JP6728776B2 - Catalyst composition, electrode for organic wastewater treatment device, and organic wastewater treatment device - Google Patents

Description

The present invention relates to a catalyst composition, an electrode for an organic wastewater treatment device, and an organic wastewater treatment device.

In recent years, as a method of recovering energy when decomposing organic wastewater such as factory wastewater, domestic wastewater, and sewage, an organic wastewater treatment system using a power-generating microorganism has been attracting attention. Here, the organic wastewater is wastewater containing organic matter, and is also called organic wastewater.

Generally, an activated sludge method, a sprinkling filter method, an anaerobic digestion method, etc. are used for the treatment of organic wastewater. While these methods using microorganisms can treat organic substances efficiently and in a short time and economically, energy for treating sludge generated from microorganisms grown after treating organic wastewater is one of the major problems.

An organic wastewater treatment system using a power-generating microorganism can recover energy by utilizing a function of generating electricity when a microorganism decomposes organic matter in wastewater. Not only that, but the amount of sludge generated is also suppressed because the energy used for the growth of microorganisms is used for power generation. From these things, it is expected as a next-generation organic wastewater treatment system.

Since the power generation function of microorganisms is utilized in this way, a key power generation device is called a microbial fuel cell.

The microbial fuel cell has a configuration in which an anode, an ion permeable membrane (diaphragm), and a cathode are arranged in order. The anode and the cathode are connected by a conducting wire.

In a microbial fuel cell, anaerobic microorganisms are settled or flowed into the surface of the anode, and a liquid containing an organic substance is flown therein. Further, air is caused to flow through the cathode so that the air comes into contact with the cathode. At the anode, protons (H ⁺ ) and electrons (e ⁻ ) are generated when microorganisms decompose organic substances. Protons pass through a proton conductive membrane that is an electrolyte, move to the cathode side, and react with oxygen in the air on the cathode side to generate electricity. As a result, the electric energy flowing through the conducting wire that connects the anode and the cathode can be recovered.

Patent Document 1 discloses a power generation method using surplus sludge, which destroys cell membranes and the like of sludge microorganisms contained in surplus sludge generated by treatment of organic wastewater and serves as a fuel source for a microbial fuel cell. .. Further, in Patent Document 1, the excess sludge is heated in the pretreatment tank, and the pH is maintained at about 1.5 by the added sulfuric acid, and the high concentration obtained in the pretreatment tank. It is also described to send the supernatant water containing the soluble organic components of the above to a microbial fuel cell.

As the cathode used in such a microbial fuel cell, from the viewpoint of system simplicity and cost, generally used is one called an air cathode configured so that oxygen in the air flows into the surface opposite to the electrolyte. The method is adopted. At the air cathode, oxygen reacts with protons and electrons from the anode to generate electricity and contribute to energy recovery. At that time, a catalyst is required to accelerate the above reaction.

Patent Document 2 discloses a microbial fuel cell having an air cathode in which a platinum catalyst is coated on one surface of carbon paper.

JP, 2006-66284, A JP, 2015-41477, A

In the microbial fuel cell, in the process of reducing sludge generated from microorganisms and recovering energy by power generation, the fundamental solution to the pollution and infiltration of air cathode organic wastewater and the deterioration of cathode performance due to electrochemical load Is difficult to do.

The air cathode described in Patent Document 2 has a configuration in which carbon fibers are used as a conductive base material and a catalyst is carried on the carbon fibers. For this reason, there is a possibility that sufficient durability may not be obtained due to contamination and infiltration with organic wastewater and an electrochemical load. Further, since expensive platinum is used, the cost merit of the air cathode cannot be obtained.

An object of the present invention is to improve the durability of a cathode used in a microbial fuel cell.

The present invention is a catalyst composition constituting an electrode used for treating organic wastewater, comprising a catalyst, exfoliated graphite, and a binder, and containing a carbonaceous material containing nitrogen as a catalyst. The content of the catalyst with respect to 100 parts by mass is 10 parts by mass or more and 50 parts by mass or less.

According to the present invention, the durability of the cathode used in the microbial fuel cell can be improved.

It is a schematic block diagram which shows the organic wastewater treatment apparatus which concerns on this invention. It is a graph which shows the evaluation result of the catalyst durability of a catalyst composition.

