Pressure-Induced Formation of Noble Metal Hydrides

Noble metals (Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) do not form hydrides with hydrogen under ambient conditions originated from the extremely low solubility of hydrogen in them. Because of such limitation, finding these hydrides under ambient conditions is scarce. Here we use a combination of particle swarm optimization technique on crystal structure prediction and first-principles calculations based on density functional theory to explore the reactivity of hydrogen with noble metals under high pressure. We demonstrated that except for Au, other noble metals can commonly form monohydrides under high pressure even at zero temperature. We find universal high pressure structure features of these monohydrides-the structures either are stable or eventually transform into closed packed fcc or hcp with hydrogen occupying the octahedral interstitial sites of the metal sublattices. Of particular interest by the introduction of hydrogen are the high pressure structural changes of these noble metals, which, however, remain remarkably stable for pure elements. Our research highlights the key role of pressure played in the formation of these noble metal hydrides.