JP7104129B2 - Electrochemical reaction single cell and electrochemical reaction cell stack - Google Patents

Description

The techniques disclosed herein relate to electrochemical reaction single cells.

A solid oxide fuel cell (hereinafter referred to as "SOFC") having an electrolyte layer containing a solid oxide is known as one of the types of fuel cells that generate power by utilizing an electrochemical reaction between hydrogen and oxygen. Has been done. The fuel cell single cell (hereinafter, simply referred to as “single cell”), which is the minimum constituent unit of SOFC, faces each other in a predetermined direction (hereinafter, referred to as “first direction”) with the electrolyte layer interposed therebetween. Includes air and fuel poles.

Conventionally, a single cell in which an electrolyte layer is arranged so as to cover a side surface of a fuel electrode has been known (see, for example, Patent Documents 1 to 3).

JP-A-2017-174605 Japanese Unexamined Patent Publication No. 2019-220461 Japanese Unexamined Patent Publication No. 2016-157637

In a single cell, the electrolyte layer and the fuel electrode may be separated from each other due to the difference in thermal expansion between the electrolyte layer and the fuel electrode. Even in a conventional single cell in which the electrolyte layer is arranged so as to cover the side surface of the fuel electrode, stress is generated at the boundary between the electrolyte layer and the fuel electrode due to the difference in thermal expansion between the two. There is a problem that the separation from the fuel electrode cannot be suppressed.

Such a problem is an electrolyte contained in an electrolytic single cell, which is a constituent unit of a solid oxide fuel cell (hereinafter referred to as “SOEC”) that generates hydrogen by utilizing an electrolysis reaction of water. It is a common issue for layers and fuel poles. In the present specification, the fuel cell single cell and the electrolytic single cell are collectively referred to as an electrochemical reaction single cell. Further, such a problem is not limited to SOFC and SOEC, but is a problem common to the electrolyte layer and the fuel electrode contained in other types of electrochemical reaction single cells.

The techniques disclosed herein can be realized, for example, in the following forms.

(1) The electrochemical reaction single cell disclosed in the present specification is an electricity comprising an electrolyte layer containing a solid oxide and an air electrode and a fuel electrode facing each other in a first direction across the electrolyte layer. In the chemical reaction single cell, a welded portion for joining the electrolyte layer and the fuel electrode is provided, and the welded portion is located at least a part of the outer periphery of the electrolyte layer and the fuel electrode in the first direction. However, it is formed so as to straddle the electrolyte layer and the fuel electrode. In this electrochemical reaction single cell, the welded portion is formed so as to straddle the electrolyte layer and the fuel electrode. This welded portion joins the electrolyte layer and the fuel electrode, and has a coefficient of thermal expansion between the coefficient of thermal expansion of the electrolyte layer and the coefficient of thermal expansion of the fuel electrode. Therefore, the welded portion plays a role of alleviating the difference in thermal expansion between the electrolyte layer and the fuel electrode. As a result, according to the present electrochemical reaction single cell, peeling between the electrolyte layer and the fuel electrode can be suppressed.

(2) In the electrochemical reaction single cell, a plurality of the welded portions are provided, and the plurality of welded portions are arranged so as to be separated from each other along the circumferential direction of the electrolyte layer and the fuel electrode. It may be configured. In this electrochemical reaction single cell, even if one weld is peeled off or damaged, the influence of the peeling or damage on the other weld is suppressed. Therefore, according to the present electrochemical reaction single cell, for example, it is possible to suppress the influence of damage to the welded portion widely as compared with the configuration in which one welded portion surrounds the entire circumference of the electrolyte layer and the fuel electrode. can.

(3) In the electrochemical reaction single cell, the welded portion is located outside the electrolyte layer in the first directional view, and is continuous with the surface of the electrolyte layer opposite to the fuel electrode. It may be configured to have a protruding portion. In the present electrochemical reaction single cell, a wider joint area between the electrochemical reaction single cell and other members can be secured when assembling the electrochemical reaction stack, as compared with the configuration in which the welded portion does not have a protruding portion.

(4) In the electrochemical reaction single cell, the boundary line between the welded portion and the fuel electrode may have an uneven shape in at least one cross section parallel to the first direction. In this electrochemical reaction single cell, the detachment of the welded portion can be suppressed by the length of the contact portion between the welded portion and the fuel electrode, as compared with the configuration in which the boundary line between the welded portion and the fuel electrode is linear. ..

(5) In the electrochemical reaction cell stack, a plurality of electrochemical reaction single cells are provided, and at least one of the plurality of electrochemical reaction single cells is the electricity of any one of the above (1) to (4). It may be configured as a single cell for chemical reaction. Thereby, it is possible to provide an electrochemical reaction cell stack in which the separation between the electrolyte layer and the fuel electrode is suppressed.

The technique disclosed in the present specification can be realized in various forms, for example, an electrochemical reaction single cell (fuel cell single cell or an electrolytic single cell), and electricity having an electrochemical reaction single cell. It can be realized in the form of an electrochemical reaction cell stack (fuel cell stack or electrolytic cell stack) having a plurality of chemical reaction units, a method for producing them, and the like.

