JP2006179233A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems of gas shortage and distribution flow failures, caused due to freezing of formed water and condensed water in a region except an electrode part of a membrane electrode assembly having an electrode catalyst, when a fuel cell starts below freezing point. <P>SOLUTION: In the fuel cell, in which a separator 11 provided with a fluid passage 16 for circulating hydrogen gas or air, is laminated on the membrane electrode assembly 21, and by installing a combustion catalyst 18 in a non-electrode region of the downstream of the fluid passage, and by reaction heat in the combustion catalyst, the downstream region of the passage is heated which is apt to cause the freezing, when starting below the freezing point. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell, and more particularly to improvement of a cell structure for improving its low-temperature startability.

As a conventional fuel cell, there is one as shown in Patent Document 1 or Patent Document 2. In the former, in order to prevent CO poisoning of the catalyst, CO oxidation catalyst is provided everywhere from the fuel gas supply line to the anode electrode, or for removing harmful substances at the same position on the cathode side. A configuration in which the catalyst is provided is disclosed. The latter discloses that the power generation is started when the outlet of the oxidant gas passage is heated to a predetermined temperature or higher.
JP-A-9-27326 JP 2003-303607 A

  In such a conventional fuel cell, there is a problem that the generated water or condensed water freezes in a region other than the electrode portion of the membrane electrode assembly having the electrode catalyst at the time of starting below freezing point, causing gas shortage and poor distribution.

  An object of the present invention is to improve the startability of a fuel cell by accelerating the temperature rise in the non-electrode region of the membrane electrode assembly to avoid freezing of water at the time of starting below freezing.

  In the present invention, a membrane electrode assembly in which an electrode composed of a fuel electrode or an oxidant electrode having an electrochemical reaction catalyst on an electrolyte membrane is formed, and a fluid passage for allowing the fuel or oxidant to flow is provided between the membrane electrode assembly and the membrane electrode assembly. A fuel cell is formed by laminating a separator formed therebetween.

  Further, a combustion catalyst is provided in the middle of the fluid passage, and it is possible to promote the temperature rise of the fuel cell by the reaction heat at the combustion catalyst when starting at a low temperature.

  By supplying, for example, a mixed fluid of fuel and oxidant to the fluid passage portion of the fuel or oxidant gas provided with the combustion catalyst, the fuel and oxidant react directly on the combustion catalyst to generate heat. Normally, an exothermic reaction occurs only in the region where the electrode catalyst is present, but as described above, heat is also generated in the combustion catalyst portion provided in the middle of the fluid passage. Freezing of generated water and condensed water in the region can be suppressed. Therefore, at the time of starting below freezing, the low temperature startability of the fuel cell can be improved by suppressing deficiency of fuel and oxidant gas and poor distribution due to freezing.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected and shown to the part which is common about each embodiment.

  FIG. 1 shows a first embodiment of the present invention, which shows an example in which the present invention is applied to a fluid passage portion on the fuel electrode side of a separator that constitutes a fuel cell together with a membrane electrode assembly. In the fuel cell according to the following embodiment, hydrogen gas is used as the fuel and air is used as the oxidant.

  In the figure, the separator 11 has a substantially rectangular plate shape, and along one side thereof, a hydrogen gas inlet manifold portion 12a, a cooling water outlet manifold portion 13b, an air inlet manifold portion 14a, and the opposite side thereof. An air outlet manifold portion 14b, a cooling water inlet manifold portion 13a, and a hydrogen gas outlet manifold portion 12b are provided along one side so that the respective fluid inlets and outlets face each other. FIG. 2 shows a membrane electrode assembly 21 laminated on the separator 11. The membrane electrode assembly 21 has the same external shape as the separator 11, and similarly to the separator 11, a hydrogen gas manifold portion 22 a, 22 b, a cooling water manifold portion 23 a, 23 b, and an air manifold portion 24 a, 24 b are provided. It is. A rectangular region sandwiched between the manifold portions located on both sides is a fuel electrode (or gas diffusion layer) 25.

