Suppressed activation energy for interfacial charge transfer of a Prussian blue analog thin film electrode with hydrated ions (Li⁺, Na ⁺, and Mg²⁺)

Interfacial charge transfer is one of the most important fundamental steps in the charge and discharge processes of intercalation compounds for rechargeable batteries. In this study, temperature-dependent electrochemical impedance spectroscopy was carried out to clarify the origin of the high power output of aqueous batteries with Prussian blue analog electrodes. The activation energy for the interfacial charge transfer, E_a, was estimated from the temperature dependence of the interfacial charge transfer resistance. The E_a values with Li⁺ and Na⁺ aqueous electrolytes were considerably smaller than those with organic electrolytes. The small E_a values with aqueous electrolytes could result from the fact that the Coulombic repulsion at the interface is largely suppressed by the screening effect of hydration.