Why is there such a small overpotential for O2 electro reduction by copper laccase?

Abstract

Quantum chemical predictions are made of the reversible potentials for the intermediates formed during the four-electron reduction of O2 by copper laccase, using three loosely associated partially ligated Cu1 centers as models for the active site. Two mechanisms are studied, the platinum surface mechanism in acid electrolyte and the proposed laccase mechanism for basic electrolyte. Both are found viable and the CuII-OH reduction step has the lowest potential and so is responsible for the predicted overpotential, which is less than for platinum electrodes, but more than in the natural laccase. Adding more ligands would be expected to reduce the predicted overpotential to the very small measured value by reducing O and OH bond strengths to the active site.