JP5480082B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell in which the gas flow is reversed between the cathode side and the anode side.

  A fuel cell generates electricity by an electrochemical reaction between fuel and its oxidant, for example, hydrogen and oxygen. In this fuel cell, a fuel gas and an oxidizing gas such as hydrogen gas are passed through a gas diffusion layer on both electrodes of an anode and a cathode formed on both membrane surfaces of an electrolyte membrane having proton conductivity (for example, a solid polymer membrane). Supply air.

  The proton conductivity of the electrolyte membrane is affected by the wet state of the electrolyte membrane, and generally decreases when the electrolyte membrane becomes insufficiently wet. For this reason, various techniques for increasing the power generation capability by maintaining the wetness of the electrolyte membrane have been proposed (for example, Patent Document 1 below).

JP 2006-156144 A

  In the technique proposed in the above publication, a part of the membrane surface of the electrolyte membrane is exposed to the flow path of the gas (air) that carries the produced water generated by power generation, and the produced water is directly given to the electrolyte membrane. ing. Since there is no electrode at the exposed portion of the electrolyte membrane, there is a concern that the electrochemical reaction through the electrolyte membrane is lowered at the exposed portion.

  The present invention has been made to solve at least a part of the above-described conventional problems, and an object of the present invention is to improve the power generation capacity by more reliably wetting the electrolyte membrane.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the following configuration is adopted.

[Application 1: Fuel cell]
A membrane electrode assembly in which electrodes are formed on both membrane surfaces of an electrolyte membrane having proton conductivity; an anode-side diffusion layer provided on one electrode surface of the membrane electrode assembly; and the other membrane electrode assembly. A fuel cell comprising a cathode side diffusion layer provided on an electrode surface, wherein the gas flow in the cathode side diffusion layer and the anode side diffusion layer is reversed,
A bottomed recess is provided on the surface of the anode side diffusion layer opposite to the membrane electrode assembly,
The gist is that the recess is located on the inflow side of the gas flowing into the anode side diffusion layer.

  In the anode side diffusion layer of the fuel cell having the above-described configuration, the fuel gas passes through the bottomed concave portion on the inflow side (hereinafter referred to as the anode inflow side) and then flows downstream, so that the fuel gas is bottomed. When passing through the recess, water or water vapor (hereinafter collectively referred to as a water component) entering the recess is taken away downstream. Then, the water component distribution (water component concentration) is shifted between the membrane electrode assembly sandwiching the anode-side diffusion layer at the bottom of the bottomed recess and the inner region of the recess, and the bottom of the bottomed recess Since the water component can permeate, the water component moves from the membrane electrode assembly toward the inner region of the recess.

  On the other hand, since the gas flow is reversed between the anode side diffusion layer and the cathode side diffusion layer facing each other across the membrane electrode assembly, the anode inflow side is the downstream side of the oxidizing gas flow in the cathode side diffusion layer. (Hereinafter referred to as the cathode downstream side). On the cathode side, water is generated along with the electrochemical reaction, and the generated water is carried by the oxidizing gas flowing in the cathode side diffusion layer and increases on the downstream side of the cathode. In other words, the region where the water component moves from the membrane electrode assembly toward the inner region of the recess on the anode side diffusion layer side, and the region where the cathode side diffusion layer tends to generate excessive water sandwich the membrane electrode assembly. Match. In addition, since the generated water diffuses and penetrates even in the membrane electrode assembly, the generated water in the cathode side diffusion layer diffuses and passes through the membrane electrode assembly and then enters the inside of the recess from the membrane electrode assembly. Move towards the area.

  Since such a phenomenon continues during the passage of the fuel gas in the anode side diffusion layer, that is, during the gas supply for battery power generation, the membrane electrode assembly, more specifically, the electrolyte membrane contained therein, has a cathode side diffusion. It becomes naturally wet due to the diffusion and penetration of the generated water from the layer. As a result, according to the fuel cell having the above-described configuration, the electrolyte membrane can be more reliably wetted to increase the power generation capacity. Moreover, since the membrane / electrode assembly has the bottom surface of the bottomed concave portion of the anode-side diffusion layer joined to the electrode on the anode inflow side, the electrolyte membrane contained in the membrane / electrode assembly can be used for all power generation. It can be used in the area, so that the power generation capacity does not decrease.

