CO gas sensor and CO gas concentration measuring method

• US 6,090,268 A
• Filed: 05/15/1998
• Issued: 07/18/2000
• Est. Priority Date: 04/22/1996
• Status: Expired due to Term

• Current Assignee: IMRA Japan Kabushikikaisha
• Original Assignee: IMRA Japan Kabushikikaisha
• Inventors: Kunimatsu, Keiji, Akita, Hidemi
• Primary Examiner(s): Tung, T.
• Assistant Examiner(s): McNeil, Jennifer C.
• Application Number:
  US08/981,624
• Time in Patent Office: 795 Days
• Field of Search: 429/19, 429/22, 204/421, 204/424, 204/425, 204/426, 204/431, 204/432, 205/782, 205/783, 205/783.5
• US Class Current: 205/782
• CPC Class Codes: G01N 27/4045 for gases other than oxygen
• CPC Class Codes: G01N 33/004 CO or CO2

Abstract

A CO gas sensor according to the present invention includes a gas collecting container for collecting a measured gas therein; a detecting section provided within the gas collecting container and having at least a pair of electrodes positioned through electrolyte; and a voltage applying apparatus for applying voltage to the detecting section. One of the electrodes of the detecting section is a detection electrode having the capability of adsorbing at least one of hydrogenous gas and CO gas when a voltage is applied and then oxidizing it. By introducing a measured gas into a gas collecting container of the CO gas sensor and carrying out electrolysis according to a potential sweep method or a pulse method with the measured gas being in contact with the detecting section, a CO gas concentration in the measured gas can be measured based on an electrical current value obtained at the detecting section and changes of the electrical current with elapse of time. According to the CO gas sensor of the present invention, it is possible to accurately carry out detection and measurement of the concentration of CO gas when CO gas is to be detected or measured even in a gaseous atmosphere containing a relatively large amount of hydrogen gas and CO₂ gas.

Claims

1. A method for detecting CO concentration in a gas containing CO and hydrogen in an amount in excess of the CO, said method comprising:

providing a CO gas sensor including a detection electrode, a counter electrode and an electrolyte interposed between the detection electrode and the counter electrode;

contacting the gas with the detection and counter electrodes;

impressing voltages on said electrodes, while in contact with said gas, to obtain a change of hydrogen ionization current corresponding to CO adsorption by said detection electrode; and

determining the change in hydrogen ionization current as a measure of CO concentration in the gas.

2. A method according to claim 1 wherein the determined change is a decrease in hydrogen ionization current due to adsorption CO by the detection electrode.

3. A method according to claim 2 wherein said decrease in hydrogen ionization current is measured for a predetermined period of time at a voltage producing CO adsorption by the detection electrode.

4. A method according to claim 2 wherein the determined change is determined as a period of time elapsed in reaching a predetermined fraction of an initial hydrogen ionization current.

5. A method according to claim 1 wherein said determining includes generation of a cyclic voltammogram.

6. A method according to claim 5 wherein the CO gas sensor further includes an electrolyte solution with the electrodes immersed therein in a spaced relationship, wherein said contacting includes saturating the electrolyte with the gas, and wherein the hydrogen ionization current is allowed to stabilize at each voltage and then determined.

7. A method according to claim 5 wherein the electrodes are in a container, wherein said contacting is by introducing the gas into the container and wherein said determining is conducted after the concentration of CO in the gas within the container has stabilized.

8. A method according to claim 1 wherein the imposed voltage is a pulsed voltage.

9. A method according to claim 8 wherein the change is determined as a period of time required to reach a predetermined fraction of an initial hydrogen ionization current and wherein the determination of CO concentration is made by applying the determined period of time to a, analytical curve for a relationship between CO concentration and the inverse of the time required to reach the predetermined fraction after initiation of hydrogen ionization current.

10. A method according to claim 8 wherein said determining is by applying a ratio of a hydrogen ionization current at time t to a hydrogen ionization current at time O to a langmuir analytical graph for CO adsorption.

11. A method according to claim 8 wherein said determining includes determination of a ratio of the detected decrease in the hydrogen ionization current to an initial hydrogen ionization current and applying the determined ratio to an analytical graph for a relationship between the CO concentration and ratios of decrease in hydrogen ionization current to initial hydrogen ionization current.

12. A method according to claim 8 wherein said determining includes determination of an initial speed of decrease in hydrogen ionization current and applying the determined speed to a predetermined plot of initial speeds of decrease in hydrogen ionization current versus CO concentration.

13. A method according to claim 1 wherein said gas is a reforming gas.

14. A method according to claim 1 wherein the imposed voltage is set to avoid reduction of CO₂.

15. A method according to claim 1 comprising imposing a first voltage which produces a first hydrogen ionization current without adsorption of CO and a second voltage which produces adsorption of CO by the detection electrode and a second hydrogen ionization current less than said first hydrogen ionization current, and wherein said change is a difference between said first and second hydrogen ionization currents.

16. A method according to claim 1 wherein the impressed voltage is a pulsed voltage which varies between a CO oxidation potential and a CO adsorption potential.