JP4770120B2 - Direct liquid fuel type fuel cell system - Google Patents

Description

  The present invention relates to a direct liquid fuel type fuel cell system in which an organic solvent such as methanol, isopropanol, butanol, dimethyl ether or the like is mixed with water, for example, as a liquid fuel and directly supplied to a fuel electrode. In this specification, the direct liquid fuel cell system may be simply referred to as a fuel cell system, and the proton conductive polymer solid electrolyte membrane may be simply referred to as a proton conductor membrane.

  In the direct liquid fuel type fuel cell system, it is necessary to manage the fuel concentration in the liquid fuel, for example, the methanol concentration in the methanol-water fuel. It has been proposed that a sensor using MEA as a fuel concentration sensor is provided separately from the fuel cell stack, and a constant voltage is applied to the sensor MEA to monitor the output current. However, this method requires a fuel concentration sensor in addition to the stack, and has a short life because a constant voltage is applied to the MEA. The MEA is a composite of a proton conductive polymer solid electrolyte membrane, a fuel electrode, and an air electrode. When the fuel electrode and the air electrode are supported by a carbon sheet or the like, the carbon sheet may be included in the MEA. In addition, the fuel cell stack is formed by connecting single cells composed of MEAs and separators in series, and may be simply referred to as a stack for simplicity.

An object of the present invention is to make it possible to detect a liquid fuel concentration without using a fuel sensor separate from the fuel cell stack.
An additional problem with the present invention is that the liquid fuel concentration deviates from the optimum value to the low concentration side or deviates from the high concentration side using a monitor cell that detects that the liquid fuel concentration deviates from the optimum value. Is to enable feedback to the liquid fuel concentration.
Another additional problem of the present invention is to make it possible to configure a monitor cell that easily measures the liquid fuel concentration using the MEA or separator of the fuel cell stack.
Still another additional problem of the present invention is that the MEA of the monitor cell is slightly changed so that the liquid fuel concentration can be discriminated from the optimum value to the low concentration side or the high concentration side. Is to make it.

A direct liquid fuel type fuel cell system according to the present invention includes a fuel cell stack in which a plurality of M E A each including at least a proton conductive polymer solid electrolyte membrane, a fuel electrode, and an air electrode are stacked with a separator interposed therebetween. The fuel cell stack includes a monitor cell that is driven by fuel and that supplies air and liquid fuel from a separator to M E A that includes at least a proton conductive polymer solid electrolyte membrane, a fuel electrode, and an air electrode. Connected to the monitor cell and connected to the monitor cell, the liquid fuel concentration is reduced by driving in a large current region where the output is lower than the optimum fuel concentration regardless of whether the liquid fuel concentration is higher or lower than the optimum value. It is detected that the liquid fuel concentration deviates from the optimum value, and the liquid fuel concentration deviates from the optimum value to the high concentration side (Rich R) or to the low concentration side (Lean L) Whether it has is provided with a discriminating means for discriminating from the behavior of the output of said monitor cell.

Preferably, the discriminating unit discriminates whether the liquid fuel concentration is deviated from the optimum value to the high concentration side or the low concentration side from the behavior of the output of the monitor cell after the high concentration liquid fuel is replenished. When the high-concentration liquid fuel is replenished, the output of the monitor cell does not approach the optimum concentration in the case of rich, but the output approaches the optimum concentration output in lean.
Preferably, the determination unit determines whether the liquid fuel concentration is deviated from an optimum value to a high concentration side or a low concentration side by switching the resistance from a small value to a large value . If the resistance value is decreased, the output of the monitor cell increases as the fuel concentration is lower (FIG. 5), so it is possible to determine whether the resistance is rich or lean.
Preferably, by directly starting the liquid fuel type fuel cell under the condition that the liquid fuel concentration is deviated from the optimum value to the high concentration side, and controlling so that the liquid fuel concentration does not shift from the optimum value to the low concentration side, The output of the discrimination means is kept on the high density side. The direct liquid fuel type fuel cell system may be started at a fuel concentration higher than the initial optimum concentration in order to facilitate startup. Therefore, if the fuel cell is started at a fuel concentration higher than the optimum concentration and thereafter controlled so that the fuel concentration does not change to a concentration lower than the optimum concentration, even if the monitor cell cannot determine whether it is rich or lean, the optimum fuel concentration or a little higher than this A direct liquid fuel type fuel cell system can be controlled at a high fuel concentration. In addition, if the fuel cell is started under conditions that deviate from the optimum value to the low concentration side, not only does it take a long time to start due to a delay in the temperature rise of the stack, but the cell may be deteriorated due to inversion, etc. It is not preferable.

