Metal Porphyrins for Oxygen Reduction in PEMFC

A short literature review on alternative catalysts for the cathodic oxygen reduction in acid (H2SO4) and polymer electrolyte membrane fuel cell (PEMFC) with special emphasis on pyrolyzed macrocycles and precursor materials from metals, organic molecules and N-containing elements has been conducted. Furthermore, various catalytic materials comprising two different concentrations of iron and cobalt tetramethoxyphenyl porphyrins and perovskites were prepared by both the impregnation and precipitation reactions. Screening tests of the individual catalytic materials and their mixtures were carried out in half-cell measurements using the rotating disc electrode (RDE) in 0.5M H2SO4 and at room temperature. Cyclic voltammograms were recorded at a scan rate of 10 mV s-1 both with and without rotations. The peak potential at 0 rpm was used to study and compare the catalytic activities towards oxygen reduction reaction (ORR). Concentrations of 30wt% Fe and Co/TMPP have shown increased performance characteristics, while those with lower or increased contents, acid-treated and mixed with perovskite have displayed lower activities. Polarization data for the catalyst containing 30wt% FeTMPP was also obtained. Acid leaching of the pyrolysis products has resulted in substantial decrease of the metals from the pyrolysis products supported on carbon. TEM, BET-surface area and EDX analyses on the samples have shown high aggregation of the metals with crystalline structure, surface areas depending on the compositions of the catalysts and increased surface concentration of the metals with absence of nitrogen on the moiety.