A perspective view showing an external configuration of the fuel cell stack 100 in the present embodiment. Explanatory drawing which shows the XZ cross-sectional structure of the fuel cell stack 100 at the position of II-II of FIG. Explanatory drawing which shows the YZ cross-sectional structure of the fuel cell stack 100 at the position of III-III of FIG. Explanatory drawing which shows the XZ cross section configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. Explanatory drawing which shows the YZ cross section configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. Explanatory drawing schematically showing the structure of the joint portion between the electrolyte layer 112 and the fuel electrode 116.

A. Embodiment:
A-1. Constitution:
(Structure of fuel cell stack 100)
FIG. 1 is a perspective view showing an external configuration of the fuel cell stack 100 in the present embodiment, and FIG. 2 is an explanatory view showing an XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II of FIG. FIG. 3 is an explanatory view showing a YZ cross-sectional configuration of the fuel cell stack 100 at the positions III-III of FIG. Each figure shows XYZ axes that are orthogonal to each other to identify the direction. In the present specification, for convenience, the Z-axis positive direction is referred to as an upward direction, and the Z-axis negative direction is referred to as a downward direction, but the fuel cell stack 100 is actually in a direction different from such an orientation. It may be installed. The same applies to FIGS. 4 and later. The vertical direction is an example of the first direction in the claims.

The fuel cell stack 100 includes a plurality of power generation units 102 (seven in this embodiment) and a pair of end plates 104 and 106. The seven power generation units 102 are arranged side by side in a predetermined arrangement direction (vertical direction in this embodiment). The pair of end plates 104 and 106 are arranged so as to sandwich an aggregate composed of seven power generation units 102 from above and below.

A plurality of holes (eight in this embodiment) penetrating in the vertical direction are formed on the peripheral edge of each layer (power generation unit 102, end plates 104, 106) constituting the fuel cell stack 100 in the vertical direction. The holes formed in each layer and corresponding to each other communicate with each other in the vertical direction to form a communication hole 108 extending in the vertical direction from one end plate 104 to the other end plate 106. In the following description, the holes formed in each layer of the fuel cell stack 100 to form the communication holes 108 may also be referred to as the communication holes 108.

A bolt 22 extending in the vertical direction is inserted into each communication hole 108, and the fuel cell stack 100 is fastened by the bolt 22 and the nuts 24 fitted on both sides of the bolt 22. As shown in FIGS. 2 and 3, between the nut 24 fitted on one side (upper side) of the bolt 22 and the upper surface of the end plate 104 forming the upper end of the fuel cell stack 100, and the bolt. An insulating sheet 26 is interposed between the nut 24 fitted on the other side (lower side) of the 22 and the lower surface of the end plate 106 forming the lower end of the fuel cell stack 100. However, in the place where the gas passage member 27 described later is provided, the insulating sheets arranged on the upper side and the lower side of the gas passage member 27 and the gas passage member 27 between the nut 24 and the surface of the end plate 106, respectively. 26 is intervening. The insulating sheet 26 is made of, for example, a mica sheet, a ceramic fiber sheet, a ceramic dust sheet, a glass sheet, a glass-ceramic composite agent, or the like.

The outer diameter of the shaft portion of each bolt 22 is smaller than the inner diameter of each communication hole 108. Therefore, a space is secured between the outer peripheral surface of the shaft portion of each bolt 22 and the inner peripheral surface of each communication hole 108. As shown in FIGS. 1 and 2, near the midpoint of one side (the side on the positive side of the X-axis of the two sides parallel to the Y-axis) on the outer circumference of the fuel cell stack 100 around the Z-axis direction. In the space formed by the positioned bolt 22 (bolt 22A) and the communication hole 108 through which the bolt 22A is inserted, the oxidant gas OG is introduced from the outside of the fuel cell stack 100, and the oxidant gas OG is introduced into each of the spaces. It functions as an oxidizer gas introduction manifold 161 which is a gas flow path supplied to the power generation unit 102, and is inside the opposite side (the side on the negative side of the X-axis of the two sides parallel to the Y-axis). The space formed by the bolt 22 (bolt 22B) located near the point and the communication hole 108 through which the bolt 22B is inserted is an oxidizer off-gas OOG which is a gas discharged from the air chamber 166 of each power generation unit 102. Functions as an oxidant gas discharge manifold 162 that discharges the fuel to the outside of the fuel cell stack 100. In this embodiment, for example, air is used as the oxidant gas OG.

Further, as shown in FIGS. 1 and 3, the midpoint of one side (the side on the positive side of the Y-axis of the two sides parallel to the X-axis) on the outer circumference of the fuel cell stack 100 around the Z-axis direction. In the space formed by the bolt 22 (bolt 22D) located in the vicinity and the communication hole 108 through which the bolt 22D is inserted, the fuel gas FG is introduced from the outside of the fuel cell stack 100, and the fuel gas FG is introduced into each of the spaces. A bolt that functions as a fuel gas introduction manifold 171 to be supplied to the power generation unit 102 and is located near the midpoint of the opposite side (the side on the negative side of the Y axis of the two sides parallel to the X axis). The space formed by the 22 (bolt 22E) and the communication hole 108 through which the bolt 22E is inserted is a fuel off-gas FOG, which is a gas discharged from the fuel chamber 176 of each power generation unit 102, outside the fuel cell stack 100. It functions as a fuel gas discharge manifold 172 that discharges to. In the present embodiment, for example, a hydrogen-rich gas obtained by reforming city gas is used as the fuel gas FG.

