Separators and fuel cells used in fuel cells

Abstract

The present invention provides a separator for use in fuel cells that suppresses the backflow of water from the fuel gas exhaust manifold port into the fuel gas flow path. [Solution] The separator used in the fuel cell has a manifold hole for supplying fuel gas, The fuel gas includes a manifold hole for discharging fuel gas, and a fuel gas flow path system for circulating the fuel gas to the power generation section of the fuel cell, comprising: a first flow path section that directs the fuel gas from the supply manifold hole toward the power generation section; a second flow path section that supplies the fuel gas to the power generation section opposite to the power generation section; and a third flow path section that directs the fuel gas from the power generation section toward the discharge manifold hole. The third flow path section is a low-hydrophilic flow path located near the discharge manifold hole, and comprises a low-hydrophilic flow path having a low-hydrophilic surface that is lower than the surface of other flow paths in the adjacent gas flow path system.

Description

Technical Field

[0001] The present disclosure relates to a separator used in a fuel cell and a fuel cell.

Background Art

[0002] For example, a fuel cell such as a polymer electrolyte fuel cell (PEFC) is configured by laminating a power generation unit, which is a membrane electrode gas diffusion layer composite (MEGA) in which a polymer electrolyte membrane is sandwiched between an anode and a cathode, via a separator.

[0003] The separator on the anode side of the MEGA is formed with a fuel gas supply manifold hole for supplying fuel gas to the MEGA, a fuel gas discharge manifold hole, and a groove serving as an anode gas flow path for guiding anode gas to the anode side gas diffusion layer.

[0004] When water is generated in the MEGA during operation of the fuel cell. For example, in order to effectively discharge the water generated at the anode or the like, there is a technique of subjecting the fuel gas flow path to a hydrophilic treatment so as to discharge it from the discharge manifold hole together with the fuel gas (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, for example, at the time of operation stop or the like, generated water may flow backward from the vicinity of the fuel gas discharge manifold hole into the fuel gas flow path toward the MEGA side due to capillary action or the like. Leaving the MEGA exposed to the generated water in such a state may cause a decrease in the power generation performance of the fuel cell.

[0007] This specification provides a fuel cell in which the backflow of water (generated water) from the fuel gas discharge manifold hole of the separator into the fuel gas flow path is suppressed.

[0008] The technology disclosed herein is embodied in a separator for use in a fuel cell. The separator comprises a fuel gas supply manifold hole, a fuel gas discharge manifold hole, and a fuel gas flow path system for circulating the fuel gas to the power generation section of the fuel cell, the fuel gas flow path system comprising: a first flow path section that directs the fuel gas from the supply manifold hole toward the power generation section; a second flow path section that supplies the fuel gas to the power generation section opposite to the power generation section; and a third flow path section that directs the fuel gas from the power generation section toward the discharge manifold hole. The third flow path section comprises a low-hydrophilic flow path located near the discharge manifold hole, the low-hydrophilic flow path having a low-hydrophilic surface that is lower than the surface of other adjacent flow paths in the gas flow path system.

[0009] With this separator, when water around the discharge manifold hole reaches the low-hydrophilic channel, its low-hydrophilic surface prevents water movement based on capillary action within the low-hydrophilic channel. Therefore, when the fuel cell is stopped, the phenomenon of water flowing back towards the power generation section is suppressed or avoided. On the other hand, in channels other than the low-hydrophilic channel, water discharge is promoted when the fuel cell is running. Therefore, exposure of the separator and power generation section to water is suppressed or avoided both during operation and when the fuel cell is stopped. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows the relationship between the MEGA and separator in a fuel cell. [Figure 2] This is a diagram showing a cross-section of MEGA. [Figure 3] This diagram shows the surface of the separator corresponding to the MEGA fuel gas. [Modes for carrying out the invention]

[0011] A separator for use in a fuel cell disclosed herein comprises a fuel gas supply manifold hole, a fuel gas discharge manifold hole, and a fuel gas flow path system for circulating the fuel gas to a power generation section of the fuel cell, the fuel gas flow path system comprising: a first flow path section that directs the fuel gas from the supply manifold hole toward the power generation section; a second flow path section that supplies the fuel gas to the power generation section opposite to the power generation section; and a third flow path section that directs the fuel gas from the power generation section toward the discharge manifold hole, wherein the third flow path is a low-hydrophilic flow path located near the discharge manifold hole and has a low-hydrophilic surface that is lower than the surface of other flow paths in the adjacent gas flow path system.

