JPH021919B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a cathode for water electrolysis, and particularly to an electrode catalyst-ion membrane assembly capable of performing water electrolysis at low voltage and a method for manufacturing the same. 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. The gist of the present invention is particularly directed to a water electrolysis method using such a cation exchange membrane, in which a Raney nickel or Raney cobalt ternary alloy is bonded to the cation exchange membrane as a cathode electrode catalyst. As the base metal electrode catalyst, nickel, nickel porous material, nickel composite oxide, etc. are usually used. For example, the electrode disclosed in Japanese Unexamined Patent Publication No. 112785/1985, which the present applicant had already proposed, has greater effects in terms of lower hydrogen overvoltage and durability than previously known electrodes. be. However, as a result of further detailed study, the inventors of the present invention discovered that some of the electrodes disclosed in the above publication may not necessarily have sufficient durability, and as a result of making earnest efforts to solve this problem, This is what led to the discovery of the present invention. The cause of the loss of durability is common to nickel-based electrode catalysts. Therefore, the idea of the present invention is
The same applies to nickel-based electrode catalysts other than those described in Publication No. 11278. Further, the present invention is effective in the case of a direct bonded body of an electrode catalyst and an ion membrane, since the same drawbacks as that of a nickel-based catalyst are found. As mentioned above, so-called SPE water electrolysis, in which water electrolysis is performed by bonding electrode catalysts to each side of an ion membrane, is a new energy-saving hydrogen production method that can replace the conventional method of using asbestos as a diaphragm. In this type of electrolysis method, a low hydrogen overvoltage cathode as described above is preferably used as the cathode. However, during the electrolysis operation, the operation may be stopped for various reasons, and in this case, when the operation is restarted, hydrogen An increase in overvoltage was observed. As a result of deep investigation into this phenomenon, the present inventors found that the electrode activity deteriorates due to the nickel or cobalt in Raney nickel particles or Raney cobalt particles, which are active components of the electrode, changing into nickel hydroxide or cobalt hydroxide (i.e., hydrogen In order to prevent this deterioration, known metal particles consisting of a first component such as nickel or cobalt and a second component such as aluminum, zinc, magnesium, or silicon are used. The present invention was completed based on the discovery that the inclusion of a third specific component in a component X, in which the electrode active metal particles are composed of nickel and/or cobalt,
An alloy in which component Y selected from aluminum, zinc, silicon magnesium, and component Z selected from group metals of the periodic table are in the range surrounded by points A, B, C, D, and E in Figure 1. Durable low hydrogen overvoltage electrode catalyst A: X = 99wt% Y = 0wt% Z = 1wt% B: X = 79wt% Y = 20wt% Z = 1wt% C: X = 50wt% Y = 20wt% Z = 30wt% D :X=42wt% Y=16wt% Z=42wt% E: Or component X consisting of cobalt, component Y selected from aluminum, zinc, magnesium silicon, and component Z selected from group metals of the periodic table are located at points A', B', C', D' and E in Figure 2. A method for manufacturing a highly durable ion membrane-electrode catalyst assembly for water electrolysis, characterized in that the electrode-active metal particles made of an alloy in the range surrounded by ' are used as a cathode and are bonded to the ion membrane by pressure bonding A':X = 59wt% Y = 40wt% Z = 1wt% B': X = 39wt% Y = 60wt% Z = 1wt% C': X = 25wt% Y = 60wt% Z = 15wt% D': X = 25wt% Y = The main points are: 50wt% Z=25wt% E': X=35wt% Y=40wt% Z=25wt%. Here, FIG. 1 is a ternary component diagram of a component X consisting of nickel and/or cobalt, a component Y selected from aluminum, zinc, and magnesium, and a component Z selected from group metals of the periodic table. It is necessary that the alloy composition of the metal particles in the cathode falls within the range surrounded by points A, B, C, D, and E in FIG. Preferably F,
The range is G, H, E. Here, the amounts of X, Y, and Z components of points F, G, and H are (95, 0, 5), respectively.
(85, 10, 5), (46, 10, 44). The effects of the present invention are due to the inclusion of a group metal of the periodic table as a component of the alloy composition, but why does the inclusion of a group metal prevent the formation of hydroxides of nickel or cobalt? However, the details have not yet been clarified. however,
The present inventors have discovered that titanium, among group metals,
It has been found that tin zirconium is optimal for achieving the effects of the present invention. That is, when using titanium or tin zirconium among group metals, a low hydrogen overvoltage can be maintained for a longer period of time even under more severe environmental conditions. The reason why it is preferable for the metal particles of the cathode of the present invention to have a composition surrounded by ABCDE in FIG. 1 is because particles having a composition outside the above range may not be able to maintain a low hydrogen overvoltage over a long period of time. The average particle diameter of the metal particles described above is related to the porosity of the electrode surface and the dispersibility of particles during electrode production, which will be described later, but it is sufficient if it is between 0.1 μ and 100 μ. Among the above ranges, from the viewpoint of the porosity of the electrode surface, it is preferably 0.1 μ to 50 μ, more preferably 0.1 μ to 10 μ. Furthermore, the particles of the present invention are preferably superficially porous in order to achieve a lower hydrogen overpotential of the electrode. Furthermore, it is preferable that the inside of the particles be porous. As for the degree of porosity, it is preferable that the degree of porosity is considerably large; however, if porosity is created during the process, 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%. Incidentally, the above-mentioned porosity is a value measured by a known water displacement method or nitrogen adsorption method. Although various methods can be used to make the material porous, for example, it is preferable to remove part or all of the metal component Y from an alloy consisting of components X, Y, and Z to make it porous. In such a case, it is particularly preferable to treat an alloy in which components X, Y, and Z are uniformly blended in predetermined proportions with caustic alkali treatment to remove at least a portion of the metal component Y. In the case of the membrane-electrode assembly of the present invention, for example, when producing hydrogen by electrolyzing an alkaline aqueous solution, it is not necessarily necessary to treat it with caustic alkali before installing it in an electrolytic cell, and the catholyte used is Because of the caustic alkaline conditions, the metal of component Y is gradually removed during electrolysis and can become the desired cathode. Various composition combinations of the above metal particles can be used, and a typical example is Ni.
