JP5630408B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly to an internal structure of a fuel cell.

  A fuel cell has a structure in which an electrolyte membrane is sandwiched between both electrodes of a cathode and an anode. A cathode gas (oxidizing gas) containing oxygen such as air is in contact with the cathode while an anode gas containing hydrogen ( When the fuel gas is in contact with the anode, an electrochemical reaction occurs between the electrodes, and as a result, a voltage is generated between the electrodes. In general, fuel cells are required to have mutually contradictory characteristics of efficiently discharging generated / condensed water to the gas flow path and supplying a sufficiently humidified gas evenly to the electrolyte membrane. The

  Various fuel cell structures have been proposed. For example, Patent Document 1 includes a gas diffusion layer for a fuel cell including a gas diffusion layer base material and a conductive water repellent layer. A fuel cell is described in which the conductive water-repellent layer contains a conductive material and a water-repellent material and has pores with a pore size distribution range of 0.2 μm to 2 μm.

JP 2009-59524 A

  However, although the fuel cell described in Patent Document 1 is intended to improve drainage from the electrode, the inventor has intensively studied, and in the conductive water-repellent layer having the above-described configuration, It has been found that the water permeability may be reduced to an unfavorable level, and as a result, the drainage from the electrode and its vicinity may not be sufficiently improved.

  Therefore, the present invention has been made in view of such circumstances, and includes a gas diffusion layer having a water repellent portion, and can sufficiently and stably improve drainage from the electrode and its vicinity. An object is to provide a fuel cell.

In order to solve the above problems, a fuel cell according to the present invention is provided with a membrane electrode assembly in which a cathode and an anode are disposed on both sides of an electrolyte membrane, and on both sides of the membrane electrode assembly, and A cathode gas flow path through which the cathode gas flows, a separator defining an anode gas flow path through which the anode gas flows, and a gas diffusion layer disposed between the membrane electrode assembly and the separator. The gas diffusion layer has a water-repellent part disposed on the membrane electrode assembly side and having pores, and a substrate part disposed on the separator side, and an average pore size distribution range of pores in the water-repellent part Is 0. It is set to more than 2 μm to 0.6 μm.

In the fuel cell according to the present invention configured as described above, moisture generated in the vicinity of the membrane electrode assembly (the cathode thereof) hits the gas diffusion layer against the water repellent part that contacts the membrane electrode assembly and the separator. It passes through the base material portions in contact with each other and is discharged to the gas flow path side of the separator. At this time, the average pore size distribution range of the pores formed in the water-repellent part is 0.00. By being a 2 [mu] m super ～0.6Myuemu, with water penetration pressure of the water repellent portion is sufficiently suppressed, the degree of saturation of the pores of the water-repellent part (occupancy degree of the interior space of the pores by water, i.e. An excessive increase in one of the indices indicating the degree of water clogging is suppressed. Thereby, it can suppress that the fluidity | liquidity of the water which distribute | circulates a water repellent part is inhibited, and can improve the drainage property from the vicinity of a membrane electrode assembly.

  Therefore, according to the fuel cell of the present invention, it is possible to increase the drainage from the electrode and its vicinity sufficiently and stably more than before, and thereby the output is lowered to an inconvenient level or unstable. It is possible to improve the driving performance by suppressing the occurrence of the above.

It is sectional drawing which shows typically a part of structure of suitable one Embodiment of the fuel cell by this invention. (A)-(C) is sectional drawing which expands and schematically shows a part of fuel cell shown in FIG. 1, (B) corresponds to the thing of embodiment among these, and (D ) Is a graph showing changes in water permeation pressure and saturation of the water repellent part with respect to the diameter of the pores formed in the water repellent part of the gas diffusion layer.

  Hereinafter, embodiments of the present invention will be described in detail. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. Furthermore, the following embodiment is an illustration for explaining the present invention, and is not intended to limit the present invention only to the embodiment. Furthermore, the present invention can be variously modified without departing from the gist thereof.

