JP2013191475A - Catalyst ink for fuel cell and coating sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst ink which can form an excellent catalyst layer for cathode fuel cell, by using a carbon-based catalyst that is safe and inexpensive when compared with a platinum-based catalyst, and exhibiting excellent coating properties for a proton conductive polymer solid electrolyte membrane.SOLUTION: The catalyst ink used for formation of the electrode of a solid polymer fuel cell is a carbon catalyst ink for fuel cell containing a nitrogen atom-containing carbon catalyst, a proton conductive polymer electrolyte, a solvent having a boiling point of 70-130°C, and water. A catalyst coating sheet is produced by coating a proton conductive polymer electrolyte membrane with the catalyst ink, and then drying the membrane.

Description

  The present invention relates to a catalyst ink composition for a fuel cell that does not use a noble metal, and a coated sheet thereof, which are used for a polymer electrolyte fuel cell.

  A fuel cell is a system that takes out electricity by a chemical reaction between hydrogen and oxygen, and produces only water, so that the load on the environment is small, and has attracted attention as a power generation method that replaces oil, natural gas, and nuclear power.

A battery cell of a polymer electrolyte fuel cell includes a proton permeable polymer solid electrolyte membrane, and a membrane electrode assembly (Membrane Electrode Assembly) composed of an anode-side and cathode-side electrode catalyst layer sandwiching the electrolyte membrane from both sides. (Hereinafter abbreviated as MEA), a gas diffusion layer (hereinafter abbreviated as GDL) is provided outside each catalyst layer, and a separator is further provided outside.
Conventionally, platinum-supported carbon has been mainly used as an electrode layer catalyst, but platinum is limited in its reserves and is expensive, so as a cathode-side electrode catalyst, research on platinum alternative catalysts using carbon as the main raw material has been conducted. Has been done. This carbon-based catalyst is advantageous in that it has no risk of being ignited during production unlike a platinum catalyst and is inexpensive. However, the performance is still not sufficient as compared with a noble metal catalyst using platinum or the like, and it is necessary to use a large amount of the catalyst in order to improve the catalyst performance.

  When platinum-supported carbon particles are used as a catalyst, as disclosed in Patent Document 1, cracking can be prevented by using a solvent having a boiling point of 120 to 150 ° C. However, when a carbon-based catalyst is used, the amount of catalyst, that is, the coating amount must be increased as compared with the platinum catalyst, so that the degree of occurrence of cracking increases, and when the MEA is produced, the solid polymer electrolyte membrane There is a problem that the transferability to is poor.

  Patent Documents 2, 3 and 4 disclose examples using a carbon catalyst. However, in consideration of mass productivity, it has been clarified whether or not a carbon catalyst film can be formed by a normal coating method. Absent.

JP 2010-140699 A JP 2009-295441 A JP 2010-221126 A JP 2011-195351 A

  The problem to be solved by the present invention is that a good catalyst layer for a cathode fuel cell can be formed by using a carbon-based catalyst that is safer and cheaper than a platinum-based catalyst, and a proton conductive polymer solid electrolyte It is an object of the present invention to provide a catalyst ink excellent in applicability to a film.

The present invention is a catalyst ink used for forming an electrode of a polymer electrolyte fuel cell, comprising a carbon catalyst containing a nitrogen atom, a proton conductive polymer electrolyte, a solvent having a boiling point of 70 to 130 ° C., and water. The present invention relates to a carbon catalyst ink for a fuel cell.
The present invention also relates to the carbon catalyst ink for a fuel cell according to claim 1, wherein the water content in the ink is 1 to 30% by weight and the total solid content in the ink is 15 to 50% by weight.
Furthermore, the present invention relates to a catalyst-coated sheet obtained by coating and drying the ink according to any one of claims 1 to 2 on a proton conductive polymer electrolyte membrane.

According to the present invention, by using a nitrogen atom-containing carbon catalyst as a fuel cell catalyst, the catalyst activity is obtained and the dispersibility in the polymer electrolyte solution is also improved.
Furthermore, in the present invention, by using a solvent having a boiling point of 70 to 130 ° C., it becomes easy to apply and dry the catalyst ink on the solid polymer electrolyte, and the water content in the ink is further reduced to 10% by weight or less. Formation of the catalyst coating layer is facilitated.

