Intrinsic Thermal Conductivity of Mg\(_{2}\)NiH\(_{4}\) at High Pressures: A First-Principles Study

Abstract

To realize a hydrogen energy-based society, an efficient solid-state hydrogen-storage material is crucial. Among candidate materials, the storage performance and thermal management during the hydrogenation–dehydrogenation processes need to be improved by optimizing the thermofluid dynamics and thermal conductivity. A common approach is to add a thermally conductive material; however, few studies have tried to enhance the intrinsic thermal conductivity of solid-state hydrogen-storage materials because of their many crystalline phases depending on the temperature, pressure, and hydrogen concentration. We employed a first-principles anharmonic lattice dynamics to calculate the lattice thermal conductivity of the solid-state hydrogen-storage material Mg\(_{2}\)NiH\(_{4}\) considering various structures that correspond to the unresolved crystalline phases observed in previous high-pressure experiments. Our results revealed that the thermal conductivity of Mg\(_{2}\)NiH\(_{4}\) has a non-trivial dependence on pressure that is driven by complex modulations of the vibrational characteristics. Moreover, the room-temperature thermal conductivities of the crystalline phases are below 20 W m\(^{-1}\) K\(^{-1}\) at pressures below 10 GPa, which was attributed to the large mass contrast of constituent elements and the structural complexity. These findings provide valuable insights for the thermal engineering of hydrogen-storage units based on Mg\(_{2}\)NiH\(_{4}\).