After we have understood the diffusion process of H + and H through the layers of h-BN, we have to answer the intriguing question: what is the force which drives the diffusion? In other words, what is responsible for the directional diffusion of both species? In the case of H + , one would assume that Coulomb repulsion between the protons and the electric field gradient between the electrodes can serve as the driving force for the diffusion. For the H atom, the only driving mechanism can be a concentration gradient, which requires the interaction of H atoms with each other. In the gas phase, the formation of H 2 is associated with a large exothermic reaction energy of -4.5 eV (both experimental and our theoretical value) . Confined in the h-BN lattice, this energy somewhat reduces to -3.46 eV (calculated in a 7 ×7×2 supercell model). This energy still suggests that H atoms, even if they manage to enter the h-BN lattice as atomic species, strongly prefer recombination inside the lattice, unless there is a substantial kinetic barrier preventing recombination.