[0012] In another embodiment of the separator, the first, second, and third channel portions of the separator, other than the low-hydrophilic channel, may have surfaces that have been treated to be hydrophilic. In this embodiment, the low-hydrophilic channel is given a low-hydrophilic surface by not being treated to be hydrophilic. This results in a separator that can be manufactured easily and at low cost.

[0013] Another embodiment of the separator may provide the discharge manifold hole in the fuel cell at a position corresponding to the vicinity of one corner of the lower end of the separator in the direction of gravity, and the low hydrophilic flow path at a position corresponding to the vicinity of the lower end of the third flow path in the direction of gravity. In this embodiment, by providing the low hydrophilic flow path on the lower end side in the direction of gravity, water is concentrated in the low hydrophilic flow path on the lower end side in the direction of gravity due to gravity, thereby more effectively suppressing or avoiding backflow of water.

[0014] Another embodiment of the separator may include a stainless steel substrate. Fe ions may leach from the stainless steel substrate. In this embodiment, even if Fe ions leach from the stainless steel, the water containing Fe ions is prevented from reaching the power generation section, particularly the electrolyte membrane. Therefore, even when using a low-cost stainless steel substrate, degradation of the electrolyte membrane due to the Fenton reaction by Fe ions can be effectively suppressed.

[0015] A fuel cell disclosed herein may be a fuel cell comprising any of the separators described above. With this fuel cell, water discharge is promoted during operation of the fuel cell, and backflow of water from the discharge manifold hole is suppressed or avoided when the fuel cell is stopped. As a result, deterioration of the power generation unit due to water or components that may be contained in the water is suppressed.

[0016] In this specification, the fuel cell is not particularly limited, but for example, a polymer electrolyte fuel cell (PEFC) may be preferred. Furthermore, the fuel cell can employ various cooling methods, such as cooling with a liquid refrigerant like water.

[0017] Hereinafter, the fuel cells disclosed herein will be described with reference to the drawings as appropriate. Figure 1 shows an exploded view of the MEA-encapsulated resin composite (hereinafter also simply referred to as the composite) 4 that constitutes the cell 2 of a fuel cell which is a PEFC, and the two separators 12a and 12b that sandwich it. Figure 2 shows an enlarged view of the cross section along line II-II in Figure 1. Figure 3 shows a view of separator 12a from the side opposite to the fuel electrode side of the MEA 4.

[0018] Figure 1 shows the structure of cell 2, which constitutes fuel cell 1. Cell 2 comprises a membrane electrode and gas diffusion layer assembly (MEGA) 4 and separators 12a and 12b that are in contact with the MEGA 4. In cell 2, the MEGA 4 and separators 12a and 12b are stacked along a third direction Z, which is perpendicular to the first direction X, which is the direction of gravity in Figure 1. A stack 1a is formed by stacking an appropriate number of cells 2 along the third direction Z.

[0019] As shown in Figure 2, MEGA4 comprises a membrane electrode assembly (MEA) 6 and gas diffusion layers 8a and 8b on its surfaces 6a and 6b, respectively, which are diffusion layers for fuel gas and oxidizer gas. The membrane electrode assembly 6, although not shown, is bonded so that an electrolyte membrane is sandwiched between the fuel electrode and the air electrode.

[0020] The electrolyte membrane is, for example, a proton-conducting ion-exchange membrane formed from a solid polymer material. The fuel electrode and air electrode are both made of known materials. Gas diffusion layers 8a and 8b are provided for the fuel electrode and air electrode of MEA6, respectively. These gas diffusion layers 8a and 8b are formed from a conductive material such as a gas-permeable carbon porous body. MEGA4 to MEA6 are examples of power generation units as described herein.

[0021] As shown in Figure 1, MEGA4 is held in place by a frame 10 that surrounds it. The frame 10 is, for example, a plate-like body made of resin, and holds MEGA4 in place through an opening in its center.

[0022] The separators 12a and 12b are, for example, plate-like members having stainless steel substrates 13a and 13b. On the surfaces of the stainless steel substrates 13a and 13b, conductive layers made of a conductive material such as carbon are formed. On a surface 14a of the separator 12a facing the fuel electrode side of MEGA4, a fuel gas flow path system 20a for allowing a fuel gas to flow between the separator 12a and the gas diffusion layer 8a is provided. On a surface 14b of the separator 12b facing the oxygen electrode side of MEGA4, an oxidant gas flow path system 20b for allowing an oxidant gas to flow between the separator 12b and the gas diffusion layer 8b is provided. The fuel gas flow path system 20a and the oxidant gas flow path system 20b will be described in detail later.

