JPH0696771A - Gas diffusive electrode - Google Patents

Abstract

PURPOSE:To reduce hydrogen ion in using a reaction layer as a negative electrode and efficiently generate hydrogen gas from the negative electrode by providing an electrical insulating hydrophilic porous layer and an electrical insulating water repellent porous layer on both surfaces of the reaction layer. CONSTITUTION:In the center of a reaction layer 1 formed by tangling a hydrophilic part and a water repellent part in contact to each other, an electric collector 2 is nipped and built therein. An electrical insulating hydrophilic porous layer 3 is bonded to the layer 1, and an electrical insulating water repellent porous layer 4 to the other surface of the layer 1. Since the layers 3, 4 are provided on both the surfaces of the layer 1 in this way, the layer 1 is never exposed to a flowing electrolyte. The layer 1 is thus protected, the electrolyte is moved to the layer 2 only by diffusion, so that metal ions are never reduced, and hydrogen ions are diffused to the layer 1 and positively reduced in the hydrophilic part by the collector 2 to form hydrogen gas, which thus can be extremely efficiently taken out from the water repellent layer surface of the electrode.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improvements in gas diffusion electrodes for use in electrochemical reactors.

[0002]

2. Description of the Related Art A conventional gas diffusion electrode is composed of a hydrophilic part made of hydrophilic carbon black and polytetrafluoroethylene (sometimes supporting a catalyst), a water-repellent carbon black and polytetrafluoroethylene. And a gas diffusion layer made of polytetrafluoroethylene are joined to one surface of the reaction layer formed by interposing and in contact with each other. This gas diffusion electrode as the cathode,
When platinum 2 is used as an anode to oxidize Fe ²⁺ to Fe ³⁺ and H ₂ is generated at the cathode, Fe ³⁺ oxidized at the anode is reduced at the cathode to become Fe ²⁺ . Therefore, it is improved by bonding a hydrophilic porous layer to the surface of the reaction layer. However,
The gas diffusion electrode has a problem in that it is necessary to provide an air chamber on the gas diffusion layer side, and it is impossible to use the gas diffusion electrode as it is in the electrolytic solution.

[0003]

Therefore, the present invention, when used as a cathode, does not reduce metal ions in the electrolytic solution and reduces hydrogen ions to prevent hydrogen ions from moving to the cathode. An object of the present invention is to provide a gas diffusion electrode in which gas is efficiently generated from the cathode.

[0004]

In the gas diffusion electrode of the present invention for solving the above-mentioned problems, a current collector is sandwiched at the center of a reaction layer which is constituted by a hydrophilic part and a water-repellent part which are interdigitated and in contact with each other. It is built in, and the hydrophilic layer having electrical insulation and the water repellent porous layer having electrical insulation are bonded to both surfaces of the reaction layer.

[0005]

In the gas diffusion electrode constructed as described above, the electrically insulating hydrophilic porous layer is provided on one surface of the reaction layer. Therefore, when the gas diffusion electrode is used as a cathode, electrolysis that permeates the hydrophilic porous layer. Since the liquid cannot move due to convection but only diffuse movement, the electrolytic solution containing the metal ions oxidized on the anode side is not supplied to the reaction layer. Therefore, the cathode does not reduce metal ions. Then, the hydrogen ions pass through the electrically insulating hydrophilic porous layer having a high transmittance without being hindered from moving to the cathode, and are actively reduced by the current collector at the hydrophilic part in the reaction layer to become hydrogen gas, and the reaction It occurs from the water repellent part in the layer and the electrically insulating water repellent porous layer on the other surface. The porosity of the porous layer is preferably 60% or more from the viewpoint of suppressing power loss due to electric resistance during electrolysis. The pore size of the porous layer is preferably 10 μm or less for the purpose of moving the electrolytic solution only by diffusion.

[0006]

