Optimized oxygen-rich carbon nanofiber film via nitric acid oxidation for high-performance zinc-ion capacitor cathodes and flexible energy storage devices

This study reports a method for preparing oxygen-rich carbon nanofiber film (OCNF) as a high-performance anode material for zinc-ion capacitors through hydrothermal nitric acid oxidation of carbon nanofiber film (CNF). By optimizing the nitric acid oxidation duration, OCNF exhibited exceptional hydrophilicity, electrical conductivity, and an abundance of oxygen-containing functional groups, which significantly enhanced the electrochemical performance of zinc-ion capacitors. Notably, OCNF-6h samples demonstrated high initial charge-discharge capacity (155.48 mAh g −1 at 0.2 A g −1 ) and remarkable long-term stability (retention rate of 94.5 % after 5000 cycles), along with high energy density (109.16 Wh kg −1 at 140.49 W kg −1 ). Notably, flexible OCNF-based devices maintain performance under 180°bending, enabling durable wearable energy storage solutions. This work highlights that the nitric acid oxidation strategy promotes the storage and diffusion of Zn 2+ on carbon-based material surfaces, presenting a promising new material for energy storage and flexible energy storage devices.