JP2006092793A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of restraining catalyst degradation reaction. <P>SOLUTION: This fuel cell system comprises a fuel cell 2 having a membrane electrode assembly 16 having a catalyst layers 5 on both main surfaces of proton exchange membrane 4 and comprising a fuel cell 2 and being equipped with a gas diffusion electrode 6a of a fuel electrode 14a and a gas diffusion electrode 6c of an oxidizer electrode 14c, respectively on the outside of the catalyst layer 5, and separators 3a, 3c comprising a fuel gas flow passage 7 and an oxidizer gas flow passage 8 for supplying fuel gas and oxidizer gas, respectively to the gas diffusion electrode 6a and the gas diffusion electrode 6c. In such a fuel cell system, the gas diffusion electrode 6a, the gas diffusion electrode 6c and the separators 3a, 3c are constituted by divided elements 17a and 17c which are divided into a plurality of elements by an insulation member 10 vertically in the flow direction of the fuel gas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in a fuel cell system. In particular, the present invention relates to a control method for suppressing deterioration of a fuel cell at start / stop.

  2. Description of the Related Art As a conventional fuel cell, a battery configured by stacking unit cells by arranging a plurality of divided electrodes on a plane is known. A single-layer matrix is sandwiched between the fuel electrode and the oxidant electrode formed by the divided electrodes. Mixing of fuel gas and air is prevented by the matrix, and handling performance at the time of assembly is reduced without causing a decrease in electric capacity and an increase in cost without using a partition plate or the like in the reaction surface between the divided electrodes. (For example, refer to Patent Document 1).

Japanese Patent Laid-Open No. 7-6772

  When the fuel cell is started / stopped, the fuel cell and the oxidant gas are mixed in the reaction gas channel on the fuel electrode side to form a local cell, thereby causing a deterioration reaction of the catalyst layer. In particular, when the fuel gas flow path and the oxidant gas flow path are configured in parallel, the deterioration of the catalyst layer on the outlet side of the oxidant electrode flow path tends to become remarkable, which is one of the factors that determine the fuel cell durability. It has become one.

  In the prior art described above, since the divided electrodes are electrically connected, it is difficult to suppress the deterioration reaction of the catalyst layer at the time of starting / stopping as in the case of the conventional fuel cell.

  In view of the above problems, an object of the present invention is to provide a fuel cell that can suppress a deterioration reaction of a catalyst layer.

  The present invention provides a membrane electrode assembly having catalyst layers on both main surfaces of an electrolyte membrane, and a fuel gas diffusion electrode and an oxidant gas diffusion electrode disposed on both sides thereof, and the fuel gas diffusion electrode and the oxidation membrane. And a separator having gas flow paths for supplying fuel gas and oxidant gas to the oxidant gas diffusion electrode, respectively, the fuel gas diffusion electrode, the oxidant gas diffusion electrode, and the separator. In addition, it is constituted by a divided body divided into a plurality of parts by an insulating member substantially perpendicularly to the flow direction of the fuel gas.

  The fuel gas diffusion electrode, the oxidant gas diffusion electrode, and the separator are configured by a divided body that is divided into a plurality of portions by an insulating member substantially perpendicular to the flow direction of the fuel gas. Thereby, since the movement of the electrons between divided bodies can be prevented, the deterioration reaction of the catalyst layer can be suppressed.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of the fuel cell stack 1, and FIG.

