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Rhodium Oxide Surface-Loaded Gas Sensors

Authors :
Anna Staerz
Inci Boehme
David Degler
Mounib Bahri
Dmitry E. Doronkin
Anna Zimina
Helena Brinkmann
Sina Herrmann
Benjamin Junker
Ovidiu Ersen
Jan-Dierk Grunwaldt
Udo Weimar
Nicolae Barsan
Source :
Nanomaterials, Vol 8, Iss 11, p 892 (2018)
Publication Year :
2018
Publisher :
MDPI AG, 2018.

Abstract

In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic study of sensors based on rhodium-loaded WO3, SnO2, and In2O3—examined using X-ray diffraction, high-resolution scanning transmission electron microscopy, direct current (DC) resistance measurements, operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and operando X-ray absorption spectroscopy—is presented. Under normal sensing conditions, the rhodium clusters were oxidized. Significant evidence is provided that, in this case, the sensing is dominated by a Fermi-level pinning mechanism, i.e., the reaction with the target gas takes place on the noble-metal cluster, changing its oxidation state. As a result, the heterojunction between the oxidized rhodium clusters and the base metal oxide was altered and a change in the resistance was detected. Through measurements done in low-oxygen background, it was possible to induce a mechanism switch by reducing the clusters to their metallic state. At this point, there was a significant drop in the overall resistance, and the reaction between the target gas and the base material was again visible. For decades, noble metal loading was used to change the characteristics of metal-oxide-based sensors. The study presented here is an attempt to clarify the mechanism responsible for the change. Generalities are shown between the sensing mechanisms of different supporting materials loaded with rhodium, and sample-specific aspects that must be considered are identified.

Details

Language :
English
ISSN :
20794991
Volume :
8
Issue :
11
Database :
Directory of Open Access Journals
Journal :
Nanomaterials
Publication Type :
Academic Journal
Accession number :
edsdoj.b3ff4e78c7cb4cb2826fc84ca0680dc0
Document Type :
article
Full Text :
https://doi.org/10.3390/nano8110892