Oxyhydride Synthesis through Facile Water Dissociation on the Electride Intermetallic LaScSi

The simultaneous presence of hydride (H^-) and oxide (O^2-) anions in an inorganic material is thermodynamically challenging. Oxyhydrides have always been synthesized from an oxide precursor, by using high-temperature solid-state reaction using a mixture of oxide and hydride, topochemical reduction at mild temperatures, or high-pressure synthesis. Here, we introduce a novel and unprecedented synthesis route for transition metal oxyhydrides, where the starting material is not an oxide but an intermetallic compound, LaScSi. The topochemical synthesis of LaScSiO_<i>x</i>H_<i>y</i> (<i>x</i> ≈ 0.5, <i>y</i> ≈ 1) occurs through water dissociation, highlighting the exceptional catalytic behavior of the electride-type parent material. The topochemical insertion of oxygen and hydrogen transforms LaScSi into a more two-dimensional material and modifies its electronic properties, altering its transport properties, from three-dimensional metallic to semimetallic. This innovative path to oxyhydrides is also of fundamental interest for catalysis: it could open the way for new methods of hydrogen production and storage, especially in water splitting, bypassing traditional processes such as electrolysis or photocatalysis.