Moreover, the formation and decomposition of metal hydrides is accompanied by electron transfer as well as chemical adsorption and desorption of H2molecules on surfaces/interfaces. However, the role of electron transfer and heterogeneous interfaces has received little attention in the hydrogen storage community, unlike more conventional electrochemical systems such as batteries. In fact, metal hydrides for hydrogen storage share much in common with electrochemical devices. For example, in hydrogen storage hydrogen gas reacts with solid metal phases and forms metal hydrides during hydrogenation, similar to the way oxygen gas reacts with metal ions in metal-air batteries during discharge. In subsequent dehydrogenation or charging processes, these materials likewise release hydrogen or oxygen gases, respectively. Processes in hydrogen storage are driven by hydrogen pressure- and temperature-dependent chemical potentials, while chemical potential and voltage are analogous driving forces in electrochemical systems.
As a part of the DOE Hydrogen Storage Materials — Advanced Research Consortium (HyMARC), we have been leveraging the similarities between these systems to introduce new modeling concepts to study heterogeneous interfaces in metal hydrides for hydrogen storage. We have categorized interfaces into three groups: intercalation, sharp, and diffuse interfaces, based on whether lattice deformation occurs between phases and the extent of variations of composition and strain profiles (see Table 1). In this talk, we will provide examples of how different computational techniques can be deployed for each of these three different types of interfaces. In addition, we will show how a description of chemical reaction kinetics can be included to model reactive and diffuse interfaces for systems comprised of cations and reactive molecular anions. The chemical reaction kinetics of molecular phases at the interfaces and the interface heterogeneity issue are addressed using large-scale ab initio molecular dynamics, enabling us to study spatial and temporal properties of the reactive diffuse interface. In this manner, we expect to better understand the energetics, composition, and structure of metal hydride interfaces, and further studies on electron transfer, hydrogen reaction and transport at and along the interfaces will enable us to optimize system performance.
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This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.