JPH10102273A - Water electrolytic cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water electrolytic cell for producing high-purity hydrogen and oxygen in the water electrolysis using a solid high molecular electrolyte. SOLUTION: The water electrolytic cell 10 is provided with a solid high molecular electrolyte 1 consisting of a fluororesin cation-exchange membrane, the catalytic electrodes (anode 3 and cathode 2) set on both sides of the electrolyte and the feeders 5 and 4 furnished respectively on the catalytic electrodes and prepared by plating the surface of a metallic sintered compact with platinum. Both sides of the electrolyte 1 are plated with a platinum-group metal 43 at >=0.05mg/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a water electrolysis cell. More specifically, the present invention relates to a water electrolysis cell capable of producing high-purity oxygen and hydrogen.

[0002]

2. Description of the Related Art In recent years, attention has been paid to a highly efficient water electrolysis method using a solid polymer electrolyte membrane. Hereinafter, the principle and structure of a typical water electrolysis cell using a solid polymer electrolyte membrane will be described with reference to the drawings. FIG. 2 shows a schematic sectional view thereof.
As shown in FIG. 2, the structure of the water electrolysis cell 10 is such that feeders 4 and 5 (expanded metal) and current-carrying plates 6 and 6 are provided on both sides of the solid polymer electrolyte membrane 1 to which the catalyst electrodes 2 and 3 are joined. And a cathode compartment 11 and an anode compartment 12 separated by the solid polymer electrolyte membrane 1. The mechanism of water electrolysis by the water electrolysis cell 10 is that water is supplied to the cathode chamber 11 and the anode chamber 12 and a direct current is applied between the electrodes 2 and 3 so that oxygen is generated in the anode chamber 12 and generated simultaneously. The hydrogen ions move through the solid polymer electrolyte membrane 1, obtain electrons in the cathode chamber 11, and become hydrogen gas. Conventionally, (1) electroless plating and (2) hot pressing have been known as methods for bonding a catalyst electrode to such a solid polymer electrolyte membrane.

However, each of these methods has the following problems. (1) Electroless plating method This method is a wet processing method in which a catalyst electrode is formed by reducing and depositing a catalyst electrode on the surface of a solid polymer electrolyte membrane. The contact resistance between the membrane and the catalyst electrode is small, and the bonding strength is large. (For example, Japanese Patent Publication No. 58-47471). However, because of the plating method, only a metal can be bonded, and thus an oxide or the like cannot be directly used as an electrode. Further, if the film is not sufficiently stretched, plating cannot be performed uniformly, and there is a problem that it is difficult to increase the size. (2) Hot pressing method This method is a dry processing method in which an electrode film containing a catalyst is prepared in advance and this is thermocompression-bonded to the surface of a solid polymer electrolyte membrane to form a bonded body (for example, Kosho 58
No. 15544). For this reason, any of metal and oxide can be used as the catalyst species, but the thickness of the electrode is increased, the contact resistance is large, and the bonding strength is low. Also, with this method, it was difficult to produce a film in which the catalyst was uniformly dispersed in the electrode.

[0004] In order to solve these problems, the present inventors have proposed a water electrolysis cell having a novel structure (Japanese Patent Application No. Hei 8-8).
No. 12714). The first feature is that the power supply bodies 4 and 5 are each made of a metal (for example, titanium) powder sintered body whose surface is plated with platinum. The second feature is that, for example, a mixture of iridium oxide or ruthenium oxide and a polymer electrolyte is coated on the sintered body to form the anode 3, for example, a mixture of platinum black and a polymer electrolyte. The purpose of the present invention is to form the cathode 2 by applying it on the body. With such a structure, a water electrolysis cell which is easier to manufacture than the conventional method and has a low cell voltage is realized.

[0005]

However, the above-mentioned water electrolysis cell contains several tens ppm of oxygen in the generated hydrogen,
The generated oxygen contains 1-2% hydrogen as an impurity.
Oxygen, which is an impurity in hydrogen, becomes a solid, for example, when liquefying hydrogen, and may cause serious damage to the liquefaction apparatus. . Further, it is extremely dangerous to generate oxygen containing 1 to 2% of hydrogen which is close to the explosion limit (4% or more), and it is important to reduce the concentration of hydrogen in oxygen.

