Introduction. Recently, Hu et al. reported hydrogen isotope separation by sieving through the interstitial space of layered materials, namely, hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS 2 ). While the difference in the entry barrier of the hydrogen isotopes into the interstitial space of the layered materials was found to be the driving factor for the isotope separation, there is no conclusive picture yet on the chemical interaction of interstitial hydrogen with the layered materials, and on the transport mechanism through them. Spatial confinement has a strong impact on the chemical properties of molecules. The layers of h-BN, MoS 2 , and graphene are chemically very stable, if not inert, and the interlayer interactions impose pressure on the intercalated species. So, the chemistry in the interstitial space of a layered material is expected to be significantly different from the surface-adsorbed counterpart.