JP5234878B2 - Fuel cell - Google Patents

Description

  The present invention generally relates to fuel cells and membrane electrode assemblies thereof.

  Fuel cells continue to show strong sales potential around the world as an alternative to traditional energy sources. There are various types of fuel cells, all of which generate electric power through a chemical reaction. One fuel cell of increasing importance is the proton exchange membrane fuel cell (PEMFC), which can operate at relatively low temperatures (typically from room temperature to 120 ° C.).

FIG. 1 represents a general conventional type of PEMFC, generally indicated by reference numeral 10. The PEMFC (10) has an electrode membrane assembly (MEA) (15) in the center. The MEA (15) includes a proton exchange membrane (20) having an anode catalyst layer (32) disposed on the surface and a cathode catalyst layer (42) placed on the opposite side. The auxiliary layer (34) on the anode side is disposed on the anode catalyst layer (32), and the auxiliary layer (44) on the cathode side is disposed on the cathode catalyst layer (42). In practice, the auxiliary layers (34), (44) are typically made from a microporous material with a high surface area to volume ratio, such as carbon paper or cloth. This microporous layer serves to physically assist the disposed catalyst layer. Finally, in order to ensure proper intimate contact between the proton exchange membrane (20), the catalyst layers (32), (42), and the auxiliary layers (34), (44), the membrane (20) and each layer are 120 The MEA (15) is formed by being pressed by a hot press at a temperature of from 150 to 150 ° C. The fuel cell (10) is then completed by attaching the MEA (15) between the pair of fluid flow plates (36), (46). The anode-side fluid flow plate (36) includes an inlet (37), an outlet (38), and a distribution pipe. The cathode-side fluid flow plate (46) includes an inlet (47), an outlet (48), and a distribution pipe (49). In practice, the fuel cell (10) is arranged as one of many fuel cells stacked. In a stack, the bipolar plates have tubes / conduit on both sides and these flow field plates are called bipolar plates.

  Considering the performance and configuration of this conventional structure, several drawbacks become apparent. First, the manufacture of MEA (15) requires a very delicate process in practice, which must be performed very strictly for the fuel cell to function correctly. Next, compared to what the theoretical model presents, the amount of catalyst supported to reach sufficient performance is extremely large.

  It is an object of the present invention to address at least some of the aforementioned drawbacks.

  According to a first aspect, the present invention comprises a proton exchange membrane disposed between an anode catalyst layer and a cathode catalyst layer such that the membrane surface and the catalyst layer surface engage with each other in an interface region. The surface in the interface region may provide an electrode membrane assembly for a fuel cell having a surface structure formed from a nanoimprinting process.

  By utilizing the nano-scale surface structure formed in the interface region, the effective reaction zone (between the catalyst layer and the membrane) increases, resulting in improved power generation and reduced catalyst loading on the catalyst layer. Can also be achieved. The use of nanoimprinting technology to form the surface structure is particularly advantageous in that the arrangement of the surface structure can be accurately managed. In this respect, nanoimprinting technology is difficult to control the formed surface structure and prevent contamination, and forms other surface structures such as mechanical wear and plasma etching that are difficult to use in practice. This is an advantage over the previous technology.

  The surface structure is preferably on the membrane.

  In some embodiments, the surface structure may be formed in only one interface region, but is preferably formed in the interface regions on both the anode side and the cathode side.

According to a second aspect, the present invention provides:
An electrode membrane assembly comprising a proton exchange membrane disposed between the anode catalyst layer and the cathode catalyst layer;
An anode-side bipolar plate with a contact surface joined to the anode catalyst layer,
A cathode-side bipolar plate having a contact surface joined to the cathode catalyst layer;
The contact surface may provide a fuel cell having a surface structure formed from a nanoimprinting process.

By using a nanoscale surface structure formed on a bipolar plate , distribution in a conventional diffusion permeation layer is possible. This is advantageous as it allows the construction of smaller fuel cells. Furthermore, if the bipolar plate is made of a polymer, it is possible to construct an all-polymer fuel cell, which is attractive for medical use.

  In the present invention, the expression “from the nanoimprinting process” is understood to include surface structures that occur as a result of the nanoimprinting process, whether directly or indirectly.

  Thus, according to a third aspect of the present invention, the present invention provides a method for producing a fuel cell component by nanoimprinting, the method comprising providing a mold having a pattern for nanoimprinting, and a fuel cell. A manufacturing method may be provided that includes providing a component and nanoimprinting the pattern directly on the component. According to a fourth aspect, there is provided a method for producing a fuel cell component by nanoimprinting, the method comprising: providing a mold having a pattern for nanoimprinting; providing a pattern support template; and said pattern support A manufacturing method may be provided that includes nanoimprinting the pattern on a template and forming the component from its constituent material in the pattern support template.

