Preparation And Supercapacitive Properties Of Nickel-cobalt Based Selenides

As a new energy storage device,supercapacitor which has been widely used in many fields has aroused great research interest of many researchers because of its high power density,long cycle life,fast charge-discharge and green environmental protection.In general,in order to improve the electrochemical performance,electrode materials are required to possess these merits,such as high electrochemical activity,large specific surface area and good electrical conductivity.Ni-Co selenides have drawn particular attention because they are just in line with the above-mentioned impressive properties.The electroconductibility of these materials is high,in which the transition metal elements can provide Faraday reaction,improving the specific capacity,and the synergistic effect of Ni/Co ions also benefit to further enhance the electrochemical performance.In addition,besides the traditional three electrode test methods,the assembly of asymmetric supercapacitors can not only improve the energy density,but also help to evaluate the practical value of the synthesized electrode materials.In this work,we used Ni-Co selenides as the research object,and successfully synthesized a series of new and hierarchical structured electroactive materials which were used as electrode materials for supercapacitor,exhibited excellent and tunable electrochemical performance.The details are summarized briefly as follows:Firstly,hierarchical nanosheet-based Ni Se microspheres were successfully fabricated using a facile one-step solvothermal method,in which ethylenediamine and N,N-dimethylformamide?DMF?were used as the mixed solvent.The evolutionof this morphology and the effects of cetyltrimethylammonium bromide were also explored by controlling the reaction time and the amount of surfactant respectively.The as-synthesized Ni Se microspheres exhibited the ideal performance when employed as the electrode materials of supercapacitors.This study provides a valuable reference for the preparation of nickel selenides electrode materials with special morphologies.Secondly,large-scale uniform Ni Se nanowires in situ grown on nickel foam?NF?were prepared by a facile solvothermal route.Next,a series of ternary materials possessing different proportions of Ni and Co were fabricated by a Co-exchange method using the Ni@Ni Se material as a template,which effectively achieved morphology inheritance from the parent material.To explore the electrochemical performance,all the synthetic materials were assembled into asymmetric supercapacitor devices.Among which,the Ni@Ni_0.8Co_0.2Se//active carbon?AC?device exhibited a high specific capacitance of 86 F/g at a current density of 1 A/g and an excellent cycling stability with virtually no decrease in capacitance after 2000 continuous charge-discharge cycles.This device still delivered an energy density of17 Wh/kg even at a high power density of 1526.8 W/kg.These superior electrochemical properties of Ni@Ni_0.8Co_0.2Se as an electrode material for supercapacitor devices confirmed the synergistic effect between Co and Ni ions,suggesting their potential application in the field of energy storage.At last,a hollow porous biomass carbon material was used as a substrate,and the acanthosphere-like Ni-Co precursors which were uniformly distributed on the substrate were successfully synthesized using a facile solvothermal method,in which deionized water and ethanol were used as the mixed solvent and nickel nitrate,cobalt nitrate and urea as reactants.Then,component-controllable?Ni,Co?Se_2?1-x?S_2x?0 ? x? 1?acanthospheres were perfectly fabricated through a simple chemical vapor deposition method.These composites,which were directly used as electrode materials for binder-free supercapacitors,exhibit excellent electrochemical properties and other different characteristics.For example,Ni-Co-S/CTs had the highest specific capacity,while Ni-Co-Se/CTs had the best rate performance.