The anodic oxidation of cerium(II1) a t platinum, gold and glassy carbon electrodes was investigated by rotating disc voltammetry in sulphuric and perchloric acid solutions. Conditional potentials, limiting currents and charge-transfer kinetic parameters were obtained and the results are discussed. The absence of chemical corrosion and mixed potentials indicated that glassy carbon is the best electrode material. Current efficiencies were calculated.
Keywords : Cerium(I V ) ; rotating disc electrode ; charge-transfer kinetic fiarametersCerium(1V) is a popular oxidising agent and has been used in coulometric titrations with success.1-18 Most of the work has been carried out at platinum, but gold3 and carbon pastelg have also been used. Vetter,20 Fronaeuszl and Fronaeus and Ostman22 studied the reduction of cerium(1V) in sulphuric and perchloric acids. The rate-determining step is the electron transfer reaction Ce(1V) + e -+ Ce(II1)A survey of the literature indicated that every group who had studied this system and measured kinetic parameters had approached the problem by studying the reduction of cerium(1V) rather than the oxidation of cerium(II1). As it is the anodic reaction that is involved in coulometric titrations with cerium( IV) we decided to study the anodic reaction directly .The purpose of this work was to study the effect of experimental parameters on the chargetransfer kinetic parameters. Both background and cerium( IV) generation reactions were studied for the purpose of evaluating generation current efficiencies.
Experimental ApparatusA conventional three-electrode potentiostat was built by using general-purpose FET operational amplifiers. A separate control unit provided the initial and ramp potentials, which, when fed into the potentiostat bridge circuit, allowed control of the working electrode potential.The rotating disc electrode with interchangeable tips has been described elsewhere.23Voltammograms were recorded on a Hewlett-Packard Moseley 7035 X -Y recorder.Potentials of the working electrode with respect to a specially designed calomel electrode24Rotation frequencies of the working electrode were measured on an S.E. Laboratories (Engin-were measured on an S.E. Laboratories (Engineering) Ltd. digital voltmeter, Model SM 215. eering) Ltd. crystal timer, Model SM 200.
Reagents and Materialsacids, which were of Aristar grade (BDH Chemicals).All of the reagents used were of AnalaR grade (Hopkin and Williams), except for mineral Specially distilled water25 was used. Certified-grade volumetric glassware was cleaned with an alcoholic potassium hydroxide solution.
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