JPH04118858A - Low temperature type fuel cell - Google Patents

Abstract

PURPOSE:To improve the polarization property and the reliability by improving the gas diffusing property and the ion conductivity of an electrode catalyst layer, and preventing to block a gas passage by the electrolyte. CONSTITUTION:Strip-form hydrophilic layers 11 and gas diffusing layers 12 are laminated alternatively. To the main surface of an electrode catalyst layer 20, an electrolyte layer and an electrode substrate are provided respectively. Such an electrode catalyst layer is produced by dispersing the catalyst particles carrying precious metal particles and a fluorinated hydrocarbon resin in the water sufficiently, and adding an organic solvent making into a paste. This paste is mixed and churned sufficiently so as to make the fluorinated hydrocarbon resin particles into a fiber. Then, an organic solvent made by adding and mixing a fluorinated hydrocarbon resin to a carbon fluoride is added and mixed to produce a paste. These two sorts of pastes are superposed and extruded to form in a specified thickness. In this case, the thickness of the hydrophilic layer 11 is made in the scope 0.1 to 2mum. The resultant multi-layer membranes are laminated and put in a mold and pressed. After pressing it, it is cut square to the laminating direction. Then after a baking, and a binding process to the electrode substrate, an electrode is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a cathode for a low-temperature fuel cell, and particularly to an electrode catalyst layer having excellent gas diffusivity.

(Prior Art) Low-temperature fuel cells include phosphoric acid fuel cells and solid polymer electrolyte fuel cells.

The electrode structure of a phosphoric acid fuel cell is shown in FIG. The electrode has an electrode substrate 34 made of a porous carbon material with excellent electrical conductivity, and an electrode catalyst layer made of a uniform mixture of a catalyst carrier 32 supporting a noble metal 31 such as platinum, and a fluororesin 33 as a water repellent material. Further, a matrix layer 38 made of a mixture of silicon carbide (not shown), which has excellent electrical insulation properties, and fluororesin (TI!J, not shown) as a binding material is laminated on the electrode. The matrix layer 38 is impregnated with phosphoric acid, which is an electrolyte, and the electrode catalyst layer 35 is supplied with the electrolyte from the matrix layer 38 and the reaction gas from the electrode substrate 34 . Although not shown in the drawings, other electrodes are arranged in the matrix layer 38 symmetrically with respect to the matrix layer 3B, and each electrode serves as an anode or a cathode. Inside the electrode catalyst layer 35, the catalyst (solid)
A three-phase interface between the electrolyte (liquid) and the reactant gas (gas) is formed, an electrochemical reaction occurs, and electrical energy can be taken out of the system.

[Problem to be solved by the invention]

However, in the cathode of a conventional fuel cell as described above, oxygen diffusion within the electrode catalyst layer is poor, so when operating at high current density, which requires a large amount of oxygen, sufficient oxygen is not supplied and the characteristics deteriorate. . Furthermore, in the high current density region, the characteristics are also degraded due to the influence of ionic resistance inside the electrode catalyst layer.

In addition, during long-term operation, phosphoric acid, which is an electrolytic solution, moves from the matrix to the cathode, fills the pores, and blocks the gas passage, causing a problem in which the characteristics (j) gradually deteriorate. To prevent this, wet the catalyst layer.
<It is possible to prevent the electrolyte from entering the catalyst layer, but if a large amount of PTFE, which is a water repellent, is used to make the catalyst layer difficult to wet, the PTFE will clog the gas passages and deteriorate the properties. Moreover, in this case, there was also the problem that the PTFE covered the surface of the platinum catalyst, reducing the platinum specific surface area.

This invention was made in view of the above points, and its purpose is to improve the gas diffusivity and ion conductivity of the electrode catalyst layer, and to avoid clogging of the gas passage by the electrolyte, thereby achieving excellent polarization characteristics and stability at low temperatures. The objective is to provide a type fuel cell.

[Means to solve the problem]

The above objects are achieved according to the present invention by 1) comprising an electrode catalyst layer 20, an electrolyte layer, and an electrode substrate, the electrolyte layer being disposed on one main surface of the electrode catalyst layer, and supplying hydrogen ions to the electrode catalyst layer; , the electrode substrate is arranged on the other main surface of the electrode catalyst layer and supplies oxygen to the electrode catalyst layer, and the electrode catalyst layer includes a strip-shaped hydrophilic layer 11 and a gas diffusion layer 1.
2) in the fuel cell according to claim 1, the hydrophilic layer has a density of 2n or less, or 3) claim 1 In the described fuel cell, this is achieved by the gas diffusion layer being composed of fluorocarbon and fluororesin.

The hydrophilic layer is a hydrophilic layer containing a catalyst, and an electrochemical reaction occurs in the catalyst. ! An electrolyte is supplied to the aqueous layer from the electrolyte layer. Since the electrode substrate has flood control properties, electrolyte does not move to the electrode substrate.

The gas diffusion layer has flood control properties and limits the supply of electrolyte from the electrolyte layer. Gas is supplied to the gas diffusion layer from the electrode substrate. The gas that has diffused through the gas diffusion layer stops diffusing at the electrolyte layer.

[Effect]

The gas diffusion layer is difficult to contain an electrolyte therein, and gas is easily diffused therein. ! The electrolyte membrane develops without interruption within the water layer, making it easier for ions to move.The utilization rate of the catalyst also increases.

Since the gas reaches the catalyst by being dissolved in the hydrophilic layer rather than the gas diffusion layer, there is no problem of gas passage blockage caused by electrolyte.

Fluorinated carbon has water control properties and does not melt during the electrode firing process, so by using a fluororesin as a binder, both water control properties and gas diffusivity can be improved.

