Ammonia gas sensor and method for measuring concentration of ammonia gas

Patent metadata

Field	Value
Publication number	US-2017184538-A1
Application number	US-201615370069-A
Country	US
Kind code	A1
Filing date	Dec 6, 2016
Priority date	Dec 24, 2015
Publication date	Jun 29, 2017
Grant date	—

Abstract

Provided is a gas sensor which is capable of preferably sensing an ammonia gas, and has excellent durability. A mixed-potential gas sensor includes a sensor element composed of an oxygen-ion conductive solid electrolyte, and a heater provided inside the element. The sensor element includes on a surface thereof a sensing electrode formed of a cermet including Pt, Au and an oxygen-ion conductive solid electrolyte, and also includes a reference electrode formed of a cermet of Pt and an oxygen-ion conductive solid electrolyte, and a porous electrode protective layer whose porosity is 5 to 40% covering at least the sensing electrode. The Au abundance ratio in a surface of noble metal particles forming the sensing electrode is 0.4 or more. The concentration of an ammonia gas is determined on the basis of a potential difference occurring between the sensing electrode and the reference electrode when the sensor element is disposed in a measurement gas and heated to 400° C. to 800° C.

First claim

What is claimed is:

1 . A mixed-potential gas sensor for sensing an ammonia gas in a measurement gas, said sensor comprising:
a sensor element composed of an oxygen-ion conductive solid electrolyte, said sensor element comprising: a sensing electrode formed of a cermet of a noble metal and an oxygen-ion conductive solid electrolyte, said sensing electrode being provided on a surface of said sensor element; a reference electrode formed of a cermet of Pt and an oxygen-ion conductive solid electrolyte; and an electrode protective layer being a porous layer that covers at least said sensing electrode, wherein said noble metal includes Pt and Au, an Au abundance ratio is 0.4 or more, said Au abundance ratio being an area ratio of a portion covered with said Au to a portion at which said Pt is exposed in a surface of noble metal particles forming said sensing electrode, a porosity of said electrode protective layer is 5% or more and 40% or less, and said gas sensor determines a concentration of said ammonia gas on the basis of a potential difference between said sensing electrode and said reference electrode.

2 . The ammonia gas sensor according to claim 1 , further comprising:
a heater which is provided inside said sensor element, and heats said sensor element, wherein said sensor element is disposed in said measurement gas and heated to an element control temperature of 400° C. or higher and 800° C. or lower by said heater, and said ammonia gas sensor determines the concentration of said ammonia gas on the basis of a potential difference occurring between said sensing electrode and said reference electrode.

3 . The ammonia gas sensor according to claim 2 , wherein
said element control temperature is 450° C. or higher and lower than 700° C.

4 . The ammonia gas sensor according to claim 3 , wherein
said element control temperature is 450° C. or higher and 650° C. or lower.

5 . The ammonia gas sensor according to claim 1 , said sensor element further comprising:
a reference gas introduction space separated from a space in which said measurement gas is present, into which a reference gas is introduced, wherein said reference electrode is disposed under an atmosphere of said reference gas.

6 . The ammonia gas sensor according to claim 5 , said sensor element further comprising:
a reference gas introduction layer being a porous layer that is in communication with said reference gas introduction space, wherein said reference electrode is covered with said reference gas introduction layer.

7 . The ammonia gas sensor according to claim 5 , wherein
said reference electrode is disposed so as to be exposed to said reference gas introduction space.

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

9 . The ammonia gas sensor according to claim 8 , wherein
said sensing electrode and said reference electrode are covered with an electrode protective layer.

10 . A mixed-potential gas sensor for sensing an ammonia gas in a measurement gas, said sensor comprising:
a sensor element composed of an oxygen-ion conductive solid electrolyte; and a heater which is provided inside said sensor element, and heats said sensor element, wherein said sensor element comprises: a sensing electrode formed of a cermet of a noble metal and an oxygen-ion conductive solid electrolyte, said sensing electrode being provided on a surface of said sensor element; and a reference electrode formed of a cermet of Pt and an oxygen-ion conductive solid electrolyte, said noble metal includes Pt and Au, an Au abundance ratio is 0.4 or more, said Au abundance ratio being an area ratio of a portion covered with said Au to a portion at which said Pt is exposed in a surface of noble metal particles forming said sensing electrode, and said sensor element is disposed in said measurement gas and heated to an element control temperature of 450° C. or higher and lower than 700° C. by said heater, and said ammonia gas sensor determines a concentration of said ammonia gas on the basis of a potential difference occurring between said sensing electrode and said reference electrode.

11 . The ammonia gas sensor according to claim 10 , wherein
said element control temperature is 450° C. or higher and 650° C. or lower.

12 . The ammonia gas sensor according to claim 10 , said sensor element further comprising:
a reference gas introduction space separated from a space in which said measurement gas is present, into which a reference gas is introduced, wherein said reference electrode is disposed under an atmosphere of said reference gas.

13 . The ammonia gas sensor according to claim 12 , said sensor element further comprising:
a reference gas introduction layer being a porous layer that is in communication with said reference gas introduction space, wherein said reference electrode is covered with said reference gas introduction layer.

14 . The ammonia gas sensor according to claim 12 , wherein
said reference electrode is disposed so as to be exposed to said reference gas introduction space.

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

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

17 . A method for measuring a concentration of an ammonia gas in a measurement gas using a mixed-potential gas sensor, said gas sensor comprising:
a sensor element composed of an oxygen-ion conductive solid electrolyte; and a heater which is provided inside said sensor element, and heats said sensor element, wherein said sensor element comprises: a sensing electrode formed of a cermet of a noble metal and an oxygen-ion conductive solid electrolyte, said sensing electrode being provided on a surface of said sensor element; a reference electrode formed of a cermet of Pt and an oxygen-ion conductive solid electrolyte; and an electrode protective layer being a porous layer that covers at least said sensing electrode, said noble metal includes Pt and Au, an Au abundance ratio is 0.4 or more, said Au abundance ratio being an area ratio of a portion covered with said Au to a portion at which said Pt is exposed in a surface of noble metal particles forming said sensing electrode, and the porosity of said electrode protective layer is 5% or more and 40% or less, said method comprising the steps of: a) disposing said sensor element in said measurement gas; b) heating said sensor element disposed in said measurement gas to an element control temperature of 400° C. or higher and 800° C. or lower by said heater; and c) determining the concentration of said ammonia gas on the basis of a potential difference occurring between said sensing electrode and said reference electrode with said sensor element held at said element control temperature.

18 . The method for measuring the concentration of an ammonia gas according to claim 17 , wherein
said element control temperature is 450° C. or higher and lower than 700° C.

19 . The method for measuring the concentration of an ammonia gas according to claim 18 , wherein
said element control temperature is 450° C. or higher and 650° C. or lower.

20 . A method for measuring a concentration of an ammonia gas in a measuremen

Assignees

• Ngk Insulators Ltd

Inventors

• Okamoto Taku
• Sakurai Takayuki
• Hirata Noriko
• Nakayama Yuki

Classifications

• G01N27/4067

  Means for heating or controlling the temperature of the solid electrolyte · CPC title

• G01N27/301

  Reference electrodes · CPC title

• G01N33/0054

  Ammonia · CPC title

• G01N27/4074 Primary

  for detection of gases other than oxygen · CPC title

• G01N27/4077

  Means for protecting the electrolyte or the electrodes · CPC title