  The reason is that when the amount of the catalyst applied is increased, the absolute amount of water contained is also increased, and there is a concern that the proton conductive polymer electrolyte used as the base material may deteriorate or the wettability to the base material may decrease. By setting the water content to 1 to 30% by weight or less, swelling and deterioration of the proton conductive polymer electrolyte can be prevented and good wettability can be maintained. Furthermore, by setting the total solid content of the ink to 15 to 50% by weight, it is possible to prevent the ink from spreading unnecessarily due to the solvent and to prevent the coating from cracking when the catalyst coating amount is increased.

  As a result, it is possible to avoid the problem due to transfer failure when the coating amount is increased by direct coating on the proton conductive polymer electrolyte membrane. Therefore, according to the present invention, it is possible to provide a catalyst-coated sheet using a catalyst ink having a good coating performance, which is inexpensive, safe and does not use a noble metal.

  Embodiments of the present invention will be described below. In the present specification, “carbon catalyst ink for fuel cell” may be abbreviated as “carbon catalyst ink”, and “catalyst coated sheet” may be abbreviated as “coated sheet”.

(1) Carbon catalyst containing nitrogen atom The carbon catalyst containing nitrogen atom is obtained by heat-treating a carbon material and a precursor of nitrogen atom containing at least one organic pigment.

  Further, instead of the organic pigment, after dissolving and dispersing a precursor of a nitrogen atom containing one or more macrocyclic compounds not containing a noble metal element, it is deposited on the surface of the carbon material, washed and dried, and the dried product A carbon catalyst can also be obtained by heat-treating.

  Macrocyclic compounds that do not contain organic pigments or noble metal elements contain one or more nitrogen atoms or metal elements that are considered to be important factors in the catalytic activity of the carbon catalyst in the present invention. By using it as a raw material, a catalytic activity function can be efficiently introduced on the surface of the carbon material.

  Furthermore, the carbon catalyst in the present invention can contain a resin component or a natural material in addition to the nitrogen atom precursor. Therefore, organic pigments that easily sublimate and macrocyclic compounds that do not contain a noble metal element are also likely to remain in the heat treatment and can be suitably used as a raw material for the carbon catalyst.

(Carbon material)
The carbon material used in the carbon catalyst of the present invention includes carbon black (furnace black, acetylene black, ketjen black, medium thermal carbon black), activated carbon, graphite, carbon nanotube, carbon nanofiber, carbon nanohorn, graphene nanoplatelet And nanoporous carbon.

  The carbon material in the previous period has various physical properties and costs such as particle diameter, shape, BET specific surface area, pore volume, pore diameter, bulk density, DBP oil absorption, surface acid basicity, surface hydrophilicity, and conductivity depending on the type and manufacturer. Therefore, select the most suitable material according to the intended use and required performance.

Examples of commercially available carbon materials used in the present invention include Ketjen Black manufactured by Akzo Corporation such as Ketjen Black EC-300J and EC-600JD;
Furnace blacks manufactured by Tokai Carbon, such as Toka Black # 4300, # 4400, # 4500, and # 5500;
Furnace Black made by Degussa such as Printex L;
Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULT
Furnace black made by Colombian, such as RA, Conductex SC ULTRA, 975 ULTRA, PUER BLACK100, 115, and 205;
# 2350, # 2400B, # 2600B, # 30050B, # 3030B, # 3230B, # 3350B, # 3400B, and # 5400B furnace black manufactured by Mitsubishi Chemical Corporation;
Furnace black from Cabot, such as MONARCH 1400, 1300, 900, Vulcan XC-72R, and Black Pearls 2000;
Furnace black manufactured by TIMCAL, such as Ensaco 250G, Ensaco 260G, Ensaco 350G, and SuperP-Li;
Acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd. such as Denka Black, Denka Black HS-100 and FX-35;
Carbon nanotubes manufactured by Showa Denko KK such as VGCF, VGCF-H, VGCF-X;
Carbon nanotubes manufactured by Meijo Nanocarbon Co., Ltd .;
graphene nanoplatelets made by XGSciences such as xGnP-C-750, xGnP-M-5;
Nano-carbon produced by Easy-N;
However, it is not limited to these.

(Organic pigment)
Examples of the organic pigment used in the carbon catalyst include various pigments used in printing inks, inkjet inks, color filter resist inks, and the like. Such pigments include soluble azo pigments, insoluble azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, perylene pigments, perinone pigments, dioxazine pigments, anthraquinone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments. , Anthanthrone pigments, indanthrone pigments, flavanthrone pigments, pyranthrone pigments, diketopyrrolopyrrole pigments, and the like, and phthalocyanine pigments correspond to the macrocyclic compounds containing no noble metal element.

