Flexible Asymmetric Photo-Microsupercapacitor Based on Pseudobrookite-Type Iron Titanate and V₂CT_X MXene for Solar-Assisted Energy Storage

The integration of solar energy harvesting with electrochemical storage represents a promising strategy for next-generation microsystems. Here, we report a flexible asymmetric photo-microsupercapacitor (photo-MSC) based on pseudobrookite-type iron titanate (FeTi₂O₅) and V₂CT_x MXene electrodes fabricated on PET substrates. Iron titanate was synthesized from ilmenite via a sustainable route with a potential acid recovery system, yielding defect-rich nanopowder with a direct band gap of ∼2.31 eV and sub-bandgap states that enhance visible-light absorption. The asymmetric configuration leverages complementary charge storage mechanisms using diffusion-controlled pseudocapacitance in iron titanate and fast surface-capacitive behavior in MXene, delivering an areal capacitance of 78.99–361.67 mF cm⁻². Under simulated solar illumination, capacitance increases by 45.8% at 50 mV s⁻¹, with an energy density rising from 64.36 to 93.93 µWh cm⁻² and power density from 5.80 to 8.45 mW cm⁻². This photo-enhancement originates from efficient photogenerated carrier separation at the iron titanate/MXene heterojunction, confirmed by reduced charge-transfer resistance and improved carrier dynamics under illumination. The device further demonstrates excellent mechanical flexibility (∼92% capacitance retention at 180° bending) and practical energy delivery capability. This work establishes pseudobrookite iron titanate as a sustainable photoactive electrode material for integrated solar energy storage microsystems.