JP3999934B2 - Solid oxide fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell, and more particularly to a fuel cell that operates while supplying a reaction gas in which a fuel and an oxidant are mixed to an anode and a cathode.
[0002]
[Prior art]
In general, a fuel cell has a basic unit in which a cell in which a cathode and an anode are arranged facing each other through an electrolyte plate or an electrolyte membrane is sandwiched between a pair of plate substrates on which gas channels are formed. A structure in which a plurality of units are stacked.
[0003]
When the fuel cell is operated, generally, air as an oxidant is supplied to the channel on the cathode side, fuel gas is supplied to the channel on the anode side, and the supplied fuel gas is supplied to the anode and cathode of the fuel cell. Then, the oxidant is reacted electrochemically to generate electricity.
In such a fuel cell, a gas-impermeable material is used for the electrolyte membrane so that air and fuel gas are not mixed in the unit, and air and fuel gas are also transmitted between adjacent stacked units. To prevent mixing, gas-impermeable plates are inserted between the units, and the plate substrate is made of a gas-impermeable material. I keep it.
[0004]
On the other hand, in recent years, there has been proposed a non-membrane type fuel cell that generates power while flowing a reaction gas of the same composition in which a fuel and an oxidant are mixed on the anode side and the cathode side.
For example, in Japanese Patent Publication No. 2810977, a mixture of a fuel gas and an oxidant gas is used in which two electrodes having different catalytic capacities for a partial oxidation reaction of hydrocarbons are printed on the same surface of an electrolyte sheet. A fuel cell capable of generating electricity is disclosed, and in this case, there is an advantage that the cost can be reduced because the gas seal material and the separator are unnecessary and the structure of the apparatus is simple. However, in this type, it is necessary to control so that the mixing ratio of the fuel gas and the oxidant gas is within an appropriate range.
[0005]
By the way, in any type of fuel cell, in order to obtain good power generation performance, the composition of the reaction gas flowing through the channel is adjusted so as to fall within a range suitable for the reaction in the entire region of the cell, It is desirable to react uniformly in the entire region.
[0006]
[Problems to be solved by the invention]
However, in general, in a fuel cell, the reaction gas flows along the surface of the cell as described above, and the reaction gas is used for the reaction at the electrode and the reaction product is mixed. The composition of the reaction gas is considerably different between the gas inlet side region and the outlet side region. That is, the composition of the reaction gas varies in the cell plane.
[0007]
Therefore, since it is difficult to keep the composition of the reaction gas within an appropriate range in the entire region from the inlet side region to the outlet side region of the channel, the reaction becomes uneven between the regions in the cell, and the temperature is not uniform. There is a problem that it tends to be uniform, and therefore, it is difficult to obtain good power generation performance.
Further, in the type using the mixed gas of the fuel gas and the oxidant gas, it is necessary to control the mixing ratio as described above, but there is a problem that this control becomes difficult if the composition of the reaction gas varies.
[0008]
The present invention has been made in view of such problems, and in a fuel cell that generates power using a mixed gas of a fuel gas and an oxidant gas, by suppressing variations in the reaction gas composition in the cell plane. The purpose is to obtain better power generation performance than before.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a fuel cell according to the present invention includes a cell in which an anode catalyst layer and a cathode catalyst layer are disposed on a gas permeable electrolyte plate, and a fuel and an oxidant on the anode catalyst layer and the cathode catalyst layer. And a gas supply means for supplying a reaction gas in which is mixed.
[0010]
According to the fuel cell of the present invention, since the reaction gas can pass through the electrolyte plate and travel between the anode catalyst layer and the cathode catalyst layer, the reaction gas composition becomes non-uniform between the regions in the cell. Can be alleviated.
As the electrolyte plate having gas permeability, a gas impermeable electrolyte plate that has been used conventionally and having one or more holes penetrating the electrolyte plate can be used.
[0011]
A cell stack can also be formed by stacking a plurality of such cells.
In this case, in the electrolyte plate of each cell, it is preferable to shift the positions of the holes formed in the adjacent electrolyte plates.
