JP2909307B2 - Fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a fuel cell, an electrolyte matrix, and a stacked body in which a plurality of single fuel cells each including a oxidizer electrode, a gas separator, and a cooling plate are stacked. It relates to a fuel cell.

[0002]

2. Description of the Related Art Conventionally, as a method for supplying a fuel gas to a fuel cell stack, there has been a method disclosed in Japanese Patent Publication No. 62-23434. This means that one laminate is divided into a first laminate and a second laminate, a fuel gas is supplied to the first laminate, the exhaust gas is supplied to the second laminate, and the first laminate is Was increased by at least one cell compared to the number of stacked single cells included in the second stacked body (hereinafter referred to as the number of downstream cells). Things. Such a flow type in which the exhaust gas of the first stacked body is supplied to the second stacked body is generally called a serial flow system.

The above-described fuel cell is intended to prevent a decrease in flow velocity due to consumption of fuel gas by reducing a fuel gas space on the downstream side. An object of the present invention is to reduce the utilization factor to avoid a local fuel deficiency due to uneven fuel supply and to prevent the cell from being corroded. This effect of corrosion prevention is described in “Corrosion, Vol. 46, P628-P633 (1990)”, which shows empirical data when the number of upstream cells and the number of downstream cells are the same.
Also, the mechanism by which the corrosion of a cell occurs due to an increase in the fuel utilization rate is described in J. Am. Electrochem. S
oc. Vol. 137, P3079-P3085 (1990)
It is described in.

[0004] By supplying a fuel gas containing methane reformed carbon monoxide to a phosphoric acid fuel cell stack in which the number of upstream cells is actually twice the number of downstream cells, we conducted an operation test. Was. When the fuel utilization rate is increased to 90%, the decrease of the cell voltage near the cooling plate of the downstream cell becomes remarkably large,
The voltage of the cell turned negative, and it became impossible to operate. This is because, in the downstream cell, the hydrogen partial pressure decreases with the consumption of hydrogen in the upstream cell, and the concentration of carbon monoxide relatively increases. It was presumed that the effects of CO poisoning became significant. Note that the fuel utilization rate of 90% is a utilization rate necessary for increasing the efficiency of the fuel cell.

A method for solving this problem is disclosed in
There is one disclosed in Japanese Patent Application Laid-Open No. 3-29463. This is a method of removing water vapor from the exhaust gas of the upstream cell and increasing the hydrogen partial pressure of the fuel gas supplied to the downstream cell. However, there is a disadvantage that the cost is increased because a device for removing water vapor is required.

[0006]

The conventional phosphoric acid type fuel cell is configured as described above, and cannot operate stably up to a fuel utilization rate of about 90%. In addition, there is a problem that the cost is increased in the method of removing water vapor for stable operation. The present invention has been made in order to solve the above-described problems, and has as its object to provide a fuel cell that can operate stably without increasing the cost even when the fuel utilization rate increases. .

[0007]

According to a first aspect of the present invention, there is provided a fuel cell comprising a fuel cell and a fuel cell. The fuel cell is divided into a first fuel cell and a second fuel cell. The number of single cells of the first stacked body is smaller than the number of single cells of the second stacked body.

[0008] The fuel cell according to the present invention is characterized in that the stack is composed of a first stack to which fuel gas is supplied and a first stack .
The first laminate is divided into a second laminate, which is electrically connected in series and supplied with the exhaust gas, and has different electrode reaction areas of the single cells of the first laminate and the second laminate. It was made.

Further, in the fuel cell according to a third aspect of the present invention, the stack is divided into a first stack to which fuel gas is supplied and a second stack to which exhaust gas is supplied. A first current collector and a second current collector provided at both ends of the laminate, a third current collector provided between the first laminate and the second laminate, and the first current collector being provided; Plate and said third
Due to loads inserted between the current collector and the third current collector and between the third current collector and the second current collector, respectively, the total current of the power generation reaction between the first stacked body and the second stacked body. The values are different.

[0010]

In the fuel cell according to the first aspect of the present invention, the number of the upstream cells as the first stacked body is made smaller than the number of the downstream cells as the second stacked body, so that the fuel supplied to the downstream cells is reduced. The concentration of hydrogen contained in the gas can be kept high, the concentration of carbon monoxide can be kept low, and the effect of CO poisoning in the cells near the cooling plate can be kept low, so that it can operate stably even at high fuel utilization. be able to.

In the fuel cell according to the second aspect of the present invention, the electrode reaction areas of the upstream cell and the downstream cell are made different, so that the ratio of the hydrogen consumption between the upstream and downstream in the serial flow system is constant. The operating current densities of the cells upstream and downstream can be adjusted, and the cell characteristics (cell voltage) upstream and downstream can be arbitrarily set.

