JP2007242449A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of starting up stably in a shorter time even in the atmosphere below freezing point. <P>SOLUTION: In the fuel cell system which has a membrane electrode structure including a solid polymer electrolyte membrane, and an electrode catalyst layer and a gas diffusion layer to pinch the solid polymer electrolyte membrane, and which has separators provided with flow passages to respectively supply a fuel gas containing hydrogen to a fuel electrode of the electrode catalyst layer and an oxidizer gas containing oxygen to an oxygen electrode of the electrode catalyst layer, and which is provided with a fuel cell stack 111 wherein cells pinching the membrane electrode structure by the separators are laminated by the number necessary to obtain a prescribed output, and wherein power generation is carried out by electrochemical reaction of the fuel gas (hydrogen) and the oxidizer gas (oxygen) to be respectively supplied to the fuel electrode (anode) and the oxidizer electrode (cathode), provided with a hydrogen supply system to supply hydrogen to the anode, and provided with an oxygen supply system to supply air to the cathode, the gas containing oxygen is mixed by an anode oxygen supply pump 151 and supplied to the fuel electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that can be stably started in a shorter time even in a sub-zero atmosphere.

  The fuel cell system supplies hydrogen as a fuel gas to the fuel electrode of the fuel cell, supplies air as the oxidant gas to the oxidant electrode of the fuel cell, and causes the hydrogen and oxygen in the air to react electrochemically. To obtain generated power. Such a fuel cell system is highly expected to be put into practical use, for example, as a power source for automobiles, and research and development for practical use are being actively carried out.

  As a fuel cell used in a fuel cell system. For example, a solid polymer type fuel cell is known as being suitable for mounting in an automobile. A solid polymer type fuel cell is provided with a solid polymer membrane as an electrolyte membrane between a fuel electrode and an oxidant electrode. In this solid polymer type fuel cell, the solid polymer membrane functions as an ionic conductor, a reaction occurs in which the fuel gas hydrogen is separated into hydrogen ions and electrons at the fuel electrode, and an oxidant gas is generated at the oxidant electrode. A reaction for generating water from oxygen, hydrogen ions and electrons in (air) is performed.

  In a vehicle equipped with such a fuel cell system, when the vehicle is stopped in a low temperature environment, moisture present in the fuel cell or in the reaction gas path may freeze, and the electrolyte membrane due to freezing may be frozen. There is a problem that the fuel cell system cannot be started due to inhibition of the progress and arrival of the reaction gas, clogging of the reaction gas path, and locking of the circulation means. Note that when sub-zero power generation is performed, water generated by an electrochemical reaction hinders the supply of the oxidant gas to the catalyst, and thus power generation is possible only until the generated water shuts off the gas supply to the catalyst.

Therefore, in order to deal with such a problem, for example, in US Pat. No. 5,798,186, an external circuit (mainly an electrical resistor) is installed as a temperature raising means of the fuel cell stack, and fuel is supplied to the external circuit. A technique has been proposed in which the temperature of the fuel cell stack is raised by the heat generation of the external circuit by connecting the battery stack and supplying power.
US Patent Publication US 5,798,186

  However, even with the technique disclosed in Patent Document 1 described above, in power generation from a sub-zero atmosphere, the temperature of the fuel cell stack rises when the current is taken out from the fuel cell stack, and the humidification by the supply gas and the amount of diffusive moving water are reduced. Until it becomes large, it is necessary to limit the extraction current (that is, output limitation). For example, in the case of a vehicle fuel cell system mounted on an automobile, there is a situation that a sufficient warm-up operation is required.

  In other words, if the solid polymer electrolyte membrane does not contain sufficient water in the membrane, the proton conductivity decreases and as a result the fuel cell stack performance decreases, but in order to prevent the fuel electrode from drying out in sub-zero power generation. There is no other way to reduce electroosmotic water, and the amount of electroosmotic water is proportional to the amount of protons that move, so the extraction current must be very small.

  The present invention has been made in view of the above-described conventional circumstances, and an object thereof is to provide a fuel cell system that can be stably started in a shorter time even in a sub-zero atmosphere.

  In order to solve the above object, the present invention provides a membrane electrode structure including a solid polymer electrolyte membrane, an electrode catalyst layer and a gas diffusion layer sandwiching the solid polymer electrolyte membrane, and a fuel electrode of the electrode catalyst layer And a separator provided with a flow path for supplying a fuel gas containing hydrogen to the oxygen electrode of the electrode catalyst layer and an oxidant gas containing oxygen, respectively, and sandwiching the membrane electrode structure with the separator And a fuel cell that generates power by an electrochemical reaction of a fuel gas and an oxidant gas supplied to the fuel electrode and the oxidant electrode, respectively, and a fuel gas to the fuel electrode. A fuel gas supply means for supplying oxygen, an oxidant gas supply means for supplying an oxidant gas to the oxidant electrode, and an anode oxygen supply means for mixing and supplying a gas containing oxygen to the fuel electrode. Features To.

  In the fuel cell system according to the present invention, gas containing oxygen can be mixed and supplied to the fuel electrode by the anode oxygen supply means, so that water can be supplied to the solid polymer electrolyte membrane even under conditions where it is difficult to supply water to the membrane such as a subzero atmosphere. As a result, a fuel cell system that can be stably started in a shorter time can be realized even in a sub-zero atmosphere.

  Hereinafter, embodiments of the fuel cell system of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. A fuel cell system 100 according to the present embodiment is used as a driving power source of a fuel cell vehicle, for example, and includes a fuel cell stack 111 that generates power by supplying hydrogen and air as shown in FIG.

