Gas sensor

• US 4,474,648 A
• Filed: 04/23/1981
• Issued: 10/02/1984
• Est. Priority Date: 04/30/1980
• Status: Expired due to Term

• Current Assignee: City Technology Ltd. (Honeywell International Inc.)
• Original Assignee: City Technology Ltd. (Honeywell International Inc.)
• Inventors: Hobbs, Bryan S., Chan, Yat S., Tantram, Anthony D. S., Finbow, John R.
• Primary Examiner(s): Tung, T.
• Application Number:
  US06/256,283
• Time in Patent Office: 1,258 Days
• Field of Search: 204/1 T, 204/1 K, 204/195 R, 204/195 P, 204/400, 204/415, 204/431-433
• US Class Current: 205/783
• CPC Class Codes: G01N 27/4045 for gases other than oxygen

Abstract

An electro-chemical cell for quantitatively detecting an acidic or an alkaline gas, e.g. carbon dioxide, includes a sensing electrode 9 which is connected to a top cap 12 by a contact strip 8 and is accessible to the gas to be tested through a hole 13. The electrode 9 comprises an electro-chemical couple whose potential is pH-dependent (e.g. silver/silver oxide for carbon dioxide) the active material being supported by a nickel gauze to give good current collection. A counter electrode 2 without significant gas access is immersed in an electrolyte 3 whose pH is such that it will change following adsorption of the gas being tested for. A wicking separator 7 ensures an electrolytic path between the two electrodes. The components are contained within a metal can 1, the top cap 12 being held by folding over the rim 5. An insulating grommet 6 is fitted between the two electrodes. When using silver/silver oxide for the sensing electrode 9, the counter electrode may be of the same material and the electrolyte may be potassium carbonate. The current flowing between the electrodes is a measure of the concentration of gas being detected. A reference electrode 14 may also be included.

Claims

1. A method of quantative detection of carbon dioxide by means of an electrochemical cell comprising a sensing electrode which is in contact with an electrochemical couple whose potential is pH dependent, a counter electrode without significant carbon dioxide access and an electrolyte in contact with both electrodes whose pH is such that it will change following absorption of the carbon dioxide being tested for and low impedance means for measuring the current flowing between the sensing and counter electrodes, this current being a measure of the concentration of the carbon dioxide being detected, wherein the flux to the sensing electrode of the carbon dioxide being tested for is controlled by a gas phase diffusion barrier which restricts the access of carbon dioxide and which comprises at least one narrow defined capillary passage or a combination thereof with a porous membrane for the diffusion of carbon dioxide, wherein the carbon dioxide being tested for is absorbed in the vicinity of the sensing electrode which is pH sensitive, thus changing the pH of the electrolyte in the vicinity of the pH sensitive sensing electrode and hence the potential of the sensing electrode, wherein as a consequence of said low impedance means for measuring the current flowing between the sensing and counter electrodes the potential change is restricted and current flows instead to redress pH imbalance, which current provides a signal dependent on the concentration of the carbon dioxide being tested for.

2. An electro-chemical cell for quantitatively detecting carbon dioxide comprising a sensing electrode to which access of the carbon dioxide to be tested is provided via a gas phase diffusion barrier which restricts the access of carbon dioxide and which comprises at least one narrow defined capillary passage or a combination thereof with a porous membrane for the diffusion of carbon dioxide, said sensing electrode being in contact with an electrochemical couple whose potential is pH dependent, a counter electrode without significant carbon dioxide access and an electrolyte in contact with both electrodes whose pH is such that it will change following absorption of the carbon dioxide being tested for and low impedance means for measuring current flowing between the sensing and counter electrodes, this current being a measure of the concentration of carbon dioxide being detected.

3. A cell as claimed in claim 2 including also a third, reference electrode without significant carbon dioxide access and means arranged to maintain said sensing electrode substantially at the potential characteristic of said electro-chemical couple in said electrolyte, in the absence of said carbon dioxide being detected.

4. A cell as claimed in claim 2 or claim 3 for the detection of carbon dioxide in which the pH of said electrolyte is between 4 and 14.

5. A cell as claimed in claim 2 or claim 3 for the detection of carbon dioxide in which the pH of said electrolyte is between 8 and 14.

6. A cell as claimed in claim 2 in which said pH-sensitive electro-chemical couple in conact with said sensing electrode is Ag₂ O/Ag.

7. A cell as claimed in claim 2 in which said pH-sensitive electro-chemical couple in contact with said sensing electrode is HgO/Hg.

8. A cell as claimed in claim 3 in which said third reference electrode contains an Ag₂ O/Ag couple.

9. A cell as claimed in claim 8 in which said electrolyte contains a solid hydroxide of a metal selected from the group comprising barium, calcium and magnesium, said electrolyte being separated from said sensing electrode by an anion-exchange membrane.

10. A cell as claimed in claim 3 in which said third reference electrode contains an HgO/Hg couple.

11. A cell as claimed in claim 10 in which said electrolyte contains a solid hydroxide of a metal selected from the group comprising barium, calcium and magnesium, said electrolyte being separated from said sensing electrode by an anion-exchange membrane.

12. A cell as claimed in claim 2 in which said electrolyte contains a solid hydroxide of a metal selected from the group comprising barium, calcium and magnesium.