  Preferably, the monitor cell is configured using other cells in the fuel cell stack, a common MEA, and a common separator. The monitor cell may use a different member from the other cells of the fuel cell stack (single cell made up of MEA and separator), but if the same MEA and separator with the same air supply and fuel supply pattern are used, the manufacturing process will be improved. Simple.

The direct liquid fuel type fuel cell system according to the present invention also includes a fuel cell stack in which a plurality of M E A each including at least a proton conductive polymer solid electrolyte membrane, a fuel electrode, and an air electrode are stacked via a separator. The fuel cell stack includes a monitor cell that is driven by fuel and that supplies air and liquid fuel from a separator to M E A that includes at least a proton conductive polymer solid electrolyte membrane, a fuel electrode, and an air electrode. And connecting a resistor to the monitor cell, and driving the monitor cell under the condition that the supply of the liquid fuel is restricted, it is detected that the liquid fuel concentration is out of the optimum value.

  In order to restrict the supply of liquid fuel to the monitor cell, the fuel supply groove of the separator of the monitor cell may be narrower than the grooves of other cells. However, if the cross-sectional area of the groove is changed or the groove is partially filled, a problem occurs in the reproducibility. Therefore, preferably, the MEA of the monitor cell and the other MEAs of the fuel cell stack include a diffusion control film on the opposite side of the proton conductive polymer solid electrolyte membrane of each of the fuel electrode and the air electrode, and the fuel electrode of the monitor cell. The liquid permeability of the diffusion control membrane on the side is made lower than the diffusion control membrane on the fuel electrode side of the other MEA, thereby limiting the supply of liquid fuel to the monitor cell. For example, if the number of carbon sheets on the fuel electrode side in the monitor cell is increased as compared with other cells, the liquid permeability can be easily reduced. Similarly, even if the content of a hydrophobic polymer such as PTFE in the carbon sheet is increased or the density of the carbon sheet is increased, the liquid permeability can be lowered.

  In the present invention, a monitor cell is attached to the fuel cell stack, and a resistor is connected to the monitor cell, so that the fuel cell stack is driven in a large current region where the output is reduced regardless of whether the liquid fuel concentration is higher or lower than the optimum value. For example, as shown in FIG. 5, when the monitor cell is driven at a larger current density than the other cells of the fuel cell stack, the output voltage to the resistor decreases regardless of whether the liquid fuel concentration is higher or lower than the optimum concentration. This is because when the concentration is higher than the optimum fuel concentration, polarization due to crossover of fuel components such as methanol to the air electrode side becomes significant. Further, when the concentration is lower than the optimum fuel concentration, the diffusion of the liquid fuel to the fuel electrode is delayed, so that the output voltage of the monitor cell is lowered. For these reasons, it can be detected by the monitor cell that the concentration of the liquid fuel deviates from the optimum fuel concentration. Next, if the determination means determines whether the liquid fuel concentration deviates from the optimum value to the high concentration side or the low concentration side, the liquid fuel concentration can be feedback-controlled.

  In determining whether the liquid fuel concentration deviates from the optimum value to the high concentration side or the low concentration side, for example, the output of the monitor cell after replenishing the high concentration liquid fuel is monitored. When it is out of the high concentration side, the output of the monitor cell does not increase even if high concentration liquid fuel is supplied. On the other hand, when it is out of the low concentration side, if the high concentration liquid fuel is replenished, the output of the monitor cell increases. Therefore, after the high concentration liquid fuel is replenished, if the output of the monitor cell increases, it is deviated to the low concentration side, otherwise it can be determined that it is deviated to the high concentration side.

