JPH053045A - Flat plate solid electrolyte type fuel cell - Google Patents

Abstract

PURPOSE:To form a module having less temperature gradient and voltage gradient by supplying a fuel discharged from a single cell unit or a cell stack to an adjacent unit or stack. CONSTITUTION:A lanthanum chromite separator films A are stacked on both surfaces of a single cell C such that an anode film being stacked on one surface of a solid electrolyte film, a cathode film on the other surface and distributers B and D are provided between the film A and the cell C so as to form a single cell unit. A plurality of the units are combined so as to form a cell stack. Discharged fuels from the unit or the stack are sequentially supplied to an adjacent unit or stack. In such a way, by turning a gas passage up in the stack, the gas concentration gradient, i.e., calorific value, between neighboring units is completed so that a module, the temperature gradient and the voltage gradient per unit area of which being small, can be formed with easy mass production.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat plate solid oxide fuel cell.

2. Description of the Related Art Solid oxide fuel cells are considered to be advanced fuel cells of the first generation phosphoric acid fuel cells and the second generation molten carbonate fuel cells, and are regarded as third generation fuel cells. ing. In this solid oxide fuel cell,
The flat plate solid oxide fuel cell is a more advanced fuel cell because it has higher power generation efficiency and higher output density than the cylindrical solid oxide fuel cell. The flat plate solid oxide fuel cell has a configuration similar to that of the phosphoric acid fuel cell or the molten carbonate fuel cell in its form. That is, a single cell having a positive electrode film / electrolyte film / negative electrode film structure in which a positive electrode film and a negative electrode film are laminated on both surfaces of a flat plate-like electrolyte film and a separator (also called an interconnector or a bipolar plate) are alternately laminated. Configured. Between the separator and the unit cells, a distributor for sandwiching a fuel gas and air and a distributor electrically connecting the unit cells are sandwiched. A plate with a rib or a corrugated plate is often used for this distributor in order to rationally distribute the gas, and a porous material is used for the electrode portion or the joint portion with the electrode so that the gas is well distributed. Industrially, zirconia is used as the electrolyte membrane, lanthanum chromite or an alloy is used as the separator membrane, lanthanum manganite or lanthanum cobaltite as the positive electrode, and nickel-zirconia cermet, nickel-as the negative electrode.
Ceria cermet or the like is used. By the way, there are some technical difficulties in the flat plate solid oxide fuel cell. One is that it is difficult to manufacture an airtight and thin flat plate of an electrolyte membrane or a lanthanum chromite separator membrane having a sufficiently large area. For this reason, forming a thin film on the support has been studied, but since the electrolyte membrane and the separator membrane are made of ceramics, the size industrially possible is the phosphoric acid type in consideration of strength and good product ratio. Alternatively, it is expected to be much smaller than the molten carbonate fuel cell. The second of the technical difficulties is when the electrolyte membrane with a small area is laminated,
In a solid oxide fuel cell, a very large temperature gradient is generated per unit area, and correspondingly, thermal stress is generated, which increases the possibility of destroying the ceramic film. In addition, the gradient of the voltage per unit area becomes large, which may cause a decrease in power generation efficiency. Next, this will be specifically described. Generally, there is one dilemma in fuel cells.
That is, it is necessary to increase the fuel consumption rate in order to increase the power generation efficiency with respect to the input fuel, and normally 70 to 85% of the fuel is consumed and the remainder is waste gas. However, the output voltage of the fuel cell is governed by the gas partial pressure ratio between the positive and negative electrodes. In other words, if the fuel consumption advances and the combustion residual gas, steam, and carbon dioxide partial pressure on the fuel side increase, the voltage decreases, and if the residual gas on the air side and nitrogen increase, the voltage decreases. This causes an increase in the internal resistance of the fuel cell and a gradient in the temperature inside the cell. Because the partial pressure of fuel gas and oxygen at the inlet is high and the partial pressure at the outlet is low, the voltage at the inlet is high on the unit cell and low at the outlet, and should flow in the direction perpendicular to the unit cell surface. This is because the electric current also flows in the single cell plane direction. Further, when the voltage at the inlet is high and the voltage at the outlet is low, the amount of power generation at the inlet is large and the amount of heat generated is large, so that a large temperature gradient is formed. Although these problems exist in general fuel cells, they become serious problems especially in flat plate solid oxide fuel cells. Because the unit cell area is small, not only the potential gradient per unit length becomes large and the power generation efficiency decreases, but also the temperature gradient due to heat generation becomes large, the thermal stress increases, and there is a possibility that the cell warps and eventually breaks. Because there is. By the way, the first major cause of the generation of the temperature gradient in the battery is the gas concentration difference between the inlet and the outlet. The second cause is the size of a single cell, and the difference in concentration per unit length is large. Thirdly, the constituent material of the solid oxide fuel cell is composed of ceramics having relatively low thermal conductivity, and the removal of heat depends on the heat transfer by gas. Therefore, one solution is to reduce the gas concentration gradient per unit area of the single cell and increase the gas flow rate per unit area. However, this is a kind of dilemma, and in a fuel cell of a normal design, there is no difference in concentration between the inlet and the outlet, which means that the fuel consumption rate is reduced, and the power generation efficiency is reduced. Will be invited.

