Electrochemical studies of Ni(OH) ₂ , NiO, and Ni ₃ S ₂ nanostructures on Ni‐foam toward binder‐free positive electrode for hybrid supercapacitor application

Abstract

Summary 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.