JP2014032752A - Fuel cell and fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote the longevity of a fuel cell body.SOLUTION: The fuel cell includes a fuel cell body which includes a fuel gas passage configured such that a fuel electrode and an oxidant electrode are arranged while sandwiching an electrolyte membrane, and fuel gas containing hydrogen passes through the fuel electrode, and an oxidant gas passage configured so that an oxidant gas passes through the oxidant electrode, and an oxygen-based gas introduction section located at a predetermined position on the downstream side of the inlet of the fuel gas passage and on the upstream side of the outlet thereof, and introducing an oxygen-based gas containing oxygen to the fuel gas passage from the outside.

Description

  Embodiments described herein relate generally to a fuel cell and a fuel cell system.

  The fuel cell generates electric power from an electrochemical reaction between hydrogen in the fuel gas introduced into the fuel electrode (anode electrode) and oxygen in the oxidant gas introduced into the oxidant electrode (cathode electrode).

  Hydrogen as a fuel is obtained from a hydrocarbon-based raw fuel such as natural gas, propane gas or kerosene by fuel processing in a reformer. The reformer performs a process of decomposing the hydrocarbon system into carbon dioxide and hydrogen by a steam reforming reaction as shown in the following chemical formula (1) or a partial oxidation reaction as shown in the chemical formula (2).

CH ₄ + 2H ₂ O → 4H ₂ + CO ₂ (1)
CH ₄ + O ₂ → 2H ₂ + CO ₂ (2)
Here, a small amount of carbon monoxide (CO) is also produced in the reformer. It is well known that when this carbon monoxide is introduced into the fuel electrode of the fuel cell body, it is adsorbed on the surface of the catalyst and the catalytic activity is lowered.

  In order to suppress this decrease in the activity of the fuel electrode, it is common to use a selective oxidation reactor (PROX) disposed downstream of the reformer as a means for reducing the content (concentration) of carbon monoxide. is there. PROX mixes an oxidant gas in the fuel gas generated by the reformer, and converts carbon monoxide to carbon dioxide by an oxidation reaction represented by the following chemical formula (3).

CO + 1 / 2O ₂ → CO ₂ (3)
Further, it has been confirmed that the carbon monoxide concentration in the fuel gas can be reduced to 10 ppm or less by combining the PROX and the shift transformer.

US Pat. No. 4,910,099

  As described above, the carbon monoxide concentration in the fuel gas can be reduced to a certain extent, but it is still difficult to suppress the decrease in the catalytic activity of the fuel electrode. For example, since a solid polymer electrolyte type fuel cell is operated at a low temperature of 60 to 80 ° C., the catalytic activity of the fuel electrode is lowered even with carbon monoxide having a concentration of about 10 ppm.

  For example, the following countermeasures can be considered for such a problem.

  As a first countermeasure, an alloy such as platinum-ruthenium or platinum-palladium is used as a catalyst contained in the fuel electrode. Since such an alloy component promotes the desorption reaction of carbon monoxide adsorbed on platinum, it is possible to suppress deterioration in the performance of the fuel cell due to carbon monoxide. However, there is a limit to the concentration of carbon monoxide that can be suppressed by the alloy catalyst, and when excessive carbon monoxide is mixed in the fuel gas, the performance of the fuel cell is significantly reduced.

  As a second countermeasure, air is mixed into the fuel gas on the fuel inlet side of the fuel cell to reduce the amount of carbon monoxide in the fuel gas. In this case, since an oxidation reaction of carbon monoxide shown in the chemical formula (3) occurs in the fuel electrode, the amount of carbon monoxide is reduced, and a decrease in catalyst activity can be suppressed.

  Although it is possible to suppress a decrease in the catalytic activity of the fuel electrode by such measures, on the other hand, due to the following factors, an electrolyte membrane, for example, a solid polymer electrolyte membrane in a solid polymer electrolyte type fuel cell (Hereinafter referred to as “polymer film”) is shortened.

One is that when air is mixed into the fuel gas on the fuel inlet side in order to reduce the influence of carbon monoxide, hydrogen and oxygen react at the fuel electrode of many unit cells, and hydrogen peroxide (H ₂ O ₂ ) is generated, and OH radicals, which are intermediate products generated during the production of hydrogen peroxide, degrade the chemical bonds of the polymer film. That is, if air is continuously introduced into the fuel electrode during the operation of the fuel cell, the polymer membrane of the fuel cell body deteriorates and the life of the polymer membrane is shortened.

