Temperature and pH Dependence of Oxygen Reduction Catalyzed by Iron Fluoroporphyrin Adsorbed on a Graphite Electrode

The graphite electrode surface adsorbed by 5,10,15,20-tetrakis(pentafluorophenyl)-21 H , 23 H -porphine iron (III), abbreviated as Fe III TPFPP , displays strong electrocatalytic activity toward O 2 reduction. The surface adsorption of Fe III TPFPP was investigated at different pH levels and temperatures by cyclic voltammetry. The kinetics of catalyzed O 2 reduction at different temperatures, as measured by cyclic voltammetry and a rotating disk electrode, was analyzed and the corresponding reaction mechanism was proposed. A four-electron/four-proton process was found to be the dominating pathway for catalyzed O 2 reduction. Furthermore, an increase in temperature from 20 to 70°C was shown to significantly enhance the reduction rate. The implication of such non-noble electrocatalysts for the cathode reaction in low-temperature proton exchange membrane fuel cells is discussed.