JP2008041517A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the startability of a fuel cell in a low-temperature environment. <P>SOLUTION: A cathode-side separator 140 has ribs 141, and a plurality of grooves 145 formed on tops of the respective ribs 141. A water-absorbing resin 160 is arranged on each groove 145. The water-absorbing resin 160 absorbs water produced by an electrochemical reaction of this fuel cell. Thereby, the groove 145 is brought into a state that water is always kept therein. Conductive members 150 are arranged on surfaces of the ribs 141 on a gas diffusion layer side to cover the grooves 145. Thereby, moisture included in the water-absorbing resins 160 arranged in the grooves 145 are frozen and expanded in a low-temperature environment to deform the conductive members 150 in the fuel cell 10. As a result, contact resistance between the conductive members 150 and the separator 140 is increased to increase a calorific value, whereby the temperature of the fuel cell 10 can be raised to a value suitable for its operation in a short time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell that generates power by an electrochemical reaction between hydrogen and air.

  Examples of the fuel cell include a polymer electrolyte fuel cell. A polymer electrolyte fuel cell includes a proton conductive electrolyte membrane, a plurality of cells each having a pair of electrode layers (anode, cathode) disposed on both sides of the electrolyte membrane, and a separator sandwiching the electrolyte membrane and electrode layers Configured. A catalyst for promoting an electrode reaction is supported on the electrode. When a fuel gas containing hydrogen is supplied to the anode, the fuel gas is separated into protons and electrons by the catalyst. Protons conduct through the electrolyte membrane and electrons move through the external circuit to the cathode. When an oxidizing gas containing oxygen is supplied to the cathode, the oxidizing gas reacts with protons and electrons to generate water. In this way, current flows as electrons move from the anode to the cathode, and the fuel cell generates electricity.

JP 2004-47149 A JP 2005-293928 A JP 2005-293902 A

  When the electrolyte membrane or catalyst used in the fuel cell is in a low temperature environment (for example, 0 ° C. or lower), the proton conductivity and catalytic activity of the electrolyte membrane are lowered, and the power generation efficiency of the fuel cell is lowered. For this reason, in a low temperature environment, there is a problem that it is necessary for a long time from the start of the fuel cell to the temperature suitable for the operation of the fuel cell.

  The present invention has been made in view of such a problem, and an object of the present invention is to shorten the time until the temperature of the fuel cell rises to an appropriate operating temperature in the start-up process of the fuel cell in a low temperature environment.

  In order to solve at least a part of the problems described above, a first configuration of the present invention provides a fuel cell. A fuel cell according to a first configuration of the present invention includes an electrolyte membrane, an electrode layer that forms a membrane electrode assembly together with electrolyte membranes formed on both surfaces of the electrolyte membrane, and a membrane electrode assembly. The gist is to include a pair of separators formed on a surface facing the joined body and having a protruding portion having a recessed portion at the top, and a conductive member disposed on the recessed portion.

  According to the fuel cell of the first configuration of the present invention, the water generated by the electrochemical reaction is held in the depression formed on the protruding portion of the separator, and is frozen and expanded in a low temperature environment. The space between the separator and the conductive member spreads. As a result, the contact resistance between the separator and the conductive member increases, and the amount of heat generated during power generation of the fuel cell increases, so the time required for the temperature of the fuel cell body to reach the optimum operating temperature can be shortened, and the fuel cell can be started. Can be improved.

  In the fuel cell of the present invention, the projecting portion may form a gas flow path.

  According to the fuel cell of the present invention, since the conductive member is disposed on the protruding portion, the conductive member can be disposed without hindering the flow of gas from the gas flow path to the membrane electrode assembly.

  In the fuel cell of the present invention, a moisture retaining means for retaining moisture may be further provided in the recess.

  According to the fuel cell of the present invention, the evaporation of moisture can be suppressed, and the state in which moisture is always held in the recess can be maintained.

  In the fuel cell of the present invention, the moisture retaining means may include at least one of a resin having a water absorption property or a hydrophilic property and a fiber.

  Since a resin / fiber having water absorption or hydrophilicity can be easily prepared, the fuel cell of the present invention can be easily used for a fuel cell.

