Gas sensor and method for manufacturing gas sensor

Patent metadata

Field	Value
Publication number	US-10816501-B2
Application number	US-201615347086-A
Country	US
Kind code	B2
Filing date	Nov 9, 2016
Priority date	Nov 17, 2015
Publication date	Oct 27, 2020
Grant date	Oct 27, 2020

Abstract

A gas sensor with excellent detection sensitivity is provided. A sensing electrode, which is provided in a mixed-potential gas sensor for measuring a concentration of a predetermined gas component of a measurement gas to sense the predetermined gas component, is formed of a cermet of a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal includes Pt and Au. A range of at least 1.5 nm from a surface of a noble metal particle included in the sensing electrode is a Au enriched region having a Au concentration of 10% or more.

First claim

What is claimed is:

1. A mixed-potential gas sensor for measuring a concentration of a predetermined gas component of a measurement gas, the gas sensor comprising:
a sensor element mainly made of an oxygen-ion conductive solid electrolyte;
a sensing electrode located on a surface of said sensor element; and
a reference electrode including a cermet of Pt and an oxygen-ion conductive solid electrolyte,
wherein
said sensing electrode includes a cermet comprising a plurality of noble metal particles and oxygen-ion conductive solid electrolyte particles,
said noble metal particles each comprise an alloy of Pt and Au,
for at least one of the plurality of noble metal particles, a range of at least 1.5 nm from a surface of each of the at least one of the plurality of noble metal particles is a Au enriched region having a Au concentration of 10% or more, and
the gas sensor determines the concentration of said predetermined gas component based on a potential difference between said sensing electrode and said reference electrode.

2. The gas sensor according to claim 1 , wherein said Au concentration is a value calculated from an expression
Au concentration (%)=100×Au detection value/(Au detection value+Pt detection value)

where a Au detection value and a Pt detection value are values in Auger spectrum obtained by performing a measurement on the surface of said at least one of the plurality of noble metal particles by Auger electron spectroscopy.

3. The gas sensor according to claim 2 , further comprising
an electrode protective layer that is a porous layer covering at least said sensing electrode.

4. The gas sensor according to claim 3 , wherein
said sensor element further includes a reference gas introduction space into which a reference gas is introduced, said reference gas introduction space separated from a space containing said measurement gas, and
said reference electrode is placed in an atmosphere of said reference gas.

5. The gas sensor according to claim 3 , wherein said sensing electrode and said reference electrode are disposed on the surface of said sensor element.

6. The gas sensor according to claim 2 , wherein
said sensor element further includes a reference gas introduction space separate from a space containing said measurement gas, into which a reference gas is introduced, and
said reference electrode is placed in an atmosphere of said reference gas.

7. The gas sensor according to claim 2 , wherein said sensing electrode and said reference electrode are disposed on the surface of said sensor element.

8. The gas sensor according to claim 1 , further comprising an electrode protective layer that is a porous layer covering at least said sensing electrode.

9. The gas sensor according to claim 8 , wherein
said sensor element further includes a reference gas introduction space into which a reference gas is introduced, said reference gas introduction space separated from a space containing said measurement gas, and
said reference electrode is placed in an atmosphere of said reference gas.

10. The gas sensor according to claim 8 , wherein said sensing electrode and said reference electrode are disposed on the surface of said sensor element.

11. The gas sensor according to claim 1 , wherein
said sensor element further includes a reference gas introduction space into which a reference gas is introduced, said reference gas introduction space separated from a space containing said measurement gas, and
said reference electrode is placed in an atmosphere of said reference gas.

12. The gas sensor according to claim 11 , wherein
said sensor element further includes a reference gas introduction layer that is a porous layer in communication with said reference gas introduction space, and
said reference electrode is covered with said reference gas introduction layer.

13. The gas sensor according to claim 11 , wherein said reference electrode is exposed to said reference gas introduction space.

14. The gas sensor according to claim 1 , wherein said sensing electrode and said reference electrode are disposed on the surface of said sensor element.

15. The gas sensor according to claim 14 , wherein said sensing electrode and said reference electrode are covered with an electrode protective layer.

16. The gas sensor according to claim 1 , wherein said predetermined gas component comprises at least one of a hydrocarbon component or a carbon monoxide component.

17. A method for manufacturing a mixed-potential gas sensor for measuring a concentration of a predetermined gas component of a measurement gas, said gas sensor comprising:
a sensor element mainly made of an oxygen-ion conductive solid electrolyte;
a sensing electrode located on a surface of said sensor element; and
a reference electrode including a cermet of Pt and an oxygen-ion conductive solid electrolyte,
wherein
said sensing electrode includes a cermet comprising a plurality of noble metal particles and oxygen-ion conductive solid electrolyte particles,
said noble metal particles each comprise an alloy of Pt and Au,
for at least one of the plurality of noble metal particles, a range of at least 1.5 nm from a surface of each of the at least one of the plurality of noble metal particles is a Au enriched region having a Au concentration of 10% or more,
the gas sensor determines the concentration of said predetermined gas component based on a potential difference between said sensing electrode and said reference electrode,
said method comprising:
(a) preparing a plurality of green sheets each comprising said solid electrolyte;
(b) applying a conductive paste whose weight ratio of Au to a noble metal component is 10 wt % or more to one of said plurality of green sheets to form a pattern of said sensing electrode;
(c) forming a laminated body of said plurality of green sheets including the green sheet on which the pattern of said sensing electrode has been formed; and
(d) firing said laminated body to integrally fire said sensing electrode with said solid electrolyte,
wherein in said step (d), a Au vapor pressure near the pattern of said sensing electrode is set to 10 −6 atm or more when the laminated body is fired.

18. The method according to claim 17 , wherein in said step (d), when said laminated body is fired, said laminated body is enclosed by a predetermined member to set a Au vapor pressure near the pattern of said sensing electrode to 10 −6 atm or more.

19. The method according to claim 17 , wherein said Au concentration is a value calculated from an expression
Au concentration (%)=100×Au detection value/(Au detection value+Pt detection value)

where a Au detection value and a Pt detection value are values in Auger spectrum obtained by performing a measurement on the surface of said at least one of the plurality of noble metal particles by Auger electron spectroscopy.

20. The method according to claim 18 , wherein said Au concentration is a value calculated from an expression
Au concentration (%)=100×Au detection value/(Au detection value+Pt detection value)

where a Au detection value and a Pt detection value are values in Auger spectrum obtained by performing a measurement on the surface of said at least one of the plurality of noble metal particles by Auger electron spectroscopy.

Assignees

• Ngk Insulators Ltd

Inventors

• Nakayama Yuki
• Hirata Noriko
• Okamoto Taku
• Nakasone Osamu

Classifications

• G01N27/4074

  for detection of gases other than oxygen · CPC title

• G01N33/0047

  Organic compounds · CPC title

• G01N27/301

  Reference electrodes · CPC title

• G01N27/4075 Primary

  Composition or fabrication of the electrodes and coatings thereon, e.g. catalysts · CPC title