JP5531222B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell employed in a polymer electrolyte fuel cell.

  As one type of fuel cell, a solid polymer fuel cell using a membrane made of a fluorine-based polymer or a hydrocarbon-based polymer as an electrolyte membrane is known. Such a polymer electrolyte fuel cell is generally introduced with an electrolyte membrane composed of an ion exchange membrane that selectively permeates cations (hydrogen ions) and a fuel gas (hydrogen gas or the like) of the electrolyte membrane. A fuel electrode (anode electrode) composed of a catalyst layer and a gas diffusion layer disposed on the surface, and an oxidant electrode (cathode) composed of a catalyst layer and a gas diffusion layer disposed on the surface into which the oxidant gas (air, etc.) is introduced Membrane Electrode Assembly (MEA) composed of an electrode).

In the polymer electrolyte fuel cell of the above-described type, when fuel gas and oxidant gas are supplied, on the fuel electrode side, a reaction that ionizes hydrogen gas into hydrogen ions and electrons occurs (the following formula 1), The ionized hydrogen ions (cations) move through the electrolyte membrane to the oxidant electrode side. On the oxidant electrode side, a reaction for generating water from oxygen, hydrogen ions and electrons in the air (Formula 2) occurs.
H ₂ → 2H ⁺ + 2e ⁻ Formula 1
2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O... Formula 2

  When the above reaction occurs, hydrogen ions ionized on the fuel electrode side move with water in the electrolyte membrane toward the oxidant electrode side (that is, hydrate with water retained in the electrolyte membrane). This moves from the fuel electrode side to the oxidant electrode side). Therefore, as the reaction proceeds, a phenomenon (so-called dry-up phenomenon) in which the water content of the electrolyte membrane on the fuel electrode side decreases occurs. When the dry-up phenomenon occurs, the water for moving the hydrogen ions is insufficient, the electric resistance when the hydrogen ions permeate the electrolyte membrane increases, and the power generation efficiency of the fuel cell decreases.

  On the other hand, during the operation of the polymer electrolyte fuel cell, the ambient temperature of the MEA changes from a temperature substantially equal to the outside air temperature to about 80 ° C. As such, when the ambient temperature of the MEA changes, the gas saturation vapor pressure of the water vapor (humidified water) supplied together with the hydrogen gas changes, so that a large amount of condensed water (surplus water) is generated in the vicinity of the fuel electrode. Sometimes. When a large amount of surplus water is generated in this manner, the water content of the polymer electrolyte membrane on the fuel electrode side increases, but a state where the surplus water adheres to the fuel electrode (so-called flooding phenomenon) occurs. When the flooding phenomenon occurs, the supply of hydrogen gas that diffuses in the gas phase using the pores of the catalyst layer constituting the fuel electrode as a conduction path is hindered, so that the ionization reaction in the fuel electrode is reduced and the oxidizer electrode The hydrogen ions and electrons that move to the side decrease, and the power generation efficiency of the fuel cell decreases as in the case where the dry-up phenomenon occurs.

  As described above, in order to keep the power generation efficiency of the polymer electrolyte fuel cell high, it is indispensable to appropriately secure the water content of the MEA, particularly the electrolyte membrane. Therefore, as a method of optimizing the humidity control in the power generation part of the fuel cell, as in Patent Document 1, the water is generated on the hydrogen electrode side by forming a catalyst layer on the fuel electrode side using a hydrogen storage alloy. To reduce the decrease in hydrogen ion conductivity due to dry-up, or as disclosed in Patent Document 2, a water retention layer is inserted between the MEA catalyst layer and the gas diffusion layer to absorb the generated water. Methods for reducing the occurrence have been proposed.

JP 2007-73252 A JP 2004-158387 A

  However, the method of forming a catalyst layer on the fuel electrode side using a hydrogen storage alloy as in Patent Document 1 requires a large amount of hydrogen storage alloy, and thus the thickness of the catalyst layer must be increased. In addition, the structure is complicated and the manufacturing cost is extremely high. Further, as in Patent Document 2, the method of inserting the water retention layer between the catalyst layer and the gas diffusion layer has to increase the thickness of the water retention layer, and the structure is complicated as in the method of Patent Document 1. At the same time, the manufacturing cost becomes extremely high.

  An object of the present invention is to solve the above-mentioned problems of the conventional fuel cell, and to produce a simple structure at low cost, and to improve the power generation efficiency of the fuel cell due to the occurrence of a flooding state and the occurrence of a dry-up state. An object of the present invention is to provide a practical fuel cell capable of suppressing the decrease.

