Effect of water content in the Nafion matrix and the pH of the electrolyte solution on the charge transfer in the oxidation of the Ru(bpy)32+ complex

Potential-step chronoamperospectrometry (PSCAS) was employed to investigate charge transport in one-electron oxidation of the Ru(bpy)(3)(2+) complex in a Nafion film. The polymer-coated electrode was prepared by two methods: mixture casting and adsorption. The electroactive fraction of Nafion[Ru(bpy)(3)(2+)] prepared by the former method was lower than that prepared by the latter. If the charge transfer distance between the adjacent complexes is considered to be the same in the two systems, higher electroactivity for the adsorption system can be ascribed to the localization of the complex in the hydrophilic region of the Nafion and the localization factor can be calculated. The localization factor was found to decrease with increasing water ratio-in the mixed solvent used for casting the film, which leads to an increase in volume of the hydrophilic region. The lifetime of photoexcited Ru(bpy)(3)(2+) became shorter with increasing pH showing that movement of the complex was suppressed at higher H+ concentration. This was ascribed to a shrinkage of the hydrophilic region in Nafion morphology. Rapid counterion migration under the potential step at low pH would result in a longer charge transfer distance and a faster charge transfer rate. (C) 1999 Elsevier Science Ltd. All rights reserved.