  By switching the value of the resistance connected to the monitor cell, it can also be determined whether the liquid fuel concentration deviates from the optimum value to the high concentration side or to the low concentration side. As shown in FIG. 5, in a region where the current density is small, polarization due to crossover on the air electrode side becomes a factor governing the output voltage of the monitor cell. In this case, the output voltage decreases as the liquid fuel concentration increases (FIG. 5). 5). Therefore, by increasing the resistance value and driving the monitor cell in a small current region or measuring the electromotive force, it can be determined which side the fuel concentration deviates from the optimum concentration. When this discriminant value is used in combination with the output voltage of the monitor cell when driven in the large current region, the liquid fuel concentration can be feedback-controlled.

  The direct liquid fuel cell system may be activated at a liquid fuel concentration higher than the optimum value in order to facilitate activation. Therefore, in such a case, the fuel concentration at the time of startup is higher than the optimum value. If feedback control is performed so that the liquid fuel concentration does not fall below the optimum value with the monitor cell, the liquid fuel concentration will be less than the optimum value or the optimum value. Feedback control can be performed while maintaining a slightly high concentration side.

  The monitor cell of the present invention can be configured using an MEA that is basically common to other cells of the fuel cell stack or a common separator. That is, the size, material, and structure of the MEA and separator can be made common to those of other cells. Moreover, the structure of the air supply groove and the fuel supply groove of the separator can be made common to other separators. For this reason, the monitor cell of this invention can be easily attached to a fuel cell stack, and can supply air and fuel like other cells. For these reasons, it is not necessary to provide a sensor, that is, a monitor cell, separately from the fuel cell stack.

  The invention also limits the supply of liquid fuel to the monitor cell. Then, the output voltage of the monitor cell is governed by the diffusion of the liquid fuel to the fuel electrode, and the output increases as the fuel concentration increases until reaching a certain value, and the output gradually decreases when the fuel concentration falls below the certain value. Furthermore, since it drops rapidly when the lower limit value is lower than a certain value, the actual liquid fuel concentration can be obtained. When the fuel concentration exceeds a certain value and exceeds the upper limit value, the output decreases.

  Even in this case, the shape of the MEA or separator of the monitor cell may be the same as the MEA or separator of other cells of the fuel cell stack, and in order to restrict the supply of fuel to the fuel electrode of the monitor cell, the fuel electrode side The liquid permeability of the diffusion control membrane such as the carbon sheet may be lower than that of the diffusion control membrane on the fuel electrode side of other MEAs. For example, a plurality of carbon sheets may be stacked, the content of a hydrophobic component such as PTFE (polytetrafluoroethylene) in the carbon sheet may be increased, or the density of the carbon sheet may be increased. If it does in this way, liquid permeability of liquid fuel to the fuel electrode of a monitor cell can be reduced simply and correctly.

  In the following, an optimum embodiment for carrying out the present invention will be shown.

  1 to 11 show examples and their characteristics. FIG. 1 shows a layout of the fuel cell system 2. Reference numeral 4 denotes a fuel cell stack, in which a plurality of single cells composed of MEAs and separators are stacked in series. As the MEA, for example, a proton conductive polymer solid electrolyte membrane provided with a fuel electrode and an air electrode on both surfaces is used. In particular, the fuel electrode and the air electrode are each supported by a carbon sheet such as hydrophobic carbon paper. The carbon sheet is a support for the fuel electrode and the air electrode, and at the same time serves as a flow path for liquid fuel and air to the fuel electrode and the air electrode, and also serves as a conductive path to the fuel electrode and the air electrode. For example, a carbon material is used for the separator, an air supply groove and a fuel supply groove are provided, and fuel and air are supplied through the carbon sheet.

