JP7093665B2 - Polyelectrolyte thin film - Google Patents

Description

The present invention relates to a polyelectrolyte thin film.

Since the electrolyte membrane in a fuel cell is a very important component, high performance has been proposed. In order to further increase the ion conductivity of the electrolyte membrane, it is common to increase the ion exchange group concentration, that is, decrease the ion exchange group equivalent (hereinafter, also referred to as “EW”). Ion conductivity can also be improved by reducing the film thickness of the electrolyte membrane to reduce the membrane resistance (Non-Patent Document 1). However, when the EW becomes low or the film thickness becomes small, the electrolyte membrane tends to swell during battery operation, and the strength decreases. Therefore, it has been proposed to use a porous membrane as a reinforcing material (for example, Patent Documents 1 and 2).

International Publication No. 2016/056430 US Pat. No. 7,811,694

Journal of Membrane Science 364 (2010) 183-193

Using a porous membrane as a reinforcing material complicates the manufacturing process. Therefore, a method that does not use a reinforcing material is desired. When the reinforcing material is not used, it is necessary to optimize the balance between the film thickness and the strength, which are in a trade-off relationship. At present, the polyelectrolyte has an EW of 800 to 1100 g / mol and a film thickness of about 25 to 250 μm. Membranes are commercially available (eg, Nafion®, Aquivion®, etc. sold by Sigma-Aldrich). However, there is a demand for a polyelectrolyte membrane with higher ionic conductivity and strength. In view of such circumstances, it is an object of the present invention to provide a polyelectrolyte thin film having high ionic conductivity and strength.

The inventors have solved the above-mentioned problems by increasing the ionic conductivity by reducing the film thickness, reducing the bulk portion and increasing the surface portion, and increasing the EW above a certain value to improve the strength. That is, the above-mentioned problem is solved by the following invention.
[1] A polymer electrolyte membrane having an ion exchange group equivalent of more than 1100 g / mol and a thickness of 8 μm or less.
[2] The polymer electrolyte according to [1], wherein the thickness is 6 μm or less.
[3] The polymer electrolyte according to [1], wherein the thickness is 3 μm or less.
[4] The polymer electrolyte according to any one of [1] to [3], wherein the thickness is 0.1 or more.
[5] A fuel cell provided with the polymer electrolyte membrane according to any one of the above [1] to [4].

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a polymer electrolyte thin film having high ionic conductivity and strength.

Hereinafter, the present invention will be described in detail. In the present invention, "X to Y" includes X and Y which are fractional values.
1. 1. Polyelectrolyte film (1) Ion exchange group equivalent The polyelectrolyte film of the present invention has an ion exchange group equivalent (EW) of more than 1100 g / mol. The EW is not limited as long as it exceeds 1100 g / mol, but is preferably 1200 g / mol or more, and more preferably 1300 g / mol or more.

Examples of the ion exchange group include an acid type functional group for cation exchange and a base type functional group for anion exchange. The former is suitable for PEMFC and the latter is suitable for AEMFC. Examples of the acid type functional group include a sulfonic acid group, a phosphoric acid group, a carboxylic acid group and the like. Among these, a sulfonic acid group is preferable because it has excellent proton conductivity. Examples of the basic functional group include a quaternary basic functional group such as a quaternary ammonium group or a quaternary pyridyl group.

(2) Film thickness The thickness of the polyelectrolyte membrane of the present invention is 8 μm or less. The upper limit of the thickness is preferably 6 μm or less, more preferably 3 μm or less, further preferably 2 μm or less, and particularly preferably 1 μm or less. The lower limit of the thickness is not limited, but is preferably 0.1 μm or more, and more preferably 0.5 μm or more.

(3) Material As the polyelectrolyte membrane of the present invention, a polymer in which an ion exchange group is introduced into a known polymer can be used. Further, since the thickness of the polyelectrolyte film of the present invention is extremely thin, a composition in which a water-insoluble inorganic electrolyte or an organic electrolyte is dispersed in a polymer known as a polyelectrolyte film can also be used. Known polymers include fluoroaliphatic polymers such as polytetrafluoroethylene and polytrifluorostyrene, aromatic polyethers such as polyetherketone, polyetheretherketone, and polyethersulfone, aromatic polyimides, and polybenz. Examples include aromatic polymers such as imidazole. The introduction of the ion exchange group can be carried out according to a known method. Examples of the water-insoluble inorganic electrolyte include Li ₃ PO ₄ , Li ₃ PO ₄ N _x , LiBO ₂ N _x , Li ₄ SiO ₄ -Li ₃ PO ₄ , Li ₄ SiO ₄ -Li ₃ VO ₄ . .. Examples of the water-insoluble organic electrolyte include carbonic acid esters such as propylene carbonate, diethyl carbonate and ethylene carbonate.

