Preparation And Electrochemical Characteristics Of Pyrolyzed Carbon Supported Non Precious Metal Polypyrrole Catalyst For Oxygen Reduction Reaction

Environmentally energy conversion systems attract growing attentionto fulfill the energy requirements in the future. Proton exchangemembrane fuel cells （PEMFCs） are promising sources of clean energy byconverting chemical energy directly into electricity. In practice, catalystsare needed to promote the electrochemical reactions of hydrogenoxidation at the anode and oxygen reduction at the cathode in PEMFCs,especially the sluggish oxygen reduction reaction （ORR）. At present,carbon supported Pt and its alloys have been proved and accepted to bethe most efficient catalyst for ORR. However, high cost and limitedresources of the noble metal platinum and its low utilization haveconstrained the commercialization of PEMFCs. Therefore, developmentof low cost and efficient non-precious metal electrocatalysts for ORR hasbecome an urgent task for worldwide fuel cell people, and numerousefforts have been made in recent decades Among various non-precious metal electrocatalysts for ORR, carbonsupported transitional metal based nitrogen-containing catalysts （M-N/C）have been considered as the most promising replacement for the existingplatinum-based catalysts for ORR in PEMFCs, and extensive researcheshave been conducted on M-N/C catalysts. The results showed that thecatalytic performance of M-N/C catalysts towards ORR is closely relatedwith the used metal type and its precursor and content, nitrogen resourceand its content, heat treatment temperature and time as well as thestructure of the catalysts. In order to achieve higher activity toward ORR,this work was conducted to prepare catalysts by using cobalt acetate andiron acetate as a metal source, polypyrrole as a nitrogen source,p-Toluenesulfonic acid （TsOH） as sadditive, and commercially availablecarbon black as a support. Effects of catalysts composition, the usedmetal type and its precursor and content and heat treatment temperaturewere extensively investigated. Furthermore, we also optimized thepreparation process of catalysts to achieve better catalytic performance.It is revealed that the used amount of pyrrole has much moreapparent effect than TsOH on elemental contents in the Co-PPy-TsOH/Ccatalysts. Increase in the usage of both pyrrole and TsOH is helpful foraccelerating four-electron-transfer ORR, but only that of pyrrole isbeneficial for catalytic activity improvement. Besides, the content of eachelement has also been found to affect the electrochemical performance of the Co-PPy-TsOH/C catalysts. Through the CVs test,CoFe₂-PPy-TsOH/C catalysts showed the best catalytic performanceamong the studied alloy catalysts with both iron and cobalt, and800℃has been found to be the best temperature to synthesizeCoFe₂-PPy-TsOH/C catalyst with the optimal performance, agreeing wellwith the previously reported results in literatures for similar M-N/Ccatalysts. Furthermore, the synthesis procedure of the Co-PPy-TsOH/Ccatalyst has also been optimized to obtain better performance.