title: High Energy Density Aqueous Electrochemical Capacitors with a KI-KOH Electrolyte.
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.
authors: Department of Chemistry, Oregon State University , Corvallis, Oregon 97331, United States.
authors: Xingfeng
authors: X
authors: Wang
authors: Department of Chemistry, Oregon State University , Corvallis, Oregon 97331, United States.
authors: Raghu S
authors: RS
authors: Chandrabose
authors: Department of Chemistry and Biochemistry, University of Oregon , Eugene, Oregon 97403, United States.
authors: Sang-Eun
authors: SE
authors: Chun
authors: Department of Chemistry, Oregon State University , Corvallis, Oregon 97331, United States.
authors: Tianqi
authors: T
authors: Zhang
authors: Brian
authors: B
authors: Evanko
authors: Department of Chemistry, Oregon State University , Corvallis, Oregon 97331, United States.
authors: Zelang
authors: Z
authors: Jian
authors: Department of Chemistry and Biochemistry, University of Oregon , Eugene, Oregon 97403, United States.
authors: Shannon W
authors: SW
authors: Boettcher
authors: Galen D
authors: GD
authors: Stucky
authors: Department of Chemistry, Oregon State University , Corvallis, Oregon 97331, United States.
authors: Xiulei
authors: X
authors: Ji
keywords: KI and KOH mixture; aqueous electrochemical capacitor; high energy; high power; iodate; redox electrolyte