  The other is, for example, in a fuel cell that employs an internal humidification method in which the fuel gas or oxidant gas to be introduced is humidified with moisture evaporating from the separator, if the gas introduction unit is insufficiently humidified, The molecular film is deteriorated by drying. Even in fuel cells that use an external humidification system that adds water vapor to the fuel gas or oxidant gas in advance, the humidified water may condense before being introduced into the fuel cell, or the power consumption of the humidifier may be minimized. In this case, humidification of the gas introduction part is insufficient, and the polymer film of the gas introduction part is deteriorated by drying.

  Further, even in a fuel cell using a pure hydrogen gas as a fuel gas, if the humidification of the gas introduction part is insufficient, the polymer film of the fuel cell main body deteriorates and the life of the polymer film is shortened.

  The problem to be solved by the invention is to provide a fuel cell and a fuel cell system capable of extending the life of the fuel cell main body.

  In the fuel cell of the embodiment, a fuel electrode and an oxidant electrode are disposed with an electrolyte membrane interposed therebetween, a fuel gas channel configured to allow a fuel gas containing hydrogen to pass through the fuel electrode, and an oxidant gas to oxidize the fuel cell. A fuel cell main body having an oxidant gas flow path configured to pass through the agent electrode; and located downstream of the fuel gas flow path inlet and upstream of the fuel gas flow path outlet And an oxygen-based gas introduction part for introducing an oxygen-based gas containing oxygen from the outside into the fuel gas flow path.

FIG. 1 is a perspective view showing an appearance of an external gas manifold type fuel cell according to the first embodiment. FIG. 2 is a conceptual diagram showing the flow of fuel gas and the like inside the fuel cell stack provided in the fuel cell of FIG. 1 when viewed horizontally from a direction perpendicular to the longitudinal direction. 3A is a diagram showing a shape of the fuel inlet / outlet manifold provided in the fuel cell of FIG. 1 when viewed horizontally from the stack side, and FIG. 3B is a diagram showing the fuel cell of FIG. It is a figure which shows the shape at the time of seeing the fuel return manifold with which it is provided horizontally from the stack side. FIG. 4 is a graph for explaining the CO concentration in the fuel cell stack 1. FIG. 5 is a perspective view showing the external appearance of an internal gas manifold type fuel cell according to the second embodiment. FIG. 6 is a conceptual diagram showing the flow of fuel gas and the like inside when the fuel cell stack provided in the fuel cell of FIG. 5 is viewed horizontally from the direction perpendicular to the longitudinal direction. FIG. 7 is a perspective view showing the appearance of the fuel cell according to the third embodiment. FIG. 8 is a graph for explaining the utilization rate of the fuel gas. FIG. 9A is a conceptual diagram showing the flow of fuel gas and the like inside the first stack provided in the fuel cell of FIG. 7 when viewed horizontally from the direction perpendicular to the longitudinal direction. FIG. 9B is a conceptual diagram showing the flow of fuel gas and the like inside when the second stack provided in the fuel cell of FIG. 7 is viewed horizontally from the direction perpendicular to the longitudinal direction. FIG. 10A is a diagram showing a shape of the fuel inlet / outlet manifold provided in the fuel cell of FIG. 7 when viewed horizontally from the stack side, and FIG. 10B is a diagram of the fuel cell of FIG. It is a figure which shows the shape at the time of seeing the fuel return manifold with which it is provided horizontally from the stack side. FIG. 11 is a graph for explaining the CO concentration in the fuel cell stack. 12A is a view showing a modification of the shape when the fuel inlet / outlet manifold provided in the fuel cell of FIG. 7 is viewed horizontally from the stack side, and FIG. 12B is a view of FIG. It is a figure which shows the modification of the modification at the time of seeing the fuel return manifold with which a fuel cell is equipped from the stack side horizontally. FIG. 13A is a view showing a modification of the shape when the fuel inlet / outlet manifold provided in the fuel cell of FIG. 7 is viewed horizontally from the stack side, and FIG. 13B is a view of FIG. It is a figure which shows the modification of the shape at the time of seeing the fuel return manifold with which a fuel cell is equipped from the stack side horizontally. FIG. 14 is a perspective view showing an appearance of a fuel cell system according to the fourth embodiment. FIG. 15 is a perspective view showing an appearance of a fuel cell system according to the fifth embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

(First embodiment)
The first embodiment will be described with reference to FIGS. 1 to 3.

  FIG. 1 is a perspective view showing the appearance of the fuel cell according to the first embodiment.

