First-Principles Study of Ti-Deficient Ti₃C₂ MXene Nanosheets as NH₃ Gas Sensors

Sensitive gas sensors are becoming increasingly important in toxic gas detection and environmental monitoring. The applications of conventional gas sensors are limited due to their low sensitivity or high operating temperature. MXenes with high conductivity are conducive to the rapid transmission of electrons and are suitable as highly sensitive NH3 gas sensors. Considering the limited research on the experimental details and sensing mechanism of MXene-based NH3 gas sensors, our research focuses on precisely controlling the atomic structure of MXenes to improve the performance of NH3 gas sensors. The atomic structures of a typical monolayer Ti3C2O2 MXene and its Ti-deficient counterpart as the NH3 gas sensor are systematically studied through first-principles calculations and the nonequilibrium Green’s function method. The Ti-deficient Ti3C2O2 MXene has a relatively stronger physical interaction with NH3 and is comparatively more suitable as a highly sensitive NH3 gas sensor. Atomic-level device simulations show that the current has a greater change when NH3 is adsorbed on the surface of Ti-deficient Ti3C2O2. These detailed calculations provide substantial theoretical support and a useful design scheme to improve the sensitivity of MXene-based gas sensors by deliberately introducing Ti vacancies in the MXene.