Investigating the\nAnnealing Effects of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>X</i></sub> MXene for Stable and\nSelective Low-Concentration Hydrogen Detection

Titanium carbide (Ti<sub>3</sub>C<sub>2</sub>T<sub><i>X</i></sub>), a member of the MXene family, is widely used in\ndiverse\napplications, which include gas sensors, energy storage, electrochromic\ndevices, biosensors, etc. However, its effectiveness in gas sensing\nis notably lacking, indicating the need for further research in this\nfield. This study investigates a detailed analysis of the effects\nof annealing on pristine titanium carbide, particularly emphasizing\nits ability to detect H<sub>2</sub> selectively. Annealing Ti<sub>3</sub>C<sub>2</sub>T<sub><i>X</i></sub> at 300 °C\nin the presence of air results in the formation of partially oxidized\nMXene (Ti<sub>3</sub>C<sub>2</sub>T<sub><i>X</i></sub>/TiO<sub>2</sub>), which enhances conductivity and yields a response of 62\n± 5% to 4% H<sub>2</sub> and 6.6% to 50 ppm of H<sub>2</sub>,\nwith a response time of less than 1 min. In contrast, pure Ti<sub>3</sub>C<sub>2</sub>T<sub><i>X</i></sub> shows a reduced\nconductivity and a weak response of 1.0%. The 300 °C annealed\nMXene sensor, with its operating temperature optimized at 300 °C,\nexhibits a strong selectivity toward H<sub>2</sub> compared to CH<sub>4</sub>, NH<sub>3</sub>, and CO due to the combined properties of\nMXene and TiO<sub>2</sub>. In addition, the instability issues within\nthe pristine MXene contribute to its diminished sensitivity, and an\neffective enhancement can be realized through variation of the annealing\ntemperatures. A detailed investigation was carried out to understand\nthe underlying mechanisms influencing gas sensing in partially oxidized\nMXene, emphasizing structure-based depletion layer formation using\ndetailed material characterization techniques, including X-ray photoelectron\nspectroscopy, thermogravimetric analysis, and X-ray diffraction. Finally,\nthe sensor prototype is assembled by combining a microheater and an\ninterdigitated electrode with the optimized sensing material inside\nthe TO8 package.