JP7263269B2 - Solid oxide electrochemical stack - Google Patents

Description

Embodiments of the present invention relate to solid oxide electrochemical stacks.

One of the new energies is hydrogen. Fuel cells, which convert chemical energy into electrical energy by electrochemically reacting hydrogen and oxygen, are attracting attention as a field of utilization of this hydrogen. Fuel cells have high energy utilization efficiency and are being developed as large-scale distributed power sources, household power sources, and mobile power sources.

Fuel cells are divided into solid polymer, phosphoric acid, molten carbonate, and solid oxide types, depending on the temperature range and the type of materials and fuels used. A solid oxide fuel cell (SOFC) that obtains electrical energy through an electrochemical reaction using an oxide electrolyte has attracted attention. In the production of hydrogen, there is an electrolysis reaction of water, and research is underway on a high-temperature steam electrolysis method (SOEC) in which water is electrolyzed at a high temperature in the form of water vapor. The operating principle of SOEC is the reverse reaction of SOFC and also uses an electrolyte consisting of solid oxides.

An electrochemical cell is a laminate of at least an air electrode, an electrolyte, and a fuel electrode, each using materials with different properties. The air electrode and the fuel electrode are porous, and different gases are supplied to the air electrode and the fuel electrode with a dense electrolyte interposed therebetween. The cathode and anode are electrical conductors, and the electrolyte is an ionic conductor that does not conduct electricity. The shape of the electrochemical cell includes a flat plate type, a cylindrical type, a cylindrical flat plate type, and the like. For example, a flat plate type electrochemical cell has a shape in which an air electrode, an electrolyte, a fuel electrode, and the like are laminated in a flat plate shape.

A stack of a plurality of such cells is generally called a stack. For example, in the case of a flat plate electrochemical cell, the stack consists of a plurality of flat plate cells, different gases are supplied to the cathode and anode of each cell, and the cells are electrically connected in series. have a possible structure. Cells are separated from each other by separators, which separate the gas from each cell, and since the separators are conductive, they also play a role of electrical conduction between cells. Gas supply and discharge channels for each cell are also generally formed in the separator.

FIG. 4 shows an example of a stack structure using planar electrochemical cells. A fuel electrode support type cell 15 is taken as an example of the flat plate type electrochemical cell. There is no particular limitation on the gases to be flowed to the air electrode side and the fuel electrode side of the cell, but FIG. 4 shows an example in which air is flowed to the air electrode side of the cell 15 and hydrogen is flowed to the fuel electrode side, assuming the case of power generation. rice field.

The cell 15 is mainly composed of a porous air electrode (oxygen electrode) 11 , a dense electrolyte 12 , a porous hydrogen electrode (fuel electrode) 13 and a porous support 14 . In the stack, the portion where the cell 15 is installed has a dense electrolyte 12 , and the electrolyte 12 separates the atmospheres of the hydrogen electrode 13 and the air electrode 11 .

On the other hand, it is necessary to separate the atmospheres of the hydrogen electrode 13 and the air electrode 11 with some kind of dense member where the cell 15 is not installed. In the example shown in FIG. 4, the atmospheres of adjacent cells 15 are separated by dense separators 21, and the atmospheres of the hydrogen electrode 13 and the air electrode 11 of the same cell 15 are separated from each other over the dense electrolyte 12 of the cell 15. A partition plate 22 is provided to separate the hydrogen electrode 13 and the air electrode 11 .

A gas sealing material 31 is disposed on the contact surface between the partition plate 22 and the separator 21, the contact surface between the partition plate 22 and the cell 15, and the contact surface when the separator 21 is composed of a plurality of parts, in order to prevent gas leakage. There are many things. As the gas seal material 31, for example, a glass seal material, a compressive seal material, or the like is used. In the stack configuration of FIG. 4, a sealing material 31' having a certain thickness is provided, particularly on the air electrode 11 side of the cell 15, because it is necessary to secure a space for air flow.

The materials used as the gas seal materials 31 and 31' must be stable at high operating temperatures of 600 to 1000°C, have a coefficient of thermal expansion close to that of the joining members such as the separator 21, and have insulating properties. It is very limited because it is necessary to satisfy conditions such as Glass seal materials are considered to meet these requirements and are promising, and are used in many stacks.

The deterioration behavior of SOFC and SOEC gas seal materials including glass seal materials is largely unknown, but it has become clear that glass seal materials deteriorate in the gas atmosphere of SOFCs and SOECs. For example, boron is often included in the glass seal material to adjust the heat resistance temperature and thermal expansion coefficient required for the glass seal material. However, boron reacts with water vapor, degrading the glass sealing material itself, and the transpired boron may react with and degrade other members such as cells. Although many parts of materials other than boron are not clarified, it is fully conceivable that they react with SOFC/SOEC gases, evaporate after reaction, or react with other members.

Therefore, there is a demand for the development of a technology that can easily prevent the deterioration of the glass seal material and the deterioration of the surrounding members due to the evaporation of the glass seal material, which are problems of solid oxide electrochemical stacks.

