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

Abstract

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.

Morphological, Structural, and Optical Features of Thermally Annealed Slag Powders Generated from the Iron and Steel Industry: A Source of Disordered Iron Oxide Composites

“…The high-intensity peaks of the untreated and treated composites at 600 • C are linked to the reaction of the incident excitation wavelength of the laser and the optical transition of α-Fe 2 O 3 [40] . The peaks at 252 cm −1 and 527 cm −1 correspond to the A 1g mode, and those at 322 cm −1 , 435 cm −1 , and 635 cm −1 correspond to the E g mode, respectively [41][42][43]. The additional peak observed at around 683 cm −1 was attributed to the presence of magnetite content [43].…”

“…Notably, the shift in the peak positions to wavenumbers is ascribed to the high amount of disorder introduced in the iron oxide material crystal lattices during the production process. The characteristic carbon peak of the material was absent in the spectral range of the vibrational modes, indicating that the sample has poor crystallinity [42].…”

Hydrogen-Assisted Thermal Treatment of Electrode Materials for Electrochemical Double-Layer Capacitors

“…Commercial activated carbon, few-layer graphene (FLG, BeDimensional S.p.A.), produced by wet-jet milling exfoliation of graphite, − and PVDF were mixed with an 80:10:10 weight ratio in NMP (1:3 solid/liquid weight content ratio) using a planetary centrifugal mixer until obtaining a homogenized slurry. − The as-produced slurry was subsequently deposited onto a pyrolytic graphite sheet by doctor blading using a MSK-AFA-H200A coater (MTI Corp.) and dried at 70 °C in a vacuum oven (Binder, VD 53-UL) overnight to remove solvent residues. In the resulting EDLC electrodes, the mass loading of the electrode materials was ∼4 mg cm –2 to be compatible with practical requirements, as recommended in ref .…”

Functionalized Metallic 2D Transition Metal Dichalcogenide-Based Solid-State Electrolyte for Flexible All-Solid-State Supercapacitors

“…In this scenario, electrochemical double layer capacitors (EDLCs) represent a type of supercapacitors that have attracted considerable attention because of their high power density (>10 kW kg –1 ) and excellent electrochemical stability over hundreds of thousands of charge–discharge cycles, − complementing the characteristics of high-capacity energy storage systems, e.g., lithium-ion batteries, , or other energy storage units, including electrochemical (e.g., flow batteries, pseudocapacitors), , chemical (e.g., power-to-gas-to-power), thermal (e.g., molten salt technology), and mechanical (e.g., pumped hydroelectric storage) ones. Among supercapacitors, EDLCs exclusively rely on nonfaradaic charge storage, namely the ion adsorption and the swapping of co-ions for counterions at electrode–electrolyte interfaces, determining the double layer capacitance. − To further extend the applications of supercapacitors, flexible solid-state supercapacitors (FSSSCs) have attracted significant interest because of their distinctive mechanical properties (e.g., bendability and foldability), , lightness and safety (absence of leakage of toxic and corrosive electrolytes), , which, ideally, can be coupled with the main features of traditional EDLCs (e.g., high power density and long-term operation). − These properties turn FSSSCs into suitable candidates for portable and wearable electronics, including biomedical implants and health monitoring devices. − …”

“…8,9 Meanwhile, they also play a crucial role in developing decentralized power networks, i.e., the so-called "microgrids", for small-scale self-sufficient organizations 10,11 and even portable and wearable electronics. 12−15 In this scenario, electrochemical double layer capacitors (EDLCs) represent a type of supercapacitors that have attracted considerable attention because of their high power density (>10 kW kg −1 ) 16 and excellent electrochemical stability over hundreds of thousands of charge−discharge cycles, 17−19 complementing the characteristics of high-capacity energy storage systems, e.g., lithium-ion batteries, 20,21 or other energy storage units, including electrochemical (e.g., flow batteries, pseudocapacitors), 22,23 chemical (e.g., power-to-gasto-power), 24 thermal (e.g., molten salt technology), 25 and mechanical (e.g., pumped hydroelectric storage) 26 ones. Among supercapacitors, EDLCs exclusively rely on nonfaradaic charge storage, namely the ion adsorption and the swapping of co-ions for counterions at electrode−electrolyte interfaces, determining the double layer capacitance.…”