High energy density aqueous electrochemical capacitors with a KI-KOH electrolyte

Xingfeng Wang, Raghu S. Chandrabose, Sang Eun Chun, Tianqi Zhang, Brian Evanko, Zelang Jian, Shannon W. Boettcher, Galen D. Stucky, Xiulei Ji

Research output: Contribution to journalArticlepeer-review

86 Scopus citations

Abstract

We report a new electrochemical capacitor with an aqueous KI-KOH electrolyte that exhibits a higher specific energy and power than the state-of-the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx-/I- couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx-/I- redox couple for the positive electrode, which pins the positive electrode potential to be 0.4-0.5 V vs Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach -1.1 V vs Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectroscopy and Raman spectrometry confirm the formation of IO3- ions (+5) from I- (-1) after charging. Based on the total mass of electrodes and electrolyte in a practically relevant cell configuration, the device exhibits a maximum specific energy of 7.1 Wh/kg, operates between -20 and 50 °C, provides a maximum specific power of 6222 W/kg, and has a stable cycling life with 93% retention of the peak specific energy after 14 000 cycles.

Original languageEnglish
Pages (from-to)19978-19985
Number of pages8
JournalACS applied materials & interfaces
Volume7
Issue number36
DOIs
StatePublished - 16 Sep 2015

Keywords

  • KI and KOH mixture
  • aqueous electrochemical capacitor
  • high energy
  • high power
  • iodate
  • redox electrolyte

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