Vanadium doping enhances the photo-capacity of Fe2O3 nanoflowers: a promising photo-electrode for aqueous iron ion photo-capacitors

Abstract

Photo-rechargeable capacitors have become popular as renewable energy storage devices comprising photo energy harvesting and energy storage component materials. Certain nanostructures that can perform the dual function of energy harvesting and storing it for future use are endorsed to mitigate the problems originating from joining these two modules that work separately. Herein, we report V⁵⁺ doped Fe₂O₃ nanoflowers in situ grown on nickel foam as a single material with energy harvesting and storing capability. It exhibits high-capacity values of ∼280 mA h g⁻¹ in the dark and ∼360 mA h g⁻¹ under illumination with enhanced cycling stability in an aqueous alkaline medium at 2 A g⁻¹. Cyclic voltammetry studies suggest a capacity enhancement of 89.3% at a scan rate of 1 mV s⁻¹ for the Fe₂O₃ nanoparticles after doping with V⁵⁺. This nanostructure emerged as a potential photocathode for photo-rechargeable capacitors (iron ions in tetramethylene glycol dimethyl ether as electrolyte) with high initial charge and discharge capacities of 413 mA h g⁻¹ and 496.6 mA h g⁻¹ respectively at a current density of 500 mA g⁻¹ and excellent cycling stability. The photo-capacitor significantly enhanced capacity values from 95 mA h g⁻¹ (dark) to 150 mA h g⁻¹ under illumination at 3A g⁻¹.