Study On The Preparation And Catalytic Activity Of Carbon Suppored Metalloporphyrins Catalysts

Platinum and its alloys are good catalysts for oxygen reduction reaction(ORR) used for fuel cell in low temperature condition, however, these are easily poisoned by CO and the high cost which limit its application as catalyst and the development of industrialization of Fuel Cells. Metalloporphyrins compounds show good electrocatalytic activity for oxygen reduction both in acid and alkaline solutions. It is considered as the most promising catalyst material to replace the noble metal for ORR in fuel cells. The three basic precursors of metalloporphyrins, containing non-noble metal, nitrogen sources and carbon support, show the same catalytic activity as metalloporphyrins chelates and this is investigated as a new study direction for these catalysts. This paper applied microwave and mechanically mixing to prepare catalysts and studied the influence factores for catalytic activity. Focusing on carbon support and synthesis technology, we prepared Co-TMPP based catalysts with good catalytic activity and high stability and investigated the catalytic performance and mechanism of catalysts for ORR by means of electrochemical and physical testing methods.1. CoTMPP/MWNT electrocatalyst was synthesized by microwave method and its microstructure was characterized using transmission electron microscopy. The activities of the CoTMPP/MWNT for ORR were evaluated by rotating disc electrode (RDE) and rotating ring disc electrode (RRDE) technique, respectively. Compared to the traditional organic synthesis, CoTMPP/MWNT electrocatalys which prepared by microwave synthesis has shown better performance for oxygen reduction reaction (ORR) and the half wave potential shifted 110 mV positively. CoTMPP/MWNT electrocatalys shows 10 mV higher on-set potential for oxygen reduction and 21% lower reduction current loss in comparison to CoTMPP/BP2000. That means that multiwalled carbon nanotube supported CoTMPP electrocatalyst has higher catalytic activity and better stability than CoTMPP/BP2000. The number of electrons exchange during ORR and the percentage of peroxide (% H2O2) produced by the reaction were calculated to be 3.63 and 18.65%, respectively.2. Composite electrocatalysts based on transition metal Co are synthesized for oxygen reduction reaction (ORR) by mechanically mixing three basic precursors containing carbon black, cobalt acetate and Tetramethoxy-phenylporphyrin (TMPP). The influence of various mixing processes, solvents, pyrolysis temperature and precursor ratios on the ORR activity of electrocatalysts was investigated by means of their electrochemical characteristics. Levich-Koutecky plots showed that the number of transferred electrons during ORR on these catalysts varies between 2 and 4. A pyrolyzed mixture synthesized by ultrasonication shows better activity for ORR than that by ball milling. The solvent was found to have significant effect on the performance of catalysts in acidic media. The catalyst synthesized in water, a poor solvent of TMPP, had better activity than that synthesized in good solvent of TMPP, such as N, N-Dimethylformamide and acetic acid. The optimal pyrolyzed temperature was observed at 600°C. Various mole ratio and Co/carbon weight ratio were examined. Maximum activity was found at 1:1 TMPP/Co mole ratio and 5% Co/carbon weight ratio.