When the thickness of the hydrophilic layer is set to 2 ira or less, dissolved oxygen from the gas diffusion layer easily reaches the catalyst.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a perspective view showing an electrode catalyst layer of a low temperature fuel cell according to an embodiment of the present invention. Strip-shaped hydrophilic layer 11
and gas diffusion layers are alternately stacked.

Although not shown, an electrolyte layer and an electrode substrate are arranged on the main surface of the electrode catalyst layer, respectively.

Such an electrode catalyst layer is prepared as follows. A paste was prepared by thoroughly dispersing catalyst particles carrying noble metal particles and 20% by weight of fluororesin in water, and adding and mixing a 100% solvent such as ethylene glycol or isopropyl alcohol. This paste was thoroughly kneaded, and an aqueous solvent containing 20% by weight of a fluororesin was added to the 0-order fluorinated carbon in which the fluororesin particles were made into fibers and well entangled, and mixed to prepare a paste.

The above two types of pastes are superimposed and molded using an extruder, folded in half and repeated about 10 times, and finally molded to a predetermined thickness. At this time, the number of repetitions and the final molding thickness are selected so that the thickness of the hydrophilic layer is in the range of 0.1 to 2-2.

A 30 cm square block is created by stacking the multilayer films thus obtained. Put this into a mold and press. After pressing, cut perpendicular to the stacking direction to a thickness of 0.5 mm.

Subsequently, the electrode is produced through firing and bonding to the electrode substrate.

FIG. 2 is a diagram showing the dependence of fuel cell voltage on the thickness of the hydrophilic layer. The current density was 300e+^/-. When the thickness of the hydrophilic layer exceeds 2μ, the battery voltage drops rapidly. This is because it takes time for dissolved oxygen from the gas diffusion layer to reach the catalyst in the hydrophilic layer, increasing concentration polarization. However, when the thickness of the hydrophilic layer is 2 μ or less, oxygen replenishment is rapid, and the battery voltage shows a high value of 780 mV with little polarization. This good oxygen replenishment is achieved by the gas diffusion layer and the hydrophilic layer of 2 uVA or less. It is what was done. The conventional battery voltage at the above current density is 7
It is 60mV.

Note that the electrode catalyst layer according to the present invention can also be used as a cathode of a solid polymer electrolyte fuel cell. In this case, a solid polymer electrolyte is used for the electrolyte layer. The hydrophilic layer can be impregnated with a solution of a polymer electrolyte.

Alternatively, instead of the fluorinated carbon, an acetylene blank may be used, 60% by weight of a fluororesin is mixed therein, an organic solvent is added, and the gas diffusion layer 12 is composed of the acetylene blank and the fluororesin.

〔Effect of the invention〕

According to this invention, 1) It has an electrode catalyst layer, an electrolyte layer, and an electrode substrate, the electrolyte layer is arranged on one main surface of the electrode catalyst layer and supplies hydrogen ions to the electrode catalyst layer, and the electrode substrate has the following features: The electrode catalyst layer is arranged on the other main surface of the electrode catalyst layer and supplies oxygen to the electrode catalyst layer. 2) In the fuel cell according to claim 1, the hydrophilic layer has a thickness of 2n or less, or 3) In the fuel cell according to claim 1, the gas diffusion layer is made of fluorocarbon and fluororesin. The reaction gas is supplied to the hydrophilic layer through the gas diffusion layer, which does not easily contain electrolyte and allows gas to easily diffuse.The reaction gas melts into the hydrophilic layer from the gas diffusion layer, and is then dissolved in the form of dissolved oxygen. It can easily reach the catalyst. In this way, a high reaction gas supply to the catalyst, which is required for high current densities, can be achieved.

When the thickness of the hydrophilic layer is 2 μm or less, the reaction gas dissolved in the hydrophilic layer can reach the catalyst more easily than the gas diffusion layer by diffusion in the liquid.

Carbon fluoride is water repellent and does not contain an electrolyte when forming a gas diffusion layer.

In addition, fluorinated carbon does not melt during the electrode firing process and does not block the gas diffusion path. In this way, fluorinated carbon is bonded with fluororesin to form a gas diffusion layer and improve gas diffusion. be able to.

In the hydrophilic layer, the electrolyte membrane is well developed without interruption, allowing ions to move easily, and resistive polarization becomes small at high current densities. In addition, the electrolyte membrane is well developed and makes sufficient contact with the catalyst, increasing the utilization rate of the catalyst.

In addition, since the reactive gas is dissolved in the hydrophilic layer rather than the gas diffusion layer and reaches the catalyst, the problem of gas diffusion path clogging by the electrolyte is solved, and the reliability of the battery is improved.

In this way, a low-temperature fuel cell with excellent polarization characteristics and reliability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an electrode catalyst layer of a low temperature fuel cell according to an embodiment of the present invention, and FIG. 2 is a perspective view showing an electrode catalyst layer of a low temperature fuel cell according to an embodiment of the present invention. A diagram showing thickness dependence, and FIG. 3 is a cross-sectional view showing a conventional battery. OVa water layer, 12: gas diffusion layer, 2o: electrode catalyst layer.

Claims (1)

[Claims] 1) An electrode catalyst layer, an electrolyte layer, and an electrode substrate, the electrolyte layer being disposed on one main surface of the electrode catalyst layer and supplying hydrogen ions to the electrode catalyst layer; The electrode catalyst layer is arranged on the other main surface of the electrode catalyst layer and supplies oxygen to the electrode catalyst layer. A low-temperature fuel cell that is characterized by 2) A low-temperature fuel cell according to claim 1, wherein the hydrophilic layer has a thickness of 2 μm or less. 3) A low-temperature fuel cell according to claim 1, wherein the gas diffusion layer is composed of fluorocarbon and fluororesin.