Fuel cell

Abstract

To provide a fuel cell provided with a separator having excellent durability in a cell environment when the fuel cell operates.SOLUTION: A fuel cell includes a power generation part and a laminate of a cell formed by a separator 12 arranged on both surfaces of the power generation part. The separator 12 includes a stainless steel base material 13 and a film 20 covering a surface 13a of a power generation part side of the stainless steel base material 13. The film 20 includes a titanium layer 22 on the surface 13a of the stainless steel base material 13, includes a carbon layer 28 on the outmost surface of the power generation part side, and includes a titanium carbide containing layer 26 containing titanium carbide and a titanium oxide containing layer 24 containing titanium oxide, from a side close to the carbon layer 28, between the titanium layer 22 and the carbon layer 28.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a fuel cell and a separator used in a fuel cell.

Background Art

[0002] For example, a fuel cell such as a polymer electrolyte fuel cell (PEFC) includes a plurality of structural units in which a membrane electrode gas diffusion layer composite (MEGA) sandwiching a polymer electrolyte membrane between an anode electrode and a cathode electrode is sandwiched by separators. Grooves serving as gas (hydrogen, oxygen, etc.) flow paths are formed in the separators.

[0003] As a separator for a PEFC, on the MEGA side of a metal substrate such as stainless steel, a titanium layer is provided on the surface of the stainless steel, and further, a conductive carbon layer is provided, so that the contact resistance of the separator can be reduced and the corrosion resistance can be improved (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, when a titanium layer and a carbon layer are formed by a PVD method, a titanium carbide layer is formed between the titanium layer and the carbon layer at that time. Depending on the in-cell environment during the operation of the fuel cell, it has been found that the carbon layer peels off due to the oxidation of the titanium carbide layer.

[0006] This specification provides a fuel cell including a separator having excellent durability in the in-cell environment during the operation of the fuel cell.

[0007] The technology disclosed in this specification is embodied in a fuel cell. The fuel cell includes a stack of cells composed of a power generation unit and separators disposed on both sides of the power generation unit. The separator includes a stainless steel base material and a film covering the surface of the stainless steel base material on the power generation unit side. The film includes a titanium layer on the surface of the stainless steel base material and a carbon layer on the outermost surface on the power generation unit side. Between the titanium layer and the carbon layer, from the side closer to the carbon layer, there are provided a titanium carbide-containing layer containing titanium carbide and a titanium oxide-containing layer containing titanium oxide.

[0008] According to this fuel cell, by providing a titanium oxide-containing layer in the film, peeling of the carbon layer due to oxidation of the titanium carbide-containing layer can be suppressed. As a result, the durability of the separator due to the in-cell environment during operation of the fuel cell is improved.

[0009] According to the disclosure of this specification, a separator provided with the above-described surface treatment film is also provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] In this specification, the fuel cell is not particularly limited, but for example, a polymer electrolyte fuel cell (PEFC) may be suitable in some cases. Also, the fuel cell can adopt various cooling forms such as a cooling form using a liquid refrigerant such as water or an air-cooling type.

[0012] Hereinafter, the fuel cell disclosed in this specification will be described with appropriate reference to the drawings. FIG. 1 shows an MEA-inclusive resin composite (hereinafter, also simply referred to as a composite) 4 constituting a cell 2 of a fuel cell that is a PEFC, and two separators 12 sandwiching the same.

[0013] FIG. 1 shows the structure of the cell 2 that constitutes the fuel cell 1. The cell 2 includes a membrane electrode and gas diffusion layer assembly (MEGA) 4 and a separator 12 that abuts on the MEGA 4 so as to partition the MEGA 4.

[0014] The MEGA 4 includes a membrane electrode assembly (MEA) 6 and gas diffusion layers 10a and 10b disposed on both sides thereof. The membrane electrode assembly 6 is composed of an electrolyte membrane 7 and a pair of electrodes 8a and 8b joined so as to sandwich the electrolyte membrane 7. The electrolyte membrane 7 is, for example, a proton-conductive ion exchange membrane formed of a solid polymer material. The electrodes 8a and 8b are a fuel electrode (anode) and an air electrode (cathode), respectively, and are both composed of known materials. The gas diffusion layers 10a and 10b are formed of a conductive member such as a carbon porous body having gas permeability. The EMGA 4 to MEA 6 is an example of a power generation unit in this specification.

[0015] The separator 12 is a plate-like member having a stainless steel base material 13. The separator 12 has a corrugated shape, faces the gas diffusion layers 10a and 10b of the MEGA 4, and forms flow paths 9a and 9b for hydrogen, which is a fuel gas, and air, which is an oxidant gas, between the separator 12 and the gas diffusion layers 10a and 10b, respectively. The surface 13b of the separator 12 that does not face the MEGA 4 is not particularly limited, but is appropriately provided with a surface treatment film and is joined, for example, to the separator 12 of another cell 2 laminated adjacent thereto.

[0016] Figure 2 is a schematic cross-sectional view showing an enlarged part of the separator for explaining the surface configuration of the separator 12. In the separator 12, a surface treatment film 20 composed of multiple layers is provided on the surface of the surface 13a of the stainless steel substrate 13 as the metal substrate facing MEGA4. As shown in Figure 2, the surface treatment film 20 includes a titanium layer 22 on the surface of the surface 13a. Further, a carbon layer 28 is provided on the surface of the surface 13a closest to MEGA4. Furthermore, between the titanium layer 22 and the carbon layer 28, there are provided a titanium carbide-containing layer 26 and a titanium oxide-containing layer 24 from the side closer to the carbon layer 28. The surface treatment film 20 is an example of the film in this specification.

