JPS6344832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for electrolyzing water, particularly with a low oxygen overvoltage.
This invention relates to a water electrolysis method using a highly durable anode.

Reflecting the recent energy situation, hydrogen is attracting attention from many quarters as a new energy source to replace oil. Industrial hydrogen production methods can be roughly divided into water electrolysis methods and coke or petroleum gasification methods. Although the former method uses readily available water as a raw material, it requires a large number of electrolytic equipment, is insufficiently adaptable to excess or insufficient current, and suffers from deterioration due to carbonation of the electrolyte and floor space.
Many issues remain, including equipment costs. On the other hand,
The latter method is generally complicated to operate, requires fairly large equipment, and has problems such as considerable equipment costs.

As a means to solve the above problems, a method has recently been proposed in which water is electrolyzed in an electrolytic cell using a cation exchange membrane to produce hydrogen.

It is well known that so-called ion exchange membrane electrolysis is applied to salt electrolysis, but an aqueous alkaline solution such as caustic potash is supplied to an anode chamber separated by a cation exchange membrane, and water or dilute alkali is supplied to a cathode chamber. Water electrolysis, in which electrolysis is carried out by supplying an aqueous solution, requires anode chamber conditions that are significantly different from salt electrolysis, and nickel is considered to be a practical anode, especially under such alkaline conditions.

On the other hand, anodes made mainly of noble metals such as platinum, palladium, and ruthenium, their alloys, or oxides of these conventionally used for salt electrolysis are not only expensive, but also have the following problems: Therefore, it cannot be used practically as an anode for water electrolysis.

That is, since ruthenium and palladium gradually dissolve in alkali, their durability is poor.

The present inventors have made extensive studies to solve the above-mentioned problems, and as a result, they have provided a new method that can electrolyze water at low voltage. A method for electrolyzing water in an electrolytic cell comprising an anode and a cathode, the anode containing particles containing a metal selected from nickel, cobalt, and silver, a part of which is exposed on the surface. The gist of the present invention is a water electrolysis method characterized in that the anode is provided with a layer made of at least one metal selected from nickel, cobalt, and silver on an electrode core.

The cathode used in the present invention is not particularly limited, and cathodes used in conventional salt electrolysis, such as cathodes etched with iron, stainless steel, etc., can be used. Of course, it is also possible to use the anode used in the present invention as a cathode.

As the cation exchange membrane, known fluorine-containing cation exchange membranes can be used, and among them, perfluorinated carbon membranes having carboxylic acid groups as ion exchange groups (for example, JP-A-51-140899, (disclosed in Kaisho 52-48598) is durable,
Particularly preferred from the viewpoint of low electrolysis voltage.

Next, the anode used in the present invention will be explained. The anode used in the present invention contains particles containing a metal selected from nickel, cobalt, and silver.
It is necessary that a layer consisting of at least one metal selected from nickel, cobalt, and silver is provided on the electrode core so that some parts are exposed on the surface, and the electrode surface contains a large number of particles. is attached, and when viewed macroscopically, the electrode surface becomes microporous.

Thus, the anode has many particles containing nickel, cobalt, and silver on the electrode surface, and as mentioned above, the electrode surface is microporous.
The active surface of the electrode becomes larger accordingly, and the synergistic effect of these makes it possible to effectively reduce the oxygen overvoltage. Furthermore, since the particles are firmly attached to the electrode surface by the layer made of the above-mentioned metal, they are difficult to deteriorate, and the sustainability of the above-mentioned low oxygen overvoltage can be dramatically extended.

Furthermore, the above-mentioned effects also improve the initial performance of the electrode.

The material of the electrode core may be any suitable conductive metal such as Ti, Zr, Fe, Ni, V, Mo,
A metal selected from Ou, Ag, Mn, platinum group metals, graphite, Cr, or an alloy selected from these metals can be used. Of these, Fe, Fe alloy (Fe-Ni alloy,
It is preferable to use Ni, Ni alloy (Ni-Cu alloy, Ni-Cr alloy, etc.) Cu, Cu alloy, etc. (Fe-Cr alloy, Fe-Ni-Cr alloy, etc.).

