Cation–Water Dynamics in Prussian Blue Analogues Cathodes

Prussian blue analogues (PBA) cathodes are emerging as promising electrode materials for post-Li batteries due to their open framework, high theoretical capacity, and fast ion diffusion channels. Their large interstitial sites facilitate the reversible intercalation of both small and bulky cations, enabling efficient charge storage. These interstitial spaces, however, can also accommodate water molecules, which significantly influence the charging mechanism and, consequently, the electrochemical performance of PBA. Since water is nonelectroactive at the working potential of PBA cathodes, monitoring the dynamics of H₂O during charging is a challenging task. As a result, a comprehensive understanding of its contribution to the electrochemical behavior of PBA is still lacking. To address this issue, electrochemical quartz crystal microbalance with dissipation monitoring is employed to investigate NiPBA electrodes during the insertion/extraction of Na⁺, K⁺, and Cs⁺. This study is further supported by systematic electrochemical analysis in practical battery configurations and advanced X-ray diffraction measurements, providing deeper insights into the cation-water dynamics in PBA electrodes.