In such a fuel cell, when supplying the reaction gas, it is preferable to pass through one of the anode catalyst layer and the cathode catalyst layer, and then pass through the other layer, which is orthogonal to the cell. More preferably, the reaction gas is supplied in the direction.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
(About fuel cell configuration)
FIG. 1 is a perspective view (partial cross section) showing a configuration of a fuel cell according to the present embodiment.
[0013]
This fuel cell 1 is composed of a fuel gas and an oxidizer in a state where a cell 10 having an anode 20 on one side of a solid electrolyte plate 11 and a cathode 30 on the other is sandwiched between a pair of current collecting plates 41 and 42. The reaction gas mixed with the agent gas is fixed in the housing 50 that circulates inside.
FIG. 2 is a diagram schematically showing a cross section of the fuel cell 1.
[0014]
The electrolyte plate 11 is a plate made of ion conductive ceramics, and one that is generally used as an electrolyte plate of a solid oxide fuel cell, such as stabilized zirconia (YSZ), is used. However, one or a plurality of through-holes 11a are opened over the entire plate so that gas can permeate.
The form of the through-hole 11a may be a fixed-shaped hole (for example, a circular hole) or an indeterminate hole, but is preferably opened so that a large number of holes are uniformly distributed over the entire plate.
[0015]
As for the opening ratio of the through-holes 11a (ratio of the through-holes 11a with respect to the apparent total area of the electrolyte plate 11), if the opening ratio is too small, the reaction gas cannot pass through, but the opening ratio is large. If the amount is too large, the electrolyte plate 11 is easily cracked and the reaction area is decreased. Therefore, it is preferably set to 1% or more and 50% or less, and more preferably 20% or more and 40% or less.
[0016]
As a method of forming the through-hole 11a, first, a dense electrolyte plate is formed by molding and baking an electrolyte material into a plate shape, and then mechanically opening the plate, and the electrolyte material There is a method of forming a porous electrolyte plate by setting the firing temperature to a lower level when the material is molded into a plate shape and fired.
The anode 20 is made of a porous electrode material in which an anode reaction selectively occurs. Specific examples of this electrode material include 25 wt% Ce _0.8 Gd _0.2 O _1.9 -containing Ni [Ni (GDC)] and 10 wt% samaria doped ceria (SDC) -containing Ni.
[0017]
The cathode 30 is made of a porous electrode material in which a cathode reaction selectively occurs. Specific examples of this electrode material include 15 wt% MnO ₂ -containing La _0.8 Sr _0.2 MnO ₃ [LSM (MnO ₂ )] and Sm _0.5 Sr _0.5 CoO ₃ .
The anode 20 and the cathode 30 are formed in layers in close contact with one surface and the other surface of the electrolyte plate 11.
[0018]
As shown in FIG. 1, the anode 20 and the cathode 30 may be formed so as to cover the through hole 11a on the surface of the electrolyte plate 11, but may be formed only in a place excluding the through hole 11a.
The current collecting plates 41 and 42 are plates made of a high-temperature heat-resistant conductive material (for example, ferritic stainless steel such as 18 chrome stainless steel or LaCoO ₃ ceramic).
[0019]
The current collecting plate 41 is fixed to the anode 20 and the current collecting plate 42 is fixed to the cathode 30 so as to be able to collect current from the anode 20 and the cathode 30.
In addition, the current collector plates 41 and 42 are provided with a large number of through holes 41a and 42a throughout so that the gas can pass through the reaction.
[0020]
Further, the current collecting plates 41 and 42 are provided with lead wires (not shown) extending to the outside of the housing 50 so that power can be taken out from the current collecting plates 41 and 42 to the outside.
The housing 50 is provided with a reaction gas inlet 51 and a reaction gas outlet 52 on opposing wall surfaces (upper and lower wall surfaces in FIG. 1) so that gas can flow through the inside and the cell 10 can be stored. Here, a slight space is provided between the inlet 51 and the current collector plate 41 and between the outlet 52 and the current collector plate 42.
[0021]
As a material of the housing 50, a heat resistant material (for example, stainless steel or ceramics) may be used. When the entire housing 50 is formed of a conductive material, the housing 50 needs to be insulated from the anode 20 and the cathode 30. . In addition to the above, the housing 50 can also serve as a positive electrode terminal and a negative electrode terminal. For example, if two metal lids are combined through an insulating material to form the housing 50 and each lid is connected to the current collector plates 41 and 42, each lid serves as a positive electrode terminal and a negative electrode terminal. Become. In this case, it is also possible to connect the current collecting plates 41 and 42 and the lids by directly contacting them.