(Macrocyclic compounds that do not contain precious metal elements)
Macrocyclic compounds are defined as compounds having 9 or more atoms (including the case where all are heteroatoms) and 3 or more bonded atoms (Coordination Chemistry of Macrocyclic Compounds, GAMelson, Plenum Pres, New York & London, 1979). In the present invention, a macrocyclic compound means a compound having an N4 structure in which four nitrogen atoms are arranged on a plane in a basic skeleton.

  The macrocyclic compound containing no precious metal element is a kind whose central metal is selected from cobalt, iron, nickel, manganese, copper, titanium, vanadium, chromium, zinc, tin, aluminum, magnesium, and organic coordination Examples thereof include a phthalocyanine compound, a naphthalocyanine compound, a porphyrin compound, and a tetraazaannulene compound to which a child is bonded. Further, a macrocyclic compound not containing a noble metal element has no problem even if an electron-withdrawing functional group or an electron-donating functional group is introduced. Among them, cobalt phthalocyanine compounds, nickel phthalocyanine compounds, and iron phthalocyanine compounds are known to be inexpensive and have high oxygen reduction activity. Therefore, carbon catalysts synthesized using them are inexpensive and have high oxygen content. Since it becomes a carbon catalyst which has a reduction activity, it is more preferable as a raw material.

(Resin component)
Resin components used for carbon catalysts include acrylic resin, polyurethane resin, polyester resin, butyral resin, phenol resin, epoxy resin, phenoxy resin, polystyrene resin, urea resin, melamine resin, alkyd resin, formaldehyde resin, polyacrylamide, silicone Resin, fluororesin, polyvinyl acetate resin, ethylene / vinyl acetate resin, ketone resin, petroleum resin, casein, shellac, gelatin, gilsonite, rosin, rosin ester, polyvinyl alcohol, polyvinyl pyrrolidone, nitrocellulose, hydroxyethyl cellulose, carboxymethyl cellulose, etc. Cellulose resins, synthetic rubbers such as styrene-butadiene rubber and fluorine rubber, and conductive resins such as polyaniline and polyacetylene. Moreover, the modified body of these resin, a mixture, or a copolymer may be sufficient.

(Natural materials)
Examples of natural materials used for the carbon catalyst include natural materials selected from the group consisting of unmodified or modified polysaccharides, natural waxes, and vegetable oils.

An example of a method for producing a carbon catalyst will be described.
Examples of the method for producing a carbon catalyst include a method including a step of producing a precursor containing at least one organic pigment and a step of heat-treating the precursor.
As a method for producing the precursor, one type of organic pigment may be used alone, but there are also cases where two or more types of organic pigments are used, or in combination with a carbon material, a resin component, or a natural material. . When two or more types of components are mixed or combined, there are methods such as dry mixing and wet mixing, and a dry processing machine or a wet processing machine can be used.

  Examples of dry processing machines include roll mills such as 2 rolls and 3 rolls, high-speed stirrers such as Henschel mixers and super mixers, fluid energy crushers such as micronizers and jet mills, attritors, and particle composites manufactured by Hosokawa Micron. Examples of the apparatus include “Nanocure”, “Nobilta”, “Mechanofusion”, Nara Machinery Co., Ltd. powder surface modification device “Hybridization system”, “Mechanomicros”, “Miraro”, and the like.

  Examples of wet processing machines include mixers such as dispersers, homomixers, or planetary mixers, homogenizers, paint conditioners (manufactured by Red Devil), ball mills, sand mills (“Dynomill” manufactured by Shinmaru Enterprises, etc.), Examples thereof include, but are not limited to, media-type dispersers such as an attritor, medialess dispersers such as a wet jet mill, and other roll mills and kneaders.

  Moreover, in the case of wet mixing, the process of drying the dispersion produced using the wet processing machine is needed. In this case, examples of the drying device to be used include a shelf dryer, a rotary dryer, a flash dryer, a spray dryer, a stirring dryer, and a freeze dryer.

In the step of heat-treating a precursor containing one or more organic pigments, the heating temperature varies depending on the organic pigment to be treated, but is usually in the range of 500 to 1000 ° C, preferably 600 to 900 ° C.
When the heating temperature in the heat treatment step is lower than 500 ° C., the organic pigment is hardly melted or thermally decomposed, and the carbon catalyst activity may be lowered. On the other hand, when the heating temperature exceeds 1000 ° C., the thermal decomposition and sublimation of the precursor of nitrogen atoms becomes intense, and nitrogen atoms and metal elements that are considered as one of the catalytic activity factors hardly remain on the carbon material surface. This is because the catalytic activity may be low.

