JP2001076739A - Separator for phosphoric acid fuel cell and fuel cell using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat resistance, acid resistance, electric characteristics, and general characteristics at a low cost by carbonizing the resin component in a compact including a resin and expansion graphite powder to manufacture a separator. SOLUTION: A resin and expansion graphite powder mixed by a dry method having good workability at a low cost are thermally molded in a die and hardened nearly completely by a heat treatment, then this separator is manufactured by carbonization in the atmosphere of inert gas such as nitrogen at 200 deg.C or above. An inexpensive powdery phenol resin hardened by ring-opening polymerization is suitable for this resin. Little gas is generated at hardening, moldability and general characteristics are good, the flow of the resin at molding is good if the average grain size is set to 1-1,000 μm, they are uniformly mixed, and the mechanical properties are not deteriorated. If the number average grain size is set to 5-100 μm for the expansion graphite powder obtained by heating, compression molding, and crushing from an interlayer compound generated by the dipping of the natural graphite having a highly developed crystal in a solution including an acid material and an oxidant, the mixing property and mechanical strength are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid type fuel cell separator and a fuel cell using the phosphoric acid type fuel cell separator.

[0002]

2. Description of the Related Art A separator impregnated with a phosphoric acid-resistant sheet-like substance is used as an electrolyte, and this is used in a phosphoric acid type fuel cell having a high operating temperature (around 200 ° C.). A high acid resistance product required from the properties and the type of electrolyte is required, and a processed product of a graphite plate has been conventionally used.

[0003] However, when a processed product of a graphite plate is used, a very high-precision cutting technique is required to form a complicated rib shape, and it takes time to finish the cutting. The separator obtained through the above process is very expensive, and the fuel cell itself using a large number of separators is naturally expensive, which has reduced the general penetration rate.
As a general-purpose separator, there is a molded product in which a synthetic resin, graphite, or the like is mixed. However, since the matrix is a general-purpose resin, the operating environment is high temperature and a strong acid or strong alkali limits the range of use.

[0004]

The inventions according to claims 1 to 6 are excellent in mass productivity and low in cost, can be used even at high temperatures, have excellent acid resistance, and have problems in general physical properties such as electric characteristics. The present invention provides a phosphoric acid type fuel cell separator. The invention according to claim 7 is to provide a high-performance phosphoric acid fuel cell having a separator which is inexpensive and has excellent heat resistance, acid resistance, electrical characteristics and general characteristics.

[0005]

The present invention relates to a phosphoric acid type fuel cell separator obtained by carbonizing a resin component in a molded product containing a resin and expanded graphite powder. Also, the present invention
The present invention relates to the above phosphoric acid type fuel cell separator, wherein the resin is a powdery phenol resin which undergoes a curing reaction by ring-opening polymerization. The present invention also relates to the above-mentioned separator for a phosphoric acid type fuel cell, wherein the powdery phenol resin has an average particle size in a range of 1 μm to 1000 μm.

The present invention also relates to the above-mentioned separator for a phosphoric acid type fuel cell, wherein the expanded graphite powder has an average particle size of 5 μm to 1000 μm. Further, the present invention relates to the phosphoric acid type fuel cell separator, wherein the carbonization temperature of the resin is 200 ° C. or higher. The present invention also relates to the phosphoric acid type fuel cell separator, wherein the carbonized atmosphere is an inert gas. Furthermore, the present invention relates to a fuel cell having the above-mentioned separator.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The separator for a phosphoric acid type fuel cell of the present invention is characterized by heat resistance, acid resistance, electric characteristics and general characteristics by carbonizing a resin component in a molded body containing a resin and expanded graphite powder. Excellent.

In the present invention, the resin used is:
It is preferable to use a powdery thermosetting resin or a thermoplastic resin. There are no particular restrictions on the structure, the number of functional groups, the type of reaction, etc., for example, solid epoxy resin, melamine resin, acrylic resin, resol type, various phenolic resins such as novolak type, powdered polyamide resin, powdered polyamideimide resin, Polyetherimide resin,
A phenoxy resin or the like is used. These resins may be used in combination with a curing agent, a curing accelerator, a curing catalyst, and the like, if necessary. For example, novolak type phenolic resin
Hexamethylenetetramine or the like is used as a curing catalyst. Among these resins, a phenol resin is preferable in view of excellent property balance, economy, workability, and the like.

