Investigation of solid-state hydrogen storage performance using multiple phase change materials

In this study, the concept of integrating multiple annular phase change materials (PCM) with a metal hydride (MH) reactor is investigated to enhance hydrogen storage efficiency. A detailed mathematical model is developed to represent hydrogen storage in the MH and latent heat storage in the PCM. The selected metal hydride is the low-temperature LaNi₅, and the three PCMs used— CaCl 2 ·6H 2 O, LiNO 3 .3H 2 O, and Na 2 CO 3 .10H 2 O—are chosen based on compatibility of their solidus and liquidus temperatures with the MH. An initial study highlights the critical importance of accounting for buoyancy effects in PCM simulations, particularly in cases where significant temperature gradients lead to density variations and strong natural convection . This effect has been overlooked in several previous studies. Incorporating the buoyancy effect into the numerical model leads to a significant reduction of approximately 27.41 % in the time required to achieve 90 % hydrogen storage, resulting in discrepancies and substantial variations in the local distribution of key parameters compared to model that do not account for this effect. The results indicate that the MH bed with LiNO 3 ·3H 2 O outperforms the MH bed with CaCl 2 ·6H 2 O by 51.6 % and Na 2 CO 3 ·10H₂O by 14.12 % in terms of hydrogen storage performance. The simulations with annular two layers of PCMs show that the combination of LiNO 3 ·3H 2 O and CaCl 2 ·6H 2 O significantly outperforms the other two possible combinations, and it is 4 % more effective for hydrogen storage compared to using LiNO 3 ·3H 2 O alone. The findings of the present study emphasize the potential of combining multiple PCMs with MH reactors to optimize the efficiency of hydrogen storage systems across various applications. • Buoyancy force in PCM modeling greatly impacts MH bed performance. • The study examined hydrogen storage using three different PCMs. • Among PCM pairs, LiNO 3 ·3H 2 O and CaCl 2 ·6H 2 O performed the best. • The study highlights the potential of combining PCMs for better hydrogen storage.