JP2005302420A - Manufacturing method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a fuel cell, which reduces the generation of a breakage of an electrolyte layer, and suppresses short circuit between a hydrogen permeable metal layer and a cathode. <P>SOLUTION: The manufacturing method of the fuel cell has: an electrolyte membrane comprising a hydrogen permeable metal layer containing hydrogen permeable metal and an electrolyte layer laminated on the hydrogen permeable metal layer and having proton conductivity; and an electrode laminated on the side opposite to the side where the hydrogen permeable metal layer is laminated in the electrolyte layer. The method includes processes of: (a) forming the electrolyte membrane on the hydrogen permeable metal layer under the prescribed temperature condition; and (b) forming the electrode on the electrolyte layer formed in the process (a), while the temperature condition hardly generating a breakage caused by thermal expansion in the electrolyte layer is held before the electrode is formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a fuel cell including a hydrogen permeable metal layer, an electrolyte layer, and an electrode.

  Conventionally, fuel cells having various structures have been proposed. For example, Patent Document 1 below discloses a fuel cell in which a palladium-based metal film having hydrogen permeability is disposed on the anode side of an electrolyte layer having proton conductivity. As such a fuel cell, for example, a solid electrolyte layer such as ceramics is formed on a hydrogen permeable metal layer which is a metal thin film, and a cathode electrode is thinly and uniformly formed on the film. A single cell can be manufactured, and the single cell and a separator as a current collector can be laminated to form a single cell. Various film forming methods can be used for manufacturing such a fuel cell. For example, using a laser ablation method, a dense solid electrolyte layer is formed on a hydrogen permeable metal layer under a high temperature condition, taken out of the chamber, and a general film formation method such as sputtering is used. Thus, the cathode electrode can be formed. In the case of forming such a plurality of films, a film forming method corresponding to the type of film is generally selected from the viewpoint of the overall film forming speed and cost.

JP-A-5-299105

  However, the fuel cell manufactured by such a method has a problem that a short circuit occurs between the hydrogen permeable metal layer and the cathode electrode. This problem is caused when the electrolyte membrane formed by forming a solid electrolyte layer on the hydrogen permeable metal layer under high temperature conditions is cooled when taken out of the apparatus used for the film formation, and the hydrogen permeability is further increased. This occurs because a defect occurs in the solid electrolyte layer due to a difference in thermal expansion between the metal layer and the solid electrolyte layer. The material for the electrode enters the defect portion on the solid electrolyte layer in the process of forming the cathode electrode, and the hydrogen permeable metal layer and the cathode electrode are short-circuited. As a result, performance degradation of the fuel cell has occurred. Such a problem is a common problem for fuel cells using solid oxides or solid polymers as the electrolyte layer.

  In view of these problems, an object of the present invention is to provide a method for manufacturing a fuel cell that reduces the occurrence of defects in an electrolyte layer and suppresses a short circuit between a hydrogen-permeable metal layer and a cathode electrode. .

  In view of the above problems, the fuel cell manufacturing method of the present invention employs the following method. That is, an electrolyte membrane comprising a hydrogen permeable metal layer containing a hydrogen permeable metal, an electrolyte layer laminated on the hydrogen permeable metal layer and having proton conductivity, and the hydrogen permeability in the electrolyte layer A method of manufacturing a fuel cell having an electrode laminated on a surface opposite to a surface on which a metal layer is laminated, wherein: (a) on the hydrogen permeable metal layer under a predetermined temperature condition, A step of forming an electrolyte layer; and (b) a defect caused by thermal expansion of the electrode on the electrolyte layer formed in step (a) before the formation of the electrode. The gist of the present invention is to provide a film forming process while maintaining difficult temperature conditions.

  According to the manufacturing method of the present invention, when forming an electrode, the temperature is maintained such that defects due to thermal expansion hardly occur on the electrolyte layer formed on the hydrogen permeable metal layer. That is, by controlling the temperature condition of the electrolyte layer formed on the hydrogen permeable metal layer, the occurrence of defects such as cracks in the electrolyte layer is suppressed. Since the electrode is formed on such an electrolyte layer, a short circuit between the hydrogen permeable metal layer and the electrode, which is caused when the electrode material enters the defect portion, can be suppressed.

  In the above fuel cell manufacturing method, the electrode is formed by the step (b) while the electrolyte membrane formed in the step (a) is held in the apparatus in which the film is formed. It is also good.

