荷电物质修饰活性炭电极及不对称电容器去离子性能

发布时间：2018-04-14 21:41

本文选题：电容去离子 + 共离子排斥　；参考：《东华大学》2017年硕士论文

【摘要】：电容去离子(Capacitive deionization,CDI)技术通过控制充电/放电循环过程来实现离子的去除。在充电的过程中,流经电极的溶液中的离子在静电场作用下被吸附到带相反电荷的电极上形成双电层而从水溶液中去除,获得淡水。充电过程结束后,通过电池短路或者反向充电的方式使吸附在电极上的离子脱附,完成电极再生。电容去离子技术与传统脱盐技术相比,具有能耗低、电极再生简单和无二次污染等特点。碳材料具有较高的比表面积和丰富的孔隙结构,常常作为电极材料用于电容去离子。然而在研究过程中,发现电极充电时候在吸附极性相反离子的同时会排斥极性相同的离子,这一过程同样会产生额外能耗,减少离子吸附总量,这一过程叫做“共离子排斥效应”。“共离子排斥效应”的产生会降低脱盐过程中的电流效率和脱盐性能。而活性炭本身导电性较差等因素制约着电容去离子技术的发展。因此,低成本高性能的新型电极材料电极的开发对电容去离子技术的推广和应用具有指导意义。本论文围绕电容脱盐中“共离子排斥效应”影响脱盐性能这一问题展开讨论。首先通过对比不同电容器池(对称活性炭电极,表面活性剂修饰活性炭电极组装的不对称电容脱盐装置以及膜电容脱盐装置)来分析恒流充电过程中的共离子排斥效应产生的现象、原因及解决方法。并通过Nafion材料对活性炭电极进行表面电荷修饰制备复合活性炭电极,组装成非对称电容脱盐装置来改善共离子排斥效应,提高电流效率,优化脱盐性能。主要结论如下:1、设计三种电容器,对比分析共离子排斥效应:通过制备对称的活性炭电容器、经过表面活性剂修饰活性炭电极组装的不对称电容器以及膜电容器三种电容脱盐装置来分析在恒流充电过程中的共离子排斥效应。利用纯活性炭电极制备的对称活性炭电容脱盐装置(AC|AC)三种不同电流密度充分充电情况下,溶液电导率先上升后下降且吸脱附平衡点所对应的充电电量保持在4.4 m Ah左右,说明对称的活性炭电极具有特定的吸附“平衡电量点”。可以通过控制操作过程中的充电电量值来提高电流效率,保证脱盐性能。利用表面活性剂修饰的活性炭电极来组装制备得到不对称电容脱盐装置(CTAB-AC||LAS-AC),发现其经荷电物质修饰后,电极的吸附“平衡电量点”比活性炭电极明显增加。说明经过表面活性剂修饰的电极有效改善共离子排斥。膜电容脱盐装置(MCDI)由于电荷选择性,在充电过程中能够有效的抑制共离子排斥,从而电流效率可达95%。然而在充电第二阶段(4.7mh A),电极极化或水电解严重消耗电量,电流效率急剧下降,脱盐量增加变缓。2、Nafion既可作为离子交换剂,也是广泛采用的电极粘合剂,实验采用Nafion为添加剂与活性炭共混,利用Nafion可以部分替代疏水性的PTFE粘合剂,制备低PTFE含量的Nafion-AC复合电极。场发射电子扫描显微镜和能谱仪(SEM-EDS)表征结果显示Nafion能够均匀的分布在活性炭电极表面,氮吸脱附测试结果表明经过Nafion掺杂改性后的复合电极,比表面积略微增大,微孔体积增加,说明Nafion分子能够有效的填补活性炭电极间的大孔结构,为离子在电极内部的传输提供媒介,较少阻碍,提高离子的传输速率;接触角表征结果表明由于Nafion的存在,降低了超疏水的PTFE含量,从而有效改善电极的亲水性;同时Nafion表面含有丰富的磺酸基团,能够有效的改善电极的离子导电性;拉伸测试证明了Nafion-AC复合活性炭电极比AC电极具有更好的机械拉伸性能。以Nafion-AC复合电极组装成不对称电容脱盐装置用于电容去离子的研究,同时探究Nafion掺杂量对电极的电化学性能和脱盐性能的影响。结果表明,当Nafion掺杂量为7.5%时,复合电极比电容值最高达到148 F/g。通过对Nafion-AC复合电极零电势的研究,当Nafion-AC复合电极用作负极时,能够有效的减少共离子排斥效应,提高电流效率,其脱盐值能够达到10.8 mg/g是纯活性炭电极的1.6倍,电流效率是纯活性炭的2.0倍。
[Abstract]:Capacitive deionization (Capacitive deionization CDI) technology by controlling the charging / discharging process to achieve ion removal. In the process of charging, ion solution flowing through the electrode in electrostatic field is adsorbed to the electric double layer and removal from aqueous solutions, obtaining fresh water formed oppositely charged electrodes on the charge. After the end of the process, the adsorption of ions on the electrode desorption by battery short-circuit or reverse charging mode, complete regeneration of electrodes. Compared with the traditional capacitive deionization desalination technology, has the advantages of low energy consumption, simple and no regeneration electrode two times pollution. Carbon materials with high specific surface area and pore structure. Often used as electrode material for capacitive deionization. But in the course of the study, found that the electrode charging time will reject the same polarity of ions in the simultaneous adsorption of opposite polarity ions, this process The same will generate additional energy consumption, reduce the amount of ion adsorption, this process is called "total ion exclusion effect." "ion exclusion effect" will reduce the current efficiency and performance of desalination desalination process. The activated carbon itself poor conductivity and other factors to restrict the development of capacitor ion technology. Therefore, with the guidance of the significance of the promotion and application of new electrode electrode with low cost and high performance of capacitive deionization technology. This thesis focuses on the capacitive desalination ion exclusion effect desalination performance of a discussion of this issue. Firstly, through the comparison of different capacitor pool (asymmetric capacitance desalting device symmetry activated carbon electrode, surfactant modified activated carbon electrode assembly and membrane capacitance) desalination device analysis of the constant current charging process of the total ion exclusion effect of the phenomenon, causes and solutions. The Nafion material for surface charge modification of activated carbon electrode composite activated carbon electrode assembly, asymmetric