Hydrogen Storage in Hydrides

Our focus concerns the thermodynamic modelling, mathematical analysis and simulations of storage problems in crystal lattices with special emphasis to understand and control the evolution of the storage process and accompanying hysteretic phenomena.

Currently we study the storage of hydrogen in metals and the storage of lithium in the cathode of modern lithium-ion batteries. Characteristic for both problems is the appearance of phase transitions and large changes of the crystal volume leading to strong coupling of diffusion and mechanical stresses.

The current model for hydrogen storage is set up for the metal magnesium, because here a solid basis of thermodynamic and chemical data is available. The model embodies the dissociation of molecular gas at the metal surface, the diffusion and formation of MgH2 in the crystal and the appearance of mechanical stresses due to local volume changes of up to 30%. It is shown that the process cycle and the hysteresis in the pressure versus hydrogen content plot is strongly influenced by mechanical effects.

Within the framework of the corresponding storage problem in lithium-ion batteries, the research group has identified the crucial phenomena that influence the storage time and capacity of the battery.

Keywords: hydrogen storage, hydrides, modelling, thermodynamics, phase transition, simulation, mathematical analysis