Palmierite‐Type Oxyhydride Ba ₃ V ₂ H _0.5 O _7.5 With Vanadium Charge Ordering

Hydride ions (H − ) are attracting increasing interest as alternative charge carriers to protons in electrochemical devices; however, the development of H – /e – mixed conductors remains challenging. Herein, we demonstrate a novel design strategy for hydride incorporation using oxide‐ion‐conducting transition metal oxides as precursors. Using Ba 3 V 2 O 8 as the precursor, we successfully synthesized the first palmierite‐type oxyhydride, Ba 3 V 2 H 0.5 O 7.5 (BVHO), via a topochemical ion exchange reaction. Structural analyses revealed that BVHO exhibits a unique crystal structure featuring a charge ordering of V 5+ or V 4+ at tetrahedral sites and V 3+ or V 2+ at octahedral sites, accompanied by a random distribution of H and O at the anion sites. Electrochemical impedance spectroscopy of a symmetric BVHO|Ba 1.75 LiH 2.7 O 0.9 |BVHO cell confirmed that BVHO functioned as a hydrogen reversible electrode. These results highlight the potential of oxide‐ion‐conducting oxides as effective precursors for creating novel oxyhydrides with distinct framework structures, thereby expanding the exploration space for H – ·e − mixed conductors.