  The fuel cell shown in FIG. 1 is, for example, a solid polymer electrolyte type fuel cell, and the fuel cell main body is on one side with a solid polymer electrolyte membrane (hereinafter referred to as “polymer membrane”) interposed therebetween. A fuel electrode is arranged, an oxidant electrode is arranged on the other side, a porous separator constituting a fuel gas flow path is arranged outside the fuel electrode of each electrode, and an oxidant gas flow is arranged outside the oxidant electrode. It has a fuel cell stack 1 in which unit cells in which porous separators constituting a path are arranged are arranged in a plurality of rows along the axial direction. Further, this fuel cell is provided with a current collector plate 2 on one outside of the fuel cell stack 1 and a current collector plate 3 on the other side, and fuel gas is supplied to the fuel gas flow path of each unit cell of the fuel cell stack 1. A fuel inlet / outlet manifold 4 is provided on the fuel inlet / outlet side of the fuel cell stack 1 as a fuel gas manifold having a gas chamber for supplying and discharging the fuel gas from the fuel gas passage, and flows through the fuel gas passage. As a fuel gas manifold having a gas chamber for turning fuel gas, a fuel return manifold 5 is provided on the fuel return portion (fuel gas turning portion) side, and a fuel inlet pipe 6 and a fuel outlet pipe 7 are provided on the fuel inlet / outlet manifold 4. The air return pipe 8 is provided in the fuel return manifold 5.

  Further, in order to function as a fuel cell, an oxidant manifold and a coolant manifold are also necessary. However, these are not directly related to the present invention, so in this embodiment, an oxidant manifold and a coolant manifold are illustrated. Is omitted (the same applies to other embodiments).

  In this embodiment, an internal humidification method in which the fuel gas or oxidant gas introduced into the fuel cell is humidified with moisture evaporating from the porous separator is employed as the polymer film humidification method. You may employ | adopt the external humidification system which adds water vapor | steam beforehand to oxidizing agent gas.

  FIG. 2 is a conceptual diagram showing the flow of fuel gas and the like inside the fuel cell stack 1 provided in the fuel cell of FIG. 1 when viewed horizontally from a direction perpendicular to the longitudinal direction. 3A is a diagram showing the shape of the fuel inlet / outlet manifold 4 provided in the fuel cell of FIG. 1 when viewed horizontally from the stack side, and FIG. 3B is a diagram of FIG. It is a figure which shows the shape at the time of seeing horizontally the fuel return manifold 5 with which a fuel cell is equipped from the stack side.

  As shown in FIG. 2, the fuel cell stack 1 has a first path 1A and a second path 1B as paths through which the fuel gas flows. Details of the fuel gas flow will be described later.

  As shown in FIG. 3A, the fuel inlet / outlet manifold 4 has two spaces 4 </ b> A and 4 </ b> B that are partitioned by a boundary between fuel gas paths. A fuel inlet pipe 6 is connected to the space 7A, and a fuel outlet pipe 7 is connected to the space 7B. The space 4A faces the first path 1A of the fuel cell stack 1, and the space 4B faces the second path 1B of the fuel cell stack 1.

  On the other hand, as shown in FIG. 3B, the fuel return manifold 5 has a space 5A inside thereof. An air introduction pipe 8 is connected to the space 5A. The space 5A faces the first path 1A and the second path 1B of the fuel cell stack 1.

  Here, with reference to FIG. 2 and FIG. 3, the fuel gas flow etc. in this embodiment are demonstrated. During operation of the fuel cell system, fuel gas, oxidant gas, and cooling water are respectively supplied to the fuel cell stack 1, but here, the flow of the fuel gas is mainly shown.

  When the fuel gas is supplied to the space 4 </ b> A of the fuel inlet / outlet manifold 4 through the fuel inlet pipe 6, the fuel gas passes through the first path 1 </ b> A of the fuel cell stack 1 and turns back in the space 5 </ b> A of the fuel return manifold 5. The fuel gas that has entered the space 5A is mixed with air introduced from the outside through the air introduction pipe 8, passes through the second path 1B of the fuel cell stack 1, and enters the space 4B of the fuel inlet / outlet manifold 4. The fuel gas that has entered the space 4B, that is, the fuel gas that has not been consumed in the fuel cell stack 1, is discharged from the fuel outlet pipe 7.

  Next, the operation of this embodiment will be described.

  The fuel gas introduced into the fuel cell usually contains a trace amount of carbon monoxide (CO). FIG. 4 shows the CO concentration in each part of the fuel cell when the CO concentration in the fuel gas is, for example, 10 ppm. When the fuel inlet of the fuel cell stack is 10 ppm and the fuel utilization rate is 67.5%, 60% of the total hydrogen consumed before reaching the fuel return part is consumed. From the fuel return part to the fuel outlet part If the remaining 40% is consumed before reaching the value, the CO concentration at each location increases as it goes downstream as described below.

