Synthesis And Characterization Of Diporphyrin Compounds And Their Electrocatalytic Activities Toword Oxygen Reduction

Transition metal-N4 macrocyclic compounds have been investigated widely as a class of promsing non-noble metal catalysts for ORR due to its good catalytic activity for oxygen reduction after high temperature treatment under acidic conditions. In this paper, in order to explore the cathodic ORR catalyst applied in fuel cell, we focus on three aspects of the catalyst preparation: pretreatment methods of the carbon support, different N-precursors choices, and heat-treatment of the catalyst. The modified electrodes were prepared based on porphyrin monomer Cobalt(II)meso-tetraphenylporphyrin(CoTMPP), Cobalt diporphyrins linked by alkanes, [Co(II)Salen], Co (phen)₃ and Co-PPy electrocatalyst, and their ORR catalytic performances were investigated by means of electrochemical and physical tests in order to explore in depth the factors which influence the ORR electrocatalysis ability.1. Electrocatalysis for Oxygen Reduction by Ketjen Black EC 300J Supported Cobalt Porphyrin Complexes after High-temperature Pyrolysis. The ORR performance of the carbon black loaded CoTMPP/KB catalyst was investigated in 0.5 M H₂SO₄ solution, as well as the influence of chemical pretreatment of carbon black and cobalt porphyrin loading method to ORR performance were explored. The carbon supports was pretreated with 6 M HNO₃ and 30% H₂O₂ respectively and the electrochemical test results show that pretreatment of the catalyst can promote the catalytic properties for ORR with more promoting effect by 6 M HNO₃. Comparing the two carbon black loading method of metal porphyrin, pyridine was proven as the better solvent, and the electrocatalyst prepared directly by CoTMPP has better catalytic performance than that made by TMPP added with cobalt salts separately. In this paper, the surface properties and the microstructures of both the carbon black KB and the electrocatalyst have been investigated by IR, XRD, TEM and nitrogen adsorption/desorption.2. Synthesis and ¹H-NMR characterization of Porphyrin Dimers and their metal complexes. The alkoxyl-chain linked and tolylene-bridged biporphyrin complexes were synthesized and we attempted to explore the synthesis routes to o/o and p/p biporphyrin bridged by–O-CH₂-R-CH₂-O- chain gradually through single hydroxyl-porphyrin→bromine-porphyrin→biporphyrin. Furthermore, we discussed the experimental conditions of synthesis and the intermediate products as well as the objectives were characterized by 1HNMR.3. The redox properties of the intermediate products and the objectives were investigated in DMSO by the Cyclic Voltammetry (CV). Meanwhile, Three kinds of carbon-supported metal porphyrin dimmers catalysts were prepared and the catalytic activity for ORR were evaluated by rotating ring-disk electrode(RRDE) technique and CV. The results show that the redox peak half-wave potential(E_1/2)of porphyrin ring moved to negative potential when there are substitute groups(-CH₃,-OCH₃) on the base of phenyl and metal ions have conjugated with porphyrin. And the alkoxy chain length have significant impacts on electrochemical properties of diporphyrin compounds.4. Electrocatalytic Activities Toword ORR was evaluated on electrocatalysts based on non-porphyrin N-precusors by RRDE technique and CV. Several carbon-supported macrocyclic metal complex catalysts were prepared by [Co(II)Salen] and Co(phen)₃ as N-precursors. The composite catalysts Co-PPy-C was synthesized by oxidative chemical polymerization method and its catalytic activity towards ORR was evaluated by CV.