Controllable Synthesis And Photo-electrochemical Characteristics Of Co-base Semiconductor Materials

In recent years,it has been found that when semiconductor process technology is below7 nm,the use of"copper"as a semi conductor material is clearly not sufficient to support the development of science and technology.Due to the advantages of cobalt such as small size,good conductivity,and low power consumption,the leading American semiconductor equipment company for applied materials has taken the lead in investing in a new process of using"cobalt"as a conductor material to replace traditional"copper".This behavior greatly promotes the development of Co based semiconductor materials.This behavior greatly promoted the development of Co-based semiconductor materials.Transition metal semiconductors（such as Co,Ni,Fe,Mn）have the advantages of low energy consumption,easy operation,and economy,and have broad application prospects in energy,optoelectronics,and catalysis.Compared to other transition metal semiconductors,cobalt based semiconductors have narrower band gaps and high conductivity.Due to the relatively low activation energy of electron transfer,they improve the electron transfer rate and charge separation efficiency.Cobalt nickel sulfide particles（NiCo₂S₄）are typical transition metal sulfides with magnetic p-type semiconductors and excellent optoelectronic properties.NiCo₂S₄contains two variable valence metals,Niand Co,respectively.In both electrochemistry and photocatalysis,due to the conversion between Ni²⁺and Ni³⁺,and between Co²⁺and Co³⁺,the electron transfer barrier is smaller.Compared with transition metal oxides,S has lower electronegativity,and S replaces O to make the band gap of sulfide smaller,thus improving the conductivity.In the process of photocatalysis,energy storage and electrocatalysis,the conduction of electrons/charges is accelerated,and more active site are added.As known,NiCo₂S₄ has received great attention in energy storage.it often appear in supercapacitors or zinc air batteries.due to its advantages such as good conductivity,simple preparation,environmentally friendly materials,theoretically larger than capacitance,and favorable electron transfer.However,poor cycling stability and structural damage during the charging and discharging process seriously restrict its development.Therefore,improving the cycling stability of NiCo₂S₄ in energy storage is the most important issue.Based on the above analysis,we developed the first part of work.Construct electrode materials with hollow structures and vacancy defects.In this work,the hollow Nanoflower（NiCo LDH）,as the substrate of the whole reaction,was decorated with the dodecahedron structure of ZIF-8.After O^2-and S^2-anion exchange reactions and simple reduction,it was formed into a r-NCS@Zn S composite electrode rich in S vacancies.Transmission electron microscopy studies confirmed the hollow structure of r-NCS@Zn S,which was well preserved after H₂reduction.Compared with solid structures,r-NCS@Zn S has a higher specific capacitance,and ESR spectra demonstrate that r-NCS@Zn S contains abundant sulfur vacancies,which play an unprecedented role in electrochemical performance.Therefore,the electrode material we prepared has the following characteristics:the hollow and internal pore structure is conducive to the diffusion and accommodation of electrolytes;Abundant sulfur vacancies contribute to enhanced electronic conductivity,rapid mass transfer and more electrochemical active site.The prepared r-NCS@Zn S sample exhibits ideal electrochemical storage performance after optimization.In addition,the all-solid-state hybrid supercapacitor based on r-NCS@Zn S shows excellent performance with an energy density of up to 47.0 Wh?kg^-1 at a power density of 641.2W?kg^-1.In the field of photocatalysis,NiCo₂S₄ is a potential photocatalyst because of its narrow bandgap,ideal conduction and valence bands.However,the low light absorption efficiency seriously restricts the development of NiCo₂S₄ in the field of photocatalysis,so it is urgent to improve the light absorption ability of NiCo₂S₄.Carbon materials play an important role in improving light absorption.As an emerging material,graphdiyne（GDY）has a high degree of conjugation,uniform pore structure,and adjustable electronic structure.These excellent characteristics make the new scientific and technological fields of GDY and its derivatives receive extensive attention.GDY was successfully synthesized by Academician Li Yuliang’s team for the first time in 2010,and then"gas-liquid"and"liquid-liquid"methods emerged one after another,providing more ideas for the synthesis of GDY.So we conducted the second part of the work:Using electrospinning technology to spin nickel,cobalt,and sulfur sources into a filamentous fiber interwoven structure.Then,NiCo₂S₄ nanofibers are generated through tube furnace carbonization.Afterwards,Cu Cl₂ is reduced to Cu Cl through Na BH₄.Finally,hexaacetylene benzene is added to generate graphdiyne in situ under the catalysis of Cu Cl.Cu Cl serves as both a necessary catalyst for generating graphdiyne and an indispensable part of composite materials,which can better utilize resources.Due to the establishment of graphyne surface heterojunction structure and the establishment of high reduction active site,the prepared photocatalyst has stronger visible light absorption ability,faster electron transfer mobility,and stronger redox ability.Characterization techniques such as XRD,XPS,SEM,ESR,FTIR,UV-Vis diffuse reflection and photoluminescence spectroscopy,electrochemical impedance spectroscopy,and photocurrent response were used to characterize the NCS@CC@GDY,The physical and chemical properties of GDY composite materials were characterized.UV-Vis diffuse reflection indicates that the composite material has strong light absorption ability in the ultraviolet region.Due to the heterogeneous structure and special electron transfer mode of NCS@CC@GDY,the reduction efficiency of Cr⁶⁺is as high as85.8%.And the possible mechanisms for improving the performance of photocatalysts in reducing Cr⁶⁺were explored.This provides an effective strategy for the design of new heterojunction composite photocatalysts.