CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2017/041992, filed Nov. 22, 2017, claiming priority based on Japanese Patent Application No. 2016-226504, filed, Nov. 22, 2016.

TECHNICAL FIELD

A technique disclosed in the present specification relates to an electrochemical reaction unit.

BACKGROUND ART

A known type of a fuel cell for generating electricity by utilizing electrochemical reaction between hydrogen and oxygen is a solid oxide fuel cell (hereinafter may be referred to as “SOFC”). A fuel-cell electricity generation unit which partially constitutes an SOFC includes a fuel-cell unit cell, a pair of interconnectors, and a separator. The fuel-cell unit cell includes an electrolyte layer, a cathode, and an anode such that the cathode and the anode face each other in a first direction and such that the electrolyte layer intervenes between these electrodes. The paired interconnectors face each other in the first direction with the fuel-cell unit cell intervening therebetween. The separator has a through hole formed therein, and a portion around the through hole is joined (e.g., bonded) to a peripheral portion of the fuel-cell unit cell, whereby the separator separates from each other a cathode chamber facing the cathode and an anode chamber facing the anode.

In the fuel-cell electricity generation unit, in some cases, a glass seal member formed through crystallization of a glass material is disposed in a space between two structural members facing each other in the first direction (e.g., the separator and the interconnector mentioned above) in order to provide electrical insulation and a gas seal between the two structural members (see, for example, Patent Document 1).

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2005-183376

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

Two structural members in contact with the glass seal member thermally expand as a result of an electricity generating operation of the fuel-cell electricity generation unit. On this occasion, because of difference in thermal expansion between the two structural members, a difference may arise between the amount by which a portion of the glass seal member located toward one structural member is stretched in a second direction orthogonal to the first direction by the one structural member and the amount by which a portion of the glass seal member located toward the other structural member is stretched in the second direction by the other structural member. Accordingly, cracking in the second direction may occur in the glass seal member. As a result, the sealing performance between the structural members may be impaired.

Such a problem arises in not only an SOFC having a flat-plate shape but also an SOFC having a cylindrical shape. Such a problem also arises in an electrolysis cell unit which partially constitutes a solid oxide electrolysis cell (hereinafter may be referred to as “SOEC”) for generating hydrogen by utilizing electrolysis of water. In the present specification, a fuel-cell unit cell and an electrolysis cell are collectively referred to as an electrochemical reaction unit cell, and a fuel-cell electricity generation unit and an electrolysis cell unit are collectively referred to as an electrochemical reaction unit.

The present specification discloses a technique capable of at least partially solving the aforementioned problems.

Means for Solving the Problem

A technique disclosed in the present specification can be implemented in the following modes.

(1) An electrochemical reaction unit disclosed in the present specification comprises a unit cell including an electrolyte layer, and a cathode and an anode which face each other in a first direction with the electrolyte layer intervening therebetween; and one or a plurality of structural members, the electrochemical reaction unit being characterized by further comprising a glass seal member which contains glass and is in contact with two members facing each other in the first direction, the two members being selected from the unit cell and the one or the plurality of structural members, and characterized in that the glass seal member contains a plurality of crystal grains each having a ratio of a vertical dimension in the first direction to a horizontal dimension in a second direction orthogonal to the first direction of 1.5 or more. According to the present electrochemical reaction unit, the glass seal member contains a plurality of crystal grains (hereinafter may be referred to as “vertically long crystal grains”) each having a ratio of a vertical dimension to a horizontal dimension of 1.5 or more. Accordingly, even when stress is developed in the glass seal member due to difference in thermal expansion between two members between which a seal is provided, by virtue of the vertically long crystal grains, vertical cracking in the first direction (vertical direction) is apt to occur in the glass seal member preferentially to horizontal cracking in the second direction (horizontal direction) and can release the stress. That is, preferential occurrence of cracking in the first direction in which two members face each other restrains occurrence of cracking in the second direction, thereby restraining the passage of gas between the two members. Therefore, there can be restrained impairment of sealing performance between two members between which a seal is provided.

(2) In the electrochemical reaction unit, the two members are the unit cell, and the structural member which at least partially faces the unit cell in the first direction. According to the present electrochemical reaction unit, there can be restrained impairment of sealing performance between the unit cell and the structural member.

(3) In the electrochemical reaction unit, the structural member which faces the unit cell is a separator which has a through hole formed therein; whose portion around the through hole is joined to a peripheral portion of the unit cell; and which separates from each other a cathode chamber facing the cathode and an anode chamber facing the anode. According to the present electrochemical reaction unit, there can be restrained impairment of sealing performance between the unit cell and the separator.

