ZnS@Fe2O3 core–shell nanorod arrays for supercapattery applications; theoretical evaluation of faradic and non-faradic behavior using Dunn’s model

Supercapattery has emerged as an ideal energy storage device that has the features of both batteries and supercapacitors. In this work, ZnS@Fe2O3 core–shell nanorod arrays supported on Ti foil have been prepared by the cost-effective, efficient, and facile two-step hydrothermal method and investigated for high performance supercapattery applications. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirm the successful synthesis of the material, while the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images clearly show the successful deposition of the Fe2O3 shell over the ZnS core. Electrochemical characterizations including cyclic voltammetry, galvanostatic charge discharge and electrochemical impedence spectroscopy have been employed to investigate the electroactive nature of the materials. It is found that the ZnS@Fe2O3 exhibits excellent specific capacitance of 681 Fg−1 at 1 Ag−1 current density within the potential window of −0.2 to 0.75 V while demonstrating a significant capacitance retention of 85 % and 95 % coulombic efficiency over 2000 cycles. The contribution of faradic and non-faradic processes during electrochemical reactions is evaluated using Dunn's model. The diffusion controlled mechanism is greater than the surface controlled mechanism in the synthesized material, which depicts the battery grade nature. Interestingly, the electrode was able to exhibit an excellent energy density of 86 Whkg−1 and a maximum power density of 4232 Wkg−1, which is significantly higher than the previously reported ZnS based and Fe2O3 based composites. A Supercapattery device has been assembled using ZnS@Fe2O3 as anode and reduced grapheme oxide (rGO) as cathode, which demonstrate a specific capacitance of 165 Fg−1 at 1 Ag−1 current density, exhibiting 66 Whkg−1 at power density of 3895 Wkg−1 with excellent retention in specific capacitance and coulombic efficiency at 15 Ag−1 after 3000 cycles.