Sensor and method for accurately measuring concentrations of oxide compounds in gas mixtures

• US 5,397,442 A
• Filed: 03/09/1994
• Issued: 03/14/1995
• Est. Priority Date: 03/09/1994
• Status: Expired due to Term

• Current Assignee: Gas Technology Institute
• Original Assignee: Gas Research Institute (GTI Energy)
• Inventors: Wachsman, Eric D.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): Bell, Bruce F.
• Application Number:
  US08/208,449
• Time in Patent Office: 370 Days
• Field of Search: 204/415, 204/424, 204/425, 204/426, 204/427, 204/428, 204/153.14, 204/153.16, 204/153.18, 204/410, 204/412, 338/34, 73/23.31, 422/94, 422/98
• US Class Current: 205/781
• CPC Class Codes: G01N 27/4074 for detection of gases other than oxygen
• CPC Class Codes: G01N 33/0031 comprising two or more sensors, e.g. a sensor array electrochemical electrode arrays G01N27/27
• CPC Class Codes: G01N 33/0037 for NOx
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

Sensors (10, 40) accurately measure the concentration of an oxide compound, such as nitrogen oxide NO_x, in a gas mixture (11) which can include oxygen O₂. The sensors (10, 40) each comprise a chamber (12, 42) adapted to receive the gas mixture (11) as well as first and second electrochemical cells (16, 17) for consuming oxygen and/or the oxide compound in the chamber (12, 42). The first electrochemical cell (16) comprises a first internal electrode (16a) inside the chamber (12, 42), a first external electrode (16b) outside the chamber (12, 42), and a first electrolyte body (14'"'"') therebetween. The second electrochemical cell (17) comprises a second internal electrode (17a) inside the chamber (12, 42), a second external electrode (17b) outside the chamber (12, 42), and a second electrolyte body (14") therebetween. The first and second electrolyte bodies (14'"'"', 14") are permeable to oxygen ions. Significantly, the first and second internal electrodes (16a, 17a) are metal oxides having a perovskite lattice structure, which generally exhibit high relative selectivity between oxide compounds, including NO_x, and O₂. The electrical characteristics of the first and second electrochemical cells (16, 17) are manipulated and/or monitored in order to determine the concentration of NO_x within the chambers (12, 42) and the gas mixture (11).

Claims

1. A sensor for accurately measuring a concentration of an oxide compound in a gas mixture, comprising:

a chamber adapted to receive the gas mixture;

a first cell means comprising a first internal electrode inside said chamber, a first external electrode outside said chamber, and a first electrolyte body therebetween, said first electrolyte body is substantially permeable to oxygen ions when said first electrolyte body is electrically biased during operation of the sensor, said first internal electrode comprising a perovskite having selectivity to reduce oxygen and, not the oxide compound, in said chamber; and

a second cell means comprising a second internal electrode inside said chamber, a second external electrode outside said chamber, and a second electrolyte body therebetween, said second electrolyte body is substantially permeable to said oxygen ions when said second electrolyte body is electrically biased during operation of the sensor, said second internal electrode comprising a metal oxide having selectivity to reduce the oxide compound in said chamber after depletion of the oxygen within said chamber;

whereby an electrical characteristic associated with said second cell means corresponds to the concentration of the oxide compound in the gas mixture.

2. The sensor of claim 1, wherein said chamber comprises an enclosure for housing said internal electrodes and an elongated aperture in the shape of a pin through which the gas mixture enters said enclosure.

3. The sensor of claim 1, wherein said chamber comprises an elongated enclosure in the shape of a tube for housing said internal electrodes, said enclosure having first and second apertures for receiving and expelling the gas mixture respectively, said first and second internal electrodes disposed in succession along an axis connecting said first and second apertures, said first internal electrode disposed along said axis between said first aperture and said second internal electrode.

4. The sensor of claim 1, wherein said second internal electrode comprises a perovskite.

5. The sensor of claim 4, wherein said perovskite is selected from the group consisting of LaRuO₃ and LaMnO₃.

6. The sensor of claim 1, wherein said first and second electrolyte bodies are portions of a singular wall of said chamber.

7. The sensor of claim 1, wherein said first and second electrolyte bodies comprise zirconia.

8. The sensor of claim 1, wherein said perovskite is selected from the group consisting of La₂ CuO₄, LaNiO₃, LaFeO₃, LaCoO₃, LaMnO₃, and LaSrCoO₃.

