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

## TL;DR

This study reports the synthesis of a novel hydrogen-storing salt NaCl(H₂) at high pressures and temperatures, revealing its structure, stability, and potential for hydrogen storage applications.

## Contribution

It provides experimental evidence and theoretical predictions for new NaCl-hydrogen compounds formed under extreme conditions, expanding understanding of salt-hydrogen interactions.

## Key findings

- NaClHₓ formed at >1500 K and >40 GPa with a specific crystal structure.
- NaClHₓ remains stable down to 17 GPa upon pressure release.
- Prediction of a hydrogen-rich phase NaCl(H₂)₄ stable above 40 GPa.

## 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$_{\textit{x}}$ with $\textit{P}$6$_{3}$/$\textit{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$_\textit{x}$ remains stable down to 17 GPa. Our calculations suggest the observed NaClH$_{\textit{x}}$ is NaCl(H$_{2}$). Besides, a hydrogen-richer phase NaCl(H$_{2}$)$_{4}$ is predicted to become stable at pressures above 40 GPa.