Superior supercapacitance exhibited by acid insoluble Ni(OH)2 in the form of its nanocomposite with rGO

Abstract

The solubility of Ni(OH)<inf>2</inf> in acids was been the major impediment that has been preventing the usage of acid electrolytes like 1 M H<inf>2</inf>SO<inf>4</inf> in supercapacitors and batteries that contain Ni(OH)<inf>2</inf> as electrode material. This impediment is successfully removed and impressive energy storage characters were achieved from an electrode made up of Ni(OH)<inf>2</inf> in the presence of acid electrolyte of 1 M H<inf>2</inf>SO<inf>4.</inf> This acid insoluble form of Ni(OH)<inf>2</inf> was achieved by synthesizing it in situ in the presence of graphene oxide by chemical reduction method to produce the stable nanocomposite of reduced graphene oxide (rGO) and Ni(OH)<inf>2</inf>. The insolubility of Ni(OH)<inf>2</inf> in 1 M H<inf>2</inf>SO<inf>4</inf> was carefully studied for nearly six months and proved to be a factual observation. Remarkably, the rGO/Ni(OH)<inf>2</inf> composite exhibited the better energy storage performance in the presence of 1 M H<inf>2</inf>SO<inf>4</inf> in relation with conventional methods that involve basic electrolytes like NaOH and KOH for Ni(OH)<inf>2</inf>. The supercapacitor containing rGO/Ni(OH)<inf>2</inf> composite and 1 M H<inf>2</inf>SO<inf>4</inf>, was stable in storing and delivering the energy without deterioration up to 31,500 cycles, with an uniqueness of increase in energy storage with increase in cycles of energy storage and delivery. Remarkably, two type of faradaic processes are observed to be contributing to the total energy storage of Ni(OH)<inf>2</inf>, of which one is unprecedented. The superior specific energy (E) and specific capacitance (C<inf>s</inf>) achieved are 130.7175 W h kg−1 (comparable with Li-ion batteries of 3 V) and 653.5947 F g−1 at 1 A g−1. This superior C<inf>s</inf> is higher than the theoretical C<inf>s</inf> expected from this composite for this specific composition (rGO33.33 % and Ni(OH)<inf>2</inf> 66.66 %) (1571 F g−1) and higher than the theoretical C<inf>s</inf> of Ni(OH)<inf>2</inf> (2082 F g−1). It is expected that this study would be an inevitable attraction and take the applicability of Ni(OH)<inf>2</inf> to higher level and make it one of the meritorious materials for future energy storage. © 2022 Elsevier Ltd