JP3888326B2 - Operation method of polymer electrolyte fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell that uses an electrochemical reaction to generate power, for example, used in an electric vehicle.
[0002]
[Prior art]
As is well known, a fuel cell, which is a typical example of an electrochemical device, contacts a pair of electrodes via an electrolyte, supplies fuel to one electrode, and supplies an oxidant to the other electrode, thereby oxidizing the fuel. Is an apparatus that converts chemical energy directly into electrical energy by electrochemically starting up the battery.
Although there are several types of fuel cells depending on the electrolyte used, in recent years, solid polymer fuel cells using a solid polymer electrolyte membrane as an electrolyte have attracted attention as fuel cells that can obtain high output. Yes.
[0003]
In the fuel cell, when hydrogen gas is supplied to the fuel electrode and oxygen gas is supplied to the oxidant electrode and current is taken out from the external circuit, the following reaction occurs.
Fuel electrode reaction: H ₂ → 2H ⁺ + 2e ^- ... (1)
Oxidant electrode reaction: 2H ⁺ + 2e ^- + 1 / 2O ₂ → H ₂ O ... (2)
If a catalyst such as platinum on the electrode acts effectively at this time, the reaction proceeds smoothly with almost no overvoltage in the reaction of the above formula (1).
On the other hand, when a hydrocarbon such as methanol that is easy to handle is used as the fuel, it is supplied after being reformed into hydrogen by a reaction such as the following formula (3) by a reformer.
Reforming reaction: CH _Three OH + H ₂ O → 3H ₂ + CO ₂ ... (3)
However, a small amount of CO is mixed into the fuel by the shift reaction of the following formula (4).
Shift reaction: CO ₂ + H ₂ → CO + H ₂ O ... (4)
Especially in electrochemical devices such as polymer electrolyte fuel cells with low operating temperatures, the catalyst is poisoned by the incorporation of several tens of ppm of carbon monoxide (CO), increasing the overvoltage of the fuel electrode (anode) reaction. Therefore, the problem is that the characteristics deteriorate.
[0004]
Therefore, in order to reduce the influence of poisoning due to CO, various devices have been made conventionally. Basically, the development of a catalyst composition that is less affected by CO poisoning and the development of a method for selectively removing CO in fuel.
[0005]
Regarding the catalyst composition, it has been reported that when a platinum-ruthenium alloy (Pt · Ru) is used, high characteristics can be maintained up to a CO concentration of 100 ppm. ("CO poisoning characteristics of the electrode catalyst for polymer electrolyte fuel cells" 35th Battery Symposium Abstracts 3D19, p299-300 (1994))
[0006]
As a method for selectively removing CO in the fuel, a method for removing air by adding air in the catalyst layer (Canadian Patent No. 1,305,212) or a small amount of air in the fuel cell fuel is used. There is a report of a method of mixing ("Characteristic evaluation of three-dimensional electrode / membrane bonding type PEFC", 36th Battery Symposium Abstracts 1C07, p225-226 (1995)).
It has been confirmed that such selective oxidation by air mixing oxidizes CO in the fuel and reduces the CO concentration to such an extent that it is not poisoned.
[0007]
[Problems to be solved by the invention]
However, in the improvement by the catalyst composition, even if Pt · Ru has a high CO concentration, the characteristics are unstable, and this alone is still insufficient as a poisoning countermeasure.
In addition, in selective oxidation by air mixing, the fuel gas is diluted with nitrogen, which is the main component of air, and the characteristics are deteriorated due to burning and consumption of a large amount of hydrogen at the same time, or inert gas is retained. There is a drawback that the hydrogen gas is deficient and the battery member is corroded.
Also, if the amount of air is too small, CO cannot be removed sufficiently, and it is important to control the amount of air according to the amount of fuel and the CO concentration. It was difficult.
