High-throughput experimentation in resistive gas sensor materials development
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The review describes the workflow of a high-throughput screening process for the rapid identification of new and improved gas sensor materials. Multiple nanoparticulate metal oxides were synthesized via the polyol method, and material diversity was achieved by volume and/or surface doping. The resulting materials were applied as thick films on multielectrode substrates to serve as chemiresistors. This high-throughput approach including automated preparation, complex impedance measurements, and evaluation procedures enables reproducible measurements and their visual representation. Selected examples demonstrate the state of the art for applying high-throughput impedance spectroscopy in search of new sensitive and selective gas sensing materials as well as in analyzing structure–property relations.
I. INTRODUCTION
Gas sensors are widely used in different fields of application, like in intelligent process management, environmental protection, security, and medical diagnostics. To fulfill the growing demands of these rapidly evolving fields, the fast development of highly sensitive and selective gas sensor materials is essential. Most commonly applied gas sensors are metal oxidebased conductometric or resistive sensors, so-called chemiresistors. These sensors rely on a change in electrical resistance upon surface reactions with reactive analyte gas(es). That achievement goes back to Brattain and Bardeen1 for Ge and to Heiland2,3 for the semiconducting ceramic ZnO. Then, Seiyama et al.4,5 and Taguchi6 further developed the concept toward the first commercial product—a fire alarm sensor. The metal oxides, which are in use today, are predominantly SnO2, ZnO, TiO2, WO3, and In2O3.7 More recent examples are mainly based on ternary oxides, such as rare-earth perovskites, LnBO3 (Ln 5 lanthanide series; B 5 Cr and Fe), which are also applied as materials in electrodes of fuel cells,8 (photo) catalysts,9,10 and magneto-optics.11 In particular, several orthoferrites of which LaFeO3 and SmFeO3 are the best studied materials among this class of substances12,13 have
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Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2012.344 574
J. Mater. Res., Vol. 28, No. 4, Feb 28, 2013
http://journals.cambridge.org
Downloaded: 14 Mar 2015
been investigated with respect to CH3OH14 and NO2 sensitivity.15 Most recently, LaFeO3 has been the subject of first-principles studies of the molecular oxygen adsorption on Fe ion sites,16 and LnFe0.9Mg0.1O3 (Ln 5 Nd, Sm, Gd, and Dy) has been tested for C2H5OH sensitivity.17 Ilmenite oxides, such as CoTiO3, in combination with Ta2O318 have been applied for humidity detection, while the p-type semiconductor CoTiO3 was initially published as an ethanol detecting material in 1999.19 A way to overcome the limitations of such oxides in terms of selectivity is the application of foreign elements or oxides for surface and volume doping. The material doping widens up the parameter space since, besides the chemi
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