Sulfur-Doped Porphyrinic Carbon Nanostructures Synthesized with Amorphous MoS2 for the Oxygen Reduction Reaction in an Acidic Medium

Abstract

To develop doped carbon nanostructures as non-precious metal cathode catalysts, nanocomposites were synthesized by using SBA-15 and 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin-iron(III) chloride with different ratios of amorphous MoS₂ precursor. From various analyses, it was found that, during pyrolysis at 900 °C under an N₂ atmosphere, the amorphous MoS₂ precursor decomposed into Mo and S, facilitating the formation of graphene sheet-like carbon with MoC and doping of sulfur in the carbon. In the nanocomposite formed from 10 wt % MoS₂ precursor (denoted as Mo/S/PC-10), most of the MoS₂ was decomposed, thus forming S-doped carbon, which was grown on the MoC phase without crystalline MoS₂ . Furthermore, Mo/S/PC-10 exhibited better performance in the oxygen reduction reaction (specific activity of 1.23 mA cm^-2 at 0.9 V and half-wave potential of 0.864 V) than a commercial Pt catalyst, owing to a heteroatom-doped carbon nanostructure with a fairly high specific surface area. In the polarization curve of the unit-cell performance measured at 80 °C under ambient pressure, Mo/S/PC-10 as a cathode catalyst exhibited an optimal power density of 314 mW cm^-2 and a current density of 280 mA cm^-2 at 0.6 V.

Keywords: carbonaceous materials; doping; electrocatalysis; fuel cells; nanostructures.