  As shown in FIG. 1, the fuel cell stack 1 is configured by stacking a plurality of unit cells 2. The unit cell 2 has a fuel electrode 14a composed of a catalyst layer 5a and a gas diffusion electrode 6a on one surface of the polymer electrolyte membrane 4, and an oxidant electrode 14c composed of a catalyst layer 5c and a gas diffusion electrode 6c on the other surface. A membrane electrode assembly 16 is provided. One surface of the membrane electrode assembly 16 is provided with a separator 3a provided with a fuel gas channel 7 through which fuel gas flows, and the fuel gas is supplied to the catalyst layer 5a via the gas diffusion electrode 6a. The other surface is provided with a separator 3c provided with an oxidant gas flow path 8 through which an oxidant gas flows, and the oxidant gas is supplied to the catalyst layer 5c via the gas diffusion electrode 6c. As shown in FIG. 1, the fuel gas channel 7 and the oxidant gas channel 8 are configured in parallel to each other. Further, the inlet portion and the outlet portion of the fuel gas flow path 7 and the oxidant gas flow path 8 are provided at positions that substantially overlap each other in the stacking direction, and the fuel gas and the oxidant gas flow in substantially the same direction during normal operation. Configure as follows. Furthermore, the unit cell 2 includes a seal 9 along the outer edge of the membrane electrode assembly 16 to prevent a short circuit between the electrodes 14a and 14c and to prevent mixing of reaction gases.

  The gas diffusion electrode 6 a of the fuel electrode 14 a is constituted by a divided electrode 61 a that is divided substantially perpendicularly to the flow direction of the fuel gas flow path 7. Further, the cathode-side gas diffusion electrode 6 c is constituted by a divided electrode 61 c that is divided substantially perpendicularly to the flow direction of the oxidant gas flow path 8. Here, the divided electrode 61a constituting the gas diffusion electrode 6a and the divided electrode 61c constituting the gas diffusion electrode 6c are divided into substantially the same shape.

  Further, the anode-side separator 3 a is constituted by a divided separator 31 a that is divided perpendicularly to the flow direction of the fuel gas flow path 7. Further, the cathode-side separator 3 c is constituted by a divided separator 31 c that is divided substantially perpendicularly to the flow direction of the oxidant gas flow path 8. Here, the divided separator 31a constituting the separator 3a and the divided separator 31c constituting the separator 3c are divided into substantially the same shape.

  Further, the gas diffusion electrode 6 a and the separator 3 a are divided at the same location in the flow axis direction of the fuel gas flow channel 7. Further, the gas diffusion electrode 6 c and the separator 3 c are divided at the same place in the flow channel axial direction of the oxidant gas flow channel 8.

  That is, the separators 3a and 3c and the gas diffusion electrodes 6a and 6c are divided into a plurality of parts in the flow direction of the reaction gas. In other words, the divided separators 31a and 31c and the divided electrodes 61a and 61c stacked in the stacking direction have the same length in the flow direction of the reaction gas flow paths 7 and 8. In addition, an insulating member 10 is provided at a divided portion of the gas diffusion electrode 6 and the separator 3 in order to maintain electrical insulation between the divided electrode 61 and the divided separator 31. The divided cells 17a and 17c are constituted by the divided separators 31a and 31c and the divided electrodes 61a and 61c, and the plurality of divided bodies 17a and 17c are arranged via the insulator 10, thereby constituting the unit cell 2.

  Such divided bodies 17a and 17c have the same shape between the stacked unit cells 2, and the divided bodies 17a and 17c are stacked to form the divided stack 15. Each of the divided stacks 15 is connected to the external load 12 via the switch 11a.

  In FIG. 1, the number of divisions of the separators 3a and 3c and the gas diffusion electrodes 6a and 6c is three. That is, the fuel cell stack 1 is composed of three divided stacks 15, but this is not restrictive.

   Further, the catalyst layer 5 is divided and configured in the same manner as the divided electrode 61 by applying catalyst-supporting carbon to the gas diffusion electrode 6. Alternatively, when applying to the electrolyte membrane 4, it is preferable to avoid applying the catalyst-supporting carbon to the portion facing the insulating member 10. Alternatively, when the catalyst layer 5 is formed using other members, the constituent members may be divided.

  Next, the state at the time of starting and stopping of this embodiment will be described. First, the local electrode generation mechanism at the start-up when using a normal undivided unit cell 102 will be described with reference to FIG.

