JP5624009B2 - Membrane electrode assembly - Google Patents

Description

  The present invention relates to a membrane electrode assembly of a fuel cell using a fiber sheet.

  In a polymer electrolyte fuel cell, water is required to maintain proton conductivity of the polymer electrolyte membrane, and a humidified reaction gas is supplied. However, in recent fuel cells, in order to improve the utilization rate of the catalyst, the pores (voids) in the catalyst electrode layer are enlarged using the pore former, and the fuel gas efficiently reaches the catalyst. In addition, the water dischargeability in the catalyst electrode layer is increasing. For this reason, power generation performance is improved in a highly humid environment with abundant moisture, but in a low humid environment, water necessary for maintaining the proton conductivity of the solid polymer membrane is discharged, resulting in power generation. There was a problem that the performance deteriorated.

  As a means for solving the above-described problems, as shown in FIG. 3, a solid high layer in which a water retention layer 33 for improving water retention is provided between the catalyst electrode layer 32 and the gas diffusion layer 34. An electrode for a molecular fuel cell is disclosed (for example, see Patent Document 1). The water retention layer 33 is formed by mixing an ion conductive polymer having a water retention effect and carbon fiber as a pore former, and by providing the water retention layer 33, the relative humidity in the reaction gas is low. Even so, the solid polymer film 31 retains sufficient water to maintain proton conductivity.

  However, the water retaining layer 33 described in the above-mentioned Patent Document 1 is a paste in which an ion-conductive polymer 21 having a water absorption property, carbon fibers 22 as a pore former, and conductive carbon particles 23 are mixed. Is formed by coating and drying. As shown in FIG. 2A, the structure is a state in which the ion conductive polymer 21, the carbon fiber 22, and the carbon particle 23 are mixed, and the ion conductive polymer 21 exists in the gap between the carbon fibers 22. . A hole (gap) 24 is formed between these materials. In such a structure, in a highly humid environment, as shown in FIG. 2B, the ion conductive polymer 21 absorbs moisture and swells, so that the ion conductive polymer 21 in which the holes 24 swell is swelled. There is a problem that the performance of the fuel cell is deteriorated by obstructing gas permeation.

JP 2004-158388 A

  Therefore, the present invention has been made to solve the above-described problems, and even when the hygroscopic material swells in a highly humid environment, the gap (hole) of the water retention layer is not blocked, and gas permeation is inhibited. An object of the present invention is to provide an excellent membrane electrode assembly for a fuel cell that does not occur.

Membrane electrode assembly of the present invention, on both sides of the electrolyte membrane, in turn, a catalyst electrode layer comprising a catalyst, a membrane electrode assembly for a fuel cell gas diffusion layer are laminated, at least of the electrolyte membrane in one aspect, the water-retaining layer without further comprises a catalyst between the catalyst electrode layer and the gas diffusion layer is provided with, before Symbol moisture-holding layer, a conductive carbon material to the fibers of the sheet made of hygroscopic material der those covering is, the hygroscopic material is characterized in that a polymer electrolyte resin.

In the membrane electrode assembly of the present invention, at least one surface of the electrolyte membrane, between the coercive aqueous layer and the gas diffusion layer, a configuration is a preferred embodiment to provide a water-repellent layer.

  According to the membrane / electrode assembly of the present invention, instead of using carbon fiber as the pore former, the moisture-absorbing material can be swollen by forming the moisture-absorbing material itself into a fibrous shape and making the water retaining layer porous. The pores between the fibers are not blocked, and gas permeation is not hindered.

  According to the present invention, even if the hygroscopic material swells in a highly humid environment, the gap (hole) of the water retention layer is not blocked, and the excellent membrane electrode assembly of a fuel cell that does not inhibit gas permeation Can be provided.

It is the conceptual diagram which showed an example of the water retention layer which consists of a fiber sheet in the membrane electrode assembly of the fuel cell of this invention. It is the conceptual diagram which showed an example of the water retention layer in the membrane electrode assembly of the conventional fuel cell. It is the conceptual diagram which showed a part of membrane electrode assembly of a fuel cell.

  Hereinafter, the membrane electrode assembly of the fuel cell of the present invention will be specifically described with reference to the drawings. FIG. 1 is a conceptual diagram showing an example of a water retention layer made of a fiber sheet in a membrane electrode assembly of a fuel cell according to the present invention, and FIG. 2 shows an example of a water retention layer in a membrane electrode assembly of a conventional fuel cell. FIG. 3 is a conceptual diagram, and FIG. 3 is a conceptual diagram showing a part of a membrane electrode assembly of a fuel cell. As shown in FIG. 3, the membrane electrode assembly of the fuel cell of the present invention has a catalyst electrode layer 32, a water retention layer 33, a water repellent layer 34, and a gas diffusion layer 35 on a solid polymer membrane 31. It is the structure provided in order.

