Light-driven enhancement in the pseudocapacitance of nanosized ZnO particles and carbon nanotube-based photo-rechargeable supercapacitors†

Photo-rechargeable supercapacitors (PRSCs), which simultaneously harvest and store solar energy, have received significant attention in the technological field for powering portable and autonomous devices. Unlike separate devices such as supercapacitors and solar cells, creating a single device that efficiently converts and stores solar energy presents a challenge for researchers. We fabricated a two-electrode configuration-based PRSC using bifunctional photoactive nanosized zinc oxide particles (NZPs) that simultaneously facilitate energy conversion and storage in the device. Multi-walled carbon nanotubes (MWCNTs) are used as a counter electrode with NZPs as a photoactive material, and their electrochemical characteristics are examined under dark and light conditions. The electrochemical energy storage capacity of the PRSC demonstrates ∼44% relative capacitance enhancement at a scan rate of 50 mV s⁻¹ under light illumination. This enhancement is attributed to the pseudocapacitive charge storage process, which is initiated in the presence of light, as observed from electrochemical measurements. The PRSC achieved a maximum voltage of 0.65–0.7 V under light illumination without the application of any external current. Additionally, the device demonstrated an excellent capacitance retention of 88% and stability over 1500 cycles at a current density of 20 mA g⁻¹ under light illumination. The overall efficiency of the PRSC is ∼0.47%, making it suitable for future practical application in smart, portable, and photo-sensitive devices owing to its unique simultaneous energy conversion and storage feature.