【作者】 徐茂文；

【导师】 力虎林；

【作者基本信息】 兰州大学 ， 物理化学， 2008， 博士

【摘要】 锰有7种不同的氧化态(Mn⁷⁺、Mn⁶⁺、Mn⁵⁺、Mn⁴⁺、Mn³⁺、Mn²⁺、Mn⁺),其对应的氧化物及其混合价态的氧化物在电、磁、催化等方面均表现出优越的物理及化学性能,是非常重要的能源材料。纳米科学的兴起为锰基氧化物的研究和应用注入了新的活力。本论文在综述当前锰基氧化物研究和应用的基础上,结合多种新兴纳米材料的制备手段构筑了一系列新型形貌和微结构的锰基氧化物,并对其电化学性能进行了测试和评价,系统地研究了材料的合成方法-微结构特征-电化学性质三者之间的关系,深入地认识了锰基化合物的结构特征及其应用,制备出一些性能优异的锰基化合物,并将其应用于化学能源系统,探讨其广泛应用的可行性。主要进行了以下的研究工作:（1）利用铜做还原剂,首次在水热反应条件下,不借助任何模板剂的作用,得到了中空结构的海胆状α-MnO₂。通过大量实验研究了反应时间、反应温度对产物结构和形貌的影响。结果发现,随着反应时间的增长,样品由实心球→空心球→纳米线逐渐转化,符合“奥斯特瓦尔德熟化”机理。随着反应温度的升高,产物由纳米线逐渐转化为规则的多面体结构,而且晶体结构也逐渐变化。这说明产物形貌的变化属于动力学控制过程,而热力学控制过程更容易引起晶体结构的变化。此外,通过比表面积、阻抗谱图分析、循环伏安和充放电测试,研究了不同形貌α-MnO₂的电化学行为。分析了样品微结构对其电化学性能的影响。（2）利用不同的反应介质对制备的球形γ-MnO₂进行再处理,发现反应体系的酸碱性对产物的晶体结构和形貌有很大的影响。通过大量实验,对水热反应的可控合成有了进一步的认识。（3）利用水热法合成了分布均匀的β-MnO₂纳米管,并以其为载体,首次合成了Pd/β-MnO₂纳米管复合材料,并研究了其作为直接甲醇燃料电池催化剂的可行性,对于拓展和开发新型的燃料电池电催化剂材料具有重要的指导意义。（4）以高分子聚合物作为模板,利用改进的还原法制备了中孔无定形MnO₂。并利用TG-DTG,XRD,TEM,BET和电化学测试,详细探讨了材料的微结构和化学性能之间的关系。研究结果表明,材料比表面积的提高,不但可以提高材料的双电层电容,而且其氧化还原活性位也大大增多,其法拉第电容也随之增加。为制备性能优异的多孔电极材料提供了一种简单可行的方法。（5）利用微波辅助高温法制备了具有理想尖晶石结构和规则形貌的LiCr_0.15Mn_1.85O₄。所得材料粒径分布均匀,颗粒表面光滑平整。采用微波对样品的前驱体进行处理,不但可以缩短样品的焙烧时间,大大节约了制备锰酸锂的成本,而且由于微波是从前驱体的内部开始升温,避免了前驱体表面碳化后,影响内部晶体的生成,也减少了晶体的团聚现象。另外微波加热速率快,可以避免材料合成过程中晶粒的异常长大,能够在短时间、低温下合成纯度高、粒度细、分布均匀的材料。（6）利用有特殊孔道结构的SBA-15氧化硅分子筛为模板,用蔗糖作碳源,制备了具有大比表面积和均匀孔分布的介孔碳。其表面积为1020 m²/g,孔分布主要在3-6纳米之间,是理想的双电层电容器的电极材料。（7）研究了LiCr_0.15Mn_1.85O₄和介孔碳在水体系的电化学行为,并探索了将锰酸锂作为正极材料,介孔碳作为负极材料,组成水体系的电化学混合型电容器的可行性,进一步提高了电化学电容器的性能。更多还原

