【作者】 宋文生；

【导师】 王宇新；

【作者基本信息】 天津大学 ， 化学工程， 2004， 博士

【摘要】 直接甲醇燃料电池（DMFC）具有结构简单、燃料补充方便、体积和质量比能量密度高等特点，有望成为未来理想动力源之一，用作移动动力电源和便携式电源。DMFC能否顺利地实现商业化和民用化，其电解质膜、电极材料和催化剂起着关键的作用。通用的Nafion?电解质膜和Pt或Pt合金催化剂价格昂贵，且膜存在甲醇“穿透”问题。为此，本文从非贵金属在碱性介质中具有高活性这一点出发，寻找合适的电解质膜。碳酸盐（如K2CO3）系中强碱盐，其作为DMFC电解质时，一可放宽电极催化剂的选择范围；二可抑制CO2进入电解质溶液中。我们提出了将碳酸盐聚合物膜用于DMFC的新思路并采取三种方法制备出K2CO3掺杂型电解质膜。第一，在聚丙烯酰胺凝胶中嵌入K2CO3，利用凝胶中的水分子来保证碳酸盐发生电离，制备出K2CO3掺杂聚丙烯酰胺凝胶电解质膜。第二，为提高K2CO3掺杂聚丙烯酰胺凝胶电解质膜的强度，选择聚醚砜微孔膜作增强材料，让聚合在膜微孔内发生，制成增强型K2CO3掺杂聚丙烯酰胺凝胶电解质膜。第三，分两种途径直接掺杂高聚物，一是选择水溶性聚丙烯酰胺或聚四氟乙烯水乳液，使K2CO3在其水相中溶解后制成复合膜；二是K2CO3颗粒直接掺杂热塑性聚氨酯弹性体或尼龙6和聚己内酰胺负载K2CO3掺杂聚砜制备出复合膜。研究发现，K2CO3掺杂型电解质膜的电导率均比较高，且随温度的升高而增加，增加幅度大于Nafion膜；增强型K2CO3掺杂聚丙烯酰胺凝胶电解质膜和支撑型K2CO3掺杂水溶性聚丙烯酰胺复合膜在甲醇液态进料的DMFC中应用时，电池放电性能比较稳定，并具有一定的阻醇作用。此外，K2CO3掺杂高聚物制备复合膜的方法为制备其它的离子传导性电解质膜提供了有益的借鉴。从碳酸盐水溶液与CO2平衡的开放体系入手，考察了温度对碳酸盐体系中各组分浓度的影响；阐明了为什么碳酸盐电解质体系具有抑制甲醇氧化产物CO2进入溶液的功能；在对碳酸盐体系中负离子浓度分析的基础上，探讨了DMFC中使用碳酸盐电解质时电极反应机理。更多还原

【Abstract】 Direct methanol fuel cells (DMFC) are characterized by simple structure, convenient fuel supply and high energy density. DMFC will be one of the ideal power sources in the future for mobile, portable and stationary applications. Present electrolyte membrane, electrode materials and catalysts in DMFC are not satisfactory. Commercial Nafion? electrolyte membrane, Pt or Pt alloy catalysts are expensive, and methanol crossover in Nafion? electrolyte membrane leads to not only a waste of fuel but also poor fuel cell performance. The aim of this study is to explore alternative membranes based on the fact that catalyst of non-noble metals shows high activity in alkaline media. Metal carbonate is an alkali salt with moderate basicity. When a metal carbonate, e. g. K2CO3 is used as electrolyte in DMFC, the potential advantage is both widened selection of catalysts and resistance of CO2 uptake in the electrolyte. We initiated the idea of using membrane composed of polymer matrix and embedded metal carbonate as the electrolyte in DMFC and K2CO3 electrolyte membranes have been prepared through three methods. Firstly, the gel electrolyte membrane of K2CO3 doped polyacrylamide is prepared by dispersing ionic species, K2CO3, to a solution of acrylamide and bisacrylamide followed by polymerization and gelation. Their ambient temperature conductivity is in the range 10-2 to 10-1S/cm. Secondly, to enhance the strength of the above-mentioned gel electrolyte, microporous membrane of polyethersulfone (PES) is used as supporting material and gelation takes place in the micropore of PES membrane. The reinforced gel electrolyte membrane of K2CO3 doped polyacrylamide is thus obtained. The third method is to K2CO3 powder directly dispersed in polymer. In this method, we use two ways. In one way, casting membranes are prepared by using K2CO3 in aqueous PAA solution or PTFE emulsion. In the other, membranes are prepared by K2CO3 directly being doped with thermoplastic polyurethane elastomer (TPU) and nylon 6, respectively, and that a composite membrane is prepared by polycaprolactam loading K2CO3 prior to K2CO3 being doped with polysulfone (PSF). The results show that K2CO3 doped solid electrolyte membranes have rather high electricity at ambient temperature and electricity increase with the increasing of temperature. The stable performance of the membranes used in DMFC can be maintained. <WP=5>The component concentration in an equilibrium system of aqueous carbonate solution and CO2 under varying temperature is analyzed. The equilibrium relation in such a system determines the exclusion of CO2 by an aqueous metal carbonate electrolyte. On the basis of the above analysis, the mechanism of a DMFC with carbonate electrolyte is discussed.更多还原