| Energy shortage and environmental pollution are two major problems facing human society at present.Exploring and researching new clean and renewable energy is the key to solve the problem of energy shortage and environmental pollution in the future.Solar energy has the characteristics of abundant reserves,clean and pollution-free as a clean renewable energy.It is one of the most promising new energy sources to solve future energy and environmental problems.The photoelectrochemical water splitting technology can convert low-density solar energy into high-density hydrogen energy,and it has high theoretical solar energy conversion efficiency.It will be one of the most potential technologies to convert solar energy into hydrogen energy for solving future energy and environmental problems.In the past decades,the photoelectrochemical water splitting technology has got rapid development.However,the low efficiency of photoelectrochemical water splitting was unable to meet the needs of practical application and has become the key to restrict its further development and wide application.Therefore,it is of great significance to explore a new type of photoelectrochemical electrodes with high efficiency and to improve the efficiency of photoelectrochemical water splitting for furtherly promoting the development and wide application of photoelectrochemical technology.Oxynitrides are a kind of semiconductor material with excellent quality,which has important applications in many fields.Compared with oxide semiconductors widely studied,valence bands of oxynitride semiconductors are usually composed of N 2p and O 2p orbital hybrids.It can satisfy the requirements of energy band position and energy band width of semiconductor materials for photocatalytic water splitting at the same time,and it has become the best choice for preparing efficient photocatalytic water splitting electrodes.However,the materials usually have the poor crystallinity and many defects because that oxynitrides nanoparticles are generally prepared by nitriding oxide precursors with high temperature.Therefore,the photochemical water splitting efficiency of semiconductor photoelectrodes is usually low due to the relatively backward preparation technology,which has become a bottleneck restricting their photochemical water splitting activity.For the above problems,this paper chooses perovskite-structured oxynitride semiconductor materials MTaO2N(M = Ca,Sr)as the main research object.From the crystallographic point of view,we explore a new method to prepare MTaO2N nanomaterials through the study of its growth and preparation process.The composition and electronic structure of the materials were controlled by nanomaterial micro-structure control technology to further improve the photoelectrochemical water splitting activity of MTaO2N photoelectrodes.The chief research contents are as fo lows:In the first chapter,we systematically introduced the basic principle of photoelectrochemical water splitting technology,the parameters affecting its performance and the ways to improve the efficiency of photoelectrochemical water splitting decomposition.In particular,the preparation of perovskite oxynitride semiconductor materials and the research progress of photoelectrochemical water splitting are systematically introduced.The significance and main research contents of this paper are put forward.In the second chapter,we explore a new method of preparing CaTaO2N material by one-step molten salt method.Compared with the traditional solid-state reaction method,the method innovatively uses CaCl2 as both reactant and molten salt.Perovskite oxynitride semiconductor materials can be obtained by one-step reaction,which not only omits the preparation of oxide precursors,but also further reduces the synthesis temperature and reaction time of the materials.Moreover,the prepared CaTaO2N is higher than the materials prepared by traditional methods on the crystallinity and photoelectrochemical properties.In the third chapter,we further studied and explored the preparation method,synthesis conditions,growth mechanism and its photoelectrochemical water splitting activity of SrTaO2N materials with molten salt method.The results show that the SrTaO2N prepared by molten salt method has better crystallinity and fewer defects than the samples prepared by solid-state synthesis,so it has better photochemical activity.Meanwhile,it proves that the one-step molten salt method is a general type of MTaO2N perovskite nitrogen oxide semiconductor material.In the fourth chapter,a series of SrxBa(1-x)TaO2N and SrxCa(1-x)TaO2N solid solution materials were synthesized by molten salt reaction method for the first time on the basis of MTaO2N semiconductor materials prepared by one-step molten salt method.The experimental results show that SrxBa(1-x)TaO2N and SrxCa(1-x)TaO2N solid solution materials have better photoelectrochemical properties than MTaO2N solid solution materials.This experiment provides a new idea for tuning the composition of MTaO2N perovskite nitride semiconductor materials,then tuning their electronic structure and optimizing their photoelectrochemical properties.In the fifth chapter,this paper summarizes the chief research contents and innovations of this thesis,discusses the main problems and shortcomings of the current work and proposes the research work to be carried out in the next step at the same time.In summary,as a kind of semiconductor photoelectrode material with important application prospects and excellent performance,oxynitride semiconductor materials are of great significance to further promote the development and practical application of photoelectrochemical water splitting technology.In this paper,we explored and studied the new method of preparing MTaO2N perovskite oxynitride semiconductor materials and solid solution starting with the basic method of crystal growth starting with the basic method of crystal growth and through studing the growth process of MTaO2N(M = Ca,Sr)oxynitride semiconductor materials.This study provides a method for further improving the photochemical water splitting performance,exploring and preparing a new type of high-efficiency nitrogen oxynitride semiconductor photochemical electrodes.It is of great significance to further promote the development and practical application of photochemical water decomposition technology. |
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