ZnO-embedded activated carbon nanofibers derived from electrospun ZIF-7/metal salt/PAN fibers for flexible supercapacitors

The wearable electronics market is growing exponentially and has benefited considerably from a versatile electrospinning technique capable of fabricating freestanding, binder-free fibers. Using this method in the current study, electrospun fibers were produced from a polymer-salt-ZIF-DMF solution. The obtained fibers were annealed to prepare Fe-ZnO/carbon nanofibers (CNFs), which exhibited a wide potential window of 0–1.6 V in an aqueous electrolyte (6 M KOH). Moreover, the composite fibers exhibited a large interfacial area between the electrode and electrolyte and reduced the ion transport distance during operation. Consequently, a high capacitance of 499 mF·cm–2 was attained at a current density of 5 mA·cm–2. Notably, high energy densities of 0.23–0.18 mWh·cm–2 were achieved owing to the excellent synergy between ZIF-7-derived ZnO and Fe-activated CNFs. The energy density of Fe-ZnO/CNF was approximately four times higher than that of ZnO/CNF at a power density of 16 mW·cm–2. Electrochemical stability testing through 10,000 galvanostatic charging–discharging cycles revealed a capacitance retention of ∼95 %. Practical applications and bendability tests of environmentally benign flexible supercapacitors underscored the potential of the freestanding electrodes in fabricating wearable, portable electronic devices.