脱盐是缓解淡水资源短缺的有效方式之一，电驱动型脱盐技术在多样化水质需求的场景中具有广泛应用前景。流动电极型电容去离子技术（Flow Electrode Capacitive Deionization，FCDI）突破了固态电极材料的离子吸附容量限制，具有驱动电压低、可连续运行、处理高盐度水等优点，在近年来研究中受到广泛关注。针对流动电极内电荷传递过程复杂问题，本研究构建电化学特性测试系统与分析模型，解析流动电极内电荷传递特点，确定FCDI脱盐性能提升的关键要素；解析颗粒本征特性、电极流动状态、集电体结构对流动电极导电性的影响，针对颗粒与颗粒间、颗粒与集电体间的电荷传递进行优化，提升FCDI脱盐性能。论文主要成果如下：构建流动电极交流阻抗谱测试系统与分析模型，量化流动电极内部电子电阻、离子电阻及流动电极与集电体间接触电阻；发现流动电极内电子电阻大于离子电阻及接触电阻，是限制FCDI脱盐性能的关键因素。对比两种粉末活性炭构成的FCDI脱盐性能差异发现，其主要原因是流动电极的导电性不同。粉末活性炭适度疏水化可增强颗粒间接触，促进流动电极中电子传递；通过表面修饰和热法两种改性方式，增强粉末活性炭疏水性和导电性，对应FCDI平均盐去除速率由0.87 μmol·cm-2·min-1分别提升至1.26和1.72 μmol·cm-2·min-1。折线型流道设计可改变电极流态，增加颗粒间接触，降低流动电极中电子传递阻力，循环流量15 mL·min-1时，FCDI平均脱盐速率由0.87 μmol·cm-2·min-1提升至1.05 μmol·cm-2·min-1；不同流道类型FCDI的脱盐速率均随电极循环流量增加而增加；折线流道和循环流量提升均增加电极流动能耗。利用钛网作为集电体，构建膜集电型FCDI，降低电极内部电荷传递距离，电子电阻降低了45%，平均脱盐速率提升了88%；进一步优化钛网参数，FCDI平均脱盐速率提升了59%；24 h持续运行，流动电极可在膜电极表面更新而无沉积层形成。
Desalination is one of the effective ways to alleviate the water shortage. Electrically driven desalination technology has promising applications in scenarios with diverse water quality needs. Flow electrode capacitive deionization(FCDI) breaks through the limitation of electrode materials on ion adsorption capacity and has the advantages of low voltage, continuous operation, and treatment of high salinity water, etc., which has received wide attention in recent years. To explore the complex charge transport process in the flow electrode, an electrochemical characterization test system and analytical model were constructed for quantitatively charactering the charge transport within the flow electrode and identifying the key elements for improving desalination performance of FCDI in this study. In addition, the effects of particle intrinsic characteristics, electrode flowing state, and current collector on the conductivity of the flow electrode were analyzed. By facilitating charge transport among carbon particles in flow electrode and that from these particles to current collectors, the desalination performance of FCDI was improved. The obtained conclusions are as follows.The alternating current impedance spectrum test system and analytical model of the flow electrode were constructed to quantify the electronic resistance, the ionic resistance inside the flow electrode and the contact resistance between the flow electrode and the current collector. It was found that the electronic resistance inside the flow electrode was greater than the ionic resistance and the contact resistance, and thus was recognized as the key factor limiting the desalination performance of FCDI.Different performances were found in FCDI devices with two types of powdered activated carbon, which was primarily attributed to the conductivity of flow electrode. Moderate hydrophobization of powdered activated carbon could enhance inter-particle contact and promote electron transport in the flow electrode. Then the hydrophobicity of the powdered activated carbon was enhanced by both surface modification and thermal method, and correspondingly increased the average salt removal rate of FCDI from 0.87 μmol·cm-2·min-1 to 1.26 and 1.72 μmol·cm-2·min-1, respectively.The zigzag flow channel design can change the electrode flow state, increase the contact between particles, and reduce the electron transfer resistance in the flow electrode. And the average salt removal rate of FCDI was enhanced from 0.87 μmol·cm-2·min-1 to 1.05 μmol·cm-2·min-1 at the circulation flow rate of 15 mL·min-1. The salt removal rate of FCDI with different flow channel patterns increased with the electrode circulation flow rate. Besides, both the zigzag flow channel and faster circulation flow rate increased the energy consumption for electrode flowing.Using titanium mesh as the current collector, a membrane-electrode assembly FCDI was constructed, which decreased the charge transport distance, reduced the electronic resistance by 45%, and increased the average salt removal rate by 88%. By further optimizing the titanium mesh parameters, the average salt removal rate of FCDI was improved by 59%. In 24 h continuous operation, the flow electrode could be renewed on the membrane and electrode surface without deposit layer formation.