  According to this method of manufacturing a fuel cell, the electrolyte membrane is held in the apparatus in which the film is formed until the electrode is formed. That is, the electrolyte membrane moves to the electrode deposition step as it is under the temperature condition atmosphere at the time of deposition. Therefore, cooling by taking out the electrolyte membrane can be avoided, and occurrence of defects in the electrolyte layer can be suppressed. As a result, a short circuit between the hydrogen permeable metal layer and the electrode can be suppressed.

  The temperature condition held in step (b) of the method for manufacturing a fuel cell having the above-described configuration is a temperature difference within ± 100 ° C. based on the temperature condition at the time of film formation in step (a). Also good. According to this manufacturing method, the electrode is formed while maintaining the temperature within a range of ± 100 ° C. from the temperature condition during the formation of the electrolyte layer. By maintaining the temperature within this range, stress applied to the electrolyte layer due to thermal expansion can be relaxed, and defects in the electrolyte layer can be suppressed.

In the method of manufacturing a fuel cell having the above configuration, the electrolyte layer formed in the step (a) is a SrZrO ₃ perovskite as a proton conductive ceramic layer, and the temperature maintained in the step (b) The conditions may be such that the temperature difference from the temperature condition during the film formation in the step (a) is in the range of −75 ° C. to + 40 ° C.

According to this manufacturing method, the electrode is formed while maintaining a temperature difference within the range of −75 ° C. to + 40 ° C. from the temperature of forming the electrolyte layer. In particular, when the electrolyte layer is a SrZrO ₃ -based perovskite, the load stress caused by thermal expansion can be within an allowable range with respect to the strength of the electrolyte layer. Therefore, the frequency with which defects occur in the electrolyte layer can be significantly reduced.

  Step (b) of the method for producing a fuel cell having the above-described structure is a step of forming the electrode on the electrolyte layer while maintaining the temperature condition during the film formation in the step (a). It is also good. According to this manufacturing method, the electrode is deposited while maintaining the same temperature condition as in step (a). Therefore, no defects occur in the electrolyte layer during electrode formation, and the occurrence of a short circuit can be suppressed.

  In the manufacturing method of the fuel cell having the above-described configuration, any method may be used as a method for forming the electrolyte layer and the cathode electrode as long as the temperature condition during the film formation is controlled. The film formation in a) and the step (b) can be performed by a laser ablation method in which a film material is evaporated by laser irradiation.

  According to this manufacturing method, the electrolyte layer and the electrode are formed by laser ablation. In particular, a dense electrolyte layer can be formed by using a laser ablation method. Subsequent to the formation of the electrolyte layer, the temperature is controlled and the electrode is formed by a laser ablation method. By performing a series of manufacturing by such one film forming method, management of temperature conditions can be facilitated.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. Fuel cell structure:
B. Manufacturing method of MEA:
C. Temperature conditions:

A. Fuel cell structure:
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a single cell constituting a fuel cell as one embodiment of the present invention. The fuel cell of this example is a hydrogen separation membrane type fuel cell provided with a hydrogen separation membrane that separates hydrogen from fuel gas, and a plurality of single cells 10 shown in FIG. 1 are stacked to provide fastening force from both ends. A stack structure in which a plurality of single cells 10 are connected in series. The fuel cell of this example is a cross flow type in which the flow direction of the anode gas and the flow direction of the cathode gas are orthogonal directions. However, for the sake of simplicity, FIG. Yes.

  As shown in FIG. 1, this single cell 10 mainly includes gas separators 60, 70, an electrolyte membrane 50, and a cathode electrode 40 that serve as a flow path for a fuel gas and an oxidizing gas used for an electrochemical reaction in a fuel cell. MEA100 (Membrane-Electrode Assembly) etc. which are integrally provided, and the MEA100 is sandwiched between gas separators 60 and 70 from both sides. Although illustration is omitted here, in order to adjust the internal temperature of the stack structure, a refrigerant flow path through which a refrigerant for cooling the fuel cell passes is provided between each single cell or each time a predetermined number of single cells are stacked. It may be provided.

  The gas separators 60 and 70 are made of a conductive material such as carbon or metal, and are formed of a dense material that does not allow fuel gas and oxidant gas to permeate. The surface of the gas separator 60 has a concavo-convex shape that forms a fuel gas channel 65 that guides the fuel gas to the inside of the single cell 10, and the surface of the gas separator 70 has an oxidizing gas channel 75 that guides the oxidizing gas to the inside of the unit cell 10. The uneven shape to be formed is formed respectively.

