JPS5911675B2 - Catalyst electrode structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to catalytic electrodes and membrane-electrode structures, and more particularly to electrodes particularly useful in the electrolysis of halides.

Needless to say, the method of electrolyzing a compound to generate one of its constituent elements as a gas is a conventionally known technique.

By the way, some recently developed electrolytic devices for gas generation include cells that use an electrolyte made of a solid polymer ion exchange membrane. In this type of device, catalytic electrodes using a suitable catalyst are placed on either side of an ion transport membrane, such as a sulfonated fluorinated hydrocarbon resin ion exchange membrane. Due to the oxidation reaction, one of the component elements (for example, hydrogen when electrolyzing water or hydrogen chloride, or sodium when electrolyzing an alkali metal halide such as sodium chloride) becomes an ion at the position of one electrode. is generated in the state of Such ions are transported across the ion exchange membrane and reduced at the other electrode to produce electrolytic products such as molecular hydrogen, sodium hydroxide, etc. Electrolytic cells using solid polymeric ion exchange membranes are particularly advantageous in that they are efficient, small in size, and do not contain any corrosive electrolytes. Various metals and alloys have been used as part of the catalytic electrodes incorporated into such electrochemical cells.

It is clear that the performance of the catalyst present at the gas generating electrode determines the effectiveness and efficiency of the electrolysis cell and thus the economy of the electrolysis process. The selection of a catalyst and its effectiveness within an electrolytic cell is complicated by factors such as the surface area of the catalyst, the formation of oxides of its components on the catalyst surface, contaminants in the reactants, and the nature of the reactions occurring within the cell. exists in Therefore, it is, and indeed always has been, difficult to predict whether a catalyst useful in one electrolytic cell will have application in another device. No. 3,992,271 describes an improved catalytic electrode for oxygen evolution comprising a platinum-iridium alloy which has been found to provide significant improvements in performance and efficiency. Also, U.S. Patent No. 40394
No. 90 describes another catalytic electrode for oxygen generation using a reduced oxide of platinum-ruthenium.

Such platinum-ruthenium catalysts are not only substantially cheaper than platinum-iridium catalysts due to the use of relatively inexpensive materials such as ruthenium for alloying with platinum, but also in the case of platinum-iridium electrodes. It has been found to be more effective because it has a lower oxygen overpotential than However, attempts to use an electrocatalyst made of reduced oxide of ruthenium to generate halogen using an electrode of an aqueous halide solution have not necessarily been successful due to the harsh electrode conditions in the cell (electrolytic tank). Nakatsuta.

In other words, since the reduced oxides of platinum group metals dissolve in the acidic environment that exists during the electrolysis of hydrogen halides and the electrolysis of alkali metal halide solutions (often acidic solutions), a large amount of catalyst is removed from the membrane during chlorine generation. may be lost. Thus, not only is there a tendency for catalyst to be lost due to dissolution of the platinum group metals, but there is also a tendency for cell efficiency to decrease due to increased electrode overvoltage, thus making long-term operation impossible. This is often the case. Now, the advantages of the present invention will become apparent by themselves as the description progresses.

The novel electrocatalysts associated with the present invention include at least one catalyst treated in the presence of oxygen using high temperatures sufficient to increase resistance to aggressive electrolytic conditions by thermal stabilization. Contains reduced oxides of platinum group metals.

Such electrocatalysts may also optionally contain reduced oxides of other platinum group metals (e.g., iridium), and may include graphite and valve metals (e.g., oxides, nitrides,
Conductive fillers such as carbides and sulfides can optionally be included in proportions up to 50% (by weight). Examples of useful platinum group metals include platinum, palladium, iridium, rhodium, ruthenium, and osmium, although the thermally stabilized reduced oxides of ruthenium are preferred for chlorine and other halogen generation. The reduced oxide of ruthenium is preferred because it has been found to have a very low overpotential relative to chlorine as well as being stable in the electrolytic environment. As previously mentioned, such electrocatalysts may consist of a reduced oxide of only one platinum group metal (eg, a reduced oxide of ruthenium, platinum, iridium, etc.).

However, mixtures of two or more thermally stabilized reduced oxides of platinum group metals have been found to be more stable.
An example of such a mixture is a reduced oxide of ruthenium containing up to 25% (by weight), preferably from 5 to 25% (by weight) of reduced oxide of iridium, calculated as metal. However, iridium is slightly more expensive than ruthenium.
Conductive fillers such as graphite have low overpotentials relative to halogens, are substantially cheaper than oxides of platinum group metals, and can be easily incorporated without reducing the effectiveness of the catalyst.

The addition of reduced oxides of valve metals such as titanium, tantalum, niobium, tungsten, vanadium, zirconium and hafnium in addition to graphite can further stabilize the electrocatalyst and further increase its resistance to harsh electrolytic conditions. Such thermally stabilized reduced oxides of platinum group metals and fillers added thereto (1) perfluorinated hydrocarbon resin particles such as those sold by Dubon under the trade name "TeflOn". By bonding, it is formed into an electrode.

That is, catalyst particles and resin particles are mixed, optically filled into a mold, and then sintered into a suitable shape by heating. The molded article is then bonded to at least one surface of the membrane by heating and pressure. In this way, novel electrode structures and integrated membrane-electrode structures can be obtained. A novel method for producing such electrocatalysts involves forming oxides of at least one platinum group metal and optionally one or more valve metals, reducing such oxides to a partially oxidized state, and The process consists of heating in the presence of oxygen using a high enough temperature to stabilize the reduced oxide, followed by the optional addition of graphite.

The novel features believed to be inherent in the invention are pointed out in the appended claims.

The structure and method of operation of the present invention, as well as other objects and advantages, may, however, be best understood from the following description, taken in conjunction with the accompanying drawings. Novel electrocatalysts comprising thermally stabilized reduced oxides of platinum group metals, alone or together with other platinum group metals or optional valve metals, are partially reduced and thermally stabilized permanent oxides. It can be prepared by any suitable method as long as it provides a catalyst.

