三维阳极自呼吸微流体燃料电池传输特性及性能强化

发布时间：2018-06-25 23:27

  本文选题：微流体燃料电池 + 物质传输　； 参考：《重庆大学》2014年博士论文

【摘要】：近年来移动互联网技术的高速发展使得各种高性能移动电子设备不断出现（如智能手机、平板电脑等），对高效可靠的微型电源提出了更高的要求。而传统的锂离子电池不能满足长期连续运行的要求，微型直接甲醇燃料电池（μDMFC）则面临着水管理困难、膜老化降解等技术挑战，因此必须研究开发新型的高性能微型电源。微流体燃料电池利用多股流体在微通道中平行层流流动的特点来分隔燃料和氧化剂，去除了质子交换膜以及由膜引起的一系列问题（如水管理困难、膜老化降解、成本较高等），是最有前景的高性能微型电源之一。 但是现阶段微流体燃料电池的性能主要受到阳极侧燃料和阴极侧氧化剂传输的限制。已有研究表明采用空气自呼吸电极可以消除阴极侧传质限制，，但燃料的传质限制还未得到有效缓解。微流体燃料电池阳极产生的CO2气泡还会对平行层流造成扰动，引起对流混合和燃料渗透。此外，目前对微流体燃料电池的理论研究工作还比较有限，尚不能较好地为结构设计和优化运行提供理论依据。 针对以上问题和不足，本文从工程热物理学科角度出发，立足于强化传输和提高电池性能，分别构建了具有可渗透阳极、单根三维阳极和容积式三维阵列阳极的空气自呼吸微流体燃料电池，对电池的物质传输特性和性能特性进行了实验和理论研究。研究内容主要包括：（1）构建了具有可渗透阳极的空气自呼吸微流体燃料电池，研究了运行参数对电池性能的影响；并建立三维数学模型，研究了具有可渗透阳极的电池中的燃料传输特性和燃料渗透特性；（2）研究了在曲面电极表面制备高效催化剂层的方法，表征和比较了电极的物理化学特性、电化学特性和催化能力；并构建了具有单根三维阳极的空气自呼吸微流体燃料电池，研究了运行参数和电解液酸碱性对电池性能的影响；（3）构建了具有容积式三维阵列阳极的空气自呼吸微流体燃料电池，在酸性电解液中研究了运行参数、阳极及隔离棒排列方式对电池性能的影响；并研究了碱性电解液中电池的性能特性；（4）对具有容积式三维阵列阳极的空气自呼吸微流体燃料电池建立了三维数学模型，研究了流体流速、燃料浓度、电流和电势的分布规律，研究了运行参数和结构参数对物质传输和电池性能的影响。主要研究成果如下： 1)具有可渗透阳极的空气自呼吸微流体燃料电池的性能随燃料浓度增加逐渐升高，但当燃料浓度达到2M后发生燃料渗透，使电池性能降低。增加流量可强化反应物传输、提高电池性能，流量过高时（20mL h-1）电池内部发生水力失稳使性能下降。相比于平面阳极，可渗透阳极性能较高、反应电流分布均匀，且在小流量（50μL min-1）时阴极寄生电流密度较小。 2)采用反复沉积浸渍方法制备的钯催化剂层具有均匀的“岛状”结构和多层结构；并具有活性高、抗氧化性强的Pd（111）晶面和更均匀的三相（电解液、催化剂、反应物）界面分布；还具有高电化学活性面积、高催化剂利用率以及优良的甲酸氧化能力和抗COads毒化能力。 3)酸性电解液中具有单根三维阳极的空气自呼吸微流体燃料电池产生的CO2气泡聚并为气弹，会减小阳极催化反应面积并阻碍燃料传输、增大欧姆内阻。气泡动态行为对放电电流影响较大。碱性电解液中电池的最高功率密度比酸性电解液中高188.3%。 4)对于具有容积式三维阵列阳极的空气自呼吸微流体燃料电池，去除最靠近阴极的两根隔离棒后电池性能提高。CO2气泡被限制在阳极及隔离棒阵列中，气泡周期性动态行为会对放电曲线造成周期性扰动。电池最高功率密度达到21.5mWcm-3，最大电流密度为118.3mAcm-3，最高燃料利用率可达87.6%。阳极及隔离棒顺排排列时电池性能较低。 5)当燃料浓度、流量相同时，碱性电解液中具有容积式三维阵列阳极的空气自呼吸微流体燃料电池的最高输出功率为36.7mW，最大输出电流为229.0mA，分别比酸性电解液中提高171.0%和207.3%。碱性电解液中电池性能随着燃料浓度、电解液浓度和反应物流量的上升先均升高后趋于恒定。电池后段发生燃料传输限制使阴极电势发生反转。运行工况最优时电池的最高输出功率为50.4mW，达到国际先进水平。 6)数值模拟结果表明：自呼吸阴极附近的空腔中电解液流速较快。各阳极产电量不相等，上层阳极输出电流较高。低流量下电池发生燃料传输限制，而高流量下电池性能受欧姆内阻控制。阳极后段发生燃料传质限制时局部离子电势上升使阴极电势反转。容积式阵列阳极中自补偿机制可提高下层阳极后段的反应电流。 7)具有顺排阳极及隔离棒的电池性能较低。电池性能随电池长度线性变化，最高输出功率随电池长度的变化率为0.99mW mm-1，而最高体积功率密度随电池长度的变化率为-0.46mW cm-3mm-1。同时采用直径较大的阳极和直径较小的隔离棒时电池后段会发生传质限制。减少或去除隔离棒不会引起严重的燃料渗透，减少隔离棒后电池性能上升。水平方向扩展更有利于实现单电池的放大化。
[Abstract]:In recent years , the high - speed development of mobile Internet technology has made various high - performance mobile electronic devices ( such as smart phones , tablets , etc . ) to meet the requirements of high - efficiency and reliable miniature power supply , and the traditional lithium - ion battery can not meet the requirements of long - term continuous operation , and the micro direct methanol fuel cell ( 渭DMFC ) is faced with technical challenges such as water management difficulty and membrane aging degradation .

