Zeolitic imidazolate framework-8 (ZIF-8)-derived nanoporous carbons (NPCs) have become more attractive in the energy storage sector due to their excellent characteristics, such as their porosity, available specific surface area, and charge storing ability. In this work, we further modify ZIF-8NPC by using Co3O4 nanoflakes together with polyaniline (PANI) in a controlled in situ polymerization on the surface of ZIF-8NPC to form a Co3O4-PANI@ZIF-8NPC nanocomposite. The as-prepared nanocomposite shows a high specific capacitance of 1407 F g−1 at 1 A g−1 with remarkable rate capability and cyclic stability. An asymmetric supercapacitor (ASC) with Co3O4-PANI@ZIF-8NPC as a positive electrode and ZIF-8NPC as a negative electrode shows a high energy densities of 52.81 W h kg−1 (at a power density of 751.51 W kg−1) and 18.75 W h kg−1 (at a power density of 7500 W kg−1), along with a high cyclic stability as evidenced by retaining 88.43% of the initial capacitance after 10,000 cycles at 10 A g−1. The remarkable electrochemical performance mentioned above is attributed to a synergistic effect between the high conductivity provided by PANI, the increased number of pseudocapacitive active sites provided by CO3O4, and the high surface area with a suitable pore size distribution provided by ZIF-8NPC. The results demonstrate that the as-prepared electrode materials can be a good alternative for applications in supercapacitors and other energy storage devices. Display omitted •A unique Co3O4-PANI@ZIF-8NPC nanocomposite is designed for supercapacitor applications.•An asymmetric supercapacitor, Co3O4-PANI@ZIF-8NPC//ZIF-8NPC, was assembled and tested.•The synergetic effect between the Co3O4 and PANI-enhanced ZIF-8NPC delivered excellent electrochemical performance.•The ASC showed a high energy density of 52.81 W h kg−1 at a power density of 751.51 W kg−1.