Controllable Preparation Of MOFs Derived Iron Nanocomposites And Study On Supercapacitor Performance

As a promising energy storage device,supercapacitors have attracted extensive attentions due to their high power density,excellent safety,and low cost.Compared with other energy storage devices,the low energy density of supercapacitors limits its further practical applications.Therefore,improving the energy density of supercapacitors as much as possible without changing their advantages is the key to expanding their application scenarios.Recently,enormous research progress have been made on the cathode materials,and the specific capacitance of most Co and Ni based cathode materials has been surpassed 1000 F g^-1.However,the exploration of anode materials is obviously lagging behind,and the specific capacity of commonly used carbon anode materials is usually less than 200 F g^-1.Therefore,the anode and cathode is serious mismatched,which significantly limits the output energy density of supercapacitors.Therefore,the development of high-performance anode materials is urgent need.Due to the good redox reaction and wide negative potential window(-1.2-0 V),Iron-based nanomaterials are considered as potential anode materials of supercapacitor,but the related low conductivity and poor stability limit their supercapacitor performance.To solve these shortage of Fe-based nanomaterials,metal-organic frameworks(MOFs)with the ultra high specific surface area are employed as precursors,and a series of high-performance iron-based nanocomposite electrode materials are prepared by shell coating,element doping and controllable vulcanization processes.The conductivity,ion transport rate,and specific surface area are optimized by those process,and the inherent defects of iron-based materials are well addressed.Furthermore,high-performance hybrid supercapacitors are fabricated by the as-prepared iron-based materials as negative electrode,and boosted energy density are achievd.The main research contents are as follows:1.Controllable preparation of MIL-88A-derived FeS2/Co1-x S and their supercapacitor properties:In this work,using hexagonal prism-shaped MIL-88A as a sacrificial template,a Fe/Co-LDH hierarchical nanostructures is prepared by an alkali etching and co-precipitation reaction of Co and Fe elements,which is further vulcanized to fabricated the target FeS₂/Co_1-xS heterogeneous nanomaterials with hollow structure.Relevant characterizations show that the unique hollow structure of FeS₂/Co_1-xS enrich the pore structure inside the material to facilitate the rapid mass transfer of the electrolyte and the synergistic effect of iron and cobalt bimetals effectively improves the conductivity of iron-based materials and increases the electron transfer rate..Therefore,the optimized FeS₂/Co_1-xS material exhibits a high specific capacity of 743 F g^-1 at 1 A g^-1.Furthermore,a NCS//FeS₂/Co_1-xS hybrid supercapacitor is assembled by FeS₂/Co_1-xS with the reported NCS cathode material.The NCS//FeS₂/Co_1-xS hybrid supercapacitor displays a prominent energy density(64Wh kg^-1)and an excellent cycle durability(retaining 81.3%of the initial capacity after6000 cycles).2.Preparation of MIL-88A derived FeS2/Fe2O3@S-rGO and their of Supercapacitor Performance:In this work,to solve the poor conductivity of iron-based materials,the graphene materials with high conductivity is involved in Fe-based nanomaterials.First,uniformly distributed MIL-88A nanoparticles on graphene oxide nanosheets are prepared by solvothermal method;then,a FeS₂/Fe₂O₃hetero-junction coupled with S-functionalization GO(FeS₂/Fe₂O₃@S-rGO)are successfully constructed by precise control of vulcanizing agent The unique heterostructure of FeS₂/Fe₂O₃@S-rGO can provide more active sites for enhanced specific capacity;and the three-dimensional S-rGO network can not only effectively enhance the electrical conductivity but also provides abundant pores and channels for improved diffusion rate of the electrolyte,which dramatically enhance the electrochemical stability of FeS₂/Fe₂O₃@S-rGO.Therefore,FeS₂/Fe₂O₃@S-rGO exhibits an outstanding specific capacity as high as 219.4 m Ah g^-1(790 F g^-1)at 2 A g^-1.In addition,a NCS//FeS₂/Fe₂O₃@S-rGO hybrid supercapacitor is assembled with2D/3D Ni₃S₂/Co₃S₄(NCS)as the positive electrode and FeS₂/Fe₂O₃@S-rGO as the negative electrode.A high specific capacity is reached 114.2 m Ah g^-1(274 F g^-1),and a corresponding high energy density of 85.63 Wh kg^-1 is achieved at the power density of 0.75 k W kg^-1,which is significantly better than most reported hybrid supercapacitors.3.The fabrication of Co-MOF derived high-performance supercapacitor positive and negative materials for the fabrication of high-energy-density supercapacitors:In this work,through cationic shell coating and controlled etching process,M₃S₂/MS₂hollow triangular array electrode materials doped with trimetallic elements(M/Co/V,M=Ni or Fe)are successfully prepared by using Co-MOF nanoarray as precursor.When the introduced metal element is Ni element,the CNVS positive electrode material is obtained,while the CFVS negative electrode material is obtained for the introduced Fe element.The Ni/V-or Fe/V-doped Co₃S₂ nanoparticles are randomly distributed on Co/Ni-or Co/Fe-doped VS₂ nanosheets to form a M₃S₂/MS₂hetero-interface,which can not only increases the reaction kinetics,but also provide more electroactive sites for deep redox reactions.Therefore,CNVS display an outstanding specific capacity of 6556 m F cm^-2 at 5 m A cm^-2,CFVS display an outstanding specific capacity of 6195 m F cm^-2 at 5 m A cm^-2.Subsequently,CNVS//CFVS hybrid supercapacitor devices are fabricated with CNVS as the positive electrode and CFVS as the negative electrode,and the energy density can achieved0.73 m Wh cm^-2(0.4 m W cm^-2),and excellent cycle performance and only 13.6%capacity loss after 5000 cycles.