Preparation Of Double-ligand MOFs Materials And Application In Supercapacitors

Supercapacitors（SCs）have high energy storage capacity,good stability,flexible operating temperature and environmental friendliness.Among them,MOFs and MOFs derived metal compound electrode materials have become one of the research hotspots in the field of energy storage due to their adjustable structure and large energy storage capacity.However,the structural instability and poor electrical conductivity of MOFs materials restrict their practical applications.In order to solve the above problems,MOFs(NiCo_2/1MOF_bd)with adjustable structure have been synthesized by using a double-ligand strategy with the multi-component synergetic effect.Then,using MOFs as precursors or templates,metallic compounds（NiCo P）with different nanostructures and excellent functions are prepared;or one-dimensional MXene fibers are simultaneously introduced into MOFs to fabricate composites（Ni（Co）₃S₄@MXene-fibers）.The relationships between the structure and performance of these three electrode materials are studied,and the specific research contents are as follows:（1）By means of a simple hydrothermal method,dual-ligand MOFs materials(NiCo_2/1MOF_bd)have been obtained via the coordination of metal ions with trimesic acid and 1,4-diazabicyclo[2.2.2]octane.The coordination effect of multiple components is used to improve its electrochemical performance.Researches indicate that the specific capacitance of NiCo_2/1MOF_bd is as high as 1365 F/g at a current density of 1 A/g,and it still maintains 88.5%of the initial value at 10 A/g.And the asymmetric device NiCo_2/1MOF_bd//AC exhibits a high energy density of 50.6 Wh/kg at a power density of 850.0W/kg.（2）The composites（Ni（Co）₃S₄@MXene-fibers）have been prepared by a two-step hydrothermal method.One-dimensional MXene fibers are introduced into MOF-based electrode materials of supercapacitor for the first time.The structure and electrochemical properties of Ni（Co）₃S₄@MXene-fibers are investigated.The results demonstrate that the MXene fibers can not only avoid the massive accumulation of MOFs-derived metal sulfides,but also control the overall morphology,so as to construct a structure with rapid charge transfer ability.This construction is conducive to the redox reaction of the active substances loaded on the surface of the composite materials.The electrochemical studies illustrate that the Ni（Co）₃S₄@MXene-fibers has a excellent energy storage performance.That is its specific capacitance is 1508 F/g at a current density of 1 A/g.For an asymmetric device Ni（Co）₃S₄@MXene-fibers//AC,it also has a high energy density of 63.3 Wh/kg at a power density of 850.0 W/kg,and maintains a cycle stability of 71.4%after 20,000 charge-discharge cycles.（3）A flower-like bimetallic nickel-cobalt phosphide（NiCo P）has been prepared by phosphating NiCo-MOFs at low temperature.It is found that this unique flower-like structure can not only exposes more active sites,but also produces many surface voids along with the Kirkendall effect.Hence,the structure promotes the rapid transport of ions in the electrolyte during the electrochemical reaction process and improves overall electrochemical performance.Electrochemical tests show that the specific capacitance of optimized NiCo P-1/1 is as high as 1545 F/g at the current density of 1 A/g.The NiCo P-1/1//AC has a high energy density（62.4 Wh/kg）at a power density of 850.0 W/kg,and a high energy density of41.0 Wh/kg is also obtained at a higher power density of 8500 W/kg.