No.sub.x sensor using electrochemical reactions and differential pulse voltammetry (DPV)

• US 5,554,269 A
• Filed: 04/11/1995
• Issued: 09/10/1996
• Est. Priority Date: 04/11/1995
• Status: Expired due to Term

• Current Assignee: Gas Technology Institute (GTI Energy)
• Original Assignee: Gas Research Institute (GTI Energy)
• Inventors: Joseph, Jose P., Oh, Seajin
• Primary Examiner(s): Tung, T.
• Application Number:
  US08/420,121
• Time in Patent Office: 518 Days
• Field of Search: 204/153.1, 204/153.14, 204/400, 204/434, 204/421-429, 205/781
• US Class Current: 204/424
• CPC Class Codes: G01N 27/4065 Circuit arrangements specially adapted therefor
• CPC Class Codes: G01N 27/419 Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells

Abstract

A sensor system accurately measures nitrogen oxide (NO_x) in a gas mixture via the use of at least one electrochemical sensing cell and differential pulse voltammetry (DPV). The sensor system has a sensor with an electrochemical sensing cell for producing an electrical signal (current, voltage, etc.) indicative of an amount of the nitrogen oxide within the gas mixture. The sensing cell has an electrolyte interposed between an anode electrocatalyst and a cathode electrocatalyst. Significantly, a DPV mechanism is connected to the sensing cell for enhancing the sensitivity and selectivity of the electrolyte associated with the sensing cell. The DPV mechanism has (1) a pulse superimposition mechanism for combining a pulse with a sensing cell bias imposed upon the sensing cell; (2) a measurement mechanism for measuring the electrical signal before and during superimposition of the pulse to derive first and second sample signals; and (3) a concentration derivation mechanism for mathematically combining (preferably, subtraction) the first and second sample signals to derive a DPV signal which is indicative of the NO_x concentration. Optionally, based upon the material structure of the sensing cell, the sensor system may also be equipped with an electrochemical pumping cell for consuming oxygen (O₂) within the gas mixture.

Claims

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

an electrochemical sensing cell for consuming nitrogen oxide within said gas mixture and for producing an electrical signal indicative of an amount of said nitrogen oxide within said gas mixture, said sensing cell comprising an anode electrocatalyst, a cathode electrocatalyst, and a solid metal oxide electrolyte disposed therebetween; and

differential pulse voltammetry means connected to said sensing cell having;

(1) pulse superimposition means for combining a pulse with a sensing cell bias imposed upon said sensing cell;

(2) measurement means for measuring said electrical signal before and during superimposition of said pulse to derive first and second sample signals; and

(3) concentration derivation means for mathematically combining said first and second sample signals to derive a differential pulse voltammetry signal which is indicative of said nitrogen oxide concentration within said gas mixture;

wherein said sensing cell bias is imposed between said anode and cathode electrocatalysts and across said electrolyte, said cathode electrocatalyst for decomposing said nitrogen oxide said electrolyte capable of conducting oxide ions at high temperatures above 2000°

C.

2. The sensor system of claim 1, further comprising an electrochemical pumping cell for consuming oxygen within said gas mixture.

3. The sensor system of claim 2, wherein said pumping cell and said sensing cell are partially exposed to a cavity having only a single hole for ingress of said gas mixture into said cavity.

4. The sensor system of claim 1, wherein said an electrolyte comprising zirconia.

5. The sensor system of claim 1, wherein said cathode sensing cell comprises electrocatalyst comprises a metal oxide perovskite, said cathode electrocatalyst being arranged in said sensing cell to consume said nitrogen oxide.

6. The sensor system of claim 1, wherein said cathode electrocatalyst comprises gold for decomposing said nitrogen oxide.

7. The sensor system of claim 1, wherein said cathode electrocatalyst comprises platinum for decomposing said nitrogen oxide.

8. The sensor system of claim 1, wherein said bias exhibits a step function waveform.

9. The sensor system of claim 1, further comprising a porous layer shielding said cathode electrocatalyst of said sensing cell, said porous layer being permeable to said gas mixture for permitting passage of said gas mixture therethrough to said cathode electrocatalyst.

10. The sensor system of claim 1, wherein said cathode electrocatalyst comprises gold and said electrolyte comprises yttria-stabilized-zirconia.

11. A sensor system for measuring nitrogen oxide in a high temperature exhaust gas emitted from a gas combustion process, comprising:

an electrochemical sensing cell including a cathode electrocatalyst and an anode electrocatalyst sandwiching a solid metal oxide electrolyte layer that is permeable to oxide ions at high temperatures above 200°

C., wherein said sensing cell is for consuming said nitrogen oxide within said exhaust gas and for producing an electrical signal indicative of an amount of said nitrogen oxide within said exhaust gas; and

differential pulse voltammetry means connected to said sensing cell for enhancing sensitivity and selectivity of said electrolyte and for generating a differential pulse voltammetry signal indicative of said nitrogen oxide concentration in said exhaust gas.

12. The sensor system of claims 11, wherein sad DPV means includes:

(1) pulse superimposition means for combining a pulse with a sensing cell bias imposed between said cathode and anode electrocatalyst and across said electrolyte;

(2) measurement means for measuring said electrical signal before and during superimposition of said pulse to derive first and second sample signals; and

(3) concentration derivation means for mathematically combining said first and second sample signals to derive said differential pulse voltammetry signal which is indicative of said nitrogen oxide concentration within said gas mixture.

13. The sensor system of claim 11, further comprising a porous layer shielding said cathode electrocatalyst.

14. The sensor system of claim 11, further comprising an electrochemical pumping cell for consuming oxygen within said exhaust gas.

15. The sensor system of claim 14, wherein reduction reactions at said sensing cell and said pumping cell occur at different electrical potentials.

16. The sensor system of claim 14, wherein said pumping cell and said sensing cell are partially exposed to a cavity having only one hole for ingress of said exhaust gas into said cavity.