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EP-4737893-A1 - PROTON CONDUCTOR GAS SENSOR

EP4737893A1EP 4737893 A1EP4737893 A1EP 4737893A1EP-4737893-A1

Abstract

A proton conductor gas sensor (2) comprises: an MEA (20); a diffusion control plate (6); a filter (12); and a housing (4). The diffusion control plate (6) is provided with a protrusion (22) with a diffusion control hole (24) at the center and raising towards the opposite side to the MEA (20). A gap (26) is present between the protrusion (22) and the MEA (20). The output variance among proton conductor gas sensors is reduced by the protrusion.

Inventors

  • SUGITA, NORIO

Assignees

  • Figaro Engineering Inc.

Dates

Publication Date
20260506
Application Date
20251016

Claims (5)

  1. A proton conductor gas sensor (2,2',3,3') comprising: an MEA (20) having a proton conductor membrane (30); catalytic electrodes on both sides of the proton conductor membrane (30); and a pair of gas diffusion layers (32,34) on the catalytic electrodes in an opposite side to the proton conductor membrane (30); a diffusion control plate (6) in contact with one face of the MEA (20), pressing the MEA (20), and having a diffusion control hole (24) supplying atmosphere to the MEA (20); a filter (12) supplying atmosphere to the diffusion control plate (6); and a housing (4) accommodating the MEA (20); the diffusion control plate (6); and the filter (12), characterized in that said diffusion control plate (6) is provided with a protrusion (22, 27, 28) raising towards the opposite side to the MEA (20) wherein the diffusion control hole (24) is at a center portion of the protrusion (22, 27, 28), and that a gap (26) is present between the protrusion (22, 27, 28) and the MEA (20).
  2. The proton conductor gas sensor according to claim 1, characterized in that the gas sensor (2,3,3') further comprises: a sealing cap (8) fixed within the housing (4); accommodating said filter (12); and having an atmosphere introducing hole (10) at the opposite side to the diffusion control plate (6) seen from the filter (12), and an atmosphere supplying hole (14) at a side facing the diffusion control plate (6); and a gasket (16) pressing the sealing cap (8) towards the diffusion control plate (6) and making the sealing cap (8) in contact with the diffusion control plate (6), that said protrusion (22,27,28) is accommodated in the atmosphere supplying hole (14), and that said atmosphere supplying hole (14) is larger in diameter than the protrusion (22) of the diffusion control hole (6).
  3. The proton conductor gas sensor according to claim 2, characterized in that the atmosphere supplying hole (14) of the sealing cap (8) is larger in thickness than the height of said protrusion (22,27,28), and that a clearance is present between said protrusion (22,27,28) and said filter (12).
  4. The proton conductor gas sensor according to claim 3, characterized in that said sealing cap (8) is provided with a ring-like protrusion (80) around said atmosphere supplying hole (14) protruding in an opposite side to said diffusion control plate (6), and that the atmosphere supplying hole (14) of the sealing cap (8) is made larger in thickness by said ring-like protrusion (80).
  5. The proton conductor gas sensor according to claim 2, characterized in that said filter (12) is provided with a recess (84) at a portion facing said atmosphere supplying hole (14).

Description

Field of the Invention The present invention relates to a proton conductor gas sensor and particularly, a diffusion control plate that controls the diffusion of atmosphere from a sealing cap to a membrane electrode assembly (MEA) of the gas sensor. Background Art The applicant has proposed a proton conductor gas sensor that comprises an MEA, a sealing cap, and a diffusion control plate (Patent Document 1: USP 7393505B). The sealing cap is a container with two metal plates that accommodates a filter comprising activated charcoal. It introduces atmosphere through its side or top surface, processes the atmosphere through the filter, and supplies the atmosphere through an opening towards the MEA. Furthermore, the sealing cap functions as an output terminal connected to the detection electrode of the gas sensor. The diffusion control plate, which supplies atmosphere through its diffusion control hole, is present between the opening of the sealing cap and the MEA. The MEA contains a proton conductor membrane at its center, as well as catalytic electrodes on both sides of the membrane, and gas diffusion layers on and outside of both electrodes. The catalytic electrodes contain a carbon that supports electrode catalyst, such as platinum (Pt), and a proton conductor, such as Nafion (a registered trademark of the DuPont Company). The gas diffusion layers contain carbon, such as carbon black or activated charcoal. They are porous to allow gas diffusion and provide electrical conductivity. To control the hydrophobicity and hydrophilicity of the gas diffusion layers, Teflon (a registered trademark of DuPont) and Nafion are added to the layers. The output of this gas sensor is proportional to the concentration of the gas to be detected in the atmosphere. This is achieved by controlling the quantity of atmosphere provided to the MEA with the gas diffusion hole of a controlled size. The size of the hole is made accurate by creating it in a thin diffusion control plate, since a thin plate allows to accurate machining. Prior Document List Patent Document Patent Document 1: USP 7393505B Summary of the Invention: Object of the Invention: The inventor has found that the material of the MEA (e.g., one of the gas diffusion layers) sometimes enters the diffusion control hole of the diffusion control plate. This causes variance in the diffusion of the atmosphere in the gas diffusion hole. This variance results in output variance between gas sensors. The object of the invention is to prevent the gas diffusion layer material from entering the diffusion control hole of the diffusion control plate of the proton conductor gas sensor and reduce output variance between proton conductor gas sensors. Means for Solving the Problem The proton conductor gas sensor according to the invention comprises: an MEA having a proton conductor membrane; catalytic electrodes on both sides of the proton conductor membrane; and a pair of gas diffusion layers on the catalytic electrodes in an opposite side to the proton conductor membrane;a diffusion control plate in contact with one face of the MEA, pressing the MEA , and having a diffusion control hole supplying atmosphere to the MEA;a filter supplying atmosphere to the diffusion control plate; anda housing accommodating the MEA; the diffusion control plate; and the filter. The gas sensor is characterized in that the diffusion control plate is provided with a protrusion raising towards the opposite side to the MEA wherein the diffusion control hole is at a center portion of the protrusion, andthat a gap is present between the protrusion and the MEA. Preferably, the gas sensor further comprises: a sealing cap fixed within the housing; accommodating the filter; and having an atmosphere introducing hole at the opposite side to the diffusion control plate seen from the filter, and an atmosphere supplying hole at a side facing the diffusion control plate; and a gasket pressing the sealing cap towards the diffusion control plate and making the sealing cap in contact with the diffusion control plate. The protrusion is accommodated in the atmosphere supplying hole, and the atmosphere supplying hole is larger in diameter than the protrusion of the diffusion control hole. Preferably, the atmosphere supplying hole of the sealing cap is larger in thickness than the height of the protrusion, and a clearance is present between the protrusion and the filter. This prevents the contact between the protrusion of the diffusion control plate and the filter, even when the height of the protrusion is excessively high, and reduces the variance in the gas sensitivity. Preferably, the diffusion control plate is made of a metal. According to the invention, the pressure that the diffusion control plate compresses the MEA secures the electrical connection between the gas diffusion layer of the MEA and the diffusion control plate. Due to the pressure, the material of the gas diffusion layer enters sometimes the diffusion control hole