In-situ doping nickel single atoms in two-dimensional MXenes analogue support for room temperature NO₂ sensing

MXenes are promising supports for anchoring metal single atoms due to their versatile composition, well-defined nanostructures, and suitable conductivity. However, metal single atoms are usually coordinated with surface terminal groups (-O, -OH, -Cl, etc.) of MXenes via conventional wet-impregnation, resulting in limited electronic structure modification. Through a NiCl₂ molten salt etching method, we observed that Ni single atoms could be in-situ doped in the lattice of MXenes analogue TiC_0.5N_0.5 support (denoted as Ni₁/TiC_0.5N_0.5), resulting in much larger charge transfer from Ni atoms to adjacent Ti atoms, and thus increasing the electronic density of these Ti atoms. When used for NO₂ sensing, Ni₁/TiC_0.5N_0.5 exhibited excellent response sensitivity (ultra-low limit of detection ~ 10 ppb), selectivity, and good stability at room temperature. This study provides an effective strategy for producing MXenes analogue supported metal single atoms for potential application in gas sensing.