JP6609862B2 - Carbon catalyst production method, carbon catalyst - Google Patents

Description

  The present invention relates to a carbon catalyst production method and a carbon catalyst obtained by the carbon catalyst production method.

In a fuel cell, platinum is used as a redox reaction catalyst.
However, since platinum is expensive, a catalyst that does not use platinum is being developed.

As a platinum substitute catalyst, a carbon material having catalytic activity has been proposed.
In particular, it is known that a carbon material containing nitrogen has oxygen reduction activity.
For example, it has been proposed to produce a carbon catalyst containing nitrogen by using a precursor polymer compound containing nitrogen and carbonizing the precursor polymer compound (see, for example, Patent Document 1). .)

International Patent Publication No. 2004/112174

The manufacturing method described in Patent Document 1 uses a synthetic polymer such as a polyacrylonitrile polymer compound or a polyimide polymer compound as a precursor polymer compound.
Since synthetic polymers are used, the environment is burdened.
Moreover, as a platinum alternative catalyst, it is desired to have a higher catalytic activity than the carbon catalyst produced by the production method of Patent Document 1.

  In order to solve the above-described problems, the present invention provides a method for producing a carbon catalyst and a carbon catalyst that can reduce environmental burdens and achieve high catalytic activity.

The method for producing a carbon catalyst of the present invention comprises a step of mixing a protein and a metal compound, and then a step of carbonizing the mixture , using egg or soy milk as the protein, and iron or cobalt as the metal. A compound selected from iron chloride, cobalt chloride, iron acetate, and cobalt acetate is used as the metal compound .

The carbon catalyst of the present invention is a carbon catalyst used as a water electrocatalyst, comprising carbon, nitrogen in a substance obtained by carbonizing protein, and iron or cobalt, and sulfuric acid having a concentration of 0.5 M in the electrolytic solution. The absolute value of the reaction starting potential | E _H2 | as a water electrocatalyst , measured with a current of −1 mA / cm ² , is 0.18 to 0.39 V (against a reversible hydrogen electrode). Is.

  According to the above-described method for producing a carbon catalyst of the present invention, after mixing a protein and a metal (iron or cobalt) compound, the mixture is carbonized to contain a large amount of protein-derived nitrogen and have high catalytic activity. It becomes possible to manufacture the carbon catalyst which has.

According to the configuration of the carbon catalyst of the present invention described above, the absolute value | E _H2 | of the reaction start potential as a water electrocatalyst is 0.18 to 0.39 V, and therefore has high catalytic activity.

According to the above-described present invention, a carbon catalyst having high catalytic activity can be obtained.
In addition, since a compound of protein and iron or cobalt is used as a raw material, the burden on the environment can be reduced and the raw material cost can be reduced.

It is a flowchart of one Embodiment of the manufacturing method of the carbon catalyst of this invention. 3 is a voltammogram for evaluating the performance of each sample of Experiment 1 as an oxygen reduction catalyst. 4 is a voltammogram for evaluating the performance of each sample of Experiment 1 as a water electrocatalyst. It is the figure which plotted the value of _EO2 of the sample of the carbon catalyst produced using wool and a synthetic polymer as a raw material, respectively, and the value of nitrogen content of carbon after carbonization. It is a figure which shows the value of _EO2 of each sample of Experiment 3. It is a figure which shows absolute value | _i0.7V | of the current density in 0.7V of each sample of Experiment 3. It is a figure which shows absolute value | _EH2 | of _EH2 of each sample of Experiment 3. It is a figure which shows absolute value | i- _0.5V | of the current density in -0.5V of each sample of Experiment 3. It is a figure which shows the relationship between the measurement result of the cobalt content of each sample of A and B Experiment 4, and evaluation of catalyst activity. It is a figure which shows the relationship between the carbonization temperature of each sample of A, B experiment 5, and the measurement result of evaluation of catalyst activity. It is a figure which shows the relationship between the carbonization temperature of each sample of A, B experiment 5, and the measurement result of evaluation of catalyst activity. It is a figure which shows the relationship between the carbonization temperature of each sample of A, B experiment 5, and the measurement result of evaluation of catalyst activity. It is a figure which shows the relationship between the carbonization temperature of each sample of A, B experiment 5, and the measurement result of evaluation of catalyst activity. It is a figure which shows the relationship between the mixing ratio of the precursor of the carbon catalyst which concerns on this invention, and ketjen black, and the voltammogram for evaluating oxygen reduction catalyst activity. It is a figure which shows the relationship between the mixing ratio of A, B casein and carbon black, and the measurement result of water electrocatalytic activity. It is a figure which shows the relationship between the mixing ratio of A, B casein and carbon black, and the measurement result of oxygen reduction catalyst activity. It is a figure which shows the measured value of evaluation of water electrocatalyst activity of each sample of two types of carbon catalysts from which A and B raw materials differ, and the sample of a mixture. A, B It is a measurement result of the catalyst activity of each sample before and after re-heat treatment. AD is a result of differential thermal analysis of the carbon precursor before carbonization. EG is a result of differential thermal analysis of the carbon precursor before carbonization. 14 is a voltammogram showing a measurement result of water electrocatalytic activity of each sample of Experiment 12. It is a voltammogram which shows the measurement result of the water electrocatalytic activity of the sample which mixed the ketjen black, and the sample which is not mixed. AG is a spectrum of the binding energy of electrons in the 1s orbit of a nitrogen atom obtained by XPS measurement of each sample in Experiment 12.

