Study On The Nanostructure Preparation And Electrochemical Performance Of Nickel-based Metal Phosphide

Supercapacitors have always been one of the research hotspots in the field of new energy storage,showing significant advantages of high charging-discharging power,cycle stability and environmental friendliness etc.However,the comprehensive electrochemical properties of the cathode materials need to be improved,which severely limits the application of devices.In recent years,transition metal phosphides have been proved to be effective in improving the multiplier performance of devices and broadening the application field.In this paper,a simple one-step hydrothermal method was used to synthesize Ni₁₂P₅ nanowires with high conductivity,which were used as anode materials of supercapacitors to study the electrochemical performance.The mechanism of conductivity and energy storage of Ni₁₂P₅ nanowires is analyzed by the simulation results.In addition,study on the doping of transition metals and the electrochemical properties of their products show that Ni₁₂P₅nanowires have great development potential as cathode materials of supercapacitors.Researches in this paper are summarized as follows:High porosity Ni₁₂P₅ nanowires with a width of about 20 nm were prepared by one-step hydrothermal method,and the mechanism of synthesis and regulation was analyzed with tests of different reaction time and surfactant.The results show that the phosphorus ions on the surface of red phosphorus are attracted by Hexadecyl trimethyl ammonium Bromide(CTAB)to continue overflowing,forming continuous epitaxial growth nanowires until the red phosphorus is exhausted.In addition,supercapacitors packaged with Ni₁₂P₅ nanowires as cathode materials exhibit high energy density(108.2 Wh kg^-1 at 0.896 k W kg^-1)and high rate performance(48.78 Wh kg^-1 at 8.96 k W kg^-1).Through the four-probe test of Ni₁₂P₅ nanowires,the results show that the conductivity of Ni₁₂P₅ nanowires is higher than that of most transition metal compounds(13.8 S cm^-1).Furthermore,through the simulation of the crystal structure,energy band and density of state distribution of Ni₁₂P₅ nanowires,it is shown that the crystal structure gap of Ni₁₂P₅ is large,and the distribution of energy band and density of state is concentrated near the Fermi level.This distribution is conducive to providing an efficient electronic transmission channel,which contributes to the high conductivity and magnification characteristics of the material.Ni₁₂P₅nanowires have high specific capacitance(707.2 C g^-1 at 1 A g^-1)and excellent rate performance(481.7 C g^-1 at 10 A g^-1,more than 68%of that at 1 A g^-1).The above one-step hydrothermal method was used to realize doping Ni₁₂P₅ with transition metals(Fe,Co)and researches on optimizing performance were carried out.The specific capacitance of the products after doping 0.05 mmol Fe are higher than that before doping at low current density(about 750 C g^-1 at 1 A g^-1),but the multiplier performance is reduced(specific capacitance at 10 A g^-1 is 64%of that at 1 A g^-1),while doping 0.5 mmol of ferric nitrate will cause Fe₅(PO₄)₄(OH)₃·2H₂O to appear in the product,which can reduce the redox activity.With the increase of doping ratio,the products gradually changed to Ni₂P,and its performance is always lower than Ni₁₂P₅.The results also show that the morphology of the product is changed from nanowire to sheet structure with the Co doping ratio up to 1:1.Moreover,the products after doping 1.5 mmol Co exhibit higher specific capacitance(750 C g^-1 at 1 A g^-1)and rate performance(specific capacitance at 10 A g^-1 is 70%of that at 1 A g^-1).The results show that transition metal doping has great potential to improve the properties of materials.