Phase field modeling of hydrogen transport and reaction in metal hydrides

The reaction of hydrogen with metals to form metal hydrides has numerous potential energy storage and management applications. The metal hydrogen system has a high volumetric energy density and is often reversible with a high cycle life. However, improving the often poor gravimetric performance of such systems through the use of lightweight metals usually comes at the cost of reduced reaction rates or the requirement of pressure and temperature conditions far from the desired operating conditions. Most studies of reaction kinetics of such systems focus on fitting low-dimensional kinetic models to measured rates and inferring the rate-limiting process based on the quality of the fit. ork develops a methodology for describing these reactions using a multi-process model of the physical transport and energy state transitions of interstitial hydrogen atoms within a metal lattice. In its nondimensional form, this model is applicable to arbitrary geometries and dimensions using four nondimensional kinetic parameters based on the physical transport mechanisms present in the system. oposed model is then used for LaNi5 and TiCrMn to examine how the nucleation pattern, kinetic parameters, and particle aspect ratio affect the time of formation of a closed hydride layer and the apparent measured kinetics. The analysis is applied to both hydriding and dehydriding processes to show how different kinetic limitation mechanisms can manifest when considering the reciprocal reaction.