However , the performance of the micro - fluid fuel cell is mainly limited by the anode - side fuel and the cathode - side oxidant transfer . The research shows that the use of the air self - breathing electrode can eliminate the mass transfer limitation of the cathode side , but the mass transfer limitation of the fuel is not effectively mitigated . The CO2 bubbles generated by the anode of the micro - fluid fuel cell can also cause disturbance to the parallel laminar flow , thus causing convection mixing and fuel permeation .

In view of the above problems and deficiencies , this paper based on the engineering thermal physics discipline angle , based on strengthening the transmission and improving the battery performance , respectively constructed the air self - breathing micro - fluid fuel cell with permeable anode , single - root three - dimensional anode and positive - volume three - dimensional array anode . The research contents mainly include : ( 1 ) the air self - breathing micro - fluid fuel cell with permeable anode is constructed , and the influence of operating parameters on the performance of the battery is studied ;
and a three - dimensional mathematical model is established to study the fuel transmission characteristics and fuel permeation characteristics in cells with permeable anodes ;
( 2 ) The method of preparing efficient catalyst layer on the surface of curved electrode was studied . The physical and chemical properties , electrochemical characteristics and catalytic ability of the electrode were characterized and compared .
An air self - breathing micro - fluid fuel cell with single three - dimensional anode was constructed . The effects of operating parameters and electrolyte acid - alkalinity on cell performance were studied .
( 3 ) The air self - breathing micro - fluid fuel cell with positive - volume three - dimensional array anode was constructed . The influence of operating parameters , anode and isolation bar arrangement mode on cell performance was studied in acidic electrolyte .
The properties of the battery in alkaline electrolyte were studied .
( 4 ) A three - dimensional mathematical model is established for the air self - breathing micro - fluid fuel cell with positive - volume three - dimensional array anode . The distribution law of fluid flow velocity , fuel concentration , current and potential is studied . The effects of operating parameters and structural parameters on material transmission and cell performance are studied . The main research results are as follows :

1 ) The performance of the air self - breathing micro - fluid fuel cell with permeable anode gradually increases with the increase of fuel concentration , but when the fuel concentration reaches 2M , the performance of the cell decreases . The increase of the flow can enhance the transfer of the reactant , improve the performance of the battery , and the flow is too high ( 20 mL - 1 ) . The performance of the cell decreases . Compared with the planar anode , the permeable anode has high performance , the distribution of the reaction current is uniform , and the current density of the cathode is small at the small flow rate ( 50 渭L min - 1 ) .

2 ) the palladium catalyst layer prepared by adopting the repeated deposition impregnation method has uniform island - like structure and multi - layer structure ;
Pd ( 111 ) crystal plane with high activity and strong oxidation resistance and more uniform three - phase ( electrolyte , catalyst , reactant ) interface distribution ;
and also has high electrochemical activity area , high catalyst utilization rate and excellent formic acid oxidation capability and anti - COADS poisoning capability .

3 ) The CO2 bubbles generated by the air self - breathing micro - fluid fuel cell with single three - dimensional anode in the acidic electrolyte can reduce the area of the anode catalytic reaction and hinder the fuel transmission , increase the ohmic resistance , and the dynamic behavior of the bubbles influence the discharge current . The highest power density of the battery in the alkaline electrolyte is 188.3 % higher than that in the acidic electrolyte .

4 ) For the air self - breathing micro - fluid fuel cell with positive - volume three - dimensional array anode , the performance of the battery is improved after the two isolating rods closest to the cathode are removed . The CO2 bubbles are limited in the anode and the isolation rod array , and the periodic dynamic behavior of the bubbles can cause periodic disturbance to the discharge curve . The maximum power density of the battery reaches 21.5 mWcm - 3 , the maximum current density is 118.3 mAcm - 3 , and the maximum fuel utilization rate can reach 87.6 % .

5 ) When the fuel concentration and the flow rate are the same , the maximum output power of the air self - breathing micro - fluid fuel cell with positive - volume three - dimensional array anode in the alkaline electrolyte is 36.7mW , the maximum output current is 229.0 mA , and the maximum output current of the alkaline electrolyte is increased by 171.0 % and 207.3 % respectively .

6 ) The numerical simulation results show that the flow velocity of the electrolyte in the cavity near the cathode is faster . The output current of the anode is not equal , the output current of the upper layer anode is high . The battery performance under the high flow rate is controlled by the ohmic resistance . When the fuel mass transfer limit occurs in the back section of the anode , the local ionic potential rises and the cathode potential is reversed . The self - compensation mechanism in the positive displacement array anode can improve the reaction current of the back section of the lower layer anode .

7 ) The battery performance is low . The battery performance varies linearly with the length of the battery . The maximum output power varies with the battery length to 0.99 mW mm - 1 , while the highest volume power density is - 0.46 mW / cm - 3 mm - 1 with the battery length change rate . Meanwhile , mass transfer limitation can occur when the separator rod with larger diameter and smaller diameter is used . The reduction or removal of the isolation rod does not cause serious fuel permeation , and the battery performance of the separator after the isolation rod is increased . The horizontal direction expansion is more favorable for realizing the amplification of the single battery .
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM911.4


本文编号：2067993