JP2012038481A - Fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance effectiveness of deterioration suppression of a fuel battery system by a radical.SOLUTION: A secondary battery 150 is used as a power source in a situation of low request output during traffic congestion or a low-speed travel, and a fuel battery 100 is selected as the power source since the request output increases in a situation of acceleration or a high-speed travel. Further, when the fuel battery 100 is used as the power source, the fuel battery 100 is placed in power generation operation with a current density of ≥0.6 A/cm.

Description

  The present invention relates to a fuel cell system that generates power with a fuel cell.

  The fuel cell is supplied with fuel and its oxidant, for example, hydrogen gas and air as an oxygen-containing gas, to both electrodes of a membrane electrode assembly in which electrode layers are joined to both membrane surfaces of an electrolyte membrane having proton conductivity. It generates electricity through an electrochemical reaction between hydrogen and oxygen. It is known that this electrochemical reaction proceeds via proton conduction of the electrolyte membrane, water is generated at the cathode on the air supply side, and hydrogen peroxide is generated as an intermediate reaction of this water generation. Since hydrogen peroxide is a chemically unstable compound, the generated hydrogen peroxide is easily decomposed to generate hydroxyl groups, so-called radicals. Since radicals are highly active, they tend to cause oxidative degradation degradation of membrane electrode assemblies, specifically oxidative degradation degradation of the electrodes and electrolyte membranes, and eventually battery performance degradation. Various methods for maintaining are proposed (for example, Patent Document 1).

JP 2004-273209 A JP 2008-226630 A

  According to the methods proposed in these patent documents, the production of hydrogen peroxide can be suppressed, but it is difficult to prevent the production of hydrogen peroxide at all. For this reason, there is still room for hydrogen peroxide to be generated, but the degradation of the membrane electrode assembly due to radicals generated through the decomposition of the generated hydrogen peroxide, and further deterioration of the battery performance. I'm worried.

  The present invention has been made in order to solve at least a part of the above-described conventional problems, and an object thereof is to improve the effectiveness of suppressing deterioration due to radicals generated through decomposition of generated hydrogen peroxide.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the following configuration is adopted.

[Application 1: Fuel cell system]
A fuel cell having a membrane electrode assembly in which electrode layers are bonded to both membrane surfaces of an electrolyte membrane having proton conductivity;
A supply system for supplying fuel to one of the electrode layers and supplying an oxidant of the fuel to the other electrode layer;
Power generation control means for controlling power generation of the fuel cell by controlling the supply status of the fuel and the oxidant by the supply system;
Determination means for determining whether or not the fuel cell needs to be generated by the power generation control means,
The power generation control means includes
If the determination means determines that power generation of the fuel cell is necessary, the power generation of the fuel cell is controlled so that the current density per electrode area of the fuel cell is 0.6 A / cm ² or more. The gist.

In the fuel cell system having the above configuration, when the determination unit determines that the power generation of the fuel cell is necessary, the power generation control unit controls the power generation of the fuel cell, and the generated power can be output. The power generation control of the fuel cell at this time is such that the current density per electrode area of the fuel cell is 0.6 A / cm ² or more. At this current density, proton conduction of the electrolyte membrane of the membrane electrode assembly is performed. The electrochemical reaction through the substrate proceeds actively. For this reason, a relatively large amount of water is generated in the power generation region in the membrane electrode assembly, and the electrolyte membrane is sufficiently wetted by a large amount of water (generated water). Under such a sufficiently wet state of the electrolyte membrane, even if radicals are generated by the generation and decomposition of hydrogen peroxide, the radicals are considered to be decomposed or quenched by the generated water.

  As a result, according to the fuel cell system having the above configuration, the oxidative degradation of the electrolyte membrane due to radicals can be suppressed with high effectiveness. Thereby, the range of the adoption of the membrane material used for an electrolyte membrane spreads, and versatility increases. In addition, the oxidative degradation deterioration due to radicals can also occur in the electrode layer of the membrane electrode assembly, but the radical quenching or decomposition due to the large amount of generated water also occurs in the electrode layer bonded to the electrolyte membrane. Oxidative decomposition degradation of can be suppressed with high effectiveness, and through these, according to the fuel cell system having the above configuration, the cell performance can be maintained.

The fuel cell described above can be configured as follows. For example, the power generation control of the fuel cell when the determination unit determines that the power generation of the fuel cell is necessary can be performed such that the current density does not exceed 4.0 A / cm ² . In general, when a fuel cell is subjected to high load power generation with a current density exceeding 4.0 A / cm ² , power generation occurs near or exceeds the upper limit of the battery capacity, so that the output can be reduced and the fuel consumption can be reduced. It is pointed out that the power generation efficiency from the relationship also decreases. Therefore, in the above-described aspect, it is possible to suppress the deterioration described above, while suppressing a decrease in output of the fuel cell and a decrease in power generation efficiency.

