Preparation And Modification Of Nickel Phosphide Electrode Materials

The application of supercapacitors is limited due to the low energy density and small working window.The characteristics of the electrode material itself will have a great influence on the electrochemical performance of the supercapacitor.Transition metal phosphides can provide high energy density and specific capacitance due to strong Faraday pseudocapacitance reactions.In addition,transition metal phosphides have higher conductivity due to metalloid properties,and are very promising electrode materials in the field of supercapacitors.However,the electrochemical performance of electrode materials is not only affected by the morphology,structure and characteristics of the material,but also by external conditions.In this work,Ni₂P with a three-dimensional network structure loaded on nickel foam was prepared under different reaction conditions to improve the specific capacitance and cycle stability of the supercapacitor electrode material.The conductivity,specific capacitance and cycle stability of the electrode material were improved by composite modification with MXene material.The specific research contents are as follows:（1）Using Ni（NO₃）₃·9H₂O as nickel source,Na H₂PO₂ as phosphorus source,and nickel foam as substrate,Ni₂P growing on the nickel foam surface was successfully prepared by hydrothermal phosphating method.XRD,SEM and EDS were used to characterize the structural morphology of the materials.The results show that Ni₂P grows uniformly on the nickel foam,showing a three-dimensional network structure,which makes the material have more active sites and can fully contact with the electrolyte.The electrochemical performance test results show that the specific capacity of the electrode material reaches 1512 F g^-1 when the voltage range is 0-0.5 V,the electrolyte is 1 mol·L^-1 KOH and the current density is 0.5 A g^-1.After 200 cycles,the capacity retention rate is 76%.The supercapacitor assembled by Ni₂P/NF has been tested.It has high magnification performance.After 200 cycles,the capacity retention rate is 79%,showing good cycle stability.（2）In order to explore the effects of different phosphating temperature,phosphating time and phosphorus-nickel ratio on the properties of nickel phosphide,Ni₂P/NF was prepared by the same method at different phosphating temperatures（300°C,350°C,400°C,450°C）,different phosphating times（1 h,2 h,3 h）and different phosphorus-nickel ratios（7.5:1、8:1,8.5:1,9:1）.The structural morphology characterization and electrochemical performance tests of materials prepared under different conditions showed that high temperature will destroy the surface nanosheet-like three-dimensional network structure,and the collapse of the structure will lead to accumulation,which is not conducive to the penetration and ion transfer of the electrolyte,so that the specific capacity is greatly reduced;The prolongation of phosphating time will increase the crystallinity of Ni₂P,but it will also affect the surface morphology of phosphide,and the long phosphating time leads to serious material accumulation,and the porosity is greatly reduced,which seriously affects the specific capacity of nickel phosphide;With the increase of phosphorus content,nickel phosphide gradually changed from pure Ni₂P to a mixture of Ni P and Ni₂P,and the crystallinity increased.The nanosheets grow laterally and accumulate,the specific surface area of the active substance gradually decreases,and the porosity decreases,resulting in a decrease in the specific capacity.（3）Multilayer Ti₃C₂T_x MXene was prepared by Li F+HCl etching Ti₃Al C₂ as a substrate,and precursors 3Ni（OH）₂·2H₂O and Ni₂P were introduced into the MXene layer and surface by hydrothermal phosphating method to prepare precursors 3Ni（OH）₂·2H₂O@MXene composites Ni₂P@MXene composites.The structural morphology characterization of the prepared composites showed that the precursors 3Ni（OH）₂·2H₂O and Ni₂P were successfully introduced into the surface and interlayer of MXene,and the layer spacing of MXene was increased,thereby providing greater storage and transport space for ions,which was conducive to the penetration of electrolyte.The electrochemical performance of the composite was tested,and the results showed that the specific capacitance of the best precursor 3Ni（OH）₂·2H₂O@MXene composite is 621 F g^-1,which is 49%higher than the specific capacitance of 3Ni（OH）₂·2H₂O;The specific capacitance of the best performing Ni₂P@MXene composite is 1756 F g^-1,which is 23%higher than the specific capacitance of Ni₂P.Compared with 3Ni（OH）₂·2H₂O@MXene composite materials,the specific capacity growth rate is lower,which may be caused by structural collapse caused by phosphating.In the impedance test,the intrinsic resistance is 1.22Ω,which is higher than that of Ni₂P of 1.28Ω,indicating that the conductivity of the material is improved,and the cyclic stability is also 96.6%higher than Ni₂P.