Patent Publication Number: US-11658326-B2

Title: Cell stack device, module, and module housing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a national stage application of International Application No. PCT/JP2020/028911, filed on Jul. 28, 2020, which designates the United States, the entire contents of which are herein incorporated by reference, and which is based upon and claims the benefit of priority to Japanese Patent Application No. 2019-158561, filed on Aug. 30, 2019, the entire contents of which are herein incorporated by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a cell stack device, a module, and a module housing device. 
     BACKGROUND ART 
     In recent years, various fuel cell stack devices have been proposed as next-generation energy sources in which a plurality of fuel cells are arranged, each of the fuel cells being a type of cell capable of generating electrical power by using a fuel gas (hydrogen-containing gas) and an oxygen-containing gas (air). 
     In such a fuel cell stack device, for example, lower ends of the plurality of fuel cells are bonded to a holding member by a fixing material (see Patent Document 1). 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: JP 2013-157191 A 
     SUMMARY OF INVENTION 
     A cell stack device according to an aspect of an embodiment of the present disclosure includes a cell stack, a holding member, and a positive electrode terminal. The cell stack is constructed by stacking a plurality of cells. The holding member holds the cells. The positive electrode terminal functions as a positive electrode when power generated by the cell stack is output to the outside. Furthermore, the potential of the positive electrode terminal is not more than that of the holding member. 
     Furthermore, a module of the present disclosure includes the cell stack device described above in a housing container. 
     Moreover, a module housing device of the present disclosure includes, in an outer case, the module described above and an auxiliary device for operating the module. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1 A  is a cross-sectional view illustrating an example of a cell according to an embodiment. 
         FIG.  1 B  is a side view illustrating an example of a cell according to an embodiment when viewed from an air electrode side. 
         FIG.  1 C  is a side view illustrating an example of the cell according to the embodiment when viewed from an interconnector side. 
         FIG.  2 A  is a perspective view illustrating an example of a cell stack device according to the embodiment. 
         FIG.  2 B  is a cross-sectional view taken along the line X-X illustrated in  FIG.  2 A . 
         FIG.  2 C  is a top view illustrating an example of the cell stack device according to the embodiment. 
         FIG.  3 A  is a diagram illustrating an example of a power system including a cell stack device of a reference example. 
         FIG.  3 B  is a diagram illustrating an example of a magnitude relationship of potentials of respective parts in the cell stack device of the reference example. 
         FIG.  3 C  is a diagram for explaining a phenomenon that occurs in the cell stack device of the reference example. 
         FIG.  3 D  is a diagram for explaining a phenomenon that occurs in the cell stack device of the reference example. 
         FIG.  3 E  is a perspective view illustrating another example of a holding body. 
         FIG.  3 F  is a perspective view illustrating another example of a holding body. 
         FIG.  3 G  is an enlarged cross-sectional view of a bonding part between another example of a holding body and a cell (corresponding to  FIGS.  3 C and  3 D ). 
         FIG.  4 A  is a diagram illustrating an example of a power system including the cell stack device according to the embodiment. 
         FIG.  4 B  is a diagram illustrating a magnitude relationship of potentials of respective parts in the cell stack device according to the embodiment. 
         FIG.  5 A  is a diagram illustrating an example of a power system including a cell stack device according to a first modification of the embodiment. 
         FIG.  5 B  is a diagram illustrating a magnitude relationship of potentials of respective parts in the cell stack device according to the first modification of the embodiment. 
         FIG.  6    is an external appearance perspective view illustrating an example of a module according to the embodiment. 
         FIG.  7    is an exploded perspective view schematically illustrating an example of a module housing device according to the embodiment. 
         FIG.  8    is a cross-sectional view illustrating a cell stack device according to a second modification of the embodiment. 
         FIG.  9    is an enlarged cross-sectional view illustrating a structure of a cell according to the second modification of the embodiment. 
         FIG.  10    is a diagram illustrating an example of a power system including the cell stack device according to the second modification of the embodiment. 
         FIG.  11    is a diagram illustrating another example of a power system including the cell stack device according to the second modification of the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of a cell stack device, a module, and a module housing device disclosed in the present specification will be described with reference to the accompanying drawings. The disclosure is not limited by the following embodiments. 
     Furthermore, it is noted that the drawings are schematic and the dimensional relationship between elements, the proportions of elements, and the like may differ from realistic ones. Even between the drawings, there may be a case where portions having different dimensional relationships, proportions, and the like from one another are included. 
     Configuration of Cell 
     First, an example of a solid oxide fuel cell will be described as a cell constituting a cell stack device according to an embodiment with reference to  FIGS.  1 A to  1 C . 
       FIG.  1 A  is a cross-sectional view illustrating an example of a cell  1  according to an embodiment,  FIG.  1 B  is a side view illustrating an example of the cell  1  according to the embodiment when viewed from an air electrode  5  side, and  FIG.  1 C  is a side view illustrating an example of the cell  1  according to the embodiment when viewed from an interconnector  6  side.  FIGS.  1 A to  1 C  illustrate an enlarged part of each configuration of the cell  1 . 
     In the example illustrated in  FIGS.  1 A to  1 C , the cell  1  is of a hollow flat plate type and has an elongated plate shape. As illustrated in  FIG.  1 B , the shape of the entire cell  1  when viewed from the side is, for example, a rectangle having a side length of 5 cm to 50 cm in a length direction L and a length of 1 cm to 10 cm in a width direction W orthogonal to the length direction L. The total length (thickness direction T) of the cell  1  is 1 mm to 5 mm. 
     As illustrated in  FIG.  1 A , the cell  1  includes a support substrate  2  that is conductive, an element part, and the interconnector  6 . The support substrate  2  has a columnar shape having a pair of opposing first flat surface n 1  and second flat surface n 2 , and a pair of arc-shaped side surfaces m that connect the first flat surface n 1  and the second flat surface n 2 . 
