(Invited) Atomistic Simulations of Hydrogen Storage Materials
Authors: Zhou Xiaowang , Spataru Catalin , Stavila Vitalie , Allendorf Mark D. , Kang ShinYoung , Heo Tae Wook , Wood Brandon C. 
Published: February 2020

Solid state hydrogen storage materials possess good volumetric and gravimetric hydrogen storage densities and can be more attractive hydrogen storage media for hydrogen fuel cell vehicles. However, the current hydrogen storage materials are limited by their slow hydrogen storing and releasing kinetics. Understanding thermodynamic and kinetic foundations that limit the current storage materials is critical for accelerated material improvement. To achieve this understanding, we have been developing and applying atomistic simulation tools to study various classes of hydrogen storage materials. Here we present three cases. First, we have developed a series of molecular dynamics methods to study diffusional phase transformation hydrides, such as PdHx. This allows us to analytically quantify bulk and interfacial diffusivities, surface and interfacial energies, surface segregation, lattice constants, Gibbs free energy, and elastic constants, all as a function of temperature and composition. We then implemented all these properties in phase field codes and directly simulated the hydrogenation and dehydrogenation of PdHx at the engineering scale. Second, we have developed a high-fidelity Mg-H bond order potential to study the structural phase transformation hydrides, such as MgH2. We demonstrate that this potential not only captures the property trends for a variety of selected phases, but also ensures direct molecular dynamics simulation of formation and decomposition of the crystalline MgH2 phase. This new capability, not demonstrated in the past, opens up opportunities to explore in great details mechanisms of hydrogenation and dehydrogenation processes. Finally, we discuss our recent progress on developing a Mg-B-H ternary potential that can be used in atomistic simulations to study thermodynamics and kinetics behaviour of complex metal hydrides based on magnesium and boron.
Acknowledgement - Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. A portion of this work was performed under the auspices of Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The authors gratefully acknowledge research support through the Hydrogen Storage Materials—Advanced Research Consortium (HyMARC), from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract Numbers DE-AC04-94AL85000 and DE-AC52-07NA27344. The views expressed in the article do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.