JP2013157178A - Method of manufacturing electrode material whose base substance is carbon and fuel battery using electrode material manufactured by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode material whose base substance is carbon capable of performing oxidation reduction of hydrogen and reduction at noble potential of oxygen with no use of catalyst metal such as platina, and to provide a fuel battery which uses the electrode material manufactured by the method.SOLUTION: A carbon material is processed by ultrasonic radiation in a solution of an arbitrary ratio between hydrophilic organic compound and water. Then, with the carbon material as an electrode, an aqueous solution containing carbamic acid and ethanol is subjected to electrolytic oxidation, and the carbon material, in which a carbon atom on the surface of the carbon material is covalent-bonded to nitrogen-containing functional group and the surface is covalent-bonded to the nitrogen-containing functional group, is subjected to electrolytic reduction treatment in strong acid. And then, it is reacted with sulfuric acid in which sodium nitride is dissolved for diazotation, thereby forming an electrode material whose base substance is the carbon in which diazo group and sulfonic acid group acting as electron suction group are bonded on the surface. An electrode material whose base substance is the above stated carbon is used to constitute a fuel battery.

Description

  The present invention relates to a method for producing a carbon-based electrode material and a fuel cell using the electrode material produced thereby.

  Conventionally, conductive carbon materials have been widely used as battery electrodes, electrochemical sensor electrodes, and the like. However, its catalytic activity is not always satisfactory (see Non-Patent Document 1), and a technology such as catalyst loading has been developed to promote oxidation and reduction of hydrogen.

  For example, Patent Document 1 below discloses a fuel cell electrode in which metal fine particles such as platinum are dispersedly supported on the pore surface walls of a porous carbon film.

JP 2004-335459 A

“Fuel Cell Electrode Catalyst” Akiko Aramata p. 114 Hokkaido University Library Publication Association (2005)

  However, in the above conventional technique, since expensive platinum is used as a catalyst, there is a problem that the cost is increased. Therefore, the above problem can be solved if the oxidation-reduction characteristics of the electrode can be maintained and improved without using an expensive catalyst metal such as platinum.

  An object of the present invention is to provide a method for producing a carbon-based electrode material capable of performing hydrogen oxidation-reduction and oxygen reduction at a noble potential without using a catalyst metal such as platinum, and an electrode material produced thereby. It is to provide a used fuel cell.

  In order to achieve the above object, one embodiment of the present invention is a method for producing a carbon-based electrode material, wherein the carbon material is contained in a solution of an alcohol-containing hydrophilic organic compound and water in an arbitrary ratio. The carbon material after the electrolytic reduction treatment is subjected to the ultrasonic irradiation treatment, the nitrogen-containing functional group is covalently bonded to the surface of the carbon material, the carbon material having the nitrogen-containing functional group covalently bonded to the surface is subjected to electrolytic reduction treatment, Is diazotized by reaction in sulfuric acid in which sodium nitrite is dissolved.

  Further, after the diazotization, each process is repeated in the order of the electrolytic reduction process, the diazotization, and the electrolytic reduction process.

  Further, the hydrophilic organic compound is a lower alcohol including ethanol and propanol.

  Further, an aqueous solution containing a carbamic acid and a hydrophilic organic compound containing a lower alcohol is subjected to electrolytic oxidation using the carbon material as an electrode, thereby covalently bonding a nitrogen-containing functional group to the surface of the carbon material. Features.

  The carbon material may be composed of any of glassy carbon, carbon nanotube, carbon felt, plastic molded carbon, or diamond electrode.

  Another embodiment of the present invention is a fuel cell, characterized in that an electrode material produced by the above-described method for producing an electrode material based on carbon is used for at least one of a hydrogen electrode and an oxygen electrode. To do.

  According to the present invention, there is provided a method for producing a carbon-based electrode material capable of performing hydrogen oxidation-reduction and oxygen reduction at a noble potential without using a catalyst metal such as platinum, and an electrode material produced thereby. The used fuel cell can be obtained.

