fuel cell device

Abstract

By draining the water that accumulates in the reservoir section of the outermost channel of the multiple channels, the fuel cell system achieves both drainage and moisture retention. [Solution] The fuel cell device comprises an electrolyte membrane, a pair of catalyst layers, a pair of gas diffusion layers, and a pair of separators. The separator has multiple flow channels arranged in a line to supply fluid to the electrolyte membrane covered by the catalyst layers through the gas diffusion layers. At the downstream end of the outermost flow channel closest to the edge of the separator, the fluid velocity decreases, and a reservoir is formed where water generated by the electrochemical reaction at the reaction surface consisting of the electrolyte membrane covered by the catalyst layers accumulates. The catalyst layers defining the reaction surface are formed in a shape that avoids the reservoir formed at the downstream end of the outermost flow channel.

Description

Technical Field

[0001] The present invention relates to a fuel cell device formed by stacking a plurality of fuel cells.

Background Art

[0002] There exists a fuel cell device formed by stacking a plurality of fuel cells, such as a solid polymer fuel cell mounted on a vehicle. In a fuel cell, a membrane electrode assembly (MEA) is sandwiched between an anode electrode to which fuel (hydrogen) is supplied and a cathode electrode to which air (oxygen) is supplied. Electricity and water (or water vapor) are generated by the electrochemical reaction between hydrogen and oxygen in the membrane electrode assembly. Along with the power generation of the fuel cell, water or water vapor (hereinafter referred to as "generated water") is generated on the cathode side. The generated water is necessary for wetting or moisturizing the reaction membrane that undergoes an electrochemical reaction in the membrane electrode assembly. However, when the generated water becomes excessive, the performance of the fuel cell deteriorates. Therefore, it is necessary to drain the water appropriately.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the cathode of a fuel cell, there is a risk of excess water being present due to the movement of water from the anode to the cathode by electroosmosis and the generation of water by electrode reactions at the cathode. Specifically, this can lead to "flooding," where water vapor condenses into water droplets within the porous cathode gas diffusion layer, blocking the pores and hindering gas permeability in the cathode gas diffusion layer. Patent Document 1 discloses a fuel cell that uses a fastening load adjustment means to adjust the fastening load of part or all of the laminate constituting a single fuel cell (single cell) in order to suppress flooding. An electric actuator operated by an external electrical signal is used as the fastening load adjustment means. Specifically, a flooding operation mode is selectively executed, in which the electric actuator is extended to increase the fastening load of the single cell when flooding occurs, and a normal operation mode is selectively executed, in which the electric actuator is shortened to decrease the fastening load of the single cell when flooding is resolved.

[0005] However, accurately detecting the occurrence and resolution of flooding in a single cell is difficult. Repeatedly adjusting the fastening load mechanically applied to the laminate by extending and retracting an electric actuator can easily reduce the mechanical strength of the laminate, potentially leading to a decrease in power generation performance. Furthermore, providing an electric actuator for each individual cell complicates the structure of each cell. If the amount of moisture generated differs from cell to cell, adjusting the fastening load for each cell also becomes complicated.

[0006] To solve the above-mentioned problems, the embodiment of the present invention aims to provide a fuel cell device that can achieve both drainage and moisture retention of a fuel cell by draining the water that accumulates in the water reservoir at the downstream end of the outermost channel of a plurality of channels formed in a separator for supplying fuel or air to the fuel cell. [Means for solving the problem]

[0007] A fuel cell device according to an embodiment of the present invention comprises an electrolyte membrane, a pair of catalyst layers flanking the electrolyte membrane, a pair of gas diffusion layers flanking the electrolyte membrane and the pair of catalyst layers, and a pair of separators flanking the electrolyte membrane, the pair of catalyst layers, and the pair of gas diffusion layers. The pair of separators has a plurality of flow channels aligned to supply fluid to the electrolyte membrane covered by the pair of catalyst layers through the pair of gas diffusion layers. The plurality of flow channels include the outermost flow channels closest to the edges of the pair of separators, and at the downstream end of the outermost flow channels, the fluid velocity decreases, forming a reservoir where water generated by the electrochemical reaction at the reaction surface consisting of the electrolyte layer covered by the pair of catalyst layers accumulates. The pair of catalyst layers defining the reaction surface are formed in a shape that avoids the reservoir formed at the downstream end of the outermost flow channels. [Effects of the Invention]

[0008] Embodiments of the present invention enable the drainage of water accumulating in the water reservoir at the downstream end of the outermost channel of a plurality of channels formed in a separator for supplying fuel or air to a fuel cell, thereby achieving both drainage and moisture retention for the fuel cell. [Brief explanation of the drawing]

[0009] [Figure 1] (A) An exploded perspective view of a fuel cell cell constituting a fuel cell device according to an embodiment of the present invention, and (B) a cross-sectional view of the fuel cell cell. [Figure 2] (A) A plan view of a separator with a flow channel structure that is symmetrical with respect to a reference line, and (B) A plan view of a separator with a flow channel structure that is asymmetrical with respect to a reference line. [Figure 3] This is a plan view showing the relationship between a separator with an asymmetrical IDFF-type flow channel structure and the reaction surface. [Figure 4] This is a plan view showing the relationship between a separator with an asymmetrical IDFF-type flow channel structure and the size and shape of the reaction surface according to the present invention. [Figure 5](A) Cross-sectional view AA of the laminate on the cathode side of the fuel cell, and (B) Cross-sectional view BB of the laminate on the cathode side of the fuel cell. [Figure 6] (A) An enlarged cross-sectional view showing the movement of water on the reaction surface when wet in the moisture-retaining region adjacent to the outermost channel of the fuel cell, and (B) An enlarged cross-sectional view showing the movement of water on the reaction surface when dry in the moisture-retaining region adjacent to the outermost channel of the fuel cell. [Figure 7] (A) A plan view of a separator equipped with a parallel flow channel structure according to a first modified example of the embodiment of the present invention, and (B) A plan view of a separator equipped with a parallel flow channel structure according to a second modified example of the embodiment of the present invention. [Figure 8] (A) A plan view of the separator showing the gas supply path in the water storage mode for moisture generated in the fuel cell, and (B) A plan view of the separator showing the gas supply path in the water drainage mode for moisture generated in the fuel cell. [Figure 9] (A) A plan view of the separator showing the refrigerant supply path in the water storage mode for moisture generated in the fuel cell, and (B) A plan view of the separator showing the refrigerant supply path in the water drainage mode for moisture generated in the fuel cell. [Modes for carrying out the invention]

