Unveiling the impact of reaction temperature on hydrothermally synthesized nickel phosphate hydrate for supercapacitors

Abstract

Transition metal phosphates have engrossed a hefty amount of interest in the field of energy storage owing to their fascinating characteristics. Herein, this study reports nickel phosphate hydrate (NP) deposited on nickel foam using a facile hydrothermal method. The X-ray diffraction (XRD) technique confirms the formation of NP on the nickel foam having a monoclinic structure and an “I2/m” space group. The scanning electron microscopy (SEM) studies revealed a stacked micro-sheet-like structure. The electrochemical measurements were examined under a potential window of −0.2 to 0.55 V Vs SCE in a 1 M KOH electrolyte delivering a maximum areal capacitance of 6333.33 mF cm−2 at a current density of 10 mA cm−2. The synthesized electrodes’ charge storage kinetics were diffusion-driven. Moreover, the electrode produced an energy density of 316.67 µWh cm−2 along with an impressive cyclic retention of ∼89 % over 1000 charge–discharge cycles. A hybrid supercapacitor device was fabricated with N5//AC as the electrodes shows 94.44 % of its initial capacitance retention after 5000 cycles.