【Abstract】 There are seven oxidation states (Mn⁷⁺、Mn⁶⁺、Mn⁵⁺、Mn⁴⁺、Mn³⁺、Mn²⁺、Mn⁺) in manganese oxides, and their corresponding and mixed valence oxides show extraordinary physical and chemical properties in electricity, magnetic and catalysts. At present, it is also a kind of important power sources materials which can be used widely. In particular, the spring-up of nanomaterials further fuels-up the activity of the research and development of manganese oxides.In this thesis, we have reviewed the recent developments of manganese oxides in synthesis and application. Through the means of improving synthetic method, optimizing preparation condition, we have obtained a series of manganese oxides with different crystal structure and novel morphologies. Besides, we have investigated the structure properties, electrochemical performance and the correlations between them using different testing technologies such as TG-DTG, XRD, FESEM, TEM, HRTEM, BET as well as some electrochemical measurements. The main content is as follows:（Ⅰ） Various hollow sphere and urchin structuredα-MnO₂ have been synthesized by a simple and facile hydrothermal method for the first time. The effect of reaction time and reaction temperature on the structure and morphology of samples has also been studied systemically. The experimental results indicated that the products grew from solid sphere to hollow sphere, further to nanorods gradually with the increasing of reaction time, which is the result of Ostwald ripening process. With the increasing of hydrothermal reaction temperature,α-MnO₂ transformed intoβ-MnO₂, its morphology also changed correspondingly, from nanorods into polyhedral particles. The results indicated different shapedα-MnO₂ materials were kinetically controlled products, which were formed at lower temperature, whereasβ-MnO₂ was a thermodynamically controlled product, which was formed at higher temperature. The novel hollow sphere or urchin structuredα-MnO₂ materials possessed high loosely mesoporous cluster structure consisting of thin plates or nanowires and exhibited enhanced rate capacity and cycleability. The good cycleability and high rate capability coupled with the low cost and environmentally benign nature of manganese may make this material attractive for large applications. Furthermore, the hydrothermal method has excellent reliability, selectivity, and efficiency for synthesizing inorganic materials with uniform and distinct morphologies.（Ⅱ） Usingγ-MnO₂ sphere as raw material, by controlling reaction temperature and reaction atmosphere, different nanostructured products were prepared via hydrothermal treatment. The results of FESEM investigation indicated that the sample can maintain its spherical morphology of starting materials in ammonia solution, while it unlayed into nanowires in- water atmosphere, which revealed that the reaction atmosphere has significantly influence on the microstructure and morphology of the resulting products.（Ⅲ）β-MnO₂ nanotube was first proposed as catalyst supporting material in our experiment. Pd/β-MnO₂ nanotubes composites were prepared via a simple and facile reductive process. Electrochemical study indicated that Pd/β-MnO₂ composites had a better electrocatalytic activity than that of Pd/C for methanol oxidation in NaOH solution. It implies that Pd/β-MnO₂ nanotubes may be a good candidate for noble metal catalyst supports and have potential application in preparing catalysts for direct methanol fuel cells. It open a new way for searching good catalyst supporting material.（Ⅳ） Mesoporous amorphous MnO₂ was synthesized by an improved reduction reaction and using supramolecular as template. Its amorphous structure was determined by TEM and XRD analysis. The amorphous MnO₂ annealed at 200℃exhibited the maximum specific capacitance of 298.7 F/g in a 2 mol/L KOH electrolyte at 5 mA. The prepared mesoporous amorphous MnO₂ showed ideal capacitive nature, high specific capacitance and long cycle life, so it is suitable to be used as electrode material for electrochemical capacitors. It is believed that the main part of the capacitance comes from the pseudocapacitive surface redox process. When the specific surface area of MnO₂ electrode material increase, not only the double layer capacitance will increase, the redox active sites will also increase subsequently, so the pseudocapacitance will increase significantly.（Ⅴ） Spinel-type LiCr_0.15Mn_1.85O₄ has been efficiently fabricated via improved microwave assisted sintering method. The prepared LiCr_0.15Mn_1.85O₄ powders have ideal spinel structure, regular shape and narrow particle size distribution. The results of the experiments indicated that microwave not only reduced the sintering time, but also saved the cost significantly. In the microwave irradiation field, since the microwave heated not from the outside but from the inside of the precursor and thus it provided a uniform heating environment which could shorten the synthesizing time, effectively avoided the growing of crystal grain exceptionally and overcome the agglomeration of particles.（Ⅵ） Mesoporous carbon with large specific surface area （1020 m²/g） and uniform pore size distribution （3-6 nm） has been successfully synthesized by using SBA-15 as template, sucrose as carbon sources. The result of electrochemical measurement indicated that it is a good electrode material for double-layer capacitor.（Ⅶ） The electrochemical performance of LiCr_0.15Mn_1.85O₄ and mesoporous carbon in aqueous electrolyte was studied respectively. A hybrid aqueous supercapacitor using LiCr_0.15Mn_1.85O₄ as anode and mesoporous carbon as cathode materials was setup in our experiment. The results of electrochemical measurement indicated that LiCr_0.15Mn_1.85O₄ has a potential as good electrode materials in hybrid aqueous supercapacitor.更多还原