  The method for producing a carbon catalyst of the present invention uses various proteins to add and mix a metal compound, and carbonize the mixture to produce a carbon catalyst. And iron or cobalt is used as a metal.

Preferably, after carbonization, a step of removing metal (iron or cobalt) is further performed to produce a carbon catalyst. The removal of iron or cobalt can be performed using an acid, for example hydrochloric acid.
By performing the step of removing the metal, at least a part (a part or the whole) of the metal in the mixture at the time of carbonization is removed in the obtained carbon catalyst.

The carbon catalyst of the present invention is a carbon catalyst formed by carbonizing a mixture of various proteins and an iron or cobalt compound.
The carbon catalyst of the present invention contains nitrogen because it is derived from a protein obtained by carbonizing a mixture of a protein and an iron or cobalt compound. In the carbon catalyst of this invention, it is preferable that 2 mass% or more of nitrogen is contained in the carbon catalyst.

And in the carbon catalyst of this invention and the manufacturing method of the carbon catalyst of this invention, as protein, protein-containing fibers, such as wool (wool), cashmere, animal hair and skin, silk, casein, soy milk, a chicken egg, etc. Protein-containing foods can be used.
For protein-containing fibers such as wool, waste fibers or duvets can be used as raw materials. And by using these raw materials, it can be expected to reduce the disposal cost of the waste material.
In protein-containing foods, it is also possible to use cracked eggs or foods that have expired. By using these raw materials, it can be expected to reduce the disposal cost of chicken eggs and food.

In the method for producing a carbon catalyst of the present invention, various iron compounds and cobalt compounds can be used as the iron or cobalt compound. Examples thereof include iron chloride, cobalt chloride, iron nitrate, cobalt nitrate, cobalt acetate, iron sulfate, cobalt sulfate, and cobalt oxide.
More preferably, a water-soluble iron salt or a water-soluble cobalt salt is used as the iron or cobalt compound. By using a water-soluble salt, mixing with protein can be performed easily and more uniformly. Examples of the water-soluble iron salt and the water-soluble cobalt salt include chlorides, nitrates, acetates, and sulfates of the above-described iron or cobalt compounds.
Further, when a water-soluble protein is used as the protein, the protein and the iron salt or cobalt salt can be mixed uniformly. Moreover, the mixing ratio of protein and metal salt (iron salt or cobalt salt) can be freely changed.

In the method for producing a carbon catalyst of the present invention, the carbonization temperature is preferably 800 to 1200 ° C.
Moreover, it is preferable that the mixing ratio of the compound of protein, iron, or cobalt is 1-15 mass parts with respect to 100 mass parts of proteins, and the metal component of iron or cobalt in a compound is 3-5 mass parts. It is more preferable.

According to the method for producing a carbon catalyst of the present invention, by performing carbonization after mixing a protein and an iron or cobalt compound, a carbon catalyst containing a large amount of protein-derived nitrogen and having high catalytic activity is obtained. can get.
Further, by performing carbonization after mixing the protein and the iron or cobalt compound, higher catalytic activity can be obtained as compared with the case where only the protein is carbonized. Even if iron or cobalt is removed by acid treatment after carbonization, high catalytic activity can be obtained. This is presumably because an interaction with the protein occurs due to the presence of an iron or cobalt compound during carbonization.
In addition, when carbonization is performed after mixing a protein and an iron or cobalt compound, the carbonization is performed by mixing a nitrogen-containing synthetic polymer (for example, polyacrylonitrile) and an iron or cobalt compound. In comparison, higher catalytic activity is obtained. This is because the nitrogen content after carbonization is higher than when carbonized by mixing a synthetic polymer containing nitrogen and an iron or cobalt compound. This is probably because many of them remain.
Further, by using iron or cobalt, higher catalytic activity can be obtained as compared with the case where a metal other than iron and cobalt (calcium, magnesium, nickel, titanium, etc.) is used.
Moreover, since the compound of protein and iron or cobalt is used as a raw material, compared with the case where a synthetic polymer is used, the load to an environment can be reduced and the raw material cost can be reduced.

Furthermore, the carbon catalyst obtained by the production method of the present invention exhibits high activity in terms of activity as an oxygen reduction catalyst and activity as a water electrolysis catalyst.
Thereby, oxygen reduction and water electrolysis can be performed with the same carbon catalyst.

  In particular, when cobalt is used, the activity as a water electrolysis catalyst is further increased as compared with the case where iron is used.

In addition, about the carbon catalyst based on this invention produced from the mixture of wool and a metal salt, and the carbon catalyst produced from the mixture of the phenol resin which is a synthetic polymer, and a metal phthalocyanine, X-ray-diffraction measurement and an X-ray-spectral-analysis apparatus (XPS) ) Spectrum measurement revealed that the structure of the carbon catalyst and the state of the nitrogen atom were different.
From the results of X-ray diffraction measurement, it was found that the carbon catalyst prepared from a mixture of wool and a metal salt does not have a nanoshell structure like a carbon catalyst prepared from a mixture of a phenol resin and a metal phthalocyanine.
Moreover, from the measurement result of the spectrum by XPS, it was found that the N1s spectrum was different between a carbon catalyst prepared from a mixture of wool and a metal salt and a carbon catalyst prepared by carbonizing only wool.

In addition, a carbon catalyst obtained by carbonizing a mixture of a protein and a metal salt has a smaller carbon 002 plane spacing required by X-ray diffraction measurement than a carbon catalyst obtained by carbonizing a protein alone. all right. Even when the metal is removed after carbonization, the 002 plane spacing remains small.
Therefore, it can be determined from the 002 plane spacing that a metal salt is used during carbonization.

