Electrochemical studies of Ni(OH)2, NiO, and Ni3S2 nanostructures on Ni-foam toward binder-free positive electrode for hybrid supercapacitor application

Self-supported, porous, and binder-free hexagonal nanosheets of Ni(OH)(2) [HS-Ni(OH)(2)], hexagonal nanosheets of NiO [HS-NiO], and hexagonal-nanosheet/ nanoporous-grain like Ni3S2 [HSNG-Ni3S2] were successfully grown on 3D Ni-foam at different stages of hydrothermal synthesis using Ni-foam as a precursor source for the cost-effective fabrication of positive electrode for hybrid supercapacitor (SC) application. Comparative analysis revealed that the HSNG-Ni3S2 exhibited a maximum areal capacitance of 1286 mF cm(-2) at 0.5 mA cm(-2), far more than the 217 mF cm(-2) of HS-NiO and 129 mF cm(-2) of HS-Ni(OH)(2), with remarkable capacitance retention of 97% for 5000 charge-discharge cycles. The porous binder-free electrode design, improved interfacial conductivity, and easy ionic diffusion are responsible for the remarkable performance of HSNG-Ni3S2. Furthermore, the aqueous alkaline hybrid SC assembled by HSNG-Ni3S2 as a positive electrode with activated carbon as a negative electrode delivered a maximum areal capacitance of 225.4 mF cm(-2) at 1 mA cm(-2) with remarkable stability up to 92.2% for 5000 charge-discharge cycles. This study presents insightful electrochemical properties of binder-free designed Ni-based Ni(OH)(2), NiO, and Ni3S2 electrodes for low-cost and environmental-friendly energy storage systems.