The fuel cell stack 100 is provided with four gas passage members 27. Each gas passage member 27 has a hollow cylindrical main body 28 and a hollow cylindrical branch 29 branched from the side surface of the main body 28. The hole of the branch portion 29 communicates with the hole of the main body portion 28. A gas pipe (not shown) is connected to the branch portion 29 of each gas passage member 27. Further, as shown in FIG. 2, the hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22A forming the oxidant gas introduction manifold 161 communicates with the oxidant gas introduction manifold 161. The hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22B forming the oxidant gas discharge manifold 162 communicates with the oxidant gas discharge manifold 162. Further, as shown in FIG. 3, the hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22D forming the fuel gas introduction manifold 171 communicates with the fuel gas introduction manifold 171 and fuel gas. The hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22E forming the discharge manifold 172 communicates with the fuel gas discharge manifold 172.

(Structure of end plates 104 and 106)
The pair of end plates 104 and 106 are flat plate-shaped conductive members that are substantially rectangular in the Z-axis direction, and are made of, for example, stainless steel. One end plate 104 is located above the power generation unit 102 located at the top, and the other end plate 106 is located below the power generation unit 102 located at the bottom. A plurality of power generation units 102 are sandwiched by a pair of end plates 104 and 106 in a pressed state. The upper end plate 104 functions as a positive output terminal of the fuel cell stack 100, and the lower end plate 106 functions as a negative output terminal of the fuel cell stack 100.

(Structure of power generation unit 102)
FIG. 4 is an explanatory view showing an XZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 2, and FIG. 5 is an explanatory view showing the XZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross-sectional structure of two power generation units 102.

As shown in FIGS. 4 and 5, the power generation unit 102 includes a single cell 110, a separator 120, an air pole side frame 130, an air pole side current collector 134, a fuel pole side frame 140, and a fuel pole side. It includes a current collector 144 and a pair of interconnectors 150 that form the uppermost layer and the lowermost layer of the power generation unit 102. Holes corresponding to the communication holes 108 through which the above-mentioned bolts 22 are inserted are formed in the peripheral edges of the separator 120, the air pole side frame 130, the fuel pole side frame 140, and the interconnector 150 around the Z axis direction.

The interconnector 150 is a flat plate-shaped conductive member that is substantially rectangular in the Z-axis direction, and is made of a material containing Cr, for example, ferritic stainless steel. The interconnector 150 ensures electrical continuity between the power generation units 102 and prevents mixing of reaction gases between the power generation units 102. In the present embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by two adjacent power generation units 102. That is, the upper interconnector 150 in a certain power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of the power generation unit 102. Further, since the fuel cell stack 100 includes a pair of end plates 104 and 106, the power generation unit 102 located at the top of the fuel cell stack 100 does not have the upper interconnector 150 and is located at the bottom. The power generation unit 102 does not include the lower interconnector 150 (see FIGS. 2 and 3).

The single cell 110 includes an electrolyte layer 112, an air electrode (cathode) 114 arranged above the electrolyte layer 112, a fuel electrode (anode) 116 arranged below the electrolyte layer 112, and an electrolyte. An intermediate layer 180 arranged between the layer 112 and the air electrode 114 is provided. The single cell 110 of the present embodiment is a fuel pole support type single cell that supports other layers (electrolyte layer 112, air pole 114, intermediate layer 180) constituting the single cell 110 by the fuel pole 116.

The electrolyte layer 112 is a flat plate-shaped member that is substantially rectangular in the Z-axis direction, and is a dense layer (with a low porosity). The electrolyte layer 112 contains solid oxides (eg, YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), CSZ (calcia-stabilized zirconia)). As described above, the single cell 110 of the present embodiment is a solid oxide fuel cell (SOFC) that uses a solid oxide as an electrolyte.

The air electrode 114 is a substantially rectangular flat plate-shaped member smaller than the electrolyte layer 112 in the Z-axis direction, and is a porous layer having a porosity higher than that of the electrolyte layer 112. The air electrode 114 is a perovskite-type oxide represented by ABO ₃ (for example, lanthanum strontium cobalt iron oxide (LSCF), lanthanum strontium iron oxide (LSF), lanthanum strontium cobalt oxide (LSC), lanthanum strontium manganese oxidation. (LSM), lanthanum nickel iron oxide (LNF), etc.) are contained.

The fuel electrode 116 is a substantially rectangular flat plate-shaped member having substantially the same size as the electrolyte layer 112 in the Z-axis direction, and is a porous layer having a porosity higher than that of the electrolyte layer 112. Although not shown, in the present embodiment, the fuel electrode 116 includes a substrate layer constituting the lower surface of the fuel electrode 116, and a functional layer located between the substrate layer and the electrolyte layer 112. The functional layer of the fuel electrode 116 is a layer that mainly exerts a function of reacting oxygen ions supplied from the electrolyte layer 112 with hydrogen or the like contained in the fuel gas FG to generate electrons and water vapor, and exhibits electrons. It contains Ni, which is a conductive substance, and an oxygen ion ion conductive oxide (for example, YSZ). Further, the substrate layer of the fuel electrode 116 is a layer that mainly exerts a function of supporting the functional layer, the electrolyte layer 112, and the air electrode 114, and Ni, which is an electron conductive substance, and an oxygen ion conductive oxide ( For example, YSZ) and is included.

