The d-p orbital coupling enhancing the kinetics of magnesium-based hydrogen storage materials: Catalytic mechanism and principle

Magnesium-based hydrogen storage materials have garnered significant interest owing to their plentiful availability and elevated gravimetric hydrogen density; yet, their utilisation is constrained by slow kinetics and substantial thermodynamic stability. Recently, dual-atom catalysts (DACs) composed of transition metals have surfaced as a potent approach to enhance the kinetics of hydrogenation and dehydrogenation in Mg/MgH₂. Nonetheless, the collaborative effect of DACs and N-modified confinement materials on H₂ adsorption and H^- dissociation processes is still ambiguous. In response to this, a collection of 3d/4d transition metal-based TM₁/TM₂-N-CNTs-Mg/MgH₂ heterostructure models was developed. Our density functional theory (DFT) computations indicate that Cr/Mn-N-CNTs and Mo/Tc-N-CNTs systems markedly diminish the hydrogenation/dehydrogenation energy barriers of Mg/MgH₂ by 0.7–1.03 eV and 1.33–2.19 eV, respectively. This improvement is chiefly ascribed to D-band interaction with DACs and the ensuing hybridisation with N p-orbitals, which triggers an electron shuttling phenomenon that hastens electron transfer between Mg and H orbitals, thus markedly enhancing kinetic performance. The suggested electron shuttling action generated by d-p hybridisation offers theoretical insights for the development of efficient Mg/MgH₂ hydrogen storage systems.