JPH1121687A - Solid polymer type water electrolytic cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the fall of a catalyst and to suppress an increase in cell voltage by using an ion-exchange membrane-catalytic electrode joined body with an electrode composed of three layers, i.e., substrate layer, intermediate layer and coating layer, consisting of platinum as the anode or anode and cathode. SOLUTION: Iridium catalyst and/or ruthenium catalyst beds are preferably formed in the intermediate layer. Meanwhile, an ion-exchange membrane- catalytic electrode joined body with an electrode composed of two layers, i.e., substrate layer and coating layer of platinum, as the anode or anode and cathode is used as the ion-exchange membrane, and a catalyst bed is preferably formed in the substrate layer. The catalyst bed is preferably formed with Ir and/or IrO2 , Ir2 O3 and/or Ru or Ru and/or RuO2 . The catalyst bed is sandwiched between the substrate layer of platinum and coating layer or the coating layers of platinum, hence the catalyst bed poorly adhesive to the platinum of the substrate layer or ion-exchange membrane is physically held by platinum, and the falling of the catalyst bed attendent on the elecrolysis of a solid polymer- type water electrolytic cell is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte water electrolysis cell, and more particularly to an electrode structure thereof.

[0002]

2. Description of the Related Art In a solid polymer type water electrolysis cell using an ion exchange membrane as a solid polymer electrolyte as an electrolyte, for example, an anode made of a platinum group metal is provided on one of both sides of the ion exchange membrane and the other is made of platinum. A basic unit is an ion exchange membrane-catalyst electrode assembly in which a cathode made of a group metal is integrally joined, and while applying water to the anode chamber, a voltage is applied between the two electrodes. More hydrogen is obtained.

Anode: H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e ⁻ Cathode: 2H ⁺ + 2e ⁻ → H ₂ Total reaction: H ₂ O → _1/2 O ₂ + H ₂ Here, the cell pressure of the cell during electrolysis (V _t ) is the theoretical decomposition voltage (E ₀ ), the anode and cathode overvoltages (η _a , η _c ), and
The total loss (IR).

V _t = E ₀ + η _a + η _c + IR In the cell voltage, the ratio of the anode overvoltage (η _a ) is the largest. Therefore, in order to reduce the production cost of hydrogen obtained by water electrolysis, the overvoltage is low. An iridium-based catalyst or a ruthenium-based catalyst is used as an anode of an ion exchange membrane-catalyst electrode assembly. When a perfluorosulfonate membrane is used as the ion exchange membrane, since the membrane has a strong acidity, platinum (Pt) having high acid resistance is used for the underlayer, and an iridium-based catalyst having a low overvoltage is further provided thereon.
Or an ion exchange membrane formed with a ruthenium-based catalyst layer
A catalyst electrode assembly is used.

As a method for integrally joining these catalysts to an ion exchange membrane, an electroless plating method (Japanese Patent Publication No. 56-3687)
3. JP-B-58-47471, JP-B-59-4207
8, Japanese Patent Publication No. 2-20709) and a hot press method (Japanese Patent Application Laid-Open No. 52-78788, '97 64th Annual Meeting of the Institute of Electrical Chemistry, P91).

[0006]

The ion-exchange membrane-catalyst electrode assembly using an iridium-based catalyst or a ruthenium-based catalyst disclosed in the above-mentioned patents and the like can be obtained by directly converting an iridium-based catalyst and / or a ruthenium-based catalyst. After bonding to an ion exchange membrane or bonding platinum (Pt) as an underlayer,
An iridium catalyst or a ruthenium catalyst is directly bonded to an ion exchange membrane. That is, the iridium-based catalyst and / or the ruthenium-based catalyst form the surface layer of the electrode.

However, an iridium-based catalyst or a ruthenium-based catalyst has poor adhesion to an ion-exchange membrane or to platinum as an underlayer, and is relatively difficult to gasify by oxygen gas generated by electrolysis. The catalyst drops off quickly, and the cell voltage during water electrolysis increases. Therefore, if the same water electrolysis cell is used for a long time, there is a problem that the production cost of hydrogen increases with time.

