JP2902651B2 - Electrode for oxygen electrode exhibiting high equilibrium oxygen electrode potential and method for producing the same - Google Patents

Description

The present invention is suitable for a cathode of a fuel cell such as an oxygen-hydrogen battery, an oxygen electrode for a hydrogen oxidation reaction such as carbon monoxide and nitrogen oxide, and the like. It relates to an oxygen electrode reaction electrode that can be used.

[Prior art] First, the present inventor is the world's first oxygen electrode reaction electrode consisting of a simple metal-oxide mixture that can stably maintain an equilibrium oxygen electrode potential of 1.23 V _vs. RHE for more than one year. A reaction electrode, an IrO ₂ -coated platinum electrode, and an IrO ₂ platinum-coated graphite electrode were developed (see Japanese Patent Application No. 62-249170 {Patent No. 2520266}).

These electrodes are obtained by providing an electrode activator layer made of IrO _{2 on the} surface of an electrode substrate made of platinum or platinum graphite.

Here, an oxygen-hydrogen battery is a device in which a hollow porous electrode made of graphite, platinum, nickel, or the like is inserted into an electrolyte solution as described in Japanese Patent Application No. 62-249170 (Patent No. 2520266). When hydrogen is injected into one electrode (positive electrode) and oxygen is injected into the other electrode (negative electrode), and the two electrodes are connected by a conductor, a current flows by the following reaction. It is widely known from the past.

Positive electrode reaction: H ₂ → 2H ⁺ + 2e (cathode: hydrogen electrode) Negative electrode reaction: O ₂ + 4H ⁺ + 4e → H ₂ O (anode: oxygen electrode) The positive electrode serves as a cathode, and the side into which electrons flow (negative electrode in the above) serves as an anode.

Incidentally, the electromotive force in the oxygen-hydrogen battery is obtained as a hydrogen equilibrium potential. The oxygen equilibrium potential is obtained by subtracting the standard hydrogen electrode potential at the cathode from the equilibrium potential at the anode, and the value theoretically obtained from a thermodynamic viewpoint is 1.23 V _vs. RHE.

However, an anode material that can stably obtain an oxygen equilibrium potential close to the theoretical value has hardly been obtained until now. For example,
With a Pt / PtO ₂ electrode, no equilibrium potential is obtained, the resting potential is the most noble at 1.15 V, i _o 10 ^-9 A / cm ² , and it is stable for only a few days. In the case of a Ru ₂ O ₃ or PbO ₂ carbon electrode, the resting potential ≦ 0.9 V, i _o = 10 ⁻⁶ A / cm ² ,
And it is stable for a few days.

The reason why an oxygen equilibrium potential close to the theoretical value cannot be stably obtained in this way is that dissociative adsorption of oxygen is inhibited on the electrode surface when oxygen is introduced into the electrode at the anode, and complicated reactions occur on the electrode surface. It is considered that the potential changes due to progress.

"Problems to be Solved by the Invention" By the way, in order to put these electrodes into practical use, the former IrO ₂ -coated platinum electrode was unsatisfactory because the platinum plate (foil) was expensive, resulting in a high price.

Further, the latter IrO ₂ platinum-coated graphite electrode has the disadvantages that it is structurally vulnerable and is dispersed by vigorous oxidation. The present invention has been made in view of the above circumstances, showing the world's first 1.23V _vs. RHE selected equilibrium oxygen electrode potential as an oxygen electrode reaction electrode consisting of a simple metal-oxide mixture, the equilibrium oxygen electrode An object of the present invention is to provide an electrode for an oxygen electrode reaction capable of maintaining a potential at room temperature for a long period of at least one month or more, and a method for producing the same.

"Object of the Invention" The present invention has been made in view of the above circumstances, and can stably realize an equilibrium oxygen electrode potential similarly to the excellent oxygen electrode reaction electrode to which the present inventors have previously applied for a patent. Another object of the present invention is to provide an oxygen electrode reaction electrode which is structurally strong, has excellent corrosion resistance, and is inexpensive, and a method for producing the same.