  In a fuel cell for practical use, a fuel cell is constituted by a stack in which a large number of cells composed of the separator 11 and the membrane electrode assembly 21 are stacked. Each of the manifold portions forms a series of supply passages or discharge passages when the fuel cell stack is configured, and distributes fluids such as hydrogen gas, cooling water, and air to the cells, or discharge fluids from the cells. Has the function of gathering.

  The separator 11 is provided with a large number of ribs 15 having protrusions or protrusions in a substantially rectangular region from the inlet manifold portion 12a of hydrogen gas to the outlet manifold portion 12b on the other end side. A serpentine (meandering) fluid passage 16 through which hydrogen gas flows is formed between the electrode surfaces (gas diffusion layer 25) of the membrane electrode assembly 21 stacked adjacent to each other. Although not shown, a fluid passage for allowing air to flow is formed on the back side of the separator 11 so as to face the oxidant electrode surface of another adjacent membrane electrode assembly.

In this embodiment, a combustion catalyst is provided in a non-electrode region of the fluid passage 16 of the separator 11, that is, a region not opposed to the gas diffusion layer 25 of the membrane electrode assembly 21. More specifically, in this separator 11, the regions 17a and 17b in the vicinity of the hydrogen gas inlet manifold portion 12a and the outlet manifold portion 12b shown in the figure serve as the non-electrode regions, and therefore, the non-electrode in the vicinity of the outlet manifold portion 12b. The region 17b is covered with the combustion catalyst 18. Various combustion catalysts 18 such as Fe, Co, Cr, Ni, Ru, Pd, Cu, Zn, and Pt can be applied, but they are activated at a relatively low temperature from the viewpoint of improving the startability below freezing point. From the viewpoint of cost, a non-noble metal type is preferable. In addition, Fe or Cu-based materials are used because when Fe or Cu is eluted as ions in the water produced by the combustion reaction, it promotes the deterioration of the electrolyte membrane by H ₂ O ₂ that is a by-product of the electrochemical reaction during power generation. It is desirable to avoid.

  FIG. 3 shows a configuration example of a fuel cell system having a fuel cell stack composed of the separator 11 and the membrane electrode assembly 21. This is a fuel cell system having a hydrogen circulation line 32 including pure hydrogen as a fuel gas and including a hydrogen circulation pump 31. Hydrogen is supplied to the fuel electrode side of the fuel cell stack 34 through a hydrogen supply line 33 from a hydrogen storage means (not shown) such as a high-pressure hydrogen cylinder or a hydrogen storage alloy. Excess hydrogen gas discharged from the fuel cell stack 34 to the hydrogen discharge line 35 is re-supplied to the hydrogen supply line 33 via the hydrogen circulation line 32 having the hydrogen circulation pump 31. A valve 36 is provided in the hydrogen discharge line 35, and the valve 36 is normally closed when recirculating. However, when the valve 36 is opened as necessary, the exhaust hydrogen gas can be discharged to the exhaust side as it is. it can. On the other hand, air is supplied to the oxidant electrode side of the fuel cell stack 34 from a pressure increasing means (not shown) such as a compressor via the air supply line 37, and the reacted air is discharged from the air discharge line 38 to the outside. Reference numeral 39 denotes a control device that controls electric power extracted from the fuel cell stack 34.

  In the fuel cell system, electric power is generated by an electrochemical reaction in the fuel cell stack 34 with the supply of hydrogen gas and air. When starting below freezing, the water generated during this reaction freezes in the passage 16 of the separator 11, which may hinder gas flow and cause startup failure. On the other hand, under the configuration of the present embodiment, the moisture can be prevented from freezing by the reaction heat generated in the portion of the combustion catalyst 18, so that it is possible to smoothly start the fuel cell below freezing point. Become. On the fuel electrode side, the water generated by the direct reaction between hydrogen gas and oxygen in the air often freezes in the downstream area of the passage 16, which tends to cause poor distribution of hydrogen gas in the downstream area of the fuel electrode. On the other hand, in the present embodiment, the combustion catalyst 18 is provided in the non-electrode region 17b near the hydrogen gas outlet, so that the vicinity of the downstream region of the passage 16 can be heated to efficiently avoid the freezing of moisture. .

