Nonprecious Metal Catalysts for Oxygen Reduction Based on First Row Transition Metal Brominated Corrole Complexes

Lior Elbaz, Chemistry, Bar Ilan University, Ramat-Gan, Israel
Naomi Levi, Chemistry, Bar Ilan University, Ramat-Gan, Israel
Ariel Friedman, Chemistry, Bar Ilan University, Ramat-Gan, Israel
Bar Gavriel, Chemistry, Bar Ilan University, Ramat-Gan, Israel
Zeev Gross, Chemistry, Technion, Haifa, Israel
Atif Mahammed, Chemistry, Technion, Haifa, Israel

Fuel cell technology raised new interest over the past two decades due to the increasing oil prices, non-sustainability of fossil fuel and the consequences of combustion on air pollution and climate changes. Two aspects limit the practicality and energy conversion efficiency in polymer electrolyte membrane fuel cells: the rate-limiting oxygen reduction reaction at the cathode and the low abundance and high cost of platinum, which still remains the most efficient catalyst.

Significant effort has been made to develop alternative non-precious metal catalysts (NPMCs) for oxygen reduction. Many of those catalysts have been inspired by biological processes in that their active centers consist of transition metal complexes such as metallo-porphyrins. So far, studies conducted with such catalysts show that their activity and stability is lower than that of the state-of-the-art platinum based catalysts. In most recent years a new class of NPMCs has shown great promise; the metallo-corroles.

A series of first row transition metal β-pyrrole-brominated 5,10,15-tris(penta-fluorophenyl)- Corroles [M(tpfc)Br_8, M=Mn, Fe, Co, Ni and Cu] were synthe-sized and tested as catalysts for oxygen reduction in acidic aqueous solutions. Both the reduced form and the oxidized forms of these corroles were chara-cterizes by means of NMR, EPR and UV-vis measurements. Rotating Ring-Disk electrode (RRDE) was used to test the kinetic performance of these corroles in the catalytic reaction of oxygen reduction (ORR). The corroles were adsorbed on a high surface area carbon powder (BP2000) prior to electro-chemical measurements, to create a unique composite material. The comparison between the corroles with different metal centers showed a favorable catalytic performance of the ORR in the case of the Co-Corrole, which showed an onset potential of only 0.8V vs. RHE.