Aero-gel based CeO2 nanoparticles: synthesis, structural properties and detailed humidity sensing response

In this work, we present aero-gel based cerium oxide (CeO2) nanoparticles for the relative humidity (%RH) sensing application. X-ray diffraction (XRD) and N-2 adsorption-desorption isotherms revealed that the synthesized CeO2 nanoparticles (NPs) possessed a face centered cubic (fcc) structure with a high surface area (268 m(2) g(-1)). The high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and selected area electron diffraction (SAED) studies confirmed that the shape of CeO2 NPs was spherical and they possessed a polycrystalline nature. X-ray photoelectron spectroscopy (XPS) studies revealed the presence of both trivalent (Ce3+) and tetravalent (Ce4+) oxidation states of ceria. The CeO2 NPs' response towards %RH was explored by measuring the important sensing attributes (response/recovery, linearity, hysteresis, repeatability and stability) at 11-98%RH and at room temperature. An impressive impedance change of 4.5 orders of magnitude was observed along with a swift response (4.6 s) time and rapid recovery (2.7 s) time. Moreover, the prepared sensor showed negligible hysteresis, excellent stability and good reversible response in the complete 11-98%RH range.