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional flat plate solid oxide fuel cell and minimizes the temperature gradient and voltage in a single cell without lowering the fuel consumption rate. It is an object of the present invention to provide a flat plate solid oxide fuel cell which is made uniform and reduces irreversible loss associated with power generation and has improved power generation efficiency and output density.

A plate type solid oxide fuel cell of the present invention for achieving the above object (hereinafter, may be abbreviated as a fuel cell) has a positive electrode film on one surface of a solid electrolyte film. A separator film is laminated on each of the positive electrode film side and the negative electrode film side of a single cell having a negative electrode film laminated on the other surface, and a distributor is provided between the positive electrode film and the separator film and between the negative electrode film and the separator film. Characterized in that a plurality of single cell units each provided with are assembled to form a cell stack, and the fuel discharged from the single cell or the cell stack is supplied to the adjacent single cell or cell stack. Is. That is, the fuel cell of the present invention, as described in detail below, makes the gas flow paths in the cell stack folded back to make the gas concentration gradient between adjacent single cells, that is, the calorific value complementary, and the flow path. Is increased, that is, by adopting the long flow path method, the gas flow rate per unit area is increased, the heat transfer amount is increased, and heat is effectively removed. Alternatively, the cell stack is divided into multiple blocks, the fuel consumption rate in each block is reduced, and waste gas containing a large amount of remaining fuel is supplied to the next block to reduce the difference in gas concentration between the inlet and outlet. It can also be achieved by doing. This method is effective not only for fuel but also for air, but normally, air can be supplied several times as much as fuel, and it is performed, and therefore the consumption rate can be reduced. Therefore, the effect is not as great as that for fuel, but it is enough for fuel. Here, the cell stack means a separator (A) and a distributor.
(B), single cell (C) and distributor (B)
It is an assembly obtained by assembling a plurality of single cell units each of which is laminated in the order of A / B / C / B. Since the single cell unit is a flat plate type, the cell stack has a shape in which the flat plate surfaces of other single cell units are sequentially stacked on the flat plate surface of the single cell unit (hereinafter referred to as a horizontal stack type cell stack) and the cell stack. Is divided into a plurality of cell blocks, and a plurality of these cell blocks are sequentially stacked with a single cell unit standing (hereinafter referred to as a vertically stacked cell stack). First, the principle of the present invention will be described with reference to the horizontally stacked cell stack illustrated in FIG. Now, assume a cell stack in which rectangular single cells on sides a and b are stacked in n layers. Single cells are stacked in order of T1, T2, ..., Tn
And number. It is assumed that the amount of fuel or air supplied is nQ. Normally this gas is on the inlet side (x) of the laminated cell
, Tn are uniformly supplied to the unit cells T1, T2, ..., Tn, and discharged from the outlet side (y). Now, the gas of nQ is supplied to T1, the waste gas of T1 is supplied to T2, and similarly, it will be supplied to the next single cell one after another. In this case, the final gas consumption rate is set to 80%. Assuming this, the gas flow rate per unit area is nQ / ab,
The gas concentration gradient is 0.80 Q / nb in the case of unidirectional flow. That is, it is possible to increase the gas flow rate per unit area to make the heat removal by the gas flow more effective, to equalize the gas concentration gradient per unit area, and to equalize the voltage and the heat generation amount. The same effect can be obtained not by using a single cell but by using a stack in which cells are stacked. On the other hand, when the gas flow path is not lengthened, as shown in FIG. 2, the gas is supplied from the inlet side (x) of the laminated cell to the single cells T1, T2, ...
, Is evenly supplied to Tn and discharged from the outlet side (y). If the gas consumption rate is set to 80%, the fuel gas concentration at the inlet is 100% and the fuel gas concentration at the outlet is 20%.
%, Combustion waste gas concentration becomes 80%. Therefore, the gas flow rate per unit cell area is Q / ab, and the gas concentration gradient is
It becomes 0.80 Q / b. Now, the gas introduction system to the cells and stacks of the fuel cell is roughly divided into so-called external gas manifold and internal gas manifold, and a flat plate solid oxide fuel cell having a gas distribution system as shown in FIG. 1 is realized. It is clear that both internal and external methods are possible to achieve this. In addition to the method of folding back for each single cell as shown in FIG. 1, T1, T2, ..., Tn of FIG.
Can be performed not only as a single cell but also as a cell stack. Furthermore, the present inventors have found that the vertically stacked stacking type, which was impossible with the conventional fuel cell, is possible with the flat plate type solid oxide fuel cell, and the features of the present invention and the solid oxide type fuel cell. We considered a stack format that makes use of the, and manufactured it in the field. That is, in the conventional phosphoric acid type and molten carbonate type, since the electrolyte is a liquid, the cell can be installed only horizontally in order to prevent electrolyte leakage and deviation.
However, in a solid oxide fuel cell, the electrolyte is solid, and there is no problem even if it is placed vertically. The vertical arrangement rather has the advantage of reducing the load on the lower cell when a large number of cells are stacked. More specifically, when a cell stack in which T1, T2, ..., Tn in FIG. 1 are blocked as shown in FIG. 3 is used, the gas outlet (Y
The blocks may be arranged side by side so that the entrance of T2 comes to the side), and the whole connected in this way may stand vertically. Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE FIG. 4 is a schematic view of the manufactured cell stack. FIG. 5 is a schematic diagram thereof. In FIG. 4, A is a lanthanum chromite separator doped with calcium (hereinafter abbreviated as LCC), and B is lanthanum manganite doped with strontium in yttria-stabilized zirconia (hereinafter abbreviated as YSZ) and LCC.
