EQCM Analysis of Redox Behavior of CuFe Prussian Blue Analog in Mg Battery Electrolytes

A wide variety of ions and molecules can be accommodated in the framework structure of Prussian blue (PB) and its analogs (PBAs). Mono- and polyvalent ions accommodated in the PB framework structure and PBAs can be extracted or re-inserted by redox reactions of transition metal ions composing the framework for charge compensation. In the present work, we report the detailed mechanism of the electrochemical inseration/extraction of Mg 2 + ions and the effect of anions on the redox chemistry of a PBA composed of Cu and Fe ions by electrochemical quartz crystal microbalance and X-ray absorption spectroscopy. Furthermore, we evaluated the PBA as an active material using aqueous and organic electrolytes for Mg battery systems, and clarified that the redox potential of CuFe-PBA is approximately 3 V vs. Mg/Mg 2 + in both aqueous and organic electrolytes.