Dual-step pulsed electrodeposition enables microstructural control and redox kinetics in iron oxide films

This work investigates the effect of deposition parameters on the structural and electrochemical performance of iron oxide thin films fabricated via direct reverse-pulsed hydrothermal electrodeposition (RP-HED) and dual-step reverse-pulsed hydrothermal electrodeposition (DRP-HED). By systematically varying the duty cycle (0.1, 0.25, and 0.5) and pulse frequency (10, 100, and 500 Hz), we correlated the changes in film morphology, crystallinity, surface wettability, and capacitive behavior. XRD analysis revealed that the DRP-HED samples possessed smaller crystallite sizes (22-35 nm) and more stable lattice constants (a = 8.371-8.394 Å) compared to RP-HED counterparts. Contact angle measurements showed improved surface energy, with the lowest contact angle of 62.16° observed for the DRP-HED sample at a 0.5 duty cycle and 10 Hz. Electrochemical characterization demonstrated that the DRP-HED sample prepared at a duty cycle of 0.25 and 10 Hz achieved the highest specific areal capacitance of 22.22 mF cm^{- 2} at 2.5 mA cm^{- 2}, along with a smaller IR drop and extended discharge time. The DRT analysis confirmed a dominant mid-frequency relaxation peak, indicating efficient redox kinetics and reduced polarization. The results affirm that DRP-HED, particularly under optimized pulsing parameters, provides a tunable and scalable route for engineering high-performance iron oxide electrodes for supercapacitor applications.