| As a new type of electrochemical energy storage device,supercapacitors have been widely used in household appliances,transportation,military,aerospace and other fields because of their fast charging speed and long service life.The performance of supercapacitors mainly depends on the structure and properties of electrode materials,and current electrode materials,such as carbon materials,metal oxides,conductive polymers,etc.,limit the large-scale application of supercapacitors in the field of energy storage because of their poor structural adjustability,high electrical resistance,and poor cycle stability.Metal phosphides have become a hot spot in the study of energy systems because of their metal-like properties and good electrical conductivity.At present,the preparation of metal phosphides requires additional phosphorus sources.On the one hand,it will cause uneven distribution of phosphorus in the material,poor controllability of the product structure,and low proportion of active sites;On the other hand,the low ignition point of phosphorus makes the production process a certain safety hazard.Phosphate-based metal organic framework(MOFs)materials have received extensive attention in the field of energy storage because of their large specific surface area,adjustable structure,uniform pore size,and uniform distribution of metal and non-metal elements.In view of this,this article focuses on the idea of preparing metal phosphides from high-temperature pyrolysis of phosphate-based MOFs,using SEM,TEM and other technical means to analyze the morphology and structure of the material,and using electrochemical analysis methods to conduct detailed research on the performance of its supercapacitors.The main content and results are as follows:1.Ni_xP with a core-shell structure and Co_xP with a network structure were prepared by high-temperature pyrolysis of phosphate-based Ni-MOFs and Co-MOFs.Experimental results show that the particle size of Ni_xP is about 60～80 nm,and the specific capacitance of Ni_xP-800-450 reaches 870 F/g at a current density of 1 A/g.After1500 cycling,the capacitance retention rate is 71%.The specific capacitance of Co_xP-900-450 is 184 F/g.After 3000 cycling,the capacitance retention rate is still 100%.Ni_xP-800-450 and carbon cloth were respectively used as the positive electrode and negative electrode material,and they were assembled the asymmetric supercapacitor.The energy density of the supercapacitor reaches to 18.63 Wh/Kg at a current density of 1 A/g,the power density is 936.2 W/Kg.2.A phosphate-based Ni-MOFs/ZIF-8 composite was prepared by using ZIF-8 as a template,and a series of ZIF-8-Ni_xP/C materials were prepared by a high-temperature pyrolysis method.The experimental results show that the specific capacitance of ZIF-8-Ni_xP/C-950-450-26 reaches 856 F/g at a current density of 1 A/g.After 3500 cycling,the capacitance retention rate reached 97%.The introduction of ZIF-8 template can effectively increase the specific surface area of Ni_xP particles,accelerate the transfer speed of electrolyte ions in the electrode material,and improve the performance of its supercapacitor.3.The phosphate-based Ni-MOFs/CNT composite was synthesized in one step,and a series of Ni_xP/CNT materials were prepared by the high-temperature pyrolysis method.The size of Ni_xP particles obtained by this method is reduced to 15～30 nm.The electrochemical test results show that the specific capacitance of Ni_xP/CNT-5 is 1000 F/g at a current density of 1 A/g.After 6000 cycling,the capacitance retention rate remains at 100%.Ni_xP/CNT-5 and carbon cloth were respectively used as the positive electrode and negative electrode material,and they were assembled the asymmetric supercapacitor.The energy density of the supercapacitor reaches to 23.22 Wh/Kg at a current density of1 A/g,the power density is 950.1 W/Kg,which shows better super electrical performance. |