  Of the flow paths of the gas separators 60 and 70, the fuel gas flow path 65 contains hydrogen-rich gas obtained by reforming hydrocarbon fuel as fuel gas, and the oxidant gas flow path 75 contains air as oxidizing gas. Are supplied respectively. The gas separators 60 and 70 have a function of collecting electricity generated by an electrochemical reaction between hydrogen in the supplied hydrogen-rich gas and oxygen in the air.

  The MEA 100 includes a hydrogen permeable metal layer 20 as a hydrogen separation membrane, an electrolyte membrane 50 including an electrolyte layer 30, a cathode electrode 40, and the like.

  The hydrogen permeable metal layer 20 is a layer made of a metal having hydrogen permeability, and can be formed of, for example, palladium (Pd), a Pd alloy, or the like. The hydrogen permeable metal layer 20 selectively permeates only hydrogen contained in the hydrogen rich gas out of the hydrogen rich gas supplied through the fuel gas flow path 65. In this embodiment, this hydrogen permeable metal layer 20 has a function as a hydrogen separation membrane, a catalyst function for activating hydrogen ionization (proton), and a function as an anode electrode. The hydrogen permeable metal layer 20 may be a composite metal film in which vanadium (V) is used as a base material and palladium (Pd) is laminated on both surfaces thereof.

The electrolyte layer 30 is made of a solid electrolyte having proton conductivity and is an electrically insulating layer. For the electrolyte layer 30, for example, BaCeO ₃ , SrCeO ₃ , SrZrO ₃ based perovskite or pyrochlore which are solid oxides can be used. The electrolyte layer 30 is formed as a thin film on the dense hydrogen permeable metal layer 20. Therefore, the film resistance can be reduced by reducing the thickness.

  The cathode electrode 40 is a metal layer formed on the electrolyte layer 30 and can be formed of, for example, Pd. The cathode electrode 40 can be formed of a noble metal having catalytic activity that promotes an electrochemical reaction. In order to promote the electrochemical reaction, a catalyst layer such as platinum (Pt) may be provided.

B. Manufacturing method of MEA:
Next, the manufacturing method of MEA100 which comprises said fuel cell is demonstrated. FIG. 2 is a process diagram showing a manufacturing process of the MEA 100. In this embodiment, a laser ablation method, which is a method for irradiating a target material with a laser and forming a film of atoms, molecules, ions, etc. emitted from the target material on a substrate, is used as a method for manufacturing the MEA 100. Since this method does not depend on the internal gas pressure like the sputtering method and the vapor deposition method, it is suitable for producing a material containing a gas such as oxygen.

  As shown in FIG. 2, when manufacturing the MEA 100, first, a hydrogen permeable metal substrate constituting the hydrogen permeable metal layer 20 is prepared, and this is placed in a film formation chamber KL, and the temperature in the chamber KL is set. The temperature rises to about 500 (° C.) (step S200). As a result, the temperature of the substrate also rises to around 500 (° C.). In this embodiment, the substrate is produced using a Pd alloy as the hydrogen permeable metal. In this process, the inside of the chamber KL in which the hydrogen permeable metal substrate is set is depressurized to a predetermined pressure, and a predetermined amount of oxygen is supplied in a high temperature atmosphere. The supplied oxygen is used for forming an electrolyte layer described later.

Subsequently, a solid oxide constituting the electrolyte layer 30 is used as a target material, and the target material is irradiated with a laser to form a solid oxide on a hydrogen permeable metal substrate (step S210). As the solid oxide used for this film formation, the aforementioned SrZrO ₃ perovskite is used. Of these atoms emitted by laser irradiation of the target material, the oxygen component is difficult to reach the substrate, but by incorporating oxygen in the high-temperature atmosphere supplied in step S200 described above, it is uniform and dense. A simple electrolyte layer 20 is formed.

  In this way, the ambient temperature of the state in which the electrolyte membrane 50 in which the electrolyte layer 30 is laminated on the hydrogen permeable metal layer 20 is managed as it is, and the target material is changed to the electrode material of the cathode electrode 40 (step S220). That is, the electrolyte membrane 50 on which the electrolyte layer 30 is formed moves to the formation of the cathode electrode 40 while being held in the chamber KL. As the target material, palladium constituting the cathode electrode 40 is used. In this step, oxygen that is no longer needed is exhausted from the chamber KL, and the chamber KL is in a vacuum state.

