Carbon-α-Fe2O3 Composite Active Material for High-Capacity Electrodes with High Mass Loading and Flat Current Collector for Quasi-Symmetric Supercapacitors

In this work, we report the synthesis of an active material for supercapacitors (SCs), namely α-Fe₂O₃/carbon composite (C-Fe₂O₃) made of elongated nanoparticles linearly connected into a worm-like morphology, by means of electrospinning followed by a calcination/carbonization process. The resulting active material powder can be directly processed in the form of slurry to produce SC electrodes with mass loadings higher than 1 mg cm⁻² on practical flat current collectors, avoiding the need for bulky porous substrate, as often reported in the literature. In aqueous electrolyte (6 M KOH), the so-produced C-Fe₂O₃ electrodes display capacity as high as ~140 mAh g⁻¹ at a scan rate of 2 mV s⁻¹, while showing an optimal rate capability (capacity of 32.4 mAh g⁻¹ at a scan rate of 400 mV s⁻¹). Thanks to their poor catalytic activity towards water splitting reactions, the electrode can operate in a wide potential range (−1.6 V–0.3 V vs. Hg/HgO), enabling the realization of performant quasi-symmetric SCs based on electrodes with the same chemical composition (but different active material mass loadings), achieving energy density approaching 10 Wh kg⁻¹ in aqueous electrolytes.