As the phenol resin, a phenol resin which undergoes a curing reaction by ring-opening polymerization, which has a small amount of gas generated during the curing reaction, has good moldability, and has good various properties, is particularly preferably used. As the phenol resin that undergoes a curing reaction by ring-opening polymerization, a resin in the form of a powder is preferable.

Embedded image The resin having a dihydrobenzoxazine ring shown in (1) is excellent in moldability, heat resistance and the like, and is preferred. This resin causes a ring-opening polymerization reaction by heating, and can form a crosslinked structure having excellent properties without using a catalyst or a curing agent and without generating volatile components.

The resin containing a dihydrobenzoxazine ring is represented by the general formula (b)

Embedded image (Wherein the hydrogen bonded to the aromatic ring may be substituted with a substituent except for one of the ortho positions of the hydroxyl group) and a general formula (c)

Embedded image (Wherein R ¹ is a hydrocarbon group, and the hydrogen bonded to the aromatic ring may be substituted with a substituent), which has the effect of suppressing generation of volatile gas. It is preferable because the molar ratio of general formula (b) / general formula (c) is 4/1 to 1/9 in view of heat resistance and the like. This ratio can be adjusted by the ratio of the materials used and the like.

In the chemical structural units represented by the general formulas (b) and (c), the substituent which may be substituted in place of hydrogen bonded to an aromatic ring is not particularly limited, but a methyl group And an alkyl group having 1 to 10 carbon atoms such as an alkyl group such as an ethyl group and a propyl group. In the general formula (b), one of the ortho positions of the hydroxyl group has hydrogen for a curing reaction. Further, in the general formula (c), examples of the hydrocarbon group represented by R1 include those having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a cyclohexyl group, a phenyl group and a substituted phenyl group.

When the number of the general formula (b) contained in one molecule is m and the number of the general formula (c) is n in one molecule, m is 1 or more and n is 1 Anything above is acceptable,
It is preferable that m + n is 3 to 10 on a number average in terms of characteristics of the cured product, for example, heat resistance.

The above-mentioned chemical structural units may be directly bonded to each other, or may be bonded via various groups.
Such groups include, as organic groups, alkylene groups,
Preferred examples include hydrocarbon groups such as xylylene groups, and specifically,

Embedded image Wherein R ² is a hydrogen atom or a methyl group,
Ethyl group, propyl group, isopropyl group, phenyl group,
A substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms), and a linear alkylene group having 5 to 20 carbon atoms. This can be selected according to the type of the compound having a phenolic hydroxyl group used as a raw material.

The resin containing a dihydrobenzoxazine ring can be synthesized, for example, from a compound having a phenolic hydroxyl group, formaldehyde, and a primary amine. As a method for synthesizing a resin containing a dihydrobenzoxazine ring from these materials, a mixture of a compound having a phenolic hydroxyl group and a primary amine is preferably added to formaldehydes heated to preferably 70 ° C. or more, Is 70 ° C to 110 ° C, more preferably 90 ° C
The reaction is carried out at a temperature of from 100 ° C to 100 ° C, preferably for 20 minutes to 120 minutes, and then dried under reduced pressure at a temperature of preferably 120 ° C or lower.

Examples of the compound having a phenolic hydroxyl group include bisphenol compounds such as bisphenol A, bisphenol F, and biphenol; low-molecular phenol compounds such as trisphenol compounds and tetraphenol compounds; and phenol resins. Phenol resins include phenol or xylenol, t
-Monophenolic compounds such as alkylphenols such as butylphenol and octylphenol, resorcinol, polyphenol compounds such as bisphenol A and novolak resins or resol resins obtained by reacting formaldehydes, phenol-modified xylene resins,
Melamine-modified phenolic resin, polybutadiene-modified phenolic resin and the like can be mentioned.

