Study On Graphene/TiO₂ Based Nanomaterials:Structure Optimization And Photoelectrochemical Peroperties

The use of solar energy to produce electric energy or hydrogen energy from the photoelectrochemical properties of semiconductor materials is a promising means of renewable energy storage.However,due to the electron-hole recombination induced by thestructuredefectsandintrinsicpropertiesofsemiconductors,the photoelectrochemical application is limited to a great extent.Taking these above into account,in this thesis,using TiO₂ as a basis for combining graphene or graphite carbon nitride,we tried to constructe nano architecture to optimize electron transfer channels in the photoelectricchemical reactions,which are aimed to enhance the photoelectrochemical properties of the composite materials.The thesis mainly carried out the following three aspects:1.The impacts of Ti O₂ nanostructures on photoelectrochemical properties.The electron transfer and photoelectrochemical cell performances based on TiO₂nanostructure electrodes were researched firstly.The photoanodes based on TiO₂nanoparticles,TiO₂ nanotube arrays,and TiO₂ microsheeets had been fabricated via blade-coating,anodic oxidation,and hydrothermal process,respectivily.Optical performance research found that the microsheets structure possesses superior light scattering as compared to nanoparticles and nanotube arrays,especially particle structure,which means higher light harvesting ability.Further photoelectrochemical study found that the nanotube arrays and microsheets have superior electron transfer properties,and nanoparticles has more dye-adsorbed content due to larger specific surface area.Therefore,the solar cell based on nanoparticles achieved a photoelectric conversion efficiency?PCE?of 3.85%.Then,a TiO₂ photoelectrode on flexible Ti substrate for dye-sensitized solar cells was constructed via layer-by-layer assembly of1D nanotube arrays?bottom layer?,3D microsized leaves?intermediate layer?,and 0D TiO₂ nanoparticles?top layer?by anodic oxidation,hydrothermal approach and screen coating,respectively.The novel 1D-3D buxus-liked bilayer presents superior light scattering and favorable charge-collection.After integrating 14?m TiO₂ nanoparticles with a 12?m buxus-liked double layered photoanode,an excellent power conversion efficiency of 8.02%(short circuit current density J_SC=17.03 mA cm^-2,open circuit voltage V_OC=0.78 V and fill factor FF=60.4%)was obtained,which outperformed that of a cell based on titanium nanotube arrays-TiO₂ nanoparticles?6.30%?with a similar film thickness.The research idea is very promising in the design and development of solar cells'electron transfer layer.2.Graphene-assisted improve electron transfer ability of TiO₂ based photoanode of photoelectrochemical cells.Achieving efficient charge transport is one of the biggest challenges in TiO₂nanostructured electrode-based photoelectrochemical cells.Firstly,the impact of TiO₂nanopartilces'thickness on the photoelectrochemical properties of graphene-TiO₂nanoparticles had been studied.The thickness of nanoparticles could be controlled by controlling the content of graphene oxide.The research found that with increasing the content of graphene,the electron transfer rate boost distinctly.However,it should be noted that too much graphene oxide content increased the exposure of graphene,which lead to high recombination of electron-hole pairs.The solar cells based on the series of composites had been fabricated.The research of photoelectrochemical performance shows that the composite with 10 mg graphene exibits the highest PCE of 7.33%.In order to further reduce the elctron transfer loss among TiO₂ nanoparticles,inspiredbyexcellentdirectionalchargetransportandwell-known electro-conductibility of one dimensional?1D?anatase TiO₂ nanostructured materials and graphene respectively,we report planting ordered single-crystalline anatase TiO₂nanorod clusters on graphene sheet?rGO/ATRCs?via a facial one-pot solvothermal method.The hierarchical rGO/ATRCs nanostructure can serve as an efficient light-harvesting electrode for photoelectrochemical cells.In addition,the obtained high-crystallinity anatase TiO₂ nanorods in rGO/ATRCs possess lower density of trap states,thus facilitating the diffusion-driven charge transport and suppressing the electron recombination.Moreover,the novel architecture significantly enhances the trap-free charge diffusion coefficient,which contributes to superior electron mobility properties.By virtue of more efficient charge transport and higher energy conversion efficiency,the rGO/ATRCs developed in this work show significant advantages over conventional rGO-TiO₂ nanoparticle counterparts in photoelectrochemical cells.3.Tailoring TiO₂ nanotube-interlaced graphite carbon nitride nanosheets for improving visible-light-driven photocatalytic performance.Rapid recombination of photoinduced electron-hole pairs is one of the major defects in graphitic carbon nitride?g-C₃N₄?based photocatalysts.To address this issue,perforated ultralong TiO₂ nanotube-interlaced g-C₃N₄ nanosheets?PGCN/TNTs?were prepared via a template-based process by treating g-C₃N₄ and TiO₂ nanotubes polymerized hybrids in alkali solution.Shortened migration distance of charge transfer was achieved from perforated PGCN/TNTs on account of cutting redundant g-C₃N₄nanosheets,leading to subdued electron-hole recombination.When PGCN/TNTs were employed as photocatalysts for H₂ generation,their in-plane holes and high hydrophilicity not only accelerate cross-plane diffusion to dramatically promote the photocatalytic reaction in kinetics,but also supply plentiful catalytic active centers.By having these unique features,PGCN/TNTs exhibit superb visible-light H₂-generation activity of 1364?mol h^-11 g^-1??>400 nm?and a notable quantum yield of 6.32%at420 nm,which is much higher than that of bulk g-C₃N₄ photocatalysts.This study demonstrates an ingenious design to weaken the electron recombination in g-C₃N₄ for significantly enhancing its photocatalytic capability.