Solubility in Metals:

Hydrogen dissolves as atoms in metals.  Those atoms occupy octahedral and tetrahedral locations inside the lattice.  The hydrogen apparently exists inside nonhydriding metal lattices as deuteron, proton, or triton, along with the electron in a metal conduction band.  A few metals are endothermic (chemical change because of absorption of heat) hydrogen absorbers and others are exothermic (chemical change which releases heat), and solubilities vary considerably (approximately 10 to 15 orders of magnitude) at room temperature.

The solubility of hydrogen within endothermic absorbers rises as the temperature increases. The reverse is true for exothermic absorbers and the solubility decreases as the temperature increases. For several hydride phases, plots of decomposition overpressure as a function of inverse temperature yield negative enthalpies or heats of establishment.