Computational Understanding of Effect of Alkali Earth Metal Dopants on Dehydrogenation Thermodynamics of MgH₂ Nanoparticles

Efficient hydrogen storage is crucial for realizing the potential of hydrogen as an alternative energy source. Metal hydrides, particularly MgH₂, have shown promise due to their stability and high storage capacity. However, their high operating temperatures pose challenges. Doping MgH₂ with elements such as Be and Ca is strategically explored to improve performance. This study investigates how dopant type, concentration, and configuration influence the particle size effect on hydrogenation/dehydrogenation reaction thermodynamics. It is revealed that both Be and Ca dopants, irrespective of their configurations (whether positioned on the surface or within the subsurface), enhance the reduction in the reaction temperature of MgH₂ caused by the particle size reduction. This impact is more pronounced for Be dopants compared to Ca dopants. In a similar logic, subsurface doping scenario is better for pronouncing this impact enhances than surface doping scenario. Further investigation highlights that the destabilization of MgH₂, which is induced by Be/Ca dopants, is primarily attributed to the electronic localization of the local Mg–Be/Ca environment, leading to a reduction in the dehydrogenation reaction temperature by weakening the Mg–H bonds. These findings provide valuable insights into reducing reaction temperatures in metal hydrides, crucial for practical hydrogen storage applications.