JP3097690B1 - Polymer electrolyte fuel cell - Google Patents

Abstract

The present invention provides a solid oxide fuel cell including a stainless steel separator having extremely low poisoning of each electrode-supported catalyst due to eluting metal ions. SOLUTION: Impurities such as S, P, V, Ni and Cu are reduced, and the content of Cr and Mo is reduced to Cr: 10.5 to 35.
%, Mo: 0.5 to 5%, and 12% ≦ Cr + 3Mo
A solid oxide fuel cell including a stainless steel separator satisfying ≦ 43%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell used as a small distributed power source for a vehicle or a home.

[0002]

2. Description of the Related Art A fuel cell is a cell that generates DC power using hydrogen and oxygen, and is a solid electrolyte fuel cell, a molten carbonate fuel cell, a phosphoric acid fuel cell, and a polymer electrolyte fuel cell. and so on. The name of the fuel cell is derived from the constituent materials of the "electrolyte" part that forms the basis of the cell.

At present, fuel cells that have reached the commercial stage include a phosphoric acid fuel cell and a molten carbonate fuel cell.
Approximate operating temperatures of the fuel cell are 1000 ° C. for a solid oxide fuel cell, 650 ° C. for a molten carbonate fuel cell, 200 ° C. for a phosphoric acid fuel cell, and 80 ° C. for a polymer electrolyte fuel cell.

A solid oxide fuel cell has an operating temperature of 80
Since it is easy to start and stop at low temperatures around ℃ and the energy efficiency can be expected to be about 40%, it can be used as an emergency dispersed power source for small business establishments and telephone offices, a small household dispersed power source using city gas as fuel, hydrogen gas It is expected to be put to practical use worldwide as a power source for low-pollution electric vehicles using methanol or gasoline as fuel.

[0005] The above-mentioned various fuel cells are referred to by a common name of "fuel cell", but when considering the constituent materials of the respective cells, it is necessary to consider them completely different. The performance required by the presence or absence of corrosion of the constituent materials due to the electrolyte used, the presence or absence of high-temperature oxidation that begins to become apparent at around 380 ° C, the presence or absence of sublimation and reprecipitation of the electrolyte, the presence of condensation, etc. Because it is completely different. In fact, the materials used are also various, ranging from graphite-based materials to Ni clad materials, high alloys, and stainless steels.

[0006] It is hardly conceivable to apply the materials used in commercially available phosphoric acid fuel cells and molten carbonate fuel cells to the constituent materials of polymer electrolyte fuel cells.

FIG. 1 is a view showing the structure of a polymer electrolyte fuel cell. FIG. 1 (a) is an exploded view of a fuel cell (single cell), and FIG. 1 (b) is a perspective view of the whole fuel cell. It is. As shown in FIG. 1, the fuel cell 1 is an aggregate of single cells. In the single cell, as shown in FIG. 1A, a solid polymer electrolyte membrane 2 has a fuel electrode membrane (anode) 3 laminated on one surface and an oxidant electrode membrane (cathode) 4 laminated on the other surface. It has a structure in which separators 5a and 5b are overlapped on both surfaces.

A typical solid polymer electrolyte membrane 2 includes:
There is a fluorine ion exchange resin membrane having a hydrogen ion (proton) exchange group.

The fuel electrode film 3 and the oxidant electrode film 4 include
A catalyst layer made of a particulate platinum catalyst, graphite powder, and, if necessary, a fluororesin having a hydrogen ion exchange group is provided so as to come into contact with a fuel gas or an oxidizing gas.

The flow path 6a provided in the separator 5a
From the fuel gas (hydrogen or hydrogen-containing gas) A to supply hydrogen to the fuel electrode film 3. Also, the separator 5
An oxidizing gas B such as air is flown from a flow path 6b provided in b, and oxygen is supplied. The supply of these gases causes an electrochemical reaction to generate DC power.

