【作者】 刘淑芳；

【导师】 贺晓慧；

【作者基本信息】 南昌大学 ， 材料物理与化学， 2011， 硕士

【摘要】 直接甲醇燃料电池(DMFC)具有结构紧凑、质量轻、燃料来源丰富及存储携带方便等优点,是目前优先发展的能源技术之一。质子交换膜(PEM)是直接甲醇燃料电池的核心组件之一。当前广泛使用的Nafion(?)膜,因为高的甲醇渗透率、高温及低湿条件下质子传导率大幅降低和成本高昂等制约了其大规模应用。开发高性价比的新型质子交换膜已成为燃料电池研究中的新热点。降冰片烯类单体的加成型聚合物的主链结构刚性极高,加上其坚固的环状结构限制了COC聚合物沿着主链的自由移动,因而呈现出较高的玻璃化转变温度。由于此材料无不饱和的双键,三键或芳香环结构,因此通常此种材料具备较佳的耐热温度与抗老化性能。其热裂解温度可高于400℃以上,此外,此材料更具低渗水性。基于该类高分子本身兼具：成膜性佳、热稳定度高、化学稳定度高以及耐电压性质等优点,因此是适合开发作为直接甲醇燃料电池用质子交换膜材料的环烯烃材料。本文以双-(β-酮萘亚胺)镍(Ⅱ)与B(C6F5)3的二元催化体系制备了降冰片烯的酯衍生物与降冰片烯的醚衍生物的共聚物,此聚合物脱酯后与2-溴-2-甲基-丙酰溴反应获得原子转移自由基聚合(ATRP)所需的大分子引发剂P(BN/NOH)Br。以HEMA作为单体,用此引发剂引发对甲基丙烯酸羟乙酯的原子转移自由基聚合得到以聚功能化降冰片烯为主链,侧链含多羟基的聚合物。将产物溶于四氢呋喃中加入4.5-咪唑二羧酸和H3PO4超声分散均匀成膜,加热时,这种聚合物和4.5-咪唑二羧酸通过PHEMA所带的-OH和4.5-咪唑二羧酸(IDA)所带的-COOH之间的酯化反应进行交联,加入的磷酸(H3PO4)与IDA形成咪唑-磷酸络合物,进行质子传输。在0.5 mol/L的H2SO4溶液中,膜的质子传导率随H3PO4含量的增加而增大,随温度的升高而升高,80℃时膜的最大质子传导率为0.0043 S/cm。聚合物的结构已通过核磁共振(1H NMR)和红外(FT-IR)谱图得到证明,[P(BN/NOH)Br-g-PHEMA]膜展示了好的机械性能(弹性模量为810.5 MPa)和高的热稳定性(高达320℃),分别由万能试验机(UTM)和热重分析(TGA)得到。我们用双-(β-酮萘亚胺)镍(Ⅱ)/B(C6F5)3催化体系制备了5-降冰片烯-2-甲基丁基醚(BN)及5-降冰片烯-2-亚甲氧基-己氧基联苯(BphN)的乙烯基加成型共聚物(P(BN/BphN)),并用浓硫酸作为磺化试剂对其进行磺化,得到磺化共聚物SP(BN/BphN),通过控制磺化时间控制磺化度,流延法成膜。为了得到甲醇透过率低、IEC值高的磺酸膜,将最长磺化时间控制为8h。此时膜的IEC值为1.11meq/g,高于Nafion(?) 115(0.88 meq/g);甲醇透过率为7.5×10-7 cm2/s,低于Nafion(?) 115(13 x 10-7 cm2/s)。随着磺化度的增大,SP(BN/BphN)膜的吸水率、甲醇透过率、质子传导率都增大；同时,质子传导率随着温度的升高而增大。因为低吸水率,SP(BN/BphN)膜的质子传导率低于Nafion(?)115,导致单电池性能不佳。通过透射电镜(TEM),扫描电镜(SEM)观察到SP(BN/BphN)膜中的微相分离及离子簇。SP(BN/BphN)膜具有优异的氧化稳性、良好的耐热性能、足够的机械强度,有望成为DMFC质子交换膜材料。更多还原