As the formaldehyde, those which generate formaldehyde such as formalin, paraformaldehyde and hexamethylenetetramine can be used in addition to formaldehyde. Examples of the primary amine include aliphatic amines such as methylamine and cyclohexylamine, and aromatic amines such as aniline and substituted aniline. From the viewpoint of heat resistance, aromatic amines are preferred.

The mixing ratio of these compounds is not particularly limited. For example, a hydroxyl group of a compound having a phenolic hydroxyl group (at least one of its ortho positions is hydrogen)
It is preferred that the primary amine be reacted at a ratio of 0.2 to 0.9 mol and the formaldehydes at a ratio of at least twice the molar amount of the primary amine per 1 mol.

When a powdery phenolic resin is used as the resin, there is no particular limitation on the particle size distribution, but the mixing property with powdered carbon material such as expanded graphite powder (particularly in the case of the dry mixing method), and the resin at the time of molding. In consideration of the flowability of the particles, the number average particle diameter is preferably in the range of 1 μm to 1000 μm, and is preferably 5 μm.
The range of m to 500 μm is more preferable. When the number average particle size is less than 1 μm, the particles aggregate (block), not only workability is poor, but also uniform mixing with the expanded graphite powder becomes difficult, and the mechanical properties of the obtained separator tend to decrease. On the other hand, if it exceeds 1000 μm,
As described above, uniform mixing with the expanded graphite powder becomes difficult, and the mechanical properties of the obtained separator tend to decrease.

The expanded graphite powder used in the present invention is, for example, a step of dipping raw graphite in a solution containing an acidic substance and an oxidizing agent to form a graphite intercalation compound, and heating the graphite intercalation compound to form graphite crystals. It can be obtained by including a step of expanding the C-axis direction into expanded graphite, a step of compressing and molding the expanded graphite, and a step of washing and drying the pulverized powder with water as required.

The raw material graphite is not particularly limited, but is preferably graphite having a high degree of crystal development, such as natural graphite, quiche graphite, and pyrolytic graphite. Natural graphite is preferred in consideration of the balance between the obtained characteristics and economy. The natural graphite used is not particularly limited.
Commercial products such as F48C (trade name, manufactured by Nippon Graphite Co., Ltd.) and H-50 (trade name, manufactured by Chuetsu Graphite Co., Ltd.) can be used.

The acidic substance used in the processing of the raw graphite is as follows:
Generally, sulfuric acid or a mixture of sulfuric acid and nitric acid is used. The concentration of the acid is preferably 95% by weight or more. The amount of the acidic substance to be used is not particularly limited, and is determined by a target expansion ratio. For example, 1 to 100 parts by weight of graphite is used.
It is preferable to use 100 to 1000 parts by weight.

As the oxidizing agent used together with the acidic substance, it is preferable to use hydrogen peroxide or hydrochloric acid since a good expanded graphite powder can be obtained. When hydrogen peroxide is used as the oxidizing agent, the concentration of hydrogen peroxide is not particularly limited, but is preferably 20 to 40% by weight. Although the amount is not particularly limited, it is preferable to mix 5 to 60 parts by weight of hydrogen peroxide with respect to 100 parts by weight of graphite.

There is no particular limitation on the method of converting the graphite into expanded graphite. As a known method, the graphite is immersed in an acidic substance which is a mixed solution of sulfuric acid or sulfuric acid and nitric acid, and furthermore, such as hydrogen peroxide or hydrochloric acid. A method of generating a graphite intercalation compound by adding an oxidizing agent and performing a treatment, followed by washing with water and rapid heating to expand the C-axis direction of the graphite crystal. As a result, the expanded graphite becomes a worm-like shape, and becomes a complicatedly entangled form having no directionality.

In the production of the expanded graphite powder, the expanded graphite is used in a density of 0.5 g / cm ^{3 to} 1.8 g / cm ³ , preferably 0.7 g / cm ³ .
^A sheet is formed by pressing with a roll, a press or the like so as to have a density of ^{3 to} 1.7 g / cm ³ , further increasing the contact between the expanded graphites, crushing them, and classifying them as necessary. be able to. When a sheet having a density of less than 0.5 g / cm ³ is used, the electrical characteristics are not significantly improved, while a sheet having a density of more than 1.8 g / cm ³ requires a large pressure during production, Workability and productivity tend to decrease.