  In the fuel cell of the present invention, of the pair of separators, a depression may be formed in the protruding portion of the cathode side separator disposed on the cathode electrode layer side of the membrane electrode assembly.

  In a fuel cell using a proton conductive electrolyte membrane, water is generated in the cathode electrode layer, so that the wet state on the cathode electrode layer side is good. Therefore, according to the fuel cell of the present invention, it is possible to efficiently maintain a state in which moisture is retained in the recessed portion.

  The second configuration of the present invention provides a fuel cell. An electrolyte membrane, an electrode layer that is formed on both surfaces of the electrolyte membrane and forms a membrane electrode assembly together with the electrolyte membrane, a membrane electrode assembly is sandwiched, and a projecting portion is formed on a surface facing the membrane electrode assembly A pair of separators, disposed on at least a part of the top of the projecting portion, have conductivity, and are disposed between the projecting portion and the membrane electrode assembly. And a conductive member.

  According to the fuel cell of the second configuration of the present invention, the water generated by the electrochemical reaction is held on the protruding portion of the separator by the moisture holding means, and is frozen and expanded in a low temperature environment. The holding means and the contact resistance between the moisture holding means and the conductive member are increased. Since the amount of heat generated at the time of power generation by the fuel cell increases due to the increase in contact resistance, the time required for the temperature of the fuel cell body to reach the proper operating temperature can be shortened, and the startability of the fuel cell can be improved.

  The moisture retaining means of the present invention may include at least one of a water-absorbing or hydrophilic resin and fiber.

  According to the fuel cell of the present invention, a resin / fiber having water absorption or hydrophilicity can be easily prepared. Therefore, according to the fuel cell of the present invention, it can be easily used for a fuel cell.

  In the fuel cell according to the present invention, the conductive member and the moisture retaining means are provided between at least the cathode electrode layer of the membrane electrode assembly and the cathode separator disposed on the cathode electrode layer side of the pair of separators. It may be arranged.

  According to the fuel cell of the present invention, since the conductive member and the moisture retaining means can be arranged on the cathode electrode layer side in a good wet state, moisture can be efficiently retained.

  The fuel cell of the present invention may further include a porous gas diffusion layer disposed between the membrane electrode assembly and the separator.

  According to the fuel cell of the present invention, gas diffusion efficiency can be improved, and power generation efficiency can be improved.

  In the present invention, the various aspects described above can be applied by appropriately combining or omitting some of them.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on examples with appropriate reference to the drawings.
A. First embodiment:
A1. Fuel cell schematic configuration:
The configuration of the fuel cell in the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is an exploded perspective view illustrating a schematic configuration of a fuel cell in the first embodiment. FIG. 2 is a cross-sectional view schematically showing an AA cross section of the fuel cell in the first embodiment. In the first embodiment, the manifold for supplying the fuel gas and the oxidizing gas to the fuel cells is omitted. A fuel cell 10 shown in FIG. 1 represents one of a plurality of fuel cells constituting an individual polymer fuel cell.

  As shown in FIG. 1, the fuel cell 10 includes a MEGA 50, separators 130 and 140, and a conductive member 150. The separators 130 and 140 are disposed so as to sandwich the MEGA 50 and the conductive member 150.

  2, the MEGA 50 includes an electrolyte membrane 100, an anode electrode catalyst layer 110 formed on one surface of the electrolyte membrane 100, a cathode electrode catalyst layer 111 formed on the other surface of the electrolyte membrane 100, and each electrode. Gas diffusion layers 120 and 121 are provided outside the catalyst layers 110 and 111.

  The electrolyte membrane 100 is a proton conductive thin film formed of a polymer material, for example, a fluorine resin. For example, Nafion (registered trademark) is used for the electrolyte membrane 100.

  The anode electrode catalyst layer 110 and the cathode electrode catalyst layer 111 are electrodes formed from a material having catalytic activity that promotes an electrochemical reaction. As the material having catalytic activity, for example, materials generally used in solid polymer electrolyte fuel cells such as platinum-supporting carbon and platinum-ruthenium alloy-supporting carbon can be used.

