Understanding the structural evolution of Au/WO 2.7 compounds in hydrogen atmosphere by atomic scale in situ environment
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y Lab of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, China International Laboratory for Quantum Functional Materials of Henan, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China 3 School of Mechanical and Mining Engineering and Centre for Microscopy and Microanalysis, The University of Queensland, St Lucia, QLD 4072, Australia 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 8 May 2020 / Revised: 26 June 2020 / Accepted: 29 June 2020
ABSTRACT 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/WO2.7 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/WO2.7 compound. Swing and sintering processes of the Au particles on the WO2.7 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.
KEYWORDS in situ environmental TEM, H2 sensing, Au/WO2.7, gas-solid interface
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Introduction
Hydrogen (H2) sensing in air is crucial since H2 is a reducing gas and one of the most important carrier gases as a fuel gas and a clean energy resource. Hydrogen has been used for a wide variety of applications including fuel cells, cars with a H2 engine, and industrial processes such as ammonia production, petroleum refining, the metallurgical industry and fine organic synthesis [1]. Noble metal-decorated semiconductor oxides are typical superior sensor materials since it can create enhanced sites for gas molecular adsorption and lower the activation energy. Increasing attention has been paid to the novel properties of supported noble metal nanoparticles (NPs) on transition metal oxides. Among them, tungsten oxide has been extensively studied due to its distinctive properties of electrochromism, photochromism, ability to sense gases, photocatalysis, photoluminescence and so on [2–5]. Ultrafine Au NPs supported on tungsten oxides exhibit extraordinarily high activity for low-temperature catalytic combustion, partial oxidation of hydroca
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