Study On The Photoelectrochemical Performance Of WO₃ Nano Photocatalysts

WO3,a visible-light responsive photocatalyst,absorbs light up to 480 nm with several intriguing advantages such as low cost,harmlessness,and stability in acidic and oxidative conditions.In this paper,the relationship between the morphology control and photocatalytic activity of WO3 is analyzed in detail.Furthermore,some main strategies for improving photocatalytic activity of WO3.Besides,the preparation methods,photocatalytic enhancement factors and possible photocatalytic mechanisms for the WO3/semiconductor composites were described.It is anticipated that this review could offer guidelines for designing novel WO3-based photocatalysts with low cost and high efficiency,which can possess promising prospects of application to meet the urgent demands of highly efficient solar energy conversion in the areas of renewable energy and environmental purification.Finally,the main conclusions and future perspectives of WO3-based photocatalysts were pointed out.This thesis consists of four parts which its the main contents are as follows:1.A short review was given on the progress of semiconductor materials.We introduced the model and research method of photocatalytic hydrogen evolution.Meanwhile,how to synthesis improved composite material,the principle of the photoelectric catalysis method and its application were elaborated in photocatalytic hydrogen evolution.2.In this chapter,porous WO3 nanosheets were prepared.First,plain WO3 nanosheets were prepared by hydrothermal method in aqueous solution of tungsten oxide in aqua regia.Next,plain WO3 nanosheets were simultaneously etched with polyvinylpyrrolidone(PVP)and L-ascorbic acid as oxidant and reductant to obtain porous WO3 nanofilms.And calcined at high temperature to obtain WO3 with better crystal form.The samples were characterized by SEM,XRD and XPS techniques.The photoelectrochemical properties of the samples were characterized by I-V,I-t,Voc decay and EIS techniques.The results showed that the porous WO3 nanosheets films exhibited higher photocatalytic activity of the photocatalytic oxidation of water activity.The photocurrents of WO3 nanosheet films can achieve 0.75 m A·cm-2(0.6 V vs SCE),and the photocurrents of porous WO3 nanosheet films can achieve 1.4 m A·cm-2(0.6 V vs SCE).3.In this part,Graphitic carbon nitride(g-C3N4)has been studying as a metal-free photocatalyst and has led to various attractive progress,but rapid recombination of photogenerated charge carriers substantially limits its performance.Here,we establish g-C3N4-based heterojunction type II photoanodes on transparent conducting substrate via coupling with rod-like.In these composites,g-C3N4 film grown by electrophoretic deposition of exfoliated g-C3N4 firstly serves as guest material.The optimized type II WO3/g-C3N4 composite exhibits enhanced photocurrent of 0.82 m A·cm-2 at 1.23 V vs RHE and incident photo-to-current conversion efficiency(IPCE)of 33% as compared with pure WO3 nanorods(0.22 m A·cm-2 for photocurrent and 15% for IPCE).The enhancement can be attributed to accelerated charge separation in heterointerface because of suitably aligned band gap between WO3 and g-C3N4,as confirmed by optical spectra and ultraviolet photoelectron spectroscopy(UPS)analysis.The photocatalytic process and mechanism of g-C3N4-based heterojunctions are proposed and it potentially explains the origin of enhanced photoelectrochemical performance.4.Here,we successfully establish g-C3N4-based heterojunction nonmediator assisted Z-scheme photoanodes on transparent conducting substrate via coupling with nanoparticulate WO3.Relative to pure g-C3N4 film(with photocurrent of several microampere and IPCE of 2%),largely improved photocurrent of 0.22 m A·cm-2 and IPCE of 20% with Z-scheme g-C3N4/WO3 composite are acquired.This achievement and fundamental information supplied here indicate the importance of rational designing heterojunction photoelectrode to improve performance of single semiconductor.Especially for those materials,such as pure g-C3N4,and WO3,their photoactivities are strongly restricted by high recombination rate.