  The fuel cell described above can be configured as follows. For example, the bottomed concave portion can be a maximum from the gas inflow side portion to the center of the anode side diffusion layer. Since the anode side diffusion layer supplies fuel gas to one electrode surface of the membrane electrode assembly, if the anode side diffusion layer has a recess over the entire surface of the anode side diffusion layer opposite to the membrane electrode assembly, Then, the fuel gas passes through the recess and the efficiency of supplying the fuel gas to the electrode surface of the membrane electrode assembly is deteriorated. Therefore, if the formation area of the recess is defined as described above, in the formation area of the recess, gas can be supplied from the bottom part of the recess to the electrode surface, and also passes through the anode side diffusion layer outside the formation area of the recess. At this time, since the gas is supplied to the electrode surface, it is possible to suppress a decrease in the efficiency of gas supply.

  In addition, the recesses may be multi-row bottomed groove portions, and the groove portions may extend downstream from the gas inflow side portion of the anode side diffusion layer. In this way, the flow of gas passing through each groove is made uniform as compared with a recess that is only recessed at the bottom. Therefore, the diffusion permeation of the generated water from the cathode side diffusion layer occurring at the bottom part of each groove portion is substantially uniform for each groove portion, so that it is desirable that the electrolyte membrane contained in the membrane electrode assembly is evenly moistened.

  In this case, it is more desirable to extend the groove part in parallel with the flow direction of the gas flowing through the anode side diffusion layer, because the gas flow flowing through each groove part becomes more uniform.

  Further, a separator bonded to the anode side diffusion layer is provided, and the separator is provided with a gas flow path for defining the gas flow direction in the anode side diffusion layer on the anode side diffusion layer side. It can be provided in a row, and ribs between the multiple rows of gas flow paths can be brought into contact with ribs between the multiple rows of the groove portions. In this way, it is easy to make the gas flow flowing through each groove uniform.

  Further, if the recess has an electrolyte resin having proton conductivity while allowing gas to pass through the recess, the water content in the anode-side diffusion layer is maintained by holding the water component by the ion exchange group of the electrolyte resin in the recess. Can be increased. Normally, when the fuel cell continues to operate at a high temperature, the moisture tends to become insufficient. However, as described above, the lack of moisture can be compensated by the water retention in the anode side diffusion layer, so that the power generation capacity can be maintained. In this case, due to the moisture retention by the electrolyte resin in the recess, it is possible to suppress a decrease in power generation capacity even when supplying fuel gas in a non-humidified state.

  In addition, pores can be formed by holding conductive powder with an electrolyte resin having proton conductivity on the surface of the anode side diffusion layer on the membrane electrode assembly side. By so doing, the water component is retained in the pore layer to increase the amount of water in the anode side diffusion layer and compensate for the lack of moisture during high temperature operation, so that the power generation capacity can be maintained. In this case, the pores are preferably continuous pores.

It is explanatory drawing which decomposes | disassembles and shows the schematic structure of the single cell 15 which comprises the fuel cell 10 of a present Example by a perspective view. It is explanatory drawing which shows this single cell 15 roughly in cross section. It is a graph which shows the relationship between the length of the groove part 30 with respect to the cell full length L of the single cell 15 at the time of supplying hydrogen gas without humidification, and a generated voltage. It is a graph which shows the relationship between the fabric weight at the time of formation of the anode side MPL layer 23a, and the moisture content in the said MPL layer. It is a graph which shows the relationship between the fabric weight and the layer thickness at the time of formation of the anode side MPL layer 23a. It is a graph which shows the relationship between the layer thickness of the anode side MPL layer 23a at the time of supplying hydrogen gas without humidification, and a generated voltage. It is a graph which shows the mode of dependence with respect to the cell temperature of the power generation voltage and cell internal resistance at the time of generating electric power by supplying hydrogen gas without humidification. It is explanatory drawing which decomposes | disassembles and shows the schematic structure of the single cell 15A of a modification in a perspective view. It is explanatory drawing which shows schematically the cross section of the single cell 15A of this modification. It is explanatory drawing which decomposes | disassembles and shows the schematic structure of the single cell 15B of the modified example which has arrange | positioned the multi-row groove part 30 diagonally in the gas flow direction. It is explanatory drawing which shows schematically the cross-sectional view of the single cell 15C of the modification which has the recessed part 30A which lined up the groove part 30 of multiple rows, and was depressed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded explanatory view showing a schematic configuration of a single cell 15 constituting the fuel cell 10 of the present embodiment, and FIG. 2 is an explanatory diagram schematically showing the single cell 15 in a sectional view. . The fuel cell 10 of the present embodiment has a stack structure in which a plurality of single cells 15 having the configuration shown in FIGS. The fuel cell 10 of the present embodiment is a solid polymer fuel cell, but can be similarly applied to different types of fuel cells, for example, solid oxide fuel cells.

