La2O3-sensitized SnO2 nanocrystalline porous film gas sensors and sensing mechanism toward formaldehyde

In this work, a smart platform was reported with an ability to rapidly screen the gas sensing properties of metal oxide gas sensors which were loaded on a single material chip with a capability of 36 sensor films. Among the SnO2-based material sensitized with various catalysts (Mo, Pd, Cd, Mn, Pt, Y, La, Ce, Pr, Sm, Gd) in different concentrations, a significant enhancement of sensing performance was observed for the film with surface functionalized La. To intrinsically investigate its sensitization mechanism, the changes in microstructure and surface valence of the SnO2-based materials were characterized by XRD, SEM, XPS, PL, HRTEM and EDX. It is demonstrated that the hydrated lanthanum chloride transformed to La2O3 with an intermediate of LaOCl during the sintering process of the samples. Thus, the sensitization mechanism of La2O3 can be concluded into two items: (1) numerous of oxygen vacancies are newly created on the SnO2 surface through the LaOCl to La2O3 transformation resulted in the enhancement of gas-sensing properties; (2) the chemisorbed peroxide O22− on La2O3 surface has the ability to cause an H-abstraction reaction with hydrocarbon, which may account for the decrease of optimum temperature toward formaldehyde.