  A monitor cell 6 is provided at one end of the fuel cell stack 4, for example. 8 is a fuel tank, and 10 is a liquid fuel such as methanol-water. Here, the fuel cell stack 4 is driven by being submerged in the liquid fuel 10. Of course, the fuel cell stack 4 may not be housed in the fuel tank 8 and fuel may be supplied from the fuel pump. An air pump 12 supplies air to each single cell of the fuel cell stack 4 and the monitor cell 6. 14 is a radiator for cooling the exhaust air, 16 is a gas-liquid separator using a gas-liquid separation membrane, etc., recovering water from the exhaust air cooled by the radiator 14 and returning it to the fuel tank 8, Prevents the liquid level from dropping. Reference numerals 18 and 18 denote, for example, a pair of CO2 outlets that discharge CO2 generated in the fuel cell stack 4 from the fuel tank 8. Reference numeral 19 denotes a liquid level sensor for detecting the liquid level height of the liquid fuel 10.

  20 is a fuel cassette, 21 is a drainage reservoir, 22 is a fuel reservoir composed of an elastic bag, and 23 is a movable wall between them. High concentration liquid fuel is supplied to the fuel tank 8 via a high concentration fuel pump 24. Supply. As the high-concentration liquid fuel, for example, a fuel such as methanol 50 wt% -water 50 wt% is used, and 26 is a filter. Then, moisture and the like are collected from the exhaust air of the fuel cell stack 4 by the gas-liquid separator 16, and the remaining air is guided to the drainage reservoir 21. When the liquid level of the fuel tank 8 is high, the radiator 14 is turned off, and moisture and the like are collected in the drainage reservoir 21. From the waste liquid reservoir 21, by-products such as methanol and formic acid are removed by the filter 26, and the exhaust air is discharged. Reference numeral 30 denotes a control unit of the fuel cell system 2, which is an air pump 12 or a high-concentration fuel pump based on signals from the monitor cell 6 (output voltage to the resistor and monitor cell temperature) and the liquid level obtained by the liquid level sensor 19. 24, radiator 14 etc. are controlled.

  FIG. 2 shows the structure of the monitor cell 6. The MEAs to be used include the MEA 32 shown on the upper right side in FIG. 2 and the MEA 34 shown on the lower right side, and any of these may be used. The MEAs 32 and 34 have the same size, the same structure, material, and composition as the other MEAs of the fuel cell stack 4 except for the points specifically pointed out.

  In the MEA 32, 35 is a proton conductive polymer solid electrolyte membrane, for example, using a Nafion 117 membrane (Nafion is a registered trademark of DuPont), 36 is an air electrode, 38 is a fuel electrode, and 37 and 39 are hydrophobic carbons. It is a sheet. Reference numeral 40 denotes a carbon sheet added to the fuel electrode side. The air electrode 36 includes a platinum catalyst supported on carbon, a PTFE binder, a proton conductive polymer solid electrolyte, and the like, and the fuel electrode 38 includes a platinum-ruthenium catalyst supported on carbon, a PTFE binder, a proton conductive polymer solid electrolyte, and the like. Become. The carbon sheets 37, 39, and 40 are obtained by adding a hydrophobic binder such as PTFE to a porous carbon base material such as carbon paper, and have a thickness of about 150 to 300 μm, for example, 250 μm. The MEA 32 is characterized in that an additional carbon sheet 40 is provided on the fuel electrode side.

  The MEA 34 is exactly the same as the MEA used in the other cells of the fuel cell stack 4, and there is one carbon sheet for each of the air electrode side and the fuel electrode side. One of the MEAs 32 and 34 is sandwiched between, for example, carbonaceous separators 42 and 44, liquid fuel is supplied from the fuel supply groove 45, and air is supplied from the air supply groove 46. The fuel supply groove 45 passes through the separator 42 from the bottom to the top of FIG. 1 and supplies liquid fuel to the fuel electrode by convection or diffusion. In addition, air is supplied to the air supply groove 46 from a hole 47 that passes through the separators 42 and 44, and air is discharged from the hole 48. In this way, air is supplied to the entire fuel cell stack and the monitor cell 6 by one air pump 12, and exhaust air is discharged to the radiator 14 side. 49 is a temperature sensor for measuring the temperature of the monitor cell 6, 50 and 51 are fixed resistors, for example, the resistor 50 is 0.1Ω, the resistor 51 is 10Ω, etc. 52 is a switch, and any of the fixed resistors 50 and 51 Select. 54 is a voltmeter for output measurement.