Further, in the fuel cell according to the third aspect of the present invention, the total current value of the power generation reaction of the upstream cell and the downstream cell is made different, so that the hydrogen consumption of the whole fuel cell is constant, but the upstream of the serial flow. , And the operating current density of the cell can be simultaneously adjusted, and the cell characteristics (cell voltage) at the upstream and downstream can be arbitrarily set.

[0013]

【Example】

Embodiment 1 FIG. Hereinafter, first, theoretical considerations performed by the present inventors according to the present invention will be described. The advantage of using more upstream cells than downstream cells as in the prior art is that the actual fuel utilization of the downstream cells is reduced. Conversely, the disadvantages are that the hydrogen concentration in the downstream cell decreases and the C
O concentration increases. Therefore, quantitative analysis was performed on the real fuel utilization rate, hydrogen concentration, and CO concentration of the downstream cell. First, regarding the real fuel utilization rate of the downstream cell, the nominal fuel utilization rate (the fuel utilization rate of the whole stack) is calculated as U _F
(100% = 1), and the real fuel utilization rates of the upstream cell and the downstream cell are U _FU and U _FD (100% = 1), respectively. If the ratio between the number of upstream cells and the number of downstream cells is α (= the number of upstream cells / the number of downstream cells), U _FU and U _FD are expressed by equations (1) and (2), respectively. FIG. 3 shows the change with respect to the nominal fuel utilization rate. In FIG. 3, the horizontal axis represents the nominal fuel utilization rate (U _F ;%), and the vertical axis represents the real fuel utilization rate (U _FU , U _FD ;
%), And the region indicated by the arrow A at the top indicates a corrosion dangerous region. Here, a case where the first laminate (upstream cell) and the second laminate (downstream cell) have the same electrode area and current value will be described. _{U FU = {α / (1} + α)} × U F ··· (1) U FD = U F / (1 + α-α × U F) ··· (2) in FIG. 3 alpha = 0.5, 1, 2 shows that the real fuel utilization rate is significantly improved in the upstream cell, and that in the downstream cell, the larger the α is, the more the real fuel utilization rate is improved. As indicated by arrow A, when the actual fuel utilization rate becomes 90% or more, the risk of corrosion of the oxidant electrode increases.

FIG. 4 is a graph showing the nominal fuel utilization factor U _F (%) when U _FD becomes 90% on the vertical axis and α on the horizontal axis. As can be seen from this graph, for example, when α = 1, U _F is 94.7%, which indicates that there is a margin in the fuel utilization rate of about 4.7%. That is, the nominal fuel utilization rate is 9
Because Takamara not the U _FD up to 4.7% does not reach 90%, it can be seen that the risk of corrosion is substantially reduced.
FIG. 4 shows that the larger the value of α, the higher the effect of preventing corrosion of the oxidant electrode. However, even if it is assumed that the reforming rate of methane to hydrogen is reduced due to the malfunction of the reformer, it is unlikely that the nominal fuel utilization rate is much higher than 90%. Even if the rate is improved, the prevention effect is sufficient. Therefore, it is considered that the corrosion effect is sufficient even when α is about 0.3. In addition, regarding the danger of corrosion when the fuel utilization rate is increased, the Abstracts of the 1989 National Meeting of the Institute of Electrical Engineers of Japan, pages 11-212 to 11
Pp. 213, which shows that the risk of corrosion increases with increasing fuel utilization at an accelerated rate.

Next, regarding the hydrogen concentration and CO concentration of the downstream cell, the hydrogen concentration at the inlet side of the upstream cell is represented by P (H
₂ ), the CO concentration is P (CO) (100% =
1) Then, the hydrogen concentration P _D (H ₂ ) at the downstream cell inlet side,
The CO concentration P _D (CO) is expressed by Expression (3) and Expression (4), respectively. _{P D (H 2) = (} α + 1-α × U F) / {(α + 1) / P (H 2) -α × U F} ··· (3) P D (CO) = (α + 1) × P ( CO) / {α + 1- α × U F × P (H 2)} ··· (4) reforming of methane is carried out excessively added water vapor at about 600 to 800 ° C., hydrogen through the CO converter rich Is supplied to the fuel cell. The ratio of carbon to steam during this reforming reaction is generally called S / C, and usually S / C = 2 to 2.
At 4, a reforming reaction is performed. At this time, the composition of the reformed gas supplied to the fuel cell is 55 to 80% of hydrogen, 0.1 to 3.0% of carbon monoxide, and the remainder is carbon dioxide, water vapor and the like. Such a composition is not limited to methane, and the same applies to a case where methane or propane is used as a raw material.

