Filling Vacancies in a Prussian Blue Analogue Using Mechanochemical Post-Synthetic Modification

Mechanochemical grinding of polycrystalline powders of the Prussian blue analogue (PBA) Mn[Co(CN)$_{\textbf6}$]$_{\textbf{2/3}}\boldsymbol\Box_{\textbf{1/3}}\cdot\boldmath x$H$_{\textbf 2}$O and K$_{\textbf 3}$Co(CN)$_{\textbf 6}$ consumes the latter and chemically modifies the former. A combination of inductively-coupled plasma and X-ray powder diffraction measurements suggests the hexacyanometallate vacancy fraction in this modified PBA is reduced by approximately one third under the specific conditions we explore. We infer the mechanochemically-driven incorporation of [Co(CN)$_{\textbf 6}$]$^{\textbf 3-}$ ions onto the initially-vacant sites, coupled with intercalation of charge-balancing K$^+$ ions within the PBA framework cavities. Our results offer a new methodology for the synthesis of low vacancy PBAs, unlocking novel, high capacity PBA battery materials.