JPS6341991B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for electrolyzing water, and in particular to a method for electrolyzing water using a low oxygen overvoltage and 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 high 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.

Various types of water electrolysis devices are possible, but the one usually used is one in which an anode chamber and a cathode chamber containing an anode and a cathode are arranged on both sides of a liquid-permeable or liquid-impermeable diaphragm. . In the case of water electrolysis, a caustic alkaline aqueous solution is supplied to the anode chamber, water or a dilute caustic alkaline aqueous solution is supplied to the cathode chamber, and as a result of electrolysis, hydrogen is generated at the cathode and oxygen is generated at the anode. In such an anode for gas generation, ions containing calcium, magnesium, silicon, manganese, etc., S:O ₃ ^-2 , etc. dissolved in the caustic alkali aqueous solution that is the anolyte are deposited on the anode, such as oxides and It is known to deposit on the anode as a hydroxide. In the anode for gas generation, it is thought that the speed of reduction and electrodeposition is increased by the stirring effect of the electrolytic solution due to gas generation.

An anode suitable for use in the above electrolytic method has not yet been found.

The present invention provides a method for electrolyzing water using an anode that effectively prevents the above-mentioned phenomenon and makes the generated oxygen gas bubbles large enough to easily separate from the electrode surface, resulting in a decrease in cell voltage. An anode body for gas generation consisting of a porous surface layer provided on a liquid-impermeable basic surface, in which a non-electronically conductive substance is finely and uniformly distributed over the entire electrode surface. This water electrolysis method is characterized in that water is electrolyzed using an electrode body which is discontinuously attached as an anode.

The anode body used in the present invention is a nickel plating bath in which metal particles such as Raney nickel particles, which are developed or undeveloped, are dispersed in a liquid-impermeable electrode substrate such as iron, as disclosed in JP-A-54-112785. It may be obtained by immersing it in a liquid and electroplating it.
The electrode base surface may be etched or sandblasted as disclosed in Japanese Patent No. 115626.

The anode body used in the present invention has a porous surface layer provided on the surface of a liquid-impermeable base body for gas generation. It is attached to. Here, finely uniform and discontinuous means:
The non-electronically conductive substance is a relatively small deposit, and the deposit is uniformly distributed on the electrode surface in the form of an unconnected island or a band of several to dozens of islands connected. This refers to the state in which the material is attached to the surface. In general, it is thought that the aforementioned silicon, calcium, magnesium, and manganese that adhere during electrolysis are relatively likely to adhere to convex parts, and therefore, the non-electronically conductive substances are formed in the form of islands or bands so as to cover the convex parts of the electrode surface. Although it is thought that it is preferable to attach it to the substrate, this is not necessarily the case, and various other ideas are possible.

Further, it is thought that the generated fine oxygen bubbles easily combine to form large bubbles due to the effect of the attached non-conductive layer.

In the present invention, it is important to use a non-electronically conductive substance as the substance to be attached to the surface layer of the electrode. When an electronically conductive substance is deposited, it acts as an electrode, which is disadvantageous because prevention of the deposition of inhibitory substances such as the above-mentioned compounds cannot be achieved.

Such non-electronically conductive materials include various electrically insulating or ionically conductive inorganic and organic materials such as glass, enamel, ceramics,
Polymeric substances etc. can be used. From the viewpoint of durability, it is preferable to use a non-water-soluble material that is solid under the operating conditions of the electrode body.Furthermore, from the viewpoint of achieving strong adhesion to the electrode surface layer and easily controlling the amount of adhesion, organic Polymeric substances can be preferably employed.

