X-ray absorption spectroscopic study of sodium iodide and iodine mediators in a solid-state supercapacitor

By Mansour, Azzam N.; Zhou, Juanjuan & Zhou, Xiangyang
Published in Journal of Power Sources NULL 2014

Abstract

In situ X-ray absorption spectroscopy was used to provide the redox states of the NaI/I2 mediators in an all-solid-state mediator-enhanced supercapacitor during the charge/discharge processes. Results show that in the charge process from -0.08 (open-circuit voltage (OCV)) to 0.80 V at constant current of 5 mA, all of the I- ions were oxidized to I2. However, in the discharge process from +0.80 V to OCV at constant current of -5 mA, only I 3 - ions were detected indicating that the I2 molecules were reduced to I 3 - ions. Upon a negative polarization from OCV to -0.80 V at constant current of -5 mA, the I 3 - ions were reduced to I- ions. Based on combined in situ XAS and cyclic voltammetry data, we show that the I-/I2 redox couple proceeds via the formation of I 3 - ions as an intermediate step.

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