Anode side: H ₂ → 2H ⁺ + 2e Cathode side: (1/2) O ₂ + 2H + 2e ⁻ → H ₂ O The functions required of the polymer electrolyte fuel cell separator are:
(1) a function as a “flow path” for uniformly supplying fuel gas in a plane on the fuel electrode side, and (2) water generated on the cathode side,
A function as a "flow path" that efficiently discharges air and oxygen from the fuel cell together with the carrier gas such as air and oxygen outside the system. (3) Between single cells that maintain low electrical resistance and good electrical conductivity as electrodes for a long time And (4) the function as a "partition wall" between the anode chamber of one cell and the cathode chamber of an adjacent cell in an adjacent cell.

Until now, the use of a carbon plate as a separator material has been intensively studied. However, the carbon plate has a problem that it is easily cracked. Further, the machining cost for flattening the surface and the gas flow path are reduced. There is a problem that the machining cost for forming is very high. Each is a fatal issue, and there are situations that can make commercialization of fuel cells themselves difficult.

[0013] Among carbons, a heat-expandable graphite product has been receiving the most attention as a material for a polymer electrolyte fuel cell separator because it is extremely inexpensive. However, in order to reduce the gas permeability and impart the function as the partition wall, the resin impregnation and firing must be performed “a plurality of times”. In addition, there are many issues to be solved in the future, such as machining costs for securing flatness and forming grooves,
At present, it has not been put to practical use.

[0014] In response to the study of the application of such graphite materials, attempts have been made to apply stainless steel to the separator for the purpose of cost reduction.

Japanese Patent Application Laid-Open No. 10-228914 discloses a fuel cell separator made of a metal member and having a gold plating directly applied to a contact surface of a unit cell with an electrode. Stainless steel, aluminum, and Ni-iron alloy are listed as metal members, and SUS304 is used as stainless steel. In the present invention,
It is said that since the separator is plated with gold, the contact resistance between the separator and the electrode is reduced, and the conduction of electrons from the separator to the electrode is improved, so that the output voltage of the fuel cell is increased.

JP-A-8-180883 discloses a solid polymer electrolyte fuel cell in which a passive film formed on the surface uses a separator made of a metal material that is easily formed by the atmosphere. I have. Stainless steel and titanium alloy are mentioned as metal materials. In the present invention, a passivation film is always present on the surface of the metal used for the separator, and the degree of ionization of water generated in the fuel cell is reduced due to the fact that the surface of the metal is hardly chemically attacked. The fuel cell is said to be reduced, and a decrease in the electrochemical reactivity of the fuel cell is suppressed. Further, it is said that the electrical contact resistance value is reduced by removing the passive body film at the portion of the separator that contacts the electrode film or the like and forming a noble metal layer.

However, even if a metal material such as stainless steel provided with a passivation film on the surface disclosed in the above-mentioned publication is used for the separator as it is, the corrosion resistance is not sufficient and the metal is eluted, and the metal eluted. The supported catalyst performance is degraded by ions (hereinafter, referred to as poisoning of the supported catalyst).
In addition, corrosion products such as Cr-OH and Fe-OH generated after elution have a problem that the contact resistance of the separator increases. At present, noble metal plating is applied.

The application of metal materials to separators so far has only been applied, and is far from practical use.

As a separator, which can be applied “pure” without expensive surface treatment and has excellent electric conductivity in a battery environment and stainless steel excellent in corrosion resistance, the production cost of a fuel cell will increase. This is a drastic decrease, and the commercialization of polymer electrolyte fuel cells and the expansion of applications can be expected.

[0020]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the need for expensive surface treatment, to minimize the poisoning of each electrode-carrying catalyst by metal ions eluted, and to reduce the contact electric contact with electrodes by corrosion products. An object of the present invention is to provide a solid oxide fuel cell provided with a stainless steel separator in which the increase in resistance and the increase in contact resistance due to the strengthening of a passive film are small.

[0021]

The gist of the present invention is as follows.

(1) A plurality of unit cells in which a fuel electrode membrane and an oxidant electrode membrane are stacked with the solid polymer electrolyte membrane at the center, and a fuel gas And a oxidizing gas to generate DC power, wherein the separator is made of a ferritic stainless steel having the following chemical composition.

