Controlled Reversible Redox Behavior at Zeolitic Imidazolate Framework-8 Coupled Iron–Metal Organic Framework for High-Performance Planar Hybrid Capacitor

A hybrid entity of zeolitic imidazolate framework (ZIF-8) integrated with Fe MOFs was developed via a sonochemical route holds promising potential for enhanced performance as a hybrid capacitor. The design is to harvest the pseudocapacitive properties of Fe MOFs (Fe2+/Fe3+) coupled with the high surface area of ZIF-8 at the graphite sheet (GS) electrode. Thereby, a hybrid composite has been formed between Fe MOFs and ZIF-8, revealing a mesoporous structure with high surface area (428 m2 g–1), greater than either Fe MOF or ZIF-8 standalone. The composite in three-electrode testing shows tremendous performance of 290 mAh g–1 specific capacity at 1 Ag-1, exceeding Fe MOF’s and ZIF-8’s performance, such as 142 and 125 mAh g–1, respectively. Moreover, a solid-state planar asymmetric supercapacitor was fabricated and evaluated, employing the prepared composite as the cathode and activated carbon as the anode. The assembled device exhibited a high energy density of 163 Wh kg–1 at a power density of 991 W kg–1, and retained 95.8% of its original capacity after 10,000 charge–discharge cycles, confirming its superior electrochemical performance and long-term durability. Thus, the findings underscore the synergistic benefits of integrating ZIF-8 and Fe MOFs at economically viable, simple GS electrodes, highlighting the composite’s potential for a wide range of high-performance energy storage applications.