JP2005174829A - Fuel cell system and operation method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system suppressing degradation of a fuel cell stack accompanied by repeating start and stop of operation. <P>SOLUTION: The fuel cell system comprises a fuel cell stack stacking a plurality of single cells, a fuel generator generating a raw material gas to a fuel gas, a gas cleaner cleaning the raw material gas, a humidifier humidifying an oxidant gas, a power circuit taking out electric power from the fuel cell stack, a measurement part measuring the voltage and the resistance of the single cell, and a controller controlling the fuel cell stack, the fuel generator, the gas cleaner, the humidifier, the power circuit, and the measurement part; wherein the internal resistance of the single cell at the time of the stop of operation is 1.0 Ωcm<SP>2</SP>or larger. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system and an operation method thereof. More specifically, the present invention relates to a fuel cell system that suppresses deterioration such as a voltage drop of a fuel cell stack that accompanies repeated start / stop of operation, and an operation method thereof.

A polymer electrolyte fuel cell will be described as an example of a conventional fuel cell. In a fuel cell, electric energy and thermal energy are obtained mainly by the reaction between hydrogen and oxygen. The reaction shown in Formula 1 occurs at the fuel electrode, and the reaction expressed by Formula 2 occurs at the air electrode. The total reaction is represented by Formula 3.
2H ₂ → 4H ⁺ + 4e ⁻ (Formula 1)
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (Formula 2)
2H ₂ + O ₂ → 2H ₂ O (Formula 3)

In the fuel electrode, a mixture or alloy of Pt and Ru is used as a catalyst in order to prevent a decrease in catalytic function due to adsorption of carbon monoxide on the Pt catalyst. As shown in Formula 3, since the reaction product generated by the reaction is only water, the fuel cell has a feature that it does not discharge substances that adversely affect the environment.
However, since it is not necessary to operate the fuel cell until it does not require electrical energy or heat energy, there is a need for a "start / stop type" operation method that starts when necessary and stops when not needed. .

As this operation method, for example, there is a method of simply stopping the supply of the oxidant gas and the fuel gas when the operation of the fuel cell is stopped. Patent Document 1 proposes a method of enclosing humidified inert gas at the time of stopping / storage in order to keep the polymer electrolyte membrane in a water retaining state even when the fuel cell is stopped / stored. Further, in Patent Document 2, in order to improve durability, in order to prevent oxidation of the oxygen electrode or adhesion of impurities to the oxygen electrode, power generation is performed with the supply of the oxidant gas stopped, and it remains in the fuel cell. There has been proposed a method for performing an operation that consumes oxygen.
JP-A-6-251788 JP 2002-93448 A

However, if the fuel cell is repeatedly started and stopped, the air electrode is oxidized and impurities are easily adsorbed to the air electrode. On the other hand, oxygen is mixed in the fuel electrode, and the potential is increased, so that the catalyst is easily eluted. For this reason, there exists a problem that the electric power generation voltage of a fuel cell will fall.
In order to prevent such a problem, in order to stop the fuel cell after sealing the humidified inert gas in the fuel cell, or to prevent the oxidation of the air electrode and the adhesion of impurities to the air electrode, After generating electricity with the supply stopped and not only consuming oxygen remaining in the fuel cell, but also maintaining the potential of the air electrode and the fuel electrode at 0 to 0.5 V with respect to the standard hydrogen electrode, Attempts have been made to stop operation.

However, these methods cannot sufficiently suppress the deterioration (voltage drop) of the fuel cell during operation stop, and the potential of the fuel electrode rises as the stop time becomes longer. In addition, even when there is no increase in the potential of the fuel electrode, the pores in the electrode are blocked by the condensation of humidified water at the time of stopping, so a battery is formed locally in a minute region inside the electrode, The above-described deterioration occurs partially. In particular, when stopping for a long period of time, the potential of the fuel electrode increases due to the inflow of air into the fuel cell, and the catalytic action of the electrode decreases due to the formation of a local cell.
SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a fuel cell system that suppresses deterioration of a fuel cell stack that accompanies repeated start / stop of operation and an operation method thereof.