[0008]
Japanese Patent Application Laid-Open No. 7-105967 discloses that a fuel cell for removing CO is disposed on a fuel supply path of a main fuel cell, and a fuel discharge path of the fuel cell for removing CO is connected to a fuel supply path of the main fuel cell. A fuel cell having the above structure is described.
The reformed gas mainly composed of hydrogen is first supplied to a fuel cell for removing CO, and hydrogen as fuel is consumed by the reaction of the above formula (1), but at the same time, CO contained in the fuel is fuel electrode. Adsorbed on the catalyst. On the other hand, when the oxygen is supplied to the oxidizer electrode, the reaction of the above formula (2) is performed. By adjusting the supply pressure, oxygen passes through the electrolyte membrane and reaches the fuel electrode on the opposite side. The oxidation reaction of the following formula (5) occurs on the fuel electrode, and the poisonous substance CO adsorbed on the fuel electrode is CO. ₂ Therefore, only a very small amount of CO after being adsorbed and removed by the CO removing fuel cell is introduced into the main fuel cell.
Oxidation reaction: CO + 1 / 2O ₂ → CO ₂ ... (5)
However, there is still a problem that a part of hydrogen in the fuel reacts with oxygen and is consumed at the same time as the oxidation reaction of the formula (5), and the power generation efficiency is lowered. There is also a problem that extra power is required to allow oxygen to permeate by pressure.
[0009]
The present invention has been made to solve the above-described problems, and an object thereof is to prevent deterioration of characteristics due to poisoning of a catalyst or the like while suppressing a decrease in power generation efficiency of a fuel cell.
[0010]
[Means for Solving the Problems]
An operation method of a polymer electrolyte fuel cell according to a first configuration of the present invention includes a unit cell in which electrodes having gas diffusibility are arranged on both surfaces of an ion conductive electrolyte membrane, and one electrode of the unit cell. A fuel cell main stack portion in which fuel is sequentially stacked with a gas separator that supplies an oxidant gas to the other electrode, and the number of stacks of the unit cells and the separator is less than the main stack portion, and a current path from the main stack portion Has an independent sub-laminate part, and both ends of the main laminate part and the sub-laminate part are sandwiched between a pair of current collector plates, and a pair of current collector plates arranged at both ends of the main laminate part The first load is connected to the pair of current collector plates disposed at both ends of the sub-stacking portion, and the second load is connected to the main load after passing the fuel and oxidant gas through the sub-stacking portion. In the operation method of a polymer electrolyte fuel cell that supplies power to the stack and generates electricity Te, the current value of the sub-laminate in order to prevent a decrease in the voltage of the sub-laminate operation The second load is adjusted so as to decrease from the middle.
[0011]
The solid polymer fuel cell operating method according to the second configuration of the present invention, in addition to the first configuration, driving The battery is replaced with a unit cell whose characteristics have not deteriorated every predetermined time.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a general configuration of a polymer electrolyte fuel cell unit cell used in a fuel cell according to the present embodiment, and FIG. 2 shows a fuel having a main stack portion and a sub stack portion according to the first embodiment. It is a schematic diagram which shows the structure of a battery. In FIG. 1, reference numeral 1 denotes an ion conductive solid electrolyte membrane, for example, a polyperfluorosulfonic acid membrane. Reference numeral 2 denotes a cathode (oxidant electrode) having gas diffusibility, and 3 denotes an anode (fuel electrode) having gas diffusibility, and an electrically conductive porous material such as carbon paper is used for these. Reference numerals 4 and 5 denote catalyst layers (4: platinum catalyst, 5: Pt · Ru catalyst), and the electrolyte membrane 1, electrodes 2, 3, and catalyst layers 4, 5 constitute a unit cell 10. 8 and 9 are separator plates, which are made of an electrically conductive material that does not pass gas, such as a carbon plate. Reference numerals 6 and 7 denote gas flow paths surrounded by the separator plates 8 and 9 and the unit cell 10.
