Determining internal porosity in Prussian blue analogue cathode materials using positron annihilation lifetime spectroscopy

Prussian blue analogues (PBAs), A_xM[M'(CN)_6]_1-y·zH_2O , are a highly functional class of materials with use in a broad range of applications, such as energy storage, due to their porous structure and tunable composition. The porosity is particularly important for the properties and is deeply coupled to the cation, water, and [M'(CN)_6]^n- vacancy content. Determining internal porosity is especially challenging because the three compositional parameters are dependent on each other. In this work, we apply a new method, positron annihilation lifetime spectroscopy (PALS), which can be employed for the characterization of defects and structural changes in crystalline materials. Four samples were prepared to evaluate the method’s ability to detect changes in internal porosity as a function of the cation, water, and [M'(CN)_6]^n- vacancy content. Three of the samples have identical [M'(CN)_6]^n- vacancy content and gradually decreasing sodium and water content, while one sample has no sodium and 25