JP2004259457A - Reversible cell for hydro electrolysis and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reversible cell for hydro electrolysis and a fuel cell which can resolve the problems in machining/assembling dimensional accuracy associated with size increase and attain cost reduction, by adopting a flexible structure for a bipolar plate which is an important component part in the size increase and high performance of the reversible cell. <P>SOLUTION: The reversible cell includes at least one set of constitutional unit, consisting of a bipolar plate 1/a gas diffuser 2/an MEA 3/a gas diffuser 2/a bipolar plate 1, and the unit is sandwiched and pressurized by end plates 5. The polar plate 1 is a 0.2-3 mm thin-plate titanium or titanium alloy plate, molded by the superplasticity machining method. Mechanical damages to the gas diffuser and the MEA are reduced, and stable performance of the reversible cell over long term can be attained. When this constitutional unit is sandwiched and pressurized by the end plates, dimensional deviation of the gas diffuser or the MEA is absorbed due to the elastic effect of the bipolar plates, and the entire surface contact can be attained at a low pressure. As a result, the mechanical damages to the gas diffuser or the MEA are reduced, and the stable performance of the reversible cell in the long term can be attained. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is configured to have both functions of a water electrolysis tank for producing hydrogen and oxygen, and a fuel cell for obtaining electric power by electrochemically performing a combustion reaction using hydrogen as fuel and oxygen as an anode active material. Integrated reactor (referred to as “reversible cell” in this specification), in particular, a reversible cell for water electrolysis and a fuel cell using a polymer electrolyte membrane.
[0002]
[Prior art]
Using a polymer electrolyte membrane, a water electrolyzer (PEWE: Proton Exchange membrane type Water Electrolysis, hereinafter referred to as PEWE) for electrolyzing water to produce hydrogen and oxygen, and supplying hydrogen and oxygen in reverse. 2. Description of the Related Art A polymer electrolyte fuel cell (PEFC: Proton Exchange membrane type Fuel Cell, hereinafter referred to as PEFC) for generating power has been conventionally known. Since water electrolysis, which converts electrical energy into chemical energy to obtain hydrogen and oxygen, and a fuel cell, which converts chemical energy into electrical energy to generate electricity, are reversible reactions, they are integrated like a secondary battery. It is possible.
[0003]
Actually, since the two types of modules, PEFC and PEWE, have similar basic structures, research has been conducted on a polymer electrolyte fuel cell-water electrolysis reversible cell integrating these two modules. For a reversible cell using a polymer electrolyte membrane, Sweet et al. Disclose that 15 times of charging / discharging of a ULFC having an electrode area of 40 cm ² was performed (Intersociality Energy Conversion Conference p. 1.1227). -1.1232, 1993).
[0004]
In addition, Mitssky et al. Of Lawrence Livermore National Laboratory introduced that a reversible cell using a polymer electrolyte membrane was put to practical use in “Portable Fuel Cell International Conference” held in Switzerland in 1999 (F. Millitsky, B. Myers, AH Weisberg, T. M. Molter, and WF Smith, "Reversible (Unitized) PEM Fuel Cell, Internated presentation, Portable Cellphone, USA , June 21-24 (1 99);. Feature Artcle, Fuel Cells Bulletin, No.11 Aug (1999); UCRL-JC-134538). Here, a two-cell stack having an electrode area of 46 cm ² and a one-cell stack having an electrode area of 93 cm ² are introduced.
[0005]
In Japan, development of a reversible cell using such a polymer electrolyte membrane has been conducted. For example, Patent Document 1 discloses a catalyst material suitable for a reversible cell, and Patent Document 2 discloses a reversible cell for an automobile. Patent Literature 3 discloses a system for mounting the reversible cells for power load leveling, respectively.
[0006]
The reversible cell is basically a bonded body (MEA: Membrane Electrode Assembly, which is referred to as “MEA” in this specification) in which an electrode catalyst made of a platinum group metal is transferred and bonded to one solid polymer membrane. And two porous gas diffusers and two bipolar plates or end plates are laminated in the order of bipolar plate / gas diffuser / MEA / gas diffuser / dipolar plate. The structure has one or more (usually many) cells of the zero-gap diaphragm chamber type having one oxygen electrode chamber and one hydrogen electrode chamber per cell.