S: 0.005% or less, P: 0.025% or less, V: 0.2% or less, Ni: 0.2% or less, Cu: 0.2% or less, Cr: 10 0.5 to 35%, Mo: 0 to 6%, rare earth element: 0 to 0.1%, and (Cr + 3Mo) in the range of 10.5 to 43% (2) In ferritic stainless steel Si and Mn
, By weight, Si content 0.3% or less, Mn 0.4%
The polymer electrolyte fuel cell according to the above (1), which is:

(3) The content of C and N in the ferritic stainless steel is, by weight%, C: 0.018% or less, and N:
0.018% or less, and the total content of C and N is 0.0
The polymer electrolyte fuel cell according to the above (1) or (2), wherein the content is 25% or less.

(4) The ferritic stainless steel is made of Ti
And one or two of Nb, and Ti is 0.2% by weight or less, and 6 (C% + N%) to 25 (C
% + N%), and the above (1) to (3), in which Nb is 0.3% or less and in the range of 6 C% to 25 C%.
The polymer electrolyte fuel cell according to any one of the above.

The separator has the four functions described above. That is, a) a function as a "flow path" for uniformly supplying a fuel gas in-plane on the fuel electrode side, b) air generated on the cathode side by reacting air from the fuel cell,
Function as a "flow path" to efficiently discharge out of the system together with carrier gas such as oxygen, c) Function as an electrical "connector" between single cells that maintains low electrical resistance and good electrical conductivity as an electrode for a long time And d) adjacent cells have a function as a "partition wall" between the anode chamber of one cell and the cathode chamber of the adjacent cell. In some cases, the functions are shared by a plurality of plates. As used herein, the term “separator” refers to a plate having at least one of the above four functions.

The present inventors have developed a polymer electrolyte fuel cell having a separator made of stainless steel,
In an environment where the separator is placed, various tests were performed using a single cell with the aim of reducing as much as possible the metal ions eluted from the stainless steel surface. as a result,
Achieved the present invention based on the following findings a) An environment where the pH of the separator is 1 to 3 (hereinafter, referred to as
In this case, austenitic stainless steel has insufficient corrosion resistance and metal is eluted remarkably, making it unsuitable for a separator.

B) In a separator environment, ferritic stainless steel exhibits good corrosion resistance, but general ferritic stainless steel elutes metal to an extent that affects battery performance.

C) When the metal is eluted, the corrosion product (Fe
(Mainly a hydroxide), which causes an increase in the contact electric resistance and has a remarkable adverse effect on the performance of the supported catalyst, so that the battery performance represented by electromotive force is deteriorated in a short time.
In addition, the cation conductivity of the fluorinated ion exchange resin membrane having hydrogen ion (proton) exchange groups is adversely affected.

D) In order to prevent the elution of the metal, among the impurities in the ferritic stainless steel, S, P, V,
The content of Ni and Cu must be reduced at the same time, and the passivation film must be strengthened.

E) Even if the passivation film is strengthened, if the passivation film thickness is increased, the contact electric resistance is increased and the battery efficiency is significantly reduced.

F) In order to strengthen the passivation film without thickening it and to suppress metal elution in the separator environment, the content of Cr and Mo is (Cr% + 3 × Mo%) of 1
It is necessary to be within the range of 2 to 43%.

G) By actively adding Mo, corrosion resistance is ensured. However, even if Mo is eluted, the influence on the performance of the catalyst supported on the anode and the cathode is relatively small.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reason why the chemical composition of the ferrite stainless steel separator provided in the polymer electrolyte fuel cell of the present invention is specified will be described in detail below.
In addition,% display of the following components shows weight%.

S: The amount of S in steel must be 0.005% or less. S is a Mn-based sulfide, a Cr-based sulfide, a Fe-based sulfide, a Ti-based sulfide, a composite non-metal with these composite sulfides and oxides, depending on the coexisting element in the steel and the amount of S in the steel. Most are precipitated as inclusions.
However, in a separator environment, non-metallic inclusions of any composition, although varying in degree, act as a starting point of corrosion, and are harmful to maintaining passivation and suppressing corrosion elution of metals.

