A smart and nanostructured perovskite for selective NO sensing in a broader temperature range

Abstract

BaTiO3 based perovskites and their doped compounds are known as highly catalytic active materials and thus are potentially interesting candidates for gas sensing. This work reports the synthesis and processing of Rh-integrated BaTiO3 nanoparticulate powders and their application for gas sensing investigations. The synthesis of nanoparticles is achieved by means of the oxalic co-precipitation route and further processed by spray-drying prior deposition on sensor platforms with Pt-interdigital electrodes (IDE). Sensor characterization carried out under humid air environment conditions and at gas temperatures varying from RT to 900°C. The powder was characterized by means of SEM, XRD, XPS and Raman spectroscopy. While XRD and Raman spectroscopy show the presence of a single phase identified as tetragonal BaTiO3, EDX and XPS reveal the presence of Rh and oxidation state of the different elements. The SEM reveals a morphology of spherical nanoparticles (70 nm) with the slightly increasing BET measured surface area related to the presence of Rh. Sensor tests yield excellent sensor signal at the lower temperature range (250-400°C) in dry air and very good response from 450 to 900 °C in the presence of as high as 10 % of relative humidity. The humidity at high temperatures has a strong positive effect on the observed good sensor performance. The NO-selectivity of the sensor is excellent from 250 to 900° C, also in the presence of CO at higher temperatures. The subsequent hydrogen treatment at high temperature appears to play an activation role resulting in a better sensing property of the material. The reason for this phenomenon is investigated and believed to be related to Rh-diffusion out of the lattice resulting in a high concentration of oxygen vacancies.