  When the fuel gas is introduced into the fuel gas passage 107 from the state where oxygen is mixed in the fuel gas passage 107 and the oxidant gas passage 108, the fuel gas containing hydrogen is upstream in the fuel gas passage 107. Then, air containing oxygen exists on the downstream side, and a local battery is formed on the fuel electrode 114a side. As a result, protons are deficient in the electrolyte membrane 104 in the downstream region of the fuel gas channel 107, and a proton concentration gradient is generated in the electrolyte membrane 104. As a result, the potential difference between the catalyst layer 105 and the electrolyte membrane 104 increases, and corrosion of the catalyst-supporting carbon and dissolution of the catalyst metal occur as shown in the following equation (1) in the downstream region.

C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ (1)
In addition, even when the fuel gas is purged with air, for example, when the fuel gas is purged with air, a region where the fuel gas exists and a region where the fuel gas does not exist are generated in the fuel gas flow path 107. It is formed.

Therefore, in the present embodiment, the switch 11a is opened under the condition that the gas in the oxidant gas flow path 8 is replaced from air to fuel gas or from fuel gas to air. As a result, the electrons e ⁻ cannot move between the anode-side divided bodies 17a through the separator 3a on the fuel electrode 14a side and the gas diffusion electrode 6a. Similarly, electrons e− cannot move between the cathode-side separator 3c and the cathode-side divided body 17cc through the gas diffusion electrode 6c. Therefore, the local battery is generated only while the boundary between the fuel gas and the oxidant gas (hydrogen / air front) flows along the respective divided bodies 17a and 17c, and the potential difference is small.

  Thereby, since the local deterioration of the catalyst layer 5 due to the generation of a local battery at the start / stop of the fuel cell stack 1 can be prevented, the durability of the fuel cell stack 1 can be improved.

  Next, the effect of this embodiment will be described.

  The fuel cell system has a catalyst layer 5 on both main surfaces of the electrolyte membrane 4, and a membrane electrode joint formed by disposing the gas diffusion electrode 6a of the fuel electrode 14a and the gas diffusion electrode 6c of the oxidant electrode 14c on the outside thereof. And a separator 3a, 3c provided with a fuel gas channel 7 and an oxidant gas channel 8 for supplying fuel gas and oxidant gas to the gas diffusion electrode 6a and gas diffusion electrode 6c, respectively. A battery 2 is provided. In such a fuel cell system, the gas diffusion electrode 6a, the gas diffusion electrode 6c, and the separators 3a, 3c are divided into a plurality of divided bodies 17a, 17c by the insulating member 10 substantially perpendicular to the flow direction of the fuel gas. It consists of. Thereby, local deterioration of the catalyst layer 5 at the time of starting or stopping can be prevented.

  In the electric circuit connecting the divided body 17 and the external load 12, a switch 11 a is provided for each divided body 17. By opening the switch 11a, the corrosion current flowing between the divided bodies 17 can be cut off when the local battery is generated.

  Next, a second embodiment will be described with reference to FIG. Hereinafter, a description will be given centering on differences from the first embodiment. The electric circuit connecting the divided body 17 and the external load 12 is provided with a coil 11 b for each divided electrode 61.

  A coil 11b is used in place of the switch 11a as means for interrupting the electrical connection between the divided bodies 17 at the time of starting and stopping. Corrosion current due to the generation of local cells at the start / stop of the fuel cell stack 1 occurs in a short time of 1/10 second level. Therefore, by connecting the divided bodies 17 via the coil 11b, it is possible to suppress the electron movement due to the generation of the local battery without requiring complicated control. The size (number of turns) of the coil 11b can be set according to the length of the gas flow paths 7 and 8 along the divided body 17, and is set in advance by experiments or the like here. As a result, it is possible to prevent local deterioration of the catalyst layer 5 due to the generation of local cells when the fuel cell stack 1 is started / stopped, and the durability of the fuel cell stack 1 can be improved.

  Next, a third embodiment will be described with reference to FIG. Hereinafter, a description will be given centering on differences from the first embodiment.

  A diode 11c is used in place of the switch 11a as means for interrupting the electrical connection between the divided bodies 17 at the time of starting and stopping. That is, the diode 11 c is provided for each divided body 17 in the electric circuit connecting the divided body 17 and the external load 12.