  Furthermore, regarding the atmosphere in the heat treatment process, it is necessary to carbonize the precursor of nitrogen atoms by incomplete combustion as much as possible, and to leave nitrogen elements and metal elements in the vicinity of the surface of the carbon material. A gas atmosphere or a reducing gas atmosphere in which hydrogen is mixed in nitrogen or argon is preferable. Further, in order to suppress a reduction in the amount of nitrogen element in the carbon catalyst during the heat treatment, the heat treatment can be performed in an ammonia gas atmosphere containing a large amount of nitrogen element.

(2) Proton Conducting Polymer Electrolyte Examples of the proton conducting polymer electrolyte include ion exchange resins that are organic fluorine-containing polymer compounds. For example, perfluorocarbon sulfonic acid resin, sulfonated polyether ketone, sulfonated polysulfide, sulfoalkylated polyethersulfone, sulfoalkylated polysulfide and the like can be mentioned. Examples of commercially available products include “Mafion” (registered trademark, manufactured by DuPont), “Flemion” (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like.

(3) Solvent having a boiling point of 70 to 130 ° C. Examples of the solvent used in the present invention include a solvent having a boiling point of 70 to 130 ° C. Furthermore, a solvent that is freely miscible with water is more preferable. When the coating temperature is less than 70 ° C., drying is fast, and thus cracking is likely to occur when the coating is applied thick. On the other hand, if it exceeds 130 ° C., the solvent tends to remain in the coating depending on the drying conditions, and the proton conductive polymer electrolyte membrane tends to be softened and deformed. Moreover, it is because the dispersion | distribution particle | grains of a proton conductive polymer electrolyte will be easy to be formed in a liquid by using the solvent freely mixed with water. Here, mixing freely with water means mixing with an arbitrary mixing ratio.

  Examples of the solvent having a boiling point of 70 to 130 ° C. include ester solvents, ketone solvents, glycol ether solvents, aliphatic solvents, aromatic solvents, alcohol solvents, glycol solvents, ether solvents, and the like. It is also possible to mix two or more types.

  Examples of the alcohol solvent include ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, t-butyl alcohol, sec-amyl alcohol, 2-methyl-1-butanol, t -Amyl alcohol, sec-isoamyl alcohol, neoamyl alcohol, etc. are mentioned.

  Examples of the glycol ether solvent include ethylene glycol monomethyl ether and propylene glycol monomethyl ether.

  Examples of the ester solvent include ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate and the like.

  Examples of the ketone solvent include methyl ethyl ketone, methyl propyl ketone, diethyl ketone, butyl methyl ketone, and methyl isobutyl ketone.

Examples of the aliphatic type include n-heptane, octane, isooctane, cyclohexane, and methylcyclohexane. Examples of the aromatic type include toluene, and other examples include dimethyl carbonate.

  Among the above solvents, alcohol-based, glycol-based and ketone-based solvents are preferable, and among them, ethanol, propylene glycol monomethyl ether, and methyl ethyl ketone are preferable from the viewpoint of drying property and film-forming property.

(4) Production of carbon catalyst ink In the carbon catalyst ink of the present invention, carbon catalyst particles containing nitrogen atoms are mixed by dispersing a proton conductive polymer electrolyte, a solvent having a boiling point of 70 to 130 ° C., and water. Can be manufactured. Further, if necessary, various commonly used additives such as a plasticizer, a lubricant, a dispersant, an antifoaming agent, a surface tension adjusting agent, an antistatic agent, an antioxidant, and a chelating agent can be included. Furthermore, other commonly used organic / inorganic fillers may be included within the range not contrary to the object of the present invention. The dispersion is performed by a conventionally known method, for example, using a ball mill, an attritor, a sand mill, a jet mill, a three roll mill, a paint shaker or the like.

  The carbon catalyst ink of the present invention contains water. The content is preferably in the range of 1 to 30% by weight in the ink. If it contains more than 30% by weight of water, it may cause cracking of the coating after coating and agglomeration of the carbon catalyst particles. If it is less than 1% by weight, the proton conductive polymer electrolyte may This is because handling becomes worse.

  The total solid content of the carbon catalyst ink of the present invention is preferably 15 to 50% by weight. More preferably, it is 20 to 40% by weight. When it is less than 15% by weight, unnecessary spreading of the catalyst particles is likely to occur during the drying process, and cracking of the coating tends to occur. On the other hand, when it exceeds 50% by weight, the fluidity of the carbon catalyst ink is lowered and it becomes difficult to handle.