In FIG. 2, 11 is a fuel cell stack, 12 is a fuel cell main stack, 13 is a fuel cell sub-stack, 14 is a humidifier, and 15 to 17 are current collectors. 50 main cells 10 are stacked on the main stack 12 and three single cells are stacked on the sub stack 13, and air and fuel are supplied from the humidifier 14 to the sub stack 13 and the main stack 12 in this order. . The current of the main laminated part 12 is taken out from the current collecting plates 15 and 16, and the current of the sub laminated part 13 is taken out from the current collecting plates 16 and 17, respectively. Reference numerals 12a and 13a denote loads connected between the current collecting plates 15 and 16 and between the current collecting plates 16 and 17, respectively.
[0013]
Next, the case where hydrogen is supplied as fuel will be described. The air and hydrogen humidified by the humidifying unit 14 are first supplied to the sub-stacking unit 13 and distributed to each of the three cells (unit cells) in the sub-stacking unit, and by the reactions of the above formulas (1) and (2) After power generation, the power is supplied to the main laminated portion 12 and generated by the same reaction.
[0014]
3 (a) and 3 (b) show changes in voltage and output at each part when power generation is performed. In the figure, “a” indicates changes in voltage and output of the main laminated portion, and “a” indicates changes in voltage and output of the sub laminated portion, both of which are 500 mA / cm ² The change when operating at a constant current of. Although the output of the main laminated portion 12 did not change during the operation for 2000 hours, it was found that the output of the sub laminated portion 13 was greatly reduced. Therefore, when the load 13a between the current collector plates 16 and 17 is adjusted to reduce only the current value of the sub-stacked portion 13 from the middle, the amount of decrease in both voltage and output is reduced as shown in FIG. I was able to.
[0015]
Further, when the sub-stacked portion 13 is analyzed after operation, a metal in the piping material such as Fe or Cr and a metal ion such as Ca or Na are detected, and impurities in the supply gas accumulate in the electrolyte film to cause resistance. It was found that the characteristics increased and the characteristics deteriorated. Therefore, when only the sub-stack portion 13 is replaced every 1500 hours, the main stack portion 12 and the sub-stack portion 13 are not deteriorated in characteristics even after 5000 hours, and the high characteristics are maintained. I can do it now.
[0016]
As described above, according to the first embodiment, the impurities in the supply gas are removed by accumulating in the sub-stacked portion 13 to prevent the impurities from flowing into the main stacked portion 12 to deteriorate the characteristics. Yes. In addition, the sub-stacking unit 13 controls the load to suppress a decrease in output due to impurity accumulation.
Therefore, it is possible to prevent deterioration of characteristics due to impurities in the supply gas while suppressing reduction in power generation efficiency of the fuel cell.
[0017]
Reference Example 1
Next, Reference Example 1 will be described. The structure of the polymer electrolyte fuel cell unit and the structure of the fuel cell stack are the same as those of the first embodiment shown in FIGS. 1 and 2, and here, a methanol reforming simulation gas (hydrogen) containing 1000 ppm of CO as fuel. 75%, carbon dioxide 25%).
The air and the methanol reforming simulation gas humidified by the humidifying unit 14 are first supplied to the sub-stacking unit 13 and distributed to the three cells in the sub-stacking unit, and by the reactions of the above formulas (1) and (2) After power generation, the power is supplied to the main laminate 12 and generated by the same reaction.
[0018]
In this reference example, the load per unit cell (single cell) of the sub-stack unit 13 is continuously controlled by controlling the load 13a of the sub-stack unit 13 so that the anode potential of the sub-stack unit 13 exceeds the oxidation potential of CO. To vibrate.