[0023] The surfaces of the separators 12a and 12b that do not face MEGA4 are joined to the separators 12b and 12a of other cells 2 that are laminated adjacent to each other.

[0024] The stack 1a in which such cells 2 are laminated includes a fuel gas supply manifold 100 and a fuel gas discharge manifold 102 for allowing hydrogen, which is a fuel gas, to flow through MEGA4. Further, the stack 1a includes an oxidant gas supply manifold 200 and an oxidant gas discharge manifold 202 for allowing oxygen or air, which is an oxidant gas, to flow through MEGA4. Furthermore, the stack 1a includes a coolant supply manifold 300 and a coolant discharge manifold 302 for allowing a coolant such as water to flow to cool the cells 2.

[0025] Corresponding to such manifolds 100, 102, 200, 202, 300, and 302, the separator 12a includes a fuel gas supply manifold hole 100a, a discharge manifold hole 102a, an oxidant gas supply manifold hole 200a, a discharge manifold hole 202a, a coolant supply manifold hole 300a, and a discharge manifold hole 302a.

[0026] Furthermore, the separator 12b and the frame are also provided with manifold holes 100b, 102b, 200b, 202b, 300b, exhaust 302b, and manifold holes 100c, 102c, 200c, 202c, 300c, and 302c, corresponding to these manifolds 100, 200, and 300.

[0027] Next, with reference to Figure 3, the fuel gas flow path system 20a in the separator 12a will be described. As shown in Figure 3, the fuel gas flow path system 20a includes a first flow path section 22 that directs fuel gas from the supply manifold hole 100a toward the MEGA 4, a second flow path section 24 that supplies fuel gas to the MEGA opposite the MEGA 4, and a third flow path section 26 that directs fuel gas from the MEGA 4 toward the discharge manifold hole 102a. This fuel gas flow path system 20a is formed by bending a stainless steel base material 13a into an uneven shape. These flow paths are formed in a concave shape that opens toward the MEGA 4 in the direction of the paper in Figure 3.

[0028] The first flow path section 22 is formed between a supply manifold hole 100a formed near the upper end A in the direction of gravity of the separator 12a and one edge 28 in the second direction Y of the MEGA 4. The first flow path section 22 has a plurality of first flow paths 22a. The plurality of first flow paths 22a are formed from the supply manifold hole 100a toward the edge 28 of the MEGA 4. The plurality of first flow paths 22a can be arranged in any pattern so as to guide the fuel gas to the MEGA 4. That is, each first flow path 22a may be a single first flow path 22a that extends continuously to the edge 28 or its vicinity in any pattern, or the plurality of first flow paths 22a may be arranged in any pattern so as to be close enough to guide the fuel gas to the MEGA 4 toward the edge 28 or its vicinity.

[0029] The second flow channel section 24 is formed to face the MEGA 4. The second flow channel section 24 has a plurality of second flow channels 24a. The plurality of second flow channels 24a are formed to extend from the edge 28 or its vicinity to the edge 30 or its vicinity. Each second flow channel 24a, like the first flow channel 22a, has a plurality of second flow channels 24a arranged in any pattern so that fuel gas can be supplied to the MEGA 4.

[0030] The third flow channel section 26 is formed between the edge 30 of the MEGA 4 and the discharge manifold hole 102a. The discharge manifold hole 102a is formed near the corner B at the lower end in the direction of gravity of the separator 12a. The third flow channel section 26 has a plurality of third flow channels 26a. The plurality of third flow channels 26a are formed from the edge 30 of the MEGA 4 or its vicinity toward the opening edge of the discharge manifold hole 102a or its vicinity. Typically, they are formed in a comb-like pattern toward the edge 30 of the MEGA 4 toward the opening edge of the discharge manifold hole 102a. The plurality of third flow channels 26a are arranged in an arbitrary pattern so as to guide the fuel gas from the MEGA 4 to the discharge manifold hole 102a, similar to the first flow channel 22a.

