JP2010144203A - Cathode for hydrogen peroxide production - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for producing hydrogen peroxide with high efficiency even by the use of an acidic electrolyte in the electrode used for electrochemical production of hydrogen peroxide. <P>SOLUTION: A cathode is used for the production of hydrogen peroxide by reducing oxygen on the electrode and is obtained by supporting a conductive carbon oxide obtained by oxidizing a conductive carbon on a conductive base material or the conductive carbon oxide obtained by molding a conductive carbon oxide containing a binder. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cathode for use in the production of electrochemical hydrogen peroxide.

  As an industrial method for producing hydrogen peroxide, an auto-oxidation method using alkylanthraquinone is used. However, since a large amount of organic solvent needs to be added and many by-products and catalysts are deteriorated, there are disadvantages such as requiring various separation steps and regeneration steps. On the other hand, various methods for producing hydrogen peroxide by electrochemically reducing oxygen have been studied (see Patent Document 1).

  The electrochemical method has an advantage that hydrogen peroxide solution can be produced on-site with a simple and safe apparatus. Therefore, many studies have been made mainly by paper makers, but there are the following problems. 1) When an alkaline electrolyte is used and a cation exchange membrane is used for the bipolar membrane, hydrogen peroxide can be obtained with high current efficiency, but theoretically, only hydrogen peroxide water with a high alkali concentration can be obtained, and its application is limited. . 2) When an acidic electrolyte is used, the current efficiency is low, and various electrodes have been studied so far, but the current efficiency is 60% or less (see Patent Documents 2 and 5).

In the method of producing hydrogen peroxide by electrochemically reducing oxygen, when an alkaline electrolyte is used and a cation exchange membrane is used as a diaphragm, the following reaction occurs on the cathode, and the hydrogen peroxide An aqueous solution is produced with high efficiency.
_{O 2 + H 2 O + 2Na} + + 2e - → NaOOH + NaOH (E 0 -0.08V)
However, since 2 equivalents of alkali are mixed in the product liquid with respect to hydrogen peroxide, the aqueous solution has a high alkali concentration and its application is limited.
On the other hand, when an acidic electrolytic solution is used, a reaction of the following formula occurs, and an acidic aqueous solution of hydrogen peroxide is obtained without increasing or decreasing by-products.
O ₂ + 2H ⁺ 2e ⁻ → H ₂ O ₂ (E ⁰ +0.69 V)
However, it is generally said that the current efficiency is lowered because a side reaction such as a reduction reaction to water and a decomposition reaction are likely to occur simultaneously.
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (E ⁰ + 1.23V)
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O (E ⁰ +1.77 V)
2H ₂ O ₂ → 2H ₂ O + O ₂

  In addition, a method for producing hydrogen peroxide from hydrogen and oxygen using a fuel cell system has been proposed (see Non-Patent Document 1). This is because the cation exchange membrane is a diaphragm, the anode side is platinum black, the cathode side is gold mesh or graphite as the catalyst electrode, and oxygen gas is blown into the cathode chamber into which hydrogen gas and hydrochloric acid aqueous solution are introduced into the anode chamber. It produces hydrogen peroxide.

Furthermore, as a method for efficiently generating hydrogen peroxide at a high concentration, an intermediate chamber formed between the inside of the anode and the inside of the cathode, an anode chamber outside the anode, and a cathode chamber outside the cathode are provided. An apparatus that has a three-tank structure, and that the intermediate chamber is further divided into a cathode-side intermediate chamber and an anode-side intermediate chamber by an anion exchange membrane, and an aqueous electrolyte solution is introduced into the cathode-side intermediate chamber and the anode-side intermediate chamber Has been proposed in which hydrogen is supplied to the anode chamber and oxygen is supplied to the cathode chamber to generate hydrogen peroxide or the like in the cathode-side intermediate chamber (see Patent Documents 3 to 5). In these methods, the use of an alkaline electrolyte dramatically improves the reactivity at a high current density of 100 mA / cm ² or more and a maximum hydrogen peroxide accumulation concentration of 8.5% by weight. However, alkaline electrolyte has a high alkali concentration of hydrogen peroxide, and acidic electrolyte has low current efficiency.

