Quantifying nuclear quantum effects in metal hydrides for hydrogen storage

• Applicant: Dr. Kai Sellschopp
• Subject Area: Theoretical Chemistry: Molecules, Materials, Surfaces ; Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale ; Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 506703280

In the course of the energy transition towards a sustainable cyclic economy, hydrogen (H2) will play a significant role due to its high mass-specific energy density, its availability, and its application potential in the chemical industry. Metal hydrides (MHs) present a promising possibility of storing hydrogen with low losses and security risks, while having a high volumetric storage density. However, the thermodynamics and kinetics of the hydrogenation, which determine the application temperature and the speed of charging/discharging, respectively, still offer some optimization potential. In this regard, theoretical studies can identify promising materials and provide deeper insight into the processes during the hydrogenation reaction on the atomic scale. So far, simulations neglect the possibility of significant nuclear quantum effects (NQE), such as delocalization and tunneling, of the proton in hydrogen, which directly influences the thermodynamic stability and the kinetics of MHs.Therefore, the aim of this project is to study and quantify the influence of NQE on the accuracy of theoretical models for MHs thoroughly for the first time. To achieve this, computationally demanding path-integral and ring-polymer molecular dynamics calculations will be performed employing ab-initio and machine-learned (ML) force fields. First, the well-known magnesium hydride (MgH2) system will be investigated, testing and adapting the methods for the rest of the project. Then, the study will move on to alloyed magnesium hydrides and further technologically relevant interstitial MHs. In order to reduce the computational costs and to facilitate the transition to new materials, the modelling process will be automatized, and ML force-fields will be trained in each step. Quantifying the NQE in MHs for the first time will not only improve the accuracy of theoretical predictions, but also provide deeper insight into relevant processes at the atomic scale. Furthermore, it enables future studies to make an informed decision about including or neglecting NQE. In addition, implementing the results in multi-scale simulations and ML models will improve their accuracy.The project will be performed at the Institute for Hydrogen Technology of the Helmholtz-Zentrum Hereon in Geesthacht, where leading theoretical and experimental experts on hydrogen storage in MHs work together to understand and improve these systems on different scales. Collaborations with modelling groups at the Max-Planck-Institute for the Structure and Dynamics of Matter (MPSD) and the Lawrence Livermore National Laboratory (LLNL), which contribute their expertise on modelling NQE and interstitial MHs on different scales, respectively, are also part of the project. A short research visit to LLNL will foster the collaboration and promote international mobility.

• DFG Programme: WBP Position