  Subsequently, by irradiating the changed target material with laser, the cathode electrode 40 made of palladium is formed on the electrolyte layer 30 formed on the hydrogen permeable metal layer 20 (step S230), and the MEA 100 is completed. In this step, the thickness of palladium is reduced, and the cathode electrode 40 is formed as a porous body.

  In the manufacturing method using the laser ablation method, the cathode electrode 40 is formed under the same temperature condition after the formation of the electrolyte layer 30. That is, the temperature of the electrolyte membrane 50 in a series of processes for manufacturing the MEA 100 is maintained at about 500 (° C.).

  As a general film formation method for the cathode electrode 40, a sputtering method that is excellent in energy efficiency and has a high film formation rate is often used. In this case, after forming a dense electrolyte layer on the hydrogen permeable metal layer using a laser ablation method, it is taken out from the chamber KL and a cathode electrode is formed using a sputtering method.

  In the manufacturing method of the present embodiment, the electrolyte membrane 50 is retained in the chamber KL throughout the manufacturing process. Therefore, the electrolyte membrane 50 in a high temperature state is suppressed from being taken out from the chamber KL and cooled. As a result, the materials having different coefficients of thermal expansion (the hydrogen permeable metal layer 20 and the electrolyte layer 30) contract with cooling, and the generation of defects due to stress during contraction on the electrolyte layer 30 side of the thin film is suppressed. Therefore, defects in the electrolyte layer 30 can be reduced, and the electrolyte layer 30 can be made thinner.

  Furthermore, even if the electrolyte layer 30 is deficient due to cooling after the cathode electrode 40 is manufactured while maintaining the temperature condition, the electrode material is suppressed from entering the deficient portion. Therefore, a short circuit between the hydrogen permeable metal layer 20 and the cathode electrode 40 due to the formation of the cathode electrode 40 can be suppressed.

  The MEA 100 manufactured in this way is sandwiched between gas separators 60 and 70 from both ends as shown in FIG. In the single cell 10, the occurrence of a short circuit between the hydrogen permeable metal layer 20 and the cathode electrode 40 is suppressed. The fuel cell stack is manufactured by stacking a predetermined number of the single cells 10 in series.

  The fuel cell stack manufactured by the method of the present embodiment can suppress a decrease in power generation performance. That is, the suppression of the short circuit of each single cell 10 has a great effect in suppressing the decrease in power generation performance by stacking the plurality of single cells 10.

  In this embodiment, the film formation of the electrolyte layer 30 and the cathode electrode 40 is performed using the laser ablation method. However, if the temperature condition is controlled, the film formation method may be changed according to each film. good. That is, it is possible to use the sputtering method for forming the cathode electrode 40 as long as the temperature condition for forming the electrolyte layer 30 on the hydrogen permeable metal layer 20 is maintained.

  In this embodiment, the temperature for forming the electrolyte layer 30 and the cathode electrode 40 is set to about 500 (° C.), but the temperature for forming the two layers is not necessarily equal. If the difference in film forming temperature between the two is within a range of about ± 100 (° C.), it is effective to reduce defects in the electrolyte layer 30 due to thermal expansion.

C. Temperature conditions:
The frequency of defects in the electrolyte layer due to the difference in film formation temperature described above varies depending on the material of the electrolyte layer to be formed. FIG. 3 is an explanatory diagram showing the relationship between the film forming temperature difference and the stress applied to the electrolyte layer when SrZrO ₃ -based perovskite (hereinafter referred to as perovskite) is used as the material of the electrolyte layer. The horizontal axis in FIG. 3 indicates the temperature difference (° C.) from the temperature at which the perovskite is formed, and the vertical axis indicates the maximum principal stress (MPa) applied to the perovskite.

  As shown in the figure, the stress applied to the perovskite increases almost linearly as the temperature difference becomes larger with reference to the temperature at which the perovskite is formed. For example, when the cathode electrode is formed at a temperature 100 (° C.) higher than that at the time of forming the perovskite, a tensile stress of about 130 (MPa) is applied to the perovskite. When the cathode electrode is formed at a temperature lower by 100 (° C.) than when the perovskite is formed, a compressive stress of about 130 (MPa) is applied to the perovskite.