US Pat. No. 4,431,494 JP 2007-162033 A JP 2001-236968 A JP-A-2005-76043 JP 2005-281577 A Electrochimica Acta, Vol. 35, no. 2,319,1990

  In a cathode for producing hydrogen peroxide electrochemically by reducing oxygen on a conventional cathode, hydrogen peroxide can be generated efficiently when an alkaline electrolyte is used as the electrolyte. In the case of using an acidic electrolyte, there are problems that the reaction rate is lowered and the current efficiency is low. An object of the present invention is to provide a cathode capable of efficiently producing hydrogen peroxide not only with an alkaline electrolyte but also with an acidic electrolyte in a cathode for producing hydrogen peroxide.

  As a result of intensive studies to solve the above problems, the present inventors have been able to efficiently produce hydrogen peroxide in an acidic electrolyte by using a conductive carbon oxide for the cathode, and in an alkaline electrolyte as well. It has been found that the hydrogen peroxide generation ability is improved. That is, the present invention relates to a cathode for producing hydrogen peroxide by reducing oxygen on an electrode, and using a conductive carbon oxide.

  The cathode for producing hydrogen peroxide according to the present invention has an ability to generate hydrogen peroxide in an alkaline electrolyte as compared with a conventional electrode using graphite, and has a higher reaction rate and efficiency in an acidic electrolyte. Improve and produce hydrogen peroxide with high efficiency. Furthermore, since an acidic electrolyte solution can be applied, it is possible to simplify the device structure by bonding the anode and the cation exchange membrane, thereby shortening the distance between the electrodes and improving the reaction rate. Further, since hydrogen peroxide can be generated in a relatively thin acidic solution, purification is easy, and application to oxidation reagent applications can also be expected.

The present invention is described in detail below.
The cathode of the present invention is an electrode for directly producing hydrogen peroxide electrochemically by reducing oxygen on the cathode. The cathode of the present invention can be used in an electrochemical hydrogen peroxide production apparatus such as a hydrogen peroxide production apparatus by electrolytic synthesis or a hydrogen peroxide production apparatus by a fuel cell system.
An electrode using a conductive carbon oxide is used for the cathode of the present invention. The conductive carbon oxide is obtained by oxidizing conductive carbon.

  As the conductive carbon used as a raw material, various carbon materials having electrical conductivity can be used. However, in order to improve the reaction rate, the contact area with the aqueous solution is increased, and further, in order to prevent gas diffusion, fine particles are used. Conductive carbon is preferred. As such conductive carbon, one kind selected from activated carbon, graphite, carbon black, acetylene black, carbon fiber, vapor grown carbon fiber, carbon nanotube, fullerene, and ketjen black is used alone, or two or more kinds are used. Can be used in combination.

Conductive carbon oxide is obtained by oxidizing the conductive carbon described above. Examples of the oxidation treatment method include air oxidation, sulfuric acid oxidation, nitric acid oxidation, permanganic acid oxidation, and anodic oxidation. For example, when nitric acid oxidation is performed, conductive carbon is oxidized by adding conductive carbon to concentrated nitric acid and stirring. The treated conductive carbon oxide is washed with water, filtered and dried by a conventionally known method to become a conductive carbon oxide used for the electrode.
It is considered that at least a part of the conductive carbon is oxidized by the treatment, and a structure having, for example, a carboxyl group, a hydroxyl group, a lactone ring, or the like is obtained.

  The cathode using the conductive carbon oxide is an electrode used in the present invention. However, in order to use as an electrode, the shape and conductivity as an electrode are required. There is no problem as long as the conductive carbon oxide is obtained by oxidizing electrode-shaped conductive carbon, but when particulate conductive carbon is used, it needs to be processed into an electrode shape.

As a method of processing into an electrode shape, there is a method of supporting conductive carbon oxide particles on a substrate. The substrate is preferably a conductive substrate for use in electrodes. Also, apply conductive carbon oxide to one side of the conductive substrate, and apply oxygen to the coated surface of the conductive carbon oxide without applying conductive carbon oxide to the other side. By providing an oxygen supply surface for supply, an electrode capable of efficiently supplying oxygen is obtained. In this case, a porous conductive substrate is preferably used as the conductive substrate. As the conductive and porous substrate, carbon paper, carbon cloth or the like is preferably used. Thus, when dividing into an oxygen supply part and a reaction part, since a reaction part is immersed in electrolyte solution, it is necessary to isolate electrolyte solution in an electrode surface. Therefore, a substrate that has been subjected to a water repellent treatment is usually used. Water repellent treatment of carbon paper or carbon cloth is generally performed by sintering Teflon (registered trademark) fine particles.
A conductive carbon oxide is applied on a conductive substrate having an arbitrary shape. For bonding the conductive carbon oxide to the substrate, there is a method of using an adhesive. For example, a Nafion solution having high proton conductivity and conductive carbon oxide particles can be suspended, applied onto the substrate, dried, and sintered to be bonded. Thereby, the cathode processed into the electrode shape is completed.