  The single cell 15 includes both electrodes of an anode 21 and a cathode 22 on both sides of the electrolyte membrane 20. The anode 21 and the cathode 22 are formed on both membrane surfaces of the electrolyte membrane 20 to form a membrane electrode assembly (MEA). In addition, the single cell 15 includes an anode-side gas diffusion layer 23, a cathode-side gas diffusion layer 24, and gas separators 25 and 26 that sandwich the electrode-formed electrolyte membrane 20 from both sides, and both gas diffusion layers correspond to each other. It is joined to the electrode. The gas separator 25 is provided with an in-cell fuel gas flow channel 47 for flowing a fuel gas containing hydrogen on the anode side gas diffusion layer 23 side. The gas separator 26 is provided with an in-cell oxidizing gas flow path 48 through which an oxidizing gas containing oxygen (air in this embodiment) flows, on the cathode side gas diffusion layer 24 side. Although not described in FIGS. 1 to 2, an inter-cell refrigerant flow path through which a refrigerant flows can be formed between adjacent single cells 15, for example.

  The electrolyte membrane 20 is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluorine-based resin, and exhibits good electrical conductivity in a wet state. The anode 21 and the cathode 22 include a catalyst (for example, platinum or a platinum alloy), and are formed by supporting these catalysts on a conductive carrier (for example, carbon particles).

The anode side gas diffusion layer 23 and the cathode side gas diffusion layer 24 can be formed of a conductive member having gas permeability, such as carbon paper or carbon cloth. The anode-side gas diffusion layer 23 includes a plurality of bottomed grooves 30 in multiple rows on the surface of the diffusion layer opposite to the anode 21 in the MEA, that is, on the surface on the gas separator 25 side as shown. The relationship between the groove 30 and the flow of hydrogen gas will be described later. The anode side gas diffusion layer 23 has an anode side MPL layer (Micro Porous Layer) 23a on the surface of the diffusion layer on the anode 21 side in the MEA. The anode-side MPL layer 23a holds carbon particles, which are conductive powder, with an electrolyte resin having proton conductivity (in this embodiment, a fluorine-based resin constituting the electrolyte membrane 20). Creates pores. The anode-side MPL layer 23a can be formed by various methods. For example, a slurry in which carbon particles are dispersed in a fluororesin solution is applied to the surface of the anode-side gas diffusion layer 23 and dried. , With a layer thickness of about 100 to 200 μm. Further, the so-called basis weight per unit area of the anode-side MPL layer 23a can be defined, and in the present embodiment, it is set to 2.6 to 5.3 mg / cm ² . In addition, it can replace with the anode side MPL layer 23a, and can also be used as the hydrophilic chemical | medical agent layer which has a water retention function.

  The cathode side gas diffusion layer 24 has a cathode side water repellent layer 24a on the surface of the diffusion layer on the cathode 22 side in the MEA. The cathode side water repellent layer 24 a is formed by spraying a water repellent on the surface of the cathode side gas diffusion layer 24.

  The gas separators 25 and 26 are made of a gas-impermeable conductive member, for example, a dense carbon made by compressing carbon and impermeable to gas, baked carbon, or a metal material such as stainless steel. The gas separators 25 and 26 are members that form the wall surfaces of the in-cell fuel gas flow path 47 and the in-cell oxidizing gas flow path 48 described above, and the surface has an uneven shape for forming the gas flow path. Is formed.

  Although not shown in FIGS. 1 and 2, a plurality of holes are formed at predetermined positions near the outer peripheries of the gas separators 25 and 26. The plurality of holes overlap each other when the gas separators 25 and 26 are laminated together with other members and the fuel cell 10 is assembled, thereby forming a flow path that penetrates the fuel cell 10 in the lamination direction. That is, a manifold for supplying and discharging fuel gas, oxidizing gas, or refrigerant is formed with respect to the in-cell fuel gas channel 47, the in-cell oxidizing gas channel 48, or the inter-cell refrigerant channel.