Fuel return part: 10 ppm × 100 / (100-67.5 × 0.6) ≈17 ppm
Fuel outlet: 10 ppm × 100 / (100-67.5) ≈31 ppm
In general, as the CO concentration increases, the voltage drop increases, and therefore, it is easily affected by the performance deterioration particularly on the downstream side where the CO concentration increases. In order to suppress the performance degradation, a method of reducing the amount of carbon monoxide in the fuel gas by mixing air into the fuel gas supplied to the fuel gas side electrode is effective.

On the other hand, the fuel gas introduction part is a place where the polymer film is easily damaged due to drying, and when air is mixed before the fuel gas is introduced, hydrogen and oxygen react with each other at the fuel electrode, resulting in hydrogen peroxide. It has been confirmed that (H ₂ O ₂ ) is produced. The OH radical, which is an intermediate product generated when hydrogen peroxide is generated, degrades the chemical bond of the polymer film. That is, if air is continuously introduced into the fuel electrode during the operation of the fuel cell, the polymer membrane of the fuel cell body deteriorates and the life of the polymer membrane is shortened. Thus, the fuel inlet portion where the deterioration due to drying and the chemical deterioration due to the introduction of air overlap is most easily damaged in the plane. Therefore, by introducing air from the air introduction pipe 8 provided in the fuel return manifold 5, damage to the fuel inlet can be suppressed and the CO concentration downstream of the fuel gas having a high CO concentration can be reduced. The gas introduced from the air introduction pipe 8 is not limited to air, and any gas other than air may be applied as long as it is an oxygen-based gas containing oxygen.

Comparison of three cases of voltage life and polymer life: (1) no oxygen gas introduction, (2) oxygen gas introduction (fuel inlet), (3) oxygen gas introduction (fuel return) The following table shows the results of the verification. Here, it is assumed that the oxygen-based gas is air.

  The voltage life and polymer film life are shown as relative values when the case (3) is 1.0. In case (1), since there is no air introduction, the voltage life is as short as 0.4. On the other hand, the polymer membrane life is not deteriorated due to air introduction, and is as long as 1.1. Is 0.4. In case (2), air is introduced from the fuel inlet and the voltage life is as long as 1.1. However, since air is introduced from the fuel inlet, the deterioration of the fuel inlet is large. The lifetime of the polymer film is 0.9. For case (3), the introduction of air from the fuel return part suppresses the decrease in the voltage life and suppresses the decrease in the polymer film life at the fuel inlet, so the total life is 1.0. And showed the best results among the three cases.

  As described above, according to the present embodiment, it is possible to achieve both the suppression of the decrease in the voltage life and the suppression of the decrease in the life of the polymer membrane, and the life of the fuel cell body can be extended.

  In this embodiment, the fuel cell stack 1 is exemplified as a two-pass flow configuration including the first path 1A and the second path 1B. However, the present invention is not limited to this, and the stack includes three or more paths. It is good also as a structure.

(Second Embodiment)
The second embodiment will be described with reference to FIGS. 5 and 6.

  FIG. 5 is a perspective view showing the appearance of the fuel cell according to the second embodiment. FIG. 6 is a conceptual diagram showing the flow of fuel gas and the like inside when the fuel cell stack 21 provided in the fuel cell of FIG. 5 is viewed horizontally from a direction perpendicular to the longitudinal direction.

  In the above-described first embodiment, the fuel cell stack 1 is provided with the fuel inlet / outlet manifold 4 and the fuel return manifold 5, the fuel inlet pipe 6 and the fuel outlet pipe 7 are provided in the fuel inlet / outlet manifold 4, and the air Although the configuration in which the introduction pipe 8 is provided in the fuel return manifold 5 has been shown, in this second embodiment, not such a configuration, but on the back side of the current collector plate 23 of one of the current collector plates 22 and 23, A fuel inlet manifold 24A having a gas chamber for supplying fuel gas to the fuel gas passage, a fuel outlet manifold 24B having a gas chamber for discharging the fuel gas from the fuel gas passage, and the fuel gas passage. A fuel return manifold 25 having a gas chamber for turning back the fuel gas is arranged so that the fuel inlet pipe 26 and the fuel outlet pipe 27 are aligned. The air inlet pipe 28 is provided in the current collector plate 23, and the fuel inlet pipe 26, the fuel outlet pipe 27, and the air inlet pipe 28 penetrate the current collector plate 23, respectively, and the fuel inlet manifold 24A, the fuel outlet manifold 24B, and the fuel return, respectively. It is configured to be connected to each gas chamber of the manifold 25.

  Other configurations and operations are the same as those in the first embodiment.

  As described above, according to the present embodiment, there is an effect similar to that of the first embodiment, and it is possible to achieve both suppression of the decrease in voltage life and suppression of the decrease in life of the polymer film, and the long life of the fuel cell main body. Can be achieved.