A fuel cell system of the present invention includes a pair of separators having a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the electrolyte membrane, and a flow path for supplying fuel gas and oxidant gas to the pair of electrodes, respectively. A fuel cell stack in which a plurality of single cells made of plates are stacked, a fuel generator that generates the fuel gas from a raw material gas, a gas cleaning unit that cleans the raw material gas, and a humidifying unit that humidifies the oxidant gas A power circuit unit that extracts power from the fuel cell stack, a measurement unit that measures the voltage and resistance of the unit cell, the fuel cell stack, a fuel generator, a gas cleaning unit, a humidification unit, a power circuit unit, and a measurement And an internal resistance of the unit cell when the operation of the fuel cell system is stopped is 1.0 Ω · cm ² or more.

It is preferable that the measurement unit includes a high frequency resistance meter.
The control unit supplies the dry inert gas to the fuel cell stack while maintaining the temperature of the operation before stopping the operation of the fuel cell system, thereby reducing the internal resistance of the unit cell. It is preferable to control to 1.0 Ω · cm ² or more.
It is preferable that the control unit supplies the dried inert gas to the fuel cell stack while maintaining the temperature of the operation.

The control unit controls the internal resistance of the unit cell to 0.3 Ω · cm ² or less by supplying a humidified inert gas to the fuel cell stack before starting the operation of the fuel cell system. It is preferable.
It is preferable that the inert gas is a source gas purified by the gas cleaning unit.

It is preferable that the inert gas is a humidified raw material gas generated at a temperature of 300 ° C. or lower in the fuel generator at start-up.
It is preferable that the inert gas is a raw material gas humidified in the humidification unit using heat and water generated in the fuel generator at the time of startup.
It is preferable that after the raw material gas is supplied to the fuel cell stack, it is used as a combustion fuel for the fuel generator.

Further, the operating method of the fuel cell system of the present invention includes a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the electrolyte membrane, and a gas flow for supplying fuel gas and oxidant gas to the pair of electrodes, respectively. Before stopping the operation of the fuel cell system including a fuel cell stack in which a plurality of unit cells each having a pair of separator plates are stacked, the dry inert gas is supplied to the fuel cell stack, and the unit cell Including the step (1) of setting the internal resistance of the substrate to 1.0 Ω · cm ² or more.

In the step (1), the fuel cell stack is preferably maintained at an operating temperature.
Before starting the operation of the fuel cell system, including a step (2) of supplying a humidified inert gas to the fuel cell stack so that the internal resistance of the unit cell is 0.3 Ω · cm ² or less. preferable.
It is preferable to include a step (3) for purifying the source gas, and in the steps (1) and (2), the purified source gas is used as the inert gas.

Preferably, the method includes a step (4) of generating the fuel gas from the source gas and a step (5) of humidifying the source gas, and the humidified source gas is used as the inert gas in the step (2).
It is preferable to humidify the source gas in the step (5) using the heat and water generated in the step (4).

According to the present invention, the dry inert gas is supplied to the fuel cell stack before the operation of the fuel cell system is stopped, and the internal resistance of the unit cell in the fuel cell is set to 1.0 Ω · cm ² or more, so that dew condensation is achieved. It is possible to suppress the formation of a local battery due to the water. In addition, even if air enters from the outside during stoppage, the proton conductivity of the polymer electrolyte membrane is low and the reactivity is low, so that oxidation of the air electrode, adhesion of impurities to the air electrode, and catalyst component of the fuel electrode Deterioration of the electrode due to elution can be suppressed.

Further, by supplying an inert gas humidified before startup to the fuel cell stack and setting the internal resistance to 0.3 Ω · cm ² or less, an increase in internal resistance due to heat generated at startup can be suppressed.
With the above effect, it is possible to provide a fuel cell system capable of suppressing deterioration of the fuel cell stack due to repeated start / stop of operation.
Further, it is possible to provide a method of operating a fuel cell system that can reliably and easily suppress deterioration of the fuel cell stack due to repeated start / stop of operation.

