【作者】 袁伟；

【导师】 汤勇；

【作者基本信息】 华南理工大学 ， 机械制造及其自动化， 2012， 博士

【摘要】 作为燃料电池技术领域的重要分支，被动式自呼吸直接甲醇燃料电池（以下简称PAB-DMFC）由于具有最接近实用的操作特性及高能量密度，在便携式电源领域正吸引着广泛关注和研究。然而，由于PAB-DMFC完全自主运行，其操作条件很难达到最优，而且在被动工作模式下电池内部的质、热传递机制受到很大限制，因而其性能往往远低于主动式DMFC。在此背景下，从PAB-DMFC的结构着手进行优化成为改善电池性能的现实可行的方式。为此，本文以PAB-DMFC单池为研究对象，基于传统结构层面及新型多孔流场结构层面对电池进行优化设计并研究其作用机理，主要研究内容包括：1. PAB-DMFC的结构设计及其多孔流场板的制造与表征结合可视化设计方法及实验策略，详细讨论了传统电池组件（集电板/流场板、膜电极）的设计及制造方法，在此基础上提出集成多孔流场板的新型PAB-DMFC的设计思路。重点研究了基于多齿刀具切削金属纤维工艺及高温固相烧结工艺的多孔流场板制造方法，特别是基于Deform三维有限元模拟及SEM技术对金属纤维的成形过程及形貌进行详细表征。针对PAB-DMFC的特殊应用环境，对多孔流场板包括多尺度微观形貌、宏观结构特征、流体渗透性、亲/疏水性、导电性及耐腐蚀性等在内的关键物性参数进行系统表征及评估。2. PAB-DMFC的多结构参数耦合影响机制基于传统结构设计方案，在PAB-DMFC两极采用相同结构配置的情况下，对其在多结构耦合条件下的性能表现进行比较研究，结合电池内部的质、热传递机制（如反应物供给、产物排放、甲醇穿透等）对关键组件结构参数的影响机制进行定性分析，并通过正交方法对包括耦合因素在内的各结构参数对电池典型特性指标（最大功率密度、极限电流密度和开路电压）的影响权重进行定量描述，最终得到最优结构组合。在考察结构影响的同时，还研究了操作参数（甲醇浓度、操作时间、强迫空气对流、换液操作等）对PAB-DMFC性能的影响机制以及电池的动态特性。3. PAB-DMFC的两极结构差异化影响机制进一步研究PAB-DMFC两极采用不同结构配置时的结构因素对电池性能的影响机制，重点考察了质子交换膜、碳纤维扩散介质（碳纸型和碳布型）以及集电板（不同形式及开孔率）对电池性能及开路特性的影响。通过比较电池在包含和取消阴极扩散层情况下的性能详细评估了阴极扩散层在氧气传输和水热管理方面的功能特性。在两极结构差异化条件下，深入研究了甲醇浓度、操作方位、阴极强迫空气对流及环境温度等操作参数对电池性能的影响，同时利用数字成像法及红外热像分析法对阳极的气泡行为以及阴极的温度特性进行定性分析。4.多孔流场板在PAB-DMFC中的性能研究通过与采用传统结构的PAB-DMFC进行比较，详细分析了多孔流场板在传质方面的功能特性及其结构参数（孔隙率和厚度）对电池性能的影响机制。同时考察了多孔流场板装配方式及集电板参数对电池性能的影响。针对采用多孔流场板的PAB-DMFC，系统考察了其在不同操作条件（甲醇浓度、操作方位、环境温度、阴极强迫空气对流）下的性能，并对其动态特性进行了定性描述。本文研究结果表明，对PAB-DMFC的结构进行优化须考虑关键组件结构的耦合影响以及两极结构的差异化影响。优化准则的核心在于衡量不同组件结构参数及其组合是否有利于电池内部的质、热传递机制，特别是在反应物传递、产物排放以及甲醇穿透抑制方面是否能够实现较好的平衡。当PAB-DMFC阳极采用多孔流场结构后，电池的性能得到明显改善，不仅提高了电池的能量密度和功率密度，还延长了电池的工作时间。更多还原

