high pressure gas cylinders (up to 800 bar);
liquid hydrogen in kryogenic tanks (at 21 K);
adsorbed hydrogen on materials with a large specific
surface area (at T < 100 K);
absorbed on interstial sites in a host metal (at ambient
pressure and temperature);
chemically bond in covalent and ionic compounds (at
ambient pressure);
oxidation of reactive metals, e.g. Li, Na, with water.