Facile synthesis of a binary composite from watermelon rind using response surface methodology for supercapacitor electrode material

Abstract

The electrode material is critical to the performance of a supercapacitor. Therefore, developing a cost-effective and efficient electrode is an essential step toward broader applications for energy storage devices. This paper reports the development of a novel binary composite from watermelon rind (BCWR) as a nitrogen-rich and high stability precursor for a supercapacitor's electrode. BCWR has been successfully synthesized via one-pot self-purging pyrolysis of watermelon rind waste impregnated with nickel ferrite (NiFe2O4). The effects of process parameters such as pyrolysis temperature, pyrolysis time and biomass to metal oxide ratio were investigated by response surface methodology (RSM). The statistical analysis showed the optimal synthesis condition for BCWR to be 600 °C pyrolysis temperature, 15 min pyrolysis time, and 75:25 ratio of watermelon rind (WR) to NiFe2O4. Furthermore, the predicted model and experimental results for the specific capacity of BCWR were determined to be 191 Cg−1 and 187 Cg−1 at 5 mV s−1. With the experimental validation based on structural, chemical and morphological and electrochemical properties determined by X-Ray Diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), field emission electron scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDX), cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectrometry (EIS) we find that watermelon rind biochar (WRB) and BCWR can be considered as a superior alternative for electrode materials for energy storage applications. Two-electrode cells device configuration of BCWR/WRB supercapattery exhibited high power density and energy density of 750.00 W kg−1 and 28.33 Wh kg−1 respectively at 1 Ag−1 current density. Besides, the calculated charge transfer resistance of the BCWR/WRB supercapattery is 42.35 Ohms.