  FIG. 1 is a sectional view schematically showing a part of the configuration of a preferred embodiment of a fuel cell according to the present invention. The fuel cell stack 10 is a solid polymer fuel cell (PEMFC) provided with a solid polymer separation membrane (electrolyte membrane), and is mainly mounted on a fuel cell vehicle or the like. The fuel cell stack 10 (fuel cell) has a stack structure in which a plurality of unit cells 20 are stacked (only one unit is shown in the figure). The unit cell 20 includes gas diffusion layers 22 on both sides outside of an MEA 21 (Membrane Electrode Assembly) in which a cathode 2a and an anode 2b (both electrode catalyst layers) are arranged with the electrolyte membrane 2 interposed therebetween. A power generator 23 in which 22 is integrally formed by a seal gasket (not shown), and a cathode separator 26 and an anode separator made of a conductive metal material such as stainless steel or titanium for isolating adjacent power generators 23, 23. 28.

  The separator that separates the adjacent power generators 23 and 23 is, for example, a stack of the cathode separator 26, an intermediate plate (not shown; mainly used as a flow path for cooling water), and the anode separator 28 described above. The unit cell 20 is defined as described above in order to form a three-layer stacked unit and to be consistent with the drawing.

  Further, a cathode gas flow path 30 through which cathode gas flows is defined between the cathode separator 26 and the power generation body 23, and further, anode gas is interposed between the anode separator 28 and the power generation body 23. A circulating anode gas channel 40 is defined. It should be noted that the peripheral edges of the power generator 23, the cathode separator 26, and the anode separator 28 have a cathode inlet and a cathode outlet communicating with the cathode gas channel 30, and an anode inlet and a cathode communicating with the anode gas channel 40. The anode outlet (both not shown) is provided.

  Here, FIGS. 2A to 2C are cross-sectional views schematically showing an enlarged part of the fuel cell stack 10 shown in FIG. 1. Mainly, the cathode 2 a of the MEA 21 and the cathode gas channel 30 are mainly shown. The cross-sectional structure of the gas diffusion layer 22 arrange | positioned between the separators 26 in which the is defined is shown. For the sake of illustration, the three aspects of FIGS. 2A to 2C are also shown for mutual comparison. Of these, FIG. 2B corresponds to the present embodiment, and FIG. The mode shown in FIG. 2 (A) and FIG. 2 (C) is a so-called comparative example.

  As shown in the figure, the gas diffusion layer 22 has a water repellent part 221 disposed on the cathode 2a side and a base material part 222 adjacent thereto. The water repellent portion 221 is composed of, for example, a microporous layer (MPL) made of a coating thin film mainly composed of a water repellent resin such as PTFE (polytetrafluoroethylene) and a conductive material such as carbon black. A plurality of pores H are formed.

  FIG. 2D shows the results of the test evaluation conducted by the present inventors. The water repellent part 221 with respect to the diameter (μm) of the pores H formed in the water repellent part 221 of the gas diffusion layer 22 is shown. It is a graph which shows the water permeability pressure (kPa) of this, and the change of the saturation (%) of the pore H of the water-repellent part 221 mentioned above. In the figure, a black circle plot represents the hydraulic pressure (left vertical axis), and a black square plot represents the saturation (right vertical axis).

As is apparent from the test evaluation results, when the diameter of the pores H is less than 0.1 μm, the water permeation pressure of the water repellent portion 221 tends to increase rapidly. In this case, as schematically shown in FIG. 2A, the pores H of the water-repellent part 222 of the gas diffusion layer 22 are blocked by the water W generated by power generation and staying without being discharged from the cathode 2a side. For example, oxygen molecules (O ₂ ) contained in the cathode gas flowing through the base material portion 222 are inhibited from flowing into the cathode 2a from the pores H, and as a result, sufficient oxygen is supplied to the cathode 2a. It becomes difficult to supply gas.