Particularly preferable materials for the electrode core are Fe, Cu, Ni,
These are Fe-Ni alloy and Fe-Ni-Cr alloy.

The structure of the electrode core can be made into any suitable shape and size depending on the structure of the electrode used. The shape can be, for example, plate-like, porous, net-like (for example, expanded metal), or blind-like.
These may be shaped like a flat plate, a curved plate, or a cylinder.

Particles containing metals selected from nickel, cobalt, and silver as anode active particles include such metals alone, particles of metals or alloys mainly composed of such metals, or surface layers of these metals or alloys. Particles consisting of a composite having the following properties are employed.

In addition, when using metals or alloys mainly composed of the above metals, metals other than the above metals can be used, depending on their content, but metals that do not have an excessively negative effect on the reduction of oxygen overvoltage can be used, such as Al, Zn,
Mg, Sn, Si, Sb, etc. can be used. The average particle size of the particles is related to the porosity of the electrode surface and the dispersibility of the particles during electrode manufacturing, which will be described later, but is between 0.1μ and 100μ.
If so, it is sufficient.

Among the above ranges, from the viewpoint of the porosity of the electrode surface, it is preferably 0.9 μ to 50 μ, more preferably 1 μ to 30 μ.

Preferably, the particles are superficially porous to achieve a lower oxygen overpotential of the electrode.

This surface porosity does not mean only that the entire surface of the particle is porous; it is sufficient that only the portion exposed from the layer made of the metal mentioned above is porous.

The degree of porosity is preferably as large as possible; however, if the degree of porosity is excessively high, the mechanical strength of the particles decreases, so it is preferable that the porosity is 20 to 90%. More preferably within the above range
35-85%, particularly preferably 50-80%.

The above porosity is a value measured by a known water displacement method or the like.

Various methods can be used to make the material porous. For example, there is a method to make it porous by removing metals other than Ni, Co, and Ag from an alloy mainly composed of Ni, Co, and Ag. Other methods include converting Ni, Co, and Ag into carbonyl compounds and thermally decomposing them to obtain porous metals; thermally decomposing organic acid salts of Ni, Co, and Ag;
Porous metals can be obtained by heating oxides of Ni, Co, and Ag in a hydrogen-reducing atmosphere to obtain porous metals. Of these, in terms of workability, Ni,
From alloys mainly composed of Co and Ag, such Ni, Co,
A method that removes metals other than Ag is preferred. In such cases, an alloy of a first metal selected from Ni, Co, and Ag and a second metal selected from Al, Zn, Mg, Sn, Si, and Sb is used as the particle material, and the caustic Particularly preferred is a method in which at least a portion of the second metal is removed by alkali treatment. Such alloys include Ni-Al alloy, Ni-Zn alloy, Ni-
Mg alloy, Ni-Sn alloy, Ni-Si alloy, Co-Al alloy, Co-Zr alloy, Co-Mg alloy, Co-Si alloy,
Co-Sn alloy, Ag-Al alloy, Ag-Zn alloy, Ag-
Mg alloy, Ag-Sn alloy, Ag-Si alloy can be used.
Among these, Ni-Al alloy, Co
-Al alloy and Ag-Al alloy are preferred. Such preferred alloys include specifically undeveloped Raney Nickel, Raney Cobalt, and Raney Cobalt.
cobalt) and Raney Silver. Among these, Ni--Al alloy, specifically undeveloped Raney nickel, is particularly preferred.

In the present invention, the metal used in the layer for attaching particles may be a metal that has alkali resistance and can firmly attach the particles, but in particular, metals selected from Ni, Co, and Ag may be used. It is preferable to use at least one type of metal. In particular, it is preferable to use the same type of metal as the main metal of the particles.

