晶种生长法制备类水滑石薄膜材料及其电化学性能研究

发布时间：2018-11-28 17:13

【摘要】：无机功能薄膜材料在微电子设备、化学和生物传感、能量转化及储存等方面具有重要的应用。晶体粒子的成核及生长过程显著影响无机薄膜的微结构,比如比表面积、孔隙、粒子取向性及晶体形貌等特性。水滑石(LDH)作为无机层状功能材料在催化、吸附、聚合物添加剂、药物传输、环境修复及能量储存等方面具有广泛的应用。将LDH构筑成二维薄膜材料拓宽了其性能应用。目前为止,LDH薄膜的制备方法包括原位生长、物理沉积、电化学沉积等手段,其中原位生长法制备的薄膜具有粒子与基体间结合力强、易于控制晶体取向等特点,最具应用前景。然而,水热条件下原位生长LDH薄膜存在组分局部聚集、薄膜组成不均匀等问题,这将影响到薄膜材料的性能。创新LDH薄膜的制备技术提高其应用性能具有较为重要的研究意义本论文尝试采用晶种生长法(seeded growth method,也叫做二次生长法,secondary growth method)在镍箔和泡沫镍基体上制备了NiAl-LDH薄膜,并将其用作碱性镍氢电池阳极材料,测试其电化学性质。主要的实验结果如下：(1)首先采用水热法制备了纳米NiAl-LDH晶种,晶体粒子尺寸20-30 nm左右,能够形成稳定的胶体溶液。然后,通过浸渍提拉在基体表面涂覆上LDH晶种层。最后在水热条件下进行二次生长制备LDH薄膜。论文研究了晶种法LDH薄膜的晶体组成、薄膜结构、形貌等特点,并与原位生长法制备的薄膜相比较。表征研究了薄膜随着反应时间的演化过程,推测了薄膜原位及二次生长的过程机制,发现二次生长时LDH晶种具有加速晶体晶化速率的作用,所制备的薄膜材料具有更为均匀的晶体组成。(2)论文将两种方法制备的NiAl-LDH薄膜用作镍氢电池阳极材料,测试其电化学性质,发现晶种法薄膜材料具有更好的充放电性能,更高的比放电容量及稳定性。当充放电电流密度为30 mA g-1时,晶种法薄膜的充电电压平台长而低,放电电压平台长而高,薄膜的比放电容量为216mAhg-1,而原位生长法薄膜的为173 mAh g-1。在50圈循环测试中,晶种法薄膜的比放电容量具有更高的稳定性。推测该薄膜具有更高的结晶度和均匀的组分分布,由此有利于降低质子扩散阻力,并稳定电活性材料的结构。(3)最后,本论文尝试采用晶种法制备了MgAl-LDH薄膜,使用与上述NiAl-LDH薄膜相同的二次生长制备工艺,分别在钛片及不锈钢片基体上得到了MgAl-LDH薄膜材料。通过与原位法薄膜对比,发现晶种法薄膜的晶体结晶度更高,晶型更完整,同时生长的薄膜表面晶体更密第进一步证实了LDH晶种在二次法薄膜生长过程中加速晶体晶化的作用。
[Abstract]:Inorganic functional thin films have important applications in microelectronic equipment, chemical and biological sensing, energy conversion and storage. The nucleation and growth process of crystal particles significantly affect the microstructure of inorganic films, such as specific surface area, porosity, particle orientation and crystal morphology. As inorganic layered functional materials, hydrotalcite (LDH) has been widely used in catalysis, adsorption, polymer additives, drug transport, environmental remediation and energy storage. The properties and applications of LDH thin films are broadened by using LDH as two-dimensional thin-film materials. Up to now, the preparation methods of LDH thin films include in situ growth, physical deposition, electrochemical deposition and so on. The films prepared by in situ growth method have the characteristics of strong adhesion between particles and substrates, and easy to control the crystal orientation. The most promising application. However, in situ growth of LDH thin films under hydrothermal conditions, there are some problems such as local aggregation of components and uneven composition of the films, which will affect the properties of the films. It is of great significance to improve the performance of LDH thin films by means of innovative preparation techniques. In this paper, we try to prepare NiAl-LDH films on nickel foil and foamed nickel substrates by seed growth method (seeded growth method,), also known as secondary growth method (, secondary growth method). It was used as anode material for alkaline Ni-MH battery and its electrochemical properties were tested. The main experimental results are as follows: (1) the nanocrystalline NiAl-LDH seeds were prepared by hydrothermal method. The size of the nanoparticles is about 20-30 nm, which can form a stable colloidal solution. Then, the surface of the substrate was coated with LDH seed layer by dipping Czochralski. Finally, LDH thin films were prepared by secondary growth under hydrothermal conditions. In this paper, the crystal composition, structure and morphology of LDH thin films prepared by seed method are studied and compared with those prepared by in situ growth method. The evolution process of the film with reaction time was studied, and the mechanism of in situ and secondary growth of the film was inferred. It was found that the LDH seed had the function of accelerating the crystallization rate of the film during the secondary growth. The prepared thin films have more uniform crystal composition. (2) the NiAl-LDH thin films prepared by two methods are used as anode materials for Ni-MH batteries, and their electrochemical properties are tested. It is found that the film has better charge-discharge performance, higher specific discharge capacity and stability. When the charge / discharge current density is 30 mA g ~ (-1), the charging voltage platform is long and low, and the discharge voltage platform is long and high. The specific discharge capacity of the film is 216mAhg-1, while that of the in-situ growth thin film is 173 mAh g-1. In 50 cycles, the specific discharge capacity of the seed film is more stable. It is inferred that the film has higher crystallinity and uniform component distribution, which is beneficial to reduce the proton diffusion resistance and stabilize the structure of the electrically active material. (3) finally, the MgAl-LDH thin film is prepared by the method of crystal seeding. MgAl-LDH thin films were prepared on titanium and stainless steel substrates using the same secondary growth process as above mentioned NiAl-LDH thin films. Compared with the in-situ thin films, it is found that the crystal crystallinity and crystal form of the seeded thin films are higher, and the surface crystals of the films grown are more dense. The effect of LDH seed on accelerating the crystallization of the thin films in the secondary growth process is further confirmed.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2

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