(4) In the electrochemical reaction unit, the two members are a first structural member and a second structural member which face each other in the first direction. According to the present electrochemical reaction unit, the glass seal member contains vertically long crystal grains. Accordingly, even though stress is generated in the glass seal member due to thermal expansion difference between the first structural member and the second structural member, since, by virtue of the vertically long crystal grains, vertical cracking extending in the first direction (vertical direction) is apt to occur in the glass seal member preferentially to horizontal cracking extending in the second direction (horizontal direction), horizontal cracking can release the stress. That is, preferential occurrence of cracking in the first direction in which the first structural member and the second structural member face each other restrains occurrence of cracking in the second direction, thereby restraining the passage of gas between the first structural member and the second structural member. Therefore, there can be restrained impairment of sealing performance between the first structural member and the second structural member.

(5) In the electrochemical reaction unit, one of the first structural member and the second structural member is an interconnector. Therefore, there can be restrained impairment of sealing performance between the interconnector and the structural member which faces the interconnector.

(6) The electrochemical reaction unit may be configured such that the vertical dimension of at least one of the crystal grains is 30% or more of a thickness of the glass seal member in the first direction. According to the present electrochemical reaction unit, since the vertical dimension of at least one of the crystal grains is 30% or more of the thickness of the glass seal member in the vertical direction (first direction), vertical cracking is apt to occur in the glass seal member further preferentially to horizontal cracking. Therefore, there can be more effectively restrained impairment of sealing performance between the unit cell and the structural member or between the first structural member and the second structural member.

(7) The electrochemical reaction unit may be configured such that the vertical dimension of at least one of the crystal grains is 50% or more of a thickness of the glass seal member in the first direction. According to the present electrochemical reaction unit, since the vertical dimension of at least one of the crystal grains is 50% or more of the thickness of the glass seal member in the vertical direction (first direction), even if horizontal cracking occurs, the development of the horizontal cracking is apt to be restrained by the crystal grains. As a result, there can be more effectively restrained impairment of sealing performance between the unit cell and the structural member or between the first structural member and the second structural member.

(8) An electrochemical reaction cell stack disclosed in the present specification is configured such that at least one of the electrochemical reaction units is an electrochemical reaction unit as recited in any one of (1) to (7) above.

(9) The present specification discloses a production method for an electrochemical reaction unit which includes a unit cell including an electrolyte layer, and a cathode and an anode facing each other in a first direction with the electrolyte layer intervening therebetween, one or a plurality of structural members, and a glass seal member containing glass and being in contact with two members facing each other in the first direction, the two members being selected from the unit cell and the one or the plurality of structural members, and in which the glass seal member contains a plurality of crystal grains each having a ratio of a vertical dimension in the first direction to a horizontal dimension in a second direction orthogonal to the first direction of 1.5 or more, comprising: a step of preparing the unit cell and the one or the plurality of structural members; a step of disposing between the two members a seed layer containing at least one element of Ba, Ca, Mg, Al, La, Ti, Cr, Zr, and Ce, and glass; and a step of forming the glass seal member by, in a state in which the seed layer and the glass are disposed between the two members, melting the glass, followed by crystallization. The present production method for an electrochemical reaction unit can form between the two members the glass seal member containing vertically long crystal grains, by disposing between the two members a seed layer containing at least one element of Ba, Ca, Mg, Al, La, Ti, Cr, Zr, and Ce, and glass, and melting the glass, followed by crystallization.

(10) In the production method for an electrochemical reaction unit, the two members are the unit cell, and the structural member which at least partially faces the unit cell in the first direction. The present production method for an electrochemical reaction unit can form between the unit cell and the structural member the glass seal member containing vertically long crystal grains by disposing a seed layer containing at least one element of Ba, Ca, Mg, Al, La, Ti, Cr, Zr, and Ce, and glass between the unit cell and the structural member, and melting the glass, followed by crystallization.

(11) In the production method for an electrochemical reaction unit, the two members are a first structural member and a second structural member which face each other in the first direction. The present production method for an electrochemical reaction unit can form between the first structural member and the second structural member the glass seal member containing vertically long crystal grains by disposing a seed layer containing at least one element of Ba, Ca, Mg, Al, La, Ti, Cr, Zr, and Ce, and glass between the first structural member and the second structural member, and melting the glass, followed by crystallization.

The technique disclosed in the present specification can be implemented in various modes; for example, an electrochemical reaction unit (fuel-cell electricity generation unit or electrolysis cell unit), an electrochemical reaction cell stack (fuel cell stack or electrolysis cell stack) including a plurality of electrochemical reaction units, and a production method therefor.