The thickness of the layer of the present invention depends on the particle size of the particles employed, but it is sufficient if it is 20 to 200 microns, and more preferably 25 to 150 microns. This is because, in the present invention, some of the particles described above are attached to the electrode core while being buried in the metal layer. In order to facilitate understanding of such a state, a cross-sectional view of the electrode surface of the present invention is shown in FIG. As shown in the figure, a layer 2 made of metal is provided on an electrode core 1, and part of particles 3 are contained in this layer so as to be exposed from the surface of the layer. The ratio of particles in layer 2 is 5~
Preferably it is 80wt%, more preferably
It is 10-50wt%. In addition to such a state, Ni, Co, Ag, Cu, etc. may be present between the electrode core and the layer containing particles.
By providing an intermediate layer made of a metal selected from the following, the durability of the electrode can be further improved. Such an intermediate layer may be of the same type or a different type from the metal of the above-mentioned layer, but from the viewpoint of adhesion between the intermediate layer and the above-mentioned layer, it is preferable that these intermediate layers and the metals of the layer are of the same type. Preferably. The thickness of the intermediate layer is from 5 to 5 from the viewpoint of mechanical strength etc.
100μ is sufficient, more preferably 20~
80μ, particularly preferably 30-50μ.

To facilitate understanding of the electrode provided with such an intermediate layer, a cross-sectional view of the electrode is shown in FIG.

1 is an electrode core, 4 is an intermediate layer, 2 is a layer containing particles, and 3 is particles.

As is clear from Figures 1 and 2, when looking at the electrode surface microscopically, many particles are exposed on the electrode surface, but when looking macroscopically, the surface layer is It has become porous.

As mentioned above, the degree of porosity is also related to the reduction in oxygen overpotential, so that the purpose can be sufficiently achieved if the degree of porosity is 1000 μF/cm ² or more in electric double layer capacity. Within the above range, preferably 2000 μF/cm ² or more,
Particularly preferably, it is 5000 μF/cm ² or more. Electric double layer capacity is the capacitance of an electric double layer formed when positive and negative ions are relatively distributed over a short distance near the electrode surface when the electrode is immersed in an electrolyte solution. indicates the actually measured differential capacity.

This capacitance increases as the electrode surface becomes larger. Therefore, when the electrode surface becomes porous and the electrode surface area increases, the electric double layer capacity of the electrode surface also increases. Therefore, due to the electric double layer capacity,
The electrochemically effective electrode surface area, that is, the degree of porosity of the electrode surface can be determined.

Note that the electric double layer capacity varies depending on the temperature at the time of measurement, the type and concentration of the electrolyte solution, the electrode potential, etc. Therefore, the electric double layer capacity of the present invention is the value measured by the following method. means.

Test piece (electrode) in 35wt% NaOH aqueous solution (25℃)
A platinum plate with black platinum, which has an apparent area approximately 100 times that of the test piece, is inserted as a counter electrode, and the cell impedance in this state is measured using a Kohlrausch Pritzge to determine the electric double layer capacity of the test piece. seek.

Various methods can be employed as specific means for attaching the electrode surface area, such as a dispersion plating method, a melt spraying method, a sintering method, etc., and a dispersion plating method is particularly preferred.

The dispersion plating method is an aqueous solution containing the metal that forms the metal layer, in which particles mainly made of nickel, for example, are dispersed in a bath, and an electrode core is used as a cathode.
Plating is performed to eutectoid the metal and particles on the electrode core.

For example, when a nickel layer is used as the metal layer, plating baths include all-nickel chloride bath, high nickel chloride bath, nickel chloride-nickel acetate bath, high nickel sulfate bath, black nickel bath, nickel sulfate bath, hard nickel bath, A nickel borofluoride bath, a nickel phosphate plating bath, or a nickel alloy bath may be employed.

When a cobalt layer is employed as the metal layer, a cobalt chloride bath, a cobalt sulfamate bath, a cobalt ammonium sulfate bath, a cobalt sulfate bath, or a plating bath of a soluble organic acid cobalt salt may be employed.

When using a silver layer as the metal layer, use a silver plating bath (AgCN36g/, KCN60g/,
K ₂ CO ₃ 15g/) can be adopted.

In the present invention, it is preferable to employ the baths described above, but the present invention is not limited to these, and various Ni plating baths, Co plating baths, and Ag plating baths can be employed.

