Electrochemical reduction of oxygen by metalloporphyrin ion-complexes with heat treatment

The catalytic activity and stability of carbon powders supporting metalloporphyrin ion-complexes for electrochemical reduction of oxygen have been studied in acidic solutions. The carbon catalysts were prepared by adsorption of an electrostatic aggregation of two metalloporphyrins, metal tetrakis(N-methyl-4-pyridyl) porphyrin (TMPyP, cationic) and metal tetrakis(sulphophenyl)porphyrin (TPPS, anionic), to carbon powders dispersed in a solution. Treatment of the carbon catalysts in an argon atmosphere at 800°C enhances the activity and stability. The catalyst prepared using the FeTMPyP-FeTPPS aggregate shows a high activity comparable to that of platinum particles and reduces molecular oxygen through a four-electron process. The electrostatic aggregation of iron porphyrins forms active sites on the carbon surface and these sites persist even after heat treatment, causing a high activity for oxygen reduction.