Preparation Of Metal Formic Acid Organic Framework Based Metal Sulfide And Its Application In Supercapacitors

Supercapacitor is a kind of environmental protection and economic energy storage device.With high energy density,stable performance,short charging time and little affected by environment,supercapacitor has been widely used in military,transportation,aerospace and other fields.The main factor affecting the performance of supercapacitors is the composition and structure of the electrode materials.Therefore,the research of high performance electrode materials is the focus of current research.Among the energy storage materials,hollow structure metal sulfides have the advantages of good electrical conductivity,large specific surface area,environment friendly,high capacity and good stability.Therefore,hollow structure metal sulfides are one of the ideal energy storage materials.As porous crystalline materials,metal organic frameworks（MOFs）are considered to be the ideal precursors for the synthesis of hollow and porous materials.However,it is still a challenge to make the MOFs materials industrialized.Therefore,it is necessary to develop a simple,economical and effective way to synthesize hollow and porous materials with MOFs.In this paper,metal formic acid organic frameworks（MFFs）were used as precursors to synthesize the nanostructured hollow metal sulfides by simple ion exchange reaction.And the electrochemical performance of the hollow metal sulfides electrode materials were investigated.The main research contents are as follows:Firstly,uniform NiS hierarchical hollow cubes were facilely fabricated by an anion exchange reaction of low-cost Ni formate framework precursor（[CH₃NH₃][Ni（HCOO）3]）with S2-.The formation mechanism of the hierarchical hollow structure was explored completely.When evaluated as electrode materials for supercapacitors,NiS hierarchical hollow cubes exhibited high specific capacitance(874.5 F g^-1 at 1 A g^-1)and good cycling stability（retention of 90.2% after 3000 cycles）.Moreover,the as-fabricated asymmetric supercapacitor achieves an enhanced energy density of 34.9 Wh kg^-1 at a power density of 387.5 W kg^-1.When using two asymmetrical button capacitors as a power supply,one blue round light-emitting diode（LED 0.5 W）can be powered efficiently for more than 30 minutes.In addition,two red or a yellow LED can also be lighted up for 10 min.Secondly,[CH₃NH₃][Co（HCOO）3] precursors with different morphologies were prepared by adjusting the ratio of formic acid and methylamine at room temperature by simple stirring method.Based on the morphological inheritance of MOFs,hollow cube structure and hollow microframes Co3S4 were synthesized by a simple ion exchange.In order to exert the application value of the synthetic hollow Co3S4,the capacitance characteristic of the synthesized Co3S4 sample can be evaluated.The test results show that hollow cube structure Co3S4 has a specific capacitance of 546.5 F g^-1 at 1 A g^-1 and the capacitance maintained 96% after constant current charge and discharge 10,000 times,while hollow microframes Co3S4 has a specific capacitance of up to 497.0 F g^-1 at 1 A g^-1 and capacitance maintenance of 94% after 10,000 cycles.Thirdly,three different morphologies [CH₃NH₃][NiCo2（HCOO）3] precursors were prepared by adjusting the reaction solvent,the addition order of formic acid and methylamine.Then,hollow cube,hollow ellipsoid and microflower shaped NiCo2S4 were prepared by simple ion exchange reactions.When used as the electrode materials for supercapacitor,microflower shaped NiCo2S4 has the highest specific capacitance(at 1 A g^-1,specific capacitance of 1229 F g^-1)and good cycling stability(retention of 85% after 5000 cycles at a current density of 5 A g^-1).The NiCo2S4 nanocomposite and carbon fiber were constructed as asymmetric capacitors.Moreover,the as-fabricatedasymmetric supercapacitor using microflower shaped NiCo2S4 and carbon nanofiber,had an enhanced energy density of 37.2 Wh kg^-1 at a power density of 400 W kg^-1.