FIG. 5 shows the change of P _D (H ₂ ) by U _F when P (H ₂ ) = 60% (0.6), and the horizontal axis shows the nominal fuel utilization rate (U _F). ;%), the hydrogen concentration on the vertical axis (P _D (H ₂₎ and P (H _2);%) is a graph showing a. It can be seen that at α = 2, the hydrogen concentration at the downstream cell inlet side drops to the 30% range at 90% U _F. Also,
FIG. 6 shows U _F of P _D (CO) when the CO concentration is 1%.
The horizontal axis shows the nominal fuel utilization rate (U
_F;%), carbon monoxide concentration on the vertical axis (P _D (CO) and P
It is a graph which shows (CO);%). 90% at α = 2
It can be seen that the CO concentration has increased to near 2% at U _F. CO poisoning is caused by inhibiting the adsorption of H ₂ molecules to platinum by specific adsorption of CO on a platinum catalyst. The lower the hydrogen concentration, the higher the CO concentration, and the lower the operating temperature, The influence of CO poisoning is great, and the cell voltage drops significantly.

FIG. 7 shows the hydrogen concentration (P _D (H ₂ );
%) And carbon monoxide _{(P D (CO);%} ), a graph showing the relationship taking α on the horizontal axis. It can be seen that as α increases, P _D (H ₂ ) decreases and P _D (CO) increases.

On the basis of the above theoretical considerations, the inventors of the present invention actually used a phosphoric acid fuel cell stack of 18 cells as shown in FIG. The methane reforming gas was supplied by changing the ratio of the partition plate attached to the fuel gas manifold to various values, and the change in the output voltage of the cell near the cooling plate was examined. FIG. 1 is a configuration diagram showing a phosphoric acid type fuel cell according to one embodiment of the present invention. In the figure, reference numeral 1 denotes a single cell, which comprises a fuel electrode 2, an electrolyte matrix 3, and an oxidant electrode 4. The single cell 1, the cooling plate 5 and the gas separation plate 6 are sequentially laminated to constitute a phosphoric acid type fuel cell alone.
Reference numeral 7 denotes a first stacked body (hereinafter, referred to as an upstream cell) to which fuel gas is supplied from the direction of arrow B, and reference numeral 8 denotes a second stacked body (hereinafter, referred to as downstream cell) to which the exhaust gas is supplied.

Using this phosphoric acid type fuel cell stack, the ratio of the number of upstream cells to the number of downstream cells is changed to supply reformed gas of methane, and the change in the output voltage of the cells near the cooling plate 5 is monitored. The result of the examination is shown in FIG. In the figure, the horizontal axis is α, and the vertical axis is the cell voltage V near the cooling plate 5 when U _F = 90% under a load of 200 mA / cm ² . In the figure, 11 to 13
11 shows the case where the concentration of water vapor supplied to the fuel cell body, that is, the concentration of hydrogen is different, 11 shows the result when the hydrogen concentration is 62%, 12 shows the result when the hydrogen concentration is 60%, and 13 shows the result when the hydrogen concentration is 58%. From the results of FIG. 2, when α is larger than 1, 200 m
At A / cm ² , it was found that the cell voltage sharply decreased. On the other hand, α = 0.29 (4 upstream cells: 14 downstream cells), α = 0.5 (9 upstream cells: 9 downstream cells), α = 0.8 (8 upstream cells) In the example of (cell: 10 downstream cells), it was found that the cell voltage was stable and stable operation was possible. That is, the operation can be stably performed when α is smaller than 1.

As described above, by making the number of single cells of the first stack smaller than the number of single cells of the second stack, the concentration of hydrogen contained in the fuel gas supplied to the downstream cells is kept high. The carbon monoxide concentration can be kept low, and stable operation can be achieved even when the fuel utilization is increased. In addition, there is no need to provide steam removal equipment conventionally provided between the upstream cell and the downstream cell, and it is possible to prevent an increase in cost. Note that, in the above example, the case where a reformed gas of methane was used was shown, but the same result would be obtained by using a reformed gas such as methanol or propane. It is clear from similarities.
Further, it is apparent from the results of FIG. 2 that the cell voltage changes with α = 1 as an inflection point even when the hydrogen concentration of the reformed gas changes. Even if α is 1 or more, stable operation can be achieved if the fuel utilization is lower than 90%. However, the risk of corrosion of the oxidant electrode increases when the fuel utilization rises to 90% or higher. The effect of preventing corrosion by using a serial flow cannot be sufficiently exhibited. Therefore,
Even if the fuel utilization rate is 90%, it can be operated stably,
In addition, the range of 0 <α <1 where the fuel utilization is sufficient, and more preferably the range of 0.3 <α <1 where the margin of the fuel utilization of 2% or more is expected.