Hereinafter, an organic wastewater treatment device (microbial fuel cell) using the catalyst composition according to one embodiment of the present invention will be described.

FIG. 1 schematically shows an example of the configuration of an organic wastewater treatment device.

In the figure, an organic wastewater treatment device 100 (microbial fuel cell) includes an anode 101, a cathode 103, and an organic wastewater tank 105. The cathode 103 has a base material and a catalyst. Microorganisms are arranged on the anode 101. An ion permeable film 102 is attached to the surface of the cathode 103. A gas supply unit 104 is provided at the center of the cathode 103. Oxygen or air can be supplied to the gas supply unit 104. That is, the cathode 103 functions as an air cathode. The organic wastewater is continuously supplied from the organic wastewater supply passage 106 to the organic wastewater tank 105, and is discharged from the organic wastewater discharge passage 107. The anode 101 and the cathode 103 are electrically connected by a conductive wire. A load 108 is provided on the conductive wire.

As shown in this figure, in the case of a microbial fuel cell, the cathode 103 is preferably an air cathode.

<Cathode>
The catalyst composition used for the cathode 103 will be described.

The cathode is produced by applying a catalyst composition to a base material and drying.

The catalyst composition uses a carbonaceous material containing nitrogen (nitrogen-containing carbonaceous material) as a catalyst, and further contains exfoliated graphite (exfoliated graphite) and a binder for binding them. By uniformly dispersing the nitrogen-containing carbonaceous material that is the catalyst and the exfoliated graphite in the binder, the contact surface between the catalyst and oxygen in the air is widened, the oxygen reduction reaction is promoted, and the cathode performance is improved. improves. Further, even if carbon of the nitrogen-containing carbonaceous material is corroded in the process of continuous power generation, exfoliated graphite having a stable structure among carbonaceous materials may function as an electron conductor necessary for the oxygen reduction reaction. it can. As a result, the durability of the cathode performance can be improved.

In the present specification, oxygen reduction means either of the reactions represented by the following reaction formulas (1) and (2).

_{O 2 + 2H 2 O + 4e} - → 4OH - ... reaction formula (1)
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O... Reaction formula (2)
The nitrogen-containing carbonaceous material has a structure containing nitrogen in at least a carbon network structure, and it is considered that the oxygen reduction reaction proceeds in the vicinity of the nitrogen. The shape is irregular.

The catalyst may be supported on amorphous amorphous carbon.

The content of nitrogen in the nitrogen-containing carbonaceous material is preferably 0.001 or more and 0.3 or less when the number of carbon atoms in the nitrogen-containing carbonaceous material is 100. When it is 0.001 or more, the oxygen reduction performance is improved. When it is 0.3 or less, the carbon network structure of the catalyst can be maintained, and the reduction of oxygen reduction performance can be suppressed.

The nitrogen-containing carbonaceous material can be further doped with an arbitrary metal element to improve its catalytic performance. Specific examples include transition metals such as Ni, Fe, Co and Cu, and alkali metals such as K, Na, Cs, Mg, Ca, Sr and Ba. Among these, Fe is particularly desirable. These metal elements may be contained alone or in plural. These metal elements play the role of forming catalytically active sites involved in the oxygen reduction reaction in the calcination stage of the catalyst manufacturing process. In particular, when Fe is added as a metal element, it becomes possible to form a catalytically active site that exhibits high oxygen reduction activity.

The content of the metal element contained in the nitrogen-containing carbonaceous material is 0.005 or more and 0.3 or less when the number of carbon atoms contained in the nitrogen-containing carbonaceous material is 100. Is desirable. If it is less than 0.005, the effect is not exhibited, and if it is more than 0.3, the reaction surface area of the catalyst is lowered due to the coagulation and coarsening of the metal, so that the oxygen reduction performance is deteriorated.

The content of the catalyst in the exfoliated graphite is 10 parts by mass or more and 50 parts by mass or less based on 100 parts by mass of the exfoliated graphite. If it is less than 10 parts by mass, the catalytic effect cannot be obtained, and if it is more than 50 parts by mass, the reaction surface area is reduced due to aggregation of the catalysts, and there is a concern that desired performance cannot be obtained.

