JPS5846828B2 - Manufacturing method of gas diffusion electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a battery such as a fuel cell or an oxygen-metal battery;
The purpose of this project is to improve the manufacturing method of gas diffusion electrodes used in salt electrolyzers and other electrochemical devices.
without sacrificing the current-voltage characteristics of the gas diffusion electrode.
The purpose is to improve the service life by increasing the mechanical strength.

Many proposals have already been made regarding methods of manufacturing gas diffusion electrodes used in fuel cells and other electrochemical devices.

For example, Japanese Patent Publication No. 45-38100 discloses a catalyst layer consisting of a mixture of a catalyst material and polytetrafluoroethylene as a water-repellent binder on one side of a porous metal plate, and a porous polytetrafluoroethylene as a water-repellent layer. A method of manufacturing a gas diffusion electrode has been proposed in which an ethylene oxide film and a metal mesh as a reinforcing body are sequentially crimped.

In this manufacturing method, when the porous polytetrafluoroethylene membrane was relatively thick, the metal mesh was well attached to the surface of the porous polytetrafluoroethylene membrane, and a reinforcing effect was observed.

However, in order to improve the gas diffusivity and current-voltage characteristics, it is necessary to make the polytetrafluoroethylene membrane thinner, but in this case, the pressure of the metal mesh must be relatively high. , the membrane is partially cut, and on the other hand, if the crimp pressure is reduced to prevent the membrane from being cut by the mesh, the polytetrafluoroethylene membrane surface and the metal mesh will separate when the electrode bends, causing the metal mesh to separate. The disadvantage is that the reinforcing effect is lost.

On the other hand, for example, Japanese Patent Publication No. 46-24823 proposes a gas diffusion electrode in which a catalyst layer and a porous polytetrafluoroethylene membrane are arranged between two porous metal plates.

Electrodes with this structure are certainly extremely superior in terms of mechanical strength, but the gas diffusion rate through the pores of the porous metal plate placed on the gas side is not fast enough. The drawback was that it was difficult to operate at high current densities such as , 100-400 mA/ci.

The present invention eliminates the drawbacks of conventional gas diffusion electrodes.

In other words, instead of using a metal net or a porous metal plate whose entire surface is made of micropores as a reinforcing body placed on the gas side of the gas diffusion electrode described above, it is possible to cover the gas diffusion electrode with a microporous metal layer that combines the advantages of both. In addition, it uses a metal plate with an opening.

A metal plate coated with a microporous metal layer and having openings is produced in this way.

That is, first, a core made of metal with openings such as a metal net or expanded metal is prepared, and a dispersion obtained by dispersing metal powder in a cross material such as an aqueous polyvinyl alcohol solution is sprayed onto this core. , immersing the core in the dispersion liquid.

In addition, in this spraying and dipping step, the entire opening of the core should not be blocked.

When first sintered in a sintering furnace, a microporous layer of metal is formed on the surface of the metal core.

When the thus obtained metal plate having openings covered with a microporous metal layer is crimped onto porous polytetrafluoroethylene lumbosacral in the conventional gas diffusion electrode manufacturing method, even if the crimping pressure is high, the metal microporous Because of the porous layer, there is no need to cut the porous polytetrafluoroethylene membrane, and because of the openings, gas diffusion is inhibited compared to when using a porous metal plate on the entire surface. That's not true.

Furthermore, when a microporous metal layer is treated with a water repellent such as polytetrafluoroethylene or tetrafluoroethylene-hexafluoropropylene copolymer, these water repellents simultaneously form porous polytetrafluoroethylene. It also has the advantage of having an adhesive effect on fluorinated ethylene films.

An embodiment of the present invention will be described in detail below.

On one side of a porous nickel plate with a porosity of 80%, a thickness of 1 mm, a length of 110 mm, and a width of 110 mm, an aqueous suspension of activated carbon powder containing silver and nickel and polytetrafluoroethylene as catalyst metals was placed. The mixed dispersion was applied to the end of the porous nickel so as to leave a width of 1101 nm, and once dried to remove moisture.

Next, an aqueous suspension (solid content: 55%) of a copolymer of tetrafluoroethylene and hexafluoropropylene is sprayed onto the surface and dried again.

Next, the porosity was 40%, the thickness was 0.05 mm, and 100
The above-mentioned tetrafluoroethylene-hexafluoropropylene copolymer was sprayed onto a porous polytetrafluoroethylene membrane with a width of 100 mm and a pressure of 100 kg/cwt, and further heated at 250°C. By heat treatment, a body of the gas diffusion electrode is obtained which basically consists of three layers: a porous nickel plate layer, a catalyst layer and a porous polytetrafluoroethylene membrane layer.

On the other hand, a metal plate having openings covered with a microporous metal layer is manufactured as follows.

First, a nickel expanded metal core having a diamond-shaped opening is prepared.

The longer one of the diagonals of the opening is 5 ken, and the shorter one is 2 ken.

Next, a viscous dispersion liquid consisting of 100 parts of carbonyl nickel powder, 1.5 parts of polyvinyl alcohol, and 100 parts of water is prepared.

Next, the viscous liquid mixture is sprayed onto both sides of the core until the diagonal lengths of the openings are 3.2 mm and 0.2 mm, respectively.

After that, it was heated for 3 hours at 1000℃ in an ammonia decomposition gas atmosphere.
Sinter for 0 minutes.

