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Abstract:
Iron oxide (Fe2O3) is attractive for energy storage due to its low cost, abundance, and eco-friendliness, but suffers from poor cyclic stability and capacitance fading. Here, we systematically investigate how calcination temperature influences the structure, morphology, and electrochemical properties of surfactant-assisted self-assembled iron oxide nanoflowers. Variation of calcination temperature from 300 °C to 600 °C strongly affects the phase, crystal structure, morphology, surface area, porosity, and electrochemical properties of the oxides. The low-temperature calcination of iron oxide at 300 °C leads to a distinctive mesoporous flower-like morphology, high surface area (145.76 m2 g−1), and mixed-phase (maghemite and hematite) composition with low crystallinity, resulting in the highest specific capacitance (182.3 F g−1 at 1 A g−1), low internal resistance with enhanced capacitive behavior. In contrast, samples calcined at higher temperatures than 300 °C exhibit reduced surface area, enhanced phase purity (pure hematite), and diminished electrochemical activity. A low-cost pouch-type asymmetric capacitor is fabricated using Fe2O3 nanoflowers calcined at 300 °C and activated carbon, delivering 24.33 μWh cm−2 energy density, 448.91 μW cm−2 power density, and 78.8% capacitance retention with 97% coulombic efficiency after 10,000 cycles. These results underscore the pivotal role of calcination temperature in optimizing Fe2O3 nanostructures for efficient energy storage.

Keywords:
Iron oxide nanoflowers, Calcination temperaturę, Phase-morphology correlation, Pseudocapacitance, Asymmetric electrochemical capacitor