(Hereinafter abbreviated as LSM) is a positive electrode side distributor which is impregnated and overcoated. C is a single cell composed of a positive electrode film / electrolyte film / negative electrode film. The positive electrode was LSM, the negative electrode was nickel zirconia cermet (hereinafter abbreviated as NY), and the electrolyte was YSZ. D is NY for YSZ and LCC foam
Is a distributor that is impregnated and overcoated. These constituent materials were manufactured as follows. First, as a separator, LCC powder was mixed with a binder polyvinyl butyral, a plasticizer dibutyl phthalate, a dispersant fish oil, a defoaming agent Triton X, a solvent isopropanol and toluene to form a slurry, and the slurry was formed into a film by a doctor blade method.
Next, the same slurry was impregnated into a polyurethane foam foam film to form a foam film. This green film is a foam film /
Co-fired with doctor blade membrane / foam membrane. As the electrolyte membrane, a doctor blade membrane and a foam membrane were formed from YSZ powder in the same manner as the separator, and the doctor blade membrane / foam membrane was laminated and fired. On one side of the separator composite membrane thus prepared, the foam membrane was impregnated and top-coated with NY slurry,
NY slurry was applied as a negative electrode to the side of the electrolyte membrane where the foam film was not attached. The NY-impregnated foam film and the NY electrode surface were put together, and a polyurethane foam film was impregnated with NY on the mating surface to form a separator / single cell composite film, and the composite film was laminated and fired. That is, the structure is LCC foam film / LCC separator film / NY-LC.
The C foam membrane / NY foam membrane / NY electrode / YSZ electrolyte membrane / YSZ foam membrane / LCC foam membrane / LCC separator membrane / NY-LCC foam membrane are repeatedly laminated. Since the fired cell stack is not yet coated with the positive electrode material LSM on the positive electrode side, LSM slurry is
The combined portion of the CC and YSZ foam film was impregnated to give a positive electrode function and conductivity as a distributor.
Further, in FIG. 4, a portion corresponding to a corner of the stack is preferably provided with an airtight reel in order to prevent cross leak of fuel and air. For this purpose, it is effective to apply a YSZ or LCC paste in a green state to the relevant portion before firing the composite film, and to further enhance the airtightness by overcoating the whole when integrally firing. Is effective. The cell stack manufactured as described above is shown in FIG.
The fuel cell was constructed as shown in FIG. 11 so that the gas flowing out from one cell stack could be supplied to the next cell stack. 6 and 7 are longitudinal sectional views,
8, FIG. 9, FIG. 10 and FIG. 11 are transverse sectional views. 1
Is a containment vessel, 2 and 3 are gas manifolds for air, 4,
Reference numerals 5, 6, 7, and 8 are parts that constitute the fuel gas manifold, and 9 is a spacer that also serves as a seal. 2,
3 has air introducing / exhausting holes Y1 and Y2 in the upper portion in FIGS. 7 and 8, but it is essentially the same in either the lower portion or the upper and lower portions. The air gas manifolds 2 and 3 form a box and are installed facing each other. As shown in the figure, it may be divided into several parts to be manufactured and combined. Of the components that make up the fuel-side gas manifold, two are installed vertically and are box-shaped to enclose the vertical cross section of the cell stack. Reference numeral 8 is for preventing an electrical short circuit between the cell stacks and for hermetically sealing. 8 is covered with 2 at the upper and lower ends, but is further covered with a C-shaped 7 in the middle. This is because a bonding material is packed between the cell stacks 7 and 8 and the airtight seal is effectively made. Reference numeral 5 is a plate-shaped member, which serves as a bus bar for electrically connecting the cell stacks in series and as a spacer. Further, 6 is also plate-like, and is an insulator such as zirconia installed at a position equivalent to 6 and also functions as a spacer like 6. Reference numeral 9 denotes a spacer, which also has a function of separating the air supply side and the air discharge side. For fuel cells, cross-leakage of fuel and air reduces efficiency, and in some cases there is a possibility of explosion due to air-fuel mixture, so it should be avoided as much as possible. When manufacturing this cell stack, the whole part is not integrated and the parts other than the cell stack are box-shaped or plate-shaped. Therefore, the parts are easy to manufacture, but the problem of airtightness is concerned. However, the cross leak of fuel and air does not cause a problem in this embodiment. The reason is that the inside of the stack is hermetically separated into the air side and the fuel side by the separator, and the outside of the fuel side is doubly wrapped by the plate or box as shown in FIG. 6-11. Even if air leaks, it is against the containment vessel, and even if fuel leaks there, the operating temperature is 10
Since it is as high as 00 ° C, it burns at the leak point, so there is no danger of explosion due to the air-fuel mixture. In other words, since it is sufficient to prevent excessive leakage, the required airtightness can be achieved by overcoating the sealing material when the airtightness is insufficient. The box-shaped or plate-shaped parts that connect these cell stacks together are made of YSZ in order to achieve the same coefficient of thermal expansion. However,
The bus bar for connecting the cells in series, only the component 15, needs to be electrically conductive, and thus is manufactured by LCC. These parts are usually manufactured by injection molding or slip casting, but in the present invention, a doctor blade film is attached on both sides of a YSZ foam film, and YSZ paste is applied on the side surfaces to form a thick plate. The plate was formed in a plate shape or assembled into a box shape, and the joint surface was coated with paste and integrally fired. (Paragraph) Fuel is supplied from X1,
A long gas flow path is provided by successively raising the fuel side passages of the cell stack. As shown in the figure, the air side of the stack is sealed against the X1 side during the stack manufacturing process, so that no cross leak with the air occurs. Air is supplied from Y1 and flows through the cell stack up and down on the paper surface in FIG. 6 and left and right on the paper surface in FIG.

