Synergistic Acceptor-Donor Interplay of Nd <sub>2</sub> Sn <sub>2</sub> O <sub>7</sub> Pyrochlore based Sensor in Selective Detection of Hydrogen
Aida Raauf, David Graf, Yakup Gönüllü, Praveen Kumar Sekhar, Michael Frank, Sanjay Mathur
Abstract
Nanostructured thin film of Nd 2 Sn 2 O 7 pyrochlore obtained by solution processing of a single molecular precursor with Nd-Sn ratio of 1:1 was found to show unprecedently high selectivity towards hydrogen sensing in the temperature range 200 °C–450 °C. Formation of crystalline Nd 2 Sn 2 O 7 upon annealing the xerogel in air at 800 °C was confirmed by powder X-ray diffraction analysis. The heat-treated pyrochlore films exhibited a porous structure with interconnected grains confirmed by scanning electron microscope images. The gas sensing behavior of the device towards various analyte gases (H 2 , CO, CH 4 , NO 2 , NH 3 ) showed remarkably high selectivity towards H 2 , while no sensor response against other reducing and oxidizing gases was monitored. The highest sensitivity towards H 2 was detected at 300 °C with a linear trend observed in the sensitivity values and H 2 concentration (5%–30%). Intercorrelated analysis of sensor characteristics, surface spectroscopy before and after hydrogen treatment and implications of unique crystallographic features of the pyrochlore lattice demonstrated a novel defined subsequent detection mechanism, which strongly differs from conventional binary oxides like SnO 2 . The significant increase in operating temperature upon H 2 exposure is apparently caused by the exothermic reaction between pyrochlore and molecular hydrogen to generate highly reactive hydride species during the detection mechanism. The high efficiency and reproducibility of the investigated sensor devices indicates the potential of Nd 2 Sn 2 O 7 based sensors for hydrogen safety applications.