     The element part is provided on the first flat surface n 1  of the support substrate  2 . The element part has a fuel electrode  3 , a solid electrolyte layer  4 , and an air electrode  5 . In the example illustrated in  FIG.  1 A , the interconnector  6  is provided on the second flat surface n 2  of the cell  1 . 
     As illustrated in  FIG.  1 B , the air electrode  5  does not extend to a lower end of the cell  1 . At the lower end of the cell  1 , only the solid electrolyte layer  4  is exposed on a surface of the first flat surface n 1 . As illustrated in  FIG.  1 C , the interconnector  6  may extend to the lower end of the cell  1 . At the lower end of the cell  1 , the interconnector  6  and the solid electrolyte layer  4  are exposed on the surface. As illustrated in  FIG.  1 A , the solid electrolyte layer  4  is exposed on surfaces of the pair of arc-shaped side surfaces m of the cell  1 . The interconnector  6  need not extend to the lower end of the cell  1 . 
     Hereinafter, respective constituent members constituting the cell  1  will be described. 
     The support substrate  2  is provided therein with gas flow paths  2   a  through which a gas flows.  FIG.  1 A  illustrates an example in which the support substrate  2  has six gas flow paths  2   a  extending along the length direction. The support substrate  2  has gas permeability and allows fuel gas to permeate to the fuel electrode  3 . The support substrate  2  illustrated in  FIG.  1 A  has conductivity. The support substrate  2  can collect electricity generated in the element part via the interconnector  6 . 
     The material of the support substrate  2  contains, for example, an iron group metal component and an inorganic oxide. For example, the iron group metal component may be Ni and/or NiO. For example, the inorganic oxide may be a specific rare earth element oxide. 
     As the material of the fuel electrode  3 , a generally known material may be used. The fuel electrode  3  can be formed from a porous conductive ceramic, for example, a ceramic containing a solid solution of a calcium oxide, a magnesium oxide, or a rare earth element oxide in ZrO 2  and Ni and/or NiO. As the rare earth element oxide, for example, Y 2 O 3  or the like is used. Hereinafter, a solid solution of a calcium oxide, a magnesium oxide, or a rare earth element oxide in ZrO 2  is referred to as stabilized zirconia. In the present disclosure, stabilized zirconia also includes partially stabilized zirconia. 
     The solid electrolyte layer  4  is an electrolyte and bridges ions between the fuel electrode  3  and the air electrode  5 . At the same time, the solid electrolyte layer  4  has a gas blocking property and makes it difficult for fuel gas and oxygen-containing gas to leak. 
     The material of the solid electrolyte layer  4  is, for example, a solid solution of 3 mol % to 15 mol % of a rare earth element oxide in ZrO 2 . As the rare earth element oxide, for example, Y 2 O 3  or the like is used. Another material may be used as the material of the solid electrolyte layer  4  as long as it has the above characteristics. 
     The material of the air electrode  5  is not particularly limited as long as it is generally used for an air electrode. The material of the air electrode  5  may be, for example, a conductive ceramic such as a so-called ABO 3  type perovskite type oxide. 
     The material of the air electrode  5  may be, for example, a composite oxide in which Sr and La coexist in the A site. Examples of such a composite oxide include La x Sr 1-x Co y Fe 1-y O 3 , La x Sr 1-x MnO 3 , La x Sr 1-x FeO 3 , La x Sr 1-x CoO 3 , and the like. Here, x is 0&lt;x&lt;1 and y is 0&lt;y&lt;1. 
     Furthermore, the air electrode  5  has gas permeability. The open porosity of the air electrode  5  may be 20% or more, and is particularly in the range of 30% to 50%. 
     As the material of the interconnector  6 , a lanthanum chromite-based perovskite type oxide (LaCrO 3 -based oxide), a lanthanum strontium titanium-based perovskite type oxide (LaSrTiO 3 -based oxide), or the like may be used. These materials have conductivity, and are neither reduced nor oxidized even when they come into contact with a fuel gas such as a hydrogen-containing gas, and an oxygen-containing gas such as air. 
     Furthermore, the interconnector  6  is dense and makes it difficult for the fuel gas flowing through the gas flow paths  2   a  formed in the support substrate  2  and the oxygen-containing gas flowing outside the support substrate  2  to leak. The interconnector  6  may have a relative density of 93% or more, particularly 95% or more. 
     Configuration of Cell Stack Device 
     Next, a cell stack device  10  according to the present embodiment using the aforementioned cell  1  will be described with reference to  FIGS.  2 A to  2 C .  FIG.  2 A  is a perspective view illustrating an example of the cell stack device  10  according to the embodiment,  FIG.  2 B  is a cross-sectional view taken along line X-X illustrated in  FIG.  2 A , and  FIG.  2 C  is a top view illustrating an example of the cell stack device  10  according to the embodiment. 
     As illustrated in  FIG.  2 A , the cell stack device  10  includes a cell stack  11  having a plurality of cells  1  arranged (stacked) in the thickness direction T (see  FIG.  1 A ) of the cells  1 , and a fixing member  12 . 
     The fixing member  12  has a fixing material  13  and a holding member  14 . The holding member  14  holds the cells  1 . The fixing material  13  fixes the cells  1  to the holding member  14 . Furthermore, the holding member  14  has a holding body  15  and a gas tank  16 . The holding body  15  and the gas tank  16 , which constitute the holding member  14 , are made of metal and have conductivity. 
     As illustrated in  FIG.  2 B , the holding body  15  has an insertion hole  15   a  into which the lower ends of the plurality of cells  1  are inserted. The lower ends of the plurality of cells  1  and the inner wall of the insertion hole  15   a  are bonded by the fixing material  13 . 
