Optimized V‐Doped Defective TiO2/α‐(Fe2O3)1‐x(Cr2O3)x Heterojunctions for Photo‐Assisted Supercapacitor Devices: Insights on the Materials Integrity and Dual Conversion‐Storage Mechanism

Abstract

Abstract Energy conversion and storage integrated power units suffer from multiple engineering issues. Replacing two devices (solar cell and supercapacitor assembly) with one device (photo‐enhanced supercapacitor‐ PSC) requires materials with emerged dual solar‐electrochemical storage attributes. Herein, a propitious approach is developed to fabricate all visible light‐enhanced semisolid flexible PCS. Nanoflakes‐based p‐n junction α‐(Fe2O3)1‐x(Cr2O3)x photocathode is synthesized directly on industrial waste stainless steel mesh (316L‐SS). Alongside, three TiO2‐based electrodes are utilized as positive photoactive electrodes. Tuning the optical properties of TiO2 is displayed via doping with mixed valence vanadium (V4+/V5+) together with thermal hydrogen annealing. This is revealed via the reduction of the bandgap energy from 2.89 to 2.15 eV, which can be ascribed to the induced oxygen vacancies. The device can sustain up to 1.6 V potential window with 91% stability after 350 successive charge/discharge cycles with the possibility of performance regeneration to its 100% retention. An illustration of the photo‐storage mechanism is proposed based on the X–ray photoelectron spectroscopy, X–ray crystallography, and band position/alignment results. Quasi‐reversible water splitting/formation is concluded as the main storage mechanism in the semisolid state electrolyte under illumination conditions.

Keywords

• flexible functional device
• nanoporous stainless steel
• oxygen deficiency
• photo‐storage mechanism
• photo‐supercapacitor