Study On Construction And Photoelectrocatalytic Hydrogen Generation Of One-Dimensional Nanostructured TiO₂ Array Composite Electrodes

Due to the constant demand for energy and environment,human beings have been facing the most serious energy crisis and environmental problems throughout history.Based on the human’s needs for the healthy and sustainable requirement of human society and the desire to leave the beautiful earth to the descendants of human beings,all countries in the world paid more and more attentions to energy conservation and environmental protection.Promoting the development and utilization of solar energy,hydrogen energy and other clean energy and reducing the burning of fossil fuels have become the efficient ways to solve these problems.Due to the good optical and electrical properties,as a photocatalytic material,TiO2 has been widely used for hydrogen generation,pollutants degradation,C resources conversion and so on.The one-dimensional TiO2 nanotube/rod arrays composite is an excellent photoelectrocatalytic material for simple preparation process,the excellent structure,high recyclability and no secondary pollution.However,there were two major problems faced by one-dimensional TiO2 nanotube/rod arrays in photoelectrocatalytic hydrogen production:(1)TiO2 semiconductor with the band gap of 3.0 eV or 3.2 eV can absorb the UV light which accounts for less than 5%of sunlight,which results in low utilization of sunlight;(2)the photogenerated carrier recombination rate is high,resulting in low light quantum efficiency.Therefore,researchers have made many efforts to improve the photoelectrocatalytic activity of TiO2 semiconductors using a variety of methods.This work is amied at improving the photelectricatalylic activity of one-dimensional nanostructured TiO2 arrays tbrough coupling semiconductors.Two kinds of photoelectrocatalytic electrodes with unique structures were constructed,and their photoelectrochemical properties,transfer mechanism of photogenerated carriers and photocatalytic hydrogen production ability are investigated.The main research contents are displayed as follows:1.Three-dimensional(3D)Bi2MoO6-Pd-TiO2 nanotube arrays were constructured by electrochemical methods in which the Pd nanoparticles and Bi2MoO6 nanosheets were deposited on successively on TiO2 nanotube arrays,and used in the photoelectrocatalytic hydrogen generation.Firstly,noble metal Pd nanoparticles with a particle diameter size of 20-30 nm were successfully modified on the inner and outer walls of TiO2 nanotubes by electrodeposition.Secondly,the Bi2MoO6 nanosheets synthesized by the oil bath method were decroated on the Pd-Ti02 nanotube arrays through electrophoretic deposition.The 3D Bi2MoO6-Pd-TiO2 photocatalysts were successfully synthesized.The UV-visible absorption spectra showed that this composite electrode had an enhanced absorption in the wavelength range of 250-750 nm.Compared the photoelectrocatalytic activity of Bi2MoO6-Pd-TiO2 nanotube arrays with those of TiO2、Pd-TiO2、Bi2MoO6-TiO2 and Pd-Bi2MoO6-TiO2 nanotube arrays,it was found that the Bi2MoO6-Pd-TiO2 ternary composite electrode had the highest photogenerated carrier separation and transfer rate and the highest photoelectrocatalytic activity.The highest photocatalytic hydrogen production rate of B12MoO-6-pd-TiO2 nanotube arrays was 25.13μmol·cm-2·h-1 under the visible light irradiation,which was 20 times higher than that of pure TiO2 nanotube arrays.The Pd nanoparticles in Bi2MoO6-Pd-TiO2 nanotube array composite can help anchor Bi2MoO6 nanosheets on the Pd-TiO2 and form a 3D structure,which not only help to enhance the visible light absorption of the composite,but also facilitate to collect the photogenerated electrons on the conduction band of Bi2MoO6 and tiransfer to the conduct band of TiO2 rapidly,and thus promote the separation of the photogenerated charges.2.WO3-,nanowires loaded TiO2 nanorod array composite electrodes were prepared by hydrothermal method.Firstly TiO2 nanorod arrays with diameter of about 100 nm and rod length of about 1.2μm were synthesized on FTO conductive glass by hydrothermal method.Secondly,the blue WO3-x nanowires with oxygen defects were deposited on the TiO2 nanorod arrays by solvothermal method.The"spider web"like WO3-X nanowires were uniformly bridged on the TiO2 nanorods.Compared with pure TiO2 nanorod arrays.The WO3-x-TiO2 nanorod arrays displayed slightly en hanced visible light response,higher photoelectrocatalytic activity and photoelectrocatalytic hydrogen generation ability.The highest photoelectrocatalytic hydrogen production rate of WO3-X-TiO2 photoelectrode reached 69.55μmol·cm-2·h-1,which was about 11 times than that of pure Ti02 nanorod arrays.Due to the presence of oxygen vacancies in WO3-x-TiO2 nanorod arrays,the conduction band position of the WO3-x was lower than WO3.Under the light illumination,the photogenerated electrons on the conduction band of WO3-X could combined with the photogenerated holes on the valepnce band of TiO2.Therefore,the spatial separation of photogenerated electrons on the conduction band of TiO2 and the photogenerated holes on the valence band of WO3-X could be achieved As a result,the photoelectrocatalytic activity of the WO3-X-TiO2 photoelectrode was greatly improved.In particular,in the absence of sacrificial agents,the photogenerated holes on the valence band of WO3-X also can oxidize the water,realizing the photoelectrocatalytic decomposition of pure water.