In each of the examples of the first embodiment, the first laminate and the second laminate have the same electrode reaction area. Focusing on the composition of the fuel gas supplied to the downstream cell, corrosion prevention of the cell and CO deposition are prevented. The idea is to reduce poisons. However, in any case, since the exhaust gas of the upstream cell is supplied to the downstream cell in the serial flow method, the hydrogen concentration of the downstream cell cannot be higher than that of the upstream cell, and the operation of the power generation reaction between the upstream cell and the downstream cell. If the current density is the same and the operating temperature conditions are the same (actual serial flow type fuel cells
Under these conditions, the characteristics of the downstream cells (specifically, cell voltage) are lower than those of the upstream cells, and the power generation efficiency of the entire fuel cell is reduced.

Embodiment 2 FIG. FIG. 8 is a cross-sectional view of a main part of the fuel cell according to the second embodiment. 8, reference numeral 21 denotes a fuel cell stack, and reference numerals 21a and 21b denote a first stack and a second stack, respectively.
Represents a laminate. 22a is a fuel supply header, 22b is a fuel discharge header, 22c is an intermediate header, 23 is an air side header, 24 is a current collector, 25 is an insulating plate, and 26a is a second
The upstream cells stacked in the stacked body 21a, and the downstream cells 26b stacked in the second stacked body 21b. Here, the number of the upstream cells 26a stacked on the first stacked body 21a is N
a, the number of downstream cells 26b stacked on the second stacked body 21b is represented by Nb. In addition, I shown in the figure indicates the total current generated by the fuel cell stack 21.

FIG. 9 shows an upstream cell 26a and a downstream cell 26b.
27a and 27b are electrode reaction portions of the upstream cell 26a and the downstream cell 26b, respectively, and 28a and 28b are electrode sealing portions of the upstream cell 26a and the downstream cell 26b, respectively. In the case of the present embodiment, the cell outer size of the upstream cell 26a and the downstream cell 26b is the same, but the electrode sealing portion 28a of the upstream cell 26a.
Is larger than the electrode sealing portion 28b of the downstream cell 26b, and the electrode reaction area Sa of the electrode reaction portion 27a of the upstream cell 26a is smaller than the electrode reaction area Sb of the electrode reaction portion 27b of the downstream cell 26b. . In the drawing, ia and ib represent operating current densities in the upstream cell 26a and the downstream cell 26b, respectively.

Next, the operation and operation will be described. The fuel supplied from outside is supplied from the fuel supply header 22a to the first
It enters the laminated body 21a, performs a power generation reaction in the cell 26a, and is discharged to the intermediate header 22c. The discharged gas is successively supplied from the intermediate header 22c to the second stacked body 21b, performs a power generation reaction in the cell 26b, and is discharged as exhaust gas through the fuel discharge header 22b. That is, the fuel supplied from the outside flows from the fuel supply header 22a to the fuel discharge header 22b in the cells 26a in the first stacked body 21a and the cells 26b in the second stacked body 21b.
It has the opportunity to be used as fuel for two power generation reactions. The air side can be configured and operated in the same manner as the fuel side. However, in the case of this embodiment, air is supplied in parallel to the first stacked body 21a and the second stacked body 21b, that is, in parallel to all cells. The case of discharging is shown.

On the other hand, the first laminate 21a and the second laminate 21
Since b is electrically connected in series, the same amount of current flows through the first laminate 21a and the second laminate 21b.
That is, the cell 26a in the first laminate 21a and the second laminate 2
The cell 26b in 1b also generates the same amount of current on the entire electrode reaction surface, so that the hydrogen consumption per cell is the same. Assuming that the current value in the fuel cell stack 21 is I,
Hydrogen consumption Ca in first laminate 21a and second laminate 2
The hydrogen consumption Cb in 1b is expressed as follows using the proportionality constant k. Ca = k × Na × I (5) Cb = k × Nb × I (6) Assuming that the amount of hydrogen in the fuel supplied from the outside is qH, the entire fuel cell stack 21 Fuel (hydrogen) utilization rate η and first
The fuel utilization ηa of the stacked body 21a and the fuel utilization ηb of the second stacked body 21b are represented by the following equations. η = {(Na + Nb) × k × I / qH} × 100 (%) (7) ηa = (k × Na × I / qH) × 100 (%) (8) ηb = ｛k × Nb × I / (qH−k × Na × I)｝ × 100 (%) (9) From Equations (7) to (9), ηa = Na / (Na + Nb) × η (( 10) ηb = [100 × Nb / ｛(100−η) × Na + 100 × Nb}] × η (11) Therefore, when the fuel utilization rate η of the entire fuel cell stack is given, the first stack The fuel utilization rates ηa and ηb of the body 21a and the second stacked body 21b are determined only by the number of upstream cells and the number of downstream cells. Η = ηa + ηb−ηa × ηb / 100 (12) 0 ≦ η, ηa, ηb ≦ 100 which can be considered in normal use
The following relationship is satisfied in the range of (%). η> ηa, ηb Assuming that the hydrogen component ratio of the fuel supplied to the fuel cell stack 21 is χ (0 to 1.0) and that all the water generated during the power generation reaction is discharged to the air side, Supply header 22
a and the intermediate header 22c and the fuel discharge header 22
The respective hydrogen component ratios χa, χb, χc at b are as follows. χa = χ (13) χc = ｛(qH-Ca) / (qH-χ × Ca)｝ × χ (14) χb = [｛qH- (Ca + Cb)｝ / ｛qH-χ ( Ca + Cb)｝] × χ (15)

