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Preparation of iron oxides , modification and application in the field of new energy

Author: ChengFeng
Tutor: HuangKeLong
School: Central South University
Course: Applied Chemistry
Keywords: Iron oxides Photo-electrochemical water splitting Nanorod arrays Surfactant carbonization Lithium-ion batteries
CLC: TQ138.11
Type: Master's thesis
Year: 2011
Downloads: 167
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Abstract


Iron oxides are abundant on earth and environmental friendly. The research about them in the field of new energy sources has attracted many researchers’attention. In this dissertation, the application of iron oxides in photo-electrochemical water splitting and lithium ion batteries were investigated.a-Fe2O3 nanorod arrays were prpepared via aqueous chemical growth method and thermal treatment at 500℃. As-prepared samples were characterized by XRD, SEM and UV-visible optical absorbance spectra. Open circuit potential, linear sweep voltammetry and Mott-Schottky measurement were conducted to investigate the influence of doping on the photoelectrochemical performance of a-Fe2O3 thin films in configuration of photoelectrochemical cells. Results showed that the three samples had the same direct band gap (2.24 eV) and indirect band gap (1.85 eV). They also had the same photocurrent onset potential (-0.22 V vs. SCE). Their photocurrents were 3.1910-5 A·cm-2,1.98×10-5 A·cm-2 and 1.51×10-5A·cm-2 at an applied potential of 0.2 V vs. SCE and their charge carrier concentrations were 3.648×1018 m-3,2.462×1018 m-3 and 1.647×1018 m-3 for Co-doped, Ni-doped and undoped a-Fe2O3, respectively. Doping did not change the phase, the morphology, the optical absorbance characteristics, the surface electrocatalysis and the energy band position of a-Fe2O3 thin films. The main effect of doping was to increase the charge carrier concentration and then achieved a good conductivity, which improved the photoelectrochemical performance of a-Fe2O3 thin films.Oleic acid-capped a-Fe2O3 nanoparticles with different morphologies were first prepared as precursors by a simple hydrothermal method. Then various iron oxides were obtained by annealing the precursor under Ar, namely surfactant carbonization. The carbonization condition of oleic acid groups was determined by FTIR and TGA analysis. The phase evolution of iron oxides with the annealing temperature increasing was evidenced by XRD. Cyclic voltammetry (CV) and galvanostatic discharge/charge measurement were employed to evaluate the electrochemical performance of as-prepared Fe3O4/C nanocomposites. Results showed that the nanoparticles with small size and pseudocubic shape were synthesized when the dosage of sodium oleate was stoichiometric ratio to that of Fe+ and oleic acid exceeded over the stoichiometric value. Rod-shaped and spindle-shapedα-Fe2O3 particles were prepared when a smaller amount of sodium oleate was used and the alkalinity increased. A series of iron oxides including a-Fe2O3/C, a-Fe203/Fe304/C and Fe3O4/C were obtained via annealing oleic acid-capped a-Fe2O3 under Ar for 2 h at 300℃,400℃and 500℃, respectively. As anode materials for lithium-ion batteries, the Fe3O4/C composite exhibited excellent cycling performance (691.7 mAh·g-1 after 80 cycles at 0.2 C) and rate capability (520 mAh·g-1 after 20 cycles at 2 C).

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CLC: > Industrial Technology > Chemical Industry > Inorganic compounds, the chemical industry of the metal elements > Inorganic compounds of the first the Ⅷ family metal elements > Inorganic compounds of iron elements > Inorganic compounds of iron
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