Identifying pseudocapacitance of Fe₂O₃ in an ionic liquid and its application in asymmetric supercapacitors
2014
Sun, Shixiong | Lang, Junwei | Wang, Rutao | Kong, Lingbin | Li, Xiaocheng | Yan, Xingbin
Pseudocapacitance is commonly associated with surface or near-surface reversible redox reactions, as observed with transition metal oxides in alkaline aqueous electrolytes. Here, we demonstrate that pseudocapacitive behavior of Fe₂O₃ can occur in a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) ionic liquid (IL), and it is closely related to the chemical state variation between Fe³⁺ and Fe²⁺ on the surface of a Fe₂O₃ electrode during the charging/discharging process. By taking advantage of such pseudocapacitance, we prepared a promising electrode material, i.e., graphene nanosheet-supported Fe₂O₃ nanoparticles (denoted as Fe₂O₃@GNS), and then built high-performance asymmetric supercapacitors (ASs) using Fe₂O₃@GNS as the battery-type electrode material, commercial activated carbon (AC)/or activated polyaniline-derived carbon nanorods (denoted as APDC) as the capacitor-type electrode material, and EMIMBF₄ IL as the electrolyte. The as-made ASs are able to work reversibly in a full operation voltage region of 0–4 V and exhibit very high energy density. Especially, the AS of Fe₂O₃@GNS//APDC achieves an extremely high energy density of 177 W h kg⁻¹ and shows a superior combination of high energy and power density (the energy density still remains 62.4 W h kg⁻¹ even at a high power density of 8 kW kg⁻¹).
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