INDUSTRIAL APPLICABILITY As described above, by supplying fuel discharged from a stack forming one cell or block to the next cell or stack one after another, a unit similar to a stack composed of only large cells is provided. It is possible to construct a module having a small temperature gradient and a small voltage gradient per area. As a result, it is possible to avoid the production of large-area cells, which is difficult with ceramics, and it is possible to configure a manufacturing process that enables mass production with few defective products. In addition, the gas manifold can be separately manufactured into simple parts that are easy to manufacture and small parts, which facilitates mass production.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention showing a fuel supply method to a cell stack by a long flow path method.

FIG. 2 is a schematic diagram showing a normal fuel supply method to a cell stack.

FIG. 3 is an explanatory diagram showing an arrangement state of cell stacks.

FIG. 4 is a schematic diagram of an external gas manifold type cell stack.

FIG. 5 is a schematic diagram of an external gas manifold type cell stack.

FIG. 6 is a vertical sectional view taken along the line GG ′ of the fuel cell (vertical stacking type) of the present invention.

FIG. 7 is a vertical sectional view taken along the line FF ′ of the fuel cell (vertical stacking type) of the present invention.

FIG. 8 is a cross-sectional view taken along the line AA ′ of the fuel cell (vertical stacking type) of the present invention.

FIG. 9 is a cross-sectional view taken along the line BB ′ of the fuel cell (vertical stacking type) of the present invention.

FIG. 10 is a cross-sectional view taken along the line CC ′ of the fuel cell (vertical stacking type) of the present invention.

FIG. 11 is a transverse cross-sectional view of the fuel cell (vertical stacking type) of the present invention taken along the line DD ′.

[Explanation of symbols]

 2,3 Air gas manifold 4,5,6,7,8 Fuel gas manifold

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Tokiya 1-1-1 Higashi, Tsukuba-shi, Ibaraki Industrial Technology Institute of Chemical Research

Claims (1)

Claim: What is claimed is: 1. A positive electrode film is laminated on one surface of a solid electrolyte membrane, and a separator film is laminated on the positive electrode film side and a negative electrode film side of a single cell in which a negative electrode film is laminated on the other surface. A cell stack is formed by collecting a plurality of single cell units each having a distributor provided between the positive electrode film and the separator film and between the negative electrode film and the separator film, and discharged from the single cell or the cell stack. A flat plate solid oxide fuel cell, characterized in that fuel is supplied to adjacent single cells or cell stacks.