−Al−Ti, Ni−Al−Sn, Ni−Zn−Ti, Ni−Zn
−Sn, Co−Al−Ti, Co−Al−Sn, Co−Zn−
Ti, Co−Zn−Sn, Ni−Mg−Ti, Ni−Mg−
Possible examples include Sn, Co-Mg-Ti, and Co-Mg-Sn. Furthermore, it is conceivable that Ti is replaced with Zr. Among these, a particularly preferable combination is Ni-Al-Ti,
It is Co-Al-Ti. In the present invention, the alloy particles as described above are bonded onto the ion exchange membrane, but there is no need for this bonding to be particularly limited. A method is preferably used. The conditions for such caustic alkali treatment vary depending on the composition of the starting metal particles, but in the case of metal particles with the composition described below, the caustic alkali concentration (NaOH equivalent) is 10 to 100% by weight (NaOH equivalent) of 10 to 35% by weight. It is preferable to immerse it in a ℃ aqueous solution for 0.5 to 30 hours. The reason for this is that the component Y was selected on the condition that it should be removed as easily as possible, and the component Z should be removed as little as possible. In the case of the present invention, the metal particles include a component X made of nickel and/or cobalt, and a component Y selected from aluminum, zinc, and magnesium.
It is necessary that the component Z selected from the group metals of the periodic table is an alloy within the range surrounded by points A', B', C', D' and E' in FIG. The reason for this is that if it deviates from this range, it may not be possible to secure a sufficient amount of adhesion during the bonding process with the membrane, or even if bonding is possible, the adhesion strength may be low. This is because the activity as an electrode catalyst is not sufficient. Therefore, A′~
If it deviates slightly from the range shown by E', the initial hydrogen overvoltage will be slightly higher and the resistance to oxidation due to short circuits, which will be described later, will decrease, but if it deviates significantly, the mechanical strength will be low and the initial overvoltage will be high, making it no longer practical. This is because it cannot be provided. The thus obtained ionic membrane-electrode catalyst assembly is then treated with caustic alkali (e.g., immersed in an aqueous caustic solution) as necessary to elute and remove at least a portion of the metal of component Y in the metal particles, The particles are rendered porous. The conditions in such a case are as described above. In addition, when an alloy of the components X, Y, and Z described above is used as particles, it is preferable to perform the caustic alkali treatment as described above, but it is preferable to perform the caustic alkali treatment as described above. It may be attached to an alkaline water electrolyzer to actually perform electrolysis. In such a case, the metal of component Y is eluted during the electrolysis process, and the overvoltage of the electrode is reduced. However, although the aqueous caustic alkaline solution produced is slightly contaminated by the eluted metal ions of component Y, this generally does not pose a problem. In the present invention, the electrode catalyst used as an anode is not particularly limited, and may be any of various noble metals that are effective as an anode catalyst, such as rhodium, iridium, platinum, and the like. Furthermore, a nickel-based electrode catalyst may also be used. These may be directly bonded to the membrane, or an electrode body may be used that is bonded to another core body by various methods such as dipping, chemical plating, electroplating, spraying, etc. . It goes without saying that in this water electrolysis method, it is preferable that the oxygen overvoltage is as low as possible. Further, as the cation exchange membrane used in the present invention, known fluorine-containing cation exchange membranes can be used, and among them, perfluorinated carbon membranes having carboxylic acid groups as ion exchange groups (e.g.,
No. 140899, disclosed in Japanese Patent Application Laid-Open No. 52-48598)
is particularly preferable from the viewpoint of durability and low voltage. Next, examples of the present invention will be described. Examples 1 to 11 An alloy powder (500 mesh passes) having the composition shown in Table 1 was prepared, 25 g of methyl cellulose was added to 15 g of the powder, kneaded for 45 minutes, and 3 c.c. of cyclohexanol and 1 c.c. of cyclohexanone were added. was added and kneaded for 15 minutes to obtain a catalyst paste. CF ₂ =
CF ₂ and CF ₂ = CFO (CF ₂ ) ₃ Copolymer with COOCH ₃ , ion exchange capacity 1.90 meq/g resin, 5 mg/cm ² of each of the above alloy powders on one side of a cation exchange membrane with a film thickness of 150 μm. , applied by screen printing machine. On the other side of the ion membrane, 3 mg/g of separately prepared rhodium black was added.
cm ² applied. Next, heat this at 150℃ and 250Kg/cm ² for 10
Pressed for a minute. 80℃, 15% NaOH aqueous solution for 20
Hydrolyzed for hours. Here, a part of the electrode catalyst was peeled off and the composition was analyzed. Next, a Ni mesh was used as a current collector, and the rhodium black side was used as an anode at 35%
Electrolysis was performed under the conditions of NaOH, 90° C., and 20 A/dm ² . The following short circuit test was conducted on the third day after the start of electrolysis. First, the power supply from the DC power supply was stopped, and the anode and cathode were connected outside the container using a copper conductor wire, and the battery was left as it was for about 15 hours. During this time, the current flowing from the cathode to the anode was observed. In addition, after stopping electrolysis, approximately 3
The catholyte temperature was maintained at 90° C. for a period of time and then allowed to cool naturally. After cooling for 15 hours, the electrode was taken out and the hydrogen overvoltage was measured. Table 1 shows the results. This is almost the same as the pre-test performance. In addition, the electrode catalyst-membrane assembly of Example 2 was added to 40%
It was immersed in NaOH aqueous solution at 100°C for one week. To ensure sufficient contact with air, the depth of the container was made shallow to 7 cm, and the top of the container was left open. The hydrogen overvoltage of this electrode was measured before and after the immersion test. The hydrogen overvoltage is approximately
There was almost no change before and after the test at 0.08V.