[0010] A fuel cell 10 constituting a fuel cell device according to an embodiment of the present invention will now be described. Figure 1(A) is an exploded perspective view showing the overall configuration of the fuel cell 10. Figure 1(B) is a cross-sectional view of the fuel cell 10. Each component of the fuel cell 10 is assigned an alphanumeric code, with the code "a" assigned to the anode side component to which fuel (hydrogen) is supplied, and the code "c" assigned to the cathode side component to which air (oxygen) is supplied.

[0011] The fuel cell cell 10 is composed of an electrolyte membrane 11, a pair of catalyst layers 12 (12a, 12c) covering both sides of the electrolyte membrane 11, a pair of micro-porous layers (MPL) 13 (13a, 13c) formed on the outside of the pair of catalyst layers 12, a pair of gas diffusion layers (GDL) 14 (14a, 14c) formed on the outside of the pair of micro-porous layers 13, and a pair of separators 15 (15a, 15c) covering the gas diffusion layers 14 from the outside. To supply fuel (hydrogen) to the anode side, separator 15a has a plurality of flow channels Cha facing the gas diffusion layer 14a. To supply air (oxygen) to the cathode side, separator 15c has a plurality of flow channels Chc facing the gas diffusion layer 15c. The flow channel structure of the fuel cell cell 10 is formed by the plurality of flow channels Ch (Cha, Chc).

[0012] The gas diffusion layer 14 is a porous material composed of carbon fibers and has multiple pores. The water-repellent layer 13 is a porous material with multiple pores that are smaller than those of the gas diffusion layer 14. Therefore, the water-repellent layer 13 has the property of being less likely to accumulate water inside compared to the gas diffusion layer 14.

[0013] In reality, the electrolyte membrane 11 is about 10 μm thick, the catalyst layer 12 is about 10 μm thick, the water-repellent layer 13 is about 20 μm to 30 μm thick, and the gas diffusion layer 14 is about 200 μm thick. In other words, the gas diffusion layer 14 is about 10 times thicker than the water-repellent layer 13, and water produced by the electrochemical reaction between the electrolyte membrane 11 and the catalyst layer 12 tends to accumulate more easily in the gas diffusion layer 14 compared to the other layers.

[0014] The reaction gases supplied through multiple flow channels Ch formed in a pair of separators 15, namely hydrogen gas and oxygen gas, pass through the pores of the gas diffusion layer 14 and the water-repellent layer 13 to reach the electrolyte membrane 11 where a pair of catalyst layers 12 are formed, and electricity is generated by an electrochemical reaction. In order to effectively utilize the reaction surface of the electrochemical reaction in the electrolyte membrane 11 where the pair of catalyst layers 12 are formed, a flow channel structure with symmetry is usually adopted so that the reaction gases can diffuse uniformly on the reaction surface. Symmetry refers to a flow channel structure that is vertically symmetrical with respect to a central line perpendicular to the direction in which the reaction gases flow from the inlet to the outlet.

[0015] The flow path structures formed in the separator 15 include an inter-digitated flow field (IDFF) where the inlet and outlet flow paths are not connected, a parallel shape where multiple flow paths are formed in parallel, and a serpentine shape where a single flow path meanders from the inlet to the outlet of the reaction gas. The multiple flow paths are formed between multiple protrusions formed in the separator 15.

[0016] Next, the IDFF-type flow channel structure formed in the separator 15 will be described. Figures 2(A) and 2(B) are plan views of the separator 15 formed with an IDFF-type flow channel structure. The vertical direction of the paper in Figures 2(A) and 2(B) corresponds to the left-right direction of the separator 15 when the separator 15 is placed horizontally. Specifically, Figure 2(A) shows a flow channel structure Fs that is symmetrical with respect to the reference line RL. Figure 2(B) shows a flow channel structure Fd that is asymmetrical with respect to the reference line RL. In the IDFF-type flow channel structure, multiple flow channels are formed between meanderingly connected convex sections, and the gas inlet flow channel Fin and the gas outlet flow channel Fout are arranged individually and alternately, and are not connected to each other. Therefore, the reaction gas introduced into the inlet flow channel Fin is transmitted to permeate into the gas diffusion layer 14 which has multiple pores. After that, the reaction gas that has permeated through the gas diffusion layer 14 is transmitted to the outlet flow channel Fout. That is, the reaction gas flows from the inlet flow channel Fin through the gas diffusion layer 14 to the outlet flow channel Fout. The arrow GF indicates the flow direction of the reaction gas from the inlet to the outlet.

