Giant hydrogen storage capacity of 11.23% and high thermoelectric response in Li3AlH6: A potential candidate for fuel cell and energy harvesting technologies

In recent years, the exploration of hydrogen storage (HS) aspects in complex hydrides has gained significant importance. Here, using first-principles calculations under hydrostatic ([111]) strain, we investigated the Li3AlH6 hydride in terms of its potential for HS application and energy harvesting. The computed formation enthalpy (∆Hf) of −31.66 kJ/mol·H2 for the unstrained system is close to the ideal value of −40 kJ/mol·H2, resulting in a hydrogen desorption temperature (Tdes.) of 244 K. It is interesting to note that ∆Hf and Tdes. values are maintained within the optimal range against ±5% strain, indicating the material’s durability and acceptability for outdoor conditions. With a very high gravimetric and volumetric capacity of 11.23 wt% and 122.49 gH2/L, it exhibits a colossal hydrogen storage capability. Additionally, the materials’ mechanical stability is confirmed by the Born stability criteria, where the material’s covalent bonding is further suggested by the computed G/B ratio and Poisson’s ratio. Also, the system displays dynamic stability as no imaginary frequencies exist in the phonon dispersion curves. For the considered strain range, an insulating behavior of the system with an energy gap of 3.4-2.98 eV is revealed. Ultimately, it is discovered that tensile strains enhance thermoelectric performance because of enhanced phonon scattering, which leads to a large figure of merit of 0.78 at 1050 K, making it a promising material for producing electricity from heat. Thus, the current study indicated that Li3AlH6 is an optimistic compound for HS and energy harvesting applications.