Regulating surface terminals and interlayer structure of Ti₃C₂T_x for superior NH₃ sensing

MXene materials have exhibited potential in electrochemistry, particularly in gas sensing, due to their excellent conductivity, large specific surface area of layered materials, and unique functional groups. However, the gas sensing performance of intrinsic 2D MXene materials is often limited by their fluorine-containing terminals and interfacial structure. In this study, based on intrinsic Ti₃C₂T_x, we employed alkali treatment and annealing to prepare oxygen-rich Ti₃C₂(OH)_x/Ti₃C₂O_x with expanded interlayer spacing, achieving enhanced gas sensing performance for NH₃. The surface chemistry and structure of the sensing materials have been optimized through the synergistic regulation of MXene's unique surface terminations and the intercalation effect of layered materials. Compared to intrinsic Ti₃C₂T_x, the interlayer spacing of oxygen-rich Ti₃C₂(OH)_x/Ti₃C₂O_x increased from 9.1 Å to 12.1 Å. The surface terminations of oxygen-rich Ti₃C₂(OH)_x/Ti₃C₂O_x have been defluorinated and oxygenated. The maximum response value of oxygen-rich Ti₃C₂(OH)_x/Ti₃C₂O_x to NH₃ was 35.66, approximately twice that of the original Ti₃C₂T_x at an NH₃ concentration of 200 ppm. DFT (Density functional theory) calculations and DRIFT (In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy) tests explained the interaction between the surface terminals and NH₃, indicating good selectivity and sensitivity of oxygen-rich Ti₃C₂(OH)_x/Ti₃C₂O_x to NH₃. The results demonstrated that the synergistic effects of surface chemistry and structural engineering are crucial for MXene to optimize the electrochemical performance, particularly the gas sensing performance. This provides a feasible approach for the performance optimization of intrinsic MXene materials.