Electrochemical Properties of Barium Titanium Oxyhydride toward CO 2 Reduction

Mixed-anion compounds containing multiple anions are attractive solid-state materials whose properties can be controlled by the kind of anion introduced and its concentration. Recently, oxyhydrides, in which hydride ions (H–) are introduced into metal oxides, have been developed. These materials are known to serve as catalyst supports in thermocatalytic reactions such as ammonia synthesis and methanation. Although oxyhydrides have strong potential as catalysts because of their high electron-donating ability and metallic conductivity, their performance as catalysts themselves has not been adequately elucidated. In this study, we explored the electrocatalytic properties of barium titanate oxyhydride, BaTiO3–xHx, for the electrochemical CO2 reduction reaction (eCO2RR) and investigated the correlation between its hydride content (x) and catalytic activity. BaTiO3–xHx exhibited eCO2RR activity in acetonitrile, an aprotic solvent, and the activity varied with x. For BaTiO3–xHx electrocatalysts with an x value greater than 0.5, the formic acid Faradaic efficiency increased and methanol and ethanol were formed. The reduced species of titanium formed by the introduction of hydride ions may be a key factor. This finding indicates that introducing hydride ions into metal oxide hosts is an effective strategy to induce eCO2RR activity.