Influence of the Molecular and Mesoscopic Structure on the Electrocatalytic Activity of Pyrolysed CoTMPP in the Oxygen Reduction

Novel oxygen reduction electrocatalysts are obtained by thermolysis of chelates such as cobalt- tetramethoxyphenylporphyrin (CoTMPP) in presence of the foaming agent FeC2O4. EXAFS spectra point to the presence of molecular Fe-N4 and Co N4 centres embedded in a graphite-like matrix. The foaming agent provokes the generation of a porous material (800 m2/g) exhibiting a high fraction of mesopores (5 to 30 nm). Adding elemental sulphur to the precursors CoTMPP and FeC2O4, the catalytic activity in ORR of the final catalyst significantly improves due to an increase of mesopores and the formation of extended graphene layers in a glassy carbon-type material. The added sulphur not only facilitates the removal of inorganic by-products formed in the process of pyrolysis, but also provides an appropriate environment for catalytic centres so that the formation of undesired H2O2 is significantly decreased. In RDE measurements a catalytic activity in ORR equal to commercial platinum catalysts has been achieved.

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