  The gas diffusion layers 120 and 121 are formed of carbon paper or carbon cloth having gas permeability and conductivity. The gas diffusion layers 120 and 121 diffuse fuel gas and oxidizing gas into the electrode catalyst layers 110 and 111.

  Since the separator 130 is disposed on the anode side and the separator 140 is disposed on the cathode side, hereinafter, in the first embodiment, the separator 130 is referred to as the anode side separator 130 and the separator 140 is referred to as the cathode side separator 140.

  The anode separator 130 has an elongated protrusion 131. Hereinafter, in the present embodiment, the protrusion 131 is referred to as a rib 131. In the anode separator 130, a gas flow path 132 is formed by each rib 131.

  The cathode side separator 140 has an elongated protrusion 141. Hereinafter, in the present embodiment, the protruding portion 141 is referred to as a rib 141. In the cathode side separator 140, a gas flow path 142 is formed by each rib 141. The cathode separator 140 further includes a plurality of grooves 145 formed at the top of each rib 141. The groove 145 corresponds to the “dent” of the present application. An enlarged view of the groove 145 is shown together with FIG.

  In each groove 145, a resin / fiber having water absorption or hydrophilicity is arranged. In this embodiment, as shown in the enlarged view X of FIG. 1, a water absorbent resin 160 is disposed. For example, Nafion (registered trademark) can be used as the water absorbent resin 160. The water absorbent resin 160 absorbs water generated in the electrochemical reaction of the fuel cell. As a result, water is always held in the groove 145.

  The conductive member 150 corrodes in the environment within the fuel cell, such as a conductive plate having substantially the same shape as the surface of each rib 141 on the gas diffusion layer side, such as a carbon thin plate, a gold-plated copper plate, or a titanium nitride thin plate. In addition, it has conductivity. As shown in FIGS. 1 and 2, the conductive member 150 is disposed on the gas diffusion layer side surface of the rib 141 so as to cover the groove 145. The thickness of the conductive member 150 is preferably 0.5 mm or less in order to make the fuel cell thin, although it depends on the material to be selected.

  The fuel battery cell 10 according to the first embodiment has the above-described configuration, so that moisture contained in the water absorbent resin 160 disposed in the groove 145 is frozen and expanded in a low temperature environment and becomes conductive. The sex member 150 is deformed. As a result, the contact resistance between the conductive member 150 and the cathode-side separator 140 increases, and the amount of heat generated when the fuel cell 10 is started up increases, so that the temperature of the fuel cell 10 is suitable for operation in a short time. Can rise to temperature.

A2. Regarding temperature rise at startup:
The temperature rise at the start of the fuel cell will be described in detail with reference to FIGS. 3 and 4. FIG. 3A is a plan view schematically showing the cathode side separator 140 and the conductive member 150 in a normal temperature environment in the first embodiment. FIG. 3B is an enlarged plan view showing a portion of a circle Y in FIG. FIG. 4A is a plan view schematically showing the cathode separator 140 and the conductive member 150 in a low temperature environment in the first embodiment. FIG. 4B is an enlarged plan view showing a portion of a circle Z in FIG. FIGS. 3A and 4A are plan views showing a side surface of the cathode separator 140 from the B side shown in FIG.

  As shown in FIG. 3A, in a normal temperature environment, the water-absorbing resin 160 containing moisture is accommodated in the groove 145, and the conductive member 150 is in contact with the rib 141 of the cathode-side separator 140. . Therefore, when the fuel cell is started, the electrons that have moved from the anode-side separator 130 to the cathode-side separator 140 through the external circuit in a normal temperature environment have good conductivity as shown by arrows in FIG. Pass through member 150.

  On the other hand, as shown in FIG. 4A, in a low temperature environment, the moisture contained in the water absorbent resin 160 freezes and expands, causing the conductive member 150 to deform. Due to the deformation of the conductive member 150, the space between the cathode separator 140 and the conductive member 150 is expanded as shown by hatching in FIG. The contact surface with 150 becomes rough and the contact resistance increases. Therefore, when the fuel cell is started, as shown in FIG. 4B, in a low temperature environment, electrons that have moved from the anode side separator 130 to the cathode side separator 140 through the external circuit are shown in FIG. As indicated by the arrow, it cannot move well to 150, and the amount of heat generation increases in the vicinity of the contact surface between the cathode-side separator 140 and the conductive member 150 as compared with the low temperature environment.

