Decoration of Zeolitic Imidazole Framework With Carbon Nano-Onions for Enhancing Electrochemical Performance of ZIF-(67 and 8) for Supercapacitor

Abstract

The development of affordable and sustainable nanomaterials for energy storage is a top priority and a major focus within the global research community. Among these, carbon nano-onions (CNOs) have emerged as a promising material for supercapacitors due to their distinctive morphology, high surface reactivity, and microporous structure. Zeolitic imidazole frameworks (ZIFs), known for their vast surface area and electrically active inorganic centers, have emerged as a potential material for energy storage. In this context, the ZIF rhombic dodecahedron is homogenously decorated with CNOs (size < 100 nm) to form a nanocomposite of CNOs/ZIF (67 and 8) utilizing a simple solvothermal technique. The samples have been characterized by Fourier transform infrared spectroscopy and X-ray diffraction techniques, which confirm the successful synthesis of the samples. The produced material displays a distinct rhombic dodecahedral shape, significant porosity, and a large specific surface area (SSA) confirmed by N₂ sorption studies. The as-prepared samples are further tested as electrode material for supercapacitors, and among them, the CNO/ZIF-67 nanocomposite surpasses in terms of SSA, electron and ion transport speed, and structural stability, leading to improved electrochemical performance. The specific capacitance of 1064.2 F g⁻¹ at a current density of 2 A g⁻¹ is observed for CNO/ZIF-67 in a 1 M H₂SO₄ aqueous electrolyte in a three-electrode system. Subsequently, a symmetric supercapacitor (SSC) is constructed to investigate the system's capacitive behavior. Notably, the SSC exhibited a peak device-specific capacitance of 325.40 F g⁻¹ at 2 A g⁻¹, a high energy density of 24.51 Wh kg⁻¹, and achieved a maximum power density of 2.4 kW kg⁻¹. The practical functionality of the device was demonstrated by connecting two symmetrical supercapacitors in series, effectively powering a red LED. These results highlight new opportunities for structural engineering in CNO and metal–organic framework-based electrode materials, paving the way for advancements in future energy storage technologies.