Are Fractal-Like Structures Beneficial for Supercapacitor Applications? A Case Study on Fe2O3 Negative Electrodes

The question of whether fractal-like structures are beneficial for supercapacitor applications is investigated by hydrothermally synthesizing Fe2O3 in fern, flake, and microsphere morphologies with similar specific surface areas. Their negative electrodes are prepared by supporting them on nickel foam (NF). The fractal dimensions (FDEIS) of these morphologies estimated from electrochemical impedance spectroscopy are ∼2.50, ∼2.36, and ∼2.19, respectively. The Fern@NF electrode exhibits the highest specific capacitance (C sp) of ∼2708 and ∼104 F g–1 at 1 and 5 A g–1, respectively, with an ∼94% capacitance retention after 2000 cycles. The capacitive (nonfaradaic) surface charge storage contribution from cyclic voltammetry increases with FDEIS from microspheres to ferns. Interestingly, such an increase in FDEIS leads to a decrease in the estimated impedance (Z CPE) in that order enhancing the performance of ferns. Hence, fractal-like structures are beneficial for supercapacitor applications by promoting capacitive surface charge storage through low Z CPE. The emphasis of this work is to study the effect of fractal dimension on the charge storage performance of Fe2O3 electrodes, which is scarcely addressed in the literature. The methodology presented here can be useful in designing/synthesizing a novel supercapacitor material possessing fractal-like structures with a potential for scale-up and commercialization.