JP2013168311A - Fuel cell system - Google Patents

Abstract

A fuel cell system capable of suppressing a decrease in power generation efficiency while suppressing cost.
A fuel cell that generates hydrogen by supplying hydrogen and air to a fuel cell having a plurality of cells using a low EW ionomer in a catalyst layer, and electrochemically reacting the hydrogen and oxygen in the air in the cell. In the system, when the output difference ΔP between the target output Pt and the measured output P in the fuel cell exceeds a predetermined value, the target calorific value is calculated from the relationship between a preset ionomer shrinkage rate Δδ and the calorific value Q. Qt is obtained, the target output voltage Et is calculated from the target calorific value Qt, and the target stoichiometric ratio STt is obtained from the relationship between the preset output voltage E and the stoichiometric ratio ST, and the fuel is set so as to be the target stoichiometric ratio STt. A diffusion resistance suppression operation for supplying air to the battery is performed.
[Selection] Figure 2

Description

  The present invention relates to a fuel cell system including a fuel cell in which a low EW ionomer is used for a catalyst layer.

  In recent years, a fuel cell system that uses a fuel cell that generates electric power by an electrochemical reaction of reaction gases (fuel gas and oxidizing gas) as an energy source has attracted attention. The fuel cell system supplies hydrogen as a fuel gas to the anode of the fuel cell and supplies air as an oxidizing gas to the cathode, and causes an electrochemical reaction between the fuel gas and the oxidizing gas to generate an electromotive force. It is.

  A fuel cell used in a fuel cell system includes a first catalyst layer formed on an electrolyte membrane and a second catalyst layer thicker than the first catalyst layer formed on the first catalyst layer. In the electrode catalyst layer for a fuel cell, the catalyst support density and the electrolyte ratio of the catalyst support carbon particles constituting the first catalyst layer are higher than those of the second catalyst layer, and the EW value and water immersion pH of the electrolyte ionomer are the second catalyst layer. A lower one is known (for example, see Patent Document 1).

JP 2010-198844 A

  By the way, when the sulfonic acid equivalent EW (Equivalent Weight) of the ionomer of the catalyst layer is high, the catalyst layer is dried up at a high temperature and the output is reduced. Therefore, in the fuel cell system, it is effective to lower the sulfonic acid equivalent EW of the ionomer of the catalyst layer in order to efficiently generate power in the fuel cell without high temperature and humidity. However, in the fuel cell using the low EW ionomer, the diffusion resistance increases due to the swelling of the ionomer in the normal temperature range, leading to a decrease in output, and there is a possibility that the actual output cannot be sufficiently obtained with respect to the target output.

  In this case, it is conceivable to provide a determination device for determining the moisture content of the catalyst layer and control the moisture content of the catalyst layer based on the determination result of this determination device, but the cost of adding a new determination device is considered. Invite up.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a fuel cell system capable of suppressing a decrease in power generation efficiency while suppressing cost.

In order to achieve the above object, the fuel cell system of the present invention comprises:
This is a fuel cell system in which hydrogen and air are supplied to a fuel cell having a plurality of cells using a low EW ionomer in the catalyst layer, and the hydrogen and oxygen in the air are electrochemically reacted in the cell to generate electricity. And
When the output difference between the target output of the fuel cell and the actually measured output exceeds a predetermined value, a target heat generation amount is obtained from a preset relationship between the ionomer contraction rate and the heat generation amount, and the target heat generation amount is determined from the target heat generation amount. The output voltage is calculated, and further, the target stoichiometric ratio is obtained from the relationship between the preset output voltage and the stoichiometric ratio, and the diffusion resistance suppressing operation for supplying air to the fuel cell so as to be the target stoichiometric ratio is performed. .

  According to this configuration, when the diffusion resistance suppression operation is performed and air is supplied to the fuel cell so as to achieve the target stoichiometric ratio, the catalyst layer generates heat with the target calorific value, and the ionomer swelling of the catalyst layer is suppressed. The Thereby, the increase in the diffusion resistance due to the swelling of the ionomer can be suppressed to suppress the output decrease, and the output from the fuel cell can be set as the target output.

  In particular, the power generation efficiency can be maintained in a good state even during cold power generation where ionomer swelling easily occurs. That is, it is possible to suppress a decrease in power generation efficiency without incurring a cost increase by newly providing a determination device for determining the moisture content of the catalyst layer.