In order to solve the above problems, a separator provided with a plurality of fuel gas passages is disposed on the fuel electrode surface side of a membrane electrode assembly comprising an electrolyte membrane, a fuel electrode and an oxidant electrode, and an oxidant for the membrane electrode assembly A fuel cell in which a separator provided with a plurality of oxidant gas passages is disposed on the electrode surface side, and a fuel gas having a relatively high humidity flows into the tip of each fuel gas passage. a first inflow path, relatively humidity and a second inlet passage for introducing the low fuel gas Rutotomoni, the tip of each oxygen-containing gas channel, respectively, the relatively high humidity oxidizing gas a first inflow passage for flowing, the second inflow path and characterized in that e Bei the for relative humidity to flow into the low oxidizing gas.

  The fuel cell of the present invention can easily manage the humidity of the fuel cell stack by controlling the supply amount of each gas having different humidity. Therefore, according to the fuel cell of the present invention, the power generation efficiency of the fuel cell can be maintained high. In addition, when dry-up occurs, a sufficiently humidified gas is supplied to the fuel cell stack, and when flooding occurs, a gas that can afford to take in the generated water is supplied to the fuel cell stack. The state can be quickly returned to an appropriate state. Therefore, according to the fuel cell of the present invention, the life of the fuel cell power generation facility can be extended.

  Hereinafter, an embodiment of a fuel cell according to the present invention will be described in detail with reference to the drawings.

Reference example

FIG. 1 is an explanatory view showing a vertical cross section of a fuel cell of a reference example. A fuel cell 1a includes a membrane electrode assembly (MEA) 2, a fuel electrode side separator 3, and an oxidant. It is composed of a pole-side separator 4 and a seal member 5. The MEA 2 is a fuel electrode (anode electrode) comprising an electrolyte membrane 6 made of an ion exchange membrane that selectively permeates hydrogen ions, and a catalyst layer and a gas diffusion layer disposed on the surface of the electrolyte membrane 6 where hydrogen gas is introduced. 7 and an oxidant electrode (cathode electrode) 8 including a catalyst layer and a gas diffusion layer disposed on a surface into which the oxidant gas (air) is introduced.

  FIG. 2 shows the surface of the separator 3 on the fuel electrode side. The separator 3 is made of a gas-impermeable material, and the fuel gas is applied to the surface (joint surface with the fuel electrode 4). A concave groove-like fuel gas passage 9 is provided for circulation. The fuel gas passage 9 includes a plurality of first passages 10 and 10 for allowing a relatively high humidity fuel gas to pass therethrough, and a plurality of second passages 11 and 11 for allowing a relatively low humidity gas to pass therethrough. have. Each of the first passages 10 and 10 and each of the second passages 11 and 11 is formed in a meandering manner by a horizontal groove that is long in the left-right direction and a vertical groove that connects the horizontal grooves to each other. The edges are alternately folded in the order of the edge → the edge on the right side → the edge on the left side → the edge on the right side. The first passages 10 and 10 and the second passages 11 and 11 are in a state of being arranged in parallel in the vertical direction and the horizontal direction at a predetermined interval.

  On the other hand, the separator 4 on the oxidant electrode side is also made of a gas-impermeable material, like the separator 3 on the fuel electrode side, so that the oxidant gas can flow through the surface joined to the oxidant electrode 8. The grooved oxidant gas passage 12 is provided. The oxidant gas passage 12 includes a plurality of first passages 13 and 13 for allowing a fuel gas having a relatively high humidity to pass therethrough, and a plurality of second passages 14 and 14 for allowing a gas having a relatively low humidity to pass therethrough. And have. Each of the first passages 13 and 13 and each of the second passages 14 and 14 includes horizontal grooves that are long in the left-right direction, as well as the first passages 10 and 10 and the second passages 11 and 11 of the separator 3. Are formed in a meandering manner by vertical grooves that connect the horizontal grooves to each other, and are alternately folded in the order of the left edge, the right edge, the left edge, the right edge, and so on. It is in the state. And it has the state arrange | positioned in parallel with the up-down direction and the left-right direction at predetermined intervals.

  In the fuel cell 1a, the fuel gas passage 9 of the separator 3 faces the fuel electrode 7 side, and the oxidant gas passage 12 of the separator 4 faces the oxidant electrode 8 side. , 10 and the second passages 11 and 11) and the oxidant gas passage 12 (the first passages 13 and 13 and the second passages 14 and 14), the seal member 5 is provided with the separators 3 and 4 and the MEA 2. Each of the separators 3 and 4 is formed by laminating the front and back surfaces of the MEA 2 in a state where the separators 3 and 4 are fitted in the recessed portions provided at the periphery of the MEA 2.

