Electrochemical capacitors with KCl electrolyte |
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| Institution: | 1. Institute of Solid State Chemistry, UB RAS, 91 Pervomayskaya Str., 620990 Yekaterinburg, Russia;2. Ural Federal University, 19 Mira Str., 620002 Yekaterinburg, Russia;1. Institut Charles Gerhardt, UMR 5253 CNRS Université Montpellier 2 34095 Montpellier cedex 05, France;2. CIRIMAT, UMR 5085 CNRS Université Paul Sabatier 118 route de Narbonne, 31062 Toulouse, France;3. Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, France;4. Department of Materials Science and Engineering & A.J. Drexel Nanotechnology Institute Drexel University 3141 Chestnut St., Philadelphia, PA 19104, United States;1. Division of Advanced Materials Engineering, Chonbuk National University, Jeonbuk, 54896 Republic of Korea;2. Hydrogen and Fuel Cell Research Center, Chonbuk National University, Jeonbuk, 54896 Republic of Korea |
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| Abstract: | Potassium manganese dioxide KxMnO2 + δ·nH2O and amorphous MnO2 in a mild 2 M KCl aqueous electrolyte prove to be excellent electrodes for faradaic electrochemical capacitors. The KxMnO2 + δ·nH2O materials were prepared by direct thermal decomposition of KMnO4 and contained a large amorphous/crystalline ratio. A sample decomposed at 550 °C gave a specific cyclic capacitance between ?0.2 and +1.0 V/SCE of 240 F·g?1, which corresponds to nearly one-third of the Mn(IV) ions participating in the faradaic reaction. Excellent cyclability at 12 mA·cm?2 was found for 100 cycles. On short-circuit, K0,31MnO2,12·0,63 H2O in 2 M KCl and pH 10.6 aqueous solution gave an initial current density of 0.58 A·cm?2 and a total released charge of 4.6 C·cm?2 compared with 0.32 A·cm?2 and 11.1 C·cm?2 for RuOOH·nH2O in 5.3 M H2SO4. Similar results obtained with amorphous MnO2 demonstrate that alkali ions can be used as the working ion in a faradaic supercapacitor, which frees the search for new materials from the constraint of working in a strong-acid aqueous medium. |
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