The intermediate layer 180 is a flat plate-shaped member that is substantially rectangular in the Z-axis direction. The intermediate layer 180 is formed of, for example, a solid oxide having ionic conductivity such as SDC (samarium-doped ceria), GDC (gadolinium-doped ceria), LDC (lanthanum-doped ceria), and YDC (yttrium-doped ceria).

The separator 120 is a frame-shaped member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed near the center, and is formed of, for example, metal. The peripheral portion of the hole 121 in the separator 120 faces the peripheral edge of the surface of the electrolyte layer 112 on the side of the air electrode 114. The separator 120 is joined to the electrolyte layer 112 (single cell 110) by a joining portion 124 formed of a brazing material (for example, Ag wax) arranged at the opposite portion thereof. The separator 120 partitions the air chamber 166 facing the air pole 114 and the fuel chamber 176 facing the fuel pole 116, and a gas leak from one electrode side to the other electrode side at the peripheral edge of the single cell 110. It is suppressed.

The air electrode side frame 130 is a frame-shaped member in which a substantially rectangular hole 131 penetrating in the vertical direction is formed near the center, and is formed of, for example, an insulator such as mica. The hole 131 of the air electrode side frame 130 constitutes an air chamber 166 facing the air electrode 114. The air electrode side frame 130 is in contact with the peripheral edge of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral edge of the surface of the interconnector 150 facing the air electrode 114. .. Further, the air electrode side frame 130 electrically insulates between the pair of interconnectors 150 included in the power generation unit 102. Further, in the air electrode side frame 130, the oxidant gas supply communication hole 132 that communicates the oxidant gas introduction manifold 161 and the air chamber 166, and the oxidant gas that communicates the air chamber 166 and the oxidant gas discharge manifold 162. A discharge communication hole 133 is formed.

The fuel electrode side frame 140 is a frame-shaped member in which a substantially rectangular hole 141 penetrating in the vertical direction is formed near the center, and is formed of, for example, metal. Hole 141 of the fuel electrode side frame 140 constitutes a fuel chamber 176 facing the fuel electrode 116. The fuel electrode side frame 140 is in contact with the peripheral edge of the surface of the separator 120 facing the electrolyte layer 112 and the peripheral edge of the surface of the interconnector 150 facing the fuel electrode 116. Further, in the fuel electrode side frame 140, a fuel gas supply communication hole 142 that communicates the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel gas discharge communication hole 143 that communicates the fuel chamber 176 and the fuel gas discharge manifold 172. And are formed.

The fuel electrode side current collector 144 is arranged in the fuel chamber 176. The fuel electrode side current collector 144 includes an interconnector facing portion 146, an electrode facing portion 145, and a connecting portion 147 connecting the electrode facing portion 145 and the interconnector facing portion 146. For example, nickel or nickel alloy. , Stainless steel, etc. The electrode facing portion 145 is in contact with the surface of the fuel pole 116 opposite to the side facing the electrolyte layer 112, and the interconnector facing portion 146 is on the surface of the interconnector 150 facing the fuel pole 116. Are in contact. However, as described above, since the power generation unit 102 located at the bottom of the fuel cell stack 100 does not have the lower interconnector 150, the interconnector facing portion 146 in the power generation unit 102 is the lower end plate. It is in contact with 106. Since the fuel pole side current collector 144 has such a configuration, the fuel pole 116 and the interconnector 150 (or the end plate 106) are electrically connected to each other. A spacer 149 formed of, for example, a mica is arranged between the electrode facing portion 145 and the interconnector facing portion 146. Therefore, the fuel pole side current collector 144 follows the deformation of the power generation unit 102 due to the temperature cycle and the reaction gas pressure fluctuation, and the fuel pole 116 and the interconnector 150 (or the end plate 106) via the fuel pole side current collector 144 follow. Good electrical connection with is maintained.

The air electrode side current collector 134 is arranged in the air chamber 166. The air electrode side current collector 134 is composed of a plurality of substantially square columnar current collector elements 135, and is made of a material containing Cr, for example, ferritic stainless steel. The air electrode side current collector 134 is in contact with the surface of the air electrode 114 opposite to the side facing the electrolyte layer 112 and the surface of the interconnector 150 on the side facing the air electrode 114. However, as described above, since the power generation unit 102 located at the top of the fuel cell stack 100 does not have the upper interconnector 150, the air electrode side current collector 134 in the power generation unit 102 has an upper end plate. It is in contact with 104. Since the air electrode side current collector 134 has such a configuration, the air electrode 114 and the interconnector 150 (or the end plate 104) are electrically connected to each other. A conductive bonding layer for bonding the air electrode 114 and the current collector 134 on the air electrode side may be interposed. The air electrode side current collector 134 and the interconnector 150 may be configured as an integral member.

A-2. Operation of fuel cell stack 100:
As shown in FIGS. 2 and 4, the oxidant gas OG is supplied via a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the oxidant gas introduction manifold 161. Then, the oxidant gas OG is supplied to the oxidant gas introduction manifold 161 through the holes of the branch portion 29 and the main body portion 28 of the gas passage member 27, and the oxidizer gas introduction manifold 161 oxidizes each power generation unit 102. It is supplied to the air chamber 166 through the agent gas supply communication hole 132. Further, as shown in FIGS. 3 and 5, the fuel gas FG is supplied via a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the fuel gas introduction manifold 171. Then, the fuel gas FG is supplied to the fuel gas introduction manifold 171 through the holes of the branch portion 29 and the main body portion 28 of the gas passage member 27, and the fuel gas supply communication of each power generation unit 102 is performed from the fuel gas introduction manifold 171. It is supplied to the fuel chamber 176 through the hole 142.