  Exemplary embodiments of the invention will now be described with reference to the accompanying drawings.

  FIG. 2 shows a first embodiment of the invention. This embodiment and each of the subsequent embodiments have properties common to the conventional type of FIG. Hereinafter, the same reference numerals will be used to refer to similar parts. Referring to FIG. 2, the PEMFC 10 has an electrode membrane assembly (MEA) (15) in the center. The MEA (15) includes a semipermeable membrane type proton exchange membrane generally made of an ionomer. The membrane (20) is designed so that protons (hydronium ions) can pass through it, but gas such as oxygen and hydrogen cannot pass through it. A suitable material for the membrane is Naflon (registered trademark) manufactured by DuPont. The MEA (15) also includes an anode catalyst layer (32) disposed on the membrane (20) and a cathode catalyst layer (42) disposed on the opposite side of the membrane. A suitable catalyst for both layers (32), (42) is noble metal platinum. The diffusion layers (34) and (44) are as described in the context of the conventional type of FIG. The method of constructing the MEA (15) is also basically the same as the hot press method. However, in the construction of the first embodiment of the present invention, and according to the present invention, prior to hot pressing the parts of the MEA (15), both sides of the membrane (20) are nanoimprinted in a pattern of surface structure. A plurality of patterns are possible for the surface structure, and some basic figures are listed in FIGS. 7A shows a cylindrical structure, FIG. 7B shows a rectangular structure, FIG. 7C shows a truncated cone structure, and FIG. 7D shows a pyramidal structure. The height of the structure is usually about 100 nm. The spacing between structures is usually about 10 nm. The diameter of the cylindrical and frustoconical bottom is usually about 10 nm. The bottom surface area of the rectangular structure and the pyramid structure is set to be the same as the bottom surface of the cylindrical shape and the truncated cone structure.

  When the MEA (15) is hot-pressed, the nanoimprinting surface of the membrane (20) and one surface of the anode catalyst layer (32), and the other nanoimprinting surface of the membrane (20) and the cathode catalyst layer (42). Are joined together at the interface regions (50) and (60), respectively. It will be appreciated that the effective contact area between the catalyst layers (34), (42) and the membrane (20) is dramatically increased compared to the conventional MEA represented in FIG. . The fuel cell (10) is then completed by mounting the MEA (15) between the fluid flow plates (36), (46). According to the invention, the fluid flow plate has surface structures (36a), (46a) nanoimprinted on its inner surface. The anode fluid flow plate (36) includes an inlet (37) and an outlet (38). The cathode-side fluid flow plate (46) includes an inlet (47) and an outlet (48).

In actual operation, fuel (basically a hydronium ion source) is supplied from an inlet (37) installed in the anode bipolar plate (36). In this embodiment of the invention, the fuel is methanol and is supplied directly to the fuel cell. As fuel enters the inlet (37), it is pooled in a conduit network formed by a surface structure (36a) carved in the anode bipolar plate (36). This conduit network facilitates the wide diffusion and distribution of fuel over the surface of the bipolar plate (36) from where it flows to the diffusion layer (34) where the fuel is further diffused and distributed. When the anode catalyst layer (32) is reached, the fuel is oxidized, thereby releasing protons and electrons. Protons and electrons follow separate paths to the cathode catalyst layer (42). Protons pass through the proton exchange membrane (20), and electrons pass through an external circuit (70) that produces an electric current. When returning to the cathode catalyst layer (42), the electrons recombine with protons, and at the same time, combine with oxygen supplied through the inlet (47) of the cathode field flow (46) to generate water. The anode side discharge port (38) discharges unused fuel and at the same time discharges a by-product, ie, carbon dioxide, due to a half reaction occurring on the anode side. The cathode side discharge port discharges by-product, that is, water due to a half reaction occurring on the cathode side.

  The anodic reaction is seen to be confined to the three-stage boundary of fuel, membrane, and catalyst. Thus, the reactive surface area increased by the pattern of surface structures nanoimprinted on the membrane appears to improve effective catalyst utilization. A similar localized reaction with a three-step boundary is considered to occur at the cathode, and a similar advantage is thought to be caused by the nanoimprinted surface structure in the cathode side membrane.

