All-solid-state flexible symmetric light-driven supercapacitor based on indium oxide-modified carbon nanotube bifunctional photoelectrodes

Abstract

Light-driven supercapacitors (LDSCs) enable sustainable energy storage in flexible forms for portable devices and transportation. Flexible carbon-based electrodes offer promising conductivity, lightness, strength, durability, high surface area, porosity and flexibility. Carbon nanotubes decorated with indium oxide prepared by hydrothermal treatment serve as a flexible photoelectrode that integrates both photoactive and energy storage functionalities in LDSCs. The In₂O₃@CNT electrode significantly improves the electrochemical performance compared to pure In₂O₃ and bare CNTs due to the superior electrical conductivity and larger specific surface area. This improvement is due to the synergistic integration of In₂O₃ with carbon nanotubes, which optimize the charge transport and accessibility of the active sites. Consequently, the optimized In₂O₃@CNT electrode delivered a high capacitance of 0.9 mAh/cm² at a current density of 0.08 mA/cm². Under illumination, the specific capacitance of the electrode reached 1.4 mAh/cm², which corresponds to a 1.55-fold increase compared to conditions in the dark. The device showed exceptional flexibility when assembled into a flexible symmetrical LDSC with a sandwich structure. It achieved a specific capacitance of 1.2 mAh/cm², an energy density of 1.77 mWh/cm² and a power density of 53.15 mW/cm². Light-assisted operation resulted in a remarkable increase in specific capacitance compared to dark conditions, suggesting that charges generated by light increase conductivity and accelerate charge transfer processes. In addition, the effects of simultaneous double-sided illumination on the characterization of this device were evaluated, with the results indicating that the capacitance under double-sided illumination exceeds that under single-sided illumination. Overall, the study provides a practical and simple approach to increase the light absorption efficiency and overall performance of flexible LDSCs.