[0007]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-342965
[Patent Document 2]
JP-A-2002-135911
[Patent Document 3]
JP, 2002-142386, A
[Problems to be solved by the invention]
Some of the present inventors, aiming an increase in the size of the reversible cell, a prototype MEA with an electrode area of 100 cm ² greater than 93cm ^2, which have been published, are intensively developed important technologies in the size .
[0011]
The reversible cell and the PEFC are the same in the basic components, but in order to make the PEFC reversible, the materials of the components must be suitable for water electrolysis, that is, the materials differ. Further, in the case of PEFC, it is necessary to make each component have water repellency in order to quickly discharge water generated by burning hydrogen from the reaction site. In the case of a reversible cell, however, the repellency during fuel cell operation is required. It is required to have both functions of water and hydrophilicity during the operation of water electrolysis in a well-balanced manner.
[0012]
In the case of PEFC, a bipolar plate used for laminating single cells composed of one MEA is composed of a carbon material such as graphite. This is because carbon-based materials have resistance to hydrogen oxidation and oxygen reduction atmospheres. When these materials are used in PEWE, they are exposed to a highly oxidizing environment that generates oxygen, and are consumed as carbon dioxide. Resulting in. For this reason, a titanium material plated with platinum is used for the double electrode plate of PEWE.
[0013]
The multipole plate is provided with grooves serving as flow paths. In the conventional reversible cell, these flow paths have been produced by machining or press molding. Then, a gas diffuser / MEA / gas diffuser is laminated between a bipolar plate having such a large number of grooves, thereby forming a reversible cell. If uniform contact between these laminates is not sufficient, the contact resistance will be high, and as a result, the internal resistance during fuel cell or water electrolysis will be high, and a high efficiency energy converter cannot be obtained. In the case of PEFC, there is a porous body such as a flexible carbon fiber material, and the deviation in dimensional accuracy is absorbed by the flexible carbon fiber material, but in the case of a reversible cell, a carbon-based material cannot be used. Unless the dimensional accuracy of each is improved, there is a problem that uniform mutual contact of the laminates cannot be realized.
[0014]
On the other hand, since the laminate sandwiched between the bipolar plates is a porous body and a polymer film, it is very difficult to make the dimensional accuracy uniform. Therefore, the processing dimensional accuracy and assembly dimensional accuracy required for the bipolar plate become high, and this is a more difficult problem to achieve when the size of the reversible cell is increased.
[0015]
An object of the present invention is to increase the size and performance of a reversible cell, to provide a flexible structure to a bipolar plate, which is an important component, to solve the problem of processing and assembly dimensional accuracy accompanying the increase in size. An object of the present invention is to provide a cost-effective reversible cell of a water electrolysis and fuel cell.
[0016]
[Means for Solving the Problems]
The reversible cell of the water electrolysis and fuel cell according to the present invention has at least one set of constituent units consisting of a bipolar plate / gas diffuser / MEA / gas diffuser / bipolar plate, and this unit is sandwiched between end plates. In the pressurized water electrolysis and fuel cell reversible cells, the bipolar plate is characterized by being a thin titanium plate or a titanium alloy having a thickness of 0.2 to 3 mm formed by a superplastic working method. .
[0017]
A preferred embodiment of the bipolar plate is a valve metal such as titanium, particularly a titanium alloy suitable for superplastic working, for example, a titanium alloy of Ti-4.5Al-3V-2Fe-2Mo. More specifically, Al: 3.0 to 5.0 wt. %, V: 2.1 to 3.7 wt. %, Mo: 0.85 to 3.15 wt. %, O: 0.15 wt. %, And further contains one or more of Fe, Ni, Co and Cr, and 0.85 wt. % ≦ Fe (wt.%) + Ni (wt.%) + Co (wt.%) + 0.9 × Cr (wt.%) ≦ 3.15 wt.% % And 7 wt. % ≦ 2 × Fe (wt.%) + 2 × Ni (wt.%) + 2 × Co (wt.%) + 1.8 × Cr (wt.%) + 1.5 × V (wt.%) + Mo (wt.%) %) ≦ 13 wt. %, And the balance is a titanium alloy consisting of Ti and unavoidable impurities, or Al: 3.0 to 5.0 wt. %, V: 2.1 to 3.7 wt. %, Mo: 0.85 to 3.15 wt. %, O: 0.15 wt. %, And further contains one or more of Fe, Ni, Co and Cr, and 0.85 wt. % ≦ Fe (wt.%) + Ni (wt.%) + Co (wt.%) + 0.9 × Cr (wt.%) ≦ 3.15 wt.% % And 7 wt. % ≦ 2 × Fe (wt.%) + 2 × Ni (wt.%) + 2 × Co (wt.%) + 1.8 × Cr (wt.%) + 1.5 × V (wt.%) + Mo (wt.%) %) ≦ 13 wt. %, The balance being Ti and unavoidable impurities, and a titanium alloy having an α crystal grain size of 5 μm or less is preferable. In this case, it is desirable to apply platinum plating with a thickness of 0.3 μm or more to prevent insulation by the anodic oxide film (titanium oxide).
