JP3406399B2 - Electrode for electrochemical and electrolytic method using the electrode - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an electrolytic reaction using an aqueous electrolytic solvent, and efficiently suppresses the generation of oxygen gas and hydrogen gas. Electrochemical electrode for obtaining a product and an electrolysis method using the electrode, more particularly, used for organic electrolysis, an electrochemical electrode and an electrode for obtaining a target organic compound with high selectivity. It relates to the electrolysis method used. 2. Description of the Prior Art Water is without doubt the best electrolytic solvent in view of conductivity, safety, low cost, stability and all other aspects. However, the only problem is that the efficiency of the target electrolytic reaction is reduced due to the simultaneous occurrence of oxygen gas and hydrogen gas due to the electrolytic oxidation and reduction of water itself. This is particularly remarkable in electrolysis using organic molecules that are hydrophobic (water repellent) as compared with water molecules as a starting material, and is a serious problem in the organic electrolysis industry. The use of non-aqueous solvents has long been adopted as a method to solve this problem, but non-aqueous solvents are inferior to water in all of the above points,
There is no practical application of electrolysis using a non-aqueous solvent electrolyte. As a method for suppressing the generation of oxygen gas and hydrogen gas using an aqueous electrolytic solution, a method of performing electrolysis using a hydrophobic electrode has recently been proposed (JP-A-3-131585). However, these techniques have a certain effect on suppressing the generation of oxygen gas and hydrogen gas, but are extremely limited. That is, many electrolysis reactions, particularly electrolysis reactions of organic substances, require an oxygen and hydrogen source, and in most cases, water plays the role. However, in the conventional hydrophobic electrode, since water is excluded from the electrode surface, which is a reaction field of the electrolytic reaction, although it has the effect of suppressing the generation of oxygen gas and hydrogen gas, water, which is essential as a source of oxygen and hydrogen, is not used. Since it is not present on the surface, the reaction selectivity must be reduced due to the occurrence of undesired side reactions, causing the aforementioned problems. As one method for responding to this, there has been disclosed a technique of forming a coating made of a hydrophobic substance and a hydrophilic substance on the surface of an electrode (JP-A-3-56684). However, this electrode is a so-called coated electrode, and the coating film is non-conductive, so that it is necessary to make the film thickness extremely thin. There is a problem of film peeling, and there is a limit. That is, the function cannot be stably exhibited for a long period of time. [0005] In order to preferably carry out the electrolytic reaction, water is used as an electrolytic solvent, the generation of oxygen gas and hydrogen gas by the electrolytic reaction of water itself is suppressed, and water as a source of oxygen and hydrogen essential for the electrolytic reaction is used on the electrode surface. Attracting the reaction substrate (mostly more hydrophobic than water) to the electrode surface,
There are five requirements for maintaining the conductivity and durability of the electrode. In order to satisfy these factors at the same time, the electrodes must have mutually contradictory properties of hydrophobicity, hydrophilicity and electrical conductivity in the body. This is impossible in principle at the molecular level. [0006] The object of the present invention is to combine the above contradictory properties,
It is an object of the present invention to provide an electrochemical electrode having various requirements for preferably performing the above-described electrolytic reaction. [0007] The present invention provides an electrochemical electrode characterized in that three components of a conductive substance, a hydrophobic non-conductive substance and a hydrophilic non-conductive substance are finely dispersed, And an electrode for electrochemical use in which an electrode material composed of the three components is formed on a conductive substrate, and an electrolytic method using these electrodes. Further, the particle size of the three components dispersed is from 0.1
50 μm, and their volume ratio is 1: (0.1 to 0.8