"Means for Solving the Problems" The basic configuration of the electrode for oxygen electrode reaction exhibiting a high equilibrium oxygen electrode potential according to the present invention consists of a platinum layer and iridium oxide on the surface of an electrode substrate made of stainless steel, titanium or nickel. The layer is an oxygen electrode reaction electrode having an active layer laminated in a state of being in contact with each other, characterized in that an equilibrium oxygen electrode potential of 1.23 V _vs. RHE is obtained in the electrolytic solution. .

In the above basic configuration, Ir ⁴⁺ having a strong electron accepting property can be freely expressed in the iridium oxide layer, and the equilibrium oxygen electrode potential of 1.23 V _vs. RHE is maintained at room temperature for one month or more.

Next, in the above configuration, it is preferable that the electrolytic solution is an aqueous solution of H ₃ BO ₃ or an aqueous solution of H ₃ PO ₄ .

Further, the present invention provides an oxygen-hydrogen battery having a configuration in which an oxygen electrode reaction electrode, which is one electrode, and the other electrode are inserted into an electrolyte, and both electrodes are connected by a conductor. On the oxygen electrode reaction electrode, the oxygen electrode reaction electrode side, which is one electrode in the electrolytic solution, O ₂ 4H
^The reaction represented by the formula +++ 4e → H ₂ O may be performed, and the reaction represented by the formula H ₂ → 2H ⁺ + 2e may be performed on the other electrode side in the electrolytic solution.

Further, an oxygen electrode reaction electrode, which is used in an oxygen-hydrogen battery having a configuration in which an oxygen electrode reaction electrode and one electrode, which are one electrode, are inserted into the electrolytic solution, and both electrodes are connected by a conductor. Then, on the oxygen electrode reaction electrode side which is one electrode in the electrolytic solution, a reaction represented by the formula of O ₂ + 4H ⁺ + 4e → H ₂ O is performed, and on the other electrode side in the electrolytic solution, H ₂ → The reaction represented by the formula of 2H ⁺ + 2e is performed, and the elementary reaction on the oxygen electrode reaction electrode side in the electrolytic solution is performed by the electron transfer step represented by the formula of (H ₂ O) ads → (OH) ads + H ⁺ + e. And (OH) ads through Oads, O ₂ ads and O ₂
It may be characterized by having a reaction that occurs as follows.

An oxygen electrode reaction electrode used for an oxygen-hydrogen battery having a configuration in which an oxygen electrode reaction electrode and the other electrode, which are one electrode, are inserted into the electrolyte, and both electrodes are connected by a conductor. On the oxygen electrode reaction electrode side, which is one electrode in the electrolyte, a reaction occupied by the formula O ₂ + 4H ⁺ + 4e → H ₂ O takes place. On the other electrode side in the electrolyte, H ₂ → The reaction represented by the formula 2H ⁺ + 2e is performed, and the elementary reaction on the oxygen electrode reaction electrode side in the electrolytic solution is performed by an electron transfer step represented by the formula (H ₂ O) ads → (OH) ads + H ⁺ + e. , (OH) OADS from ads, it comprises a O ₂ through the ads generated a O ₂ reaction, the (OH) OADS from ads, O ₂ through the ads generated a O ₂ reaction equilibrium is a, the _{(H 2 O) ads → (} OH) ads + H + + e becomes the oxygen conductive by electron transfer step represented by the formula The overall reaction in the reaction electrode side is rate-limiting, it may be understood that the electron transfer stage is activated by the active layer.

The electrode substrate in each of the above structures may be formed in a plate shape or a porous shape.

On the other hand, by depositing a platinum layer on the surface of an electrode substrate made of stainless steel, titanium or nickel, and then depositing an iridium oxide layer, an electrode exhibiting an equilibrium oxygen electrode potential of 1.23 V _vs. RHE in the electrolyte is obtained. Obtainable.

Next, a platinum layer is electrodeposited on the surface of an electrode substrate made of stainless steel, titanium or nickel, and then a slurry containing an iridium element is applied, and then a heat treatment is performed to obtain an equilibrium oxygen electrode potential in the electrolyte of 1.23. V
_vs RHE can be obtained.

