Recessed microelectrodes as a platform to investigate the intrinsic redox process of Prussian blue analogs for energy storage application

The determination of the intrinsic properties of solid active material candidates is essential for their performance optimization. However, macroscopic electrodes and related analytical techniques show challenges concerning the number of additional influencing parameters. We explore recessed microelectrodes (rME) as a platform that allows for a binder-free investigation of Prussian Blue analogues (PBA), a family of promising battery materials. The enhanced diffusion using microelectrochemical tools is indispensable to assess the intrinsic material performance, overcoming the limitation of cation diffusion from the electrolyte to the solid interface during (dis)charging cycles and allowing the investigation of limiting steps in the coupled ion-electron transfer process. The intrinsic electrochemical performance of PBAs was studied in a three-electrode configuration by means of cyclic voltammetry and galvanostatic (dis)charging in aqueous Na+-containing electrolyte. We extended the evaluation to the role of the electrolyte on the performance of cathodic and anodic processes of a Mn-based PBA. Ex-situ and operando chemical characterization were coupled to support the microelectrochemical results.