  Next, an embodiment of the carbon catalyst production method of the present invention will be described. A flowchart of an embodiment of the method for producing a carbon catalyst of the present invention is shown in FIG.

First, in step S1 of FIG. 1, a protein and an aqueous solution of a metal salt or a suspension of a metal compound are mixed. As the metal salt, the aforementioned iron or cobalt salt is used.
Of the metal compounds (iron and cobalt compounds), for example, CoO is not dissolved in water, so it is a suspension.
Since fibers such as wool do not dissolve in water, when fibers are used as proteins, the fibers are dispersed in an aqueous solution or suspension.

Next, in step S2, it is dried to remove moisture.
The drying method is not particularly limited, and any drying method such as air drying, hot air drying, reduced pressure drying, freeze drying and the like can be used.

Thereafter, in step S3, a carbonization process is performed.
Next, in step S4, the carbonized material is pulverized using a ball mill or the like.

In step S5, the pulverized product is acid-treated. For example, the treatment for 2 hours at 70 ° C. is repeated 3 times using 1 M hydrochloric acid.
By this acid treatment step, the metal salt or metal compound mixed in step S1 is removed.

  In this way, a carbon catalyst can be produced from protein.

  A carbon catalyst was actually produced, and various characteristics such as catalytic activity were examined.

<Experiment 1>
Characteristics such as catalytic activity were compared between the case of carbonization by mixing metal salts and the case of carbonization of only proteins without mixing metal salts.

Example 1
Wool and aqueous cobalt chloride solution were mixed using wool (wool) as protein and cobalt chloride (CoCl ₂ ) as metal salt. The mixing ratio was 5 parts by mass of metal in the metal salt (cobalt chloride) with respect to 100 parts by mass of protein.
After drying, carbonization was performed. The carbonization temperature was set to 1000 ° C., and the carbonization was carried out by holding at 1000 ° C. for 1 hour in a nitrogen stream.
After carbonization, it was pulverized with a ball mill.
Next, the acid treatment with 1 M hydrochloric acid at 70 ° C. for 2 hours was repeated three times to remove cobalt.
Thus, the sample of Example 1 was obtained.
Hereinafter, this sample is referred to as “wool-CoCl ₂ -1000”.
In addition, about other samples, a sample is described similarly with a raw material (protein or synthetic polymer), a metal salt, and carbonization temperature.

(Comparative Example 1)
The wool (wool) was carbonized. The carbonization temperature was set to 1000 ° C., and the carbonization was carried out by holding at 1000 ° C. for 1 hour in a nitrogen stream.
After carbonization, it was pulverized with a ball mill.
In this way, a sample of Comparative Example 1 was obtained.
Hereinafter, this sample is described as “wool-1000”.

(Evaluation of catalyst performance)
About each sample, the performance as an oxygen reduction catalyst and the performance as a water electrolysis catalyst were evaluated.
Using a potentiostat (ALS 700 series) and its accessory rotating ring disk electrode (RRDE manufactured by BAS), sulfuric acid with a concentration of 0.5M was used as the electrolyte, and the counter electrode was made into glassy carbon. With the reference electrode as a reversible hydrogen electrode (RHE), the performance of each catalyst was evaluated at room temperature and at an electrode rotational speed of 1500 rpm.

The evaluation of the performance as an oxygen reduction catalyst was carried out using a scanning range of 1 to 0 V vs. As RHE, a voltammogram, a potential at which a current of −10 μA / cm ² starts to flow (reaction starting potential) E _O2, and an absolute value | i _0.7V | of the current density at a voltage of 0.7 V were measured.
The voltammogram of each sample is shown in FIG. 2, and E _O2 and | i _{0.7 V} | are shown in Table 1.

The reaction start potential E _O2 indicates that the higher the value, the higher the performance of the catalyst.
The absolute value | i _0.7V | of the current density at a voltage of 0.7V indicates that the higher the value, the higher the performance of the catalyst.
From FIG. 2 and Table 1, it can be seen that the catalytic activity is improved by adding a metal salt (CoCl ₂ ) to wool.

Evaluation of the performance as a water electrocatalyst was performed by changing the scanning range from 0 to 1 V vs. As RHE, a voltammogram, a potential E _{H2 at} which a current of −1 mA / cm ² starts to flow, and a current density i _{−0.5 V} at a voltage of −0.5 V were measured.
The voltammogram of each sample is shown in FIG. 3, and E _H2 and i _{−0.5 V} are shown in Table 2.

The potential E _{H2 at which} a current of −1 mA / cm ² starts to flow indicates that the smaller the absolute value, the higher the performance of the catalyst.
The current density i _−0.5 V at a voltage of −0.5 V indicates that the higher the absolute value, the higher the performance of the catalyst.
From FIG. 3 and Table 2, it can be seen that the catalytic activity is improved when a metal salt (CoCl ₂ ) is added to the wool and carbonized.