(4) Characteristics The polymer electrolyte membrane of the present invention has excellent ionic conductivity and strength. Generally, when the film thickness of the polyelectrolyte membrane becomes small, it tends to swell and the strength tends to decrease. However, as described above, the polyelectrolyte membrane of the present invention has a high EW, that is, a low ion exchange group concentration, so that the electrolyte membrane does not easily swell during battery operation, and thus has excellent strength and durability. In general, when the EW is high, the ionic conductivity decreases, but since the polyelectrolyte membrane of the present invention has an extremely small film thickness, the membrane resistance is low and excellent ionic conductivity is exhibited.

Since the polymer electrolyte membrane of the present invention has a high EW, that is, a low ion exchange group concentration, in addition to the above, it has excellent film forming property, excellent chemical stability, and excellent heat resistance. In addition, since the ion exchange group concentration is low, it dissolves not only in highly polar organic solvents such as NMP and DMSO but also in relatively low polar organic solvents such as DMF and THF, so that it has a wide range of organic solvent selectivity. .. Further, since the ion exchange group concentration is low, the polyelectrolyte membrane of the present invention has an advantage that it can be produced at low cost.

Generally, as the water content of the polyelectrolyte membrane decreases, the ionic conductivity decreases. The conventional polymer electrolyte membrane has a problem that the ionic conductivity is lowered because the water content is inclined so that the water content on the cathode side is high and the water content on the anode side is low during the operation of the battery. However, since the polyelectrolyte membrane of the present invention has a small film thickness, backdiffusion in which water moves from the cathode side to the anode side is likely to occur, and the ion conductivity can be maintained without the above-mentioned inclination of the water content. It also has an effect.

2. 2. Manufacturing Method Although the polymer electrolyte membrane of the present invention can be manufactured by a known method, it is preferably manufactured by the CCG (Catalyst Coated on GDL) method because the film thickness is extremely small. The CCG method is a method of applying a catalyst layer to a gas diffusion layer. In the present invention, it is preferable to produce by a method including the following steps.
Step 1: A step of forming a catalyst layer on a gas diffusion layer and a step 2: a composition containing a polymer and a solvent or a dispersion medium for forming a polyelectrolyte film are prepared, and the composition is placed on the catalyst layer. The process of applying to form an electrolyte film.

(1) Step 1
A known gas diffusion layer can be used. Catalyst metals include platinum, palladium, rhodium, iridium, ruthenium, iron, titanium, nickel, cobalt, gold, silver, copper, chromium, manganese, molybdenum, tungsten, aluminum, silicon, renium, zinc, tin, or any of these. Examples thereof include alloys, but platinum is preferable. The carrier is a support for supporting the catalyst metal, and is preferably carbon, metal nitride, metal carbide, or metal oxide. Further, the carrier is preferably porous, and particularly preferably porous carbon. The carrier is preferably in the form of particles, and the average particle size thereof is preferably about 10 to 100 nm. This step can be carried out as known, but a composition containing catalyst particles, a carrier, a polymer forming a polymer electrolyte membrane, and a solvent or a dispersion medium is prepared and applied onto the gas diffusion layer. It is preferable to form a catalyst layer.

Examples of the polymer forming the polyelectrolyte film include the above-mentioned ones. As the solvent or dispersion medium, known aprotic polar solvents are preferable. Examples thereof include DMF, DMSO, NMP, NEP, THF and the like. The method of applying the composition to the gas diffusion layer is not limited, but it is preferable to spray the composition.

(2) Step 2
In this step, a composition obtained by removing the catalyst and the carrier from the composition prepared in the previous step is prepared, and by spraying the composition, for example, a polymer electrolyte membrane having a desired thickness can be formed on the catalyst layer. When the spray method is carried out at normal pressure, it takes time to form a film, so it is preferable to use a dispersion liquid in which a polyelectrolyte is dispersed in a mixed solvent of water and alcohol. Alternatively, a solvent having an appropriate vapor pressure such as DMF may be used as the solvent.

In addition to the spray method, a transfer method (decal), a screen printing method, or a spin coating method can be used to form a polyelectrolyte film having a desired thickness on the catalyst layer. Alternatively, the composition may be impregnated with one side of a plate-shaped GDL or GDE to form a polyelectrolyte film having a desired thickness.

3. 3. Fuel cell The fuel cell provided with the polyelectrolyte membrane of the present invention is excellent in power generation efficiency and durability. Known materials can be used as the electrode, catalyst layer, and gas diffusion layer of the fuel cell.

[Example 1]
A polyether sulfone containing a sulfonic acid group (EW = 1200 g / mol) is dissolved in DMSO to prepare a 10 wt% concentration polyether sulfone solution. An electrode having a catalyst layer formed on a GDL (gas diffusion layer) is prepared, a sulfonated polyether sulfone solution is sprayed onto the electrode, and the mixture is dried (60 to 200 ° C.) to form a thin film.

Claims (3)

A single polyelectrolyte layer having an ion exchange group equivalent of 1200 g / mol or more and a thickness of 8 μm or less. The polymer electrolyte layer according to claim 1, wherein the thickness is 1 μm or less. The fuel cell provided with the polyelectrolyte layer according to claim 1.