The selectivity of oxygen reduction by prolysed iron porphyrin supported on carbon

The selectivity of oxygen reduction at pyrolysed FeTPP-Cl on carbon black was studied in acidic electrolyte using the RRDE. First the applicability of RRDE theory to RRDE porous disk electrodes was tested. It was observed that the collection efficiency for these systems decreases with increasing rotation frequency. By compensating for these variations in collection efficiency a Wroblowa analysis could be performed. It was concluded that the desired 4-electron reduction plays a dominant role only at high potentials, where the current densities are low, at lower potentials the production of hydrogen peroxide predominates. The direct formation of water was related to the possibility of the Fe(IV)O intermediate adduct being formed. Hydrogen peroxide reduction and decomposition were also studied with the RRDE, using a CoTSPc/polypyrrole ring electrode. It was found that hydrogen peroxide decomposition plays a major role in the consecutive reactions of hydrogen peroxide. The decomposition reaction was found to be independent of the potential, making a radical decomposition catalysed by the FeN4-sites most likely.