Flexible and Transparent Supercapacitor Electrodes Based on V ₂ O ₅ Nanostructures for Energy Storage Applications

Wearable, transparent, environmentally compatible, and cost-effective electronic devices are the prerequisites for future advanced technology. This work employs a cost-effective method to demonstrate a flexible, transparent supercapacitor electrode for sustainable energy storage applications. Transparent vanadium pentoxide (V 2 O 5 ) was reactively sputter-coated at room temperature (RT) onto an eco-friendly poly(vinyl alcohol) (PVA) substrate for supercapacitor electrode fabrication. In particular, it was fabricated in two different layers with an interface that facilitated the current collection. The sputtered material was systematically studied using various materials characterization tools. The field emission scanning electron microscopy (FESEM) images of the V 2 O 5 surface revealed the nanocauliflower-like morphology. The nanogranules and pores of the cauliflower contributed to enhanced supercapacitor performance. Two-electrode electrochemical measurements in a 1 M Na 2 SO 4 aqueous electrolyte demonstrated a voltage window of 1.3 V and a specific capacitance of 178.7 F/g (6.25 mF/cm 2 ) at a scan rate of 10 mV/s. It delivered a power density of 9.6 kW/kg (0.14 mW/cm 2 ) and an energy density of 7.8 Wh/kg (0.195 μWh/cm 2 ). The device exhibited a capacitance retention of 82% and 67.3% after 10,000 and 18,000 charging–discharging cycles, respectively, along with excellent mechanical flexibility. In addition, the electrode exhibited 70% transmittance in the visible region and demonstrated rapid device disposal in both normal water and moist soil. Therefore, the biodegradable PVA substrate, environmentally friendly Na+-ion storage, and nontoxic V 2 O 5 layer have enabled a cost-effective, flexible, and transparent supercapacitor device.