In the fuel cell system having the above-described configuration, the secondary battery capable of charging and discharging electric power, and the fuel cell and the secondary battery are selected as a power source to be supplied to an external load, A power selection unit that supplies power to the load from the selected power source; and a power detection unit that detects required power required to be output to the load. When determining whether or not the power generation is necessary according to the required power, and determining that the fuel cell needs to generate power, the power selection unit can select the power source as the fuel cell. In this way, for example, when the required power is generated power at a current density of 0.6 A / cm ² or more, it is determined that the fuel cell needs to generate power and the fuel cell is set to 0. 0 as described above. Power generation can be controlled at a current density of 6 A / cm ² or more, and the generated power can be supplied to the load. That is, according to the above aspect, the load can be operated with the required power by the generated power of the fuel cell while suppressing the oxidative decomposition deterioration of the membrane electrode assembly due to radicals. In this aspect, from the viewpoint of power selection, the fuel cell is selected as the power source of the load under the situation where the power generation of the fuel cell is controlled so that the current density is 0.6 A / cm ² or more. It means to do.

In the above aspect, the power generation means has a capacity means for detecting a charge capacity of the secondary battery, and the required power detected by the power detection means is generated power at a current density lower than 0.6 A / cm ^2. When the required power cannot be covered by the charge capacity of the secondary battery detected by the capacity detecting means, it is determined that the fuel cell needs to generate power, and the current density of the fuel cell is 0.6 A / cm ^2. Power generation control is performed so as to achieve the above, and the secondary battery can be charged with surplus generated power. If it carries out like this, after suppressing the oxidative decomposition degradation of the membrane electrode assembly by a radical, a secondary battery can be charged, operating a load with the required electric power by using a fuel cell or a secondary battery as a power source. From the viewpoint of the charge capacity of the secondary battery, this aspect selects the secondary battery as the load power source when the required power can be covered by the charge capacity of the secondary battery, and operates the fuel cell. It means that it can be avoided.

Further, the fuel cell system having the above-described configuration further includes power detection means for detecting required power required to be output to an external load, and the determination means determines that the fuel cell needs to generate power. Power consumption including surplus generated power exceeding the required power detected by the power detection means, including charging a secondary battery capable of charging and discharging power. It is possible to turn to the mode. According to this aspect, the power generation control of the fuel cell at a current density of 0.6 A / cm ² or more suppresses the oxidative degradation deterioration of the membrane electrode assembly due to the radicals described above, and the surplus power of the generated power The secondary battery can be charged. The surplus power after the secondary battery is fully charged can be used for other power consumption, for example, power consumption in a heating element for heating.

Further, in the fuel cell system having the above-described configuration, the fuel cell is further provided as an aggregate of a plurality of battery units, further comprising power detection means for detecting required power required to be output to an external load. It is configured to generate power for each battery unit, collect the generated power for each battery unit, and supply the fuel and the oxidant to the supply system for each battery unit, The determination means determines whether or not the power generation control means needs to generate power for each battery unit according to the required power detected by the power detection means, and the power generation control means The supply status in the supply system may be controlled for each battery unit, power generation for each battery unit may be controlled, and the collected generated power may be output. According to this aspect, for the battery unit for which power generation control is required according to the required power, the above-described radical membrane electrode assembly by controlling power generation at a current density of 0.6 A / cm ² or more. Oxidative degradation degradation can be suppressed. In this case, in the battery unit in which the power generation control is not required, the supply of fuel and oxidant and the power generation control are not performed. Therefore, radicals are not generated, and oxidative decomposition of the membrane electrode assembly by radicals does not cause a problem.

  The present invention is naturally applicable to a fuel cell operation method, a vehicle equipped with a fuel cell system, and a stationary power generation system in which the fuel cell system is installed and the fuel cell is used as a power generation source.

1 is an explanatory view schematically showing a fuel cell vehicle 10 as an embodiment of the present invention in plan view. FIG. It is a graph which shows the relationship between the current density at the time of electric power generation, and the molecular weight fall rate of the electrolyte membrane of MEA about the modeled battery cell. It is explanatory drawing which shows roughly the relationship between the driving | running | working condition of the fuel cell mounted vehicle 10, the request | requirement output at that time, and the source | sauce of this output. 3 is a flowchart showing a state of power source selection and power generation control of the fuel cell 100 performed by a control device 200. It is a flowchart which shows the mode of the electric power generation control of the fuel cell 100 in another Example. It is explanatory drawing which shows roughly the structure of 100 A of fuel cells in another Example. It is a flowchart which shows the mode of the electric power generation control of 100 A of fuel cells.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view schematically showing a fuel cell vehicle 10 as an embodiment of the present invention in plan view.

  As shown in the figure, the fuel cell-equipped vehicle 10 has a fuel cell system 20 mounted on a vehicle body 12. The fuel cell system 20 includes a fuel cell 100, a hydrogen gas supply system 120 including a hydrogen gas tank 110, an air supply system 140 including a motor-driven compressor 130, a secondary battery 150, and a DC-DC converter 160. Prepare. The fuel cell system 20 supplies the generated power of the fuel cell 100 or the charging power of the secondary battery 150 to a load such as the motor 170 for driving the front wheels FW.