【Abstract】 Direct methanol fuel cell (DMFC) with a compact structure, light weight, abundant fuel source and easi to be carried and stored, is one of priority development of the energy technologies.The proton exchange membrane (PEM), is the key component of the DMFCs. Nafion(?), one of the perfluorosulfonic acid membranes, is the current state-of-the-art PEM material. However, several drawbacks of Nafion(?), such as high cost, high methanol permeability, low humidity and a major reduction in conductivity at high temperatures, have led researchers to investigate promising alternatives.Vinyl addition type polynorbornenes have both high rigidity main chain and strong polymer ring structure which limits the COC to move freely along the main chain, show a higher glass transition temperature. Because all this materials that don’t have unsaturated double bond, triple bond or aromatic ring structure, usually have excellent heat resistance and anti-aging properties. Its thermal decomposition temperature is higher than 400℃. This material also has low water permeability. Based on its good film-forming, thermal stability, high chemical stability, and dielectric properties etc., the vinyl addition type polynorbornene is suitable for development as a direct methanol fuel cell proton exchange membrane material.The graft copolymer poly(butoxymethylenenorbornene-co-norbornenemethylene bromoisobutyrylate) grafted poly(hydroxy ethyl acrylate) [P(BN/NOH)Br-g-PHEMA] was synthesized by the atom transfer radical polymerization (ATRP) of hydroxy ethyl acrylate (HEMA) from the copolymer prepared by two functional norbornene monomers via vinyl addition mechanism. The graft copolymer [P(BN/NOH)Br-g-PHEMA] is further crosslinked with 4,5-imidazole dicarboxylic acid (IDA) and then doped with phosphoric acid (H3PO4) to form imidazole-H3PO4 complexes. The results showed that the polynorbornene backbone and crosslinked micromorphology produced low methanol permeability of the membranes (from 1.5×10-7 to 3.8×10-6 cm2/s) and endowed the membranes with good mechanical properties (from 692.7 to 159.7 MPa of elastic modulus, from 2.7 to 22.7% of elongation at break, from 14.4 to 5.5 MPa of tensile strength at break) and excellent thermal stability (up to 280℃). Furthermore, the proton conductivities of the membranes increased with increasing temperature and increasing contents of IDA/H3PO4 in the membranes.The vinyl addition type copolymer Poly(butoxymethylene norbornene-co-biphenyl oxymethoxy norbornene) (P(BN/BphN)) was synthesized by using bis-(β-ketonaphthylimino)nickel(Ⅱ)/B(C6F5)3 catalytic system. P(BN/BphN) was sulfonated with concentrated sulfuric acid (98%) as sulfonating agent in a component solvent. Degree of sulfonation (DS) was controlled by the reaction time and the SP(BN/BphN) membranes were obtained by solution casting method. The ion exchange capacity (IEC), DS, water uptake and methanol permeability of the SP(BN/BphN)s were increased with the sulfonated time. The sulfonated time was controlled to be 8h as the highest to obtain lower methanol permeability. The methanol permeability of the SP(BN/BphN) membranes were in the range of 1.8×10-7 to 7.5×10-7 cm2/s, which were lower than the value 1.3×10-6 cm2/s of Nafion(?)115. FTIR,1H NMR were involved to confirm the structure of achieved monomer, copolymer and sulfonated copolymers. The proton conductivity of SP(BN/BphN) membranes increased with the increase of IEC values, temperature and water uptake. Water uptake of the SP(BN/BphN) membranes were lower than that of Nafion(?) 115 and lead to low proton conduction. Microscopic phase separation occurred in SP(BN/BphN) membrane and domains containing sulfonic acid groups were investigated by TEM and SEM. SP(BN/BphN) membranes had good mechanical properties, high thermal stability and excellent oxidative stability.更多还原