On the Influence of Sulphur on the Pyrolysis Process of FeTMPP Cl based Electro Catalysts with Respect to Oxygen Reduction Reaction ORR in Acidic Media

Pyrolysis of chloroiron tetramethoxyphenyl porphyrin FeTMPP Cl in the presence of iron oxalate sulphur leads to the formation of higly porous and active catalysts for the oxygen reduction reaction ORR . In order to clarify the influence of sulphur the pyrolysis process is analyzed by thermogravimetry TG and by high temperature X ray diffraction HT XRD . In the absence of sulphur iron carbide FexC is formed which catalyses the proceeding graphitisation of the pyrolysis products. As a result catalytic active centres are decomposed by this reaction. This can be avoided by the addition of sulphur because iron monosulphide FeS; troilite is formed instead of FexC. Furthermore, FeS can easily be removed in a successive etching step so that nearly all inactive by products can be removed. The results are in accordance with the higher electrochemical performance of the sulphur containing catalyst