[0017] In the flow path structure Fs having the symmetry shown in Fig. 2(A), three outlet-side flow paths Fout (Fout1 to Fout3) are alternately arranged with respect to the four inlet-side flow paths Fin (Fin1 to Fin4). Therefore, the outlet-side flow path area of the flow path structure Fs is smaller than the inlet-side flow path area, and the gas outlet is narrower than the gas inlet. Further, the reference line RL passes through the central outlet-side flow path Fout2, and two inlet-side flow paths Fin1, Fin2 and one outlet-side flow path Fout1 are arranged in the upper portion, and two inlet-side flow paths Fin3, Fin4 and one outlet-side flow path Fout3 are arranged in the lower portion. Therefore, the flow path structure Fs has symmetry between the upper portion and the lower portion of the reference line RL passing through the central outlet-side flow path Fout2. In the flow path structure Fs shown in Fig. 2(A), an even number of inlet-side flow paths Fin and an odd number of outlet-side flow paths Fout are arranged, but the "symmetry" is not limited to this. For example, an odd number of inlet-side flow paths Fin and an even number of outlet-side flow paths Fout may be arranged, and the reference line RL may be set to pass through the central inlet-side flow path Fin.

[0018] Regarding the fuel cell 10 including the separator 15 having the flow path structure Fs with symmetry, when analyzing the gas pressure gradient in the gas diffusion layer 14 by simulation, the pressure at the gas inlet is high and the pressure at the gas outlet is low, and a certain gas pressure gradient is formed. In the symmetric flow path structure Fs, the gas flows evenly from the gas inlet to the gas outlet without convection in the space of the inlet-side flow path Fin. Therefore, in the flow path structure Fs, an imbalance in the gas pressure gradient does not occur, and it is difficult for a phenomenon such as excessive generated water to accumulate in the vicinity of the outlet side of the outermost flow path.

[0019] In the channel structure Fd having the asymmetry shown in Fig. 2(B), four outlet-side channels Fout (Fout1 to Fout4) are formed for the four inlet-side channels Fin (Fin1 to Fin4). That is, the number of inlet-side channels and the number of outlet-side channels of the channel structure Fd are the same, and the inlet-side channel area and the outlet-side channel area of the channel structure Fd are the same. Further, the reference line RL, which is a line segment that bisects the separator 15 vertically (horizontally), passes through the ridge portion of the separator 15 between the second inlet-side channel Fin2 and the third outlet-side channel Fout3. Two inlet-side channels Fin1 and Fin2 and two outlet-side channels Fout1 and Fout2 are arranged in the upper portion of the channel structure Fd, and two inlet-side channels Fin3 and Fin4 and two outlet-side channels Fout3 and Fout4 are arranged in the lower portion. However, since the channel structure Fd does not have symmetry such that the number of inlet-side channels Fin and the number of outlet-side channels Fout is an even number to an odd number or an odd number to an even number, it has asymmetry.

[0020] In the channel structure Fd having asymmetry, since the inlet-side channel area and the outlet-side channel area are the same, compared with the channel structure Fs having symmetry, the gas pressure gradient is generally smaller and tends to be unbalanced. Therefore, for the fuel cell 10 including the separator 15 having the channel structure Fd, when analyzing the gas pressure gradient in the gas diffusion layer 14 by simulation, the pressure at the gas inlet is slightly lower than that of the channel structure Fs, and the gas pressure gradient between the gas inlet and the gas outlet becomes smaller. In particular, the gas flow velocity in the vicinity of the outlet side of the outermost edge channel becomes small, and when water is generated as the fuel cell 10 generates electricity, it becomes difficult to discharge the generated water, and there is a possibility that the generated water accumulates.

[0021] Next, we will explain the relationship between the separator 15, which has an asymmetrical flow channel structure Fd, and in particular the cathode separator 15c, which is prone to generating water, and the electrode area of ​​the fuel cell cell 10. The electrode area (hereinafter referred to as the "reaction surface") is formed by coating the electrolyte membrane 11 with a catalyst layer 12. That is, by adjusting the coating area of ​​the catalyst layer 12 on the electrolyte membrane 11, the shape and size of the reaction surface can be adjusted, thereby adjusting the amount of electricity generated by the electrochemical reaction and the amount of water generated. Typically, the catalyst 12 is coated on the electrolyte membrane 11 in such a way that it forms a reaction surface RS that covers the entire surface of the electrolyte membrane 11 with a shape and size that covers the entire flow channel structure Fd of the separator 15.

[0022] The embodiment of the present invention is characterized by setting the shape and size of the reaction surface RS so as to avoid the water storage portion WS of the separator 15. Figures 3 and 4 show plan views of the cathode separator 15c, but the shape and size of the reaction surface RS of the electrolyte membrane 11 coated with the catalyst layer 12 so as to cover the flow channel structure Fd of the cathode separator 15c are different. In the embodiment of the present invention, the cathode separator 15c will be described, but the anode separator 15a is configured similarly. As described above, the cathode separator 15c (hereinafter simply referred to as "separator 15c") has four inlet flow channels Fin1 to Fin4 and four outlet flow channels Fout1 to Fout4 formed alternately in the vertical direction of the paper.

[0023] Figure 3 is a plan view showing the relationship between a separator 15c having an asymmetrical IDFF-type channel structure Fd and a reaction surface RSn having a shape and size that covers the entire channel structure Fd. In Figure 3, the reaction surface RSn of the electrolyte membrane 11 coated with a catalyst layer 12 is formed to cover the entire channel structure Fd of the separator 15c. In an asymmetrical channel structure Fd, an imbalance in the gas pressure gradient occurs, which can cause generated water to accumulate, for example, at the downstream end or near the outlet of the outermost channel, potentially making power generation impossible. In addition, because gas is not supplied locally in the channel structure Fd, the catalyst layer 12 is more prone to deterioration.

