JP2005310468A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell in which risk is scarce for a deterioration to occur with an electrocatalyst caused by an excessive rise of temperature during a warming up operation at the starting time. <P>SOLUTION: In the fuel cell provided with an anode electrode and a cathode electrode arranged on both sides of an electrolyte and with separators respectively arranged outside of the anode electrode and the cathode electrode, this is provided with a fluid flow passage which is arranged at least one separator and makes a fluid circulate from the face far separated from the face contacted with the electrode, and an exothermic reaction promoting means that is arranged at a fluid flow passage and makes the fluid generate exothermic reaction. The fluid is made to be circulated through the fluid flow passage at the starting time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell.

An electrochemical reaction that is a source of electricity generation in a fuel cell proceeds in the following steps. First, hydrogen delivered to the fuel electrode through the groove formed in the separator is decomposed into hydrogen ions and electrons in the presence of the catalyst.
Fuel electrode (anode) side: H ₂ → 2H ⁺ + 2e ⁻ (Formula 1)
The generated hydrogen ions pass through the electrolyte membrane, which is an ion conductor, and move to the air electrode. Since the electrolyte membrane has a property of allowing only ions to pass through, the generated electrons cannot pass through the electrolyte membrane and move to the air electrode through an external circuit. In a fuel cell, electricity is generated by such movement of electrons. On the other hand, the oxygen delivered to the air electrode reacts with hydrogen ions and electrons that have moved to the air electrode, thereby generating water.
Air electrode (cathode) side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (Formula 2)

For electric vehicle applications, fuel cells are required to generate electrical energy immediately after startup. At normal living temperatures (eg, about 15 ° C.), the fuel cell can draw current immediately, so it can be started in a reasonable amount of time and then to its preferred operating temperature (about 80 ° C.) until the internal resistance of the fuel cell. It is possible to quickly raise the temperature by heating using (hereinafter referred to as “IR heating”). However, rapid startup becomes difficult under cold conditions (for example, a low temperature of 0 ° C. or lower). At such a low temperature, the rate at which the electrochemical reaction represented by the above (formula 1) and (formula 2) generated in the MEA (membrane electrode assembly) occurs is greatly reduced. This reduces the amount of current that can be drawn from the fuel cell, limiting IR heating that can be introduced into the fuel cell. The cause of this decrease in response rate has not been precisely clarified. The conduction of H ⁺ ions in the solid polymer electrolyte becomes very poor at low temperatures, or the catalytic efficiency for electrochemical ionization of H ₂ and / or O ₂ becomes very poor at these temperatures. Therefore, it is considered that a significant amount of current cannot be drawn from the stack, and further, no corresponding IR heating occurs.

  Furthermore, in such a low-temperature environment, the entire fuel cell is completely cooled down, so that a little heat of reaction is generated by the electrochemical reaction or a slight amount of IR heating is generated. There is also a problem that the residual moisture from the water or water newly generated by the above reaction is condensed and frozen, and the gas flow path of the air electrode and the fine gas permeation holes of the diffusion layer are blocked.

Patent Document 1 discloses a technique for raising the temperature of a fuel cell by mixing hydrogen in an oxidant gas at the time of start-up, supplying it to the cathode, and causing an exothermic reaction on the cathode catalyst.
JP 2001-189164 A

  However, in the technique disclosed in Patent Document 1, the electrode catalyst may be excessively heated by the combustion of hydrogen and oxygen to deteriorate. Therefore, an object of the present invention is to provide a fuel cell in which the electrode catalyst is less likely to be deteriorated by an excessive temperature rise caused by a warm-up operation at the time of startup.

In order to solve the above problems, the present invention takes the following means. That is,
The invention according to claim 1 is a fuel cell comprising an anode electrode and a cathode electrode disposed on both sides of an electrolyte, and a separator disposed on the outside of the anode electrode and the cathode electrode, respectively. A fluid channel that is disposed in at least one of the separators and that circulates fluid to a surface away from a surface that contacts the electrode of the separator, and an exothermic reaction promoting unit that is disposed in the fluid channel and causes the fluid to react exothermically. The fuel cell is characterized in that a fluid is circulated through the fluid flow path at startup.
The invention according to claim 2 is the fuel cell according to claim 1, wherein the exothermic reaction promoting means is a catalyst.
According to a third aspect of the present invention, in the fuel cell according to the second aspect, the catalyst is configured to make the exothermic reaction in the fluid flow path uniform.
The invention according to claim 4 is the fuel cell according to any one of claims 1 to 3, wherein the fluid is a mixture of a hydrogen-containing gas supplied to the anode and an oxygen-containing gas supplied to the cathode. It is a gas.