  As schematically shown in the figure, the fuel cell 100 is a battery of a power generation unit including a membrane electrode assembly (MEA) in which both electrodes (electrode layers) of an anode and a cathode are bonded to both sides of an electrolyte membrane. The stack structure is formed by stacking cells, and is located below the vehicle floor between the front wheel FW and the rear wheel RW. The MEA electrolyte membrane in the fuel cell 100 is a solid polymer electrolyte membrane having proton conductivity, and in this embodiment, either a hydrocarbon electrolyte membrane or a fluorine electrolyte membrane can be adopted. As the hydrocarbon electrolyte membrane, an inexpensive hydrocarbon electrolyte membrane obtained by sulfonating an engineering plastic polymer such as polyether ether ketone, polyether sulfone, polyether imide, or polyphenylene ether can be used. Here, the MEA manufacturing method will be briefly described.

  First, fine particles of platinum (Pt) as a catalyst are dispersed in an electrolyte solution having proton conductivity, and the dispersion is applied to both membrane surfaces of the above hydrocarbon electrolyte membrane by a technique such as spray coating. Then, anode and cathode electrode layers are formed on both surfaces of the hydrocarbon electrolyte membrane. Next, a carbon paper or the like having gas diffusion permeability is thermocompression bonded to this electrode layer to form a gas diffusion layer to obtain an MEA.

  The fuel cell 100 includes a hydrogen gas supply system 120 and an air supply system 140 (described later) that supply hydrogen gas and air to both electrode layers (anode electrode layer and cathode electrode layer) of a battery cell sandwiching the MEA with a separator (not shown). Receive supply. The fuel cell 100 generates electric power by causing an electrochemical reaction between hydrogen in the supplied hydrogen gas and oxygen in the air in each battery cell, and drives a load such as the motor 170 with the generated power. The power generation status of the fuel cell 100 is measured by the current sensor 102, and the measurement result is output from the current sensor 102 to the control device 200 described later.

  The hydrogen gas supply system 120 includes a hydrogen supply path 121 from the hydrogen gas tank 110 to the fuel cell 100, and a circulation path 122 that circulates unconsumed hydrogen gas (anode offgas) to the hydrogen supply path 121. The hydrogen gas supply system 120 uses hydrogen gas at a flow rate that is the sum of the flow rate adjusted by the flow rate adjustment valve 123 of the hydrogen supply route 121 and the circulation flow rate adjusted by the circulation pump 124 of the circulation route 122 as fuel. Supply to the anode of the battery 100. This hydrogen gas supply amount is determined by the control device 200 described later based on the operation of the accelerator 180, and is a supply amount corresponding to the load required for the fuel cell 100. The hydrogen gas supply system 120 appropriately discharges the anode off-gas to the atmosphere through the opening / closing adjustment of the opening / closing valve 126 of the discharge pipe 125 branched from the circulation path 122.

  The air supply system 140 includes an oxygen supply path 141 that reaches the fuel cell 100 via the compressor 130 and a discharge path 142 that discharges unconsumed air (cathode offgas) to the atmosphere. The air supply system 140 adjusts the flow rate of the air taken from the open end of the oxygen supply path 141 by the compressor 130 and then supplies the air to the cathode of the fuel cell 100, while discharging the flow rate adjustment valve 143 of the discharge path 142. The cathode off-gas is discharged to the atmosphere through the discharge path 142 at a flow rate adjusted in step (1). When air supply and cathode off-gas discharge are performed by the air supply system 140 as described above, the air supply system 140 supplies air by the compressor 130 after setting the discharge flow rate adjustment valve 143 to a predetermined opening degree. Even in the air supply amount at this time, similarly to the hydrogen gas, the supply amount is determined by the control device 200 based on the operation of the accelerator 180 and corresponds to the load required for the fuel cell 100. The fuel cell system 20 has a cooling system (not shown) that cools the fuel cell 100 by circulating supply of a cooling medium in addition to the above-described supply system. However, this cooling system is not directly related to the gist of the present invention. Description is omitted.

  The secondary battery 150 is connected to the fuel cell 100 via the DC-DC converter 160 and functions as a power source different from the fuel cell 100. In this embodiment, since it is assumed that the fuel cell 100 is operated under a predetermined power generation state as will be described later, the secondary battery 150 supplies the charging power to the motor 170 in the operation stop state of the fuel cell 100. Supply. As the secondary battery 150, for example, a lead-rechargeable battery, a nickel metal hydride battery, a lithium ion battery, or the like can be employed. A capacity detection sensor 152 is connected to the secondary battery 150, and the sensor detects the charging status of the secondary battery 150 and outputs the detected charge amount to the control device 200.

  The DC-DC converter 160 has a charge / discharge control function for controlling charge / discharge of the secondary battery 150, and controls charge / discharge of the secondary battery 150 in response to a control signal from the control device 200. The voltage level applied to the motor 170 is variably adjusted.

