| Fuel cells are getting more and more attention because of their high efficiency and environmentally friendly nature. In the fuel cell’s electrode reactions including the anodic hydrogen oxidation reaction (HOR) and the cathodic oxygen reduction reaction (ORR), the rate of ORR is much slower than that of HOR, making the ORR the dominant limiting factor in fuel cell performance even when Pt-based catalysts are used. At present, all of the non-precious metal catalysts (NPMCs) have much less catalytic activity and stability than Pt-based catalysts. While transition metal-nitrogen catalysts (abbreviated as TM-N/C) and nitrogen-doping carbon catalyst (N/C), have attracted significant attention because of their reasonable activity and remarkable selectivity towards the ORR.This paper use urea, melamine, melamine as nitrogen source, Co(OAc)2· 4H2O and FeCl·6H2O as metal precursor, BP2000 as a carrier for carbon, then the catalyst were heat treatmented at 600,700,800,900 and 1000℃ showed a good electrocatalysis of oxygen reduction reaction (ORR). The influence of the dosage of the nitrogen source, metal source, heat treatment temperature and acid treatment of catalysts for electro-catalysis performance was examined. And it is compared with the current commercial 20% Pt/C catalyst. Composition and structure of the catalysts had been characterized using X-ray diffraction (XRD), fourier transform infrared spectrum (FT-IR), X-ray photoelectron spectroscopy (XPS) methods. ORR dynamics mechanism on the catalyst was put forward, and based on this, the catalytic activity and catalytic mechanism were discussed. The results showed that:(1) Through three different synthetic methods of the grinding method, ultrasonic method and magnetic heating mixing method for preparation of catalyst Co0.25-N0.32/C0.32-800 using melamine as the nitrogen source, the catalyst prepared though ultrasonic method was best by cyclic voltammograms experiment.(2) Catalyst TM-N/C-t showed good electro catalysis activity ORR, which using urea, dicyanodiamine and melamine as nitrogen source, Co(OAc)2·4H2O and FeCl3·6H2O as source of metals, BP2000 as as carbon carrier, and then heat-treatment under the high temperature at 600,700,800,900 and 1000℃.(3) The metal source and heat treatment temperature had an impact on catalytic activity, and the second was the dosage of nitrogen source. But the species of nitrogen source had a little effect on catalytic activity.(4)The catalyst TM-N/C-t prepared in this paper had better electrocatalysis ORR activity and methanol resistance than commercial 20% Pt/C catalyst.(5)Through the test of XRD, XPS, FT-IR and CVs for the contrast experiments, it was concluded that Co-N-C, N-C, Co-N may be the active sites of catalyst Co-N/C-800, and active site Co-N-C electrocatalysis activity for ORR was best.(6) Through XPS analysis and fitting corresponding Nls peak in the catalyst Co0.25-Nx/C0.32-800 of prepared using different dosage of melamine and comparision the percentage of different kinds of nitrogen, the type of nitrogen in Co-N-C active site was concluded. And through the study of the CVs and XPS analysis for the catalyst before and after acid treatment, it stated that acid treatment can reduce electrocatalysis activity ORR.(7) According to the theory of irreversible reaction process of the cyclic voltammograms and calculated the catalysts Co-N/C-800 prepared using urea, dicyanodiamine and melamine as nitrogen source, cobalt acetate as source of metal source, it was found that the electrocatalysis ORR of catalysts Co-N/C-800 was 2 and 4 electronic mixing process, and mainly in 4 electronicreaction mechanism. That is to say, the mainly catalytic ORR process of the catalysts prepared in this paper directly transformed oxygen to the water. |
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