JP2011210386A - Cathode catalyst, method of manufacturing the same, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode catalyst improving power generating performance more by activating an oxygen reducing reaction in an oxygen side electrode (a cathode), and to provide a method of manufacturing the same and a fuel cell using the same.SOLUTION: The fuel cell includes: an electrolyte layer 4 capable of moving an anion component; and a fuel side electrode 2 and the oxygen side electrode 3 arranged opposite to each other with the electrolyte layer 4 between them. The oxygen side electrode 3 includes a cathode catalyst including: a first catalyst including a transition metal and a polypyrrole; and a second catalyst, in which a cobalt oxide including CoOis dispersed in carbon. With this structure, the oxygen reducing reaction in the oxygen side electrode 3 can be improved, and as a result, power generating performance of the fuel cell can be improved.

Description

  The present invention relates to a cathode catalyst, a method for producing the same, and a fuel cell, and more particularly to a cathode catalyst used for a cathode of a fuel cell, a method for producing the same, and a fuel cell using the cathode catalyst.

  To date, various fuel cells such as alkaline type (AFC), solid polymer type (PEFC), phosphoric acid type (PAFC), molten carbonate type (MCFC), and solid electrolyte type (SOFC) are known as fuel cells. ing. These fuel cells are being studied for use in various applications such as automobile applications.

  For example, a polymer electrolyte fuel cell includes a fuel-side electrode (anode) to which fuel is supplied and an oxygen-side electrode (cathode) to which oxygen is supplied. These electrodes are formed from a solid polymer membrane. Are arranged opposite to each other with an electrolyte layer interposed therebetween. In this fuel cell, hydrogen gas is supplied to the anode and air is supplied to the cathode, so that an electromotive force is generated between the anode and the cathode to generate electric power.

  As such a polymer electrolyte fuel cell, for example, a fuel side electrode (anode), an oxygen side electrode (cathode) containing a composite (carbon composite) composed of polypyrrole and carbon carrying cobalt, and There has been proposed a fuel cell including an anion exchange resin solid polymer membrane sandwiched (see, for example, Patent Document 1).

  According to such a fuel cell, the oxygen reduction reaction at the oxygen side electrode (cathode) is activated by making the oxygen side electrode (cathode) contain a composite of polypyrrole and carbon carrying cobalt as a cathode catalyst. Power generation performance can be improved.

International publication pamphlet WO2008 / 117485

  However, in recent years, there is a demand for a fuel cell that is more excellent in power generation performance than the fuel cell described in Patent Document 1.

  Accordingly, there is a demand for a cathode catalyst capable of activating the oxygen reduction reaction at the oxygen side electrode (cathode) and further improving the power generation performance as compared with the cathode catalyst described in Patent Document 1.

  On the other hand, for example, in addition to the cathode catalyst described in Patent Document 1, it is also considered to contain a catalyst such as metallic cobalt in the oxygen side electrode (cathode). However, even in such a case, the required power generation performance may not be sufficiently obtained.

  An object of the present invention is to provide a cathode catalyst capable of activating an oxygen reduction reaction at an oxygen side electrode (cathode) and further improving power generation performance, a method for producing the same, and a fuel cell using the cathode catalyst. There is to do.

In order to achieve the above object, a cathode catalyst of the present invention is a cathode catalyst used for an oxygen-side electrode of a fuel cell, and includes a first catalyst containing a transition metal and polypyrrole, and a cobalt oxide containing Co ₃ O ₄ . And a second catalyst dispersed in carbon.

  Further, in the cathode catalyst of the present invention, the second catalyst obtains a catalyst precursor by heating the cobalt compound and carbon at 400 to 700 ° C. in a non-oxidizing atmosphere, and the catalyst precursor is oxidized. It is suitable to be obtained by heating at 100 to 350 ° C. in an atmosphere.

The method for producing a cathode catalyst of the present invention includes a step of obtaining a first catalyst containing a transition metal and polypyrrole, a step of obtaining a second catalyst in which cobalt oxide containing Co ₃ O ₄ is dispersed in carbon, Mixing the first catalyst and the second catalyst to obtain a cathode catalyst, wherein the step of obtaining the second catalyst heats the cobalt compound and carbon at 400 to 700 ° C. in a non-oxidizing atmosphere. Thus, the method includes a step of obtaining a catalyst precursor and a step of heating the catalyst precursor at 100 to 350 ° C. in an oxidizing atmosphere.

  The fuel cell of the present invention includes an electrolyte capable of moving an anion component, and a fuel side electrode and an oxygen side electrode arranged to face each other with the electrolyte interposed therebetween, and the oxygen side electrode is the cathode catalyst described above. It is characterized by containing.

Since the cathode catalyst of the present invention contains a first catalyst containing a transition metal and polypyrrole and a second catalyst in which cobalt oxide containing Co ₃ O ₄ is dispersed in carbon, the oxygen reduction reaction at the oxygen side electrode As a result, the power generation performance of the fuel cell can be improved.

In addition, according to the method for producing a cathode catalyst of the present invention, a cobalt precursor and carbon are heated at 400 to 700 ° C. in a non-oxidizing atmosphere to obtain a catalyst precursor, and the catalyst precursor is oxidized in an oxidizing atmosphere. The second catalyst in which cobalt oxide containing Co ₃ O ₄ is dispersed in carbon can be easily manufactured by heating at 100 to 350 ° C. below. Therefore, the cathode catalyst can be efficiently produced by mixing the first catalyst and the second catalyst.