  As a hydrogen supply system (hydrogen supply means), a hydrogen high pressure tank 115, a hydrogen pressure regulating valve 128, a hydrogen supply path, a three-way valve 117, an oxygen concentration sensor 152, a hydrogen circulation channel, a fuel circulation pump 116, and an outlet pipe 125 are provided. The air supply system (air supply means) includes an air filter 112, an air compressor 113, an air supply path 126, a humidifier 114, and a bypass line 127 (the line switching valve is not shown). A path, a refrigerant circulation pump 119, a cooling fan 122, a refrigerant heat exchanger 123, a refrigerant inlet temperature sensor (temperature detecting means) 120, and a refrigerant outlet temperature sensor (temperature detecting means) 121 are provided.

  An anode oxygen supply pump 151 is provided as anode oxygen supply means for supplying a mixture of oxygen-containing gas to the anode (fuel electrode), and the supply pipe of the anode oxygen supply pump 151 is connected to the hydrogen supply path of the hydrogen supply system. Communicate.

  Further, the fuel cell stack 111 is provided with a fuel cell temperature sensor (temperature detection means) 124, and current taken from the fuel cell stack 111 is supplied to the external circuit 131. Further, the fuel cell system 100 of the present embodiment includes a hydrogen supply system, an air supply system, a cooling system 200, and a hydrogen supply system, an air supply system, a cooling system based on detection signals from various sensors of the external circuit 131 and other various sensors. This is a configuration including a system control device 141 that controls each component of the system 200 and the external circuit 131.

  In the fuel cell stack 111, an anode (fuel electrode) supplied with hydrogen as a fuel gas and a cathode (oxidant electrode) supplied with air as an oxidant gas are overlapped with an electrolyte interposed therebetween to form a power generation cell. In addition, it has a stack structure in which a plurality of power generation cells are stacked in multiple stages, and converts chemical energy into electrical energy by an electrochemical reaction based on hydrogen and oxygen in the air. In each power generation cell of the fuel cell stack 111, a reaction occurs in which hydrogen supplied to the anode is separated into hydrogen ions and electrons, the hydrogen ions pass through the electrolyte, and the electrons generate power through an external circuit, Each moves to the cathode. At the cathode, oxygen in the supplied air reacts with hydrogen ions and electrons that have moved through the electrolyte to produce water, which is discharged to the outside.

  As the electrolyte of the fuel cell stack 111, for example, a solid polymer electrolyte membrane is used in consideration of high energy density, low cost, light weight, and the like. The solid polymer electrolyte membrane is made of an ion (proton) conductive polymer membrane such as a fluororesin ion exchange membrane, and functions as an ion conductive electrolyte when saturated with water.

  An outline of the configuration of the single fuel cell 10 of the fuel cell stack 111 of this embodiment is shown in FIG. The solid polymer electrolyte membrane 12 is sandwiched between the electrode catalyst layers (the anode catalyst layer 13 and the cathode catalyst layer 14) and further sandwiched between the gas diffusion layers (the anode gas diffusion layer 15 and the cathode gas diffusion layer 16) from the outside, and membrane electrode bonding is performed. A body (MEA) 11 is formed, a gas flow path for supplying hydrogen (fuel gas) is provided on the anode (fuel electrode) side, and an air separator (oxidant electrode) side is provided with air (oxidant electrode). A cathode separator 18 having a gas flow path for supplying gas is provided on the surface.

  In this embodiment, hydrogen is used as the fuel gas and air is used as the oxidant gas. In addition, since a perfluorosulfonic acid membrane is used as the solid polymer electrolyte membrane 12, a perfluorosulfonic acid polymer was also used in the residual water retention mechanism in consideration of bonding properties.

  The voltage of each power generation cell of the fuel cell stack 111 is monitored by a cell voltage monitor (not shown), and the information is sent to the system control device 141 that controls the operation of the entire fuel cell system 100. . The fuel cell stack 111 is provided with a fuel cell temperature sensor 124 that detects the temperature of the fuel cell stack 111, and its output is sent to the system control device 141. The system control device 141 monitors the power generation state and temperature state of the fuel cell stack 111 based on information from the cell voltage monitor and output from the fuel cell temperature sensor 124.

  In order to generate power in the fuel cell stack 111, it is necessary to supply hydrogen as fuel gas and air as oxidant gas to the anode (fuel electrode) and cathode (oxidant electrode) of each power generation cell. In the system 100, a hydrogen supply system and an air supply system are provided as mechanisms for that purpose.

  In the air supply system, the electric motor driven by the power supply from the fuel cell stack 111 and the air compressed by the air compressor 113 are sent to the humidifier 114 via the air supply path 126 and humidified by the humidifier 114. Then, it is sent to the cathode of the fuel cell stack 111. As the humidifier 114, a device using a water vapor exchange membrane that uses moisture in the exhaust or a device that supplies pure water from the outside can be used.

  In the hydrogen supply system, the hydrogen supplied from the high-pressure hydrogen tank 115 passes through the hydrogen supply path, is regulated to a desired pressure by the hydrogen pressure regulating valve 128, and joins the exhaust hydrogen circulated by the hydrogen circulation pump 116. After that, the fuel cell stack 111 is sent to the anode.

  In particular, in the present embodiment, an appropriate amount of oxygen by the anode oxygen supply pump 151 is mixed with hydrogen supplied to the anode of the fuel cell stack 111 under predetermined conditions (when the temperature of the fuel cell number tack 111 is lower than the predetermined temperature). And supplied to the fuel cell stack 111. At this time, in the anode catalyst layer 13 of the fuel cell stack 111, the mixed oxygen and hydrogen react to generate water, which is absorbed into the solid polymer electrolyte membrane 12. That is, oxygen is supplied so that the water balance of the membrane on the anode side is balanced.