In particular, in the case of Ni-plated baths and Co-plated baths, the bath
It is preferable to control the pH between 1.5 and 4.5. The reason for this is that Ni-containing particles and Co-containing particles generally have oxygen attached to their surfaces, but such attached oxygen inhibits the adhesive strength of the particles when they are attached to the electrode core. It is used to remove such adhering oxygen on the particle surface in the plating bath.
This is because a plating bath with a pH of 1.5 to 4.5 is preferable. In addition, for the above effect, it is also effective to have Cl ions present in the bath, in which case the Cl ion concentration can be reduced.
It is recommended that the amount be 135g/bath or more. It is more preferable to set the pH to 1.5 to 4.5 and the Cl ion concentration to 135 g/bath or more.

A specific preferred means for obtaining the co-electrodeposited layer as described above will be explained.

The electrode core is immersed in a bath in which particles containing metal selected from nickel, cobalt, and silver are dispersed, and while a diaphragm placed in the bath is vibrated,
Plating is performed while stirring the bath with a bubbler, or the linear velocity of the bath is increased from 5 to 300 while circulating the plating bath between the plating tank and the bath storage tank.
It is best to plate as cm/sec.

When using the former method, the frequency is 5 to 500.
times/minute, preferably 10 to 300 times/minute, more preferably 50 to 150 times/minute, and the shaking width is 5 times the height of the plating tank.
~30%, preferably 10-25%, more preferably 15
~25%, bubbling gas amount is 1d of bottom area of plating tank
0.1-100/ ^min , preferably 1-50/m2
minutes, more preferably 5 to 35 minutes.

In the latter method, the linear velocity of the bath is preferably 10 to 200 cm/sec, more preferably 15 to 120 cm/sec.

The proportion of such particles in the bath is 1 g/~
It is preferable to set the amount to 200 g/cm from the viewpoint of improving the adhesion of particles to the electrode surface. Also, the temperature conditions during dispersion plating work are 20 to 80℃, and the current density is
It is preferable that it is 1A/dm ^<2> -20A/dm ^<2> .

It goes without saying that additives for reducing strain, additives for promoting eutectoid deposition, etc. may be added to the plating bath as appropriate.

Furthermore, in order to further strengthen the adhesion between the particles and the metal layer, it is of course possible to perform heating, re-plating with Ni after dispersion plating, etc., as appropriate.

In this way, an electrode is obtained in which particles are attached to the electrode core through the metal layer.

Thereafter, if necessary, the alloy particles are treated with caustic alkali (for example, immersed in an aqueous caustic solution) to elute and remove at least a portion of metals other than Ni, Co, and Ag in the alloy particles, thereby making the particles porous.

In such a case, the concentration of the caustic aqueous solution is
It is preferable to use NaOH at 5 to 40 wt% and at a temperature of 20°C to 150°C.

Example 1 Undeveloped Raney nickel powder (Ni50% by weight,
Al50% by weight) in a total nickel chloride bath (NiCl ₂ .
It was dispersed at a ratio of 10 g/in 6H ₂ O 300 g/, H ₃ BO ₃ 38 g/). The thus obtained dispersion with a pH of 2.2 was supplied to an electroplating tank. The electroplating tank has a perforated plate that moves up and down at the bottom of the tank, and a bubbler that releases gas such as nitrogen is placed above the perforated plate.

Nickel electrodes (anodes) with the same area are provided on both sides of the tank, and a plate to be plated (iron expander) connected to a negative power source is placed in the center of the tank.

The width of the perforated plate is 20% of the tank height, and the frequency is 100.
The bubbler vibrates at a rate of 10 times per minute, and the bottom area of the tank is
Plating was performed by introducing nitrogen gas at a rate of 10/min/ ^dm2 . The plating conditions were 40° C. and a current density of 3 A/dm ² for 1 hour. The resulting plating layer had a thickness of approximately 150 μm and was uniform over the entire surface, and the proportion of Raney nickel particles contained therein was 30% by weight.

The plated board thus obtained was heated to 20% at 80°C.
It was treated in an aqueous NaOH solution for 1 hour.

_{Then , the anode} A water electrolytic cell was assembled by disposing the above anode on the chamber side and the electrode prepared above as a cathode on the cathode chamber side.

Then, supply 30% KOH aqueous solution to the anode chamber,
Supply water to the cathode chamber to adjust the KOH concentration in the anode and cathode chambers.
Electrolysis was carried out at 90°C while maintaining the temperature at 20%.