[0031] The third flow channel section 26 has a low-hydrophilic flow channel 40 in part. The low-hydrophilic flow channel 40 is a flow channel or a portion thereof that has a low-hydrophilic surface with lower hydrophilicity than the other parts excluding the low-hydrophilic flow channel 40. The low-hydrophilic flow channel 40 is one or more third flow channels 26a or a portion thereof that are closest to the lower end in the direction of gravity of the third flow channel section 26. There may be one or more low-hydrophilic flow channels 40. The low-hydrophilic flow channel 40 only needs to have a low-hydrophilic surface in at least a portion of the flow channel range extending from the vicinity of the opening edge of the discharge manifold hole 102a of the third flow channel section 26 to the edge 30 of the MEGA 4. The low-hydrophilic surface may be only a portion of the vicinity of the discharge manifold hole 102a of a continuous low-hydrophilic flow channel 40.

[0032] The low-hydrophilicity channel 40 suppresses the backflow of water from the discharge manifold hole 102a. For this reason, the low-hydrophilicity channel 40 has lower hydrophilicity compared to the third channel section 26 and / or the second channel section 24 adjacent to the low-hydrophilicity channel 40 in the fuel gas flow path system 20a.

[0033] For example, the water contact angle of the low-hydrophilic channel 40 is smaller than the water contact angle of the adjacent third channel section 26 and / or second channel section 24. The water contact angles of the channels of the third channel section 26 and / or second channel section 24 are greater than 70°, 75° or more, 80° or more, 85° or more, and 88° or more, while the water contact angles of at least a portion of the third channel section 26 and / or second channel section 24 adjacent to the low-hydrophilic channel 40 are 50° or less, 40° or less, 30° or less, and 28° or less.

[0034] The contact angle of water can be measured using the following method. The measuring device is a camera-equipped instrument that reads the angle of the liquid dropped onto the surface to be measured. The liquid used is pure water (ion-exchanged water), in a volume of 0.8 to 1.0 μl, and is dropped onto the surface to be measured using a wet-liquid method. After 10 seconds have elapsed since dropping, the contact angle of the droplet is read by the camera-equipped instrument. The contact angle measurement is performed on a separator 12a that is clean enough to accurately measure the contact angle of water in the low-hydrophilic channel 40. For example, the separator 12a should be washed by a standard method and the measurement should be performed within 24 hours. To maintain surface cleanliness until measurement, it should be stored in an atmosphere isolated from in-process work, such as in a case with a lid or a desiccator. The contact angle is measured as the average value of the contact angles at multiple points.

[0035] The low-hydrophilic channel 40 can be formed in the fuel gas flow path system 20a of the separator 12a near the discharge manifold hole 102a, having a low-hydrophilic surface lower than the surface of the adjacent fuel gas flow path system 20a. Specifically, the low-hydrophilic channel 40 is formed by performing a hydrophilization treatment on the conductive film on the surface 14 of the stainless steel substrate 13a in the area other than the low-hydrophilic channel 40. In this way, hydrophilization and partial dehydration of the fuel gas flow path system 20a can be achieved simultaneously. A conductive layer is formed on the surface of the fuel gas flow path system 20a of the stainless steel substrate 13a. The hydrophilization treatment is a treatment that increases hydrophilicity by adding or increasing hydrophilic groups (OH, CHO, COOH, etc.) to the surface of the conductive layer using active oxygen generated by ultraviolet irradiation. Such a hydrophilization treatment can be performed, for example, by irradiating the low-hydrophilic channel 40 with ultraviolet light while shielding it with a mask that does not transmit ultraviolet light. Furthermore, such a hydrophilization treatment can be performed, for example, after the formation of the fuel gas flow path system 20a.

[0036] Furthermore, the low-hydrophilic channel 40 can be created by various methods, including not performing any hydrophilic treatment. Those skilled in the art will know that this type of hydrophilization treatment can also be performed by, for example, ozone treatment, plasma treatment, heat treatment, etc.

[0037] The other separator 12b may be equipped with a known oxidizer gas flow path system 20b. A stack 1a in which cells 2 equipped with such separators 12a and 12b are stacked can be provided as a fuel cell 1 assembled together with other known elements.

[0038] As described above, the separator 12a suppresses or prevents backflow of water (generated water) at the fuel electrode of MEGA4, thereby suppressing or preventing problems caused by the separator and MEGA4, especially the electrolyte, being exposed to water.

[0039] Furthermore, in the separator 12a described above, various modifications known for separators for fuel cells can be applied, as long as they do not interfere with the effect of the low-hydrophilic channel 40. For example, the low-hydrophilic surface of the low-hydrophilic channel 40 may be formed by applying a layer containing a water-repellent compound such as a silicon resin or fluororesin, or by applying a water-repellent fine uneven surface. In addition, although the separator 12a is provided with a stainless steel base material 13a, it is not limited to this, and a base material containing a known resin material can be used. Furthermore, the separator 12a may be provided with various intermediate layers in addition to the conductive layer.