It is a figure which shows the structural example of the electrolytic oxidation apparatus of the ammonium carbamate aqueous solution. It is a figure which shows the structural example of the apparatus which electrolytically reforms the carbon material which the amino group and the diazo group couple | bonded in strong acid aqueous solution. 6 is a diagram illustrating a configuration example of a fuel cell according to Example 3. FIG. It is a figure which shows the relationship between the output of a fuel cell, and an electric current at the time of using the electrode material produced by changing the mixing ratio of the ammonium carbamate / ethanol / ethanol in the pure aqueous solution in electrolytic oxidation treatment. It is a figure which shows the relationship between the mixing ratio of ethanol, and the maximum output of a fuel cell. It is a figure which shows the relationship between an output when oxygen or air is supplied to the fuel cell using the electrode material in case the mixing ratio of ethanol is 70%. It is a figure which shows the cyclic voltammogram of 1M sulfuric acid aqueous solution at the time of using electrode material (III) for an electrode.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described.

  In this embodiment, the carbon material is subjected to ultrasonic irradiation treatment in a solution of an alcohol-containing hydrophilic organic compound and water in an arbitrary ratio, and a nitrogen-containing functional group is covalently bonded to the surface of the carbon material by electrolytic oxidation treatment. Then, the carbon material having a nitrogen-containing functional group covalently bonded to the surface is subjected to electrolytic reduction treatment, and the carbon material after the electrolytic reduction treatment is reacted with a strong acid in which sodium nitrite is dissolved to diazotize the carbon with the substrate. It is characterized by manufacturing an electrode material.

  The carbon material has conductivity necessary as an electrode material, and graphite or the like is preferable. For example, glassy carbon, carbon nanotube, carbon felt, plastic molded carbon, diamond electrode, or the like can be used.

  Examples of the nitrogen-containing functional group covalently bonded to the carbon atom on the surface of the carbon material include an amino group and a diazo group. In order to covalently bond the amino group and the diazo group to the carbon atom on the surface of the carbon material, the carbon material is used as an electrode, for example, by electrolytically oxidizing an aqueous solution containing carbamic acid and the above hydrophilic organic compound, Directly bonded to carbon atoms on the surface, then decarboxylated to form amino groups, and diazo groups generated by further decarboxylation by binding of the carbamate radicals generated by electrolysis to the amino groups and carbon on the surface of the carbon material. A method of directly introducing into a atom by a covalent bond is preferable.

  As the hydrophilic organic compound, for example, lower alcohols including ethanol and propanol can be used. As the aqueous solution containing the carbamic acid and the hydrophilic organic compound, an aqueous solution of ethanol or the like to which ammonium carbamate, ammonium carbonate, or ammonium hydrogen carbonate is added can be preferably used.

  In this embodiment, when the carbon material is subjected to ultrasonic irradiation treatment in a solution of a hydrophilic organic compound such as ethanol and water in an arbitrary ratio, an aqueous solution containing carbamic acid and the hydrophilic organic compound is subsequently electrolytically oxidized. In addition, an aqueous solution containing carbamic acid is likely to penetrate into the surface of the hydrophobic carbon material. For this reason, the surface area of the carbon material to which the nitrogen-containing functional group is covalently bonded is increased, and the catalytic activity can be improved.

  An example in which an amino group and a diazo group are directly covalently bonded to a carbon atom on the surface of a carbon material by the above process is shown below.

  The structural formula (Chemical Formula 1) shows a partial structure of the carbon material, and the number of hexagonal lattice structures of carbon atoms and the number of amino groups and diazo groups are represented by the structural formula (Chemical Formula 1). It is not limited to those.

  Next, the carbon material having a nitrogen-containing functional group (amino group and diazo group) covalently bonded to the surface is subjected to electrolytic reduction treatment in an aqueous solution. As the strong acid in this case, a strong acid such as sulfuric acid and an aqueous solution such as a phosphate buffer can be used. As a result, when electrolytic reduction is performed in sulfuric acid, an electron-withdrawing group including a sulfonic acid group is introduced into a carbon atom on the surface of the carbon material by covalent bonding.

  The reaction in the case of introducing a sulfonic acid group by electrolytically reducing a carbon material having an amino group and a diazo group bonded to the surface in an aqueous sulfuric acid solution is shown below.

