Homogeneous catalysis of cathodic reduction of oxygen in copper–cystamine aqueous solutions

Abstract

The copper cystamine complex is a suitable system for the homogeneous catalysis of oxygen cathodic reduction in aqueous solutions. A steady state cathodic current density of 3.2 mA/cm2 at 0.2 V and an overvoltage decrease of 400 mV was observed in oxygen-saturated solutions of equimolar concentrations of CuII ions and cystamine (5 × 10–2 mol dm–3) at pH 4.5. For a given value of Cl– ion concentration and pH the catalytic current can be expressed by: Icat=k[CuII]0[O2].

The optical, magnetic and kinetic properties of the catalyst were investigated. The results suggest that the CuII ion, although initially reduced to CuI, is stabilized by the disulphide bridge. It is also suggested that because the bridge is a two electron mediator for the reduction of oxygen, the potential barrier of the first electron reduction can be overcome.