JP2007073356A - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell for improving the stability of output and output efficiency, by uniformizing quantity of reaction gas distributed and supplied to respective power generating cells from a manifold. <P>SOLUTION: A fuel cell stack is formed by constituting a power generating cell 5, by arranging a fuel electrode layer 3 and an air electrode layer 4 on both surfaces of a solid electrolyte layer 2, arranging a fuel electrode current collector 6 and an air electrode current collector 7 outside the power generating cell 5, and by arranging separators 8, having a gas flow passage 11, 12 outside the current collectors 6, 7. Unevenness of total pressure loss caused by separator flow passage pressure loss and current collector flow passage pressure loss is restrained to 10% or lower, by arranging at the separator 8 a pressure loss control means which increases the pressure loss of the gas flow passages 11, 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid oxide fuel cell that enables an equal flow distribution of reaction gas to each power generation cell.

  In recent years, fuel cells that directly convert chemical energy of fuel into electrical energy have attracted attention as high-efficiency and clean power generation devices. In particular, solid oxide fuel cells have been researched as third-generation power generation fuel cells. Development is underway.

A solid oxide fuel cell has a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer (cathode) and a fuel electrode layer (anode) from both sides. An oxidant gas (oxygen) is supplied to the air electrode layer side, and a fuel gas (H ₂ , CO, etc.) is supplied to the fuel electrode layer side. The air electrode layer and the fuel electrode layer are both porous layers so that the reaction gas can reach the interface with the solid electrolyte layer.

In the power generation cell, oxygen supplied to the air electrode layer passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer. It is ionized to (O ²⁻ ). This oxide ion diffuses and moves in the solid electrolyte layer toward the fuel electrode layer and reaches the vicinity of the interface with the fuel electrode layer, where it reacts with the fuel gas to produce reaction products (H ₂ O, produce CO _2, etc.), releasing electrons to the fuel electrode layer. Electrons generated by the electrode reaction can be taken out as an electromotive force at an external load on another route.

A flat-plate-type solid oxide fuel cell stacks a large number of power generation cells on both sides with a current collector (fuel electrode current collector, air electrode current collector) and separator interposed therebetween, and the stacking direction from both ends The load is applied to each component of the laminate (stack) so that the components are pressed and adhered to each other.
The separator has a function of electrically connecting the power generation cells and supplying a reaction gas to the power generation cells, and a fuel gas passage and an oxidant gas for guiding the fuel gas to the fuel electrode layer inside. And an oxidant gas flow path for guiding the gas to the air electrode layer side.
The current collector is composed of a sponge-like porous metal having a current collecting function, a gas permeation function, a uniform gas diffusion function, a cushion function, and the like.

In order to continuously perform a stable power generation reaction in the fuel cell stack, it is extremely important that the reaction gas is uniformly supplied (equal flow distribution) to each of a large number of stacked power generation cells. Patent Documents 1 and 2 and the like are disclosed as prior arts related to the uniform flow of reaction gas. These are techniques for improving the battery performance by adjusting the pressure loss of the gas flow path through which the reaction gas flows to improve the gas flow distribution performance.
JP-A-6-267564 JP 7-161366 A

By the way, in a flat plate type fuel cell, each reaction gas is distributed and supplied into each separator through a manifold provided along the stacking direction, and passes through each current collector through a gas flow path of each separator. It has the distribution form supplied to each power generation cell.
As described above, the current collector is a sponge-like porous metal body having a gas permeation function, a uniform gas diffusion function, a cushion function, etc. in addition to the current collection function. Or the like, or the load applied to the current collector during stack assembly, for example, causes variations in the flow path pressure loss of the current collector. Incidentally, at present, the variation in the pressure loss due to the current collector lot is as large as about 15%.

  In such a power generation cell, the flow rate distribution of the gas introduced from the manifold to each power generation cell becomes uneven due to such a pressure loss difference between the current collectors, and the gas supply amount is insufficient (the pressure loss of the gas flow path is large). As a result, the voltage drops, and the battery performance as a whole decreases.

