Synthesis Of Self-supported Ni-based Nanoarrays And Their Application In Supercapacitor

Supercapacitors（SCs）have become a focus in the field of materials science and energy storage due to their long cycle life and high power density.In the system,the electrode material is undoubtedly one of the very important components in determining the performance of the overall device.Therefore,the development of new electrode materials with excellent electrochemical properties plays an important role in the practical application of supercapacitors.Nickel-based materials with good thermal and chemical stabilities,high electrochemical activity and low cost have demonstrated great potential for pseudocapacitor application.Since pseudocapacitors rely on fast faradic reactions to store charges,they require the electrode material to have high electrical conductivity in order for fast charge transfer during these redox reactions.However,nickel-based compounds such as hydroxides/sulfides/phosphides are semiconductors in nature which have intrinsically low conductivities,resulting in a lower actual capacitance.In order to overcome the above problem,a series of self-supported nickel-based nanoarray materials with excellent performance were synthesized and applied in supercapacitor.The main research works are as follows:（1）Self-supported urchin-like Ni₃S₂ nanoparticles were successfully synthesized on a nickel foam substrate by a one-pot hydrothermal method.An asymmetric supercapacitor（ASC）was assembled with the sample as the cathode and activated carbon（AC）as the anode,and the device manifested an areal capacitance of 1.26 F cm^-2 at a current rate of 2 mA cm^-2.In addition,this ASC was capable of lighting up 8 red light-emitting diodes（LEDs）.（2）Ni₂P@Carbon nanowires were prepared on nickel foam by two-step method including a hydrothermal synthesis followed by a gaseous phosphorization.It was discovered that the average molecular weight of the polyvinylpyrrolidone（PVP）used in the synthesis and the phosphorization temperature have significant effects on the morphology and electrochemical properties of the final product.The results showed that the asymmetric supercapacitor assembled with the Ni₂P@Carbon sample prepared using PVP-10k and phosphorized at 300℃ delivered a capacitance of 3.7 F cm^-2 at a current density of 2 mA cm^-2.The ASC could reach a high energy density of about 122.8 Wh kg^-1 at a power density of 150 W kg^-1.Besides,it also had the ability to easily power up 16red LEDs.Therefore,it is of great application value.（3）NiCo alloy was first synthesized on nickel foam by a simple electrodeposition method,which was then phosphorized to obtain a self-supported NiCoP sample with the surface covered with nanopyramid arrays.The asymmetric supercapacitor assembled with this self-supported NiCoP as the active material can achieve a capacitance of 10.3 F cm^-2 at 2 mA cm^-2.After 3000 cycles at a current density of 25 mA cm^-2,the capacitance retention is almost 100%.