Stability Mechanisms of Unconventional Stoichiometric Crystals Exampled by Two-Dimensional Na2Cl on Graphene under Ambient Conditions

Abstract

Compounds harboring active valence electrons, such as unconventional stoichiometric compounds of main group elements including sodium, chlorine, and carbon, have conventionally been perceived as unstable under ambient conditions, requiring extreme conditions including extra-high pressure environments for stability. Recent discoveries challenge this notion, showcasing the ambient stability of two-dimensional Na2Cl and other unconventional stoichiometric compounds on reduced graphene oxide (rGO) membranes. Focusing on the Na2Cl crystal as a case study, we reveal a mechanism wherein electron delocalization on the aromatic rings of graphene effectively mitigates the reactivity of Na2Cl, notably countering oxygen-induced oxidation--a phenomenon termed the Surface Delocalization-Induced Electron Trap (SDIET) mechanism. Theoretical calculations also show a substantial activation energy barrier emerges, impeding oxygen infiltration into and reaction with Na2Cl. The remarkable stability was further demonstrated by the experiment that Na2Cl crystals on rGO membranes remain almost intact even after prolonged exposure to a pure oxygen atmosphere for 9 days. The discovered SDIET mechanism presents a significant leap in stabilizing chemically active substances harboring active valence electrons under ambient conditions. Its implications transcend unconventional stoichiometric compounds, encompassing main group and transition element compounds, potentially influencing various scientific disciplines.