Two-dimensional Transition Metal Dichalcogenieds Combined With TiO₂ Nanoarrays For Photoelectrochemical Hydrogen Evolution

TiO₂ nanoarray is one of the specific forms which is highly ordered,possesses larger specific area and allows the vertical transfer of electrical charges across the length of nanoarrays.It is expected to have potential applications in photocatalyst and solar cells.However,the power conversion efficiency of TiO₂ under visible light is still low due to its wide band gap?³.2 eV?and the rapid recombination rate of photogenerated electron–hole pairs.In order to address these obstacles,exfoliated WS₂ and MoS₂ nanosheets were introduced to promote the PEC responses of TiO₂nanoarrays.The main results of this thesis are as follows:?1?TiO₂ nanorod arrays?TiO₂ NAs?were obtained using a facile hydrothermal method.Highly ordered and large-scale TiO₂ nanorods are vertically aligned on the FTO substrate.The average diameter of the nanorods is about 200 nm,and the mean length is about 3?m.The maximum PEC hydrogen generation efficiency of 0.15%is observed for the pristine TiO₂ NAs under AM 1.5 G illumination?100 mW/cm²?.?2?The WS₂ nanosheets with mixed phase were prepared by sonication-assisted lithium intercalation.Then,TiO₂ NAs/WS₂ nanocomposite was obtained utilizing a drop-casting method.The samples were characterized by XRD,SEM,TEM,Raman,XPS and UV-vis spectra,indicating the suceessful exfoliation of bulk WS₂ and prosperous fabrication of TiO₂/WS₂ composite.Parallel experiments reveal that the TiO₂ NAs/WS₂ photoanode with optimized WS₂ loading?0.1 mg?displays significantly enhanced PEC performance,which is about 140%higher than that of the TiO₂ NAs.The higher PEC performance is attributed to the energy band structure of the TiO₂ NAs/WS₂ composite,allowing photogenerated holes could flow from TiO₂ to WS₂,and be eliminated by oxidizing water.Furthermore,exfoliated WS₂ nanosheets in the experiment are in the mixed phase?1T and 2H?,while 1T phase is metallic with high electric conductivity.Thus,charge transportation rate in TiO₂ NAs/WS₂composite could be promoted greatly,obtaining photoanode with high activities.?3?The 1T-MoS₂ nanosheets were prepared by sonication-assisted lithium intercalation according to our previous studies with slight modification.Utilizing a drop-casting method,the TiO₂ NAs/1T-MoS₂ composite was synthesized.TiO₂NAs/2H-MoS₂ composite was prepared by annealing TiO₂ NAs/1T-MoS₂ under nitrogen atmosphere at 500°C for 30 min.A series of characterization methods was performed to demonstrate the successful preparation of ideal samples.Parallel experiments reveal that the TiO₂ NAs/1T-MoS₂ composite with optimized 1T-MoS₂loading?0.1 mg?exhibits the highest photo-electric conversion efficiency,which is about 440%and 93%higher than those of the TiO₂ NAs and the TiO₂ NAs/2H-MoS₂counterpart,respectively.This result can be explained by the easier transfer of the photogenerated holes from TiO₂ NAs to the 1T-MoS₂ nanosheets,owing to the larger impetus and better electrical conductivity of 1T-MoS₂.On the other hand,stronger interaction is present in the case of TiO₂ NAs/1T-MoS₂ composite,thus leading to enhanced charge separation efficiency.