JP5476753B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell.

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas has attracted attention as an energy source. This fuel cell has a structure in which a catalyst layer and a gas diffusion layer are bonded to both surfaces of an electrolyte membrane as gas diffusion electrodes, respectively. In such a fuel cell, the catalyst layer generally contains carbon black carrying a catalyst metal such as platinum and an electrolyte.

JP 2005-35396 A JP 2006-085929 A JP 2007-257886 A

Yoshiaki Nakayama, et al., “High-volume synthesis of carbon nanocoils, nanochaplets and related materials by green engineering and development research on highly functional composite materials”, Internet <URL: http://www.osaka.jst.go.jp/ kadai / pdf / h1305.pdf>

  By the way, in the fuel cell, in order to reduce the internal resistance and improve the power generation performance, it is required to ensure the contact property between the electrolyte membrane, the catalyst layer, and the gas diffusion layer. Therefore, the electrolyte membrane, the catalyst layer, and the gas diffusion layer are generally joined by hot pressing. Since the surface of the electrolyte membrane is smooth between the electrolyte membrane and the catalyst layer, sufficient contact can be ensured by the hot pressing. Moreover, between the electrolyte membrane and the catalyst layer, the hot press causes mutual diffusion of the electrolyte between the two, and the contact property is further improved.

  However, it has been difficult to ensure sufficient contact between the catalyst layer and the gas diffusion layer. That is, generally, as the gas diffusion layer, carbon paper having a pore diameter of several tens of microns, carbon cloth, or the like is used, and the surface has irregularities equivalent to the pore diameter. For this reason, even the hot pressing described above does not fill the void at the interface between the catalyst layer and the gas diffusion layer, and a contact failure occurs between the catalyst layer and the gas diffusion layer.

  The present invention has been made in order to solve the above-described problems. In a fuel cell including a catalyst layer and a gas diffusion layer on both surfaces of an electrolyte membrane, the contact between the catalyst layer and the gas diffusion layer is provided. It aims at improving.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A fuel cell including a catalyst layer and a gas diffusion layer on both surfaces of an electrolyte membrane, wherein at least one of the catalyst layers is disposed between the electrolyte membrane and the gas diffusion layer. A carbon nanotube oriented in a direction perpendicular to the surface of the electrolyte membrane and having elasticity in a direction perpendicular to the surface of the electrolyte membrane, and the fuel cell includes the carbon nanotube in the perpendicular direction. A fuel cell comprising a load application unit that applies a load within the elastic range of the above.

  In the fuel cell of Application Example 1, the unevenness of several tens of microns existing on the surface of the gas diffusion layer described above is filled with carbon nanotubes having an outer diameter of nanometer order provided in the at least one catalyst layer, The contact property between at least one catalyst layer and the gas diffusion layer can be improved.

  Furthermore, in the fuel cell of Application Example 1, the elasticity of the carbon nanotube absorbs a change in thickness due to swelling / shrinkage of the electrolyte membrane and suppresses an increase in contact resistance between the electrolyte membrane, the catalyst layer, and the gas diffusion layer. You can also. The increase in contact resistance between the current collector (separator) disposed in contact with the gas diffusion layer and the gas diffusion layer can also be suppressed by the elasticity of the carbon nanotube.

It is explanatory drawing which shows schematic structure of the fuel cell stack 100 as one Example of this invention. 4 is an explanatory diagram showing a relationship between a surface pressure and strain applied in a direction perpendicular to the surfaces of a catalyst layer A and a catalyst layer B. FIG. 3 is an explanatory diagram showing an elastic range of a catalyst layer 12. FIG. It is explanatory drawing which shows typically the effect by the catalyst layer 12 of an Example.

Hereinafter, embodiments of the present invention will be described based on examples.
A. Fuel cell stack configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell stack 100 as an embodiment of the present invention. In FIG. 1, a side view of the fuel cell stack 100 is shown together with a cross-sectional view of single cells constituting the fuel cell stack 100.

  The fuel cell stack 100 includes a stacked body in which a plurality of single cells are stacked. Each single cell is configured by providing a frame-shaped seal member 14 for preventing leakage of fuel gas and oxidant gas at the peripheral edge of the membrane electrode assembly 10 and sandwiching them with a separator 20. Each separator 20 is formed with a gas flow path for flowing fuel gas or oxidant gas and a cooling water flow path (not shown). The number of single cells stacked in the fuel cell stack 100 can be arbitrarily set according to the output required for the fuel cell stack 100.

  The membrane electrode assembly 10 is formed by joining an anode and a cathode to both surfaces of an electrolyte membrane 11 having proton conductivity. Each of the anode and the cathode includes a catalyst layer 12 and a gas diffusion layer 13. In this embodiment, a solid polymer membrane is used as the electrolyte membrane 11. Further, as the gas diffusion layer 13, carbon paper having conductivity and gas diffusibility is used. The membrane electrode assembly 10, particularly the catalyst layer 12, will be described in detail later.