): Desirably (0.1 to 0.8). Hereinafter, the present invention will be described in detail. The electrochemical electrode of the present invention comprises three components of a conductive material, a hydrophobic non-conductive material, and a hydrophilic non-conductive material, and these are finely dispersed in each other. Are formed on a conductive substrate. Examples of the electrode conductive material include metals such as nickel, zinc, lead, and silver, metal oxides and carbon, and examples of the hydrophobic non-conductive material include fluororesin, fluorinated graphite, and fluorinated pitch. Silica gel, alumina, zirconia, polyvinyl alcohol, cellulose and the like can be used as the conductive non-conductive substance. Among the above three substances, a substance having conductivity, that is, a metal, a metal oxide, and carbon causes a predetermined electrolytic reaction as an electrode catalyst, and a substance having hydrophobicity, that is, a fluororesin, fluorinated graphite, and fluorine. Activated pitch or the like attracts a starting material of an electrolysis reaction that is more hydrophobic than water to the surface of the electrode catalyst and participates in the desired electrolysis reaction, and the hydrophilic material, that is, silica gel, alumina, zirconia,
Polyvinyl alcohol, cellulose, and the like attract and secure the water required as the oxygen and hydrogen sources required for the electrolytic reaction to the electrode surface in a state where the water itself is electrolyzed and oxygen and hydrogen gas are not generated. Therefore, when an electrode material having conductivity, hydrophobicity, and hydrophilicity is formed by mixing and mixing particles of the above three types of materials, the electrode material is preferably used as an electrode used in the above-mentioned electrolytic reaction. The condition will be satisfied. In other words, the electrochemical electrode according to the present invention has, at the particle level, contradictory physical properties such as hydrophobicity and hydrophilicity, which are impossible at the molecular level, and also has electrical conductivity in addition to the above physical properties. High current efficiency can be obtained while suppressing generation of gas, and further, the reaction selectivity can be appropriately controlled. Further, the electrode according to the present invention can suppress an increase in the cost of the electrolytic process without substantially increasing the electrolytic voltage. The electrode material is usually formed in a layer on the surface of the electrode substrate, but the electrode material itself may constitute an electrode. In any case, it is necessary that the respective material particles and the like are uniformly dispersed and mixed. For example, the electrode material is constituted by any of the following three types. The respective particles are sufficiently mixed, and if necessary, a small amount of a binder is added, and the mixture is molded into a predetermined shape by pressing and / or heating. In this case, for example, a metal or a metal oxide is used as a conductive material, and hydrophobic non-conductive material particles are used as binders, and 0.1 to 10 μm PTFE particles are used as a binder.
Using silica gel fine particles etc. as a hydrophilic non-conductive substance,
1: (0.1-0.8) :( 0.1-0.8) by volume ratio respectively
Then, a uniform paste-like substance is formed using solvent naphtha as a solvent, applied on an electrode substrate, and sintered at a temperature of about 350 ° C. to form an electrode substance layer on the electrode substrate. 10-1000k to increase strength
g / cm ² may be applied. Alternatively, the paste substance may be put into a mold and molded to form a single electrode. In addition to the binder, graphite fluoride or fluoride pitch may be added as a hydrophobic non-conductive substance. [0013] The paste material in the above method is put into a mold and molded into a sheet, and this sheet is joined to the surface of the electrode substrate in a thin film by hot pressing. The particles of the non-conductive substance are electrodeposited on the electrode substrate together with the conductive substance by a composite plating method. In this case, for example, 100 to 10 g of hydrophobic non-conductive substance particles and hydrophilic non-conductive substance particles of about 0.1 to 50 μm are added to a plating bath usually used for plating metal or metal oxide.
Liter, 1-20 g of cationic or neutral surfactant /
Liters, and perform composite plating under appropriate plating conditions on the electrode substrate surface using an insoluble counter electrode,
An electrode active material layer is formed. EXAMPLES Next, examples relating to the production of an electrode for electrochemical use according to the present invention and electrolysis using the electrode will be described.