     The gas tank  16  has an opening for supplying a reaction gas to the plurality of cells  1  via the insertion hole  15   a  and a recessed groove  16   a  provided around the opening. An outer peripheral end of the holding body  15  is bonded to the gas tank  16  by a bonding material  21  filled in the recessed groove  16   a  of the gas tank  16 . 
     In the example illustrated in  FIG.  2 A , the fuel gas is stored in an internal space formed by the holding body  15  and the gas tank  16 , which constitute the holding member  14 . A gas circulation pipe  20  is connected to the gas tank  16 . The fuel gas is supplied to the gas tank  16  through the gas circulation pipe  20 , and is supplied from the gas tank  16  to the gas flow paths  2   a  (see  FIG.  1 A ) inside the cells  1 . The fuel gas supplied to the gas tank  16  is generated by a reformer  82  (see  FIG.  6   ) to be described below. 
     Hydrogen-rich fuel gas may be produced, for example, by steam reforming a raw material. The fuel gas produced by steam reforming contains steam. 
     The example illustrated in  FIG.  2 A  includes two rows of cell stacks  11 , two holding bodies  15 , and the gas tank  16 . Each of the two rows of cell stacks  11  has a plurality of cells  1 . Each of the cell stacks  11  is fixed to a corresponding one of the holding bodies  15 . The gas tank  6  has two through holes on the upper surface thereof. Each of the holding bodies  15  is disposed in a corresponding one of the through holes. The internal space is formed by one gas tank  6  and two holding bodies  15 . 
     The insertion hole  15   a  has, for example, an oval shape in the top view. The length of the insertion hole  15   a , for example, in the arrangement direction of the cells  1 , that is, the thickness direction T, is larger than a distance between two end current collection members  17  located at both ends of the cell stack  11 . The width of the insertion hole  15   a  is, for example, larger than the length of the cell  1  in the width direction W (see  FIG.  1 A ). 
     As illustrated in  FIG.  2 A , the fixing material  13  is filled in the bonding portion between the inner wall of the insertion hole  15   a  and the lower end of the cell  1  and is solidified. Consequently, the inner wall of the insertion hole  15   a  and the lower ends of the plurality of cells  1  are bonded and fixed, respectively, and the lower ends of the cells  1  are bonded and fixed to each other. The gas flow path  2   a  of each of the cells  1  communicates with the internal space of the holding member  14  at the lower end. 
     The fixing material  13  and the bonding material  21  have oxide ion conductivity. The fixing material  13  and the bonding material  21  can use a material having lower conductivity. As a specific material of the fixing material  13  and the bonding material  21 , amorphous glass or the like may be used, or particularly, crystallized glass or the like may be used. 
     As the crystallized glass, for example, any of SiO 2 —CaO-based, MgO—B 2 O 3 -based. La 2 O 3 —B 2 O 3 —MgO-based. La 2 O 3 —B 2 O 3 —ZnO-based, and SiO 2 —CaO—ZnO-based materials may be used, or, particularly, a SiO 2 —MgO-based material may be used. 
     As illustrated in  FIG.  2 B , a conductive member  18  for electrically connecting adjacent ones of the cells  1  in series is interposed between adjacent ones of the cells  1 . More specifically, the space between the adjacent ones of the cells  1  corresponds to the space between the fuel electrode  3  of one of the adjacent cells  1  and the air electrode  5  of the other one of the adjacent cells  1 . 
     As illustrated in  FIG.  2 B , the end current collection members  17  are connected to the outermost ones of the cells  1  in the arrangement direction of the plurality of cells  1 . The end current collection member  17  is connected to a conductive part  19  protruding outward from the cell stack  11 . The conductive part  19  has a function of collecting electricity generated by power generation of the cells  1  and sending the collected electricity to the outside.  FIG.  2 A  does not illustrate the end current collection members  17 . 
     As illustrated in  FIG.  2 C , in the cell stack device  10 , two cell stacks  11 A and  11 B are connected in series and function as one battery. Therefore, the conductive part  19  of the cell stack device  10  is divided into a positive electrode terminal  19 A, a negative electrode terminal  19 B, and a connection terminal  19 C. 
     The positive electrode terminal  19 A functions as a positive electrode when power generated by the cell stack  11  is output to the outside, and is electrically connected to the end current collection members  17  on a positive electrode side in the cell stack  11 A. The negative electrode terminal  19 B functions as a negative electrode when power generated by the cell stack  11  is output to the outside, and is electrically connected to the end current collection members  17  on a negative electrode side in the cell stack  11 B. 
     The connection terminal  19 C electrically connects the end current collection members  17  on the negative electrode side in the cell stack  1 I A and the end current collection members  17  on the positive electrode side in the cell stack  11 B. 
     Reference Example 
     A reference example illustrated in  FIGS.  3 A to  3 C  will be described.  FIG.  3 A  is a diagram illustrating an example of a power system  100  including the cell stack device  10  of the reference example, and  FIG.  3 B  is a diagram illustrating an example of a magnitude relationship of potentials of respective parts in the cell stack device  10  of the reference example. Furthermore,  FIGS.  3 C and  3 D  are diagrams for explaining a phenomenon occurring in the cell stack device  10  of the reference example. 
     As illustrated in  FIG.  3 A , the power system  100  connects the cell stack device  10  to a power conditioning subsystem (PCS)  101 , and supplies power generated by the cell stack device  10  to a power system  102  via the PCS  101 . 
     Specifically, the PCS  101  converts DC power generated by the cell stack device  10  into AC power, and supplies the AC power to the power system  102 . Therefore, both the positive electrode terminal  19 A and the negative electrode terminal  19 B of the cell stack device  10  are connected to the PCS  101 . 
     Furthermore, in the power system  100  illustrated in  FIG.  3 A , as illustrated in  FIG.  3 B , when the electromotive force of the cell stack device  10  is set to 2A (V), the potential of the positive electrode terminal  19 A is +A (V) and the potential of the negative electrode terminal  19 B is −A (V). The electromotive force of the cell stack device  10  is, in other words, the electromotive force of the cell stack  11 . 
