Synthesis And Characterization Of Non Precious Metal Catalysts For The Proton Exchange Membrane Fuel Cell Cathode

Recently, Pt-based catalysts remain the best proton exchange memberane fuel cell (PEMFC) cathode catalysts for oxygen reduction reaction (ORR). However, Pt is a rare and precious metal. Both instability and high cost of Pt-based catalysts represent two main obstacles limiting the commercial applications of PEMFCs. Therefore, non-noble metal catalysts known for their high efficiency and low cost ought to be a long-term choice. In this paper, we synthesized three systems of non-noble metal catalysts:(1) The non-precious metal catalysts of pyrolyzed Vitamin B12as carbon-supported transition metal based macrocycles for ORR were synthesized. Pyrolysis was carried out at temperatures of300℃,500℃,700℃, and900℃in an N2-atmosphere. Electrocatalytic measurements show that a significant enhancement in intrinsic activity and onset potential for the ORR is observed when the temperature is increased from300℃to500℃, while a further increase to900℃results in a decrease in catalytic activity. The optimal pyrolysis temperature is500℃. The ORR onset potential of the catalyst obtained at500℃is0.78V.(2) Polyaniline (PANI) was used as precursors to prepare PANI-M-C non-precious metal catalysts by a soft template method. Electrochemical measurements show that the PANI-Fe-C catalyst obtained at850℃has the highest electrocatalytic activity among these catalysts. The ORR onset potential of PANI-Fe-C catalyst is measured to be0.87V. This catalyst contains more carbon lattice distortion and graphite nitrogen than the others, which make good explanations for the excellent ORR performance.(3) We designed a new synthetic method for a series of novel PANI-tungsten carbide (WC) catalysts for ORR. The PANI-WC catalysts were synthesized from pyrolysis of the prepared PANI nanofibers as both nitrogen and carbon precursors and WC particles. Electrocatalytic measurements for PANI-WC catalysts with different polymerization times of PANI and WC loading show that the catalyst with PANI in16h and5.0wt.%WC performs the best electrocatalytic activity. The ORR onset potential is measured to be0.87V and undergoes four-electron transfer processes.