<Experiment 2>
A variety of proteins, nitrogen-containing synthetic polymers, and metal salts were prepared to prepare carbon catalysts.
As the protein, wool (wool), dog hair, cashmere, high nitrogen-containing casein, silk, chicken egg, soy milk, feathers, cowhide, and gelatin were prepared. As the wool, Merino top wool was used. The hair of the dog was used after washing the hair loss of a Golden Retriever dog. As the high nitrogen content casein, MP Biomedicals (from milk) was used. The soy milk was lyophilized from Kibun non-adjusted soy milk. As the gelatin, Wako Pure Chemical gelatin was used as it was.
As a synthetic polymer containing nitrogen, polyacrylonitrile and a phenol resin were prepared.
For the metal salt, CoCl ₂ , FeCl ₃ , Co (NO ₃ ) ₂ , Fe (NO ₃ ) ₃ , Co (CH ₃ COO) ₂ , Fe ₂ (SO ₄ ) ₃ are prepared as iron or cobalt salts, As other metal salts, CaCl ₂ , ZnCl ₂ , ZrCl ₄ , TiCl ₄ , SnCl ₂ , Ni (NO ₃ ) ₂ , and MgSO ₄ were prepared.
Also, cobalt phthalocyanine (CoPc) and iron phthalocyanine (FePc) were prepared for mixing with the synthetic polymer.

Here, the nitrogen content as a precursor before carbonization is shown in Table 3 for some of the above-described various proteins, synthetic polymers, mixtures of proteins and metal salts, and mixtures of synthetic polymers and phthalocyanines. Shown in
In the numerical values in Table 3, the nitrogen content of polyacrylonitrile-FePc, phenol resin-CoPc, and phenol resin-FePc is calculated on the assumption that a metal is added at a mass ratio of 3 to the synthetic polymer 100. The nitrogen content of the metal salt is calculated assuming that 5 parts by mass of metal in the metal salt is mixed with 100 parts by mass of wool.

Phenol resin does not contain nitrogen, and polyacrylonitrile contains a large amount of nitrogen.
Wool and casein contain more than 10% nitrogen.

Using the above-mentioned various raw materials, precursors before carbonization were prepared using protein alone, a mixture of protein and metal salt, and a mixture of synthetic polymer and metal phthalocyanine, respectively. The mixing ratio of protein and metal salt was 5 parts by mass of metal in the metal salt with respect to 100 parts by mass of protein.
And using each precursor, the sample of the carbon catalyst was produced according to the process of Example 1 of Experiment 1, or Comparative Example 1. For some of the precursors, samples with a carbonization temperature of 800 ° C. were prepared.
About each produced sample, _EO2 was measured like Experiment 1, and the nitrogen content of carbon was measured with the X ray photoelectron analyzer about a part of sample.
The measurement results are shown in Tables 4 and 5. Table 4 shows the result of the sample of the carbon catalyst according to the present invention, and Table 5 shows the result of the sample of other carbon catalyst (protein alone, using a metal salt other than iron or cobalt, using a synthetic polymer). .

As can be seen from Table 4, in the carbon catalyst sample according to the present invention, E _O2 is as high as 0.80 or more.
As can be seen from Table 5, when a protein alone or a metal salt other than iron or cobalt is used, E _O2 is a low value of less than 0.80.
In addition, when a synthetic polymer is used, E _O2 is about the same or lower than that of the sample of the carbon catalyst according to the present invention.
Furthermore, when Table 3 and Table 5 are compared about nitrogen content, when a synthetic polymer is used, nitrogen content has decreased before and after carbonization, and it has decreased remarkably especially in the case of polyacrylonitrile. I understand that.

Samples of carbon catalysts prepared using wool and synthetic polymer as raw materials described in Table 4 and Table 5, respectively, and carbon catalyst samples prepared using the same raw materials and metals as those samples. The value of _O2 and the nitrogen content of carbon after carbonization were measured. The two values for each sample are plotted and shown in FIG.
As can be seen from FIG. 4, wool-iron and wool-cobalt contain a certain amount (2% by mass or more) of nitrogen, and the content of nitrogen is higher than when synthetic polymer is used as a raw material. The value of E _O2 is as high as 0.8 V or higher.

<Experiment 3>
Example 1 of Experiment 1 with respect to each sample shown in Table 3 to Table 5 of Experiment 2 and FIG. 4 and a sample in which 100 parts by mass of protein other than silk or wool and 5 parts by mass of metal in a metal salt were mixed. Samples of carbon catalyst were prepared following the steps of No. 1 and Comparative Example 1.
For each sample prepared, evaluated similarly oxygen reduction catalyst activity as in Experiment 1 to measure the current density with a value and 0.7V of E _O2. The value of _{EO 2} of each sample is shown in FIG. 5, and the absolute value | i _0.7V | of the current density at 0.7 V of each sample is shown in FIG.
Also, for each sample prepared, evaluated similarly water electrolysis reaction catalyst activity as in Experiment 1 to measure the current density with a value and -0.5V of E _H2. The absolute value of _{E H2} of each sample _{| E H2} | is shown in Figure 7, the absolute value of the current density at -0.5V for each sample _| showing the Figure 8 | _{i -0.5V.}
In FIG. 5 to FIG. 8, the measured values of the sample carbonized with the protein alone are distinguished by attaching an asterisk (*) at the end of the bar graph.

E _O2 in FIG. 5, the catalyst larger value means that a high performance.
From the results of FIG. 5, it can be seen that a carbon catalyst having a high oxygen reduction catalytic activity can be obtained by mixing and carbonizing a protein and a metal salt.

The absolute value | i _0.7V | of the current density in FIG. 6 means that the larger the absolute value, the higher the performance of the catalyst.
From the results of FIG. 6, it can be seen that the sample carbonized by mixing the protein and the metal salt shows a higher current density in the oxygen reduction reaction than the sample carbonized by the protein alone. In particular, when iron or cobalt is used for the metal salt, it is remarkable. It should be noted that soymilk shows a high current density even when carbonized alone, but this is considered to be due to the fact that soymilk contains a metal compound.

| E _H2 | in FIG. 7 means that the smaller the absolute value, the higher the performance of the catalyst.
From the results of FIG. 7, it can be seen that a carbon catalyst having a high water electrolysis reaction catalytic activity can be obtained by mixing and carbonizing a protein and a metal salt. In particular, it can be seen that the effect is large when a cobalt salt is used as the metal salt, and the effect is small when other metal salts are used.