The average particle size of the expanded graphite powder is not particularly limited, but considering dry mixing with a powdery resin, etc.
The number average particle size is preferably in the range of 5 μm to 1000 μm,
The range of 25 μm to 500 μm is more preferable. Here, when the expanded graphite powder having a number average particle size of less than 5 μm is used, the mechanical strength of the molded separator tends to decrease. On the other hand, when the expanded graphite exceeding 1000 μm is used, the powdery resin and Tends to decrease, and it becomes difficult to obtain a uniform molded body.

The mixing ratio of the resin and the expanded graphite powder used in the present invention is as follows: resin / expanded graphite powder = 10/90 to 50/50
(Weight ratio) is preferably in the range of 20/80 to 60/40.
Is more preferable. Here, when the mixing ratio of the resin and the expanded graphite powder exceeds 10/90, the mechanical strength tends to sharply decrease, while when it is less than 50/50, the conductivity tends to sharply decrease.

The method of mixing the resin and the expanded graphite powder is not particularly limited, and the dry mixing method using a shaker, a mixer or the like is preferable in terms of cost and workability. There is no particular limitation on the molding method of the obtained mixture. For example, in the case of molding by a compression molding method, the mixed powder or tablet (for the purpose of measuring work efficiency, the powder is preformed to reduce the accumulation). The resulting block is filled in a separator molding die and thermoformed.

The separator molded product obtained by the above method is further post-cured to form a separator molded product in which the used resin is completely cured. In the case of a phosphoric acid type fuel cell separator, as described above, the separator containing a cured product of a general resin is exposed to a strong acid atmosphere and a high temperature. Decreases electrical properties. The present invention relates to a separator molded product obtained by curing the used resin obtained above almost completely, further at 200 ° C.
This is achieved by heat treatment in the above inert gas and carbonizing the cured resin.

The furnace used for the heat treatment is not particularly limited, but a batch furnace or a continuous furnace is used. Also, there is no particular limitation on the heat treatment time, the furnace volume,
The temperature can be set arbitrarily according to the temperature rising speed, the operating temperature range, the number of processed sheets, and the like. Further, as a method for setting optimal heat treatment conditions (temperature and time), measurement of mechanical strength, electrical properties and dimensions of the obtained heat treated molded product is effective. There is no particular limitation on the inert gas used for the heat treatment, but nitrogen gas is preferred in view of economy.

The size, thickness, shape and the like of the fuel cell separator according to the present invention are not particularly limited. FIG. 1 shows a perspective view of an example of the fuel cell separator of the present invention. In general, the fuel cell separator 1 is provided with ribs as shown in FIG. 1 in order to secure a flow path of a reaction gas. 2 is a rib, and 3 is a groove. FIG. 1A shows a configuration in which ribs are provided on both surfaces, and FIG. 1B shows a configuration in which ribs are provided on one surface.

[0031]

The present invention will be described below with reference to examples. Example 1 (1) Production of Expanded Graphite Powder 600 g of sulfuric acid (concentration 99% by weight) and 200 g of nitric acid (concentration 99% by weight) were put into a 3 liter glass beaker. This was mixed with 400 g of graphite F48C (fixed carbon: 99% by weight or more, trade name, manufactured by Nippon Graphite Co., Ltd.) and stirred for 6 minutes with a stirring motor (60 rpm) equipped with a glass splash. (Concentration 35% by weight)
Stir for 15 minutes. After the stirring, the graphite oxide and the acid component were separated by filtration under reduced pressure, and the obtained graphite oxide was transferred to another container.
One liter of water was added, the mixture was stirred for 10 minutes, and washed graphite oxide and washed water were separated by filtration under reduced pressure.

The obtained washed graphite oxide was transferred to an enamel vat, leveled, and heat-treated in a dryer heated to 120 ° C. for 1 hour to dry the water. Add 850 more
5 minutes in a heating furnace heated to a temperature of
cm ³ of expanded graphite was obtained. After cooling, the expanded graphite is rolled and processed into a sheet having a density of 1.0 g / cm ³ , and the obtained sheet is pulverized by a coarse pulverizer (Rosoplex (trade name) manufactured by Hosokawa Micron Corporation). Then, it was pulverized with a fine pulverizer (free pulverizer M-3 (trade name) manufactured by Nara Machinery Co., Ltd.) to obtain an expanded graphite powder having an average particle size of 130 μm.