  The present invention has been made in view of such problems, and by stabilizing the amount of reaction gas distributed and supplied from the manifold to each power generation cell, the battery output is stabilized and the output efficiency is improved. An object of the present invention is to provide a solid oxide fuel cell.

  That is, according to the present invention, the fuel cell layer and the air electrode layer are arranged on both surfaces of the solid electrolyte layer to constitute the power generation cell, and the fuel electrode current collector and the air electrode current collector are disposed outside the power generation cell. Solid oxidation is performed by arranging a current collector, placing a separator provided with a reaction gas flow path outside the current collector, and supplying the reaction gas from the gas flow path of the separator to the power generation cell through the current collector. In the solid fuel cell, the separator is provided with a pressure loss control means for increasing the pressure loss of the gas flow path, and the variation in the total pressure loss due to the separator flow path pressure drop and the collector flow path pressure drop is suppressed to 10% or less. It is characterized by that.

  The present invention described in claim 2 is characterized in that in the solid oxide fuel cell according to claim 1, pressure loss control means for increasing the pressure loss in the cross-sectional area of the gas flow path is provided.

  Further, according to a third aspect of the present invention, in the solid oxide fuel cell according to the first or second aspect, the pressure loss control means for increasing the pressure loss with the length of the gas flow path is provided. It is characterized by having.

  According to a fourth aspect of the present invention, in the solid oxide fuel cell according to any one of the first to third aspects, the pressure loss is reduced by a gas flow restricting mechanism at an inlet portion of the gas flow path. It is characterized by having an increasing pressure loss control means.

  According to the present invention, the pressure loss control means increases the separator channel pressure loss and absorbs the variation in the collector channel pressure loss, whereby the total pressure loss due to the separator channel pressure loss and the collector channel pressure loss varies. The sticking can be suppressed to 10% or less. As a result, it is possible to distribute the reaction gas to each power generation cell in a uniform manner, the power generation performance of each power generation cell is made uniform, and the battery output can be stabilized and the output efficiency can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a flat plate type solid oxide fuel cell to which the present invention is applied, FIG. 2 shows the structure of a single cell according to the present invention, FIG. 3 shows an example of a separator, and FIG. FIG. 5 shows the ratio of the total pressure loss due to the separator channel pressure loss and the collector channel pressure loss to the separator channel pressure loss.

  As shown in FIG. 2, the unit cell 10 includes a power generation cell 5 in which a fuel electrode layer 3 and an air electrode layer 4 are disposed on both surfaces of a solid electrolyte layer 2, and a fuel electrode current collector disposed outside the fuel electrode layer 3. 6, an air electrode current collector 7 disposed outside the air electrode layer 4, and a separator 8 disposed outside each current collector 6, 7.

Among these components, the solid electrolyte layer 2 is composed of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer 3 is composed of a metal such as Ni or a cermet such as Ni—YSZ, and the air electrode layer. 4 is composed of LaMnO ₃ , LaCoO ₃ or the like, the fuel electrode current collector 6 is composed of a sponge-like porous sintered metal plate such as Ni, and the air electrode current collector 7 is a sponge-like porous material such as Ag. It consists of a sintered metal plate.
The porous metal has a current collecting function, a gas permeation function, a gas diffusion function, a cushion function, a thermal expansion difference absorption function, and the like.

The separator 8 is composed of a rectangular stainless steel plate having a thickness of 2 to 3 mm, and has a function of electrically connecting the power generation cells 5 and supplying a reaction gas to the power generation cells 5. The gas is introduced from the edge of the separator 8 and discharged from the substantially central portion 11 a of the surface of the separator 8 facing the anode current collector 6, and the oxidant gas is introduced from the edge of the separator 8. The separator 8 has an oxidant gas flow path 12 that is discharged from substantially the center 12a of the surface of the separator 8 that faces the air electrode current collector 7.
The fuel gas channel 11 and the oxidant gas channel 12 are rectangular in cross section with a cross section of about 3 × 1.5 mm, and each is formed in a spiral shape (see FIG. 3).