  By using the diode 11c, the electron movement to the external load 12 can be ensured, and the electron movement to the other divided body 17 can be prevented. As a result, it is possible to prevent local deterioration of the catalyst layer 5 due to the generation of local cells when the fuel cell stack 1 is started / stopped without requiring complicated control, thereby improving the durability of the fuel cell stack 1. can do.

  Next, a fourth embodiment will be described. Using the fuel cell stack 1 shown in the first embodiment, the switch 11a is switched at the timing shown in FIGS.

  First, switching of the switch 11a at startup will be described with reference to FIG.

  When the fuel cell stack 1 is stopped and stored, the fuel cell stack 1 is connected to the external load 12 and connected to the switch 11a in order to prevent an open circuit voltage. Immediately after start-up, the fuel gas and the oxidant gas are supplied in a state where the switch 11a is opened and the electrical connection between the divided bodies 17 is cut off.

After a predetermined time t _{1 has} elapsed, the switch 11a is connected to start taking out power. The predetermined time t ₁ is a time required until the gas supply is stabilized. Here, the predetermined time t ₁ is a time until the fuel gas reaches the fuel gas passage 7. The predetermined time t ₁ is obtained from the fuel gas flow rate Mf and the fuel electrode total flow path volume V _{c, cell} in the fuel cell stack 1 as follows.

t ₁ = V _{c, cell} / Mf
Alternatively, the time until the fuel gas is distributed may be obtained in advance by an experiment, and this may be set as the predetermined time t ₁ . Alternatively, a hydrogen sensor may be installed on the outlet side of the fuel gas channel 7 and, when hydrogen is detected, it may be determined that the fuel gas has spread to the fuel gas channel 7 and the switch 11a may be connected.

  Next, switching of the switch 11a when stopped will be described with reference to FIG.

During operation of the fuel cell stack 1, the switch 11 a is connected and the external load 12 is connected to extract electric power. When the stop control of the operation of the fuel cell stack 1 is started, the switch 11a is opened. In this state, air is introduced into the oxidant gas passage 8 and the fuel gas passage 7 for purging. And stopping the introduction of air When the predetermined time t ₂ has elapsed exit purge, also stops the operation while preventing an open circuit voltage by connecting the switch 11a.

The predetermined time t ₂ is a time required for the oxidant gas to reach the oxidant gas flow path 8 and the fuel gas flow path 7. For example, it is obtained as follows from the oxidant gas flow rate Mo supplied to the fuel electrode 14a and the fuel electrode total flow path volume V _{c, cell} in the fuel cell stack 1.

t ₂ = V _{c, cell} / Mo
Or by experiment, the fuel gas channel 7 is obtained in advance the time until spread the air, which may be set as the predetermined time t _2. Alternatively, a hydrogen sensor is installed on the outlet side of the fuel gas flow path 7, and when hydrogen is no longer detected, it is determined that the oxidant gas has spread to the fuel gas flow path 7, the purge is terminated, and the switch 11a is connected. May be.

  Next, the effect of this embodiment will be described. Only the effects different from those of the first embodiment will be described below.

  At the time of startup, the supply of fuel gas is started with all the switches 11a opened. Thereby, the corrosion current which flows between the division | segmentation electrodes 61 can be interrupted | blocked at the time of local battery generation | occurrence | production at the time of starting.

  Further, at the time of stop, the air purge of the fuel gas passage 7a is performed with the switch 11a fully opened. Thereby, the corrosion current which flows between the division | segmentation electrodes 61 can be interrupted | blocked at the time of local battery generation | occurrence | production at the time of a stop.

  Next, a fifth embodiment will be described. Hereinafter, a description will be given centering on differences from the first embodiment.

  In the fuel cell stack 1, each of the divided stacks 15 in which the divided bodies 17 are stacked includes the voltage sensor 13. Here, the gas diffusion electrode 6 and the separator 3 of the fuel cell stack 1 are divided into three to be provided with three divided stacks 15, and further, three voltage sensors 13 are provided.

