Electrochemically induced mass exchange between electrolyte and Fe(bpy)32+-impregnated Nafion membrane Original Research Article

The mass exchange properties of a Fe(bpy)32+-impregnated Nafion membrane have been investigated with spectrophotometry, electrochemistry, and quartz microbalance measurements (QCM). When all of the anionic charges in the Nafion membrane are neutralized by Fe(bpy)32+, the membrane becomes water-repellent. Poorly hydrated tetraethylammonium ion more effectively replaces the complex in this membrane than well-hydrated cations such as Na+, K+, and Ca2+. Poorly hydrated anions (e.g. ClO4−) also facilitate the cation-exchange leaching of Fe(bpy)32+ from the membrane. When this membrane is spread over the surface of an electrode, the mass transfer is influenced by the electrical potential applied to the electrode. Applying positive potential facilitates the electrolyte invasion into the membrane, and thereby the leaching of Fe(bpy)32+ due to cation-exchange is enhanced. QCM measurements have revealed that cations partitioned into the membrane are excluded out of the membrane by the oxidation of Fe(bpy)32+, and that cations are repartitioned into the membrane by the cathodic potential sweep.