In the above reaction, a carbon material having an amino group and a diazo group bonded to the surface is electrolytically reduced in an aqueous sulfuric acid solution, whereby the diazo group is reduced to an electron donating hydrazino group. At that time, HSO ₃ ⁺ ions formed by cleavage of H ₂ SO ₄ (sulfuric acid) into HSO ₃ ⁺ and OH ⁻ attack the electron-rich carbon atom (C ⁻ ) in the ortho position with respect to the hydrazino group. As a result, a sulfonic acid group is introduced. In this way, the electrode material (I) having a nitrogen-containing functional group (amino group or hydrazino group) and a sulfonic acid group covalently bonded to the surface is produced. The structural formula of this electrode material (I) is shown below.

The electrode material (I) has a hydrazino group bonded to a carbon atom on the surface. In addition, a sulfonic acid group (SO ₃ ⁻ ) is also bonded to the surface carbon atom.

  The electrode material (I) is oxidized in air to become an electrode material (II) shown below.

In the electrode material (II), a diazo group in which a hydrazino group is oxidized is bonded to a surface carbon atom. In addition, a sulfonic acid group (SO ₃ ⁻ ) is also bonded to the surface carbon atom, and the diazo group and the sulfonic acid group are stabilized by forming an ion pair, and the diazo group is reduced by denitrification. It is preventing. Unlike diazo groups, hydrazino groups and azo groups are stable unless oxidized or reduced by electrolysis or oxygen. The diazo group in the following structural formula may be an azo group.

  When the electrode material (II) is reacted in sulfuric acid in which sodium nitrite is dissolved and diazotized, the electrode material (III) is generated.

  The electrode material (III) is an example of a carbon-based electrode material according to this embodiment. In the electrode material (III), the amino group bonded to the carbon atom on the surface is changed to a diazo group by diazotization, and the number of diazo groups is increased as compared with the electrode material (II). Thus, the cyclic voltammogram of the 1M sulfuric acid aqueous solution measured using the electrode material (III) shows that the oxidation-reduction wave of hydrogen was measured using the 1M (mol / liter) sulfuric acid aqueous solution measured using the electrode material (II). As compared with the cyclic voltammogram, the oxygen reduction wave shifts in a noble direction as it increases greatly. This is presumably because the diazo group acts as an electron transfer catalyst site for hydrogen redox and oxygen reduction. The position of the oxygen reduction wave shifts in the base direction due to diazotization with sodium nitrite, but returns to the initial position when similar electrolytic reduction is performed again in sulfuric acid. As a result, it is understood that the ratio of the number of sulfonic acid groups to the number of diazo groups needs to be large in order for the oxygen reduction catalyst site to work effectively. When the electrolytic reduction process is performed again in sulfuric acid after the diazotization, the ratio of the number of sulfonic acid groups to the number of diazo groups can be increased. Furthermore, if the diazotization and the electrolytic reduction treatment are repeated after the above electrolytic reduction treatment, the ratio of the number of sulfonic acid groups to the number of diazo groups can be further increased.

  Since the electrode material based on carbon according to the present embodiment manufactured as described above has improved electrode characteristics such as redox characteristics, etc., an electrode for electrolytic production of hydrogen (electrolysis of water), a fuel cell It is suitable to use for electrodes, electrochemical sensors, oxygen reduction catalyst electrodes, biosensors and the like. When the electrode material based on carbon according to the present embodiment is used as an electrode for a fuel cell, hydrogen reduction and oxygen reduction at a noble potential can be performed without using a catalyst metal such as platinum. . Moreover, when using as an electrode for electrolytic production of hydrogen, it can be used at least for the cathode, but may be used for both the cathode and the anode.

  Examples of the present invention will be described below. However, the present invention is not limited to the examples described below.

Example 1
(1) A nitrogen-containing functional group was covalently bonded to a carbon atom on the surface of the carbon material by the following procedure.

  A carbon felt having a size of 1 × 6 × 0.5 cm was selected as a carbon material, which was immersed in a mixed solution of ethanol and pure water in an arbitrary ratio, and subjected to ultrasonic irradiation treatment for 1 hour. The ultrasonic irradiation apparatus used at this time was Branson 1510.

  Next, 0.1 M (mol / liter) ammonium carbamate / ethanol / pure aqueous solution was electrolytically oxidized using the carbon felt subjected to the ultrasonic irradiation treatment as a working electrode. The ammonium carbamate / ethanol / pure aqueous solution in this case was prepared by dissolving ammonium carbamate in the above mixed solution. The electrolytic oxidation was performed using a silver-silver chloride electrode (Ag / AgCl) as a reference electrode, a potential of +1.1 V (vs. Ag / AgCl), and an electrolysis time of 1 hour.