  In starting the fuel cell stack 1, when the switch 11a is opened, the voltage of the unit cell 2 generally increases from about 0V to about 0.95V. In the fuel cell stack 1, the unit cells 2 are stacked, so that the output of the voltage sensor 13 is the sum of the stacks of the unit cells 2. For example, at the time of start-up, supply of fuel gas and oxidant gas is started in a state where the switch 11a is opened. The switch 11a is connected and power extraction is started. Thereby, the holding time of the open circuit voltage state can be reduced as much as possible.

  Similarly, at the time of stop, when air is introduced as a purge gas and then drops to a predetermined voltage, the switch 11a is connected.

  Next, the effect of this embodiment will be described. Only the effects different from those of the first embodiment will be described below.

  Each of the divided stacks 15 formed by laminating a plurality of divided bodies 17 is provided with a voltage sensor 13, and the switch 11 a switches to the external load 12 in order from the divided stack 15 having a voltage at which it is determined that the assumed gas is supplied. 11a is connected. Here, the gas assumed at the time of start-up is fuel gas, and the gas assumed at the time of stop is air. The voltage determined to be supplied refers to a voltage that can be estimated to be a state in which the fuel gas flow path 7 is filled with fuel gas or air. Thereby, the holding time of the open circuit voltage can be shortened, and deterioration of the catalyst layer 5 due to the open circuit voltage can be suppressed.

   In the above embodiment, the gas diffusion electrode 6, the catalyst layer 5, and the separator 3 are all divided, but this is not a limitation, and at least the gas diffusion electrode 6 and the separator 3 are formed in a division.

  Thus, the present invention is not limited to the best mode for carrying out the invention, and various modifications can be made within the scope of the technical idea described in the claims. Not too long.

  The present invention relates to a fuel cell system. In particular, an appropriate effect can be obtained by applying it to a vehicle-mounted fuel cell system that repeatedly starts and stops.

1 is a schematic configuration diagram of a fuel cell system according to a first embodiment. It is a figure which shows the condition of polar battery generation | occurrence | production at the time of starting / stopping. It is a schematic block diagram of the fuel cell system by 2nd Embodiment. It is a schematic block diagram of the fuel cell system by 3rd Embodiment. It is a timing chart of switch change at the time of starting by a 4th embodiment. It is a timing chart of switch change at the time of a stop by a 4th embodiment. It is a schematic block diagram of the fuel cell system by 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Unit cell 3 Separator 31 Split separator 4 Electrolyte membrane 5 Catalyst layer 6 Gas diffusion electrode 61 Split electrode 7 Oxidant gas flow path 8 Fuel gas flow path 10 Insulating member 11a Switch 11b Coil 11c Diode 12 External load 13 Voltage Detection means 15 Divided stack 16 Membrane electrode assembly 17 Divided body

Claims (7)

A membrane electrode assembly comprising a catalyst layer on both main surfaces of the electrolyte membrane, and a fuel gas diffusion electrode and an oxidant gas diffusion electrode disposed on both sides thereof; and
A separator having a gas flow path for supplying fuel gas and oxidant gas to the fuel gas diffusion electrode and oxidant gas diffusion electrode, respectively,
The fuel gas diffusion electrode, the oxidant gas diffusion electrode, and the separator are constituted by a divided body that is divided into a plurality of parts by an insulating member substantially perpendicular to the flow direction of the fuel gas. Battery system.   The fuel cell system according to claim 1, wherein a switch is provided for each of the divided bodies in an electric circuit connecting the divided bodies and an external load.   The fuel cell system according to claim 1, wherein a coil is provided for each of the divided bodies in an electric circuit connecting the divided bodies and an external load.   The fuel cell system according to claim 1, wherein a diode is provided for each of the divided bodies in an electric circuit connecting the divided bodies and an external load.   The fuel cell system according to claim 2, wherein at the time of startup, the supply of fuel gas is started with all the switches open.   3. The fuel cell system according to claim 2, wherein when the operation is stopped, the fuel gas is purged with air while the switch is fully opened. Each of the divided stacks formed by stacking a plurality of the divided bodies is provided with voltage detection means,
The fuel cell system according to any one of claims 2, 5, and 6, wherein the switch is connected to an external load in order from a divided stack having a voltage at which it is determined that an assumed gas is supplied.

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