Organic polymeric substances that can be suitably employed in the present invention include various synthetic or natural resins or elastic bodies. Specifically, the synthetic polymeric substances include tetrafluoroethylene, chlorotrifluoroethylene, Fluorine-containing olefins such as vinylidene fluoride, vinyl fluoride, and hexafluoropropylene; chlorine-containing olefins such as vinyl chloride and vinylidene chloride; olefins such as ethylene, propylene, butene-1, and isobutylene; aromatic compounds such as styrene Unsaturated compounds; dienes such as butadiene, chloroprene, and isoprene; nitriles and nitrile derivatives such as acrylonitrile, methacrylonitrile, methyl acrylate, and methyl methacrylate; homopolymers and copolymers such as polyurethanes, Polyurethane urea, polyurea, polyamideimide, polyamide, polyimide, polysiloxane,
Polyketals, polycondensates or polyaddition polymers such as polyarylene ether, and these polymers also include -COOH, -COONa, -SO ₃ H, -
SO ₃ Na, ―CH ₂ N (CH ₃ ) ₃ Cl, ―CH ₂ N
(CH ₃ ) ₃ OH, -CH ₂ , -CH ₂ N (CH ₃ ) ₃ (C ₂ H ₄ OH)
Cl, _-CH2N ( _CH2 ) ₂ ( _C2H4OH ) _OH , _-CH2N
(CH ₃ ) ₂ , -CH ₂ NH (CH ₂ ) -, which have ion-exchange groups and exhibit ion conductivity, as well as natural polymers such as natural rubber, cellulose, and polypeptides. etc. are exemplified.

In the present invention, when selecting a non-electronically conductive substance, the use conditions of the anode body, such as atmosphere, electrolyte,
The required chemical resistance, heat resistance, mechanical strength, etc. are set based on the type of gas generated, temperature, amount of gas generated, etc.
Furthermore, it is desirable to consider the adhesion force to the electrode surface layer, the operability in the adhesion work, etc. That is, when applied to the anode in water electrolysis, homopolymers or copolymers of fluoroolefins with excellent alkali resistance and heat resistance, such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexane, etc. fluoropropylene copolymer,
Perfluoropolymers such as tetrafluoroethylene-perfluoro-5-oxa-6-hebdate copolymer are preferably selected.

The method for depositing the non-electronically conductive substance described above on the anode is not particularly limited, and various methods can be adopted, but from the viewpoint of controlling the amount of deposit, dipping methods and spraying methods using a solution or dispersion of the substance are preferred. Alternatively, suitable methods include electrophoresis and the like. According to the method exemplified above, the non-electronically conductive material can be deposited finely, uniformly and discontinuously on the anode surface.

Then, the electrode in which the non-electronically conductive substance is held in the porous layer together with the solvent or dispersion medium is dried, or is dried and then fired to be firmly attached to the surface of the anode. Regardless of the dipping method, electrophoresis method, or spraying method, it is desirable that the solution or dispersion be sufficiently stirred to have a uniform concentration, otherwise the non-electronically conductive substance will not be present on the anode. It does not adhere uniformly to the surface.

The amount of the non-electronically conductive substance deposited is preferably 0.3 to 10 c.c. per m ² of apparent electrode surface area. This amount of adhesion is the apparent electrode surface area of the non-electronically conductive material 1
It is expressed as the value of the deposited weight (g) per m ² divided by the density of the material. The reason for limiting the amount of adhesion as described above is that if the amount of adhesion is less than 0.3cc/ ^m2 , it is not possible to effectively prevent metals or insoluble salts in the electrolyte from depositing on the electrode surface. Ten
If it is more than cc/m ² , the effective surface of the electrode will be reduced too much.

In order to control the non-electronically conductive substance within the above range, when using the dipping method, the concentration or viscosity of the solution or dispersion must be controlled within an appropriate range to regulate the amount of pick-up or increase or decrease the number of pick-ups; Also,
In the case of a spraying method, it can be appropriately controlled by increasing or decreasing the amount of coating or the number of times of spraying, and in the case of an electrophoresis method, by regulating the amount of current applied by controlling the current density or the current application time. According to studies by the present inventors, when using the dipping method, it is desirable from an operational standpoint that the concentration of the solution or dispersion is 0.1 to 5% by weight, preferably 0.5 to 5% by weight. In addition, in the case of a dispersion, the particle size of the non-electronically conductive substance varies depending on the porosity of the cathode surface (distribution of unevenness and depth and width of unevenness), but is 0.05 to 2μ, preferably 0.1 to 1μ. It is better to do so.

Next, one example of a preferred method for manufacturing the anode body used in the present invention will be described. As such an anode, it is preferable to use a co-electrodeposited Raney alloy as disclosed in JP-A No. 54-112785. An anode body is obtained in which the particles are co-electrodeposited on the substrate by electroplating as a cathode.

