Layered Composite:Synthesis And Performance Of Energy Conversion And Storage

With the progress and development of society,the environment problems caused by energy consumption are becoming more and more serious.Thus,in order to meet the needs of human production and life,it is very important to develop new renewable and eco-friendly clean energy.To resolve above problems,photocatalytic H2 production,lithium ion battery and supercapacitor have emerged as three kinds of attractive approaches of energy convertion and store.Photocatalytic H2 production is an important way of convertint solar energy into clean and eeco-friendly hydrogen,it can not only alleviate the increasingly serious energy crisis can also solve the environmental pollution.The lithium ion battery has many advantages such as long cycle life,high energy density and environmental friendly,which has been widely applied in portable electronic devices and electric vehicles as an energy storage and conversion of the device.As an efficient and clean energy storage and conversion device,supercapacitors have attracted great attention due to their high power density,long life and fast charge and discharge.Based on this,in order to meet the demand of the development of energy conversion,it is very important to design new electrode materials and photocatalyst.The goal of this dissertation is to design and synthesize novel layed composite based on the analyses of restrictive factors of Photocatalytic H2 production,lithium ion battery and supercapacitor,thus improving the application in energy convertion.The details of this dissertation are summarized briefly as follows:?1?g-C₃N₄ has been extensively studied because of its low cost,no metal component,good stability and high efficient photocatalytic activity.However,the bulk gC₃N₄ has poor surface area,the high recombination rate and low efficient photocatalytic activity,which severely limits the application of g-C₃N₄ in photocatalytic hydrogen production.Based on this,in this study,a holey structured g-C₃N₄ with edge oxygen doping?HS g-C₃N₄-O?was successfully obtained using photo-Fentonreaction.First,we prepared bulk g-C₃N₄ through pyrolysis.Second,bulk g-C₃N₄ was oxidized and exfoliated into g-C₃N₄ thin sheets with abundant oxygen-containing groups.Thus,the gC₃N₄ thin sheets with abundant oxygen-containing groups as active defective sites can be partially oxidized and etched,leaving behind carbon vacancies,which gradually extend into nanopores.The as-resulted HS g-C₃N₄-O demonstrated a narrow band gap of 2.434 eV and high surface area of 348 m² g^-1.The band gap of bulk g-C₃N₄ is 2.7 eV,after edge doping with oxygen,the band gap of HS g-C₃N₄-O is significantly reduced to 2.434 eV,suggesting more visible light harvesting capability.The result is reasonable becausean oxygen atom owns one more electron than an N atom does,naturally,the substitution of N sites by O atoms would offer extraelectrons in the HS g-C₃N₄-O.The H2 evolution rate of HS g-C₃N₄-O?202.56 umol/h?is much higher than bulk g-C₃N₄?70.65 umol h-1?and g-C₃N₄ thin sheets?122.56 umol h-1?.?2?Baesd on the understanding of the electrical conductivity of the capacitor electrode material and the low capacitance of the double layer capacitor electrode material,we proposed the first oriented design and fabricate the?metal-organic framework?-Polyaniline sandwich structure composites as novel hybrid electrode material for highperformance supercapacitor,the electrode material shows agood electrochemistry in supercapacitor.Metal-organic frameworks?MOFs?as an emerging class of porous materias built by metal ions and organic linker.Recently,MOFs have received much attention as promissing template or precursor to prepare carbon material.In addition,polyaniline?PANI?as a kind of pseudocapacitance material,which has been considered as a kind of electrode material with excellent development ability,because of its advantage such as easy access to raw materials and simple synthesis.In this paper,we fabricate nover carbonized MOF/PANI sandwich structure composites through in situ polymerization of aniline monomer in the presence of carbonized Zn-MOF suspension.Carbonized Zn-MOF is synthesized from 8-hydroxyquinoline,zinc acetate and via calcination process.The specific capacitance of MOF/PANI has been approach to be as high as 477 F g^-1 at a current density of 1 A g^-1.The carbonized MOF could show a good electrical conductivity toimprove the electrical conductivity of carbonized MOF/PANI composite,and also enhances the ability of PANI storage electrolyte and electrochemical activity.Moreover,the carbonized MOF plays a key role to improve the performance electrode material.?3?Commercial graphite electrodes have a theoretical capacity of only 372 mA h g^-1,which could not meet the requirements in some application fields.Thus,Thus,developing new anode material with higher capacity and excellent cyclic stability is crucial for lithium ion battery.Among the many alternative materials,molybdenum disulfide?MoS₂?as layered transition-metal sulfide has received a great deal of attention due to its unique property and high specific capacity.The adjacent layers spacing of MoS₂ is 0.615 nm,significantly larger than that of graphite?0.335 nm?.Furthermore,the van der Waals forces between the layers are relatively weak.With assisted of chitosan,the bulk MoS₂ can be well directly exfoliated into few-layer MoS₂ nanosheets in aqueous solution by mean of direct sonication.After that,we fabricate the few-layered MoS₂ nanosheets embedded in N-doped porous carbon frameworks as high-performance LIB anode materials based on direct pyrolysis and KOH activition of MoS₂/CS foams.As a consequence,due to the synergistic effect,the flake-like MoS₂/NDPC composites with high specific surface area and porous structures exhibited high rate capability and longlife cycling performance when used as LIB anode.The MoS₂/NDPC composites can deliver discharge capacity as high as 1260 m A h g^-1 at 0.1 A g^-1 and 434 mA h g^-1 at 10 A g^-1 after 50 cycles.At current density of 5 A g^-1,the MoS₂/NDPC-0.5 also depicted a discharge capacity of 496 mA h g^-1 after 1000 cycles.For MoS₂/NDPC composites,the embedded MoS₂ nanosheets of MoS₂/NDPC composites can facilitated fast Li-ion transport and the N-doped porous carbon frameworks enhanced the electronic conductivity and retain the structure integrity.?4?Baesd on the understanding of restraining factor of lithium ion battery,we report a facile route to fabricate metal-organic-framework-derived layered ZnCo₂O₄ involving room temperature synthesis and subsequent thermal calcination.In this paper,the formation of metal organic frameworks?MOFs?by using 8-hydroxyquinoline as an organic ligand and Zn²⁺ and Co²⁺ through complexation.In the process of the formation of MOFs,the presence of?bond of 8-hydroxyquinoline formates layered structure.After that,layered ZnCo₂O₄ formed through the ?bond rupture in the process of calcination.The as-obtained ZnCo₂O₄ as a electrode material for lithium ion battery delivers a high reversible capacity of 1640.8 mAh g^-1 at a current density of 100 mA g^-1 after 50 cycles.The unique layered ZnCo₂O₄ possesses large specific surface area,which can enlarge the contact area with electrolyte and facilitate the Li+ ion diffusion and electron transition.