FIG. 4 shows 500 mA / cm for both the main laminated portion 12 and the sub laminated portion 13. ² 2 shows a change with time in voltage (20 seconds) when power generation is performed at a constant current of (a), in which (a) shows a voltage change in the main laminated part 12 and (a) shows a voltage change in the sub laminated part 13. The voltage A of the sub-layered portion 13 oscillates with an amplitude (0.18 to 0.58 V) per unit cell at a cycle of 3 seconds, but the voltage of the main layered portion 12 is 0.6 V per unit cell. Even if a fuel having a high CO concentration of 1000 ppm was supplied without vibration, a DC voltage of 30 V with a stable voltage could be obtained. At this time, the CO concentration at the inlet of the sub-layered portion 13 was 1000 ppm, but the CO concentration at the inlet of the main laminated portion 12 was reduced to 100 ppm. This is because CO in the fuel is adsorbed by the catalyst of the fuel electrode, and the anode potential reaches the CO oxidation potential when the voltage of the sub-stacking portion 13 oscillates and is decomposed by the reaction of the following formula (6). it is conceivable that.
CO + H ₂ O → CO ₂ + 2H ⁺ + 2e ^- (6)
At this time, CO reacts with surrounding moisture to form carbon dioxide and hydrogen ions, but the hydrogen ions reach the cathode side and can be used for the fuel cell reaction of the above formula (2).
[0019]
As described above, according to this reference example, CO reacts with water to form carbon dioxide and hydrogen ions in the sub-stacking portion 13 and wastes hydrogen in the fuel as disclosed in JP-A-7-105967. Furthermore, hydrogen ions are obtained by this reaction and can be used for the fuel cell reaction.
Therefore, it is possible to prevent deterioration in characteristics due to CO in the supply gas while suppressing reduction in power generation efficiency of the fuel cell.
[0020]
Reference Example 2
Reference Example 2 of the present invention will be described. The structure of the laminate and the gas supply conditions are almost the same as in Reference Example 1, but in this reference example, the amount of water flowing through a cooling water pipe (not shown) is adjusted to control the temperature during power generation in the main laminate section. 12 (specifically, for example, the temperature of the separator plate located at the center of the laminate) is adjusted to 80 ° C., and the sub-stack portion 13 (similarly, the temperature of the separator plate) is adjusted to 60 ° C.
[0021]
Next, the operation will be described. FIG. 5 shows that the current density is 500 mA / cm in both the main laminated portion and the sub laminated portion. ² 2 shows a change with time in voltage (20 seconds) when power generation is performed at a constant current, where A represents a voltage change in the main laminated portion and A represents a voltage change in the sub laminated portion. The voltage A of the sub-layered portion 13 oscillates with an amplitude of 0.4 V per unit cell (0.1 to 0.5 V) at a cycle of 1.5 seconds, but the voltage of the main layered portion 12 is 0.5 per unit cell. A stable DC voltage of 31 V could be obtained without vibration at 62 V. At this time, the CO concentration at the inlet of the sub-stacking portion 13 was 1000 ppm, but the CO concentration at the inlet of the main stacking portion 12 was 50 ppm, and the temperature was not changed between the main stacking portion 12 and the sub-stacking book 13 and Reference Example 1 Compared to a significant drop. In general, it was found that CO was more easily adsorbed at a lower temperature, and that CO in the fuel was adsorbed more in the sub-laminate 13 having a lower temperature, and the decomposition efficiency of CO decomposed when the voltage oscillated increased.
The temperatures of the main laminate 12 and the sub laminate 13 are determined by the type of electrolyte membrane, catalyst, etc., but the main laminate 12 is set to the highest power generation efficiency and the temperature of the sub laminate 13 is set higher than that. Lower it.
[0022]
Reference Example 3
Hereinafter, Reference Example 3 of the present invention will be described. This reference example relates to a fuel cell system including a reformer having a CO selective oxidation unit at the front stage of the fuel cell shown in FIG. 2, for example.
When the load fluctuates, the CO concentration at the reformer outlet changes due to a temperature change in the reformer. In this reference example, the amount of air supplied to the CO selective oxidation unit according to the change in the CO concentration. By controlling the value to the optimum value, fluctuations in CO concentration are suppressed while preventing waste of hydrogen.