     Furthermore, the holding member  14  made of metal and having conductivity is grounded in order to ensure stable operation of the cell stack device  10 . The holding member  14  includes the holding body  15  and the gas tank  16 . That is, the potential of the holding body  15  (holding member  14 ) is 0 (V). The potential of the holding body  15  may be a potential slightly deviated from the just intermediate potential between the potential of the positive electrode terminal  19 A and the potential of the negative electrode terminal  19 B. 
     Due to such a magnitude relation of the potentials, as illustrated in  FIG.  3 C , a potential difference occurs between the cell  1  in the vicinity of the positive electrode terminal  19 A having a potential of approximately +A (V) and the holding body  15  having a potential of 0 (V). 
     Due to such a potential difference, as illustrated in  FIG.  3 C , oxygen ions (O 2− ) in an oxide film formed on the surface of the holding body  15  are attracted to the cell  1  side, and metal ions (M + ) in the oxide film are attracted to the holding body  15  side. That is, a reduction reaction of the oxide film occurs in an interface between the fixing material  13  and the holding body  15 . 
     Consequently, this causes a loss of the oxide film on the surface of the holding body  15  in the interface with the fixing material  13 , and such a loss causes a gap C to be formed between the fixing material  13  and the holding body  15  as illustrated in  FIG.  3 D . The formation phenomenon of the gap C is likely to occur between the cell  1  in the vicinity of the positive electrode terminal  19 A and the holding body  15  between which there is a large potential difference, and the formation of such a gap C may reduce the durability of the cell stack device  10 . 
     The holding body  15  may be a flat plate-shaped holding body  15  as illustrated in  FIG.  3 E . In such a case, for example, an internal space is formed by bonding the gas tank  16  to the lower surface or side surface of the holding body  15  that has a flat plate shape. Furthermore, as illustrated in  FIG.  3 F , the holding body  15  may be a holding body  15  having a plurality of insertion holes  15   a . In such a case, the cells  1  may be inserted into the plurality of insertion holes  15   a  of the holding body  15  in a one-to-one manner, or a plurality of cells  1  may be inserted into each of the plurality of insertion holes  15   a  of the holding body  15 .  FIG.  3 G  is a cross-sectional view of a bonding portion between the holding body  15  that has a flat plate shape and the cell  1 . Furthermore, the holding body  15  may be integrally formed with the gas tank  16 . Even in such a holding body  15 , the gap C is formed between the fixing material  13  and the holding body  15 . 
     Embodiment 
     Subsequently, the cell stack device  10  according to the embodiment will be described with reference to  FIGS.  4 A and  4 B .  FIG.  4 A  is a diagram illustrating an example of the power system  100  including the cell stack device  10  according to the embodiment, and  FIG.  4 B  is a diagram illustrating a magnitude relationship of potentials of respective parts in the cell stack device  10  according to the embodiment. 
     As illustrated in  FIG.  4 A , in the power system  100  according to the embodiment, the positive electrode terminal  19 A of the cell stack device  10  and the PCS  101  are connected to a ground potential  31  via a noise reduction unit  32 . That is, in the cell stack device  10  according to the embodiment, the positive electrode terminal  19 A is grounded by being connected to the ground potential  31 . 
     Consequently, as illustrated in  FIG.  4 B , the potential of the positive electrode terminal  19 A can be set to 0 (V), which is the same as that of the holding body  15  (holding member  14 ). In such a case, the potential of the negative electrode terminal  19 B is −2A (V). 
     That is, in the embodiment, there is no potential difference between the cell  1  in the vicinity of the positive electrode terminal  19 A and the holding body  15  described in the above reference example, which makes it possible to prevent a reduction reaction from occurring in the interface between the fixing material  13  and the holding body  15 . 
     Consequently, according to the embodiment, it is possible to reduce the loss of the oxide film on the surface of the holding body  15  in the interface with the fixing material  13 . As a consequence, the gap C is not easily formed between the fixing material  13  and the holding body  15 . That is, according to the embodiment, it is possible to improve the durability of the cell stack device  10 . 
     Furthermore, in the embodiment, the noise reduction unit  32  may be provided between the positive electrode terminal  19 A and the ground potential  31 . In the noise reduction unit  32 , for example, a coil  32   a  and a resistor  32   b  are connected in series between the positive electrode terminal  19 A and the ground potential  31 , and a capacitor  32   c  is connected in parallel with the resistor  32   b.    
     In the embodiment, by providing the noise reduction unit  32  between the positive electrode terminal  19 A and the ground potential  31 , it is possible to reduce noise included in DC power supplied from the cell stack device  10 . Consequently, according to the embodiment, the PCS  101  can stably convert DC power into AC power. 
     The circuit configuration of the noise reduction unit  32  illustrated in  FIG.  4 A  is merely an example and other circuit configurations can also be adopted. 
     First Modification 
     Subsequently, the cell stack device  10  according to a first modification of the embodiment will be described with reference to  FIGS.  5 A and  5 B .  FIG.  5 A  is a diagram illustrating an example of the power system  100  including the cell stack device  10  according to the first modification of the embodiment, and  FIG.  5 B  is a diagram illustrating a magnitude relationship of potentials of respective parts in the cell stack device  10  according to the first modification of the embodiment. 
     The first modification is different from the embodiment in that a separate battery  33  is provided between the positive electrode terminal  19 A and the ground potential  31 . A positive electrode of the battery  33  is connected to the ground potential  31  via the noise reduction unit  32 . Furthermore, a negative electrode of the battery  33  is connected to the positive electrode terminal  19 A. 
     As illustrated in  FIG.  5 B , when the electromotive force of the battery  33  is B (V), the potential of the positive electrode terminal  19 A can be set to −B (V) lower than the potential 0 (V) of the holding body  15  (holding member  14 ). In such a case, the potential of the negative electrode terminal  19 B is −B−2A (V). 