A preferred method of reduction involves the addition of a thermally decomposable platinum group metal halide (e.g. ruthenium chloride) alone or if desired together with an appropriate amount of various thermally decomposable platinum group metal or valve metal halides in an excess amount of sodium nitrate. A modification of the Adanls method for preparing platinum group metals by adding .

Adams' platinum group gold preparation method was published in the Journal of the American Chemical Society (JOU).
rnalOftheAnleri-CarlChemi
R. Adams and R. L. CalSOciety), No. 45, p.
R.Adams & R.L.Schri
ner). In this case, finely divided halides of platinum group metals (e.g. chloroplatinic acid for platinum, ruthenium chloride for ruunium, ruthenium chloride for titanium) are added according to the same weight ratio of metals as desired in the final alloy product. It is convenient to mix titanium chloride for tantalum, and tantalum chloride for tantalum. After addition and mixing of excess sodium nitrate, the mixture is melted in a silica dish at 500-600°C for 3 hours. The desired platinum group metal oxide (ie, ruthenium oxide, platinum ruthenium oxide, ruthenium iridium oxide, ruthenium titanium oxide, etc.) can be obtained by thoroughly washing the residue to remove remaining nitrates and halides. The suspension of mixed acids thus obtained is then partially reduced. Reduction of the platinum group metal oxide can be accomplished by any suitable known method, such as electrochemical reduction or hydrogen introduction at room temperature, as long as the oxide is not completely reduced to the free metal state. According to a preferred embodiment, the oxide is reduced by the use of electrochemical reduction techniques (i.e. electrochemical reduction in an acidic medium). The resulting product (oxide) is thoroughly dried, for example by using a heat lamp, ground, and then passed through a 400 mesh nylon sieve.
A fine powder of a reduced oxide of a platinum group metal is obtained. The reduced oxide of the platinum group metal thus obtained is then heated in an acidic hydrogen halide environment and in the presence of oxygen using a temperature and time sufficient to obtain a stable catalyst in the presence of halogen. It is thermally stabilized by this.

As discussed below, such thermal stabilization results in a catalyst that exhibits much better corrosion resistance in the presence of halogen (eg, chlorine) halide solutions (eg, hydrochloric acid). It is also believed that such thermal stabilization produces catalyst particles having a large average pore diameter and a stable thin oxide film on the outside of the reduced oxide particles. This stabilization of the reduced oxide particles results in improved mechanical properties for bonding to solid polymer electrolyte membranes and resistance to dissolution in hydrochloric acid or other acidic halide solutions or to generated halogens. It will be improved. For this purpose, it is preferable to heat the reduced oxide at 350-750°C for 30 minutes to 6 hours;
More preferably, the reduced oxide is heated at 600° C. for 1 hour. Furthermore, it has been found that in order to optimize the electrolytic activity of such a catalyst and an electrode containing the same, it is sufficient to make the catalyst particles into a powder state as fine as possible.

That is, the surface area of the catalyst particles measured by the BET nitrogen absorption method is at least 25 m2/9, preferably 50 to 1
It turned out that 50m2/9 would be sufficient. For producing gas permeable electrode structures comprising catalyst particles and fluorinated hydrocarbon polymer particles, U.S. Pat.
Catalyst particles may be mixed with a Teflon dispersion to form a bonded electrode structure as described in the '484 specification.

When bonding the electrodes, it is desirable to mix the Teflon dispersion with the catalyst with care so that it contains little or no hydrocarbons. If the Teflon dispersion contains hydrocarbons as organic surfactants, a loss of surface area of the catalyst occurs. A reduction in the surface area of the catalyst is clearly undesirable. This is because it can adversely affect the efficiency and efficacy of the catalyst. Therefore, dispersions of Teflon (ie, polytetrafluoroethylene) particles that are substantially free of hydrocarbons should be used in the manufacture of electrode structures. Examples of suitable Teflon particles that may be used in the manufacture of electrode structures include those sold by Dubon under the trade name "Teflon T-30." A mixture of noble metal particles and Teflon particles or graphite and reduced oxide particles is filled into a mold and then shaped by heating.

Next, the molded article thus obtained is bonded and embedded into the surface of the membrane by heating and pressurizing. For example, if an electrode structure is bonded to the surface of an ion exchange membrane as described in the above-mentioned US Pat. No. 3,297,484,
A gas permeable particle mixture is bonded together. Also,
In some cases it is preferable to embed it in the surface of the membrane. The novel membrane-electrode structure thus prepared comprises a solid polymer electrolyte membrane capable of selective ion transport and a reduced oxide of a platinum group metal (as described above) bonded to at least one side of such membrane. It consists of a thin, porous, gas-permeable electrode (containing an electrocatalyst).

A second electrode can also be bonded to the other side of the membrane,
The electrodes in that case may contain the same electrocatalyst or any other suitable cathode material. Preferably, the selective ion transport membrane is a stable hydrous cation exchange membrane characterized by selectivity in ion transport. Cation exchange membranes allow the passage of positively charged cations (e.g., hydrogen ions in the case of electrolysis of halides such as hydrogen chloride, and sodium ions in the case of electrolysis of aqueous alkali metal halides); Passage of negatively charged anions is suppressed. There are a variety of ion exchange resins that can be used as membranes that allow selective transport of cations.

