| With the progress of science and technology,the problem of energy exhaustion and environmental sustainable development has become a consensus.Now,there is a growing eagerly need to develop more environmentally friendly and efficient energy conversion and storage systems.The situation of electrochemical energy storage devices represented by sodium/lithium ion batteries is also a breakthrough and a challenge.The electrode material is closely related to the performance of the battery.Based on the factors of affecting the battery performance and the different energy storage mechanisms of sodium/lithium ion batteries,it is urgent to design and develop electrode materials with excellent performance.The physicochemical properties of 2D materials such as Mo S2 and graphene,due to their high surface area,versatile electronic structure,high mechanical robustness,high electrical conductivity,and desirable electrochemical characteristics,make them superior candidates for energy storage applications.Similarly,Mo S2,as a typical transition metal sulfide,has a graphene-like layered configuration and a wide energy gap.In addition,primary Mo S2 high mobility(100 cm2 vs-1)and ease of fabrication also make it stand out in the new generation of energy materials.Considering the theory of self-assembly without template method,For the regulation of Mo S2 based material structure,especially the green and rapid preparation of new hierarchically porous Mo S2 and carbon materials（amorphous carbon,carbon tube and graphene,etc.）hybrid hollow rhomboid three-dimensional frame structure materials are more difficult.In this paper,the structure regulation synthesis of Mo S2-C and Mo S2/r GO hybrid materials was studied by a facile self-templated solvothermal approach,focusing on the structural design,green controllable preparation process and formation mechanism of multistage micro-nano-structure composites.A series of electrode materials with excellent electrochemical properties were successfully prepared,and the energy storage mechanism and structure-function relationship of a new type of hybrid geometry with hierarchically porous hollow Mo S2base were preliminarily discussed.With the exploration and development of new energy products and applications,the environmental problems caused by this need to be solved urgently.NO2 is one of toxic gases emitted from vehicles and industrial processes and is the main source of acid rain and photochemical smog.Oxide semiconductor materials have been widely investigated for application in detecting toxic gases.WO3,as the most important n-type semiconductor metal oxide nanomaterials,is widely used in gas sensitive,optical（electrical）catalysis and sewage treatment.Single WO3 structure is difficult to meet the requirements of high sensitivity detection of low temperature or room temperature gas sensitivity,therefore,heterogeneous multistage 3D micro-nanostructure materials based on WO3 were designed and prepared to achieve high-performance control about gas sensor.At the same time,as an important gas sensitive material,WO3 is often used to detect toxic and harmful gases such as NO2,H2S,acetone,CO and so on.It is shown that the gas-sensitive properties of materials depend largely on their morphology and surface structure state.Therefore,the preparation of materials with special morphology and high specific surface area has become the important strategies to enhance the sensor properties.The main research results are divided into the following four parts:（1）Study on the controllable preparation and sodium storage mechanism and performance of hierarchically porous Mo S2-Carbon hollow rhomboids based on“Mn Mo O4 self-template”of transition metal Mn element.Based on the theory of in situ template-free solute thermal self-assembly and calcination pickling assisted by static electricity and coordination.Using molybdenyl acetylacetonate（Mo O2（acac）2）as molybdenum source,manganese（II）acetylacetonate（Mn（acac）2）as manganese source,glucose as carbon source and thiourea as sulfur source,by adjusting the proportion of metal（Mo:Mn）ions,the content of carbon source and the concentration of the system,a layered porous hollowγ-Mn/Mo S2-C rhombohedral structure composite was successfully synthesized.Then,the hollow rhomboid Mo S2-C was obtained by high temperature annealing and washing with concentrated hydrochloric acid,it has been clarified that the obtained MCHRs assembled underlyingly from ultrathinγ-Mn S and carbon co-hybridized Mo S2 nanosheets under the structure-direction of Mn Mo O4·0.49H2O self-templating.The sample was applied for superior-performance anode of sodium ion batteries.The prepared MCHRs anode of sodium ion batteries exhibited a reversible capacity of 506 m A h g-1 at 0.1 A g-1,ultrahigh rate capabilities up to 10 A g-1 with 310 m A h g-1,and exceptional stability over 3000 cycles.The reason is due to the three-dimensional nanostructured conductive network formed by the close doping of micro-nano rhombic Mo S2 and C,which greatly shorted the electron transfer and sodium ion transmission path,and thus was shown good electrochemical properties.the sodium storage performance of Mo S2-C electrode is greatly improved on account of the synergistic effect of Mo S2and C.In addition,it was analyzed by XRD,SEM and other data by the phase transition and morphology evolution of intermediate products in different reaction stages,and the formation mechanism of MCHRs was studied.This study provides inspiration for the rational design of hierarchically porous hollow nanostructures with specific geometries as an excellent electrode material for outstanding performance energy storage equipment.