The Preparation And Electrochemical Properties Of Novel Nanomaterials For Energy Conversion And Storage Application

Owing to the non-renewability, low conversion efficiency and pollution caused in the use of traditional fossil oil and gas, scientists have made great effort on searching green power with high energy efficiency, which results in the developments of energy conversion and storage technology such as fuel cells, supercapacitors and Li ion batteries. Energy conversion and energy storage are two aspects to effectively use energy, significantly, a novel concept called Self-Charging Power Cell has been proposed recently, which shows a promising possibility to fulfill the integration of energy conversion and energy storage. However, no matter energy conversion or storage, one of the most crucial technologies is the use of materials. In the light of the concerns above, in this thesis, we have fabricated various nanostructural materials by using simple methods, and investigated their morphologies and electrochemical properties, which is considered to prepare the integrative devices of energy conversion and storage. The main conclusions show as follows:1. Scalable sawtooth-shaped nickel-based submicrowires were fabricated by hydrazine reduction method under magnetic field. The submicrowires were about500-700nm in diameter and10-30pm in length. The slow supply of Ni2+(Co2+) ions as Ni (Co) source in reaction solution was a controlling factor in the formation of sawtooth-shaped structure. The electrochemical results showed that compared with Ni nanoparticles and smooth Ni submicrowires, sawtooth-shaped nickel-based submicrowires exhibited higher activity and stability on methanol oxidation reaction, which could be ascribed to the sawtooth-shaped structure that combined the advantages of both the geometry of submicrowire and the morphology of nanoparticle. In addition, due to the bi-functional effect of Ni and Co, sawtooth-shaped NiCo submicrowires showed better electrochemical properties than sawtooth-shaped Ni submicrowires, which facilitated the electron transport. Therefore, because of its simplicity, low cost and high yield, it was believed that this kind of sawtooth-shaped submicrowire was a promising non-precious anode catalyst for alkaline fuel cell application.2. By using AgNO3as Ag source, Ag nanowires were prepared in ethylene glycol system, and then in ammonium hydroxide-ethanol aqueous solution, they were effectively embedded into the nitrogen-doped graphene nanosheets to get nitrogen-doped graphene/Ag nanowires composites. Ag nanowires embedded in graphene nanosheets created many porous channels in the composites, which hindered the restacking of graphene, resulting in more accessible surface area of nitrogen-doped graphene, larger active sites for oxygen reduction reaction, improved O2and OH" ion transport. Due to the synergetic effect of nitrogen-doped graphene and Ag nanowires, nitrogen-doped graphene/Ag nanowires composites showed better catalytic properties than pristine nitrogen-doped graphene and Ag nanowires, the composites were expected to be an effective cathode catalyst in alkaline fuel cell.3. At first,α-MnO2nanotubes were fabricated in hydrothermal reaction. Without any surface modifications, α-MnO2nanotube/Co3O4nanoparticles hybrid were prepared in the precursor solution of Co(NO3)2and NH4F, and the addition of NH4F and concentration of precursor solution played important roles in the final morphology of product. The hybrid showed a bead-on-string structure with big CO3O4nanoparticle (-120nm) dispersed on a-MnO2nanotube at the high concentration. At low concentration, a-MnO2nanotube was fully covered by a layer of thin CO3O4nanoparticles (～10-20nm), which facilitated the charge transfer, hindered the dissolution of Mn species and allowed ion transport into a-MnO2nanotube backbone; in addition, both of a-MnO2nanotubes and CO3O4nanoparticles contributed to the capacitance, as a result, the hybrid with thin CO3O4nanoparticles exhibited better specific capacitance and rate capacity than pure a-MnO2nanotubes and physical mixture of a-MnO2nanotubes and CO3O4nanoparticles, the remaining capacitance value after2000cycles could retain87.5%of the original capacitance at the first cycle. This well-designed hybrid structure showed promising charge storage performance, which demonstrated an alternative way to construct high-performance supercapacitor without the use of carbon-and conductive polymer-based materials.4. An unique three-dimensional branched single-crystal β-Co(OH)2nanowire array was prepared and supported on Ni foam for the first time. The specific morphology was formed by the splitting crystal growth effect combined with the specific topological structure of β-Co(OH)2. And then the branched β-Co(OH)2nanowire array was used as scaffold to load a layer of MnO2nanosheets, after annealing at450℃, branched Co3O4/MnO2core-shell nanowire array was constructed. At a current density of10mA/cm2, the branched Co3O4/MnO2core-shell nanowire array exhibited0.99F/cm2of area capacitance and still retained69.3%of the initial capacitance (1.43F/cm2at1mA/cm2). Such excellent electrochmical performance was ascribed to the unique configuration and the strong synergistic effect from the porous CO3O4 nanowire core and the ultrathin MnO2shell. This new branched β-Co(OH)2nano wires was considered as an exceptional material in supercapacitor and other electrochemistry devices.5. Branched MOS2nanotubes with bamboo-like structure were prepared by simple thermal decomposite of (NH4)2MoS4precursor by using anodized aluminum oxide template. The structure and morphology of the branched nanotubes were characterized by scanning electron microscopy and high-resolution transmission electron microscopy, and the possible formation mechanism of bamboo-like sections in nanotube was discussed. The final morphology of nanotubes were determined by the coating state of (NH4)2MoS4in the nanochannel of anodized aluminum oxide template, and the length and diameter of nanotubes depended on the thickness and inner diameter of corresponding templates, the wall thickness of M0S2nanotubes resulted from the remaining amount of (NH4)2MoS4. The formed bamboo-like structure was attributed to the Mo-S chemical bond and the wetting state between precursor solution and the nanochannel of template.