As the above-mentioned electrode substrate, a plate-like one or a porous body can be used.

The active layer is a layer in which platinum and iridium oxide are present in contact with each other, and may be a layer in which two layers of a platinum layer and an iridium oxide layer are provided. In the case of a two-layer structure, any layer may be a lower layer.

The electrode substrate is desirably plate-shaped or porous.

As a method for producing this electrode for oxygen electrode reaction, when the electrode substrate is plate-like, a method of depositing platinum on the surface of the electrode substrate and then depositing iridium oxide or depositing the platinum. After that, a method of applying a slurry containing an iridium element and then performing a heat treatment is preferable.

Here, as the slurry containing the iridium element, a slurry containing iridium ions and a slurry containing IrO ₂ are preferable.

The heat treatment performed after the application of the slurry is performed at a temperature at which iridium in the slurry is sufficiently fixed on the electrodeposited substrate on which platinum has been deposited.

In the case of producing an electrode for oxygen electrode reaction comprising a porous electrode substrate, a method of depositing platinum on the surface of the porous electrode substrate and then depositing iridium oxide or a slurry containing an iridium element is used. A method of applying and heat-treating is preferred.

In order to deposit platinum, it is desirable to use a high-frequency furnace and perform it under vacuum.

[Operation] In the oxygen reaction electrode of the present invention, the active layer composed of platinum and iridium oxide is supported by an electrode substrate composed of stainless steel, titanium or nickel. Also, on the surface of the electrode substrate, a platinum layer and an iridium oxide layer are provided.
Since the active layers are stacked in a state where they are in contact with each other, the electron transfer stage on the electrode side in the electrolytic solution is activated, and a noble value of 1.23 V _vs. RHE is obtained as the equilibrium oxygen electrode potential.

"Example" (Example 1) A plate made of stainless steel, a plate made of titanium, and a plate made of nickel were used as electrode substrates, and 50 mg / cm _{2 of} platinum was electrodeposited on these electrode substrates, and then an iridium complex ( Na
₂ was immersed in an aqueous solution of IrO ₄ ) to electrodeposit IrO ₂ .

The electrodes thus obtained were immersed in a 1N aqueous solution of H ₃ BO ₃ and H ₃ PO ₄ at 25 ° C., and the resting potential was measured in an oxygen atmosphere at 1 atm. It was confirmed that an equilibrium oxygen electrode potential of 1.23 V _vs RHE could be realized. This potential is maintained for two months.

In addition, it was confirmed that these electrodes could be prepared only by using a small amount of Pt, and were inexpensive. It was also confirmed that these electrodes were structurally strong and had corrosion resistance enough to withstand long-term use.

Example 2 Platinum was vacuum-deposited on sponge-like stainless steel, sponge-like titanium and sponge-like nickel in a high-frequency furnace. The coating thickness of the platinum was several tens to several hundreds of microns. Next, a slurry containing IrO ₂ was applied to these, followed by heat treatment.

The static potential of these electrodes was measured in the same manner as in Example 1. As a result, 1.23 V _vs. RHE was obtained after 10 to 20 minutes. These behaviors were similar to the oxygen electrode reaction electrode proposed in Japanese Patent Application No. 62-249170.

Also, it was confirmed that these electrodes also had practically sufficient strength and corrosion resistance.

(Example 3) Electrodes having different surface conditions were prepared.

Electrode on which Ir is deposited on a stainless steel plate and then oxidized.

Apply a solution containing Ir ⁴⁺ to a stainless steel plate, and then
Electrode heated at 700 ° C.

Electrode after depositing IrO ₂ on stainless steel plate, depositing Pt, and then anodizing and anodic polarization.

Electrode after depositing Pt on stainless steel plate, depositing IrO ₂ , and then subjecting to negative and positive polarization treatment.

These electrodes were placed on 1.0 NH ₃ BO _{3 at} Po ₂ = 1 atm and T = 25 ° C.
As a result of measuring the resting potential by immersion in an aqueous solution, a stainless steel plate was provided with an active layer composed of Ir4 ^+, which has strong electron-accepting properties, and platinum, which is active in an electron transfer reaction. It was confirmed that it would be a reaction electrode.

