Mechanistic understanding of transition-metal-decorated biphenylene for highly selective NO2 and NH3 detection

Abstract

Here, we employ density functional theory (DFT) in combination with ab initio molecular dynamics (AIMD) simulations to examine the sensing performance of biphenylene doped with selected transition-metal dopants (M@BP), specifically Fe, Co, and Ni, on NO2 and NH3. The results indicate that NO2 exhibits stronger interaction than NH3, with adsorption energies ( Eads ) exceeding -3.0 eV. In contrast, the Eads values for NH3 are around -1.30 eV. Bader charge and electron density difference (EDD) analyses reveal that charge is transferred from the M@BP monolayers to NO2. In contrast, the charge transfer occurs in the opposite direction for NH3, indicating distinct chemical adsorption mechanisms. Additionally, the electron localization function (ELF) results indicate partial ionic bonding and localized charge sharing between the metal sites of M@BP and the gas molecules. Variations in the work function, alongside calculated sensitivity (S) values, demonstrate that M@BP is exceptionally responsive to NH3, with S values of 13.4 %, 8.7 %, and 13.7 % for Fe@BP, Co@BP, and Ni@BP, respectively. These materials exhibit strong potential as reusable gas sensors capable of operating at temperatures above 500 K while maintaining practical recovery times. Moreover, AIMD simulations confirm the thermal stability of Co@BP and Ni@BP, whereas Fe@BP exhibits instability at 600 K. These findings suggest that M@BP possess a strong affinity for NH3, tunable electronic properties, and excellent thermal stability, making them promising candidates for selective, reusable high-temperature gas-sensor applications.