| In recent years, the problem of electromagnetic interference (EMI) has drawn considerable attention due to the explosive growth in the application of electronic devices such as mobile phone, local area network, personal computers and radar systems. The conventional absorbing materials such as ferrites and metallic materials have been studied widely. Although presenting good absorption properties these materials are too heavy. An alternative approach is coating support media of low density with polymer or metallic materials. The recent development in absorber technology is to produce absorbers that are thin, flexible and strong. Carbon nanotubes, grapheme and SiC are exactly suitable as a supporting media for this purpose because of their low density, good thermal and chemical stabilization.Graphene, one-atom thick planar sheet of hexagonally arrayed sp2 carbon atoms, exhibits excellent physical and chemical properties, which makes it promising for potential applications in many technological fields, such as nanoelectronics, sensors, nanocomposites, batteries, supercapacitors and hydrogen storage. Especially, graphene has potential application as a heterogeneous catalyst support in direct methanol fuel cells. In comparison with CNTs, graphene not only possesses similar stable physical properties but also larger surface areas. Combination of graphene and functional nanoparticles may lead to materials with interesting properties for a variety of applications, and they are specifically expected to have enhanced electrocatalytic activity. The contents of this thesis are as follows:1. Ni1-xCox Palloy nanoparticles (x=0.25,0.50,0.75), with diameters in the range of 8-18nm were uniformly attached on the surface of multi-walled carbon nanotubes (MWNTs) by electroless plating, which were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), X-ray diffraction analysis (XRD), vibrating sample magnetometer (VSM) and vector network analyzer, respectively. Magnetization measurement indicates that both coercivities and saturation magnetizations decreased linearly with increasing Ni concentration in Ni-Co-P deposits. The complex permittivities of MWNTs-olefin matrix composites also decreased linearly with increasing Ni concentration while the complex permeabilities increased slightly, which were measured in the range of 2-18GHz. The microwave absorbing properties enhanced with increasing Co concentration and a maximum reflection loss of-26.84dB was obtained at the frequency of 7.75GHz when the matching thickness was 2.5mm and x=0.75.2. Silicon carbide particles reinforced nickel-cobalt-phosphorus matrix composite coatings were prepared by two-step electroless plating process (pre-treatment of sensitizing and subsequent plating) for the application to lightweight microwave absorbers, which were characterized by scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), vibrating sample magnetometer (VSM) and vector network analyzer, respectively. The results show that Ni-Co-P deposits are uniform and mixture crystalline of a-Co and Ni3P and exhibit low specific saturation magnetization and low coercivity. Due to the conductive and ferromagnetic behavior of the Ni-Co thin films, high dielectric constant and magnetic loss can be obtained in the microwave frequencies. The maximum microwave loss of the composite powder less than-32 dB was found at the frequency of 6.30 GHz with a thickness of 2.5mm when the initial atomic ratio of Ni-Co in the plating bath is 1.5.3. A magnetic hybrid of chemically converted graphene (CCG) and nickel nanoparticles was synthesized by chemical reduction using hydrazine as a reducing agent. The Ni/CCG hybrid was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM). The results show that Ni nanoparticles were uniformly dispersed on the surface of CCG sheets and its main particle sizes were distributed in the range of 35-40nm. Magnetic measurement indicates that Ni/CCG exhibits typical ferromagnetic behavior, which makes it promising applications in electronic-magnetic nanodevices, absorbing mateials and data storage systems.4. We have investigated a simple approach for the deposition of platinum (Pt) nanoparticles onto surfaces of graphite oxide (GO) nanosheets with particle size in the range of 1-5 nm by ethylene glycol reduction. During Pt deposition, a majority of oxygenated functional groups on GO was removed, which resulted in a Pt/chemically converted graphene (Pt/CCG) hybrid. The electrochemically active surface areas of Pt/CCG and a comparative sample of Pt/multi-walled carbon nanotubes (Pt/MWCNT) are 36.27 m2/g and 33.43 m2/g, respectively. The Pt/CCG hybrid shows better tolerance to CO for electro-oxidation of methanol compared to the Pt/MWCNT catalyst. Our study demonstrates that CCG can be an alternative two-dimensional support for Pt in direct methanol fuel cells.
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