  By setting the perovskite allowable stress with respect to the relationship between the temperature difference and the stress, an allowable temperature difference range can be specified. For example, based on the tensile strength of the perovskite, the stress on the tensile side and the stress on the compression side taking into account the safety factor are set. In the example shown in FIG. 3, the allowable stress on the compression side is set to 100 (MPa), and the allowable stress on the tensile side is set to 50 (MPa). In other words, the hatched area shown in the figure shows a range in which the frequency (probability) at which defects (cracks) occur in the perovskite that is the electrolyte layer is low.

The temperature difference that falls within the shaded range is an allowable temperature difference range in which almost no defects are generated in the electrolyte layer. In the case of the SrZrO ₃ -based perovskite that is the electrolyte layer 30 of the present embodiment, the cathode electrode 40 is maintained while maintaining a temperature difference within the range of −75 (° C.) to +40 (° C.) from the deposition temperature of the electrolyte layer 30. It is preferable to perform the film formation. In other words, the allowable temperature difference range of the SrZrO ₃ perovskite is in the range of −75 (° C.) to +40 (° C.).

In FIG. 3, the SrZrO ₃ perovskite has been described as an example. However, the temperature difference is similarly applied to other electrolyte layer materials, particularly BaCeO ₃ and SrCeO ₃ perovskite used in solid oxide fuel cells. The range of allowable temperature difference can be specified from the relationship between stress and stress. A short circuit between the hydrogen permeable metal layer 20 and the cathode electrode 40 can be suppressed by forming the cathode electrode while maintaining the temperature difference within such a range.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and can of course be implemented in various forms without departing from the spirit of the present invention. . In this embodiment, the laser ablation method has been described as a method for forming each layer, but an evaporation method or the like may be used.

It is a cross-sectional schematic diagram which shows schematic structure of the single cell which comprises the fuel cell as one Example of this invention. It is process drawing which shows the manufacturing process of MEA. It is explanatory drawing which shows the relationship between the film-forming temperature difference at the time of using perovskite as a material of an electrolyte layer, and the stress concerning an electrolyte layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Single cell 20 ... Hydrogen-permeable metal layer 30 ... Electrolyte layer 40 ... Cathode electrode 50 ... Electrolyte membrane 60, 70 ... Gas separator 65, 75 ... Gas flow path 100 ... MEA

Claims (6)

An electrolyte membrane comprising a hydrogen permeable metal layer containing a hydrogen permeable metal, an electrolyte layer laminated on the hydrogen permeable metal layer and having proton conductivity, and the hydrogen permeable metal layer in the electrolyte layer A method of manufacturing a fuel cell having an electrode laminated on a surface opposite to the surface laminated with
(A) depositing the electrolyte layer on the hydrogen permeable metal layer under a predetermined temperature condition;
(B) The electrode is formed on the electrolyte layer formed in the step (a) while maintaining a temperature condition in which defects due to thermal expansion are unlikely to occur in the electrolyte layer before the film formation. A method for producing a fuel cell, comprising: forming a membrane. A fuel cell manufacturing method according to claim 1,
A method of manufacturing a fuel cell, wherein the electrode is formed in the step (b) while the electrolyte membrane formed in the step (a) is held in an apparatus in which the film is formed. A method for producing a fuel cell according to claim 1 or 2,
The temperature condition held in the step (b) is a fuel cell manufacturing method in which the temperature difference within ± 100 ° C. is based on the temperature condition during the film formation in the step (a). A method of manufacturing a fuel cell according to claim 3,
The electrolyte layer formed in the step (a) is a SrZrO ₃ perovskite as a ceramic layer having proton conductivity,
The temperature condition held in the step (b) is a method for manufacturing a fuel cell, wherein a temperature difference from the temperature condition at the time of film formation in the step (a) is within a range of −75 ° C. to + 40 ° C. A method of manufacturing a fuel cell according to any one of claims 1 to 4,
The process (b) is a method of manufacturing a fuel cell, wherein the electrode is formed on the electrolyte layer while maintaining the temperature conditions during the film formation in the step (a). A method for producing a fuel cell according to any one of claims 1 to 5,
The film formation in the step (a) and the step (b) is a method of manufacturing a fuel cell, which is a laser ablation method in which a film material is evaporated by laser irradiation.

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