EXAMPLE An example of the gas diffusion electrode of the present invention will be described with reference to FIG. 1. Reference numeral 1 denotes a reaction layer composed of a hydrophilic part and a water repellent part in contact with each other. The current collector 2 is sandwiched and built in. An electrically insulating hydrophilic porous layer 3 is bonded to one surface of the reaction layer 1, and an electrically insulating water-repellent porous layer 4 is bonded to the other surface of the reaction layer 1.
The reaction layer 1 comprises hydrophilic carbon black having an average particle size of 390Å and water-repellent carbon black having an average particle size of 420Å,
Polytetrafluoroethylene powder with an average particle size of 0.3 μm is 4:
Thickness 0.1mm, width 100mm, mixed and molded in the ratio of 3: 3,
50 mg of platinum catalyst is supported on hydrophilic carbon black in a 100 mm long sheet. The current collector 2 is made of titanium expanded metal (about 50 mm thick).
(Mesh) is platinum-plated. The electrically insulating hydrophilic porous layer 3 is formed by mixing and molding silicon carbide powder having an average particle size of 0.5 μm and polytetrafluoroethylene having an average particle size of 0.3 μm in a ratio of 9: 1 to a thickness of 0.5. mm, width 100 mm,
A sheet with a length of 100 mm, a porosity of 70%, and a pore diameter of 10 μm or less. The electrically insulating water-repellent porous layer 4 has an average particle size of
Thickness of 0.3 μm polytetrafluoroethylene dispersion
Spray 0.1mm, width 100mm, length 100mm, 320 ℃
It was heat treated in. Thus the gas diffusion electrode 5 thus configured, for example, in an electrolytic tank 6 as shown in FIG. 2, arranged in the hydrophilic porous layer 3 side to face the insoluble electrode 7, Fe ⁺⁺ to the electrolytic cell 6 Electrolyte solution 8 consisting of a 5M hydrochloric acid solution containing 1.5 M / l of Fe and ³⁺ Fe ³⁺ was flowed in as indicated by an arrow, and electrolysis was carried out at 0.2 A / cm ^{2 using} gas diffusion electrode 5 as a cathode and insoluble electrode 7 as an anode. However, Fe ⁺⁺ is oxidized on the anode side to become Fe ³⁺ . Fe oxidized on the anode side
^The electrolytic solution containing ³⁺ does not supply to the reaction layer 1 because it only diffuses and moves in the hydrophilic porous layer 3 on the cathode side. Therefore, Fe ³⁺ is not reduced at the cathode. The H ⁺ in the electrolytic solution 8 passes through the hydrophilic porous layer 3 without being hindered from moving to the cathode, and is actively reduced by the current collector 2 in the hydrophilic portion of the reaction layer 1 to H ₂ (hydrogen gas). Then, hydrogen gas is generated from the gas diffusion electrode 5 through the water-repellent porous layer 4 of the reaction layer 1. The hydrogen evolution overvoltage at this time was 50 mV, and the amount of hydrogen gas obtained was 97% in terms of current efficiency. In the above example, the hydrophilic porous layer 3 and the water-repellent porous layer 4 are bonded to each other one by one, but as shown in FIG. 3, the hydrophilic and water-repellent porous layers may be bonded to each surface in a band shape. . At this time, when the hydrophilic porous layer 3 is bonded to one surface of the reaction layer, it is desirable that the water repellent porous layer 4 is bonded to the other surface.
Further, as shown in FIG. 4, it is also possible to place anodes on both sides.
Further, when H ₂ was bubbled from the lower portion of this electrode to form an anode, hydrogen was oxidized and Fe ²⁺ was not oxidized. Furthermore, this electrode was able to reversibly carry out the reaction of Extra 1.

[Outer 1]

On the other hand, as a conventional example, a gas diffusion electrode, in which a 0.5 mm glass filter film is formed as a hydrophilic porous layer on one surface of a reaction layer and a gas diffusion layer is bonded on the other surface, is the same as in the above embodiment When used for electrolysis, hydrogen overvoltage is
At 62 mV, the amount of hydrogen gas obtained was 68% in terms of current efficiency. This was because the gas diffusion layer was electrically conductive and Fe ³⁺ generated was reduced.

[0008]

As can be seen from the above description, in the gas diffusion electrode of the present invention, since the porous layers are provided on both sides of the reaction layer, the reaction layer is not exposed to the flowing electrolytic solution.
Therefore, the reaction layer is protected and the movement of the electrolytic solution to the reaction layer is only diffusion, the metal ions are not reduced, the hydrogen ions are diffused in the reaction layer, and the current collector positively in the hydrophilic part. It is reduced to hydrogen gas and can be taken out from the surface of the water repellent layer of the electrode extremely efficiently. Conversely, hydrogen can be oxidized to hydrogen ions, and the metal ions are not oxidized at this time. Thus, the reaction between the gas and the ion can be reversibly caused without changing the valence of the coexisting ion.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part showing an embodiment of a gas diffusion electrode of the present invention.

FIG. 2 is a cross-sectional view showing an example of use of the gas diffusion electrode of the present invention.

FIG. 3 is an enlarged cross-sectional view of a main part showing another embodiment of the gas diffusion electrode of the present invention.

FIG. 4 is a cross-sectional view showing another example of use of the gas diffusion electrode of the present invention.

[Explanation of symbols]

 1 Reaction Layer 2 Current Collector 3 Electrically Insulating Hydrophilic Porous Layer 4 Electrically Insulating Water-Repellent Porous Layer 5 Gas Diffusion Electrode

Claims (1)

[Claims] 1. A current collector is sandwiched and incorporated in the center of a reaction layer composed of a hydrophilic part and a water repellent part which are assembled and in contact with each other. A gas diffusion electrode in which an electrically insulating water-repellent porous layer is joined.