(2) Production of phenolic resin (resin containing dihydrobenzoxazine ring) to undergo ring-opening polymerization 1.9 kg of phenol, formalin (37% by weight aqueous solution)
1.0 kg and 4 g of oxalic acid were charged into a 5-liter flask and reacted at reflux temperature for 6 hours. Subsequently, the internal pressure was reduced to 6666.1 Pa (50 mmHg) or less to remove unreacted phenol and water, thereby synthesizing a phenol novolak resin. The obtained resin has a softening point of 84 ° C (ring and ball method),
The trinuclear to polynuclear / binuclear ratio was 92/18 (peak area ratio by gel permeation chromatography).

Next, 1.7 kg of the synthesized phenol novolak resin (corresponding to 16 mol of hydroxyl groups) was mixed with 0.93 kg (corresponding to 10 mol) of aniline, and the mixture was mixed at 80 ° C. with 5 kg.
After stirring for an hour, a uniform mixed solution was prepared. Next, 1.62 kg of formalin was charged into a 5-liter flask, and 90
C., and the above novolak / aniline mixed solution was added little by little over 30 minutes. After the addition, 30
For 2 minutes at 100 ° C. for 2 hours
Condensed water was removed by reducing the pressure to 666.1 Pa (50 mmHg) or less to obtain a resin containing a dihydrobenzoxazine ring in which 71 mol% of the reactive hydroxyl groups were dihydrobenzoxazinated. That is, the resin containing a dihydrobenzoxazine ring contains the above-mentioned general formula (b) and the general formula (c) at a molar ratio of 1 / 2.45 for the former / the latter. Thereafter, the above-mentioned resin was pulverized with a pulverizer to obtain a powdery phenol resin with little gas generated during the reaction.

The amount of the hydroxyl group that can react in the phenol novolak resin is calculated as follows. That is, 1.7 kg of the phenol novolak resin (corresponding to 16 moles of hydroxyl groups)
Aniline 1.4 (corresponding to 16 moles), formalin 2.
The resin was reacted with 59 kg to synthesize a resin in which a dihydrobenzoxazine ring was introduced into all of the reactive hydroxyl groups. Excess aniline and formalin were removed during drying, yielding 3.34 kg. This indicates that, in the phenol novolak resin, the amount of the hydroxyl group capable of reacting was 14 mol and the dihydrobenzoxazine was cyclized.

(3) Production of separator for phosphoric acid type fuel cell 80 g of expanded graphite powder obtained in Example 1 (1) and 20 g of phenol resin powder obtained in (2) (expanded graphite powder / phenol resin = 80) / 20 (weight ratio) was weighed into a plastic bag, air was put into the bag, and the bag was inflated, and dry-mixed for 1 minute to obtain a mixed powder, in which the materials were uniformly mixed.

20 g of the mixed powder was dispensed and uniformly filled in a separator molding die heated to 180 ° C.
70 ton compression molding machine heated to ℃, gauge pressure 40kg
The molding was performed under the conditions of f / cm ² (3.92 MPa) and a molding time of 10 minutes. The obtained molded separator had a good appearance of 140 mm in length, 180 mm in width and a density of 1.3 g / cm ³ in which a rib-like projection having a height of 2 mm was formed on one surface.

Next, the molded product of the separator obtained above was sandwiched between two iron plates having a thickness of 3 mm, placed in a drier heated to 200 ° C., and heat-treated for 1 hour. It was completely reacted. Next, the obtained molded product was fixed with a deformation preventing jig, placed in a muffle furnace using an industrial nitrogen atmosphere heated to 250 ° C., and heated to 400 ° C. in 2 hours.
Heat treatment was performed for 10 hours at 00 ° C. to carbonize (carbonize) the resin. The carbonized phosphoric acid fuel cell separator had good appearance without swelling or cracks.