Just two such resins are the so-called sulfonic acid cation exchange resins and carboxylic acid cation exchange resins. More preferred sulfonic acid cation exchange resins include hydrated sulfonic acid groups (
SO3H. H2O) as an ion exchange group. Since the ion exchange groups in the membrane are bonded and fixed to the polymer main chain, the electrolyte concentration does not change. As indicated above, particularly preferred are fluorinated hydrocarbon resins and sulfonic acid cation exchange resins. Examples of cation exchange polymers of this type include those sold by Dubon under the tradename NafiOr!.
Such naphionic membranes are made of a hydrous copolymer of polytetrafluoroethylene (PTFE) and polyfluorinated sulfonyl vinyl ether containing sulfonic acid side groups.
EC) depends on the number of M9 equivalents of sulfonic (SO3) acid groups per polymer 19 (NEW).

The greater the concentration of sulfonic acid groups, the greater the ion exchange capacity and hence the cation transport capacity of the membrane. However, as the ion exchange capacity of the membrane increases, the water content increases and therefore the membrane's ability to reject salts decreases. by the way,
In the case of electrolysis of an alkali metal halide solution, caustic alkali is produced on the cathode side, so the rate at which the caustic alkali moves from the cathode side to the anode side increases with the ion exchange capacity. Such reverse migration reduces the current efficiency (CE) of the cathode and also causes the evolution of oxygen at the anode side. Such oxygen evolution has undesirable consequences in terms of its effect on the anode-side catalytic electrode. Therefore, an ion exchange membrane suitable for electrolysis of salt water has an ion exchange capacity of 1500
Although m9 equivalent, water content is small (5-15%)
A cation exchange membrane of about 51 μ (2 mil) with a large salt exclusion ability and a large ion exchange capacity (1100 m
It is a laminate consisting of cation exchange membranes of approximately 102μ (4 mils) bonded with Teflon cloth. An example of such a laminate is that sold by DuPont under the trade name Nafion 315. There are various other laminates that use a thin film of resin with a low water content (5-15%) as the layer on the cathode side to optimize the salt rejection ability. Examples of such laminates include Nafion 355, 376, 390, 227 and 21
4 can be mentioned. In the case of laminates bonded by Teflon cloth, the membrane and Teflon cloth can be separated by reflux heating in 70% HNO3 for 3 to 4 hours, in addition to the conventionally preferred immersion in caustic alkaline. It can be said that it is desirable to keep it clean. In the case of electrolysis of hydrogen halides such as hydrogen chloride, simple forms of membranes such as Nafion 120 can be used as ion transport membranes since the problem of back migration of caustic and other salts does not exist.

In the case of saline electrolysis, a stack containing a chemically modified layer 2 to 4 mils thick with sulfonamide or carboxylic acid groups as a barrier layer on the cathode side, which also requires a low water content. You can also use objects.

Next, referring to FIG. 1, an electrolytic cell 1 for halogen generation is shown.
0 is shown.

Such a cell 10 consists of a cathode jacket 11 and an anode jacket 12 separated by a solid polymeric electrolyte membrane 13. Both sides of the membrane 13, which is preferably a permselective hydrous cation exchange membrane, are coated with a thermally stabilized reduced oxide of ruthenium (RuOx) or reduced oxide of iridium (RuOx).
IrOx), thermally stabilized ruthenium-iridium (
Ru-1r), ruthenium-titanium (Ru-Ti), ruthenium-tantalum (Ru-Ta) or ruthenium-
Particles of tantalum-iridium (reduced oxide of ruthenium-graphite with RuTa-r, or a combination of the above and reduced oxides of graphite and other valve metals, bonded with a perfluorinated hydrocarbon resin such as Teflon) A cathode 14, visible in the figure, is bonded and preferably embedded on one side of the membrane 13. On the opposite side of the membrane 13, not visible in the figure, an anode are bonded and preferably embedded. Current collectors 15 and 16 consisting of metal screens are crimped onto these electrodes. Such membrane-electrode assembly is connected to the envelope element 11 by means of gaskets 17 and 18. and 12. Gaskets 17 and 18 are connected to the cell environment, i.e., caustic, chlorine, oxygen, and aqueous sodium chloride in the case of saline electrolysis (or sodium chloride in the case of hydrogen halide electrolysis). EPDM is made of a material that is inert to hydrogen (hydrogen and hydrogen bromide).
Filled rubber gaskets sold by OreComp2my. In operation, an aqueous solution of an alkali metal halide (eg, sodium chloride) or hydrogen halide (eg, hydrogen chloride) is introduced through the anolyte inlet tube 19 leading to the anode chamber 20 .

The used anolyte and halogen (eg chlorine) are removed through the outlet pipe 21. In the case of saline electrolysis, an inlet tube 22 leading to the cathode chamber 11 is provided, by means of which a catholyte, i.e. water or (more dilute than that produced electrochemically at the electrode-electrolyte interface) sodium hydroxide, is introduced. It becomes possible to introduce an aqueous solution. Note that in the case of electrolysis of hydrogen halide (for example, hydrogen chloride), a catholyte is not required, and therefore the introduction tube 22 can be omitted. In a saline electrolysis cell, water serves two independent functions.

That is, some of the water is electrolyzed to produce hydroxide ions (0H), which then combine with sodium ions transported through the membrane to produce caustic (i.e., sodium hydroxide). , thereby diluting the high concentration of caustic generated at the membrane-electrode interface and thus inhibiting the back-diffusion of caustic through the membrane to the anode side. Tube 23 serves to remove excess catholyte and electrolysis products (ie caustic in the case of saline electrolysis and hydrogen in the case of saline or hydrogen chloride electrolysis).
A power cable 24 is drawn into the cathode chamber, and an anode chamber 2
An equivalent cable (not shown) is routed to 0.
These cables have a metal screen 1 for power supply.
5 and 16 or any other suitable current collector. Next, FIG. 2 illustrates the reactions that occur within the cell during electrolysis of an aqueous solution of an alkali metal halide (eg, saline), and is useful for understanding the function of the cell in the electrolysis process.