  According to the first aspect of the present invention, since an exothermic reaction does not occur on the electrode catalyst, there is no possibility that the electrode catalyst deteriorates.

  According to the invention described in claim 2, an exothermic reaction can be performed with a simple configuration.

  According to the invention described in claim 3, it is possible to warm up efficiently by making the heat generation in the separator surface uniform.

  According to the fourth aspect of the invention, since the gas supplied to the fuel cell is used, it is not necessary to separately supply an exothermic reaction gas. There is no need to provide a member therefor.

  The fuel cell of the present invention comprises an anode electrode and a cathode electrode disposed on both sides of the electrolyte, and a separator disposed on the outside of the anode electrode and the cathode electrode, respectively. And a fluid flow path that allows fluid to flow to a surface away from the surface that contacts the electrode of the separator, and an exothermic reaction promoting means that is disposed in the fluid flow path and causes the fluid to exothermically react. A fluid is circulated through the flow path.

  FIG. 1 is a partially broken perspective view showing a fuel cell of the present invention. The illustrated fuel cell 100 is configured by stacking a plurality of unit cells C1, C2,. In FIG. 1, the cell C1 arranged on the foremost side is shown broken away from the middle in the surface direction, and the stacked structure of the unit cell C1 appears. This will be described in the section of FIG. In the stacking direction of the fuel cell 100 which is a stack of unit cells C1, C2,..., Manifolds penetrating each cell are formed on both sides of the cell. On the left side of the figure, a hydrogen gas inlet manifold 1, a cooling medium inlet manifold 2, and an air inlet manifold 3 are provided in order from the top. On the other hand, on the right side of the drawing, a hydrogen gas discharge manifold 4, a cooling medium discharge manifold 5, and an air discharge manifold 6 are provided in order from the top.

  In FIG. 1, the flow of the cooling medium flowing through the cooling medium flow path (see also FIG. 2) formed in the cell C1 on the near side is indicated by arrows. When the outside air temperature is a low temperature of, for example, 0 ° C. or less, a mixed gas of hydrogen and air is circulated through the cooling medium flow path, which will be described later.

  FIG. 2 is a diagram showing two cross-sections of the fuel cell unit cell according to the present invention arranged along a plane perpendicular to the cell stacking direction. Here, in correspondence with FIG. 1, the unit cell on the left side of the drawing is C1, and the unit cell on the right side is C2. In FIG. 2, the unit cells C1 and C2 are shown separated from each other, but this is for convenience of explanation. In an actual fuel cell, the unit cells are arranged in close contact with each other. Has been. The left and right unit cells C1, C2 have the same configuration. In the following description, the left unit cell C1 will be described, and the right unit cell C2 having the same configuration will be denoted by the same reference numerals as those of the unit cell C1 except that the unit cell C1 functions in combination with the unit cell C1. The description is omitted.

  The unit cell C1 is provided with an MEA (Membrane Electrode Assembly) 21 at the center thereof, and an anode side separator 23 is disposed on the left side and a cathode side separator 24 is disposed on the right side. In the figure, the MEA 21 is represented as a single body, but actually, it is composed of an electrolyte in the center, an anode (fuel electrode) on both sides, and a cathode (air electrode). And a diffusion layer disposed on the outer side and in contact with the separator.

  Hydrogen gas flow paths 23 a to 23 f are formed on the surface of the anode separator 23 facing the MEA 21. Cooling medium flow paths 23g to 23l are formed on the surface of the anode separator 23 opposite to the side where the hydrogen gas flow paths 23a to 23f are formed. On the other hand, air channels 24 a to 24 f are formed on the surface of the cathode separator 24 facing the MEA 21. Further, cooling medium flow paths 24g to 24l are formed on the surface of the cathode separator 24 opposite to the side where the air flow paths 24a to 24f are formed.