  In order to cause the combustion reaction in the combustion catalyst 18, it is necessary to provide means for supplying fuel and oxygen to the portion of the combustion catalyst 18, but the fuel that operates using hydrogen gas and air as the reaction gas as described above. In a battery system, such a supply means is not necessarily provided. That is, in the fuel cell system as described above, it takes several hours for the temperature of each part of the system to reach below freezing after the operation is stopped. During this time, the fuel electrode of the hydrogen supply line 33 and the fuel cell stack 34 is required. The neighborhood, the inside of the hydrogen discharge line 35 and the hydrogen circulation line 32 are replaced with air due to the influence of air intrusion from the outside and the cross leak from the air electrode side of the fuel cell stack 34. For this reason, when hydrogen gas is initially introduced into the fuel cell stack 34 at the time of starting below freezing, a mixture of hydrogen and air is naturally supplied to the fuel electrode. Thereby, in the combustion catalyst 18, a combustion reaction can be obtained within a limited time by the mixture of hydrogen and air.

  However, when a combustion catalyst is provided on the air electrode side, it is necessary to provide a fuel supply means for the combustion reaction. As such supply means, for example, as shown by a broken line in FIG. 3, a fuel distribution line 41 that connects the hydrogen supply line 33 and the air supply line 37 and a valve 42 that opens and closes the fuel distribution line 41 are provided. In this case, at the beginning of the system below freezing point, the valve 42 is opened prior to the start of air supply, and the pressurized hydrogen gas from the hydrogen supply line 33 is introduced into the air supply line 37 in a required amount. Thereafter, the supply of air is started after the valve 42 is closed. As a result, since a mixed gas of hydrogen and oxygen is supplied to the air electrode side at the beginning of startup, it is possible to cause a combustion reaction in the combustion catalyst provided on the air electrode side. When the combustion catalyst is provided in the fluid passage on the air electrode side, the freezing of moisture tends to occur in the downstream area of the passage on the fuel electrode side as described above. If provided, freezing can be prevented efficiently.

  4 and 5 show a second embodiment of the present invention. This is an example in which the combustion catalyst 18 is provided on the side of the membrane electrode assembly 21 similar to that shown in FIG. A gas diffusion layer 26 (see FIG. 5) exists in the same region so as to overlap the fuel electrode 25 in the figure. Around the fuel electrode 25 and around each manifold, there is a seal material impregnated portion 54 in which the substrate of the gas diffusion layer 26 is impregnated with a seal material. The gas and cooling water existing inside the diffusion layer are sealed so as not to leak to the outside.

In the region near the hydrogen outlet manifold portion 22b, the base material of the gas diffusion layer 26 is not impregnated with the sealing material, and is formed on the surface of the material (for example, carbon fiber) constituting the porous base material of the gas diffusion layer 26. A combustion catalyst 18 is supported. Further, hydrophilicity is imparted to the region. In order to impart hydrophilicity, the base material of the gas diffusion layer 26 is impregnated with an oxide such as SnO ₂ , ZnO ₂ , SiO ₂ , ZrO ₂ , and TiO ₂ .