A concrete calculation using the above equation is as follows. Now, suppose that the number of upstream cells Na and the number of downstream cells Nb are both equal to 150 (cells), the generated current value I of the fuel cell stack is 600 (A), and the flow rate of the supplied fuel is 6,500 (mol / h). Now, consider the case where the hydrogen component ratio in the fuel is 60%, that is, χ = 0.6. When the unit of the amount of hydrogen is represented by (mol / h), k is k ≒ 0.0187.
Thus, from Equations (5) and (6), the hydrogen consumption in each stacked body is Ca = Cb ≒ 1,679 (mol / h). The amount of hydrogen qH in the supplied fuel is qH = 6500 × χ
= 3,900 (mol / h), the equation (10),
From (11) and equations (12) to (14), the fuel utilization and the hydrogen component ratio are as follows. η ≒ 86 (%) ηa ≒ 43 (%) ηb ≒ 76 (%) χa = 0.6 χb = 0.46 χc = 0.17 For comparison, a normal fuel flow method is used for all cells in parallel. Considering the case, the values of the overall fuel utilization rate η and the hydrogen component ratio χc in the exhaust gas do not change, but the cell exit hydrogen amount of each cell of the fuel cell stack greatly differs. The residual hydrogen amount at each cell outlet in the case of the parallel flow and the serial flow is as follows. Parallel flow; (qh-Ca-Cb) / (Na + Nb) {1.8 (mol / h / cell) Serial flow [upstream]; (qh-Ca) / Na {14.8 (mol / h / cell)} [Downstream]; (qh-Ca-Cb) /Nb≒3.6 (mol / h / cell) As described above, the downstream cell of the serial flow has about twice as much hydrogen as the parallel flow, and the upstream cell has about 8 times as much hydrogen. The remaining amount is a major feature of the serial flow method. In this way, in the serial flow, the remaining amount of hydrogen is large,
Since the hydrogen deficiency state can be avoided, the corrosion of the cell can be prevented.

However, as can be seen from the above example, in the serial flow method, there is a large difference between the hydrogen component in the upstream cell and the hydrogen component in the downstream cell. In the case of the above example, the average hydrogen component between the inlet and the outlet in the upstream cell and the downstream cell is specifically as follows. Upstream hydrogen component; χu = (χa + χc) /2≒0.53
(Inlet / outlet average value) Downstream hydrogen component; χd = (χc + χb) /2≒0.32
(Inlet / outlet average value) As described above, since the hydrogen partial pressure is different between the upstream cell and the downstream cell, if the operating conditions (current density,
If the operating temperature is the same, the cell voltage of the upstream cell is better than that of the downstream cell, as a matter of course. Therefore, in Embodiment 2 of the present invention, the countermeasures are taken by changing the electrode reaction areas of the upstream cell and the downstream cell. Specifically, the electrode reaction area Sb of the downstream cell 26b is larger than the electrode reaction area Sa of the upstream cell 26a. Here, the total current flowing through the fuel cell stack 21 is I,
Assuming that the current density ia in the upstream cell 26a and the current density ib in the downstream cell 26b are I = Sa × ia = Sb × ib (16), ia (= I / Sa)> ib (= I / Sb )

In general, the current density and cell voltage of a single cell of a fuel cell show characteristics as shown in FIG. That is, the higher the current density, the lower the cell voltage. Further, as shown in FIG. 10, the characteristic curve changes depending on the hydrogen partial pressure. That is, the higher the hydrogen partial pressure, the better the cell characteristics. In the second embodiment of the present invention, the upstream cell 26a is connected to the downstream 26b as described above.
By increasing the operating current density while increasing the hydrogen partial pressure as compared with, the upstream cell and the downstream cell can be operated at points A and B so that they have the same cell voltage as shown in FIG. is there.

Embodiment 3 FIG. Note that, in the second embodiment. In the above, the case where the electrode reaction area Sa of the upstream cell 26a is smaller than the electrode reaction area Sb of the downstream cell 26b has been described, but even if the electrode reaction area Sa of the upstream cell 26a is larger than the electrode reaction area Sb of the downstream cell 26b. Good. When the operating conditions of the upstream cell and the downstream cell are different (for example, the upstream cell operates at a low temperature and the downstream cell operates at a high temperature), depending on the operating conditions of the first stacked body and the second stacked body, such a method is preferable. In some cases, the characteristics of the entire battery can be improved or made uniform.