[0024] Figure 4 is a plan view showing the relationship between a separator 15c having an asymmetrical IDFF-type flow channel structure Fd and a reaction surface RSd having the shape and size according to the present invention. In Figure 4, the reaction surface RSd of the electrolyte membrane 11 coated with the catalyst layer 12 is formed in a shape and size that avoids the reservoir section WS near the downstream end or outlet side of the outermost flow channel of the flow channel structure Fd of the separator 15c where generated water tends to accumulate. The shape and size of the reservoir section WS depend on the gas flow velocity and gas pressure gradient. If the reservoir section WS is defined as the area on the electrolyte membrane 11 where the catalyst layer 12 is not coated, a certain area may be determined and set in advance through experimentation or simulation. By forming the reaction surface RSd to avoid the reservoir section WS, moisture accumulates in the gas diffusion layer 14c and catalyst layer 12c located in the reservoir section WS that the reaction surface RSd avoids. Therefore, generated water can be retained without hindering the power generation performance of the fuel cell cell 10. In practice, the generated water is stored in a portion of the gas diffusion layer 14c located near the downstream end or outlet of the outermost channel of the channel structure Fd.

[0025] As a modification of the present embodiment, the electrolyte membrane 11 may be covered with the catalyst layer 12 in order to form a reaction surface RSd that avoids the entire outermost channel of the channel structure Fd. In this case, the electrolyte membrane 11 covered by the catalyst layer 12 does not exist in the outermost channel of the channel structure Fd, and the size of the reaction surface RSd is substantially reduced. As a result, the outermost channel of the channel structure Fd substantially does not participate in power generation.

[0026] Figures 5(A) and 5(B) are cross-sectional views of the cathode-side laminate of the fuel cell cell 10. Compared to the separator 15c shown in Figure 4, Figure 5(A) is a cross-sectional view (AA) of the gas upstream side near the gas inlet, and Figure 5(B) is a cross-sectional view (BB) of the gas downstream side near the gas outlet. That is, the cathode gas, which consists of oxygen-containing air, flows in the direction from the cross-sectional view (AA) shown in Figure 5(A) to the cross-sectional view (BB) shown in Figure 5(B). In Figures 5(A) and 5(B), the gas outlet side flow path Fout and the gas inlet side flow path Fin are arranged from left to right on the page in the order of flow paths Fout1, Fin1, Fout2, Fin2, Fout3, Fin3, Fout4, and Fin4. Note that the inlet side flow path Fin4 is the outermost flow path where moisture tends to accumulate.

[0027] In Figure 5(A), a gas diffusion layer 14c, a water-repellent layer 13c, a catalyst layer 12c, and an electrolyte membrane 11 are formed on the separator 15c in the region demarcated by the gasket GS. The superstructure of the electrolyte membrane 11, i.e., the anode-side laminated structure, is shown in Figure 1(B), and its explanation is omitted here.

[0028] Figure 5(A) is an AA cross-sectional view of the area near the upstream side of the gas, and therefore the catalyst layer 12c is formed over the entire surface of the electrolyte membrane 11. In addition, moisture W1 to W8 moves between the multiple flow channels Fin1 to Fin4 and Fout1 to Fout4 and the gas diffusion layer 14c. Moisture W1 to W8 is not limited to the water generated during power generation of the fuel cell cell 10, but also includes moisture contained in the cathode gas. In Figure 5(A), moisture W1 to W8 does not accumulate in the flow channels Fin1 to Fin4 and Fout1 to Fout4, but is uniformly present and moves between the gas diffusion layer 14c and the water-repellent layer 13c.

[0029] Figure 5(B) is a cross-sectional view of BB near the upstream side of the gas flow, where the inlet channel Fin4, which is the outermost channel, is not covered by the electrolyte membrane 11 and the catalyst layer 12c. Therefore, the amount of water W8m in the inlet channel Fin4, which is the outermost channel, is relatively small and moves to the gas diffusion layer 14c. Gas convection weakens in the region near the outlet of the outermost channel or in the region at the downstream end of the gas flow (hereinafter referred to as the "water retention region R"). The water retention region R includes the outermost channel and the gas diffusion layer 14c in its vicinity. In the water retention region R, the gas pressure gradient is small and the gas flow velocity is small, so once water permeates, it is difficult to discharge. Therefore, the water generated at the reaction surface on the upstream side of the outermost channel and the water contained in the gas tend to remain in the water retention region R. Furthermore, when moisture generated at the reaction surface near the moisture retention region R flows towards the outermost channel and reaches the moisture retention region R, it becomes difficult for the moisture to be discharged from the moisture retention region R where the gas flow velocity decreases. When moisture remains in the moisture retention region R, it absorbs heat from its surroundings, causing the temperature to drop, which increases the relative humidity and makes it easier for water vapor in the gas to condense.

[0030] On the other hand, even if moisture remains in the moisture retention region R, since there is no reaction surface near the moisture retention region R, the moisture does not inhibit gas diffusion to the reaction surface and does not hinder power generation associated with the electrochemical reaction at the reaction surface. In other words, according to the present embodiment, moisture can be stored in a specific location that does not hinder the electrochemical reaction of the fuel cell cell 10. Furthermore, when the reaction surface of the fuel cell cell 10 dries out, the residual moisture can be used to moisturize the reaction surface. Generally, in power generation by fuel cell devices, the presence of a certain amount of moisture on the reaction surface reduces the conductivity resistance of protons, allowing for more efficient power generation.