[0008]

Means for Solving the Problems Platinum (P) is used for the ion exchange membrane.
solid polymer type water having an electrode composed of three layers of an underlayer, an intermediate layer, and a coating layer composed of platinum (Pt) as an anode or an ion exchange membrane-catalyst electrode assembly having an anode and a cathode A solid polymer having an electrolytic cell or an ion-exchange membrane-catalyst electrode assembly in which an electrode composed of a base layer and a coating layer made of platinum (Pt) is sequentially used as an anode or an anode and a cathode. The above-mentioned problem is not solved by forming an iridium-based catalyst and / or a ruthenium-based catalyst layer in an intermediate layer and in an underlayer in the former.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the solid polymer type water electrolysis cell of the present invention, as described above, an iridium catalyst and / or
An underlayer made of platinum (Pt);
Similarly, by being sandwiched between a coating layer made of platinum (Pt) or an ion-exchange membrane and a coating layer made of platinum (Pt), an iridium-based base layer having poor adhesion to platinum (Pt) or an ion-exchange membrane is used. Since the catalyst and / or the ruthenium-based catalyst layer is physically held by platinum, it is possible to prevent the iridium-based catalyst and / or the ruthenium-based catalyst layer from falling off due to the water electrolysis.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to preferred embodiments.

(Embodiment 1) Platinum (Pt) -iridium (Ir) -platinum (P
An ion-exchange membrane-catalyst electrode assembly was prepared using the three-layered electrode of t) as an anode and a cathode. FIG. 1 is a cross-sectional view of an ion exchange membrane-catalyst electrode preparation holder, wherein 1 is an ion exchange membrane, 2 is an acrylic resin holder, and 3 is a packing.

1. Pretreatment of ion exchange membrane: Perfluorosulfonic acid type ion exchange membrane (Dafon, Nafion
-117) Both surfaces were roughened by sandblasting, boiled with 4N hydrochloric acid, and washed with purified water.

2. Attachment to holder: The film was sandwiched between acrylic resin holders shown in FIG. 1, and the area in contact with a plating solution described later was defined as φ80 mm (50 cm ² ).

3. Formation of underlayer: Tetraammineplatinum (〓) salt solution [Pt (NH ₃ ) ₄ ] ^{2+ on} both sides of the film
, And allowed to stand for 2 hours. Then, 1 mg / cm ² of platinum (Pt) was deposited on the surface of the film with a 0.05% NaBH ₄ solution to form an underlayer.

4. Preparation of the intermediate layer: 2 mg of a plating solution composed of potassium hexachloroiridate and hydrazine hydrochloride solution was added to both surfaces of the film, and hydrazine hydrochloride was added so that the pH was maintained at about 2.5. /
cm ² of iridium (Ir) was deposited.

5. Preparation of coating layer: A plating solution composed of hexachloroplatinic acid, hydrazine hydrochloride, and an aqueous ammonia solution was added to both surfaces of the film, and while adding aqueous ammonia so that the pH was maintained at about 4, platinum (platinum) was formed on the intermediate layer. P
t) was precipitated at 1 mg / cm ² .

(Example 2) An ion-exchange membrane-catalyst electrode assembly having an electrode composed of two layers of iridium (Ir) -platinum (Pt) as an anode and a cathode was formed on the ion-exchange membrane by the following procedure. Created.

1. Pretreatment of ion exchange membrane: Perfluorosulfonic acid type ion exchange membrane (Dafon, Nafion
-117) Both surfaces were roughened by sandblasting, boiled with 4N hydrochloric acid, and washed with purified water.

2. Mounting on Holder: The film was sandwiched between acrylic resin holders shown in FIG. 1, and the area in contact with a plating solution described later was defined as 50 cm ² .

3. Preparation of underlayer: An iridium ammonium chloride (NH ₄ ) IrCl ₆ aqueous solution was put on both surfaces of the film, left for 2 hours, and then 0.05% NaBH ₄ solution was used.
Iridium (Ir) was deposited at 1 mg / cm ^{2 on the} film surface to form an underlayer.

4. Preparation of coating layer: A plating solution composed of hexachloroplatinic acid, hydrazine hydrochloride, and an aqueous ammonia solution was added to both surfaces of the film, and while adding aqueous ammonia so that the pH was maintained at about 4, platinum (platinum) was formed on the intermediate layer. P
t) was precipitated at 1 mg / cm ² .

Example 3 Iridium oxide / ruthenium oxide / platinum (IrO ₂ .RuO _2.
An ion-exchange membrane-catalyst electrode assembly was prepared in which an electrode composed of two layers of a Pt) mixed catalyst layer and a platinum (Pt) layer was used as an anode and a cathode.

1. Preparation of underlayer: iridium oxide: ruthenium oxide: platinum (IrO ₂ : RuO ₂ : Pt) 7:
A mixed solution of a powder catalyst containing NaClion (Aldrich, Nafion solution) having the same composition as the ion exchange membrane and a tetrafluoroethylene (PTFE) dispersion containing the powder catalyst in a ratio of 2: 1 was mixed with ethylene tetrafluoride and hexafluoride. After forming a film (φ80 mm) on a propylene copolymer (FEP) film and drying, both surfaces of a perfluorosulfonic acid-type ion-exchange membrane (Dafon, Nafion-117) are hot-pressed at 130 ° C. at 130 ° C. Transferred and joined.