In a situation where the fuel cell is operating, a separator made of ferritic stainless steel and a M
In the gap between EA (Membrane Electrode Assembly)
Due to the battery reaction and / or oxygen concentration difference battery corrosion, the pH in the gap is lowered and micro battery corrosion is likely to occur. However, sulfide-based nonmetallic inclusions are corrosion starting points and acceleration factors at that time. Have a big impact. S content in normal mass-produced steel exceeds 0.005% and 0.008%
Before and after, it is necessary to reduce it to 0.005% or less in order to prevent the above harmful effects. The desirable S content in steel is 0.002% or less, and the most desirable S content level in steel is less than 0.001%, the lower the better.

P: The amount of P in steel must be 0.025% or less. Normal stainless commercial steel content levels are on the order of 0.026-0.035%. P is an unavoidable impurity and, along with S, is a harmful element that has a considerable effect on poisoning of the anode and cathode catalyst layers. The lower the better.

V: V in steel must be 0.2% or less. In general, V is contained as an impurity in a Cr source, which is an essential melting raw material when smelting stainless steel, and it is unavoidable to mix V to some extent. However, the eluted V
Has a considerable adverse effect on the performance of the catalyst supported on the anode and cathode parts. From the viewpoint of maintaining battery characteristics, the allowable upper limit is 0.2%, and the lower the better, the better.

Cu, Ni: Cu or Ni in the steel must be 0.2% or less for both or both. In general, even trace amounts of Cu and Ni, which are as small as impurities, have an effect of improving the corrosion resistance of stainless steel in a low pH environment. However, in the separator environment, even if a small amount of Cu and Ni ions are eluted in the passive state, the poisoning of the anode and cathode catalyst layers is affected, so the upper limit must be 0.2%. It is desirable that the amount of Cu and Ni in the steel be low, including contamination from scrap.
Since u and Ni have the effect of increasing the passivation ability of ferritic stainless steel and suppressing metal elution in the passivated state, and as a result, improving the battery performance, the upper limit is 0.2.
%.

Cr, Mo: Cr and Mo are both basic alloying elements for ensuring corrosion resistance. The higher the content, the higher the corrosion resistance, but the higher the Cr content, the lower the room temperature toughness tends to be. If the Cr content exceeds 35%, mass production becomes difficult. If it is less than 10.5%, it becomes difficult to secure the corrosion resistance required for a separator even if other elements are changed.

Mo is an element to be contained if necessary.
An effect of improving the corrosion resistance is obtained with a small amount as compared with r. 0.5
%, The effect of Mo is not clear. In the case where it is contained, if it is contained in excess of 6%, it is difficult to avoid precipitation of intermetallic compounds such as a sigma phase, and production becomes difficult due to the problem of embrittlement of steel. By positively containing Mo, corrosion resistance is ensured. Even if Mo is eluted, the effect on the performance of the catalyst supported on the anode and the cathode is relatively minor, and the cation conductivity of the fluorinated ion exchange resin membrane having hydrogen ion (proton) exchange groups is also affected. The adverse effects are small.

(Cr% + 3Mo%): As the stainless steel for the separator, it is in a passivated state in an environment of 70 ° C. to 100 ° C. at most, which is the operating temperature of the polymer electrolyte fuel cell, and it is continuous. In addition, it is necessary that the contact electric resistance is low. It is necessary to suppress the increase in the thickness of the passive film and the formation of corrosion products within a practical range. As a necessary condition for this, the content of Cr and Mo needs to have a corrosion index (Cr% + 3Mo%) in the range of 12 to 43%.

The pH at 25 ° C. is determined to be appropriate as a simulated environment inside the battery in an actual operating state.
At 80 ° C. of a sulfuric acid aqueous solution ”is at least necessary. For this purpose, 0.2V vs.
Passive maintenance current density in SCE is 50 μA / cm ²
Desirably less than.

