Pyrolysis of Self-Assembled Iron(III) Porphyrin on Carbon toward Efficient Oxygen Reduction Reaction

Abstract

We report a simple solubility-induced self-assembly of iron(III) meso-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (FeCPP) on carbon black (BP2000) combined with subsequent pyrolysis, leading to the synthesis of new types of non-precious metal electrocatalysts (NPMEs). In both alkaline and acidic media, the obtained NPMEs demonstrate oxygen reduction reaction (ORR) activity comparable to that of commercial 20% Pt/C and much better than that synthesized by pyrolysis of mechanically blended FeCPP and carbon without self-assembly. Especially, the half-wave potential of our electrocatalyst is 0.79 V (vs. RHE) in 0.1 M HClO4 aq., representing a highly active NPME in acid. Additionally, our electrocatalysts are superior to commercial Pt/C in terms of durability during accelerated durability test (ADT) in both acidic and alkaline media. The H2O2 and HO2− yield of the electrocatalyst is less than 6.5% and 0.8%, respectively, in acidic and alkaline media. The high ORR activity should be closely correlated with the self-assembly process, allowing well dispersion of FeCPP on carbon and forming a relatively high density of ORR active sites after pyrolysis. Interestingly, it appears that Fe-N-C sites and iron oxides should be the major contributor of the ORR activity in acidic media based on electrochemical SCN− poisoning and acid-treatment experiments.