(Third embodiment)
The third embodiment will be described with reference to FIGS.

  FIG. 7 is a perspective view showing the appearance of the fuel cell according to the third embodiment.

  The fuel cell shown in FIG. 7 is, for example, a solid polymer electrolyte type fuel cell, and the fuel cell main body has a fuel electrode disposed on one side and a oxidant electrode disposed on the other side with a polymer membrane interposed therebetween. And a unit cell in which a porous separator constituting the fuel gas flow path is arranged outside the fuel electrode of each electrode, and a porous separator constituting the oxidant gas flow path is arranged outside the oxidant electrode. The fuel cell stack 41 is arranged in a plurality of rows along the axial direction. Further, in this fuel cell, the fuel cell stack 41 has a two-stage configuration including a first stack 49 and a second stack 50, and a current collecting plate 42 is provided outside the first stack 49, whereby the second stack As a fuel gas manifold provided with a current collecting plate 43 outside 50, a separator plate 51 between the stacks, and a gas chamber for supplying fuel gas to the fuel gas flow path of each unit cell of the fuel cell stack 41 The fuel inlet / outlet manifold 44 is provided on the fuel inlet / outlet side of the fuel cell stack 41, the fuel return manifold 45 is provided on the fuel return portion side, and the fuel inlet pipe 46 and the fuel outlet pipe 47 are provided on the fuel inlet / outlet manifold 7. In addition, an inter-stack communication channel 52 is provided outside the fuel inlet / outlet manifold 44. The inter-stack communication channel 52 guides fuel gas from a lower space in the fuel inlet / outlet manifold 44 to a higher space in the same fuel inlet / outlet manifold 44. It is assumed that the number of unit cells is smaller in the second stack 50 than in the first stack 49 (for example, a ratio of 75% to 25%).

  Further, in order to function as a fuel cell, an oxidant manifold and a coolant manifold are also necessary. However, these are not directly related to the present invention, so in this embodiment, an oxidant manifold and a coolant manifold are illustrated. Is omitted (the same applies to other embodiments).

  By the way, as one of the methods for increasing the efficiency, there is a method of improving the fuel utilization rate (ratio of consumption to the amount of fuel supply). In the case of a plant equipped with a reformer that converts fuel into hydrogen, the fuel gas discharged from the fuel cell is used as a heat source, but in the case of a pure hydrogen fuel plant, hydrogen that is not used for power generation is exhausted. Therefore, improving the fuel utilization rate is effective in improving the plant efficiency.

  In the fuel cell in which the fuel cell stack has a two-stage configuration including two stacks as in the present embodiment, 75% of the total number of unit cells in the fuel cell is the first stack, and the remaining 25% unit cells. Is the second stack, as shown in FIG. 8, the utilization rate of each stack can be made lower than the overall utilization rate in all the areas. For example, when the overall fuel gas utilization rate is 90%, the actual utilization rate of the fuel gas in the first stack is 90% × 0.75 = 67.5%, and the fuel gas in the second stack The actual utilization ratio of 0.25 / {(100% / 90%) − 0.75} × 100≈69.2%, and the utilization ratio of each stack without changing the overall utilization ratio of the fuel gas It is possible to increase the flow rate of the fuel gas supplied to the individual stacks without decreasing the flow rate, that is, without changing the overall flow rate of the fuel gas. Such a method is effective in improving the plant efficiency because the entire fuel gas flow rate can be reduced. Therefore, in the present embodiment, such a method is applied to the first stack 49 and the second stack 50 described above.

  FIG. 9A is a conceptual diagram showing the flow of fuel gas and the like in the interior when the first stack 49 provided in the fuel cell of FIG. 7 is viewed horizontally from the direction perpendicular to the longitudinal direction. FIG. 9B is a conceptual diagram showing a flow of fuel gas and the like inside the second stack 50 provided in the fuel cell of FIG. 7 when viewed horizontally from a direction perpendicular to the longitudinal direction. FIG. 10 (a) is a view showing the shape of the fuel inlet / outlet manifold 44 provided in the fuel cell of FIG. 7 when viewed horizontally from the stack side, and FIG. 10 (b) is a view of FIG. It is a figure which shows the shape at the time of seeing horizontally the fuel return manifold 45 with which a fuel cell is equipped from the stack side.

  As shown in FIG. 9A, the first stack 49 has a first path 49A and a second path 49B as paths through which the fuel gas flows. Further, as shown in FIG. 9B, the second stack 50 includes a first path 50A and a second path 50B as paths through which the fuel gas flows. As can be seen from FIGS. 9A and 9B, the first stack 49 and the second stack 50 have a common two-stage path configuration. Details of the fuel gas flow will be described later.