  As described above, since the unit cell C1 and the unit cell C2 are actually arranged in contact with each other, the cooling medium flow formed on the cathode separator 24 of the unit cell C1 shown on the left side of the drawing. The path 24g forms a flow path integrally with the cooling medium flow path 23g formed in the anode separator 23 of the unit cell C2 shown on the right side of the drawing. Similarly, the cooling medium flow paths 24h to 24l are formed integrally with the cooling medium flow paths 23h to 23l, respectively.

In a normal operation state of the fuel cell 100, the hydrogen gas supplied to the hydrogen gas inlet manifold 1 is circulated through the hydrogen gas passages 23a to 23f formed in the anode separator 23, thereby the catalyst of the anode. It is supplied to the layer and decomposed into hydrogen ions and electrons.
Anode side: H ₂ → 2H ⁺ + 2e ⁻
Then, the generated hydrogen ions pass through the electrolyte which is an ionic conductor and move to the cathode. Since the electrolyte has a property of allowing only ions to pass therethrough, the generated electrons cannot pass through the electrolyte and move to the cathode through an external circuit. In the fuel cell 100, electricity is generated by the movement of the electrons. Excess hydrogen not involved in the reaction is guided to the outside of the fuel cell 100 through the hydrogen gas discharge manifold 4.

On the other hand, the air supplied to the air inlet manifold 3 is circulated through the air flow paths 24a to 24f formed in the cathode separator 24 and supplied to the air electrode. Then, oxygen contained in the air reacts with hydrogen ions and electrons that have moved to the cathode, thereby generating water.
Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O
Excess air that did not participate in the reaction and water (including steam) generated as a result of the reaction are guided from the air discharge manifold 6 to the outside of the fuel cell 100.

  In such a normal operation state of the fuel cell 100, the temperature of the fuel cell that generates power most efficiently is said to be around 80 ° C. However, the above reaction is an exothermic reaction, and there is IR exotherm due to the flow of electricity in the fuel cell, and cooling is required because the temperature of the fuel cell rises above the optimum temperature. Therefore, in a normal operation state, relatively low temperature air or cooling water is circulated through the cooling medium flow path to optimize the fuel cell temperature.

  On the other hand, since the temperature of the fuel cell is lower than the optimum temperature at the start, it is preferable to quickly raise the temperature to the optimum temperature. In particular, when the ambient temperature is 0 ° C. or less, water generated by the power generation of the fuel cell freezes in the fuel cell, and the air and hydrogen gas in the fuel cell may not be sufficiently circulated. There is. Therefore, in one aspect of the present invention, when the fuel cell is started, heat generation promotion means is provided in a flow path that is used as a cooling medium flow path during normal operation, and heat generation is promoted in the flow path by the heat generation promotion means. The fluid was allowed to circulate.

  The type of fluid flowing through the flow path is not particularly limited in the present invention. For example, a mixture of hydrogen-containing gas supplied to the anode and air (oxygen-containing gas) supplied to the cathode Can be used.

  The type of heat generation promotion means is not particularly limited in the present invention, but an oxidation catalyst can be preferably used when the fluid to be used is the above-mentioned mixed gas of hydrogen-containing gas and air. Furthermore, the oxidation catalyst is preferably configured to make the exothermic reaction in the fluid flow path uniform. As a method for making the exothermic reaction in the fluid flow path uniform, for example, it is conceivable to lower the catalyst concentration on the side close to the cooling medium inlet manifold 1 and increase the concentration on the outlet side. Further, different types of catalysts may be used on the entrance side and the exit side. Furthermore, the surface area of the catalyst may be different between the inlet side and the outlet side.

By taking such a configuration, it was a problem in the prior art,
(1) When attempting to heat with electricity, the secondary battery capacity becomes too large.
(2) When the cooling water is to be heated by burning the fuel, the entire system is heated, so the efficiency is low and it takes too much time.
(3) When the fuel is mixed with the cathode air and burned in the combustor and supplied to the fuel cell body to be heated, the generated water is frozen in the fuel cell.
(4) When fuel is mixed with the cathode air and burned in the power generation catalyst layer to be heated, the produced water freezes in the fuel cell and accelerates the deterioration of the MEA due to local overheating. .
While avoiding such problems, it is possible to cause an exothermic reaction with a simple configuration, and it is possible to warm up efficiently by making the heat generation in the separator surface uniform. Further, since the gas supplied to the fuel cell is used, it is not necessary to supply a gas for exothermic reaction separately. There is also an advantage that it is not necessary to provide a member therefor.