  The fuel cell 10 of the present embodiment supplies hydrogen gas from the left side in FIG. 1 when flowing hydrogen gas from the hole in the vicinity of the outer periphery of the gas separator 25 to the in-cell fuel gas passage 47. In addition, air is supplied from the right side in FIG. 1 when air flows from the hole near the outer periphery of the gas separator 26 to the in-cell oxidizing gas channel 48. That is, in the fuel cell 10 of the present embodiment, the gas flow in the anode side gas diffusion layer 23 and the cathode side gas diffusion layer 24 are reversed, and the gas inflow side 23b side of the anode side gas diffusion layer 23 is the same. In addition, the above-described bottomed groove portions 30 are provided in multiple rows. In the fuel cell 10 of this embodiment, the hydrogen gas that has flowed into the anode gas diffusion layer 23 from the gas inflow side 23b is the anode gas diffusion layer 23 that contacts the bottom portion 23c of the groove 30 and the anode downstream of the groove 30. It is supplied to the anode 21 while diffusing with the side gas diffusion layer 23. As for the air, the air that has flowed into the cathode-side gas diffusion layer 24 in a direction opposite to that of hydrogen gas is supplied to the cathode 22 while being diffused by the cathode-side gas diffusion layer 24. In this case, FIGS. 1 to 2 show a partial range of the single cell 15, and in FIG. 1, three rows of groove portions 30 are located on the gas inflow side 23 b, but the number of rows of the groove portions 30 is It is determined by the size of the single cell 15.

  Here, the dimension of the groove part 30, the layer thickness of the anode side MPL layer 23a, the basis weight, and the like will be described. FIG. 3 is a graph showing the relationship between the length of the groove 30 and the generated voltage with respect to the total cell length L of the single cell 15 when hydrogen gas is supplied without humidification. As shown in the figure, the length of the groove 30 is zero, that is, in the fuel cell 10 having the groove 30 on the gas inflow side 23b side as shown in FIG. If the length of 30 is 2/5 of the total cell length L, a significant increase in the generated voltage is observed. If the cell length is about ½ of the total cell length L, a higher power generation capacity can be obtained with certainty than the comparative example described above. There was found. Moreover, when the groove part 30 exceeds 1/2 of the cell full length L, the power generation capacity is reduced, and when the entire cell full length L is reached, the power generation capacity is inferior to that of the comparative fuel cell having no groove part 30. There was found. This is because if the groove part 30 becomes long, the downstream side of the groove part 30 overlaps with a region where the amount of generated water is small because it is upstream in the cathode side gas diffusion layer 24, and even in such a region, the water component described later takes away. This is probably because drying of the anode side gas diffusion layer 23 is promoted. If the groove portion 30 extends over the entire length L of the cell, the amount of fuel gas that passes through the groove portion 30 increases, and accordingly, gas diffusion from the anode side gas diffusion layer 23 to the MEA (specifically, the anode 21). Since the supply does not proceed, it is considered that the power generation capacity is inferior to that of the comparative fuel cell having no groove 30.

  In this case, if the depth of the groove part 30 is made smaller than the thickness of the anode side gas diffusion layer 23, the groove part 30 has a bottom and the bottom part 23 c can be left in the anode side gas diffusion layer 23. Therefore, it may be determined as appropriate in consideration of the power generation capacity required for the fuel cell 10.

The influence of the groove 30 was examined from other viewpoints. In general, when the electrolyte membrane 20 is insufficiently wetted, the proton conductivity of the electrolyte membrane 20 decreases, so that the power generation capability decreases and the internal resistance value of the single cell 15 increases. About the comparative example fuel cell which does not have the groove part 30, and the fuel cell 10 of the present Example which has the groove part 30 in the length of 2/5 of the cell total length L (hereinafter, this is simply referred to as the fuel cell 10 having the groove part 30) Both fuel cells were operated in a steady state, gas supply was stopped and power generation was stopped, and then drying was performed for 30 seconds, and the cell internal resistance after the drying was measured. The cell internal resistance per unit area of the comparative fuel cell having no groove 30 was 0.338 Ω / cm ² , whereas the fuel cell 10 having the groove 30 was 2.054 Ω / cm ² . This phenomenon will be described below from the relationship with the power generation capacity improvement seen in FIG. Normally, drying is not performed after the operation is stopped. Therefore, even in the comparative example fuel cell having no groove 30 and the fuel cell 10 having the groove 30, an increase in cell internal resistance is not a problem.