9. A sensor for accurately measuring a concentration of an oxide compound in a gas mixture, comprising:

a chamber adapted to receive the gas mixture;

a first cell means comprising a first internal electrode inside said chamber, a first external electrode outside said chamber, and a first electrolyte body therebetween, said first electrolyte body is substantially permeable to oxygen ions when said first electrolyte body is electrically biased during operation of the sensor, said first internal electrode comprising a perovskite having selectivity to reduce the oxygen and, not the oxide compound; and

a second cell means comprising a second internal electrode inside said chamber, a second external electrode outside said chamber, and a second electrolyte body therebetween, said second electrolyte body is permeable to said oxygen ions when said second electrolyte body is electrically biased during operation of the sensor, said second internal electrode comprising a material having selectivity to concurrently reduce both the oxygen and the oxide compound;

whereby first and second electrical characteristics associated with said first and second cell means are measured and the concentration of the oxide compound in the gas mixture is determined by mathematically combining said first and second electrical characteristics.

10. The sensor of claim 9, wherein said chamber comprises an enclosure for housing said internal electrodes and an elongated aperture in the shape of a pin through which the gas mixture enters said enclosure.

11. The sensor of claim 9, wherein said chamber comprises an elongated enclosure in the shape of a tube for housing said internal electrodes, said enclosure having first and second apertures for receiving and expelling the gas mixture respectively, said first and second internal electrodes disposed in succession along an axis connecting said first and second apertures, said first internal electrode disposed along said axis between said first aperture and said second internal electrode.

12. The sensor of claim 9, wherein said second internal electrode is a perovskite.

13. The sensor of claim 12, wherein said perovskite is selected from the group consisting of LaRuO₃ and LaMnO₃.

14. The sensor of claim 9, wherein said first and second electrolyte bodies are portions of a singular wall of said chamber.

15. The sensor of claim 9, wherein said first and second electrolyte bodies comprise zirconia.

16. The sensor of claim 9, wherein said perovskite is selected from the group consisting of La₂ CuO₄, LaNiO₃, LaFeO₃, LaCoO₃, LaMnO₃, and LaSrCoO₃.

17. The sensor of claim 9, wherein said second internal electrode is selected from the group consisting of Pt and Rh.

18. The sensor of claim 9, wherein said second internal electrode comprises a perovskite selected from the group consisting of LaRuO₃ and LaMnO₃.

19. A method for accurately measuring a concentration of an oxide compound in a gas mixture, comprising the steps of:

exposing the gas mixture to a first internal electrode comprising a perovskite and a second internal electrode comprising a metal oxide;

selectively reducing the oxygen with said first internal electrode without substantially depleting the oxide compound in the gas mixture;

reducing the oxide compound with said second internal electrode after said first internal electrode depletes the oxygen; and

measuring electrical characteristic associated with said second internal electrode to determine the concentration of the oxide compound in the gas mixture.

20. The method of claim 19, further comprising the steps of:

measuring the electrical current between said first internal electrode and a first external electrode;

measuring the electrical current between said second internal electrode and a second external electrode.

21. The method of claim 19, further comprising the steps of:

measuring the voltage between said first internal electrode and a first external electrode;

measuring the voltage between said second internal electrode and a second external electrode.

22. The method of claim 19, wherein the oxide compound is NO_x.

23. A method for accurately measuring a concentration of an oxide compound in a gas mixture, comprising the steps of:

exposing the gas mixture to first internal and second internal electrodes, said first electrode comprising a perovskite;

selectively reducing the oxygen with said first internal electrode without substantially depleting the oxide compound in the gas mixture;

reducing both the oxygen and the oxide compound with said second internal electrode;

measuring first and second electrical characteristics associated with said first internal and second internal electrodes respectively; and

determining the concentration of the oxide compound in the gas mixture by mathematically combining said first and second electrical characteristics.

24. The method of claim 23, further comprising the steps of:

measuring the electrical current between said first internal electrode and a first external electrode;

measuring the electrical current between said second internal electrode and a second external electrode.

25. The method of claim 23, further comprising the steps of:

measuring the voltage between said first internal electrode and a first external electrode;

measuring the voltage between said second internal electrode and a second external electrode.

26. The method of claim 23, wherein the oxide compound is NO_x.