The intrinsic stability of SACs can be well-explained by the thermodynamic diagram in Figure . When the free-energy change from nanoparticles to single atoms is negative, nanoparticles can be dispersed to single atoms spontaneously, leading to the thermodynamic stability of SACs. However, even if the free-energy change is positive, single atoms can be kinetically stable when the aggregation barrier is sufficiently high to prevent sintering. In this regard, the metal-substrate interaction (or binding energy of single atoms, Ebind) is a suitable descriptor to predict the thermodynamic stability of SACs. For instance, stable SACs will not be formed on the basal plane of graphene and 2H-phase MoS2 owing to their weak interaction. The presence of defects (such as steps and vacancies), dopants, and surface terminations significantly improve the stability of single atoms via surface trapping. Several examples of SACs with higher thermal stability than their supported nanoparticle analogues have been reported. Apparently, a stronger metal-support interaction (or Ebind) implies a lower mobility of atomic species on the support, but this does not truly reflect the diffusion activation barrier (Ea). This suggests that a thermodynamic metric of binding energies alone cannot explain the kinetic stability in most SAC systems. A more detailed study by E. J. M. Hensen et al. revealed the importance of the cohesive energy of bulk metal (Ec) for the prediction of Ea, which reflects the intrinsic chemical reactivity of single atoms. As shown in Figure , the diffusion activation barrier has a strong linear dependency on the ratio of (Ebind) /Ec for various SAC systems on reducible metal oxides (CeO2, TiO2), stable metal oxides (MgO, ZnO), perovskite (SrTiO3), and two-dimensional materials (MoS2 and graphene). Indeed, the ratio of Ebind/Ec serves as a correction factor to Ebind by comparing the affinity of a single metal atom to the support surface and bulk metal. This provides a simple model for screening thermodynamics to the kinetics of metal adatom on a support.