The absolute value | i− _0.5V | of the current density in FIG. 8 means that the higher the absolute value, the higher the performance of the catalyst.
From the results shown in FIG. 8, it can be seen that a carbon catalyst having high water electrolysis reaction catalytic activity can be obtained by mixing and carbonizing a protein and a metal salt. It can be seen that the effect is particularly great when a cobalt salt is used as the metal salt.
Further, comparing FIG. 7 and FIG. 8, it can be seen that the influence of the addition of the metal salt is larger than the potential in terms of current, and that the effect is particularly remarkable when a cobalt salt is used as the metal salt.

<Experiment 4>
The catalytic activity was evaluated by changing the addition amount of the metal salt, and the appropriate addition amount was examined.
Water-soluble casein was used as the protein, and water-soluble cobalt chloride was used as the metal salt so that they could be mixed in a uniform ratio.
As for the mixing ratio, cobalt chloride was added so that the content of metallic cobalt was 1 g, 3 g, 5 g, and 10 g with respect to 100 g of casein.
Casein and cobalt chloride were mixed with each other, and the dried mixture was carbonized at 1000 ° C. for 1 hour in the same manner as in Experiment 1. Then, acid treatment was performed to remove cobalt to prepare a sample of a carbon catalyst.

About the obtained carbon catalyst sample, as an evaluation of the oxygen reduction catalytic activity, the value of E _O2 , a current density of 0.7 V, and a current density of 0.5 V were measured, respectively, and as an evaluation of the water electrolysis reaction catalytic activity, the current density of the current density and -0.4V value of E _H2 and -0.5V were measured.
FIG. 9A shows the relationship between the cobalt content of each sample and the measurement result of the evaluation of the oxygen reduction catalytic activity. FIG. 9B shows the relationship between the cobalt content of each sample and the measurement result of the evaluation of the water electrolysis reaction catalytic activity. Shown in In addition, in FIG. 9A and FIG. 9B, each measured value is shown by the absolute value. The measured value of E _H2 indicates that the smaller the absolute value, the higher the performance of the catalyst, and the other measured value indicates that the higher the absolute value, the higher the performance of the catalyst.

9A and 9B show that E _O2 and E _H2 hardly depend on the concentration of the metal, but the current density is lower than the other samples when the metal is 1 g.
Therefore, when mixing casein and a cobalt salt, it is desirable to mix a cobalt salt so that metallic cobalt may be 3-5g per 100g of casein. This is because the effect does not change even if the cobalt salt is added in excess of 5 g.

<Experiment 5>
The catalyst activity was evaluated by changing the temperature of the carbonization process, and an appropriate carbonization temperature was examined.
Wool was used as the protein, and CoCl ₂ , Co (NO ₃ ) ₂ , FeCl ₃ , and Fe (NO ₃ ) ₃ were used as the metal salts, respectively.
The mixing ratio was 5 parts by mass of metal in the metal salt with respect to 100 parts by mass of wool.
A plurality of each sample was prepared, and the carbonization temperature was changed to 800 ° C., 900 ° C., 1000 ° C., 1100 ° C., and 1200 ° C., and the carbon catalyst sample was prepared in the same manner as in Experiment 1.

About the obtained carbon catalyst sample, as an evaluation of the oxygen reduction catalytic activity, the value of E _O2 , a current density of 0.7 V, and a current density of 0.5 V were measured, respectively, and as an evaluation of the water electrolysis reaction catalytic activity, the current density of the current density and -0.4V value of E _H2 and -0.5V were measured.
The measurement results when CoCl ₂ is used are shown in FIGS. 10A and 10B, the measurement results when Co (NO ₃ ) ₂ is used are shown in FIGS. 11A and 11B, and the measurement results when FeCl ₃ is used are shown. FIG. 13A and FIG. 13B show the measurement results when Fe (NO ₃ ) ₃ is used as shown in FIG. 12A and FIG. 12B. FIG. 10A, FIG. 11A, FIG. 12A, and FIG. 13A show the relationship between the carbonization temperature of each sample and the measurement results of the evaluation of the oxygen reduction catalyst activity, and the measurement of the carbonization temperature of each sample and the evaluation of the water electrolysis reaction catalytic activity. The relationship of the results is shown in FIGS. 10B, 11B, 12B, and 13B. In each figure, each measured value is shown as an absolute value. The measured value of E _H2 indicates that the smaller the absolute value, the higher the performance of the catalyst, and the other measured value indicates that the higher the absolute value, the higher the performance of the catalyst.

From the results of FIGS. 10 to 13, a certain degree of high catalytic activity is obtained in the range of 900 to 1200 ° C. In the case of 800 degreeC, a catalyst activity may become low compared with 900-1200 degreeC.
It turns out that carbonization should just be performed in the range of 900-1200 degreeC for 1 hour.