Si: The amount of Si in the steel is preferably 0.3% or less. Si is a deoxidizing element as effective as Al in mass-produced steel. However, the eluted Si has a considerable effect on the poisoning of the anode and cathode catalyst layers, and is obviously harmful from the viewpoint of maintaining battery characteristics. Production at around 0.25% is most desirable from the viewpoint of mass production cost reduction, but it is desirably less than 0.2% in a separator environment. Even more desirable is less than 0.1%.

Mn: The Mn content in steel is desirably 0.4% or less. Usually, Mn has an effect of fixing S in steel as Mn-based sulfide, and has an effect of improving hot workability. Further, it may be positively added as a deoxidizing element or a Ni balance adjusting element. However, while the passive state is maintained, the elution of the metal progresses little by little. However, when the amount exceeds 0.4%, the eluted Mn ions are less likely to poison the anode and cathode catalyst layers. Influence. Desirably, it is less than 0.1%. If the Mn is 0.45 or less, it can be manufactured without problems such as hot cracking during mass production. Increase in manufacturing cost is hardly a problem.

C, N: C and N in the steel are 0.018% or less, N is 0.018% or less, and 0.025% in C% + N% value for the purpose of improving room temperature toughness. It is desirable to make the following. C and N are intrusive elements and cause deterioration of base metal toughness, corrosion resistance and toughness of a welded portion of high-purity ferritic stainless steel. Strictly limiting C and N is a measure against room temperature toughness, which is a problem in the process of manufacturing a hot-rolled coil of high-purity ferritic stainless steel, and can avoid an increase in manufacturing cost. Room temperature toughness improves as C and N in the steel are made extremely low, so the lower the better, the better.

Ti: If necessary, Ti is contained in an amount of 0.2% or less and in a range of 6 times or more and 25 times or less of the (C% + N%) value. Ti is an element that should be reduced because it poisons the anode and cathode catalyst layers. However, from the viewpoint of ensuring productivity in mass production and ensuring workability of a thin plate, Ti is contained in a minimum amount as necessary.

When weldability is not required, (C% +
(N%) value × 6 times or more and 10 times or less is most desirable. When weldability is required, the value is most preferably 10 times or more and 16 times or less of the (C% + N%) value. In order to avoid the occurrence of plate surface flaws due to inclusions, the content is desirably 0.1% or less. If it is contained more than necessary, it may cause deterioration of the performance of the anode and cathode catalysts due to elution of the metal in the passive state.

Nb: Nb is an element to be contained if necessary, and is an alloy element having a stronger bonding force with C and N in steel than Cr, like Ti. Nb is 0.3% or less and C%
× 6 to C% × 25 [that is, Nb (%) / C (%) = 6 to
25%]. It is extremely effective in improving toughness including the cold room toughness of hot rolled coils. However, Nb eluted due to corrosion accumulates as a corrosion product on the corroded surface and has a harmful effect of increasing the contact electric resistance. Therefore, it is preferable that the Nb content is low from the viewpoint of base metal performance only. However, if it is determined that it is necessary to improve the workability of the cold-rolled steel sheet material by ensuring the performance of the welded portion or simultaneously containing Nb and Ti, the minimum necessary amount is added.

Rare earth element (REM): The rare earth element has an extremely strong bonding force with S in the molten steel stage, and thus has the effect of rendering S harmless. Therefore, if necessary, it may be added in the form of misch metal. A sufficient effect can be obtained when the content is 0.1% or less.

If necessary, an element other than the above elements may be contained. For example, in order to improve the hot workability, it is preferable to contain Ca, Mg or B of 0.1 or less.

[0052]

EXAMPLES Ferritic stainless steels having 28 kinds of chemical compositions shown in Table 1 were melted in a high-frequency induction heating type 150 kg vacuum melting furnace. As the melting raw material, a commercially available raw material having a small amount of impurities was carefully selected and used, and the amount of impurities in the steel was adjusted.