[0040] According to the disclosure in the specification, the following aspects are included: [1] A separator used in a fuel cell, A manifold port for supplying fuel gas, The aforementioned fuel gas discharge manifold hole, A fuel gas flow path system for circulating the fuel gas to the power generation section of the fuel cell, comprising: a first flow path section that directs the fuel gas from the supply manifold hole toward the power generation section; a second flow path section that supplies the fuel gas to the power generation section opposite to the power generation section; and a third flow path section that directs the fuel gas from the power generation section toward the discharge manifold hole, Equipped with, The separator comprises a third flow channel, which is a low-hydrophilic flow channel located near the discharge manifold hole, and which has a low-hydrophilic surface that is lower than the surface of other flow channels in the adjacent gas flow channel system. [2] The separator according to [1], wherein the first channel portion, the second channel portion, and the third channel portion of the separator, other than the low hydrophilic channel portion, have surfaces that have been treated to be hydrophilic. [3] The separator according to [1] or [2], wherein the separator is provided with the discharge manifold hole at a position corresponding to the vicinity of one corner of the lower end of the separator in the direction of gravity within the fuel cell, and the low hydrophilic flow path is provided at a position corresponding to the vicinity of the lower end of the third flow path in the direction of gravity. [4] The separator comprises a stainless steel base material. The separator according to any one of [1] to [3]. A fuel cell comprising a separator as described in any of [5][1] to [4]. [6] A method for manufacturing a separator used in a fuel cell, The separator comprises a fuel gas supply manifold hole, a fuel gas discharge manifold hole, and a fuel gas flow path system for circulating the fuel gas to the power generation section of the fuel cell, the fuel gas flow path system comprising: a first flow path section that directs the fuel gas from the supply manifold hole toward the power generation section; a second flow path section that supplies the fuel gas to the power generation section opposite to the power generation section; and a third flow path section that directs the fuel gas from the power generation section toward the discharge manifold hole; and the separator comprises a fuel gas flow path system, With respect to the flow path system of the separator, a step of forming a low-hydrophilic flow path having a low-hydrophilic surface that is lower than the surface of the adjacent fuel gas flow path system, near the discharge manifold hole of the third flow path, A manufacturing method that includes the following features. [7] The manufacturing method according to [6], wherein the step of forming the low hydrophilic channel is a step of hydrophilizing the surface of the fuel gas channel system while shielding the area corresponding to the low hydrophilic channel. [8] The manufacturing method according to [6], wherein the hydrophilization treatment includes ultraviolet irradiation.

[0041] Although embodiments have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0042] 1 Fuel cell, 1a Stack, 2 Cell, 4 MEGA, 6 MEA, 8a Fuel gas diffusion layer, 8b Oxidizer gas diffusion layer, 10 Flame, 12a, 12b Separator, 13a, 13b Stainless steel substrate, 14a Surface of separator 12a facing MEGA, 20a Fuel gas flow path system, 22 First flow path section, 24 Second flow path section, 26 Third flow path section, 40 Low hydrophilic flow path

Claims

1. A separator used in fuel cells, A manifold port for supplying fuel gas, The aforementioned fuel gas discharge manifold hole, A fuel gas flow path system for circulating the fuel gas to the power generation section of the fuel cell, comprising: a first flow path section that directs the fuel gas from the supply manifold hole toward the power generation section; a second flow path section that supplies the fuel gas to the power generation section opposite to the power generation section; and a third flow path section that directs the fuel gas from the power generation section toward the discharge manifold hole, Equipped with, The third flow path is a low-hydrophilic flow path located near the discharge manifold hole, and the separator comprises the low-hydrophilic flow path having a low-hydrophilic surface that is lower than the surface of other flow paths in the adjacent fuel gas flow path system.

2. The separator according to claim 1, wherein the first channel portion, the second channel portion, and the third channel portion of the separator, other than the low hydrophilic channel portion, have surfaces that have been treated to be hydrophilic.

3. The separator according to claim 2, wherein the separator is provided with the discharge manifold hole at a position corresponding to the vicinity of one corner of the lower end of the separator in the direction of gravity within the fuel cell, and the low hydrophilic flow path is provided at a position corresponding to the vicinity of the lower end of the third flow path in the direction of gravity.

4. The separator according to claim 3, wherein the separator comprises a stainless steel base material.

5. A fuel cell comprising a separator according to any one of claims 1 to 4.

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