【作者】 朱建慧；

【导师】 黄新堂；

【作者基本信息】 华中师范大学 ， 凝聚态物理， 2014， 博士

【摘要】 随着纳米材料这一概念的提出以及电子显微镜技术的发展,纳米材料逐渐引起了科学工作者的广泛关注和浓厚的研究兴趣。由于尺寸较小,比表面积较大,纳米材料具有一些不同于块体材料的特殊性能,包括电子能级的不连续性,量子尺寸效应,小尺寸效应,表面效应和宏观量子隧道效应等。将纳米材料应用作为电极材料时,它的电化学性质也会发生不连续、显著的变化,例如,临界电流密度在较小的电极和电极阵列上将显著增大等。作为一门研究电能和化学能之间的相互转化及其转化过程中有关规律的学科,电化学应用技术至今已经成为国民经济的重要组成部分。它被广泛地应用于社会生产的诸多方面,包括电化学新能源体系的开发和利用,电化学传感器的开发,金属的表面精饰,电化学腐蚀和防腐以及无机、有机化合物的电解合成等。纳米材料在电化学新能源体系包括锂离子电池和超级电容器以及电化学传感器方面的应用已经非常广泛,并且取得了显著的成果。在本论文中我们集中以镍基纳米材料及其复合物为例,探索了这些纳米结构大面积可控生长的方法,并将它们直接应用于电化学器件(包括电化学超级电容器,锂离子电池和电化学无酶传感器),对其性能进行了研究。主要研究内容包括以下几个方面：(1)利用简单的水热反应法,在不锈钢基底上生长得到了Ni2(OH)2CO3纳米片阵列,我们分析了这种纳米结构的生长条件,接下来通过在惰性气氛中煅烧这种Ni2(OH)2CO3,最终可以得到多孔的NiO纳米片网状结构阵列。这种NiO纳米片阵列可以直接应用作为超级电容器的电极,并且具有较高的比电容(电流密度为0.67A/g时,其比容量可达到270F/g)：较好的大电流充放电倍率性能(电流密度扩大到13.35A/g时,比容量仍然保持有236F/g)以及较好的循环寿命(4000次充放电循环容量保持率为93%)。为了近一步改善超级电容器的性能,增大器件的能量密度,我们又通过简单的、不借助模板辅助的两步法,在不锈钢基底上实现了C/CoNi3O4层状纳米复合物网状结构的生长。这种复合物具有纳米片结构上均匀生长纳米线的有趣结构,并且纳米片相互连接,形成网状,经过煅烧后,纳米片和纳米线由于失去水分和CO2,形成了多孔结构,导致材料具有较大的比表面积(128.1m2/g)；同样地这种结构和基底之间也具有紧密的结合力,可以直接应用作为超级电容器的电极。这种材料同样具有优越的电化学性能,相比较上述NiO纳米片阵列结构电极,其比电容,倍率性能以及循环寿命等性能都得到了显著的增强：在三电极测试体系中,当充放电电流密度为0.5mA/cm2时,其比容量高达1299F/g；该电极的倍率性能优越,当放电电流增大至50mA/cm2,该电极的比容量仍高达1018.2F/g,其容量保持率仍可达～78%。与活性炭电极组成两电极体系时,在1mA/cm2的充放电速率下,其电容量为64.7F/g。当电流密度达到100mA/cm2,即电容器可在几秒钟之内完成一次充放电时,其功率密度高达13.0KW/kg,能量密度为19.2Wh/kg。此外,该电容器具有较长的循环寿命,经5000次循环后,其比容量几乎无衰减。这些都充分证明了Ni基材料时一种颇有前景的超级电容器材料。(2)采用上述Ni2(OH)CO3纳米片阵列为基底,经一步水热法可得到Ni2(OH)CO3/SnO2三维复合物纳米阵列,相互交错的Ni2(OH)2CO3纳米片阵列组成网状结构,在每个纳米片上面均匀地生长着SnO2的纳米棒；经过浸泡葡萄糖和加热/还原的过程,我们可以得到终产物Ni/SnOx/C。这种Ni/SnOx/C复合物保持了前驱体的三维网状结构,碳包覆SnOx纳米棒均匀地生长在金属Ni纳米阵列网状结构上。此外,这种生长在不锈钢基底上的Ni/SnOxC复合物材料可直接用作锂离子微型电池的负极材料,它展示了比较大的面积比容量,优越的倍率性能以及稳定的循环性能,电流密度为-0.1mA/cm2时,面积比容量可以达到～1.75mAh/cm2,即使当电流密度增大27倍达至(?)2.8mA/cm2时,这种电极的比容量仍然保持有～0.11mAh/cm2,此外,三维Ni/SnOx/C复合物电极经过100次循环,电容量的保持率为72%。相比较SnOX纳米棒阵列电极材料,这种三维结构复合物电极的各种电化学性能都更加优越。接下来,通过水热的方法,我们可以将超薄的Ni(OH)2纳米片均匀地包裹在过渡金属氧化物的表面,其中包括MnO2纳米线和CoO纳米线阵列,然后在弱还原性的气氛中对这种复合物进行加热,即可以得到终产物MnO@Ni纳米线和三维CoO@Ni纳米阵列结构。应用于锂离子电池负极材料时,这两种材料都展示出优越的电化学性能,相比较纯的MnO纳米线和CoO纳米线阵列电极,复合物电极的比容量、倍率性能以及循环性能都得到了改善,对于MnO@Ni纳米线电极,在充放电电流为0.3A/g时,循环250次,其比容量依然可以保持有644.8mAh/g;其倍率性能也相当优越,当充放电电流密度从0.3A/g上升到6.4A/g,其容量仍然保持有314mAh/g,这些都由于单纯的MnO纳米线电极。对于CoO@Ni复合物阵列电极电流密度为0.3A/g时,经过100次循环,其可逆容量保持率高达95.1%,远远高于CoO电极的16%。电流密度从0.15A/g上升到4.8A/g时,其比容量保持率为42%。这些数据充分证明了金属Ni包覆可以极大地改善整个电极的性能：此外,我们提供了一种简单普适的制备三维金属网状结构包覆活性材料的方法,对于电极材料的发展起到了积极推动作用。(3)同样地,以上述Ni2(OH)2CO3纳米片阵列为前驱体,在还原气氛中对Ni2(OH)2CO3进行加热处理,可以得到CNTs/Ni纳米复合物阵列。这种CNTs/Ni纳米复合物仍然可以保持相互交错的纳米片阵列结构,和前驱体Ni2(OH)2CO3纳米阵列相似,都具有网状薄膜的形貌在纳米片上均匀地生长着卷曲的相互缠绕的多壁CNTs。这种CNTs/Ni复合物可以直接应用作为无酶葡萄糖传感器的电极,在探测葡萄糖方面表现出优越的性能,它的探测极限较低,线性范围宽,灵敏度高。在信噪比为3时,探测极限可达到1μm,它的探测线性范围可达0.5-10mM,此外,它具有很高的灵敏度,可以达至到～1381μAmM-1cm-2。此外这种CNTs/Ni纳米阵列电极还具有一些其他的优良性能,包括良好的可重复型,稳定性以及抗干扰性等。我们首次应用简单的CVD方法制备出了这种CNTs/Ni复合物纳米阵列并将它直接应用作为无酶葡萄糖传感器的电极。成本较低,便于制备及良好的电化学催化能力等优点使这种CNTs/Ni纳米阵列成为一种颇有应用前景的葡萄糖传感器电极材料。更多还原

