Electrochemical Oxidative Fluorination of an Oxide Perovskite

We report the successful electrochemical intercalation of F-ions into a densely packed perovskite oxide from a liquid electrolyte at room temperature. Using galvanostatic oxidation and electrochemical impedance spectroscopy coupled with operando X-ray diffraction, we show that roughly 0.5 equivalents of F-ions can be inserted onto the vacant A-site of the perovskite ReO3. Density functional theory calculations indicate that the intercalated phase is thermodynamically unfavorable compared to other less densely packed polymorphs of ReO3F. Pairing X-ray spectroscopy, neutron total scattering measurements, and magic-angle spinning 19F NMR confirms a rapid decomposition of the product on removal from the cell but nevertheless, these results clearly demonstrate that small anions like fluoride can be intercalated into solids as readily as alkali cations at room temperature, which opens new opportunities to electrochemically fluorinate many new materials.