  As another method for processing into an electrode shape, there is a method in which conductive carbon oxide particles are mixed and molded so as to contain a binder. When the conductivity of the conductive carbon oxide is small, conductive carbon particles can also be added. Any binder may be used as long as it can form a conductive carbon oxide and maintain the strength as an electrode. However, when the oxygen supply unit and the reaction unit are separated, since the reaction unit is immersed in the electrolyte solution, it is necessary to isolate the electrolyte solution with the electrode. In this case, a water-repellent binder such as Teflon (registered trademark) particles is used.

  By using the above graphite oxide electrode as a cathode, an anode as a counter electrode, and an electrolyte between both electrodes, a hydrogen peroxide production apparatus is obtained. The electrolyte of the present invention is a liquid electrolyte in which an electrolytic cell is filled with an electrolytic solution, but a solid electrolyte such as Nafion (registered trademark) may be used. When using a liquid electrolyte, an ion exchange membrane is usually installed as a diaphragm in an electrolytic cell. Thereby, it is possible to prevent hydrogen peroxide generated at the cathode from being decomposed at the anode. Hydrogen peroxide is generated regardless of whether the liquid electrolyte is alkaline or acidic. In any case, a cation exchange membrane is preferred as the ion exchange membrane. When an anion exchange membrane is used, hydrogen peroxide tends to pass through the anion exchange membrane in alkalinity, so that the generation efficiency is deteriorated. On the other hand, in the case of acidity, protons in the cathode electrolyte are reduced, so that it is necessary to supply an acid to the cathode electrolyte, and only low concentration hydrogen peroxide can be generated. The cation exchange membrane used here is not particularly limited, but a fluorine-based resin that is durable against an oxidizing agent such as hydrogen peroxide is preferably used.

When hydrogen peroxide is produced by an apparatus having an electrolyte between the cathode and the anode of the present invention and the electrode, an external voltage can be used to supply electrons to the cathode as in an electrolytic reaction. Further, as in the fuel cell system, electrons can be supplied by performing an oxidation reaction at a potential lower than the electrode potential at which oxygen is reduced to hydrogen peroxide at the anode. As an example, the oxidation reaction of hydrogen at the anode is shown.
Alkalinity: H ₂ + 2OH ⁻ → 2H ₂ O + 2e ⁻ (E ⁰ −0.828V)
Acidity: H ₂ → 2H ⁺ + 2e ⁻ (E ⁰ 0.0V)

  The required structure of the anode used for the counter electrode differs between a method of applying an external voltage between the cathode and the anode and a method of using the fuel cell system. In the method of applying an external voltage, the electrolyte is usually electrolyzed at the anode to generate electrons. Examples of the application of the voltage between the cathode and the anode include a method of applying a voltage to both electrodes with a DC power supply, and a method of using a potentiostat and a reference electrode such as Ag / AgCl as shown in FIG. Is not to be done. There are various kinds of anodes that can be used, and platinum electrodes and carbon electrodes are mentioned from the viewpoint of durability. In addition, in order to lower the required voltage, an electrode having a low oxygen generation overvoltage has been intensively studied.

When using a fuel cell system, it is necessary to perform an oxidation reaction at a potential lower than the electrode potential at which oxygen is reduced to hydrogen peroxide at the anode. Oxidation of the raw material at the anode produces protons or cations and electrons. Examples of raw materials capable of such a reaction include hydrogen, methanol, ethanol, and dimethyl ether. Although hydrazine, borohydrides, base metals such as aluminum and the like are possible, they are usually more expensive than hydrogen peroxide. At present, hydrogen or methanol is preferred as a practical raw material. The reaction at both anodes is shown below.
H ₂ → 2H ⁺ + 2e ⁻ (E ⁰ 0.0V)
CH ₃ OH + H ₂ O → 6H ⁺ + 6e ⁻ + CO ₂ (E ⁰ + 0.02V)

  As the electrode catalyst used here, platinum or ruthenium containing platinum or ruthenium is generally used in the case of hydrogen, or in the case of methanol. These catalysts are usually supported on a carbon support. Moreover, since it is preferable to isolate the raw material part from the electrolyte solution side which is a reaction part, the electrode which apply | coated the catalyst to the single side | surface of carbon paper is generally used.