This anode body is then replaced with a non-electronically conductive material, e.g.
The anode body is immersed in a dispersion liquid in which PTFE particles are dispersed, the anode body is impregnated with the dispersion liquid, and then dried and fired to fix the PTFE particles, which is a non-electronically conductive substance, on the anode body.

When using the above method, it is preferable to use either an alloy of the first metal and the second metal or an alloy obtained by removing at least a part of the second metal as the particles having anode activity. However, the former is more preferable for the reasons described below.

In the former method, particles are co-electrodeposited in the form of an alloy, a non-electronically conductive material is deposited thereon, and then at least a portion of the second metal is removed. The reason why this is preferable has not yet been fully elucidated, but in the process of removing the second metal, part of the attached non-electronically conductive material is removed at the same time, resulting in unevenness on the anode surface, for example. This seems to be due to the removal of non-electronically conductive substances that have adhered to the deep part of the body.

The anode body thus obtained can be widely used as an anode body for gas generation, but is particularly suitable as an anode for water electrolysis.

Next, a method for electrolyzing water using the anode body thus obtained will be described.

Cation Exchange Membrane Method The present invention is characterized by using the above-mentioned anode as a water electrolysis method, and known ones can be used as the cathode and cation exchange membrane used in the method of the present invention. That is, 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 also 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, but 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.

Thus, the method of the present invention comprises an anode as described above;
By arranging a cathode through a cation exchange membrane and supplying a caustic aqueous solution to the anode side and water or a dilute caustic alkali aqueous solution to the cathode side for electrolysis, hydrogen and It provides a water electrolysis method that can produce oxygen.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Total nickel chloride bath (NiCl ₂ -6H ₂ O 300g/,
_Unexpanded Raney nickel alloy powder (Ni50% manufactured by Kawaken Fine Chemical Co. _, Ltd.,
Add 10 g of aluminum (50% Al, 200 mesh passes) and mix well to form a thick layer in advance.
Dispersion plating was performed on an expanded iron substrate (5 x 5 cm) with a 20μ nickel plating base. The plating conditions were as follows: pure nickel was used for the anode, current density was 3 A/dm ² , pH = 2.2, and plating was performed at a temperature of 40° C. for 1 hour. The composite plating layer had a thickness of about 200μ, and the content of Ni--Al alloy particles in the plating layer was about 38%.

The surface porosity is 2.5×10 ⁵ /cm ² of convexities formed by Raney nickel alloy particles, and the thickness of the electrodeposited layer is approximately
It was 200μ.

After washing this sample with pure water and drying it, a PTFE aqueous dispersion (Teflon 30J manufactured by Mitsui Fluorochemical Co., Ltd.: solid content concentration 60% by weight, average particle size 0.3μ) was applied.
After being immersed in a solution diluted 30 times with pure water for about 5 minutes, the droplets hanging down at the lower end of the electrode were absorbed with paper, and then dried in a dryer. Then, 350°C in a nitrogen gas atmosphere.
℃ for about 1 hour. After cooling, it was immersed in a 20% caustic soda aqueous solution and treated at 80°C for 2 hours to extract aluminum.

The amount of the PTFE particles deposited was 1.7 cc/m ² .

Next, the oxygen overvoltage of this electrode body was measured in a 30% caustic potassium aqueous solution at a temperature of 90° C. and a current density of 20 A/dm ² and found to be 180 mV. Next, the developed Raney nickel dispersed plating sample was placed as an anode and a cathode, and both were connected to a perfluorocarboxylic acid type cation exchange membrane (Asahi Glass's "Flemion").
While supplying 30% KOH aqueous solution to the anode chamber and water to the cathode chamber using an electrolyte layer separated by a
Electrolysis was performed while maintaining the KOH concentration at 20%. At this time, about 100 ppm of Na ₂ SiO ₃ as Si was constantly dissolved in the anode chamber. Even after electrolysis was carried out at 90°C and 20 A/dm ² for about 30 days, the oxygen overvoltage was about 180 mV, which was the same as when the operation started.