As a method for reducing impurities in hydrogen and oxygen generated by water electrolysis, for example, a surface resistance value of 10 to 1000 Ω / c is applied to the anode side surface of the solid polymer electrolyte membrane.
It is disclosed that an m-th platinum group metal layer is provided (JP-A-3-107488). In this method, the platinum plating amount is required to be 0.4 mg / cm ² or more, and the plating time is extremely long. Further, the purity is not always satisfactory, that is, 99.98% of oxygen and 99.89% of hydrogen.

The present invention has been made in view of the above-mentioned problems, and has been made to improve a water electrolysis cell. In a water electrolysis method using a solid polymer electrolyte, a water electrolysis method for producing high-purity hydrogen and oxygen gas is provided. The purpose is to provide a cell.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies on a method for producing high-purity hydrogen and oxygen. It has been found that high-purity hydrogen and oxygen can be produced in water electrolysis by using a polymer electrolyte membrane. That is, according to the present invention, a solid polymer electrolyte comprising a fluororesin-based cation exchange membrane, catalyst electrodes (anode and cathode) provided on both surfaces thereof, and metal sintering provided on the catalyst electrodes respectively A water electrolysis cell comprising a power feeding body having a body surface plated with platinum and comprising a solid polymer electrolyte plated with a platinum group metal on the surface.

In a preferred embodiment, there is provided a water electrolysis cell characterized in that the plating amount of the platinum group metal is 0.05 mg / cm ² or more.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the water electrolysis cell of the present invention will be specifically described below with reference to the drawings. FIG.
1 is a schematic sectional view schematically showing a water electrolysis cell of the present invention. As shown in FIG. 1, the water electrolysis cell of the present invention comprises a solid polymer electrolyte 1 comprising a fluororesin-based cation exchange membrane,
Catalyst electrodes (anode and cathode) provided on both sides
2 and power feeders 5 and 4 provided with platinum plating on the surface of a metal sintered body provided on each of the catalyst electrodes thereof. This is based on the finding that high-purity hydrogen and oxygen can be obtained by plating a platinum group metal 43 of at least 05 mg / cm ² (a plating amount on one side, the same applies hereinafter).
Although the reason is not necessarily clear, hydrogen diffused in the film from the cathode 2 side and oxygen diffused from the anode 3 side are burned and consumed by the catalyst metals 2 and 3 on the counter electrode side film surface, respectively. It is considered that the amount mixed as impurity gas is reduced. Hereinafter, each component will be described.

1. Solid Polymer Electrolyte Membrane Examples of the solid polymer electrolyte membrane 1 used in the present invention include a fluorinated resin-based cation exchange membrane having a sulfone group, a carboxyl group or a phosphone group.
Specifically, NAFION (registered trademark, the same applies hereinafter) 11
2, 115, 117, 450 (manufactured by DuPont) or the like can be preferably used.

2. Platinum Group Metal Plating Examples of the platinum group metal plated on both surfaces of the solid polymer electrolyte 1 include metals having high hydrogen-oxygen combustion catalytic ability, such as platinum, palladium, and rhodium. Of these, platinum or palladium is preferred. The method for plating these platinum group metals on the solid polymer electrolyte membrane is not particularly limited, but a known electroless plating method can be used. For example, after the solid polymer electrolyte membrane is impregnated with metal ions in a platinum group metal ion-containing aqueous solution (adsorption bath), the solid polymer electrolyte membrane may be immersed in a reducing agent-containing solution (reduction bath). More specifically, the platinum group metal ion-containing aqueous solution is obtained by adding ammonia water to ammineplatinic nitrite and boiling to form an ammine complex platinum, and it is desirable that excess ammonia is sufficiently volatilized. The concentration of ammine platinate nitrite is 0.2-2 g / 1,
Preferably it is 0.25 to 1 g / 1. If it is less than 0.2 g / 1, the concentration is so low that a sufficient amount of adsorption cannot be obtained, and
If it exceeds 1, it becomes difficult to control the amount of adsorption, and the cost increases because of expensive chemicals. The reducing bath is an aqueous solution of sodium borohydride, and the concentration is 0.01 to 0.1% by weight, preferably 0.03 to 0.06% by weight. 0.
If the content is less than 01% by weight, reduction takes time, and
Exceeding the cost increases. Preferred immersion conditions in the adsorption bath are as follows: temperature is 30 to 80 ° C., time is 30 minutes to 2 hours,
Preferred immersion conditions in the reducing bath are as follows:
The time is 30 minutes to 1 hour. In the present invention, under these conditions, a platinum group metal of 0.05 mg / cm ² or more, preferably 0.05 to 0.
3 mg / cm ² , particularly preferably 0.05 to 0.2 mg
/ Cm ² plating. Plating amount is 0.05mg / cm ²
If the amount is less than the above, the combustion reaction does not proceed sufficiently and the purity of the gas is deteriorated.If the amount of plating is large, the amount of platinum that is required to burn the impurities is plated, and an extra cost is required. Becomes 3. As shown in FIG. 1, a platinum plating 42 is provided on the surface of a sintered body 41 of a metal powder (for example, titanium, tantalum, zirconium, niobium, nickel, stainless steel, etc.). A porous power feeder having a gas-liquid flow path structure can be manufactured by a sintering method by using a material that has been subjected to a sintering process or a product obtained by sintering a product obtained by applying a platinum plating to the surface of the powder. Hei 8-12714).