An embodiment of the fuel cell system of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of a fuel cell system of the present invention.
The fuel cell stack 1 is configured by stacking a plurality (n) of single cells (C1 to Cn). The unit cell includes a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the electrolyte membrane, and a pair of separator plates each having a gas flow path for supplying fuel gas and oxidant gas to the pair of electrodes.
On the air electrode side of the fuel cell stack, an oxidant gas control device 2 that controls the supply amount of the oxidant gas based on the voltage and internal resistance of the fuel cell stack, and a total heat exchange type humidification as a humidifier for humidifying the oxidant gas An oxidant gas supply pipe 13 in which a vessel 9 and a hot water humidifier 10 are installed is connected.

On the other hand, on the fuel electrode side, a fuel gas supply pipe 12 provided with a fuel generator 3 that generates fuel gas from the source gas and a gas cleaning unit 8 that cleans the source gas is connected.
The fuel gas supply pipe 12 and the oxidant gas supply pipe 13 are provided with solenoid valves 71 to 79 for switching gas flow paths. A power circuit unit 6 is connected to a current collector plate (not shown) of the fuel cell stack 1, the voltage of each cell (C1 to Cn) is detected by the voltage detector 4, and the internal resistance of the cell is a high frequency resistance. It is measured by a measuring unit such as 11 in total. The control unit 5 controls the fuel cell stack, the fuel generator, the gas cleaning unit, the humidification unit, the power circuit unit, and the measurement unit, and in particular, is output from the power circuit unit 6 based on the detected voltage and internal resistance. The amount of electric power generated, the amount of fuel gas generated by the fuel generator 3, and the opening and closing of the valves in the electromagnetic valves 71 to 79 are controlled.

  Next, an operation method of the above-described fuel cell system of the present invention will be described with reference to Table 1 and FIGS. Table 1 shows a process (sequence) of the operation method of the fuel cell system of the present invention, and FIGS. 2 to 5 respectively show the average value of the internal resistance of the single cell, the temperature of the fuel cell stack, the power generation in each step of Table 1. The transition of the average value of electric power and cell voltage is shown. Here, a case where 70 unit cells are stacked (when n = 70) is shown.

First, during normal operation (step 1), humidified air is supplied to the air electrode, and humidified reformed gas (SRG) is supplied to the fuel electrode to generate power. At this time, the battery temperature is 70 ° C., the average voltage of each unit cell is about 0.75 V, and the generated power is 1 kW.
When stopping the operation of the fuel cell system, the process includes a step (1) of supplying the inert gas dried before the stop to the fuel cell stack and setting the internal resistance of the unit cell to 1.0 Ω · cm ² or more. Perform the operation.

By this operation, the formation of the local battery in the electrode can be suppressed at the time of stopping. Even when oxygen is introduced from the outside during shutdown, the proton conductivity of the polymer electrolyte membrane is low and the reactivity is low. Therefore, oxidation of the air electrode, adsorption of impurities to the air electrode, and elution of catalyst components at the fuel electrode It is possible to suppress electrode deterioration due to.
The internal resistance of the unit cell in step (1) is preferably 1.0 to 3.0 Ω · cm ² . If it exceeds 3.0 Ω · cm ² , the change in water content will increase and the volume change due to repeated swelling and shrinkage of the polymer electrolyte membrane will increase when drying at stop and humidification at startup are repeated. , The electrode is easily damaged.

  First, in step 2, the gas supplied to the air electrode is switched to a dry inert gas, and external output is stopped. At this time, the battery voltage gradually decreases, and the average voltage of the unit cells is about 0.10 to 0.15V. This is because the inside of the air electrode is replaced with an inert gas, and hydrogen in the fuel electrode naturally diffuses into the air electrode, thereby bringing the potentials of both electrodes closer to each other. Note that in the configuration of a normal fuel cell, the flow volume of the air electrode and the flow volume of the fuel electrode are almost the same, and when hydrogen and oxygen diffuse and react, there is an excess of hydrogen. It approaches 0V with respect to the standard hydrogen electrode.

Next, in step 3, dry inert gas is supplied to both electrodes until the internal resistance of the unit cell in the fuel cell stack becomes 1.0 Ω · cm ² or more. In steps 2 and 3, the temperature of the fuel cell stack is maintained at 70 ° C.
That is, in Table 1, step (1) described above corresponds to step 3.
In Step 4 where the internal resistance of the unit cell in the fuel cell stack is 1.0 Ω · cm ² or more, the gas flow paths of the fuel electrode and the air electrode are sealed, the gas flow is stopped, the battery temperature is lowered, and the operation is performed. To stop.

