Synthesis of doped ZIF-8@ZIF-67 hybrid nanocomposites: a strategy for enhancing supercapacitor performance for energy storage device

Abstract Developing advanced materials are vital to maximizing supercapacitor performance potential. This study examined Co-, Zn-, and Pb-doped ZIF-8@ZIF-67 nanocomposites for enhanced supercapacitor performance. The structural, morphological, optical, and electrochemical properties were analyzed using X-ray diffraction, scanning electron microscopy (SEM), ultraviolet-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and cyclic voltammetry (CV), respectively. X-ray diffraction analysis shows that the hybridization and doping of the nanocomposites were successful. The SEM images revealed a distinct morphological difference with Pb-doped composites demonstrating a combination of two different kinds of nanoparticles, while the energy-dispersive spectroscopy (EDS) analysis shows the successful incorporation of the dopants in the hybridized framework. In addition, optical analysis revealed improved absorbance and reduced band gap values ranging from 2.35 eV, 1.95 eV, and 1.58 eV for Co-, Zn-, and Pb-doped composites, respectively. Electrochemical analyses showed a pseudocapacitive behavior as demonstrated by the redox peaks in the CV plots. As the scan rate increases, the specific capacitance decreases. At 5 mV/s, Co-, Zn-, and Pb-doped electrodes have estimated specific capacitances of 987.50 F/g, 962.50 F/g, and 969.32 F/g, respectively. The low charge transfer resistance observed in the Nyquist plot suggested excellent capacitive performance. Based on the galvanostatic charge- discharge testing, Pb-doped ZIF-8@ZIF-67 demonstrated the highest specific capacitance of 428.63 F/g and energy density of 2.366 Wh/kg at 2.0 A/g. The Co/ZIF-8@ZIF-67 electrode demonstrated the highest power density of 8969.98 W/kg, while Zn/ZIF-8@ZIF-67 gave the maximum capacitance retention of 85.2% after 4800 cycles. According to these results, hybrid ZIF-8@ZIF-67 nanocomposites, especially the Pb-doped varieties, show potential for energy storage devices.