Preparation Of Transition Metal Composites And Their Application In Supercapacitor

The accumulation and storage of energy is one of the most important topics of our time.Global carbon reduction targets can be met by beefing up energy storage.Solar and wind energy,due to their variable sources,require efficient storage to ensure consistent supply.Supercapacitors（SCs）,also known as electrochemical capacitors,have been identified as a key part of the solution to this problem.However,their energy density is relatively low,so it is urgent to further study the development of high performance supercapacitors so that they can be used for efficient large capacity power storage.This has a great relationship with the structure and electrochemical performance of the electrode material itself.Therefore,the exploration and preparation of electrode materials with high quality structure plays a key role in improving the electrochemical performance of SCs.In this paper,core-shell Cu（OH）₂@Ni（OH）₂nanocomposites were prepared by in situ chemical oxidation reaction and chemical bath deposition.In addition,multilayer Ni（OH）₂ nanosheets（MgCo₂O₄@Ni（OH）₂/NF）were prepared on the surface of Nickel-based MgCo₂O₄ nanowires by hydrothermal method and calcination method and used as electrode materials for supercapacitors.Specific methods and steps are as follows:1.A novel core-shell hybrid electrode material of nickel hydroxide（Ni（OH）₂）supported on copper hydroxide nanorod arrays（Cu（OH）₂ NAs）,which is constructed on the copper foam（CF）as the substrate by in situ chemical oxidation reaction accompanied by chemical bath deposition.As a result,it has been found that the pre-fabricated Cu（OH）₂@Ni（OH）₂ electrode has revealed a remarkable areal capacitance of 9.27 F cm^-2 and good cycling performance（retained 92.38%after 6000 cycles）compared to its counterpart Cu（OH）₂ nanorods（88.57%）.Additionally,the Cu（OH）₂@Ni（OH）₂materials,as a positive electrode,can also be employed to assemble a hybrid supercapacitor（HSC）while activated carbon（AC）has been chosen as the negative electrode.As a result,the constructed HSC device with the desired working voltage of0-1.5 V can light up the light emitting diode（LED）indicator,proving the potential practicability of the pre-fabricated HSC device.2.MgCo₂O₄@Ni（OH）₂（MC@NH）nanocomposites on nickel foam（NF）were synthesized by facile two step techniques.The first one is hydrothermal reaction through which precursor of MgCo₂O₄ nanowires are prepared,while the second one is a calcination process,through which Ni（OH）₂ nanosheets are loaded on the surface of MgCo₂O₄ nanowires to yield the core-shell structured MgCo₂O₄@Ni（OH）₂（MC@NH）nanocomposites on nickel foam（NF）.This special core-shell structure gifts the nanocomposite with enormous active sites which can accelerate the REDOX reaction.It also completely gets rid of the use of binder and other conductive agent,thus largely reduces the resistance.The specific capacitance of the MC@NH/NF composite is 1520F g^-1 at 1 A g^-1,which is better than those of the individual MgCo₂O₄ electrode materials and Ni（OH）₂ electrode materials owning to synergistic effect among them.To explore the practical application of the device,a quasi-solid state asymmetric supercapacitor（ASC）is assembled with the MC@NH/NF and activated carbon（the AC）as positive electrode and negative electrode.At 10 A g^-1 current density,capacitance and coulombic efficiency can still be maintained at 97.21%and 98.16%after 12000 cycles,respectively,evidencing the good operation stability of the as-assembled MC@NH/NF//AC-ASC device.