Ethanolamine-Induced Hydrophilic Transition in Coaxial Electrospun C-MNF for Co ₃ O ₄ Nanoneedle Growth toward Flexible Supercapacitors

Hydrophilic modification of materials is crucial for optimizing the performance of flexible supercapacitors, which are promising energy-storage devices for flexible and wearable electronics. However, enhancing the wettability of coaxial electrospun membranes to facilitate the uniform growth of active materials and improve electrochemical performance remains a key challenge. Herein, we propose a hydrophilic modification strategy using ethanolamine (MEA) heat treatment, which significantly enhances the wettability of coaxial electrospun CNT/MOF-5/PAN/PVDF (C-MNF) membranes and promotes the uniform in situ growth of Co₃O₄ nanoneedles. Characterization results reveal that hydrophilic modification improves the penetration and diffusion of Co²⁺ ions within the substrate, optimizing the nucleation and growth environment for Co₃O₄ crystals. By integrating multiple mechanisms such as Zn²⁺/Co²⁺ ion exchange, Fe³⁺-induced oxidation, and spontaneous crystal transformation, the material's interface structure and electrochemical performance were synergistically enhanced. The resulting Co₃O₄@C-MNF composite electrode achieved a mass-specific capacitance of 310 F g^-1 at 0.5 A g^-1, with good rate performance (250 F g^-1 at 10 A g^-1) and low interfacial resistance (∼51 Ω). A symmetric supercapacitor device constructed with the modified material exhibited a maximum energy density of 4.94 Wh kg^-1, high cycling stability (94.2% capacity retention after 8000 cycles), and stable output in various bending states. These results highlight the potential of the device for flexible, wearable energy storage applications and provide an approach and material system for the design of high-performance flexible supercapacitors.