  Further, the cooling system 200 removes the heat generated by the power generation of the fuel cell stack 111 and keeps the fuel cell stack 111 at an appropriate temperature. The cooling water (refrigerant) pumped by the refrigerant circulation pump 119 absorbs heat through the fuel cell stack 111, passes through the cooling water circulation path, exhausts heat to the outside of the system by the refrigerant heat exchanger 123, and again It is pumped to the fuel cell stack 111 by the cooling water circulation pump 119. Further, while monitoring the coolant temperature with the coolant inlet temperature sensor 120, the coolant outlet temperature sensor 121, etc., the coolant circulation flow rate is controlled by the coolant circulation pump 119, and the temperature is adjusted to an appropriate temperature for power generation of the fuel cell stack 111.

  Further, the system control device 141 is configured as a microcomputer having, for example, a CPU, ROM, PROM, RAM, peripheral interface, etc., and includes various sensors for the hydrogen supply system, air supply system, cooling mechanism, external circuit 131, and other The detection signals from the various sensors are read, and various control signals are output according to the judgments on the detected values and the calculation results, thereby controlling the operation of each part of the fuel cell system 100.

  The system control device 141 includes a temperature determination unit, a first film wet state detection unit, a second film wet state detection unit, and a gas supply control unit as components, which are programs executed on the CPU. It represents the functional unit of. Further, the recording means for recording the stop operation condition when the fuel cell system 100 is stopped is realized by a PROM or the like (any writable nonvolatile recording medium may be used).

  The temperature determination unit determines whether or not the temperature of the fuel cell stack 111 detected by the temperature detection unit (the fuel cell temperature sensor 124 or the refrigerant inlet temperature sensor 120 and the refrigerant outlet temperature sensor 121) is equal to or lower than a predetermined temperature. Note that the temperature detection of the fuel cell stack 111 can also be performed by detecting the actual temperature by the fuel cell temperature sensor 124 or by estimating the temperature by the refrigerant inlet temperature sensor 120 and / or the refrigerant outlet temperature sensor 121 as in this embodiment. Alternatively, when these sensors are not installed, it may be estimated by an outside air temperature sensor. Here, the estimated temperature can be calculated by a correction formula based on the structural specifications of the fuel cell stack 111, the operation time at the previous operation, the elapsed time from the end of the previous operation to the present, and the like.

  The first membrane wet state detection means and the second membrane wet state detection means detect the wet state of the solid polymer electrolyte membrane, respectively.

  Further, the gas supply control means, when it is determined by the temperature determination means that the temperature is equal to or lower than the predetermined temperature before taking out the load from the fuel cell, the anode (fuel electrode) is detected by the anode oxygen supply pump 151 (anode oxygen supply means). Gas containing an oxygen amount corresponding to the film wet state detected by the first film wet state detection means is mixed and supplied, and during power generation of the fuel cell stack 111, the temperature is determined to be lower than a predetermined temperature by the temperature determination means. Is determined, the anode oxygen supply pump 151 (anode oxygen supply means) mixes a gas containing oxygen corresponding to the film wet state detected by the second film wet state detection means into the anode (fuel electrode). Supply.

  Next, before explaining the operation at the start of the fuel cell system of the present embodiment, the principle of the conventional problem and the countermeasures according to the present invention will be described with reference to FIGS. Here, FIG. 3 is an explanatory view for schematically explaining the water behavior in the conventional single fuel cell, and FIG. 4 is an explanatory view for schematically explaining the water behavior in the single fuel cell of the present invention.

  If the solid polymer electrolyte membrane 12 does not contain sufficient water, the proton conductivity is lowered and, as a result, the fuel cell stack performance is lowered. Therefore, it is important as a fuel cell stack design to control the water in the solid polymer electrolyte membrane 12.

  As shown in FIG. 3, the water movement phenomenon in the solid polymer electrolyte membrane 12 is roughly divided into the following two. That is, the first is diffusion movement (flux Qr) due to a water concentration gradient, and the second is electroosmosis (flux Qd) that occurs because protons are attracted during proton movement. In addition to this, there is a movement between the anode gas and the membrane (flux Qa) and a movement between the cathode gas and the membrane (flux Qc), and these are combined to achieve water balance.

  During normal temperature operation, the amount of water diffusion (flux Qr) in the solid polymer electrolyte membrane 12 is relatively large, and humidified hydrogen (fuel gas) can be supplied to the anode. The amount of water lost from the water (flux Qd) can be generated by balancing the amount of diffusion water (flux Qr) from the cathode to the anode and the amount of humidified water (flux Qa) from the humidified gas.

  However, during sub-zero power generation (for example, at −30 ° C.), when the diffusion coefficient in the membrane was measured with the perfluorosulfonic acid polymer membrane used in this example, the amount of diffusion water (flux Qr) was significantly higher than that at room temperature. ) Is known to decrease. Further, since the gas temperature to be supplied is low, the saturated vapor pressure is low, and the amount of water supplied to the anode by the humidified gas can hardly be expected. That is, in sub-zero power generation, there is no other way to reduce the electroosmotic water in order to prevent the anode from being dried out, and the amount of electroosmotic water (flux Qd) is proportional to the amount of protons that move, so the extraction current is very I agree that it must be small.

