Synergistic Acceptor-Donor Interplay of Nd2Sn2O7 Pyrochlore based Sensor in Selective Detection of Hydrogen

Abstract

Nanostructured thin film of Nd2Sn2O7 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 Nd2Sn2O7 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 (H2, CO, CH4, NO2, NH3) showed remarkably high selectivity towards H2, while no sensor response against other reducing and oxidizing gases was monitored. The highest sensitivity towards H2 was detected at 300 °C with a linear trend observed in the sensitivity values and H2 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 SnO2. The significant increase in operating temperature upon H2 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 Nd2Sn2O7 based sensors for hydrogen safety applications.