties of catalysts for the synthesis of tran-sition metal doped carbon-nitrogen-based material,enriched the types of ORR cata-lysts. |
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