JPH0395870A - Solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To enhance the energy efficiency of a solid electrolyte fuel cell to enhance its output density by making the structure of an oxygen electrode as thick as possible to maintain the strength of each unit cell and also to reduce electric resistance on the side of the oxygen electrode. CONSTITUTION:Flat single cells 7a...7h are each formed by connection of its component pieces in square so as to form a stack of cells. A predetermined fuel gas passage and a predetermined air passage are provided between single cells and the output density is determined by the thickness of each single cells. Each single cell comprises a solid electrolyte layer and a fuel electrode layer sequentially formed on an oxygen electrode, and the oxygen electrode is formed thick enough to maintain the strength of each single cell without using another reinforcing material, and in addition, electric resistance is reduced on the side of the oxygen electrode due to the thick structure. Thus each single cell does not require reinforcing material and so the structure is thinned after all.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid oxide fuel cell, and particularly to a solid oxide fuel cell having a high power generation output density. [Prior Art] Fuel cells, which have recently attracted attention as a low-pollution energy source, generate electrical energy by continuously supplying fuel as an active material and oxidizing agent from the outside, which are the sources of electromotive reactions. This battery is capable of continuously discharging reactive substances. Among fuel cells, solid oxide fuel cells are attracting attention as they have no fear of electrolyte leakage and have a high reaction rate, and are designed to increase output by stacking many single cells. As an application related to this, for example, the patent application No. 1-1 proposed by the present inventors
No. 114793 etc. can be mentioned.

FIG. 4 is a perspective view of a single cell unit of the solid electrolyte fuel cell according to the prior application. This single cell unit is plate-shaped, and includes a base plate 21, an oxygen electrode membrane (hereinafter also referred to as an oxygen side electrode) 23 laminated on the surface of the base plate 21, and a solid electrolyte membrane (hereinafter simply referred to as a solid electrolyte). ) 22, a fuel electrode WX (hereinafter also referred to as fuel-side electrode) 24, and current collectors 28 disposed at both ends of the base plate 2l. Note that 25 indicates a battery unit in unit of a single cell.

FIG. 5 shows a structure in which the single cell units 26 of FIG. 4 are connected in parallel.
Rectangular single cells 27 (a-f) with stepwise different sizes
FIG. 2 is a perspective view showing a cell stack unit in which cell stacks are further stacked in parallel. The battery part 25 of each single cell is connected to the battery part 25 of the adjacent single cell, and the base plate 21 is connected to the base plate 2 of the adjacent single cell.
1 and are arranged to face each other. A fuel cell stack is formed by connecting these cell stack units in series via an intermediate connecting conductor 30, and a solid oxide fuel cell is formed by arranging a large number of fuel cell stacks on a substrate. For example, hydrogen gas is introduced into the fuel flow path facing the fuel-side electrode 24 of the solid oxide fuel cell constructed in this manner, and air is introduced into the air flow path facing the base plate 21, so that each electrode An electrode reaction occurs between the electrodes, and the generated electrical energy is collected and extracted to the outside. [Problem to be solved by the invention] In the solid electrolyte fuel cell according to the above-mentioned prior application, a base plate is used as a strength member of the single cell unit, and the single cell unit becomes thicker accordingly. The stacking expansion pitch in the plane when stacking becomes large, which is an obstacle to improving the power generation output density of the fuel cell stack as a whole. Further, in such a solid oxide fuel cell, there is a problem that the oxygen side electrode has a large electrical resistance, making it difficult to improve energy efficiency.

An object of the present invention is to solve the problems of the prior art described above and to provide a solid oxide fuel cell that has good energy efficiency and further improves output density.

[Means to solve the problem]

In order to achieve the above object, the present inventors have found that in order to improve the output density, it is necessary to make the single cell unit as thin as possible and increase the number of stacked single cell units (or single cells) per unit area. In addition, we focused on the fact that it is effective to make the oxygen side electrode as thick as possible in order to reduce the electrical resistance of the oxygen side electrode, and if we made the oxygen side electrode thicker by a certain amount to give it strength, we could eliminate the base plate. The present invention was achieved by discovering that not only can a single cell be made thinner, but also the electrical resistance of the oxygen side electrode can be reduced.

That is, the present invention provides a solid oxide fuel cell having a large number of polygonal single cells arranged in parallel with each other, each of which has an oxygen electrode made of an electron conductor or a mixed conductor. It is characterized by comprising a membrane, and a fuel electrode membrane consisting of an oxygen ion conductive solid electrolyte membrane and an electron conductor, which are sequentially laminated on the oxygen electrode membrane.

[Effect]

By constructing a single cell unit from an oxygen-side electrode and a solid electrolyte and a fuel-side electrode laminated thereon, if the oxygen-side electrode is made thicker by a predetermined amount, the electrical resistance of the oxygen-side electrode decreases, reducing energy loss. is reduced, and the strength of the single cell unit can be sufficiently maintained without using a base plate.

