In Situ Insights into the Formaldehyde Sensing Mechanism of SnO2/NiO: The Critical Role of Lattice Oxygen.

Owing to the synergistic effect of hetero-materials and the improvement of the oxygen vacancy (VO) concentration, construction of heterostructural materials represents an effective strategy for developing highly sensitive sensors for trace formaldehyde detection. However, the traditional sensing mechanism neglects the role of lattice oxygen (OLat). Moreover, conventional characterizations often fail to identify the specific component of the composite that is responsible for providing reactive OLat. Herein, we report a high-performance formaldehyde sensor based on SnO2/NiO heterostructures, exhibiting an exceptional response (ΔI/Iair = 8.75 @ 1 ppm), an ultralow detection limit (4 ppb), and high selective coefficients (SF/SOthers) ranging from 49 to 533.5. Through in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT) calculations, we present direct experimental evidence that the OLat of NiO within the SnO2/NiO heterostructure actively participates in the sensing process. Furthermore, we elucidate the underlying mechanism, demonstrating that the participation of OLat plays a significant role in enhancing the sensor's response value. This study advances the fundamental understanding of gas-sensing mechanisms based on heterostructures.