  The increase in the cell internal resistance appears due to a decrease in proton conductivity due to insufficient wetting of the electrolyte membrane 20, so that the fuel cell 10 has a slight increase after the power generation is stopped. Insufficient wetting of the electrolyte membrane 20 occurred during the drying period. Such insufficient wetting of the electrolyte membrane 20 is caused by the anode side gas diffusion layer 23 in the bottom portion 23c (see FIG. 2) of the groove portion 30 and the MEA bonded to the anode side gas diffusion layer 23 in the bottom portion in the groove 30. This corresponds to insufficient wetting of the electrolyte membrane 20 due to the water component being extracted. That is, in the fuel cell 10 of the present embodiment, it can be said that the bottomed groove portion 30 causes the water component to be extracted into the groove of the groove portion 30. Nevertheless, the improvement in power generation capacity as shown in FIG. 3 can be explained as follows.

  In the anode side gas diffusion layer 23 of the fuel cell 10 having the groove portion 30, the hydrogen gas flows into the anode side gas diffusion layer 23 from the gas inflow side 23 b, passes through the bottomed groove portion 30, and then flows downstream. Flowing. When the hydrogen gas flowing in this way passes through the bottomed groove part 30, it takes away the water component entering the inside of the groove part 30 to the downstream side. Then, the water component distribution (water component concentration) is shifted between the MEA sandwiching the anode-side gas diffusion layer 23 corresponding to the bottom portion 23c of the bottomed groove 30 and the inner region of the groove 30. In this case, since the anode side gas diffusion layer 23 corresponding to the bottom portion 23c of the bottomed groove portion 30 can transmit the water component, the water component moves from the MEA including the electrolyte membrane 20 toward the inner region of the groove portion 30. Will go on.

  On the other hand, the anode-side gas diffusion layer 23 and the cathode-side gas diffusion layer 24 facing each other across the MEA including the electrolyte membrane 20 have the opposite gas flow as described above. In the cathode gas diffusion layer 24, the gas inflow side 23b in 23 is the downstream side of the air flow (cathode downstream side). At the cathode 22, water is generated along with the electrochemical reaction, and the generated water is carried by the air flowing through the cathode side gas diffusion layer 24 and increases on the downstream side of the cathode. That is, the region where the movement of the water component from the MEA toward the inner region of the groove portion 30 on the anode side gas diffusion layer 23 side and the region that tends to generate excessive water in the cathode side gas diffusion layer 24 form the electrolyte membrane 20. Matches across the MEA. In addition, since the generated water diffuses and penetrates even in the MEA including the electrolyte membrane 20, the generated water in the cathode side gas diffusion layer 24 diffuses and passes through the MEA including the electrolyte membrane 20, and then from the MEA. It moves toward the inner area of the groove 30.

  Such a phenomenon continues during the passage of the hydrogen gas groove 30 in the anode side gas diffusion layer 23, that is, during the gas supply for battery power generation, so that the MEA, specifically, the electrolyte membrane 20 included therein is used as the cathode. Due to the diffusion permeation of the generated water from the side gas diffusion layer 24, it naturally becomes wet. As a result, it can be said that in the fuel cell 10 of the present embodiment having the groove portion 30, the electrolyte membrane 20 can be more reliably wetted to increase the power generation capability, and this result is reflected in FIG. 3. Moreover, the MEA including the electrolyte membrane 20 is formed on the entire surface of the anode-side gas diffusion layer 23, more specifically on the outer surface of the anode-side gas diffusion layer 23 corresponding to the bottom portion 23c of the groove 30 on the gas inflow side 23b and on the downstream side of the groove 30. The anode 21 is joined to the outer surface of the anode side gas diffusion layer 23. Therefore, gas can be supplied from the anode side gas diffusion layer 23 corresponding to the bottom portion 23c of the groove 30 on the gas inflow side 23b to the anode 21, and the anode 21 can also be supplied from the anode side gas diffusion layer 23 on the downstream side of the groove 30. Therefore, the gas supply efficiency can be suppressed, and the electrolyte membrane 20 included in the MEA can be used in all the power generation regions, so that the power generation capacity is not reduced.