In the fuel cell system configured as described above, an output difference determination unit that determines whether or not an output difference between the target output of the fuel cell and the actual output exceeds a predetermined value;
A target calorific value calculation unit for obtaining a target calorific value from the relationship between the ionomer contraction rate and the calorific value set in advance;
A target output voltage calculation unit for calculating a target output voltage from the target heat generation amount;
A target stoichiometric ratio calculating unit for obtaining a target stoichiometric ratio from a relationship between a preset output voltage and a stoichiometric ratio;
An air supply amount control unit configured to control an air supply amount to the fuel cell so as to be the target stoichiometric ratio.

  According to the fuel cell system of the present invention, it is possible to suppress a decrease in power generation efficiency while suppressing costs.

1 is a configuration diagram schematically showing one embodiment of a fuel cell system according to the present invention. It is a flowchart which shows diffusion resistance suppression control. It is a map figure which shows the relationship between the shrinkage | contraction rate of an ionomer, and the emitted-heat amount. It is a map figure which shows the relationship between an output voltage and stoichiometric ratio.

  First, the overall configuration of the fuel cell system according to the present invention will be described. This fuel cell system is an in-vehicle power generation system for a fuel cell vehicle. In addition to a fuel cell system mounted on a vehicle, a fuel cell system for any moving body such as a ship, an aircraft, a train, a walking robot, or the like, for example, a fuel cell However, it can also be applied to stationary fuel cell systems used as power generation equipment for buildings (housing, buildings, etc.).

  In the fuel cell system 1 shown in FIG. 1, the air as the oxidizing gas is supplied to the air supply port of the fuel cell 20 via the air supply path 11. The air supply path 11 is provided with an air filter A1 that removes particulates from the air, a compressor A2 that pressurizes the air, and a humidifier A3 that adds required moisture to the air. The air filter A1 is provided with an air flow meter (flow meter) (not shown) that detects the air flow rate. The compressor A2 is driven by a motor. This motor is driven and controlled by a control unit 50 described later.

  Air off-gas (oxidation off-gas) discharged from the fuel cell 20 is discharged to the outside through the exhaust passage 12. The exhaust passage 12 is provided with a pressure adjustment valve A4 and a humidifier A3. The pressure adjustment valve A4 functions as a pressure regulator (pressure reduction) that sets the supply air pressure to the fuel cell 20. The control unit 50 sets the supply air pressure and the supply air flow rate to the fuel cell 20 by adjusting the rotation speed of the motor that drives the compressor A2 and the opening area of the pressure adjustment valve A4.

  Hydrogen gas as fuel gas is supplied from a hydrogen supply source 30 to a hydrogen supply port of the fuel cell 20 through a hydrogen supply path 31. The hydrogen supply source 30 corresponds to, for example, a high-pressure hydrogen tank, but may be a so-called fuel reformer, a hydrogen storage alloy, or the like.

  In the hydrogen supply path 31, a shutoff valve H1 that supplies or stops supplying hydrogen from the hydrogen supply source 30, a hydrogen pressure regulating valve H2 that adjusts the supply pressure of hydrogen gas to the fuel cell 20 by reducing the pressure, and the fuel cell 20 A shutoff valve H3 for opening and closing between the hydrogen supply port and the hydrogen supply path 31 is provided. As the hydrogen pressure regulating valve H2, for example, a pressure regulating valve that performs mechanical pressure reduction can be used, but a valve whose valve opening degree is linearly or continuously adjusted by a pulse motor may be used.

  The hydrogen gas that has not been consumed in the fuel cell 20 is discharged as hydrogen offgas (fuel offgas) to the hydrogen circulation path 32 and returned to the downstream side of the hydrogen pressure regulating valve H2 in the hydrogen supply path 31. The hydrogen circulation path 32 includes a gas-liquid separator H11 that collects moisture from the hydrogen off-gas, a drain valve H12 that collects the collected product water in a tank (not shown) outside the hydrogen circulation path 32, and a hydrogen pump that pressurizes the hydrogen off-gas. H13 is provided. The operation of the hydrogen pump H13 is controlled by the control unit 50. The hydrogen off gas merges with the hydrogen gas in the hydrogen supply path 31 and is supplied to the fuel cell 20 for reuse.

