| Due to incompletely filled d-shells of transition metals, metal oxides/hydroxides nanostructure materials are given a variety of unique properties, which make them potentially of great use in biosensors, gas sensors, electrochromic devices, solar cells, supercapacitors, photodetectors, light-emitting diodes, and so on. Among these application fields, photodetectors and supercapacitors are attracting great interest from researchers. Currently, increasing researches are focusing on the development of novel metal oxide nanostructured materials with new morphologies and higher performance. The research focuses of this thesis are the rearch and development of three types of new metal oxide/hydroxide based supercapacitor electrode materials. In addition, some research of novel metal oxide based photodetector materials were also presented in this thesis. In this thesis, firstly, we fabricated a two-dimensional ordered porous SnO2monolayer nanofilm with the monolayer polymer colloid crystal nanofilm prepared from oil-water interfacial self-assembly as the template, and employed it to construct the photoresponsive nanodevice. In the second part, we prepared reduced graphene oxide (RGO)-MnO2hollow sphere (HS) hybrid electrode materials for supercapacitor electrodes, using a solution-based ultrasonic co-assembly process followed by a thermal treatment at vacuum. In the third part, we employed a novel one-step hydrothermal method to grow Ni(OH)2-MnO2hybrid films with ultrathin nanosheets and porous nanostructures on three-dimensional macroporous nickel foam for pseudocapacitor electrodes. In the fourth part, we used one-step hydrothermal method to grow nickel-cobalt layered double hydroxide hybrid films on three-dimensional macroporous nickel foam, and then employed it as positive electrode materials and utilized porous RGO as negative electrode materials to construct asymmetric supercapacitor. All the research content and main results are shown as follows:(1) In the second chapter, monodispersed poly(styrene-co-acrylic acid)(PSA) spheres were firstly synthesized by emulsifier-free emulsion polymerization. Then, polymer monolayer colloid crystal nanofilm was fabricated using PSA micropheres by the oil-water interfacial self-assembly method. Moreover, we discussed the effect of ethanol inducer amount on the quality of formed colloid crystal nanofilms. After that, monolayer ordered porous metal oxide nanofilms were prepared by filling the voids of polymer nanofilm with metal oxide sol-gel precursors, then calcining the resulting composite at high temperature to remove polymer template. In this process, we also studied the influence of precursor solution concentration on the morphology of formed monolayer porous nanofilm. In addition, this method was extended to fabricate SnO2, TiO2, ZnO, and CeO2monolayer ordered porous semiconducting nanofilms. Then, SnO2monolayer ordered porous nanofilm was took as an example and fabricated into a photoresponse nanodevice. The response of as-fabricated device to light wavelength, light on and off, and light power intensity, were investigated. Experiment results showed that a photocurrent of232.3μA was recorded at a low applied voltage of1.0V, which exceeded those of some other oxide semiconductor photodetector materials. Moreover, the fitting of the dependence of photocurrent to the light intensity gave a power function law, suggesting that this device possesses ultrahigh sensitivity and certain quantitative detection ability. Therefore, it may have applications in photodetectors, photoelectronic switches, and solar cells.(2) In the third chapter, graphene oxide was prepared from graphite powder using Hummers method. MnO2HS were synthesized as previously reported references. Based on hydrogen bonding and electrostatic interactions, graphene oxide-MnO2HS hybrid electrode materials were fabricated from graphene oxide, MnO2HS, and acetylene black (as electrical conductor), using a solution-based ultrasonic co-assembly process. They were then reduced to RGO-MnO2HS hybrid electrode materials by a thermal treatment at vacuum. After that, as-obtained hybrid materials were fabricated into hybrid electrodes, the cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) measurements were employed to evaluate their capacitance properties. In addition, the effects of electrode fabrication methods and MnO2nanostructures on the capacitance of as-obtained electrodes were also studied. The results revealed that as-fabricated RGO-MnO2HS hybrid electrode exhibited profoundly improved specific capacitance (578F g-1) and energy density (69.8Wh Kg-1). These values were far larger than those reported for graphene-MnO2based hybrid supercapacitor electrode materials.(3) In the fourth chapter, Ni(OH)2-MnO2hybrid films with ultrathin nanosheets and porous nanostructures, supported on three-dimensional macroporous nickel foam, were fabricated by a hydrothermal co-deposition process without using any adscititious alkali source. This reaction also employed nickel nitrate and manganese chloride as precursors, and a cationic gemini surfactant G12as the nanostructure growth assisting agent. Then, the nickel foam supporting hybrid nanosheets were acted directly as the working electrodes to evaluate their pseudocapacitive properties. In addition, we also compared the morphology and capacitance property of as-obtained hybrid films prepared with different Ni:Mn feeding mole ratios, or with different G12feeding amounts, or using urea and hexamine as adscititious alkali source. The results showed that as-obtained hybrid film exhibited ultrahigh specific capacitance (2628.0F g-1) and energy density (81.2Wh Kg-1). Both values were significantly higher than those of other similar pseudocapacitive materials.(4) In the fifth chapter, nickel-cobalt layered double hydroxide (Ni-Co LDH) hybrid films with ultrathin nanosheets and porous nanostructures supported on three-dimensional macroporous nickel foam, were fabricated by a hydrothermal co-deposition process with nickel nitrate and cobalt chloride as precursors, without using any adscititious alkali source and oxidant. Then, the Ni-Co LDH hybrid nanosheets supported on nickel foam were acted directly as the working electrodes to evaluate their pseudocapacitance. In addition, we also made the comparison in the morphology, crystal structure and capacitance property of as-obtained hybrid films prepared with different Ni:Co feeding mole ratios, or using urea and hexamine as adscititious alkali source. Experimental results showed that the as-obtained Ni-Co LDH hybrid films supported on nickel foam exhibited ultrahigh specific capacitance (2682.0F g-1) and energy density (77.3Wh Kg-1) in0-0.5V. Both values were obviously higher than those of all the previously reported electrodes based on nickel-cobalt oxides/hydroxides. In addition, three-dimensional porous freeze-dried RGO was prepared by a freeze-drying of GO (preparation using Hummers method) followed by a thermal reduction at vacuum. Then, it was fabricated into RGO electrode, and the electrochemical properties were investigated. It was found that RGO electrode displayed excellent electric double-layer capacitance at-1to0V. The as-obtained specific capacitance was comparable to those of the other graphene based supercapacitor materials. Lastly, we used the as-obtained Ni-Co LDH as the positive electrode materials and the RGO as the negative electrode materials to fabricate a asymmetric supercapacitor, and measured its electrochemical properties. The results showed that the electrochemical window of as-prepared quasi-asymmetric supercapacitor can extend to0-1.6V, the energy density (187.7Wh Kg-1) has significantly exceeded those of all the previously reported nickel or cobalt oxide/hydroxide based asymmetric supercapacitors. |
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