Severe inhibition of the diffusion and electroactivity of Cu(bpy)(2)(2+) complexes incorporated in Nafion(R) coatings on electrodes

The Cu(bpy)(2)(2+) complex (bpy = 2,2'-bipyridine) is readily incorporated by Nafion(R) coatings in amounts that can exceed the normal cation exchange capacity of the Nafion(R). The voltammetric responses of the incorporated complex are unusual in that, after the usual initial increases, the currents for reduction of Cu(bpy)(2)(2+) to Cu(bpy)(2)(+) diminish as the quantity of complex incorporated in the Nafion(R) grows. Quartz crystal microbalance measurements indicate that ca. 25 H2O molecules are expelled from Nafion(R) coatings for every Cu(bpy)(2)(2+) complex that is incorporated. The inhibition of the voltammetric response is attributed to large decreases in the physical diffusion rates of Cu(bpy)(2)(2+) in the resulting highly loaded, dehydrated Nafion(R) coatings, The contrasting behavior of Os(bpy)(3)(2+), Ru(bpy)(3)(2+) and Co(bpy)(3)(2+) complexes are noted and possible reasons for the behavioral differences are suggested.