  The control device 200 is configured by a so-called microcomputer including a CPU, a ROM, a RAM, and the like that execute a logical operation, and receives various sensor inputs from the accelerator 180 and controls various controls of the fuel cell vehicle 10. For example, the control device 200 obtains the required power for the motor 170 according to the operation state of the accelerator 180, and the required power is obtained by the power generation of the fuel cell 100, or is charged with the charging power of the secondary battery 150. The electric power is supplied to the motor 170. When the required power of the motor 170 is obtained by the power generation of the fuel cell 100, the gas supply amount in the hydrogen gas supply system 120 and the air supply system 140 is controlled so as to meet the required power. Further, the control device 200 controls the DC-DC converter 160 according to the required power to the motor 170.

  In the fuel cell-equipped vehicle 10 of the present embodiment, the fuel cell 100 is subjected to a power generation operation under a predetermined condition to be described later after determining whether or not the power generation operation of the fuel cell 100 is necessary. Will be described. FIG. 2 is a graph showing the relationship between the current density during power generation and the molecular weight reduction rate of the MEA electrolyte membrane for a modeled battery cell. The graph of FIG. 2 was obtained through the following durability test.

  A single battery cell to be tested is a battery cell having an MEA using a hydrocarbon electrolyte membrane (for example, an electrolyte membrane obtained by sulfonating polyetheretherketone) as described above. Electric power was generated by supplying hydrogen gas and air under low humidification conditions of a cell temperature of 95 ° C., an anode dew point of 45 ° C., and a cathode dew point of 55 ° C. Then, while variously changing the current density per electrode area of the MEA at the time of this power generation, an endurance test that continues the repeated cycle of power generation and non-power generation over 200 hours is performed, and the hydrocarbon electrolyte membranes before and after the test are tested. The molecular weight change (decrease rate) was determined with an analyzer such as a mass analyzer. In this case, after the durability test for 200 hours, the catalyst (Pt) was removed from the MEA, and the molecular weight change (decrease rate) of the hydrocarbon-based electrolyte membrane itself before and after the durability test was measured. In addition, since the molecular weight of the hydrocarbon electrolyte membrane itself before the durability test was measured in advance prior to the test, the molecular weight reduction rate was calculated from the measured value of the molecular weight of the hydrocarbon electrolyte membrane itself before and after the durability test. .

A sample A in FIG. 2 is a measurement value obtained by performing an endurance test on the battery cell in a repetitive cycle of 30 seconds of non-power generation and 20 seconds of power generation under the above-mentioned low humidification gas supply conditions. In this case, the power generation condition of the battery cell in the power generation period (20 seconds) of each cycle is a current density of 0.6 A / cm ² .

Sample B in FIG. 2 is a measurement value obtained by performing an endurance test on the battery cell in a repeated cycle of 10 seconds of non-power generation and 10 seconds of power generation under the above-mentioned low humidification gas supply conditions. In this case, the power generation condition of the battery cell in the power generation period (10 seconds) of each cycle is a current density of 1.2 A / cm ² .

Sample C in FIG. 2 is a measurement value obtained by performing an endurance test on the battery cell in a cycle of 30 seconds of non-power generation and 60 seconds of power generation under the above-mentioned gas supply conditions with low humidification. In this case, the power generation condition of the battery cell in the power generation period (60 seconds) of each cycle is a current density of 0.1 A / cm ² .

A sample D in FIG. 2 is a measurement value obtained by performing an endurance test on the battery cell in a cycle of non-power generation for 180 seconds and power generation for 60 seconds under the above-mentioned gas supply condition with low humidification. In this case, the power generation condition of the battery cell in the power generation period (60 seconds) of each cycle is a current density of 0.1 A / cm ² .

Sample E in FIG. 2 is a measurement value obtained by performing an endurance test on a battery cell in a cycle of 30 seconds of non-power generation and 180 seconds of power generation under the above-mentioned gas supply conditions with low humidification. In this case, the power generation condition of the battery cell in the power generation period (180 seconds) of each cycle is a current density of 0.4 A / cm ² .

As shown in FIG. 2, the sample A was only about 3% even in the molecular weight reduction rate. Therefore, in sample A, it is assumed that the hydrocarbon electrolyte membrane hardly deteriorates. Even in Sample B, the molecular weight reduction rate was only about 2%. Therefore, even in the sample B, it is assumed that the hydrocarbon-based electrolyte membrane hardly deteriorates. The molecular weight reduction rate of 2 to 3% is almost equal to the upper limit of the maximum measuring ability of the analyzer. In addition, although it is not illustrated about the case where a battery cell is generated with a current density greater than 1.2 A / cm ² , if the battery cell is generated with a high load exceeding 4.0 A / cm ² , the upper limit of the battery capacity Since the power generation is in the vicinity or beyond this, the output can decrease, and the power generation efficiency in relation to the fuel consumption also decreases. In the range from 0.6 to 1.2 A / cm ² , the molecular weight decrease rate has changed at the upper limit of measurement to approximately the same level, so that the battery cell is at a current density of 4.0 A / cm ² or less. Even if power is generated, it is assumed that the deterioration of the hydrocarbon-based electrolyte membrane can be suppressed in substantially the same manner as in Samples A to B.

  On the other hand, in Sample C, a molecular weight reduction rate of 40% was observed. That is, in sample C, it is assumed that the hydrocarbon-based electrolyte membrane is greatly deteriorated although the generated power is smaller than in samples A to B. This deterioration of the electrolyte membrane is considered to be caused by a decrease in molecular weight, and it is assumed that the decrease in molecular weight is caused by oxidative decomposition by radicals generated through the decomposition of hydrogen peroxide generated during the power generation period in the durability test. .