     That is, in the first modification, since a potential difference opposite to the potential difference described in the above reference example can be generated, an oxidation reaction opposite to the reduction reaction can occur in the interface between the fixing material  13  and the holding body  15 . 
     Consequently, even though the oxide film on the surface of the holding body  15  in the interface with the fixing material  13  may grow due to the oxidation reaction, it is possible to reduce the loss of the oxide film. Therefore, according to the first modification, the gap C is not easily formed between the fixing material  13  and the holding body  15 , which makes it possible to improve the durability of the cell stack device  10 . 
     The battery  33  is an example of a negative voltage application unit that applies a negative voltage to the positive electrode terminal  19 A. That is, such a negative voltage application unit is not limited to the battery  33 , and may have any configuration as long as it can apply a negative voltage to the positive electrode terminal  19 A with respect to the ground potential  31 . 
     Furthermore, in the first modification, the noise reduction unit  32  may be provided between the positive electrode terminal  19 A and the ground potential  31  as in the embodiment. With this, it is possible to reduce noise included in DC power supplied from the cell stack device  10 , and thus the PCS  101  can stably convert DC power into AC power. 
     Module 
     Next, a module  80  according to the embodiment of the present disclosure using the cell stack device  10  described above will be described with reference to  FIG.  6   .  FIG.  6    is an external appearance perspective view illustrating the module  80  according to the embodiment, and illustrates a state in which a front surface and a rear surface, which are a part of a housing container  81 , are taken out and the cell stack device  10  of a fuel cell housed inside is taken out to the rear. 
     As illustrated in  FIG.  6   , the module  80  includes the housing container  81  and the cell stack device  10  housed in the housing container  81 . The reformer  82  is disposed above the cell stack device  10 . 
     The reformer  82  generates fuel gas by reforming raw fuel such as natural gas and kerosene, and supplies the generated fuel gas to the cell  1 . The raw fuel is supplied to the reformer  82  through a raw fuel supply pipe  83 . The reformer  82  may include a vaporizing part  82   a  for vaporizing water and a reforming part  82   b . The reforming part  82   b  includes a reforming catalyst (not illustrated) and reforms the raw fuel into the fuel gas. The reformer  82  such as that described above can perform steam reforming which is a highly efficient reforming reaction. 
     The fuel gas generated by the reformer  82  is supplied to the gas flow paths  2   a  (see  FIG.  1 A ) of the cell  1  through the gas circulation pipe  20 , the gas tank  16 , and the fixing member  12 . 
     Furthermore, in the module  80  having the configuration described above, the temperature in the module  80  during normal power generation is 500° C. to 1.000° C. due to the combustion of gas and power generation of the cells  1 . 
     In the module  80  such as that described above, by providing the cell stack device  10  having high durability, which is less likely to form the gap C as described above, the module  80  having high durability can be acquired. 
     Module Housing Device 
       FIG.  7    is an exploded perspective view illustrating an example of a module housing device  90  according to the embodiment. The module housing device  90  according to the embodiment includes an outer case, the module  80  illustrated in  FIG.  6   , and an auxiliary device (not illustrated). The auxiliary device operates the module  80 . The module  80  and the auxiliary device are housed in the outer case.  FIG.  7    does not illustrate a part of the configuration. 
     The outer case of the module housing device  90  illustrated in  FIG.  7    has columns  91  and an outer plate  92 . A partition plate  93  vertically divides the inside of the outer case. The space above the partition plate  93  in the outer case is a module housing chamber  94  for housing the module  80 , and the space below the partition plate  93  in the outer case is an auxiliary device housing chamber  95  for housing the auxiliary device that operates the module  80 .  FIG.  7    does not illustrate the auxiliary device that is housed in the auxiliary device housing chamber  95 . 
     Furthermore, the partition plate  93  has an air circulation port  96  for causing the air in the auxiliary device housing chamber  95  to flow toward the module housing chamber  94 . The outer plate  92  constituting the module housing chamber  94  has an exhaust port  97  for exhausting the air in the module housing chamber  94 . 
     In the module housing device  90  such as that described above, by providing the module housing chamber  94  with the module  80  having high durability as described above, the module housing device  90  having high durability can be acquired. 
     So far, although the present disclosure has been described in detail, the present disclosure is not limited to the aforementioned embodiment, and various changes, improvements, and the like can be made without departing from the gist of the present disclosure. 
     The aforementioned embodiment has exemplified a vertical stripe type cell stack device in which so-called “vertical stripe type” cells are stacked, the cells being provided with only one power generation element part including a fuel electrode, a solid electrolyte layer, and an air electrode on the surface of a support substrate. The present disclosure can be applied to a horizontal stripe type cell stack device in which so-called “horizontal stripe type” cells are stacked, the cells including power generation element parts provided at a plurality of locations separate from each other on the surface of a support substrate, adjacent power generation element parts being electrically connected to each other. 
     Furthermore, the aforementioned embodiment has exemplified the case where a hollow flat plate type support substrate is used. The present disclosure can also be applied to a cell stack device using a cylindrical support substrate. Furthermore, the present disclosure can also be applied to a flat plate type cell stack device in which a so-called “flat plate type” cell is stacked in the thickness direction. 
     Furthermore, the aforementioned embodiment gives an example in which a fuel electrode is provided on a support substrate and an air electrode is disposed on the surface of a cell. The present disclosure can also be applied to an opposite arrangement, that is, a cell stack device in which an air electrode is provided on a support substrate and a fuel electrode is disposed on the surface of a cell. 
