Hydrogen is the lightest element in the periodic table. It is a main component in most organic materials and forms hydrides with high hydrogen content when introduced into many metals. The hydrogen nuclei (protons) are highly mobile in the metal hydride lattices and at lower temperatures there are strong effects of quantum tunnelling. This makes metallic hydrides interesting from a basic point of view, at the same time as their storage capacity is of potential use for energy systems with hydrogen as an energy carrier.
Hydrogen is the simplest atom for studies of quantum effects, as well as a single proton in a metallic lattice is the simplest impurity problem. Already at this level, there are fundamental problems to be solved, such as the screening of the proton charge by conduction electrons, the vibrational states of the H-atom and the transfer of H-atoms between different sites in the lattice by over-barrier or tunnelling processes. Complication arises when a proton is bound to another impurity or two or more protons are quantum correlated.
The interest in hydrogen as an energy carrier has increased considerably during the last decades. The energy related research at Materials Physics is focused on new lightweight materials for hydrogen storage. Magnesium (Mg) is considered to be one of the most promising base material. The aim of the research is to enhance the hydrogen absorption rate and to overcome the problems connected with the high absorption/desorption temperatures by alloying Mg with other metals.
Hydrogen is highly relevant for vacuum technology and the outgassing of materials is completely dominated by hydrogen at the lowest accessible pressures. Understanding of the hydrogen uptake of materials is therefore highly useful for obtaining desired material properties in this context.
Finally, the presence of hydrogen often modifies the properties of materials. This allows the tailoring of material properties such as magnetic, electric, optical as well as mechanical and elastic properties.