Structural Control And Electrochemical Properties Of Ni-based Hydroxide And Sulfide Composites

Due to the depletion of fossil energy and the deterioration of environment,the exploitation and utilization of clean and renewable energy has become the primary task of all countries in the world.Nevertheless,there are intermittent and regional restrictions in the development of new energy in the practical application process.Therefore,the exploitation of new energy conversion and storage equipment is crucial for the utilize of renewable energy.As one of the most common storage devices,due to the advantages of high specific capacitance,high power density and reliable cycle stability,supercapacitors are regarded as an energy storage equipment with great application value.As the most crucial part of supercapacitor,electrode materials have been extensively researched.Among them,nickel-based hydroxide and sulfide are considered to be the most promising electrode materials attributed to its high specific capacitance,good redox activity,low cost and environmental friendliness.However,there exist still some problems such as low conductivity and poor stability in application.In order to solve these problems,researchers have done a lot of efforts.In this paper,the Ni(OH)2 electrode was firstly prepared by hydrothermal method,and then the Ni-Co LDHs electrode was synthesized by low temperature co-precipitation method.In addition,using Ni(OH)2 as the precursor,the sulfide and composite materials were obtained by further hydrothermal vulcanization treatment,which further improved the electrochemical performance of the materials.(1)The self-assembled flower-like nickel hydroxide was obtained by one-step hydrothermal method.Herein,the influence of(NH4)6Mo7024·4H2O as complexing agent on the morphology and performance of the prepared nickel hydroxide electrode material was mainly studied.The results show that with the increase of the amount of(NH4)6Mo7O24·4H2O,the morphology of the prepared electrode material changes from a hexagonal sheet to a flower-like structure,eventually,due to the massive addition of(NH4)6Mo7O24·4H2O,the flower-like structure was damaged and collapsed.When the molar ratio of Ni(Ac)2-4H2O to(NH4)6Mo7O24-4H2O is 8:1,the Ni(OH)2 electrode materials posses the best electrochemical properties,showing an ultrahigh specific capacitance,excellent rate performance and prominent multiplier performance.(2)The Ni-Co LDHs were prepared by low temperature co-precipitation method.By changing the molar ratio of Ni2+to Co2+in the reaction solution,Ni-Co LDHs materials with different compositions were obtained.Results show that when the molar ratio of Ni2+to Co2+is 4:1,the small size of flower structure was obtained with higher specific surface area.Due to the unique morphology of electrode materials and high specific surface area(254.5 m2 g-1),the specific capacitance of Ni-Co LDHs were respectively 1495,1305 and 1142 F g-1 at the current density of 1,5 and 10.A g-1,which possess high specific capacitance and good multiplier performance.(3)The flower-like nickel hydroxide obtained in the first step was used as the precursor,which was further treated by hydrothermal vulcanization to obtain more excellent electrode materials.In the case of NaBH4 and N2H4·H2O as reducing agents,the effects of sulfurization time,the molar ratio of Ni2+to S2-and sulfurization temperature on the structure and properties of electrode materials were investigated.When NaBH4 is used as the reducing agent,the synthesized material is a mixture of?-Ni(OH)2.Ni3S2,?-NiS,and Ni3S4 at the sulfurization time,the molar ratio of Ni2+to S2-and sulfurization temperature of 12 h,1:1 and 120?,respectively,which possesses a three-dimensional porous composite structure of nanoparticles and nanosheets.Due to the heterostructure and more electron transport channels,the specific capacitance of the electrode material is respectively 1278 Fg-1 and 714.6 F g-1 at the current density of 1A g-1 and 10 A g-1,which shows good electrochemical performance.When N2H4·H2O is used as the reducing agent,the obtained material is the pure phase Ni0.96S at the sulfurization time,the molar ratio of Ni to S and sulfurization temperature were 12 h,1:2 and 120?,resectively,which possesses a three-dimensional structure assembled by nanoparticles.Due to its high conductivity and characteristic microstructure,the specific capacitance reaches 1657.5 Fg-1 at the current density of 1 A g-1 and has excellent rate performance and cycling performance.As electrode material of supercapacitor,it has potential application prospect.