[0018]
Superplasticity refers to the property of being continuously deformed when a force exceeding a certain limit is applied and not returning to its original state. Superplastic working is a processing method utilizing such properties. Titanium and titanium alloys exhibit superplasticity at high temperatures, making use of this property to apply a technology to form difficult molded products that have complex shapes and high strength, and have problems with productivity and economics. It is called processing or superplastic forming. It is desirable that grooves serving as flow paths provided in the bipolar plate are provided at a pitch of about 0.1 to 2 mm in depth and about 0.5 to 3 mm in width, and the bipolar plate is sandwiched between these. It is necessary to have a complicated special shape for providing a function required for the reversible cell, such as a groove for fixing a gasket for shielding the space of the gas diffuser / MEA / gas diffuser from the outside. Yes, superplastic working is suitable as a technique for forming such a complicated shape.
[0019]
In the present invention, the reason why the thickness of the bipolar plate subjected to superplastic working is limited to 0.2 to 3 mm is that, when the thickness is 0.2 mm or less, a groove provided in advance is deformed when pressed due to insufficient strength. This is because if it is 3 mm or more, it does not have sufficient flexibility to absorb the deviation of the dimensional accuracy of the present invention.
[0020]
The MEA constituting the laminate of the present invention is suitable for hydrogen oxidation and hydrogen generation, and oxygen generation and oxygen reduction, such as platinum group metals such as Pt, Ir or Ru, or oxides / hydroxides thereof. A fine powder of an active metal catalyst is formed as a catalyst layer composed of a mixture of a solid polymer electrolyte and PTFE (polytetrafluoroethylene) on both opposite surfaces of a solid polymer electrolyte membrane. As the solid polymer electrolyte, a commercially available cation exchange membrane of perfluorosulfonic acid type, for example, Nafion, Aciplex, Flemion or the like is usually used.
[0021]
In the present invention, as the material of the base material of the gas diffuser, a valve metal is suitable for the material disposed on the oxygen electrode chamber side, and in particular, inexpensive Ti is suitably used. In the case of the arrangement on the hydrogen electrode chamber side, valve metal is of course suitable, but other than that, stainless steel or carbon can be used. The aggregate of the fibers constituting the gas diffuser has a fiber diameter of 30 to 100 μm from the viewpoints of gas and water flow, pressure loss, permeability of a liquid used for applying Pt and PTFE, and the like. And a non-woven fabric having a porosity of 70 to 90% and a thickness of about 0.3 to 1.0 mm is preferable. The non-woven fabric has a mechanical strength capable of maintaining a thickness of 0.3 to 0.7 mm even under a stress of ^{20 to} 150 kgf / cm ² applied when placed in a cell or pre-compressed. And those having flexibility.
[0022]
The base material of the gas diffuser disposed on the oxygen electrode chamber side needs to be a valve metal, and therefore, for the purpose of securing conductivity, electroplating, electroless plating, or thermal decomposition of a compound, Preferably, a coating is applied. When Ti is also used for the gas diffuser disposed in the hydrogen electrode chamber, Pt coating may be applied to prevent hydrogen embrittlement. If the coating amount of Pt is 0.4 to 20 mg / cm ² , a sufficient effect can be obtained.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the following description, the upper and lower parts refer to the upper and lower parts of the figure.
[0024]
FIG. 1 and FIG. 2 show an embodiment of the reversible cell of the water electrolysis and fuel cell of the present invention.
