Hydrogen-Storing Salt NaCl(H${}_2$) Synthesized at High Pressure and High Temperature

Abstract

X-ray diffraction and Raman scattering measurements, and first-principles calculations are performed to search for the formation of NaCl-hydrogen compound. When NaCl and H${}_2$ mixture is laser-heated to above 1500 K at pressures exceeding 40 GPa, we observed the formation of NaClH${}_{\text{x}}$ with $\text{P}$6${}_3$/$\text{mmc}$ structure which accommodates H${}_2$ molecules in the interstitial sites of NaCl lattice forming ABAC stacking. Upon the decrease of pressure at 300 K, NaClH${}_{\text{x}}$ remains stable down to 17 GPa. Our calculations suggest the observed NaClH${}_{\text{x}}$ is NaCl(H${}_2$). Besides, a hydrogen-richer phase NaCl(H${}_2$)${}_4$ is predicted to become stable at pressures above 40 GPa.