Potentiometric NOx sensors based on yttria-stabilized zirconia with zeolite modified electrode

1. A NO X potentiometric sensor for determining the concentration of NO X in a gas stream comprising:

a tube, said tube having an end, an interior and an exterior;

a cap member comprising yttria-stabilized zirconia disposed on said end of said tube so as to close said end of said tube, said cap member having an interior surface exposed to the interior of said tube and an exterior surface;

a first electrode disposed on said interior surface of said cap member;

a second electrode disposed on said exterior surface of said cap member; and

a zeolite coating disposed on said first electrode, said zeolite coating capable of oxidizing NO in said gas stream to NO 2 such that said first electrode is exposed to a higher concentration of NO 2 than said second electrode.

2. The NO X potentiometric sensor according to claim 1 additionally comprising a potentiometer, said potentiometer in electrical communication with said first electrode and said second electrode so as to measure a potential difference between said first electrode and said second electrode.

3. The NO X potentiometric sensor according to claim 1 wherein said tube comprises alumina.

4. The NO X potentiometric sensor according to claim 1 wherein said first electrode comprises a material selected from the group consisting of platinum, gold and Cr 2 O 3 .

5. The NO X potentiometric sensor according to claim 1 wherein said second electrode comprises a material selected from the group consisting of platinum, gold and Cr 2 O 3 .

6. The NO X potentiometric sensor according to claim 1 wherein said zeolite is zeolite Y.

7. A NO X potentiometric sensor for determining the concentration of NO X in a gas stream comprising:

a tube comprising yttria-stabilized zirconia, said tube having an exterior surface and an interior surface;

a first electrode disposed on said exterior surface of said tube;

a second electrode disposed on said interior surface of said tube; and

a zeolite covering said first electrode, said zeolite coating capable of oxidizing NO in said gas stream to NO 2 such that said first electrode is exposed to a higher concentration of NO 2 than said second electrode.

8. The NO X potentiometric sensor according to claim 7 additionally comprising a potentiometer, said potentiometer in electrical communication with said first electrode and said second electrode so as to measure a potential difference between said first electrode and said second electrode.

9. The NO X potentiometric sensor according to claim 7 wherein said first electrode comprises a material selected from the group consisting of platinum, gold and Cr 2 O 3 .

10. The NO X potentiometric sensor according to claim 7 wherein said second electrode comprises a material selected from the group consisting of platinum, gold and Cr 2 O 3 .

11. The NO X potentiometric sensor according to claim 7 wherein said zeolite is zeolite Y.

12. The NO X potentiometric sensor for determining the concentration of NO X in a gas stream comprising:

a substrate comprising yttria-stabilized zirconia;

a first electrode disposed on said substrate;

a second electrode disposed on said substrate; and

a zeolite coating disposed on said second electrode, said zeolite coating capable of oxidizing NO in said gas stream to NO 2 such that said second electrode is exposed to a higher concentration of NO 2 than said first electrode.

13. The NO X potentiometric sensor according to claim 12 additionally comprising a potentiometer, said potentiometer in electrical communication with said first electrode and said second electrode so as to measure a potential difference between said first electrode and said second electrode.

14. The NO X potentiometric sensor according claim 12 wherein said first electrode comprises a material selected from the group consisting of platinum, gold and Cr 2 O 3 .

15. The NO X potentiometric sensor according claim 12 wherein said second electrode comprises a material selected from the group consisting of platinum, gold and Cr 2 O 3 .

16. The NO X potentiometric sensor according claim 12 wherein said zeolite is zeolite Y.

17. The NO X potentiometric sensor according to claim 12 wherein said substrate, said first electrode and said second electrode are shielded from direct contact by an exhaust gas by a porous member that permits said exhaust gas to travel through said porous member such that said exhaust gas indirectly contacts said first and said second electrodes, said porous member additionally protecting said substrate, said first and said second electrodes from degradation caused by said exhaust gas.

18. A NO X potentiometric sensor for determining the concentration of NO X in a gas stream comprising:

a yttria-stabilized zirconia substrate;

a first electrode disposed on said yttria-stabilized zirconia substrate;

a second electrode disposed on said yttria-stabilized zirconia substrate;

a zeolite coating disposed on said first electrode, said zeolite coating capable of oxidizing NO in said gas stream to NO 2 such that said first electrode is exposed to a higher concentration of NO 2 than said second electrode.

19. The NO X potentiometric sensor according to claim 18 wherein said first electrode comprises a material selected from the group consisting of platinum, gold, and Cr 2 O 3 .

20. The NO X potentiometric sensor according to claim 18 wherein said second electrode comprises a material selected from the group consisting of platinum, gold, and Cr 2 O 3 .

21. The NO X potentiometric sensor according to claim 18 wherein said first electrode and said second electrode are constructed from the same material.

22. The NO X potentiometric sensor according to claim 18 wherein said zeolite is zeolite Y.