(5) Application of carbon catalyst ink The carbon catalyst ink of the present invention is a conventionally known method such as gravure printing, flexographic printing, or screen printing on at least one surface of a film such as “Nafion” (registered trademark, manufactured by DuPont). After being applied by rotary screen printing, spray coating, die coating, lip coating, knife coating, dip coating, curtain coating, roll coating, etc., it is usually dried at 40 to 100 ° C., preferably 50 to 70 ° C. A coated sheet having a carbon catalyst layer on one side is obtained.

  The carbon catalyst ink of the present invention has a water content of 10% by weight or less in the catalyst ink, a total solid content of the ink of 30 to 70% by weight, and further contains a solvent having a boiling point of 70 to 130 ° C. Therefore, since it has excellent film form performance, it varies depending on the coating method, but it can be directly applied in the range of 0.5 to 8.0 mg / cm 2 by weight after drying, and undergoes a transfer process. The MEA can be manufactured without any problem.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples. In the examples, “part” represents “part by weight” and “%” represents “% by weight”.

The following measuring instruments were used for the analysis of the carbon catalyst and the surface-treated carbon material as a precursor.
-XRD (X-ray diffraction measurement); X'Pert PRO MPD manufactured by PANalytical
CHN elemental analysis: Perkin Elmer 2400 type CHN elemental analysis ICP emission spectroscopic analysis: SPECTRO SPECTRO ARCOS FHS12
SEM (scanning electron microscope); SEM S-4300 manufactured by Hitachi, Ltd.

[Example of carbon catalyst synthesis (1)]
Pigment Black 1 (BASF) and Ketjen Black (Lion EC-600JD) were weighed at a weight ratio of 1: 1, and dry mixed in a mortar to obtain a precursor.
The precursor powder was filled in an alumina crucible, heat-treated at 800 ° C. for 1 hour in a nitrogen atmosphere in an electric furnace, and the resulting carbide was pulverized in a mortar to obtain a carbon catalyst (1).
The obtained carbon catalyst had a molar ratio N (nitrogen) / C (carbon) of 0.01 based on CHN elemental analysis.

[Preparation Example of Proton Conductive Polymer Electrolyte Dispersion]
The proton conductive polymer electrolyte dispersion used in the present invention was prepared as follows. A commercially available Nafion solution (manufactured by Wako Pure Chemical Industries, Ltd., Nafion 20% by weight dispersion) was distilled off using a rotary evaporator and the solvent was replaced, and a solid content 35% by weight dispersion (solvent: water / ethanol = 15). / 50, weight ratio).

[Example 1]
In accordance with the formulation shown in Table 1, 10 parts by weight of the carbon catalyst (1) obtained in Synthesis Example 1 above, 14.3 parts by weight of the proton conductive polymer electrolyte dispersion obtained in the above Preparation Example, and 25.3 ethanol. Part by weight and 0.4 part by weight of water were mixed and dispersed for 10 minutes using a paint shaker to obtain a carbon catalyst ink.

[Examples 2 to 10]
A carbon catalyst ink was obtained in the same manner as in Example 1 except that the formulation in Table 1 was changed.

The carbon catalyst ink obtained in the examples was evaluated by the following method.
[Evaluation of coating state]
The carbon catalyst ink was applied onto a proton conductive polymer film, Nafion NR212 (manufactured by DuPont, thickness of about 51 μm) at a speed of 3 m / min using a 10 mil doctor blade. After coating, it was dried at 80 ° C. for 30 minutes using a hot air drying oven to obtain a coated sheet. The obtained coated sheet was observed at 500 times using a digital microscope (manufactured by Keyence, VHX-900 type). The evaluation of the coated sheet was in accordance with the following evaluation criteria.

○: No cracks or uneven coating (very good)
Δ: Cracks and coating unevenness (good)
×: Very many cracks and coating unevenness (defect)

  When the fuel cell was created using the said application | coating sheet, all showed the favorable characteristic.

Claims (3)

  A catalyst ink used for forming an electrode of a polymer electrolyte fuel cell, comprising: a carbon catalyst containing nitrogen atoms; a proton conductive polymer electrolyte; a solvent having a boiling point of 70 to 130 ° C .; and water. Carbon catalyst ink for batteries.   The carbon catalyst ink for fuel cells according to claim 1, wherein the content of water in the ink is 1 to 30% by weight and the total solid content in the ink is 15 to 50% by weight.   A catalyst-coated sheet obtained by coating and drying the ink according to claim 1 on a proton-conductive polymer electrolyte membrane.