Ni(OH)₂ nanoflakes electrodeposited on Ni foam-supported vertically oriented graphene nanosheets for application in asymmetric supercapacitors

Highlights: • Ni(OH)₂/vertically oriented graphene nanosheets (V-GNs) was prepared. • Ni(OH)₂/V-GNs had enhanced specific capacitance, cycling reversibility and stability. • Performance of Ni(OH)₂/GNs/NF-AC asymmetric supercapacitor was studied. - Abstract: Binderless Ni(OH)₂ nanoflakes grown on Ni foam (NF)-supported vertically oriented graphene nanosheets (V-GNs) has been fabricated as a positive electrode material for asymmetric supercapacitor (ASC), coupled with activated carbon (AC) as a counter electrode material. The introduction of V-GNs leads to dense growth of nanocrystalline β-Ni(OH)₂ that is confirmed by X-ray diffraction, transmission electron microscopic and scanning electron microscopic analyses. The electrochemical performances of the Ni(OH)₂/GNs/NF electrode are characterized by cyclic voltammetry and charge–discharge tests, which exhibit high specific capacitance of 2215 F g⁻¹ at a scan current density of 2.3 A g⁻¹, enhanced cycling stability and high rate capability. The Ni(OH)₂/GNs/NF-AC-based ASC can achieve a cell voltage of 1.4 V and a specific energy density of 11.11 Wh kg⁻¹ at 0.5 mA cm⁻² with a nearly 100% coulombic efficiency at room temperature