Entropy stabilization of deformed regions characterized by an excess volume for hydrogen storage applications

Abstract

A general framework using the universal equation of state is given to quantify the excess entropy present in deformed regions of metals and metal hydrides characterized by an excess volume. The conditions under which the excess entropy leads to a stabilization of the deformed regions with respect to multiple hydriding/dehydriding cycles are determined. The impact of the energy barrier created by the excess entropy on the recrystallization rate of the deformed regions is quantified using a homogeneous nucleation and crystal growth model. At high temperature, due to the energy barrier, metal hydride systems containing a large excess volume can have a recrystallization rate that is several orders of magnitude smaller than the recrystallization rates of regions containing low excess volume. This entropy stabilization can create a regime where the reduced enthalpy of formation of the metal hydride could be maintained over multiple cycles because of the increased stability of the nanostructures responsible for the reduction in the enthalpy of formation.