  In the fuel cell stack 100, end plates 30 are disposed at both end portions of the stacked body in the stacking direction of the single cells with current collector plates and insulating plates (not shown) interposed therebetween, and these are fastened to the fastening rods. 40 and a nut 42 are used for fastening. By fastening each end plate 30, a pressing force is applied in the stacking direction of the single cells. At this time, the pressing force (load) applied in the stacking direction of the single cells is selected within the elastic range of the catalyst layer 12 described later. Members that apply a pressing force in the stacking direction of the single cells, such as the separator 20, the end plate 30, the fastening rod 40, and the nut 42, correspond to the load application unit in the present invention. Each end plate 30 is made of metal such as steel in order to ensure rigidity. Each current collecting plate is provided with an output terminal, and the power generated by the fuel cell stack 100 can be output from these output terminals.

  In the fuel cell stack 100, the end plates 30 and the fastening rods 40 are, for example, the end portions of the fastening rods 40 in the through holes (reference numerals omitted) formed in the four corners of the end plates 30 in the thickness direction. It is fixed by inserting the male screw part formed in the above and screwing the nut 42 having the female screw formed on the inner wall into the male screw part. Note that the thickness of the portion of the fastening rod 40 excluding the male screw portion is set to be larger than the size of each through hole formed in each end plate 30, and in the stacking direction of the single cells in the fuel cell stack 100. The length is defined by the length of the portion of the fastening rod 40 excluding the male screw portion regardless of the magnitude of the load applied to each single cell.

B. Membrane electrode assembly:
In the membrane electrode assembly 10 used in the fuel cell stack 100 of the present embodiment, the catalyst layer 12 has an electrolyte membrane 11 in order to improve the contact between the catalyst layer 12 and the gas diffusion layer 13 as described later. It has carbon nanotubes oriented in the direction perpendicular to the surface and having elasticity in the perpendicular direction. Hereafter, the manufacturing process of the membrane electrode assembly 10 of a present Example is demonstrated.

  First, a plurality of carbon nanotubes oriented perpendicular to the surface of the substrate are grown on the substrate by, for example, a CVD (Chemical Vapor Deposition) method. Here, “vertically oriented” does not need to be strictly oriented vertically. For example, by forming growth nuclei for growing carbon nanotubes on the substrate at a high density in advance, brush-like carbon nanotubes oriented almost perpendicular to the surface of the substrate grow on the substrate. . In addition, the inventor of the present application has determined whether the carbon nanotubes grown in a brush shape on the substrate have elasticity in the vertical direction with respect to the surface of the substrate, and the elastic range in the vertical direction is a growth condition of the carbon nanotubes. It was found that it changes depending on the difference. The growth conditions of the carbon nanotubes constituting the catalyst layer 12 are determined so that the grown carbon nanotubes have elasticity in the direction perpendicular to the surface of the substrate.

  Next, a platinum salt solution is dropped on the entire surface of the carbon nanotubes grown in a brush shape, dried and baked and reduced, thereby supporting platinum on the carbon nanotubes. Then, an ionomer dispersion solution (for example, Nafion dispersion solution (“Nafion” is a registered trademark)) is dropped onto carbon nanotubes carrying platinum, and the carbon nanotubes carrying platinum are ionomers (electrolytes). A member to be the catalyst layer 12 is produced.

  Next, the member produced by the above-described process, that is, carbon nanotubes carrying platinum and having a surface coated with an electrolyte is thermally transferred to both surfaces of the electrolyte membrane 11 respectively. By doing so, catalyst layers 12 are formed on both surfaces of the electrolyte membrane 11, which are oriented in a substantially vertical direction with respect to the surface of the electrolyte membrane 11 and have carbon nanotubes having elasticity in the vertical direction. And the membrane electrode assembly 10 is produced by sandwiching the formed article in which the catalyst layers 12 are formed on both surfaces of the electrolyte membrane 11 with carbon paper (gas diffusion layer 13) and bonding them by hot pressing.

C. Load characteristics of carbon nanotubes in the catalyst layer:
As described above, the inventor of the present application has the case where the carbon nanotubes grown in a brush shape on the substrate have elasticity in the direction perpendicular to the surface of the substrate, depending on the growth conditions of the carbon nanotubes. And found that there is. This knowledge was obtained by performing a load test using a load cell on catalyst layer A and catalyst layer B produced using carbon nanotubes grown under different growth conditions. The production conditions of the catalyst layer A and the catalyst layer B other than the carbon nanotube growth conditions are the same.