[0031] Next, the manner of water movement in the aforementioned water retention region R will be explained. Figures 6(A) and 6(B) are enlarged cross-sectional views of the water retention region R near the outermost channel (inlet channel Fin4) in Figure 5(B). Specifically, Figure 6(A) shows the manner of water movement when the reaction surface is wet, and Figure 6(B) shows the manner of water movement when the reaction surface is dry. In Figures 6(A) and 6(B), the same reference numerals are used for components that are the same as in Figure 5(B).

[0032] As shown in Figure 6(A), moisture W7 moves from the outlet channel Fout4 to the gas diffusion layer 14c, and also to the water-repellent layer 13c. In the inlet channel Fin4, which is the outermost channel, moisture W8m moves toward the gas diffusion layer 14c. However, since the reaction surface is wet, it is expected that liquid water moves from the catalyst layer 12c toward the gas diffusion layer 14c along arrows Mt1 and Mt2. Therefore, in the inlet channel Fin4, liquid water dl1, dl2, dl3, and dl4 each move toward the gas diffusion layer 14c. In this way, when the reaction surface is wet, moisture and liquid water accumulate in the reservoir WS of the moisture retention region R (particularly the region corresponding to the gas diffusion layer 14c near the downstream end of the outermost channel) and are then drained.

[0033] Figure 6(B) assumes that the temperature of the fuel cell 10 has risen compared to the wet state of the reaction surface shown in Figure 6(A), resulting in a dry state of the reaction surface. In this case, if moisture remains in the moisture retention region R, a temperature gradient will be generated between the moisture retention region R and the reaction surface when the reaction surface dries. As a result, the remaining moisture flows from the moisture retention region R towards the reaction surface, and the reaction surface near the moisture retention region R is partially moistened. By moistening the dry reaction surface, the activity of the electrochemical reaction is improved, and the decrease in the power generation performance of the fuel cell cell 10 can be suppressed.

[0034] In contrast to the wet state of the reaction surface shown in Figure 6(A), even in the dry state of the reaction surface shown in Figure 6(B), moisture W7 moves from the outlet channel Fout4 to the gas diffusion layer 14c, as well as to the water-repellent layer 13c. However, in the inlet channel Fin4, which is the outermost channel, moisture W8d moves towards the gas diffusion layer 14c. In Figure 6(B), since the reaction surface is dry, it is assumed that the liquid water accumulated in the reservoir WS moves along arrows Mt3 and Mt4. Therefore, in the inlet channel Fin4, liquid water dl5 and dl6 move towards the gas diffusion layer 14c, respectively. Thus, in the dry state of the reaction surface, moisture and liquid water accumulated in the reservoir WS of the moisture retention region R move towards the reaction surface, allowing the reaction surface to be moisturized.

[0035] In this embodiment, as shown in Figures 3 and 4, an IDFF-type flow channel structure Fd is formed in the cathode separator 15c, but the invention is not limited thereto. For example, instead of the IDFF-type flow channel structure Fd, a parallel-type flow channel structure Fp in which a plurality of flow channels communicating from the gas inlet to the gas outlet are arranged in parallel may be applied. Even in the parallel-type flow channel structure Fp, a water reservoir that easily retains moisture can be formed near the downstream end of the outermost flow channel.

[0036] Figures 7(A) and 7(B) show the first and second modified examples in which a parallel flow channel structure Fp is formed on the separator 15c.

[0037] In the first modified example shown in Figure 7(A), multiple channels F1 to F9 are arranged in parallel to allow gas to flow according to a constant pressure gradient. Here, channels F1 to F8 are formed with the same channel width d, for example, at a pitch of 0.5 mm. In order to form a reservoir WS1 for retaining generated water at the downstream end of channel F9, which is the outermost channel, the upstream side of channel F9 is formed with the same channel width d as the other channels, and the downstream side of the convex section of channel F9 is partially narrowed, thereby expanding the channel width on the downstream side of channel F9 from d to d1. In this way, by expanding the width of the downstream end of channel F9, the gas pressure gradient is reduced and the gas flow velocity is reduced, making it easier for generated water to temporarily remain in the reservoir WS1. In addition to changing the channel width at a predetermined position, the channel width may also be widened in a tapered manner as a method for expanding the channel width on the downstream side of channel F9.

[0038] In the second modified example shown in Figure 7(B), similar to the first modified example in Figure 7(A), multiple channels F1 to F8 are arranged in parallel with the same channel width d, for example, at a pitch of 0.5 mm. In the outermost channel, channel F10, the channel width is increased to d2, for example, at a pitch of 1 mm, and the gas pressure is reduced compared to the other channels F1 to F8. As a result, the gas flow velocity in channel F10 decreases, and a reservoir WS2 is formed at the downstream end of channel F10 where generated water tends to accumulate.

[0039] Next, a method for switching the gas supply direction (or gas supply path) in the flow path structure Fd of the separator 15 of the fuel cell cell 10 will be described. In the fuel cell cell 10, gas is basically supplied to multiple flow paths in a way that prevents uneven distribution of gas flow. However, by controlling the opening and closing of valves V1 to V4 provided at the four corners of the separator 15, it is possible to intentionally create an uneven distribution of gas flow to facilitate the storage of moisture generated during gas supply and to promote the drainage of that moisture.

[0040] Figures 8(A) and 8(B) are plan views of a separator 15 on which an asymmetrical flow path structure Fd forming a gas supply path is formed, with valves V1 to V4 provided at the four corners of the separator 15. Valves V1 and V2 are located on the gas inlet side, and valves V3 and V4 are located on the gas outlet side. In Figures 8(A) and 8(B), valves in the "closed" state are marked with an "×". The approximate gas flow direction (or gas supply path) GP is indicated by multiple arrows. By appropriately switching valves V1 to V4 on the gas inlet and outlet sides, the degree of water retention in the reservoir WS near the downstream end of the outermost flow path can be adjusted.