  As shown in FIG. 10A, the fuel inlet / outlet manifold 44 is divided into four spaces 44A, 44B, and 44C that are partitioned between the stacks and between the fuel gas paths. , 44D. A fuel inlet pipe 46 is connected to the space 44A, a fuel outlet pipe 47 is connected to the space 44D, and both spaces 44B and 44C are connected to both via the openings 53 and 54 provided in the fuel inlet / outlet manifold 44. The aforementioned inter-stack communication flow path 52 that connects the space outside the fuel inlet / outlet manifold 44 is connected. The space 44A is opposed to the first path 49A of the first stack 49, the space 44B is opposed to the second path 49B of the first stack 49, and the space 44C is the first of the second stack 50. The space 44 </ b> D is opposed to the second path 50 </ b> B of the second stack 50.

  On the other hand, as shown in FIG. 10B, the fuel return manifold 45 has two spaces 45 </ b> A and 45 </ b> B that are partitioned between the stacks inside. An air introduction pipe 48 is connected to the space 45A. The space 45A is opposed to the first path 49A and the second path 49B of the first stack 49, and the space 45B is opposed to the first path 50A and the second path 50B of the second stack 50. Yes.

  Here, with reference to FIG. 9 and FIG. 10, the fuel gas flow etc. in this embodiment are demonstrated. During operation of the fuel cell system, fuel gas, oxidant gas, and cooling water are respectively supplied to the fuel cell stack 41. Here, the flow of the fuel gas is mainly shown.

  When the fuel gas is supplied to the space 44 </ b> A of the fuel inlet / outlet manifold 44 through the fuel inlet pipe 46, the fuel gas passes through the first path 49 </ b> A of the first stack 49 and turns back in the space 45 </ b> A of the fuel return manifold 45. . The fuel gas that has entered the space 45 </ b> A mixes with air introduced from the outside through the air introduction pipe 48, passes through the second path 49 </ b> B of the first stack 49, and enters the space 44 </ b> B of the fuel inlet / outlet manifold 44. The fuel gas that has entered the space 44B passes through the inter-stack communication flow path 52 via the opening 53 of the fuel inlet / outlet manifold 7 and enters the space 44C via the opening 54 of the fuel inlet / outlet manifold 44. The fuel gas that has entered the space 44C passes through the first path 50A of the second stack 50, turns back in the space 45B of the fuel return manifold 45, passes through the second path 50B of the second stack 50, and enters the fuel inlet / It enters the space 44D of the outlet manifold 44. The fuel gas that has entered the space 44 </ b> D, that is, the fuel gas that has not been consumed in the fuel cell stack 41 is discharged from the fuel outlet pipe 47.

  In the present embodiment, the fuel cell stack 41 is illustrated as having a two-stage configuration including the first stack 49 and the second stack 50. However, the present invention is not limited to this and includes three or more stacks. It is good also as a structure of 3 steps | paragraphs or more. When the fuel cell stack 1 has an N-stage configuration including N stacks, the space facing the fuel outlet of the i-th stack (i is an integer not less than 1 and not more than N-1) and the i + 1-th stack An inter-stack communication channel 52 that communicates with the space facing the fuel inlet is provided outside the fuel inlet / outlet manifold 44, respectively.

  Next, the operation of this embodiment will be described.

  The fuel gas introduced into the fuel cell usually contains a trace amount of carbon monoxide (CO). FIG. 11 shows the CO concentration in each part of the fuel cell when the CO concentration in the fuel gas is, for example, 10 ppm. When the fuel inlet of the fuel cell stack is 10 ppm and the fuel utilization rate is 90%, 60% of the hydrogen consumed in each stack is consumed before reaching the fuel return part, and the fuel return part is connected to the fuel outlet part. If the remaining 40% is consumed by the time it reaches, the CO concentration at each location becomes higher as it goes downstream as described below.

Fuel return part of first stack 49: 17 ppm
Fuel outlet of first stack 49, fuel inlet of second stack 50: 31 ppm
Fuel return part of second stack 50: 53 ppm
Fuel outlet of second stack 50: 100 ppm
In general, as the CO concentration increases, the voltage drop increases, and therefore, it is easily affected by the performance deterioration particularly on the downstream side where the CO concentration increases. In particular, compared with the first embodiment, the fuel utilization rate of each stack is almost the same as a little less than 70%. However, since the overall fuel utilization rate is as high as 90%, the CO concentration decreases toward the downstream of the cell. Remarkably high. In order to suppress the performance degradation, a method of reducing the amount of carbon monoxide in the fuel gas by mixing air into the fuel gas supplied to the fuel gas side electrode is effective.