capacitor desalination device to improve the total ion exclusion effect, improve current efficiency, optimize the desalination performance. The main conclusions are as follows: 1. The design of three kinds of capacitors, comparative analysis of total ion exclusion effect: activated carbon capacitor by symmetry, after surfactant modified activated carbon electrode assembly of asymmetric capacitor and three capacitor film capacitor desalination device to analysis in the constant current charging process of the total ion exclusion effect. Symmetric active carbon capacitor active carbon electrode pure desalting device prepared by using (AC|AC) three different current density full charge, charging electricity conductivity increased first and then decreased and the adsorption desorption equilibrium point corresponding to the 4.4 m on the Ah, that the activated carbon electrode with symmetric specific absorption With "power balance." can increase the current efficiency by charging power control in the process of operation, ensure the desalination performance. Activated carbon electrode modified by surfactant assembly prepared by asymmetric capacitance desalting device (CTAB-AC||LAS-AC), found the charged material modified electrode, the adsorption equilibrium power point "obviously increased than that of activated carbon electrode. The electrode with surfactant modified to effectively improve the total ion exclusion. The membrane capacitance desalting device (MCDI) due to the charge selectivity, can effectively inhibit the total ion exclusion in the charging process, and the current efficiency was up to 95%. but in the second stage charging (4.7mh A), or the electrode polarization water electrolysis serious energy consumption, current efficiency decreased sharply, desalination increased slow.2, Nafion can be used as ion exchange agent, electrode adhesives are also widely used, using Nafion As the additive and activated carbon blended by Nafion can partially replace the hydrophobic adhesive PTFE, Nafion-AC composite electrodes were prepared with low PTFE content. Field emission scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) results show that Nafion can be uniformly distributed on the surface of activated carbon electrode, nitrogen adsorption desorption test results show that the composite electrode after Nafion doping, the specific surface area increased slightly, the micropore volume increased, indicating that Nafion molecules can fill the pore structure of activated carbon electrode effectively, provide the media, for ion transport within the electrode less obstacles, improve the transmission rate of ions; contact angle. The results showed that due to the presence of Nafion, reduce the the content of PTFE super hydrophobic, which can effectively improve the hydrophilic electrode; at the same time, the surface of Nafion containing sulfonic groups rich, can improve the ionic conductivity of the electrode effectively; tensile test It is shown that the tensile mechanical properties of Nafion-AC composite activated carbon electrode is better than that of AC electrode. The Nafion-AC composite electrode assembly asymmetric capacitance desalting device for capacitive deionization, and explore the Nafion doping on the electrochemical performance of the electrodes and the desalination performance was studied. Results show that when the Nafion content was 7.5%, the composite electrode the specific capacitance is up to 148 F/g. through the research on the Nafion-AC composite electrode potential zero, when the Nafion-AC composite electrode used as anode, which can effectively reduce the total ion exclusion effect, improve the current efficiency, the desalination value can reach 10.8 mg/g is 1.6 times higher than that of pure activated carbon electrodes, current efficiency is 2 times higher than that of pure activated carbon.

【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P747

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