  In the case of the MEA 32 of FIG. 2 (using two carbon sheets 39 and 40 on the fuel electrode side), the output voltage to the resistor (hereinafter simply output) is within a range where the liquid fuel concentration is practically controlled. Since it increases with the liquid fuel concentration, the liquid fuel concentration can be easily obtained from the output voltage of the monitor cell. In the case of the MEA 34, even if the liquid fuel concentration is shifted to a higher concentration side or a lower concentration side than the optimum value, the output voltage of the monitor cell is lowered, so that the liquid fuel concentration is shifted to the higher concentration side, It is necessary to determine whether it is shifted to the low concentration side.

  The configuration of the control unit 30 for determination is shown in FIG. Reference numeral 60 denotes an AD converter that inputs the output voltage and temperature of the monitor cell 6, and reference numeral 62 denotes a rich / lean storage unit that stores either rich (high concentration side) or lean (low concentration side). The resistance switching unit 64 switches the value of the fixed resistance of the monitor cell 6 and determines whether it is rich or lean. The interval monitoring unit 66 monitors the change in the output voltage of the monitor cell 6 after replenishing the high-concentration liquid fuel. If the output voltage increases, the interval monitoring unit 66 is on the lean side. If the output voltage does not increase, the interval monitoring unit 66 is on the rich side. It shall be. The fuel pump drive unit 68 drives the high concentration fuel pump 24 according to the detection result of the liquid fuel concentration. Further, after the high-concentration fuel pump is replenished with high-concentration liquid fuel, there is a delay of about 30 seconds to 1 minute for the output voltage of the monitor cell 6 to change. Regardless of the voltage, the addition of high-concentration liquid fuel is prohibited.

  FIG. 4 shows the output of the monitor cell when the supply of liquid fuel to the fuel electrode is restricted. The white symbols in the figure indicate the output voltage to the load resistance of the monitor cell, and the black symbols indicate the output power. “1M normal” is a result when the methanol concentration in the liquid fuel is 1M and one carbon sheet is attached to the fuel electrode side. The other results are obtained when two carbon sheets are used on the fuel electrode side and the thickness is changed twice. The double thickness of 0.8M to 2.5M indicates the methanol concentration in the liquid fuel concentration.

With the output voltage of the monitor cell, the output voltage increases with the fuel concentration up to about 2.0M. In particular, when the current density is driven at about 150 to 250 mA / cm ² , the output voltage varies significantly depending on the fuel concentration. Also, if the thickness of the carbon sheet is doubled, the output voltage is smaller than when one carbon sheet is used, and 1M when the carbon sheet is made into one sheet at a methanol concentration of about 1.5M to 2.5M. The output voltage is about. In the output density, the influence of the methanol concentration appears more clearly, and at a concentration of 1M when there is one carbon sheet, an output almost equivalent to 1.5M to 2.5M can be obtained with two carbon sheets. From these facts, when the MEA 32 of FIG. 2 is used, it is possible to easily obtain the fuel concentration and perform feedback control.

FIG. 5 shows the characteristics when one carbon sheet is formed on the fuel electrode side, and the methanol concentration was changed in the range of 0.5M to 3M. When the current density is small, the output voltage increases as the methanol concentration decreases. This is because the polarization increases and the output voltage decreases as the methanol crossover to the air electrode increases. For example, when driving in a large current region of 250 mA / cm ² or more, the output voltage decreases even if the fuel concentration increases or decreases from an optimal fuel concentration of about 1M. This method cannot identify whether the fuel concentration is higher or lower than the optimum fuel concentration. For this purpose, an additional algorithm shown in FIGS. 6 to 8 is used.

