JP2015018661A - Separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the performance of a conventional separator for fuel cell furthermore.SOLUTION: In the separators 3, 4 for fuel cell forming a gas flow channel and a conductive path between a membrane electrode assembly 2 and the separators, a rough surface region 5 having a surface of fine uneven shape subjected to roughening is provided, at least partially, on a principal surface facing the membrane electrode assembly 2. Conductivity between the membrane electrode assembly 2 and the separators is enhanced by increasing the contact area with the membrane electrode assembly 2 by the fine uneven shape of the rough surface region 5.

Description

  The present invention relates to a fuel cell separator used for constituting a single cell together with a membrane electrode assembly.

  Conventional fuel cell separators include those described in Patent Document 1, for example. The fuel cell separator described in Patent Document 1 has a metal base layer and a conductive carbon layer located on at least one main surface of the metal base layer. And said separator ensures the outstanding electroconductivity by making the intensity ratio of D band peak intensity measured by the Raman scattering light analysis of a conductive carbon layer and G band peak intensity 1.3 or more. However, the corrosion resistance is further improved.

JP 2010-153353 A

  This type of fuel cell separator forms a single cell together with a membrane electrode assembly, and further stacks a plurality of single cells to form a fuel cell. In such a fuel cell, in order to improve the performance of the entire battery, it is very important to improve the performance of the single cell and its components, that is, the components such as the separator described in Patent Document 1. .

  The present invention has been made in view of the above-described conventional situation, and is a fuel cell separator that constitutes a single cell together with a membrane electrode assembly, and can improve conductivity between the membrane electrode assembly. It aims at providing the separator for fuel cells.

  The fuel cell separator according to the present invention forms a gas flow path and a conductive path between the membrane electrode assembly. This separator for a fuel cell has a structure having a rough surface area in which the surface is made fine irregularities by roughening treatment on at least a part of the main surface facing the membrane electrode assembly. As a means to solve.

  The fuel cell separator of the present invention partially contacts the membrane electrode assembly and forms a conductive path with the membrane electrode assembly. At this time, the surface is finely uneven by roughening treatment. Since the rough surface region is formed into a shape, the contact area with the membrane electrode assembly is increased by the fine uneven shape, and the conductivity between the membrane electrode assembly can be improved.

FIG. 2 is a perspective view (A) of a fuel cell stack and a perspective view (B) in an exploded state for explaining a fuel cell stack structure of the present invention. It is the top view (A) which shows the single cell shown in FIG. 1 in the decomposition | disassembly state, and sectional drawing (B) of a single cell. It is a top view of the separator in a 1st embodiment. It is a graph which shows the relationship between roughening processing time and surface roughness. It is graph (A) which shows the relationship between an electrical resistance and a surface pressure, and explanatory drawing (B) which shows the measuring apparatus of an electrical resistance. It is the graph (A) which shows the relationship between the current density in 2nd Embodiment, and a gas flow path, and the top view (B) of a separator. It is the graph (A) which shows the relationship between the current density in 3rd Embodiment, and a gas flow path, and the top view (B) of a separator.

<First Embodiment>
As shown in FIG. 1B, the fuel cell stack FS shown in FIG. 1 includes at least two cell modules M in which a plurality of single cells C as power generation elements are stacked and integrated, and the cell module M And a seal plate P interposed therebetween. The unit cell C and the seal plate P in the illustrated example each have a rectangular plate shape having substantially the same vertical and horizontal dimensions. In FIG. 1B, two cell modules M and one seal plate P are shown, but in reality, a larger number of cell modules M and seal plates P are stacked.

  The fuel cell stack FS has end plates 56A and 56B arranged at both ends in the stacking direction of the cell modules M, and fastened to the stacking end surfaces (upper and lower surfaces in FIG. 1) on the long side of the single cell C. The plates 57A and 57B are provided, and the reinforcing plates 58A and 58B are provided on the laminated end surface on the short side. Each of the fastening plates 57A, 57B and the reinforcing plates 58A, 58B has a size over the entire length in the stacking direction of the stacked body A composed of the cell module M and the seal plate P, and is connected to both end plates 56A, 56B by bolts (not shown). .