  Examples of the alkaline electrolyte used in the present invention include an aqueous solution of hydroxide such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, an aqueous solution of carbonate such as sodium carbonate and potassium carbonate, and an ammonium salt such as ammonium chloride and ammonium sulfate. Although what filled the electrolytic vessel with aqueous solution and these liquid mixture is mentioned, It is not limited to these. A hydroxide aqueous solution is preferably used as the electrolytic solution having excellent electrical conductivity. Examples of the acidic electrolyte include, but are not limited to, an electrolytic solution in which an electrolytic cell is filled with hydrochloric acid, sulfuric acid, nitric acid and a mixture thereof. Sulfuric acid is preferably used as the electrochemically stable electrolyte.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1
(Oxidation of graphite)
Concentrated nitric acid 383 g was added to 10 g of ketjen black (Lion Corporation EC-600JD), and the mixture was stirred at 48 ° C. for 24 hours. After cooling, it was washed 6 times with 2.5 L of ion exchange water and filtered. The obtained particles were dried under reduced pressure to obtain 10 g of ketjen black oxide.
(Preparation of cathode)
In a round bottom flask, 0.2 g of the above ketjen black oxide was weighed as an electrode catalyst, and the inside of the flask was replaced with argon gas. To this, 1.5 g of isopropanol and 1.0 g of a 5% Nafion solution were added, and the mixture was stirred and dispersed twice by an ultrasonic cleaner to obtain a ketjen black oxide dispersion. Place a water repellent treated carbon paper on the bottom of a 100 ml beaker, put the ketjen black oxide dispersion into this, dry at room temperature on carbon paper (TGP-H-060) manufactured by Toray Industries, and then further at 80 ° C. It was dried for 10 minutes and then heated at 130 ° C. for 1 hour under an argon stream to obtain a ketjen black oxide electrode. From the amount of change in the weight of the carbon paper, the amount of the coating was 0.9 mg / cm ² .

(Preparation of anode)
In a round bottom flask, 0.5 g of 50% platinum / Vulcan (N.E. Chemcat) was weighed as an electrode catalyst, and the inside of the flask was replaced with argon gas. To this, 2.0 g of isopropanol and 1.0 g of a 5% Nafion solution were added, and the mixture was stirred and dispersed twice with an ultrasonic cleaner to obtain a platinum / Vulcan dispersion. Place the water-repellent treated carbon paper on the bottom of a 100 ml beaker, put the platinum / Vulcan dispersion above onto this paper, dry at room temperature on the carbon paper, and then dry at 80 ° C. for another 10 minutes, followed by 130 ° C. under an argon stream. For 1 hour to obtain a platinum / Vulcan electrode. From the weight change amount of the carbon paper, the amount of the coated material was 0.65 mg / cm ² .

(Hydrogen peroxide generation reaction)
Using the reaction cell (inner diameter 2.4 cm) shown in FIG. 1, a cathode chamber, a current collector (see FIG. ² , opening area 3.14 cm ² , thickness 0.2 mm), cathode, cathode side intermediate chamber (thickness 5 mm) ), Nafion 117 membrane (DuPont), anode-side intermediate chamber (thickness 5 mm), anode, current collector (see FIG. ² , opening area 3.14 cm ² , thickness 0.2 mm), stacked with anode chamber, outside Pressed with metal fittings. The cathode chamber, cathode-side intermediate chamber, anode-side intermediate chamber, and anode chamber are made of acrylic, and the current collector plate is gold-plated SUS plate. Subsequently, 20 g of a 2N sodium hydroxide aqueous solution was externally circulated in the cathode side intermediate chamber by a pump, and the 2N sodium hydroxide aqueous solution was continuously supplied to the anode side intermediate chamber at a rate of 10 g / hour. Next, oxygen gas was supplied to the cathode chamber and hydrogen gas was supplied to the anode chamber at 30 ml / min. Here, the voltage between the cathode and the anode was measured and found to be 0.888V. Subsequently, when the anode and the cathode were short-circuited via a non-resistance ammeter (Hokuto Denko HM-104), an average current value of 812 mA was observed. When the cross-sectional area of the reaction cell and the effective area, the current density becomes 180 mA / cm ^2. The reaction was continued for 10 minutes and all the catholyte was collected and found to be 20.2 g. When the catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.41 wt%. That is, the amount of hydrogen peroxide produced is 2.44 mmol. The current efficiency was determined by the following formula and found to be 96%.
Theoretical production amount (mmol) = average current value (mA) × time (seconds) / 96500 (C / mol) / 2
Current efficiency (%) = hydrogen peroxide production (mmol) / theoretical production (mmol) × 100

