空气污染物对DMFC阴极毒化机理及抑制策略研究

Direct methanol fuel cells (DMFC) has been considered as a promising portable and mobile power source due to its high energy density,low pollution, abundence resources and easily storage of fuel. However, the insufficient durability of DMFC is still a key issue hindering the commercial application. Air contaminants can degrade the cell’s performance and durability by attacking the cathode of the cells. So it is necessary to study the contamination mechanism and to establish the efficient mitagation method regarding air contaminants.In this project, the contaminative effects of sulfid,nitrid,chloride and their mixtures responsible for the insufficient durability of DMFC will be studied on the basis of special characteristics of DMFC, such as the high-loading catalyst, the water-rich micro enviroments and potential changes due to dynamic operation. The single cell and stack will be adopted to investigate the contaminative characteristics of several key factors, such as pollution sources species, concentration, temperature, current and voltage,etc. A multyple methold that contains in situ analysis and electrochemical process, which is based on the combined FTIRS-MS-electrochemical workstation instrument , rotating disk electrode,rotating ring disk electrode, and contact angle meter, will be developed for revealing the contamination mechanism by testing potential,adsorption states,intermindiates,products,wettability of carbon supports and gas diffusion layer. According to the effects of cathode potential’ changes on the contamination process during dynamic opertation of DMFC,a method for on-line mitagation of air contamination will be explored through dynamic opertation.The results of this work may provide theoretical support for the optimization of DMFC systems.

直接甲醇燃料电池（DMFC）比能量高、环境污染小、燃料来源丰富、便于储存，在便携移动电源领域具有良好的应用前景。然而耐久性问题仍然是DMFC商业化的障碍。空气污染物会攻击阴极导致电池性能和耐久性降低，因此开展其毒化机理和抑制策略研究十分必要。本项目针对DMFC阴极高催化剂载量、富水微环境和动态运行时电位变化特征，研究硫化物、氮化物、氯化物和硫氮混合物等对DMFC阴极的污染问题。通过单电池和电池堆研究污染物种、浓度、温度和电流电压等对阴极性能的影响规律。在线分析手段和电化学方法相结合，通过旋转圆盘电极、旋转环盘电极、电化学工作站-傅里叶红外光谱-在线质谱联用装置和接触角测量仪等分析电位、吸附态、中间物、产物、扩散层及载体润湿性质的变化，研究污染物毒化机理。分析电池动态操作时阴极电位的变化对毒化过程的影响，探索动态操作在线抑制污染物毒化的方法。研究成果将为优化DMFC性能提供理论依据。

直接甲醇燃料电池的运行条件及操作策略与性能、寿命和成本密切相关，是该研究领域的热点。空气中污染物对电池性能的影响是DMFC长期稳定运行面临的挑战之一。同时，从化石燃料中获得的低成本工业甲醇中多碳醇杂质含量高达20-2000ppm，这些杂质物种将严重影响电池性能与耐久性。本项目系统地研究了阴极侧空气进料中的污染物(SO2、NO2等)对电池性能的影响，分析了不同污染物毒化行为的过程机制，针对SO2的毒化行为提出4种恢复缓解策略。同时，研究了工业甲醇代替色谱纯甲醇进料条件对电池性能与耐久性的影响，深入分析工业甲醇中的杂质的毒化作用机制，提出2种恢复缓解策略。主要结论如下：相同浓度SO2毒化造成的DMFC电池性能损失明显小于PEMFC电池性能损失，100ppmSO2混合气导致DMFC恒流放电(100mA·cm-2)下电压在3h内衰减11.1%。SO2毒化造成电池阴极电化学活性比表面积减小，氧还原反应电荷转移电阻增大，导致电池整体性能衰减。干空气吹扫自恢复后电池电压仍有12.3%的衰减。负载间歇加载操作峰值功率密度恢复了31.9%，I-V变载操作恢复了21.6%，外加电场施加脉冲电压恢复了35.6%，恢复效果最优。100ppmNO2混合气导致DMFC恒流放电(100mA·cm-2)下电压6h内衰减13.1%。电池阴极催化剂Pt表面NO2吸附较少，对电化学活性比表面积及氧还原反应电荷转移电阻影响较小。混合物(50ppmSO2和50ppmNO2)毒化导致DMFC恒流放电(100mA·cm-2)下电压5h内衰减18.6%。工业甲醇中杂质物种乙醇和异丙醇不完全氧化生成的乙醛和丙酮在电催化剂表面的吸附是造成电池性能快速衰减的主要原因。根据乙醛和丙酮在电催化剂表面氧化困难，但可在0V附近被还原为乙醇和异丙醇的特性，提出一种在线电化学脉冲方法。通过施加脉冲电位使吸附在催化剂表面的羰基物种还原并从催化剂表面脱附，有效提升了电池性能和耐久性。以工业甲醇为燃料在线电化学脉冲法使电池性能衰减速率大幅度降低(由3.86mV·h-1降低至0.05mV·h-1)，该方法在电池中得到实际的应用。