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

采用气体扩散电极的氧气去极化阴极因其节能和减少二氧化碳排放而被认为是一种很好的纯碱电解方法。用氧阴极取代析氢阴极可以显著降低电池电压，这就是这些电极反应的电位差。使用氧阴极可以节省30%到40%的能源。然而，采用气体扩散电极的氧阴极还没有得到实际应用。其中一个原因是，当气体扩散电极在高温的高浓度碱性溶液中使用时，电解液在电解过程中渗透到气体扩散电极中的供气层。碱性溶液的渗透改变了电极的性能，这是因为反应部位的气-液-固三相界面面积减小。氧在气体扩散电极上的还原动力学已被广泛研究，b…由于对电极特性或电极退化机理的定量数据不足，研制新型气体扩散电极还没有获得更多的基础数据。因此，有必要对电极的退化进行量化。本研究的目的是提高气体扩散电极在高温下对高浓度碱性溶液的稳定性。用等效电路交流阻抗法研究了气体扩散电极上氧还原的阴极性质。用电荷转移电阻和双电层电容定量测定了电解液对气体扩散电极的渗透作用。对比使用不同寿命的银和铂催化剂的电极，阴极电位和奈奎斯特曲线的直径都随着寿命的延长而增大。银催化剂的电极性能优于铂催化剂。用XPS对气体扩散电极的表面进行了分析。碳、聚四氟乙烯和银上的电极表面脱落，吸附了钠和氧。通过阴极过电位模拟，探讨了电极退化的机理。阴极过电位的增加受薄膜厚度的影响大于电解液对气体扩散层渗透率的影响。较少

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