  In the algorithm of FIG. 6, the operation of the liquid fuel cell system is started on the high concentration side, and the initial value for determining whether it is rich or lean is rich. And when the monitor cell rises in temperature, the output is stable, and feedback control is possible, the output voltage of the monitor cell does not reach the optimum value, and the liquid fuel concentration is constantly kept slightly higher than the optimum value, Feedback control of fuel concentration. Note that the temperature signal of the monitor cell is also used in the feedback control of the fuel concentration. In addition, the fuel consumption rate by the fuel cell stack can be estimated from the output of the fuel cell stack, etc. Therefore, it can be estimated to some extent how much the fuel concentration is lowered while the high concentration liquid fuel is not replenished. As a result, if it is clear that the initial value is on the high concentration side, feedback control can be performed by estimating whether the liquid fuel concentration is rich or lean thereafter.

  In the algorithm of FIG. 7, load resistance switching is used instead of using the state at the start of operation of the fuel cell system. That is, the load resistance is always reduced, the monitor cell is driven in a large current region, and feedback control is applied to the liquid fuel concentration. Then, the value of the load resistance is increased intermittently or at the initial stage when feedback control becomes possible, and the rich or lean is discriminated using the output of the monitor cell in the small current region of FIG.

  In the algorithm of FIG. 8, it is determined whether the output is rich or lean from the behavior of the output of the monitor cell after the high-concentration liquid fuel is added. When the output of the monitor cell decreases and is lean, a high concentration liquid fuel is added, and thereafter, the addition of the high concentration fuel is prohibited for a time period during which the output of the monitor cell responds. If the output increases during this time, the liquid fuel concentration is deviated to the lean side, and if it does not increase, it is the rich side.

  FIG. 9 schematically shows an example using a transient response when the value of the load resistance of the monitor cell is switched. The solid line in the figure shows the behavior when the liquid fuel concentration is a normal value (optimum value), the broken line shows the behavior when the concentration is low, and the chain line shows the behavior when the concentration is high. When the liquid fuel concentration is low, the increase in output when the load resistance is changed from a small value to a large value is large. On the other hand, when the liquid fuel concentration is shifted to the high concentration side, the increase in output when the load resistance is switched from a small value to a large value is small, and the output drops when the load resistance is maintained at a large value. Is big.

  10 and 11 show the control results in the embodiment. The horizontal axis of the figure shows the operation time from the start of the fuel cell system. In the control, the output voltage y (MC) from the monitor cell is used in mV, the monitor cell temperature is T in ° C, and the output voltage is shown in the figure. When the value falls below the value on the right side of the control equation, a high-concentration methanol aqueous solution was added, and thereafter, for example, addition of the methanol aqueous solution was prohibited for 1 minute, and whether it was rich or lean was determined from the output behavior during this period. Note that MCC represents a control voltage determined by a control equation. The methanol concentration in the liquid fuel is indicated by a broken line with a value measured by a separate sensor. As apparent from FIG. 10, the feedback control of the liquid fuel concentration was successful, and the liquid fuel type fuel cell system could be directly driven with a stable output.

In the embodiment, the following effects can be obtained.
(1) A monitor cell can be configured using a single cell similar to the single cell of the fuel cell stack.
(2) By limiting the fuel supply to the fuel electrode of the monitor cell, the liquid fuel concentration can be easily obtained.
(3) When a monitor cell that is exactly the same as a single cell of the fuel cell stack is driven in a large current range, it can be detected that the fuel concentration is outside the optimum fuel concentration, and if it is determined whether it is rich or lean, the fuel concentration is fed back. Can be controlled.

The figure which shows the layout of the fuel cell system of an Example The figure which shows the structure of the monitor cell used in the Example Block diagram of discriminating means in the control unit used in the embodiment Characteristic diagram of the monitor cell with increased diffusion resistance to the fuel electrode by stacking carbon sheets Characteristic diagram of a monitor cell that is exactly the same as a single cell for power generation The flowchart which shows the example of the algorithm which controls the density | concentration of liquid fuel using the monitor cell of FIG. The flowchart which shows the other algorithm which performs density | concentration control of liquid fuel using the monitor cell of FIG. The flowchart which shows the further another algorithm which controls the density | concentration of liquid fuel using the monitor cell of FIG. The figure which shows typically the transient characteristic of a monitor cell output at the time of switching load resistance using the monitor cell of FIG. FIG. 8 is a characteristic diagram showing characteristics of the fuel cell system when the fuel concentration is controlled by the algorithm of FIG. FIG. 10 is a characteristic diagram showing the output and temperature of the fuel cell system in the process of obtaining the data of FIG.