When starting the operation of the fuel cell system, an operation including the step (2) of supplying a humidified inert gas to the fuel cell stack before starting the power generation and setting the internal resistance of the unit cell to 0.3 Ω · cm ² or less. I do. By this operation, an increase in internal resistance due to heat generation can be suppressed during startup.
The internal resistance of the unit cell in step (2) is preferably 0.1 to 0.3 Ω · cm ² . The internal resistance of the cell during operation is about 0.1 Ω · cm ² .
In step 5, the humidified inert gas is supplied to the air electrode and the fuel electrode while the temperature of the fuel cell stack is increased until the internal resistance of the single cell in the fuel cell stack becomes 0.3 Ω · cm ² or less. By this step 5, the polymer electrolyte membrane which was in a dry state during the stop is humidified, and the fuel cell stack returns to a state where power generation is possible.
That is, in Table 1, step (2) described above corresponds to step 5.

In step 6, the gas supplied to the fuel electrode is switched to humidified reformed gas (SRG), and the unit cell is operated for a while with the average voltage of the cell being about 0.10 to 0.15V. At this time, hydrogen moves from the fuel electrode to the air electrode by natural diffusion, whereby the electrode catalyst is reduced and cleaned.
In step 7, the gas supplied to the air electrode is switched to humidified air to generate 1 kW of power.
When operated by the above method, it is possible to suppress deterioration of the fuel cell stack due to repeated start / stop of operation.

  As the inert gas used above, the raw material gas cleaned by the gas cleaning unit 8 can be used. For example, when a city gas containing methane, propane, or the like is used as a source gas, a purified gas obtained by removing an odorant (S component) contained in the city gas as an impurity is used as an inert gas. This removal of impurities is performed to prevent poisoning of Pt contained in the catalyst layer.

As the dry inert gas used in Steps 2 and 3, for example, a raw material gas that has passed through the bypass 3b provided between the fuel generators 3 via the gas cleaning unit 8 is used.
The humidified inert gas used in Steps 5 and 6 is, for example, a raw material gas that has passed through the fuel generator 3 at 300 ° C. or lower via the gas cleaning unit 8. When the temperature of the fuel generator 3 is 300 ° C. or lower, the raw material gas is not reformed into a hydrogen-containing gas, and only the raw material gas is humidified.

Further, in the humidified inert gas, for example, the raw material gas that has passed through the connecting pipe 12 a that connects the fuel gas supply pipe and the air supply pipe after passing through the gas cleaning unit 8 is generated in the fuel generator 3. What was humidified with the hot water humidifier 10 using heat and water can be used.
The raw material gas supplied to the fuel cell stack 1 as an inert gas can be reused as a combustion fuel for the fuel generator 3.

Since the source gas can be used as the inert gas in this way, it is not necessary to separately provide an apparatus for supplying an inert gas such as a nitrogen gas cylinder. Therefore, deterioration of the fuel cell stack can be easily suppressed without complicating the fuel cell system and without cost.
Examples of the present invention will be specifically described below, but the present invention is not limited to them.

A fuel cell stack having the configuration shown in FIG. 6 was produced by the following method. FIG. 6 is a schematic longitudinal sectional view showing a part of the fuel cell stack.
(1) Production of membrane / electrode assembly Acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd., particle size: 35 nm) as carbon powder and aqueous dispersion of polytetrafluoroethylene (PTFE) (Daikin Kogyo Co., Ltd.) A water repellent ink containing 20% by weight of PTFE as a dry weight was obtained by mixing with D1). This ink was applied and impregnated on carbon paper (TGPH060H manufactured by Toray Industries, Inc.) as a base material for a gas diffusion layer, and then heat-treated at 300 ° C. with a hot air dryer, and a gas diffusion having a thickness of about 200 μm. Layers 23a and 23b were obtained.