Example 2
(Production of cathode)
The same operation as in Example 1 was performed.
(Production of anode)
The same operation as in Example 1 was performed.
(Hydrogen peroxide generation reaction)
The same operation as in Example 1 was performed. However, air was allowed to flow through the cathode chamber at 500 ml / min using an air compression device. An average current value of 722 mA was observed. The current density is 160 mA / cm ² . That is, the reaction rate is 89% compared to the oxygen source. The reaction was continued for 10 minutes and all the catholyte was collected to find 20.0 g. When this catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.38 wt%. That is, the amount of hydrogen peroxide produced is 2.24 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 99.6%.
Next, the catholyte was changed to an aqueous solution of 4.0 wt% hydrogen peroxide and 9.4 wt% sodium hydroxide. As a result, the current value was 628 mA. The reaction rate is 77% compared to the result of 0% overwater concentration.

Example 3
(Preparation of cathode)
The same operation as in Example 1 was performed. However, the ketjen black oxide was oxidized in concentrated nitric acid at 50 ° C. for 200 hours to obtain a ketjen black oxide electrode.
(Production of anode)
The same operation as in Example 1 was performed.
(Hydrogen peroxide generation reaction)
The same operation as in Example 1 was performed. However, the above ketjen black oxide electrode was used for the cathode, and 10% sulfuric acid was used for the electrolyte. After the electrolytic solution was filled in the cell, the electrolytic solution was not circulated. After flowing hydrogen and oxygen, the voltage between the cathode and the anode was measured and found to be 0.663V. Subsequently, when the anode and the cathode were short-circuited via a non-resistance ammeter (Hokuto Denko HM-104), an average current value of 155 mA was observed. Assuming that the cross-sectional area of the reaction cell is an effective area, the current density is 34 mA / cm ² . The reaction was continued for 15 minutes, and the catholyte was recovered and found to be 2.46 g. When the catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.79 wt%. That is, the amount of hydrogen peroxide produced is 0.57 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 79%.

Example 4
(Production of cathode)
The same operation as in Example 3 was performed.
(Preparation of anode)
The same operation as in Example 1 was performed.
(Hydrogen peroxide generation reaction)
The reaction cell shown in FIG. 3 was used. That is, the apparatus configuration without the anode-side intermediate chamber of the apparatus of FIG. The Nafion 117 membrane and the anode were adhered in advance by hot pressing at 120 ° C. 10% sulfuric acid was used as the electrolytic solution, and the electrolytic solution was not circulated after filling the cell with the electrolytic solution. Hydrogen and oxygen were circulated. When the anode and the cathode were short-circuited via a non-resistance ammeter (Hokuto Denko HM-104), an average current value of 234 mA was observed. The reaction rate was 151% compared to Example 3. When the cross-sectional area of the reaction cell is an effective area, the current density is 52 mA / cm ² . The reaction was continued for 10 minutes, and the catholyte was recovered and found to be 2.27 g. When this catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.80 wt%. That is, the amount of hydrogen peroxide produced is 0.54 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 78%.

Example 5
(Production of cathode)
The same operation as in Example 1 was performed. However, the ketjen black oxide was oxidized in concentrated nitric acid at 50 ° C. for 100 hours to obtain a ketjen black oxide electrode.
(Preparation of anode)
In a round bottom flask, 0.1 g of carbon black (Tokai Carbon 7100F) was weighed, and the inside of the flask was replaced with argon gas. To this, 2.0 g of isopropanol and 1.0 g of 5% Nafion solution were added, and the mixture was stirred and dispersed twice by an ultrasonic cleaner to obtain a carbon black dispersion. Place the water-repellent treated carbon paper on the bottom of a 100 ml beaker, put the above carbon black dispersion on it, dry at room temperature on the carbon paper, then dry at 80 ° C for another 10 minutes, then at 130 ° C under argon stream A carbon black electrode was obtained by heating for 1 hour. From the amount of change in weight of the carbon paper, the amount of the coating was 0.30 mg / cm ² .