  FIG. 3 is a diagram illustrating an example of a fuel cell system including the fuel cell 100. The illustrated fuel cell system 30 includes a fuel cell 100 main body, a hydrogen storage tank 31, and an air pump 32. At the time of cold start, the on-off valves 41, 42 are closed, and the on-off valves 33, 35, 36 are opened. The air sent from the air pump 32 is supplied from the hydrogen storage tank 31 and mixed with hydrogen that has passed through the on-off valve 33. Then, the mixed gas is supplied through the passage 34 to the coolant flow paths 23g to 23l (24g to 24l) of the fuel cell 100. The surface of the cooling medium flow paths 23g to 23l (24g to 24l) is coated with an oxidation catalyst as an exothermic reaction promoting means, and performs an oxidation reaction at a position where hydrogen and oxygen in the mixed gas are separated from the MEA. Heat is generated and the entire fuel cell 100 is warmed. The water (steam) generated by the oxidation reaction and the remaining mixed gas not involved in the reaction are discharged to the outside through the on-off valve 36.

  When the temperature of the fuel cell 100 is raised to a predetermined temperature, the on-off valves 41 and 42 are opened, and the on-off valves 33, 35, and 36 are closed. Hydrogen in the hydrogen storage tank 31 is supplied to the hydrogen gas passages 23a to 23f of the unit cells C1 and C2 from the passages branched through the on-off valve 41, and the air sent from the air pump 32 is supplied to the on-off valve 42. Then, the air is supplied from the branched passages to the air flow passages 24a to 24f of the unit cells C1 and C2, respectively, and supplied to the original power generation of the fuel cell 100. With this configuration, the fuel cell system 30 can be configured with minimal use of new members for warm-up.

  In the present invention, the above-described catalyst may be used as the exothermic reaction accelerating means. However, the present invention is not limited to this, and any other type may be used as long as it causes an exothermic reaction of the fluid. When an oxidation catalyst is used as the exothermic reaction promoting means, examples of usable catalysts include Pd (palladium), Pt (platinum), Ru (ruthenium), Ag (silver), Co (cobalt), Au (gold), Ni (nickel), Cu (copper), Mn (manganese), Fe (iron), etc. can be mentioned.

  In the above description, an example in which the cooling medium flow path is used as the flow path of the fluid to be circulated at start-up has been shown. However, a separate flow path may be formed on the surface away from the surface where the separator contacts the electrode. Good.

It is a partially broken perspective view which shows the fuel cell of this invention. It is a figure which shows two cross sections at the time of cut | disconnecting the fuel cell unit cell of this invention along the surface orthogonal to the lamination direction of a cell. It is a figure which shows a fuel cell system.

Explanation of symbols

Unit cell 1 Hydrogen gas inlet manifold 2 Coolant inlet manifold 3 Air inlet manifold 4 Hydrogen gas outlet manifold 5 Coolant outlet manifold 6 Air outlet manifold 21 MEA
DESCRIPTION OF SYMBOLS 23 Anode side separator 24 Cathode side separator 23a-23f Hydrogen gas flow path 24a-24f Air flow path 23g-23l, 24g-24l Cooling medium flow path 30 Fuel cell system 31 Hydrogen storage tank 32 Air pump 33, 35, 36, 41 42 Open / close valve 34 Passage 100 Fuel cell

Claims (4)

An anode electrode and a cathode electrode disposed on both sides of the electrolyte;
Further, a fuel cell comprising a separator disposed on each of the anode electrode and the cathode electrode,
A fluid flow path that is disposed in at least one of the separators and allows fluid to flow to a surface away from a surface that contacts the electrode of the separator;
An exothermic reaction accelerating means arranged in the fluid flow path and causing the fluid to react exothermically,
A fuel cell characterized by causing the fluid to flow through the fluid flow path at the time of startup. The fuel cell according to claim 1, wherein the exothermic reaction promoting means is a catalyst. The fuel cell according to claim 2, wherein the catalyst is configured to make an exothermic reaction in the fluid flow path uniform. 4. The fuel cell according to claim 1, wherein the fluid is a mixed gas of a hydrogen-containing gas supplied to the anode and an oxygen-containing gas supplied to the cathode.

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