Reversible hydrogen storage in NaF-Al composites

This work demonstrates that hydrogen can be reversibly stored in a composite of NaF and Al. NaF and Al reacts to a mixture of Na3AlF6 and NaAlH4 via hydridofluoride phases of the form Na3AlH6−xFx. The analysis of thermodynamics based on literature standard enthalpies of formation yields the technically favourable enthalpy of reaction of roughly 35 kJ/mol H2 for a theoretical gravimetric hydrogen storage capacity of 3.3 wt%. Reaction mechanisms are discussed with respect to substitution of hydrogen by fluorine in complex hydrides.