  In this way, the fuel cell stack FS has a case-integrated structure as shown in FIG. 1A. Each cell module M and the seal plate P are constrained and pressurized in the stacking direction, and each unit cell C is predetermined. In order to maintain good gas sealing performance and electrical conductivity.

  As shown in FIG. 2, the single cell C has a structure in which the membrane electrode assembly 2 is sandwiched between separators 3 and 4 on the anode side and the cathode side. The membrane electrode assembly 2 of this embodiment integrally has a resin frame 1 around it. Each of the frame 1 and the separators 3 and 4 has a rectangular plate shape having substantially the same vertical and horizontal dimensions.

  The frame 1 is integrated with the membrane electrode assembly 2 by resin molding. The membrane electrode assembly 2 is arranged at the center thereof, and three manifold holes H1 to H6 are provided at both ends on the short side. Are arranged.

  The membrane electrode assembly 2 is generally called an MEA (Membrane Electrode Assembly). As shown in FIG. 2B, for example, an electrolyte layer 11 made of a solid polymer is combined with a fuel electrode layer (anode) 12. It has a structure sandwiched between the air electrode layer (cathode) 13. The fuel electrode layer 12 and the air electrode layer 13 in the illustrated example have catalyst layers 12A and 13A and gas diffusion layers 12B and 13B made of a conductive porous body from the electrolyte layer 11 side. In the membrane electrode assembly 2, anode gas (hydrogen) is supplied to the fuel electrode layer 12 and cathode gas (hydrogen) is supplied to the air electrode layer 13 to generate power by an electrochemical reaction.

  Each of the separators 3 and 4 is a metal plate member having an inverted shape, and is made of stainless steel, for example, and can be formed into an appropriate shape by pressing. Each of the separators 3 and 4 has a central portion corresponding to the membrane electrode assembly 2 formed in a wave shape in a cross section in the short side direction. This wave shape is continuous in the long side direction as shown in the figure.

  Accordingly, each of the separators 3 and 4 has a corrugated convex portion in contact with the membrane electrode assembly 2 and a corrugated concave portion serving as a gas flow path at a central portion corresponding to the membrane electrode assembly 2 in a wave shape. . More specifically, as shown in FIG. 2 (B), the separators 3 and 4 have the top portions (shown in cross section) of the corrugated convex portions 3A and 4A as the gas in the fuel electrode layer 12 and the air electrode layer 13. The diffusion layers 12B and 13B are in contact with each other. Further, the gas flow path composed of the corrugated recesses is formed along the long side direction of the single cell C. Further, the separators 3 and 4 have manifold holes H1 to H6 similar to the manifold holes H1 to H6 of the frame 1 at both ends on the short side.

  In the frame 1 and the separators 3 and 4, the manifold holes H1 to H3 shown on the left side of FIG. 2 are for cathode gas supply (H1), cooling fluid supply (H2), and anode gas discharge (H3). The respective flow paths are formed in communication with each other in the stacking direction. Also, the manifold holes H4 to H6 shown on the right side of FIG. 2 are for anode gas supply (H4), cooling fluid discharge (H5), and cathode gas discharge (H6), and communicate with each other in the stacking direction. The flow path is formed. The supply and discharge may be partially or entirely reversed in positional relationship.

  Further, a seal member S is continuously arranged around the peripheral edge of the frame 1 and the separators 3 and 4 and around the manifold holes H1 to H6. These sealing members also function as adhesives, and airtightly join the frame 1 and membrane electrode assembly 2 to the separators 3 and 4. Further, the seal member S disposed around the manifold holes H1 to H6 has an opening at a corresponding portion in order to supply fluid according to each layer while maintaining the airtightness of each manifold.

  The unit cell C is formed by stacking a predetermined number of cell modules M. At this time, a flow path of the cooling liquid (for example, water) is formed between the adjacent single cells C, and a flow path of the cooling liquid is also formed between the adjacent cell modules M. Therefore, the seal plate P is disposed between the cell modules M, that is, in the flow path of the coolant.