2. Preparation of coating layer: The film was sandwiched between holders made of acrylic resin shown in FIG. 1, and the area in contact with a plating solution described later was defined as 50 cm ² (φ80 mm). further,
A plating solution consisting of hexachloroplatinic acid, hydrazine hydrochloride, and an aqueous ammonia solution was added to both sides of the film, and the pH was adjusted.
While maintaining the pH at about 4, platinum (Pt) was deposited at a concentration of 1 mg / cm ² on the underlayer while adding aqueous ammonia.

The ion-exchange membrane-catalyst electrode assembly obtained by bonding the various electrodes obtained in Examples 1 to 3 above was assembled in a water electrolysis cell, the actual electrolysis was performed, and the results of measuring the change over time in the cell voltage were shown. As shown in FIG. For comparison, Examples 1 to 3 were used.
In the above, a similar test was performed on a conventional water electrolysis cell using an ion-exchange membrane-catalyst electrode assembly without a coating layer made of platinum (Pt). In FIG. 2, A to C are water electrolysis cells of the present invention using the ion-exchange membrane-catalyst electrode assembly obtained in Examples 1 to 3, respectively. This is a conventional water electrolysis cell using an ion exchange membrane-catalyst electrode assembly without a coating layer made of platinum (Pt).

The electrolysis conditions are shown below.

Electrolytic current density: 2 A / cm ² Operating temperature: 60 ° C. From FIG. 2, the water electrolysis cells (A to C) of the present invention have almost no change in cell voltage with time due to electrolysis, and have a higher concentration than platinum (Pt). In conventional water electrolysis cells (DF) using an ion-exchange membrane-catalyst electrode assembly in which no coating layer is provided, the cell voltage increases with time with electrolysis. As a result of disassembly of the water electrolysis cell, the ion exchange membrane-catalyst electrode assembly of the water electrolysis cells (A to C) of the present invention hardly saw any electrode falling off, but the conventional water electrolysis cell (D In ~ F), partial dropout of the electrode was confirmed.

[0028]

As described above, the solid polymer type water electrolysis cell according to the present invention has no electrode falling off even during long-term operation.
Since there is no increase in cell voltage, the cost of hydrogen produced by water electrolysis is reduced. Therefore, it is very important to contribute to the industry.

[Brief description of the drawings]

FIG. 1 is an ion-exchange membrane-catalyst electrode preparation holder-cross-sectional view

FIG. 2 is a graph showing the characteristics of the solid polymer type water electrolysis cell of the present invention with the lapse of time of an electrolysis cell.

Claims (6)

[Claims] An underlayer, an intermediate layer, and an intermediate layer made of platinum (Pt).
A solid polymer water electrolysis cell comprising an anode or an ion exchange membrane-catalyst electrode assembly in which an electrode composed of three layers of a coating layer made of platinum (Pt) is used as an anode or an anode and a cathode. 2. A solid electrode comprising an anode or an ion-exchange membrane-catalyst electrode assembly in which an electrode composed of two layers of a base layer and a coating layer made of platinum (Pt) is used as an anode or an anode and a cathode. Molecular water electrolysis cell. 3. The method according to claim 1, wherein the intermediate layer comprises an iridium-based catalyst,
2. The polymer electrolyte water electrolysis cell according to claim 1, wherein the cell is formed of a catalyst layer containing a ruthenium-based catalyst. 4. An underlayer comprising an iridium catalyst or / and
The polymer electrolyte water electrolysis cell according to claim 2, wherein the cell is formed of a catalyst layer containing a ruthenium-based catalyst and a ruthenium-based catalyst. 5. The method according to claim 1, wherein the intermediate layer is made of iridium (Ir) or / and / or
_2. The solid polymer according to claim 1, wherein the solid polymer is formed of a catalyst layer containing iridium oxide (IrO ₂ , Ir ₂ O ₃ ) or / and ruthenium (Ru) or / and ruthenium oxide (RuO ₂ ). Type water electrolysis cell. 6. An underlayer comprising iridium (Ir) or / and / or
_3. The solid polymer according to claim 2, wherein the solid polymer is formed of a catalyst layer containing iridium oxide (IrO ₂ , Ir ₂ O ₃ ) or / and ruthenium (Ru) or / and ruthenium oxide (RuO ₂ ). 4. Type water electrolysis cell.