After a porous feeder having a gas-liquid flow path structure is manufactured by a sintering method, a catalyst electrode is supported. Platinum (Pt) is plated as a preceding step. The reason for this is
In order to reduce the contact resistance related to the cell voltage at the time of energization, especially on the anode side, Ti or the like undergoes anodization and the insulating T
This is to prevent the formation of an oxide film such as i. T
When an oxide film such as i is formed, the cell voltage increases.

The method of plating Pt on a sintered body of Ti or the like is the same as the method of plating a platinum group metal on a solid polymer electrolyte. In the present invention, a metal (for example, titanium, tantalum, zirconium, niobium, nickel, stainless steel, etc.) whose surface is subjected to platinum plating as described above may be subjected to sintering as described above.

4. Catalyst electrode As the physical properties required for the catalyst electrode used in the present invention,
(1) good conductor of electricity, (2) acid resistance, (3) oxidation resistance,
Although there are (4) reduction resistance and (5) heat resistance, a metal or oxide having a small oxygen overvoltage on the anode side and a small hydrogen overvoltage on the cathode side is used to reduce the cell voltage which greatly affects the cost of water electrolysis. Must be used. Metals with a small oxygen-hydrogen overvoltage are generally of the platinum group. As the metal of the catalyst electrode 3 on the anode side used in the present invention, iridium or ruthenium having a low oxygen overvoltage or ruthenium and oxides thereof, or a mixture containing them is preferable. As the metal of the catalyst electrode 2 on the cathode side, a hydrogen overvoltage Is preferred. The catalyst electrode can be formed on the metal sintered body by various known methods. For example, a thermal decomposition method, an electrolytic plating method, an electroless plating method, a coating method, and the like can be used. Is the most convenient.

(1) Anode In the embodiment of the present invention, as shown in FIG. 1, a mixture of iridium oxide or ruthenium oxide and a polymer electrolyte is used as the anode 3. In the present invention, as a method of providing iridium oxide or ruthenium oxide on the porous power feeder, in the present invention, a liquid polymer electrolyte having the same composition as a solid polymer electrolyte membrane (for example, NAFION 117 or the like) used in water electrolysis. (NAFION emulsion: manufactured by Aldrich Chemical Company) and a powdery catalyst (I
rO ₂ or RuO ₂ ) to form a paste, and then apply it to the surface of the power supply with a brush or the like, or spray it using a spray method, and then dry it to form an electrode. IrO ₂ or RuO ₂ used preferably has a particle size of 0.5 to 100 μm, particularly preferably 0.5 to 1 μm in consideration of the specific surface area, catalytic activity and the like.
As the state of the paste, the concentration of the catalyst metal is 5 to 70.
% By weight, preferably 10 to 50% by weight. 5% by weight
If it is less than 70%, the catalyst metal cannot be provided because it permeates into the sintered body, and if it exceeds 70% by weight, it does not become a paste. An arbitrary set amount (support amount) can be obtained by changing the amount of the catalyst metal. A preferable loading amount is 0.5 mg / cm ^{2 to} 10 mg / cm
² , more preferably 1.5 to 4 mg / cm ² .
If it is less than 0.5 mg / cm ² , the performance as an electrode will be poor, and if it exceeds 10 mg / cm ² , the cost will be high. When applied with a brush and then dried, the organic solvent coexisting with the liquid polymer electrolyte is removed, and the catalyst metal is provided on the surface of the porous power feeder in a state like a film in which the catalyst metal and the polymer electrolyte are mixed. Further, the surface is overcoated with the same liquid polymer electrolyte as above to form a polymer electrolyte layer. The coating amount is 0.01 μm
To 100 μm, preferably 0.5 μm to 10 μm. If it is less than 0.01 μm, it is somewhat difficult to suppress peeling of the film, and if it exceeds 100 μm, the film is strong but the cell voltage becomes high. The film is dried at a drying temperature of 8
About 30 to 60 minutes at 0 to 150 ° C. is sufficient.

