Seed-Assisted Growth of Nickel-MOFs on Electrospun Carbon Nanofibers for Superior Asymmetric Supercapacitors

Metal–organic frameworks (MOFs) represent a promising class of electrode materials for electrochemical energy storage systems due to their tunable morphology, high surface area, and chemical composition. However, the poor electron transport characteristics of MOFs have hindered their application in supercapacitor electrodes. Here, we report the seed-assisted synthesis of a freestanding composite featuring hydrangea flower-like Ni-MOF structures anchored on cobalt oxide (CoO_x)-embedded carbon nanofibers (Co-CNFs) as electrodes for superior asymmetric supercapacitors. The CoO_x nanoparticles serve as seeds that promote nucleation and modulate the growth of the Ni-MOF particles over the Co-CNF surface. The resulting Ni-MOF@Co-CNF composite exhibits a significantly high specific capacitance of 491 F g^–1 at a current density of 0.1 A g^–1 in a three-electrode system, surpassing the performance of both the individual components and the Ni-MOFs deposited onto the CNFs without any seed. This enhancement is accredited to the synergistic effect between Co-CNF and Ni-MOF, facilitating efficient dispersion of reaction active sites and promoting fast electron transfer through the conductive CNF matrix. The asymmetric supercapacitor (ASC) device with Ni-MOF@Co-CNF as a positive electrode demonstrates a specific capacitance of 126 F g^–1 (301 mF cm^–2) at a current density of 0.5 A g^–1. The ASC device exhibited a high energy density of 44.8 Wh kg^–1 (428.4 Wh cm^–2) at a power density of 0.4 kW kg^–1 (3.82 kW cm^–2). Furthermore, the quasi-solid-state ASC device (SASC) delivered a remarkable energy density of 35.6 Wh kg^–1 (340 Wh cm^–2) at a power density of 0.4 kW kg^–1 (3.82 kW cm^–2) with excellent cycling durability (∼89% capacitance retention after 10,000 charge/discharge cycles). This study highlights the significant potential of Ni-MOF@Co-CNF as electrodes in electrochemical energy storage applications.