【作者】 杨娟；

【导师】 丁旵明；

【作者基本信息】 华东师范大学 ， 无机化学， 2014， 硕士

【摘要】 全被动式直接甲醇燃料电池(DMFC)有理论比能量密度高、结构紧凑、系统简单、微型化潜力大、燃料来源丰富、价格低廉、环境友好等特点,使其作为小型电子设备的便携式电源备受青睐,被视为可替代传统电池成为便携式设备的首选能源。然而,还存在能量效率低、甲醇渗透、阴极“水淹”和成本高等问题难以达到实际应用的要求。针对这些难题,近几年的研究热点围绕着全被动式DMFC的核心部件膜电极集合(MEA)展开。本论文聚焦于优化MEA的结构,旨在降低甲醇从阳极到阴极的渗透速率、缓解阴极水淹、提高催化剂的利用率和通过降低催化剂的载量减少成本。通过一系列的优化提高电池性能加快DMFC的实用步伐。论文主要工作包括以下三个部分：1.针对于目前电池中存在的甲醇渗透和阴极水淹问题：通过测定甲醇渗透率,详细研究了阳极支撑层的聚四氟乙烯(PTFE)含量对全被动式直接甲醇燃料电池(DMFC)甲醇传质和电池性能的影响。膜电极集合体均使用相同的阳极催化层,膜和阴极。实验结果表明：随着阳极支撑层PTFE含量的提高,甲醇渗透速率明显减小当PTFE的含量较高时,甲醇传质阻力较大,会导致电池在很低的电流密度下就出现传质控制区。发现采用PTFE质量分数为40wt.%的支撑层,DMFC以9M甲醇为燃料时,电池的最大功率密度可达32mW cm-2,以40mA cm-2恒电流放电时展现了更好的稳定性。进一步证明了适当提高阳极支撑层的憎水性有助于DMFC放电稳定性的提高和更大浓度甲醇的使用,既减少了甲醇的渗透,又缓解了阴极的“水淹”问题。2.通过合成一种新的材料碳纳米管打孔石墨烯(G-CNT),代替传统的碳粉(XC-72R)作为DMFC的微孔层结构。新材料是把碳纳米管和石墨烯结合起来,所以其兼具了两者的优点如：好的导电能力、优良的亲水性、均匀的孔径分布等。用G-CNT作为阳极微孔层(MPL)材料制备的MEA表现了很好的电池性能。在25℃条件下,电池的最大功率密度可达41.6mW cm-2。通过循环伏安测试,电化学活性面积提高约36.1%。G-CNT制备的阳极微孔层具有均匀的网格结构,没有裂痕,一定程度上减少了甲醇从阳极到阴极的渗透。网状结构有助于催化剂向微孔层的渗透,增多阳极催化剂的活性位点提高其利用率,显著提高电池性能。3.针对目前燃料电池贵金属催化剂载量高致其成本较高的问题。利用电化学沉积法,借助氧化铝模板(AAO)将氯铂酸还原在孔道中,制备出一定程度上纳米有序的Pt纳米线。成功的将AAO模板通过粘结剂和基底结合起来,基底是用碳纳米管制备的微孔层。通过增大催化剂的比表面积,增多电化学反应的活性位点来提高电池性能。用循环伏安、阻抗等电化学手段对其制备的MEA进行表征,发现阴极的电化学活性面积明显提高,电荷传递电阻减小等。归因于纳米阵列的催化层结构可以最大化三相界面,增多催化剂的活性位点,有助于电化学反应的彻底的进行,显著提高了电池性能。更多还原

【Abstract】 The advantages of its high energy density, portable and lightweight, easy refueling, especially environmently friendly and so on, have made the passive DMFC batteries regarded as a powerful candidate for next-generation mobile power sources. However, the poor performance in energy efficiency, methanol permeability, water flooding problem in the cathode and high cost cause present passive DMFC batteries far away from satisfaction. To solve these problems, researchers from all over the world have conducted much investigation around membrane assembly electrode (MEA). This thesis focuses on the structure of anodic micro layer and cathodic catalyst layer. By new reasonable structure design, we aim to reduce methanol permeability from the anode to cathode, mitigate water flooding problem and increase catalyst utilization. The main researches include the following three aspects:1. The effect of the anode backing layer consisting of carbon papers with different polytetrafluoroethylene (PTFE) contents on the methanol mass transfer and cell performance of a passive direct methanol fuel cell (DMFC) was investigated by methanol permeability measurement. The membrane electrode assemblies (MEAs) were fabricated with the same anode catalyst layer, membrane and cathode. The experimental results showed that the methanol permeability decreased with the increase of PTFE contents in anode backing layer. It was found that PTFE-treated backing layer results in a lower limiting current density, which could be attributed primarily to the increased mass transfer resistance. However, the fuel’s concentration can be increased as the increase of PTFE contents on anode backing layer, leading to higher energy density of passive DMFC system. Moreover, the use of a PTFE-treated backing layer also can decrease water transfer from the anode to the cathode, thus mitigating water flooding problem in the cathode. 2. Graphene-carbon nanotubes (G-CNTs) were prepared as the anodic micro porous layer (MPL) carbon material for passive direct methanol fuel cell (DMFC). It includes some merits that are composed of good electrical conductivity, excellent hydrophilicity and uniformly pores distribution. The addition of G-CNTs into the anodic MPL significantly improves the cell’s performance. The maximal power density of ca.41.6mWcm-2at a temperature of ca.25℃was achieved with G-CNTs as anodic MPL material. A. C. impedance analysis indicates that the increased performance of the passive DMFC with the addition of G-CNTs into anodic MPLs could be attributed to the improvement in catalyst utilization, which was verified by CO stripping measurements that showed ca.36.1%increase in the electrochemical active surface area for the electrode with G-CNTs within MPL over that with Vulcan XC-72R carbon.3. Ordered Pt nanowires were prepared via electrodeposition using anodic aluminium oxide template by cyclic voltammery. A high surface area nanowire array electrode of the catalyst has significantly improved its capability compared with a catalyst Pt-black electrode. In this work, AAO films were successfully bonded on the surface of micro porous layer and it is the first time that it was used as a template to synthesize a high catalytic activity surface area and ordered nanowire array electrode for direct methanol fuel cell which showed good cell performance and low charge transfer resistance.更多还原