Electrochemical supercapacitor and water splitting electrocatalysis applications of self-grown amorphous Ni(OH) 2 nanosponge-balls

A promising self-growth (caused by surface modification due to oxidation/reduction) approach for the synthesis of nickel hydroxide (Ni(OH) 2 ) nanosponge-balls on Ni-foam (NiF) electrode surface as a multifunctional electrode material for applications like energy storage and electrocatalysis is explored. Extensive physical and chemical characterizations carried out through advanced analytical techniques reveal the distinctive nanosponge-ball-type surface morphology of the Ni(OH) 2 @NiF, confirming the successful hydroxilation of the NiF electrode surface to Ni(OH) 2 @NiF. In terms of energy storage, on using Ni(OH) 2 @NiF electrode as a half-cell electrode material, an impressive specific capacitance of 803.08 F.g -1 at a current density of 6 mA.cm -2 is obtained, highlighting its energy storage potentiality. When integrated it into an asymmetric supercapacitor (ASC) alongside Bi 2 O 3 @NiF through the Ni(OH) 2 @NiF//Bi 2 O 3 @NiF, a remarkable power density of 2250 Wkg -1 at an energy density of 96.5 Wh kg -1 with  exceptional cycling stability of 83.33 % even after 3500 cycles is confirmed. Moreover, on using the Ni(OH) 2 @NiF electrode as electrocatalyst, a robust activity with ultra-low overpotentials of 240 mV and 158 mV and Tafel slopes 62 mV dec ‑1 and 127 mV dec ‑1 are obtained for the oxygen evolution reaction and the hydrogen evolution reaction activities in a 6 M KOH electrolyte solution at a current density of 10 mA cm -2, respectively, suggesting importance of the developed Ni(OH) 2 @NiF electrode material in both energy storage and water splitting, into hydrogen and oxygen, applications.