Development of Energy-saving Process of Chlor-Alkali Membrane Cell with Gas-diffusion Electrode

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Oxygen depolarized cathodes with gas-diffusion electrode has been expected as an excellent method for soda electrolysis because of its energy-saving and CO_2-reducing. Replacing hydrogen-evolving cathodes with oxygen cathodes significantly reduces cell voltage, which is the potential difference of these electrode reactions. The use of oxygen cathodes can lead to energy saving of 30 to 40 %. However, oxygen cathodes using gas diffusion electrode have not been practically applied yet. As one of the reasons, when a gas diffusion electrode is used in high concentrated alkaline solution at high temperature, the electrolyte solution penetrates to the gas supply layer in the gas diffusion electrode during electrolysis period. The penetration of the alkaline solution changes the electrode performance because of the decrease in the interface area of the gas-liquid-solid phase at the reaction site. The kinetics of oxygen reduction on a gas diffusion electrode has been extensively investigated, b … More ut basic data in developing the new gas diffusion electrode have not been obtained because of the quantitative data on the electrode characteristic or the mechanism of the electrode degradation are not sufficient. Therefore, it is necessary to have quantification of the electrode degradation. The purpose of this study is to improve the stability of gas-diffusion electrode for high concentrated alkaline solution at high temperature. The cathodic properties of oxygen reduction on the gas diffusion electrode were examined by AC impedance method using an equivalent circuit. The effect of the penetration of the electrolyte into gas diffusion electrode was determined quantitatively by using charge-transfer resistance and the double-layer capacitance. Comparing the electrodes using Ag and Pt catalysts of different life time, the cathode potentials and the diameter of the Nyquist plots were increased with increasing life time. The electrode characteristics using Ag catalyst was more excellent than using Pt catalyst. The surfaces of the gas diffusion electrodes were analyzed by XPS. The surfaces of the electrodes on carbon, PTFE and silver were failed away and adsorbed sodium and oxygen. The mechanism of the electrode degradation was discussed by the cathodic overpotential simulation. The increase of cathodic overpotential was affected by increasing the thickness of the thin-film than the penetration of the electrolyte into gas diffusion layer. Less