That is, an aqueous solution of sodium chloride is introduced into the anode chamber 20 separated from the cathode chamber by the cation exchange membrane 13. The membrane 13 consists of a layer 26 of high water content (20-35% based on the dry weight of the membrane) located on the anode side and a layer 26 of low water content (5-35% based on the dry weight of the membrane) located on the cathode side.
15%) and high ion exchange capacity layer 27 with Teflon cloth 2.
This is a composite membrane consisting of 8 bonded parts. The barrier layer on the cathode side may also be a thin layer of a low water content polymer obtained by chemical modification on the cathode side. By way of example, the polymer is modified so that the cathode side of the membrane has a sulfonamide substituent. By changing the cathode side to a weakly acidic type (sulfonamide type) in this way, the water content in this part of the membrane is reduced, and the salt-repelling ability of the membrane is therefore increased. As a result, back diffusion of sodium hydroxide through the membrane toward the anode side is suppressed. In the case of salt water electrolysis, a membrane with a laminated structure is preferable to prevent the back movement of sodium hydroxide, but a homogeneous membrane with a low water content (for example, Nafion 1
50, perfluorinated carboxylic acid resin, etc.) can also be used. Of course, in the case of electrolysis of hydrogen halides (eg, hydrogen chloride, hydrogen bromide, etc.), the ion transport membrane may be a simple homogeneous membrane such as the conventionally preferred Nafion 120 membrane. As shown in the figure, a catalyst consisting of a reduced oxide of a noble metal bonded with Teflon is pressed onto the surface of the membrane 13.

Such catalysts contain at least one thermally stabilized reduced oxide of a platinum group metal, such as a reduced oxide of ruthenium, iridium or ruthenium-iridium, and also a reduced oxide of titanium, niobium or tantalum and graphite. may contain. Current collectors 15 and 16 are crimped onto the surface of the catalyst electrode, as partially shown for simplicity, and are connected to the positive and negative electrodes of a power source for supplying electrolytic voltage between the electrodes of the cell, respectively. There is. When an aqueous solution of an alkali metal halide (eg, an aqueous solution of sodium chloride) is introduced into the anode chamber, electrolysis at the anode 29 results in the evolution of chlorine, as illustrated by bubble formation 30. Theoretically, chlorine is generated at the interface of one electrode membrane, but it goes to the electrode surface via the porous voltage. On the other hand, sodium ions (Na) pass through the membrane 13 to the cathode 14.
will be transported to the location. A stream 31 of water or an aqueous sodium hydroxide solution is introduced into the cathode chamber as catholyte. Such catholyte flows along the surface of the Teflon-bonded cathode 14, thereby diluting the caustic generated at the membrane-cathode interface, so that the caustic alkali flows into the membrane 13.
Back-diffusion to the anode side through the oxide is suppressed. A portion of the catholyte water is electrolyzed at the cathode 14 to produce hydroxide ions and hydrogen gas.

Such hydroxide ions combine with sodium ions transported through the membrane 13, thereby producing sodium hydroxide at the membrane-electrode interface. Such sodium hydroxide readily wets the Teflon forming part of the electrode and migrates to the surface where it is diluted by water flowing along the surface of the electrode. Although diluted with water as the catholyte, a concentrated sodium hydroxide solution in the range of 4.5-6.5M is produced at the cathode.

Therefore, some of the sodium hydroxide moves back along the membrane 13 toward the anode, as shown by arrow 33. Such back migration of sodium hydroxide is a diffusion process caused by the concentration gradient and electrochemical ion transport towards the anode. The sodium hydroxide transported to the anode side is oxidized to water and (as indicated by bubble formation 34)
Produces oxygen. Needless to say, since this is a parasitic reaction that reduces the current efficiency of the cathode, it should be suppressed by using a membrane with a large salt-repelling ability on the cathode side.
Besides its effect on current efficiency, the evolution of oxygen at the anode is undesirable because it can have a detrimental effect on the electrode and membrane, especially if the electrode contains graphite. Moreover, since such oxygen dilutes the chlorine generated at the anode, treatment to remove oxygen is also necessary. In addition,
If the anolyte is acidified, the sodium hydroxide that has migrated back turns into water instead of oxygen, making it possible to further suppress the generation of oxygen. The reactions in each part of the saline electrolysis cell are the same as those related to the electrolysis of hydrogen halide (for example, hydrogen chloride) described below. 1V-141 ``-? -1 et al▼? The novel device described herein for the aqueous electrolysis of common salt or hydrogen chloride is characterized in that the catalytic sites in the electrode include a cation exchange membrane and an ion exchange group ( Sulfonic acid group SO, H-H2
O or carboxylic acid group COOH-H2O) (5).

As a result, the anode and cathode chambers (usually "electrolyte R
There is almost no voltage drop (called "drop"). It takes
The electrolyte 1R drop is unique to current devices in which the electrode and membrane are separated, and can reach about 0.2 to 0.5 V. The elimination or substantial reduction of such voltage drops, of course, constitutes one of the principal advantages of the present invention, as it clearly has a very significant effect on the overall cell voltage and economics of the electrolysis process. Moreover, since chlorine is generated directly at the anode-film interface, there is no voltage drop caused by the so-called "bubble effect.""Bubbleeffect" refers to losses due to gas mixing and transport resulting in blockage of the electrolyte path between the electrode and the membrane. As mentioned above, in conventional devices, the catalytic electrode for chlorine generation is isolated from the membrane. Since the gas is generated at the electrode,
A layer of gas is formed in the space between the membrane and the electrode. As a result, the electrolyte path between the membrane and the electrode is blocked and the voltage drop increases because the passage of sodium ions (Na+) is thus blocked. According to a preferred embodiment:
In the anode consisting of a reduced oxide of a noble metal bonded with Teflon, a reduced oxide of ruthenium, iridium or ruthenium-iridium is used in order to minimize the resistance overvoltage at the anode.