     Furthermore, in the aforementioned embodiment, a fuel cell, a fuel cell stack device, a fuel cell module, and a fuel cell device are illustrated as examples of the “cell”, the “cell stack device”, the “module”, and the “module housing device”; however, in other examples, an electrolytic cell, an electrolytic cell stack device, an electrolytic module, and an electrolytic device may be the “cell”, the “cell stack device”, the “module”, and the “module housing device”, respectively. 
       FIG.  8    is a cross-sectional view illustrating a cell stack device  200  according to a second modification of the embodiment. As illustrated in  FIG.  8   , the cell stack device  200  according to the second modification includes a cell stack  210  in which a plurality of plate-shaped cells  201  are stacked. Furthermore, in the cell stack device  200  according to the second modification, the cell stack  210  is interposed between a positive-electrode-side end current collection member  220  and a negative-electrode-side end current collection member  221 . 
     The cell  201  of the second modification has an element part  202 , a separator  203 , an air-electrode-side frame  204 , a fuel-electrode-side frame  205 , an air-electrode-side current collector  206 , a fuel-electrode-side current collector  207 , and an interconnector  208 . 
       FIG.  9    is an enlarged cross-sectional view illustrating a structure of the cell  201  according to the second modification of the embodiment. As illustrated in  FIG.  9   , the element part  202  of the second modification has an air electrode  202   a , a solid electrolyte layer  202   b  located on a lower surface of the air electrode  202   a , and a fuel electrode  202   c  located on a lower surface of the solid electrolyte layer  202   b . The air electrode  202   a  is located on a side of the element part  202  in contact with the air-electrode-side current collector  206 , and the fuel electrode  202   c  is located on a side of the element part  202  in contact with the fuel-electrode-side current collector  207 . 
       FIG.  8    will be described again. The separator  203  is a frame-shaped member having a through hole penetrating the separator  203  in the vertical direction near the center thereof. The material of the separator  203  may be, for example, a metal. A peripheral portion of the through hole in the separator  203  faces a peripheral edge portion of the surface of the solid electrolyte layer  202   b  (see  FIG.  9   ) on a side of the air electrode  202   a  (see  FIG.  9   ). The separator  203  is bonded to the solid electrolyte layer  202   b  at the facing portion. 
     The separator  203  divides the cell  201  into an air chamber  264  facing the air electrode  202   a  and a fuel chamber  265  facing the fuel electrode  202   c  (see  FIG.  9   ), which makes it difficult for gas to leak from one electrode side to the other electrode side at the peripheral edge portion of the element part  202 . 
     The air-electrode-side frame  204  is a frame-shaped member having a through hole penetrating the air-electrode-side frame  204  in the vertical direction near the center thereof. The material of the air-electrode-side frame  204  may be, for example, an insulator such as mica. The air-electrode-side frame  204  comes into contact with a peripheral edge portion of a surface on a side of the separator  203 , which is opposite to a side of the separator  203 , which faces the solid electrolyte layer  202   b , and a peripheral edge portion of a surface on a side of the interconnector  208 , which faces the air electrode  202   a.    
     Since the cell  201  located at the uppermost position in the cell stack  210  does not have the upper interconnector  208 , the air-electrode-side frame  204  in the cell  201  comes into contact with the end current collection member  220 . 
     The through hole of the air-electrode-side frame  204  constitutes the air chamber  264  facing the air electrode  202   a . Furthermore, the air-electrode-side frame  204  electrically insulates adjacent interconnectors  208  from each other. 
     The fuel-electrode-side frame  205  is a frame-shaped member having a through hole penetrating the fuel-electrode-side frame  205  in the vertical direction near the center thereof. The material of the fuel-electrode-side frame  205  may be, for example, metal. The through hole of the fuel-electrode-side frame  205  constitutes the fuel chamber  265  facing the fuel electrode  202   c.    
     The fuel-electrode-side frame  205  comes into contact with a peripheral edge portion of a surface on a side of the separator  203 , which faces the solid electrolyte layer  202   b , and a peripheral edge portion of a surface on a side of the interconnector  208 , which faces the fuel electrode  202   c.    
     The air-electrode-side current collector  206  is disposed in the air chamber  264 . The air-electrode-side current collector  206  is composed of a plurality of columnar conductive members arranged at predetermined intervals. The material of the air-electrode-side current collector  206  may be, for example, stainless steel. 
     The air-electrode-side current collector  206  comes into contact with a surface on a side of the air-electrode  202   a , which is opposite to a side of the air electrode  202   a , which faces the solid electrolyte layer  202   b , and a surface on a side of the interconnector  208 , which faces the air electrode  202   a . Since the cell  201  located at the uppermost position in the cell stack  210  does not have the upper interconnector  208 , the air-electrode-side current collector  206  in the cell  201  comes into contact with the end current collection member  220 . 
     That is, the air-electrode-side current collector  206  electrically connects between the air electrode  202   a  and the interconnector  208 , or between the air electrode  202   a  and the end current collection member  220 . The air-electrode-side current collector  206  and the interconnector  208  may be formed as an integrated member. 
     The fuel-electrode-side current collector  207  is disposed in the fuel chamber  265 . The fuel-electrode-side current collector  207  is composed of a plurality of columnar conductive members arranged at predetermined intervals. The material of the fuel-electrode-side current collector  207  may be, for example, stainless steel. As illustrated in  FIG.  9   , the fuel-electrode-side current collector  207  may have an electrode facing part  207   a , an interconnector facing part  207   b , a connection part  207   c , and a spacer  207   d , for example. 
     The electrode facing part  207   a  faces the fuel electrode  202   c  of the element part  202 . The interconnector facing part  207   b  faces the interconnector  208  (or the end current collection member  221 ). The connection part  207   c  connects the electrode facing part  207   a  and the interconnector facing part  207   b . The electrode facing part  207   a , the interconnector facing part  207   b , and the connection part  207   c  may all be made of metal, or may be integrally formed with one another, for example. 
