DFT Investigation on Transition-Metal Cr-, Mo-, and W-Doped MXene Nb2CO2 Nanosheets: Implications for High-Performance H2, CO, and H2S Gas Sensors

As a prominent member of the two-dimensional (2D) material family, MXenes possess abundant active sites, a large specific surface area, metallic conductivity, and tunable surface chemistry, making them promising candidates for the fabrication of high-performance gas sensors. In this study, DFT calculations using the PBE-D3 method were employed to investigate the properties of transition metal-doped MXene Nb2CO2 (doped with Cr, Mo, and W) and to systematically evaluate their gas sensing performance toward H2, CO, and H2S. The gas sensing performance of the materials was analyzed from the perspective of adsorption energy, charge transfer, bond length variations of target gas molecules, density of states (DOS), and projected density of states (PDOS). The results revealed that transition metal doping significantly enhances the gas sensing capabilities of Nb2CO2. From the perspective of sensing materials, Cr-, Mo-, and W-doped Nb2CO2 are suitable for CO gas sensor fabrication, while W-doped Nb2CO2 exhibits superior performance for H2 sensing. From the perspective of target gases, a high-performance H2 gas sensor can be fabricated by using W-doped Nb2CO2. Due to the lower adsorption energy of the H2 molecule on the surface of W-doped Nb2CO2 and the larger amount of charge transferred between them, the sensor may operate at room temperature. High-performance CO gas sensors can be developed by using Cr-, Mo-, and W-doped Nb2CO2. For the same reason, a CO gas sensor based on W-doped Nb2CO2 may also operate at room temperature. Additionally, Mo-doped Nb2CO2 emerges as an optimal candidate for developing a high-performance H2S gas sensor. These findings provide valuable insights into the rational design and optimization of MXene-based gas sensors for the effective detection of H2, CO, and H2S.