When the oxidant gas OG is supplied to the air chamber 166 of each power generation unit 102 and the fuel gas FG is supplied to the fuel chamber 176, power is generated by the electrochemical reaction of the oxidant gas OG and the fuel gas FG in the single cell 110. Will be. This power generation reaction is an exothermic reaction. In each power generation unit 102, the air pole 114 of the single cell 110 is electrically connected to one of the interconnectors 150 via the air pole side current collector 134, and the fuel pole 116 is via the fuel pole side current collector 144. It is electrically connected to the other interconnector 150. Further, the plurality of power generation units 102 included in the fuel cell stack 100 are electrically connected in series. Therefore, the electric energy generated in each power generation unit 102 is taken out from the end plates 104 and 106 that function as the output terminals of the fuel cell stack 100. Since the SOFC generates electricity at a relatively high temperature (for example, 700 ° C. to 1000 ° C.), the fuel cell stack 100 is a heater (for example, after the start-up, until the high temperature can be maintained by the heat generated by the power generation. It may be heated by (not shown).

As shown in FIGS. 2 and 4, the oxidant off-gas OOG discharged from the air chamber 166 of each power generation unit 102 is discharged to the oxidant gas discharge manifold 162 through the oxidant gas discharge communication hole 133, and further oxidized. The fuel cell stack 100 is passed through the holes of the main body 28 and the branch 29 of the gas passage member 27 provided at the position of the agent gas discharge manifold 162, and the gas pipe (not shown) connected to the branch 29. It is discharged to the outside of. Further, as shown in FIGS. 3 and 5, the fuel off-gas FOG discharged from the fuel chamber 176 of each power generation unit 102 is discharged to the fuel gas discharge manifold 172 through the fuel gas discharge communication hole 143, and further, the fuel gas. Through the holes of the main body 28 and the branch 29 of the gas passage member 27 provided at the position of the discharge manifold 172, and through a gas pipe (not shown) connected to the branch 29, to the outside of the fuel cell stack 100. It is discharged.

A-3. Detailed configuration for joining the electrolyte layer 112 and the fuel electrode 116:
Next, a detailed configuration for joining the electrolyte layer 112 and the fuel electrode 116 in the single cell 110 constituting the fuel cell stack 100 of the present embodiment will be described. FIG. 4 shows an enlarged joint portion (X1) between the electrolyte layer 112 and the fuel electrode 116. FIG. 6 is an explanatory diagram schematically showing the structure of the joint portion between the electrolyte layer 112 and the fuel electrode 116. In FIG. 6, the air electrode 114 and the like are omitted. Note that FIG. 6 schematically shows an SEM image (for example, 90 times) of the joint portion between the electrolyte layer 112 and the fuel electrode 116 in an SEM (acceleration voltage 15 kV) showing a cross section parallel to the vertical direction. be.

As shown in FIGS. 4 and 6, the single cell 110 includes a welded portion 200 that joins the electrolyte layer 112 and the fuel electrode 116. The welded portion 200 is formed by melting and solidifying an electrolyte layer forming material (for example, YSZ) and a fuel electrode forming material (for example, Ni) by a melt welding method ((Y, Zr, Ni) Ox ( _x ). Determined by charge neutral condition)). The method for specifying the welded portion 200 is as follows. Elemental analysis of the cross section of the junction between the electrolyte layer 112 and the fuel electrode 116 using an energy dispersive X-ray spectroscope (EDS) attached to a scanning electron microscope (SEM) or a transmission electron microscope (TEM). By doing so, the type of element of the welded portion 200 is confirmed. Next, from the composition ratio of the welded portion 200 based on the confirmation result, it can be specified that the electrolyte layer 112 and the fuel electrode 116 are melted and solidified.

The welded portion 200 is located at least a part of the outer circumference between the electrolyte layer 112 and the fuel electrode 116 in the vertical direction. The welded portion 200 is formed so as to straddle the electrolyte layer 112 and the fuel electrode 116 in the vertical direction. In other words, the welded portion 200 is arranged so as to be in contact with both the side surface of the electrolyte layer 112 and the side surface of the fuel electrode 116. More specifically, the welded portion 200 is arranged so as to continuously contact and cover the side surface of the electrolyte layer 112, the side surface of the fuel pole 116, and the boundary between the electrolyte layer 112 and the fuel pole 116. There is.

The thickness D of the welded portion 200 (see FIG. 4) is, for example, 10 μm or more. The thickness D of the welded portion 200 is, for example, 30 μm or less. The length L (see FIG. 4) of the welded portion 200 in the vertical direction (Z-axis direction) is, for example, 30 μm or more. The vertical length L of the welded portion 200 is, for example, 80 μm or less. In the present embodiment, the vertical thickness of the electrolyte layer 112 is 10 μm or less, the vertical thickness of the functional layer of the fuel pole 116 is 20 μm or less, and the vertical thickness of the substrate layer of the fuel pole 116 is vertical. The thickness of is 1000 μm or less.

