The copper cystamine complex is a suitabIe system for the homogeneous catalysis of oxygen cathodic reduction in aqueous solutions. A steady state cathodic current density of 3.2 mAlcm2 at 0.2V and an overvoltage decrease of 400mV was observed in oxygen-saturated solutions of equimolar concentrations of CuII ions and cystamine (5 x mol dm-3) at pH 4.5. For a given value of C1-ion concentration and pH the catalytic current can be expressed by :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.
The electroreduction of O2 in Co(@ + NH3 solutions has been investigated using the rotating disc electrode technique. It was found that the electroactive species, in the potential range 0 to -1 V against s.c.e., are O2 and the peroxo complex [(NH3)5Co-02-Co(NH3)5]+4. The electroactivity of the complex was shown by the appearance of a new cathodic wave and by the linear increase of the limiting current of this wave with the peroxo complex concentration. It is suggested that four electrons are involved in the reduction of the complex on a Pt rotating disc electrode. Its diffusion coefficient was calculated to be 8 . 6 ~ cm2 s-I. The decomposition of the peroxo complex to form a mononuclear complex of Co(n1) was a slow process (k = 3 . 0 ~ s-l).
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