【作者】 田植群；

【导师】 古国榜； 沈培康；

【作者基本信息】 华南理工大学 ， 环境工程， 2004， 博士

【摘要】 燃料电池是一种不经过燃烧直接以电化学反应方式将燃料的化学能转变为电能的发电装置,是一种绿色能源技术。对解决目前世界面临的“能源短缺”和“环境污染”这两大难题具有重要意义,被认为是21世纪的最为重要的能源动力之一。其中,低温燃料电池如质子交换膜燃料电池(PEMFC)、直接甲醇燃料电池(DMFC),具有工作温度低,启动快,能量转化率高等特点,是未来电动汽车、野外电站、便携式电源的理想替代电源,是燃料电池优先发展的类型之一。电催化剂、质子导电膜、电极为低温燃料电池的关键材料。价格昂贵是目前低温燃料电池商业化最大的问题,这主要是电池的关键材料成本过高所引起,其中电催化剂占有很大的比重。因此发展新型催化剂制备技术,制备高活性催化剂,提高其利用率,降低用量,对降低燃料电池成本具有重要意义。 本文研究了一种利用微波介电加热技术,制备负载型贵金属催化剂的新方法,其在快速性、方便性、经济性、设备简易性等方面与其他方法相比具有突出的优势,是一种快速制备高活性纳米催化剂的全新方法。本研究利用此方法,制备了不同负载量的Pt/C(VulcanXC-72)、Pt/多壁碳纳米管(MCNTs)催化剂,采用XRD、TEM、XPS、EDX以及循环伏安法、计时电流法、计时电位法等方法进行了表征,同时以此催化剂,采用低粘度醇为预分散剂,高粘度醇为稳定剂的催化剂浆料制备技术,进行了PEMFC、DMFC研究。 TEM和XRD分析表明,Pt在碳载体上的固定沉积过程所用的微波加热程序,对最终Pt粒径大小和分布的控制具有显著地影响,其中分别采用微波加热10s停留90s和100s的微波加热程序制备的40%Pt/C催化剂IMH-90s和IMH-100s的Pt粒径为3.2nm和3.0nm,并且具有非常均匀的分布。SEM和UV研究表明此方法制备的催化剂的粉体颗粒在10μm左右,与E-TEK公司催化剂相比具有更小的粉体粒径和更容易的分散特性;通过电化学活性面积的测定和对甲醇氧化性能的研究表明IMH-90s和IMH-100s与E-TEK催化剂相比具有更大的电化学活性面积和更高的甲醇氧化电流密度。同时通过调整微波加热程序制备的60%Pt/C催化剂与同类E-TEK相比,其具有更均匀的分布,Pt粒径为4nm左右,并且拥有更高的电化学活性。 采用XRD、TEM、XPS等表征方法研究了微波调控法制备Pt/MCNTs催化剂的制备机制及影响因素,发现Pt以二价和四价Pt的氧化物沉积在MCNTs表面,进一步还原后,Pt大部以零价Pt的形式存在;Pt的粒径更多还原

【Abstract】 Fuel cell is a device that can turn chemical energy into electrical energy through electrochemical reaction without combustion and is of great importance in solving the scarcity of energy sources and environmental pollution, so it is regarded as one of the most important power resources in the 21 century. Low temperature fuel cells such as PEMFC DMFC can work at low temperature with the advantages of quick start and high energy efficiency. They can be potentially used for electric car field power plant and potable equipment. The most difficult problem in the commercialization of low temperature fuel cells is the high cost. Effective solutions to this problem include developing catalyst preparation technique, preparing highly active catalyst, increasing the utilization of catalyst and decreasing the amount of catalyst used.This thesis investigates a new method to prepare carbon supported precious metal catalyst with intermittent microwave heating (IMH) process. This new method has the advantages of rapid, convenient, economic and easy comparing with other methods. Based on this method Pt/C (VulcanXC-72) and Pt/multi-walled carbon nanotubes (MCNTs) catalysts with different loadings were prepared. The catalysts were characterized by XRD, TEM, XPS, EDX, Cyclic voltammograms(CV) method, chrono-amperometric method, chronopotentiometric method and their application in PEMFC and DMFC were studied at the different conditions.TEM and XRD results showed that in the preparation of Pt/C the intermittent microwave heating procedure of Pt deposition had an obvious influence on the size and distribution of Pt particle. The average particle size of Pt in IMH-90 and IMH-100s (prepared by the procedure of 10s heating and 90s or100s intermission) were 3.2nm and 3.0nm respectively and Pt particles were uniformly dispersed on carbon. SEM and UV results showed that the as-prepared catalyst had an uniform diameter of 10 μm. Compared with E-TEK catalyst our catalyst powder size is smaller and is easier to be dispersed in solvents. Catalysts prepared by IMH-90s and IMH-100s had bigger electrochemical active area (EAA) and higher methanol oxidation activity. The 60%Pt/C catalyst with the Pt diameter of 4nm that was prepared by adjusting microwave heating procedure had more uniformly dispersed diameter and higher electrochemical activity compared with E-TEK catalyst.XRD, TEM and XPS were used to characterize the mechanism and influencing factors of the preparation of Pt/MCNTs catalysts with IMH method. Pt existed on the surface of MCNTs in the state of Pt( II) and Pt(IV) oxide, before the reduction and most of transferred to after reduction. The diameter and dispersion of Pt were influenced by the pretreatment of MCNTs, microwave heating procedure and the structure of MCNTs. Methanol oxidation on these catalysts were studied with CV and current-potential polarization. The results showed that catalysts supported on MCNTs pretreated with H2SO4+HNO3 and prepared with the heating procedure IMH-lOOs have highest electrochemical activity and best methanol oxidation performance.The dispersion of the catalysts in different solvents was studied with Zeta potential method. The results showed that the dispersion of the agglomerate Pt/C catalysts depended on the property of the solvent. In this work the catalyst was most uniformly dispersed when isopropanol was used as solvent with the smallest size. Membrane electrode assembly(MEA) was fabricated with isopropanol as disperser and 1,2-propanediol as stabilizing reagent. The performance of H2/O2 single cell reached 0.58V, 1A cm"2 using O2 as cathode. 40W PEMFC stack was fabricated with the performance of 43W at 35°C and 74W at 50"C at atmosphere pressure.DMFC was studied with the current-potential polarization curve. It was found that its performance was largely influenced by the catalyst loading of the anode. Optimized loading was PtRu(l:l):3.4 mg cm"2, DMFC could reach the power density of 115.8 mW cm"2 at 90°C, 2 mol dm’3 methanol,O2 pressure 0.2MPa and 95.8 mW cm"2 at atmosphere pressure, The performance was largely influenced by methanol concentration, 02/air pressure, 02/air flux, and temperature. The DMFC with the self-breathing cathode can discharge steadily.更多还原