Electron transfer kinetics at redox polymer/solution interfaces using microelectrodes and twin electrode thin layer cells

The M(III) states of poly-[Ru(vbpy)₃]²⁺ and of [Os(bpy)₂(vpy)₂]²⁺ films electropolymerized onto Pt disk microelectrodes and onto one of the electrodes in twin electrode thin layer cells (TETLC), respectively, have been used to mediate oxidations of other metal polypyridine complexes NL²⁺₃ in acetonitrile solutions. Steady state mediation currents in TETLC experiments could be observed even when the formal potential of NL²⁺₃ was as much as 570 mV more positive than that of the mediating polymer film. Measured rate constants k₁₂Γ of the mediation reactions, which occur at the polymer solution interface, agree with rotated disk data where previous determinations are available and with the established Gibbs energy-rate correlation for others. An analysis is presented of the slowest case of mediation reaction kinetics, where permeation of NL²⁺₃ into the polymer volume becomes of concern, that suggests that it too is dominated by electron transfers at the polymer/solution interface.