（2）Based on the controlled preparation and sodium storage mechanism and performance of hierarchically porous 3D architectures with Mo S2-C hollow rhomboids.Theγ-Mn S/Mo S2-C material obtained in the previous chapter was used as a precursor for hydrothermal treatment,then it was subjected to hydrothermal treatment and calcined at 700℃with Ar/H2 mixture,finally,the Mn S was removed by acid etching.In other words,the hollow rhomboids Mo S2-C/r GO composites with 3D morphology and structure were synthesized by controlling the reactant precursor mass and regulating the GO concentration.Due to this morphology,the rhomboid Mo S2-C is tightly wrapped by the graphene layer,which increased the conductivity and structural stability of the electrode material,shortened electron transport path,increased electrode/electrolyte contact area and provided more active sites（holding more lithium ions）.As a result,Mo S2-C/r GO have higher specific capacity,better rate performance and longer cycle stability than the correspondingγ-Mn S/Mo S2-C.The unique hybrid structures can provide shortened electric/ion diffusion paths and large void buffer space,thus boosting the conductivity of electrode and maintain the structural integrity.When evaluated as an anode for lithium ion battery,the as-fabricated Mo S2-C/r GO electrode exhibits superior reversible capacity(850 m A h g-1 after 100 cycles at 1 A g-1)and stable cycling performance(490 m A h g-1 after 2000 cycles at 10 A g-1).This study clarifies that the Mo S2-C/r GO composite is a promising lithium anode material for large-scale energy storage.This also highlights the synergistic effect of r GO and Mo S2-C in rhomboids and the stabilizing effect of carbon doping on their structure,thus improving the electrochemical performance of Mo S2-C/r GO composites.（3）Careful preparation and gas sensing properties of 3D hierarchical carpet-like WO3microflowers with based on surfactant were studied.During the hydrothermal process,WO3 can be evolved by the alcoholysis of WCl6（0.2 g）followed by dehydrogenation,subsequent WO3 crystal growth can be induced by using oleic acid（2 m L）as directing reagent,and then the hierarchical carpet-like WO3 microflowers were made with hydrothermal treatment by using oleic acid as an oriented growth reagent.The as-synthesized WO3 microflowers show a triclinic crystal structure and are basically hierarchical assemblies of carpet-like nanosheets made up of the subunit of bundle-like nanowires.Based on the morphology evolution process,for example,by regulating the temperature,time and the dose of oleic acid of the hydrothermal reaction and so on,a possible crystal growth and nanostructure assembling mechanism were proposed,and the oleic acid plays an important role in the directional crystal growth and microstructure self-assembly of WO3.It was studied about the sensing performance of WO3 on toxic gas NO2.The prepared WO3 microflowers sensor exhibits a gas sensing response of about 228 when exposed to 10 ppm of toxic NO2 gas at 200°C.（4）The 3D hierarchical cactus-like WO3 with Mo dopants microflowers assembled with 2D nanosheets were designed and exploited for the first time as research on fast sensing mechanism and performance.3D hierarchical cactus-like Mo-doped WO3 with microflowers assembled with 2D nanosheets have been prepared by a facile one-pot method with oleic acid was used as a directional template reagent for crystal growth.Based on the evolution of morphology,we propose a possible self-assembly mechanism of crystal growth and micro-nano structure.The doping and surfactant oleic acid plays an important role in the WO3 crystal growth process.Mo atoms are successfully introduced into the 3D nano-architecture and subsequently applied to fabricate chemical sensors.The Mo-doped WO3 sensors exhibit highly enhanced gas sensing performance including low working temperature,excellent sensitive and fast response for NO2.Especially,the optimal working temperature can be lowered from200°C to 140°C after Mo dopants.The sensitivity is highly improved from 285 of the intrinsic WO3 to 10 ppm of the 2 wt.%Mo doped WO3 for NO2.Furthermore,the response and recover times were calculated as 34 s and 24 s,respectively,illustrating a faster detection.Based on the characterizations of Raman,UV-vis and XPS spectroscopies,the remarkable enhancement of NO2-sensing performance is primarily attributed to the rich oxygen vacancies resulting from the Mo dopants.Besides,the oxygen species chemisorbed onto the surface and defects in the lattice established by Mo doping may also be the underlying reasons for enhanced charge carrier density and rapid reactions with NO2.Therefore,doping of non-noble metal elements is a facile and effective way to enhance the gas-sensing properties of semiconducting metal oxides. |
PDF Full Text Request