  FIG. 1 shows a configuration example of the electrolytic oxidation apparatus for the ammonium carbamate aqueous solution. In FIG. 1, 0.1M ammonium carbamate / ethanol / pure aqueous solution is placed as an electrolyte in a plastic container 10 having a diameter of 2.5 cm and a depth of 5 cm, and carbon felt (industrial carbon felt GF manufactured by Nippon Carbon Co., Ltd.) is used as a working electrode 12. -20-5F) having a substantially spherical shape attached to the tip of the platinum wire 14, a platinum wire having a diameter of 0.5 mm as the counter electrode 16, and a silver-silver chloride electrode (Ag / AgCl) as the reference electrode 18 Then, constant potential electrolytic oxidation was performed. Ammonium carbamate used a special grade made by Merck, and ethanol used a special grade made by Wako Pure Chemical Industries.

  The constant potential electrolytic oxidation is performed by using a potentiostat / galvanostat (HA-151 manufactured by Hokuto Denko) as the potentiostat 20, and applying a constant potential (1.1V) to the reference electrode 18 to the working electrode 12. Went for hours. In addition, the ammonium carbamate / ethanol / pure aqueous solution was stirred by the stirrer 22 during constant potential electrolysis. After the electrolytic oxidation treatment, the carbon felt as the working electrode 12 was washed with distilled water to produce a carbon material (structure formula 1 above) in which an amino group and a diazo group, which are nitrogen-containing functional groups, were bonded.

(2) The carbon material (Structural Formula 1) to which the amino group and diazo group were bonded obtained in the above procedure (1) was electrolytically modified in a strong acid aqueous solution by the following procedure.

  FIG. 2 shows a configuration example of an apparatus for electrolytically reforming the above carbon material to which an amino group and a diazo group are bonded in a strong acid aqueous solution. The same elements as those in FIG. In FIG. 2, a working electrode 12 in which a 1M sulfuric acid aqueous solution is placed in a plastic container 10 as an electrolytic solution, and a carbon felt bonded with an amino group and a diazo group obtained in the procedure (1) is attached to the tip of a carbon rod 24, and the procedure described above. Constant potential electrolytic reduction was performed by a three-electrode method using a platinum wire as the counter electrode 16 and a silver-silver chloride electrode as the reference electrode 18 used in (1). As the carbon rod 24, a writing instrument (mechanical pencil) core was used. The sulfuric acid aqueous solution used was 1M sulfuric acid (for volumetric analysis) manufactured by Wako Pure Chemical Industries, Ltd.

  The potentiostatic electrolytic reduction uses a potentiostat / galvanostat (HAB-151 manufactured by Hokuto Denko) as the potentiostat 20, a constant potential (−1.0 V vs. Ag / AgCl) with respect to the working electrode 12 and the reference electrode 18. ) Was applied for 20 hours. In addition, the sulfuric acid aqueous solution was stirred with the stirrer 22 during constant potential electrolysis. When the electrolytic reduction treatment was continued, the electrolytic reduction current flowing between the working electrode 12 and the counter electrode 16 increased, and hydrogen gas was generated from the periphery of the working electrode 12 and oxygen gas was generated violently from the periphery of the counter electrode 16. Thereby, a sulfonic acid group is introduced on the surface of the carbon felt having an amino group and a diazo group bonded to the surface. Further, the diazo group becomes a hydrazino group (see Chemical Formula 2).

  After the electrolytic reduction treatment, the carbon felt as the working electrode 12 is washed with distilled water, and the amino group and hydrazino group, which are nitrogen-containing functional groups, are bonded, and the sulfonic acid group is formed on the surface by electrolytic modification in sulfuric acid. Electrode material (the electrode material (I) (Chemical Formula 3)) covalently bonded to the carbon atoms was prepared.

  Further, the electrode material (I) is oxidized in the air to become an electrode material (II) (Chemical formula 4) in which the hydrazino group becomes a diazo group.