As a result of improving the effect of the three-stage reaction, a thinner catalyst layer becomes possible. In the conventional type of FIG. 1, the range of the catalyst loading amount was 0.3 mg / cm ² to several mg / cm ² , but in the embodiment of FIG. 2, the catalyst loading amount can be greatly reduced.

FIG. 3 shows a second embodiment of the present invention. This embodiment differs from the first embodiment in that the diffusion layers (34), (44) are removed. In actual operation, the fuel cell functions in the same manner as the first embodiment of FIG. Diffusion layers (34) and (44) are particularly common features in low temperature fuel cells. Therefore, it is a remarkable advantage in the second embodiment that only the nano-imprinting surface structure can be used to deliver a necessary reactant to the catalyst layer and to remove the substance from the catalyst layer. Since this embodiment does not require a diffusion auxiliary layer, there is an advantage in the ease of manufacturing. Also, on the whole scale, the distribution by diffusion auxiliary layer and the fact that the bipolar plate does not require a network of distribution conduits (39), (49) allows a more compact structure suitable for small fuel cells. . Furthermore, because bipolar plates can be made from polymers, this embodiment of the present invention can be implemented as an all-polymer structure that is very well suited for medical applications.

FIG. 4 shows a third embodiment of the present invention, and the applicant used this embodiment to clearly show many advantages of the present invention. In this example, a 183 micron thick Naflon® (117) film (20) was patterned using a 130 ° C. nanoimprinting technique. A pattern of 1 micron high and 5 micron diameter pillars spaced at 5 micron intervals was formed on both sides of the membrane (20). After the pattern was applied, the membrane was continuously subjected to timed immersion in distilled water, hydrogen peroxide, distilled water, sulfuric acid and finally distilled water. Submersion other than the first washing with distilled water was performed at a temperature of 80 ° C. for 2 hours. Thereafter, a platinum layer having a thickness of 20 nm is disposed on the nano-imprinting film 20 by sputtering to form the anode catalyst layer 32, and a platinum layer having a thickness of 20 nm is formed by sputtering. 20) was provided to form a cathode catalyst layer (42) on the other side. Thereafter, the film (20) A commercially available diffusion auxiliary made of carbon paper (34), sandwiched between (44), was placed between the conventional bipolar plate. The overall electrode area was 5 cm ^2. Dry hydrogen and air gas were supplied to the fuel cell at 1 atmosphere and heated to 80 ° C. The amount of catalyst supported was about 0.04 mg / cm ² and the maximum power density was about 50 mW / cm ² . FIG. 5 also shows similar IV properties of a fuel cell in which the membrane (20) is not nanoimprinted. The improvement of output density was remarkable.

  FIG. 6 shows the structure of the fourth embodiment of the present invention. A small fuel cell unit (10) was built around a 51 micron thick Naflon (112) membrane (20), and the membrane (20) was patterned as in the third embodiment. After patterning, the membrane was continuously subjected to timed immersion in the order of distilled water, hydrogen peroxide, distilled water, sulfuric acid, and distilled water. Water immersion other than the first washing with distilled water was performed at a temperature of 80 ° C. for 1 hour.

The bipolar plates (36), (46) of this example are made of a silicon wafer with a back coating (51) with a 2 micron thick SiO ₂ layer. The fuel inlet (37) and the fuel outlet (38) of the cathode side wafer are connected, and the air inlet (47) and the outlet (48) are connected by a conduit pattern (36b) formed by dry etching. And (46b). The purpose of the conduit pattern is to deliver the reactants to the catalyst layer and to remove the material from the catalyst layer. The area of the overall conduit pattern is 10.5 × 11 mm.

In this example, catalyst layers (32) and (42) each having a platinum layer having a thickness of 20 nm were formed on a nanoimprinting film. Further, as a current collector, a Ti seed layer having a thickness of 10 nm and a platinum layer having a thickness of 100 nm are disposed on the bipolar plate . A Ti layer is first disposed for better bonding.

  By using passively 1M methanol solution and air as an oxidant at the cathode, an open circuit voltage of 0.7 V could be obtained. This is a great advantage over similar arrangements where only a voltage of 0.2V was obtained and the membrane was not nanoimprinted. This open circuit voltage has been shown to greatly improve the power generation capacity.

There are at least two basic processes for nanoimprinting proton exchange membranes and liquid flow plates. In the method shown as A in FIG. 8, the mold (100) having the pattern (102) that is desired to be imprinted is transformed into a proton exchange membrane (20) or a bipolar plate (20) at room temperature or higher. 36), a standard direct nanoimprinting process used to be pushed directly to (46). The finished product is indicated by (110).

