When a gas diffusion electrode is used in high concentrated alkaline solution at the high temperature, the electrolyte solution penetrates to the gas supply layer in the gas diffusion electrode during electrolysis period. Penetration of the alkaline solution deteriorates the electrode performance because of the decrease in the interface area of the gas-liquid-solid phase at the reaction site. Nafion thin film or plasma-polymerized film were coated on the surface of the electrodes in order to improve the stability of electrode. The cathodic properties of oxygen reduction on the gas diffusion electrode were examined by AC impedance method. Comparing the electrodes covered with 4 kinds of different thickness Nafion, the diameter and the intersect resistance of Nyquist plots were increased with increasing membrane thickness. Nafion thickness is required less than 10 mu m to ignore the charge transfer resistance. From the acceleration test with ELAT electrodes covered with Nafion thin film or plasma-polymerized film, a charged-thin film was found to minimize the penetration of alkaline solution into the electrode.
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