(3) The electrode material (II) obtained in the above procedure (2) was immersed in 1M sulfuric acid in which 0.1M sodium nitrite dissolved in ice for 3 hours for diazotization. Sodium nitrite used Wako Pure Chemical Industries grade 1 grade. Thereby, nitrite ions react with the primary amine bonded to the surface of the electrode material in sulfuric acid to generate a diazo group. As a result, the electrode material (III) (Chemical Formula 5) was produced as an example of an electrode material based on carbon.

(4) The procedures (2) and (3) were repeated once, and then procedure (2) was further performed. As a result, the ratio of the number of sulfonic acid groups to the number of diazo groups covalently bonded to carbon atoms on the surface of the electrode material (III) can be increased.

Example 2
Using the electrode material (III) prepared in Example 1 (ethanol concentration at the time of ultrasonic irradiation treatment is 80% by volume) as an electrode, cyclic voltammetry of 1M sulfuric acid aqueous solution was performed, and cyclic voltammogram was measured. Cyclic voltammetry was performed under the following conditions using an Electrochemical Polarization System HZ-3000 manufactured by Hokuto Denko Corporation.

<Implementation conditions for cyclic voltammetry>
The working electrode 12, to which the carbon rod 24 was connected, the counter electrode 16 of the platinum wire and the silver-silver chloride reference electrode 18 were placed in a 1M sulfuric acid aqueous solution, and the reaction was carried out in a potential range of + 1.0V to -0.4V. The potential sweep rate was 40 mV / sec, and the measurement was performed at room temperature. The potential range was determined each time according to the purpose of the experiment.
FIG. 7 shows a cyclic voltammogram of a 1M sulfuric acid aqueous solution when the electrode material (III) is used for an electrode. In FIG. 7, the vertical axis represents the response current value, and the horizontal axis represents the potential of the electrode material. As shown in FIG. 7, when the electrode material (III) produced in Example 1 is used, it can be seen that a hydrogen oxidation-reduction wave and an oxygen reduction wave appear greatly as a battery.

Example 3
Using the electrode material (III) obtained in Example 1, a fuel cell was produced and a discharge operation was performed.

  FIG. 3 shows a configuration example of the fuel cell according to the third embodiment. The fuel cell used was a minicell marketed by Tsukuba Materials Information Laboratory, and the positive and negative electrodes were composed of the electrode material (III). In FIG. 3, an electrode material (III) is disposed between a current collector 30a provided with a gas introduction pipe 26a and a gas exhaust pipe 28a and a current collector 30b provided with a gas introduction pipe 26b and a gas exhaust pipe 28b. And an oxygen electrode 32 and a hydrogen electrode 34, and a cation exchange membrane 36 (Selemion manufactured by Asahi Glass Co., Ltd.) separating the oxygen electrode 32 and the hydrogen electrode 34, and gaskets 38a and 38b made of fluororesin (PTFE). Is sealed (sealed). The oxygen electrode 32 and the hydrogen electrode 34 were impregnated with 0.1 M phosphate buffer (pH = 7.0).

  The oxygen electrode 32 of the fuel cell configured as described above is supplied with oxygen gas through the gas introduction pipe 26a and the gas exhaust pipe 28a, and the hydrogen electrode 34 is supplied with hydrogen gas through the gas introduction pipe 26b and the gas exhaust pipe 28b. To measure the electromotive force between the lead wires (between the current collector 30a and the current collector 30b) when discharging from a lead wire (not shown) connected to the current collector 30a and the current collector 30b. A power generation test was conducted.

  FIG. 4 shows a fuel in the case of using electrode material (III) prepared by changing the mixing ratio of ammonium carbamate / ethanol / ethanol in a pure aqueous solution in electrolytic oxidation treatment (procedure (1) in Example 1). The relationship between battery output and current is shown. In FIG. 4, the horizontal axis represents the current value (mA), and the vertical axis represents the output (mW) of the fuel cell. Moreover, 0% (A), 20% (B), 50% (C), 60% (D), 70% (E), and 80% (F) are selected as the mixing ratio (volume%) of ethanol. did. In the example of FIG. 4, the gas flow rate supplied to the oxygen electrode 32 and the hydrogen electrode 34 is 5 ml / min for oxygen gas and 2 ml / min for hydrogen gas.