  Also in Sample D, a 45% reduction in molecular weight was observed. That is, even in the sample D, as in the sample C, it is assumed that the hydrocarbon-based electrolyte membrane is greatly deteriorated due to oxidative decomposition due to radicals.

  In Sample E, a 27% molecular weight reduction rate was observed. That is, even in the sample E, as in the samples C to D, it is assumed that the hydrocarbon electrolyte membrane is largely deteriorated due to oxidative decomposition due to radicals.

From the durability test plotted in FIG. 2, it was found that the deterioration of the hydrocarbon-based electrolyte membrane can be remarkably suppressed if the battery cell is operated for power generation at a current density in the range of 0.6 to 4.0 A / cm ² . Based on this knowledge, the fuel cell-equipped vehicle 10 of the present embodiment performs fuel cell power generation control and motor drive as described below.

FIG. 3 is an explanatory diagram schematically showing the relationship between the traveling state of the vehicle 10 equipped with the fuel cell, the required output at that time, and the source of this output. As shown in the figure, in the fuel cell-equipped vehicle 10 of the present embodiment, the secondary battery 150 (see FIG. 1) is used as a power source in a situation of low demand output such as traffic jam or low speed running, and acceleration or high speed running situation Below, since a request | requirement output also increases, the fuel cell 100 (refer FIG. 1) is selected as a power source. In addition, when the fuel cell 100 is used as a power source, the fuel cell 100 is operated for power generation at a current density of 0.6 A / cm ² or more. FIG. 4 is a flowchart showing a state of power source selection and power generation control of the fuel cell 100 performed by the control device 200.

  As shown in the figure, the control device 200 first senses the depression state of the accelerator 180 and reads the required load power YP required for the motor 170 (step S100). At the time of reading, in addition to the depression state of the accelerator 180, the load required power YP is calculated in consideration of the vehicle speed of the fuel cell-equipped vehicle 10, the operation position of a shift lever (not shown) (for example, parking position, drive position), and the like. It can also be read.

Next, the control device 200 determines whether or not the read load required power YP is equal to or higher than the generated power when the fuel cell 100 is operated for power generation at a current density of 0.6 A / cm ² (step S110). If a positive determination is made here, the process proceeds to step S120 in order to cover the required load power YP at that time with the generated power of the fuel cell 100. In step S120, the fuel cell 100 is selected as the power source of the motor 170, and then the power generation of the fuel cell 100 is controlled at a current density of 0.6 A / cm ² or more. In this case, the control device 200 controls the power generation of the fuel cell 100 with a current density sufficient to cover the load required power YP. For example, if the generated power when the load request power YP has power generation control of the fuel cell 100 at a current density of 0.6 A / cm ^2, the control unit 200, the fuel cell 100 of 0.6 A / cm ² current density Power generation is controlled at. Similarly, if the required load power YP is generated power when the fuel cell 100 is controlled to generate power at a current density of 2.0 A / cm ² , the control device 200 controls the fuel cell 100 to a current of 2.0 A / cm ² . Power generation is controlled by density. That is, in step S120, the control device 200 performs power generation control of the fuel cell 100 at a current density corresponding to the load required power YP, but the power generation control of the fuel cell 100 at this time is 0.6 to 4.0 A / cm. The power generation is controlled at a current density in the range of ² . The control device 200 controls the power generation of the fuel cell 100 in this way, outputs the generated power (= load required power YP) to the motor 170 (step S130), and drives the motor 170 with the load required power YP (step S150). ).

On the other hand, if it is determined in step S110 that the load required power YP is generated when the fuel cell 100 is in a power generation operation at a current density lower than 0.6 A / cm ² , the control device 200 determines that this load required power is In order to cover YP with the charging power of the secondary battery 150, the process proceeds to step S 150 and the secondary battery 150 is selected as the power source of the motor 170. Next, the control device 200 reads the battery capacity BP of the secondary battery 150 from the sensor output of the capacity detection sensor 152 (step S160), and determines whether or not the required battery power YP can be covered by this battery capacity BP (step S170). ). If the battery capacity BP makes an affirmative determination that the required load power YP can be covered, the control device 200 discharges the secondary battery 150 with power that matches the required load power YP, and converts the required load power YP into the DC-DC converter 160. To the motor 170 (step S130), and the motor 170 is driven with the required load power YP (step S150).

If it is determined in step S170 that the battery capacity BP of the secondary battery 150 cannot cover the required load power YP, the process proceeds to step S180 to charge the secondary battery 150. In step S180, power generation control is performed on the fuel cell 100 at a current density of 0.6 A / cm ² or more. Since step S180 is a result of receiving a negative determination (YP <0.6 A / cm ² generated power) in step S110, if power generation control is performed on the fuel cell 100 at a current density of 0.6 A / cm ² or more, The generated power exceeds the load demand power YP. Therefore, in step S180, the secondary battery 150 is charged with the surplus generated power, and in subsequent step S130, the generated power of the load required power YP is output to the motor 170, and the motor 170 is supplied with the load required power YP. Drive (step S150). In this case, in step S180, the power generation of the fuel cell 100 is controlled at a current density of 0.6 A / cm ² or the power generation is controlled at a predetermined current density in the range of 0.6 to 4.0 A / cm ^2. Can be.