In addition, by not using a substrate plate, the thickness of the single cell unit as a whole becomes thinner than that of conventional ones, and the number of stacked single cells per unit plane can be increased, making it possible to make solid electrolyte award-type fuel cells power generation output density will be improved.

In the present invention, a single cell unit refers to the smallest unit of a battery constituting a solid electrolyte fuel cell, and this single cell unit consists of a flat oxygen side electrode and a solid layered on the oxygen side electrode. It consists of an electrolyte and a fuel side electrode.

As a molding material for the oxygen side electrode, for example, La+-x
S rx MnO3, Lal-x S rx COO3
, Ca. XCe. A berovskite such as Mn03 is used, which has a suitable particle size, e.g.
After being pulverized to 1 μm to 0.5 μm or less, it is mixed with a solvent such as polyvinyl alcohol (PVA), dibutyl phthalate (DBP), and other blowing agents to form a slurry, and after being shaped and dried, it is It is fired at °C to form a flat oxygen side electrode. Although the thickness of the oxygen-side electrode formed in this manner can be adjusted as desired, it is typically formed to a thickness of about 1 mm.

In the present invention, as the solid electrolyte laminated on the oxygen side electrode, for example, a ZrOt-based solid electrolyte is used, and as the fuel side electrode material, for example, nickel-based Ni○-YSZ is used.

As a method for laminating a solid electrolyte and a fuel side electrode on the surface of an oxygen side electrode, a known CVD (chemical
vapor deposition) method, p V
D (physical vapor deposit)
ion) method, pyrolysis sintering method, slurry sintering method, etc. are used.

In the present invention, a single cell refers to a group of single cell units formed into a polygon by combining the above-mentioned single cell units in parallel.

In the present invention, a large number of single cells whose sizes are changed stepwise are formed, and these single cells are stacked concentrically so that their diagonals overlap on the same straight line to form a cell stack unit. In this case, the oxygen-side electrode of the outermost single cell is arranged so as to face the outside of the polygon, and then the oxygen-side electrodes of each single cell are arranged so as to alternately face inside or outside the polygon.

Next, this cell stack unit is further connected in series via an intermediate connecting conductor to form a fuel cell stack, and a large number of these fuel cell stacks are further arranged on a substrate to form a solid oxide fuel cell.

In the present invention, the polygon of a single cell composed of a plurality of single cell units includes an equilateral triangle, a triangle, a square, a quadrangle, a pentagon, etc., but is not particularly limited. Also,
Normally, one single cell unit is used as one side of a polygon, but two or more single cell units may be connected in parallel to form one side of a polygon. The cell stack units or fuel cell stacks are connected to each other via an intermediate connecting conductor, but this intermediate connecting conductor may be independent for each fuel cell stack, or may be connected to adjacent It may be common to two or more fuel cell stacks.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

FIG. 1 is a perspective view of a single cell unit constituting a fuel cell stack of a solid oxide fuel cell according to an embodiment of the present invention. This single cell unit is composed of an oxygen-side electrode 3, a solid electrolyte 2 and a fuel-side electrode 4 that are laminated in sequence on one side of the oxygen-side electrode 3, and the oxygen-side electrode 3, solid electrolyte 2, and fuel-side electrode 4. It mainly consists of current collectors 1 made of heat-resistant metal placed at the upper and lower ends of a battery section 5 to be protected.

FIG. 2 is a perspective view of a cell stack unit in which rectangular single cells 7 formed by connecting the single cell units 6 of FIG. 1 in parallel are further stacked in parallel on an intermediate connecting conductor 10. In the figure, it is composed of four single cell units of the same length.
8 rectangular single cells (7a, 7
b, 7c, 7d, 7e, 7f, 7g and 7h) are arranged concentrically on the intermediate connecting conductor 10 so that their diagonal lines are on the same straight line. Single cell 7a, 7c
, 7e and 7g, the inside of the rectangle becomes the fuel-side electrode 4, and the outside becomes the oxygen-side electrode 3.

Further, in the single cells 7b, 7d, 7r, and 7h, the outer side of the rectangle is the fuel side electrode 4, and the inside side is the oxygen side electrode 3. The connecting portion of each single cell unit is sealed with a gas-sealing bonding agent. Single cell 7a
The gap between and 7b, the gap between 7C and 7d, the gap between 7e and 7f, and the gap between 7g and 7h each face the fuel side electrode 4 and serve as a fuel flow path. On the other hand, single self b and 7
The gap with 0, the gap between 7d and 7e, the gap between 7r and 7g, and the inside of 7h each face the oxygen side electrode 3 and serve as an air flow path.

FIG. 3 is an explanatory diagram showing an example of the arrangement of a fuel cell stack constituting a solid electrolyte fuel cell according to an embodiment of the present invention. The figure shows a fuel cell stack 9 in which the cell stack units 8 of FIG. 2 are connected in series via an intermediate connecting conductor 10, and this fuel cell stack 9 includes
Intermediate connection conductor 10 common to two fuel cell stacks
and are regularly arranged on the substrate 17. The substrate 17 is provided with an air passage hole 11 for supplying oxygen to the outermost oxygen-side electrode 3 of each fuel cell stack 9. Further, below the substrate 17, a fuel supply pipe 12 for supplying fuel to each fuel-side electrode 4 and a fuel discharge pipe 13 for discharging excess fuel are arranged.

