锌-空气电池空气电极研究

【作者】 王承霞；

【导师】 张建民；

【作者基本信息】 郑州大学 ， 物理化学， 2004， 硕士

【摘要】 据环保部门分析，汽车尾气污染是造成空气污染的重要方面，汽车排放的有害气体已成为地球生态环境的最大污染源，致力于绿色环保汽车的研究是汽车工业发展的主要道路，其中一个重要方向是开发电动汽车。电动汽车的解决方案有多种，其中，锌-空气电池具有一般电池无法比拟的优势，成为近年来化学电源研究开发的热点之一。锌-空电池是当前电池领域中的最新科技，它具有比能量高、性能稳定、无污染、价格低廉、原料丰富易得等优点，被称为是“面向21世纪的绿色能源”。空气电极是锌-空气电池的重要组成之一，影响空气电极性能的主要因素是氧还原催化剂和空气电极结构，本文的工作主要集中在这两方面，主要结果有： 1．以涂AgNO₃等作为催化剂，制作多孔、疏水、透气的空气电极，在此基础上，以Hg-HgO做参比电极，制作电池模型，确定制备空气电极的最优工艺条件：电极层PTFE含量约35wt％，集流网是孔径为0.147mm的铜网，电极层厚度在0.3mm以内，电极厚度控制在0.5mm左右；电极层烧结温度为350℃，烧结后，对电极层进行疏水处理，即用丙酮浸渍至少8h；电极成型，电极层依次排列为：气体扩散层|集流网|催化层，成型压力为26MPa。 2．活性炭作为催化剂的载体，它的性质对电极性能有较大的影响。空气电极的重要特点之一是内部多孔，孔的状态是影响电极性能的关键因素，凡是影响孔性质的因素都会影响电极性能。过筛优化处理活性炭，不但有利于提高电极性能，而且使电极的稳定性得以提高。过筛优化处理活性炭，不但改善传输路径，使传质电阻减小，而且使催化剂的有效面积增大，提高电极性能，使电极性能稳定性改善；用半经验方程E=E⁰—b log i—Ri（E⁰=E^r—b log i⁰）对实验数据进行曲线拟合，结果显示过筛处理活性炭对还原反应的Tafel斜率（b）影响不大，但对交换电流密度（i⁰）和电极电阻（R）影响较大。Tafel斜率（b）保持不变，说明活性炭过筛处理后，空气电极氧还原的机理没有发生变化。空气电极吸附氧气主要发生在活性炭的微孔，随着活性炭粒径的减小，微孔数目随之增加，吸附的氧气量也随之增加，而孔容积增加，则使电极内部有更大空间存储氧气，这两者都使催化剂表面积被润湿的程度加强，即以催化剂为中心的三相界面增大，从而提高电极效率；另一方面，太多微孔存在，在电极内部会发生电解质滞留，阻碍传质的顺利进行，而使电阻增大。活性炭未处理与过筛300目的活性炭，动力学参数最为接近（表4一2），但极化曲线（图4一1）显示，活性炭未处理的电极电压发生急剧降低，极化较大。最终实验结果表明，过筛300目优化处理活性炭，电极性能最佳。 3.空气电极在负载催化剂的过程中引入有机物，使电极性能下降，这是用微乳液等技术将催化剂负载到活性炭上需要首先解决的问题，否则不能充分发挥纳米催化剂的高效性一般说来，洗涤处理活性炭，是提高电极性能的有效方法。对不同的有机物进行试验，它们对电极性能影响排序为:正丁醇+二甲苯+十二烷基苯磺酸钠性能，（DBS）>无水乙醇>十二烷基苯磺酸钠。实验表明，有机物的引入影响电极可以推论洗涤溶剂的选择，也应该影响电极性能，但这方面有待深入、地研究。用微乳液及十二烷基苯磺酸钠溶液处理活性炭电极的极化曲线显示，系统随着电流密度的增大，用微乳液处理活性炭的电极电压变化最明显，也就是说，用微乳液处理活性炭对电极性能影响最大。 4.用微乳液技术负载催化剂，首要解决的问题是选择适当的溶剂对已负载催化剂的活性炭进行洗涤，常见溶剂是无水乙醇。试验的微乳液体系是:C0C12溶液用量为3.omL，二甲苯7.0ml，DBS4.0ml，正丁醇用量60ml，Na0H溶液4.0ml。试验CoO的负载量约为7.omg左右，与银的负载量相当，且性能相近，实验结果表明，微乳液技术应用于空气电极的制备是可行的。更多还原

【Abstract】 The alkaline zinc-air battery, as an environmentally friendly electrochemical power sources for electromotive cars, has recently been attracted considerable attention because of a variety of advantages of the battery, such as high specific energy, flat discharge voltage and low cost of raw materials. Air electrode is extensively equipped in zinc-air battery, and the two main factors of electrode performance influenced, which were mainly researched in this article, are the oxygen reduction electrocatalyst and the structure of air electrode. The major results and conclusions are summarized as follows:Air electrode: AgNC>3 + (catalyst), PTFE, copper network etc.Reference electrode: Hg/ Hg OElectrolyte: 30%NaOHA semi-cell model was composed of the above three electrodes.The optimum condition for air electrode preparation were given as follows: PTFE content in the electrode layer was 35 wt %, the collecting current net was the copper network of aperture 147 mm, the thickness of the electrode layer was in 0.3mm, the electrode layer was sintered at 350 C, and the electrode layer was soaked in acetone for 8 hours at least to waterproof. The air electrode was composed of catalyst layer, the collecting current net and waterproof layer, which sequence in turn was diffusion layer, active layer, collect current collector net. The compacting pressure was 26MPa.2. Active carbon is the catalyst carrier, which was related to electrode performance. Air electrode is porous. The hole in air electrode was a key factor to the electrodes performance. Optimizing active carbon by sieving was the very essential, in the one hand, which improved transmitting route, in the other hand, which have the effective areas of catalyst increased. Sieving pretreatment for 300 eyes was optimum.The organic chemicals had the electrode performance dropped, when it was introduced in the procedure of electrode preparation, which should be solved primarily when air electrode was prepared by microemulsion technology. Generally speaking, Electrode performance was improved by washing the active charcoal. Effect of organicmatter on electrode performance was in order: n-Butanol + Xylene +Dodecyl benzene sulfonic acid sodium salt(DBS) > Ethanol > DBS. Because organic chemicals influenced the electrode performance in order, washing solvent was concluded to influence the electrode performance, too, which deserved probing into deeply and systematically. Polarization curves of electrodes using active carbon pretreated with different organic chemicals showed that voltages of electrode with active carbon pretreated with microemulsion change the most sharply. That is to say, microemulsion influenced the electrode performance mostly.4. The question solved primarily was to choose the proper solvent to wash the active carbon loaded catalyst, when catalyst was loaded with microemulsion technology. In the general, wishing solvents are the ethanol. The microemulsion was composed of the volume of CoCl2 solution 3.0ml, Xylene 7.0ml, DBS 4.0ml, n-Butanol 60 ml, NaOH solution 4.0ml. The mass of CoO loaded was 7.0 mg or so, which equaled with the quantity of the silver loaded, furthermore, the electrode performance was close. Loading catalyst with microemulsion technology was feasible to the air electrode preparation.更多还原