Design And Photoelectrochemical Property Of Heterostructured Semiconductor

Among various renewable energy sources,solar energy is regarded as promising one meeting the imperative societal demand for sustainable clean energy owing to its inexhaustibility,universality,high capacity,and environmental friendliness.Over the past 40 years,numerous efforts have been made to explore the solar energy conversion technology and devices,however,due to the unsatisfactory solar conversion efficiency and high cost,they can not meet requirements for sustainable development of modern society.Metal oxide semiconductors possess wide band gap and mainly response to ultraviolet light,but the ultraviolet light energy accounted for less than 5%of the solar spectrum,resulting to the low utilization of solar energy.The semiconductors exhibit sluggish charge transfer process and toilless photo-generated carriers recombination on the surface or within the catalyst,thus the photo-excited electron cannot be timely transferred to take part in the reaction,leading to the relative low quantum efficiency.Due to the poor carrier mobility and huge surface reaction kinetics obstacles,the existing light energy conversion efficiency cannot fulfill our requirements.What’s more,the continuous corrosion under the illumination and in electrolyte brings about the poor photo-electrochemical performance.Thus,developing highly efficient catalytic semiconductor materials is of great significance to break through the catalytic performance bottlenecks.For this situation,this thesis introduced metal doping species and fabricated novel hierarchical heterojunction with highly-matched band alignment to realize the efficient conversion of solar energy.The effect of charge transfer on the solar conversion efficiency is explored,further,the proposed mechanism and the reason of enhanced photo conversion performance is deeply investigated.The main contents are as follows:（1）A facile infiltration route has been developed for preparing hollow-structured Ti-doped SnO₂ using silica microspheres as templates,which shows hollow spherical nanostructure with a particle diameter of about 300 nm.Ti is uniformly incorporated into the lattice of SinO2 materials in the form of Ti⁴⁺.It was revealed that 20%Ti-doped SnO₂ displayed enhanced photocatalytic activity compared to that of pure SnO₂.The enhancement in photocatalytic performance of Ti-doped SnO₂ can be attributed to the homogeneous doping of Ti into the lattice of SnO₂,which prevents the recombination of electron-hole pairs and expands the range of usable excitation light to the visible-light region.（2）A facile in-situ inward etching/sacrificial template approach has been utilized to prepare DW-Cu_2-xSe/Cu₇S₄-HNBs by employing Cu₂O as templates.The QDSSC with DW-Cu_2-xSe/Cu₇S₄-HNBs CE exhibits the highest PCE of 4.38%,which is better than that of SW-Cu₇S₄-NBs（3.97%）,Pt（1.54%）and brass/Cu₂S（3.43%）.Firstly,the incorporated Cu_2-xSe has high intrinsic electron conductivity.Secondly,the unique double-walled hollow structure with larger specific surface area would provide more active sites,facilitate the diffusion velocity of electrolyte and accelerate electron transport.Thirdly,DW-Cu_2-xSe/Cu₇S₄-HNBs can effectively reflect incident light and thus improve the light utilization.Finally,the excellent long-term stability is derived from the good stability of Cu_2-xSe in electrolyte,which employed as the barrier to avoid corrosion of Cu₇S₄.（3）The fabrication of well-aligned hierarchical Cu₇S₄/TiO2/CoCr-LDH nanorod arrays is reported，using vertically aligned Cu（OH）₂ nanorod arrays as templates,which shows enhanced photoconversion efficiency（0.58%at 0.6 V）and photocurrent density(2.04 mA·cm^-2 at 1.23 V).The improved PEC performance is derived from the formation of heterojunction with highly-matched band alignment.The larger surface area would provide sufficient active sites for the water oxidation processes,multiple reaction interfaces are produced and involved in the water splitting process,and the successive modifications of Cu₇S₄ and CoCr-LDH have endowed ternary sample a surprising enhancement in both ultraviolet light absorption and charge separation efficiency.（4）N-doped graphene quantum dots embedded double-shelled CeO₂/Cu₇S₄ heterostructured nanoboxes were prepared by using Cu₂O nanocubes as templates.The DS-CeO₂/Cu₇S₄/N-GQDs-HNBs based photoanode delivers a largely enhanced photoconversion efficiency（0.82%at 0.8 V）and photocurrent density(2.75 mA cm^-2 at 1.23 V)compared to other photoanodes.The improved PEC performance is derived from the synergistic effect of heterojunction with highly matched band alignment and the unique double-shelled hollow nanoboxes.The formation of heterojunction can extend the absorption range of CeO₂,adequately utilize the light energy and accelerate the separation and transfer of photogenerated electron-hole pairs.The enlarged active surface areas and mesoporous merits would provide sufficient active sites for the water oxidation processes,offer pore channels for the gas escaping and enhance light utilization efficiency.（5）The CoWO₄ wrapped treble-shelled Cu₇S₄/CeO₂ heterostructured nanorod arrays with well-matched band alignment were rationally designed and fabricated forhigh-performance PEC water splitting via the introduction of photo-active Cu₇S₄ and CoWO₄ to CeO₂.As expected,after the formation of ternary type-Ⅱ heterostructure with hierarchical treble-shelled hollow structure,the TS-Cu₇S₄/CeO₂/CoWO₄-HNAs photoanode shows enhanced PEC performance.This can be ascribed to the broadenedoptical-response range due to co-sensitization of Cu₇S₄ and CoWO₄;the facilitated photogenerated carriers separation and enhanced surface water oxidation kinetics due to highly-matched band alignment;increased active surface areas,more active sites,motivated diffusion process of carriers and electrolyte,and higher light utilization efficiency due to construction of hollow hierarchical nanostructures;the restrained photocorrosion of Cu₇S₄ and improved photostability of photoanodes.