hydriding

Hydriding is the uptake of molecular hydrogen by a host material, typically a metal or alloy, to form a solid metal hydride. The process is central to hydrogen storage technologies and is also relevant in battery chemistry, metallurgy, and nuclear materials.

Mechanisms and thermodynamics of hydriding involve diffusion of hydrogen atoms into interstitial lattice sites and the subsequent formation of hydride phases. Absorption can be accompanied by volume expansion and sometimes by heat release or absorption, depending on temperature and the specific material. In many systems, hydrogen uptake occurs via a plateau in a pressure–composition isotherm, reflecting two-phase coexistence between the parent metal and the hydride. Kinetics are influenced by temperature, hydrogen pressure, microstructure, impurities, and the occurrence of phase transitions between hydride phases.

Materials commonly studied for hydriding include light metal hydrides such as magnesium hydride (MgH2), complex hydrides, palladium and palladium alloys, and certain layered or intermetallic alloys used for nickel–metal hydride (NiMH) batteries. Palladium can form palladium hydride (PdH_x) at modest pressures, and magnesium-based systems offer high hydrogen storage capacity, often requiring catalysts or high temperatures to improve kinetics. Hydriding also plays a role in zirconium and other cladding alloys in nuclear reactors, where hydrogen uptake can lead to zirconium hydride formation and embrittlement.

Applications of hydriding include reversible hydrogen storage for fuel cells, metal hydride batteries, and hydrogen separation or purification in some contexts. Safety considerations are important because hydrogen uptake and release can be highly exothermic and, in structural metals, hydriding can influence mechanical properties and lead to embrittlement if not managed. See also hydrogen storage, metal hydride, hydrogen embrittlement, and dehydrogenation.