[0023]
FIG. 6 is a block diagram showing a configuration of a fuel cell system including a methanol reformer having a CO selective oxidizer according to Reference Example 3 of the present invention. In the figure, reference numeral 31 denotes a methanol reformer, which has a vaporization section 31a, a catalytic combustion section 31b, a reforming section 31c, and a CO selective oxidation section 31d. 32 is a methanol tank, 33 is a water tank, 34a to c are pumps, and 41 is an air blower. In addition, 51 holds a correlation diagram of FIG. 7 described later as a table and calculates a CO concentration from the frequency and temperature of the voltage of the sub-stacking unit 13, and 52 changes based on the calculation result of the calculating unit 51. This is a control unit that controls the amount of air supplied to the CO selective oxidation unit 31d of the mass device 31, and these calculation unit 51 and control unit 52 are constituted by a microcomputer. The configuration of the fuel cell stack 11 is the same as that of the first embodiment.
[0024]
In the reformer 31, the following reaction occurs. Water and methanol sent by the pumps 34a and 34b evaporate in the vaporizing section 31a and sent to the reforming section 31c to generate hydrogen and carbon dioxide by the reaction of the formula (3). At the same time, the formula (4) Since 1 to 2% of CO is generated by the shift reaction, a small amount of air is mixed from the air blower 41 in the CO selective oxidation unit 31d to selectively oxidize and remove the CO, and then reduce the CO concentration to around 1000 ppm before fuel. The battery 11 is supplied.
In the catalytic combustion unit 31b, the fuel exhaust gas of the fuel cell 11 and air are reacted by catalytic combustion, and necessary heat is supplied in the vaporization unit 31a and the reforming unit 31c. Therefore, when the load fluctuates, the heat balance may be lost and the temperature may change.
[0025]
FIG. 7 shows 500 mA / cm. ² The relationship between the CO concentration in the fuel and the frequency of the voltage in the sub-stacked portion 13 when power is generated at a constant current is shown when a is 80 ° C. and a is 60 ° C. From the figure, it can be seen that the frequency of the voltage increases as the CO concentration increases and the operating temperature decreases. If the operating temperature and frequency are known, the supplied CO concentration can be estimated. Note that the relationship in FIG. 7 also varies depending on the current.
FIG. 8 shows the relationship between the air mixing amount and the CO concentration in the CO selective oxidation unit 31d of the reformer. From the figure, the CO concentration can be lowered by increasing the air mixing amount. It can be seen that even if the air amount is excessive, only hydrogen is consumed, and the air mixing amount needs to be an optimum value according to the state of the fuel.
[0026]
FIG. 9 relates to Reference Example 3 of the present invention and is a flowchart for controlling the amount of air supplied to the CO selective oxidation unit 31d in order to suppress fluctuations in the CO concentration at the outlet of the reformer 31, and this processing is performed by the calculation unit 51. Done in
Normally, the amount of air in the CO selective oxidation section of the reformer 31 is adjusted according to the flow rate of the fuel, but the CO concentration at the outlet of the reformer 31 may change due to a temperature change in the reformer 31 or the like. Therefore, in this reference example, not only the fuel flow rate but also the CO concentration at the outlet of the reformer 31, that is, the CO concentration supplied to the fuel cell 11 is taken into consideration, and the air supply flow rate to the CO selective oxidation unit 31 d is as follows. Control.
Step 1: The CO concentration Cs and the allowable width ΔC of the fuel to be supplied to the fuel cell 11 are set. In this reference example, the set value Cs was 50 ppm, and the allowable width ΔC was 25 ppm. This is calculated from the upper limit value of the carbon monoxide concentration at which the characteristics of the fuel cell do not deteriorate and the CO removal effect and the control accuracy in the selective oxidation unit where the hydrogen consumption in the CO selective oxidation unit 31d does not become extremely large. It can be appropriately changed according to the characteristics.