  In the fuel cell of the present invention, since the cathode catalyst of the present invention is contained in the oxygen side electrode, according to the fuel cell of the present invention, the oxygen reduction reaction in the oxygen side electrode can be activated. As a result, the power generation performance of the fuel cell can be improved.

It is a schematic block diagram which shows one Embodiment of the fuel cell of this invention. The XRD (X-ray diffraction) pattern of a catalyst precursor and a 2nd catalyst is shown. The Fourier transform image of the XAFS (X-ray absorption fine structure) of a catalyst precursor and a 2nd catalyst is shown. It is a graph which shows the result of the activity measurement of an oxygen side electrode, Comprising: The result of Example 1 and the comparative example 1 is shown. It is a graph which shows the result of the activity measurement of an oxygen side electrode, Comprising: The result of Example 1, the comparative examples 2 and 3 is shown.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a fuel cell of the present invention.

  The fuel cell 1 is a polymer electrolyte fuel cell, and includes a plurality of fuel cells S, and is formed as a stack structure in which these fuel cells S are stacked. In FIG. 1, only one fuel cell S is shown for easy illustration.

  The fuel cell S includes a fuel side electrode 2 (anode), an oxygen side electrode 3 (cathode), and an electrolyte layer 4.

  The fuel side electrode 2 includes an anode catalyst (fuel side catalyst).

  More specifically, the fuel side electrode 2 is formed of, for example, a catalyst carrier that supports an anode catalyst.

  The anode catalyst is not particularly limited, and examples thereof include platinum group elements (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt)), and iron group elements. (According to IUPAC Periodic Table of the Elements (version date 22 June 2007), etc., the same applies hereinafter) such as iron (Fe), cobalt (Co), nickel (Ni)), etc. Examples thereof include 11th (IB) group elements of the periodic table such as copper (Cu), silver (Ag), and gold (Au).

  These anode catalysts can be used alone or in combination of two or more.

  As an anode catalyst, Preferably, the 8th-10th (VIII) group element of a periodic table, More preferably, an iron group element, More preferably, nickel is mentioned.

  The supported concentration of the anode catalyst (the content ratio of the anode catalyst with respect to the total amount of the anode catalyst and the catalyst carrier) is, for example, 1% by mass or more, preferably 30% by mass or more, and usually less than 100% by mass.

  The catalyst carrier is not particularly limited, and examples thereof include resins such as anion exchange resin and proton exchange resin, and porous materials such as carbon.

  These catalyst carriers can be used alone or in combination of two or more.

  The catalyst carrier is preferably a resin.

  And in order to form the fuel side electrode 2 using the catalyst support | carrier which carry | supported the anode catalyst, a membrane-electrode assembly is formed with the electrolyte layer 4 by a well-known method, for example.

  More specifically, first, a catalyst carrier carrying an anode catalyst and an electrolyte solution are mixed to prepare a dispersion of the catalyst carrier carrying an anode catalyst. At this time, if necessary, an organic solvent such as alcohol may be appropriately added to adjust the viscosity of the dispersion. Next, the dispersion is coated on one surface of the electrolyte layer 4.

  Thus, the fuel side electrode 2 fixed on one surface of the electrolyte layer 4 can be obtained.

In addition, the usage-amount of an anode catalyst is 0.01-10 mg / cm < ² >, for example. Moreover, the usage-amount of the catalyst support | carrier which carry | supported the anode catalyst is 0.01-10 mg / cm < ² >, for example. The thickness of the fuel side electrode 2 fixed on one surface of the electrolyte layer 4 is, for example, 0.1 to 100 μm, preferably 1 to 10 μm.

  The oxygen side electrode 3 contains a cathode catalyst (oxygen side catalyst).

  In the present invention, the cathode catalyst contains a first catalyst and a second catalyst, and the first catalyst contains a transition metal and polypyrrole.

  More specifically, examples of the first catalyst include a catalyst in which a transition metal is supported on a composite composed of polypyrrole and carbon (hereinafter, this composite is referred to as “carbon composite”).

  Examples of the transition metal include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu ), Yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), lanthanum (La) ), Hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), and the like.

  These transition metals can be used alone or in combination of two or more.

  The transition metal is preferably cobalt.

  Polypyrrole is a polymer of pyrrole (monomer), and can be obtained, for example, by polymerization of pyrrole (monomer) as described later.

  In such a case, the polymerization degree of pyrrole is not particularly limited, and is appropriately set according to the purpose and application. Moreover, such polypyrrole can also contain pyrrole (unreacted pyrrole), and the content ratio is not particularly limited, and is appropriately set according to the purpose and application.

  Moreover, the compounding ratio of a polypyrrole is 1-100 mass parts with respect to 100 mass parts of carbons, for example, Preferably, it is 10-50 mass parts.

  Examples of carbon include known carbon such as carbon black.

  Although there is no particular limitation on obtaining such a first catalyst, for example, after forming a carbon composite, a transition metal is supported on the carbon composite.

  More specifically, first, 100 to 1000 parts by mass of a solvent is added to 100 parts by mass of carbon, and the solvent is stirred to prepare a carbon dispersion in which carbon is dispersed in the solvent. At this time, if necessary, an organic acid such as acetic acid or oxalic acid may be added as appropriate. The addition amount is, for example, 1 to 50 parts by mass with respect to 100 parts by mass of carbon.