  Therefore, in power generation from a sub-zero atmosphere, the extraction current is limited until the temperature of the fuel cell stack 111 rises and the humidification (flux Qa) and the amount of diffusion movement water (flux Qr) by the supply gas increase ( That is, there is a circumstance that a sufficient warm-up operation is required when mounted for automobiles.

  Therefore, in the present invention, under a predetermined condition, hydrogen supplied to the anode of the fuel cell stack 111 is mixed with an appropriate amount of oxygen by the anode oxygen supply pump 151 and supplied to the fuel cell stack 111. FIG. As shown, in the anode catalyst layer 13 of the fuel cell stack 111, the mixed oxygen and hydrogen react to generate water, which is absorbed by the solid polymer electrolyte membrane 12. That is, the amount of water (flux Qp) generated by the water generation reaction in the anode catalyst layer 13 balances the water balance of the membrane on the anode side, making it difficult to supply water to a membrane such as a sub-zero atmosphere. Even under the conditions, water can be supplied to the solid polymer electrolyte membrane, and the restriction on the extraction current (that is, the output restriction) can be relaxed relatively.

  Next, the operation at the start-up of the fuel cell system of the present embodiment configured as described above will be described with reference to FIG. Here, FIG. 5 is a flowchart for explaining start-up control in the fuel cell system of the present embodiment.

  The control flow shown in FIG. 5 can be roughly divided into two types before and after taking out the load. One is that when the solid polymer electrolyte membrane 12 is dried so that a desired current cannot be taken out as it is before the start-up, a predetermined amount of oxygen is contained in the anode before taking out the load. This is an anode humidification sequence (steps S101 to S107) for supplying hydrogen (fuel gas) to humidify the anode, and the other is to continue power generation with the temperature of the fuel cell stack 111 being lower than a predetermined temperature (below zero). This is a dry-out prevention sequence (steps S108 to S113) in which oxygen corresponding to the load is supplied to the anode when the anode side is likely to dry out.

  First, when the fuel cell stack 111 is activated, an activation start sequence is executed (step S101).

  Next, it is determined by the temperature determination means whether the temperature of the fuel cell stack 111 is lower than a predetermined temperature (step S102). Here, the temperature of the fuel cell stack 111 is obtained by actual temperature detection by the fuel cell temperature sensor 124 or estimation based on a detection value of the refrigerant outlet temperature sensor 121. When the temperature of the fuel cell stack 111 exceeds the predetermined temperature, the process proceeds to a normal activation sequence (step S103). If the temperature is lower than the predetermined temperature, the process proceeds to step S104.

  When the temperature of the fuel cell stack 111 is lower than the predetermined temperature, the first membrane wet state detection means detects the wet state of the solid polymer electrolyte membrane 12, and the membrane is wet enough to take out a desired load current. It is determined whether or not (step S104). If it is determined that the dry state exceeds the wet state threshold determined in advance by actual measurement in accordance with the wet state of the solid polymer electrolyte membrane 12, the process proceeds to step S105, where it is determined that the wet state is sufficiently wet below the wet state threshold. If so, the process proceeds to a below-zero activation sequence (step S108) for starting to take out the load.

  Here, as a method for detecting the wet state of the solid polymer electrolyte membrane 12 by the first membrane wet state detecting means, there are the following methods.

  In the first method, the wet state of the solid polymer electrolyte membrane 12 is estimated from the operation conditions at the time of the previous operation stop recorded in a PROM or the like (a writable non-volatile storage medium) or the temperature history of the outside air temperature during the stop period. It is a method to do.

  In the second method, hydrogen (fuel gas) is supplied to the anode and air (oxidant gas) is supplied to the anode to monitor the open end voltage of the fuel cell stack 111, and the open end voltage and the solid polymer electrolyte membrane 12 are monitored. This is a method for estimating the wet state of the solid polymer electrolyte membrane 12 based on the relationship between the gas permeability coefficient and the water content. That is, since the solid polymer electrolyte membrane 12 has a proportional relationship between gas permeation and membrane moisture content (wet state), gas is supplied to detect from the level of the open-circuit voltage value (OCV). . For example, when the open-circuit voltage value (OCV) is low, the amount of gas permeation is large and the membrane is in a wet state. When the open-circuit voltage value (OCV) is high, the membrane is relatively dry. I can judge.

  The third method is a method of estimating the wet state of the solid polymer electrolyte membrane by measuring or estimating the change in the electrical resistance of the solid polymer electrolyte membrane 12. For example, when the electric resistance of the solid polymer electrolyte membrane 12 is low, the membrane is in a wet state, and when the electric resistance is high. It can be judged that the film is relatively dry.

  In step S104, if the first membrane wet state detection means determines that the solid polymer electrolyte membrane 12 is in a dry state exceeding the wet state threshold, the solid polymer electrolyte is reached until the wet state threshold is reached before the load is taken out. In order to wet the membrane 12, the anode oxygen supply pump 151 is operated by the gas supply control means, and oxygen (hydrogen gas) is mixed and supplied to the anode for a time corresponding to the dry state (steps S105 to S107). .

  Here, the mixed supply time of oxygen is determined according to the value detected by the first wet state detecting means. That is, the anode oxygen supply pump 151 (pump driving power = a supply amount per unit time is known) is operated for a supply time so as to supply an oxygen amount corresponding to the detected film wet state. When the second method (estimated from the open-circuit voltage value) or the third method (estimated from the change in electrical resistance) is used as the wet state estimation method of the solid polymer electrolyte membrane 12, while supplying the mixture Since the change in the wet state of the solid polymer electrolyte membrane 12 can be detected, the supply time may be counted down every time the wet state is detected.

