Nature and pH-dependent surface chemistry of TiN in aqueous environment from ab-initio and machine learning accelerated simulations

The nature of surfaces in aqueous environment has crucial implications in a broad series of important processes in catalysis and materials chemistry. Titanium Nitride (TiN) is a widely applied system. The atomistic nature of its interface with water and its pH-dependent surface chemistry are rather unexplored. In this work, we used density functional theory calculations in conjunction with ab initio and machine learning molecular dynamics to investigate the nature of TiN in aqueous environment. We focused on the stable (1 0 0) TiN surface. Then, we adopted the grand canonical formulation of species in solution to study the acid-base equilibrium constants on the surface and we calculated the pH at the point of zero charge (pHPZC), close to 3. We compared the predicted pHPZC with experimental measurements on commercial TiN. We also predicted the dissociation free energy of water at 298 K which is ∼0.5 eV, comparable to other materials such as TiO2. The results of this study provide an atomistic description of the nature of TiN/H2O interface. They provide some information on relevant aspects for materials chemistry and catalysis applications of TiN.