  Examples of the solvent include known solvents such as water, for example, lower alcohols such as methanol, ethanol, and propanol.

  Moreover, stirring temperature is 10-30 degreeC, for example, and stirring time is 10-60 minutes, for example.

  Next, for example, 1 to 50 parts by mass, preferably 10 to 20 parts by mass of pyrrole (monomer) is added to the carbon dispersion with respect to 100 parts by mass of carbon, followed by stirring. The stirring temperature at this time is, for example, 10 to 30 ° C., and the stirring time is, for example, 1 to 10 minutes.

  Subsequently, pyrrole in the carbon dispersion is polymerized to prepare a carbon composite dispersion of carbon and polypyrrole. In order to polymerize pyrrole, for example, oxidative polymerization such as chemical oxidative polymerization and electrolytic oxidative polymerization is used. Preferably, chemical oxidative polymerization is used.

  In chemical oxidative polymerization, a catalyst for oxidative polymerization is added to a carbon dispersion containing pyrrole, and pyrrole is polymerized by stirring. Examples of the oxidation polymerization catalyst include peroxides such as hydrogen peroxide, ammonium persulfate, and benzoyl peroxide, for example, permanganate such as potassium permanganate and magnesium permanganate, such as iron (III) chloride. And a known catalyst for oxidative polymerization, preferably hydrogen peroxide. Moreover, the stirring temperature (polymerization temperature) when superposing | polymerizing pyrrole is 10-30 degreeC, for example, and stirring time is 10-90 minutes, for example.

  Thereafter, the carbon composite dispersion of carbon and polypyrrole is filtered and washed, and dried in a vacuum at 50 to 100 ° C., for example. Thereby, the dry powder of a carbon composite is obtained.

  After the carbon composite is obtained, the transition metal is supported on the carbon composite.

  More specifically, 100 to 3000 parts by mass of a solvent is added to 100 parts by mass of the carbon composite and stirred. Thus, a carbon composite dispersion liquid in which the carbon composite is dispersed in the solvent is prepared. In addition, as a solvent, the solvent mentioned above is mentioned, for example.

  On the other hand, with respect to 100 parts by mass of the carbon composite, 1 to 150 parts by mass of a transition metal is dissolved in 100 to 1000 parts by mass of a solvent as a transition metal salt or alkoxide to prepare a transition metal-containing solution.

  Examples of the transition metal salt include inorganic salts such as transition metal hydroxides, sulfates, nitrates, chlorates, chromates, and chlorides, such as transition metal formates, acetates, and oxalates. And organic salts.

  Examples of transition metal alkoxides include alcoholates such as transition metal methoxides, ethoxides, propoxides, isopropoxides, butoxides, and the like, for example, transition metal methoxyethylates, methoxypropyrate, methoxybutyrate, ethoxyethyl. Examples thereof include alkoxy alcoholates such as rate, ethoxypropylate, propoxyethylate and butoxyethylate.

  Then, the transition metal-containing solution is added to the carbon composite dispersion and stirred to prepare a mixed solution of the transition metal-containing solution and the carbon composite dispersion. The stirring temperature at this time is, for example, 50 to 100 ° C., and the stirring time is, for example, 10 to 60 minutes.

  Subsequently, the reducing agent-containing solution containing the reducing agent is added to the mixed solution until the pH of the mixed solution of the transition metal-containing solution and the carbon composite dispersion is in the range of 10 to 12, and then the mixed solution is, for example, Leave at 60-100 ° C. for 10-60 minutes. Thereby, the transition metal is supported on the carbon composite.

  The reducing agent-containing solution includes, for example, a known reducing agent such as sodium borohydride, potassium borohydride, lithium borohydride, hydrazine, and an alkali compound such as sodium hydroxide and potassium hydroxide. It can be prepared as an alkaline solution by dissolving in water or the like.

  More specifically, for example, when sodium borohydride is used as a reducing agent, first, the sodium borohydride and sodium hydroxide are dissolved in water to prepare a reducing agent-containing solution (alkaline aqueous solution). . Thus, decomposition | disassembly of sodium borohydride can be suppressed by setting it as alkaline aqueous solution (basic solution) with sodium hydroxide. Next, the reducing agent-containing solution is added to the mixed solution of the transition metal-containing solution and the carbon composite dispersion.

  The production of these carbon composites and their dispersions and the loading of transition metals on the carbon composites are preferably carried out under an inert gas atmosphere (for example, a nitrogen gas atmosphere, an argon gas atmosphere, etc.).

  Thereafter, the left mixed liquid is filtered and washed, and dried in a vacuum at 50 to 100 ° C., for example. Thereby, a dry powder of a carbon composite carrying a transition metal is obtained.

  In this method, if necessary, the dry powder of the carbon composite carrying the transition metal can be washed with, for example, water or sulfuric acid.

  In the first catalyst thus obtained, the transition metal loading concentration (the transition metal loading ratio relative to the total amount of the first catalyst) is, for example, 0.1 to 60 mass%, preferably 1 to 40 mass%. It is.

  In the present invention, the second catalyst contains cobalt oxide and carbon. More specifically, in the second catalyst, cobalt oxide is dispersed (supported) on carbon.

In the present invention, the cobalt oxide contains Co ₃ O ₄ (cobalt oxide (II, III)) as an essential component.

