Carbon Nanofibers-Assembled Tungsten Oxide as Unique Hybrid Electrode Materials for High-Performance Symmetric Supercapacitors

It is crucial to balance the energy supply and demand of wearable and mobile electrical devices for their widespread applications. Supercapacitors have attracted increasing attentions in this field due to their unique advantages. This work studied the preparation of highly graphitized WO₃–CNFs as promising flexible electrode materials for fiber-shaped supercapacitors. Tungsten oxide, a prospective energy storage material owing to its n-type semiconductor property, was integrated with carbon nanofibers (CNFs) to synthesize nanostructured WO₃–CNFs through a combined electrospinning and hydrothermal method. A variety of amounts of ammonium metatungst (AMT) were screened and WO₃-RCNFs8 (8 mg AMT in 20 mL water) was proven to deliver the maximum specific capacitance (381.40 F g^–1 at 0.5 A g^–1), capacitance retention (up to 111.87% after 5000 cycles), and high-rate capability (58.68% retention in specific capacitance at 20 versus 0.3 A g^–1). A symmetric flexible solid-state supercapacitor (SFS) device was assembled using the as-prepared WO₃–CNFs8 as electrode materials. The maximum energy density of 4.28 Wh kg^–1 with a power density of 3356.90 W kg^–1 was achieved. The superior electrochemical performances can be explained by the synergistic effect of the n-type semiconductor property of WO₃ and the excellent charge transfer ability of CNFs, which could attract more charges into the electrode throughout charging state and release them rapidly during the discharging state. The n-type semiconductor enhanced the electrochemical behavior of CNFs and played a vital role in achieving high specific capacitance. The new procedure of preparing flexible electrode materials with enhanced charge storage/release capacity was investigated, which is chiefly essential for superior-performance energy storage devices.