[0025]
The reversible cell has a plurality of component units each composed of a bipolar plate (1) / a gas diffuser (2) / MEA (3) / a gas diffuser (2) / a bipolar plate (1). A set of units is obtained by being sandwiched by end plates (5) from both ends thereof and pressed.
[0026]
A flow path (4) is formed in the bipolar plate (1). A coolant introducing plate (6) is provided so as to divide the plurality of units into two. Inside each end plate (5), an insulating plate (7) is provided near the end plate (5), and a power supply plate (8) is provided near the unit. An electric conduction plate (9) is arranged between the coolant introduction plate (6) and the units on both sides thereof, and a gas diffuser (9) arranged at the center of the bipolar plate (1) at the time of tightening. The pressure welding of 2) is not affected. Further, a space between the bipolar plate (1) and the gas diffuser (2) / MEA (3) / gas diffuser (2) sandwiched between the bipolar plate (1) is provided around the periphery of the bipolar plate (1). A gasket (10) for shielding from the outside is arranged.
[0027]
FIG. 2 shows a flow path used for coolant among the flow paths (4) of the bipolar plate (1), in which a coolant introduction plate (6) is inserted between the bipolar plates (1). Thus, the flow path (4a) on the back side of the bipolar plate (1) is directly used as a flow path for the coolant, and the coolant flows directly behind the contact portion between the bipolar plate (1) and the conductive plate (9). It is made to pass.
[0028]
The bipolar plate (1) is a thin titanium or titanium alloy having a thickness of 0.2 to 3 mm formed by a superplastic working method, and fixes a gasket (11) in addition to a groove serving as a flow path (4). And a groove for the same. The grooves serving as flow paths provided in the bipolar plate (1) are provided at a pitch of about 0.1 to 2 mm in depth and about 0.5 to 3 mm in width.
[0029]
The gas diffuser (2) is composed of an aggregate of conductive nonwoven fabric, the fiber diameter of the nonwoven fabric is 30 to 100 μm, the porosity is 70 to 90%, and the thickness is about 0.3 to 1.0 mm. It has been. The surface of each fiber is coated with a fluororesin that imparts water repellency, and the coating amount is in the range of 0.06 to 1.2 mg / cm ² .
[0030]
The MEA (3) is obtained by forming a fine powder of a platinum group metal catalyst on both opposite surfaces of a solid polymer electrolyte membrane as a catalyst layer composed of a mixture of a solid polymer electrolyte and PTFE (polytetrafluoroethylene). .
[0031]
The gas diffuser (2) and the MEA (3) are pressure-bonded before pressure by the end plate (5).
[0032]
(Example)
In the above reversible cell, it is determined whether the mutual contact of the bipolar plate (1) / gas diffuser (2) / MEA (3) / gas diffuser (2) / bipolar plate (1) is uniform. In order to do this, a pressure sensitive paper with a thickness of 200 μm (manufactured by Fuji Film, for ultra-low pressure, 0.2-0.6 MPa) (3) was inserted instead of the MEA, and pressure was applied from the outside, and the relationship between the pressing force and contact Was examined. As an example of the present invention, a groove provided with irregularities having a depth of 2.8 mm and a width of 3.5 mm is formed in a thin plate of 0.5 mm titanium alloy (Ti-4.5Al-3V-2Fe-2Mo) in a range of 150 mm × 167 mm. Thus, a bipolar plate (1) provided by superplastic working was produced. As shown in FIG. 3, the bipolar plate (1) is pressurized through a titanium end plate (5) having a thickness of 20 mm, and the gas diffuser (2) and pressure-sensitive paper (3) corresponding to the MEA are spread on the pressure-sensitive paper (3). The contact state of the bipolar plate (1) was examined.
[0033]
As a comparative example, as shown in FIGS. 4 (a) and 4 (b), uneven grooves having a depth of 1 mm and a width of 2 mm were formed on a surface of a titanium plate having a thickness of 20 mm in parallel with a range of 100 mm × 100 mm by cutting machining. Similarly, pressure-sensitive paper (3) was sandwiched between two bipolar plates (11) provided with flow paths (14), and pressure was applied as shown in FIG. The contact state of the gas diffuser (2) and the bipolar plate (11) with the pressure-sensitive paper (3) corresponding to the MEA was examined.
