Influence of Sulfur on the Pyrolysis of CoTMPP as Electrocatalyst for the Oxygen Reduction Reaction

Abstract

This work presents the preparation and investigation of pyrolyzed cobalt–tetramethoxyphenylporphyrin (CoTMPP) supported by iron oxalate with and without sulfur as electrocatalysts for the oxygen reduction reaction (ORR) in acid media. A preparation method which needs no addition of carbon supports allows the structural investigation of the pyrolysis products by X-ray photoemission spectroscopy, Raman spectroscopy, and X-ray diffractometry without any interferences of a carbon support. Already with low metal loading, rotating ring disk electrode measurements reveal the high ORR activity and enhanced selectivity which are apparently caused by an increased number of catalytic centers and higher efficient ones due to a well developed porosity and a suitable molecular structure of the formed carbon. A thermogravimetric investigation of the pyrolysis process shows that the addition of sulfur to the precursor influences the carbonization of the porphyrin in a favorable way. It has been found that extended graphene layers present a particularly suitable matrix for highly active catalytic centers.