(Hydrogen peroxide generation reaction)
The reaction cell shown in FIG. 4 was used. That is, with the same cell configuration as the apparatus of FIG. 1, a reference electrode was installed in the anode-side intermediate chamber, and both electrodes and the reference electrode were connected to a potentiostat (Hokuto Denko: HA-151A). The above ketjen black oxide electrode was used for the cathode, and the above carbon black electrode was used for the anode. Further, 10% sulfuric acid was used as the electrolytic solution. After the electrolytic solution was filled in the cell, the electrolytic solution was not circulated. Using a potentiostat, the anode potential with respect to the Ag / AgCl reference electrode was set to +2.0 V, and when a voltage was applied between the cathode and the anode, an average current value of 157 mA was observed. When the cross-sectional area of the reaction cell is an effective area, the current density is 35 mA / cm ² . The reaction was continued for 10 minutes, and the catholyte was recovered and found to be 2.44 g. When this catholyte was titrated with an aqueous potassium permanganate solution, the concentration of hydrogen peroxide was 0.55 wt%. That is, the amount of hydrogen peroxide produced is 0.39 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 81%.

Example 6
(Production of cathode)
The same operation as in Example 1 was performed. However, a carbon fiber oxide electrode was obtained by using a carbon fiber powder (Showa Denko) which was oxidized with nitric acid at 100 ° C. for 24 hours as an electrode catalyst.
(Production of anode)
The same operation as in Example 1 was performed.
(Hydrogen peroxide generation reaction)
The same operation as in Example 3 was performed. However, the above carbon fiber oxide electrode was used for the cathode. 10% sulfuric acid was used as the electrolytic solution. An average current of 45 mA was observed. The current density is 10 mA / cm ² . The reaction was continued for 10 minutes, and the catholyte was recovered and found to be 2.50 g. When the catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.18 wt%. That is, the amount of hydrogen peroxide produced is 0.13 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 95%.

Comparative Example 1
(Production of cathode)
A ketjen black electrode was obtained in the same manner as in Example 1 except that ketjen black was used as the electrode catalyst.
(Preparation of anode)
The same operation as in Example 1 was performed.
(Hydrogen peroxide generation reaction)
The same procedure as in Example 1 was performed except that the above ketjen black electrode was used as the cathode.
A current value of 684 mA was observed. The current density is 151 mA / cm ² . The reaction was continued for 11 minutes, and the catholyte was recovered and found to be 20.4 g. When the catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.39 wt%. That is, the amount of hydrogen peroxide produced is 2.34 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 100%.

Comparative Example 2
(Preparation of cathode)
A ketjen black electrode was obtained in the same manner as in Example 2 except that ketjen black was used as the electrode catalyst.
(Production of anode)
The same operation as in Example 2 was performed.
(Hydrogen peroxide generation reaction)
The same procedure as in Example 2 was performed except that the above ketjen black electrode was used as the cathode.
A current value of 566 mA was observed. The current density is 125 mA / cm ² . That is, the reaction rate is 83% compared to the oxygen raw material. The reaction was continued for 10 minutes, and the catholyte was recovered and found to be 20.2 g. When the catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.29 wt%. That is, the amount of hydrogen peroxide produced is 1.72 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 98%.
Next, the catholyte was changed to an aqueous solution of 4.0 wt% hydrogen peroxide and 9.4 wt% sodium hydroxide. As a result, the current value was 475 mA. The reaction rate was 69% compared to the result with a superwater concentration of 0%.

Comparative Example 3
(Preparation of cathode)
A ketjen black electrode was obtained in the same manner as in Example 3 except that ketjen black was used as the electrode catalyst.
(Production of anode)
The same operation as in Example 3 was performed.
(Hydrogen peroxide generation reaction)
The same procedure as in Example 3 was performed except that the above ketjen black electrode was used for the cathode. A current value of 7 mA was observed. When the cross-sectional area of the reaction cell is an effective area, the current density is 1.5 mA / cm ² . The reaction was continued for 10 minutes, and the catholyte was recovered and found to be 2.38 g. When the catholyte was titrated with an aqueous potassium permanganate solution, the hydrogen peroxide concentration was 0.016 wt%. That is, the amount of hydrogen peroxide produced is 0.011 mmol. When the current efficiency was determined in the same manner as in Example 1, it was 51%.

