Co-MOF@MXene-carbon nanofiber-based freestanding electrodes for a flexible and wearable quasi-solid-state supercapacitor

Freestanding and flexible electrodes are crucial for advancing flexible and wearable energy storage devices (FW-ESD). However, the significant trade-off between mechanical flexibility and electrochemical performance of electrodes limits the development of high-performance FW-ESD. Therefore, flexible and freestanding multi-component hybrid electrodes with improved electrochemical properties are in high demand. This work reports a rational design of cobalt-metal organic framework (Co-MOF) structures on a highly flexible and electroconductive MXene-carbon nanofiber mat (MX-CNF). Further, the Co-MOF@MX-CNF was used as a starting material to derive capacitive-type Co-PC@MX-CNF and battery-type MnO₂@Co₃O₄-PC@MX-CNF functional multi-component electrodes for a high-performance flexible wearable hybrid supercapacitor (FW-HSC). Owing to their high specific surface area (SSA), wettability, conductivity, and abundant active sites, Co-PC@MX-CNF and MnO₂@Co₃O₄-PC@MX-CNF exhibited a specific capacitance of 426.7 F g⁻¹ and a specific capacity of 475.4 mAh g⁻¹ at 1 A g⁻¹, respectively, with excellent mechanical flexibility. Moreover, the two electrodes were used to fabricate an FW-HSC with an operating voltage window of 1.5 V, delivering an energy density of 72.5 Wh kg⁻¹ at a power density of 832.4 W kg⁻¹ with long-term stability (90.36 % capacitance retention). Furthermore, a series connection of two identical FW-HSC devices could power a digital clock and light up a green LED, demonstrating its potential as a power source for various wearable devices.