Study On Chemical Modification Of Nickel Based Double Metal Hydroxide And Improvement Of Pseudocapacitance Performance

Supercapacitors are a kind of potential energy storage device with the characteristics of high power density and high cycle stability,etc.However,the energy density of supercapacitors is low and cannot meet the needs of practical applications.The energy density of a supercapacitor depends on the electrode material.Ni（OH）₂ is a Pseudo-capacitance material with high theoretical specific capacitance,environmental friendliness and easy modification.This article will focus on Nickel-based hydroxide,using adding Co,phosphating and structural design methods to improve the electrochemical performance of hydroxides.（1）Using hydrothermal method,Nickel and cobalt hydroxides with different Ni/Coratios formed directly on the foamed nickel.These nickel-cobalt hydroxides with different Ni/Coratios all present nanoplate morphology.The addition of Cocan significantly reduce the charge transfer resistance of Ni（OH）₂ and improve the specific capacitance.The product（NiCoLDH）prepared with Ni（NO₃）₂ and Co（NO₃）₂ at a ratio of 3:1 has the best electrochemical performance.Thanks to the bimetallic synergistic effect and open pore structure,NiCo-3-1 has the highest specific capacitance(967.7 F g^-1,1 A g^-1)and cycling stability with 70.2%capacitance retention after 2000 cycles at20 A g^-1.（2）NiCoLDH is chemically converted into phosphides and oxides through phosphating and oxidation and the conductivity is increased.But the LDH derivated oxide specific capacitance is lower than LDH due to the difficulty of ion transport in the oxide.LDH derivated phosphides have metallic characteristics and exhibit excellent electrochemical performance.The specific capacitance of NiCoP(1635.6 F g^-1,2 A g^-1)is significantly higher than that of NiCoLDH;the rate performance has also been improved(73.6%capacitance retention under 25 A g^-1).Besides,two series-connected asymmetric supercapacitors constructed of NiCoP and reduced graphene can successfully light up an LED light.（3）Construct CoP@NiCoP composite nano-arrays in situ on the nickel foam to improve the three-dimensional space utilization rate of the electrode surface and improve electrochemical performance.Benifited form the excellent properties of phosphides and unique spatial structure,the specific capacitance of CoP@NiCoP(1911.6 F g^-1,2 A g^-1)is further improved than the simple structure of NiCoP in Chapter4.CoP@NiCoP shows outstanding rate performance(61.7%capacitance retention even at 25 A g^-1)and good cycling stability(73.3%capacitance retention after 1000 cycles at25 A g^-1).In addition,an asymmetric supercapacitor（ASC）consisted by CoP@NiCoP and the Fe₂O₃ derivated from Fe-based MOF delivers a satisfactory energy density of37.2 Wh kg^-1 at the corresponding power density of 875 W kg^-1.In this paper,the electrochemical performance of nickel-based hydroxides is improved by means of metal doping,phase transition and structure construction.Good electrochemical performance promotes the application of nickel-based hydroxides in the field of supercapacitors.