Understanding the structural evolution of Au/WO_2.7 compounds in hydrogen atmosphere by atomic scale in situ environmental TEM

Hydrogen energy is a resuscitated clean energy source and its sensitive detection in air is crucial due to its very low explosive limit. Metal oxide decorated with noble metal nanoparticles has been used for the enhancement of gas detection and exhibits superior sensitivity. Understanding the intrinsic mechanism of the detection and the enhancement mechanism is thus becoming a fundamental issue for the further development of novel metal/oxide compound gas-sensing materials. However, the correlation between the microstructural evolution, the charge transport and the complex sensing process has not yet been directly revealed and its atomic mechanism is still debatable. In this study, an Au/WO_2.7 compound was synthesized and exhibited a strongly enhanced gas sensitivity to many reductive gases, especially H₂. Aberration-corrected environmental transmission electron microscopy was used to investigate the atomic-scale microstructural evolution in situ during the reaction between H₂ and Au/WO_2.7 compound. Swing and sintering processes of the Au particles on the WO_2.7 surface were observed under heating and gaseous environments, and no injection of hydrogen atoms was suggested. First principle calculations verified the swing and sintering processes, and they can be explained by the enhancement of H₂ sensitivity.