Effect of metal atom substitutions in Li based hydrides for hydrogen storage

Abstract By using density functional theory and the full-potential linearised augmented plane wave method, the effect of alkali (AM) and transition metal (TM) atom substitutions in Li based hydrides (Li7XH8 X (AM) = Na, K, Rb and X (TM) = Ti, V, Cr) was investigated, by studying their formation energies and electron properties, aiming at improving hydrogen storage performance. The calculated formation energy values indicate that there is a gradual degradation in stability due to alkali substitutions from Na to Rb and to transition metal substitutions from Ti to Cr in Li7XH8. The found degradations of stability in Li7XH8 were better compared concomitantly with corresponding gravimetric hydrogen storage variations. The less stable phase with least variation in gravimetric hydrogen storage was found to be Li7CrH8 among all alkali and transition metal atom substitutions. The density of states and the electron density support our observations.