Probing Photo-Assisted Charge Storage Mechanism Using Bi-Fe Perovskite Oxide Electrode for Solar Supercapacitor

In this study, the rhombohedral crystalline pure phase BiFeO₃ (BFO) of irregularly shaped spherical particles of ≈100 nm and energy bandgap of ≈2.31 eV are synthesized by sol-gel auto-combustion method and explored as electrode material for photo-assisted supercapacitor. The electronic structure studies revealed that the coexistence of heterovalent Bi and Fe elements accelerated the electrochemical redox kinetics and photo-assisted charge storage properties. The resonant photoemission studies confirmed that near the Fermi level, the valence band spectra comprised the Fe3d and O2p hybridized states. The Fe-O hybridized state felicitates the charge transfer transitions (O2p (h⁺) + hυ ↔ Fe³⁺ + e^- ↔ Fe²⁺), which assists the intercalation/de-intercalation process of OH^- anions. Therefore, BFO has delivered 26.77% photo efficiency and the enhanced specific capacity of 21 Cg^-1 at 2 Ag^-1 in aq. 3m KOH under illumination, which is attributed to the accelerated photo-generated charge carrier separation and storage with surface polarization effect. BFO also delivered capacitance retention of 77.5% even after 1000 continuous GCD cycles under visible light irradiation.