  The conductive member 150 deformed by the freezing and expansion of moisture contained in the water absorbent resin 160 returns to its original shape when the frozen ice is melted by the heat generated by the fuel cell.

  According to the fuel cell of the first embodiment described above, by keeping water in the groove formed on the rib of the separator, the contact resistance between the separator and the conductive member increases in a low temperature environment. Since the amount of heat generated during the power generation of the fuel cell increases, the time required for the temperature of the fuel cell body to reach an appropriate operating temperature can be shortened, and the startability of the fuel cell can be improved.

  Further, according to the fuel cell of the first embodiment, since the grooves are formed on the ribs of the cathode-side separator 140 in a good wet state, moisture can be efficiently retained in the grooves.

  Further, according to the fuel cell of the first embodiment, the conductive member 150 is formed in substantially the same shape as the plane of the rib on the gas diffusion layer side, and the rib is arranged on the plane of the rib on the gas diffusion layer side. Therefore, the gas can be circulated satisfactorily without hindering the supply of the oxidizing gas from the gas flow path 142 to the gas diffusion layer.

  Further, according to the fuel cell of the first embodiment, since the water-absorbing / hydrophilic resin or fiber is disposed in the groove, evaporation of moisture held in the groove can be suppressed.

B. Second embodiment:
In the first embodiment, grooves are formed on the ribs of the separator, and moisture is retained in the grooves, thereby increasing the contact resistance between the separator and the conductive member and increasing the amount of heat generation in a low temperature environment. Yes. In the second embodiment, conductive and water-absorbing fibers are disposed between the rib of the separator and the conductive member.

B1. Fuel cell schematic configuration:
A schematic configuration of the fuel cell of the second embodiment will be described with reference to FIG. FIG. 5 is an exploded perspective view showing the fuel cell 20 in the second embodiment.

  As shown in FIG. 5, the fuel battery cell 20 includes a MEGA 50, gas diffusion layers 120 and 121, separators 130 and 240, a conductive member 150, and water absorbent fibers 260. The anode side separator 130 and the cathode side separator 240 are arranged so as to sandwich the MEGA 50, the conductive member 150, and the water absorbent fibers 260. In the second embodiment, the MEGA 50, the anode-side separator 130, and the conductive member 150 have the same configuration as that of the first embodiment, and thus description thereof is omitted.

  The cathode side separator 240 has a plurality of ribs 241 like the cathode side separator 140 of the first embodiment. However, 141 grooves are not formed in the rib 241 of the cathode side separator 240, and the conductive member 150 side of the rib 241 is a flat surface.

  The water-absorbing fibers 260 are conductive and water-absorbing fibers that are formed in an elongated plate shape that is formed in substantially the same shape as the conductive member 150, and the ribs 241 of the cathode-side separator 240 and the conductive member 150. It is arranged so as to be spread between. In this embodiment, the water-absorbing fiber 260 is formed of vapor grown carbon fiber (VGCF) that has been hydrophilized by surface modification using a silane coupling agent. The water absorbing fiber 260 absorbs moisture generated by an electrochemical reaction related to power generation of the fuel cell, and holds moisture between the rib 241 and the conductive member 150.

B2. Regarding temperature rise at startup:
The temperature rise at the start of the fuel cell 20 in the second embodiment will be described. As described above, the water-absorbing fibers 260 are arranged so as to be spread over the ribs 241 and are sandwiched between the conductive member 150 and the cathode-side separator 240, so that the cathode-side separator 140, the water-absorbing fibers 260, the water-absorbing fibers The conductive fiber 260 and the conductive member 150 are substantially in surface contact with each other. Therefore, when the fuel cell is started, in a normal temperature environment, the electrons that have moved from the anode side separator 130 to the cathode side separator 140 through the external circuit pass through the water absorbent fibers 260 and the conductive member 150 satisfactorily.