  The hydrogen circulation path 32 is connected to the exhaust path 12 on the downstream side of the humidifier A3 by the purge flow path 33 via the discharge control valve H14. The discharge control valve H <b> 14 is an electromagnetic shut-off valve, and operates according to a command from the control unit 50, whereby the hydrogen off gas is discharged (purged) together with the air off gas discharged from the fuel cell 20. By performing this purge operation intermittently, it is possible to prevent a cell voltage from being lowered due to an increase in the impurity concentration in the hydrogen gas.

  A cooling passage 41 for circulating the cooling water is provided at the cooling water inlet / outlet of the fuel cell 20. The cooling path 41 is provided with a radiator (heat exchanger) C2 that radiates heat of the cooling water to the outside, and a pump C1 that pressurizes and circulates the cooling water. The radiator C2 is provided with a cooling fan C3 that is rotationally driven by a motor.

  The fuel cell 20 is configured as a fuel cell stack in which a required number of single cells that receive supply of hydrogen gas and air and generate electric power through an electrochemical reaction are stacked. The electric power generated by the fuel cell 20 is supplied to a power control unit (not shown). The power control unit consists of an inverter that supplies electric power to the drive motor of the vehicle, an inverter that supplies electric power to various auxiliary devices such as a compressor motor and a motor for a hydrogen pump, and charging of power storage means such as a secondary battery. A DC-DC converter or the like that supplies power to the motors from the power storage means is provided.

  The control unit 50 is configured by a control computer system having a known configuration such as a CPU, ROM, RAM, HDD, input / output interface, display, and the like, and a required load such as an accelerator signal of a vehicle (not shown) and each part of the fuel cell system 1 Control information is received from these sensors (pressure sensor, temperature sensor, flow sensor, output ammeter, output voltmeter, etc.), and the operation of valves and motors in each part of the system is controlled.

  In the fuel cell system 1, the fuel cell 20 generates an electromotive force by causing an electrochemical reaction between hydrogen gas supplied through the hydrogen supply path 41 and air supplied through the air supply path 11. Let

  In the fuel cell system 1 according to the present embodiment, a low EW (Equivalent Weight) ionomer is used as the catalyst layer of the fuel cell 20 in order to generate electricity smoothly without high-temperature humidification. However, in the fuel cell 20 using this low EW ionomer as the catalyst layer, the diffusion resistance increases due to the swelling of the ionomer, particularly in the normal temperature range, resulting in a decrease in the output, and an actual output sufficient for the target output can be obtained. There is a risk of being lost.

  For this reason, in the fuel cell system 1 of the present embodiment, diffusion resistance suppression control that suppresses diffusion resistance is performed. In the present invention, low EW means that EW is 1000 or less.

  Next, the diffusion resistance suppression control will be described with reference to a flowchart shown in FIG. As will be apparent from the following description, the control unit 50 according to the present embodiment includes an output difference determination unit, a target heat generation amount calculation unit, a target output voltage calculation unit, a target stoichiometric ratio calculation unit, and an air supply. Functions as a quantity control unit.

  For example, in an operation in a normal temperature range, an output comparison determination is performed to compare the measured output P of the fuel cell 20 with the target output Pt (step S01). In this output comparison determination, it is determined whether or not the output difference ΔP (ΔP = P−Pt) exceeds a predetermined value. In this embodiment, the predetermined value is set to 0, and it is determined whether or not an output difference ΔP is generated and | ΔP |> 0.

  If it is determined in this output comparison determination (step S01) that the output difference ΔP has not occurred (step S01: No), the fuel cell 20 is subjected to normal control. As a result, the fuel cell 20 normally generates power (step S02).

  If it is determined in the output comparison determination (step S01) that the output difference ΔP has occurred (step S01: Yes), the subsequent diffusion resistance suppression control is performed.

First, it is necessary in the diffusion layer based on the following formula from the necessary current improvement allowance ΔI necessary for eliminating the output difference ΔP, the control voltage E, and a predetermined score β set based on the results of experiments and simulations. The required diffusion improvement allowance ΔD is calculated (step S03).
ΔI = β ・ E ・ ΔD

Next, a target ionomer shrinkage rate Δδt in the diffusion layer is calculated from the required diffusion improvement allowance ΔD and a predetermined coefficient α set based on the results of experiments and simulations (step S04).
ΔD = αΔδt

  The target ionomer shrinkage rate Δδt may be obtained from a map of the relationship between the diffusion improvement allowance ΔD and the ionomer shrinkage rate Δδ obtained in advance.