The catalyst composition of the present invention contains exfoliated graphite. _Exfoliated graphite specifically includes a 50 mass% laser diffraction diameter (X _50dif ) of 8 μm or less, a 50 mass% Stokes diameter (X _50st ) of 3.5 μm or less, and an _exfoliation index (X _50dif /X _50st ). Is exfoliated graphite of 2.2-5.

Here, the 50 mass% laser diffraction diameter (X _50dif ) is measured using a laser diffraction/scattering method, and when the mass cumulative particle size distribution curve is drawn from the small particle size side, the mass cumulative becomes 50%. Corresponds to particle size. The particle size distribution measurement using the laser diffraction method can be performed using a laser diffraction/scattering particle size distribution measurement device (for example, SALD-2100 manufactured by Shimadzu Corporation, Microtrack series MT3300 manufactured by Nikkiso Co., Ltd.).

Further, the 50 mass% Stokes diameter (X _50st ) is a particle diameter obtained from the terminal sedimentation velocity in the liquid phase sedimentation method. The 50 mass% Stokes diameter (X _50st ) can be measured using a centrifugal sedimentation particle size distribution meter (for example, Shimadzu SA-CP-4L).

Here, the _exfoliation index (X _50dif /X _50st ) is an index for evaluating the _exfoliation degree of particles, and is close to 1 when the particles are close to a lump, and is larger than 1 when the _exfoliation progresses. As a result of examination by the present inventor, the thinning index (X _50dif /X _50st ) and the aspect ratio are about 5 when (X _50dif /X _50st ) is 2.2, _{When 50dif} / _X50st ) is 3.0, the aspect ratio is about 10, and when ( _X50dif / _X50st ) is 5.0, the aspect ratio is about 50.

Exfoliated graphite in the present invention, as long as it has a size and exfoliation index within the above range, natural graphite, artificial graphite, quiche graphite, pyrolysis classified by scaly graphite/scaly graphite/earth graphite It may be any of graphite. Among them, crystallinity in the c-axis direction is developed, flaking is promoted by appropriate dry pulverization, and flaky graphite having a high aspect, that is, a large degree of flakyness is obtained, and thus scaly with good crystallinity. Graphite or flake graphite is preferred.

The binder in the present invention binds the uniformly dispersed nitrogen-containing carbonaceous material and exfoliated graphite, and further binds these catalyst compositions to the substrate.

As the binder, for example, styrene resin, styrene butadiene resin, acrylic resin, urethane resin, phenolic resin, glyxal resin, fluororesin, methacrylic resin and the like are suitable, from the viewpoint of adhesion between the catalyst composition and the substrate, Styrene butadiene resin is particularly preferred.

The content of the binder contained in the catalyst composition is preferably 1 part by mass or more and 50 parts by mass or less when the total amount of the nitrogen-containing carbonaceous material and the exfoliated graphite is 100 parts by mass. When it is lower than 1 part by mass, the binder does not spread over the nitrogen-containing carbonaceous material and exfoliated graphite, and it is difficult to obtain the effect as a binder. When it is higher than 50 parts by mass, the nitrogen-containing carbonaceous material which is a catalyst. The material is buried in the binder and the catalytic effect cannot be obtained.

As the base material of the cathode, one having electron conductivity and gas diffusivity is desirable, and for example, porous carbon (porous carbonaceous material) or expanded graphite is used. Here, expanded graphite refers to a material in which a C-axis of graphite is expansion-molded by inserting an expansion agent such as an acid between graphite layers and heating. As the raw material graphite particles of the expanded graphite, generally known artificial graphite such as natural graphite, quiche graphite, and pyrolytic graphite can be used, but in terms of easy availability, natural flake graphite, for example, flake graphite, bain. Graphite is preferable, and the particle size is 80 mesh or more, preferably 50 mesh or more, and the shape having a thick wall and needle shape is preferable because the molding work after expansion can be efficiently performed.

The desirable physical properties of expanded graphite are as follows.

The compressive fracture strength is preferably 750 kg/cm ² or more. The bulk density is desirably 0.05 g / cm ³ or more 1.4 g / cm ³ or less. Low bulk density and strength of the expanded graphite can not be maintained than 0.05 g / cm ^3, a large catalyst becomes difficult to uniformly disperse within than 1.4 g / cm ^3.