(Example 4) An oxygen electrode reaction electrode which differs from the electrode of Example 3 only in that the electrode substrate is made of nickel, and an oxygen electrode reaction electrode which differs only in that the electrode substrate is made of titanium Was manufactured and subjected to the same test.

As a result, it was confirmed that each of the electrodes had the same function and effect as those of the above-mentioned electrodes made of a stainless steel plate.

Further, the electrode composed of the electrode substrate made of titanium initially showed a higher static potential than that made of stainless steel. After that, the resting potential gradually decreased, but after 30 days, the equilibrium oxygen electrode potential was 1.23 V _vs. RHE or more. This is presumably because the oxygen species absorbed by titanium is kept well. From this result, it is considered that an electrode in which the electrode base is made of titanium is suitable for a high electromotive force battery.

Example 5 A plate made of stainless steel and a plate made of titanium were used as electrode bases, and Pt was first electrodeposited on these bases, and then IrO ₂
Was electrodeposited to produce two types of oxygen electrode reaction electrodes.

For these electrodes, the time constant of the elementary reaction was determined semi-quantitatively by the constant current transient method.

As a result, it was found that the electron transfer stage (1) described below was rate-determining and had a time constant τ ₁₀ ≒ 1 sec.

_{(H 2 O) ads → (} OH) ads + contact stage until H ⁺ is + e ...... (1) (OH ) ads generated OADS, as O ₂ through the O ₂ Ads is substantially balanced. However, when the polarization is continued for more than several hours, the activity of the absorbed oxygen species inside the electrode changes, which affects the overvoltage on the electrode surface. That is,
After the polarization, it takes a long time for the potential to return to equilibrium. For electrodes consisting of stainless steel or titanium electrode substrates,
This time is from one day to several days or tens of days.

Next, a stainless steel electrode was connected to Po ₂ = 1atm and T = 25.
It was immersed in a 1.0 NH ₃ BO ₃ aqueous solution at ℃, and the polarization curve was examined. The results are shown in FIG. The slope of the positive polarization region is b = 12
At 0 mV, this indicates that the electron transfer step (1) is a rate-limiting step.

The AC current density i ₀ = 2.3 × 10 ⁻⁷ amp / cm ² is slightly more active than that of the previously proposed IrO ₂ coated platinum electrode,
This is an effect of the surface roughness and seems to be substantially equivalent. The time constant τ ₁₀ estimated from this i ₀ is 1.
2 seconds.

From these results, it can be seen that this oxygen electrode reaction electrode is a highly active electrode equivalent to the IrO ₂ -coated platinum electrode previously proposed in Japanese Patent Application No. 62-249170.

Next, a polarization curve was similarly obtained for the titanium electrode, and when the potential change of the absorbed oxygen species was removed, almost the same result as that of the stainless steel electrode shown in FIG. 1 was obtained. .

"Effects of the Invention" As described above, the electrode of the present invention is an electrode for oxygen electrode reaction having an active layer mutually contacted with a platinum layer and an iridium oxide layer, and as an equilibrium oxygen electrode potential in an electrolytic solution, As an electrode made of a simple metal / oxide mixture, like the electrode to which the present inventors previously applied for a patent,
The world's first 1.23 V _vs. RHE is obtained, and the theoretical value of the equilibrium oxygen electrode potential can be stably realized, and there is an advantage that the amount of platinum used is small and the production can be performed at low cost.

In addition, since the electrode substrate made of stainless steel, titanium or nickel is rich in corrosion resistance and high in strength, the electrode for oxygen electrode reaction of the present invention has excellent corrosion resistance and is structurally strong, and is a practical electrode. Become.

Therefore, according to the oxygen electrode reaction electrode of the present invention, several hundred mV electromotive force is larger than before, and in addition to a practical fuel cell that can obtain about 100 times the current, an oxidation reaction having about 100 times the activity is performed. Electrode and the like can be manufactured.