Step 2: The voltage frequency f of the sub-laminate 13, the operating temperature T of the sub-laminate 13, and the current I of the sub-laminate 13 are measured.
Step 3: The calculation unit 51 estimates the CO concentration Cx in the fuel supplied to the fuel cell from the above parameters, that is, the voltage frequency f, the operating temperature T, and the current I based on FIG.
Step 4: The estimated CO concentration Cx is compared with the allowable value Cs + ΔC, and if the allowable value Cs + ΔC is exceeded, the process proceeds to step 6 to prevent the characteristics of the fuel cell from deteriorating. If not, the next step 5 is performed. Proceed with
Step 5: The estimated CO concentration Cx is compared with the lower limit value Cs-ΔC, and if it is less than the lower limit value Cs-ΔC, the process proceeds to Step 7 to suppress excessive hydrogen consumption in the CO selective oxidation unit 31d, and the upper limit value is exceeded. In the case of, return to Step 2.
Step 6: The air supply amount to the CO selective oxidation unit 31d is increased by the control unit 52.
Step 7: The control unit 52 reduces the amount of air supplied to the CO selective oxidation unit 31d.
[0027]
As described above, when the load fluctuates, the CO concentration at the outlet of the reformer 31 changes due to a temperature change in the reformer 31 or the like. As a result, the CO concentration of the fuel supplied to the fuel cell power generation section 11 changes. Before the correction control is performed, the change is 400% (250 ppm) on the positive side and 80% on the negative side with respect to the set value 50 ppm ( The fluctuation of CO concentration was suppressed to within 100% (100ppm) on the plus side and within 50% (25ppm) on the minus side by performing the correction control according to this reference example. .
As a result, the cell voltage is stabilized and the power generation efficiency is improved, and the system efficiency is improved by suppressing excessive fuel consumption.
[0028]
In the above reference example, the amount of supplied air is controlled, but the temperature of the CO selective removal unit 31d is controlled, that is, the temperature is lowered when the CO concentration is high, and the temperature is raised when the CO concentration is low. In addition, it was possible to suppress changes in the CO concentration in the fuel supplied to the fuel cell.
Further, both the supply air amount and the temperature may be controlled.
Further, in the above reference example, the CO concentration Cx in the fuel supplied to the fuel cell is estimated from the voltage frequency f, the operating temperature T, and the current I of the sub-laminate 13 based on FIG. The operation temperature T and the current I need not be measured. For example, the operation temperature need not be measured. That is, the sub-stacking portion 13 and the main stacking portion 12 have the same variation with a constant width, and the allowable CO concentration also changes depending on the temperature. Therefore, even if the actual CO concentration is not known, there is no problem in adjusting the CO concentration suitable for the main laminated portion 12.
[0029]
Reference Example 4
Next, a fuel cell system according to Reference Example 4 of the present invention will be described. The overall configuration of the system is the same as that shown in FIG.
FIG. 10 is a flowchart according to Reference Example 4 of the present invention for correcting and controlling the amount of air supplied to the CO selective oxidation unit in order to keep the CO concentration at the reformer outlet constant.
In this reference example, a change in the concentration of CO supplied to the fuel cell 11 is predicted, and the air supply flow rate to the CO selective oxidation unit 31d is optimally controlled by the following steps.
Step 11: The CO concentration Cs and the allowable width ΔC of the fuel to be supplied to the fuel cell 11 are set. In this reference example, the set value Cs was 50 ppm, and the allowable width ΔC was 15 ppm. The permissible width can be narrowed in this way because the control accuracy is improved because the control is advanced compared to the control according to the reference example 3 described above, and the permissible width can be changed according to the characteristics of the device.
Step 12: Time t = t _i The voltage frequency f of the sub-laminate 13 at _i , Operating temperature T, current I _i Measure.