To obtain a stable anode, the reduced oxide of ruthenium is stabilized against chlorine and oxygen. For this purpose, thermal stabilization is first carried out by heating the reduced oxide of ruthenium at a temperature of 550-600[deg.] C. for one hour. Next, graphite and/or 5-25% (by weight)
Preferably 25% (by weight) of reduced oxide of iridium 1
The reduced oxide of ruthenium is further stabilized by mixing with r0x or preferably 25-50% (by weight) of the reduced oxide of titanium TiOx. Reduced oxides of ruthenium, iridium and titanium (Ru-1r-Ti)
It has also been found that a ternary mixture of 0x or the reduced oxide of ruthenium, iridium and tantanyl (Ru-1r-Ta)0x bonded with Teflon is extremely effective for obtaining a stable and long-lived anode. ing. For such ternary mixtures, the composition is 5-25% (by weight) reduced oxide of iridium, about 50% (by weight) reduced oxide of ruthenium, and the balance reduced oxide of valve metal (e.g. titanium). Preferably, it consists of: In the case of a binary mixture of reduced oxides of ruthenium and titanium, the composition preferably consists of 50% (by weight) of the reduced oxide of titanium and the balance of the reduced oxide of ruthenium. Needless to say, titanium has the advantage of being much cheaper than ruthenium or iridium, making it an effective extender for stabilizing the electrode against acidic environments, hydrogen chloride, chlorine, and oxygen, as well as reducing cost. I will do it. In such an electrode structure, other valve metals such as niobium (Nb), tantalum (Ta) are used instead of titanium.
, dilbunium (Zr.) or hafnium (Hf) can also be conveniently used. Furthermore, not only reduced oxides of valve metals, but also carbide nitrides and arsenic compounds of valve metals can be used as catalyst extenders. The mixture consisting of the reduced oxide of the culprit metal and the reduced oxide of titanium or other valve metal is further homogeneously mixed with Teflon.

The Teflon content of the anode may be between 15 and 50% (by weight), but preferably between 20 and 30% (by weight). The type sold by DuPont under the trade name Teflon T-30 is used here, but other fluorinated hydrocarbon resins can be used as well. The amount of precious metal catalyst used in the anode is usually 0.6 m9/C.
d or more, but preferably 1 to 2 m9 shoulders. The current collector for the anode may be a fine-grained platinum-coated niobium screen, which is known to make good contact with the electrode surface. Alternatively, a reticulated titanium screen coated with ruthenium oxide, iridium oxide, valve metal oxide or mixtures thereof can be used as the anode current collector. Furthermore, it is also possible to use an anode current collector consisting of a titanium-palladium plate to which a platinum-coated screen is welded or glued. The cathode is preferably made of platinum black bonded with Teflon, in which case the amount of platinum black used is 0.4 to 4 m9/Clll. Like the anode, the cathode is bonded to and embedded in the surface of the cation exchange membrane. Note that the cathode is extremely thin (51-76μ (2-3
The material is porous, preferably about 13 microns (0.5 microns), and has a low Teflon content. The thickness of the cathode is believed to be extremely important.

This is because if the cathode becomes thicker, water or aqueous sodium hydroxide solution will not penetrate into the cathode, thereby reducing the current efficiency of the cathode. Therefore, a cell was fabricated with a thin (about 13-51 micron (0.5-2 mil)) platinum black cathode bonded with 15% Teflon. And 2909/
When the cell was operated at a temperature of 88 to 91° C. while supplying a saline solution to the anode side, the current efficiency of the cell was about 80% at a sodium hydroxide concentration of 5M. When using a 76μ (3 mil) thick RuOx monographite cathode, the current efficiency at a 5M sodium hydroxide concentration is 5.
It dropped to 4%. Table 1 below shows the relationship between current efficiency and cathode thickness.
It is found that best performance is obtained when the thickness does not exceed 3 mils (50.8-76.2 microns). The electrode is required to have gas permeability so that gas generated at the electrode-membrane interface can easily escape.

The electrode also needs to be porous to allow water to penetrate to the cathode-membrane interface where sodium hydroxide is produced, and to allow the supplied saline to penetrate the membrane and anode catalytic sites. This is to make it easier to reach. As a result, for the cathode, the high concentration of sodium hydroxide produced is diluted and easily reaches the cathode surface while wetting the Teflon, where it is further diluted by water flowing along the cathode surface. becomes. It is important to perform the dilution at the cathode-film interface where the sodium hydroxide concentration is highest. To maximize water penetration at the cathode, the hydrophobic Teflon content should be between 15
It should not exceed 30% (by weight). Thus, the porosity is large and the Teflon content is limited;
If the thickness is small and water or a dilute aqueous sodium hydroxide solution is used, the sodium hydroxide concentration will be limited and therefore back migration of sodium hydroxide through the membrane will be inhibited. The highly corrosive caustic alkali present in the cathode corrodes many materials, and this is especially noticeable during periods of rest, so the current collector for the cathode must be carefully selected.

Such a current collector may consist of a nickel screen that is resistant to caustic. Alternatively, such a current collector may consist of a stainless steel plate to which a stainless steel screen is welded. As a current collector for the cathode having resistance to caustic alkali, graphite or graphite with a nickel screen crimped thereon may be brought into contact with the surface of the cathode. Next, we fabricated a cell containing an ion exchange membrane embedded with electrodes consisting of reduced oxides of noble metals bonded with Teflon, and the effects of various factors on the effectiveness of the cell during saline electrolysis, among others the behavior of the cell. Tests were conducted to illustrate the voltage characteristics. Table 2 below shows the effect of various combinations of reduced oxides of noble metals on cell voltage.

That is, cells were fabricated by embedding electrodes made of various combinations of reduced oxides of noble metals bonded with Teflon into a cation exchange membrane with a thickness of 152 μm (6 mm). saline concentration, 200-200
Feed rate of 0cc/min, 3230A/M2 (300A/M2)
The cell was operated at a current density of Ft2) and a temperature of 90°C. One cell was constructed according to the prior art and included a dimensionally stable screen anode spaced from the membrane and a stainless steel screen cathode also spaced from the membrane.