[0022]
In the fuel cell 1 having such a structure, the reaction gas inlet 51 is supplied with a mixed gas in which a fuel gas and an oxidant gas are mixed.
Methane, ethane, propane, or butane can be used as the fuel gas, and air is generally used as the oxidant gas.
Here, the mixing ratio of the fuel gas and air is set so as not to fall within the explosion range in the fuel cell 1. For example, in the case of a mixed gas of methane and air, the methane concentration is set so as not to fall within this range because the methane concentration is 5.0 to 15.0 vol%. Similarly, in the case of ethane-air, propane-air, and butane-air, the explosion range is ethane concentration 3.0 to 12.5 vol%, propane concentration 2.1 to 9.5 vol%, butane concentration 1.6 vol%. Since ~ is an explosion range, set it so that it does not fall within this range.
[0023]
Then, the supplied reaction gas is uniformly dispersed in the entire area of the cell 10 as shown by the white arrow A in FIG. 2 and passes through the cell 10 as shown by the white arrow b. Used for power generation.
That is, the supplied reaction gas is first dispersed throughout the anode 20. Then, in the anode 20, the fuel gas in the reaction gas, the partial oxidation reaction _{(CH 4 + 1 / 2O 2} → CO + 2H 2 ... ▲ 1 ▼) the wake, to generate H ₂ and CO, the H ₂ and CO Reacts with oxygen ions from the cathode 30 to emit electrons (H ₂ + O ² − → H ₂ O + 2e ^{− (} 2), CO + O ² − → CO ₂ + 2e ^{− (} 3)).
[0024]
The reaction gas that has passed through the anode 20 passes through each through-hole 11 a of the electrolyte plate 11 and is dispersed throughout the cathode 30.
At the cathode 30, the reaction gas receives electrons and generates oxygen ions (O ²⁻ → O ₂ + 2e ⁻ ) (4).
Thus, the reaction gas after being used for power generation at the anode 20 and the cathode 30 is discharged as an exhaust gas from the outlet 52 as shown by the white arrow C in FIG.
[0025]
The exhaust gas also contains unreacted fuel gas, which may be incinerated with a burner or the like, or sent to another reformer to be used as reforming fuel.
Further, while the fuel cell 1 is in operation, heat is generated with power generation, but the fuel cell 1 is brought to a predetermined operating temperature (for example, 700 ° C. to 1000 ° C.) by balancing with heat radiation from the fuel cell 1. Drive while maintaining.
[0026]
(Explanation of effect)
In the conventional general fuel cell, in order to hermetically separate the reaction gas channel on the anode side and the reaction gas channel on the cathode side, a seal portion that seals the reaction gas channel is formed on the outer periphery of the electrolyte plate. However, according to the fuel cell 1 of the present embodiment, it is not necessary to form such a seal portion, and the configuration of the fuel cell can be simplified.
[0027]
Further, according to the fuel cell 1 of the present embodiment, the reactive gas flows in a direction orthogonal to the main surface of the cell 10. That is, since the reaction gas passes through the through hole 11 a of the electrolyte plate 11 and flows from the anode 20 to the cathode 30, the reaction gas is uniformly distributed over the entire region of the cell 10.
Therefore, in the entire region of the cell 10, the composition of the supplied reaction gas is uniform, the reaction is also uniform, and the in-plane temperature distribution of the cell is uniform.
[0028]
Further, since the composition of the reaction gas supplied is uniform in the entire region of the cell 10 as described above, the control of the reaction gas supply during operation is facilitated as described below.
When the reaction gas is circulated along the anode and cathode main surfaces of the cell, the reaction on the anode side (reactions (1) to (3) above) occurs exclusively, and the reaction on the cathode side (reaction (4) above). Since the reaction (2) occurs exclusively, the mixing ratio of the fuel gas and the oxidant gas greatly changes between the upstream side and the downstream side of the reactive gas on each of the anode side and the cathode side.