  In this way, the anode-side gas diffusion layer 23 can be permeated into the anode-side gas diffusion layer 23 through the anode-side gas diffusion layer 24 through the anode-side gas diffusion layer 23 corresponding to the bottom portion 23c of the groove portion 30. Even when unhumidified hydrogen gas is supplied to the layer 23, the water component can be distributed to the anode-side gas diffusion layer 23. Therefore, in the fuel cell 10 of the present embodiment, a high power generation capability can be obtained even if hydrogen gas is supplied in a non-humidified state, and the configuration for humidifying the hydrogen gas can be omitted or simplified, and the cost is reduced accordingly. Can be achieved. That is, according to the fuel cell 10 of the present embodiment, the application to the non-humidifying operation can be enhanced, and when a humidifier for gas humidification is provided, power generation by gas humidification with a small capacity humidifier. It becomes possible to drive.

  Further, in this embodiment, the bottomed grooves 30 are arranged in multiple rows on the gas inflow side 23b so as to extend downstream, and the groove 30 is made to flow in the direction of hydrogen gas flowing through the anode side gas diffusion layer 23. Since they are extended in parallel, the flow of hydrogen gas can be made substantially uniform in each groove 30. For this reason, the diffusion permeation of generated water from the cathode side gas diffusion layer 24 side that occurs in the anode side gas diffusion layer 23 corresponding to the bottom portion 23c of each groove 30 is substantially uniform for each groove 30 and is therefore included in the MEA. Wetting of the electrolyte membrane 20 becomes uniform, which is more preferable from the viewpoint of improving the power generation capability.

  In addition, in the gas separator 25 joined to the anode side gas diffusion layer 23, the flow direction of hydrogen gas in the anode side gas diffusion layer 23 is defined by the multi-row fuel gas flow paths 47 in the cell, and FIG. As shown in FIG. 2, the ribs between the multi-row in-cell fuel gas flow paths 47 are brought into contact with the ribs between the multi-row groove portions 30. Therefore, hydrogen gas can be easily and more uniformly supplied to the respective groove portions 30 from the corresponding in-cell fuel gas flow paths 47, which is further preferable in terms of improving the power generation capacity.

  Next, in the fuel cell 10 of the present embodiment, the anode side MPL layer 23a is provided in addition to the groove portion 30, and the advantages of the anode side MPL layer 23a will be described. As described above, the anode side MPL layer 23a holds the carbon particles with the electrolyte resin (fluorine resin constituting the electrolyte membrane 20) and continuously pores, and ion exchange groups (sulfone groups in the fluorine resin) of the electrolyte resin. Thus, the water component is retained in the continuous pores. FIG. 4 is a graph showing the relationship between the basis weight when forming the anode-side MPL layer 23a and the moisture content in the MPL layer, and FIG. 5 shows the basis weight when forming the anode-side MPL layer 23a and its layer thickness. FIG. 6 is a graph showing the relationship between the layer thickness of the anode MPL layer 23a and the generated voltage when hydrogen gas is supplied without humidification.

As shown in the graphs of FIGS. 4 to 5, as the basis weight of the anode side MPL layer 23a increases, the water content (water retention amount) in the anode side MPL layer 23a increases and the layer thickness also increases. On the other hand, as shown in FIG. 6, the layer thickness of the anode side MPL layer 23 a affects the power generation voltage. If the layer thickness is in the range of 100 to 200 μm, it is effective in suppressing the decrease in power generation capacity. . That is, when the layer thickness of the anode side MPL layer 23a exceeds 200 μm, the increase in the internal resistance of the anode side MPL layer 23a itself due to the increase in the layer thickness becomes remarkable, and the generated voltage is considered to decrease. On the other hand, when the layer thickness of the anode side MPL layer 23a is less than 100 μm, the water component retention in the anode side MPL layer 23a becomes insufficient, and the moisture on the anode side gas diffusion layer 23 side in the case of supplying hydrogen gas without humidification. It is thought that the power generation voltage will drop due to the shortage. Based on these findings, in the present embodiment, the anode-side MPL layer 23a has a layer thickness in the range of 100 to 200 μm, and the basis weight is 2.6 to 5.3 g / cm ² in accordance with this layer thickness. It was made the range.

  Next, advantages of the fuel cell 10 of the present embodiment provided with the groove portion 30 and the anode side MPL layer 23a will be described. FIG. 7 is a graph showing the dependence of the generated voltage and the cell internal resistance on the cell temperature when generating power by supplying hydrogen gas without humidification.

