Improving Selectivity and Catalytic Rate of Iron Porphyrin Catalysts for the Oxygen Reduction Reaction

The growing demand for sources of clean and sustainable fuel has been at the forefront of research since the turn of the 21st century. Development of hydrogen fuel cells utilizes hydrogen to meet these demands. Traditionally platinum, the most expensive component, is employed at the cathode of these cells to catalyze the oxygen reduction reaction (ORR). The drive for a cheaper alternative has led to the study of iron porphyrin complexes, inspired by cytochrome c oxidase (CcO), to catalyze ORR. However, iron porphyrin catalysts do not fully reduce all O2 to H2O, leading to the production of H2O2 breaking down the membrane of the fuel cell. Varying the first and second coordination sphere of the iron porphyrin complexes through the incorporation of anionic bound species and pendant basic groups employ a “push” and “pull” effect. These effects increase selectivity towards the production of H2O and increase the catalytic rate, 100-fold compared to the catalytic rate of CcO. In turn, these cheaper and simpler complexes can potentially replace platinum to catalyze ORR at the cathode of fuel cells.