Potassium K-edge XANES has been used to understand the location of K + within the Prussian blue structure. Differentiated K + species were clearly observed, associated with the fully intercalated Prussian white structure, partial intercalation within Prussian blue, and within the aqueous KNO 3 electrolyte. Theoretical simulations of Prussian blue, and associated XANES simulations, show that K + resides within the cavities of the structure, but located away from the center of the primitive cubic cavities (8c site) and towards the corners of the cavities (32f' position), due to structural defects or occluded water.