  On the other hand, in a low temperature environment, moisture contained in the water absorbent fibers 260 freezes and expands, and irregularities occur on the contact surface of the water absorbent fibers 260 with the cathode separator 140 and the contact surface with the conductive member 150. . Due to the unevenness, a gap is formed between the water absorbent fiber 260 and the cathode separator 140. Further, the conductive member 150 is deformed by the unevenness generated in the water absorbent fiber 260, and a gap is generated between the water absorbent fiber 260 and the conductive member 150. Due to the air gaps formed between the water absorbent fibers 260 and the cathode separator 140, and between the water absorbent fibers 260 and the conductive member 150, the respective contact surfaces become rough and the contact resistance increases. Therefore, when the fuel cell is started, in a low temperature environment, electrons that have moved from the anode side separator 130 to the cathode side separator 140 through the external circuit cannot move well to the water absorbent fibers 260 and the conductive member 150. The amount of heat generation in the vicinity of the cathode-side separator 140 increases as compared with that in a normal temperature environment.

  According to the fuel cell of the second embodiment described above, the conductive water-absorbing resin disposed on the ribs of the separator can absorb and hold water, so that the contact between the separator and the conductive member is performed in a low temperature environment. The resistance can be increased, and the amount of heat generated during power generation by the fuel cell can be increased. Therefore, the time required for the temperature of the fuel cell main body to reach the proper operating temperature can be shortened, and the startability of the fuel cell can be improved.

C. Variation:
(1) Although the groove 145 is formed in the rib 141 of the cathode separator 140 in the first embodiment described above, for example, a water receiving portion formed in a concave shape on the rib may be formed. . FIG. 6 is an enlarged view illustrating a part of the rib in the modified example. As shown in FIG. 6, a water receiver 146 is formed on the cathode-side separator 140a of this modification. In the water receiver 146, a water-absorbing resin / fiber may be further disposed. In this way, moisture evaporation can be suppressed and moisture can be efficiently retained. According to this modification, water generated by an electrochemical reaction related to power generation of the fuel cell is held in the water receiver 146 formed on the rib 141 of the cathode separator 140a, and is frozen and expanded in a low temperature environment. To do. Therefore, the contact resistance between the separator and the conductive member can be increased, and the amount of heat generated during power generation of the fuel cell can be increased.

(2) In the first embodiment described above, the separator has ribs. However, for example, the separator may have a plurality of columnar protrusions. FIG. 7 is a perspective view illustrating a cathode-side separator in this modification. As shown in FIG. 7, the cathode-side separator 340 of this modification has a plurality of columnar protrusions 370. The fuel gas flows between the protrusions 370. Each of the projecting portions 370 has a water receiving portion 346. In the water receiver 346, a water-absorbing resin / fiber may be further disposed. In this modification, as shown in FIG. 7, the conductive member 350 is disposed on the protruding portions 370 aligned in the vertical direction. According to this modification, the water generated by the electrochemical reaction related to the power generation of the fuel cell is held in the water receiver 146 formed on the protruding portion 370 of the cathode separator 340 and frozen in a low temperature environment.・ Expands. Therefore, the contact resistance between the separator and the conductive member can be increased.

(3) In the second embodiment described above, the water-absorbing fibers 260 are disposed on the ribs 241 of the cathode-side separator 240. For example, the water-absorbing fibers formed in the same shape as the separator are used as the cathode-side separator 240. You may arrange | position between the electroconductive members 150. FIG. FIG. 8 is an exploded perspective view illustrating the configuration around the cathode-side separator of this modification. As shown in FIG. 8, water-absorbing fibers 260 a formed in the same rectangular shape as the cathode-side separator 240 are disposed between the cathode-side separator 240 and the conductive member 150. In this modification, it is preferable that the water absorbent fibers 260a have a sufficient porosity so as not to hinder the flow of gas. According to this modification, it is not necessary to precisely dispose the water absorbent fibers 260a on the respective ribs, and can be easily disposed, so that the load on the manufacturing process of the fuel cell can be reduced.