This control cell was also operated under the same conditions. As can be readily seen from these data, the cell of the present invention has an operating voltage in the range of 2.9-3.6V.

When compared to a typical conventional device (cell 4), a voltage improvement of 0.6-1.5V is observed under the same operating conditions. Not to mention the resulting increased operating efficiency and economic benefits. A cell similar to cell 7 in Table 2 was made, and 90
Operated at ℃.

The cell voltage (V) was measured as a function of current density and the results are shown in Table 3. According to these data, it can be seen that as the current density decreases, the cell voltage decreases.

Incidentally, the relationship between current density and cell voltage is determined depending on the balance between operating cost and equipment cost of saline electrolysis. However, when the current density is very large (3230 and 43
It is important to note that even at 10 A/M2 (300 and 400 A/Ft2), the chlorine generator of the present invention shows a significant improvement in cell voltage (on the order of 1 V or more). Table 4 below shows the effect of cathode current efficiency on oxygen evolution.

That is, a cell was prepared by embedding an anode and a cathode consisting of a reduced oxide of a noble metal bound with Tefcan in a cation exchange membrane, and the concentration of saturated saline per square inch (6.45 cd) of electrode area was It was operated at a feed rate of 2-5 cc/min, a current density of 3230 A/M2 (300 A/Ft2), and a temperature of 90<0>C. The volume percentage of oxygen present in the chlorine thus obtained was determined as a function of the current efficiency of the cathode. Table 5 below shows the inhibitory effect that acidification of saline has on the amount of oxygen evolved.

That is, the volume percentage of oxygen present in chlorine was measured relative to the hydrogen chloride (HCl) concentration in the saline solution. As is clear from these data, the generation of oxygen by electrochemical oxidation of back-transferred OH- is reduced by preferentially chemically reacting OH- with H+ to form H2O.
Next, a cell similar to cell 1 in Table 2 was prepared and operated under a current density of 3230 A/M2 (300 A/Ft2) while supplying saturated saline acidified with 0.2 MHC1. .

The cell voltage was measured under various temperatures within the range of 35-9'C.

In addition, a cell similar to cell 7 in Table 2 was prepared, and 2150 A/M2 (200 A/Ft2) was supplied with (unacidified) 2909/l (~5 M) saline solution.
It was operated under a current density of .

Cell voltage was measured under various temperatures within the range of 35-90°C.

The data is 3230A/M2 (300A/Ft2)
It is standardized against. These data show that the best operating voltages are obtained within the temperature range of 80-90°C.

However, it should be noted that compared to a conventional electrolyser operated at 90°C, the voltage obtained for the electrolyzer of the present invention is improved by at least 0.5 V even at 35°C. The highest degree of improvement is achieved when saline electrolysis is carried out in a cell in which both electrodes are joined to the surface of the ion transport membrane.

However, performance improvements are always seen in cells where only one electrode is bonded to the surface of the ion transport membrane (hybrid cells); the improvement in such hybrid cells is slightly greater than when both electrodes are bonded. However, the improvement is quite significant (0.3 to 0.5 V lower than the voltage required for known cells).Therefore, various cells were fabricated and electrolysis of saline water was performed. By doing this, we compared the performance in fully bonded cells (cells with both electrodes bonded) with those in mixed cells (cells with only the anode or cathode bonded) and conventional non-bonded cells (cells with neither electrode bonded). .

Both cells were fabricated using Nafion 315 membranes,
Then, it was operated at a temperature of 90° C. while supplying about 2909/l saline solution. The catalysts used in the junction electrodes were 229/M2 (2f!/Ft2) platinum black for the cathode and 439/M2 (49/Ft2) for the anode.
The RuOx of 2) was graphite or RuOx. 323
The current efficiency under the current density of 0A/M2 (300A/Ft2) was almost the same for all cells (5M
(84-85% under a sodium hydroxide concentration of ).

Table 7 below shows cell voltage characteristics for various cells. As is clear from these data, the cell voltage of the complete junction cell 1 is lower by approximately 1 V than the cell voltage of the conventional (completely non-junction) control cell 6.

In addition, the cathodic junction hybrid cells 2, 3 and the anodic junction hybrid cells 4, 5 are inferior to the fully junction cell by about 0.4 to 0.6 V, but are still 0.3 to 0 V lower than the conventional fully non-junction cell.
．． Only 5V is better. It will be appreciated that the most successful apparatus for generating chlorine and other halogens from saline solutions and halides such as hydrogen chloride (as discussed below) uses contacts bonded directly to and embedded in the cation exchange membrane. This is achieved by reacting the anolyte and catholyte at the electrodes.

Such a configuration provides a significant improvement in the required cell voltage (by more than 1 V) compared to conventional devices as a result of the catalytic sites in the electrode being in direct contact with the membrane and the ion exchange groups therein. A highly efficient device can be obtained. Also,
High potency catalysts consisting of reduced oxides of noble metals thermally stabilized and bonded with fluorinated hydrocarbon resins and low overpotential catalysts consisting of reduced oxides of noble metals and graphite bonded with fluorinated hydrocarbon resins. The efficiency of the device can also be further improved by using Next, we fabricate a cell containing an ion-exchange membrane embedded with electrodes made of thermally stabilized reduced oxides of noble metals, and illustrate the effects of various factors on the effectiveness of the cell and catalyst during hydrochloric acid electrolysis. We conducted a test to find out. Table 8 below shows:
The effect of various combinations of reduced oxides of noble metals on cell voltage is shown.

