CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2017/041020 filed on Nov. 15, 2017, claiming priority based on Japanese Patent Application No. 2017-026544, filed Feb. 16, 2017.

TECHNICAL FIELD

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

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 single cell of a fuel cell (hereinafter may be referred to simply as a “single cell”), which is a constitutive unit of SOFC, includes an electrolyte layer containing a solid oxide, a cathode, and an anode such that the cathode and the anode face each other in a predetermined direction (hereinafter referred to as a “first direction”) and the electrolyte layer intervenes between these electrodes. The electrolyte layer is formed so as to contain, for example, YSZ (yttria-stabilized zirconia). The cathode is formed so as to contain, for example, LSCF (lanthanum strontium cobalt ferrite).

In the single cell, the diffusion of Sr (strontium) contained in the cathode toward the electrolyte layer and the reaction between the diffused Sr and Zr (zirconium) contained in the electrolyte layer cause generation of SrZrO3(hereinafter may be referred to as “SZO”), which is a substance of high resistance. The generation of SZO increases electric resistance in the first direction, resulting in poor electricity generation performance of the single cell. A known technique for preventing a reduction in electricity generation performance due to the generation of SZO involves disposing of an intermediate layer between the cathode and the electrolyte layer (see, for example, Patent Document 1). The intermediate layer prevents diffusion of Sr from the cathode to the electrolyte layer, thereby preventing generation of SZO. The intermediate layer is formed so as to contain, for example, GDC (gadolinium-doped ceria).

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2014-60161

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In the aforementioned conventional technique, a smaller amount of SZO contained in the single cell is more preferred. However, the present inventors have newly found that an excessively small amount of SZO contained in the single cell may cause impairment of electricity generation performance and separation between the intermediate layer and the cathode. Thus, the aforementioned conventional technique has room for improvement in terms of prevention of a reduction in the electricity generation performance of the single cell, and prevention of separation between the intermediate layer and the cathode.

Such a problem is common with an electrolysis single cell, which is a constitutive unit of a solid oxide electrolysis cell (hereinafter may be referred to as “SOEC”) for generating hydrogen by utilizing the electrolysis of water. In the present specification, a fuel cell single cell and an electrolysis single cell are collectively referred to as an “electrochemical reaction single cell.” Such a problem is also common with electrochemical reaction single cells other than SOFC and SOEC.

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

Means for Solving the Problem

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

(1) An electrochemical reaction single cell disclosed in the present specification comprises an electrolyte layer containing Zr and at least one of Y, Sc, and Ca, an anode disposed on one side of the electrolyte layer in a first direction, a cathode containing Sr and Co and disposed on the other side of the electrolyte layer in the first direction, and an intermediate layer disposed between the electrolyte layer and the cathode, the electrochemical reaction single cell being characterized by exhibiting an SrZrO3integrated value of 600 to 10,300, the SrZrO3integrated value being calculated as follows:

a 20 μm×20 μm rectangular field of view in at least one cross section parallel to the first direction and including the cathode, the intermediate layer, and the electrolyte layer is divided into 256×256 pixels, wherein two sides of the four sides forming the rectangular field of view are approximately parallel to the boundary between the intermediate layer and the electrolyte layer, and Sr intensity mapping data representing Sr intensities in the pixels are generated by means of EPMA mapping;

an Sr intensity line integrated value, which is the integrated value of Sr intensities in pixels in each of 256 pixel lines, is calculated, wherein the pixel lines are approximately orthogonal to the first direction in the Sr intensity mapping data;

an intensity curve obtained by plotting the Sr intensity line integrated values against the pixel lines has an electrolyte layer integrated value portion exhibiting the Sr intensity line integrated value of a portion of the electrolyte layer having an approximately uniform Sr intensity line integrated value, a first integrated value portion exhibiting an Sr intensity line integrated value approximately equal to the Sr intensity line integrated value of the electrolyte layer integrated value portion, and a second integrated value portion located between the electrolyte layer integrated value portion and the first integrated value portion and exhibiting an Sr intensity line integrated value larger than the Sr intensity line integrated value of the electrolyte layer integrated value portion; and