The full width at half maximum of the G band measured by Raman spectroscopy of the expanded graphite is preferably 14 cm ^-1 or more and 50 cm ^-1 or less. The R value of Raman spectroscopic analysis of the expanded graphite is preferably 0 or more and 0.5 or less. By using expanded graphite satisfying such a half band width and R value of the G band, it becomes possible to form a catalyst base composite having high oxygen reduction performance. The G band is a Raman spectrum resulting from the high crystallinity of the carbon material, and shows a peak at around 1580 cm ⁻¹ . The R value is the ratio of the spectral intensity of the D band to the G band, and is an index showing the crystallinity of the carbon material. Here, the D band has a peak at around 1350 cm ⁻¹ and is an index showing the amorphousness of the carbon material.

When the cathode according to the present invention is used in an organic wastewater treatment apparatus, since the organic wastewater is used, the wettability of the expanded graphite as a base material may affect the oxygen reduction performance of the cathode. If the hydrophilicity of the expanded graphite that is the base material is too high, the catalyst is immersed in the liquid, and the desired performance cannot be obtained. If the hydrophilicity is low, the conduction of protons inside the base material is hindered, and the desired performance cannot be obtained. In view of these, TiO ₂ , SiO ₂ , Al ₂ O _{3 and the} like may be added in order to impart hydrophilicity to the expanded graphite. In addition, the addition amount at that time is preferably 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the expanded graphite as a base material. If it is less than 0.1% by mass, the effect is not exhibited, and if it is more than 10% by mass, there is a concern that the reaction of the original catalyst may be hindered.

<Anode>
As the base material of the anode, it is desirable to use a medium that easily fixes microorganisms and can efficiently conduct electrons when decomposing organic substances to generate electricity. For example, carbon cloth (carbon woven cloth), carbon paper, carbon felt, porous carbon, a metal mesh, a member obtained by coating a metal mesh with carbon black or carbon fibers, and the like are suitable.

As the electrolyte of the organic wastewater treatment apparatus according to the present invention, the organic wastewater itself may be used, or a proton conductive electrolyte membrane that conducts protons may be used.

The material of the proton conductive electrolyte membrane is not particularly limited. As the proton conductive electrolyte membrane, for example, a fluororesin ion exchange membrane having a sulfonic acid group is used, but other membranes may be used. The sulfonic acid group has high hydrophilicity and retains high cation exchange ability. In addition, a fluororesin-based ion exchange membrane in which only a part is fluorinated or an aromatic hydrocarbon-based membrane can be used as a cheaper material. If a proton conductive electrolyte membrane is used without using organic wastewater as an electrolyte, the cost will increase, but since the protons generated by the reaction at the anode are efficiently supplied to the cathode, it is effective in improving the oxygen reduction performance of the cathode. There is.

Examples of commercially available products of the proton conductive electrolyte membrane include “Nafion ^™ 115” manufactured by DuPont, “NEOSEPTA ^™ CM-1” manufactured by Tokuyama, and “Selemion ^™ CSV” manufactured by Asahi Glass.

The thickness of the proton conductive electrolyte membrane is preferably 10 μm or more and 1 mm or less. If the thickness is less than 10 μm, there is a risk of breaking due to easy breakage. On the other hand, if the thickness is thicker than 1 mm, proton conduction may be hindered.

<Method for producing catalyst composition>
The method for producing a catalyst composition according to the present embodiment includes a catalyst producing step for producing a catalyst and a catalyst composition producing step for producing a catalyst composition by mixing the catalyst, exfoliated graphite and a binder.

In a catalyst manufacturing process for manufacturing a catalyst, a raw material containing a nitrogen compound (organic compound containing nitrogen atoms) serving as a nitrogen source, a carbonaceous material, and a liquid is mixed to prepare a catalyst precursor dispersion liquid, and a catalyst precursor is prepared. By evaporating and removing the liquid contained in the dispersion liquid, a catalyst precursor is prepared and heat treatment is performed. It is desirable to mix an inorganic metal salt with the above raw material.