As described above, in the fuel cell system 20 of this embodiment, whether or not the fuel cell 100 needs to be operated is determined according to the required load power YP required for the motor 170 for traveling the vehicle based on the operation state of the accelerator 180 or the like. To do. In other words, if the load required power YP is generated power when the fuel cell 100 is generated and operated at a current density of 0.6 A / cm ² or more, it is determined that the operation of the fuel cell 100 is necessary (step S110). The battery 100 is generated with a current density of 0.6 A / cm ² or more corresponding to the required load power YP, and the motor 170 is driven with the generated power (steps S130 to S140). That is, the fuel cell 100 is selected as the power source of the motor 170 and the motor 170 is driven under the situation where the power generation control of the fuel cell 100 is performed so that the current density becomes 0.6 A / cm ² or more.

Thus, if the fuel cell 100 is operated for power generation at a current density of 0.6 A / cm ² or more, the current density is large, and therefore, in each battery cell of the fuel cell 100, the electrochemical reaction actively proceeds, and the battery cell A relatively large amount of water is generated in the power generation region of the MEA. The power generation operation of the fuel cell 100 at a current density of 0.6 A / cm ² or more corresponds to the samples A to B in FIG. 2, and these samples A to B are the MEA electrolyte membrane (this In the examples, the deterioration of the hydrocarbon electrolyte membrane) is not observed. This is because the MEA electrolyte membrane (hydrocarbon electrolyte membrane) can be sufficiently moistened with a large amount of produced water by power generation operation at a high current density. Even if radicals are generated by the generation and decomposition of hydrogen oxide, it means that the oxidative decomposition of the electrolyte membrane can be suppressed with high effectiveness (samples A to B) as described in FIG. That is, it is considered that the radical represented by .OH is not quenched or decomposed by the generated water and thus does not cause oxidative decomposition of the electrolyte membrane. This is because the electrolyte membrane deterioration is caused in the samples A to B described in FIG. It matches what is not seen.

  As a result, according to the fuel cell system 20 of the present embodiment, the oxidative decomposition degradation of the electrolyte membrane (hydrocarbon electrolyte membrane) of the fuel cell 100 can be suppressed with high effectiveness through the transition of radicals to water. Performance can be maintained over a long period of time. Further, since the hydrocarbon-based electrolyte membrane is inexpensive and highly versatile, the use of this hydrocarbon-based electrolyte membrane for the MEA of the fuel cell 100 reduces the cost of the fuel cell system 20 and hence the fuel cell-equipped vehicle 10. Can be achieved.

Further, in the fuel cell system 20 of the present embodiment, when the power generation operation of the fuel cell 100 is performed at a current density of 0.6 A / cm ² or more according to the required load power YP, the current density exceeds 4.0 A / cm ² . I tried not to. For this reason, since the fuel cell 100 is not operated in high load power generation where the current density exceeds 4.0 A / cm ² , it is not possible to perform power generation operation near the upper limit of the cell capacity or from the relationship with the power reduction or fuel consumption due to power generation exceeding this. It is possible to suppress deterioration of the electrolyte membrane without causing a decrease in power generation efficiency.

Further, in the fuel cell system 20 of the present embodiment, when the required load power YP required for the motor 170 is small (step S110: negative determination), the fuel cell 100 is not operated for power generation. Does not cause deterioration. In addition, when the load required power YP is small, the secondary battery 150 is selected as a power source (step S150) and the load required power YP is covered by the charging power of the secondary battery 150 (step S170: affirmative). Determination) When the required power YP cannot be covered by the charging power of the secondary battery 150, the fuel cell 100 is controlled to generate power so that the current density is 0.6 A / cm ² or more (step S180), and the surplus The secondary battery 150 is charged with the generated power. For this reason, according to the fuel cell system 20 of the present embodiment, the oxidative decomposition deterioration of the MEA of the fuel cell 100 due to radicals is suppressed, and the motor 170 is used as the power source with the fuel cell 100 or the secondary battery 150 as the power source. The secondary battery 150 can be charged while being operated.

  Next, another embodiment will be described. This embodiment is characterized in that the fuel cell 100 is steadily operated when it is determined that the fuel cell 100 needs to be operated. FIG. 5 is a flowchart showing a state of power generation control of the fuel cell 100 in another embodiment.

  As shown in the figure, in this embodiment, first, it is determined whether or not the fuel cell 100 needs to generate power (step S200). For example, when the shift lever is in the parking position for a certain period, the vehicle is expected to continue to stop. During such a stop, since large electric power is not required, this routine is ended without operating the fuel cell 100. Even if the vehicle compartment audio is turned on while the vehicle is stopped, the power in such a case can be normally supplied by the secondary battery 150, and there is no problem. As will be described later, in this embodiment, the state of charge of the secondary battery 150 is kept fully charged by the surplus power of the fuel cell 100, so that the power required for starting the vehicle can be obtained using only the power of the secondary battery 150. It is also possible to cover.