Further, with the above structure, Ir ⁴⁺ having a strong electron accepting property can be freely expressed in the iridium oxide layer, and the value of 1.23 V _vs. RHE as the equilibrium oxygen electrode potential is easily maintained at room temperature for one month or more. can do.

Next, the electrolytic solution is an H ₃ BO ₃ aqueous solution or H ₃ PO ₄
It is preferably an aqueous solution.

Further, the oxygen-hydrogen battery in which the oxygen electrode reaction electrode having the above structure is configured such that the oxygen electrode reaction electrode and the other electrode, which are one electrode, is inserted into the electrolytic solution, and both electrodes are connected by a conductor. In the case of the oxygen electrode reaction electrode used in the above, the reaction represented by the formula of O ₂ + 4H ⁺ + 4e → H ₂ O is performed on the oxygen electrode reaction electrode side which is one of the electrodes in the electrolytic solution, On the other electrode side, H ₂ → 2H ⁺ + 2e
The reaction represented by the following formula is performed. The elementary reaction on the oxygen electrode reaction electrode side is (H ₂ O) ads → (OH) ads
+ H ⁺ + e, an electron transfer stage represented by the formula: (OH) ads
From OADS, consisting comprises a reaction that occurs in a O ₂ through the O ₂ Ads.

In the elementary reaction, (OH) ads is converted to Oads, Oads,
_The reaction generated as O ₂ through ₂ ads becomes equilibrium, and the entire reaction on the oxygen electrode reaction electrode side is performed by the electron transfer step represented by the formula (H ₂ O) ads → (OH) ads + H ⁺ + e. Since the rate is controlled and this electron transfer step is activated by the active layer, as an electrode made of a simple metal / oxide mixture, the same as the electrode to which the present inventors previously applied for a patent, , The first potential 1.23V _vs. RHE is obtained, and the highest potential theoretically obtained from a thermodynamic point of view, such that the potential is stably maintained for one month or more, is stably obtained for a long period of time.

Further, according to the production method of the present invention, an equilibrium oxygen electrode potential in the electrolytic solution of 1.23 V _vs. RHE is obtained, and an excellent oxygen electrode reaction electrode that can easily maintain the potential for one month or more can be obtained. . Further, by the production method of the present invention, it is possible to obtain an oxygen electrode reaction electrode which is rich in corrosion resistance and structurally strong.

Furthermore, according to the production method of the present invention, the iridium element coated on the substrate is not reduced, so that the oxygen electrode reaction electrode can be produced efficiently.

[Brief description of the drawings]

FIG. 1 is a graph showing a polarization curve measured in Example 5.

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 4/92 H01M 4/92 (72) Inventor Masayuki Kobayashi 1-7 Yukitani Otsukacho, Ota-ku, Tokyo Alps Electric Co., Ltd. (56) References JP-A-59-225740 (JP, A) JP-A-58-171589 (JP, A) JP-A-58-165252 (JP, A) JP-A-62-174394 (JP, A) 154765 (JP, A) JP-A-60-23962 (JP, A)

Claims (10)