The nitrogen compound serving as the nitrogen source may be any organic compound containing a nitrogen atom and is not particularly limited regardless of whether the molecular weight is high or low. Examples thereof include a nitrogen-containing heterocyclic compound, a nitrogen-containing aromatic ring compound, amines, imines, nitriles, and nitrogen-containing polymers.

Specifically, pyrrole and its derivatives, diazoles and their derivatives such as pyrazole and imidazole, triazoles and their derivatives, pyridine and its derivatives, diazines and their derivatives such as pyridazine, pyrimidine and pyrazine, triazines, melamine and Triazine derivatives such as cyanuric acid, quinoline, phenanthroline, purine, benzonitrile, aniline, methylamine, ethylamine, dimethylamine, trimethylamine and other aliphatic amines and their derivatives, ethylenediamine, ethanolamine, pyrrolidine, ethyleneimine, acetonitrile, nylon , Polyacrylonitrile, phthalocyanine, porphyrin, riboflavin and the like.

The inorganic metal salt is not particularly limited, but hydroxides, oxides, nitrides, sulfides, carbonides, nitrates, halides, nitrates, sulfates, carbonates and the like can be used.

The solvent that dissolves the nitrogen compound and the inorganic metal salt is not particularly limited, but since the purpose is to uniformly disperse the catalyst in the expanded graphite that is the base material, a solvent that dissolves both the inorganic metal salt and the nitrogen compound. Is desirable. For example, use of water, N-methylpyrrolidone, N-dimethylformamide, N,N-dimethylacetamide, methanol, ethanol, propanol, ethylene glycol, glycerin, dimethyl sulfoxide, tetrahydrofuran, butanol, toluene, xylene, methyl ethyl ketone, acetone, etc. You can

The ratio of the nitrogen compound and the inorganic metal salt is not particularly limited.

The heat treatment may be performed in either an active gas atmosphere such as hydrogen or ammonia, or an inert gas atmosphere such as nitrogen gas or argon gas. Further, the gas species used may be a single type or a combination of two or more types. The heating temperature in the heat treatment may be an appropriate temperature, but is preferably 300° C. or higher and 1000° C. or lower, and more preferably 600° C. or higher and 900° C. or lower. When the nitrogen compound is heat-treated to be carbonized, the temperature is preferably 600° C. or higher in order to carbonize and form a reaction site having conductivity and oxygen reducing ability. If the temperature is lower than 600° C., the carbonization is unsuccessfully progressed, and it is difficult to form a reaction site having a high oxygen reducing ability, and it is difficult to improve conductivity due to carbonization. On the other hand, when the temperature is higher than 1000° C., the crystallinity of carbon becomes high and nitrogen contained in carbon is desorbed, so that the oxygen reducing ability is lowered.

The catalyst produced in this manner can be used as a cathode of an organic wastewater treatment device (microorganism fuel cell), a cathode of a fuel cell, or a variety of organic materials by appropriately selecting a nitrogen compound, an inorganic metal salt, and a heat treatment atmosphere and temperature. It can be used as a catalyst effective for reactions and inorganic reactions. Also, the composition and structure of the catalyst-base composite should be easily confirmed by X-ray photoelectron spectroscopy, inductively coupled plasma emission spectroscopy, fluorescent X-ray analysis, X-ray diffraction analysis, scanning electron microscope, etc. You can

In the catalyst composition manufacturing step of manufacturing the catalyst composition, the above-mentioned catalyst, exfoliated graphite, and binder are uniformly mixed and manufactured in a solvent. The solvent for uniformly mixing is not particularly limited as long as the catalyst, exfoliated graphite and binder are uniformly dispersed, and it may be polar, non-polar, organic, inorganic, acidic or alkaline. For example, water, ammonia, N-methylpyrrolidone, N-dimethylformamide, N,N-dimethylacetamide, methanol, ethanol, propanol, ethylene glycol, glycerin, dimethyl sulfoxide, tetrahydrofuran, butanol, toluene, xylene, methyl ethyl ketone, acetone, etc. Can be used. The ratio of the solid component including the catalyst, exfoliated graphite, and binder to the solvent is not particularly limited.

