Elucidating the co-adsorption mechanism of H2O and NH3 onto graphene/hexagonal boron nitride heterostructures (h-BN) is critical to guide the design of new materials for application in ammonia gas sensor devices in humid environments. Here, we use first principles methods with non-empirical van der Waals density functional theory to investigate the adsorption of graphene/h-BN to NH3 + H2O. Our results show that the presence of water vapor enhances the sensitivity and the thermodynamical stability of the ammonia + graphene/h-BN through the formation of NH3•H2O clusters adsorbed directly on the graphene/h-BN. The presence of water vapor leads to the decrease of the adsorption energy to −0.613 eV, much more negative than that for the adsorption of NH3 gas, and the increasing of the electron transfer from the adsorbates to graphene/h-BN heterostructure, more twice larger than that for the adsorption of solely ammonia. Additionally, the recovery time of graphene/h-BN for the co-adsorption of NH3 + H2O is predicted to be quite short, in seconds range, in good agreement with experiment work. The results demonstrate the potential for application of graphene/h-BN for ammonia gas sensors with high performance and mechanical stability in humid environments.