  FIG. 2 is an explanatory diagram showing the relationship between the surface pressure applied in the direction perpendicular to the surfaces of the catalyst layer A and the catalyst layer B and strain. As shown in FIG. 2A, in the catalyst layer A, when a surface pressure of 1.75 (MPa) is applied in a direction perpendicular to the surface, distortion of about 24 (%) occurs, and then When the surface pressure was returned to 0 (MPa), the strain returned to about 2 (%). On the other hand, as shown in FIG. 2B, in the catalyst layer B, when a surface pressure of 1 (MPa) is applied to the surface, distortion of about 28 (%) occurs, and thereafter the surface pressure is reduced. Even when the pressure was returned to 0 (MPa), the original shape did not return with distortion of about 22 (%). That is, the catalyst layer A has elasticity in the direction perpendicular to the surface of the electrolyte membrane 11, whereas the catalyst layer B does not have elasticity in the direction perpendicular to the surface of the electrolyte membrane 11. was gotten.

  From the results of the load test described above, the catalyst layer 12 having elasticity in the direction perpendicular to the surface of the electrolyte membrane 11 is used as the catalyst layer 12 in the membrane electrode assembly 10 of this example. And the elastic range of the catalyst layer 12 (catalyst layer A) was calculated | required similarly to the load test mentioned above.

  FIG. 3 is an explanatory view showing the elastic range of the catalyst layer 12. As shown in the figure, it was found that the elastic range of the catalyst layer 12 in the direction perpendicular to the surface of the electrolyte membrane 11 (direction in which the electrolyte membrane 11 is pressed) is 0 to about 2 (MPa).

D. Effect of catalyst layer of example:
FIG. 4 is an explanatory view schematically showing the effect of the catalyst layer 12 of the example. As described above, in the manufacturing process of the membrane electrode assembly 10, the membrane in which the catalyst layer 12 is formed on both surfaces of the electrolyte membrane 11 is sandwiched between carbon papers (gas diffusion layers 13), and these are joined by hot pressing. To do.

  As shown in the upper part of FIG. 4, when the membrane having the catalyst layer 12 formed on both surfaces of the electrolyte membrane 11 is sandwiched by carbon paper (gas diffusion layer 13) and these are hot-pressed, the gas diffusion layer 13 Since there are undulations of several tens of microns on the surface, there are voids at the interface between the catalyst layer 12 and the gas diffusion layer 13 when the load is relatively small, and the catalyst layer 12 and the gas diffusion layer 13 The contact is poor. Thereafter, when the hot press load is increased, the outer diameter of the carbon nanotubes included in the catalyst layer 12 is on the order of nanometers, so that the tip of the carbon nanotubes existed at the interface between the catalyst layer 12 and the gas diffusion layer 13. The space between the catalyst layer 12 and the gas diffusion layer 13 is improved by filling the gap. Note that a load within the elastic range of the carbon nanotubes shown in FIG. 3 is selected as the load during the hot pressing.

  According to the fuel cell stack 100 of the present embodiment described above, several tens of microns existing on the surface of the gas diffusion layer 13 by the carbon nanotubes having an outer diameter of nanometer order provided in the catalyst layer 12 of the membrane electrode assembly 10. The contact between the catalyst layer 12 and the gas diffusion layer 13 can be improved.

  Furthermore, according to the fuel cell stack 100 of the present embodiment, the elasticity of the carbon nanotubes provided in the catalyst layer 12 absorbs the change in thickness due to swelling / shrinkage of the electrolyte membrane 11, and the electrolyte membrane 11, the catalyst layer 12, and the gas An increase in contact resistance with the diffusion layer 13 can also be suppressed. In addition, the elasticity of the carbon nanotube can suppress an increase in contact resistance between the separator 20 disposed in contact with the gas diffusion layer 13 and the gas diffusion layer 13.

  In the present embodiment, the catalyst layer 12 including the above-described carbon nanotubes is applied to both surfaces of the electrolyte membrane 11. However, the catalyst layer 12 may be applied to at least one surface of the electrolyte membrane 11.

DESCRIPTION OF SYMBOLS 100 ... Fuel cell stack 10 ... Membrane electrode assembly 11 ... Electrolyte membrane 12 ... Catalyst layer 13 ... Gas diffusion layer 14 ... Sealing member 20 ... Separator 30 ... End plate 40 ... Fastening rod 42 ... Nut

Claims (1)

A fuel cell comprising a catalyst layer and a gas diffusion layer on both surfaces of the electrolyte membrane,
At least one of the catalyst layers is disposed between the electrolyte membrane and the gas diffusion layer, oriented in a direction perpendicular to the surface of the electrolyte membrane, and elastic in a direction perpendicular to the surface of the electrolyte membrane. A carbon nanotube having
The fuel cell
E Bei load applying unit that applies a load within the elastic range of the carbon nanotubes in the vertical direction,
“Within the elastic range” means a fuel cell in which at least one of a residual strain of 2% or less and a linear relationship between displacement and load is satisfied .

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