How Water Attacks MXene

摘要

Two-dimensional (2D) transition metal carbidesand nitrides (MXenes) have shown outstanding performances inelectrochemical energy storage and many other applications.However, the stability of MXene remains a concern, especiallyits quick degradation in aqueous solutions under ambientconditions. Here, we report on the water/Ti3C2O2-MXeneinterfacial chemistry from first-principles molecular dynamicssimulations at room temperature. Surprisingly, we find that thewater molecules can attack the basal plane of Ti3C2O2 and pull thesurface Ti atoms out, thereby reconstructing the surface. Bytracking close encounters of water molecules and surface Ti atoms on the basal plane of Ti3C2O2, we show that the attack is initiatedby the chemisorption of a water molecule on a surface Ti atom, foEowed by the breaking of Ti-C bonds and deprotonation of thewater molecule, leading to the formation of Ti-OH on the Ti3C2O2 surface and a hydronium ion in the aqueous phase. Our findinghighlights the susceptibility of Ti3C2O2 MXene to water attack, supporting recent experimental observations. Furthermore, wedemonstrate that preventing close encounters of water molecules and the surface Ti atoms is key to the stability of the basal planeand can be realized by negatively charging the surface (thereby reorienting the O atoms of water away from the surface) orconverting the surface O to -OH groups (thereby shifting the water layer further away from the surface). Our insights and approachhighlight the importance of the reactivity of water when interfacing with 2D materials such as MXenes.