Preparation And Modification Of Nano WO 3 Film And Its Photocatalytic Decomposition Of Water Properties

Recently,nanotube or nanotube arrays-like WO₃（NAs-WO₃）as a promising photocatalyst for energy conversion is getting more and more scientific interests due to their remarkable properties.Such as the suitable electronic structure and the narrow band gap of 2.4-2.8 e V,which enable NAs-WO₃ exhibit excellent absorption in visible light region and high photocatalytic activity.Besides,the special nanotube structures with large surface area enable it to provide large number of reaction active sites and excellent electron percolation pathways for vectorial charge transfer between interfaces.However,the practical application of pure NAs-WO₃ for photocatalytic water splitting is still limited by some factors.Such as the low water oxidation kinetics,leading part of photogenerated electron-hole pairs accumulate and recombine on the surface,thus leading to its low performance for photocatalytic water splitting.Besides,the photocatalytic activity and stability of the NAs-WO₃ in neutral or weakly alkaline aqueous also need to be improved further for efficient photocatalytic water splitting.Many routes have been explored to overcome these impediments,such as ion doping,surface modification and the use of photoelectrocatalysis technology.This research is dedicated to preparing high-performance NAs-WO₃ for photocatalytic water splitting.Anodic oxidation method,modification with oxygen evolution co-catalyst（OEC）layers,and the introduction of oxygen vacancies within nanosheet arrays-like Tungsten oxide（WO₃ NSs）were taken into consideration in this work.1.NAs-WO₃ film was grown directly on tungsten substrate（W）via an anodic oxidation process.The effects of the anodic voltage,the anodic time,the concentration of fluorine ion and the calcination temperature on the morphologies and crystallinity of the as-obtained WO₃ film was studied.Then the photoelectrocatalytic activities of different nanostructured WO₃ film for water splitting were investigated in details.Experimental results showed that the as-obtained NAs-WO₃/W exhibited much enhanced PEC activity（³ times）and stability than the commercial WO₃ for overall water splitting.The special one-dimensional nanotube arrays-like morphology,the highly crystallized monoclinic structure and the strong interaction between NAs-WO₃ and W are three important factors for the excellent PEC performance of the NAs-WO₃ for water splitting.2.Photo-deposition method was used to deposit different oxygen evolution co-catalyst（OEC）layers on the surface of NAs-WO₃,which including Fe OOH,NiOOH,FeOOH/NiOOH,NiOOH/FeOOH.Then the effects of FeOOH,NiOOH on the interfacial electron-hole pairs recombination at the NAs-WO₃/OEC junction and on its water oxidation kinetics were studied.It is found that FeOOH is more favorable for surface holes capture and transfer than NiOOH,while NiOOH is more favorable for the acceleration of water oxidation kinetics than FeOOH.Thus,the synergistic effects of FeOOH and NiOOH leading to the highest PEC activity of NAs-WO₃/FeOOH/NiOOH for overall water splitting.3.Highly crystallized nanosheet arrays-like Tungsten oxide with oxygen vacancies（WO₃ NSs-Ov）which grown directly on tungsten substrate was obtained via an anodic oxidation process and annealing at high temperature in inert gas.Then the electrocatalytic activities of nanosheet arrays-like Tungsten oxide without oxygen vacancies（WO₃ NSs）and WO₃ NSs-Ov for hydrogen evolution reaction（HER）in acidic solution was investigated.It was found that WO₃ NSs-Ov exhibited much enhanced electrocatalytic activity WO₃ NSs for HER,which could be ascribed to its enhanced electrical conductivity and faster surface charges transfer rate,which resulted from the introduction of oxygen vacancies.This could be used potentially as an efficient photoelectrocatalytic（PEC）hydrogen evolution catalyst to replace platinum（Pt）.