[Table] Comparative Examples 1-2 Ni-Al and Co-Al alloy powders in Examples 1-2
It was bonded to the ionic membrane using the same method used in Example 11. A portion of the metal particles on the obtained electrode catalyst-ion membrane assembly was peeled off, and its composition was investigated. The results are also listed in Table 2. A short circuit test was conducted in the same manner as in Examples 1 to 11, and changes in hydrogen overvoltage before and after the test were measured. The results are shown in Table 2. Note that the hydrogen overvoltage before the test was approximately 0.07V. Comparative Examples 3 to 9 Membrane-electrode assemblies were manufactured in the same manner as in the example except that the composition of the alloy powder was changed to Comparative Examples 3 to 9 in Table 2. Table 2 shows the results of a short circuit test conducted in the same manner as in the examples. The hydrogen overvoltages before the short circuit test were 0.17V, 0.18V, 0.20V, 0.16V, and 0.16V for Comparative Examples 3 to 9, respectively.
It was 0.09V, 0.08V, 0.09V.

【table】 [Brief explanation of drawings]

Figure 1 shows X=Ni or Co, Y=Al or Zn, Z
The composition in the range surrounded by points A, B, C, D, and E in the diagram consisting of the three components =Ti or Sn indicates the composition of the electrode catalyst active particles for membrane bonding of the present invention. Figure 2 shows X=Ni or Co, Y=Al or Zn, Z=Ti
Or point A′ in the diagram consisting of the three components of Sn,
The composition range surrounded by B', C', D', and E' indicates the composition range of the electrode active particles used in the method of the present invention.

Claims (1)

[Scope of Claims] 1 Component X consisting of nickel and/or cobalt, component Y selected from aluminum, zinc, silicon magnesium, and component Z selected from group metals of the periodic table are located at point A in FIG. B, C, D
An ion exchange membrane and an electrode assembly in which electrode active metal particles made of an alloy electrode catalyst in the range surrounded by and E are bonded to an ion membrane as a cathode. 2 Component X consisting of nickel and/or cobalt, component Y selected from aluminum, zinc, magnesium silicon, and component Z selected from group metals of the periodic table are located at points A', B', C',
A method for producing an ion exchange membrane and an electrode assembly, characterized in that electrode active metal particles made of an alloy in the range surrounded by D' and E' are used as a cathode and are pressure-bonded to and bonded to an ion membrane.