THE ELECTRODE KINETICS OF THE CHROMOUS-CHROMIC COUPLE
CASE WESTERN RESERVE UNIV CLEVELAND OH ELECTROCHEMISTRY RESEARCH LAB
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The CrH2062CrH2O63 couple has been studied with cyclic voltammetry on a hanging mercury electrode in acidic perchlorate, chloride- perchlorate, and bromide-perchlorate supporting electrolytes at controlled ionic strength and pH. In addition to the simple hexaaquochromiumIIIII couple, the chromium chloride ion and bromide ion couple were studied. Concentrations of the reacting species at the electrode surface were computer calculated from the diffusion coefficients using the experimental current-time data, with no a priori assumptions concerning the dependence of the kinetics on potential double layer corrections were applied. For both of the halogen containing couples, the first order standard rate constants not considering surface coverage with halogen ions show a dependence on bulk halogen concentrations. The experimental free energies of activation for the hexaaquochromiumIIIII heterogeneous and homogeneous reactions were compared with the values predicted by weak interaction theory. Theory and experiment both show that the free energy of activation for an electrode reaction is about half of that for its homogeneous counterpart when the most probable distance of separation between the reactant and the electrode in the activated state is twice the radius of the reactant.
- Inorganic Chemistry
- Physical Chemistry