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, Zeolitic imidazolate framework (ZIF) rhombic dodecahedron is homogenously decorated with carbon nano-onions (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, X-ray diffraction techniques, which confirms 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 N ₂ sorption studies. The as-prepared samples further tested as electrode material for supercapacitors and among them 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 H ₂SO ₄ aqueous electrolyte in 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, 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 carbon nano-onion and metal-organic framework-based electrode materials, paving the way for advancements in future energy storage technologies.