Patent No. 5801735

As described above, in the solid oxide electrochemical stack, by preventing the glass seal material from reacting with the gas flowing through the SOFC/SOEC, deterioration of the seal itself and deterioration of surrounding members due to transpiration of the seal components are avoided. can be prevented, and a decrease in efficiency can be prevented. For this reason, in the prior art, it has been proposed to introduce a protective part (plating, etc.) to prevent deterioration of the sealing material due to the reaction between the gas and the sealing material, but this is limited to the parts where the gas collides violently. It does not protect the entire sealing material.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a solid oxide electrochemical stack that can easily prevent the deterioration of the glass seal material and the deterioration of surrounding members due to the evaporation of the glass seal material.

A solid oxide electrochemical stack of an embodiment comprises a solid oxide electrochemical cell having a porous hydrogen electrode, a porous air electrode, and a dense electrolyte; Separators for isolating physical and electrochemical cells from each other, and gas seals that are placed in areas that need to be airtightly sealed, such as plane contact surfaces where the weight of stack fastening is applied among the contact surfaces of the constituent members. wherein said gas seal material comprises a glass seal material, said glass seal material supplying gas to said hydrogen electrode and said cathode, and reaction products. It is configured so as not to be exposed to the gas flow path.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing the cross-sectional schematic configuration of the solid oxide electrochemical stack according to the first embodiment; The figure for demonstrating the positional relationship of a joining part and a glass sealing material. The figure which shows typically the cross-sectional schematic structure of the solid oxide form electrochemical stack which concerns on 2nd Embodiment. FIG. 2 is a diagram schematically showing a cross-sectional schematic configuration of an example of a solid oxide electrochemical stack;

Hereinafter, solid oxide electrochemical stacks according to embodiments will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a schematic cross-sectional structure of a solid oxide electrochemical stack according to the first embodiment. In addition, in FIG. 1, a flat plate type stack is taken as an example, but the stack shape is not limited to the flat plate type. For example, it may be cylindrical.

As shown in FIG. 1, the flat cell 15 has a structure in which a porous air electrode 11, a dense electrolyte 12, a porous hydrogen electrode 13, and a porous support 14 are laminated. A gas can pass through the interior of the air electrode 11 , the hydrogen electrode 13 , and the support 14 , but the gas cannot pass through the interior of the electrolyte 12 . The overall planar shape of the flat plate stack is, for example, rectangular. Moreover, current collectors (not shown) are often provided above and below the cells 15 .

In a solid oxide electrochemical stack, dense separators 21 separate the atmospheres between adjacent cells 15 . As for the atmospheres of the hydrogen electrode 13 and the air electrode 11 of the same cell 15 , the hydrogen electrode 13 and the air electrode 11 are separated from each other by providing a partition plate 22 on the dense electrolyte 12 of the cell 15 . A gas flow path 23 is provided in the outer peripheral portion of the cell 15 so as to penetrate the cell 15 along the stacking direction. This gas channel 23 serves as a channel for the supply gas of the hydrogen electrode 13 and the air electrode 11 and the reaction product gas.

Among the contact surfaces between the partition plate 22 and the separator 21, the contact surfaces between the partition plate 22 and the cell 15, and the contact surfaces when the separator 21 is composed of a plurality of parts, gas leak prevention is applied to the parts that need to be airtightly sealed. A glass seal member 32 is provided for this purpose. The glass sealing material 32 is configured not to be exposed to the flow paths of the supply gas of the hydrogen electrode 13 and the air electrode 11 and the reaction product gas, thereby preventing contact between the glass sealing material 32 and the gas. It's becoming

In other words, the glass sealing material 32 is arranged inside the outer edge of the contact surface, and when the contact surface is viewed from the surroundings, the glass sealing material 32 is arranged only inside that cannot be seen from the outside. . For example, as shown in the plan view shown in FIG. 2, the shape of the contact surface that contacts other members is a substantially rectangular frame shape, and there is a space in the center where the cells 15 are arranged, and gas flow paths along the four sides. When there is a separator 121 having 23, a portion where the glass seal material 32 is not disposed is provided around the outer edge of the contact surface of the separator 121 and the gas flow path 23 (outer edge portion), and only the other portions are glass-sealed. It has a configuration in which the material 32 is arranged.

In this case, as described above, the gas flow path 23 is a portion that serves as flow paths for the supply gas of the hydrogen electrode 13 and the air electrode 11 and the reaction product gas. The space in the central part is a part where the cell 15 is arranged, and this part also serves as a flow path for the supply gas of the hydrogen electrode 13 and the air electrode 11 and the reaction product gas. Therefore, the glass sealing material 32 is configured not to be exposed to the flow paths of the supply gas and the reaction product gas of the hydrogen electrode 13 and the air electrode 11 . In addition, although the outer peripheral portion is a portion that may come into contact with the outside air, it can be configured in the same manner as the gas flow path described above.

