α-Fe₂O₃-Based Core-Shell-Nanorod–Structured Positiveand Negative Electrodes for a High-Performance α-Fe₂O₃/C//α-Fe₂O₃/MnO_xAsymmetric Supercapacitor

Abstract

A α-Fe 2 O 3 /MnO x core-shell nanorod (NR)-based positive electrode is designed combining the traits of α-Fe 2 O 3 and MnO x with an ultrathin MnO x shell serving as active site for surface or near-surface based fast and reversible faradaic-reactions and α-Fe 2 O 3 NR core facilitating electron transfer toward the current collector. The α-Fe 2 O 3 /MnO x core-shell NR electrode shows ameliorated electrochemical performance in terms of capacitance and rate capability within the potential window of 0-1 V in relation to both pristine α-Fe 2 O 3 NR electrode and pristine MnO x thin film electrode. Similarly, α-Fe 2 O 3 /C core-shell NR negative electrode is also realized. The assembled α-Fe 2 O 3 /C//α-Fe 2 O 3 /MnO x core-shell NR asymmetric supercapacitor (ASC) exhibits a volumetric capacitance of ∼ 1.28 F/cm 3 at a scan rate of 10 mV/s with nearly 78% capacitance retention at the scan rate of 400 mV/s within a potential window of 0-2 V in aqueous electrolyte medium. Interestingly, the ASC delivers a maximum energy-density of ∼ 0.64 mWh/cm 3 and a maximum power-density of 155 mW/cm 3 , which are higher than the values obtained for α- By 2050, global electrical energy demand is likely to reach 28 TW.1,2 Production of such a humungous amount of carbonneutral energy would necessitate the exploitation of renewable energy sources, like solar and wind.3,4 Furthermore, electrical energy storage would be required for unimpaired integration of electricity generated from these sources to the grid. For large-scale electrochemical storage to be viable, the materials used and devices produced need to be costeffective, besides being long-lasting and safe. Indeed, high specific energy and high power densities are of lesser concern in this regard. Accordingly, chemistries that make use of aqueous electrolytes are favorable candidates for large scale energy storage. It is noteworthy that as the renewable energy resources are intermittent, it would be desirable to store the energy from these sources as quickly as possible.Recently, supercapacitors (SCs) have emerged as a new class of storage devices that can be charged quickly with higher powerdensities than storage batteries. [5][6][7] However, their energy densities still remain limited and there is a definite need to increase it to cope with the global energy demand for electric traction and nextgeneration portable electronic devices. 8 The energy density of supercapacitors can be enhanced by increasing their capacitance as well as their operating-potential window, which can be achieved more easily with asymmetric supercapacitors (ASCs) than with the symmetric supercapacitors (SSCs) since, with suitable combination of positive and negative electrode materials, the operational potential window as high as 2 V has been achieved even with aqueous electrolytes. 6,[9][10][11][12][13][14] In recent years, efforts have been expended to explore several ASCs with different electrode materials based on redox-active transition-metal oxides, like RuO 2 ,

Expanding Interlayer Spacing in MoS2 for Realizing an Advanced Supercapacitor

“…To exploit the attractive capacitive performance of MoS 2 /r-GO for realizing hybrid supercapacitors, a prototype ASC device is assembled with MoS 2 /r-GO as anode and Fe 2 O 3 /MnO 2 core/shell nanorods (NRs) as cathode materials, shown schematically in Figure a. Fe 2 O 3 /MnO 2 core/shell NRs are chosen because of their improved performance in terms of capacitance and rate capability than pristine MnO 2 within a potential window from 0 to +1 V in aqueous electrolyte as observed in our earlier studies and briefly described in Figure S13 of Supporting Information . Electrochemical comparison between electrode materials within their respective potential window is also shown in Figure b.…”

Regulating Voltage Window and Energy Density of Aqueous Asymmetric Supercapacitors by Pinecone‐Like Hollow Fe2O3/MnO2 Nano‐Heterostructure

“…Remarkably, the area of CV profile for Fe 2 O 3 /MnO 2 ‐3 NHs is far larger than that of MnO 2 , suggesting the capacitance of Fe 2 O 3 /MnO 2 ‐3 NHs electrode is higher than that of pure MnO 2 . Besides, the pure MnO 2 electrode has a polarization phenomenon when the voltage window increased to 1.0 V. In contrast, benefiting from the high oxygen evolution reaction overpotential and high redox electrochemical activity by the addition of Fe 2 O 3 , the voltage window of Fe 2 O 3 /MnO 2 ‐3 NHs electrode can reach to 1.2 V. These results indicate that the addition of Fe 2 O 3 conductive substrate can increase the capacitance performance and potential window of MnO 2 . The CV test at various scan rates indicates the stable working potential of Fe 2 O 3 /MnO 2 ‐3 NHs is 1.2 V (Figure b).…”

Nano-porous Al/Au skeleton to support MnO2with enhanced performance and electrodeposition adhesion for flexible supercapacitors

“…The supercapacitor exhibits a maximum energy density of 0.68 mW h cm −3 at a power density of 5.33 mW cm −3 , and a highest power density of 53.33 mW cm −3 . These values exceed or are comparable to some previously reported symmetric systems based on MnO 2 , such as H-ZnO 2 /MnO 2 (0.04 mW h cm −3 ), 38 FeOOH/MnO 2 (0.05 mW h cm −3 ), 39 MnO 2 /CNPs (0.05 mW h cm −3 ) 42 and some MnO 2 -based asymmetric supercapacitors, such as H-TiO 2 /MnO 2 //H-TiO 2 /C (0.30 mW h cm −3 ), 9 ZnO/MnO 2 //r-GO (0.234 mW h cm −3 ), 11 α-Fe 2 O 3 /C//α-Fe 2 O 3 /MnO x (0.64 mW h cm −3 ), 36 H-MnO 2 //RGO (0.25 mW h cm −3 ), 40 α-Fe 2 O 3 NTs//MnO 2 NRs (0.55 mW h cm −3 ), 41 N-Fe 2 O 3 //MnO 2 (0.41 mW h cm −3 ) 47 and MnO 2 /graphene//VOS@C (0.95 mW h cm −3 ). 48 Moreover, based on the nano-porous current collector, different active materials can be grown to assemble into asymmetric supercapacitor, thus widening the charge–discharge voltage window and leading to significantly enhanced energy density.…”