  The seal plate P is formed by molding a single conductive metal plate, is formed in the same rectangular plate shape and in the same size as the above-described single cell C in plan view, and on both short sides, Manifold holes H1 to H6 similar to the single cell C are formed. This seal plate P is provided with a seal member (not shown) around each of the manifold holes H1 to H6, and an outer peripheral seal member 51 and an inner peripheral seal member 52 are provided in parallel on the entire periphery thereof, The outer peripheral seal member 51 prevents rainwater and the like from entering from the outside, and the inner peripheral seal member 52 prevents leakage of the coolant flowing through the flow path between the cell modules M.

  The fuel cell separators 3 and 4 constituting the single cell C form a gas flow path and a conductive path between the membrane electrode assembly 2. The gas flow path is formed by a corrugated concave portion on the surface of the separators 3 and 4 on the membrane electrode assembly 2 side. The conductive path is formed by the corrugated convex portions 3A and 4A of the separators 3 and 4 and the gas diffusion layers 12B and 13B of the membrane electrode assembly 2 in contact therewith.

  Then, as shown in FIG. 3, the separators 3 and 4 have a rough surface region 5 whose surface is finely uneven by roughening treatment on at least a part of the main surface facing the membrane electrode assembly 2. Have. The separators 3 and 4 of this embodiment have a rough surface region 5 in the entire area facing the membrane electrode assembly 2.

  Examples of the roughening treatment include bombardment treatment and etching treatment. In particular, when the separators 3 and 4 are made of stainless steel, an ion bombardment treatment suitable for removing the oxide film on the surface is performed. Done. Further, the surface roughness of the rough surface region 5 is preferably 0.05 μm or more in terms of the center average roughness Ra. As shown in FIG. 4, the surface roughness increases as the treatment time is increased, but a sufficient value of Ra of 0.05 μm or more is obtained by roughening treatment (bombarding treatment) of at least 5 minutes or more. be able to.

  Further, the separators 3 and 4 may be subjected to a hard carbon film treatment after the rough surface region is formed. Examples of the hard carbon coating include DLC (diamond-like carbon).

  The fuel cell separators 3, 4 having the above-described configuration partially contact the membrane electrode assembly 2 and form a conductive path between the membrane electrode assembly 2. At this time, since the separators 3 and 4 have the rough surface region 5 whose surface is made into a fine uneven shape by the roughening treatment, the contact area with the membrane electrode assembly 2 is increased by the fine uneven shape, The contact area with the gas diffusion layers 12B and 13B made of a porous porous material increases. Thereby, the separators 3 and 4 can improve the electroconductivity between the membrane electrode assemblies 2.

  Here, FIG. 5A is a graph showing the relationship between the electrical resistance and the surface pressure, and shows each data of separators having different surface roughness (surface roughness). This electrical resistance was measured with a measuring apparatus shown in FIG. The measuring device includes a pair of electrodes 31 and 32 having respective metal plates 31A and 32A. A separator sample 33 and a pair of conductive members sandwiching the sample 33 are sandwiched between the electrodes 31 and 32. The porous bodies 34 and 34 are interposed.

  The sample 33 of the separator is formed with a rough surface region (5) having a rough surface formed by a roughening treatment, and here, an example in which the surface roughness Ra is 0.05 μm or more, The comparative example whose surface roughness is smaller than this was prepared. The conductive porous body corresponds to the gas diffusion layers 12B and 13B of the membrane electrode assembly 2. A predetermined load was applied between the electrodes 31 and 32 to conduct electricity, and the electrical resistance was measured while changing the surface pressure.

  As a result, as shown in FIG. 5A, in both the example and the comparative example, as the load (surface pressure) increases, the electrical resistance also decreases due to the decrease in contact resistance. The electric resistance was smaller than that of the comparative example, and in particular, the electric resistance on the low surface pressure side was clearly reduced. This is because the contact area with the conductive porous body 34 is increased by the rough surface region (5) of the sample 33.

  Thus, it was confirmed that the conductivity between the separators 3 and 4 and the membrane electrode assembly 2 is improved by the rough surface region 5. Moreover, since the electric resistance on the low surface pressure side is clearly reduced, it was confirmed that high conductivity can be obtained without applying a large surface pressure.

