Myoungsun Shin, Eun-Yeob Kim, Juhyoun Kwak, Il Cheol Jeon, "Mass transport study of Nafion® coatings saturated with [Os(bpy)3]2+ by an electrochemical quartz crystal microbalance," J. Electroanal. Chem., 394 (1), 87 - 92 (1995.09.19.)

Abstract
Ion transport out of and into the Nafion® coating on an electrode during the electrochemical processes was studied using an electrochemical quartz crystal microbalance (EQCM). After saturated loading of [Os(bpy)3]2+, the first cyclic voltammogram (CV) initiated from the lower limit showed an anodic peak around 0.85 V vs. Ag|AgCl which, according to a previous study by Anson's group, corresponds to ejection of the [Os(bpy)3]3+ complex from the Nafion® coating. However, the frequency change-potential (Df-E) curve obtained by EQCM showed an increase in the mass on the first positive scan. These contradictory results can be explained by the movement of water molecules in a direction opposite to that of [Os(bpy)3]3+ complexes. After a number of successive cycles, a steady state voltammogram was obtained. In this case the mass change was attributed mainly to the movement of the hydrated electroinactive counter-cations of the supporting electrolyte. The hydration numbers for two of the supporting electrolyte cations are in good agreement with the published results.

Keywords : Membrane electrodes, Charge transport mediators, Mass transport, Electrochemical quartz crystal microbalance