Open-Circuit Potential Drift in Intercalation Electrodes: Role of Charge Redistribution in a Prussian Blue Analog

Abstract

Prussian blue analogs (PBAs) are used as electrode materials in energy storage and water deionization cells due to their reversible cation intercalation capability. Despite extensive research on their performance and intercalation mechanisms, little attention has been given to their behavior under open-circuit conditions. Recent studies using symmetrical PBA electrodes in two electrode deionization cells reported that after constant current cycling in dilute NaCl (< 0.2 M), the cell voltage dropped under open-circuit conditions, which substantially increased the amount of energy consumed for deionization. However, it remains unclear which electrode (anode or cathode) underwent potential drift and if it was influenced by the low salinity of the electrolyte. Using a series of electrochemical experiments under different charging and discharging regimes and electrolyte compositions, we determined that charge redistribution within the electrode was the main contributor to open-circuit potential drift. A one-dimensional finite element model successfully reproduced experimental trends, corroborating the occurrence of charge redistribution. A Monte Carlo analysis of the model revealed a strong positive correlation between the simulated potential drift and a Dahmköhler number that depended on the applied current, electrode thickness, diffusion coefficient of intercalating ions, and intercalation capacity.