In such a configuration, for example, hydrogen F as a fuel supplied from the fuel supply pipework 2 enters the fuel cell stack 9 from the lower terminal 14, ascends the fuel flow path facing the fuel side electrode 4, and flows to the upper part. The fuel is emitted from a flange (not shown) provided at the top of the terminal 15 and undergoes a combustion reaction with the air similarly emitted via the air flow path, or passes through the fuel communication flow path provided in the same flange. , descends through another fuel flow path adjacent to the air flow path, then ascends through another fuel flow path, contacts all the fuel-side electrodes 4 in the same manner, and then passes through the fuel discharge pipe 13 to the system. It is discharged outside. On the other hand, air A, which is an oxygen source, is filled into the space below the base 17 from an air introduction pipe (not shown), and passes through air passage holes provided in the base 17 that communicate with the air flow path of the fuel cell stack 9. The fuel cell stack 9 enters the fuel cell stack 9 from the lower terminal 14, and after rising through the air flow path facing the oxygen side electrode 3, the upper terminal 1
5, which is released from the flange (not shown) and which undergoes a combustion reaction with hydrogen F as fuel, which is also released via the fuel flow path, or an air connection provided on the flange. After passing through the flow path, descending through another adjacent air flow path across the fuel flow path, and rising through yet another air flow path, and thereafter in the same manner, after contacting all the oxygen side electrodes 3,
The air flows out from the substrate 17 through the air passage hole l1 and comes into contact with the oxygen side electrode 3 disposed at the outermost side of each fuel cell stack.

An electrode reaction occurs between the electrodes of each single cell of the fuel cell stack 9 to which the fuel F and air A are supplied in this manner. That is, oxygen in the air flowing through the air flow path enters the oxygen side electrode, where it receives electrons from an external circuit to become oxygen ions, and then enters the solid electrolyte 2 to become a charged unit. On the other hand, hydrogen F flowing through the fuel flow path, for example, flows into the fuel-side electrode 4, where it reacts with oxygen ions in the solid electrolyte 2 to generate water and emit electrons to the outside. Similar electrode reactions occur in other fuel cell stacks 9,
Electrical energy is generated. The generated electrical energy is collected through the upper and lower terminals and taken out as more powerful electrical energy.

According to this embodiment, a single cell unit, which is the smallest cell unit constituting a fuel cell stack, is made up of an oxygen side electrode, a solid electrolyte, and a fuel side electrode without using a substrate. As the cell unit becomes thinner, the substrate area occupied by each single cell and the stacking pitch of the single cells become narrower.
The number of single cells arranged per unit substrate area can be increased, and a solid electrolyte fuel cell with high output density can be obtained.

Furthermore, since the oxygen side electrode can be made thicker by a predetermined amount to lower the electrical resistance, energy efficiency is improved.

Furthermore, manufacturing efficiency and economy are improved due to a reduction in the number of manufacturing steps due to a reduction in the number of laminated films, a reduction in the number of required materials, and the like.

Furthermore, in terms of battery characteristics, the polarization caused by gas passing through the base plate is reduced, and power generation characteristics are improved.

[Effects of the Invention] According to the present invention, since the single cell unit is constructed without using a substrate, the single cell unit becomes thinner, and the substrate area occupied by each single cell and the stacking expansion pitch of the single cells become narrower. Therefore, the number of single cells arranged per unit substrate area can be increased, and a solid oxide fuel cell with higher output density can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a single cell unit in a solid electrolyte fuel cell that is an embodiment of the present invention, and FIG. 2 is a cell stack in which the single cells in FIG. 1 are further stacked. FIG. 3 is a perspective view of a unit; FIG. 3 is a diagram showing an example of the arrangement of a fuel cell stack in a solid oxide fuel cell according to an embodiment of the present invention; FIG. 4 is a perspective view of a single cell unit according to a prior application;
FIG. 5 is a perspective view of a cell stack unit according to the preceding order. 2...Solid electrolyte, 3...Oxygen side electrode, 4...Fuel side electrode, 5...Battery part, 6...Single cell unit, 7(
a~h)...Single cell, 8...Cell stack unit, 9
...Fuel cell stack.

Claims (1)

[Claims] (1) A solid oxide fuel cell having a large number of polygonal single cells arranged in parallel with flat plate-like single cell units, wherein the single cell unit has an oxygen electrode membrane made of an electron conductor or a mixed conductor. A solid electrolyte fuel cell comprising: an oxygen ion conductive solid electrolyte membrane and a fuel electrode membrane made of an electron conductor, which are sequentially laminated on the oxygen electrode membrane.