Preparation Of Carbon - Based Catalysts For Pyrolysis Of Polyaniline - Metal Coordination Polymers And Their Catalytic Performance

With the high efficiency, low temperature of operation, and zero point-of-use emission, the polymer electrolyte fuel cells (PEMFCs) have been considered as the ideal energy conversion technologies. However, the fuel cell of high price limit its application and development. Up to now,catalysts at both the fuel cell cathode and anode are based on platinum(Pt). However, it makes catalysts to be the most expensive components due to limited resourc of Pt, and the Pt-based electrode also suffers from low tolerance to CO "poisoning". These factors make catalysts become the major cause of limiting PEMFCs commercialization. Therefore, research and development of Pt-free catalysts instead of Pt-based catalysts for the development of PEMFCs has great realistic significance.Extensive efforts have been directed to carbon catalyst in so many Pt-free catalysts. Among them, nitrogen-doped carbon catalysts has become a hotspot for research based on their good durable performance and low cost in recent years. The metal-nitrogen-carbon(M-N-C) catalysts prepared by pyrolysis of metal-coordinateing polymers are considered to be one of the most promising nitrogen-doped carbon catalysts.Transition metal salts(M= Fe, Co, FeCo) were added into the solution and different polyaniline-metal (PANI-M) coordination polymer was synthesized via chemical oxidation polymerization during the the process of the aniline polymerization. Then PANI-M coordination polymer were soaked and cleand by different solvent such as water and ethanol. Finally, the different M-N-C catalysts were prepared by pyrolysis of the coordination polymer polymer used as the nitrogen source and carbon source precursors in N2 atmosphere and 900℃. For comparison, the polyaniline(PANI) precursors without metal and the corresponding C-N nitrogen-doped carbon catalysts were prepared simultaneously. FTIR, Raman, XPS, XRD, TOP-SIMS and TEM were used to analyze the morphology, the surface chemical composition and chemical structure of the PANI-M/PANI precursors and M-N-C/C-N catalysts, studying the solvent effect on the structure of the PANI-M precursors and the electrocatalytic property of the M-N-C catalysts.The results show that some sulfide and unstable phase on its surface were reduced obviously and its surface was dedoped to some extent after the PANI-M coordination polymer was soaked and cleaned by solvent, making the doping ratio of the PANI-Fe precursors obtained by using ethanol soaking and cleaning close to ideal value of 0.5, the morphology of PANI-Fe precursors change from flake to nano-zigzag and the ORR activity of the M-N-C catalyst improve clearly. The main reason why the ORR activity of M-N-C catalyst was improved is that solvent make the morphology, the structure, the surface chemical composition and chemical state of the PANI-M precursors change, making it generate more active sites during heat-treating process to promote the electrocatalytic property improvement.On the basis of above research,14 kinds of PANI-M precursors after using ethanol soaking and cleaning and the corresponding M-N-C catalysts (M= Fe, Co, FeCo) were prepared respectively by use of different iron salts, cobalt salts and iron-cobalt salts. We use electrochemical method test the M-N-C catalysts electrocatalytic activity and study the effect of different transition metal salts on the structure of the PANI-M precursors. The results show that the content of the metal salts, the chemical valences and kinds of metal cation as well as the kinds of anion have an impact on the structure of the PANI-M precursors and the electrocatalytic property of the M-N-C catalysts.