Growth of aluminum-substituted nickel hydroxide nanoflakes on nickel foam with ultrahigh specific capacitance at high current density

Aluminum-substituted α-Ni(OH)₂ nanoflakes grown on nickel foam as electrode for application in supercapacitor were synthesized in the presence of urea through a hydrothermal route. The as-synthesized nanoflakes with ultra-thin thickness of about 12 nm presented isolated state on Nickel foam. The sample substituted with 9.8 % Al showed the highest specific capacitance of 3637 F g⁻¹ at scan rate of 5 mV s⁻¹ in 3 M KOH aqueous solution. This sample also kept high specific capacitance of 1142 F g⁻¹ at high charge and discharge current density of 32 A g⁻¹. The excellent electrochemical performance can be ascribed to the thin thickness and isolated state of these nanoflakes. The two characteristics of nanoflakes guaranteed their full contact with electrolyte during the electrochemical reactions, therefore leading to the instant and full utilization of electroactive material. During stability test, the capacitance of material still remained 81 % after 2000 charge–discharge cycles. These results demonstrated that the nanoflakes could be applied as high performance electrode material in supercapacitor.