An alternative method is shown at B in FIG. 8 and uses a mold with a pattern that is desired to be imprinted, and the mold is a pattern template (105) made of an intermediate polymer or glass material support. To nanoimprint. The intermediate (105) is then utilized as the surface on which the membrane (20) or bipolar plate (36) (46) component material is disposed and then solidified to form the finished product 110.

  It will be appreciated that what is referred to herein as a proton exchange membrane fuel cell or PEMFC is also known in the art as a polymer electrolyte membrane fuel cell.

  As used throughout this specification, the term “nanoimprinting” refers to the imprinting of surface structures of various sizes. The size range includes configurations having a single-digit number nm scale or similar size pitch. The term also sometimes refers to a configuration having a scale of up to about 100 microns.

1 is a schematic diagram of a conventional PEMFC conventional type. It is the schematic of the 1st Example of this invention. It is the schematic of the 2nd Example of this invention. It is the schematic of the 3rd Example of this invention. The performance characteristics of the third embodiment and the conventional PEMFC are compared. It is the schematic of 4th Example of this invention. Fig. 3 is a variety of patterns possible with the nano-imprinted surface structure of the present invention. A method for integrating nanoimprinting into PEMFC structural processes.

10 proton exchange membrane fuel cell 15 electrode membrane assembly 20 proton exchange membrane 32 anode catalyst layer 34 anode side auxiliary layer 36 bipolar plate or fluid flow plate 36a surface structure 42 cathode catalyst layer 44 cathode side auxiliary layer 46 bipolar plate or fluid flow Plate 46a Surface structure 47 Inlet 48 Outlet 49 Distribution pipe

Claims (6)

An anode catalyst layer (32) and a cathode catalyst layer (42);
A proton exchange membrane (15) disposed between the anode catalyst layer and the cathode catalyst layer;
An anode side diffusion layer (34) that contacts the anode catalyst layer on a surface opposite to the surface that contacts the proton exchange membrane of the anode catalyst layer, and diffuses and distributes fuel supplied to the anode catalyst layer;
An anode-side bipolar plate (36) that is in contact with the anode-side diffusion layer on the surface opposite to the surface in contact with the anode catalyst layer of the anode-side diffusion layer and supplies fuel to the anode-side diffusion layer, The anode side having a fine surface structure (36a) for diffusing and distributing the fuel on the surface in contact with the side diffusion layer, which is a fine surface structure formed from a nanoimprinting process on the surface of the anode side diffusion layer Bipolar plates,
A fuel cell assembly. A cathode side diffusion layer (44) in contact with the cathode catalyst layer on a surface opposite to the surface facing the proton exchange membrane of the cathode catalyst layer;
The surface of the cathode side diffusion layer opposite to the surface in contact with the cathode catalyst layer is in contact with the cathode side diffusion layer, and the surface in contact with the cathode side diffusion layer has a fine surface structure formed from a nanoimprinting process. cathode side bipolar plate having a fine surface structure comprising a passage of air and water there (46),
The fuel cell assembly of claim 1, comprising: A surface between the anode catalyst layer and / or cathode catalyst layer and the proton exchange membrane has a fine surface structure formed from a nanoimprinting process for increasing a reaction region, The fuel cell assembly according to claim 1 or 2. An anode catalyst layer (32) and a cathode catalyst layer (42);
A proton exchange membrane (15) disposed between the anode catalyst layer and the cathode catalyst layer;
An anode-side bipolar plate (36) that contacts the anode catalyst layer on a surface opposite to the surface that contacts the proton exchange membrane of the anode catalyst layer and supplies fuel to the anode catalyst layer, An anode-side bipolar plate having a fine surface structure (36a) for diffusing and distributing the fuel on the surface of the anode catalyst layer formed on a surface in contact with the fine surface structure formed by a nano-imprinting process ;
A fuel cell assembly. The surface of the cathode catalyst layer that is in contact with the cathode catalyst layer on the surface opposite to the surface that is in contact with the proton exchange membrane, and the surface that is in contact with the cathode side catalyst layer has a fine surface structure (46a) formed by a nanoimprinting process. The fuel cell assembly according to claim 4, comprising a cathode side bipolar plate (46). 6. The fuel cell assembly according to claim 4, wherein the fuel cell assembly has a fine surface structure formed from a nano-imprinting process on a surface between the anode catalyst layer and / or the cathode catalyst layer and the proton exchange membrane.