【作者】 练慧勤；

【导师】 曹楚南； 王建明；

【作者基本信息】 浙江大学 ， 物理化学， 2011， 博士

【摘要】 氢氧化镍电极由于其在镍基碱性电池、电化学电容器、有机电合成、传感器及电致变色装置等领域的广泛应用,最近几十年来正日益引起人们的兴趣。Ni(OH)2/Ni00H电对因其电极电位高、电化学容量大及电化学可逆性优等特性被视为最重要的氧化/还原电对之一。从Ni(OH)2到NiOOH的转化(氢氧化镍的氧化)意味着氧化性能量在氢氧化镍中的储存。考虑到氢氧化镍电极的广泛应用,探索环境友好的简易的实现氧化性能量在氢氧化镍中储存的方法无疑具有重要意义。本论文主要探究了实现氧化性能量在氢氧化镍中储存的几种方法。第三章中,以硝酸镍为主盐采用尿素均相沉淀法制备了钴取代氢氧化镍样品,并对其结构和电化学性能进行了表征与测试。X射线衍射和红外光谱结果表明,所制备的不同含钴量的样品均为典型α相,样品的结晶度随钴含量的增加而降低。电化学测试结果表明,随着样品中含钴量的增加,氢氧化镍电极的可逆性逐渐提高,其放电容量逐渐增大。随着电化学循环的进行,含钴样品的放电容量逐渐增加。含钴24.4%样品在260次循环后其放电容量达到415mAh·g-1(以纯氢氧化镍计)。钴的掺杂降低了氢氧化镍的氧化电位,同时提高了其析氧电位,这可能是导致氢氧化镍电极性能改进的原因之一。第四章中,研究了电解液组成和氢氧化镍层表面结构对二氧化钛的氧化性能量储存的影响。具有较高OH-含量的电解液有利于紫外光辐射下二氧化钛产生的氧化性能量在氢氧化镍中的储存。考察了阴极沉积电流对氢氧化镍层表面结构的影响,在1.0mA·cm-2的阴极沉积电流下获得了纳米多孔结构的TiO2-Ni(OH)2双层电极。多孔结构有利于电解液在电极内部的渗透,从而增加电化学反应的有效面积；纳米结构的颗粒可以提供高比表面积、快速的氧化还原反应和较短的固相扩散路径。上述两个因素是所制备的纳米多孔结构的TiO2-Ni(OH)2双层电极具有较好的氧化性能量储存性能的主要原因。第五章中,研究了在一个由纳米多孔结构的TiO2-Ni(OH)2双层光阳极和氧还原铂电极组成的光化学池中紫外光辐射下二氧化钛产生的氧化性能量在氢氧化镍中的储存。光阳极与铂阴极的短接,可以促进光生电子和空穴的分离,因此能够显著地改善TiO2-Ni(OH)2双层光阳极的氧化性能量储存性能。采用溶胶-凝胶法制备出了纳米结构的二氧化钛薄膜,以该薄膜为基体应用阴极电沉积法得到了纳米多孔结构的氢氧化镍膜；所制备的纳米多孔结构的TiO2-Ni(OH)2双膜电极显示了明显改进的光致氧化性能量储存性能。第六章中,采用阴极电沉积方法得到的a-Ni(OH)2膜电极作为阳极,氧还原电极作为阴极,构成Ni(OH)2-O2耦合储能体系,成功地实现了Ni(OH)2到NiOOH的转变,即氧化性能量的储存。铂电极在具有较高氧含量和较低pH值的电解液中电位较高,说明此时氧的氧化能力较强；在含有上述氧还原铂阴极的耦合储能体系中能够明显增强氢氧化镍膜电极的氧化性能量储存性能。氧化-放电循环测试结果表明,在含有由空气电极和pH=2的1.0 mol-L-1 Na2SO4溶液组成的氧还原电极的耦合储能体系中使用镍基体的氢氧化镍膜电极显示较高的循环稳定性和较好的倍率放电性能。研究还表明利用过氧化氢等其它绿色氧化剂也可实现氧化性能量在氢氧化镍中的储存。从氧化性能量储存和氢氧化镍两个角度来看,目前工作均具有重要意义。更多还原