The catalyst composition thus produced can be a catalyst composition effective for a cathode of an organic wastewater treatment device, a cathode of a fuel cell, various organic reactions and inorganic reactions. Moreover, the composition and structure of the catalyst composition can be easily confirmed by X-ray photoelectron spectroscopy, inductively coupled plasma emission spectroscopy, fluorescent X-ray analysis, X-ray diffraction analysis, scanning electron microscope, and the like. ..

[Examples] Next, examples of the present invention will be specifically described, but the technical scope of the present invention is not limited thereto.

A catalyst composition was produced according to the following examples, and the potential of the working electrode containing the catalyst composition was scanned in the electrolytic solution to accelerate the deterioration of the catalyst composition, and The current value resulting from the oxygen reduction performance was evaluated.

Hereinafter, the catalyst of the example, the catalyst composition containing the catalyst, and the electrode provided with the catalyst composition will be described.

The catalyst was prepared as follows.

First, 2.26 g of riboflavin, 0.81 g of iron (III) nitrate (Fe(NO ₃ ) ₃ ) and 2.0 g of carbon powder (Ketjen Black EC300J, manufactured by Lion Corporation) were added to 100 mL (ml) of pure water. In addition to the above, 10 mL of ethanol was further added to prepare a catalyst precursor dispersion liquid.

Next, the obtained catalyst precursor dispersion liquid was vacuum dried to remove the solvent to prepare a catalyst precursor. Then, the catalyst precursor was put into a quartz boat and heat-treated in a tubular electric furnace. Note that this heat treatment was a treatment of raising the temperature to 800° C. at a temperature rising rate of 10° C./min in a nitrogen atmosphere, and then holding the temperature at 800° C. for 1 hour.

Then, after the heat treatment, the inside of the furnace was cooled to 100° C. to obtain a catalyst powder. As a result of analyzing the composition of the obtained catalyst by X-ray photoelectron spectroscopy, the carbon content was 93.1 atomic %, nitrogen was 1.8 atomic %, oxygen was 4.5 atomic %, and Fe was 0.6 atomic %.

Next, 1.0 g of the catalyst and 10 g of exfoliated graphite were added to and mixed with 23 g of a binder solution containing 3.0% by mass of a styrene-butadiene resin (SBR: binder) to obtain a catalyst composition. ..

10 μL (microliter) of this catalyst composition was applied to a 5 mmφ glassy carbon electrode (base material), and the catalyst composition was vacuum dried to produce an electrode.

The procedure of Example 1 was repeated except that the exfoliated graphite of Example 1 was changed to 5.0 g.

The procedure of Example 1 was repeated, except that the exfoliated graphite of Example 1 was changed to 3.3 g.

The procedure of Example 1 was repeated, except that the exfoliated graphite of Example 1 was changed to 2.5 g.

The procedure of Example 1 was repeated except that the exfoliated graphite of Example 1 was changed to 2.0 g.

(Comparative Example 1)
The procedure of Example 1 was repeated, except that the exfoliated graphite of Example 1 was not added.

(Comparative example 2)
The procedure of Example 1 was repeated, except that the exfoliated graphite of Example 1 was changed to 20 g.
(Comparative example 3)
The procedure of Example 1 was repeated except that the exfoliated graphite of Example 1 was changed to 1.7 g.

(Comparative Example 4)
The procedure of Comparative Example 1 was repeated except that the binder solution containing the styrene-butadiene resin of Comparative Example 1 was changed to 3.6 g of 20% Nafion solution (“Nafion” is a registered trademark).

<Durability evaluation>
A standard three-electrode cell was assembled for the electrodes containing the catalyst compositions obtained in Examples 1, 2, 3, 4, 5 and Comparative Examples 1, 2, 3, 4 and electrochemically applied to the electrodes by potential scanning. The oxygen reduction activity at that time was evaluated by the rotating disk electrode method. Here, as described in Patent Document 1, the electrode of the microbial fuel cell is used under sulfuric acid acidity. Considering this point, the durability test was performed under the condition that the electrode was immersed in an aqueous sulfuric acid solution, as described later.

First, an electrode containing each catalyst composition was used as a working electrode. In addition, a platinum wire was used as the counter electrode and a reversible hydrogen electrode (RHE) electrode was used as the reference electrode to form a three-electrode cell.

