Effect of supporting electrolyte on the mediated reduction of [Fe(H2O)6]3+ by an osmium-containing poly(4-vinylpyridine) film

Abstract

The ability to control the mediation kinetics of [Fe(H₂O)₆]³⁺ reduction by [Os(bipy)₂(PVP)₁₀Cl]Cl films through electrode potential, film thickness and supporting electrolyte is demonstrated; bipy = 2,2′-bipyridyl, PVP = poly(4-vinylpyridine). In H₂SO₄, the mediated reduction is controlled by film thickness for surface coverages between 7 × 10^–10 and 1 × 10^–8 mol cm^–2(Lk mechanism). For surface coverages > 10^–7 mol cm^–2 total catalysis is obtained where substrate diffusion in solution limits the reduction rate (LSk mechanism). In HClO₄ the mediated reaction is of the surface type and occurs between [Fe(H₂O)₆]³⁺ still in solution and the film within a region of molecular dimensions (Sk″ mechanism). These observations are considered in relation to film structure and with regard to potential applications.