Thin films composed of Zr-doped In2O3 grains rich in fracture surfaces and cracks for photoelectrochemical water oxidation.

Zr-doped In2O3 thin films are prepared on FTO substrates by a two-step method: firstly, Zr-doped In(OH)3 thin films are hydrothermally deposited, and then converted to Zr-doped In2O3 films by heat treatment. It is found that during the phase transition from Zr-doped In(OH)3 to Zr-doped In2O3, the cuboid-like crystal grains will fragment, resulting in a large number of new surfaces and cracks. Zr doping can introduce shallow impurity levels in the band gap of In2O3, which will enhance the absorption of incident light. The substitution of trivalent In3+ ions by tetravalent Zr4+ ions provides additional donors for In2O3, which reduces the charge transfer resistance of the photoelectrochemical water oxidation and thus improves the charge transfer kinetics. These factors synergistically improve the photoelectrochemical water oxidation performance of Zr-doped In2O3. For example, at a potential of 1.5 V versus reversible hydrogen electrode, the photocurrent density of the Zr-doped In2O3 electrode during photoelectrochemical water splitting can be as high as about 3.5 times that of the undoped In2O3. Furthermore, Zr doping will also cause changes in the nucleation of some In(OH)3 grains, resulting in the formation of a small number of rod-bundle-shaped grains.

One-dimensional ZnO micro/nanostructures: deep insight into the growth mechanism and fine control of the microscopic morphology.

One-dimensional zinc oxide arrays with various finely controlled microscopic morphologies are grown on fluorine-doped tin oxide substrates by a hydrothermal method. The relationship between the microscopic morphologies and the reaction conditions are studied deeply. It is found that although all the studied reaction parameters, like reaction time, pH value, concentration of the reactants and so on, can affect the microstructures of the resultant products, what they affect, in essence, is the concentration of free Zn2+ ions of the solution. By exploring the evolution of the microstructure of the one-dimensional zinc oxide crystals, it is proved that the formation of the various microscopic morphologies is a result of the competition between the kinetic control and the thermodynamic control during the crystal growth, which in turn is mainly determined by the concentration of the free Zn2+ ions in the solution. The in-depth exploration of the growth mechanism of zinc oxide and the fine control of its microscopic morphologies is expected to provide advanced materials for current and future cutting-edge applications of zinc oxide. It is also expected that the growth mechanism reported here can provide theoretical support for achieving other oxide materials whose microstructure can be finely controlled.

Fluorine and tin co-doping synergistically improves the photoelectrochemical water oxidation performance of TiO2 nanorod arrays by enhancing the ultraviolet light conversion efficiency.

Fluorine and tin co-doped rutile TiO2 nanorod arrays are grown on fluorine-doped tin oxide substrates by a hydrothermal process and are used as photoanodes to perform photoelectrochemical water oxidation. Fluorine and tin co-doping synergistically enhances the ultraviolet light conversion efficiency of the resulting TiO2, which enables its photocurrent density of photoelectrochemical water oxidation to be more than four times that of the undoped samples. Such improvement in photoelectrochemical performance is attributed to changes in the electronic structure of the rutile TiO2 due to fluorine and tin co-doping. It is found that introducing tin into the matrix of rutile TiO2 can improve the charge separation efficiency because of the enhanced migration of photogenerated electrons from the conduction band of TiO2 to that of SnO2 that occurs at local sites, while fluorine doping can greatly reduce the recombination of the photogenerated electron-hole pairs due to the presence of the Ti3+ state that is produced to compensate for the charge difference between F- ions and O2- ions. It is envisaged that the fluorine and tin co-doped TiO2 nanorod arrays described will provide valuable platforms for wide photocatalytic applications that are not merely limited to photoelectrochemical water oxidation.