Hydrogen in Metals

Hydrogen in Metals

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. It also affects the electronic structure of the metal when absorbed.

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 fundamental 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 e.g. quantum effects or of impurities in metallic lattices. Fundamental problems include screening of the proton charge by conduction electrons, vibrational states of the H-atom and transfer of H-atoms between different sites in a lattice by over-barrier or tunnelling processes. Complications arise when a proton is bound to another impurity, or when two or more protons are quantum correlated.

Among the application possibilities there is of course hydrogen as an energy carrier, e.g. in metal hydrides, where there has been a lot of activity during the last decades. Hydrogen is also 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 these contexts.

Finally, the presence of hydrogen often modifies the properties (magnetic, electric, optical as well as mechanical and elastic) of materials. This allows tailoring of materials by hydrogen addition.