Inorganic Chemistry, Vol.51, No.8, 4694-4706, 2012
Nonprecious Metal Catalysts for Fuel Cell Applications: Electrochemical Dioxygen Activation by a Series of First Row Transition Metal Tris(2-pyridylmethyl)amine Complexes
A series of divalent first row triflate complexes supported by the ligand tris(2-pyridylmethyl)amine (TPA) have been investigated as oxygen reduction catalysts for fuel cell applications. [(TPA)M2+](n+) (M = Mn, Fe, Co, Ni, and Cu) derivatives were synthesized and characterized by X-ray crystallography, cyclic voltammetry, NMR spectroscopy, magnetic susceptibility, IR spectroscopy, and conductance measurements. The stoichiometric and electrochemical O-2 reactivities of the series were examined. Rotating-ring disk electrode (RRDE) voltammetry was used to examine the catalytic activity of the complexes on a carbon support in acidic media, emulating fuel cell performance. The iron complex displayed a selectivity of 89% for four-electron conversion and demonstrated the fastest reaction kinetics, as determined by a kinetic current of 7.6 mA. Additionally, the Mn, Co, and Cu complexes all showed selective four-electron oxygen reduction (<28% H2O2) at onset potentials (similar to 0.44 V vs RHE) comparable to state of the art molecular catalysts, while being straightforward to access synthetically and derived from nonprecious metals.