     The spacer  207   d  is located between the electrode facing part  207   a  and the interconnector facing part  207   b . The material of the spacer  207   d  may be, for example, mica. By disposing the spacer  207   d  in the fuel-electrode-side current collector  207 , the fuel-electrode-side current collector  207  can easily follow the deformation of the cell  201  due to a temperature cycle, a pressure fluctuation of the reaction gas, and the like. 
     Consequently, the cell  201  having the fuel-electrode-side current collector  207  as illustrated in  FIG.  9    can maintain a good electrical connection between the fuel electrode  202   c  and the interconnector  208  (or the end current collection member  221 ) via the fuel-electrode-side current collector  207 . 
       FIG.  8    will be described again. The interconnector  208  is a flat plate-shaped conductive member. The material of the interconnector  208  may be, for example, stainless steel. The interconnector  208  ensures electrical connection between adjacent ones of the cells  201 . Furthermore, the interconnector  208  makes it difficult for the reaction gas to be mixed between adjacent ones of the cells  201 , that is, makes it difficult for the gas to leak from one cell  201  side to the other cell  201  side. In the second modification, adjacent ones of the cells  201  share one interconnector  208 . 
     The cell  201  in contact with the end current collection member  220  or the end current collection member  221  has no interconnector  208  because the end current collection member  220  or the end current collection member  221  has the function of the interconnector  208 . 
     A positive electrode terminal  222  functions as a positive electrode when power generated by the cell stack  210  is output to the outside, and is electrically connected to the positive-electrode-side end current collection member  220  in the cell stack  210 . A negative electrode terminal  223  functions as a negative electrode when power generated by the cell stack  210  is output to the outside, and is electrically connected to the negative-electrode-side end current collection member  221  in the cell stack  210 . 
     The cell stack device  200  has communication holes  261  and  262  through which the end current collection member  220 , the cell stack  210 , and the end current collection member  221  communicate with one another, and metal bolts  231  are inserted into the communication holes  261  and  262 , respectively. 
     Furthermore, metal nuts  232  are fitted to the bolts  231  exposed to the outside from the end current collection member  220  and the end current collection member  221 , so that the plurality of cells  201  are held between the end current collection member  220  and the end current collection member  221 . That is, in the second modification, the bolts  231  and the nuts  232  form holding members  230  that hold the plurality of cells  201 . 
     A fixing material  240  is located between the end current collection member  220  and the holding member  230  and between the end current collection member  221  and the holding member  230 . The fixing material  240  of the second modification may be made of the same material as that of the fixing material  13  of the embodiment, for example. The fixing material  240  of the second modification is not limited to the same material as that of the fixing material  13  of the embodiment, and may be made of an insulating sheet, for example. 
     Either the end current collection member  220  or the end current collection member  221  may be formed with a screw hole. For example, when the end current collection member  220  is formed with a screw hole, the bolt  231  may be screwed into the screw hole. The inner wall of the screw hole and the bolt  231  may be in direct contact with each other, or the fixing material  240  may be located between the inner wall of the screw hole and the bolt  231 . In such a case, the bolt  231  is exposed to the outside from the end current collection member  221  and the metal nut  232  is fitted to the exposed bolt  231 . The fixing material  240  is located between the end current collection member  221  and the holding member  230 . 
     Instead of the bolt  231  and the nut  232 , a bolt having a flange portion may be used as the holding member  230 . The bolt having a flange portion is screwed into the screw hole of the end current collection member  220 , and the fixing material  240  is located between the flange portion of the holding member  230  and the end current collection member  221 . The screw hole may go through the end current collection member  220 , or may have a bottom portion without going through the end current collection member  220 . 
       FIG.  10    is a diagram illustrating an example of a power system  100 A including the cell stack device  200  according to the second modification of the embodiment. As illustrated in  FIG.  10   , in the power system  100 A according to the second modification, the positive electrode terminal  222  of the cell stack device  200  and the PCS  101  are connected to the ground potential  31  via the noise reduction unit  32 . 
     That is, in the cell stack device  200  according to the second modification, the positive electrode terminal  222  is grounded by being connected to the ground potential  31 . 
     With this, as illustrated in  FIG.  4 B , the potential of the positive electrode terminal  222  can be set to 0 (V), which is the same as that of the holding member  230 . The positive electrode terminal  222  and the end current collection member  220  may be electrically connected to the holding member  230 . In such a case, the potential of the negative electrode terminal  223  is −2A (v). 
     Consequently, in the second modification, there is no potential difference between the positive electrode terminal  222  and the holding member  230  as in the embodiment, which makes it possible to prevent a reduction reaction from occurring in the interface between the fixing material  240  and the holding member  230 . 
     Consequently, according to the second modification, it is possible to reduce the loss of the oxide film on the surface of the holding member  230  in the interface with the fixing material  240 . As a consequence, a gap is not easily formed between the fixing material  240  and the holding member  230 . That is, according to the second modification, it is possible to improve the durability of the cell stack device  200 . 
     The power system  100 A including the cell stack device  200  according to the second modification is not limited to the example in  FIG.  10   .  FIG.  11    is a diagram illustrating another example of the power system  100 A including the cell stack device  200  according to the second modification of the embodiment. 
     The example in  FIG.  11    is different from that in  FIG.  10    in that a separate battery  33  is provided between the positive electrode terminal  222  and the ground potential  31 . A positive electrode of the battery  33  is connected to the ground potential  31  via the noise reduction unit  32 , and a negative electrode of the battery  33  is connected to the positive electrode terminal  222 . 
     Consequently, even in the second modification, as in the first modification described above, an oxidation reaction opposite to a reduction reaction can occur in the interface between the fixing material  240  and the holding member  230 . That is, in the example in  FIG.  11   , even though the oxide film on the surface of the holding member  230  in the interface with the fixing material  240  grows due to the oxidation reaction, it is possible to reduce the loss of the oxide film. 