In addition, the cobalt oxide may optionally include other cobalt oxides such as CoO (cobalt oxide (II)), Co ₂ O ₃ (cobalt oxide (III)), Co (metal cobalt), The above transition metals (excluding cobalt) and / or oxides thereof may also be included.

  In such a case, the content of the optional component is appropriately adjusted according to necessity and application.

  Examples of carbon include carbon similar to the above, such as carbon black.

  In order to obtain such a second catalyst, for example, first, a cobalt compound and the above carbon are mixed.

  The cobalt compound is a compound containing cobalt in the molecule, and includes, for example, an inorganic salt (for example, water) of cobalt including a halide of cobalt (for example, cobalt fluoride, cobalt chloride, cobalt bromide, cobalt iodide, etc.). Cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt perchlorate, cobalt thiocyanate, diamine silver cobalt sulfate, cobalt chromate, etc.), cobalt organic salts (eg, cobalt formate, cobalt acetate, cobalt oxalate, etc.), cobalt Alkoxides (for example, cobalt alcoholates such as cobalt methoxide, cobalt ethoxide, cobalt propoxide, cobalt isopropoxide, such as cobalt methoxyethylate, cobalt methoxypropylate, cobalt methoxybutyrate, cobalt ethoxyethylene , Cobalt ethoxy propylate, cobalt propoxylates ethylate, cobalt alkoxy alcoholates such as cobalt butoxy ethylate), such as cobalt acetylacetonate.

  In these cobalt compounds, the oxidation number (divalent and / or trivalent) of cobalt is appropriately selected as necessary.

  These cobalt compounds can be used alone or in combination of two or more.

  Preferred cobalt compounds include cobalt alkoxide and cobalt acetylacetonate.

  As for the compounding ratio of a cobalt compound, a cobalt compound is 0.1-20 mass parts with respect to 100 mass parts of carbon, for example. Moreover, the compounding ratio of the cobalt compound is, for example, 0.1 to 10 parts by mass of cobalt metal in the cobalt compound with respect to 100 parts by mass of carbon.

  Although mixing in particular of a cobalt compound and carbon is not restrict | limited, Preferably, a cobalt compound and carbon are mixed in an organic solvent.

  Examples of the organic solvent include aromatic hydrocarbons (eg, benzene, toluene, xylene, etc.), aliphatic hydrocarbons (eg, hexane, cyclohexane, octane, decane, etc.), alcohols (eg, methanol, ethanol, Propanol, butanol, pentanol, hexanol, octanol, methoxyethanol, ethoxyethanol, butoxyethanol, methoxypropanol, ethoxypropanol, benzyl alcohol, furfuryl alcohol, etc.), ketones (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), Examples thereof include esters (for example, ethyl acetate, butyl acetate, etc.).

  These organic solvents can be used alone or in combination of two or more.

  The organic solvent is preferably an aromatic hydrocarbon.

  The mixing ratio of the organic solvent is not particularly limited, but is, for example, 100 to 500 parts by mass, preferably 150 to 300 parts by mass with respect to 100 parts by mass of the total amount of the cobalt compound and carbon.

  In this method, when the cobalt compound is the cobalt alkoxide, water can be added to the mixture of the cobalt compound and carbon obtained as described above to hydrolyze the cobalt compound, if necessary. . In such a case, a mixture of a cobalt compound and carbon can be obtained, for example, as a precipitate.

  In this method, the obtained mixture of cobalt compound and carbon is washed and dried as necessary, and then heated in a non-oxidizing atmosphere (hereinafter sometimes referred to as primary firing) to prepare a catalyst precursor. A body (containing cobalt) is obtained.

  As heating conditions in the primary firing, the rate of temperature rise is, for example, 2 to 10 ° C./min, preferably 3 to 6 ° C./min, and the heating temperature (temperature rise stop temperature) is, for example, 400 to 700 ° C. Preferably, it is 500-600 degreeC. Moreover, the heating time in the primary firing (the holding time at the heating temperature) is, for example, 0.5 to 3 hours, preferably 1 to 2 hours.

  When the heating temperature and heating time in the primary firing are less than the above lower limit, the cobalt compound cannot be sufficiently decomposed, and the concentration of the cobalt oxide obtained in the secondary firing described later may decrease.

  On the other hand, when the heating temperature and heating time in the primary firing exceed the upper limit, metallic cobalt may grow and the particles may become enlarged.

  In addition, as described above, the atmospheric condition in such primary firing is a non-oxidizing atmosphere.

Examples of the non-oxidizing atmosphere include atmospheric conditions that do not contain oxygen (O ₂ ), and more specific examples include an inert gas atmosphere such as a nitrogen gas atmosphere and an argon gas atmosphere.

  When the atmospheric condition of the primary firing is, for example, an oxidizing atmosphere (described later), when heated under the above conditions, carbon is oxidized to carbon dioxide and may be removed as a gas. In such a case, the cobalt oxide cannot be dispersed (supported) on the carbon, and as a result, the second catalyst may not be obtained.

  On the other hand, if the atmospheric condition of the primary firing is a non-oxidizing atmosphere, the carbon can be prevented from being removed even when heated under the above conditions, so that the carbon can be prevented from being removed. In the secondary calcination, a second catalyst in which cobalt oxide is dispersed (supported) on carbon can be obtained.

