title: Noncovalent Pi-Pi Stacking at the Carbon-Electrolyte Interface: Controlling the Voltage Window of Electrochemical Supercapacitors.
abstract: 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.
authors.forename: Mengya
authors.initials: M
authors.lastname: Li
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Westover
authors.forename: Rachel
authors.initials: R
authors.lastname: Carter
authors.forename: Landon
authors.initials: L
authors.lastname: Oakes
authors.forename: Nitin
authors.initials: N
authors.lastname: Muralidharan
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Boire
authors.affiliation: Division of Cardiovascular Medicine, Vanderbilt University Medical Center , Nashville, Tennessee 37232, United States.|Severance Biomedical Science Institute, College of Medicine, Yonsei University , Seoul 120-752, Republic of Korea.
authors.forename: Hak-Joon
authors.initials: HJ
authors.lastname: Sung
authors.forename: Cary L
authors.initials: CL
authors.lastname: Pint
keywords: electric double-layer capacitor; graphene; ionic liquids; pi−pi stacking; polymer electrolyte; porous silicon; supercapacitor