  In the present invention, the water retention layer has the greatest feature. That is, as shown in FIG. 1, the water retention layer has a configuration in which a conductive carbon material 12 is coated on a sheet of fibers 11 made of a hygroscopic material. Such fibers 11 are preferably produced by an electrospinning method. For example, an apparatus to which this electrospinning method is applied includes a spinning nozzle having a nozzle hole with a hole diameter of about 0.5 mm at the center of the tip portion, and a collector disposed about 150 mm away from the nozzle. ing. In such a configuration, a high voltage is applied to the spinning nozzle and the collector is grounded, thereby generating a large voltage difference between the spinning nozzle and the collector.

  Next, when a hygroscopic material dissolved or heat-melted in a suitable solvent is induced at the tip of the spinning nozzle and charged, an electrostatic attractive force acts between the grounded collector. Due to this electrostatic attraction, the surface of the hygroscopic material solution at the tip of the spinning nozzle is deformed into the shape of a conical Taylor cone, and when the repulsive force of the charge exceeds the surface tension, the hygroscopic material solution continuously flows from there. Released. Then, the solvent evaporates or solidifies until the released hygroscopic material solution reaches the collector, whereby the hygroscopic material fibers are spun on the collector, and the hygroscopic material fibers are laminated on the collector. A water retention layer is formed.

  Although the fibrous hygroscopic material produced in this way also absorbs moisture and swells, the pores between the fibers can be controlled even if the hygroscopic material swells by controlling the pore size between the fibers. Is not blocked and does not impede gas permeation. In the fuel cell membrane electrode assembly of the present invention, the hygroscopic material fiber forming the water retention layer preferably has a diameter of 5 to 2000 nm, more preferably about 200 nm. Moreover, it is preferable that the average hole diameter between fibers shall be 1 micrometer or more. When the water-retaining layer is formed with a paste as in the past, the diameter of the pores is about 0.1 to 0.3 μm, and when the hygroscopic material swells, it is blocked, but when it is 1 μm or more, The effect can be exhibited reliably.

  In addition, since the water retention layer in the present invention is provided between the catalyst electrode layer and the gas diffusion layer, the water retention layer is also electrically conductive in order to electrically connect the catalyst electrode layer and the gas diffusion layer. It is necessary to have. Therefore, it is essential that the fibers of the hygroscopic material in the present invention are covered with a conductive material such as carbon particles.

  Furthermore, as the hygroscopic material in the present invention, a proton conductive polymer used in a solid polymer electrolyte membrane can be used. Such polymers include perfluoro polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, polyphenylene sulfide polymers, polysulfone polymers, polyethersulfone polymers, Examples thereof include polyether ketone polymers, polyether ether ketone polymers, and polyphenylquinoxaline polymers.

  In addition, the solid polymer membrane in the membrane electrode assembly of the fuel cell of the present invention is sufficiently retained by the water retention layer having the above-described configuration, and the proton conductivity is maintained well. As such a solid polymer film, a conventionally known ion conductive electrolyte film can be used. For example, a perfluoro polymer, a benzimidazole polymer, a polyimide polymer, a polyether imide polymer Examples thereof include a film made of a molecule, a polyphenylene sulfide polymer, a polysulfone polymer, a polyethersulfone polymer, a polyetherketone polymer, a polyetheretherketone polymer, a polyphenylquinoxaline polymer, or the like.

  Furthermore, the catalyst electrode layer in the present invention can be used as a cathode a platinum-supported catalyst in which platinum is supported on a conventionally known carbon black, and a catalyst in which platinum and ruthenium are supported on carbon black as an anode. As in the case of the water retention layer, a catalyst electrode layer having a structure in which a fiber sheet is spun into a fiber and a catalyst is attached to the fiber surface may be used. As the raw material resin for the catalyst electrode layer, the resin used for the solid polymer film can be used.

  In addition, the gas diffusion layer in the present invention may be any one as long as it smoothly supplies the supplied reaction gas to the catalyst electrode layer and assists the formation of a catalyst-electrolyte membrane-gas three-phase interface. For example, carbon paper or carbon cloth having a porosity of about 80% can be used.

11 ... Hygroscopic material fiber, 12 ... Carbon particles, 21 ... Ion conductive polymer,
22 ... carbon fiber, 23 ... carbon particles, 24 ... pore, 31 ... solid polymer film,
32 ... Catalyst electrode layer, 33 ... Water retention layer, 34 ... Water repellent layer, 35 ... Gas diffusion layer, 36 ... Water

Claims (2)

A membrane electrode assembly of a fuel cell in which a catalyst electrode layer including a catalyst and a gas diffusion layer are sequentially laminated on both surfaces of an electrolyte membrane,
On at least one surface of the electrolyte membrane, a water retention layer not further comprising a catalyst is provided between the catalyst electrode layer and the gas diffusion layer,
The water retention layer is a fiber sheet made of a hygroscopic material coated with a conductive carbon material,
The membrane / electrode assembly is characterized in that the hygroscopic material is a polymer electrolyte resin. The membrane electrode assembly according to claim 1 , wherein a water repellent layer is provided between the water retention layer and the gas diffusion layer on at least one surface of the electrolyte membrane .

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