Step 13: The next instant t = t of the sub-laminate 13 _i Voltage frequency f at + Δt (0.3 seconds in this reference example) _{i + 1} , Current I _{i + 1} Measure. The temperature T _{i + 1} Was not measured because it does not change instantaneously.
Step 14: In the calculation unit 51, the above parameter, that is, the voltage frequency f of the sub-laminate 13 _i , F _{i + 1} , Operating temperature T, current I _i , I _{i + 1} To t = t in the fuel supplied to the fuel cell using the relationship of FIG. _i To t = t _i The amount of change in CO concentration between + Δt is estimated, and the amount of change in CO concentration ΔCx after a predetermined time (1.5 seconds in this reference example) is predicted. Note that the time setting here can be changed as appropriate depending on the system configuration because it depends on the time and allowable range in which the CO concentration of the supplied gas changes after the amount of air supplied to the CO selective oxidation unit 31d is changed. It is.
Step 15: The change amount ΔCx of the CO concentration after the predetermined time (1.5 seconds) predicted in Step 14 is compared with the allowable width ΔC. If the change amount ΔCx exceeds the allowable width ΔC, the process proceeds to Step 16. If not, return to Step 12.
Step 16: The air supply correction amount is calculated according to the change amount of the CO concentration after 1.5 seconds predicted in Step 14.
Step 17: The air supply amount is corrected according to the air supply correction amount obtained in Step 16. That is, when the CO concentration increases beyond the allowable width ΔC, the air supply amount to the CO selective oxidation unit 31d is increased in order to prevent deterioration of the characteristics of the fuel cell. Further, when the CO concentration becomes smaller than the allowable width ΔC, the air supply amount to the CO selective oxidation unit 31d is reduced in order to suppress excessive hydrogen consumption in the CO selective oxidation unit 31d.
[0030]
As described above, in this reference example, the change in the CO concentration after a predetermined time (1.5 seconds) is predicted from the change in the frequency of the voltage in 0.3 seconds in the sub-stacking portion 13, and the CO concentration changes. By controlling the amount of supplied air before, the CO concentration could be controlled within plus or minus 30% (50 ± 15 ppm).
As a result, the cell voltage was stabilized and the power generation efficiency was further improved as compared with Reference Example 3, and the excessive fuel consumption could be suppressed, thereby greatly improving the system efficiency.
[0031]
Although the supply air amount is controlled in the above reference example, the temperature of the reformer 31 may be controlled, and both the supply air amount and the temperature may be controlled.
In the reference example, the change amount ΔCx of the CO concentration after a predetermined time is predicted. However, the CO concentration after the predetermined time may be predicted. In this case, steps 3 to 7 in FIG. Can be controlled.
Further, in the above reference example, the change amount ΔCx of the CO concentration in the fuel supplied to the fuel cell is predicted from the voltage frequency f, the operating temperature T, and the current I of the sub-stacking portion 13 based on FIG. It is not necessary to measure all of the frequency f, the operating temperature T, and the current I. For example, the operating temperature may not be measured. That is, the sub-stacking portion 13 and the main stacking portion 12 have the same variation with a constant width, and the allowable CO concentration also changes depending on the temperature. Therefore, even if the actual CO concentration is not known, there is no problem in adjusting the CO concentration suitable for the main laminated portion 12.
