Noncovalent Pi–Pi Stacking at the Carbon–Electrolyte Interface: Controlling the Voltage Window of Electrochemical Supercapacitors
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- 作者：Mengya Li ; Andrew S. Westover ; Rachel Carter ; Landon Oakes ; Nitin Muralidharan ; Timothy C. Boire ; Hak-Joon Sung ; Cary L. Pint
- 刊名：ACS Applied Materials & Interfaces
- 出版年：2016
- 出版时间：August 3, 2016
- 年：2016
- 卷：8
- 期：30
- 页码：19558-19566
- 全文大小：523K
- 年卷期：0
- ISSN：1944-8252
文摘
A key parameter in the operation of an electrochemical double-layer capacitor is the voltage window, which dictates the device energy density and power density. Here we demonstrate experimental evidence that π–π stacking at a carbon–ionic liquid interface can modify the operation voltage of a supercapacitor device by up to 30%, and this can be recovered by steric hindrance at the electrode–electrolyte interface introduced by poly(ethylene oxide) polymer electrolyte additives. This observation is supported by Raman spectroscopy, electrochemical impedance spectroscopy, and differential scanning calorimetry that each independently elucidates the signature of π–π stacking between imidazole groups in the ionic liquid and the carbon surface and the role this plays to lower the energy barrier for charge transfer at the electrode–electrolyte interface. This effect is further observed universally across two separate ionic liquid electrolyte systems and is validated by control experiments showing an invariant electrochemical window in the absence of a carbon–ionic liquid electrode–electrolyte interface. As interfacial or noncovalent interactions are usually neglected in the mechanistic picture of double-layer capacitors, this work highlights the importance of understanding chemical properties at supercapacitor interfaces to engineer voltage and energy capability.