Size-dependent nanoconfinement effects in magnesium hydride

Nanoconfinement effect is crucial to improve the dehydrogenation kinetics of MgH₂. However, the underlying micro-mechanism for nanoconfinement effect of carbon-based carrier on MgH₂ nanoparticles is still ambiguous, hindering the design of carbon-based nanoconfined MgH₂ nanoparticles. To address this dilemma, we applied density functional theory (DFT) calculations to investigate the interaction between carbon-based carrier and MgH₂ nanoparticles. To analyze this issue, we designed various systems of carbon nanotubes nanoconfined MgH₂ nanoparticles, with the range of particle size/pore size ratio from 0.3 to 0.8. The interaction strength between carbon-based carrier and MgH₂ nanoparticles gradually increases with the increase of particle size/pore size ratio, and the dehydrogenation temperature decreases with the increase of particle size/pore size ratio. The electron of carbon-based carrier will transfer to MgH₂ nanoparticles, leading to the weakening of Mg–H bonds. The weakened Mg–H bonds corresponding to lower dehydrogenation barrier, which is consistent with the phenomenon that the dehydrogenation temperature is inversely proportional to particle size/pore size ratio in calculations and experiments. This work not only elucidates the size-dependent nanoconfinement effects on MgH₂ from a microscopic perspective, but also provides the theoretical basis for the design and development of carbon-based nanoconfined MgH₂ nanoparticles.