     Consequently, according to the example in  FIG.  11   , a gap is not easily formed between the fixing material  240  and the holding member  230 , which makes it possible to improve the durability of the cell stack device  200 . 
     Furthermore, in the examples in  FIG.  10    and  FIG.  11   , the noise reduction unit  32  may be provided between the positive electrode terminal  222  and the ground potential  31  as in the embodiment. Consequently, it is possible to reduce noise included in DC power supplied from the cell stack device  200 , and thus the PCS  101  can stably convert DC power into AC power. 
     The remaining parts in the cell stack device  200  illustrated in  FIG.  8    will be described. The communication hole  261  and the communication hole  262  of the holding member  230  may be, for example, simple bolt holes through which bolts for fixing the cell  201  are inserted. The communication hole  261  may function as a gas supply manifold that supplies the reaction gas or the oxygen-containing gas to the plurality of cells  201 . The communication hole  262  may function as a gas discharge manifold that discharges the reaction gas or the oxygen-containing gas from the plurality of cells  201 . Hereinafter, a case where the communication hole  261  functions as an oxygen supply manifold that supplies oxygen-containing gas to the plurality of cells  201  and the communication hole  262  functions as an oxygen discharge manifold that discharges the oxygen-containing gas from the plurality of cells  201  as illustrated in  FIG.  8    will be described. 
     The oxygen-containing gas flowing through the oxygen supply manifold is supplied from the communication hole  261  to the air chamber  264  via a flow path (not illustrated) formed in the air-electrode-side frame  204 . Furthermore, the oxygen-containing gas discharged from the air chamber  264  flows into the communication hole  262  via a flow path (not illustrated) formed in the air-electrode-side frame  204 . 
     A gas passage member  250  is located at an inlet of the communication hole  261 . The gas passage member  250  has a body  251  and a branch part  252 , and is interposed between the end current collection member  221  and the nut  232 . 
     A gas passage member  270  is located at an outlet of the communication hole  262 . The gas passage member  270  has a body  271  and a branch part  272 , and is interposed between the end current collection member  221  and the nut  232 . 
     Although not illustrated in  FIG.  8   , the cell stack device  200  may have communication holes different from the communication hole  261  that supplies the oxygen-containing gas to the plurality of cells  201  and the communication hole  262  that discharges the oxygen-containing gas from the plurality of cells  201 . The cell stack device  200  may have, for example, a communication hole that functions as a fuel supply manifold that supplies fuel gas to the plurality of cells  201  or a fuel discharge manifold that discharges the fuel gas from the plurality of cells  201 . Furthermore, the cell stack device  200  may have communication holes that do not have the functions of supplying and discharging gas. 
     Moreover, the cell stack device  200  may have a communication hole through which the bolt  231  is not inserted, in addition to a communication hole through which the bolt  231  is inserted. The communication hole through which the bolt  231  is not inserted may function as a gas supply manifold or a gas discharge manifold. 
     Furthermore, in the aforementioned embodiment, the example in which the cell stacks  11 A and  11 B in the cell stack device  10  are connected in series has been described; however, the cell stacks  11 A and  11 B may be connected in parallel to form one battery. 
     Furthermore, in the aforementioned embodiment, the example in which the holding member  14  is grounded has been described; however, the holding member  14  does not necessarily have to be grounded. Even in such a case, by setting the potential of the positive electrode terminal  19 A to be not more than that of the holding member  14 , the gap C is not easily formed between the fixing material  13  and the holding body  15 , which makes it possible to improve the durability of the cell stack device  10 . 
     As described above, the cell stack device  10  ( 200 ) according to the embodiment includes the cell stack  11  ( 210 ), the holding member  14  ( 230 ), and the positive electrode terminal  19 A ( 222 ). The cell stack  11  ( 210 ) is constructed by stacking the plurality of cells  1  ( 201 ). The holding member  14  ( 230 ) holds the cells  1  ( 201 ). The positive electrode terminal  19 A ( 222 ) functions as a positive electrode when power generated by the cell stack  11  ( 210 ) is output to the outside. Furthermore, the potential of the positive electrode terminal  19 A ( 222 ) is not more than that of the holding member  14  ( 230 ). With this, it is possible to improve the durability of the cell stack device  10  ( 200 ). 
     Furthermore, in the cell stack device  10  ( 200 ) according to the embodiment, the positive electrode terminal  19 A ( 222 ) and the holding member  14  ( 230 ) have the same potential. With this, it is possible to improve the durability of the cell stack device  10  ( 200 ). 
     Furthermore, in the cell stack device  10  ( 200 ) according to the embodiment, the potential of the positive electrode terminal  19 A ( 222 ) is lower than that of the holding member  14  ( 230 ). With this, it is possible to improve the durability of the cell stack device  10  ( 200 ). 
     Furthermore, in the cell stack device  10  ( 200 ) according to the embodiment, the positive electrode terminal  19 A ( 222 ) is connected to the ground potential  31 . In addition, in the cell stack device  10  ( 200 ) according to the embodiment, the noise reduction unit  32  that reduces noise is located between the positive electrode terminal  19 A ( 222 ) and the ground potential  31 . With this, the PCS  101  can stably convert DC power into AC power. 
     Furthermore, the module  80  according to the embodiment is constructed by housing the cell stack device  10  ( 200 ) described above in the housing container  81 . With this, it is possible to acquire a module  80  having high durability. 
     Furthermore, the module housing device  90  according to the embodiment is constructed by housing, in an outer case, the module  80  described above and an auxiliary device for operating the module  80 . With this, it is possible to acquire a module housing device  90  having high durability. 
     Noted that the embodiment disclosed herein is exemplary in all respects and not restrictive. Indeed, the aforementioned embodiment can be embodied in a variety of forms. Furthermore, the aforementioned embodiment may be omitted, replaced, or changed in various forms without departing from the scope of the appended claims and the purpose thereof.