Ti₃C₂ MXene-Based Composites for Hydrogen and Ammonia Gas Sensing: A Review

The unique contributions of 2D Ti₃C₂ MXenes surface, electrical, and chemical features play a crucial role in determining toxic and flammable gas-sensing behavior. Specifically, its high electrical conductivity (metallic nature), layered nanosheet structure (nanosheets), and surface termination groups (-O, -F, and -OH) collectively contribute to excellent hydrogen (H₂) and ammonia (NH₃) gas-sensing behavior. This review systematically explores the impact of pristine and modified Ti₃C₂ MXene, including its interfaces with various metals and metal oxides for enhancing H₂ and NH₃ detection. Furthermore, the significance of room temperature operation and flexible gas sensing mechanisms is explored. Notably, integration of Ti₃C₂ MXene and sulfur nanosheets demonstrates rapid response and recovery times with detection limits at ppt level. Ti₃C₂ MXene-based interfaces also exhibit excellent long-term stability under various relative humidity conditions. The selective surface termination groups (-OH and -O) facilitate the formation of hydrogen bonds with NH₃ molecules for enhancing gas adsorption and sensing selectivity. In addition, the expansion of the interlayer spacing plays a vital role in improving the gas-sensing performance. Partial oxidation of Ti₃C₂ MXene into TiO₂ increases the interlayer distance, promoting faster diffusion of gas molecules and quicker sensor response. Overall, the intrinsic properties of Ti₃C₂ MXene and its composites significantly achieve high-performance room-temperature H₂ and NH₃ gas-sensing performance.