Example 2 The same materials as in Example 1 were used except that the heat treatment conditions in the muffle furnace were raised to 800 ° C. in 3 hours and heat-treated at 800 ° C. for 10 hours. Through the same steps as in 1, a phosphoric acid fuel cell separator was obtained. The obtained phosphoric acid fuel cell separator had a good appearance as in Example 1, and had no particular problem.

Comparative Example 1 Example 1 was repeated except that the heat treatment in the muffle furnace was not performed.
A fuel cell separator was obtained using the same materials as in Example 1 and through the same steps as in Example 1.

Evaluation Next, a part of the fuel cell separators obtained in Examples 1 and 2 and Comparative Example 1 was cut into a size of 5 mm × 5 mm × 2 mm in thickness to obtain a test piece. It was immersed in phosphoric acid heated to ℃ and evaluated for changes in appearance and specific resistance. Table 1 shows the results. In addition, the phosphoric acid treatment heats a test piece to 200 degreeC, or after immersing in phosphoric acid for 8 hours,
The test piece was left in a large amount of water for 30 minutes, washed well with water, and dried under reduced pressure at 110 ° C. for 2 hours.

[0042]

[Table 1]

As shown in Table 1, the phosphoric acid type fuel cell separators of Examples 1 and 2 which were heat treated before the phosphoric acid treatment were compared with the fuel cell separator of Comparative Example 1 which was not heat treated. Thus, the specific resistance is low, and the effect of carbonizing the resin is apparent. Further, the phosphoric acid type fuel cell separators of Examples 1 and 2 according to the present invention, which were heat-treated even after the phosphoric acid treatment, had a good appearance and the specific resistance was not so different from that before the phosphoric acid treatment. It is clear that the phosphoric acid resistance has been improved. On the other hand, the fuel cell separator of Comparative Example 1 swelled, and the specific resistance could not be measured.

Separately from the above, Pt is added to the upper and lower surfaces of the electrolyte impregnated with phosphoric acid in a phosphoric acid-resistant sheet matrix.
P of carbon fiber electrode substrate having carbon on the surface
The phosphoric acid-type fuel cell is prepared by superposing the phosphoric acid-type fuel cell separator obtained above on the both outer surfaces of the carbon fiber electrode substrate, with the t-supported carbon side surface being in contact with the electrolyte. When the performance was examined, it was confirmed that the high performance could be maintained for a long time.

[0045]

The phosphoric acid fuel cell separator according to claims 1 to 6 is excellent in mass productivity and low in cost, can be used at high temperatures, has excellent acid resistance, and has good general physical properties such as electric properties. It is a separator for a phosphoric acid type fuel cell without any problem. The phosphoric acid fuel cell according to claims 7 and 8 is a high-performance phosphoric acid fuel cell having a separator which is inexpensive and has excellent heat resistance, acid resistance, electrical characteristics and general characteristics.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a phosphoric acid type fuel cell separator according to an embodiment of the present invention, in which (a) has ribs on both sides and (b) has ribs on one side. It is.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 2 Rib part 3 Groove part

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Atsushi Fujita 3-3-1 Ayukawacho, Hitachi City, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Office F-term (reference)

Claims (7)

[Claims] 1. A phosphoric acid type fuel cell separator obtained by carbonizing a resin component in a molded article containing a resin and expanded graphite powder. 2. The phosphoric acid type fuel cell separator according to claim 1, wherein the resin is a powdery phenol resin which undergoes a curing reaction by ring-opening polymerization. 3. The powdery phenol resin has an average particle size of 1 μm.
The separator for a phosphoric acid type fuel cell according to claim 1, wherein the thickness is in a range of m to 1,000 μm. 4. The expanded graphite powder has an average particle size of 5 μm to 100 μm.
4. The phosphoric acid fuel cell separator according to claim 1, wherein the thickness is in the range of 0 μm. 5. The phosphoric acid type fuel cell separator according to claim 1, wherein the carbonization temperature of the resin is 200 ° C. or higher. 6. The phosphoric acid type fuel cell separator according to claim 1, wherein the carbonizing atmosphere is an inert gas. 7. A fuel cell comprising the separator according to claim 1.