Photo-chargeable asymmetric supercapacitors based on FeVO4 dual-function photoelectrodes: A new energy harvesting and storage integrated device

The efficient utilization of sustainable sunlight offers a practical approach to improving energy storage performance through photo-assisted mechanisms. Photo-supercapacitors are innovative devices that can capture and store renewable solar energy. This work successfully synthesized a novel FeVO₄/WTNs photoelectrode consisting of pseudocapacitive iron vanadate (FeVO₄) and photosensitive tungsten-doped titania nanotubes (WTNs) and used as a new photoelectrode to achieve high capacitance. The optimized FeVO₄/WTNs (sample S3) demonstrated a maximum specific capacitance of 37 mF/cm² at a current density of 0.05 mA/cm². This value significantly exceeds the capacitance observed in pure FeVO₄ and pristine WTNs, highlighting the enhanced electrochemical performance of the composite material. Under light illumination, this electrode reached the specific capacitance of 69.11 mF/cm², which corresponds to an increase of 85.9 % compared to dark conditions. A photo-assisted asymmetric supercapacitor using FeVO₄/WTNs and FeVO₄/FTO electrodes showed a specific capacitance of 0.75 mF/cm² at 0.01 mA/cm² under light irradiation. In contrast, the device tested without exposure to light, using a conventional method, delivered a capacitance of 0.56 mF/cm² at the same current density. When photocharged to 1.2 V under unbiased conditions, this device had a specific capacitance of 0.24 mF/cm². Remarkably, the device was able to generate a voltage of 1.2 V within 200 s by photocharging alone, eliminating the need for an external bias voltage. The device exhibited exceptional stability over 10,000 galvanostatic charge/discharge cycles and maintained 87.44 % capacity in the dark and 87.61 % under illumination. In this study, a simple approach to fabricate a photochargeable supercapacitor based on the FeVO₄/WTNs electrode is presented.