High Energy Density Aqueous Electrochemical Capacitors with a KI-KOH Electrolyte (original) (raw)

We report a new electrochemical capacitor with an aqueous KIKOH electrolyte that exhibits a higher specific energy and power than the stateof- 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.

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