【作者】 邵玉艳；

【导师】 尹鸽平； 高云智；

【作者基本信息】 哈尔滨工业大学 ， 应用化学， 2006， 博士

【摘要】 质子交换膜燃料电池(PEMFC)是目前电化学能量转化领域研究开发的重点和热点。但是,PEMFC的大规模应用受到成本高、服务寿命短等因素的制约。碳纳米管(CNT)作为载体的电催化剂在氧还原和甲醇氧化等PEMFC电极反应方面表现出良好的催化活性。研究了化学气相沉积法制备的不同直径碳纳米管的抗电化学氧化性。在所有研究的CNT中,直径介于10~20 nm的CNT(D1020)的抗电化学氧化性最强。所以,本文选择D1020作为主要研究对象之一。CNT(D1020)和Vulcan XC-72电极经过在0.5 mol·L-1的H2SO4溶液中1.2 V (RHE,可逆氢电极)加速老化实验后,用X射线光电子光谱(XPS)分析电极表面的化学组成;结果表明,Vulcan XC-72被氧化的程度远高于CNT,说明CNT的电化学稳定高于Vulcan XC-72。CNT电化学稳定性高的原因归于其特殊的结构(封闭、半封闭管状结构)。因此,就电化学稳定性而言,CNT是更好的PEMFC电极材料。研究了Pt/CNT和Pt/Vulcan XC-72的电化学稳定性。Pt/CNT和Pt/Vulcan XC-72经过在0.5 mol·L-1的H2SO4溶液中1.2 V的加速老化实验后,透射电镜(TEM)和X射线衍射(XRD)的分析表明,Pt/Vulcan XC-72中Pt颗粒长大的程度高于Pt/CNT中Pt颗粒长大的程度,XPS分析表明CNT被氧化的程度低于Vulcan XC-72。用氢吸脱附法计算电极电化学表面积的变化,Pt/Vulcan XC-72电极的电化学表面积下降了49.8% ,而Pt/CNT仅下降了26.1%。所以,Pt/CNT的电化学稳定性高于Pt/Vulcan XC-72,这归因于Pt-CNT之间特殊的相互作用、载体CNT的高稳定性。Pt表面氧化层的形成会大大降低Pt/CNT的稳定性;动电位条件下,Pt/CNT的性能衰减较快;Pt颗粒越小,Pt/CNT的性能衰减越快。考察了影响Pt/CNT和Pt/Vulcan XC-72稳定性的非电化学因素,即Pt/CNT和Pt/Vulcan XC-72在气相和液相环境下的稳定性。热重分析表明,Pt/CNT在空气中的热稳定性高于Pt/Vulcan XC-72。将Pt/CNT和Pt/Vulcan XC-72置于100~175℃干燥的空气中,192 h的时间范围内,两者的质量和化学比表面积均无明显变化。Pt/CNT和Pt/Vulcan XC-72颗粒在该温度范围内的干燥空气中较为稳定。热空气处理法不是一种考察PEMFC电极材料稳定性的有效方法。又考察了Pt/CNT和Pt/Vulcan XC-72在0.1 mol·L-1的HClO4溶液中,在室温和100℃情况下的稳定性(老化处理192 h)。TEM、XRD分析均表明Pt的平均粒径明显增大,Pt/CNT中Pt粒径增大的程度低于Pt/Vulcan XC-72。水相环境加速了更多还原

【Abstract】 Proton exchange membrane fuel cells (PEMFC) have been receiving increasing attention due to its high energy efficiency and being environmentally friendly. However, PEMFCs’wide application and commercialization is hindered by two serious issues: poor durability or short life time, and high cost. Carbon nanotubes (CNT) are new promising materials of catalyst supports for PEMFCs. Previous studies reveal that CNTs supported catalysts show enhanced catalytic activity towards oxygen reduction reaction (ORR) and methanol oxidation.The effect of their diamters on the electrochemical stability of CNTs is investigated and CNTs with the diameter between 10~20 nm (D1020) show the most strong resistance to electrochemical oxidation among all the investigated CNTs. So it is selected in the following work. The electrochemical stability of CNTs and Vulcan XC-72 carbon black is investigated using an accelerated degradation test (ADT) by applying a fixed potential of 1.2 V (vs. reversible hydrogen electrode, RHE) on the two electrodes in 0.5 mol·L-1 H2SO4 for 120 h at room temperature. Cyclic voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS) analysis show that more surface oxygen is formed on the surface of Vulcan XC-72 during the electrochemical oxidation under the same conditions, which indicates that CNTs are more resistant to electrochemical oxidation than Vulcan XC-72. The strong stability of CNTs is attributed to their specific structures.The electrochemical stability of Pt/CNT and Pt/Vulcan XC-72 is investigated by applying a constant potential of 1.2 V on the two electrodes in 0.5 mol·L-1 H2SO4 for 192 h (8 days) at room temperature. Transmission Electron Microscope (TEM) images show that the sintering of Pt nanoparticles is more pronounced for Pt/Vulcan XC-72 than that for Pt/CNT. XPS analysis indicates that the oxidation degree of Vulcan XC-72 is higher than that of CNTs. The electrochemical surface area (ESA) of Pt/Vulcan XC-72 electrode decreases by 49.8% after ADT, while only 26.1% for Pt/CNT, which means that PT/CNT is more stable than Pt/Vulcan XC-72 under electrochemical operation. The enhanced stability of Pt/CNT is attributed to the specific interaction between Pt nanoparticles and CNTs and CNTs’high stability under electrochemical conditions. The electrochemical stability of Pt/CNT is closely更多还原