Surface La Vacancy-Induced Activating Surface Lattice Oxygen of LaFeO₃ for Boosting Formaldehyde Sensing Performance

The tunable physicochemical properties of LaFeO₃ show promise as a distinctive candidate for gas sensor applications. However, how to efficiently construct abundant active sites for LaFeO₃ and clarify the sensing mechanism remains a challenge. Herein, we propose a modulating surface La vacancy strategy to improve the formaldehyde (HCHO) sensing performance of LaFeO₃ by activating surface lattice oxygen. The LaFeO₃ with abundant surface La vacancies was prepared by a urea-assisted sol-gel strategy (LFO-U-CA). The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) results indicate the formation of surface La vacancies, activating more surface lattice oxygen, supported by O₂ temperature-programmed desorption (O₂-TPD) and H₂ temperature-programmed reduction (H₂-TPR). Experimentally, LFO-U-CA exhibits a high response value of 4.2 toward 10 ppm HCHO (2.5 times higher than LFO-CA@1.7), low theoretical limit of detection (LOD) of 3.3 ppb, high selectivity, and high stability and can distinguish low-concentration HCHO in simulated indoor gaseous environments. Furthermore, the LFO-U-CA sensor shows a higher response value of 31.4 to 10 ppm HCHO in Ar, confirming surface lattice oxygen as the active species. Importantly, the formation of more surface La vacancies not only reduces the electron cloud density of Fe and O sites, promoting Fe 3d-O 2p orbital hybridization, thereby strengthening Fe-O covalency and activating surface lattice oxygen, but also induces the exposure of additional surface active sites (Fe sites and oxygen vacancies thus formed) for adsorption of HCHO and O₂. This work provides a new strategy to design high-performance perovskite oxide-based gas sensors by modulating catalytic activity.