Tailoring crystallinity of 2D cobalt phosphate to introduce pseudocapacitive behavior

Abstract

The latest technological developments have catalyzed the quest for efficient electrochemical energy storage devices. Tailoring the properties of the electrode materials, such as porosity, crystallinity, electrochemical surface area, etc., can enhance the performance of electrochemical energy devices. Herein, the sonochemical synthesis of cobalt phosphate (Co3(PO4)2) followed by calcination at various temperatures (at 200, 400, 600, and 800 °C) is reported. The effect phase transformation of Co3(PO4)2 at various calcination temperatures on its electrochemical performance is evaluated. The prepared Co3(PO4)2 samples were characterized by analytical techniques such as X-ray diffraction spectroscopy (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electrons microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS). The FESEM results showed morphological changes when Co3(PO4)2 is calcined at 200, 400, 600, and 800 °C. XRD pattern revealed the phase transformations from crystalline to amorphous and then again crystalline due to the loss of water molecules from the crystal structure Co3(PO4)2. The EDS provided the elemental analysis and confirmed the high purity of the samples under investigation. The change in electrochemical behavior of the prepared samples was examined in a three-electrode cell using 1 M potassium hydroxide (KOH) electrolyte using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The Co3(PO4)2 calcined at 200 °C demonstrated excellent electrochemical performance, giving a specific capacity of 352.00 C·g−1, selected for the fabrication of supercapattery. The fabricated supercapattery (Co3(PO4)2:@200 °C//AC) produced 51.95 Wh·kg−1 energy density corresponding to the power density of 346.00 W·kg−1 at a current density of 1.0 A g−1.