Research On Transition Metal Selenide/phosphide Nanomaterials For High Performance Supercapacitors

As an important energy storage device,supercapacitors have attracted much attention due to their advantages of high power density,ultrahigh output power,Iong cycle life,fast charge/discharge process and safety.However,the energy density of commercial supercapacitors is lower than that of fuel cells and lithium ion batteries none the less,which seriously limits their further application in various fields.According to the energy density equation(E=1/2 CV2),it can be seen that to increase the energy density of the supercapacitors,not only the electrode material having a large capacitance but also the operating voltage window of the device needs to be widened.Therefore,this paper designs and prepares transition metal selenide/phosphide and composite materials as electrode materials by analyzing the factors affecting the performance of supercapacitors.After matching suitable electrolytes,new types of asymmetric supercapacitors are constructed to improve the energy density.The main research contents and results are as follows:1.Using nickel foam as nickel precursor and nucleation frame,a simple hydrothermal method was used to design and prepare a uniform vertical growth of NiSe@MoSe2 nanosheets,The NiSe@MoSe2 electrode exhibit high specific capacitance of 128.2 mAh g-1 at a current density of 1 A g-1.In addition,porous interconnected N-PMCN negative electrode materials with great nitrogen-doped(9%)and high specific capacitance(231 F g-1)were prepared by chemical activation(CaCl2)and urea as nitrogen source.Based on the unique structure and excellent electrochemical properties,a novel NiSe@MoSe2//N-PMCN ASC is assembled based on NiSe@MoSe2 nanosheets positive electrode and N-PMCN nanosheets negative electrode,which with a maximum operating voltage of 1.65 V has demonstrated a high energy density of 32.6 Wh kg'1 at a power density of 415 W kg*1,and outstanding cycling stability with 91.4%capacitance retention after 5000 cycles in aqueous electrolyte.2.A simple one-step hydrothermal method was used to design and prepare a novel NCSe microsphere material with high specific capacity without adding any template and surfactant.Its exhibit maximum specific capacity of 128.2 mAh g-1 at a current density of 0.5 A g-1.The same method was used to prepare ZnSe@BiSe nanosheets.As a negative electrode material,ZnSe@BiSe has a specific capacity of 132 mAh g-1 at a current density of 0.5 A g-1,and even when the current density is expanded by 20 times,the specific capacity still remained 75 mAh g-1.The NCSe//ZnSe@BiSe ASC operates with a voltage range of 0-1.6 V and reached a high energy density of 34.4 Wh kg-1 at a power density of 373 W kg-1.Besides,the device demonstrations a good cycling performance with capacitance retention of 70%after 2000 cycles.3.Nickel nitrate assisted polymer(gelatin)in-situ substrate-free chemical blowing pyrolysis and subsequent low-temperature phosphorization method is used to prepare the nickel phosphide nanoparticles self-inlaid carbon nanosheet frameworks(Ni2P-CNFs).The as-fabricated NbP-CNFs used as the positive electrode for supercapacitor shows high specific capacity of 145 mAh g-1 at a current density of 0.5 A g-1.To highlight,a novel aqueous asymmetric supercapacitor based on the Ni2P-CNFs positive and CNFs negative electrodes is assembled,achieving a large operating voltage of 1.65 V,high energy density of 42 Wh kg"1 at a power density of 413 W kg'1,and outstanding cycling stability with 88%capacity retention after 6000 cycles.This study provides a top-down strategy for designing the integrated and robust metallic compounds self-decorated porous carbon nanomaterials and may inspire new development for electrochemical energy storage and conversion.