In this embodiment, the single cell 110 includes a plurality of welded portions 200. As shown in FIG. 6, the plurality of welded portions 200 are arranged so as to be separated from each other along the circumferential direction of the electrolyte layer 112 and the fuel electrode 116 in the vertical view. The width W of each welded portion 200 in the circumferential direction is, for example, 50 μm or more. The distance H between the welded portions 200 located adjacent to each other in the circumferential direction is shorter than the width W of the welded portions 200. The welded portion 200 is arranged over the entire circumference of the electrolyte layer 112 and the fuel electrode 116.

At least one of the plurality of welds 200 has a protruding portion 210. The protruding portion 210 is located outside the electrolyte layer 112 in the vertical direction, and is connected to the surface (upper surface) of the electrolyte layer 112 opposite to the fuel electrode 116. In other words, the upper surface of the protruding portion 210 and the upper surface of the electrolyte layer 112 are flush with each other (see FIG. 4). In the present embodiment, the lower surface of the joint portion 124 between the separator 120 and the electrolyte layer 112 is in contact with the electrolyte layer 112 and extends to the outside of the electrolyte layer 112, and is in contact with the upper surface of the protruding portion 210. Of the plurality of welded portions 200 provided in the single cell 110, 50% or more of the welded portions 200 may have the protruding portions 210, and 80% or more of the welded portions 200 may have the protruding portions 210. May have.

As shown in FIG. 6, the boundary line B between the welded portion 200 and the fuel pole 116 is uneven in at least one cross section parallel to the vertical direction. Specifically, the boundary line B between one welded portion 200 and the fuel electrode 116 has a plurality of sets of uneven shapes.

As shown in FIGS. 4 and 6, the lower portion (the side opposite to the electrolyte layer 112) on the side surface of the fuel electrode 116 is not covered by the welded portion 200. Therefore, as compared with the configuration in which the entire side surface of the fuel electrode 116 is covered with the welded portion 200, it is possible to suppress a decrease in the diffusion of the fuel gas FG into the fuel electrode 116 due to the presence of the welded portion 200. .. Further, the welded portion 200 extends to the upper end of the side surface of the electrolyte layer 112 (the end opposite to the fuel electrode 116). Therefore, the welded portion 200 is firmly joined to the relatively thin electrolyte layer 112 so as to be caught. Further, in the welded portion 200, the thickness D of the joint portion with the fuel electrode 116 is thinner than the thickness D of the joint portion with the electrolyte layer 112. As a result, while ensuring the bonding strength with respect to the relatively thin electrolyte layer 112, it is possible to suppress the decrease in the diffusion of the fuel gas FG into the fuel electrode 116 by making it thin so as not to interfere with the fuel electrode 116 side. ..

A-4. Manufacturing method of fuel cell stack 100:
The method for manufacturing the fuel cell stack 100 of the present embodiment is as follows, for example.

(Formation of a laminate of the electrolyte layer 112 and the fuel electrode 116)
To the YSZ powder, a butyral resin, a plasticizer dioctyl phthalate (DOP), a dispersant, and a mixed solvent of toluene and ethanol are added and mixed with a ball mill to prepare a slurry. The obtained slurry is thinned by the doctor blade method to obtain a green sheet for an electrolyte layer having a predetermined thickness (for example, about 6 μm). Further, to the mixed powder of NiO powder and YSZ powder, organic beads which are pore-forming materials, butyral resin, DOP which is a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added. Mix in a ball mill to prepare a slurry. The obtained slurry is thinned by the doctor blade method to obtain a green sheet for a fuel electrode substrate layer having a predetermined thickness (for example, about 400 μm). Further, to the mixed powder of NiO powder and YSZ powder, butyral resin, DOP which is a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added and mixed by a ball mill to prepare a slurry. Prepare. The obtained slurry is thinned by the doctor blade method to obtain a green sheet for a fuel electrode functional layer having a predetermined thickness (for example, about 11 μm). After sticking each green sheet and degreasing at a predetermined temperature (for example, about 280 ° C.), firing is performed at a predetermined temperature (for example, about 1350 ° C.) for a predetermined time (for example, about 1 hour). As a result, a laminate of the electrolyte layer 112 and the fuel electrode 116 is obtained.

Next, the above-mentioned welded portion 200 is formed on the laminate of the electrolyte layer 112 and the fuel electrode 116. For example, the peripheral edge portion of the laminated body is subjected to laser processing in the vertical direction, and the peripheral edge portion of the laminated body is cut while being melted. For laser processing, for example, a well-known laser such as a CO ₂ laser, a YAG laser, or a fiber laser can be used. The welded portion 200 may be formed by peeling off a part of the melted portion after the laser processing.

(Formation of intermediate layer 180)
Polyvinyl alcohol as an organic binder and butyl carbitol as an organic solvent are added to GDC powder and mixed to adjust the viscosity to prepare a paste for an intermediate layer. The obtained intermediate layer paste is applied to the surface of the electrolyte layer 112 in the above-mentioned laser-processed laminate by, for example, screen printing, and fired at a predetermined temperature (for example, 1200 ° C.). As a result, the intermediate layer 180 is formed, and a laminate of the intermediate layer 180, the electrolyte layer 112, and the fuel electrode 116 is obtained.