The examples do not limit the invention. EXAMPLE 1 _{Ni (NH 2 SO 2) 2} .4H 2 O and 350 g / l,
NiCl ₂ at 30 g / liter, H ₃ BO ₃ at 40 g / liter, C
_{8 F 18 SO 2 NH (CH} 2) 3 N + CH 3 · I - a plating bath containing 4g / l, PTFE (1 primary particles 0.2 [mu] m, 2 primary particles 7
μm) 40 g / l and silica gel (5 μm) were uniformly suspended, and a nickel plate (3 × 3 cm) was used as a working electrode.
This is sandwiched between two platinum counter electrodes, at a temperature of 33 ° C and a current density of 20m.
By applying 2000 coulombs at A / cm ² , composite plating was performed on both sides of the nickel surface. The electrode thus obtained had a nickel plate (electrode No.) on the surface of which a composite plating layer composed of nickel as a conductive substance, PTFE as a hydrophobic non-conductive substance, and silica gel as a hydrophilic non-conductive substance was formed. .1), and the composite plating layer showed high conductivity. Comparative Example 1 The procedure of Example 1 was repeated except that silica gel was removed from the plating bath used in Example 1. Nickel as a conductive substance and a hydrophobic non-conductive substance were formed on the nickel plate surface. Forming a composite plating layer made of PTFE and forming an electrode
No.2 was manufactured. Further, the same operation as in Example 1 was performed except that PTFE was removed from the plating bath used in Example 1, and a composite plating layer comprising nickel as a conductive material and silica gel as a hydrophilic non-conductive material was formed on the surface of a nickel plate. Was formed to produce electrode No. 3. In the same manner as in Example 1 except that silica gel and PTFE were removed from the plating bath used in Example 1, a plating layer made of a conductive material, nickel, was formed on the surface of the nickel plate to form an electrode. No.4 was manufactured. Table 1 shows the comparison between the hydrophobicity of each of the electrodes Nos. 1 to 4 produced in Example 1 and Comparative Example 1 based on the contact angle with water. As can be seen from Table 1, the electrode containing PTFE which is a hydrophobic non-conductive substance has a large contact angle,
In the electrode containing no, the contact angle is small. [Table 1] EXAMPLE 2 Electrode No. 1 having a composite plating layer made of nickel as a conductive substance, PTFE as a hydrophobic non-conductive substance, and silica gel as a hydrophilic non-conductive substance, produced in Example 1. Under the following conditions, using benzaldehyde,
Electrolytic reduction of p-methylbenzaldehyde and butyraldehyde was performed. A solution of 50 mM 1 M sulfuric acid containing 150 mM of one of the above aldehydes (methanol: water = 1:
In 1), the electrode No. 1 was immersed as a cathode, and a platinum electrode was immersed as an anode, and a current of 0.33 F / mol was passed between both electrodes at a current density of 10 mA / cm ² . Thereby, either one of the corresponding reduced dimer and reduced monomer was produced. The results are shown in Table 2. Comparative Example 2 Electrolysis of aldehyde was performed under the same conditions as in Example 2 using the electrodes Nos. 2 to 4 of Comparative Example 1.
