低温熔盐中Mg基储氢合金的电沉积及其性能研究

【作者】 朱伟；

【导师】 王森林；

【作者基本信息】 华侨大学 ， 物理化学， 2008， 硕士

【摘要】 镁基储氢合金以储氢量高、密度小、资源丰富与价格低廉等一系列优点,被认为是最具有开发前景的储氢材料之一。本文从尿素-乙酰胺-NaBr低温熔盐体系中电沉积了镁基合金,并研究了该合金电化学性能。本文的主要研究内容如下:1.研究了Ni(II)、Mg(II)及La(III)分别在尿素-乙酰胺(4.27 mol·L-1)-NaBr(1.40 mol·L-1)低温熔盐中的电化学行为,循环伏安实验证实Ni(II)在该熔盐体系中的还原是一步不可逆过程,并计算了Ni(II)电还原的扩散系数D0 = 2.03×10-7 cm2·s-1和电荷传递系数α=0.42。研究发现Mg(II)和La(III)无法单独在该熔盐体系中还原析出。用计时电流曲线来表征成核过程,结果表明Ni(II)的还原是瞬间三维成核过程,并计算Ni(II)电还原的扩散系数D0 = 9.09×10-7 cm2·s-1。2.研究了Mg(II)、La(III)与Ni(II)在尿素-乙酰胺-NaBr低温熔盐体系中的共沉积行为。从循环伏安实验和对沉积膜的EDS检测发现,Ni-La、Ni-Mg及Ni-Mg-La合金可以在该体系中共沉积出来,并且是分步还原。本文用多核络合物中间体来解释上述合金的共沉积的机理。3.利用恒电位和恒电流方法制备了Ni-La、Ni-Mg及Ni-Mg-La合金薄膜。研究了沉积电位、阴极电流密度及主盐浓度比对沉积膜组成的影响。用能谱(EDS)、扫描电镜(SEM)和X射线衍射(XRD)分析了镀层结构和表面形貌。结果表明,电沉积得到的合金膜均为含非晶的多相结构。4.所制备的薄膜合金的最大放电容量和电极充放电循环稳定性顺序为:Ni-Mg-La﹥Ni-La﹥Ni-Mg。不同的合金膜电极循环伏安曲线氧化峰电流均随扫描次数增加而减小;电极放电容量越大,其循环伏安曲线氧化峰面积越大,峰电流越高。速度扫描实验表明,合金膜电极氧化峰电流与扫描速度的平方根成线性关系,说明储氢电极反应是受氢的扩散所控制。更多还原

【Abstract】 The Mg-based hydrogen storage alloys are considered as one of the most promising hydrogen storage alloys,offering the combination of great hydrogen storage capacity,low density,abundant resource and low cost.The Mg-based alloys were electrodeposited in urea-acetamide-NaBr low temperature molten salts,and the electrochemical performance of the alloys was studied.The main content in this dissertation was summarized as follows:1.The electrochemical behaviours of Ni(II)、Mg(II)、La(III) on Cu electrode was investigated in urea-acetamide(4.27 mol·L-1)-NaBr(1.40 mol·L-1) low temperature molten salts, respectively.The reduction processes of Ni(II) were proved as one step irreversibility by cyclic voltammetry experiments.The diffusion coefficient (D0) and the transfer coefficient (α) of the Ni(II) was calculated as D0=2.03×10-7 cm2·s-1 andα=0.41 respectively. Mg(II) and La(III) could not be electrochemically reduced in this molten salts independently. The nucleation processes were three-dimentional direction and instantaneous processes which was studied by chronoamperometry methods, and the diffusion coefficient (D0) was calculated as 9.09×10-7 cm2·s-1.2.The codeposition behaviors of Mg(II)、La(III) and Ni(II) were studied in low temperature molten salts by cyclic voltammetry and Energy dispersion spectrum(EDS).It was indicated that the codeposition of Ni-La、Ni-Mg and Ni-Mg-La alloys was step-by-step reduction. The codepositon mechanism was explained by the polynuclear complex of electroactive intermediates.3.The Ni-La、Ni-Mg and Ni-Mg-La alloys were prepared by constant current and potentiostatic electrodeposition. The effect of the deposition potential, current density and main salt concentration ratio on the deposits composition was investigated. The structure and surface morphology of the deposits were analyzed by EDS、Scanning Electronic Microscope(SEM) and X-ray diffraction (XRD). The results showed that the deposits were multi-phase containing amorphous phase. 4.The maximum discharge capacity and the cycle-life sequence of the deposits were both as follows: Ni-Mg-La>Ni-La>Ni-Mg. The cyclic voltammetry anodic peak current (Ip) of different alloy electrodes was decreased with increasing sweeping number,and the anodic peak area and its Ip are both proportional to electrode discharge capacity. The linear relationship between Ip and v1/2 (v is sweeping rate) indicated that the electrode discharge reaction was controlled by hydrogen atom diffusion process.更多还原