[0032]
【The invention's effect】
As described above, according to the first configuration of the present invention, a unit cell in which electrodes having gas diffusibility are arranged on both surfaces of an ion conductive electrolyte membrane, and fuel is supplied to one electrode of the unit cell and the other electrode. A fuel cell main laminated portion in which a gas separator for supplying an oxidant gas is sequentially laminated, and a sub-laminate in which the number of laminated cells and separators is smaller than that of the main laminated portion, and the current path is independent from the main laminated portion The main laminated part and the sub laminated part are sandwiched between a pair of current collector plates, and the pair of current collector plates disposed at both ends of the main laminated part have a first load However, a second load is connected to a pair of current collector plates arranged at both ends of the sub-stacking portion, and fuel and oxidant gas are supplied to the main stacking portion after passing through the sub-stacking portion. In the method for operating a polymer electrolyte fuel cell that generates electric power, The current value of the sub-laminate in order to prevent a decrease in voltage operation To reduce the second load from the middle Adjustment Therefore, it is possible to prevent deterioration of characteristics due to impurities in the supply gas while suppressing reduction in power generation efficiency of the fuel cell.
[0033]
According to the second configuration of the present invention, in addition to the first configuration, the unit cell of the sub-stacking unit includes: driving Since the battery is replaced with a unit cell whose characteristics are not deteriorated every predetermined time, high characteristics can be maintained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a unit cell according to Embodiment 1 of the present invention.
FIG. 2 is a diagram schematically showing a configuration of a fuel cell stack according to Embodiment 1 of the present invention.
FIGS. 3A and 3B are diagrams showing changes with time of each characteristic of the fuel cell stack according to Embodiment 1 of the present invention, where FIG. 3A shows voltage and FIG. 3B shows output change.
FIG. 4 is a diagram showing a change in voltage per unit cell in each stacked portion of the fuel cell according to Reference Example 1 of the present invention.
FIG. 5 is a diagram showing a change in voltage per unit cell in each stacked portion of the fuel cell according to Reference Example 2 of the present invention. .
FIG. 6 is a diagram showing a configuration of a fuel cell system according to Reference Example 3 of the present invention.
7 is a graph showing the relationship between the CO concentration in fuel and the voltage frequency according to Reference Example 3 of the present invention. FIG.
FIG. 8 is a diagram showing the relationship between the amount of air supplied to the CO selective oxidation unit and the outlet CO concentration according to Reference Example 3 of the present invention.
FIG. 9 is a flowchart for explaining a control operation according to Reference Example 3 of the present invention.
FIG. 10 is a flowchart for explaining a control operation according to Reference Example 4 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrolyte membrane, 2 cathode, 3 anode, 4, 5 catalyst layer, 6, 7 gas flow path, 10 cell, 11 fuel cell laminated body, 12 main laminated part, 13 sub laminated part, 12a, 13a load, 14 humidification Part, 15-17 current collector plate, 31 methanol reformer, 31a vaporization part, 31b catalytic combustion part, 31c reforming part, 31d CO selective oxidation part, 32 methanol tank, 33 water tank, 34a-c pump, 41 air Blower, 51 arithmetic unit, 52 control unit.

Claims (2)

A fuel in which a unit cell in which electrodes having gas diffusibility are arranged on both surfaces of an ion conductive electrolyte membrane, and a gas separator that sequentially supplies fuel to one electrode of the unit cell and oxidant gas to the other electrode A battery main laminate portion, and a sub laminate portion in which the number of stacked cells and separators is smaller than that of the main laminate portion, and a current path is independent from the main laminate portion, and the main laminate portion and the sub laminate portion Both ends are sandwiched between a pair of current collector plates, and a first load is applied to a pair of current collector plates disposed at both ends of the main laminate portion, and a pair of current collectors disposed at both ends of the sub laminate portion. In the operation method of the polymer electrolyte fuel cell, wherein a second load is connected to the electric plate, and the fuel and the oxidant gas are supplied to the main stack portion after passing through the sub stack portion, and the power is generated. In order to prevent a voltage drop in the sub-laminate, the sub-laminate Polymer electrolyte fuel cell operating method characterized by adjusting the second load to reduce from the middle of the driving current value. 2. The method for operating a polymer electrolyte fuel cell according to claim 1, wherein the unit cell of the sub-stacking unit is replaced with a unit cell whose characteristics are not deteriorated at every predetermined time during operation.

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