Gas sensor element

Abstract

A gas sensor element has a solid electrolyte body of oxygen ionic conductivity, a target gas electrode and a reference gas electrode formed on both surfaces of the solid electrolyte body, respectively, a porous diffusion resistance layer, and a catalyst support trap layer. The porous diffusion resistance layer covers the target gas electrode and through which target gases to be measured are passing. The catalyst support trap layer is formed on the outer surface of the porous diffusion resistance layer and supports noble metal catalyst. In the gas sensor element, the noble metal catalyst is made of platinum, rhodium, palladium supported in the catalyst support trap layer. In particular, an addition amount of palladium in the total amount of the noble metal catalyst is within a range of 2 to 65 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a view mainly showing a catalyst support trap layer formed on a porous diffusion resistance layer in a gas sensor element according to an embodiment of the present invention;

FIG. 2 is a view showing components forming the catalyst support trap layer in the gas sensor element of the embodiment shown in FIG. 1;

FIG. 3 is a sectional view of the gas sensor element in a direction perpendicular to a longitudinal axis of the gas sensor element of the embodiment shown in FIG. 1;

FIG. 4 is a sectional view showing an introduction path of target gases in the gas sensor element of the embodiment shown in FIG. 1;

FIG. 5 shows the measurement results of a first experiment indicating the relationship between the addition amount of palladium (Pd) in the entire amount of the noble metal catalyst supported by the catalyst support trap layer and a response time of the gas sensor element;

FIG. 6 shows the measurement results of a second experiment indicating the relationship between the time of endurance and the stoichiometric shift (as output shift) of the gas sensor element;

FIG. 7A is a partially sectional view showing the gas sensor element according to the embodiment shown in FIG. 3;

FIG. 7B is a perspective view showing the gas sensor element according to the embodiment shown in FIG. 3;

FIG. 8A is a sectional view of a catalyst support trap layer in a gas sensor element as a related-art through which target gases to be measured are passing;

FIG. 8B is a sectional view of the catalyst support trap layer in the related-art gas sensor element, which shows a state of reaching the target gases to the target gas electrode in a measurement room;

FIG. 9 is a sectional view showing a detailed catalyst support trap layer that is formed on an outer peripheral surface of a porous diffusion resistance layer in the gas sensor element as the related-art;

FIG. 10A shows components that form the catalyst support trap layer in the gas sensor element according to the related-art before breaking its endurance capability (or durability); and

FIG. 10B shows the components that form the catalyst support trap layer in the gas sensor element according to the related-art after breaking its endurance capability (or durability).

Claims

1. A gas sensor element comprising: a solid electrolyte body of oxygen ionic conductivity;a target gas electrode formed on one surface of the solid electrolyte body;a reference gas electrode formed on the other surface of the solid electrolyte body;a porous diffusion resistance layer covering the target gas electrode and through which target gases to be measured are passing;a catalyst support trap layer formed on the outer surface of the porous diffusion resistance layer and supporting noble metal catalyst,wherein the noble metal catalyst is made of platinum, rhodium, palladium supported in the catalyst support trap layer, and an addition amount of palladium in the total amount of the noble metal catalyst is within a range of 2 to 65 wt %.

2. The gas sensor element according to claim 1, wherein the addition amount of palladium is within a range of 5 to 40 wt %.

3. The gas sensor element according to claim 1, wherein the noble metal catalyst content is not more than 5 wt % of the entire content of the catalyst support trap layer.

4. The gas sensor element according to claim 2, wherein the noble metal catalyst content is not more than 5 wt % of the entire content of the catalyst support trap layer.

5. The gas sensor element according to claim 1, wherein the noble metal catalyst content is not less than 0.1 wt % of the entire content of the catalyst support trap layer.

6. The gas sensor element according to claim 2, wherein the noble metal catalyst content is not less than 0.1 wt % of the entire content of the catalyst support trap layer.

7. The gas sensor element according to claim 3, wherein the noble metal catalyst content is not less than 0.1 wt % of the entire content of the catalyst support trap layer.

8. The gas sensor element according to claim 1, wherein the catalyst support trap layer has a thickness of a range of 10 to 300 μm.

9. The gas sensor element according to claim 2, wherein the catalyst support trap layer has a thickness of a range of 10 to 300 μm.

10. The gas sensor element according to claim 3, wherein the catalyst support trap layer has a thickness of a range of 10 to 300 μm.

11. The gas sensor element according to claim 5, wherein the catalyst support trap layer has a thickness of a range of 10 to 300 μm.

12. The gas sensor element according to claim 1, wherein the gas sensor element has a width of a range of 3.0 to 5.0 mm and a thickness of a range of 1.0 to 2.5 mm.

13. The gas sensor element according to claim 1, wherein the gas sensor element is an air to fuel sensor element capable of detecting an air to fuel ratio by measuring a critical current depending on oxygen concentration in the target gases.

14. The gas sensor element according to claim 8, wherein a traveling length of the target gases passing through the porous diffusion resistance layer covering the target gas electrode is not less than 0.2 mm.

15. The gas sensor element according to claim 1, wherein the target gases are hydrogen gas and oxygen gas.

16. The gas sensor element according to claim 1, wherein a protection trap layer is made of alumina particles and formed on the outer surface of the catalyst support trap layer, and an average diameter of each alumina particle in the protection trap layer is within a range of 10 to 50 μm, an average porosity in the protection trap layer is within a range of 40 to 70%, and an average diameter of each porosity is within a range of 1 to 10 μm.