Browsing by Author "Bettelheim, Armand"

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Electroreduction of Cobalt-Amino Peroxo Complexes Part 1: Reduction of Oxygen in the Co(n) + Ammonia System
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (1), 1977) Bettelheim, Armand; Faraggi, M; Hodara, I
The electroreduction of O2 in Co(II)+ 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—O2—Co(NH3)5]+4. The electro-activity 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 × 10–6 cm2 s–1. The decomposition of the peroxo complex to form a mononuclear complex of Co(III) was a slow process (k= 3.0 × 10–6 s–1).
Electroreduction of Cobalt-Amino Peroxo Complexes Part 2: Reduction of Oxygen in the Co(n)-Ethylenediamine and Co(n)-Triethylenetetramine Systems
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (1), 1977) Bettelheim, Armand; Faraggi, M; Hodara, I
The cathodic reduction and the optical properties of the peroxo-complexes [LCo—O2—CoL]+4 with L = en (ethylenediamine) and L = trien (triethylenetetramine) have been studied. It was found that four electrons are involved in the reduction of the peroxo-complexes. The diffusion coefficients of the above complexes were calculated to be 7.0 × 10–6 and 8.8 × 10–6 cm2 s–1 respectively. The redox potentials are –0.57 V and –0.50 V (vs. s.c.e.) respectively. These complexes are unsuitable as catalysts for the cathodic reduction of oxygen because they have lower redox potentials than that of oxygen. A different behaviour was found in the cobalt-ethylenediamine system when the ratio [en] : [Co(II)]= 1. The redox potential of the complex formed in this case is –0.17 V and its optical spectrum showed two absorption bands (λmax at 350 and 310 nm.) Therefore, it is suggested that a Co(III) en complex is formed, one which was found to be a suitable homogeneous catalyst for the cathodic reduction of oxygen.
Homogeneous catalysis of cathodic reduction of oxygen in copper–cystamine aqueous solutions
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (04), 1977) Bettelheim, Armand; Faraggi, Moshe; Hodara, Isaac; Manassen, Jost
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.