  In FIG. 5, first, the supply time t1 corresponding to the dry state is set (step S105), and the oxygen mixture is supplied to the anode (step S106). Next, it is determined whether or not the supply time t1 has been reached since the oxygen mixed supply to the anode is started (supply start time t0) (step S107). If the supply time t1 has been reached, the load is taken out. The process proceeds to the starting below zero sequence (step S108) to start, and if the supply time t1 has not been reached, the process returns to step S106 to continue the oxygen mixture supply to the anode.

  Note that the supply time may be shortened by increasing the mixed supply amount of oxygen. In this case, it is preferable to increase the oxygen concentration or increase the supply amount to the anode (checking with the oxygen concentration sensor 152). . Further, the mixed supply amount of oxygen may be determined from the driving power of the anode oxygen supply pump 151 as described above, or the oxygen concentration sensor 152 is provided in the hydrogen supply path to supply the anode oxygen so as to obtain a desired concentration. The pump 151 may be controlled.

  By the above sequence (steps S101 to S107), it is possible to prevent a failure due to a significant cell voltage drop at the time of load removal due to excessive drying of the solid polymer electrolyte membrane 12.

  Next, a description will be given of the below-zero startup sequence. Even if the anode is in a wet state before the load is taken out, the water movement characteristics (water diffusion coefficient and electroosmosis coefficient under zero) of the solid polymer electrolyte membrane 12, take-out current density, time to reach a predetermined temperature, or Depending on the power generation distribution in the electrode plane, the solid polymer electrolyte membrane 12 in the vicinity of the anode catalyst layer 13 is considered to dry out.

  Therefore, in the present embodiment, even during power generation after the start of taking out the load, by detecting the wet state of the solid polymer electrolyte membrane 12, the tendency to dry out at the anode is determined, and it is determined that there is a tendency to dry out. It is supposed to supply oxygen when

  First, the wet state of the solid polymer electrolyte membrane 12 is detected by the second membrane wet state detection means, and it is determined whether or not the membrane is wet enough to extract a desired load current (step S109). If it is determined that the dry state exceeds the wet state threshold determined in advance by actual measurement according to the wet state of the solid polymer electrolyte membrane 12, the process proceeds to step S111, and the wet state is determined to be sufficiently wet below the wet state threshold. If so, go to Step S110.

  Here, as the method for detecting the wet state of the solid polymer electrolyte membrane 12 by the second membrane wet state detecting means, the second or third method in the first membrane wet state detecting means can be used.

  In step S109, when the second membrane wet state detection means determines that the solid polymer electrolyte membrane 12 is in a dry state exceeding the wet state threshold, the gas supply control means operates the anode oxygen supply pump 151, Oxygen is mixed with hydrogen (fuel gas) and supplied to the anode for a time corresponding to the dry state (step S110). Note that the mixed supply of oxygen in step S110 is continued until it is determined by the feedback control that the wet state is sufficiently wet below the wet state threshold.

  In step S109, if the second membrane wet state detection means determines that the solid polymer electrolyte membrane 12 is sufficiently wet below the wet state threshold, the gas supply control means causes the anode oxygen supply pump to The oxygen mixture supply by 151 is stopped (step S111).

  Next, it is determined by the temperature determination means whether the temperature of the fuel cell stack 111 is lower than a predetermined temperature (step S112). If the temperature of the fuel cell stack 111 exceeds the predetermined temperature, the start-up below zero is terminated (step S113), and the routine proceeds to normal operation (step S114). If the temperature is lower than the predetermined temperature, the process returns to step S109 and waits for the temperature of the fuel cell stack 111 to reach the predetermined temperature by the warm-up operation.

  The supply amount in the mixed supply of oxygen in step S110 can be accurately controlled by feedback control using the second or third method in the first film wet state detection means as described above. In the case of performing more simply, a supply amount proportional to the current value taken out to the external circuit 131 may be supplied.

  With the above sequence (steps S108 to S113), by continuing power generation while preventing dry-out of the solid polymer electrolyte membrane 12, the temperature of the fuel cell stack 111 is raised due to heat generated by the power generation and shifts to normal operation. be able to.

  As described above, in the fuel cell system of this embodiment, the membrane electrode including the solid polymer electrolyte membrane 12, the electrode catalyst layers 13 and 14 and the gas diffusion layers 15 and 16 sandwiching the solid polymer electrolyte membrane 12 is used. And separators 17 and 18 each having a flow path for supplying a fuel gas containing hydrogen to the fuel electrode 13 of the electrode catalyst layer and an oxidant gas containing oxygen to the oxygen electrode 14 of the electrode catalyst layer. The cell 10 having the membrane electrode structure 11 sandwiched between the separators 17 and 18 is stacked for several times to obtain a predetermined output, and supplied to the fuel electrode (anode) and the oxidant electrode (cathode), respectively. A fuel cell stack 111 that generates electricity by an electrochemical reaction between (hydrogen) and an oxidant gas (oxygen); a hydrogen supply system (fuel gas supply means) that supplies hydrogen (fuel gas) to the anode (fuel electrode); In a fuel cell system comprising an air supply system (oxidant gas supply means) for supplying air (oxidant gas) to a sword (oxidant electrode), an anode oxygen supply pump (anode oxygen supply means) 151 causes an anode catalyst A gas containing oxygen is mixed and supplied to the layer (fuel electrode of the electrode catalyst layer) 13.