  As shown in FIG. 5, the gas diffusion of hydrogen and air is performed so as to overlap the region where the fuel electrode 25 is provided on one side of the electrolyte membrane 51 of the membrane electrode assembly 21 and the air electrode 52 is provided on the other side. Each layer 26 is present. In the region near the hydrogen outlet manifold portion 22b where no fuel electrode or oxidant is provided, the electrolyte membrane 51 is basically sandwiched by the seal material 53 or the seal material impregnated portion 54 impregnated with the seal material inside the gas diffusion layer. However, as described above, the combustion catalyst 18 is supported on the base material of the gas diffusion layer 26 in the vicinity of the hydrogen outlet manifold portion 22b on the fuel electrode side.

  According to this embodiment, the following effects can be expected in addition to the effects of the first embodiment. That is, the region of the gas diffusion layer 26 carrying the combustion catalyst 18 is a porous portion having a large number of pores for diffusing hydrogen as a fuel. By providing the combustion catalyst 18 in the gas diffusion layer 26, the combustion catalyst In 18, the moisture generated by the direct reaction between hydrogen and oxygen in the air is generated in the pores of the gas diffusion layer 26. Therefore, the possibility that the hydrogen passage portion in the separator is directly blocked by the generated water is reduced. Further, by imparting hydrophilicity to the portion of the gas diffusion layer 26 where the combustion catalyst 18 is provided, water generated by the combustion reaction can be easily held in the pores in the gas diffusion layer 26. Further, depending on the material of the combustion catalyst 18, the base material of the gas diffusion layer 26 is made hydrophilic so that the catalyst 18 can be easily carried on that portion.

  6 and 7 show a separator and a membrane electrode assembly according to the third embodiment of the present invention, respectively. The separator 11 is configured such that the reaction gas flows in one direction along the longitudinal direction, and the fuel gas and the air are of a counterflow type in which the gas flows from the opposite ends of the separator 11. In this separator 11, a large number of fluid passages 16 are formed in parallel with ribs 15 to communicate the hydrogen inlet manifold portion 12 a on one end side with the hydrogen outlet manifold portion 12 b on the other end side. In such a so-called straight channel separator 11, a diffuser 61 is provided between the manifold portion 12 a or 12 b and the end of the fluid passage 16 so that the gas is evenly distributed to a large number of fluid passages 16. ing. In other words, the diffuser 61 on the inlet side disperses the gas from the inlet manifold portion 12a in the creeping direction and uniformly flows into each of the many fluid passages 16.

  FIG. 7 shows a membrane electrode assembly 21 applied to the separator 11, which is structurally similar to that of FIG. 5, and the rectangular region facing the fluid passage 16 when the separator 11 is laminated is as follows. A gas diffusion layer 26 exists so as to overlap with the fuel electrode 25, and the base material of the gas diffusion layer 26 is impregnated with a sealing material around the fuel electrode 25 and each manifold portion. A material impregnated portion 54 is formed. However, the gas diffusion layer 26 is not impregnated with the sealing material and the combustion catalyst 18 is supported in the region facing the diffuser 61. In this embodiment, the area where the combustion catalyst 18 is carried is larger on the fuel inlet manifold portion 22a side than on the outlet manifold portion 22b side. This is to secure an area overlapping with the diffuser connecting the fluid passage through which the air on the back side of the separator flows and the outlet manifold portion 24b as a heating area. In this case as well, it is desirable to impart hydrophilicity to the supporting region of the combustion catalyst 18.

  In this embodiment, heating by the combustion catalyst 18 is performed on each of the upstream side and the downstream side of the hydrogen gas fluid passage 16. In this case, the reaction heat in the upstream combustion catalyst 18 heats the diffuser portion of the air passage on the back side thereof by heat conduction, and suppresses freezing of moisture on the air passage side. Further, the combustion catalyst 18 on the downstream side directly heats the downstream area of the fuel passage by the reaction heat, and secures the gas flow in the portion where moisture is likely to freeze at the time of low temperature startup. In a cell having such a straight channel separator 11, the diffuser 61 becomes a relatively large non-electrode region. Therefore, by making this portion a heating region by the combustion catalyst 18, the effect of suppressing freezing of water is great. It is.