【Abstract】 As a branch of fuel cell technology, the passive air-breathing direct methanol fuel cell(PAB-DMFC) is increasingly attracting concerns from the field of portable power sources dueto its high energy density and practical properties. However, since the PAB-DMFC mainlyoperates under a self-regulating condition, the operational parameters are not always optimaland the mass and heat transfer mechanisms are inevitably limited. As a result, its performanceis mostly lower than the active DMFC system. In this situation, it is quite possible to improvethe cell performance by optimizing the fuel cell structures. To this end, this thesis focuses onstructural optimization and corresponding mechanism analysis of a single PAB-DMFC witheither a traditional flow distributor or a PMFSFD. The main contents of this thesis include:1. Structural design of PAB-DMFC&Manufacture and characterization of PMFSFDBased on visualization design and experimental strategy, this chapter provides a detaileddescription about the design and manufacturing process of the traditional PAB-DMFCcomponents including the current collector/flow distributor and membrane electrodeassembly. A design concept of incorporating newly-developed porous flow distributor namedPMFSFD is also presented. Particularly, the manufacturing process of the PMFSFD based onmetal-fiber multi-tooth cutting and high-temperature solid-phase sintering is comprehensivelyreported. The forming process and morphology of the metal fiber are characterized by usingDeform-based FEM simulation and SEM method. According to the special applicationenvironment of the PAB-DMFC, a series of important physical parameters are systematicallycharacterized and evaluated, namely the multi-scale microscopic morphology, macroscopicstructural features, fluid flow permeability, hydrophilicity and hydrophobicity, electricalconductivity and corrosion behaviors.2. Mechanisms of the coupling effects of multiple structures in a PAB-DMFCThis chapter mainly focuses on the coupling effects of multiple structures in a traditionalPAB-DMFC with the same structural configuration on both sides. A qualitative analysis isconducted by relating the cell performance to the internal mass and heat transfer mechanisms(e.g. reactant delivery, product removal and methanol crossover), while a quantitativeanalysis is also included by using the orthogonal array method to identify the dominant factors affecting the typical target variables (e.g. maximum power density, limiting currentdensity and open circuit voltage).The optimal structural combination can be finally obtained.The effects of operational parameters (e.g. methanol concentration, operating time, forced airconvection and refueling) and the dynamic characteristics of the PAB-DMFC are analyzed.3. Mechanisms of the effects of structural discrepancy on both sides of a PAB-DMFCThis chapter mainly reveals the PAB-DMFC performance with different configurations onboth sides. Especially, the effects of the membrane, carbon-fiber diffusion mediums andcurrent collectors with different patterns and open ratios are investigated. The function of thecathodic diffusion layer is reported by comparing the performances of the PAB-DMFC withand without the c-GDL. The effects of methanol concentration, operating orientation, forcedair convection and the environmental temperature are further discussed when structuraldifference is considered. In addition, the anodic bubble behaviors and cathodic self-heatingbehaviors are analyzed with the digital imaging and infrared imaging techniques.4. Performance validation of the PAB-DMFC with a PMFSFDPerformance comparison of the traditional and PMFSFD-based PAB-DMFCs is reported indetails. Especially the structural effects of the PMFSFD with different porosities andthicknesses are analyzed. Besides, this chapter also reveals the effects of PMFSFD assemblymodes and current collector openings on the cell performance. When the PMFSFD is applied,how the fuel cell is affected by various operational parameters and how it behaves under thedynamic conditions are also investigated.To summarize, the results show that, when optimizing the structures of a PAB-DMFC, theircoupling effects and difference effects on both sides must be taken into account. The core rulefor structural optimization lies in whether the structure parameters of different componentsand their combinations benefit the internal mass and heat transfer mechanisms, especially thebalance among reactant delivery, product removal and methanol crossover inhibition. Whenthe PAB-DMFC uses a PMFSFD, the performance get greatly improved, leading to not onlyhigher energy density and power density, but also a longer operating time.更多还原