[0041] Figure 8(A) is a plan view of the separator 15 showing the gas supply path GP in the water storage mode for moisture generated in the fuel cell cell 10. Here, valves V2 and V3 are open, and valves V1 and V4 are closed. In this state, the gas moves from the inlet valve V2 along the arrow to the outlet valve V3. In other words, the gas flows from the lower left to the upper right of the paper, and moisture accumulates in the water storage section WSm near the downstream side of the outermost flow path. In water storage mode, by making the distance of the gas supply path relatively long, the flow resistance of the gas increases, and the gas flow velocity decreases near the water storage section WS, making it difficult for moisture to be discharged.

[0042] Figure 8(B) is a plan view of the separator 15 showing the gas supply paths GP1 and GP2 in the water drainage mode for moisture generated in the fuel cell cell 10. Here, valves V1 and V3 are closed, and valves V2 and V4 are open. In this state, the gas moves from the inlet valve V2 along the arrow to the outlet valve V4. In other words, the gas flows from the left side to the right side of the paper. In the drainage mode, the distance of the gas supply path is relatively shorter compared to the water storage mode, which reduces the flow resistance of the gas and increases the gas flow velocity near the water storage section WSd. Therefore, it becomes easier to drain the moisture accumulated in the water storage section WSd.

[0043] In Figures 8(A) and 8(B), four valves V1 to V4 are provided to switch between gas supply paths GP and GP1 and GP2, thereby switching between water storage mode and drainage mode. However, the system is not limited to this configuration. Valve V1 on the gas inlet side is always closed, so valve V1 may be omitted. In this case, only valve V2 will be present on the gas inlet side, and it will always be open when gas is supplied. In other words, the water storage mode and drainage mode may also be switched by appropriately changing the open and closed states of valves V3 and V4 on the gas outlet side.

[0044] As a method for switching between the water storage mode and the water drainage mode for moisture generated in the fuel cell cell 10, the method is not limited to switching the valves V1 to V4 on the gas inlet and outlet sides as shown in Figures 8(A) and (B). Alternatively, the flow direction of the refrigerant supplied between the separator 15 of the fuel cell cell 10 and the separator of an adjacent fuel cell cell may be switched. Air or cooling water is used as the refrigerant to cool the fuel cell cell 10 via the separator 15. The refrigerant absorbs the heat generated when the fuel cell cell 10 generates electricity, and as a result, the temperature of the refrigerant rises. Therefore, the refrigerant temperature is low near the refrigerant inlet, but high near the refrigerant outlet. This temperature change of the refrigerant is used for moisture management in the water storage section WS (WSm, WSd).

[0045] Figure 9(A) is a plan view of the separator 15 showing the refrigerant supply path in the water storage mode of the fuel cell cell 10. At the refrigerant inlet, the refrigerant is supplied in the directions indicated by arrows C1 and C2, and then discharged in the directions indicated by arrows C3 and C4. In other words, the refrigerant is supplied from outside the outermost flow path where the water storage section WSm is formed at the downstream end, passes from the bottom to the top of the paper, and is discharged to the outside of the other outermost flow path (the flow path at the top of the paper). Near the refrigerant inlet, the temperature of the refrigerant is low, and the low-temperature refrigerant flows near the water storage section WSm of the outermost flow path. As a result, the temperature near the water storage section WSm decreases, making it easier for water to accumulate.

[0046] Figure 9(B) is a plan view of the separator 15 showing the refrigerant supply path in the water drainage mode for moisture generated in the fuel cell 10. In Figure 9(B), the refrigerant supply path is reversed compared to the refrigerant supply path shown in Figure 9(A). At the refrigerant inlet, the refrigerant is supplied in the directions indicated by arrows C5 and C6, and then discharged in the directions indicated by arrows C7 and C8. In other words, the refrigerant is supplied from outside the outermost flow path at the top of the page, passes from the top to the bottom of the page, and is discharged outside the outermost flow path (the flow path at the bottom of the page) where the water reservoir WSd is formed at the downstream end, as shown at the bottom of the page. Near the refrigerant outlet, the refrigerant absorbs the heat generated in the fuel cell 10, causing the refrigerant temperature to rise. As a result, the high-temperature refrigerant flows near the water reservoir WSd in the outermost flow path, causing the temperature near the water reservoir WSd to rise, making it easier for the liquid water to vaporize, and thus moisture is discharged near the water reservoir WSd.

[0047] Next, the features and effects of a fuel cell system equipped with a fuel cell cell 10 according to an embodiment of the present invention will be described.

[0048] (1) A fuel cell device according to an embodiment of the present invention comprises an electrolyte membrane (11), a pair of catalyst layers (12) sandwiching the electrolyte membrane (11), a pair of gas diffusion layers (14) sandwiching the electrolyte membrane (11) and the pair of catalyst layers (12), and a pair of separators (15) sandwiching the electrolyte membrane (11), the pair of catalyst layers (12), and the pair of gas diffusion layers (14). A pair of water-repellent layers (13) may be provided between the pair of catalyst layers (12) and the pair of gas diffusion layers (14). The pair of separators (15) are formed with a plurality of flow channels (flow channel structure Fd) aligned to supply fluid to the electrolyte membrane (11) covered by the pair of catalyst layers (12) through the pair of gas diffusion layers (14). The multiple flow channels include the outermost channel closest to the edges of the pair of separators (15). At the downstream end of the outermost channel, the fluid velocity decreases, forming a reservoir (WS) where water generated by the electrochemical reaction at the reaction surface (RSd), which consists of an electrolyte membrane (11) covered with a pair of catalyst layers (12), accumulates. The pair of catalyst layers (12) defining the reaction surface (RSd) are formed in a shape that avoids the reservoir (WS) formed at the downstream end of the outermost channel.