[0029]
Thus, when the distribution of the mixing ratio of the fuel gas and the oxidant gas in the fuel cell is widened, the mixing ratio of the fuel gas and the oxidant gas in the fuel cell is within a certain range (for example, a range other than the explosion range). ) Difficult to control.
In contrast, in the present embodiment, after the reaction gas is uniformly dispersed throughout the cell 10, the reaction at the cathode follows the reaction at the anode in each region. On the other hand, the mixing ratio of the fuel gas and the oxidant gas does not change so much.
[0030]
Therefore, in this embodiment, when the distribution of the mixing ratio of the fuel gas and the oxidant gas in the fuel cell is suppressed within a narrow range, for example, the mixing ratio of the fuel gas and the oxidant gas in the fuel cell is It is relatively easy to control so as not to fall within a certain range.
(Modification)
In the fuel cell 1 described above, the reaction gas is allowed to flow from the anode 20 side to the cathode 30 side, but conversely, even if it is allowed to flow from the cathode 30 side to the anode 20 side, it can be operated similarly. There are almost the same effects as described above.
[0031]
In the fuel cell 1 described above, the reaction gas is allowed to flow in a direction orthogonal to the main surface of the cell 10. However, the positions of the reaction gas inlet 51 and the outlet 52 are changed to change the anode 20 and the cathode of the cell 10. Even if it is made to flow along the surface of 30, it can be operated. In this case, there is no effect as described in FIG. 2 that the reaction gas is uniformly dispersed in the entire region of the cell 10, but the reaction gas can travel between the anode 20 and the cathode 30 through the through hole 11a. In the anode-side channel and the cathode-side channel, the problem that the mixing ratio of the fuel gas and the oxidant gas greatly changes between the upstream side and the downstream side of the reaction gas can be alleviated (ie, It has a certain level of uniformity.)
[0032]
[Embodiment 2]
FIG. 3 is a diagram schematically showing a cross section of the stacked fuel cell 2 according to the present embodiment.
The fuel cell 2 has the same configuration as the fuel cell 1 of the first embodiment, but a plurality of cells 10 are stacked, and the anode and cathode of adjacent cells 10 are connected in series, and a current collector plate 41 and 42 is different in that a high voltage can be taken out.
[0033]
In FIG. 3, the anode 20 and the cathode 30 of the adjacent cells 10 are connected by direct contact, but may be connected via an interconnector therebetween.
Even when the plurality of cells 10 are stacked in this way, the reaction gas supplied from the reaction gas inlet 51 is first uniformly dispersed in the cells 10 on the inlet 51 side, and then the plurality of cells 10 are made thick. It is used for power generation in each cell 10 while flowing while passing in the direction, and is discharged as exhaust gas from the outlet 52.
[0034]
Accordingly, since the composition of the reaction gas to be supplied becomes uniform in the entire region of each cell 10, good power generation performance can be obtained, and control of the reaction gas supply during operation is easy.
As shown in FIG. 3, in the fuel cell 2, the through holes 11 a formed in the electrolyte plates 11 of the adjacent cells 10 are positioned in a direction orthogonal to the traveling direction (vertical direction in the drawing) of the reaction gas. Are shifted from each other.
[0035]
In this case, the reaction gas passes through the through-hole 11a of one cell 10 and is then dispersed in the direction orthogonal to the traveling direction, and then flows into the through-hole 11a of the next cell 10. It is more uniformly distributed over the entire area of each cell 10.
[0036]
【Example】
Example 1
Based on the first embodiment, a test fuel cell was produced with the following specifications.
Using YSZ as the electrolyte plate material, a dense electrolyte plate having a thickness of 0.5 mm and a size of 2.2 cm × 1 cm was produced. And many pores (pore diameter of 0.1 mm) were opened in this electrolyte plate (opening ratio 30%).
[0037]
An anode material (25 wt% Ce _0.8 Gd _0.2 O _1.9 -containing Ni) is applied to the surface of the electrolyte plate, and a cathode material (15 wt% MnO ₂ -containing La _0.8 Sr _0.2 MnO ₃ ) is applied to the back surface, followed by firing. Produced. The size of each electrode was 0.5 cm × 2 cm.