Example 2 Ni-Al alloy powder approximately 38% in the same manner as Example 1
An undeveloped Raney nickel electrode containing Immediately, it was developed using a 20% caustic soda aqueous solution at 80°C for 2 hours. Then, as in Example 1, PTFE
Dispersion adhesion treatment was performed. The amount of PTFE particles deposited was 1.9 cc/m ² . Using this, electrolysis was carried out in the same manner as in Example 1 in the presence of Si ions.
The oxygen overvoltage was 180 mV at the initial stage of electrolysis, and approximately 185 mV after 30 days of electrolysis.

Example 3 A developed Raney nickel electrode coated with polystyrene dipartition was obtained in the same manner as in Example 1. As the polystyrene dispersion, a 5-fold dilution of polystyrene uniform latex (solid content concentration 10%, average particle size 0.11 μm) manufactured by Dow Chemical Company was used. Further, it was dried at 90°C and was not heated at a higher temperature. The amount of polystyrene deposited was 2 c.c./m ² .

Next, water electrolysis was performed using this electrode in the same manner as in Example 1. However, the electrolysis temperature was 70°C. about 30
The oxygen overvoltage after electrolysis for 1 day was about 180 mV, which was the same as at the beginning of the test.

Example 4 An electrode containing Ni--Al alloy powder was produced in the same manner as in Example 1. Separately prepared tetrafluoroethylene-propylene-glycidyl ether copolymer (Aflas for coating film formation manufactured by Asahi Glass Co., Ltd.: molecular weight approximately 2.5
After being impregnated with a butyl acetate solution (concentration: 2%) of 10,000 yen), it was heat-treated at 150° C. for 1 hour without using any hardening agent. Thereafter, Al extraction treatment was performed in the same manner as in Example 1. The amount of the above copolymer deposited was 1.2 cc/m ² . Next, using this anode, oxygen overvoltage measurements and electrolytic tests were performed in the same manner as in Example 1. After about 30 days of electrolysis, the oxygen overvoltage was 180 mV, which was the same as at the start of the test.

Example 5 Expanded metal made of Ni-Fe alloy (5 x 5 cm,
Ni/Fe=15/85) was subjected to alkaline etching treatment in 65% NaOH at 165°C for 50 hours. This sample was immersed in a dispersion prepared by diluting the PTFE dispersion described in Example 1 15 times, then dried (100°C), and fired (350°C, 1 hr; in a N ₂ gas atmosphere).
I went there. Next, alkaline etching treatment was performed again under the conditions of 65% NaOH and 165°C for 20 hours.
The amount of PTFE deposited was 0.9cc/ ^m2 .

Next, an electrolytic test similar to that in Example 1 was conducted. about 30
The oxygen overvoltage was 180 mV and did not change during daily operation.

Example 6 An electrode containing Raney nickel alloy powder was produced in the same manner as in Example 1. After washing this with water, an aqueous dispersion of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) (Teflon 120 manufactured by Mitsui Fluorochemical Co., Ltd.: solid content concentration 56% by weight)
After soaking for 10 minutes in a 30-fold diluted solution of
After absorbing the hanging droplets at the lower end of the electrode with paper, the electrode was dried and fired at 300° C. for 1 hour in an argon gas atmosphere. Thereafter, Al was extracted in the same manner as in Example 1. The electrode body was coated with the above FEP at 1.9 cc/m ² . Thereafter, an electrolytic test was conducted in the same manner as in Example 1 using this electrode body. The oxygen overvoltage after about 30 days of electrolytic testing was 180 mV, the same as at the start of the test.

Comparative Example 1 An electrode containing Ni--Al alloy particles was produced in the same manner as in Example 1. Immediately in 20% NaOH aqueous solution,
Activation was performed by extracting Al at 80°C. This was subjected to an electrolytic test in the presence of Si ions in the same manner as in Example 1. After about 20 days, the oxygen overvoltage will start at 100mV.
It rose to 200mV.

Comparative Example 2 Ni-Fe alloy (Ni/Fe=
An alkali etched electrode of 15/85) was obtained.
However, the etching treatment time was set to 130 hours.
This sample was subjected to an electrolytic test in the same manner as in Example 1. about
After 30 days, the oxygen overpotential increased from the initial value of 180 mV to 340 mV.

