Construction Of Tungsten Oxide-based Heterostructures And Oxygen-deficient Structures And Their Applications

As a typical n-type semiconductor,tungsten oxide material can be widely used in photocatalysis,electrocatalysis and electrochromic intelligent windows.It has become one of the hotspots in the fields of environment and energy.As an energy material,tungsten oxide is inexpensive,rich in sources and exhibits good chemical stability and light corrosion resistance,thus it can be used for large-scale applications.There are many species of tungsten oxide,including stoichiometric WO₃,sub-stoichiometric WO_3-x containing oxygen deficient and hydrated tungsten oxide containing crystalline water?WO₃·nH₂O?.In practical applications,the morphology,dimension,structure and other factors will greatly affect the performance of tungsten oxide material.Compared with bulk materials,low-dimensional nanomaterials have greater specific surface area and carrier transport property;However,the differences in structure can reflect different performances.Compared with WO₃,the oxygen vacancies in the sub-stoichiometric WO_3-x structure act as shallow donors to improve the conductivity and donor density,thereby enhancing the surface species?such as CO₂,H₂,NO₂,etc.?adsorption.In addition,restricted by the photocatalytic mechanism,when the tungsten oxide used as single photocatalyst,the photogenerated electrons and holes are easily recombined,thus affecting the photocatalytic efficiency.However,the formation of semiconductor/semiconductor heterostructures with other semiconductors?such as TiO₂?can promote the effective separation of photogenerated electrons and holes,and avoid the recombination of photogenerated electron-hole pairs.Based on these factors,this paper mainly carried out the following researches:?1?With the assistance of supercritical CO₂,we successfully obtained the WO₃·H₂O nanosheets with several layers.The ultrathin nanosheets obtained by dimensional regulation have a large specific surface area and can expose more active sites.Then we used a simple and novel method,that is,under the supercritical CO₂ environment,to form a similar Van der Waals heterostructures-TiO₂/WO₃·H₂O heterostructures.The untrathin TiO₂ nanosheets was fabricated by our previous work.The lamellar structures were fully stacked.When used as a photocatalyst,the heterostructures exhibit a good photocurrent response and excellent degradation efficiency for methyl orange compared with pure TiO₂ and WO₃·H₂O nanosheets.It is found that the photogenerated electrons of TiO₂ is transferred to WO₃·H₂O under light,and the holes of WO₃·H₂O is transferred to TiO₂,which prevents the recombination of photogenerated electron-hole pairs.Thus,it promotes the separation of photogenerated electron and holes,thereby improving the photocatalytic activity.?2?For safety reasons,we used NaBH4 instead of common H₂ to carry out hydrogenation of commercial WO₃ at high temperature to prepare sub-stoichiometric WO_3-x containing oxygen deficient.The results show that after the high temperature hydrogenation,the edge of WO₃ forms disorder region,indicating the formation of oxygen vacancies,and when the hydrogenation temperature increases to 400?,the disorder region expands,indicating that the oxygen vacancy content is increased.According to the UV-vis-NIR spectra,it is found that after hydrogenation,WO_3-x exhibits a characteristic peak at 1050 nm in the near-infrared region,showing a surface plasmon resonance.Then the samples were subjected to electrocatalytic hydrogen evolution test.The results show that the hydrogenation efficiency of hydrogenated WO_3-x sample at 400? is obviously improved.Its Tafel slope is 66 mV dec-1,which is much lower than that of the bulk WO₃?113 mV dec-1?.Moreover,the hydrogenated WO_3-x shows great advantage over other WO₃-based materials reported by literatures as electrocatalyst.