  When the fuel cell 1a configured as described above is used, a fuel gas having a high humidity is passed through the first passages 10 and 10 of the fuel gas passage 9, and a fuel gas having a low humidity is passed through the second passages 11 and 11. The oxidant gas having a high humidity is passed through the first passages 13 and 13 of the oxidant gas passage 12, and the oxidant gas having a low humidity is passed through the second passages 14 and 14. By doing so, the moisture and generated water in the supply gas move to a relatively dry portion, so that the occurrence of flooding and dry-up can be reduced.

  In the fuel cell 1a, as described above, the fuel gas passage 9 causes the first passages 10 and 10 to flow down the gas and the gas having a humidity different from that of the gas flowing down the first passages 10 and 10 down. The first passages 13 and 13 for flowing down the gas, and the gas flowing down the first passages 13 and 13, and the second passages 11 and 11. It is comprised from the 2nd channel | paths 14 and 14 for flowing down the gas from which humidity differs. Therefore, according to the fuel cell 1a, the humidity of the fuel cell stack can be easily managed by controlling the supply amount of each gas having different humidity. Therefore, according to the fuel cell 1a, the power generation efficiency of the fuel cell can be maintained high. In addition, when dry-up occurs, a sufficiently humidified gas is supplied to the fuel cell stack, and when flooding occurs, a gas that can afford to take in the generated water is supplied to the fuel cell stack. The state can be quickly returned to an appropriate state. Therefore, according to the fuel cell 1a, the life of the fuel cell power generation facility can be extended.

The structure of the fuel cell 1b of the example is substantially the same as the structure of the fuel cell 1a of the reference example , but the shape of the separator on the fuel electrode side and the separator on the oxidant electrode side is the same as that of the fuel cell 1a. Is different. FIG. 3 shows the surface of the separator of the fuel battery cell 1b of the embodiment. The separator 21 on the fuel electrode side has a plurality of fuel gases to circulate on the surface (joint surface with the fuel electrode 4). The fuel gas passages 23a, 23b, 23c. Each of the fuel gas passages 23a, 23b, 23c,... Is formed in a groove shape that is long in the left-right direction, and is arranged in parallel in the vertical direction. 4 conceptually shows the tip portions of the fuel gas passages 23a, 23b, 23c,..., And each fuel gas passage 23a, 23b, 23c,. Are provided with a first inflow passage 24 for injecting a high-fuel gas and a second inflow passage 25 for injecting a gas with relatively low humidity.

On the other hand, the separator 22 on the oxidant electrode side is also made of a gas-impermeable material, like the separator 21, and has a recess for circulating the oxidant gas on the surface joined to the oxidant electrode 8. A plurality of grooved oxidant gas passages 26a, 26b, 26c... Are provided. Like the fuel gas passages 23a, 23b, 23c,... Of the separator 21, the oxidant gas passages 26a, 26b, 26c,. In particular, a first inflow passage 27 for flowing in an oxidant gas having a relatively high humidity and a second inflow passage 28 for flowing in an oxidant gas having a relatively low humidity are provided. The other structure of the fuel cell 1b is the same as the structure of the fuel cell 1a of the reference example .

  When the fuel battery cell 1b configured as described above is used, the number of gas passages through which sufficiently humidified gas flows according to the amount of generated current, and gas passages through which gas that can afford to take in generated water is passed. Adjust the number of. That is, when the generated current is small, the number of gas passages through which sufficiently humidified gas flows is larger than the number of gas passages through which there is room for taking in generated water to prevent dry-up. For example, in the fuel gas passages 23b, 23c, 23e, 23f, 23h, 23i, 23k, 231 and 23n, fuel gas with relatively high humidity is supplied from the first inflow passage 24, and the fuel gas passages 23a, 23d, In 23g, 23j, and 23m, fuel gas with relatively low humidity is supplied from the second inflow passage 25. On the other hand, when the generated current is large, flooding is prevented by increasing the number of gas passages through which gas that can afford to take in the generated water flows through more than the number of gas passages through which sufficiently humidified gas flows. For example, in the fuel gas passages 23b, 23c, 23e, 23f, 23h, 23i, 23k, 231 and 23n, fuel gas having a relatively low humidity is supplied from the second inflow passage 25, and the fuel gas passages 23a, 23d, In 23g, 23j, and 23m, fuel gas with relatively high humidity is supplied from the first inflow passage 24. By doing so, the moisture and generated water in the supply gas move to a relatively dry portion, so that the occurrence of flooding and dry-up can be reduced.

