Synthesis And Electrochemical Performance Of Nickel Cobalt Pseudocapacitor

Supercapacitor is a new type energy storage device with the advantages of high power density, long cycle life, and no pollution. Supercapacitors have many potential applications in transportation, electrical devices and so on. Generally, to obtain excellent electrochemical performance, electrode materials are required to possess these merits, such as rich redox reactions, huge surface area and high electrical conductivity. Binary materials, like NiCo2O4、NiCo2S4, have aroused great interest because they own the above-mentioned impressive properties. Rich redox reactions ensure the high capacitance, high surface area and electrical conductivity guarantee electrons and ions rapid transport and transfer, which indicate excellent cycling performance and rate capability. Moreover, it is important to avoid the usage of polymer binder, which could greatly hinder the diffusion of electrolyte.In this work, a facile strategy is developed to synthesize Nickel-Cobalt hydroxide microspheres electrodepositioned on NiCo2O4 nanowire arrays which were grown on Ni foam directly as a binder-free electrode. The morphology of (Ni-Co)(OH)2 microspheres changes with the electrodeposition time. According to the experiment results, the pore size reaches the maximum and the electrochemical performances achieve the best when the electrodeposition time is 10 min. The as-prepared hybrid electrode delivers excellent performance of 6 F cm-2 at the current density of 2 mA cm-2 and the corresponding specific capacitance is 1132 F g-1. The capacitance could retain 90% after 2000 charging-discharging cycles.We also synthesized NiCo2S4/Co9S8/Ni hybrid electrode material through two-step hydrothermal. According to the results of the repeated charging/discharging measurement, its capacitance could increase to 314% of the initial value after the first 5000 cycles due to a progressive activation. The highest areal specific capacitance could reach 8.08 F cm-2 and the corresponding mass specific capacitance was 2068 F g-1. However, then the capacitance would decrease dramatically. After investigating the causes of the decline and extending the voltage range, the capacitance could increase again.