Study On The Electrochemical Properties Of Modified Electrodes Based On Carbon Nanofibers

Carbon nanomaterials such as nano-onion, nano-diamond, carbon nanotubes (CNTs), and carbon nanofibers (CNFs) have attracted considerable attention in both the research and industrial fields, due to their novel unique electronic, chemical, thermal and mechanical properties. However, CNFs, due to their high tensile strength, modulus, and relatively low cost, are drawing significant perspectives in a number of potential applications, especially in heterogeneous catalysis. CNFs can appears to be more attractive as catalytic materials than other carbon nanomaterials. One of the advantages of CNFs is used as catalysts and catalyst supports. Hence their commercial applications as catalysts and catalyst supports can be foreseen in the near future.Three different microstructure CNFs, including the platelet CNFs (PCNFs), the fish-bone CNFs (FCNFs), and the tube CNFs (TCNFs), were used as catalysts and catalyst supports. In the dissertation, study on some electrochemical properties of modified electrodes based on CNFs. Pt/CNFs catalysts was prepared through electrodeposited and an impregnation chemical reduction method. Their electrocatalytic activities toward methanol oxidation reaction (MOR), and oxygen reduction reaction (ORR) in direct oxidation methnol fuel cells have been studied. Glassy carbon (GC) electrodes modified by CNFs were fabricated and compared for amperometric detection of H2O2. The thin films of TiO2 supported by CNFs were prepared by sol-gel method and their photoelectrochemical properties were studied. The main results and conclusion can be summarized as following:1. Using the electrodeposition method, platinum nanoparticles have been deposited on CNFs surfaces and the mean particle size is about 50 nm by HRSEM, and the electrocatalytic activities of different modified electrodes were investigated. The comparative tests conclude that Pt/PCNFs have the best electrocatalytic performance among all carbon-supported Pt-based catalysts prepared in this study.2. Making use of an impregnation-chemical reduction method, Pt/PCNFs catalyst has been fabricated and platinum nanoparticles has a small particle size (ca.2-5 nm) and uniform distribution by HRTEM. Additionally, the kinetics of ORR at Pt/PCNFs modified electrode has also been investigated, its has high exchange current density, and the peak current (ip) is linearly related to the square root of the scan rate (υ1/2), and exhibites the ORR be controlled by the diffusion process of oxygen. The results imply that the Pt/PCNFs has good potential applications in proton exchange membrane fuel cells.3. According to electric properties of carbon nanomaterials, different types of operable, inexpensive, reagentless, and simple H2O2 sensors have been developed and studied. The highest electrocatalytic performance was observed for PCNFs/GC among three types of H2O2 sensors. The amperometric response of PCNFs/GC retained over 90% of the initial current of the first day up to 21 days. The linear range is from 1.80×10-4 to 2.62×10-3 mol/L with a correction coefficient larger than 0.999 and with a detection limit of 4.8μmol/L H2O2 (S/N =3). The relative standard deviation for detecting 1.80×10-4 mol/L H2O2 (N=8) is 2.1% with an average response of 0.64μA. The results show that PCNFs and FCNFs are very promising candidates for development of high-performance biosensors.4. Utilizing PCNFs and FCNFs as supports and ITO as electroconductive substrate, modified films TiO2 photoelectrodes were developed by sol-gel method. The nanocomposites have been extensively characterized by SEM, XRD, UV-Vis spectra. Photoelectrochemical activities were evaluated by I–E, OCP-Time, IPCE measurements. The experiments demonstrated that the ITO/PCNFs/TiO2 photoelectrode shows a higher photoelectrochemical response and sensitivity for irradiation than ITO/FCNFs/TiO2 and ITO/TiO2 photoelectrodes. This is likely because of the specific microstructure of the PCNFs, which possesses large numbers of active edge sites and provides many favorable sites for electron transfer as well as a very large working surface area. Additionally, a synergetic effect is observed for the CNFs/TiO2 composite photoelectrodes under visible light irradiation. This synergetic effect could be reasonable to ascribe to photoelectrons injection into the CNFs rather than conduction band of TiO2 semiconductor in the nanocomposite. Electrons transfer to CNFs with the formation of a hole in the valence band of TiO2 semiconductor. This work is partially supported by the National Science Foundation of China (No. 20673028), and National 863 project of China (No. 2006AA05Z121).