Zeolitic Imidazolate Framework-8 and redox-additive electrolyte based asymmetric supercapacitor: A synergetic combination for ultrahigh energy and power density

In the present work, the electrochemical study of the synthesized electrode (ZIF-8 at 300 degrees C named as Z1) material was done in a three-and two-electrode (device) assembly using non redox-additive (6 M NaOH) and redox-additive (0.35 M K4(Fe(CN)6).3H2O in 6 M NaOH) electrolyte (RAE). X-ray diffraction (XRD) of Z1 sample confirmed the cubic phase with I-43 m space group. The hexagonal-type morphology was revealed by high -resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) analysis. The formation of narrow mesopores with average pore diameter of 1.53 nm and a large specific surface area of 1272 m2/g was confirmed by Brunauer-Emmett-Teller (BET) examination. The thermal stability of pristine ZIF-8 is investigated by Thermogravimetric analysis (TGA). In the three-electrode system, the Z1 sample as electrode reveals the pseudocapacitive (in NaOH) and battery-like redox behavior (in RAE). The fabricated electrode provides the specific capacitance of 30.6 F/g (1 A/g) and 33.1 F/g (10 mV/s) in NaOH. Moreover, the Z1 electrode exhibited an excellent specific capacity of 500.0C/g (at 10 A/g) and 532.5C/g (at 10 mV/s) in RAE. Additionally, an asymmetric supercapacitor (ASSC) device was assembled via RAE with activated carbon (AC) as an anode and Z1 as a cathode to investigate the practical feasibility. The constructed device in 0.0-2.0 V voltage window provides a significant power density of 20,000 W/Kg (for an energy density of 38.89 Wh/kg at 40 A/g) and an outstanding energy density of 75 Wh/kg (for a power density of 10,000 W/kg at 20 A/g). It exhibits good capacitance retention (80 % at 20 A/g) after 1500 cycles. Furthermore, three ASSC devices are connected in series to illuminate green, yellow, white, and red Light Emitting Diodes, thus demonstrating the potential realistic advantage of the current research work in supercapacitive energy storage devices.