  As described above, the anode oxygen supply pump (anode oxygen supply means) 151 can mix and supply oxygen-containing gas to the fuel electrode, so even under conditions where it is difficult to supply water to the solid polymer electrolyte membrane 12 such as a subzero atmosphere. Water can be supplied to the solid polymer electrolyte membrane 12 and the restriction on the extraction current can be relatively relaxed. As a result, a fuel cell system that can be stably started in a shorter time in a sub-zero atmosphere is realized. can do.

  Further, in the fuel cell system of the present embodiment, the temperature of the fuel cell stack 111 is detected or estimated by the fuel cell temperature sensor 124 or the refrigerant inlet temperature sensor 120 and the refrigerant outlet temperature sensor 121 (temperature detection means), and the system control device 141, the temperature determination means determines whether or not the temperature detected by the temperature detection means is equal to or lower than a predetermined temperature, and the first membrane wet state detection means detects the wet state of the solid polymer electrolyte membrane 12. In the gas supply control means, when the temperature determination means determines that the temperature is equal to or lower than the predetermined temperature before the load is taken out from the fuel cell stack 111, the anode oxygen supply pump (anode oxygen supply means) 151 causes the anode catalyst layer (electrode) Oxygen corresponding to the membrane wet state detected by the first membrane wet state detecting means on the fuel electrode 13 of the catalyst layer) Mixing the gas containing it is supplied.

  As described above, since the gas containing oxygen corresponding to the wet state of the solid polymer electrolyte membrane 12 is mixed and supplied to the anode catalyst layer 13, oxygen is not excessively supplied to the anode to cause anode flooding. In addition, it is possible to prevent deterioration in fuel consumption due to supplying oxygen more than necessary even without flooding.

  Further, in the fuel cell system of the present embodiment, the temperature of the fuel cell stack 111 is detected or estimated by the fuel cell temperature sensor 124 or the refrigerant inlet temperature sensor 120 and the refrigerant outlet temperature sensor 121 (temperature detection means), and the system control device 141, the temperature determination means determines whether or not the temperature detected by the temperature detection means is equal to or lower than a predetermined temperature, and the second membrane wet state detection means detects the wet state of the solid polymer electrolyte membrane 12, In the gas supply control means, when the fuel cell stack 111 is determined to be below a predetermined temperature by the temperature determination means during power generation, the anode oxygen supply pump (anode oxygen supply means) 151 causes the anode catalyst layer (electrode catalyst layer). Gas containing an oxygen amount corresponding to the film wet state detected by the second film wet state detection means. Mixture to be supplied.

  Thus, when it is determined by the second membrane wet state detection means that the solid polymer electrolyte membrane 12 has a tendency to dry, oxygen corresponding to the wet state of the solid polymer electrolyte membrane 12 is supplied to the anode catalyst layer 13. Since the gas to be mixed is supplied, it is possible to prevent the output from decreasing due to dryout during power generation.

  Further, in the fuel cell system of the present embodiment, in the system controller 141, the film wet state detected by the first film wet state detection unit or the second film wet state detection unit is previously determined by the film wet state determination unit. It is determined whether or not the dry state is based on the set threshold value, and the gas supply control means determines that the anode oxygen supply pump (anode oxygen supply) only when the film wet state determination means determines that it is in the dry state. Means) 151 mixes and supplies oxygen-containing gas to anode catalyst layer (fuel electrode of electrode catalyst layer) 13.

  As described above, the oxygen-containing gas is mixed and supplied to the anode catalyst layer only when it is dryer than the threshold set in advance by the membrane wet state determination means, so that water is supplied to the solid polymer electrolyte membrane 12. In the case where it is not necessary, the sequence for supplying oxygen can be omitted, and the start-up time can be shortened. Further, since unnecessary oxygen supply is not performed, deterioration of fuel consumption can be prevented.

  In the fuel cell system of this embodiment, in the system control device 141, the stop operation condition at the time of stopping the operation of the fuel cell system is recorded in the recording means (PROM or the like), and the first membrane wet state detecting means is recorded. Thus, the wet state of the solid polymer electrolyte membrane 12 is estimated based on the previous stop operation condition recorded in the recording means. Thus, since the wet state / dry state of the solid polymer electrolyte membrane 12 is estimated from the operating conditions at the time of the previous stop of the fuel cell system, the supply amount according to the dry state can be determined, and as a result, anode flooding is performed. In addition, it is possible to prevent deterioration of fuel consumption caused by supplying oxygen more than necessary even without flooding.

  Further, in the fuel cell system of the present embodiment, in the system controller 141, the first membrane wet state detecting means or the second film wet state detecting means uses hydrogen (fuel gas), cathode ( Air (oxidant gas) is supplied to each of the oxidant electrodes to monitor the open end voltage of the fuel cell stack 111, and based on the relationship between the open end voltage and the gas permeability coefficient and water content of the solid polymer electrolyte membrane 12. The wet state of the solid polymer electrolyte membrane 12 is estimated. As a result, the detection accuracy is improved, so that it is possible to appropriately determine whether or not oxygen can be supplied and the supply amount.

  In the fuel cell system of the present embodiment, the system controller 141 uses the first membrane wet state detection unit or the second membrane wet state detection unit to measure a change in the electrical resistance of the solid polymer electrolyte membrane 12 or By estimating, the wet state of the solid polymer electrolyte membrane 12 is estimated. As a result, the wet / dry state of the solid polymer electrolyte membrane 12 during power generation can be detected in real time, and the dry out can be ensured in advance even if there are dynamic factors such as fluctuations in the amount of load taken out. Can be prevented.