(2) Cathode In the embodiment of the present invention, a mixture of platinum black and the above-mentioned polymer electrolyte is used as the cathode 2 as shown in FIG. The platinum black used has a particle size of 0.1 to 10
μm, especially 0.5 to 1 μm, is preferable in consideration of the specific surface area, catalytic activity and the like. The method for manufacturing the electrode is the same as described above. The amount of Pt black supported is 0.5 to 10
mg / cm ^2, and preferably 2~3mg / cm ^2.
If it is less than 0.5 mg / cm ² , the performance as an electrode will be poor, and if it exceeds 10 mg / cm ² , the cost will be high.

[0018]

EXAMPLES The present invention will be described more specifically with reference to the following examples.

Example 1 Platinum was plated on both surfaces of a commercially available cation exchange membrane (trade name: Nafion 117, manufactured by DuPont) by an adsorption-reduction method. In the adsorption bath, 1.65 g of ammine platinum nitrite (Pt amount 1 g /
Liter) and 1 cc of aqueous ammonia (29% by weight), and the mixture was boiled for about 30 minutes until the smell of ammonia disappeared.
The bath temperature was adjusted to 50 ° C., and the ion exchange membrane was immersed in this for about 90 minutes to adsorb Pt in the form of ammine complex ions. Next, the ion-exchange membrane was immersed in a 0.05% by weight aqueous solution of sodium borohydride (reduction bath) at 40 ° C., and the adsorbed Pt ions were reduced and precipitated. The platinum plating amount thus obtained was about 0.27 mg / cm ² , and the surface resistance was about 5 × 10 ⁶ Ω / □. The amount of platinum plating was measured by re-dissolving the platinum plated on the film in aqua regia and its weight. The surface resistance was measured by drying the film at 150 ° C. for 1 hour, leaving it in a constant temperature and humidity room at 23 ° C. and 30% for 3 days, adjusting the humidity, and then measuring in accordance with JIS K6911. IrO ₂ powder (manufactured by Tokuriki Honten) and Nafion dispersion liquid (Aldrich) were applied to a substrate obtained by plating platinum on a titanium sintered body (particle size: 150 μm, sintering temperature: 850 ° C., 2 hours, dimensions: 78 × 78 × 4 mm). An anode, a paste obtained by mixing Pt black powder (manufactured by Tokuriki Honten) and Nafion dispersion liquid (manufactured by Aldrich Chemical Co.) was applied to the anode, which was then dried at 150 ° C. for 30 minutes. The resultant was dried for 30 minutes as a cathode, and water electrolysis was carried out using the above ion exchange membrane in a cell having the structure shown in FIG. Current density 1-3 A / cm ² , 8
At 0 ° C., the amount of generated gas, purity, and cell voltage were measured. Table 1 shows the results.

[Table 1] ──────────────────────────────────── Sample No. Current density Bath voltage Hydrogen purity Oxygen purity Current efficiency [%] (A / cm ² ) [V] [%] [%] Hydrogen oxygen ──────────────────────── ──────────── Pt117-1 1 1.78 100.000 100.000 98.6 98.9 2 2.05 100.000 100.000 98.9 99.1 3 2.21 100.000 100.000 99.0 99.1 ───────────────── ───────────────────

Comparative Example The procedure of Example 1 was repeated except that the cation exchange membrane (Nafion 117) was not plated with platinum. Table 2 shows the results.

