VI. Nonstationary Processes at Polymer-Coated Rotating Disk Electrodes. A Study of [Ru(bpy)₂CI(PVP)₅]CI Films as Three-Dimensional Mediators

The mediation of the oxidation of [Fe(CN)₆]^4-0.2M NaC1O₄by [Ru(bpy)₂Cl(PVP)₅]Cl coatings on glassy carbon electrodes is investigated by rotating disk electrode (RDE) and hydrodynamically modulated rotating disk electrode studies (HMRDE). RDE studies show the faradaic current due to the substrate and mediator along with any background current due to the polymer while HMRDE senses processes occurring at polymer electrolyte interface and distinguishes between the current due to species present in solution and within the film. Both techniques confirm that the mediation process is extremely fast under the conditions employed and that the effect of background electrolyte anion is considerable. Evidence of migration of [Fe(CN)₆]^4-into the polymer in solutions of CIO₄^-at high pH is found for low background electrolyte concentrations. The polymer is shown to behave as a three-dimensional mediator. The effect of the nature of the substrate on the rotating disk experiments is also considered.