  The illustrated graph shows a comparative fuel cell that does not include the groove 30 and the anode-side MPL layer 23a, a reference fuel cell that includes the groove 30 but does not include the anode-side MPL layer 23a, and a groove that includes the anode-side MPL layer 23a. 10 shows the dependence of the generated voltage and the cell internal resistance on the cell temperature for the reference fuel cell having no 30, and the fuel cell 10 of the present embodiment having the groove 30 and the anode MPL layer 23a. As shown in the figure, in the region Tx where the cell temperature is low, in the comparative example fuel cell, both reference fuel cells, and the fuel cell 10 of this example, there is no significant difference between the generated voltage and the cell internal resistance. When the value rises, in the comparative fuel cell, a significant decrease in voltage and an increase in cell internal resistance are observed, and the battery performance decreases. In the reference fuel cell having either the groove 30 or the anode side MPL layer 23a, a higher cell capacity can be obtained than in the comparative example fuel cell, and in the fuel cell 10 of the present embodiment having both the groove 30 and the anode side MPL layer 23a. Due to the synergistic effect of the groove 30 and the anode side MPL layer 23a, higher battery performance could be obtained. That is, according to the fuel cell 10 of the present embodiment, the anode of the produced water that has passed through the electrolyte membrane 20 from the cathode-side gas diffusion layer 24 by the groove 30 can be obtained even by non-humidified hydrogen gas supply that cannot occur much in normal operation. High battery performance can be obtained by diffusion penetration into the side gas diffusion layer 23 and water retention by the anode side MPL layer 23a.

  Further, in the fuel cell 10 of this example, the cathode side water-repellent layer 24 a is provided on the MEA side in the cathode side gas diffusion layer 24. Therefore, the water-repellent function of the cathode-side water-repellent layer 24 a can positively diffuse and permeate the water generated in the cathode-side gas diffusion layer 24 through the electrolyte membrane 20 and into the anode-side gas diffusion layer 23.

  Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. FIG. 8 is an exploded explanatory view showing a schematic configuration of a single cell 15A according to a modified example, and FIG. 9 is an explanatory view schematically showing the single cell 15A according to the modified example in cross section.

  As shown in the figure, the unit cell 15A of this modification is not a substitute for the unit cell 15 of the embodiment described above in the configuration of the MEA, the groove 30, the anode side gas diffusion layer 23, the cathode side gas diffusion layer 24, and the like. The groove 30 is provided with an electrolyte resin (fluorine-based resin 31) constituting the electrolyte membrane 20, and the state in which the groove 30 is provided with the fluorine-based resin 31 is indicated by 30/31 in the figure. Yes. In this case, for example, an electrolyte resin (fluorine-based resin 31) is applied to the wall surface of the groove 30 so that hydrogen gas can pass through the groove 30. In the single cell 15A of this modification, the water content in the anode-side gas diffusion layer 23 can be increased by holding the water component by the ion exchange group (sulfone group) of the electrolyte resin (fluorine resin 31) in the groove 30. The retention of the water component by the electrolyte resin (fluorine resin 31) in the groove portion 30 occurs in parallel with the removal of the water component by the hydrogen gas passing through the groove portion 30 described above. Therefore, in this modification, the moisture content in the anode-side gas diffusion layer 23 can be increased while wetting the electrolyte membrane 20 described above by removing the water component that has entered the groove 30. Normally, when the fuel cell continues to operate at a high temperature, the moisture tends to be insufficient. However, as described above, the moisture shortage can be compensated by the water retention in the fluororesin 31 of the groove 30. The power generation capacity can be maintained. In this case, the moisture retention by the fluororesin 31 in the groove 30 can suppress a decrease in power generation capacity even during the operation accompanying the supply of non-humidified hydrogen gas.

  In the single cell 15A of this modification, the water component is retained by the fluororesin 31 in the groove portion 30, and therefore the anode side MPL layer 23a can be omitted. Alternatively, the anode-side gas diffusion layer 23 may have a layer configuration in which streaky anode-side MPL layers 23a and streaky water-repellent layers along the gas flow direction are alternately arranged in a direction intersecting the gas flow. A water repellent layer may be provided instead of the anode side MPL layer 23a. In order to alternately arrange the streaky anode side MPL layer 23a and the streaky water repellent layer, a slurry spray nozzle in which carbon particles are dispersed in a fluororesin solution and a water repellent spray nozzle are used as gas. The slurry and the water repellent may be spray-applied to the surface of the anode-side gas diffusion layer 23 from an injection device alternately arranged in a direction crossing the flow of the gas and dried. In the case of a water repellent layer, a water repellent may be applied to the surface of the anode side gas diffusion layer 23 and dried. The water repellent layer thus formed on the anode side gas diffusion layer 23 functions to contribute to the removal of the water component from the groove 30. That is, in the anode-side gas diffusion layer 23 corresponding to the bottom portion 23 c, the generated water permeates from the cathode-side gas diffusion layer 24 side, so that the water-repellent layer on the surface of the anode-side gas diffusion layer 23 has the groove 30. This helps to move the water to the inner side of the water and contributes to the removal of the water component from the groove 30.