That is, cells were fabricated by embedding Teflon-bonded graphite electrodes containing various combinations of thermally stabilized reduced acids of platinum group metals and reduced oxides of titanium into a 12 mil thick hydrous cation exchange membrane. did. And 9~
Feed normality of 11N, feed rate of 70cc/min, 43
The above cell (46.5 cd (0.05 ft2) effective cell area) was operated at a current density of 10 A/M2 (400 A/Ft2) and a temperature of 30°C. Tables 9 and 10 below show the effect of time on cell voltage for the same cells operated under the same conditions. Zd Table 11 below shows the effect of feed normality over the range 7.5-10.5N.

That is, reduced oxide of noble metal (Ru-25%Ir)0
8th by adding x to the Teflon-bonded graphite electrode.
A cell similar to Cell 5 in the table was produced. And 150
Feed rate of cc/min, 4310A/M2 (400A/F
The above cell (effective cell area 46.5 c!il (0.05
ft2)) was activated. As is clear from the above examples, when hydrochloric acid is electrolyzed, chlorine gas containing almost no oxygen is generated. The catalysts used in such cells are characterized by low cell voltages and low operating temperatures (~30°C), thus achieving economical operation. Moreover, these data are valid for various current densities, especially from 3230 to
It also shows excellent performance under a current density of 4310 A/M2 (300-400 A/Ft2). This has a clear and beneficial effect on the equipment cost of the electrolyzer for chlorine generation of the present invention. Next, some tests were conducted to demonstrate the effect of thermal stabilization on reduced oxides of noble metals and valve metals. These tests demonstrate the effect on the catalyst's resistance to harsh electrolytic conditions. That is, catalysts consisting of thermally stabilized reduced oxides and non-thermally stabilized reduced oxides were exposed to high concentrations of hydrochloric acid representing extremely harsh environmental conditions. The color of the salt block was observed because the darkening of the hydrochloric acid signified loss of catalyst. The color change became more and more pronounced with increasing loss of catalyst. Table 12 below shows the results of corrosion resistance and stability tests for catalyst batches ranging from 0.5 to 209.

As is clear from these data, thermal stabilization of the reduced oxide improves the corrosion resistance of the catalyst in high concentrations of hydrochloric acid and therefore actually provides excellent safety.

It goes without saying that the catalyst has excellent resistance in chlorine or saline environments, which are less corrosive than that, and this is due to the thermal stabilization of the reduced oxide. Having observed improved corrosion resistance of thermally stabilized reduced oxides of platinum group metals, physical and chemical studies were conducted to determine the effect of thermal stabilization on various properties of the catalyst that may account for such improved corrosion resistance. We conducted a specific test.

That is, the oxide content, surface area (M2/9), total pore volume, and pore size distribution of the catalyst were measured after preparation of the catalyst by a modified Adams method, after reduction of the catalyst, and after thermal stabilization of the reduced catalyst. . The test results, detailed below, show that the surface area of the catalyst decreases slightly after reduction and then very significantly after thermal stabilization. It is believed that the reduction in oxide content during the reduction step partially explains the reduction in surface area. Although the pore size distribution of the catalyst shows a substantial change after thermal stabilization, there is nevertheless no corresponding change in the total pore volume. Therefore, it is believed that this fact is responsible for the extremely significant change (1/2) in surface area that accompanies thermal stabilization. Furthermore, since corrosion is directly related to the surface area exposed to the attack of corrosive agents, the above facts would also seem to explain the improvement in corrosion resistance. First, a catalyst consisting of ruthenium and 25 (by weight) 91) of iridium was prepared as Sample 1 by a modified Adams method.

Sample 2 was prepared by electrochemically reducing a portion of this catalyst. Next, after reduction (Ru-25%Ir)
The 0x sample was heat stabilized at 550-600°C for 1 hour. Unreduced catalyst (sample 1), reduced catalyst (Ru-2
5% 1r) 0x catalyst (sample 2) and after thermal stabilization (
The surface area of the Ru-25% Ir)0x catalyst (Sample 3) was measured by the three-point BET (Brunauer-Emmett-Teller) nitrogen absorption method, and the results (results shown in Table 13 below) The data show that the oxide content decreases after reduction and thermal stabilization as well as the decrease in surface area after reduction and thermal stabilization.The oxide surface area is larger than the non-oxide surface area. As is customary, a reduction in oxide content should have a corresponding effect on surface area. Such a reduction in oxide content partially explains the reduction in surface area, but the dramatic reduction in surface area after thermal stabilization does not completely explain the decrease in
The porosity of the catalyst was measured to determine whether thermal stabilization of the catalyst resulted in a change in porosity resulting in a reduction in surface area and improved corrosion resistance.

A catalyst sample was taken from the same batch as samples 1, 2 and 3;
Then the porosity and particle size distribution were measured. When the particle size distribution was measured by a sedimentation method, it was found that the 50% distribution point of the equivalent spherical diameter was 3.7μ after reduction and 3.1μ after thermal stabilization. Although this indicates that the outer surface of the particles is reduced, it does not explain all of the surface area reduction after thermal stabilization. On the other hand, the total pore volume was determined by the capillary condensation method and the mercury intrusion method.

Data for Samples 1, 2 and 3 are shown in Table 15 below. These data show that the total pore volume is relatively constant.

Therefore, the porosity is almost the same (even if the equivalent sphere diameter and density are calculated and then converted to porosity), and Ru-2
Regarding 5% Ir, it is within the range of 0.7 to 0.8 cc/J. At the same time, the pore size distribution within the range of 40λ to 10μ was measured. For the range 40-500λ, capillary condensation method was used.

According to this method, the pore size distribution is determined by measuring the condensation of a liquid at a given vapor pressure. Such a capillary condensation method has shown a lower measurement limit of 40 people and an upper measurement limit of 500λ. A range of more than 500 people (i.e. 500
Regarding the pores (λ~10μ), the pore size distribution was determined using the mercury intrusion method.