On the other hand, as described above, the fuel gas introduction part is a place where the polymer film is easily damaged by drying, and when air is mixed before the fuel gas is introduced, hydrogen and oxygen react at the fuel electrode. Thus, it has been confirmed that hydrogen peroxide (H ₂ O ₂ ) is generated. The OH radical, which is an intermediate product generated when hydrogen peroxide is generated, degrades the chemical bond of the polymer film. That is, if air is continuously introduced into the fuel electrode during the operation of the fuel cell, the polymer membrane of the fuel cell body deteriorates and the life of the polymer membrane is shortened. Thus, the fuel inlet portion where the deterioration due to drying and the chemical deterioration due to the introduction of air overlap is most easily damaged in the plane. Therefore, by introducing air from the air introduction pipe 48 provided in the fuel return manifold 45, damage to the fuel inlet portion can be suppressed and the downstream side of the fuel gas having a high CO concentration can be suppressed as in the first embodiment. CO concentration can be reduced. The gas introduced from the air introduction pipe 48 is not limited to air, and any gas other than air may be applied as long as it is an oxygen-based gas containing oxygen.

  According to the present embodiment, as in the first embodiment and the second embodiment, it is possible to achieve both the suppression of the decrease in voltage life and the suppression of the decrease in life of the polymer membrane, thereby extending the life of the fuel cell body. Can be planned.

  In the present embodiment, the fuel cell stack 41 includes the first path 49A and the second path 49B of the first stack 49, and the first path 50A and the second path 50B of the second stack 50. Although the case of a two-pass flow configuration is illustrated, the present invention is not limited to this, and a configuration including a stack of three or more passes may be used.

  Further, the configuration of FIG. 10 may be modified as in the configuration of FIG. 12 or the configuration of FIG. 12 shows an example in which the air introduction pipe 58 is provided in the fuel inlet / outlet manifold 44 and connected to the space 44C. FIG. 13 shows the air introduction pipe 68 provided in the fuel return manifold 45 to be connected to the space 45B. Each example is shown in FIG. Also in this case, the same effect as that obtained when configured as shown in FIG. 10 can be obtained.

(Fourth embodiment)
The fourth embodiment will be described with reference to FIG.

  FIG. 14 is a perspective view showing an appearance of a fuel cell system according to the fourth embodiment.

  The fuel cell system shown in FIG. 14 includes a fuel cell 91 corresponding to any one of the fuel cells shown in the first to third embodiments, and reforms the raw fuel into a hydrogen-rich gas. A reformer 92 that supplies gas to the fuel electrode 91 a of the fuel cell 91, an oxidant gas supply device 93 that supplies oxidant gas to the oxidant electrode 91 b of the fuel cell 91, and a coolant that cools the fuel cell 91. The apparatus includes a cooling device 94 that supplies and recovers the portion 91c and an electric control device 95 that supplies electricity extracted from the fuel cell 91 to the outside.

  In such a configuration, raw fuel gas such as city gas is supplied to the reformer 92, and the reformed hydrogen-rich fuel gas is supplied to the fuel electrode 91 a of the fuel cell 91. Further, the oxidant gas is supplied to the oxidant electrode 91b by the oxidant gas supply device 93, and the coolant is supplied to the battery cooling unit 91c by the cooling device 94. At this time, a part of the oxidant gas supplied from the oxidant gas supply device 93 is supplied to the fuel electrode 91a from the middle of the fuel gas flow path of the fuel cell 91 through the air introduction pipe 8 (not shown). The Electricity obtained by supplying the fuel gas and the oxidant gas is supplied to the outside of the fuel cell system by the electric control device 95.

  According to the fourth embodiment, it is possible to realize a fuel cell system that takes advantage of the advantages of the fuel cells shown in the first to third embodiments.

(Fifth embodiment)
The fifth embodiment will be described with reference to FIG.

  In the fifth embodiment, parts that are the same as those in the configuration of the fourth embodiment shown in FIG. 15 are given the same reference numerals, and redundant descriptions are omitted. Below, it demonstrates centering on a different part from 4th Embodiment.

  FIG. 15 is a perspective view showing an appearance of a fuel cell system according to the fifth embodiment.

  The fuel cell system shown in FIG. 15 includes a pure hydrogen gas supply device 96 in place of the reforming device 92 described above. The pure hydrogen gas supply device 96 supplies pure hydrogen gas to the fuel electrode 91 a of the fuel cell 91.

  When pure hydrogen gas is used as the fuel gas, the hydrogen concentration is 100% in any stack group consisting of multiple stages, excluding trace impurities, and there is no difference in the composition of the fuel gas between the stacks. In comparison, it is possible to operate under substantially the same conditions.