[Table 2] ──────────────────────────────────── Sample No. Current density Bath voltage Hydrogen purity Oxygen purity Current efficiency [%] (A / cm ² ) [V] [%] [%] Hydrogen oxygen ────────────────────────な し No Pt 1 1.88 99.998 98.610 97.8 98.6 2 2.12 99.997 98.980 98.4 99.3 3 2.29 99.996 99.060 98.4 99.2 ────────────────── ──────────────────

[Embodiment 2] In Embodiment 1, Embodiment 1
Example 1 except that a cation exchange membrane (Nafion 117) immersed for about 60 minutes was used in the adsorption bath used in Step 1.
Same as. Table 3 shows the results.

[0024]

[Table 3] ──────────────────────────────────── Sample No. Current density Bath voltage Hydrogen purity Oxygen Purity Current efficiency [%] (A / cm ² ) [V] [%] [%] Hydrogen Oxygen ─────────────────────────── ───────── Pt117-2 1 1.88 100.000 99.990 98.2 98.4 2 2.11 100.000 99.995 98.5 98.9 3 2.26 100.000 99.997 98.6 99.2 ──────────────────── ────────────────

Example 3 In Example 1, the amount of ammine platinum nitrite in the adsorption bath was 0.41 g (corresponding to a Pt amount of 0.25 g / l), and the amount of ammonia water (29%) was 0.1%.
The procedure was the same as that of Example 1 except that the cation exchange membrane (Nafion 117) was changed to 25 cc and immersed in the adsorption bath at 50 ° C. for 60 minutes. Table 4 shows the results.
Shown in The plating amount of platinum thus obtained was about 0.05 mg / cm ² , and the surface resistance was about 5 × 10
It was ⁶ Ω / □.

[Table 4] ──────────────────────────────────── Sample No. Current density Bath voltage Hydrogen purity Oxygen purity Current efficiency [%] (A / cm ² ) [V] [%] [%] Hydrogen oxygen ──────────────────────── ──────────── Pt117-2 1 1.75 100.000 99.962 98.5 98.8 2 2.17 100.000 99.970 98.6 99.1 3 2.27 100.000 99.979 98.7 − ───────────────── ───────────────────

Table 5 summarizes the relationship between the Pt plating conditions, the amount of Pt plating and the value of the surface resistance in the examples.

[Table 5] ──────────────────────────────────── Pt adsorption conditions Pt plating amount Surface Resistance Pt concentration (g / l) Temperature (° C) Time (min) (mg / cm ² ) (Ω / □) ─────────────────────── ───────────── Comparative example − − − − 1 × 10 ⁴ ─────────────────────────── ───────── Example 1 1.00 50 90 0.05 5 × 10 ⁶ Example 2 1.00 50 60 − − Example 3 0.25 50 60 0.27 5 × 10 ⁶ ───────────よ り From the above results, by using a solid polymer electrolyte membrane with a very small amount of platinum group metal plating, It is understood that impurities in hydrogen can be reduced to 0 and impurities in oxygen can be reduced to several hundred ppm or less.

[0029]

As described above, according to the present invention,
It is possible to provide a water electrolysis cell for producing hydrogen and oxygen, which has a low impurity concentration in a generated gas and has little risk of hydrogen explosion or a problem in secondary treatment.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view schematically showing a water electrolysis cell of the present invention.

FIG. 2 is a schematic sectional view schematically showing a conventional water electrolysis cell.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 solid polymer electrolyte membrane 2 catalyst electrode (cathode) 3 catalyst electrode (anode) 4 power supply (cathode side) 5 power supply (anode side) 6 and 7 conductive plate 10 water electrolysis cell 11 cathode chamber 12 anode chamber 41 metal powder Sintered body 42 Platinum plating 43 Platinum group metal plating

Claims (2)

[Claims] 1. A solid polymer electrolyte comprising a fluorinated resin-based cation exchange membrane, catalyst electrodes (anode and cathode) provided on both surfaces thereof, and a surface of a metal sintered body provided on each of the catalyst electrodes. A water electrolysis cell comprising a power supply body plated with platinum and a platinum group metal on both surfaces of a solid polymer electrolyte. 2. The plating amount of the platinum group metal is 0.0
^2. The water electrolysis cell according to claim 1, wherein the concentration is 5 mg / cm ² or more.