  On the other hand, Pt was supported as a catalyst on Ketjen Black (Ketjen Black EC manufactured by Ketjen Black International Co., Ltd., particle size 30 nm) as carbon powder to obtain a catalyst powder containing 50% by weight of Pt. This catalyst powder was mixed with hydrogen ion conductive polymer electrolyte and binder perfluorocarbon sulfonic acid ionomer (Aldrich, USA, 5 wt% Nafion dispersion) in a weight ratio of 2: 1. The mixture was molded to form catalyst layers 22a and 22b having a thickness of 10 to 20 μm.

The catalyst layers 22a and 22b and gas diffusion layers 23a and 23b obtained above were bonded to both surfaces of a hydrogen ion conductive polymer electrolyte membrane 21 (Nafion 112 membrane manufactured by DuPont, USA). A membrane composed of a polymer electrolyte membrane 21, an anode 24a composed of a catalyst layer 22a and a gas diffusion layer 23a, and a cathode 24b composed of a catalyst layer 22b and a gas diffusion layer 23b sandwiching the polymer electrolyte membrane 21 An electrode assembly (hereinafter referred to as MEA) 27 was obtained.
At this time, a rubber gasket 25 was joined to the outer peripheral edge of the polymer electrolyte membrane 21 in the MEA 27. The gasket 25 was formed with a manifold hole through which fuel gas, oxidant gas, and cooling water flow.

(2) Assembly of fuel cell stack An anode side separator plate 26a having a gas flow path 28a having a depth of 0.5 mm for supplying fuel gas to the anode 24a, and a depth of 0.5 mm for supplying oxidant gas to the cathode 24b A cathode separator plate 26b having a gas flow path 28b was prepared. As the separator plates 26a and 26b, graphite plates impregnated with phenol resin having an outer dimension of 20 cm × 32 cm × 1.3 mm were used. A cooling water passage 29 having a depth of 0.5 mm is formed on the surface opposite to the surface having the gas passage.

  The surface of the anode side separator plate 26a having the gas flow path 28a is superimposed on the surface of the anode 24a of the MEA 27, and the surface of the cathode side separator plate 26b having the gas flow path 28b is superimposed on the surface of the cathode 24b of the MEA 27. A battery was obtained. 70 unit cells were stacked to obtain a battery stack. At this time, the surface of the separator 26a having the cooling water flow path 29 and the surface of the separator 26b having the cooling water flow path 29 were overlapped to form a cooling unit for each single cell. Further, a rubber seal portion 30 was provided on the surface of the separator plate having the cooling portion so as to surround the cooling water flow path in order to prevent the cooling water from flowing out.

Then, a stainless steel current collector plate, an insulating plate made of an electrically insulating material, and an end plate were disposed at both ends of the battery stack, and the whole was fixed with a fastening rod, thereby producing a fuel cell stack. The fastening pressure at this time was 15 kgf / cm ² per area of the separator plate.

[Evaluation of fuel cell system]
Then, the fuel cell stack 1 obtained above was connected to the fuel cell system having the same configuration as in FIG. 1 described above, and the following operation test was performed in the same process as in Table 1 described above.

  As Step 1, 13A gas as source gas and air as oxidant gas were supplied to the fuel gas supply pipe and oxidant gas supply pipe in the fuel cell system obtained above. At this time, the cell temperature in the fuel cell stack was 70 ° C., the fuel gas utilization rate (Uf) was 70%, and the air utilization rate (Uo) was 40%. The fuel gas and air were humidified so as to have dew points of 65 ° C. and 70 ° C., respectively. As the purge gas, 13A gas that passed through the gas cleaning unit 8 was used.

Then, the times of Steps 1 to 6 in Table 1 described above are respectively set to Step 1:80 minutes, Step 2:20 minutes, Step 3:30 minutes, Step 4:48 hours, Step 5:30 minutes, and Step 6: Steps 1-6 were performed 100 cycles for 20 minutes. The operation test was performed at room temperature (27 ° C.) (Experiment No. 1).
In addition, the raw material gas cleaned in the gas purification part was used for the dry inert gas. Moreover, the raw material gas which passed the fuel generator below 300 degreeC was used for the humidified inert gas.
An operation test was conducted in the same manner as in Experiment No. 1 except that the time of Steps 1 to 6 was changed to the conditions shown in Table 2.

