Stabilizing Ti3C2O2 MXene in Water with Montmorillonite Heterostructures: Ab Initio Molecular Dynamics Study

Abstract MXenes such as Ti3C2O2 are promising for energy storage, electronics, and biomedical technologies, but water-driven oxidation limits their aqueous stability. Using ab initio molecular dynamics, we resolve the atomistic pathway of water attack on Ti3C2O2 and test its mitigation in Ti3C2O2–clay heterostructures with tunable layer composition and interlayer counterions. In the bare bilayer, chemisorption of a water oxygen at a basal Ti site triggers irreversible surface reconstruction within 6 ps. In clay-supported structures, the outcome is governed by interfacial electrostatics and ion–water structuring: Mg-substituted clay without counterions accelerates chemisorption threefold (2 ps), Al-only clay suppresses stable adsorption over 30 ps, and the Na-containing Mg-substituted heterostructure inhibits degradation because interlayer Na+ forms persistent hydration shells that sequester water from reactive basal Ti sites. Bader analysis identifies the interfacial Ti charge state as the controlling descriptor: Al-only clay reduces 67% of interfacial Ti to +1.30 e (vs +1.92 e in the bilayer), suppressing attack over the simulated window, whereas the Mg-induced charge deficit uniformly oxidizes interfacial Ti (+1.78 to +1.94 e) and reverses the direction of interfacial charge transfer. Two-dimensional maps of the electrostatic potential and local field vectors across the unhydrated interfaces rationalize these trends: Mg substitution establishes a continuous directional gradient toward the MXene basal plane, whereas intercalated Na+ generates localized potential wells that redirect the field away from reactive Ti sites. These results establish a design principle for clay-stabilized MXenes: tuning the interfacial Ti charge state and ion–water organization suppresses basal-plane oxidation while preserving MXene functionality.