On the chemistry and mobility of hydrogen in the interstitial space of layered crystals h-BN, MoS2, and graphite

Recently, transport and separation of hydrogen isotopes in the layered materials hexagonal boron nitride and molybdenum disulphide have been reported.[1] Here, based on first-principles calculations combined with well-tempered metadynamics simulations, we report the chemical interactions and mobility of protons (H+) and protium (H) atoms in the interstitial space of these layered materials. We show that both H as well as H+ can be transported between the layers of h-BN and MoS2 with low free energy barriers, while they are immobilized in graphite, in a good agreement with experiments. In h-BN and MoS2 the transport mechanism involves a hopping process between the nearby layers, which is assisted by the low-energy phonon shear modes of layers.