In the case of an alkaline electrolyte, hydrogen peroxide can be generated with a current efficiency of about 95% or more even in the conventional electrode, but the reaction rate decreases when the cathode raw material gas is changed from pure oxygen to air. In the case where ketjen black not subjected to oxidation treatment was used for the cathode of Comparative Example 2, the reaction rate decreased to 83% with respect to the pure oxygen raw material, but the ketjen black oxide of Example 2 was used. In this case, the reaction rate was 89%, and it was found that even if an inexpensive air raw material was used, a decrease in the reaction rate could be suppressed.
Furthermore, the conventional electrode has a problem that when the hydrogen peroxide production reaction proceeds, the hydrogen peroxide concentration in the electrolyte solution increases and the reaction rate further decreases. When the hydrogen peroxide concentration of the catholyte illustrated in Example 2 and Comparative Example 2 was changed to an aqueous solution of 4.0 wt% and sodium hydroxide 9.4 wt%, Example 2 using conductive carbon oxide was used. It was found that the decrease in reaction rate can be suppressed. When the cathode using the conductive carbon oxide of the present invention is used in an apparatus for producing hydrogen peroxide, there is an effect of improving the reduction in reaction rate due to the use of air and the increase in the concentration of hydrogen peroxide, which has been a problem with conventional electrodes.

  When the electrolytic solution was acidic, the reaction rate of the conventional electrode shown in Comparative Example 3 was slow, and the current efficiency was as low as 51%. On the other hand, in Examples 3 to 6 using the conductive carbon oxide of the present invention, the reaction rate was improved and the current efficiency was improved to about 80% or more, and the hydrogen peroxide production with an acidic electrolyte was practical. It became a level. If an acidic electrolyte is applicable, the anode and the cation exchange membrane can be bonded as shown in Example 4, thereby simplifying the device structure and further reducing the distance between the electrodes. The reaction rate can be improved.

1 is a schematic diagram of an apparatus used in Example 1. FIG. 1 is a schematic diagram of a current collector plate used in Example 1. FIG. FIG. 6 is a schematic view of an apparatus used in Example 4. FIG. 6 is a schematic diagram of an apparatus used in Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode chamber 2A Cathode side intermediate chamber 2B Anode side intermediate chamber 3 Cathode chamber 4 Anode 5 Cathode 6 Hydrogen inlet 7 Oxygen (air) inlet 8 Product solution outlet 9 Conductor 10 Ammeter 11 Electrolyte aqueous solution inlet 12 Ion exchange membrane 13 Electrolyte aqueous solution outlet 14 Hydrogen outlet 15 Oxygen (air) outlet 16 Current collector plate 17 Potentiostat 18 Reference electrode (Ag / AgCl)

Claims (9)

  A cathode for producing hydrogen peroxide by reducing oxygen on an electrode, wherein the cathode uses a conductive carbon oxide.   2. The conductive carbon oxide is obtained by oxidizing at least one selected from the group consisting of activated carbon, carbon black, acetylene black, carbon fiber, vapor grown carbon fiber, carbon nanotube, fullerene, and ketjen black. The described cathode.   The cathode according to claim 1 or 2, wherein the cathode has a conductive carbon oxide supported on a conductive substrate.   The cathode according to claim 3, wherein the conductive substrate is carbon paper or carbon cloth.   The cathode according to claim 1 or 2, wherein the cathode is formed by molding a conductive carbon oxide containing a binder.   A method for producing hydrogen peroxide by means of a cathode (1) according to any one of claims 1 to 5, an anode (2) and an apparatus comprising an electrolyte (3) between the cathode and the anode, the cathode (1) And an anode (2), an external voltage is applied, The manufacturing method of hydrogen peroxide characterized by the above-mentioned.   A method for producing hydrogen peroxide with a cathode (1) according to any one of claims 1 to 5, an anode (2) and an apparatus comprising an electrolyte (3) between the cathode and the anode, the anode (2) A method for producing hydrogen peroxide, wherein the oxidation reaction is performed at a potential lower than an electrode potential at which oxygen is reduced to hydrogen peroxide.   8. The method for producing hydrogen peroxide according to claim 7, wherein any one of hydrogen, methanol, ethanol, and dimethyl ether is used for the oxidation reaction of the anode (2).   6. The hydrogen peroxide production apparatus according to claim 1, wherein the cathode (1), the anode (2), and the electrolyte solution (3) are filled between the cathode and the anode.

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