<Experiment 6>
Based on the results of Experiment 2 and Experiment 3, the catalytic activity of the carbon catalyst according to the present invention was compared with that of a carbon catalyst using a synthetic polymer.
As the carbon catalyst according to the present invention, chicken egg-CoCl ₂ -1000 and chicken egg-FeCl ₃ -1000 samples using chicken eggs as proteins were prepared. Moreover, the sample carbonized only with the chicken egg was prepared as a reference example.
Each sample of Ph-1000, Ph-CoPc-1000, and Ph-FePc-1000 using a phenol resin (Ph) was prepared as a carbon catalyst using a synthetic polymer.
Each sample was evaluated for oxygen reduction catalytic activity (E _O2 , | i _0.7V |) and water electrocatalytic activity (| E _H2 |, | i _−0.5V |).
The results are shown in Table 6.

  As can be seen from Table 6, the egg-derived sample carbonized at 1000 ° C. shows higher oxygen reduction activity / water electrolysis activity than carbon derived from phenol resin.

<Experiment 7>
For the purpose of further enhancing the catalytic activity of the carbon catalyst according to the present invention, mixing with other carbon materials and mixing of carbon catalysts with different raw materials were conducted to investigate the catalytic activity.

First, a CoCl ₂ aqueous solution was added to a casein aqueous solution and mixed uniformly with a food processor, ketjen black was added and mixed uniformly again, and dried to obtain a carbon precursor. Carbonization was performed in a nitrogen stream by raising the temperature to 1000 ° C. at a rate of temperature increase of 10 ° C./min and holding at 1000 ° C. for 1 hour.
Casein -COCl _2: mixing ratio of Ketjen black is 100: 0 (no Ketjen black), 98: 2, 95: 5,75: 25 (all by weight), and instead, the carbon catalyst each sample Was made.

The sample of the obtained carbon catalyst was evaluated for oxygen reduction catalytic activity. The voltammogram of each sample is shown in FIG.
As it can be seen from FIG. 14, be mixed ketjen black, the value of E _O2 does not change, the current density is increased.

Subsequently, as in FIG. 14, casein was used as a protein, and the catalytic activity was examined by changing the types and mixing ratios of other carbon materials.
As other carbon materials, various carbon blacks such as Ketjen Black, Black Pearl, and Vulcan were prepared.
Then, a CoCl ₂ aqueous solution was added to the casein aqueous solution and mixed uniformly with a food processor, then carbon black was added and mixed uniformly again, and dried to obtain a carbon precursor. Carbonization was performed. Carbonization was performed in a nitrogen stream by raising the temperature to 1000 ° C. at a rate of temperature increase of 10 ° C./min and holding at 1000 ° C. for 1 hour.
In addition, in the measurement of FIG. 14, the mixing ratio (mass ratio) of casein-CoCl ₂ : Ketjen black was described, but in this measurement, the mixing ratio (mass ratio) of casein: carbon black was calculated in%. .
Samples of carbon catalyst were prepared by changing the type and mixing ratio of carbon black.

About the sample of the obtained carbon catalyst, water electrolysis catalytic activity and oxygen reduction catalytic activity were evaluated. Regarding the water electrocatalytic activity of each sample, the relationship between the value of E _H2 and the mixing ratio is shown in FIG. 15A, and the relationship between the value of current density and the mixing ratio is shown in FIG. 15B. Regarding the oxygen reduction catalytic activity of each sample, the relationship between the value of E _O2 and the mixing ratio is shown in FIG. 16A, and the relationship between the value of current density and the mixing ratio is shown in FIG. 16B.
From FIG. 15A, E _H2 increased with the addition amount of ketjen black until the addition amount of ketjen black was 50%, and decreased when the addition amount was 75%. From FIG. 15B, the current density has a peak when the addition amount is 50%. Moreover, both E _H2 and current density showed a difference in peak position depending on the type of carbon black.
From FIG. 16A, until a 75% amount of Ketjen Black, E _O2 is substantially constant activity irrespective of the amount of Ketjen black, the amount of addition was reduced 100%. From FIG. 16B, the current density has a peak when the addition amount is 50%. Regarding the current density, a difference was observed in the peak position depending on the type of carbon black.

Next, we a sample of carbon catalyst silk -COCl ₂ -1000, the samples of the carbon catalyst of casein -COCl ₂ -1000, were mixed in equal amounts, the evaluation of the water electrolysis catalytic activity. Samples of the mixture with the _sample, the absolute value of _{E H2 | E H2 |} is shown in FIG. 17A, FIG. 17B the absolute value of the current density of -0.5 V.
As can be seen from FIGS. 17A and 17B, the E _H2 value of the mixture did not improve simply by averaging the values for each sample, but the current density of the mixture was greater than any of the samples before mixing. It was.

<Experiment 8>
For the purpose of further enhancing the catalytic activity of the carbon catalyst according to the present invention, the carbon catalyst once produced was reheated and the change in the catalytic activity was examined.
As a sample to be reheated, wool-FeCl ₃ -1000 was prepared and the catalytic activity was measured.
Further, wool-FeCl ₃ -1000 was heat-treated at 850 ° C. for 30 minutes to obtain a reheat-treated sample. This reheat-treated sample is expressed as “wool-FeCl ₃ -1000-850”. The catalyst activity was also measured for the reheat-treated sample.
18A and 18B show a comparison of the measurement results of the catalytic activity of the two samples. FIG. 18A shows the measurement result (voltammogram) of the oxygen reduction catalyst activity, and FIG. 18B shows the measurement result (voltammogram) of the water electrolysis catalyst activity.
It can be seen from the voltammograms of FIGS. 18A and 18B that all of E _O2 , i _0.7V , E _H2 , and i _−0.5V are improved by _reheat treatment.