The pore size distribution measurements for these two ranges are shown in Tables 16 and 17 below. These data show that thermal stabilization of the catalyst leads to changes in pore distribution.

Such changes appear to be accompanied by changes in the total number of pores, thereby reducing the total surface area. Judging from the fact that the pore size distribution changes with peaks at 200λ and 1.5μ even though the total pore volume remains almost constant, many of the pores smaller than 40λ coalesce, and therefore the pore size It seems quite clear that the total number has decreased. Moreover, the pore diameter increases at 500 Å or more.
Thus, the pore diameter and internal pore area change with thermal stabilization. In short, when a catalyst is thermally stabilized, the total number of internal pores and therefore the internal pore surface area is reduced. This is believed to be the result of morphological changes that result in a decrease in the total number of pores and an increase in the pore size distribution. After all, it is clear that the decrease in surface area due to thermal stabilization of the catalyst is caused by changes in the internal pore surface area, considering that the pore size distribution changes toward larger values while the total pore volume remains relatively constant. It appears to be. The porosity (expressed in pore volume per unit weight) of catalysts consisting of thermally stabilized reduced oxides of platinum group metals ranges from 0.4 to 1.5 cc/9.

In addition, in the case of a catalyst consisting of thermally stabilized (Ru to 25% Ir) 0x, the preferred porosity is 0.7 to 048 cc/9.
It is. The pore size distribution above 500λ of the thermally stabilized catalyst ranges from 100 to 300λ and 200λ
It has a peak (maximum value) at λ.

Above 500λ, the total pore volume is maximum and the pore size distribution ranges from 0.4 to 9μ, and 1.5μ (
It has a peak (maximum value) at 50% point).

Regarding the surface area of catalysts containing thermally stabilized reduced oxides of platinum group metals, the required catalytic activity can be obtained for any platinum group metal and for any combination of platinum group metals and valve metals, etc. surface area should be kept as small as possible (to inhibit corrosion). That is, the surface area should exceed 10 m2/GO, but preferably ranges from 24 to 165 m2/GO). In addition,
In the case of a catalyst consisting of thermally stabilized (Ru to 25% Ir)Ox, the preferred surface area is 60-70 m2/9. It goes without saying that catalysts consisting of thermally stabilized reduced oxides of platinum group metals have a larger surface area than powders, blacks, etc. (which typically have a surface area of 10-15 m@2 /g). Finally, the oxide content of such catalysts may range from 2 to 25% (by weight), preferably from 13 to 23% (by weight).

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the electrolysis cell of the present invention using a solid polymer electrolyte membrane and a novel catalyst bonded to its surface, and Figure 2 shows the reactions that occur in various parts of the cell during electrolysis of an aqueous halide solution. This is a schematic diagram. In the figure, 10 is an electrolytic cell for halogen generation, 11 is a cathode jacket, 12 is an anode jacket, 13 is an electrolyte membrane, 14 is a cathode, 1
5 and 16 are current collectors, 17 and 18 are gaskets,
19 and 22 are inlet pipes, 20 is an anode chamber, 21 and 23 are outlet pipes, and 24 is a power cable.

Claims (1)

[Claims] 1. An electrolyte comprising a solid polymer ion exchange membrane impermeable to gases and liquids but capable of transporting ions, and at least one of the electrodes is made of platinum, iridium, ruthenium, palladium. a gas- and liquid-permeable catalytic electrode made of at least one conductive reduced oxide of a platinum group metal consisting of osmium, osmium, and their alloys. the catalytic electrode is bonded to one surface of the membrane in the form of particles to form an integral structure of electrolyte and electrode. A combination structure of electrolyte and electrode. 2. The structure according to claim 1, wherein the oxide is bonded to polymer particles. 3. In the structure according to claim 1 or 2, the pore size distribution curve of the thermally stabilized reduced oxide of the platinum group metal contained in the catalyst electrode has a maximum at 200 Å, and the pore size A combination structure of an electrolyte and an electrode, characterized in that the 50% point of distribution is at 1.5μ. 4. The structure of claim 3, wherein the particles have a surface area of at least 60 m^2/g. 5 having an electrolyte consisting of a solid polymeric ion exchange membrane impermeable to gases and liquids but capable of transporting ions, and at least one of the electrodes being made of platinum, iridium, ruthenium, palladium, osmium or alloys thereof; a gas and liquid permeable catalytic electrode made of at least one electrically conductive reduced oxide of a platinum group metal consisting of
In a combined electrolyte and electrode structure, the reduced oxide is thermally stabilized by treatment in the presence of oxygen at high temperature, and the catalytic electrode is bonded to one surface of the membrane in the form of particles. to form an integral electrolyte and electrode structure, wherein the reduced oxide is bound to particles of a polymer, and the catalytic electrode comprises at least one of the following valve metals: titanium, tantalum, niobium, zirconium and hafnium. An electrolyte/electrode combination structure further comprising two thermally stabilized reduced oxides. 6. In the structure according to claim 5, the pore size distribution curve after thermal stabilization of the thermally stabilized reduced oxide of the platinum group metal contained in the catalyst electrode reaches a maximum at 200 Å. A combination structure of an electrolyte and an electrode, characterized in that the 50% point of the pore size distribution is at 1.5μ. 7. A structure according to claim 6, characterized in that the particles have a surface area of at least 60 m^2/g. 8. A conductive, gas- and liquid-permeable catalyst electrode consisting of an aggregate of conductive catalyst particles combined with resin binder particles, in which the catalyst particles are made of a platinum group metal such as platinum, iridium, ruthenium, palladium, osmium, or an alloy thereof. 1. A catalytic electrode, characterized in that the reduced oxide is thermally stabilized by treatment at high temperature in the presence of oxygen. 9. The catalytic electrode according to claim 8, further comprising at least one thermally stabilized reduced oxide of a valve metal consisting of tantalum, titanium, niobium, zirconium and hafnium. .