Electrodeposition Of Transition Metal Selenide And Its Application In Asymmetric Supercapacitors

Supercapacitors are generally used in energy storage fields due to the advantages of ultra-high power density,charge/discharge efficiency,and ultra-long operate life.However,the low energy density limits its commercialization progress.On the basis of the equation:E=1/2CV²,one program is to make nano-electrode materials to increase their specific capacitance(C);the other is to assemble asymmetrical capacitor.to increase their voltage window(V).As one kind of transition metal sulfur compounds,transition metal selenides have strong metallicity and relatively high theoretical specific capacitance.In this paper,electrode materials of nickel selenide and cobalt selenide were prepared via electrochemical deposition.The influence of preparation process parameters on the morphology and electrochemical performance of electrode materials was compared and analyzed,and asymmetric supercapacitors with high energy density were assembled.The main research contents are as follows:(1)Self-supporting Ni₃Se₄ nanoparticles were successfully prepared on nickel foam substrate by different electrodeposition methods.After analysis,the electrode material prepared under the condition of-1.2 V constant potential presents a porous nanostructure and has the optimum electrochemical properties.At a charge-discharge ratio of 1 A g^-1,the mass specific capacitance is 1112 F g^-1.The capacitance of Ni₃Se₄/NF//AC asymmetric supercapacitor was over 80%after 10,000 consecutive cycles.(2)Amorphous CoSe nanoparticles were successfully prepared on nickel foam substrate by different electrodeposition methods.The results show that the electrode material prepared at a constant current of 10 m A cm^-2 presents amorphous nanoparticle structure and has the beneficial electrochemical performance.Equipped with CoSe/NF//AC asymmetric supercapacitors,and the density energetic can reach up to 39.1Wh kg^-1.There is still 91.5%coulomb efficiency,after 10,000 cycles at a charge-discharge density of 3 A g^-1.(3)Firstly,carbon nanotube arrays were grown on nickel foam collectors using a combustion method,and then cobalt selenide is electrodeposited to form a CoSe/CNTs composite electrode.The results show that the carbon nanotubes prepared under optimized conditions greatly promote the specific surface area and electrical conductivity of the electrode material.When the test charge-discharge rate was 1 A g^-1,the specific capacity of the composite was 3580 F g^-1.When the charge-discharge was 10 A g^-1,the capacity retention rate was 84.9%,which is much higher than that of directly electrodeposited CoSe electrode.The CoSe/CNTs/NF//AC asymmetric supercapacitor is assembled,and a density energetic of 43.4 Wh kg^-1 can be obtained when the power density is 800 W kg^-1.Moreover,the cycle stability of the device is very good.After10000 times of continuous charging and discharging at a current density of 2 A g^-1,it still has a capacitance retention rate of 92.7%.Two devices connected in series can continuously light up the LED for 15 minutes,which has potential application value.