Voltammetric currents of transition metal complexes in films on electrodes increase with electron self exchange (hopping) rate k(11). In films, diffusion coefficients D-f proportional to k(11)c(f)*, where k(11) sets frequency of electron hopping attempts and c(f)* film concentration sets distance between probes. Cyclic voltammetry of Nafion films on electrodes for six probes, tris(2,2'-bipyridyl) complexes, M(bpy)(3)(z+) where Mz+ is Ru2+, Os2+, Fe2+, Cr3+, Co3+, and Co2+, demonstrates D-f varies linearly with k(11)(H2O), literature k(11) measured in water. From density of Ru(bpy)(3)(2+) exchanged Nafion 1.95 g/cm(3) and nominal equivalent weight 1100, geometry establishes volume limited, z-independent c(f)* for all M(bpy)(3)(z+). For concentrations of Ru(bpy)(3)(2+) in HNO3 where either Ru(bpy)(3)(2+) :HNO3 ratio is fixed or Ru(bpy)(3)(2+) is 1 mM and HNO3 varies, c(f)* is statistically invariant. Based on aqueous titrations and dielectric constant sufficient to support ions, electron hopping is confined to hydrated domains of Nafion. From c(f)*, k(11) in Nafion k(11)(Naf) is estimated as k(11)(Naf) = 0.010 k(11)(H2O), consistent with higher ion concentration in Nafion. Measured D-f is 2 x 10(-9) cm(2)/s for Ru(bpy)(3)(2+) and Os(bpy)(3)(2+); 1 x 10(-10) cm(2)/s for Fe(bpy)(3)(2+) and Cr(bpy)(3)(3+); and 1.5x 10(-12) and 5x 10(-12) cm(2)/s for Co(bpy)(3)(2+) and Co(bpy)(3)(3+). For physical diffusion D-p less than or similar to 10(-12) cm(2)/s. A self consistent view of M(bpy)(3)(z+) self exchange in Nafion is outlined. For Os(bpy)(3)(2/3), k(11)(H2O) approximate to 4.5 x 10(8)/Ms. (C) The Author(s) 2016. Published by ECS. All rights reserved.