  In this method, the obtained catalyst precursor is then cooled to, for example, 10 to 30 ° C., if necessary, and then heated in an oxidizing atmosphere (hereinafter sometimes referred to as secondary firing).

  The heating conditions in the secondary firing may be any conditions as long as the heating temperature is lower than the heating temperature of the primary firing, the carbon is not oxidized even in an oxidizing atmosphere, and the cobalt contained in the catalyst precursor can be oxidized. Specifically, the rate of temperature rise is, for example, 2 to 10 ° C./min, preferably 3 to 6 ° C./min, and the heating temperature (temperature rise stop temperature) is, for example, 100 to 350 ° C., preferably 200-300 ° C. Moreover, the heating time in the secondary firing (holding time at the heating temperature) is, for example, 3 to 8 hours, preferably 4 to 6 hours.

  When the heating temperature and heating time in the secondary firing are less than the above lower limit, the proportion of cobalt oxide may decrease.

  On the other hand, when the heating temperature and heating time in the secondary firing exceed the above upper limit, carbon may be carbon dioxide, and cobalt oxide may not be supported.

  Moreover, as described above, the atmospheric condition in such secondary firing is an oxidizing atmosphere.

Examples of the oxidizing atmosphere include atmospheric conditions containing oxygen (O ₂ ), preferably atmospheric conditions with an oxygen concentration of 15% or more. More specific examples of such an oxidizing atmosphere include an air (atmosphere) atmosphere (oxygen concentration 21%), an oxygen atmosphere (oxygen concentration 100%), and the like.

Thereby, cobalt contained in the catalyst precursor can be oxidized, and a second catalyst in which cobalt oxide containing Co ₃ O ₄ is dispersed in carbon can be obtained.

  In order to produce the cathode catalyst, for example, first, the first catalyst and the second catalyst are obtained by the method described above.

  Next, in this method, the first catalyst and the second catalyst obtained as described above are mixed.

  In mixing, it does not restrict | limit in particular, What is necessary is just to mix physically. More specifically, for example, the first catalyst and the second catalyst obtained as described above may be dry mixed or wet mixed.

  The mixing ratio of the second catalyst in the mixing is, for example, 10 to 1000 parts by mass, preferably 25 to 400 parts by mass with respect to 100 parts by mass of the first catalyst.

  Moreover, the blending ratio of the first catalyst is, for example, 9 to 91 parts by weight, preferably 20 to 80 parts by weight with respect to 100 parts by weight of the total amount of the first catalyst and the second catalyst. A ratio is 9-91 mass parts, for example, Preferably, it is 20-80 mass parts.

  Thereby, a cathode catalyst can be obtained.

  In order to form the oxygen side electrode 3 including such a cathode catalyst, for example, a method similar to that of the fuel side electrode 2 described above is adopted, and the dispersion of the cathode catalyst is applied to the other electrolyte layer 4 (fuel side electrode). 2 is coated on the surface of the other side to the other side.

  As a result, the oxygen-side electrode 3 fixed on the other surface of the electrolyte layer 4 different from the one surface on which the fuel-side electrode 2 is fixed can be obtained. That is, the oxygen side electrode 3 is fixed to the other surface of the electrolyte layer 4, whereby the fuel side electrode 2 and the oxygen side electrode 3 are disposed to face each other with the electrolyte layer 4 interposed therebetween. The body is formed.

Further, the oxygen-side electrode 3, the amount of the cathode catalyst, for example, 0.10~0.30mg / cm ^2, preferably from 0.15~0.25mg / cm ^2. Moreover, the thickness of the oxygen side electrode 3 fixed on the other surface of the electrolyte layer 4 is, for example, 0.1 to 100 μm, and preferably 1 to 10 μm.

The electrolyte layer 4 is a layer that can move an anion component, and is formed using, for example, an anion exchange membrane. The anion exchange membrane is not particularly limited as long as it is a medium capable of transferring hydroxide ions (OH ⁻ ), which are anion components generated at the oxygen side electrode 3, from the oxygen side electrode 3 to the fuel side electrode 2. For example, a solid polymer membrane (anion exchange resin) having an anion exchange group such as a quaternary ammonium group or a pyridinium group can be used.

  The fuel cell S further includes a fuel supply member 5 and an oxygen supply member 6. The fuel supply member 5 is made of a gas impermeable conductive member, and one surface thereof is opposed to the surface of the fuel side electrode 2 opposite to the surface in contact with the electrolyte layer 4. . The fuel supply member 5 is formed with a fuel-side flow path 7 for bringing fuel into contact with the entire fuel-side electrode 2 as a distorted groove recessed from one surface. The fuel-side flow path 7 has a supply port 8 and a discharge port 9 that pass through the fuel supply member 5 formed continuously at the upstream end and the downstream end, respectively.

  Similarly to the fuel supply member 5, the oxygen supply member 6 is made of a gas impermeable conductive member, and one surface thereof is opposite to the surface in contact with the electrolyte layer 4 in the oxygen side electrode 3. Opposite contact is made with the side surface. The oxygen supply member 6 is also formed with an oxygen-side flow channel 10 for contacting oxygen (air) with the entire oxygen-side electrode 3 as a distorted groove recessed from one surface. The oxygen-side flow path 10 also has a supply port 11 and a discharge port 12 that pass through the oxygen supply member 6 continuously formed at the upstream end portion and the downstream end portion thereof.