As shown in (1), either one or both of the corresponding reduced dimer and reduced monomer were formed. As can be seen from Table 2, the electrode having a composite plating layer composed of nickel, PTFE and silica gel in Example 1 was prepared by reducing 100% selectivity to all three aldehydes with reduced dimer or reduced monomer. Electrolytically synthesized, the current efficiency was as high as 63 to 75%, whereas the electrode of Comparative Example 1 had low current efficiency and poor selectivity in many cases. [Table 2] According to the present invention, there is provided an electrode for electrochemical use wherein three components of a conductive material, a hydrophobic non-conductive material and a hydrophilic non-conductive material are finely dispersed, and the three components are An electrochemical electrode characterized in that a finely dispersed electrode material is formed on a conductive substrate. That is, the electrode substance of the present invention may be used as an electrode as it is, or may be used in the form of a thin film formed on an electrode substrate. The electrode active material of the electrochemical electrode according to the present invention has all the properties of conductivity, hydrophobicity and hydrophilicity. Among these properties, the conductive property has a function of inducing a predetermined electrolytic reaction as an electrode catalyst, and the hydrophobic property attracts a starting material of the electrolytic reaction, which is more hydrophobic than water, to the surface of the electrode catalyst, and the desired electrolysis occurs. The function to participate in the reaction, and the hydrophilicity is secured by attracting water, which is a source of oxygen and hydrogen required for the electrolytic reaction, to the electrode surface in a state where itself is electrolyzed and oxygen and hydrogen gas are not generated. Each has a function. The electrode of the present invention has all of the above-mentioned requirements for favorably carrying out the electrolytic reaction because the substances having the three kinds of properties are mixed at the particle level, that is, water is used as the electrolyte solvent. Suppress the generation of oxygen gas and hydrogen gas due to the electrolytic reaction of water itself, secure water on the electrode surface as a source of oxygen and hydrogen essential for the electrolytic reaction, and use the reaction substrate, which is mostly hydrophobic than water, on the electrode. The electrode of the present invention has the requirements of ensuring attraction on the surface and maintaining conductivity and durability. Therefore, when the electrode of the present invention is used for an electrolytic reaction, particularly for an organic electrolytic reaction, it becomes possible to obtain a target compound with a high reaction selectivity while suppressing the generation of oxygen gas and hydrogen gas, which cannot be achieved by the prior art. . The particle size of the three components, ie, the conductive material, the hydrophobic non-conductive material and the hydrophilic non-conductive material, is from 0.1 to 50 μm.
And their volume ratio is 1: (0.1-0.8) :( 0.
1 to 0.8). As each particle or the like constituting the electrode active material, a metal, a conductive material selected from metal oxides and carbon, a fluororesin, a hydrophobic nonconductive material selected from graphite fluoride and pitch fluoride, and silica gel, When a hydrophilic non-conductive substance selected from alumina, zirconia, polyvinyl alcohol, and cellulose is used, an electrochemical electrode having an optimal function can be provided. Therefore, regardless of which of the above two types of electrochemical electrodes is used, various kinds of electrolytic reactions, particularly electrolytic reactions using an aqueous electrolytic solvent, can be efficiently advanced.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-84387 (JP, A) JP-A-58-123887 (JP, A) JP-A-1-139785 (JP, A) JP-A-4- 83890 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (1)

(57) [Claim 1] An electrochemical electrode characterized in that three components of a conductive material, a hydrophobic non-conductive material and a hydrophilic non-conductive material are finely dispersed. 2. An electrode for electrochemical use wherein an electrode material in which three components of a conductive material, a hydrophobic non-conductive material and a hydrophilic non-conductive material are finely dispersed is formed on a conductive substrate. 3. The particle size of the dispersed three components is from 0.1 μm.
3. The electrode for electrochemical use according to claim 1, wherein the thickness is 50 μm. The composition ratio of the conductive material, the hydrophobic non-conductive material and the hydrophilic non-conductive material is 1: (0.1 to 0.8) by volume:
The electrode for electrochemical use according to claim 1 or 2, wherein (0.1 to 0.8). 5. The conductive material is selected from metals, metal oxides and carbon, the hydrophobic non-conductive material is selected from fluororesins, fluorinated graphite and fluorinated pitch, and the hydrophilic non-conductive materials are silica gel and alumina. 3. The method according to claim 1, wherein said zirconia is selected from the group consisting of zirconia, polyvinyl alcohol and cellulose.
The electrode for electrochemical use according to claim 1. 6. An electrolysis method comprising electrolyzing an electrolytic solution using an electrochemical electrode in which three components of a conductive material, a hydrophobic non-conductive material and a hydrophilic non-conductive material are finely dispersed. 7. An electrolytic solution using an electrochemical electrode in which an electrode material in which three components of a conductive material, a hydrophobic non-conductive material and a hydrophilic non-conductive material are finely dispersed is formed on a conductive substrate. An electrolysis method comprising performing electrolysis.