  According to the fifth embodiment, when pure hydrogen gas is used as the fuel gas, it is possible to realize a fuel cell system that further utilizes the advantages of the fuel cells shown in the first to third embodiments. Become.

  In each embodiment, since air is not introduced into the fuel gas introduction portion (fuel inlet portion) of the fuel cell stack, the range where the air upstream of the fuel gas is not introduced is affected by carbon monoxide, and the performance of the fuel cell There is a possibility of hindering the improvement. In order to prevent this, in each embodiment, it is preferable to apply a platinum-based alloy catalyst to the fuel electrode. Specifically, a platinum-ruthenium alloy catalyst or a platinum-palladium alloy catalyst. By applying these alloy catalysts to the fuel electrode, even when a carbon monoxide concentration of about several ppm is included in the fuel gas, it is possible to suppress a decrease in the performance of the fuel cell.

  In each embodiment, the case where air is used as the oxidant gas to be introduced into the fuel electrode has been described. However, other types of gas may be used as long as the gas contains pure oxygen or oxygen.

  As described in detail above, according to each embodiment, at least at a predetermined position located on the downstream side of the fuel inlet of the fuel gas passage and on the upstream side of the fuel outlet of the fuel gas passage, Since the configuration in which an oxygen-based gas containing oxygen is introduced from the outside into the fuel gas flow path, the life of the fuel cell main body can be extended.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  1, 2, 41 ... Fuel cell stack, 2, 3, 22, 23, 42, 43 ... Current collector plate, 4, 24, 44 ... Fuel inlet / outlet manifold, 24A ... Fuel inlet manifold, 24B ... Fuel outlet manifold, 5, 25, 45 ... Fuel return manifold, 6, 26, 46 ... Fuel inlet piping, 7, 27, 47 ... Fuel outlet piping, 8, 28, 48, 58, 68 ... Air introduction piping, 49 ... First stack , 50 ... second stack, 51 ... separating plate, 52 ... inter-stack communication channel, 53,54 ... opening, 91 ... fuel cell, 92 ... reforming device, 93 ... oxidant gas supply device, 94 ... cooling Device: 95 ... Electric control device, 96 ... Pure hydrogen gas supply device.

Claims (10)

A fuel electrode and an oxidant electrode are disposed with an electrolyte membrane interposed therebetween, and a fuel gas channel configured to allow a fuel gas containing hydrogen to pass through the fuel electrode, and a oxidant gas to pass through the oxidant electrode A fuel cell main body having an oxidant gas flow path formed,
Oxygen-containing gas containing oxygen from the outside to the fuel gas channel at a predetermined position located downstream from the inlet of the fuel gas channel and upstream of the outlet of the fuel gas channel. A fuel cell comprising an oxygen-based gas introduction part to be introduced.   The fuel cell according to claim 1, wherein the fuel gas contains carbon monoxide in addition to hydrogen.   The fuel cell according to claim 1, wherein the electrolyte membrane is a solid polymer electrolyte membrane.   4. An internal humidification method in which fuel gas is humidified with moisture evaporated from a separator constituting the fuel gas flow path is adopted as a method for humidifying the solid polymer electrolyte membrane. The fuel cell according to any one of the above.   The fuel cell according to claim 4, wherein the separator is porous.   6. The fuel cell main body according to claim 1, wherein a fuel cell stack in which unit cells are arranged in a plurality of rows along the axial direction has a multi-stage configuration including a plurality of stacks. The fuel cell according to any one of the above. A manifold for turning back the fuel gas flowing through the fuel gas flow path;
The fuel cell according to any one of claims 1 to 6, wherein the oxygen-based gas introduction section is provided in the manifold.   The fuel cell according to any one of claims 1 to 7, wherein the fuel electrode includes a platinum-based alloy catalyst.   9. The fuel cell according to claim 1, reforming means for reforming raw fuel into a hydrogen-rich gas and supplying the reformed gas to the fuel cell, and oxidizing gas as the fuel. An oxidant gas supply means for supplying a battery, a cooling means for supplying and recovering a coolant to the fuel cell, and an electric control means for supplying the electricity extracted from the fuel cell to the outside. Fuel cell system.   9. The fuel cell according to any one of claims 1, 3 to 8, pure hydrogen gas supply means for supplying pure hydrogen gas to the fuel cell, and oxidant gas supply for supplying oxidant gas to the fuel cell. A fuel cell system comprising: means; cooling means for supplying and recovering coolant to the fuel cell; and electric control means for supplying electricity extracted from the fuel cell to the outside.

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