Embodiment 4 FIG. Note that, as described in the second embodiment. Third embodiment. In the above, the case where the area of the sealed portion of the cell is changed as a method of changing the electrode reaction area of the first stacked body and the second stacked body has been described. It goes without saying that the same effect can be obtained even if the reaction area is changed.

Embodiment 5 FIG. In the second embodiment. Example 4 In the above, the case where the first stacked body 21a and the second stacked body 21b form the fuel cell stacked body 21 has been described, but the first stacked body and the second stacked body do not necessarily form one fuel cell. It does not need to be formed. As shown in FIG.
The stacked body 21a and the second stacked body 21b are separate fuel cells,
The first stack 21a and the second stack 21b may form a fuel cell group.

Embodiment 6 FIG. Further, in the second embodiment. Example 5 In the above, the case where the first stacked body 21a and the second stacked body 21b are electrically connected in series has been described.
A similar effect can be expected even when electrically connected in parallel as shown in FIG. At this time, since the voltages of the first stacked body and the second stacked body become equal, if the number of upstream cells and the number of downstream cells are made equal, the single cell voltage of the upstream cell and the downstream cell (in other words, cell characteristics) The current densities in the upstream cell and the downstream cell are automatically determined to be optimum values due to differences in the operating environment (hydrogen concentration, carbon monoxide concentration, utilization factor, operating temperature, etc.) in the upstream cell and the downstream cell. Conversely, even if the area is changed, it becomes difficult to grasp the operating current densities and the hydrogen consumption in the upstream cell and the downstream cell.

Embodiment 7 FIG. Further, in the second embodiment. Example 6 In the above, the case where the first stacked body 21a and the second stacked body 21b are electrically connected has been described. However, it is needless to say that the same effect can be expected without the electrical connection.

Embodiment 8 FIG. Further, in the second embodiment. -Example 7. In the above, the case where only the first stacked body and the second stacked body are provided has been described, but it is related to those skilled in the art that the same effect can be expected even when there are a plurality of stacked bodies such as third, fourth, and so on. Anything can be easily analogized.

Embodiment 9 FIG. In FIG. 14, reference numerals 21 to 26 represent the same components as in the second to eighth embodiments. However, in the embodiment, the first current collector 24a and the second current collector 24b are provided at both ends of the stacked body 21, respectively. In addition, the first laminate 21a and the second
A third current collector 24c is also provided between the stack 21b and the three current collectors 24a, 24 in the total fuel cell stack.
b, 24c are used. Further, the present invention shows a case where the cells stacked on the first stacked body 21a and the cells stacked on the second stacked body have the same electrode reaction area S and the same specifications. 29 denotes a load connected to the fuel cell stack, and 29a denotes a first current collector 24a and a third
The first load 29b connected between the current collector 24c and the second load 29b is connected between the third current collector 24c and the second current collector 24b. Za and Zb are the first loads 29a, respectively.
And the impedance of the second load 29b, Ia and Ib
Represents a current generated by the first laminate 21a and the second laminate 21b, that is, a current flowing through the first load 29a and the second load 29b, and Ic represents a current flowing through the intermediate third current collector 24c. Va indicates the output voltage of the first stacked body 21a, and Vb indicates the output voltage of the second stacked body 21b.

Next, the operation and operation will be described. The fuel supplied from outside is supplied from the fuel supply header 22a to the first
After entering the laminate 21a, it undergoes a power generation reaction in the cell 26a, and is discharged to the intermediate header 22c.
The fuel gas is supplied to the fuel cell b, undergoes a power generation reaction in the cell 26b, and is discharged as exhaust gas through the fuel discharge header 22b. That is, the fuel supplied from the outside is supplied to the fuel supply header 22.
a from the fuel discharge header 22b to the cell 26a in the first stack 21a and the cell 26a in the second stack 21b.
The point b has the opportunity to be used as fuel for the two power generation reactions, as in the second to eighth embodiments.
Embodiment 9 differs from Embodiments 2 to 8 in that the first stacked body 21a and the second stacked body 21b have the same electrode reaction area S, but the first stacked body is the same. That is, the total current value of the second stacked body 21b is different from that of the second stacked body 21b. As a result, the first laminate 21a and the second laminate 2
The current densities ia and ib in 1b also differ. ia = Ia / S (17) ib = Ib / S (18)