<Experiment 9>
The oxygen reduction reaction at the fuel cell cathode includes the following two reactions.
4H ⁺ + O ₂ + 4e → 2H ₂ O (4-electron reaction)
2H ⁺ + O ₂ + 2e → H ₂ O ₂ (two-electron reaction)
Among these reactions, when the 4-electron reaction is dominant, the activity is high and the function as a catalyst is maintained.

Four-electron reaction selectivity was investigated about the carbon catalyst which concerns on this invention, and another carbon catalyst.
As the carbon catalyst according to the present invention, a sample of wool-FeCl ₃ -1000 and a sample of wool-CoCl ₂ -1000 were prepared.
As another carbon catalyst, a phenol resin-CoPc-1000 sample and a phenol resin-FePc-1000 sample were prepared.
For each sample, the 4-electron reaction selectivity was determined by Levich plot. The results were as follows.
Wool-FeCl ₃ -1000: 94%
Wool -CoCl ₂ -1000: 88%
Phenolic resin-CoPc-1000: 47%
Phenolic resin-FePc-1000: 86%
That is, the carbon catalyst according to the present invention showed higher 4-electron reaction selectivity.

<Experiment 10>
Different types of metals to be mixed were subjected to differential thermal analysis of the carbon precursor before carbonization.
Examples of the carbon precursor include wool alone, wool-Co (NO ₃ ) ₂ , wool-Fe (NO ₃ ) ₃ , wool-FeCl ₃ , wool-TiCl ₄ , wool-Ni (NO ₃ ) ₂ , wool-MgSO ₄ Seven types of were prepared.

The results of differential thermal analysis of the above seven types of carbon precursors are shown in order in FIGS. 19A to 19D and FIGS. 20E to 20G.
In the case of the wool alone shown in FIG. 19A, an endothermic peak accompanying the crystal melting of the wool appears around 220 ° C.
When iron salt or cobalt salt shown in FIGS. 19B to 19D is added, the endothermic peak around 220 ° C. is shifted to the low temperature side.
When other metal salts shown in FIGS. 20E to 20G are added, an endothermic peak is shown at the same temperature.
From these results, there is a difference in the interaction between protein and metal salt depending on the type of metal to be added, and it is considered that the interaction is large in iron salt and cobalt salt.

<Experiment 11>
It was investigated whether the crystal structure was different between the case of carbonization by adding a metal salt to protein and the case of carbonization by protein alone.
As protein, wool was used. As the metal salt, CoCl ₂ , FeCl ₃ , MgSO ₄ , and Ni (NO ₃ ) ₂ were used.
In accordance with the steps of Example 1 or Comparative Example 1 of Experiment 1, carbonization at 1000 ° C. and removal of metal salts by acid treatment were performed to obtain carbon catalyst samples.
Each sample was pulverized and measured using an X-ray diffractometer (XRD-6100 manufactured by Shimadzu Corporation) at CuKα, 40 kV, 30 mA in a range of 2θ = 5 to 90 °. Further, the 002 plane spacing of carbon was obtained from the X-ray diffraction pattern obtained by the measurement. Table 7 shows the value of 2θ (°) at the position of the 002 plane of each sample and the value of the 002 plane spacing (Å).

From Table 7, it can be seen that when a metal salt is added to wool and carbonized, the 002 plane spacing becomes small. This tendency is remarkable in the sample having high oxygen reduction catalytic activity to which iron or cobalt is added.
Moreover, even if it removes a metal after carbonization from this result, it can be judged whether the metal salt existed at the time of carbonization.

<Experiment 12>
Using chicken eggs as protein, the catalytic activity was examined by changing the presence or absence of addition of a metal salt, the carbonization temperature, the presence or absence of carbon black mixing, and the mixing ratio. CoCl ₂ and FeCl ₃ were used as the metal salt, and Ketjen black was used as the carbon black.

(Sample without added metal salt)
After removing the eggshell of the eggs, the eggs were mixed well in a food processor and lyophilized. Thereafter, under nitrogen flow, the temperature was increased at a temperature increase rate of 10 ° C./min, and the carbonization was performed at the carbonization temperature for 1 hour. The carbonization temperature was 800 ° C and 1000 ° C. After carbonization, it was pulverized with a ball mill. In this way, samples of Egg-800 and Egg-1000 carbon catalysts were prepared.

(Sample with added metal salt)
After removing the eggshell of the chicken egg and mixing well with a food processor, a CoCl ₂ aqueous solution or an FeCl ₃ aqueous solution was added and mixed uniformly again. The metal salt was added so that the mass ratio of the metal element was 5% with respect to the solid component of the egg from which the eggshell had been removed. The metal salt was added and then lyophilized. Thereafter, carbonization and pulverization were performed in the same manner as the sample to which no metal salt was added. Furthermore, the acid treatment at 70 ° C. for 2 hours with 1 M hydrochloric acid was repeated three times to remove Co or Fe. In this way, carbon catalyst samples of Egg-Co-800, Egg-Co-1000, Egg-Fe-800, and Egg-Fe-1000 were prepared.

The water electrocatalytic activity of each sample was measured. The measurement results (voltammogram) of the water electrocatalytic activity of each sample are shown together in FIG.
From FIG. 21, in particular, three samples of Egg-Co-800, Egg-Co-1000, and Egg-Fe-1000 showed high catalytic activity, and Egg-Co-1000 showed the highest catalytic activity.