【Abstract】 As one subject studying the conversion principle and process between electrical and chemical energy, electrochemical application technology has been regarded as an important part of national economy. It has been widely used in many aspects of social production, including the development and utilization of new energy systems, the development of electrochemical sensors, the metal finishing, the electrochemical corrosion and protection, the electrolytic synthesis of organic and inorganic compounds.Along with the emergence of nanomaterials and the development of electron microscope, nanomaterials possessing distinct properties with bulk materials attract wide attention and great interest of researchers worldwide. Due to the characteristics of small dimensions and large surface areas, nanomaterials can demonstrate unique properties, including the discontinuity of electronic energy level, quantum size effect, small size effect, surface effect and macroscopic quantum tunneling effect, etc. When applied as electrode materials, nanomaterial will reveal some discontinuous and significant changes in its electrochemical properties as well. For example, the critical current density will increased significantly in the electrode with small size electrode materials. Particularly, nanomaterials have been widely used in the field of Li ion battery, supercapacitor and electrochemical sensor, and some notable achievements have been obtained already. In this thesis, we choose nickel based materials and corresponding composites as object, study the controllable synthesis and electrochemical properties of these materials systematically. The materials have been mainly applied in the devices of supercapacitor, Li ion battery and electrochemical sensors. And the main research content includes the following aspects:(1) Trough a simple hydrothermal process, Ni2(OH)2CO3nanowall arrays can grow on the stainless steel substrate. We analyze and summarize the grow conditions for this kind of nanostructure. By annealing in Ar, Ni2(OH)2CO3can evolve into NiO nanowall network arrays finally. The NiO nanowall arrays on Fe-Co-Ni can be applied as electrode for supercapacitor directly, saving the tedious electrode preparation process. This NiO nanowall arrays demonstrate high specific capacity, superior rate performance and long cycle life in three-electrode system.In order to boost the performances of supercapacitors and get high energy density, we realize the growth of C/CoNi3O4hierarchical network arrays on stainless substrate by a simple and template-free two-step method. The C/CoNi3O4nanocomposite possess intriguing structure with nanowires growing uniformly on the nanowalls, meanwhile, the nanowalls connect with each other to form a network. After glucose coating and annealing in Ar process, large quantity of mesopores appeared in the nanowalls and nanowires due to the loss of CO2and H2O during the annealing process, leading to a large surface area of128.1m2/g. This C/CONi3O4nanowall arrays grow intimately on the conductive substrate as well and can be applied directly as electrode for supercapacitors. In both two-electrode and three-electrode system, this C/CoNi3O4nanocomposite demonstrate excellent electrochemical properties, considering its enhanced specific capacity, superior rate performance and long cycle performance. These results provide strong evidence for that nickel based materials are one kind of promising electrode materials for the practical application of supercapacitors.