In order to evaluate the durability of each electrode, a three-electrode cell was subjected to a potential cycle of 100 mV/sec in a range of 0.2 V to 1.2 V in a 0.5 mmol/L sulfuric acid aqueous solution under oxygen saturation. 1000 cycles were performed at a scanning speed of 1, and the oxygen reduction activity before and after the cycle was evaluated.

The oxygen reduction activity was determined by first conducting a potential cycle from 0 V to 1.2 V in a 0.5 mmol/L sulfuric acid aqueous solution under nitrogen saturation at 100 mV/sec. The catalyst surface was washed by performing 10 cycles at a scanning speed of. Next, while rotating the working electrode at an electrode rotation speed of 400 rpm, one potential cycle was performed in the range of 0 V to 1.1 V, and the background current was measured. Then, the saturated gas was changed from nitrogen to oxygen, and while the oxygen was saturated, the working electrode was rotated at an electrode rotation speed of 400 rpm, and one potential cycle was performed in the range from 0 V to 1.1 V to The oxygen reduction current was measured. The oxygen reduction performance was evaluated by removing the background current from the measured oxygen reduction current and comparing the current values at 0.7 V.

Table 1 shows the results of the oxygen reduction activity retention rates after the cycle tests of Examples 1, 2, 3, 4, 5 and Comparative Examples 1, 2, 3, 4. The oxygen reduction activity retention rate is a value obtained by dividing the oxygen reduction activity after the cycle by the oxygen reduction activity before the cycle test in percentage.

The electrodes using the catalyst compositions of Examples 1 to 5 showed a high durability with an oxygen reduction activity retention rate after the cycle test of 85 to 100%. On the other hand, in Comparative Example 1 in which exfoliated graphite was not added and Comparative Example 4 using Nafion (registered trademark) which is a conventional binder, the results were 48% and 49%, respectively. Further, in Comparative Examples 2 and 3 in which the ratio of the catalyst to the exfoliated graphite was 0.05 and 0.6, they were 45% and 49%, respectively, which were remarkably lower than those of the Examples.

From these results, the cathode electrode using the catalyst composition was prepared by containing the catalyst, exfoliated graphite, and binder, and setting the content of the catalyst to 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of exfoliated graphite. It has been found that the durability of can be improved.

100: organic wastewater treatment device, 101: anode, 102: ion permeable membrane, 103: cathode, organic wastewater/electrolyte layer, 104: gas supply part, 105: organic wastewater tank, 106: organic wastewater supply passage, 107: organic wastewater Discharge path, 108: load.

Claims (8)

A catalyst composition constituting an electrode used for treating organic wastewater,
A catalyst, exfoliated graphite, and a binder,
The catalyst is a nitrogen-containing carbonaceous material containing nitrogen and a metal element,
A raw material containing an organic compound containing a nitrogen atom and containing no metal atom, a carbonaceous material, an inorganic metal salt and a solvent is mixed to prepare a catalyst precursor dispersion liquid, and the solvent contained in the catalyst precursor dispersion liquid. It was produced by drying and removing and heat treating
The organic compound containing the nitrogen atom and not the metal atom is riboflavin,
The inorganic metal salt is iron nitrate,
The catalyst composition, wherein the content of the catalyst is 100 parts by mass or more and 50 parts by mass or less based on 100 parts by mass of the exfoliated graphite. The catalyst composition according to claim 1, wherein
The catalyst composition, wherein the binder includes a styrene-butadiene resin. A catalyst composition according to claim 1 or 2 , wherein
The catalyst composition, wherein the metal element is Fe. A catalyst composition according to any one of claims 1 to 3 , wherein
Further, including an amorphous carbon material,
The catalyst composition, wherein the catalyst is supported on the amorphous carbon material. A catalyst composition according to any one of claims 1 to 4 , and a substrate,
The catalyst composition is an electrode for an organic wastewater treatment device, which is attached to the base material. The electrode for an organic wastewater treatment device according to claim 5 ,
The electrode for an organic wastewater treatment device, wherein the base material is a porous carbonaceous material or expanded graphite. An organic wastewater treatment device comprising the electrode for organic wastewater treatment device according to claim 5 or 6 . The organic wastewater treatment device according to claim 7 ,
The organic wastewater treatment device, wherein the electrode for the organic wastewater treatment device is an air cathode.

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