[0049] When a fluid (hydrogen and oxygen) is supplied to an electrolyte membrane (11) covered with a pair of catalyst layers (12), electricity and water (or generated water) are produced. The water accumulates in the water reservoir (WS) at the downstream end of the outermost channel of the multiple channels. The electrolyte membrane (11) covered with catalyst layers (12) does not extend to the downstream end of the outermost channel and does not participate in the electrochemical reaction. Furthermore, the catalyst layers (12) are formed in a shape that avoids the water reservoir (WS), and the water that accumulates as the flow velocity decreases at the downstream end of the outermost channel is easily discharged from the water reservoir (WS). In this way, by defining the reaction surface (RSd) corresponding to the region of the electrolyte membrane (11) covered with catalyst layers (12) to avoid the water reservoir (WS), the water reservoir (WS) is exposed from the reaction surface and water is easily discharged.

[0050] (2) Multiple flow paths may be formed by an opposing comb-shaped flow field (IDFF) in which an equal number of inlet flow paths (Fin) and outlet flow paths (Fout) are arranged alternately. A reservoir (WS) is formed at the downstream end of the outermost flow path (e.g., Fin4) which serves as the inlet flow path. As shown in Figure 4, in a separator (15) in which an asymmetrical IDFF-type fluid structure (Fd) is formed, a reaction surface (RSd) may be provided so as to avoid the reservoir (WS). The fluid pressure and flow velocity become significant at the downstream end of the outermost flow path, making it easier for water to accumulate in the reservoir (WS). However, since the reaction surface (RSd) is formed so as to avoid the reservoir (WS), good drainage can be achieved.

[0051] (3) Multiple flow channels may be formed in a parallel flow channel structure, each formed in a straight line from the upstream side to the downstream side of the fluid and aligned in parallel. As shown in Figures 7(A) and 7(B), the flow channel cross-sectional area at least downstream of the outermost flow channel (e.g., F9, F10) is formed to be larger than the flow channel cross-sectional area of ​​the other flow channels (e.g., F1 to F8), and water reservoirs (WS1, WS2) are formed at the downstream end of the outermost flow channel. In the parallel flow channel structure, as shown in Figure 7(A), the channel width at the downstream end of the outermost flow channel (F9) is enlarged, or as shown in Figure 7(B), the channel width of the outermost flow channel (F10) is enlarged compared to the channel width of the other flow channels. As a result, the fluid velocity decreases at the downstream end of the outermost flow channel, making it easier for water to accumulate in the water reservoirs (WS1, WS2). However, since the reaction surface (RSd) is formed to avoid the water reservoirs (WS1, WS2), good drainage can be achieved.

[0052] (4) A pair of gas diffusion layers (14) includes a cathode gas diffusion layer (14c), and a pair of separators (15) includes a cathode separator (15c). The fluid supplied to the multiple channels formed in the cathode separator (15c), which is positioned opposite the cathode gas diffusion layer (14c), is oxygen-containing air. Here, the cathode gas diffusion layer (14c) includes a water reservoir (WS). The gas diffusion layer (15) has multiple pores and is thicker than the nearby water-repellent layer (13), catalyst layer (12), and electrolyte membrane (11). As shown in Figure 5(B), the fluid pressure and velocity decrease at the downstream end of the outermost channel (Fin4), making it easier for water generated by the electrochemical reaction to accumulate in the water reservoir (WS). However, since the reaction surface (RSd) is formed to avoid the water reservoir (WS), good drainage can be achieved.

[0053] (5) Multiple flow channels may be arranged asymmetrically in the direction of alignment between the fluid inlet channel (Fin) and the outlet channel (Fout). When an asymmetrical IDFF-type flow channel structure (Fd) as shown in Figure 2(B) is adopted, the pressure gradient between the upstream and downstream sides of the fluid becomes smaller due to the asymmetry, and the fluid velocity decreases downstream. In particular, as shown in Figure 4, the fluid velocity decreases at the downstream end of the outermost flow channel (Fin4), making it easier for a water reservoir (WS) to form where water accumulates. However, since the reaction surface (RSd) is formed to avoid the water reservoir (WS), good drainage can be achieved.

[0054] (6) The extent of the reservoir (WS) formed at the downstream end of the outermost channel (Fin4) may be determined according to the fluid velocity or pressure gradient of the fluids flowing through the multiple channels. Since the level of fluid velocity is determined by the magnitude of the pressure gradient between the upstream and downstream sides of the fluid, the extent (or area) of the reservoir (WS) where the fluid velocity decreases may be determined according to the pressure gradient.

[0055] (7) When drying the reaction surface (RSd), moisture may be released from the water reservoir (WS). Since the moisture from the water reservoir (WS) is transferred to the reaction surface (RSd) via the gas diffusion layer (14) and the water-repellent layer (13), the wettability of the reaction surface (RSd) can be maintained, and a decrease in the power generation performance of the fuel cell device can be prevented.

[0056] (8) The fuel cell device may be configured to switch between a water storage mode and a drainage mode for the water storage sections (WSm, WSd) by controlling the opening and closing of multiple valves (V2 to V4). As shown in Figures 8(A) and 8(B), the fuel cell device may include an inlet valve (V2) connected to the inlet side of multiple flow paths and supplying fluid, a first outlet valve (V3) connected to the outlet side of multiple flow paths and discharging fluid, and a second outlet valve (V4) connected to the outlet side of multiple flow paths and positioned closer to the water storage sections (WSm, WSd) than the first outlet valve (V3). Here, by opening the first outlet valve (V3) and closing the second outlet valve (V4), a water storage mode is activated, in which moisture is retained in the water storage section (WSm), and by closing the first outlet valve (V3) and opening the second outlet valve (V4), a drainage mode is activated, in which moisture retained in the water storage section (WSd) is drained. The fluid flow path can be switched between a gas supply path in water storage mode (GP) and a gas supply path in drainage mode (GP1, GP2) by controlling the opening and closing of the first and second outlet valves (V3, V4).