[0034]
First, for the comparative example, the pressure load was increased to 2 tons, 4 tons, and 6 tons, and traces of the contact pressure recorded on the pressure-sensitive paper (3) were examined. As a result, when a load of 6 tons was applied, contact was recognized on the entire contact surface. That is, in the case of the comparative example, it was found that the entire surface could be contacted by tightening at a pressure of 6000 kg ÷ 100 cm ² = 60 kg / cm ² . On the other hand, in the example using the bipolar plate (1) provided with the concave and convex grooves by the superplastic working, a pressure-sensitive impression of the entire surface contact was observed at a tightening load of 4 tons. That is, in the case of the example, it was found that the entire surface could be contacted by tightening at 4000 kg / 250 cm ² = 16 kg / cm ² and about 1/4 pressure.
[0035]
In a reversible cell composed of a polymer electrolyte membrane, a plurality of bipolar plates (1) / gas diffusers (2) / MEA (3) / gas diffusers (2) / multipolar plates (1) are externally connected. Pressing is further performed to achieve uniform contact between the members (1), (2), and (3). In such a configuration, there are non-uniform dimensional accuracy members such as the porous gas diffuser (2) and the MEA (3), and if the bipolar plate (11) is a rigid body manufactured by machining (comparative example), It can be seen that it is necessary to increase the pressure in order to obtain contact. On the other hand, when a thin plate of titanium or a titanium alloy having a thickness of 0.2 to 3 mm (1) formed by superplastic working is used as in the present invention, the porous gas diffuser ( Since the bipolar plate (1) absorbs the dimensional deviation of the MEA (3) and the MEA (3), the entire surface can be contacted with a low pressure. When the entire surface can be contacted at a low pressure, mechanical damage to the gas diffuser (2) and the MEA (3) is small, and a long-term stable reversible cell performance can be obtained.
[0036]
【The invention's effect】
According to the reversible cell of the water electrolysis and fuel cell of the present invention, since the bipolar plate is a thin titanium or titanium alloy having a thickness of 0.2 to 3 mm formed by a superplastic working method, the bipolar plate / gas diffuser / When the component unit consisting of MEA / gas diffuser / double electrode is sandwiched between the end plates and pressurized, the dimensional deviation of the gas diffuser and MEA is absorbed by the elastic effect of the double electrode, and the whole surface can be contacted at low pressure. Can be As a result, mechanical damage to the gas diffuser and the MEA is reduced, and long-term stable performance of the reversible cell is obtained.
[Brief description of the drawings]
FIG. 1 is a vertical sectional view showing an embodiment of a reversible cell of a water electrolysis and fuel cell according to the present invention.
FIG. 2 is a horizontal sectional view of the main part.
FIG. 3 is a perspective view showing an embodiment of a water electrolysis and fuel cell reversible cell according to the present invention.
FIG. 4 is a cross-sectional view showing a bipolar plate of a comparative example of a reversible cell for water electrolysis and a fuel cell.
FIG. 5 is a perspective view showing a reversible cell of a comparative example.
[Explanation of symbols]
(1) Bipolar plate (2) Gas diffuser (3) MEA
(4) Channel

Claims (4)

A reversible cell for water electrolysis and a fuel cell having at least one set of constituent units consisting of a bipolar plate / gas diffuser / MEA / gas diffuser / bipolar plate, wherein the unit is sandwiched by end plates and pressurized. In the reversible cell for water electrolysis and fuel cell, the bipolar plate is a thin titanium sheet or a titanium alloy having a thickness of 0.2 to 3 mm formed by a superplastic working method. 2. The reversible cell for a water electrolysis and fuel cell according to claim 1, wherein the grooves serving as flow paths provided in the bipolar plate are provided at equal intervals with a depth of 0.1 to 2 mm and a width of 0.5 to 3 mm. The reversible cell for water electrolysis and fuel cell according to claim 1 or 2, wherein the gas diffuser and the MEA are pressure-bonded. The reversible cell for water electrolysis and fuel cells according to claim 1 or 2, wherein the gas diffuser is an aggregate of fibers of a conductive substance, and the surface of each fiber is coated with a fluororesin having water repellency.

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