High-Temperature Hydrocarbon Sensors Based on a Stabilized Zirconia Electrolyte and Metal Oxide Electrodes

Abstract

The sensing properties of zirconia-based electrochemical cells with various metal oxide electrodes for 0-500 ppm hydrocarbons (primarily propene), hydrogen, and carbon monoxide were studied in the presence of 10% oxygen at 600°C. The addition of 0.1 wt % manganese oxide (MnO 2 ) to an indium oxide (In 2 O 3 ) electrode significantly improved the selectivity of the parent electrode to propene over hydrogen and carbon monoxide. This addition effect was based on the promotion of nonelectrochemical oxidations of hydrogen and carbon monoxide in preference to that of propene. The sensor using the 0.1 wt % MnO 2 -added In 2 O 3 electrode was more reproducible and sensitive to the hydrocarbons than that using a gold electrode.The oxygen sensors constructed from zirconia-based solid electrolytes rarely generate different electromotive forces (emfs) from the values calculated by the Nernst equation, when the reducing gases such as carbon monoxide, 1-4 hydrogen sulfide, 5 nitrogen monoxide, 6,7 and hydrogen 8,9 coexist with oxygen. This behavior has been explained by the appearance of a mixed potential at the working electrode, where the cathodic reaction of oxygen gas and the anodic reaction of the reducing gas occur simultaneously. 10 Recently, some research groups have reported that a gold (Au) electrode shows large mixed potentials for hydrocarbons at high temperatures up to 600°C. 11-13 For example, we found that the mixed potential at the Au electrode was enhanced by increasing the carbon number of the hydrocarbons, unsaturating the C-C linkage and branching the chain structure. 12 This property meets the hydrocarbon sensing in the exhaust gases from diesel engines, because unsaturated and higher hydrocarbons significantly cause photochemical smog in the atmosphere. However, Mukundan et al. pointed out that the mixed potential at the Au electrode, especially deposited on an yttria-stabilized zirconia (YSZ), was easily affected by its surface morphology, thus resulting in a poor reproducibility of the sensing properties. 13 This is mainly because of its relatively low melting point of 1063°C. Hence, we have investigated the use of metal oxide electrodes in place of the Au electrode for the purpose of developing a more reliable hydrocarbon sensor. In this paper, we report that a 0.1 wt % manganese oxide (MnO 2 )-added indium oxide (In 2 O 3 ) electrode showed larger mixed potentials for the hydrocarbons but smaller mixed potentials for hydrogen and carbon monoxide than the Au electrode. In addition, this electrode yields much more reproducible mixed potentials for the hydrocarbons than does the Au electrode.Experimental A two-chamber cell constructed from a YSZ solid electrolyte with working, counter, and reference electrodes is used as the hydrocarbon sensor. A detailed illustration of this cell is reported in a previous paper. 12 The sintered YSZ disk (8 mol % yttria, 14 mm diam, 1.0 mm thick) was purchased from Nikkato Co., Ltd. Various metal oxide working electrodes were deposited on the YSZ surface as follows: In t...

A review of mixed-potential type zirconia-based gas sensors

“…In general, the HCs sensitivity has been reported to be enhanced with increasing carbon number within the same HCs group, as illustrated in Fig. 13 [51,58,105,107,108,110,112,[114][115][116][117][118][119][120][121][122][123]. Additionally, it was also reported by Hibino et al that HCs sensitivity increased with the order of alkane, alkene, and alkyne in the case of same carbon number (Fig.…”

“…However, the addition of a second component to the SE materials can also change its electrochemical catalytic activity. Hibino et al reported that the addition of 0.1 wt% MnO 2 to In 2 O 3 -SE decreased the electrochemical catalytic activity of SE toward H 2 and CO, while maintaining the high catalytic activity to C 3 H 6 [115].…”

Solid‐State Electrochemical Sensors for Automotive Applications

“…Recently, there have been several publications trying to address these limitations by replacing the Au electrode with an oxide or composite electrode. The electrode materials that have been reported include Au-10%Ta 2 O 5 10 , In 2 O 3 -0.1%MnO 2 , 13 and CdO. 14 In this paper we report the response of a La 0.8 Sr 0.2 CrO 3 (LSCO) electrode on a YSZ electrolyte.…”

Electrochemical Sensors: Fundamentals, Key Materials, and Applications

“…Such examples include Cr 2 O 3 þ NiO [297] for NO x sensors, CuO þ ZnO [298,299] or SnO 2 þ CdO [300] for CO sensors, and In 2 O 3 þ MnO 2 [301,302] for hydrocarbon sensors. Some examples of the outputs of NO x and CO sensors with two-phase oxide mixtures as electrodes are shown in Figure 13.24 [270,297,298,300].…”