And the fuel cell as shown in FIG. 1 was produced using this cell.
[0038]
(Example 2)
Using the cell produced in Example 1, a fuel cell was produced in which the reaction gas circulated along the surfaces of the anode and cathode as described in the modification of the first embodiment.
(Comparative example)
A cell was produced in the same manner as in Examples 1 and 2 except that pores were not formed in the electrolyte plate, and a fuel cell in which the reaction gas circulated along the surfaces of the anode and the cathode was produced.
[0039]
(Comparative test)
The fuel cells of Examples 1 and 2 and Comparative Example produced in this way were operated at an operating temperature of 950 ° C. using methane / air = 1/1 as a reaction gas. The cell voltage was measured while changing the current density within a range of 0 to 500 mA / cm ² .
FIG. 4 shows the test results, and is a characteristic diagram showing the relationship between the current density and the cell voltage measurement value.
[0040]
From the results of FIG. 4, it can be seen that in Examples 1 and 2, a higher cell voltage can be obtained than in the comparative example. It can also be seen that the cell voltage in Example 1 is higher than that in Example 2.
(Other matters)
In the first and second embodiments, the SOFC type fuel cell has been described as an example. However, the present invention is not necessarily limited to the SOFC type and generates power using a reaction gas in which a fuel gas and an oxidant gas are mixed. The present invention can be applied to a fuel cell.
[0041]
A fuel cell that generates power using a reaction gas in which a fuel gas and an oxidant gas are mixed as described above usually needs to be operated at a temperature (300 ° C. or higher) at which a partial oxidation reaction occurs. The present invention is mainly applied to a fuel cell that operates at a temperature of 300 ° C. or higher. However, the present invention is also applicable to a fuel cell that operates at a lower temperature by using a hydrogen-air mixed gas as a fuel. It is done.
[0042]
In the first and second embodiments described above, the fuel cell having the cell in which the anode and the cathode are opposed to each other with the electrolyte plate interposed therebetween has been described as an example. However, as disclosed in Japanese Patent No. 2810977, the electrolyte plate For cells with anodes and cathodes on the same side surface, opening the through holes in the electrolyte plate has the effect of making the composition of the reactant gas supplied uniform in the entire area of the cell. Play. Also in this case, it is more effective if the reaction gas is circulated in the direction orthogonal to the cell.
[0043]
【The invention's effect】
As described above, the present invention is a fuel cell that generates power using a mixed gas of a fuel gas and an oxidant gas, in which an anode catalyst layer and a cathode catalyst layer are arranged on an electrolyte plate having gas permeability. By using, it is possible to alleviate the non-uniform reaction gas composition among the regions in the cell, to obtain good power generation performance, and to easily control the supply of reaction gas during operation. .
[0044]
Moreover, a cell laminated body can be formed by laminating a plurality of such cells, and a fuel cell capable of obtaining a high voltage can be obtained.
An electrolyte plate having gas permeability is practical because it can be produced simply by opening a number of holes penetrating the electrolyte plate in a conventionally used gas-impermeable electrolyte plate.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of a fuel cell according to a first embodiment.
FIG. 2 is a diagram schematically showing a cross section of the fuel cell shown in FIG. 1;
FIG. 3 is a diagram schematically showing a cross section of a fuel cell according to a second embodiment;
FIG. 4 is a characteristic diagram showing the results of a comparative test of a fuel cell according to an example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Fuel cell 10 Cell 11 Solid electrolyte board 11a Through-hole 20 Anode 30 Cathode 41, 42 Current collecting plate 50 Housing

Claims (2)

A cell in which an anode catalyst layer and a cathode catalyst layer are disposed on an electrolyte plate having gas permeability;
A solid oxide fuel cell comprising gas supply means for supplying a reaction gas obtained by mixing a fuel and an oxidant to the anode catalyst layer and the cathode catalyst layer. A cell laminate in which a plurality of cells each having an anode catalyst layer and a cathode catalyst layer arranged on an electrolyte plate having gas permeability are laminated;
A solid oxide fuel cell comprising gas supply means for supplying a reaction gas obtained by mixing a fuel and an oxidant to the anode catalyst layer and the cathode catalyst layer .

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