Enhanced NH₃ and NO Sensing Performance of Ti₃C₂O₂ MXene by Biaxial Strain: Insights from First-Principles Calculations

In this study, we investigate the adsorption properties of CO, NH₃, and NO gases on Ti₃C₂O₂ MXene surfaces through density functional theory (DFT) calculations. A comprehensive analysis of the adsorption preferences, electronic properties, work function (φ), sensitivity (S), and recovery time (τ) was conducted, focusing on the effects of biaxial strain (ε) ranging from -2% to 4%. At free strain, toxic gases can adsorb onto the Ti₃C₂O₂ surface, with adsorption energies (Ead) of -0.096 eV (CO), -0.344 eV (NH₃), and -0.349 eV (NO), indicating moderate interactions between NH₃, NO and the Ti₃C₂O₂ surface, while CO displays weaker physisorption. Electron density difference (EDD) and electron localization function (ELF) analyses underscore the electron transfer mechanisms, supporting the enhanced sensitivity of Ti₃C₂O₂ for NH₃ and NO detection. The influence of ε on gas adsorption behaviour was also studied, demonstrating that tensile strain enhances NH₃ adsorption (Ead = -0.551 eV at ε = 4%), while NO exhibits an inverse trend under compressive strain (Ead = -0.403 eV at ε = -2%). The S based on a change rate of φ was evaluated to be around 12% and 6% for NH₃ and NO, respectively within the calculated strain range, indicating sufficient detection capability. Additionally, the τ for NH₃ and NO detection was computed. At 0% strain and 300 K, the τ values for NH₃ and NO are in the microsecond range, suggesting that detecting these gases under normal conditions poses a challenge. However, strain-tuned Ti₃C₂O₂ and lowered temperature enhance gas sensing performance, with increased τ values at tensile strain for NH₃ and compressive strain for NO. These results suggest that Ti₃C₂O₂ MXene, when tuned with biaxial strain, is a promising candidate for detecting NH₃ and NO at low to room temperatures.