| Apr 30, 2022 |
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(Nanowerk News) Graphene-based micro-supercapacitors (EG-MSCs) combine the distinct properties of graphene and the advantages of planar device configuration to maximize charge storage. Therefore, they can provide more flexible, smaller, and thinner devices.
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However, the limited electric double layer capacity of graphene and the narrow voltage window of aqueous electrolytes limit their further application.
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Recently, a joint resarch team led by Prof. WU Zhongshuai and Prof. FU Qiang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has proposed a strategy for boosting the capacitance of graphene-based planar MSCs by highly concentrated water-in-salt ambipolar redox electrolyte (ZnI2 + ZnCl2).
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This study was published in ACS Energy Letters (“Water-in-Salt Ambipolar Redox Electrolyte Extraordinarily Boosting High Pseudocapacitive Performance of Micro-supercapacitors”).
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| Graphical abstract of the work. (© ACS Energy Letters)
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Using redox-active electrolytes to boost graphene electrodes is a highly-efficient strategy to increase the capacitive performance of MSCs.
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However, previously reported redox mediators could only offer a certain capacitance for a single electrode, leading to limited energy density due to the unmatched capacitances of two electrodes.
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In this study, the researchers developed a novel highly concentrated water-in-salt ambipolar redox electrolyte where one ambipolar mediator (ZnI2) could offer two redox couples (I–/I2 and Zn/Zn2+) natively, with matched charge storage.
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These two species allowed two electrons to be oxidized at the positive electrode and to be reduced at the negative electrode synchronously and individually, thus offering a large pseudocapacitive contribution for EG-MSCs.
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They have realized high volumetric capacity of 106 mAh/cm3, energy density of 111 mWh/cm3, and long-term cycling stability with 92.1% retention after 5,300 cycles.
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In situ characterizations confirmed that these good performances were attributed to the frustrated self-discharge by suppressing the formation and diffusion of polyiodide ions of I3– and I5–.
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Moreover, EG-MSCs showed stable cycling performance at -20 °C owing to the reduced freezing point of water by strong interactions between water molecules and zinc ions.
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“This work opens a new avenue of introducing ambipolar redox mediators into highly concentrated electrolytes for high-performance MSCs,” said Prof. WU.
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