  In addition, it can also be modified as follows. In the embodiment described above, the groove part 30 along the gas flow direction is provided in the anode-side MPL layer 23a of the anode-side gas diffusion layer 23. The groove part 30 is provided in the anode-side gas diffusion layer 23 with the anode-side MPL. The hydrogen gas that has flowed in from the layer 23a may pass through the groove. Moreover, it can also be set as the simple recessed part which the groove part 30 depressed side by side. FIG. 10 is an exploded perspective view of a schematic configuration of a single cell 15B of a modified example in which the multi-row grooves 30 are arranged obliquely in the gas flow direction, and FIG. It is explanatory drawing which shows schematically the cross section of the single cell 15C of the modification which has the recessed part 30A. Even in the modified examples shown in these, it is possible to achieve the effect accompanying the wetting of the electrolyte membrane 20 by the removal of the water component by the hydrogen gas passing through the oblique groove 30 or the recess 30A. In FIG. 11, the concave portion 30 </ b> A is drawn and shown in a part of the anode-side gas diffusion layer 23. Alternatively, it may be formed wide across the diffusion layer width direction, or may be scattered on the gas inflow side 23b in this diffusion layer width.

  In the above embodiments, the polymer electrolyte fuel cell has been described as an example, but the present invention can be applied to various fuel cells such as a direct methanol fuel cell and a phosphoric acid fuel cell.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 15, 15A-15C ... Single cell 20 ... Electrolyte membrane 21 ... Anode 22 ... Cathode 23 ... Anode side gas diffusion layer 23a ... Anode side MPL layer 23b ... Gas inflow side 23c ... Bottom part 24 ... Cathode side gas diffusion Layer 24a ... Cathode-side water-repellent layer 25 ... Gas separator 26 ... Gas separator 30 ... Groove 30A ... Recess 31 ... Fluorine resin 47 ... In-cell fuel gas channel 48 ... In-cell oxidizing gas channel

Claims (6)

A membrane electrode assembly in which electrodes are formed on both membrane surfaces of an electrolyte membrane having proton conductivity; an anode-side diffusion layer provided on one electrode surface of the membrane electrode assembly; and the other membrane electrode assembly. A fuel cell comprising a cathode side diffusion layer provided on an electrode surface, wherein the gas flow in the cathode side diffusion layer and the anode side diffusion layer is reversed,
A bottomed recess is provided on the surface of the anode side diffusion layer opposite to the membrane electrode assembly,
The recesses, the The rewritable located on the inflow side of the gas, at a maximum, a fuel cell that is up to the center of the anode side diffusion layer from the inlet side portion of the gas flowing into the anode side diffusion layer. 2. The fuel cell according to claim 1, wherein the recesses are multi-row bottomed groove portions, and the groove portions extend downstream from the gas inflow side portion of the anode side diffusion layer. The fuel cell according to claim 2, wherein the groove extends in parallel with a flow direction of the gas flowing through the anode side diffusion layer. Claim 2 or is a fuel cell according to claim 3,
Furthermore,
Comprising a separator bonded to the anode side diffusion layer;
The separator is
Gas passages defining the gas flow direction in the anode side diffusion layer are provided in multiple rows on the anode side diffusion layer side, and ribs between the gas rows in the multiple rows are provided in the grooves in the multiple rows. The fuel cell is in contact with the rib between the two. The fuel cell according to any one of claims 1 to 4, wherein the recess has an electrolyte resin having proton conductivity while allowing gas to pass through the recess. The anode diffusion layer, the film on the side of the surface of the electrode assembly, according to claim 1 to claim 5 having a pore layer formed pores conductive powder held in electrolyte resin having proton conductivity The fuel cell according to any one of the above.

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