Study Of The Preparation And Photoelectrochemical Performance Of TiO₂-based Nanocomposite Films

One of the main challenges facing humanity is the shortage of the fossil fuels and environmental pollution. Hydrogen is considered to be the most attractive renewable energy due to its advantages of abundant and high energy density. Photoelectrochemical water splitting, as a promising method for converting sunlight into hydrogen energy, has attracted considerable attention. Titanium dioxide has been intensively investigated owing to its promising properties, such as suitable band gap position and superior chemical stability. However, the titanium dioxide can only absorb ultraviolet light because of a relatively large band-gap and the recombination of electron-hole pairs is very fast. Therefore, the solar-to-hydrogen efficiency based on the titanium dioxide is extremely low. Thus, the key to utilize the solar energy efficiently is to develop a composite film with high absorption in the visible light, and improve the separation efficiency of photogenerated carriers.To solve these problems above, some methods have been adopted to improve the light absorption and photoelectrochemical performance in this thesis, such as doping, p-n heterojunction, composite semiconductor and fabricating a core-shell structure. The main research content is as follows:First of all, the electrochemical reduced graphene oxide/Ti3+self-doping modification of titanium dioxide nanotube arrays are prepared by one-step elertrochemical reduction method. The best prepared condition is determined by comparing the photoelectrochemical performance of the samples. The results suggest that electrochemical reduced graphene oxide and Ti3+self-doping are existed at the same time after elertrochemical reduction process. The light absorption and the stability can be improved due to the synergistic effect of electrochemical reduced graphene oxide and Ti3+self-doping.Secondly, the bismuth oxyiodide-titanium dioxide nanotube arrays film with a p-n junction is synthesized via electrochemical deposition method. The results suggest bismuth oxyiodide is benefit for widen the absorption, and enhances the separation and migration of photogenerated charge carriers. The photocurrent density of bismuth oxyiodide/titanium dioxide composite reached to2.97mA/cm2, and the IPCE value at500nm can reach to30%.Thirdly, the photoanode of N/Si co-doped single-crystal titanium dioxide nanorods is synthesized on the Fluorinedoped tin oxide substrate with a hydrothermal method. The highest photocurrent density is obtained by changing the parameters of hydro thermal reation. Further, an integrated device combining a high efficiency CH3NH3PbI3-based pervoskite solar cell and the N/Si codoped titanium dioxide nanorods is designed to realize overall solar water splitting. The solar-to-hydrogen efficiency of this device can reache to1.1%, which is5.7times h^her than that of the titanium dioxide.Finally, the bismuth vanadate/titanium dioxide nanocomposite film with a core-shell structure is prepared by spray pyro lysis method. The resulting titanium dioxide nanorods are coated by bismuth vanadate nanoparticles as evidenced by morphology measurement. A core-shell structure is formed with the titanium dioxide core and bismuth vanadate shell. Especially, the type-II band alignment between the bismuth vanadate shell and the rutile titanium dioxide cores provides a large driving force for electrons transfer from the bismuth vanadate shell to the titanium dioxide cores.