(2) Adopting the Ni2(OH)2CO3nanowall arrays as substrate, through a one-step hydrothermal process we can obtain the3-dimensional (3D) Ni2(OH)2CO3/SnO2nanocomposite arrays. The Ni2(OH)2CO3nanowalls connect with each other to form a network structure and SnO2nanorods .grow uniformly on each nanowall, resulting the hierarchical network architecture. Through the process of glucose coating and annealing-reduction, the final product of Ni/SnOx/C can be obtained. The final product of Ni/SnO,/C remain the3D network structure, carbon coated SnOx nanorods grow uniformly on the metallic Ni nanowalls to form a network architecture. When applied as anode materials for Li ion microbatteries, this Ni/SnOx/C nanocomposite reveal high areal capacity, superior rate performance and enhanced cyclic performance, demonstrating much better performances than the pure SnOx nanorod electrode.Through the hydrothermal process, we can successfully encapsulate transitional metal oxides (including ultralong MnO2nanowires and CoO nanowire arrays on Ti foil) in the ultra-thin Ni(OH)2lamellas. After conducting heat treatment towards MnO2@Ni(OH)2and CoO@Ni(OH)2in a mild reducing atmosphere, we can get the final products of MnO@Ni nanowires and CoO@Ni nanoarrays. When applied as anode materials, both of the composites demonstrate superior electrochemical performance, with higher capacitance, superior rate performance and enhanced cycle performance. Compared with the pure MnO and CoO electrode, the performances are largely improved with the metallic Ni coating layer, bring forth strong evidence for the fact that Ni coating can enhance the electrode performance. Besides, we also put forward one simple and general method for the preparation of3D metallic network shell with metal oxide core structrue, which play a positive role in promoting the development of LIB electrode materials.(3) Adopting Ni2(OH)2CO3nanowall arrays as precursor, after conducting heat treatment towards precursor in light-reducing atmosphere, we can get the final product of CNTs/Ni nanocomposite arrays. Just like the Ni2(OH)2CO3nanowall arrays, the CNTs/Ni nanocomposite retain the interconnected nanowall arrays structure, moreover, curved multiwall CNTs distributed on the surface of nanowalls uniformly. Growing on the conductive substrate, this CNTs/Ni nanocomposite can be used directly as electrode for nonenzymatic glucose sensors. And the CNT/Ni electrode reveal superior electrochemical performances, with low detection limitation, wide detection line range and high sensitivity. Moreover, other excellent properties of the CNTs/Ni nanowall arrays electrode, such as good reproducibility, long-term stability and anti-interferences, are demonstrated as well. The good analytical capability, low cost and facile preparation method make CNT/Ni nanowall arrays promising for amperometric non-enzymatic glucose detection.更多还原