  FIG. 5 shows the relationship between the ethanol mixing ratio and the maximum output of the fuel cell (the peak height of the curve) created from the results of FIG. In FIG. 5, the horizontal axis represents the mixing ratio (volume%) of ethanol, and the vertical axis represents the maximum output (mW) of the fuel cell.

As shown in FIGS. 4 and 5, the maximum output of the fuel cell increases as the mixing ratio of ethanol increases, and the maximum output becomes the highest when the mixing ratio of ethanol is 60%. It can be seen that the maximum output decreases with increase. For example, in the case of A where ethanol is not used, the maximum output is 3 mW, whereas in the case of D where the mixing ratio of ethanol is 60%, the maximum output reaches 53 mW (8.8 mW per cm ² ). . The reason why the output is increased by mixing ethanol is that ethanol penetrates the hydrophobic surface of carbon felt to increase the hydrophilicity and increase the effective surface area to which the active site (nitrogen-containing functional group) binds. Conceivable. On the other hand, when the mixing ratio of ethanol is higher than 60%, the maximum output of the fuel cell is reduced. This is because the solubility of carbamic acid is reduced, so that sufficient amination cannot be performed, and the active site to which the nitrogen-containing functional group is bonded. This is probably because the area has become smaller.

  FIG. 6 shows the relationship between the output and current when oxygen or air is supplied to the fuel cell using the electrode material (III) when the mixing ratio of ethanol is 70%. In FIG. 6, the horizontal axis represents the current value (mA), and the vertical axis represents the output (mW) of the fuel cell. The supply rate in the case of oxygen (pure oxygen) was 5 ml / min, and the supply rate in the case of air was 20 ml / min. The supply amount of hydrogen was 2 ml / min. As shown in FIG. 6, when air is flowed, the output is slightly lower than when oxygen is flowed, but it can be seen that sufficient power can be generated even with air.

  In addition, when a long-term power generation test was carried out with a fuel cell using the electrode material (III) when the mixing ratio of ethanol was 50% and a constant current of 35 mA was applied, the cell voltage increased from the initial 0.550 V to 138. It became 0.540V after the time. As a result, it was found that extremely stable power generation can be performed for a long time.

  DESCRIPTION OF SYMBOLS 10 Plastic container, 12 Working electrode, 14 Platinum wire, 16 Counter electrode, 18 Reference electrode, 20 Potentiostat, 22 Stirrer, 24 Carbon rod, 26a, 26b Gas introduction pipe, 28a, 28b Gas exhaust pipe, 30a, 30b Current collector 32 Oxygen electrode, 34 Hydrogen electrode, 36 Cation exchange membrane, 38a, 38b Gasket.

Claims (6)

The carbon material is subjected to ultrasonic irradiation treatment in a solution of an alcohol-containing hydrophilic organic compound and water in an arbitrary ratio,
Nitrogen-containing functional groups are covalently bonded to the surface of the carbon material,
Electrolytic reduction treatment of a carbon material having a nitrogen-containing functional group covalently bonded to the surface,
The carbon material after the electrolytic reduction is reacted in sulfuric acid in which sodium nitrite is dissolved to be diazotized.
A method for producing a carbon-based electrode material.   2. The carbon-based electrode material manufacturing method according to claim 1, wherein after the diazotization, each treatment is repeated in the order of the electrolytic reduction treatment, the diazotization, and the electrolytic reduction treatment. Manufacturing method of electrode material using as a base.   3. The method for producing a carbon-based electrode material according to claim 1 or 2, wherein the hydrophilic organic compound is a lower alcohol containing ethanol and propanol. Production method.   The method for producing an electrode material based on carbon according to any one of claims 1 to 3, wherein an aqueous solution containing a carbamic acid and a hydrophilic organic compound containing a lower alcohol is used as the electrode. A method for producing a carbon-based electrode material, wherein a nitrogen-containing functional group is covalently bonded to the surface of the carbon material by electrolytic oxidation.   5. The method for producing a carbon-based electrode material according to claim 1, wherein the carbon material is any one of glassy carbon, carbon nanotube, carbon felt, plastic molded carbon, or diamond electrode. A method for producing a carbon-based electrode material, characterized by comprising:   6. A fuel cell comprising the electrode material produced by the method for producing an electrode material based on carbon according to any one of claims 1 to 5 for at least one of a hydrogen electrode and an oxygen electrode. .

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