Synthesis Of One-Dimensional Nanomaterials Based On AAO Template And Their Properties For Supercapacitor

With the development of nano-science and technology, one-dimensional (1-D) nano-materials have attracted widely interesting due to their unique property and significant potential applications. So, the synthesis of one-dimensional nanostructural materials is becoming a main field of nano-science. Anodic aluminium oxide (AAO) membrane, which is usually fabricated by anodic oxide of Al, has uniform parallel pores and high pore density. It is used as template to fabricate a series of nano-materials such as nanowire, nano-tube and nano-club. In this thesis, several nanowires were prepared with relatively simple and effective method. Their morphology and crystal structures were systemically characterized. In addition, the Ag nanowire andα-Ni(OH)2 nanowires were also assembled into the electrode of supercapacitors for study of electrochemical properties.This thesis consists of four sections as follows:(1) The preparation and characterization of porous anodic aluminaIn this section, the process of fabricating AAO template was described in detail. AAO templates with uniform pore diameter were prepared in electrolytes of oxalic acid by two-step anodic oxidation. The anodic oxide film was characterized by atomic force microscope (AFM), scanning electron microscopy (SEM), transmission electron microscope (TEM), and the X-ray diffraction (XRD), respectively. The results showed that AAO template prepared in oxalic acid has high ordered pore arrays, which consists of the separated nanopores perpendicular to the film surface, parallel to each other and with uniform pore diameter. The diameters and density of pores are about 60 nm and 1.1×1010 pores/cm2 respectively. Because of the features mentioned above, the AAO template obtained in 0.3 M oxalic acid by controlling anodic voltage can be used as a desirable template to fabricate nanowire arrays or freestanding nanowires.(2) Synthesis and characterization of Ag particle-bunch nanowiresOrdered Ag particle-bunch nanowires were fabricated by using chemical reduction approach, in which Ag ions and glycol react to form silver nanonuclei inside the nanochannels of the anodized aluminum oxide (AAO) templates, and then the silver nanonuclei grow into nanowies of linearly stacked silver particles by confining growth under controlling temperature and reaction time. The Ag particle-bunch nanowires were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and selected area election diffraction (SAED).The TEM images showed that the diameter of the particle-bunch nanowires is about 60 nm, and up to 5μm in length, which corresponds to the pore sizes of the used templates. The data of X-ray diffraction indicated that the nanowire have face-centered-cubic structure. The mechanisms of formation of these nanostructres were discussed preliminarily.(3) Synthesis of Ag nanowire and their supercapacitor propertiesSilver nanowires were synthesized in high yield by using anodic aluminum oxide (AAO) film as template and serving ethylene glycol as reductant. Structural and morphological characterizations were performed using Field emission scanning electron microscopy (FESEM),transmission electron microscopy (TEM), X-ray diffraction (XRD) and selected area electron diffraction (SAED). The electrochemical properties of silver nanowires as electrode materials of supercapacitors were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge technique in 6 mol·L^-1 KOH aqueous electrolyte. The silver nanowire electrodes showed an excellent capacitive ability. The maximum specific capacitance of 983 F g^-1 was obtained at a charge-discharge current density of 5 mA cm–2.(4) Preparation and supercapacitor properties ofα-Ni(OH)2 nanowireAlpha-nickel hydroxide nanowire with diameter of 60 nm was successfully synthesized by coordination precipitation–decomposition technique. Structural and morphological characterizations were performed using power X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The capacitive properties were evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge technique in 6 mol·L^-1 KOH aqueous electrolyte. A maximum specific capacitance of 833 F g^-1 was obtained at constant current of 5 mA,which indicated that theα-nickel hydroxide nanowire is a promising electrode material for supercapacitors.