Preparation And Electrochemical Properties Of NiCoFe Layered Double Hydroxide-based Composites

With the rapid development of current world economy,traditional fossil energy and water resources have been close to shortage,which makes the development and research of renewable energy storage devices urgent.Since electrode materials tend to be the key to energy storage devices,it is particularly important to develop electrode materials with excellent performance.Layered double hydroxides（LDH）are widely used in the research of electrode materials because of their great pseudocapacitance,excellent layered structure and low cost.However,due to the defects of easy lamellar agglomeration and poor electrical conductivity,it can usually be combined with other materials to improve its electrochemical and electrosorption properties.In this paper,NiCoFe layered double hydroxide/reduced graphene oxide composites（NCF-LDH/r GO-x）were prepared by hydrothermal synthesis,which allowed LDH nanosheets to be uniformly dispersed on graphene sheets,thus suppressing the agglomeration of LDH sheets and significantly increasing the specific surface area of the material.Moreover,the conductivity of the composites was significantly enhanced due to the doping of graphene.In addition,the carbonate-doped NiCoFe layered double hydroxides（NCFC-LDH-x）were prepared by chemical co-precipitation,this material allowed the carbonate insert into the LDH sheet layer,thereby increasing the specific surface area of the material and its contact area with the electrolyte.Finally,the electrochemical and electrosorption properties of these materials were studied and analyzed as follows:1.Firstly,NiCoFe layered double hydroxides（NCF-LDH-x）were prepared by hydrothermal synthesis,and then NCF-LDH-0.15 had the most excellent electrochemical performance by means of morphological characterization and electrochemical performance characterization,its specific capacitance reached 752 F g^-1 at 1 m V s^-1.In addition,the capacitance retention reached 86.3%at 5 A g^-1 after 5000 cycles.The NCF-LDH/r GO-x composite was subsequently combined with graphene by hydrothermal synthesis.The electrochemical performance test showed that NCF-LDH/r GO-0.15 had the best electrochemical performance.its specific capacitance reached 1652 F g^-1 at 1m V s^-1,which was 119%higher than NCF-LDH-0.15.In addition,its capacitance retention rate reached 91.7%at 5 A g^-1 after 5000 cycles.Then,the electrosorption performance of NCF-LDH-0.15 and NCF-LDH/r GO-0.15 was tested.At the constant voltage of 1.2 V,the flow rate of 20 m L min^-1 and the initial Na Cl concentration of 800 mg L^-1,the electrosorption capacity of NCF-LDH/r GO-0.15 was 86.02 mg g^-1,which was nearly 31%higher than NCF-LDH-0.15(65.59 mg g^-1).In addition,the maximum adsorption rate of NCF-LDH/r GO-0.15 reached 2.10 mg g^-1 s^-1 at the Na Cl concentration of 1600 mg m L^-1,which was about 41%higher than NCF-LDH-0.15(1.49 mg g^-1 s^-1).2.Secondly,Carbonate-doped NiCoFe layered double hydroxides（NCFC-LDH-x）were prepared by the chemical co-precipitation method.The electrochemical performance test showed that NCFC-LDH-0.15 had the best electrochemical performance,and its specific capacitance reached 2056 F g^-1 at1 m V s^-1,which was about 173%higher than NCF-LDH-0.15.In addition,the capacitance retention reached 89.1%at 5 A g^-1 after 5000 cycles.Then,NCFC-LDH-0.15 was tested for electrosorption performance and compared with NCF-LDH-0.15 for analysis.Under the test conditions of 1.2 V,flow rate of 20 m L min^-1 and initial Na Cl concentration of 800 mg L^-1,the equilibrium electrosorption capacity of NCFC-LDH-0.15 was 76.43 mg g^-1,which was nearly 17%higher than NCF-LDH-0.15(65.59 mg g^-1).In addition,the maximum adsorption rate of NCF-LDH/r GO-0.15 reached 1.65 mg g^-1 s^-1 at the Na Cl concentration of 1600 mg m L^-1,which was nearly 11%higher than NCF-LDH-0.15(1.49 mg g^-1 s^-1).