【Abstract】 Nickel hydroxide/nickel oxyhydroxide electrodes have aroused increasing attention in decades because of their extensive applications in various fields, for example, nickel-based alkaline batteries, electrochemical capacitors, electrocatalysis in organic synthesis, sensors, and electrochromic devices. Ni(OH)2/NiOOH has been identified as one of the most important redox couples due to its distinctive electrochemical properties such as high electrode potential, large electrochemical capacity and excellent electrochemical reversibility. The transition from Ni(OH)2 to NiOOH (oxidation of Ni(OH)2) implies the oxidative energy storage in nickel hydroxide. The searching on environmentally friendly and facile methods for the oxidative energy storage in nickel hydroxide undoubtedly has considerable significance. In this dissertation various techniques for oxidative energy storage in Ni(OH)2 electrodes were investigated.In the third chapter, the Co-substituted Ni(OH)2 samples were prepared by homogeneous precipitation from nickel nitrate solution in the presence of urea, and their structures and electrochemical performance were investigated. The results of XRD and IR indicated that the Ni(OH)2 samples with various Co contents are typical a-phase, and the crystallinity of the samples decreases with the increase in the cobalt content. The results of electrochemical experiments showed that as the cobalt content increases, the discharge capacity and electrochemical reversibility of the Co-substituted Ni(OH)2 samples are obviously improved. The discharge capacity of the Co-containing samples gradually increases with the electrochemical-cycling. The discharge capacity of the sample with 24.4% Co reached 415mAh per gram of pure Ni(OH)2 at the 260th cycle. It was also found that the doping of Co increases the oxygen evolution potential and decreases the oxidation potential of Ni(OH)2, which may be partly responsible for the improvement on the electrochemical performance of the Co-substituted Ni(OH)2 samples. In the fourth chapter, the effects of electrolyte composition and surface structure in Ni(OH)2 layer on storage of the oxidative energy of TiO2 have been clarified. The electrolytes with relatively high OH- content facilitate the oxidative energy storage of an UV-irradiated TiO2 photocatalyst in Ni(OH)2. The effects of cathodic deposition current density on the surface structure in Ni(OH)2 layer have been investigated. A porous nanostructured TiO2-Ni(OH)2 bilayer may be obtained by the cathodic electrodeposition at 1.0 mA cm-2. The porous structure may provide easy access of the surfaces to liquid electrolyte, leading to an increase in effective surface area for electrochemical reactions. The nanostructured particles may provide high-specific surface area, fast redox reactions, and shortened diffusion path in solid phase. The two factors are responsible for the enhanced oxidative energy storage of the obtained porous nanostructured TiO2-Ni(OH)2 bilayer.In the fifth chapter, the oxidative energy storage of an UV-irradiated TiO2 photocatalyst in Ni(OH)2 by a photochemical cell comprising a porous nanostructured TiO2-Ni(OH)2 bilayer photoanode and a Pt foil O2-ruducing cathode was investigated. The oxidative energy storage of the TiO2-Ni(OH)2 bilayer electrode is greatly enhanced when the photoanode is galvanically connected to the platinum cathode, resulting from the effective electron-hole separation. A nanostructured TiO2 film was prepared on ITO by a sol-gel method, and a porous nanostructured Ni(OH)2 layer was further obtained by a cathodic electrodeposition. The as-prepared porous nanostructured TiO2-Ni(OH)2 dilayer shows obviously improved UV-induced oxidative energy storage performance.In the sixth chapter, the oxidative energy storage in the Ni(OH)2 film electrodes, which was evaluated by means of galvanostatic discharge tests, has been successfully achieved by a designed novel system comprising a nickel hydroxide film electrode and a platinum O2-reducing cathode. It was found that the oxidative energy storage in the Ni(OH)2 film electrodes can be obviously enhanced in the coupling system containing the cathode electrolytes with higher oxygen content or lower pH value, resulting from improvement in the oxidative ability of oxygen as indicated by increase in the open-circuit potentials of the platinum electrode. The results of the oxidation-discharge cycle tests showed that the nickel hydroxide film electrode on nickel foil substrate in the galvanic couple system with air cathode using 1.0 M Na2SO4 (pH=2) as cathode electrolyte presents higher cycling stability and better rate discharge capability. It was further demonstrated that the oxidative energy storage in Ni(OH)2 can also be realized by utilizing other green oxidative agents (e.g. H2O2). From the views of both the oxidative energy storage and the oxidation of Ni(OH)2, it is reasonable to conclude that this work is of considerable importance.更多还原