First principles insights into stability of defected MXenes in water.

Two-dimensional transition metal carbides and nitrides, known as MXenes, have demonstrated remarkable performance in electrochemical energy storage and various other applications. Despite their potential, MXenes exhibit instability in aqueous solutions, and the role of defects in their aqueous stability is unclear. In this study, we report on the interfacial chemistry between water and defected TiCO MXene at room temperature using first principles molecular dynamics simulations. We investigate how defects such as O vacancy, Ti vacancy, F terminal groups, and Ti-O vacancy pair influence the chemical interaction of water molecules with the basal plane of TiCO. Our results show that water molecules can repair the surface O vacancies, by dissociating to hydroxide and hydronium. On the other hand, F terminal groups cannot effectively block water chemisorption on the surface Ti, while Ti vacancies behave as a spectator species on the surface with respect to interaction with water. TiCO with a Ti-O vacancy pair is found to behave like TiCO with an O vacancy where a water molecule dissociates and refills the vacancy. These findings enrich our understanding of water interaction with defects on the MXene surfaces.