During normal operation (step 1), the internal resistance of the unit cell was 0.1 Ω · cm ² in any of the execution numbers 1 to 12.
First, Table 3 shows the results of the operation test in execution numbers 1, 2, and 6 to 8 in which the time of step 3 is changed. In addition, the internal resistance in Table 3 shows the average value of the internal resistance of each unit cell at the end of Steps 3 and 5. Moreover, a deterioration rate shows the average value of the fall of the voltage of each single cell per cycle (steps 1-6) when starting and a stop are repeated alternately.

Under these conditions where the time of step 3 is different, different results were obtained for internal resistance during shutdown.
Here, in order for the generated power of the fuel cell stack to have a merit as a running cost with respect to the power of a general large power plant, deterioration due to repeated start and stop, that is, the voltage drop is about 80 mV or less in about 4000 cycles, that is, The allowable range is 20 μV / cycle or less. In execution numbers 1 and 2 in which the internal resistance at the time of stop was 1.0 to 3.0 Ω · cm ² , the voltage drop of the fuel cell stack was suppressed.

On the other hand, in Experiment Nos. 6 and 7 in which the internal resistance at the time of stop was 1.0 Ω · cm ² or less, the voltage drop was large. This is presumably because the dry state at the time of stoppage was insufficient, so that pores were clogged by humidified water inside the electrode, a local battery was formed, and the electrode was deteriorated. In Experiment No. 8 where the internal resistance at the time of stop was 10 Ω · cm ² , the voltage was significantly reduced. This is thought to be because the volume change due to repeated swelling and shrinkage of the polymer electrolyte membrane was large and the electrode was damaged because the change in the amount of water due to repeated drying at stop and humidification at startup was too large. It is done.
Next, Table 4 shows the results of the operation tests of execution numbers 1, 3, 9 and 10.

Under these conditions in which the temperature raising / wetting time in Step 5 was different, the results of different internal resistance values at the start were obtained. In implementation numbers 1 and 3 in which the internal resistance at startup was 0.3 Ω · cm ² or less, the voltage drop was suppressed.
On the other hand, in the experiment numbers 9 and 10 in which the internal resistance at the start exceeds 0.3, the voltage drop was large. This is considered to be because the proton conductivity of the polymer electrolyte membrane is low, the reaction resistance is increased, and the polymer electrolyte membrane is deteriorated by starting power generation with a high internal resistance at the time of startup.
Next, Table 5 shows the results of the operation tests of execution numbers 1, 2, 4 to 8, 11, and 12.

Run numbers 1 and 4 and experiment numbers 2 and 5 differed in the stop time of step 4, but the voltage drop was small regardless of the length of the stop time, and the deterioration of the fuel cell stack was suppressed.
In contrast, in Experiment Nos. 6 and 11 and Experiment Nos. 7 and 12, the stop time was longer, and in Experiment Nos. 11 and 12, the voltage drop was larger. This is presumably because, under these drying conditions in Step 3, the drying before the stop was insufficient, a local battery was formed inside the electrode, and the deterioration of the electrode progressed as the stop time increased.

  In this example, Nafion 112 was used as the polymer electrolyte membrane, but the same effect was obtained with other materials used as the polymer electrolyte membrane. Further, in this example, the test temperature was set to room temperature of 27 ° C. However, even at other temperatures, for example, Reference 1 (Handbook of Fuel Cell, vol. 3, p567, Fundamentals, Technology and Applications) described in Nafion 112 The effective internal resistance range according to the present invention can be calculated from the conductive Arrhenius plot.

  As described above, since the fuel cell system of the present invention can maintain stable performance for a long period of time, it can be applied to portable power supplies, portable device power supplies, electric vehicle power supplies, home cogeneration systems, and the like.