  Further, in the fuel cell system of this embodiment, in the system controller 141, when the gas supply control unit determines that the temperature determination unit has exceeded the predetermined temperature, the anode by the anode oxygen supply pump (anode oxygen supply unit) 151 is used. The mixed supply of the gas containing oxygen to the catalyst layer (fuel electrode of the electrode catalyst layer) 13 is stopped. Thereby, when it is not necessary to humidify the anode, wasteful fuel is not consumed and fuel consumption is not deteriorated.

  Next, FIG. 6 is a configuration diagram of a fuel cell system according to Embodiment 2 of the present invention. The fuel cell system 101 of this embodiment is used as a driving power source of a fuel cell vehicle, for example, and includes a fuel cell stack 111 that generates power by supplying hydrogen and air as shown in FIG.

  The hydrogen supply system (hydrogen supply means) includes a hydrogen high-pressure tank 115, a hydrogen supply path, a three-way valve 117, a pressure sensor 204, a hydrogen circulation passage, a fuel circulation pump 116, and an outlet pipe 125, and an air supply system (air As a supply means, an air filter 112, an air compressor 113, an air supply path 126, a pressure sensor 205, a humidifier 114, and a bypass line 127 are provided (the line switching valve is not shown), and a cooling system 200 (details in the first embodiment) (Not shown).

  In addition, as an anode oxygen supply means for mixing and supplying a gas containing oxygen to the anode (fuel electrode), the air compressor 113 of the air supply system is also used, and the hydrogen supply path of the hydrogen supply system and the (air compressor of the air supply system) A pressure regulating valve 201 and a check valve 202 for preventing a back flow from the hydrogen supply path to the air supply path 126 are installed in the communication path 203 that communicates with the air supply path 126 (downstream of 113).

  Further, the fuel cell stack 111 is provided with a fuel cell temperature sensor (temperature detection means) 124, and current taken from the fuel cell stack 111 is supplied to the external circuit 131. Further, the fuel cell system 100 of the present embodiment includes a hydrogen supply system, an air supply system, a cooling system 200, and a hydrogen supply system, an air supply system, a cooling system based on detection signals from various sensors of the external circuit 131 and other various sensors. This is a configuration including a system control device 142 that controls each component of the system 200 and the external circuit 131.

  The difference of the configuration of the fuel cell system of Example 2 from Example 1 (see FIG. 1) is that the anode oxygen supply means (communication path 203, pressure regulating valve 201 and check valve 202) and the hydrogen supply path are installed. The pressure sensor 204, the pressure sensor 205 installed in the air supply path 126, and the system controller 142.

  The system controller 142 is configured as a microcomputer having, for example, a CPU, a ROM, a PROM, a RAM, a peripheral interface, and the like as in the first embodiment, and includes temperature determination means, first film wet state detection means, 2 includes a film wet state detection means and a gas supply control means (these represent functional groups of programs executed on the CPU), and the recording means is a PROM or the like (a writable non-volatile memory). This is the same as the point realized by any recording medium.

  The operation procedure at the time of starting the fuel cell system of the present embodiment is the same as that of the first embodiment (see FIG. 5). However, in the system controller 142, before the gas supply control means takes out the load from the fuel cell. Alternatively, when it is determined by the temperature determination means that the temperature is lower than the predetermined temperature during power generation of the fuel cell stack 111, the air compressor 113 is configured such that the outlet pressure of the air compressor 113 is higher than the pressure of the hydrogen supply path of the hydrogen supply system. And controlling the mixed supply of oxygen-containing gas to the anode catalyst layer (fuel electrode of the electrode catalyst layer) 13 by adjusting the opening of the 201 pressure regulating valve.

  In other words, in this embodiment, oxygen supplied to the anode catalyst layer (fuel electrode of the electrode catalyst layer) 13 is supplied from outside air compressed and compressed by the air compressor 113 of the air supply system to the air supply path 126 and the hydrogen supply. Supply is made using the pressure difference between the path. The oxygen supply amount is controlled by the differential pressure between the air supply path 126 and the hydrogen supply path obtained from the pressure sensors 204 and 205 and the opening degree of the pressure regulating valve 201.

  As described above, in the fuel cell system of the present embodiment, the communication path 203 that connects the hydrogen supply path of the hydrogen supply system (fuel gas supply means) and the air supply path 126 of the air supply system (oxidant gas supply means). The anode oxygen supply means is also used as the air compressor 113 of the air supply system (oxidant gas supply means). This eliminates the need for a new anode oxygen supply pump 151 and does not require complicated piping, and thus can be realized with a simpler configuration and at a lower cost. In addition, the supply amount can be easily controlled in the system controller 142.

  In the fuel cell system of the present embodiment, the pressure regulating valve 201 is installed in the communication line 203. In the system controller 142, the gas supply control means is configured such that the outlet pressure of the air compressor 113 is a hydrogen supply system (fuel gas supply). The air compressor 113 is operated and controlled so as to be higher than the pressure of the hydrogen supply path of the means), and the opening of the pressure regulating valve 201 is adjusted to include oxygen to the anode catalyst layer (fuel electrode of the electrode catalyst layer) 13. Control gas mixing supply. This eliminates the need for power (anode oxygen supply pump 151) for supplying oxygen only to the anode catalyst layer (fuel electrode of the electrode catalyst layer) 13, allows a simpler configuration and lower costs, and provides fuel efficiency. Can be prevented.

