Improving stability of MXenes

Due to their superior hydrophilicity and conductivity, ultra-high volumetric capacitance, and rich surface-chemistry properties, MXenes exhibit unique and excellent performance in catalysis, energy storage, electromagnetic shielding, and life sciences. Since they are derived from ceramics (MAX phase) through etching, one of the challenges in MXenes preparation is the inevitable exposure of metal atoms on their surface and embedding of anions and cations. Because the as-obtained MXenes are always in a thermodynamically metastable state, they tend to react with trace oxygen or oxygen-containing groups to form metal oxides or degrade, leading to sharply declined activity and impaired performance. Therefore, improving the stability of MXenes-based materials is of practical significance in relevant applications. Unfortunately, there lacks a comprehensive review in the literature on relevant topics. To help promote the wide applications of MXenes, we review from the following aspects: (i) insights into the factors affecting the stability of MXenes-based materials, including oxidation of MXenes flakes, stability of MXenes colloidal solutions, and swelling and degradation of MXenes thin-film, (ii) strategies for enhancing the stability of MXenes-based materials by optimizing MAX phase synthesis and modifying the MXenes preparation, and (iii) techniques for further increasing the stability of freshly prepared MXenes-based materials via controlling the storage conditions, and forming shielding on the surface and/or edge of MXenes flakes. Finally, some outlooks are proposed on the future developments and challenges of highly active and stable MXenes. We aim to provide guidance for the design, preparation, and applications of MXenes-based materials with excellent stability and activity.