At this time, the hydrogen consumption of the first laminate 21a and the second laminate 21b is as follows: Ca = k × Na × Ia (19) Cb = k × Nb × Ib (20) Therefore, assuming that the amount of hydrogen supplied from the outside is qH, the overall fuel utilization η, the fuel utilization ηa of the upstream cell, and the fuel utilization ηb of the downstream cell are as follows. η = {(Na × Ia + Nb × Ib) × k / qH} × 100 (%) (21) ηa = (k × Na × Ia / qH) × 100 (%) (22) ηb = ｛k × Nb × Ib / (QH−k × Na × Ia)｝ × 100 (%) (23) From this, ηa = {Na × Ia / (Na × Ia + Nb × Ib)} × η (24) ηb = [100 × Nb × Ib / {(100−η) × Na × Ia + 100 × Nb × Ib}] × η (25), and the fuel utilization of the upstream cell and the downstream cell is determined by the current value flowing through the first stacked body 21a and the second stacked body 21b. But it can be adjusted. (As in the first invention, it is not determined only by the number of cells at the upstream and the downstream). The fact that the hydrogen partial pressure of the upstream cell is higher than the hydrogen partial pressure of the downstream cell does not change as long as the fuel flow system is a serial flow system.

By the way, the following relationship is established between the voltage and the current of each part shown in FIG. 14, and the connected load. Ic = Ia−Ib (26) Va = Za × Ia (27) Vb = Zb × Ib (28) From this, the average single cell voltages vca and vcb of the upstream cell 26a and the downstream cell 26b are given by: vca = Za × ia × S / Na (29) vcb = Zb × ib × S / Nb (30), so that the characteristics (single cell voltage) of the upstream cell and the downstream cell depend on the load connected to the first stacked body and the second stacked body. , Each can be adjusted. If a load having a slightly higher impedance value per unit cell (Z × S / N) than the upstream cell is connected to a downstream cell having a low hydrogen partial pressure and a characteristic curve of the single cell lower than that of the upstream cell, FIG. As shown, the single cell voltage vca of the upstream cell and the single cell voltage vc of the downstream cell
b can be made uniform.

As described above, according to the ninth embodiment, the fuel utilization and the cell characteristics of the first stack and the second stack can be adjusted by the load connected to the outside of the fuel cell. Thus, it is possible to maintain the cell corrosion prevention effect, which is a feature of the serial flow, and at the same time adjust the cell characteristics during fuel cell operation even after fuel cell assembly is completed.

Embodiment 10 FIG. In the ninth embodiment,
The case where the cell characteristics (single cell voltage) of the upstream cell and the downstream cell are made uniform by changing the total current value of the power generation reaction between the first laminate and the second laminate has been described. Depending on the pattern and the condition of the fuel gas supplied from the outside, the total current value is changed in the opposite direction to that of the ninth embodiment, not to make the cell characteristics uniform, but to increase the output of the entire fuel cell and prevent cell corrosion. It is also possible to make it.

Embodiment 11 FIG. Embodiment 9 above. Tenth embodiment. In the above, the case where the first stacked body 21a and the second stacked body 21b form the fuel cell description 21 has been described. However, the first stacked body and the second stacked body do not necessarily constitute one fuel cell. It does not need to be formed. As shown in FIG.
The first stack 21a and the second stack 21b may be separate fuel cells, and the first stack 21a and the second stack 21b may form a fuel cell group.

Embodiment 12 FIG. Further, in the above Examples 9 to 11, the method of changing the individually connected loads was described as a method of changing the total current value of the power generation reaction between the first laminate and the second laminate. The same effects as in the above-described embodiment can be expected by any method that changes the total current value of the power generation reaction of each stacked body in addition to the difference in connection and adjustment method.

Embodiment 13 FIG. Further, in the ninth embodiment. Example 12 In the above, the case where there is only the first laminate and the second laminate has been described, but it is related to those skilled in the art that the same effect can be expected even when there are a plurality of laminates such as the third, fourth,. If so, it can be easily analogized.

Embodiment 14 FIG. As shown in FIG. 17, it goes without saying that similar effects can be expected even when the embodiments 2 to 8 and the embodiments 9 to 13 are used in combination.

[0045]

As described above, according to the fuel cell of the first aspect of the present invention, the stack is divided into the first stack for supplying the fuel gas and the second stack for supplying the exhaust gas. By dividing and making the number of single cells of the first stacked body smaller than the number of single cells of the second stacked body, it is possible to operate stably even if the fuel utilization rate is increased, thereby preventing an increase in cost. There is an effect that can be.

According to the fuel cell of the second aspect of the present invention, the electrode reaction area of the single cell of the first stacked body and the electrode reaction area of the second stacked body are
By making the electrode reaction area of a single cell different,
The current density of the first laminate and that of the second laminate can be made different, and the cell characteristics downstream of the serial flow can be improved while maintaining the cell corrosion prevention effect which is a characteristic of the serial flow. There is an effect that the power generation efficiency of the entire plant can be increased.