  FIG. 8 shows a separator according to a fourth embodiment of the present invention. The separator 11 is coated with a combustion catalyst 18 on the surface portion excluding the rib-like portion of the diffuser 61 on the outlet side of the hydrogen gas fluid passage 16 and the non-electrode region excluding the portion of the diffuser 61 on the inlet side. . Since the gas diffusion layer region of the membrane electrode assembly (21) overlapping the surface in the vicinity of the inlet of the fluid passage 16 is not impregnated with the sealing material, the gas spreads through the diffusion layer, and therefore a groove-shaped passage or the like is provided. Even if not, when a mixed gas of hydrogen and air is supplied, a combustion reaction occurs on the surface of the combustion catalyst 18 near the inlet. Therefore, it is possible to obtain a fuel cell having a simple and small configuration and excellent low temperature startability.

The top view of the separator which concerns on the 1st Embodiment of this invention. The top view of the membrane electrode assembly which concerns on the 1st Embodiment of this invention. 1 is a schematic configuration diagram showing an embodiment of a fuel cell system to which a fuel cell according to the present invention is applied. The top view of the membrane electrode assembly which concerns on the 2nd Embodiment of this invention. Sectional drawing along the AA line of FIG. The top view of the separator which concerns on the 3rd Embodiment of this invention. The top view of the membrane electrode assembly which concerns on the 3rd Embodiment of this invention. The top view of the separator which concerns on the 4th Embodiment of this invention.

Explanation of symbols

11 Separator 12a Fuel (hydrogen gas) inlet manifold 12b Fuel outlet manifold 13a Cooling water inlet manifold 13b Cooling water outlet manifold 14a Oxidant (air) inlet manifold 14b Oxidant outlet manifold 15 Rib 16 Fluid passage 18 Combustion catalyst 21 Membrane electrode assembly 22a Fuel inlet manifold 22b Fuel outlet manifold 23a Cooling water inlet manifold 23b Cooling water outlet manifold 24a Oxidant inlet manifold 24b Oxidant outlet Manifold part 25 Fuel electrode 26 Gas diffusion layer 51 Electrolyte membrane 61 Diffuser

Claims (9)

A membrane electrode assembly in which an electrode composed of a fuel electrode or an oxidant electrode having an electrochemical reaction catalyst is formed on an electrolyte membrane, and a fluid passage through which the fuel or oxidant flows is formed between the membrane electrode complex. In a fuel cell formed by laminating a separator,
A combustion catalyst is provided in the middle of the fluid passage,
A fuel cell characterized in that a temperature rise at low temperature startup is promoted by a combustion action of the combustion catalyst.   The fuel cell according to claim 1, wherein the combustion catalyst is provided in a non-electrode region on the downstream side of the electrode of the membrane electrode assembly.   2. The fuel cell according to claim 1, wherein the combustion catalyst is provided in a region corresponding to a downstream region of the fuel fluid passage on the back side of the oxidant fluid passage of the separator.   The fuel cell according to claim 1, wherein the membrane electrode assembly includes a gas diffusion layer for diffusing fuel or an oxidant, and the combustion catalyst is provided on a surface of the gas diffusion layer.   The fuel cell according to claim 4, wherein hydrophilicity is imparted to a fluid passage in the vicinity of the gas diffusion layer.   The fuel cell according to claim 1, wherein the combustion catalyst is a non-noble metal catalyst excluding a Cu-based or Fe-based catalyst.   The fuel cell according to claim 1, wherein the fluid passage includes a diffuser at an inlet portion or an outlet portion thereof, and the combustion catalyst is provided in the diffuser portion.   2. The fuel cell according to claim 1, wherein a temperature rise is promoted by a reaction heat between the fuel and the oxidant on the combustion catalyst when starting at a low temperature.   The fuel cell according to claim 1, further comprising means for supplying a mixture of a fuel and an oxidant to the combustion catalyst at a low temperature startup.

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