Subnanometer Ni Clusters on MgH₂: Unveiling Charge Transfer and Hydrogen Mobility Enhancement through ab Initio Dynamics for Rational Catalyst Design.

Magnesium hydride (MgH₂) is considered a promising solid-state hydrogen storage material due to its high hydrogen capacity, low cost, and excellent reversibility. However, its practical use is still limited by high dehydrogenation temperatures and slow kinetics. To overcome these challenges, we conducted ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) to study the catalytic role of nickel (Ni) clusters (Ni₁-Ni₇) supported on the MgH₂ surface. The formation energies and binding energies of different Ni cluster configurations were calculated to identify the most stable structures. Charge density difference and Bader charge analyses showed significant charge transfer among Mg, Ni, and H atoms, which promotes hydrogen activation. Radial distribution function analysis at 298 and 500 K revealed that small clusters, especially Ni₃ and Ni₄, achieve an optimal balance between hydrogen binding strength and structural flexibility. Moreover, mean square displacement results indicated that the Ni₄ cluster markedly enhances hydrogen mobility at higher temperatures. To understand the catalytic mechanism, we analyzed the total and projected density of states (TDOS and PDOS), velocity autocorrelation function (VACF), and vibrational density of states (VDOS). The results confirm that subnanometer Ni clusters─particularly the Ni₄-2 configuration─act as efficient catalysts for enhancing the dehydrogenation performance of MgH₂, offering valuable insights for the rational design of advanced hydrogen storage materials.