Preparation Of Tungsten Oxide And Its Composite Materials And Study Of Photoelectrocatalytic Properties

Energy crisis and environmental pollution have received more and more attentions.One of promising ways is to produce H2 and O2 from water splitting via photocatalysis using sunlight.Today,most studies are focused on Ti O2 photocatalysts owing to the low cost,easy availability,non-toxicity and high stability.However,pure TiO2 has the intrinsic defects such as narrow energy band gap corresponding to the low efficiency for using sunlight,the high recombination rate between photoelectrons and holes.Meanwhile,photocatalytic H2 production from water splitting usually needs an organic compound like methanol as the sacrificial agent to consume excess photo-induced holes,leading to the enhanced cost.Moreover,the research on the synergetic photocatalytic evolution of H2 and O2 is still quite limited.WO₃ is widely used in adsorption,catalysis,energy storage and sensitive devices,etc.Hence,how to effectively enhance the electron-hole separation and how to construct high quality heterogeneous junctions is highly required for improving photocatalytic activity.Thus,we performed the following works.1.WO₃,as a good oxygen-producing material,may result in the splitting of water under the combination with the generation of hydrogen.In this chapter,we used gas-phase etching method to obtain WO₃ nano-electrodes by using tungsten sheets as precusors.We explored the photoelectrocatalytic performance for water splitting under visible light irradiation.The influence of different HF concentration etching,different gas phase etching time and different gas phase etching temperature were also investigated to the case of the surface texture of electrode material and the photoelectrochemical activity in water splitting.It was found that the WO₃ nanoelectrode material obtained by etching at 150? for 24 h in 4 M HF exhibited the highest water splitting activity.Through the characterization,such as XRD,SEM and other related electrochemical characterization,the physicochemical properties and photoelectrocatalytic properties of the as-obtained electrodes were discussed.2.By using the above-mentioned best WO₃ electrode material as a substrate,BiVO₄ film was spin-coated on WO₃ electrode with the formation of BiVO₄/WO₃ composites.Such constructed a composite photoelectrocatalytic electrode greatly increased the carrier density and the utilization efficiency of photo-generated electron-hole,thus an improved photoelectrocatalytic performance for water splitting was achieved.In this chapter,bismuth vanadate was prepared by mixing bismuth nitrate with ammonium metavanadate,then such precursor of bismuth vanadate was spin coated onto WO₃ nanomaterials and calcined in air for forming BiVO₄/WO₃ composites.The photoelectrocatalytic performance in water splitting of the as-formed hybrid electrode was investigated under visible light irradiation?? > 420 nm?.3.WO₃ electrodes were treated in various atmosphere?vacuum,hydrogen and nitrogen environment?at 200? with the formation various electrodes with oxygen vacancies.The effect of oxygen vacancy on the photoelectrocatalytic activity was investigated by using the above electrodes as photoanodes.The WO₃ electrode treated in the hydrogen atmosphere exhibited the optimal activity.This is because the treatment of hydrogen in the atmosphere of hydrogen will form oxygen vacancies,resulting in local resonance effect,thereby increasing the separation efficiency of electrons and holes.