Total and partial hydrogen restitution in TiFe-H systems

Based on density functional theory and full-potential linearised augmented plane wave method, total and partial hydrogen restitution in TiFe-H systems were investigated by formation energy and density of states calculations. The formation energy values indicate that the TiFeH4 is less stable, and the total hydrogen restitution is more reversible compared to TiFeH and TiFeH2. The partial hydrogen restitution from TiFeH4 to TiFeH has the best hydrogen reversibility among TiFe-H systems giving three hydrogen atoms with a formation energy less than half that from total hydrogen restitution in TiFeH4. The density of states (DOS) analyses of TiFe-H systems support the results obtained above. The DOS of TiFe-H systems show that the DOS structure moves towards anti-bonding states at higher energies while hydrogen density increases.