[0057] (9) The water storage section (WSm, WSd) can be switched between a water storage mode and a drainage mode by changing the supply path of the refrigerant for cooling the fuel cell device. As shown in Figures 9(A) and 9(B), when the refrigerant is circulated outside the pair of separators (15), the system can switch between a water storage mode, in which the refrigerant is supplied from a first direction (from C1, C2 to C3, C4) that is close to the outermost flow path, causing moisture to accumulate in the water storage section (WSm), and a drainage mode, in which the refrigerant is supplied from a second direction opposite to the first direction (from C5, C6 to C7, C8), causing moisture to drain from the water storage section (WSd). In the first direction, the water storage section (WSm) is cooled by the low-temperature refrigerant, making it easier for moisture to accumulate in the water storage section (WSm). In the second direction, the temperature of the refrigerant increases due to the electrochemical reaction, so the water storage section (WSd) is warmed by the high-temperature refrigerant, making it easier for moisture to vaporize. In this way, by changing the refrigerant supply path so that the temperature of the water storage sections (WSm, WSd) changes, it is possible to switch between water storage mode and drainage mode.

[0058] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0059] 10 fuel cell cells 11 Electrolyte membrane 12a, 12c catalyst layer 13a, 13c Water-repellent layer 14a, 14c Gas diffusion layer 15a, 15c Separator Cha, Chc channel dl1 to dl6 liquid water F1 to F10 channel Fin1 to Fin4 Inlet side flow path Fout1 to Fout4 Outlet side flow path Fs, Fd channel structure GS Gasket GP, GP1, GP2 gas supply routes R Moisture residual area RL reference line RSn, RSd reaction surface V1 to V4 valves W1 to W8, W8m, W8d Moisture WS, WS1, WS2, WSm, WSd Water storage section

Claims

1. Electrolyte membrane, A pair of catalyst layers sandwiching the electrolyte membrane, The electrolyte membrane and the pair of catalyst layers sandwiched between them, The system comprises the electrolyte membrane, the pair of catalyst layers, and the pair of separators sandwiching the pair of gas diffusion layers, The pair of separators have a plurality of flow channels arranged in alignment to supply fluid to the electrolyte membrane covered by the pair of catalyst layers through the pair of gas diffusion layers. The plurality of channels include the outermost channel closest to the edges of the pair of separators, and at the downstream end of the outermost channel, the fluid velocity decreases, forming a reservoir where water generated by the electrochemical reaction on the reaction surface consisting of the electrolyte membrane covered by the pair of catalyst layers accumulates. A fuel cell device characterized in that the pair of catalyst layers defining the reaction surface are formed in a shape that avoids the water reservoir formed at the downstream end of the outermost channel.

2. The fuel cell device according to claim 1, wherein the plurality of flow paths are formed by opposing comb-shaped flow fields in which an equal number of inlet flow paths and outlet flow paths are arranged alternately, and the water storage section is formed at the downstream end of the outermost flow path which serves as the inlet flow path.

3. Each of the aforementioned plurality of flow paths is formed in a straight line from the upstream side to the downstream side of the fluid, and is arranged in parallel. The fuel cell device according to claim 1, characterized in that the cross-sectional area of ​​at least the downstream side of the outermost channel is formed to be larger than the cross-sectional area of ​​other channels other than the outermost channel, and the water reservoir is formed at the downstream end of the outermost channel.

4. The fuel cell device according to claim 1, wherein the pair of gas diffusion layers includes a cathode gas diffusion layer, the pair of separators includes a cathode separator, the fluid supplied to the plurality of flow paths formed in the cathode separator arranged opposite the cathode gas diffusion layer is oxygen-containing air, and the cathode gas diffusion layer includes the water reservoir.

5. The fuel cell apparatus according to claim 2, characterized in that the plurality of flow paths are arranged asymmetrically in the alignment direction between the inlet flow path and the outlet flow path of the fluid.

6. The fuel cell device according to claim 2, characterized in that the range of the water reservoir formed at the downstream end of the outermost channel is determined according to the flow velocity or pressure gradient of the fluid flowing through the plurality of channels.

7. The fuel cell apparatus according to claim 2, characterized in that the water is released from the water reservoir when the reaction surface is drying.

8. An inlet valve connected to the inlet side of the plurality of flow paths and supplying the fluid, A first outlet valve connected to the outlet side of the aforementioned plurality of flow paths for discharging the fluid, The system includes a second outlet valve connected to the outlet side of the plurality of flow paths and positioned closer to the water reservoir than the first outlet valve, By opening the first outlet valve and closing the second outlet valve, a water storage mode is established in which the water is retained in the water storage section. The fuel cell device according to any one of claims 1 to 3, characterized in that it switches between a drainage mode, which drains the water accumulated in the water storage section by closing the first outlet valve and opening the second outlet valve.

9. The fuel cell device according to any one of claims 1 to 3, characterized in that, when circulating a refrigerant outside the pair of separators, the device switches between a water storage mode in which the refrigerant is supplied from a first direction close to the outermost flow path to cause the water to accumulate in the water storage section, and a drainage mode in which the refrigerant is supplied from a second direction opposite to the first direction to drain the water from the water storage section.

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