a straight base line is drawn by connecting a first point and a second point in the second integrated value portion, and the area of a region surrounded by the base line and the second integrated value portion is calculated as the SrZrO3integrated value, wherein the first point corresponds to the minimum Sr intensity line integrated value on the electrolyte layer side with respect to a peak pixel line at which the Sr intensity line integrated value is maximum in the second integrated value portion, and the second point corresponds to the minimum Sr intensity line integrated value on the cathode side with respect to the peak pixel line. In the present electrochemical reaction single cell, the SrZrO3integrated value, which indicates the amount of SrZrO3(i.e., a substance of high resistance), is 10,300 or less. This can prevent impairment of the performance of the electrochemical reaction single cell, which would otherwise occur due to deposition of SrZrO3. In the present electrochemical reaction single cell, the SrZrO3integrated value is 600 or more, which indicates that the cathode is fired at a certain high temperature. Thus, separation between the intermediate layer and the cathode can be prevented.

(2) In the above-described electrochemical reaction single cell, the intermediate layer may include a solid solution layer containing at least one of Gd and Sm, Ce, and Zr, and the solid solution layer may have a thickness of 0.246 μm to 0.482 μm. This configuration of the present electrochemical reaction single cell can prevent impairment of the performance of the electrochemical reaction single cell, which would otherwise occur due to an excessive increase in the thickness of the solid solution layer of high resistance. In addition, impairment of the performance of the electrochemical reaction single cell due to an increase in SrZrO3integrated value can be prevented by increasing the thickness of the solid solution layer to a certain extent.
(3) In the above-described electrochemical reaction unit, the SrZrO3integrated value in at least one cross section parallel to the first direction may be 1,600 to 9,200. In the present electrochemical reaction single cell, the SrZrO3integrated value is 9,200 or less. This can effectively prevent impairment of the performance of the electrochemical reaction single cell, which would otherwise occur due to deposition of SrZrO3. In the present electrochemical reaction single cell, the SrZrO3integrated value is 1,600 or more, and thus separation between the intermediate layer and the cathode can be effectively prevented.
(4) In the above-described electrochemical reaction single cell, the intermediate layer may include a solid solution layer containing at least one of Gd and Sm, Ce, and Zr, and the solid solution layer may have a thickness of 0.271 μm to 0.457 μm. This configuration of the present electrochemical reaction single cell can effectively prevent impairment of the performance of the electrochemical reaction single cell, which would otherwise occur due to an excessive increase in the thickness of the solid solution layer of high resistance. In addition, impairment of the performance of the electrochemical reaction single cell due to an increase in SrZrO3integrated value can be prevented effectively by increasing the thickness of the solid solution layer to a certain extent.
(5) In the above-described electrochemical reaction single cell, the SrZrO3integrated value in at least one cross section parallel to the first direction may be 3,100 to 7,800. In the present electrochemical reaction single cell, the SrZrO3integrated value is 7,800 or less. This can more effectively prevent impairment of the performance of the electrochemical reaction single cell, which would otherwise occur due to deposition of SrZrO3. In the present electrochemical reaction single cell, the SrZrO3integrated value is 3,100 or more, and thus separation between the intermediate layer and the cathode can be more effectively prevented.
(6) In the above-described electrochemical reaction single cell, the intermediate layer may include a solid solution layer containing at least one of Gd and Sm, Ce, and Zr, and the solid solution layer may have a thickness of 0.307 μm to 0.422 μm. This configuration of the present electrochemical reaction single cell can more effectively prevent impairment of the performance of the electrochemical reaction single cell, which would otherwise occur due to an excessive increase in the thickness of the solid solution layer of high resistance. In addition, impairment of the performance of the electrochemical reaction single cell due to an increase in SrZrO3integrated value can be prevented more effectively by increasing the thickness of the solid solution layer to a certain extent.
(7) In the above-described electrochemical reaction single cell, the electrolyte layer may contain a solid oxide. The configuration of the present electrochemical reaction single cell can prevent impairment of the performance of the single cell due to deposition of SrZrO3, even in the case where the impairment of the performance of the single cell due to deposition of SrZrO3is likely to occur.
(8) In the above-described electrochemical reaction single cell, the electrochemical reaction single cell may be a fuel cell single cell. According to the present electrochemical reaction single cell, impairment of electricity generation performance, which would otherwise occur due to deposition of SrZrO3, can be prevented.

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