1 is a configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. FIG. 1 is a schematic configuration diagram of a single fuel cell 10 of a fuel cell stack 111. FIG. It is explanatory drawing which illustrates typically the water behavior in the conventional fuel cell single cell. It is explanatory drawing which illustrates typically the water behavior in the fuel cell single cell of this invention. It is a flowchart explaining the starting control in the fuel cell system of an Example. It is a block diagram of the fuel cell system which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100,101 Fuel cell system 111 Fuel cell stack 112 Air filter 113 Air compressor 114 Humidifier 115 Hydrogen high-pressure tank 116 Fuel circulation pump 117 Three-way valve 119 Refrigerant circulation pump 120 Refrigerant inlet temperature sensor (temperature detection means)
121 Refrigerant outlet temperature sensor (temperature detection means)
122 Cooling fan 123 Refrigerant heat exchanger 124 Fuel cell temperature sensor (temperature detection means)
125 Outlet piping 126 Air supply path 127 Bypass line 128 Hydrogen pressure regulating valve 131 External circuit 141, 142 System control device 151 Anode oxygen supply pump (anode oxygen supply means)
152 Oxygen concentration sensor 200 Cooling system 201 Pressure regulating valve 202 Check valve 203 Communication path 204, 205 Pressure sensor 10 Fuel cell single cell 11 Membrane electrode assembly (MEA)
12 Solid polymer electrolyte membrane 13 Anode catalyst layer (electrode catalyst layer)
14 Cathode catalyst layer (electrode catalyst layer)
15 Anode gas diffusion layer (gas diffusion layer)
16 Cathode gas diffusion layer (gas diffusion layer)
17 Anode separator 18 Cathode separator

Claims (10)

A membrane electrode structure comprising a solid polymer electrolyte membrane, and an electrode catalyst layer and a gas diffusion layer sandwiching the solid polymer electrolyte membrane;
A separator provided with a flow path for supplying a fuel gas containing hydrogen to the fuel electrode of the electrode catalyst layer and an oxidant gas containing oxygen to the oxygen electrode of the electrode catalyst layer,
The cells sandwiching the membrane electrode structure between the separators are stacked for several times to obtain a predetermined output, and power is generated by an electrochemical reaction of the fuel gas and the oxidant gas supplied to the fuel electrode and the oxidant electrode, respectively. A fuel cell,
Fuel gas supply means for supplying fuel gas to the fuel electrode;
An oxidant gas supply means for supplying an oxidant gas to the oxidant electrode;
Anode oxygen supply means for mixing and supplying a gas containing oxygen to the fuel electrode;
A fuel cell system comprising: Temperature detecting means for detecting or estimating the temperature of the fuel cell;
Temperature determining means for determining whether the temperature detected by the temperature detecting means is equal to or lower than a predetermined temperature;
First membrane wet state detection means for detecting the wet state of the solid polymer electrolyte membrane;
The film detected by the anode oxygen supply means by the first film wet state detection means by the anode oxygen supply means when the temperature determination means determines that the temperature is equal to or lower than a predetermined temperature before taking out the load from the fuel cell. Gas supply control means for mixing and supplying a gas containing an oxygen amount according to the wet state;
The fuel cell system according to claim 1, comprising: Temperature detecting means for detecting or estimating the temperature of the fuel cell;
Temperature determining means for determining whether the temperature detected by the temperature detecting means is equal to or lower than a predetermined temperature;
Second membrane wet state detection means for detecting the wet state of the solid polymer electrolyte membrane;
The membrane wet state detected by the anode oxygen supply unit by the second membrane wet state detection unit by the anode oxygen supply unit when the temperature determination unit determines that the temperature is lower than a predetermined temperature during the power generation of the fuel cell. Gas supply control means for mixing and supplying a gas containing oxygen according to
The fuel cell system according to claim 1, comprising: A film wet state determination unit for determining whether the film wet state detected by the first film wet state detection unit or the second film wet state detection unit is a dry state based on a preset threshold; Have
The gas supply control means causes the anode oxygen supply means to mix and supply a gas containing oxygen to the fuel electrode only when it is determined that the film wet state determination means is in a dry state. The fuel cell system according to any one of claims 2 and 3. Recording means for recording stop operation conditions when the fuel cell is stopped;
The first membrane wet state detection means estimates the wet state of the solid polymer electrolyte membrane based on the previous stop operation condition recorded in the recording means. The fuel cell system according to any one of claims.   The first film wet state detection means or the second film wet state detection means monitors the open-circuit voltage of the fuel cell by supplying fuel gas to the fuel electrode and oxidant gas to the oxidant electrode, respectively. The wet state of the solid polymer electrolyte membrane is estimated based on the relationship between the open-end voltage and the gas permeability coefficient and moisture content of the solid polymer electrolyte membrane. The fuel cell system according to claim 1.   The first membrane wet state detection unit or the second membrane wet state detection unit estimates the wet state of the solid polymer electrolyte membrane by measuring or estimating a change in electrical resistance of the solid polymer electrolyte membrane. The fuel cell system according to any one of claims 2 to 4, wherein the fuel cell system is provided.   The gas supply control means stops the mixed supply of gas containing oxygen to the fuel electrode by the anode oxygen supply means when the temperature determination means determines that the predetermined temperature is exceeded. The fuel cell system according to any one of claims 2 to 7. A communication path connecting the fuel gas supply path of the fuel gas supply means and the oxidant gas supply path of the oxidant gas supply means;
The fuel cell system according to any one of claims 1 to 8, wherein the anode oxygen supply means is an air compressor of the oxidant gas supply means. Having a pressure regulating valve installed in the communication path;
The gas supply control means controls the air compressor so that the outlet pressure of the air compressor is higher than the pressure of the fuel gas supply path of the fuel gas supply means, and adjusts the opening of the pressure regulating valve. The fuel cell system according to claim 9, wherein a mixed supply of a gas containing oxygen to the fuel electrode is controlled.

Images