Simple redox reactions studied below the melting point of congruently melting electrolyte: (C 4H 9) 4NF · 32H 2O

Abstract

Two simple one-electron redox reactions, one involving a highly charged ionic reactant, Fe(CN) 4− 6 − e − ⇌ Fe(CN) 3− 6, and the other involving a neutral molecule, Fc(CH 2OH) 2 − e − ⇌ Fc(CH 2OH) + 2, were investigated in a congruently melting electrolyte, (C 4H 9) 4NF · 32H 2O, at temperatures below its melting point. They were studied by cyclic voltammetry and potential step chronoamperometry using a Pt ultramicroelectrode. After freezing, the shape of cyclic voltammograms changes from the near steady-state wave shape typical of radial diffusion to the peak shape typical of linear diffusion. The slow-scan cyclic voltammetric currents obtained in solid electrolyte are considerably smaller than those obtained in liquid electrolyte. Both effects are probably caused by a substantial decrease in the apparent diffusion coefficient of redox species in the solid state. Additionally the results of potential step experiments performed in the solid electrolyte at short times (⩽ 1 s) show some radial diffusion contribution. On the basis of these results it has been concluded that the redox reactant is not uniformly dispersed in the solid electrolyte, but is concentrated near the electrode surface and probably in intergrain space.