  The fuel cell 1 is formed as a stack structure in which a plurality of fuel cells S are stacked as described above. Therefore, although not shown, the fuel supply member 5 and the oxygen supply member 6 are configured as separators in which the fuel side channel 7 and the oxygen side channel 10 are formed on both surfaces.

  Although not shown in FIG. 1, the fuel cell 1 is provided with a current collector plate formed of a conductive material, and the electromotive force generated in the fuel cell 1 is provided in the current collector plate. It is taken out from the terminal.

  Further, on a test (model) basis, the fuel supply member 5 and the oxygen supply member 6 are connected by an external circuit 13, and a voltmeter 14 is interposed in the external circuit 13, thereby generating the fuel cell 1. The voltage can also be measured.

  Next, power generation by the fuel cell 1 will be described.

  In the fuel cell 1, power is generated by supplying air to the oxygen-side channel 10 and supplying fuel to the fuel-side channel 7.

The fuel supplied to the fuel side flow path 7 is a compound containing at least hydrogen, for example, hydrogen (H ₂ ), for example, methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ). Hydrocarbons such as, alcohols such as methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH), hydrazine (NH ₂ NH ₂ ), hydrazine hydrate (NH ₂ NH ₂ .H ₂ O), hydrazine carbonate _{((NH 2 NH 2) 2} CO 2), hydrazine sulfate _{(NH 2 NH 2 · H 2} SO 4), monomethyl hydrazine _(CH 3 NHNH _2), dimethylhydrazine _{((CH 3) 2 NNH 2} , CH 3 NHNHCH 3 ), Hydrazines such as carboxylic hydrazide ((NHNH ₂ ) ₂ CO), for example urea (NH ₂ CONH ₂ ), for example ammonia ( NH _3), for example, imidazole, 1,3,5-triazine, heterocyclic compounds such as 3-amino-1,2,4-triazole, e.g., hydroxylamine _(NH 2 OH), hydroxylamine sulfate _(NH 2 OH -Hydroxylamines such as H ₂ SO ₄ ). These may be used alone or in combination of two or more.

Among the fuels compounds described above, preferably a compound that does not contain carbon, i.e., hydrazine _(NH 2 NH 2), hydrazine hydrate _{(NH 2 NH 2 · H 2} O), hydrazine sulfate _{(NH 2} NH 2 · _H 2 SO ₄ ), ammonia (NH ₃ ), hydroxylamine (NH ₂ OH), and hydroxylamine sulfate (NH ₂ OH · H ₂ SO ₄ ). If the fuel is a compound that does not contain carbon, the catalyst is not poisoned by CO, so that the durability can be improved and substantially zero emission can be realized.

  In addition, the fuel may be supplied as it is, or for example, as a solution of water and / or alcohol (for example, lower alcohol such as methanol, ethanol, 1-propanol, 2-propanol). May be. In this case, the concentration of the fuel compound in the solution varies depending on the type of the fuel compound, but is, for example, 1 to 90% by mass, preferably 1 to 30% by mass. Furthermore, the fuel may supply the above-described fuel compound as a gas (for example, vapor).

Then, the power generation in the fuel cell 1, will be described more specifically, in the fuel-side electrode 2 fuel is supplied, the hydrogen from the fuel (H ₂₎ is produced by oxidation reaction of the hydrogen (H _2), hydrogen Electrons (e ⁻ ) are released from (H ₂ ), and protons (H ⁺ ) are generated. Electrons (e ⁻ ) released from hydrogen (H ₂ ) reach the oxygen side electrode 3 via the external circuit 13. That is, the electrons (e ⁻ ) passing through the external circuit 13 become current. On the other hand, in the oxygen side electrode 3, electrons (e ⁻ ), water (H ₂ O) generated by reaction from the outside or the fuel cell 1, and oxygen (O ₂₎ in the air flowing through the oxygen side flow path 10 ) React with each other to produce hydroxide ions (OH ⁻ ) (see the following reaction formula (2)). The generated hydroxide ions (OH ⁻ ) pass through the electrolyte layer 4 and reach the fuel side electrode 2. When the hydroxide ions (OH ⁻ ) reach the fuel side electrode 2, the hydroxide ions (OH ⁻ ) react with hydrogen (H ₂ ) in the fuel at the fuel side electrode 2 to generate electrons (e ^- ) And water (H ₂ O) are formed (see the following reaction formula (1)). The generated electrons (e ⁻ ) move from the fuel supply member 5 to the oxygen supply member 6 via the external circuit 13 and are supplied to the oxygen side electrode 3. By continuously performing the electrochemical reaction in the fuel side electrode 2 and the oxygen side electrode 3 as described above, a closed circuit is formed in the fuel cell 1 and an electromotive force is generated to generate power.
(1) 2H ₂ + 4OH ⁻ → 4H ₂ O + 4e ⁻ (Reaction at the fuel side electrode 2)
(2) O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (reaction at the oxygen side electrode 3)
(3) 2H ₂ + O ₂ → 2H ₂ O (reaction as a whole of the fuel cell 1)
The operating conditions of the fuel cell 1 are not particularly limited. For example, the pressure on the fuel side electrode 2 side is 100 kPa or less, preferably 50 kPa or less, and the pressure on the oxygen side electrode 3 side is 100 kPa or less. Preferably, it is 50 kPa or less, and the temperature of the fuel cell S is set to 30 to 100 ° C., preferably 60 to 90 ° C.