(57) [Claims] 1. An oxygen electrode reaction electrode having an active layer in which a platinum layer and an iridium oxide layer are laminated on a surface of an electrode substrate made of stainless steel, titanium or nickel in a state of being in contact with each other, An electrode for oxygen electrode reaction exhibiting a high equilibrium oxygen electrode potential, characterized in that an equilibrium oxygen electrode potential of 1.23 V _vs. RHE is obtained in an electrolytic solution. 2. The method according to claim 1, wherein Ir ⁴⁺ having a strong electron accepting property can be freely expressed in the iridium oxide layer, and the equilibrium oxygen electrode potential of 1.23 V _vs. RHE is maintained at room temperature for one month or more. The oxygen electrode reaction electrode exhibiting a high equilibrium oxygen electrode potential according to claim 1. 3. The method according to claim 1, wherein the electrolytic solution is an aqueous solution of H ₃ BO ₃ ,
_The electrode for oxygen electrode reaction exhibiting a high equilibrium oxygen electrode potential according to claim 1 or 2, wherein the electrode is a ₃ PO ₄ aqueous solution. 4. An oxygen electrode reaction device for use in an oxygen-hydrogen battery in which one electrode, an oxygen electrode reaction electrode, and the other electrode are inserted into an electrolyte and both electrodes are connected by a conductor. an electrode, in the oxygen electrode reaction electrode side, which is one of the electrodes in the electrolytic solution, the reaction represented by ^{_{O 2 4H + + 4e → H}} 2 O becomes expression is made, at the other electrode side of the electrolytic solution, The oxygen electrode reaction electrode exhibiting a high equilibrium oxygen electrode potential according to claim 1 or 2, wherein a reaction represented by a formula of H ₂ → 2H ⁺ + 2e is performed. 5. An oxygen electrode reaction device for use in an oxygen-hydrogen battery in which one electrode, an oxygen electrode reaction electrode, and the other electrode are inserted into an electrolyte and both electrodes are connected by a conductor. On the oxygen electrode reaction electrode side, which is one electrode in the electrolytic solution, a reaction represented by the formula O ₂ + 4H ⁺ + 4e → H ₂ O is performed, and on the other electrode side in the electrolytic solution, The reaction represented by the formula of H ₂ → 2H ⁺ + 2e is performed, and the elementary reaction on the oxygen electrode reaction electrode side in the electrolytic solution is represented by the following formula: (H ₂ O) ads → (OH) ads + H ⁺ + e Movement phase and (OH) ads to Oad
The oxygen electrode reaction electrode exhibiting a high equilibrium oxygen electrode potential according to claim 1 or 2, characterized by comprising a reaction generated as O ₂ through s and O ₂ ads. 6. An oxygen electrode reaction electrode for use in an oxygen-hydrogen battery in which one electrode, an oxygen electrode reaction electrode, and the other electrode are inserted into an electrolytic solution and both electrodes are connected by a conductor. On the oxygen electrode reaction electrode side, which is one electrode in the electrolyte solution, a reaction represented by the formula O ₂ + 4H ⁺ + 4e → H ₂ O is performed, and on the other electrode side in the electrolyte solution, The reaction represented by the formula H ₂ → 2H ⁺ + 2e is performed, and the elementary reaction on the oxygen electrode reaction electrode side in the electrolytic solution is represented by the following formula: (H ₂ O) ads → (OH) ads + H ⁺ + e Movement phase and (OH) ads to Oad
s, O ₂ through the ads will comprises a reaction that occurs in a O _2, wherein (OH) OADS from ads, O ₂ through the ads generated a O ₂ reaction is an equilibrium, the (H ₂ O) ads → (OH) ads + H ⁺ + e The electron transfer step represented by the formula determines the overall reaction on the oxygen electrode reaction electrode side, and determines that this electron transfer step is activated by the active layer. The oxygen electrode according to claim 1, wherein the electrode has a high equilibrium oxygen electrode potential. 7. The electrode for oxygen electrode reaction exhibiting a high equilibrium oxygen electrode potential according to claim 1, wherein the electrode substrate is formed in a plate shape or a porous shape. 8. An electrode substrate made of stainless steel, titanium or nickel, on which a platinum layer is electrodeposited and then an iridium oxide layer is electrodeposited to obtain an equilibrium oxygen electrode potential of 1.23 V _vs. RHE in the electrolytic solution. A method for producing an electrode for an oxygen electrode exhibiting a high equilibrium oxygen electrode potential, characterized by obtaining an electrode to be used. 9. An equilibrium oxygen electrode potential in an electrolytic solution by depositing a platinum layer on the surface of an electrode substrate made of stainless steel, titanium or nickel, applying a slurry containing an iridium element, and then subjecting the slurry to heat treatment. As 1.
A method for producing an electrode for oxygen electrode reaction exhibiting a high equilibrium oxygen electrode potential, characterized by obtaining an electrode capable of obtaining 23V _vs. RHE. 10. The electrode for oxygen electrode reaction exhibiting a high equilibrium oxygen electrode potential according to claim 8, wherein the electrode base is made of a plate or a porous body. Manufacturing method.