Explanation of symbols

2 Fuel cell system 4 Fuel cell stack 6 Monitor cell 8 Fuel tank 10 Liquid fuel 12 Air pump 14 Radiator 16 Gas-liquid separator 18 CO2 outlet 19 Liquid level sensor 20 Fuel cassette 21 Waste liquid reservoir 22 Fuel reservoir 23 Movable wall 24 High concentration fuel Pump 26 Filter 30 Control unit 32, 34 MEA
35 proton conductive polymer solid electrolyte membrane 37, 39 carbon sheet 36 air electrode 38 fuel electrode 40 carbon sheet 42, 44 separator 45 fuel supply groove 46 air supply groove 47, 48 hole 49 temperature sensor 50, 51 fixed resistance 52 switch 54 Voltmeter 60 AD converter 62 Rich / lean storage unit 64 Resistance switching unit 66 Interval monitoring unit 68 Fuel pump drive unit

Claims (7)

A fuel cell stack in which a plurality of MEAs each including at least a proton conductive polymer solid electrolyte membrane, a fuel electrode, and an air electrode are stacked via a separator is driven by air and liquid fuel, and at least a proton conductive polymer solid A monitor cell configured to supply air and liquid fuel from a separator to an MEA including an electrolyte membrane, a fuel electrode, and an air electrode is attached to the fuel cell stack,
In addition, by connecting a resistor to the monitor cell and driving in a large current region where the output is lower than the optimum fuel concentration regardless of whether the liquid fuel concentration is higher or lower than the optimum value, the liquid fuel concentration is reduced from the optimum value. Detects that it is off,
Further, a direct liquid fuel type fuel cell system provided with a discriminating means for discriminating from the behavior of the output of the monitor cell whether the liquid fuel concentration deviates from the optimum value to the high concentration side or the low concentration side. The discrimination means discriminates whether the liquid fuel concentration is deviated from the optimum value to the high concentration side or the low concentration side from the behavior of the output of the monitor cell after replenishing the high concentration liquid fuel. The direct liquid fuel type fuel cell system according to claim 1. The determination means is configured to determine whether the liquid fuel concentration deviates from an optimum value to a high concentration side or a low concentration side by switching the resistance from a small value to a large value. The direct liquid fuel type fuel cell system according to claim 1. The direct liquid fuel type fuel cell is started under the condition that the liquid fuel concentration is deviated from the optimum value to the high concentration side, and the liquid fuel concentration is controlled so as not to shift from the optimum value to the low concentration side. 2. The direct liquid fuel fuel cell system according to claim 1, wherein the output is maintained at a high concentration side. The direct liquid fuel type fuel cell system according to any one of claims 1 to 4, wherein the monitor cell is configured by using another cell in the fuel cell stack, a common MEA, and a common separator. A fuel cell stack in which a plurality of MEAs including at least a proton conductive polymer solid electrolyte membrane, a fuel electrode, and an air electrode are stacked via a separator is driven by air and liquid fuel, and at least a proton conductive polymer solid electrolyte A monitor cell configured to supply air and liquid fuel from a separator to an MEA including a membrane, a fuel electrode, and an air electrode is attached to the fuel cell stack,
A direct liquid fuel type characterized by detecting that the concentration of liquid fuel deviates from an optimum value by connecting a resistor to the monitor cell and driving the monitor cell under a condition in which supply of liquid fuel is restricted. Fuel cell system. The MEA of the monitor cell and the other MEAs of the fuel cell stack include a diffusion control membrane on the opposite side of the proton conductive polymer solid electrolyte membrane of each of the fuel electrode and the air electrode,
In addition, the liquid permeability of the diffusion control film on the fuel electrode side of the monitor cell is made lower than the diffusion control film on the fuel electrode side of another MEA, thereby limiting the supply of liquid fuel to the monitor cell. The direct liquid fuel type fuel cell system according to claim 6.

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