Example 7 An expanded iron substrate (5 x 5 cm) was coated with a nickel base plating to a thickness of about 20μ, and then coated with 238 g of NiCl ₂ 6H ₂ O and ZnCl ₂
In a plating solution consisting of 136g/H ₃ BO _{3 /} 30g/ and a current density of 1A/dm ² at a pH of 4.0,
Electroplating was performed at a temperature of 40°C for about 120 minutes. This anode was developed in a 10% NaOH aqueous solution for about 15 minutes at room temperature. The porosity of the surface of this electrode was such that uneven portions were formed by etching, the distribution of the recesses was 3×10 ⁶ cells/cm ² , and the thickness of the porous layer was approximately 50 μm. The amount of PTFE deposited was 0.6cc/ ^m2 .
After washing and drying, it was immersed in the same diluted PTFE dispersion as in Example 1, dried, and fired. Next, development was carried out in a 20% NaOH aqueous solution at 80°C for 1 hour. An electrolytic test similar to that in Example 1 was conducted using this electrode. The oxygen overvoltage after approximately 20 days of operation is approximately
The voltage was 185mV, which was almost the same as at the start of operation.

Comparative Example 3 A Ni--Zn plated electrode was prepared in the same manner as in Example 7, and immediately developed in a 20% NaOH aqueous solution at 80° C. for 70 minutes. Then, an electrolytic test was conducted in the same manner as in Comparative Example 1. After 20 days of operation, the oxygen overvoltage increased from the initial 185 mV to 400 mV.

Example 8 In total nickel chloride bath (NiCl ₂ 6H ₂ O 300g/
, H ₃ BO ₃ 38 g/), unexpanded Raney nickel alloy powder (Ni50% manufactured by Kawaken Fine Chemical Co., Ltd.,
Add 10 g of Al (50% Al, 200 mesh bath) at a rate of 10 g/stir, stir well, and then thicken in advance.
Dispersion plating was performed on an expanded iron substrate (5 x 5 cm) with a 20μ nickel plating base. The plating conditions were as follows: pure nickel was used for the anode, current density was 3 A/dm ² , pH = 2.0, and plating was performed at a temperature of 40° C. for 1 hour. The composite plating layer had a thickness of about 200μ, and the content of Ni--Al alloy particles in the plating layer was about 38%.

The surface porosity was 2.5×10 ⁵ protrusions/cm ² formed by Raney nickel alloy particles, and the thickness of the porous layer was about 200 μm. After washing this sample with pure water and drying, tetrafluoroethylene (83 mol%) and methyl perfluoro-5-oxa-6-heptenoate [CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ ] (17 mol %)
Aqueous dispersion of copolymer (average particle size
0.2μ, solid content concentration 10% by weight) for about 5 minutes, and after lifting it from the liquid, the hanging droplets at the bottom of the electrode were absorbed with paper. It was then dried in a dryer. Then, heat treatment was performed at 200° C. for about 1 hour in a nitrogen gas atmosphere. After cooling, it was immersed in a 20% caustic soda aqueous solution and treated at 80°C for 2 hours to extract aluminum. This also results in -COOCH ₃ in the attached polymer.
Almost 100% of the group was hydrolyzed to -COONa.

The amount of the copolymer particles deposited was 8.5 cc/m ² . Next, the oxygen overvoltage of this electrode body was measured in a 30% caustic potassium aqueous solution at a temperature of 90° C. and a current density of 20 A/dm ² and found to be 180 mV.

Next, Example 1 was carried out in an electrolytic cell in which the developed Raney nickel dispersed plating sample was placed as an anode and a cathode, and both were separated by a perfluorocarboxylic acid type cation exchange membrane ("Flemion" membrane manufactured by Asahi Glass Co., Ltd.).
Water electrolysis was carried out in the same manner. Electrolysis was carried out for about 30 hours, but the oxygen overvoltage was about 180 mV, the same as when the operation started.

Claims (1)

[Claims] 1. An anode body for gas generation comprising a porous surface layer provided on the surface of a liquid-impermeable substrate, in which a non-electronically conductive substance is finely uniformly and discontinuously distributed over the entire electrode surface. A water electrolysis method characterized by electrolyzing water using an attached electrode body as an anode.