  2 and 3, the left and right edges of the separator 8 are provided with a pair of gas holes 13 and 14 penetrating in the thickness direction, and one gas hole 13 is formed in the fuel gas passage 11. The other gas hole 14 communicates with the oxidant gas flow path 12, and fuel gas and oxidant gas are passed from the gas holes 13, 14 to the electrode surfaces of the power generation cells 5 through the gas flow paths 11, 12. To be supplied.

In the solid oxide fuel cell (fuel cell stack 1) of this embodiment, as shown in FIG. 1, a large number of the above-mentioned single cells 10 are stacked with ring-shaped insulating gaskets 15 and 16 interposed therebetween. The fastening plates 20 and 20 are arranged at both upper and lower ends, and the peripheral portion is fastened with bolts 21 to form an integrated structure in which the respective components are brought into close contact with each other.
By applying a load to the stack, the fuel electrode current collector 6 and the air electrode current collector 7 made of porous metal were elastically deformed somewhat, and were pressed and sandwiched between the upper and lower separators 8 with a certain degree of elasticity. Each of the gaskets 15 and 16 is connected in the stacking direction in a state where the gaskets 15 and 16 are mechanically closely attached and fixed to the gas holes 13 and 14 of the separator 8, and the fuel gas extending in the vertical direction inside the stack. An internal manifold 17 for the oxidant gas and an internal manifold 18 for the oxidant gas are formed.

  During operation, fuel gas and oxidant gas (air) supplied from the outside flow through the internal manifolds 17 and 18, and the gases pass through the gas passages 11 and 12 from the gas holes 13 and 14 of the separators 8. Then, the gas is ejected to the fuel electrode current collector 6 side and the air electrode current collector 7 side, and the ejected gas permeates and diffuses inside these current collectors 6 and 7 and is distributed and guided to each electrode surface of each power generation cell 5. Is done.

By the way, in the flat plate type fuel cell stack 1, there is a problem related to battery performance in that preferable uniform distribution of the reaction gas is not performed for each power generation cell due to variation in pressure loss in the current collector.
This is because the variation in the collector channel pressure loss is larger than the variation in the separator channel pressure loss due to the structure of the current collector. This is because it greatly affects the variation of the total pressure loss due to the body channel pressure loss. The uniform distribution of the reaction gas is particularly important in the fuel gas flow path system that directly affects the power generation reaction.
As a result of investigations and experiments by the inventors, it has been confirmed that if the variation in the total pressure loss is 10% or less, good uniform flow distribution performance can be obtained for each power generation cell.

Therefore, in the present invention, the separator 8 is provided with a pressure loss control means for increasing the pressure loss of the gas flow path, and the total pressure loss (h1 + h2) due to the separator flow pressure pressure h1 and the current collector flow pressure pressure h2 is 10%. The following were suppressed.
That is, as shown in FIG. 5, the separator flow path pressure loss h1 is increased by the pressure loss control means (desirably, the separator flow path pressure loss h1 is made larger than the current collector flow path pressure loss h2). The large variation of the pressure loss h2 itself can be absorbed and the variation of the total pressure loss (h1 + h2) can be suppressed to 10% or less. In order to reduce the variation to 10% or less, the separator flow path pressure loss h1 may be set to 120 Pa or more. Incidentally, the current collector pressure loss h2 at the rated flow rate is about 230 Pa, and the variation in the pressure loss h2 due to the lot is about 15%.
When the separator flow path pressure loss h1 is increased, the rated flow rate is obtained in the fuel gas flow path 11, and accordingly, the flow pressure of the fuel gas in the fuel gas manifold 17 needs to be increased accordingly. In order to prevent clogging of the channel during operation, it is preferable that the cross-sectional area is large and the length is short. For this reason, the lower limit of the total pressure loss (h1 + h2) is 10% (separator flow path pressure loss h1 = 120 Pa).

