Electrocatalytic activity of Fe-N/C-TsOH catalyst for the oxygen reduction reaction in alkaline media

Abstract

Pyrolyzed carbon supported ferrum polypyrrole (Fe-N/C) catalysts were synthesized with and without the dopant p-toluenesulfonic acid (TsOH) through a solvent-grinding method followed by heattreatment at the desire temperature. Both the catalysts were characterized using electrochemical techniques, such as cyclic voltammetry (CV), as well as the rotating disk electrode (RDE) technique. It was found that the catalysts doped with TsOH showed significantly better oxygen reduction reaction (ORR) activity than the undoped catalysts. The average electron transfer numbers for the catalyzed ORR were 3.899 and 3.098 for the TsOH-doped and undoped catalysts, respectively. Thermal treatment was found to be a necessary step for catalyst activity improvement. The catalyst pyrolyzed at 600 °C showed the best ORR activity: the onset potential and the potential at the current density of-1.5 mA · cm-2 for the TsOH-doped catalyst were 30 and 170 mV more positive than those for the un-pyrolyzed TsOH-doped catalyst, respectively. To clarify the effects of TsOH doping and pyrolyzation, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to analyze the morphology, structure, and composition of the catalysts. The XPS results suggest that the pyrrolic-N groups are the most active sites and sulfur species are structurally bound to carbon in the form of C-Sn-C and oxidized -SOn- bonds, which is an additional beneficial factor for the ORR. © Editorial office of Acta Physico-Chimica Sinica.