It is a figure which shows the structure of the fuel cell system of this invention. It is a figure which shows transition of the average value of the internal resistance of the single cell in the operating method of the fuel cell system of this invention. It is a figure which shows transition of the battery temperature in the operating method of the fuel cell system of this invention. It is a figure which shows transition of the electric power generation amount in the operating method of the fuel cell system of this invention. It is a figure which shows transition of the average value of the voltage of the cell in the operation method of the fuel cell system of this invention. It is a schematic longitudinal cross-sectional view which shows a part of fuel cell stack in the fuel cell system of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Oxidant gas control apparatus 3 Fuel generator 3b Bypass 4 Voltage detection apparatus 5 Control part 6 Power circuit part 71-79 Solenoid valve 8 Gas cleaning part 9 Total heat exchange type humidifier 10 Hot water type humidifier 11 High frequency Resistance meter 12 Fuel gas supply pipe 12a Connecting pipe 13 Oxidant gas supply pipe 21 Hydrogen ion conductive polymer electrolyte membrane 22a, 22b Catalyst layer 23a, 23b Gas diffusion layer 24a Anode 24b Cathode 25 Gasket 26a Anode side separator plate 26b Cathode side Separator plate 27 Membrane / electrode assembly 28a, 28b Gas flow path 29 Cooling water flow path 30 Seal part

Claims (15)

A plurality of single cells comprising a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the electrolyte membrane, and a pair of separator plates each having a flow path for supplying fuel gas and oxidant gas to the pair of electrodes, respectively. Stacked fuel cell stacks;
A fuel generator for generating the fuel gas from the raw material gas;
A gas cleaning unit for cleaning the source gas;
A humidifying section for humidifying the oxidant gas;
A power circuit unit for extracting power from the fuel cell stack;
A measurement unit that measures the voltage and resistance of the unit cell; and a control unit that controls the fuel cell stack, a fuel generator, a gas cleaning unit, a humidification unit, a power circuit unit, and a measurement unit,
The fuel cell system, wherein the internal resistance of the unit cell when the operation of the fuel cell system is stopped is 1.0 Ω · cm ² or more.   The fuel cell system according to claim 1, wherein the measurement unit includes a high frequency resistance meter. The control unit supplies the dry inert gas to the fuel cell stack while maintaining the temperature of the operation before stopping the operation of the fuel cell system, thereby reducing the internal resistance of the unit cell. The fuel cell system according to claim 1, wherein the fuel cell system is controlled to 1.0 Ω · cm ² or more.   The fuel cell system according to claim 3, wherein the control unit supplies a dry inert gas to the fuel cell stack in a state where the temperature of the operation is maintained. The control unit controls the internal resistance of the unit cell to 0.3 Ω · cm ² or less by supplying a humidified inert gas to the fuel cell stack before starting the operation of the fuel cell system. The fuel cell system according to claim 1.   The fuel cell system according to any one of claims 3 to 5, wherein the inert gas is a raw material gas purified by the gas cleaning unit.   The fuel cell system according to claim 5, wherein the inert gas is a humidified raw material gas generated at a temperature of 300 ° C. or less in the fuel generator at the time of startup.   The fuel cell system according to claim 5, wherein the inert gas is a raw material gas humidified in the humidification section using heat and water generated in the fuel generator at the time of startup.   The fuel cell system according to any one of claims 6 to 8, wherein the source gas is used as a combustion fuel of the fuel generator after being supplied to the fuel cell stack. A plurality of unit cells comprising a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the electrolyte membrane, and a pair of separator plates each having a gas flow path for supplying fuel gas and oxidant gas to the pair of electrodes, respectively. A method for operating a fuel cell system including a fuel cell stack in which the individual fuel cells are stacked,
Before stopping the operation of the fuel cell system, including a step (1) of supplying a dry inert gas to the fuel cell stack so that the internal resistance of the unit cell is 1.0 Ω · cm ² or more. A method of operating a fuel cell system characterized by the above.   The operation method of a fuel cell system according to claim 10, wherein in the step (1), the fuel cell stack is maintained at an operation temperature. The method includes a step (2) of supplying a humidified inert gas to the fuel cell stack before starting operation of the fuel cell system so that the internal resistance of the unit cell is 0.3 Ω · cm ² or less. The operation method of the fuel cell system according to 10.   13. A method for operating a fuel cell system according to claim 10 or 12, comprising a step (3) of purifying the source gas, wherein the purified source gas is used as the inert gas in the steps (1) and (2). .   13. The step (4) of generating the fuel gas from the source gas and the step (5) of humidifying the source gas, wherein the humidified source gas is used as the inert gas in the step (2). Operation method of fuel cell system.   The operation method of the fuel cell system according to claim 14, wherein the raw material gas is humidified in the step (5) using heat and water generated in the step (4).

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