Next, a specific example of the above-described pressure loss control means will be described.
The separator flow path pressure loss h1 is
Separator inlet pressure loss: (V2 ² −V1 ² ) / 2 g ·· (I) and flow path pressure loss: λl / d × V2 ² g ·· (II).
Where λ is the friction coefficient of the gas flow path, l is the gas flow path length, d is the gas flow path diameter (equivalent diameter), V1 is the gas flow velocity in the manifold, V2 is the gas flow velocity in the gas flow path, g Is the gravitational acceleration.

Therefore, in the present embodiment, based on the above formulas (I) and (II), (1) the cross-sectional area of the fuel gas passage 11 of the separator 8 (that is, the passage diameter d) is reduced as pressure loss control means. Method of increasing pressure loss (formula II), (2) Method of increasing pressure loss by increasing the gas passage length l of the fuel gas passage 11 of the separator 8 (formula II), (3) As shown in FIG. A method of increasing the pressure loss by restricting the gas flow rate (gas flow rate V2) by using the orifice portion 19 as a flow passage portion that branches and communicates with the fuel gas flow passage 11 of the separator 8 from the fuel gas manifold 17 (gas flow velocity V1) ( Formula I) was adopted.
By the pressure loss control means (1) to (3), the power generation performance of each power generation cell 5 is made uniform, and the output stability of the fuel cell stack 1 and the output efficiency can be improved.

These pressure loss control means (1) to (3) may be used individually, but may be used in combination.
Of the pressure loss control means described above, (1) and (2) can be easily manufactured because they are not easily affected by the processing tolerance during the manufacturing, but the pressure loss control by the orifice restrictor 19 in (3) It is desirable to use the pressure loss control means (1) and (2) because it has disadvantages such as clogging of the flow path due to oxide scale during long-term use and poor workability due to a complicated and highly accurate structure.

The figure which shows the external appearance of the solid oxide fuel cell to which this invention was applied. The figure which shows the structure of the single cell which concerns on this invention. The top view which shows an example of a separator. The figure which shows the gas introduction part of a separator. The figure which shows the ratio of the dispersion | variation in the total pressure loss by the separator channel pressure loss and the collector channel pressure loss with respect to a separator channel pressure loss.

Explanation of symbols

1 Solid oxide fuel cell (fuel cell stack)
2 Solid Electrolyte Layer 3 Fuel Electrode Layer 4 Air Electrode Layer 5 Power Generation Cell 6 Fuel Electrode Current Collector 7 Air Electrode Current Collector 8 Separator 11, 12 Gas Channel 19 Gas Flow Restriction Mechanism (Orifice Restriction)

Claims (4)

A power generation cell is configured by disposing a fuel electrode layer and an air electrode layer on both sides of the solid electrolyte layer, and a fuel electrode current collector and an air electrode current collector are disposed outside the power generation cell. In a solid oxide fuel cell, a separator having a reaction gas flow path is disposed, and a reaction gas is supplied from the gas flow path of the separator to the power generation cell through the current collector.
The separator is provided with a pressure loss control means for increasing the pressure loss of the gas flow path, and variation in the total pressure loss due to the separator flow path pressure loss and the current collector flow path pressure loss is suppressed to 10% or less. Solid oxide fuel cell. 2. The solid oxide fuel cell according to claim 1, further comprising pressure loss control means for increasing pressure loss with a cross-sectional area of the gas flow path. 3. The solid oxide fuel cell according to claim 1, further comprising a pressure loss control unit configured to increase a pressure loss depending on a length of the gas flow path. The solid oxide fuel cell according to any one of claims 1 to 3, further comprising pressure loss control means for increasing pressure loss by a gas flow restricting mechanism at an inlet portion of the gas flow path.

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