Surface-engineered carbon nanofibers enriched with metallic particles for effective bimetallic MOF formation toward hybrid supercapacitors

Metal-organic frameworks (MOFs) are commonly used as positive electrode materials in hybrid supercapacitors (HSCs) because of their high specific surface area, tunable pore structure, and battery-like charge-storage nature. However, the redox-mediated charge-storage mechanism in MOFs affects the rate capability and cycle stability. To address this problem, herein, bimetallic MOFs (NiCo MOFs) are successfully synthesized on surface-engineered carbon nanofibers (NiCo CNFs) enriched with metallic (Ni and Co) nanoparticles by a hydrothermal method and named NiCo MOF@NiCo CNF. In the NiCo MOF@NiCo CNF composites, the NiCo CNF can boost the electrochemical activity and simultaneously enhance the effective growth of NiCo MOF due to the presence of metal contents in the NiCo CNF, which act as nucleation points and further facilitate metal‑carbon and metal‑oxygen interactions at the surface of the NiCo CNF and NiCo MOF. The unique structure of NiCo MOF@NiCo CNF helps to improve the electrochemical performance, and the specific capacity is found to be 295.4 mA h g−1 (1063.4 C g−1) at 1 A g−1. The fabricated NiCo MOF@NiCo CNF//ZIF CNF HSC device depicts an energy density of 45.4 Wh kg−1 at a power density of 800 W kg−1 and cycle stability with a capacitance retention of 70 % after 4000 cycles, demonstrating that NiCo MOF@NiCo CNF composites are a promising electrode for supercapacitor applications. The engineered CNF surfaces with the required metallic contents can generate a unique engineered composite structure, by the effective interaction from the metal-based functional materials, to enhance the composite properties and charge-storage kinetics.