MXenes with High Thermal Stability in Air

Two-dimensional MXenes have demonstrated potential in energy storage applications. However, their oxidation in air at elevated temperatures impedes their use in extreme environments. Here, we demonstrated that mono-flake Ti₃C₂T_x has much higher stability than stacked MXene layers (multi-flake), and can withstand temperatures as high as 600°C in air. In contrast, multi-flake MXenes can readily oxidize at 300°C. We demonstrate that the facile oxidation of multi-flake MXenes is due to the inter-flake trapped and confined water, which can only be removed by vacuum-annealing at high temperatures (>500°C). Upon the removal of confined water, multi-flake films can also withstand 600°C annealing in the air without oxidation, demonstrating the significant role of confined water in MXene degradation through hydrolysis. These findings provide insight into the mechanisms of MXene degradation and provide a blueprint for producing extremely stable MXenes for various applications.