(Formation of air pole 114)
A mixed powder of a perovskite-type oxide (for example, LSCF) powder and a sulfate (for example, SrSO ₄ ) powder is prepared, and the mixed powder is prepared with polyvinyl alcohol as an organic binder and butyl carbitol as an organic solvent. To prepare a paste for air electrode by adding and mixing to adjust the viscosity. The obtained air electrode paste is applied to the surface of the intermediate layer 180 in the above-mentioned laminate of the intermediate layer 180, the electrolyte layer 112, and the fuel electrode 116 by, for example, screen printing and dried, and the air electrode paste is applied. The laminated body is fired at a predetermined temperature (for example, about 1100 ° C.). As a result, the air electrode 114 is formed, and a single cell 110 including the fuel electrode 116, the electrolyte layer 112, the intermediate layer 180, and the air electrode 114 is produced.

After producing a plurality of single cells 110 according to the method described above, an assembly step (for example, a step of attaching another member such as a separator 120 to each single cell 110, a step of laminating the plurality of single cells 110, and fastening with bolts 22). Process, etc.). As described above, the production of the fuel cell stack 100 is completed.

A-5. Effect of this embodiment:
As described above, the single cell 110 constituting the fuel cell stack 100 of the present embodiment includes an electrolyte layer 112, and air poles 114 and fuel poles 116 facing each other with the electrolyte layer 112 interposed therebetween. The single cell 110 includes a welded portion 200 that joins the electrolyte layer 112 and the fuel electrode 116. The welded portion 200 is formed by melting and solidifying the material for forming the electrolyte layer and the material for forming the fuel electrode by the melt welding method. The welded portion 200 is located at least a part of the outer circumference between the electrolyte layer 112 and the fuel electrode 116 in the vertical direction. The welded portion 200 is formed so as to straddle the electrolyte layer 112 and the fuel electrode 116.

As described above, in the present embodiment, the welded portion 200 is formed so as to straddle the electrolyte layer 112 and the fuel electrode 116. The welded portion 200 is formed by melting the electrolyte layer 112 and the fuel electrode 116, and has an intermediate composition (property) between the electrolyte layer 112 and the fuel electrode 116. Specifically, the welded portion 200 has a coefficient of thermal expansion between the coefficient of thermal expansion of the electrolyte layer 112 and the coefficient of thermal expansion of the fuel electrode 116. Therefore, the welded portion 200 plays a role of alleviating the difference in thermal expansion between the electrolyte layer 112 and the fuel electrode 116. As a result, according to the present embodiment, peeling between the electrolyte layer 112 and the fuel electrode 116 (for example, interfacial peeling or intra-layer peeling) can be suppressed.

In the present embodiment, the plurality of welded portions 200 are arranged so as to be arranged so as to be separated from each other along the circumferential direction of the electrolyte layer 112 and the fuel electrode 116. Therefore, in the present embodiment, even if one welded portion 200 is peeled off or damaged, its influence is suppressed from extending to the other welded portion 200. Therefore, according to the present embodiment, for example, as compared with the configuration in which one welded portion 200 surrounds the entire circumference of the electrolyte layer 112 and the fuel electrode 116, it is possible to prevent damage to the welded portion 200 from being widely affected. Can be done. Further, it is possible to suppress a decrease in the diffusion of the fuel gas FG into the fuel electrode 116 due to the presence of the welded portion 200.

In this embodiment, the welded portion 200 has a protruding portion 210. The protruding portion 210 is located outside the electrolyte layer 112 in the vertical direction, and is connected to the surface (upper surface) of the electrolyte layer 112 opposite to the fuel electrode 116. Therefore, according to the present embodiment, a wider joint area between the single cell 110 and other members is secured when assembling the fuel cell stack 100, as compared with the configuration in which none of the welded portions 200 has the protruding portion 210. be able to. Specifically, as shown in FIG. 4, the joint portion 124 can be arranged not only to the electrolyte layer 112 but also to the protruding portion 210 of the welded portion 200. Therefore, for example, the joining strength can be improved by increasing the joining area between the joining portion 124 and the single cell 110 (including 210). Further, by arranging the joint portion 124 so as to protrude to the outside of the electrolyte layer 112, the region on the inner peripheral side of the joint portion 124 becomes wider, so that a wide power generation region in the single cell 110 can be secured.

In the present embodiment, the boundary line B between the welded portion 200 and the fuel electrode 116 is uneven in at least one cross section parallel to the vertical direction. Therefore, according to the present embodiment, the welded portion 200 is longer in contact with the welded portion 200 and the fuel electrode 116 than in the configuration in which the boundary line B between the welded portion 200 and the fuel pole 116 is linear. Can be suppressed from falling off.

B. Modification example:
The technique disclosed in the present specification is not limited to the above-described embodiment, and can be transformed into various forms without departing from the gist thereof. For example, the following modifications are also possible.

The configuration of the single cell 110 or the fuel cell stack 100 in the above embodiment is merely an example and can be variously modified. For example, in the above embodiment, the single cell 110 includes the intermediate layer 180, but the single cell 110 may not include the intermediate layer 180. Further, in the above embodiment, the fuel pole 116 has a two-layer structure of a substrate layer and a functional layer, but the fuel pole 116 may have a single-layer structure or a three-layer or more structure. good. Further, in the above embodiment, the number of single cells 110 included in the fuel cell stack 100 is only an example, and the number of single cells 110 is appropriately determined according to the output voltage and the like required for the fuel cell stack 100.

Further, in the above embodiment, the space between the outer peripheral surface of the shaft portion of each bolt 22 and the inner peripheral surface of each communication hole 108 is used as each manifold, but instead of this, the shaft of each bolt 22 is used. Axial holes may be formed in the portion, and the holes may be used as each manifold. Further, each manifold may be provided separately from each communication hole 108 into which each bolt 22 is inserted.