On the other hand, if it is determined in step S200 that the fuel cell 100 needs to be operated, the power generation control of the fuel cell 100 is performed at a current density of 0.6 A / cm ² or more following the reading of the required load power YP (step S210) ( Step S220). Next, it is determined whether or not the read required load power YP is equal to or greater than the generated power when the fuel cell 100 is operated for power generation at a current density of 0.6 A / cm ² (step S230). Since the power generated when the fuel cell 100 is operated for power generation at a current density of 0.6 A / cm ² corresponds to the power required when the vehicle is traveling at a low speed, in step S230 the vehicle is started from a low speed. An affirmative determination is made when the vehicle is in a high-speed driving state, and a negative determination is made when the vehicle is in a temporary stop, a traffic jam, or the like.

If an affirmative determination is made in step S230, the generated power FP (= load required power YP) of the fuel cell 100 whose power generation is controlled at a current density of 0.6 A / cm ² or more is output to the motor 170 in step S220 (step S220). S240), the motor 170 is driven with the required load power YP (step S250). In step S220, the fuel cell 100 is subjected to power generation control at a current density of 0.6 A / cm ² or more, and the load required power YP (= power generation power at a current density of 0.6 A / cm ² ) can be covered. The power generation of the fuel cell 100 is controlled. For example, if the generated power when the load request power YP has power generation control of the fuel cell 100 at a current density of 0.6 A / cm ^2, the control unit 200, the fuel cell 100 of 0.6 A / cm ² current density Power generation is controlled at. Similarly, if the required load power YP is generated power when the fuel cell 100 is controlled to generate power at a current density of 2.0 A / cm ² , the control device 200 controls the fuel cell 100 to a current of 2.0 A / cm ² . Power generation is controlled by density. Meanwhile, even in the generated power when the load request power YP has power generation control of the fuel cell 100 at 0.6 A / cm ² less than the current density, the control unit 200, the fuel cell 100 0.6 A / cm ² In this case, the process proceeds to step S260 described later. That is, in step S220, the control device 200 performs power generation control of the fuel cell 100 at a current density corresponding to the load required power YP. At this time, the power generation control of the fuel cell 100 is 0.6 to 4.0 A / cm. The power generation is controlled at a current density in the range of ² .

On the other hand, if it is determined in step S230 that the load required power YP is generated when the fuel cell 100 is in a power generation operation at a current density lower than 0.6 A / cm ² , the fuel cell 100 determines that the load required power YP The power generation operation is performed so that the generated power FP exceeds. Therefore, in this case, the process proceeds to step S260, the surplus power that is the difference between the generated power FP and the load required power YP is output, and the generated power FP corresponding to the load required power YP is output to the motor 170 (step S240). ), And drives the motor 170 with the required load power YP (step S250).

In the above-described embodiment, the surplus power output in step S260 can be performed by various techniques. First, the secondary battery 150 is charged with surplus power so as to be fully charged. If there is still surplus power even when the secondary battery 150 is fully charged, the surplus power may be used for consumption. For example, while the vehicle is running, the gear speed can be reduced by one step to increase the motor rotation speed, so that power consumption can be achieved while maintaining the vehicle speed generally. Alternatively, the clutch of the power transmission mechanism can be disengaged to cause the motor to idle, thereby consuming power, consumed by another motor mounted on the vehicle, such as a motor for an air conditioner, or consumed by energizing a heater for heating. . That is, in this embodiment, the power generation control of the fuel cell 100 at a current density of 0.6 A / cm ² or more suppresses the MEA oxidative degradation as described above, and the surplus power is supplied to the secondary battery 150. It can be effectively used for other purposes such as full charge.

  Next, another embodiment will be described. FIG. 6 is an explanatory diagram schematically showing the configuration of a fuel cell 100A in another embodiment, and FIG. 7 is a flowchart showing the state of power generation control of the fuel cell 100A.

  As shown in FIG. 6, the fuel cell 100 </ b> A is configured as a battery unit assembly including a plurality of battery stacks in which a predetermined number of battery cells are stacked, and generates power for each battery unit. In this case, hydrogen gas and air are configured to be supplied to the MEA in the battery cell of each battery unit, and the supply amount is controlled for each battery unit. The fuel cell 100A is configured to collect the generated power for each battery unit and output it to the outside.

In the power generation operation of the fuel cell 100A, as shown in FIG. 7, first, it is determined whether or not the fuel cell 100 needs to generate power based on the shift lever position or the like as in the embodiment shown on the left (step S300). This routine is terminated. On the other hand, if it is determined in step S300 that the operation of the fuel cell 100 is necessary, the load required power YP is read (step S310), and the number of stacks in the fuel cell 100A that performs power generation to cover the read load power YP is calculated. Determination and power generation control of each battery cell of the determined number of stacks are performed at a current density of 0.6 A / cm ² or more (step S320). For example, the load required power YP is divided by the stack generated power SFP when each battery cell of one stack in the fuel cell 100A is operated for power generation at a current density of 0.6 A / cm ² to cover the load required power YP. The number of stacks of the fuel cell 100A that is sufficient is determined, and power generation is controlled at a current density of 0.6 A / cm ² or more for each battery cell of the determined number of stacks. Then, the collected power (= load required power YP) obtained by collecting the stack generated power SFP obtained in each stack is output to the motor 170 (step S330), and the motor 170 is driven with the load required power YP (step S330). S340).

