【作者】 李芬；

【导师】 杨基明； 徐献芝；

【作者基本信息】 中国科学技术大学 ， 流体力学， 2010， 博士

【摘要】 锌空气电池凭借其自身能量密度高、输出功率大、价格低廉、安全无污染等特点成为动力电源的首选。气体扩散电极是锌空气电池的能量转换器,其性能的优劣制约着锌空气电池的发展。气体扩散电极的性能包括将化学能转化为电能的能力(简称放电性能)和电极的循环使用寿命。本文主要致力于提高气体扩散电极输出功率和延长电极循环使用寿命方面的研究,并借助数学模型模拟气体扩散电极的工作机理。木文的主要工作包括：第一、提高气体扩散电极放电性能,包括测试气体扩散电极催化层位置特征,催化层组分材料功能,以及优化催化层材料之间的配比;从制约气体扩散电极输出功率的因素出发,通过增加气体扩散电极比表面积和催化剂的催化能力提高电极输出功率。第二,探索了引起扩散电极性能衰退的原因,确定了导致电极性能衰退的主要因素,以及该因素导致电极性能衰退的机理。第三,结合气体扩散电极中氧气在二氧化锰催化作用下的还原机理以及物质传输过程,建立气体扩散电极数学模型。取得的主要进展和成果如下：1)测试了催化层位置对气体扩散电极放电性能的影响,以及材料活性炭、乙炔黑、石墨、MnO2、PTFE各自在催化层添加量发生变化时对气体扩散电极放电性能的影响。根据使用材料的性质确定了气体扩散电极催化层材料配比。2)通过增加电极比表面积和降低电极活化极化过电位来提高气体扩散电极输出功率。具体包括在制作过程中对粘结剂PTFE经过乙醇预处理；将气体扩散电极经过不同的温度热处理；在气体扩散电极制作过程中添加造孔剂；采用新方法制作气体扩散电极双催化剂共同催化体系。3)由气体扩散电极在使用过程中呈现的现象出发,设计一系列实验,探索引起气体扩散电极性能衰退的原因。结果显示在气体扩散电极工作过程中电解液迁移是造成电极性能衰退的主要原因。根据电解液迁移的特征,探索了导致电解液迁移的动力,以及电解液迁移造成电极性能衰退的机理。4)考虑到气体扩散电极多孔结构的复杂性,对其进行合理简化。结合电极中二氧化锰催化剂作用下的氧气还原机理以及物质传递过程,建立数学模型。通过分析数值结果讨论了氧气作为反应物的溶解边界条件对各物理量演化的影响,以及不同工作环境及参数的变化对于电极性能的作用。为了解气体扩散电极的工作机理及优化设计提供了参考。更多还原

【Abstract】 With the advantages of high energy density, large power, low costs and environment harmlessness etc, zinc air batteries distinguish themselves from others batteries to be the primary choice of dynamic power. Gas diffusion electrode (GDE) is the energy convertor of zinc air battery, so the performance of it has a great impact on the development of zinc air battery. The nature of GDE consists of the capability to convert chemical energy to electric energy and the cycle life of the electrode. The targets of this dissertation include developing methods to enlarge the output power and to prolong the cycle life of GDE. Also the working mechanisms of GDE was studied by a mathematical model.The main content of this dissertation comprise:first, methods to improve the discharge performance of GDE, including testing the effect of different catalyst layer position, functions of component materials of catalyst layer, optimization of the mixture ratio of the component, increasing the specific area of GDE and improving the catalysis ability of catalysts. Second, research into the decline of GDE’s performance was conducted. The main factor responsible for it and the mechanism of the decline were confirmed. Third, a mathematical model considering the mechanism of oxygen reduction reaction (ORR) on manganese oxide-catalyzed GDE and mass transport process was developed. The main progresses are as follows:1) Measurements of the position of catalyst layer on the GDE discharge performance was made. And also that of the addition of absorbent charcoal, acetylene black, graphite, MnO2, polytetrafluoroethylene (PTFE) on the performance respectively. The mixture ratio that consists the catalyst layer was confirmed.2) The output power of GDE was enlarged by increasing the specific area of electrodes and depressing the active overpotential. The details comprised pretreatment of PTFE with ethanol, treatment of GDEs under different temperature, addition of pore-former and a new method to fabricate a dual-catalyst GDE.3) A series experiments were conducted to explore the factors that cause the decline of GDE performance. The results indicated that the migration of electrolyte was the primary cause. Further investigations were carried out on the motivation of migration and the mechanism of decline cause by migration.4) Simplification was made to describe the porous structure of GDE mathematically. A model considering the ORR mechanism and the mass transport process of species was built to simulate the operation of GDE. The numerical results showed the impact of oxygen dissolved boundary condition on the evolution of functions such as concentrations and transfer current and the effect of environmental conditions and the variation of parameters on the electrode performance. These results can be used as references to understand the chemical and physical processes occurred inside the electrode and the optimization of design.更多还原