[0017] The titanium layer 22 is formed directly on the surface 13a. The titanium layer 22 is composed of, for example, substantially titanium. Titanium binds strongly to stainless steel and carbon and has excellent corrosion resistance. The carbon layer 28 is the most distal from the surface 13a and is formed on the surface closest to MEGA4. The carbon layer 28 is composed of, for example, substantially carbon. The carbon layer 28 is composed of a crystal structure and / or an amorphous structure and may include a polycrystalline graphite structure.

[0018] The titanium carbide-containing layer 26 may be composed of TiC or may contain TiC and other components such as Ti. The titanium carbide-containing layer 26 is formed in the carbon layer 2 between the titanium layer 22 and the carbon layer 28. The titanium carbide-containing layer 26 is specified, for example, by containing TiC as a result of component analysis of the cross-section of the surface treatment film 20 by Auger electron spectroscopy as described later.

[0019] The titanium oxide-containing layer 24 may be composed of TiOx or may contain TiOx and other components such as Ti. TiOx appropriately changes according to the oxidation number of Ti and the manufacturing method. Typically, it is TiO2. The titanium oxide-containing layer 24 is formed on the side of the stainless steel substrate 13 closer to the titanium layer 22 than the titanium carbide-containing layer 26 between the titanium layer 22 and the carbon layer 28. The titanium carbide-containing layer 26 is specified, for example, by containing TiOx as a result of component analysis of the cross-section of the surface treatment film 20 by Auger electron spectroscopy as described later.

[0020] In FIG. 2, the surface treatment film 20 includes a titanium layer 22, a titanium oxide-containing layer 24, a titanium carbide-containing layer 26, and a carbon layer 28 in order from the surface 13a of the stainless steel substrate 13 toward MEGA4. These layers 22 to 28 are specified by detecting specific components, for example, by component analysis of the cross section of the surface treatment film 20 by Auger electron spectroscopy. For this reason, these layers 22 to 28 may overlap with adjacent layers or the like. For example, the titanium oxide-containing layer 24 is specified in the range including TiOx with the point including the peak of TiOx as the center in the layer thickness direction of the surface treatment film 20. The titanium carbide-containing layer 26 is specified in the range including TiC with the point including the peak of TiC as the center in the layer thickness direction of the surface treatment film 20. As a result, in the layer thickness direction of the surface treatment film 20, the titanium oxide-containing layer 24 and the titanium carbide-containing layer 26 may overlap with each other. Also, the titanium oxide-containing layer 24 may overlap with the titanium layer 22. Furthermore, the titanium carbide-containing layer 25 may overlap with the carbon layer 28.

[0021] These layers 22 to 28 in the surface treatment film 20 are not particularly limited, but can be formed, for example, by a physical vapor deposition (PVD) method such as a sputtering method or an ion plating method. For the titanium oxide-containing layer 24, for example, a method of introducing a gas containing oxygen into the chamber during the film formation of the titanium layer 22, or a method of exposing the stainless steel substrate 13 after the film formation of the titanium layer 22 to an air atmosphere or heat-treating it in an air atmosphere can be mentioned. Also, for example, by appropriately adjusting the bias voltage applied to the stainless steel substrate, the ratio of the titanium oxide-containing layer 24 and the titanium carbide-containing layer 26 can be adjusted. The film thicknesses of these layers 22 to 28 are not particularly limited and can be set as appropriate.

[0022] When the inventors conducted a power generation evaluation test on the cell 2 provided with the separator 12 having the surface treatment film 20 on the surface 13a, it was confirmed that the peeling of the carbon layer 28 could be suppressed during the operation of the fuel cell 1, particularly when the internal environment of the cell deteriorated, especially when the pH decreased or the fluorine concentration increased. Also, it was confirmed that the peeling of the carbon layer 28 could be similarly suppressed even in the vicinity of the air inlet of the oxidant gas where the condensed water generated in the cell 2 was likely to occur. It was confirmed that such an effect was due to the newly provided titanium oxide-containing layer 24 and that the peeling of the carbon layer that had peeled off due to the oxidation of the titanium carbide-containing layer 24 in the conventional separator could be suppressed by the presence of the titanium oxide-containing layer 24.

[0023] Furthermore, according to the above results, for example, it was found that it was also preferable to increase the thickness of the carbon layer 28 in order to reduce the permeation amount of the generated water in the vicinity of the air inlet of the cell 2 or the like. That is, at least in the vicinity of the air inlet of the cell 2, it is useful to partially increase the film thickness of the carbon layer 28. The partial thickening of the carbon layer 28 can be achieved, for example, by the PVD method by arranging the vicinity of the air inlet of the cell 2 at the portion facing the evaporation source. This is because according to the PVD method, the portion facing the evaporation source has the thickest film thickness.

Explanation of reference numerals

[0024] 1 Fuel cell, 2 Cell, 4 MEGA, 6 MEA, 7 Electrolyte membrane, 8a Anode, 8b Cathode, 12 Separator, 13 Stainless steel substrate, 13a Surface of the stainless steel substrate on the MEGA side, 20 Surface treatment film, 22 Titanium layer, 24 Titanium oxide-containing layer, 26 Titanium carbide-containing layer, 28 Carbon layer.

Claims

【Claim 1】 A fuel cell comprising: a stack of cells composed of a power generation unit and separators disposed on both sides of the power generation unit; wherein the separator comprises a stainless steel substrate and a film covering the surface of the stainless steel substrate on the power generation unit side; and the film has a titanium layer on the surface of the stainless steel substrate and a carbon layer on the outermost surface on the power generation unit side, and between the titanium layer and the carbon layer, from the side closer to the carbon layer, there are provided a titanium carbide-containing layer containing titanium carbide and a titanium oxide-containing layer containing titanium oxide.

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