Characterization of Polymer Electrolyte Thin Film Using an Interdigitated Microarray Electrode

Abstract

Studies have been performed on a cast-coated Nafion^® thin film deposited on an interdigitated microarray electrode in order to elucidate its basic characteristics. Conductivity dependence on relative humidity and temperature were clearly observed. Chemical activation process of the Nafion^® film by H₂O₂ and H₂SO₄ aqueous solutions effectively enhanced the AC-conductivity. Heat treatment of the Nafion^®, especially at temperature higher than 200 °C, also decreased the conductivity, which was never recovered by the chemical activation. Interestingly, after cooling in liquid nitrogen, the conductivity was perfectly recovered. Furthermore, DC current-voltage (I-V) curves were measured varying the relative humidity in order to compare with results of the AC-conductivity measurements. Two kinds of processes for water molecules in the film were strongly suggested; one concerns an ionic conduction and the other concerns an electrode reaction. When the film was exposed to methanol saturated nitrogen gas, the I-V profile dramatically changed, which indicates an irreversible change in the cast-coated Nafion^® thin film.