In the above embodiment, the single cell 110 may include one welded portion 200. Further, the welded portion 200 may be configured not to include the protruding portion 210. The boundary line B between the welded portion 200 and the fuel electrode 116 may be arcuate.

Further, the material constituting each member in the above embodiment is merely an example, and each member may be composed of another material. In the above embodiment, as a welded portion, YSZ as a material for forming an electrolyte layer and Ni as a material for forming a fuel electrode are melted and solidified (Y, Zr, Ni) Ox ( _x is a charge neutral condition. The determination) has been illustrated, but in addition to this, for example, it may be composed of a compound or a composite material of the material for forming the electrolyte layer and the material for forming the fuel electrode.

Further, in the above embodiment, it is not always necessary that all the single cells 110 included in the fuel cell stack 100 have a configuration including the welded portion 200, and at least one single cell 110 included in the fuel cell stack 100 is not realized. With respect to the above, if the configuration including the welded portion 200 is realized, it is possible to suppress the peeling of the electrolyte layer 112 and the fuel electrode 116.

Further, although the above embodiment targets the flat plate type single cell 110, the technique disclosed in the present specification can be similarly applied to other single cells other than the flat plate type.

Further, in the above embodiment, the SOFC that generates power by utilizing the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidizing agent gas is targeted, but the technique disclosed in the present specification is: It can also be applied to an electrolytic single cell, which is a constituent unit of a solid oxide type electrolytic cell (SOEC) that generates hydrogen using the electrolysis reaction of water, and an electrolytic cell stack having a plurality of electrolytic single cells. be. The configuration of the electrolytic cell stack is not described in detail here because it is known as described in, for example, Japanese Patent Application Laid-Open No. 2016-81813, but is generally the same as the fuel cell stack 100 in the above-described embodiment. It is a configuration. That is, the fuel cell stack 100 in the above-described embodiment may be read as an electrolytic cell stack, the power generation unit 102 may be read as an electrolytic cell unit, and the single cell 110 may be read as an electrolytic cell. However, during the operation of the electrolytic cell stack, a voltage is applied between both electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode), and the voltage is applied through the communication hole 108. Water vapor as a raw material gas is supplied. As a result, an electrolysis reaction of water occurs in each electrolytic cell unit, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out to the outside of the electrolytic cell stack through the communication hole 108. Even in the electrolytic cell and the electrolytic cell stack having such a configuration, the same effect can be obtained by adopting a configuration having the same welded portion 200 as in the above embodiment.

The method for manufacturing the fuel cell stack 100 in the above embodiment is merely an example and can be variously modified. For example, in the above embodiment, laser processing is adopted to form the welded portion 200, but the present invention is not limited to this, and other melt welding methods (for example, electric discharge machining) may be adopted.

22: Bolt 24: Nut 26: Insulation sheet 27: Gas passage member 28: Main body 29: Branch 100: Fuel cell stack 102: Power generation unit 104, 106: End plate 108: Communication hole 110: Single cell 112: Electrolyte layer 114: Air pole 116: Fuel pole 120: Separator 121, 131, 141: Hole 124: Joint 130: Air pole side frame 132: Oxidizing agent gas supply communication hole 133: Oxidizing agent gas discharge communication hole 134: Air pole side collection Electric body 135: Current collector element 140: Fuel pole side frame 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel pole side current collector 145: Electrode facing part 146: Interconnector facing part 147: Connecting Part 149: Spacer 150: Interconnector 161: Oxidizing agent gas introduction manifold 162: Oxidizing agent gas discharge manifold 166: Air chamber 171: Fuel gas introduction manifold 172: Fuel gas discharge manifold 176: Fuel chamber 180: Intermediate layer 200: Welded part 210: Protruding part

Claims (5)

In an electrochemical reaction single cell including an electrolyte layer containing a solid oxide and an air electrode and a fuel electrode facing each other in a first direction across the electrolyte layer.
A welded portion for joining the electrolyte layer and the fuel electrode is provided.
The welded portion is located at least a part of the outer circumference of the electrolyte layer and the fuel electrode in the first direction, and is formed so as to straddle the electrolyte layer and the fuel electrode.
An electrochemical reaction single cell characterized by that. In the electrochemical reaction single cell according to claim 1,
A plurality of the welded parts are provided.
The plurality of welded portions are arranged so as to be arranged so as to be separated from each other along the circumferential direction of the electrolyte layer and the fuel electrode.
An electrochemical reaction single cell characterized by that. In the electrochemical reaction single cell according to claim 1 or 2.
The welded portion is located outside the electrolyte layer in the first directional view, and has a protruding portion connected to the surface of the electrolyte layer opposite to the fuel electrode.
An electrochemical reaction single cell characterized by that. In the electrochemical reaction single cell according to any one of claims 1 to 3.
In at least one cross section parallel to the first direction, the boundary line between the welded portion and the fuel electrode is uneven.
An electrochemical reaction single cell characterized by that. In an electrochemical reaction cell stack having multiple electrochemical reaction single cells,
At least one of the plurality of electrochemical reaction single cells is the electrochemical reaction single cell according to any one of claims 1 to 4.
It is characterized by an electrochemical reaction cell stack.

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