Selective Capturing and Sensing Performance of M₂CO₂ (M = Sc, Ti, V) MXenes Toward Hydrogen Cyanide: A First‐Principles Modeling

Abstract This work reports the high selection and performance of early transition‐metal‐based MXenes toward the detection of hydrogen cyanide (HCN), studied by first‐principles density functional theory (DFT) calculations. On the pristine M 2 C (M = Sc, Ti, V), HCN molecules are strongly chemisorptive to surface sites via ionic bonds with adsorption energies ranging from −3.50 to −4.40 eV. The charge density difference plot exhibits a charge accumulation around the C─H bond of HCN after adsorption, leading to its pronounced elongation. On the functionalized M 2 CO 2 surfaces, HCN molecules prefer binding to Sc 2 CO 2 via electrostatic interaction with a monodentate configuration and a high binding energy of 0.85 eV, much greater than that on other surfaces, relying on the distinguishing termination pattern of the host structure. Sc 2 CO 2 shows a relatively long recovery time of ≈235 s at room temperature, however, a high sensitivity of 306% is obtained, which is much superior to that on other investigated surfaces. A slight reduction in bandgap, i.e., 0.072 eV, originating from the down‐shift of both bonding and anti‐bonding states, is the key to this distinctive performance. Ab initio molecular dynamics (AIMD) simulations reveal the stability of adsorbed HCN on the Sc 2 CO 2 surface within the studied timescale at room temperature.