A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH4 as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH4@NCMK-3 material releases H2 at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li3AlH6 intermediate observed in bulk. Moreover, >80% of LiAlH4 can be regenerated under 100 MPa H2, a feat previously thought to be impossible. Nitrogen sites are critical to these improvements, as no reversibility is observed with undoped CMK-3. Density functional theory predicts a drastically reduced Al–H bond dissociation energy and supports the observed change in the reaction pathway. The calculations also provide a rationale for the solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

Nanoencapsulation using graphene derivatives enables the facile fabrication of two-dimensional (2D) nanocomposites with unique microstructures and has been generally applied to many fields of energy materials. Particularly, metal hydrides such as MgH 2 encapsulated by graphene derivatives have emerged as a promising hybrid material for overcoming the disadvantageous properties of Mgbased hydrogen storage. Although the behavior of the graphene−Mg nanoencapsulation interface has been studied for many composite materials, the direct modification of graphene with nonmetal foreign elements for changing the interfacial behavior has been limitedly reported. In this regard, using B-doped graphene and N-doped graphene as nanoencapsulation media for tuning the interfacial behavior of graphene derivative−Mg nanoparticles, we present altered hydrogen storage kinetics of heteroatom-doped (B and N) graphene−Mg composites. The effect of heteroatom doping is studied in terms of bonding configurations and heteroatom doping concentrations. The enhancement in hydrogen uptake was observed for all of the heteroatom-doped graphene−Mg nanocomposites. On the other hand, a few samples exhibit significantly low activation energy at the early stage of desorption, which can be related to the facilitated nucleus formation. Density functional theory calculation indicates that B-doping and N-doping accelerate hydrogen absorption kinetics in different ways, aiding charge transfer and inducing surface deformation of Mg nanoparticles, respectively. Their effects can be augmented in the presence of structural defects on graphene, such as vacancies, pores, or graphene edges. These results demonstrate that hydrogen storage kinetics of Mg-based systems can be altered by utilizing heteroatom-doped graphene oxide derivatives as 2D nanoencapsulation media, suggesting that the addition of a nonmetal doping element can also be applied to Mg-based hydrogen storage by modifying the nanoencapsulation interface without forming Mg alloy phases.

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH4 as an exemplar, we demonstrate a new approach to thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH4@NCMK-3 material releases H2 at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li3AlH6 intermediate. Moreover, >80% of LiAlH4 can be regenerated under 100 MPa H2, a feat previously thought to be impossible. The nitrogen sites lower the energy barrier for regenerating the hydride by changing the density of states in the vicinity of the Fermi level, effectively acting as solvation sites for lithium ions. Theoretical calculations provide a rationale for the unprecedented solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

With global efforts to relieve the formidable impact of climate change, hydrogen is considered a viable replacement for fossil fuels without intermittency concerns of other renewable sources. Hydrogen storage plays a pivotal role in the implementation of hydrogen economy, coupling hydrogen production with fuel cell technologies. Storing hydrogen in the form of solid-state hydride materials has been studied as a future hydrogen storage technology for enabling a safe, energy-efficient, and high-energy-density system. However, hostile thermodynamic and kinetic properties of each hydride material result in insufficient hydrogen storage performance for practical applications, such as sluggish hydrogen absorption or desorption, high dehydrogenation temperatures, and sometimes limited reversibility; thus, these kinetic and thermodynamic characteristics need to be thoroughly understood depending on each hydride material. Among various strategies, nanostructuring has been regarded as a general approach to tackling such limitations regarding thermodynamic and kinetic characteristics of hydride materials. In particular, the formation of nanosized hydrides within a nanostructured scaffoldalso known as nanoconfinementis of great potential for advanced hydrogen storage because it can additionally leverage host–guest interactions at the nanointerfaces of hydride materials and scaffolds. In this context, the active tuning of such nanointerfaces brings about additional thermodynamic or kinetic changes in hydrogen sorption reactions compared to the unmodified nanoconfined hydride composites, holding great promise for tailored strategies for each metal hydride. In this Perspective, we summarize the major thermodynamic and kinetic barriers of each metal hydride and highlight the recent progress in overcoming such limits, mainly focusing on nanointerface engineering in nanoconfined metal hydrides. Further, we provide our insight and current challenges in understanding the underlying mechanisms of the interaction at the nanointerface, whereby the noticeable technological leaps can be emulated in practical systems.