【作者】 赖勤志；

【导师】 尹鸽平；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2009， 博士

【摘要】 被动式直接甲醇燃料电池（被动式Direct Methanol Fuel Cell,被动式DMFC）是直接利用甲醇水溶液或甲醇蒸汽作为燃料、氧气或空气作为氧化剂的一种燃料电池。被动式DMFC具有不使用动力泵为电极供料,完全摒弃外置的甲醇蠕动泵和空气泵的特点,减少了电池的功耗,提高了能量利用率,被认为是最有希望取代锂离子电池成为新一代便携设备电源的技术之一。本文从改善阴极水淹和阳极甲醇渗透问题着手,优化电池的运行条件,研究影响电池不同放置方式长时间放电稳定性的因素,设计新型流场结构以改善阴极水淹问题,并揭示了甲醇浓度、甲醇摩尔量、阳极流场开放面积、阳极产物等因素与甲醇渗透的相互影响关系,并在此基础上设计并研发了两种被动式DMFC电堆。研究了制约被动式DMFC性能的因素,优化了电池的运行参数。被动式DMFC中的膜电极（Membrane electrode assembly,MEA）采用恒电压0.25 V放电活化的最佳时间为36 h。甲醇溶液浓度最佳值为1.5～2.0 mol·L-1,30℃时电池的最高功率密度达到13 mW·cm^-2。较慢的物质传输速率是制约电池性能的主要因素,而温度的提高可以改善甲醇与氧气的传质过程,提高电池性能。提高阴极催化剂载量可以显著提高电池的自加热温度,提高电化学反应速率与扩散速率,对电池性能的影响更为显著,电池阴阳极催化剂载量最佳值为4.0 mg·cm^-2,20℃时电池的最高功率密度达到11.4 mW·cm^-2。空气湿度的增加对电池的极化性能影响较小,但对电池的长时间放电性能影响较大。被动式DMFC的阴阳极分别采用点状流场与平行沟槽流场时具有较好的性能。研究了阴极水淹对电池长时间放电性能的影响。电池采用阳极向上放置方式时,依靠重力的作用,能够顺利地将阴极生成的水排出,阴极水淹状况较轻,具有较好的长时间放电性能。制约电池阳极向下放置放电性能的主要因素是阳极产生的CO2阻碍了甲醇反应的通道。制约电池垂直放置方式长时间放电性能的主要原因是阴极水淹问题。针对阴极水淹问题,设计了一种新型的阴极流场结构,采用新型流场结构的电池22.2 mA·cm^-2放电10 h的电压衰减率为9.9 %,而采用传统流场的电池电压衰减率为15.3 %。新型流场可以减小电池对环境湿度的敏感度,环境相对湿度从10 %升至90 %时,电池33.3 mA·cm^-2放电5 h的电压衰减率仅上升4.4 %。研究了甲醇渗透对电池性能的影响。随着阳极流场开放面积的减小,甲醇渗透速率逐渐降低,阳极流场开放面积的降低,提高了电池使用高浓度甲醇时的极化性能。高浓度的甲醇溶液可以提高甲醇的扩散速率,在电池大电流放电的操作条件下具有较好的长时间放电性能。甲醇总量的改变并不会影响电池的放电时间与法拉第效率。设计了被动式DMFC电堆,使用表面镀金的印刷线路板作为电堆集流体时,由于存在较严重的腐蚀问题,影响电堆的长时间运行。电堆在运行过程中,各单体电池性能均一性较好,最大功率为480 mW。电堆在恒、变电流下均可稳定运行,电堆在恒电流200 mA下运行的法拉第效率为46.6 %。该电堆在连续5个放电周期内保持了较稳定的性能,电堆间歇放电的法拉第效率为43.5 %。更多还原

【Abstract】 The passive direct methanol fuel cell （DMFC） is a kind of fuel cell using methanol solution or gas as the anode, oxygen or air as the oxidants. Passive DMFCs have some advantages such as higher reliability, low cost, higher fuel utilization and higher energy density due to the absence of external devices such as a pump or fan. Therefore, passive DMFCs are regarded as one of the most promising candidate for lithium ion batteries as the power for portable devices. This thesis is aimed to improve the water flood in the cathode and methanol crossover in the anode. Cathode water flood is improved by optimizing the operating parameter, studying the long-time stability of different cell orientations and designing novel flow field. The influencing factors of methanol crossover are investigated by changing methanol concentration, the total amount of methanol and the opening area of anode flow field.The factors influencing the performance of passive DMFCs are investigated in detail. The operating conditions are optimized. The best performance of passive DMFCs could be obtained when the membrane electrode assembly （MEA） is activated at a constant voltage of 0.25 V for 36 h. The maximum power density at 30℃is 13 mW·cm^-2 with the optimal methanol concentration of 1.5^-2.0 mol·L-1. The cathode oxygen transportation is the key factor influencing the cell performance, which could be improved by increasing the temperature. The cell temperature could be raised by increasing the cathode catalyst load and thus increasing the electrochemical reaction rate and the diffusion rate. The optimal value of catalyst load for the anode and cathode are both 4.0 mg·cm^-2. The humidity of air has small effect on the power density of the cell but strongly affects the long-term performance. It is found that better performance could be obtained by using perforated flow field for the cathode but parallel one for the anode.The effects of water flood on the long-term performance are studied. Better performance could be obtained with anode facing upward which is good for water removal in cathode with the help of gravity. The shortage of the cell with anode facing downward is that CO2 bubbles produced in the anode block methanol pathway. On the other hand, the key factor influencing the long-term performance of the cell with vertical orientation is the water flood in the cathode. A novel flow field is designed to improve the cathode flood. The potential loss is 9.9 % for the novel flow field while 15.3 % for the traditional one at a constant current density of 22.2 mA·cm^-2 for 10 h. The cell with novel flow field is not sensitive to the environmental humidity. When the relative humidity increases from 10 % to 90 %, the potential loss increases by 4.4 % after discharging at 33.3 mA·cm^-2 for 5 h.The effects of methanol crossover are discussed. Methanol crossover rate decreases when reducing the opening area of anode flow field and improve the cell performance with high concentration of methanol. By using high concentration of methanol, better performance at higher current density could be obtained owing to the fast diffusion rate of methanol. The Faradic efficiency decreases when using low concentration of methanol due to the serious crossover effect. The total amount of methanol will not influence the working time and the Faradic efficiency.The passive DMFC stacks are fabricated. Long-term performance is influenced by the corrosion of gold-plated PCB flow field. The performance of each single cell is uniform. The maximum power density reaches 480 mW. The stack operate stably at both constant or varied current densities. The Faradic efficiency is 44.6 % when the stack is operating at 200 mA. The stack displays good continuous operating performance in 5 cycles. The Faradic efficiency is 43.5 % when the stack is under intermittent discharge mode.更多还原