(Sample mixed with carbon black)
Next, for Egg-Co-1000 having the highest catalytic activity, carbon black was mixed at different mixing ratios in the same manner as performed for casein in Experiment 7, and changes in catalytic activity were examined. .
Ketjen black was used as the carbon black, and a CoCl ₂ aqueous solution was added and mixed in the same manner as Egg-Co-1000. After that, Ketjen black was added and the whole was mixed. The mixing ratio of the ketjen black was varied between 0 to 50% by mass ratio of the ketjen black to the solid component of the egg from which the eggshell had been removed. After mixing CoCl ₂ and Ketjen Black, carbonization was performed at 1000 ° C., and then a sample of a carbon catalyst was prepared in the same manner as Egg-Co-1000.
The water electrocatalytic activity of each sample was measured. As a result, the best results were obtained with a sample having a ketjen black mixing ratio of 10% in both E _H2 and current density. Hereinafter, this sample is referred to as Egg-Co-1000-KB10.

Here, the measurement results (voltammograms) of water electrocatalytic activity of Egg-Co-1000 and Egg-Co-1000-KB10 are shown together in FIG. In FIG. 22, the current density on the vertical axis is expanded as compared with FIG.
From FIG. 22, it can be seen that mixing 10% of ketjen black greatly improves the catalytic activity compared to the case of not mixing.

Furthermore, six samples whose voltammograms are shown in FIG. 21 and a sample of Egg-Co-1000-KB10 were measured by XPS (X-ray photoelectron spectroscopy). The spectrum of the binding energy of the electrons of the 1s orbit of the nitrogen atom obtained by this measurement is shown in FIGS. 23A to 23G. The spectrum of Egg-800 is shown in FIG. 23A, the spectrum of Egg-1000 is shown in FIG. 23B, the spectrum of Egg-Co-800 is shown in FIG. 23C, the spectrum of Egg-Co-1000 is shown in FIG. The spectrum of Fe-800 is shown in FIG. 23E, the spectrum of Egg-Fe-1000 is shown in FIG. 23F, and the spectrum of Egg-Co-1000-KB10 is shown in FIG. 23G.
Further, from the spectrum obtained by XPS measurement of each sample, the atomic ratio N / C of nitrogen and carbon, the peak energy of the pyridine type nitrogen atom component (eV), the peak energy of the pyrrole type nitrogen atom component (eV) eV) was determined respectively. Table 8 shows the measurement results, the current density at −0.5 V of the water electrocatalytic activity determined from the voltammogram, and E _H2 for each sample.

From Table 8, in the catalyst with high water electrocatalytic activity, the peak energy of the low energy component is 398.2 eV or more. In a catalyst having low water electrocatalytic activity, the energy of the peak of the low energy component is 398.0 eV, 398.1 eV, which is lower energy.
In addition, when ketjen black is mixed, the N / C ratio and the energy of each peak of N1s are comparable as compared with the non-mixed Egg-Co-1000, but the water electrocatalytic activity is improved. Yes.

<Experiment 13>
Waste wool, including carpets and wool duvets, is difficult to be decomposed by microorganisms and emits an unpleasant odor during combustion, so that the treatment method is one of the problems.
Considering the effective use of waste wool from the standpoint of environment and resources, a carbon catalyst sample was prepared using a worn cardigan made of 100% wool as a protein raw material. As a comparative control, a carbon catalyst sample was prepared using new wool.
Water electrocatalytic activity and oxygen reduction catalytic activity were measured for each carbon catalyst sample.
The method for preparing the carbon catalyst sample and the method for measuring the water electrolysis catalytic activity and the oxygen reduction catalytic activity were the same as in the experiment described above.

Table 9 shows the current density i _−0.5 V at E _H2 and −0.5 V obtained from the measurement result of the water electrocatalytic activity of each sample. Table 10 shows the current density i _{−0.7 V} at EO ₂ and −0.7 V obtained from the measurement result of the oxygen reduction catalytic activity of each sample.

From Table 9, the _{E H2} wool (clothes) substantially equal to the wool _{(new), i -0.5 V} was about 80%.
From Table 10, E _o2 of wool (old clothes) was almost equal to wool (new), and i- _0.7V was about 60%.
From these results, it can be seen that sufficient activity can be obtained even if a carbon catalyst is produced using wool clothes as a raw material.

  The present invention is not limited to the above-described embodiments and examples, and various other configurations can be taken without departing from the gist of the present invention.

Claims (6)

Mixing a protein and a metal compound;
And then carbonizing the mixture,
Using the egg or soy milk as the protein,
As the metal, iron or cobalt is used,
A method for producing a carbon catalyst, wherein a compound selected from iron chloride, cobalt chloride, iron acetate, and cobalt acetate is used as the metal compound.   The method for producing a carbon catalyst according to claim 1, wherein a step of removing the metal is performed after the step of carbonizing.   The method for producing a carbon catalyst according to claim 2, wherein in the step of removing the metal, the metal is removed by treatment with an acid.   The method for producing a carbon catalyst according to any one of claims 1 to 3, wherein a step of carbonizing the mixture is performed after further adding carbon black to the protein and the metal compound. A carbon catalyst used as a water electrocatalyst, comprising carbon, nitrogen in a carbonized substance of protein, and iron or cobalt, and measured using sulfuric acid having a concentration of 0.5 M in an electrolytic solution, A carbon catalyst having an absolute value | E _H2 | of a reaction initiation potential as a water electrocatalyst of 0.18 to 0.39 V (vs. reversible hydrogen electrode) at which a current of 1 mA / cm ² begins to flow .   The carbon catalyst according to claim 5, wherein the protein is chicken egg or soy milk.

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