First-principles investigation of rhodium hydrides under high pressure

Hydrogen-rich compounds are being extensively explored theoretically and experimentally as potential hydrogen storage materials. In this work, we predicted a hydrogen-rich compound rhodium trihydride (RhH₃) with a high volumetric hydrogen density of 212.5 g/L by means of ab initio calculations. The RhH₃ with Pnma symmetry is thermodynamically stable and accessible through synthesis above 40 GPa. The compound is dynamically and mechanically stable at ambient pressure. Further calculation suggests a probable dehydrogenation temperature Tdes of 650.16em0ex^∘C at ambient pressure with decomposition route to Rh+H₂. High volumetric hydrogen density and moderate dehydrogenation temperature place RhH₃ as one of the best hydrogen storage materials. Our work encourages the experimental synthesis of RhH₃ at high pressure.