  Further, the separators 3 and 4 have a rough surface area 5 with a surface roughness Ra of 0.05 μm or more, so that a sufficient contact area is ensured between the membrane electrode assembly 2 and high conductivity. Can be maintained. Furthermore, said separators 3 and 4 implement | achieve the further improvement of durability and electroconductivity by performing a hard carbon film process after formation of a rough surface area | region.

  Thereby, the single cell C using the separators 3 and 4 or the fuel cell FS formed by laminating the single cells C can obtain high conductivity in the individual separators 3 and 4, thereby further improving the power generation performance. be able to.

Second Embodiment
The fuel cell separator 4 shown in FIG. 6B is disposed on the cathode side of the membrane electrode assembly, and has rough surface regions 5 and 5 on the inlet side and outlet side in the cathode gas flow direction. That is, the illustrated example is a cathode-side separator 4.

  This separator 4 is suitable for the fuel cell FS in which the humidification of the cathode gas (air) is low. In the fuel cell FS in which the humidification of the cathode gas is low, as shown in FIG. 6A, the current density distribution changes according to the oxygen concentration gradient in the gas flow direction (arrow). That is, the current density increases from the inlet side to the middle part and reaches a peak, and decreases from the middle part to the outlet side. This change in current density is approximately equal to the amount of swelling of the electrolyte membrane 11 constituting the membrane electrode assembly 2 and is also approximately equal to the local surface pressure accompanying the increase or decrease in the amount of swelling. ,

  Accordingly, the separator 4 is provided with rough surface regions 5 and 5 on the inlet side and the outlet side in the flow direction of the cathode gas, thereby increasing the contact area with the membrane electrode assembly 2 on the inlet side and the outlet side. To improve. Thereby, separator 4 can make current density distribution substantially uniform especially in fuel cell FS with low humidification of cathode gas (air).

<Third Embodiment>
The fuel cell separator 4 shown in FIG. 7B is disposed on the cathode side of the membrane electrode assembly, and has a rough surface region 5 on the outlet side in the flow direction of the cathode gas. That is, the illustrated example is a cathode-side separator 4.

  In contrast to the second embodiment, the separator 4 is suitable for the fuel cell FS in which the humidification of the cathode gas (air) is high. In the fuel cell FS in which the humidification of the cathode gas is high, as shown in FIG. 7A, the current density distribution changes according to the oxygen concentration gradient in the gas flow direction (arrow). That is, the current density decreases from the inlet side to the outlet side.

  Therefore, the separator 4 is provided with the rough surface region 5 on the outlet side in the cathode gas flow direction, thereby increasing the contact area with the membrane electrode assembly 2 on the outlet side and improving the conductivity. Thereby, separator 4 can make current density distribution substantially uniform especially in fuel cell FS with high humidification of cathode gas (air).

  The configuration of the separator for a fuel cell according to the present invention is not limited to each of the above embodiments, and the material, shape, size, number, and the like of each member are within the scope not departing from the gist of the present invention. For example, it is possible to form two or more rough surface areas, or to partially vary the roughness.

C single cell 2 membrane electrode assembly 3 anode side separator 4 cathode side separator 5 rough surface region

Claims (5)

A fuel cell separator that forms a gas flow path and a conductive path with a membrane electrode assembly,
A separator for a fuel cell, characterized by having a rough surface region having a rough surface formed by a roughening treatment on at least a part of a main surface facing the membrane electrode assembly.   2. The fuel cell separator according to claim 1, wherein the surface roughness of the rough surface region is 0.05 [mu] m or more in Ra.   The fuel cell separator according to claim 1 or 2, wherein a hard carbon film treatment is applied after the rough surface region is formed.   The fuel cell separator according to any one of claims 1 to 3, wherein the separator for a fuel cell is disposed on the cathode side of the membrane electrode assembly, and has rough surface regions on an inlet side and an outlet side in a cathode gas flow direction. .   The fuel cell separator according to any one of claims 1 to 3, wherein the fuel cell separator is disposed on the cathode side of the membrane electrode assembly and has a rough surface region on the outlet side in the flow direction of the cathode gas.

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