Synergistic Optimize the Hydrogen Storage Capacity and Dehydrogenation Properties of NaAlH ₄ via Li‐Doping

ABSTRACT

Although NaAlH ₄ is considered a promising hydrogen storage material due to its high hydrogen storage capacity (7.5 wt%), its practical application is limited by the high dehydrogenation temperature, slow reaction dynamics and limited reversibility. To solve these problems, we investigate the influence of Li‐doping on the hydrogen storage capacity, hydrogen desorption energy, electronic and optical properties of NaAlH ₄ . The results show that the theoretical hydrogen storage capacity of NaAlH ₄ increases with increasing Li‐doped concentration, reaching a maximum of 9.6 wt%. Compared with undoped NaAlH ₄ , the hydrogen storage capacity of Li‐doped NaAlH ₄ is enhanced by 28%. However, an increase in Li‐doped concentration may lead to the formation of LiH phase, which could reduce its reversible hydrogen storage capacity. Although Li‐doped NaAlH ₄ remains thermodynamically stable, its thermal stability decreases with increasing Li‐doping concentration. Compared to parent NaAlH ₄ , it is beneficial to hydrogen release. Ab‐initio molecular dynamics (AIMD) simulation further confirmed the thermodynamic stability of Li‐doped NaAlH ₄ . Furthermore, the calculated hydrogen desorption energy indicates that Li‐doped reduces the activation energy barrier for hydrogen release, which promotes hydrogen dissociation and desorption. This behavior is related to Li‐induced local charge redistribution, which weakens the bond strength between the Al–H bond in the [AlH ₄ ] group. The reduction in Al–H bond energy reduces the reaction energy barrier during the dehydrogenation process, which accelerates the hydrogen release from the NaAlH ₄ . This mechanism is further confirmed by band structure, which shows that the band gap gradually narrows with the Li‐doped concentration increases. The narrowing of the band gap enhances electronic transition near the electron free energy surface, which promotes hydrogen release.