The Future of MXenes: Exploring Oxidative Degradation Pathways and Coping with Surface/Edge Passivation Approach

The MXene, which is usually transition metal carbide, nitride, and carbonitride, is one of the emerging family of 2D materials, exhibiting considerable potential across various research areas. Despite theoretical versatility, practical application of MXene is prohibited due to its spontaneous oxidative degradation. This review meticulously discusses the factors influencing the oxidation of MXenes, considering both thermodynamic and kinetic point of view. The potential mechanisms of oxidation are systematically introduced, based on experimental and theoretical models. Typically, the surfaces and edges of MXenes are susceptible to oxidation, as the surface terminal groups are easily attacked by oxygen and water molecules, ultimately leading to structural deformation. To retard oxidative degradation, ligand mediated surface/edge passivation is suggested as a promising strategy. In this regard, detailed passivation strategies for MXenes are systematically explained based on the types of chemistry at the MXene-ligand interface-covalent bonding, electrostatic interactions, and hydrogen bonding-and the type of stabilizing moieties-organic, inorganic, biomolecules, and polymers. The retardation of oxidation is discussed in relation with the interaction type and passivating moiety. This review aims to catalyze future research to identify efficient and cost-effective ligands for the surface engineering of MXenes, enhancing their oxidation stability.