Water Durable Electride Y₅Si₃: Electronic Structure and Catalytic Activity for Ammonia Synthesis

We report an air and water stable electride Y₅Si₃ and its catalytic activity for direct ammonia synthesis. It crystallizes in the Mn₅Si₃-type structure and confines 0.79/f.u. anionic electrons in the quasi-one-dimensional holes. These anionic electrons strongly hybridize with yttrium 4d electrons, giving rise to improved chemical stability. The ammonia synthesis rate using Ru(7.8 wt %)-loaded Y₅Si₃ was as high as 1.9 mmol/g/h under 0.1 MPa and at 400 °C with activation energy of ∼50 kJ/mol. Its strong electron-donating ability to Ru metal of Y₅Si₃ is considered to enhance nitrogen dissociation and reduce the activation energy of ammonia synthesis reaction. Catalytic activity was not suppressed even after Y₅Si₃, once dipped into water, was used as the catalyst promoter. These findings provide novel insights into the design of simple catalysts for ammonia synthesis.