Preparation And Characterization Of Semiconductor Photoelectrode And Its Photoelectrochemical Properties

The purpose of this dissertation is to study the electrochemical preparation, characterization of photoelectrode (anode and cathode) of the photoelectrochemical solar cell (PEC), and their photoelectrochemical properties. The influencing factors, formed mechanism, and related photoelectric properties of TiO₂ nanotubes array photoanode were systematically investigated based on multifarious measured techniques and photoelectrochemical research methods. And the properties for hydrogen evolution of metal (or alloy) /p-Si, AC/Ni-Co and Ni-W-P/TiO₂ photocathodes were investigated. The research contents and the gained chief achievements are as follows:TiO₂ nanotube arrays were successfully fabricated by anodic oxidation method on a pure titanium sheet. Optimal reaction conditions for preparation are as follows, 20 V for oxidation voltage, 1(wt) % for concentration of HF electrolytes, 30 min for reaction time and room temperature. In this condition, the aperture size of the nanotube arrays is about 90 nm; the thickness of tube wall is about 10 nm; and the length of nanotube is about 500 nm. The structure of these samples was characterized by XRD. The results show that the structure is a mixture phase of anatase and rutile annealed at 600℃, the rate of rutile phase is about 47.7%, and the average crystalline size is about 19.0 nm.The photoelectric measurement results show that the TiO₂ nanotube arrays electrode exhibits the typical property of the n-type semiconductor. The interfacial charge transfer resistance of the electrode annealed at 600℃is minimal, the photocurrent and the signal of open-circuit potential are maximal. Its photoelectric performances are similar with the ordinary TiO₂ porous films electrode. But the photoelectric conversion efficiency of the nanotubes electrode is higher than the porous films electrode. It was mainly due to the high porosity and the large real surface area of the TiO₂ nanotube arrays.The different transition metal ions (Fe, Mn, Ni, Cu, and Zn) doped TiO₂ nanotube photoelectrodes were prepared by sel-gol method. The results show that their photoelectric performances were different, and the order of their photocurrent ranked from the highest to the lowest is Zn > Cu > Ni > Fe > Mn. This paper argued that the difference of physical chemical quality of transition metal ions was the main factor of the results. When the TiO₂ nanotube electrode doped with Zn ions has a moderate value of Ea/r and a smaller magnetic moment, it shows much higher photoelectric performance.The nanocrystalline Pd modified p-Si and the Ni-Co-P alloy modified p-Si photocathode were prepared by electrochemical technology. The results show that the overpotential for HER of these photocathodes was reduced under illumination, and its catalytic properties were increased evidently. The investigation on relationship between surface fraction and HER current density of both electrodes indicates that the surface fraction of nanoparticles on p-Si electrode has an optimal value, and these optimal fractions of both electrodes are about 35 %.The Ni-Co/AC composite electrode was prepared by composite-electrodeposition. The results show that the Ni-Co/AC composite electrode is catalytically more active than the Ni and Ni-Co alloy electrode, which is mainly due to the increase in the real surface area of the electrode. The Ni-W-P/ TiO₂ nanotube composite electrode was prepared by electrodeposition at constant potential. The experimental results show that the overpotential for HER of the composite electrode is 130 mV lower than that of Ni-W-P alloy electrode, the former shows better properties for hydrogen evolution.