  Further, a target heat generation amount Qt is obtained from the target ionomer contraction rate Δδt. As shown in FIG. 3, the target heat generation amount Qt is obtained from a map of the relationship between the ionomer contraction rate Δδ and the heat generation amount Q, which have been obtained in advance (step S05). The relationship between the shrinkage rate Δδ and the calorific value Q changes depending on the electrolyte ratio in the catalyst layer, that is, the electrolytic mass per carbon (I / C).

  For example, the relationship between the shrinkage rate Δδ and the calorific value Q is determined for each of the various catalyst layers with I / C = 0.85, I / C = 0.75, and I / C = 0.65. Then, when the electrolytic mass of the catalyst layer actually used is, for example, I / C = 0.75, the one corresponding to I / C = 0.75 in this map is selected and the target heat generation amount Qt Ask for.

Then, the target heating value Qt, the current value I and the actual measurement voltage E ₀ based on the following equation to calculate the target output voltage Et (step S06).

Qt = (E ₀ −Et) I

  Further, a target stoichiometric ratio STt is obtained from the target output voltage Et. As shown in FIG. 4, the target stoichiometric ratio STt is obtained from a map of the relationship between the output voltage E and the stoichiometric ratio ST obtained in advance (step S07).

  When the target output voltage Et and the target stoichiometric ratio STt are obtained, the fuel cell 20 is controlled to output at the target output voltage Et, and the compressor A2 is controlled so as to achieve the target stoichiometric ratio STt (step S08).

  Then, in the fuel cell 20, heat is generated in the diffusion layer of each cell, and the swelling of the ionomer is suppressed. As a result, an increase in diffusion resistance due to the swelling of the ionomer is suppressed to suppress a decrease in output, and the output P from the fuel cell 20 is set as the target output Pt.

  When the output drop of the fuel cell 20 is suppressed and the output difference ΔP does not occur between the measured output P and the target output Pt, the fuel cell 20 is operated under normal control (steps S01 and S02).

  As described above, according to the fuel cell system according to the above-described embodiment, when the diffusion resistance suppression operation is performed and air is supplied to the fuel cell 20 so as to achieve the target stoichiometric ratio STt, the catalyst layer has the target heating value. Heat is generated and the swelling of the ionomer in the catalyst layer is suppressed. Thereby, the increase in the diffusion resistance due to the swelling of the ionomer can be suppressed to suppress the output decrease, and the output P from the fuel cell 20 can be set as the target output Pt.

  In particular, the power generation efficiency can be maintained in a good state even during cold power generation where ionomer swelling easily occurs. That is, it is possible to suppress a decrease in power generation efficiency without incurring a cost increase by newly providing a determination device for determining the moisture content of the catalyst layer.

DESCRIPTION OF SYMBOLS 1 Fuel cell system 20 Fuel cell 50 Control part (Output difference determination part, target calorific value calculation part, target output voltage calculation part, target stoichiometric ratio calculation part, and air supply amount control part)

Claims (2)

This is a fuel cell system in which hydrogen and air are supplied to a fuel cell having a plurality of cells using a low EW ionomer in the catalyst layer, and the hydrogen and oxygen in the air are electrochemically reacted in the cell to generate electricity. And
When the output difference between the target output of the fuel cell and the actually measured output exceeds a predetermined value, a target heat generation amount is obtained from a preset relationship between the ionomer contraction rate and the heat generation amount, and the target heat generation amount is determined from the target heat generation amount. The output voltage is calculated, and further, the target stoichiometric ratio is obtained from the relationship between the preset output voltage and the stoichiometric ratio, and the diffusion resistance suppressing operation for supplying air to the fuel cell so as to be the target stoichiometric ratio is performed. Fuel cell system. An output difference determination unit for determining whether an output difference between the target output of the fuel cell and the actual measurement output exceeds a predetermined value;
A target calorific value calculation unit that obtains a target calorific value from a relationship between a preset shrinkage rate of the ionomer and a calorific value;
A target output voltage calculation unit for calculating a target output voltage from the target heat generation amount;
A target stoichiometric ratio calculating unit for obtaining a target stoichiometric ratio from a relationship between a preset output voltage and a stoichiometric ratio;
An air supply amount control unit for controlling the air supply amount to the fuel cell to be the target stoichiometric ratio;
A fuel cell system according to claim 1.

Images