Ultra-Stable Titanium Carbide MXene Functionalized with Heterocyclic Aromatic Amines

2D transition metal carbides (MXenes) obtained from bulk M_n+1AX_n (n = 1, 2, 3, or 4) phases are an intriguing class of crystalline solids with unique physicochemical properties for promising applications such as batteries, capacitive energy storage, and electrocatalysis. One of the obstacles that must be overcome for technical applications is that MXene flakes delaminated in aqueous conditions suffer from phase transition and/or structural decomposition over time. Herein, a simple but powerful strategy to enhance their stability by passivating vulnerable edges on the delaminated MXene (Ti₃C₂T_x) with heterocyclic aromatic amines is reported. In particular, pyrrole-functionalized MXenes are found to facilitate anti-oxidation in aqueous solutions at room temperature over 700 days, at 70 °C over 42 days, and even with a strong oxidizer (H₂O₂, 9.70 mmol) over 50 days. On the other hand, the as-prepared MXene solution lost its color within a month at room temperature, a day at 70 °C, and 5 min in the presence of H₂O₂ (9.70 mmol). Density functional theory calculations indicate that chemical interactions between MXene and pyrrole are extremely strong and involve the formation of Ti-C bonds. Furthermore, pyrrole-functionalized MXenes exhibit higher electrochemical performance than pristine MXenes as a supercapacitor.