According to the fuel cell of the third aspect of the present invention, the total current value of the power generation reaction of the first stacked body is made different from the total current value of the power generation reaction of the second stacked body. Cell characteristics can be adjusted upstream and downstream of the serial flow while maintaining the cell corrosion prevention effect, a feature of
There is an effect that the fuel cell can be optimized, for example, by increasing the power generation efficiency of the entire fuel cell plant. In addition, such adjustments for optimization can be performed even after the fuel cell plant has completed power generation operation after the completion of fuel cell assembly. This is a huge attraction for plant users who are trying to make operation a little more economical.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a phosphoric acid type fuel cell of Example 1.

FIG. 2 is a graph showing a cell ratio α between an upstream side and a downstream side and a cell voltage (V) near a cooling plate when the fuel gas supply method according to the first embodiment is applied.

FIG. 3 is a graph showing a real fuel utilization rate (U _Fu , U _FD ;%) with respect to a nominal fuel utilization rate (U _F ;%).

FIG. 4 is a graph showing the relationship between the nominal fuel utilization factor U _F and α when the real fuel utilization factor U _{FD of the} downstream cell is 90%.

[5] the nominal fuel utilization rate (U _F;%) and the hydrogen concentration (P _D
(H ₂₎ and P (H _2); is a graph showing the relationship between%).

It is a graph showing the relationship between [6] nominal fuel utilization rate (U _F;;%) carbon monoxide concentration (% P _D (CO) and P (CO)).

[7] Hydrogen Concentration _{(P D (H 2);} %) carbon monoxide concentration _{(P D (CO);%} ) is a graph showing the relationship between α against.

FIG. 8 is a sectional view of a fuel cell according to a second embodiment.

FIG. 9 is a perspective view of an upstream cell and a downstream cell according to the second embodiment.

FIG. 10 is a characteristic curve showing a general single cell current density-voltage of a fuel cell.

FIG. 11 is a characteristic curve of an upstream cell and a downstream cell of Example 2.

FIG. 12 is a sectional view of a fuel cell according to a fifth embodiment.

FIG. 13 is a sectional view of a fuel cell according to a sixth embodiment.

FIG. 14 is a sectional view of a fuel cell according to a ninth embodiment.

FIG. 15 is a characteristic curve of the upstream cell and the downstream cell of the ninth embodiment.

FIG. 16 is a sectional view of a fuel cell according to an eleventh embodiment.

FIG. 17 is a sectional view of a fuel cell according to Example 14.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single cell 2 Fuel cell 3 Electrolyte matrix 4 Oxidizer electrode 5 Cooling plate 6 Gas separation plate 7 1st laminated body 8 2nd laminated body 21 Fuel cell laminated body 21a 1st laminated body 21b 2nd laminated body 22a Fuel supply header 22b Fuel discharge header 22c Intermediate header 23 Air side header 24 Current collector 25 Insulating plate 26a Upstream cell 26b Downstream cell 27a Upstream cell electrode reaction part 27b Downstream cell electrode reaction part 28a Upstream cell seal part 28b Downstream cell seal part

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshiaki Murahashi 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi Electric Corporation Central Research Laboratory (56) References JP-A-61-49382 (JP, A) 62-62765 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 8/00-8/24

Claims (3)

(57) [Claims] 1. A fuel cell comprising a fuel cell, an electrolyte matrix, and a single cell having an oxidant electrode, a gas separator, and a plurality of fuel cells each composed of a cooling plate which are stacked to form a laminate. The stack is divided into a first stack to which fuel gas is supplied and a second stack to which exhaust gas is supplied, and the number of single cells of the first stack is reduced by the number of single cells of the second stack. A fuel cell characterized in that the fuel cell is less than the fuel cell. 2. A fuel cell comprising a single cell having a fuel electrode, an electrolyte matrix, and an oxidant electrode, a gas separator, and a plurality of fuel cells each composed of a cooling plate, which are stacked to form a laminate. The stack is connected to a first stack to which fuel gas is supplied , and electrically connected in series with the first stack.
Connected the exhaust gas is divided into a second stack supplied, also each of the single-between the first laminate and the second laminate
A fuel cell characterized in that cells have different electrode reaction areas. 3. A fuel cell comprising a fuel cell, an electrolyte matrix, and a single cell having an oxidant electrode, a gas separator, and a plurality of fuel cells each composed of a cooling plate which are stacked to form a laminate. The stack is divided into a first stack to which fuel gas is supplied and a second stack to which exhaust gas is supplied, and a first stack at both ends of the stack.
A current collector and a second current collector are provided, a third current collector is provided between the first laminate and the second laminate, and the first current collector and the third current collector are provided. The total current value of the power generation reaction between the first stacked body and the second stacked body differs depending on the loads inserted between the first current collector and the second current collector, and between the third current collector and the second current collector. A fuel cell, characterized in that: