title: Ligand effects on the overpotential for dioxygen reduction by tris(2-pyridylmethyl)amine derivatives.
abstract: A series of copper complexes based on the tris(2-pyridylmethyl)amine (TPA) ligand are examined for their oxygen reduction reaction (ORR) activity. Increasing the potential of the Cu(I/II) couple from 0.23 V vs RHE for [Cu(TPA)(L)](2+) to 0.52 V for [Cu(TEPA)(L)](2+) (tris(2-pyridylethyl)amine) at pH 7 or adding a hydrogen-bonding secondary coordination sphere does not increase the onset potential from 0.69 V vs RHE for the ORR. The underlying mechanism for the ORR is determined to be first-order in O(2) and second-order in Cu. The rate-determining step is found to not be Cu(II) to Cu(I) reduction, as seen in other systems. The rate-determining step is also not the protonation of an intermediate, but may be the reduction of a hydroperoxo intermediate. Pyrolysis of the Cu complex of TPA affords an inactive material; activity is recovered through addition of intact TPA to the electrode surface.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Avenue, Urbana, Illinois 61801, United States.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Thorseth
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Letko
authors.forename: Edmund C M
authors.initials: EC
authors.lastname: Tse
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Rauchfuss
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Gewirth