Reducing the dehydrogenation temperature of lithium hydride through alloying with germanium

Abstract

LiH is a highly stable light metal hydride with a hydrogen capacity of 12.5 wt%. However, having a dehydrogenation enthalpy, ΔH_dehy, of 181.2 kJ mol⁻¹(H₂) and a resultant T(1 bar) of 944 °C, it is not a practical hydride for most hydrogen storage applications. In the work presented here, germanium has been found to dramatically reduce the dehydrogenation temperature for LiH down to just 270 °C. The enthalpy of dehydrogenation was reduced through the formation of lithium germanides. The reaction pathway was identified in this study using in situ powder neutron diffraction, showing the successive formation of more Li-rich germanides, following the series: LiGe, Li₄Ge₂H, Li₉Ge₄, and Li₇Ge₂. The enthalpy of formation for these germanides provides the thermodynamic tuning to reduce the ΔH_dehy for the system. The 3LiH–Ge system investigated is found to be reversible with a maximum capacity of 3.0 ± 0.1 wt%.