Study On Preparation Of Bivalent Tin Complex Oxide Powder Materials And Their Photoanode Photoelectrochemical Performance

Solar photoelectrochemical(PEC)water splitting has been one of the hot spots in the energy field in the past few decades.Among them,photocatalytic materials based on metal oxides have attracted much attention due to their good chemical stability and high cost performance.Many binary oxides,such as Zn O,WO₃,Ti O₂,etc.,have been developed as good photoelectrode materials or as a key part of them.However,their energy band structure may not meet the prerequisites for light absorption of materials by high-performance solar PEC systems.Many researchers are already trying to find new semiconductors that are suitable for visible light response.The complex and changeable structure of mixed metal oxides provides a wider range of possibilities,such as introducing new orbitals to hybridize with the O_2penergy level to control the width of the band gap and the position of the valence band.In this thesis,divalent tin is selected to introduce the required hybrid energy level,and its 5s²electrons can effectively hybridize with O_2pto produce a variety of new semiconductor oxide materials with visible light absorption.Literature reports have confirmed that they often have excellent photocatalytic potential.Based on the close relationship between the photocatalytic(PC)and photoelectrocatalytic(PEC)semiconductor materials,there are often differences in the demand.This thesis selects the mixed valence tin oxide photocatalyst that has been widely reported as an example to explore the influence of the structural characteristics of divalent tin oxide on its photoelectric properties,and to seek the key differences from photocatalyst to photoelectrocatalyst.Because of the relatively simple element composition of this material and the fewer types of defects than the more complex multi-element oxide system,this thesis fully explores its structural characteristics and clarifies the core relationship between its preparation,properties and performance.Above this,this thesis further develops divalent tin oxide powder with a more suitable energy band structure for the core material of photoanode.According to the characteristics of energy band structure and ion exchange rate,the quaternary oxide pyrochlore structure is selected as the basic lattice matrix.Specifically,the defective pyrochlore crystal structure of KTa WO₆is mainly composed of the corner-sharing Ta O₆^-and WO₆^-octahedra structure.This channel allows low-valent cations to pass through,and the divalent tin ions can be effectively hybridized with the O_2porbital in the lattice matrix after being replaced,resulting in a new type of semiconductor material corresponding to visible light.Based on the aforementioned ideas,the corresponding mixed valence tin oxide(nanoflower Sn₃O₄,nanorod Sn²⁺:SnO₂),stannous tantalum tungstate Sn Ta WO_xpowder materials and corresponding photoelectrodes are synthesized.The various binary and quaternary oxides involved in this thesis are closely related,and their material chemistry,microstructure and photoelectrochemical performance are compared with each other.The specific research conclusions are as follows:1.Self-doped tin oxide Sn²⁺:SnO₂was first synthesized by solvothermal method by mixing the powder of K₂Sn₃O₇and Sn Cl₂with N-butanol in Teflon-lined stainless steel autoclaves under 200?10h.Sn₃O₄was synthesized by hydrothermal method by mixing the powder of Na₃C₆H₅O₇·2H₂O and Sn Cl₂with deionized water in Teflon-lined stainless steel autoclaves under 180?12h.We deliberately investigated photoanodes of Sn²⁺:SnO₂microrods and the Sn₃O₄structures as the model to elucidate the PEC bottlenecks.Photo-electrochemical impedance spectroscopy(Photo-EIS)indicated they had notably diverged charge transport,which can be attributed to the path length of photogenerated charges associated with their microstructures.Furthermore,the existence of residual hydroxyl groups was found to be detrimental as well.In lack of surface catalytic sites,loading of Co hydroxide cocatalyst has been observed as another necessary measure.These structural requirements could be of particular importance for the design of other tin oxides materials for PEC or photocatalytic applications.2.Sn Ta WO_xwas synthesized by molten salt method and hydrothermal method.First of all,by mixing the powder of Ta₂O₅?WO₃?K₂CO₃and heat to 900-1100?can obtain the white mesophase KTa WO₆.Then,Sn Ta WO_xwas first prepared with KTa WO₆and Sn Cl₂by molten salt method at 400?in N₂atmosphere and by hydrothermal method under room temperature or 150-200?.Besides,we studied the effects of different experimental conditions on performance and morphology.Co-catalysts Co and Ni were supported on the synthetic material,the loading methods include thermal evaporation method and urea hydrolysis deposition method,show a photocurrent of about 0.5 m A·cm^-2after Co loaded,which is the highest among present reports.Our thesis illustrates the application potential of divalent tin quaternary oxide semiconductor(Sn Ta WO_x)in the field of photocatalysis for the first time.