In the above-described embodiment, the fuel cell 100A battery stack that requires power generation control according to the load required power YP is described above by performing power generation control at a current density of 0.6 A / cm ² or more. Oxidative degradation of MEA due to radicals can be suppressed. On the other hand, in a battery stack in which power generation control is not required, supply of hydrogen gas and air and power generation control are not performed, so that no electrochemical reaction occurs and no radical is generated. Therefore, in a battery stack that does not require power generation, there is no problem with oxidative decomposition of MEA by radicals, and deterioration can be prevented.

  Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. For example, in the above embodiment, the MEA of the fuel cell 100 has a hydrocarbon-based electrolyte membrane, but it may be an MEA having another electrolyte membrane such as a fluorine-based electrolyte membrane. Further, the fuel cell system 20 can be applied as a stationary power generation system in addition to being mounted on the fuel cell vehicle 10.

DESCRIPTION OF SYMBOLS 10 ... Vehicle equipped with fuel cell 12 ... Car body 20 ... Fuel cell system 100 ... Fuel cell 100A ... Fuel cell 102 ... Current sensor 110 ... Hydrogen gas tank 120 ... Hydrogen gas supply system 121 ... Hydrogen supply route 122 ... Circulation route 123 ... Flow rate adjustment valve 124 ... circulation pump 125 ... discharge pipe 126 ... open / close valve 130 ... compressor 140 ... air supply system 141 ... oxygen supply path 142 ... discharge path 143 ... discharge flow rate adjustment valve 150 ... secondary battery 152 ... capacity detection sensor 160 ... DC- DC converter 170 ... motor 180 ... accelerator 200 ... control device FW ... front wheel RW ... rear wheel

Claims (7)

A fuel cell having a membrane electrode assembly in which electrode layers are bonded to both membrane surfaces of an electrolyte membrane having proton conductivity;
A supply system for supplying fuel to one of the electrode layers and supplying an oxidant of the fuel to the other electrode layer;
Power generation control means for controlling power generation of the fuel cell by controlling the supply status of the fuel and the oxidant by the supply system;
Determination means for determining whether or not the fuel cell needs to be generated by the power generation control means,
The power generation control means includes
When the determination means determines that power generation of the fuel cell is necessary, the power generation of the fuel cell is controlled so that the current density per electrode area of the fuel cell is 0.6 A / cm ² or more. system. ^2. The fuel cell system according to claim 1, wherein the power generation control unit controls power generation of the fuel cell such that the current density does not exceed 4.0 A / cm ² . The fuel cell system according to claim 1 or 2, wherein
Furthermore,
A secondary battery capable of charging and discharging power;
Power selection means for selecting one of the fuel cell and the secondary battery as a power source to be supplied to an external load, and supplying power from the selected power source to the load;
Power detection means for detecting required power required to be output to the load,
The determination means determines whether or not the power generation is necessary according to the required power detected by the power detection means. When it is determined that the fuel cell needs to generate power, the power selection means supplies the power source to the power selection means. A fuel cell system that causes the fuel cell to select. 4. The determination unit according to claim 3, wherein the determination unit determines that the fuel cell needs to generate power when the required power detected by the power detection unit is generated power at a current density of 0.6 A / cm ² or more. Fuel cell system. The fuel cell system according to claim 4, wherein
Capacity means for detecting the charge capacity of the secondary battery,
The determination means is generated power at a current density where the required power detected by the power detection means is less than 0.6 A / cm ^2, and the required power cannot be covered by the charge capacity detected by the capacity detection means. In the case, it is determined that power generation of the fuel cell is necessary,
The power generation control means controls the power generation of the fuel cell so that the current density becomes 0.6 A / cm ² or more, and charges the secondary battery with surplus generated power. The fuel cell system according to claim 1 or 2, wherein
Furthermore,
Comprising power detection means for detecting required power required for output to an external load;
When the determination means determines that the fuel cell needs to generate power, the power generation control means generates surplus generated power exceeding the required power detected by the power detection means. A fuel cell system that can be used for power consumption, including charging secondary batteries that can be charged and discharged. The fuel cell system according to claim 1 or 2, wherein
Furthermore,
Comprising power detection means for detecting required power required for output to an external load;
The fuel cell is configured as an assembly of a plurality of battery units, and generates power for each battery unit, and collects generated power for each battery unit,
The supply system supplies the fuel and the oxidant for each battery unit,
The determination means determines whether the power generation control means requires power generation for each battery unit of the fuel cell according to the required power detected by the power detection means,
The power generation control means controls the supply status in the supply system for each battery unit, controls power generation for each battery unit, and outputs the collected generated power.

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