Oxygen overvoltage at the anode using a Luggin capillary
When measured using SCE as a reference electrode, it was approximately 0.21V. By the way, the oxygen overvoltage of a smooth nickel plate is
It was 0.44V.

In addition, the cell voltage during water electrolysis above is 1.8V.
The cell voltage did not change even after electrolysis continued for 30 days.

Example 2 Unexpanded Raney nickel powder (Ni50% by weight,
Al50% by weight) in a total nickel chloride bath (NiCl ₂ .
It was dispersed at a ratio of 10 g/in 6H ₂ O 300 g/, H ₃ BO ₃ 38 g/). Electroplating was performed using a plating device using the thus obtained dispersion liquid with a pH of 2.0. The plating device has a dispersion liquid storage tank and a means for supplying the dispersion liquid from the storage tank to the bottom of the plating tank using a pump.Nickel electrodes (anodes) are arranged on both sides of the plating tank, and a negative electrode is placed in the center. A steel plated plate connected to a power source is placed.
After dispersion, the water is circulated between the storage tank and the peat tank.
The plating method was carried out in a plating device at a current density of 3 A/dm ² for 30 minutes while circulating a dispersion liquid at 40° C. and pH 2.1 at a rising speed of 70 cm/sec in the plating tank. The resulting plating tank had a uniform thickness of about 70 microns and was grayish black in color, and the plating layer contained about 33% by weight of Raney nickel. This plating board is 80
It was treated in a 20% NaOH aqueous solution at ℃ for 1 hour.

Using the thus obtained anode, water electrolysis was performed in the same manner as in Example 1. The oxygen overvoltage was 0.21 V, and the cell voltage was 1.8 V, and the cell voltage did not change even after 30 days of electrolysis.

Example 3 Using the same plating device as in Example 1, a cobalt bath (C ₀ SO ₄ 7H ₂ O 330g/,
H ₃ BO ₃ 30g/, C ₀ Cl ₂・6H ₂ O 30g/, 35℃,
PH4.5), C ₀ -Al alloy particles (C ₀ 50wt%,
A C ₀ -coated anode was obtained in the same manner as in Example 1, except that the proportion of particles in the bath was 50 g/50 wt % Al, average particle size 30 μ).

When this was used as an anode and water electrolysis was performed in the same manner as in Example 1, the cell voltage was 1.85 V, and the cell voltage did not change even after 30 days of electrolysis.

Note that the oxygen overvoltage of the anode was 0.26V.

Example 4 In Example 3, the cobalt bath was replaced with _CoCl2 .
Bath composition of 6H ₂ O 300g/, H ₃ BO ₃ 38g/ (PH=
2.2, Example 3 except that the temperature was changed to 45°C)
Electrolytic experiments were carried out in the same manner.

The result is that the anode overvoltage is 0.23V and the cell voltage is 1.82V.
The cell voltage did not change even after electrolysis continued for 30 days.

Example 5 As a bath, a silver bath (AgCN100g/,
KCN100g/, K ₂ CO ₃ 15g/, KOH3g/)
Example 1 except that the Raney silver developed as particles was dispersed in the bath at a rate of 100 g/d, and the plating conditions were a current density of 6 A/dm ² , 50°C, and 60 minutes. Similarly, a silver-coated anode was used. Using this, water electrolysis was performed in the same manner as in Example 1, and the cell voltage was
The cell voltage did not change even after 30 days of electrolysis at 1.75V.

Further, the anode overvoltage was 0.16V.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of the surface of one example of an anode used in the present invention, and FIG. 2 is a partial cross-sectional view of the surface of another example of the anode used in the present invention.

Claims (1)

[Claims] 1. In a method of electrolyzing water in an electrolytic cell comprising an anode and a cathode arranged through a cation exchange membrane, the anode contains particles containing a metal selected from nickel, cobalt, and silver, some of which are on the surface. A method for electrolyzing water, characterized in that the anode is provided with a layer made of at least one metal selected from nickel, cobalt, and silver on an electrode core so as to be exposed to the metal.