On the other hand, when the diameter of the pore H exceeds 0.6 μm, the saturation degree of the pore H of the water repellent portion 221 becomes excessively large. In this case, as schematically shown in FIG. 2C, the inside of the pores H of the water repellent part 222 of the gas diffusion layer 22 is filled with water W (clogged) and flows through the base material part 222. Oxygen molecules (O ₂ ) contained in the cathode gas thus made difficult to pass through the pores H, and in this case as well, it becomes difficult to supply sufficient oxygen gas to the cathode 2a.

On the other hand, in the gas diffusion layer 22 of the fuel cell stack 10, the pore diameter distribution range of the pores H is 0.1 μm to 0.6 μm, and as shown in FIG. Since the diameter is 0.1 μm or more, the water permeation pressure of the water repellent part 221 is maintained sufficiently low, and since the diameter of the pore H is 0.6 μm or less, the pore H of the water repellent part 221 is maintained. The degree of saturation can be drastically reduced. Thereby, as schematically shown in FIG. 2B, the water W can easily pass through the pores H of the water-repellent part 222 of the gas diffusion layer 22, from the cathode 2 a side to the base material part 222 side. It becomes easy to penetrate to. As a result, oxygen molecules (O ₂ ) contained in the cathode gas that has circulated through the base portion 222 are very likely to flow into the cathode 2a side through the pores H, and a sufficient amount of oxygen gas is supplied to the cathode 2a. Can be supplied.

  In other words, according to the fuel cell stack 10, the fluid permeability of the water diffusion layer 221 of the gas diffusion layer 22 is inhibited from being hindered by the water permeability pressure reducing effect in the gas diffusion layer 22, The drainage from the vicinity of the MEA 21 can be remarkably improved, and thereby the gas diffusion resistance can be sufficiently reduced. Further, the saturation reduction effect in the gas diffusion layer 22 can suppress clogging of the pores H of the water repellent part 221 of the gas diffusion layer 22, and this can also sufficiently reduce the gas diffusion resistance. it can. From the above, it is possible to reliably prevent the output of the fuel cell stack 10 from being lowered to an inconvenient level or becoming unstable, and greatly improve the driving performance, particularly the cold performance. It becomes possible.

  In addition, as above-mentioned, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the limit which does not change the summary. For example, the specific shapes of the cathode gas flow path 30 and the anode gas flow path 40 in the fuel cell stack 10 may be straight flow paths or serpentine flow paths. They may be opposed, or may be crossed or orthogonal. A fuel cell that is not configured in a stack can also be included in the configuration of the present invention. Furthermore, the pore diameter distribution shape of the pores H in the gas diffusion layer 22 is not particularly limited.

  As described above, according to the present invention, the drainage performance from the electrode and the vicinity thereof can be increased more sufficiently and stably than before, so that the output is reduced to an inconvenient level or unstable. Therefore, the present invention is widely applicable to fuel cells in general, vehicles equipped with fuel cells, devices, systems, facilities, etc., and their production. It can be used effectively.

2 Electrolyte membrane 2a Cathode 2b Anode 10 Fuel cell stack (fuel cell)
20 unit cell 21 MEA
22 Gas diffusion layer 23 Power generator,
26 Cathode separator 28 Anode separator 30 Cathode gas flow path 40 Anode gas flow path 221 Water repellent part 222 Base material part H Pore W Water

Claims (1)

A membrane electrode assembly in which a cathode and an anode are respectively disposed on both sides of the electrolyte membrane;
A separator that is provided opposite to both surfaces of the membrane electrode assembly, and that defines a cathode gas flow path through which the cathode gas flows, and an anode gas flow path through which the anode gas flows;
A gas diffusion layer disposed between the membrane electrode assembly and the separator;
With
The gas diffusion layer has a water repellent part that is disposed on the membrane electrode assembly side and has pores, and a base material part that is disposed on the separator side. The average pore size distribution range of the pores is 0. A fuel cell having a thickness of more than 2 μm to 0.6 μm.

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