Role of different aliphatic diols on the structural and morphological aspects of Ni(OH)2 synthesized by thermal decomposition via refluxing method and their effect on charge storage properties

Abstract

Batches of nanoscale layered Ni(OH)2 are synthesized by a simple thermal decomposition at 180 °C via refluxing in the presence of different aliphatic diols, e.g., 1,2–ethanediol, 1,4–butanediol and 1,6–hexanediol as solvent and also as intercalating agent, without using any precipitating agent or any hydrolyzing agent. The respective batches are named as [Ni(OH)2]ED [Ni(OH)2]BD and [Ni(OH)2]HD. The α–phase of Ni(OH)2 consisting of aggregation of non-uniform spherical morphology is formed in [Ni(OH)2]ED. While a mixture of α– and β–Ni(OH)2 phases with flaky morphology is formed in both [Ni(OH)2]BD and [Ni(OH)2]HD. The molecular sizes of the intercalating aliphatic diols impacted on increasing interlayer distances of Ni(OH)2. The cyclic voltammetry of all these batches of Ni(OH)2 exhibited faradaic process and hence qualify as battery-type charge storage materials. The specific capacity of these batches recorded at 1 A g–1 are of the order: 200 C g−1 for [Ni(OH)2]ED, 246 C g−1 for [Ni(OH)2]BD and 320 C g−1 for [Ni(OH)2]HD. The maximum specific capacity obtained for [Ni(OH)2]HD is consistent with the structural and morphological features of the material. The charge transfer mechanism has been studied by electrochemical impedance spectroscopy. The quasi–solid–state symmetric supercapacitor type charge storage device using the best performing [Ni(OH)2]HD has been constructed. The fabricated [Ni(OH)2]HD//[Ni(OH)2]HD device offered the maximum energy density of 14.2 W h kg–1 at power density of 14.2 kW kg–1. The practical application of the charge storage device is successfully demonstrated by lighting LED bulbs and operating a portable electric fan.