  Although one embodiment of the present invention has been described above, the present invention can be implemented in other forms.

  For example, in the above-described embodiment, the present invention has been described by exemplifying a solid polymer type fuel cell. The present invention can also be applied to various fuel cells such as a salt type and a solid electrolyte type.

The cathode catalyst of the present invention contains a first catalyst containing a transition metal and polypyrrole and a second catalyst in which cobalt oxide containing Co ₃ O ₄ is dispersed in carbon. The reduction reaction can be activated, and as a result, the power generation performance of the fuel cell can be improved.

In addition, according to the method for producing a cathode catalyst of the present invention, a cobalt precursor and carbon are heated at 400 to 700 ° C. in a non-oxidizing atmosphere to obtain a catalyst precursor, and the catalyst precursor is oxidized in an oxidizing atmosphere. The second catalyst in which the cobalt oxide containing Co ₃ O ₄ is dispersed in carbon can be produced by heating at 100 to 350 ° C., so the first catalyst and the second catalyst are mixed. As a result, the cathode catalyst can be efficiently produced.

  In addition, examples of the use of the fuel cell of the present invention in which such a cathode catalyst is used include a power source for a drive motor in an automobile, a ship, an aircraft, and a power source in a communication terminal such as a mobile phone.

  Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example.

Production Example 1 (Production of first catalyst)
1) Production of polypyrrole carbon composite (PPy-C) To 75 mL of pure water, 10 g of carbon (Vulcan XC-72 manufactured by E-TEK, specific surface area 250 m ² / g) and 2.5 mL of acetic acid (acetic acid concentration 100%) In addition, the mixture was stirred at room temperature (about 25 ° C.) for 20 minutes to prepare a carbon dispersion in which carbon was dispersed. Subsequently, 2 g of pyrrole (manufactured by Aldrich) was added to this carbon dispersion, and the mixture was stirred at room temperature for 5 minutes. Furthermore, 10 mL of hydrogen peroxide having a concentration of 10% was added to this carbon dispersion, and pyrrole was oxidatively polymerized by stirring at room temperature for 1 hour. Thereafter, the carbon dispersion was filtered, washed with warm water, and vacuum-dried at 90 ° C. Thereby, PPy-C dry powder in which pyrrole was polymerized on carbon was obtained.

2) Preparation of Cobalt-supported PPy-C 2 g of PPy-C dry powder obtained in 1) was added to 44 mL of pure water, stirred for 30 minutes while heating to 80 ° C., and PPy-C in which PPy-C was dispersed. A dispersion was obtained. Next, 1.1 g of cobalt nitrate (II) hexahydrate was dissolved in 11 mL of pure water to prepare a cobalt-containing aqueous solution. And this cobalt containing aqueous solution was added to PPy-C dispersion liquid, and the cobalt-PPy-C mixed liquid was obtained by stirring for 30 minutes at 80 degreeC. Subsequently, 5.23 g of sodium borohydride and 0.37 g of sodium hydroxide were dissolved in 500 mL of pure water to prepare an alkaline aqueous solution. Next, an alkaline aqueous solution was gradually added until the pH of the cobalt-PPy-C mixed solution reached 11.1, and the mixture was allowed to stand at 80 ° C. for 30 minutes. In addition, all operations up to this operation in 2) (operation for adding an alkaline aqueous solution) were performed in a nitrogen atmosphere. Thereafter, the cobalt-PPy-C mixture was filtered, washed with warm water, further washed with sulfuric acid, and then vacuum dried at 90 ° C. As a result, a dry powder of cobalt-supported PPy-C (cobalt support concentration: 10% by mass) in which cobalt was supported on PPy-C was obtained.

Production Example 2 (Production of catalyst precursor)
Cobalt ethoxyethylate toluene solution (concentration 0.833 mol / kg) in which cobalt is divalent 5.39 g (cobalt content 0.265 g) and carbon (E-TEK Vulcan XC-72, specific surface area 250 m) ^{2 /} g) and 4.97 g were mixed in 15 mL of an organic solvent (toluene).

  Next, 81 mL of pure water was added to the obtained mixture to perform hydrolysis. Then, after washing with water and drying at 60 ° C. for 12 hours, the catalyst precursor was obtained by heating (primary firing) under the following primary firing conditions.

[Primary firing conditions]
Atmosphere condition: nitrogen gas atmosphere Temperature increase rate: 5 ° C / min
Heating temperature: 550 ° C
Heating time: 1 hour The obtained catalyst precursor was allowed to cool to room temperature.

Production Example 3 (Production of second catalyst)
The catalyst precursor obtained in Production Example 2 was heated (secondary calcination) under the following secondary calcination conditions. This obtained the 2nd catalyst (cobalt oxide carrying carbon).

[Secondary firing conditions]
Atmosphere condition: air gas atmosphere Temperature increase rate: 5 ° C / min
Heating temperature: 250 ° C
Heating time: 5 hours The obtained second catalyst was allowed to cool to room temperature. The yield of the second catalyst was 5.3 g (0.265 g in terms of cobalt).

Production Example 4
A catalyst precursor was obtained in the same manner as in Production Example 2 except that carbon (Vulcan XC-72 manufactured by E-TEK, specific surface area 250 m ² / g) was not blended. Thereafter, in the same manner as in Production Example 3, a carbon unsupported cobalt oxide was obtained.
<Analysis>
The catalyst precursor obtained in Production Example 2, and the XRD (X-ray diffraction) pattern and XAFS (X-ray absorption fine structure) of the second catalyst obtained in Production Example 3 were measured, and the catalyst precursor was measured. The state of cobalt contained in each of the body and the second catalyst was analyzed.

