Preparation And Properties Of Nanoscale Electrode Materials For Fuel Cell And Electrochemical Capacitor

Fuel cell (FC) and electrochemical capacitor (EC) are two kinds of important energy storage/conversion devices that are being studied widely at present. On account of large energy conversion efficiency and green environmental conservation, PEMFC has attracted much attention all over the world. EC has already become one of the research interests related to new chemical energy sources studies because of its higher power density and longer cycle life than secondary batteries and its higher energy density compared to conventional electrical double-layer capacitors. Generally, the cost and the life of FC and EC are restricted by the material and the structure of the electrode.In this thesis, we have reviewed the newest development in the research of electrode materials of both FC and EC devices, prepared relevant electrode materials and explored their applications in these two kinds of devices in detail. The main content is as follows:1. Multi-walled carbon nanotubes (MWCNTs) were functionalized viaÏ€-Ï€interaction with benzyl mercaptan. The subsequent bonding of thiol groups with Pt offered strong adhesion of Pt nanoparticles on MWCNT surface. Thermal treatment was introduced as the essential step of catalyst preparation. The structure and morphology of the resulting Pt/MWCNT composite were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), the results show that Pt nanoparticles were highly dispersed and effectively adhered on MWCNTs. The excellent electrocatalytic activity of the Pt/MWCNT composite for the oxidation of methanol was demonstrated by cyclic voltammetry.2. A simple method is devised to deposit highly monodispersed Ag nanoparticles (about 5 nm) on MWCNTs, which started from an initial modification of Ag nanoparticles with benzyl mercaptan molecules. By simply tuning the relative ratio of Ag catalyst to MWCNTs in solution, Ag/MWCNT composite with different Ag content can be achieved. The as-prepared Ag/MWCNT composite materials showed high electrocatalytic activity towards hydrazine oxidation, which was ascribed to the high dispersion of Ag nanoparticles on MWCNT surface. 3. We report here for the first time on the synthesis of mesoporous MnO₂ nanowire array on conductive Ti/Si substrate The morphology of the material is significantly controlled by the conjunct template of anodic aluminum oxide (AAO) and the hexagonal phase of a lyotropic liquid crystalline Low-angle XRD, field emission scanning electron microscope (FESEM) and TEM studies show that the nanowire has a coarse structure, which provides a high specific surface area. Galvanostatic charge/discharge measurements reveal that this porous, three-dimensional electrode material has excellent electrochemical capacitance between potential range of -0.1-0.9 V, and a maximum specific capacitance as high as 493 F g^-1 could be achieved in Na₂SO₄ (0.5 mol L^-1) solution at a charge/discharge current density of 4 A g^-1.4.Ni(OH)₂ thin film with porous and three-dimensional (3D) nanostructures was simply fabricated on nickel foam substrate by direct current electrodeposition from aqueous solution of Ni(NO₃)₂. The morphology and composition of the electrodeposited layer coated on nickle network were characterized by FESEM and XRD Cyclic voltammetric, galvanostatic charge/discharge and electrochemical impedance spectroscopic measurements reveal that the as-prepared electrode material has ultrahigh capacitance between potential range of -0.05-0.45 V, and a maximum specific capacitance as high as 3152 F g^-1 could be achieved in 3% KOH solution at a charge/discharge current density of 4 A g^-1. The capacitive performances of Ni(OH)₂-Ni electrode are approximately dependent on the deposition temperature and the anneal temperature.