During this sintering, the polyvinyl alcohol as the cross member is thermally decomposed and dissipated, and the surface of the nickel expanded metal core is coated with a microporous nickel layer.

The average pore diameter of the microporous nickel layer is 10μ.

The thus obtained expanded nickel metal with openings covered with a microporous nickel layer was
It is cut into a size of 0x110, immersed in an aqueous suspension of polytetrafluoroethylene (solid content 60%), and then heat-treated at 380°C for 1 hour in nitrogen air to impart water repellency.

Next, an aqueous suspension of tetrafluoroethylene-hexafluoropropylene copolymer (solid content 55%) was sprayed on one side of the nickel expanded metal that had been subjected to water-repellent treatment, and the gas was diffused as described above. It is integrated onto the porous polytetrafluoroethylene membrane of the electrode body at a pressure of 100 kg/cni, and then heat-treated at 290° C. in a nitrogen stream.

Finally, the porous nickel plate and the nickel expanded metal coated with a microporous nickel layer and having openings are spot welded at the ends.

In this way, a gas diffusion electrode effective as a so-called oxygen electrode is obtained.

The cross-sectional structure of the electrode is shown in FIG.

In FIG. 1, 1 is a porous nickel plate, 2 is a catalyst layer,
3 is a bonding layer made of tetrafluoroethylene-hexafluoropropylene copolymer that bonds the catalyst layer 2 and the porous polytetrafluoroethylene membrane layer 4, and 3 is an opening covered with a microporous nickel layer. It is an expanded nickel metal with

FIG. 2 shows an enlarged cross-sectional view of a portion of a nickel expanded metal plate having openings covered with a microporous nickel layer.

In Fig. 2, 5a is a core made of nickel expanded metal, 5b is a microporous nickel coating layer, and 5c
is the opening.

Next, the gas diffusion electrode obtained in the above example is referred to as A, and instead of the nickel expanded metal having the openings in which the liquid is seeded with a microporous nickel layer in the example, the nickel expanded metal is used. B is used alone,
A porous nickel plate having porosity of about 10% on the entire surface was used as C, and a single plate test was conducted using each electrode as an air electrode using a conventional method.

In addition, a 30% caustic potassium aqueous solution was used as the electrolyte,
A nickel plate was used as the counterpart electrode.

Among the test results, the polarization characteristics are shown in Figure 3, 100mA/c4
Figure 4 shows the continuous life test results.

That is, as seen in FIG. 3, electrode A according to an embodiment of the present invention exhibits characteristics equivalent to g compared to conventional electrode B, and far superior to conventional electrode C. It can be seen that it exhibits excellent properties.

This is because in the case of electrode C, the air diffusion rate is slow due to the porous nickel plate layer placed on the gas side.
This is because in the case of electrode A or electrode B, the air diffusion rate is sufficiently fast.

On the other hand, looking at FIG. 4, electrode A, electrode B and electrode C
It can be seen that the lifespan is much longer than that of the

The cause of the end of the life of electrode B was due to peeling of the catalyst layer.

In other words, this was because the nickel expanded metal alone had no reinforcing effect.

In the case of electrode C, no peeling phenomenon was observed, but the reason for the end of its life was that it could not withstand operation at a high current density of 100 mA/c4.

As can be seen from the above test results, electrode A according to one embodiment of the present invention exhibits superior performance in both polarization characteristics and life span.

In addition, in the above-mentioned example, when forming the metal microporous layer,
Expanded metal was used as the core, but net-like,
Similar effects can be obtained with any shape as long as it has the required openings, such as a grid or striped shape.

Further, although nickel is used as the metal material in the embodiment, it can be selected as appropriate depending on the purpose of use of the electrochemical device.

Furthermore, when forming a metal microporous layer, in the example, an aqueous solution of polyvinyl alcohol was used as the wood material, and a spraying method was used. Any method may be used, and the same effect can be obtained even if a dipping method is used instead of a spraying method.

As detailed above, the present invention provides a method for manufacturing a gas diffusion electrode that exhibits excellent performance in both polarization characteristics and life span, and its industrial value is extremely high.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional structural diagram of a gas diffusion electrode according to an embodiment of the present invention, and FIG. 2 shows a nickel expander covering the microporous nickel layer of FIG. 1 and having openings. A partially enlarged cross-sectional structural diagram of the dead metal 5 is shown. FIG. 3 is a polarization characteristic comparison diagram, and FIG. 4 is a comparison diagram of life test results. DESCRIPTION OF SYMBOLS 1... Porous nickel plate layer, 2... Catalyst layer, 4... Porous polytetrafluoroethylene layer, 5
...Nickel expanded metal, 5a
... Core body, 5b ... Microporous coating layer, 5c ... Opening.

Claims (1)

[Claims] 1. In advance, a core made of metal having openings in an expanded metal shape, a net shape, or a lattice shape is coated with a material in which metal is dispersed in a wood material such as an aqueous solution of polyvinyl alcohol. An aperture metal plate coated with a microporous metal layer is prepared by coating the aperture so as to leave an aperture and then sintering, and a water repellent treatment is applied to the aperture metal plate or the aperture metal plate. A gas diffusion method characterized in that the material is pressed onto a porous polytetrafluoroethylene membrane, which is a layered body consisting of a triple layer of a porous metal plate, a catalyst layer, and a porous polytetrafluoroethylene membrane. Electrode manufacturing method.