As a result, it was confirmed that the catalyst precursor contained metallic cobalt, while no cobalt oxide (Co ₃ O ₄ ) was contained.

Moreover, it was confirmed that the second catalyst contains both metallic cobalt and cobalt oxide (Co ₃ O ₄ ).

FIG. 2 shows an XRD (X-ray diffraction) pattern of the catalyst precursor and the second catalyst, and FIG. 3 shows a Fourier transform image of XAFS (X-ray absorption fine structure). 2 and 3 also show peaks corresponding to metallic cobalt and cobalt oxide (Co ₃ O ₄ ).

Example 1
2 mg of the first catalyst obtained in Production Example 1 and 8 mg of the second catalyst (cobalt oxide-carrying carbon) obtained in Production Example 3 were mixed to obtain a mixed powder. This was used as a cathode catalyst.

Comparative Example 1
2 mg of the first catalyst obtained in Production Example 1 and 8 mg of the cobalt oxide carbon non-supported body obtained in Production Example 4 were mixed to obtain a mixed powder. This was used as a cathode catalyst.

Comparative Example 2
2 mg of the first catalyst obtained in Production Example 1 and 8 mg of the catalyst precursor obtained in Production Example 2 were mixed to obtain a mixed powder. This was used as a cathode catalyst.

Comparative Example 3
The first catalyst obtained in Production Example 1 was prepared. This was used as a cathode catalyst.
<Evaluation test>
1) Preparation of test piece A mixture of the powder obtained in each Example and each Comparative Example and a proton exchange resin (Nafion (registered trademark of DuPont)) was appropriately dispersed in an organic solvent (2-propanol) to prepare an ink. Was prepared.

  Next, 10 μL of the obtained ink was weighed with a micropipette and dropped onto a glassy carbon electrode. Thereafter, the glassy carbon was dried to obtain a test piece.

In the test piece, the amount of the catalyst supported on the electrode was 10 μg / cm ² .

2) Activity measurement of oxygen side electrode The activity of the oxygen side electrode was measured by an electrochemical measurement method (cyclic voltammetry) using a rotating disk electrode. More specifically, the potential was scanned in a 1N aqueous KOH solution deoxygenated by nitrogen bubbling to perform test piece stabilization and background measurement. Subsequently, oxygen was bubbled into this aqueous solution to saturate the oxygen, and the oxygen reduction activity of the oxygen side electrode was measured. The potential scanning range was 0.3 V (vs. RHE (reversible hydrogen electrode)) to 1.1 V (vs. RHE (reversible hydrogen electrode)), and the electrode rotation speed was 1600 rpm.

3) Measurement results The results measured in 2) are shown in FIG. 4 and FIG. 4 shows the results of Example 1 and Comparative Example 1, and FIG. 5 shows the results of Example 1, Comparative Examples 2 and 3.

  As shown in FIG. 4, the cathode catalyst of Example 1 including cobalt oxide-supported carbon as the second catalyst is superior to the cathode catalyst of Comparative Example 1 including a cobalt non-supported carbon oxide as the second catalyst. Showed oxygen reduction activity.

  This is presumably because the electric conductivity of the second catalyst is improved by supporting the cobalt oxide on carbon.

  Further, as shown in FIG. 5, the cathode catalyst of Example 1 including cobalt oxide-supported carbon as the second catalyst is used only in Comparative Example 2 including the catalyst precursor (metal cobalt) and the first catalyst. It can be seen that the oxygen reduction activity is superior to that of Comparative Example 3.

  The present invention is not limited to the above description, and various design changes can be made within the scope of the matters described in the claims.

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Fuel side electrode 3 Oxygen side electrode 4 Electrolyte layer 5 Fuel supply member 6 Oxygen supply member S Fuel cell

Claims (4)

A cathode catalyst used for an oxygen side electrode of a fuel cell,
A first catalyst comprising a transition metal and polypyrrole;
A cathode catalyst comprising: a second catalyst in which cobalt oxide containing Co ₃ O ₄ is dispersed in carbon. The second catalyst is
Obtaining a catalyst precursor by heating a cobalt compound and carbon at 400 to 700 ° C. in a non-oxidizing atmosphere, and heating the catalyst precursor at 100 to 350 ° C. in an oxidizing atmosphere The cathode catalyst according to claim 1, wherein: Obtaining a first catalyst comprising a transition metal and polypyrrole;
A step of obtaining a second catalyst in which cobalt oxide containing Co ₃ O ₄ is dispersed in carbon, and a step of obtaining a cathode catalyst by mixing the first catalyst and the second catalyst,
The step of obtaining the second catalyst comprises:
A step of obtaining a catalyst precursor by heating a cobalt compound and carbon at 400 to 700 ° C. in a non-oxidizing atmosphere; and
A method for producing a cathode catalyst, comprising a step of heating the catalyst precursor at 100 to 350 ° C. in an oxidizing atmosphere. An electrolyte capable of moving an anion component, and a fuel-side electrode and an oxygen-side electrode arranged to face each other with the electrolyte interposed therebetween,
A fuel cell, wherein the oxygen-side electrode contains the cathode catalyst according to claim 1 or 2.

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