Since the glass sealant 32 is generally applied very thinly (for example, several microns to several tens of microns in thickness), the weight of stack fastening causes the portion of the contact surface left without the glass sealant 32 to be applied. It is thought that the members are in close contact with each other, and this close contact between the members can easily prevent the gas from contacting the glass sealing material 32 .

On the other hand, on the air electrode 11 side of the cell 15, the sealing material needs to be thick in order to secure a space for flowing air. It is difficult to prevent contact with

For this reason, a sealing material having low reactivity with the supply gas of the hydrogen electrode 13 and the air electrode 11 and the reaction product gas, for example, the compressive sealing material 33 is used together. It is known that the compressive sealing material 33 has a larger leakage at the contact surface than the glass sealing material 32 . Therefore, by arranging the glass sealing material 32 on the contact surface between the compressive sealing material 33 and the other member, it is possible to prevent gas leakage from the contact surface.

Also in this case, in order to prevent deterioration of the glass sealing material 32 due to contact with gas, the glass sealing material 32 is configured not to be exposed to the flow paths of the supply gas and the reaction product gas of the hydrogen electrode 13 and the air electrode 11 . This can prevent contact between the glass seal material 32 and the gas.

That is, as in the case where the glass sealing material 32 described above is used alone, the glass sealing material 32 is arranged inside the outer edge of the contact surface, and when the contact surface is viewed from the surroundings, the glass seal material 32 is A glass sealing material 32 is provided only inside the device which is not visible.

Since the glass sealing material 32 can be made very thin by using the compressive sealing material 33 together, it is thought that the members of the contact surfaces left without applying the glass sealing material 32 are in close contact with each other. contact can be prevented.

(Second embodiment)
FIG. 3 shows a schematic cross-sectional configuration of a main part of a solid oxide electrochemical stack according to the second embodiment, and the part corresponding to the solid oxide electrochemical stack according to the first embodiment shown in FIG. are given the same reference numerals. Note that FIG. 3 shows a flat plate stack as an example, but the shape of the stack is not limited to the flat plate type.

In the solid oxide electrochemical stack according to the second embodiment, the materials and positions of the glass sealing material 34 and the glass sealing material 34' that must have a certain thickness are the same as those of the conventional stack shown in FIG. In the solid oxide electrochemical stack according to the second embodiment, the anti-reaction layer 40 is provided on the side surfaces (exposed surfaces) of the glass sealant 34 and the glass sealant 34' that requires a certain thickness. Therefore, the glass sealing material 34 and the glass sealing material 34', which requires a large thickness, are configured so as not to be exposed to the flow paths of the supply gas and the reaction product gas of the hydrogen electrode 13 and the air electrode 11, respectively.

The anti-reaction layer 40 prevents the gas from contacting the glass sealing material 34 and the thick glass sealing material 34'. can be prevented from deteriorating. As a material constituting the reaction prevention layer 40, a material having low reactivity with gas, having necessary heat resistance, and having a coefficient of thermal expansion close to that of other members, for example, a coefficient of thermal expansion of 8× It is preferable to use a ceramic material or the like within the range of 10 ⁻⁶ /K to 12×10 ⁻⁶ /K. For example, cobalt-based spinel can be preferably used.

Although several embodiments of the invention have been described above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

11 Air electrode 12 Electrolyte 13 Hydrogen electrode 14 Support 15 Cell 21, 121 Separator 22 Separator 23 Gas channel 32 ... glass sealing material, 33 ... compressive sealing material, 34 ... glass sealing material, 34' ... glass sealing material requiring a certain thickness, 40 ... reaction prevention layer.

Claims (5)

A solid oxide electrochemical cell having a porous hydrogen electrode, a porous air electrode, and a dense electrolyte;
a separator for isolating the adjacent solid oxide electrochemical cells;
A gas sealing material disposed at a portion of the contact surfaces between the constituent members that need to be airtightly sealed on the planar contact surfaces to which the weight of stack fastening is applied ;
A solid oxide electrochemical stack comprising:
The gas sealing material includes a glass sealing material, and the glass sealing material is configured so as not to be exposed to flow paths of the supply gas and the reaction product gas of the hydrogen electrode and the air electrode. Physical electrochemical stack . 2. The solid oxide type according to claim 1, wherein the glass sealing material is disposed inside the portions facing the flow paths of the supply gas and the reaction product gas of the hydrogen electrode and the air electrode. electrochemical stack. 3. The solid oxide electrochemical stack according to claim 1, wherein the sealing material having low reactivity with gas and the glass sealing material are used in combination. 2. A reaction prevention layer covering the outer side of the glass sealing material is provided at portions of the hydrogen electrode and the air electrode facing flow paths of the supply gas and the reaction product gas. A solid oxide electrochemical stack as described in . 5. The solid oxide type electricity according to claim 4, wherein the material constituting the reaction prevention layer has a thermal expansion coefficient within the range of 8×10 ⁻⁶ /K to 12×10 ⁻⁶ /K. chemical stack.

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