In the fuel cell 1b, as described above, the fuel gas passages 23a, 23b, 23c,... Have a humidity different from that of the first inflow passage 24 for allowing the gas to flow in and the gas flowing in from the first inflow passage 24. A second inflow passage 25 for inflowing gas, and an oxidant gas passage 26 having a first inflow passage 27 for inflowing gas and a gas flowing in from the first inflow passage 27 And a second inflow passage 28 for allowing gases having different humidity to flow in. Therefore, according to the fuel cell 1b, as in the fuel cell 1a of the reference example , the humidity of the fuel cell stack can be easily managed by controlling the supply amount of each gas having different humidity. The power generation efficiency of the fuel cell can be maintained high. In addition, as with the fuel cell 1a of the reference example , the humidity state can be quickly returned to an appropriate state, so that the life of the fuel cell power generation facility can be extended.

  In addition, the structure of the fuel cell according to the present invention is not limited to the above-described embodiments. The MEA, the electrolyte membrane, the fuel electrode, the oxidant electrode, the separator, the fuel gas passage (the first passage, (Second passage, first inflow passage, second inflow passage), oxidant gas passage (first passage, second passage, first inflow passage, second inflow passage) etc. As long as it does not deviate from the gist of the present invention, it can change suitably if needed.

For example, when the fuel cell of the present invention is configured as in the above reference example , the number of first and second passages constituting the fuel gas passage or the oxidant gas passage is limited to two. 1 may be sufficient and 3 or more may be sufficient. The fuel cell of the present invention is not limited to the number of first passages and the number of second passages constituting the fuel gas passage or the oxidant gas passage, and the number of first passages and the number of first passages are the same. The number of the two passages may be different. In addition, both the fuel gas passage and the oxidant gas passage are not limited to those provided with the first passage and the second passage, either the fuel gas passage or the oxidant gas passage, What provided the 2nd channel | path may be used.

On the other hand, the fuel cell of the present invention, when configured for configured as the above embodiment, the first inflow path for all the fuel gas passage or oxidizing gas passage, it is not necessary to provide a second inlet passage, one It is also possible to provide the first inflow passage and the second inflow passage in the fuel gas passage or the oxidant gas passage of the part. In addition, the fuel gas passage and the oxidant gas passage are not limited to those provided with the first inflow passage and the second inflow passage, and the first inflow into either the fuel gas passage or the oxidant gas passage. A road and a second inflow path may be provided.

 Since the fuel cell of the present invention exhibits excellent effects as described above, it can be suitably used as a cell for various fuel cells.

It is explanatory drawing which shows the vertical cross section of a fuel cell. It is explanatory drawing which shows the mode of the surface of the separator of a reference example . It is explanatory drawing which shows the mode of the surface of the separator of an Example . It is explanatory drawing which shows the front-end | tip part of a fuel gas channel and an oxidant gas channel.

1a, 1b ... Fuel cell 2. MEA
3. ・ Separator (fuel electrode side)
4. ・ Separator (oxidizer electrode side)
6. Electrolyte membrane 7. Fuel electrode 8. Oxidant electrode 9. Fuel gas passage 10. First passage 11. Second passage 12. Oxidant gas passage 13. First passage 14. Second passage 21 ... Separator (fuel electrode side)
22. ・ Separator (oxidizer electrode side)
23 ·· Fuel gas passage 24 · · First inflow passage 25 · · Second inflow passage 26 · · Oxidant gas passage 27 · · First inflow passage 28 · · Second inflow passage

Claims (1)

A separator provided with a plurality of fuel gas passages is disposed on the fuel electrode surface side of a membrane electrode assembly including an electrolyte membrane, a fuel electrode, and an oxidant electrode, and a plurality of separators are provided on the oxidant electrode surface side of the membrane electrode assembly. A fuel cell comprising a separator provided with an oxidant gas passage,
At the tip of each of the fuel gas passages, a first inflow passage for injecting a fuel gas having a relatively high humidity and a second inflow passage for injecting a fuel gas having a relatively low humidity are provided. And
A first inflow passage for allowing an oxidant gas having a relatively high humidity to flow into the tip of each of the oxidant gas passages , and a second inflow passage for allowing an oxidant gas having a relatively low humidity to flow in, respectively. fuel cell, characterized in that example Bei and.

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