Highly Sensitive Ammonia Gas Sensors at Room Temperature Based on the Catalytic Mechanism of N, C Coordinated Ni Single-Atom Active Center

Abstract Significant challenges are posed by the limitations of gas sensing mechanisms for trace-level detection of ammonia (NH 3 ). In this study, we propose to exploit single-atom catalytic activation and targeted adsorption properties to achieve highly sensitive and selective NH 3 gas detection. Specifically, Ni single-atom active sites based on N, C coordination (Ni–N–C) were interfacially confined on the surface of two-dimensional (2D) MXene nanosheets (Ni–N–C/Ti 3 C 2 T x ), and a fully flexible gas sensor (MNPE–Ni–N–C/Ti 3 C 2 T x ) was integrated. The sensor demonstrates a remarkable response value to 5 ppm NH 3 (27.3%), excellent selectivity for NH 3 , and a low theoretical detection limit of 12.1 ppb. Simulation analysis by density functional calculation reveals that the Ni single-atom center with N, C coordination exhibits specific targeted adsorption properties for NH 3 . Additionally, its catalytic activation effect effectively reduces the Gibbs free energy of the sensing elemental reaction, while its electronic structure promotes the spill-over effect of reactive oxygen species at the gas–solid interface. The sensor has a dual-channel sensing mechanism of both chemical and electronic sensitization, which facilitates efficient electron transfer to the 2D MXene conductive network, resulting in the formation of the NH 3 gas molecule sensing signal. Furthermore, the passivation of MXene edge defects by a conjugated hydrogen bond network enhances the long-term stability of MXene-based electrodes under high humidity conditions. This work achieves highly sensitive room-temperature NH 3 gas detection based on the catalytic mechanism of Ni single-atom active center with N, C coordination, which provides a novel gas sensing mechanism for room-temperature trace gas detection research.