KINETICS OF CEROUS-CERIC REDOX REACTION AT A PLATINUM ELECTRODE

The kinetics of the cerous-ceric redox couple at the smooth platinum electrode in acid solution have been investigated using the rotating disc electrode technique. The polarisation curves obtained in sulphuric acid show the retarding effect of the oxidic layer formed on the electrode, upon the ceric reduction kinetics. In perchloric acid, and to a lesser extent in nitric acid, however, some gross hysteresis effects were observed in the polarisation curves which display a region where the reduction current decreases with decreasing electrode potential. This effect cannot be accounted for on the basis of any expected influence of the oxidic layer alone, and it is suggested that the explanation should be sought in the modification of the electrical double layer at the electrode brought about by appreciable coverages with adsorbed cerous ions. The diffusion coefficient of the ceric species in sulphuric acid was measured and found to be in agreement with the value previously measured by means of the anthracene electrode. © 1968.