(4) In the first and second embodiments described above, the same number of conductive members 150 as the number of ribs are prepared. For example, a single conductive plate is prepared and the separator gas is prepared. The conductive member may be formed by forming a through hole in a region corresponding to the flow path. A conductive member according to the modification will be described with reference to FIG. FIG. 9 is a perspective view illustrating a conductive member in the present modification. As shown in FIG. 9, the conductive member 150a of this modification has a through hole 170 at a portion corresponding to the gas flow path of the separator when the separator and the conductive member 150a are overlapped. When the separator and the conductive member 150a are superposed, the hatched portions in FIG. 9 are located on the ribs of the separator. The gas flowing through the gas flow path is satisfactorily supplied to the MEGA 50 through the through hole 170 without being obstructed by the conductive member 150a. According to this modification, since the conductive member has a single plate shape, the conductive member can be easily disposed at the correct position, that is, on the rib of the separator, so that the manufacturing load can be reduced.

(5) In the first and second embodiments described above, the water-absorbing resin / fiber and the conductive member are disposed between the cathode separator and the MEGA 50, but the wet state near the anode is also good. Therefore, the water-absorbing resin / fiber and the conductive member and the conductive member may be disposed on the anode separator.

  Although various embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to these embodiments and can take various configurations without departing from the spirit of the present invention.

The disassembled perspective view explaining schematic structure of the fuel cell in 1st Example. Sectional drawing explaining the fuel battery cell in 1st Example. Sectional drawing which shows typically the cathode side separator and electroconductive member in the normal temperature environment in 1st Example. Sectional drawing which shows typically the cathode side separator and electroconductive member in the low temperature environment in 1st Example The disassembled perspective view which shows the fuel cell in 2nd Example. The enlarged view which illustrates a part of rib in a modification. The disassembled perspective view which illustrates the structure of the cathode side separator periphery in a modification. The disassembled perspective view which illustrates the structure of the cathode side separator periphery in a modification. The perspective view which illustrates the electroconductive member in a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20 ... Fuel cell 100 ... Electrolyte membrane 110 ... Anode electrode catalyst layer 111 ... Cathode electrode catalyst layer 120, 121 ... Gas diffusion layer 130 ... Anode side separator 140, 140a, 240, 340 ... Cathode side separator 131, 141, 241 ... Ribs 132 and 142 ... Gas flow paths 145 ... Grooves 146 and 346 ... Water receiving parts 150, 150a and 350 ... Conductive members 160 ...

Claims (10)

A fuel cell,
An electrolyte membrane;
An electrode layer formed on both surfaces of the electrolyte membrane and forming a membrane electrode assembly together with the electrolyte membrane;
Sandwiching the membrane electrode assembly, formed on the surface facing the membrane electrode assembly, a separator having a projecting portion having a depression at the top;
And a conductive member disposed on the recess. The fuel cell according to claim 1, wherein
The protrusion is a fuel cell that forms a gas flow path. The fuel cell according to claim 1 or 2, further comprising:
A fuel cell comprising a moisture retaining means for retaining moisture in the recess.   The fuel cell according to claim 2, wherein the moisture retaining means includes a resin having water absorption or hydrophilicity.   The fuel cell according to claim 2, wherein the moisture retaining means includes a fiber having water absorption or hydrophilicity. A fuel cell according to any one of claims 1 to 5,
The hollow portion is formed on the protruding portion of the cathode-side separator disposed on the cathode electrode layer side of the membrane electrode assembly among the pair of separators,
The fuel cell, wherein the conductive member is disposed on the depression of the cathode separator. A fuel cell,
An electrolyte membrane;
An electrode layer formed on both surfaces of the electrolyte membrane and forming a membrane electrode assembly together with the electrolyte membrane;
A pair of separators sandwiching the membrane electrode assembly and having a protruding portion formed on the surface facing the membrane electrode assembly;
A moisture retaining means disposed on at least a part of the top of the protruding portion, having electrical conductivity and retaining moisture;
A fuel cell comprising: a conductive member disposed between the protruding portion and the membrane electrode assembly.   The fuel cell according to claim 7, wherein the moisture retaining means includes a fiber having water absorption or hydrophilicity. The fuel cell according to claim 7 or 8, wherein
The conductive member and the moisture retaining means are disposed at least between a cathode electrode layer of the membrane electrode assembly and a cathode side separator disposed on the cathode electrode layer side of the pair of separators. A fuel cell. The fuel cell according to any one of claims 1 to 9, further comprising:
A fuel cell comprising a porous gas diffusion layer disposed between the electrode layer and the separator.

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