[0053]

[Table 1]

The ingot having a round cross-section was heated to 1230 ° C. for 3 hours in the atmosphere, and then hot forged with a press-type forging machine. Finished.

Thickness 30 mm, width 100 mm, length 12
A slab having a thickness of 0 mm, a thickness of 70 mm, a width of 380 mm, and a length of 550 mm is hot-rolled into a hot-rolled steel sheet having a thickness of 6 mm, and then gradually cooled under heat insulating material wrapping conditions simulating the temperature history immediately after the end of hot rolling in mass production. did. A Charpy impact test was conducted to examine the hot rolled coil toughness at room temperature. The test piece was JIS Z2202 No. 4 half size. The slab was cut into a slab having a thickness of 62 mm by cutting the slab surface by machining to remove oxide scale on the surface.
This slab was heated to 1200 ° C. in the air and hot-rolled to a thickness of 4 mm, and then gradually cooled under heat insulating material winding conditions simulating the temperature history immediately after the end of hot rolling in mass production.

The hot-rolled steel sheet was subjected to a solution treatment for 4 minutes at the following temperature in accordance with the chemical composition, and was forcibly air-cooled. No. 25 hot-rolled steel sheet in Table 1… 830 ° C No. 11 to 15 and 16 to 23 hot-rolled steel sheet in Table 1 ... 900 ° C No. Hot-rolled steel sheets 1 to 10 930 ° C Hot-rolled steel sheets No. 24 and 29 in Table 1 980 ° C Hot-rolled steel sheets No. 26 and 27 in Table 1 Steel plate 1080 ° C. Each temperature was set to a temperature at which recrystallization proceeds and an intermetallic compound forms a solid solution. Furnace time was approximately 20 minutes.

Next, the hot-rolled steel sheet subjected to the solution treatment was cold-rolled using a multi-stage Sendzimer-type roll rolling mill while sandwiching intermediate annealing on the way to finish it to a thickness of 0.3 mm. The final finish annealing was performed in a bright annealing furnace in a hydrogen atmosphere having a dew point of −50 ° C. or less, and the temperature was the same as the annealing temperature of the hot-rolled material. The holding time was 1 minute, and the oven time was about 3 minutes.

From this cold rolled annealed material, a test piece for evaluating a passive film in a separator simulated environment having the following dimensions and a separator for loading into an actual polymer electrolyte fuel cell were formed by press molding. Made.

For No. 27 of Comparative Example, a test piece for a simulated environment and a separator were prepared, and then gold plating was applied to one side of a thickness of 5 μm.

Test specimen for simulated environment: thickness 0.3 mm, width 1
0 mm, length 10 mm Separator: thickness 0.3 mm, length 80 mm, width 80 mm Gas flow path: height 0.8 mm, spacing between peaks 1.2 mm
(Corrugating) These surfaces are shot Si
Mechanically shot-polished using C abrasives, 5% H
Ultrasonic cleaning was performed for 15 minutes in NO ₃ + 3% HF at 40 ° C. Further, immediately before the test, alkali spray degreasing treatment using 6% sodium hydroxide aqueous solution was performed. Distilled water immersion cleaning was performed three times, and distilled water spray cleaning was further performed for 4 minutes to dry with a cool air dryer, and then subjected to each test.

As a test in a simulated environment, a sulfuric acid aqueous solution having a pH of 2.6 at 25 ° C. adjusted with sulfuric acid as a special grade reagent was heated to 80 ° C., and the test piece was immersed in the solution for 6 hours. In addition to evaluating the presence or absence of passivation from corrosion weight loss, generation of hydrogen bubbles from the material surface, color change of the test solution,
0.2V vs S
The passivation current density at CE was measured.

The results of the Charpy impact test and the test results in the simulated separator environment are as shown in Table 2.

[0063]

[Table 2]

As is clear from Table 2, in the example of the present invention,
It is in a passivated state in a sulfuric acid aqueous solution having a pH of 2.6 at 25 ° C. at a temperature of 80 ° C., and the “passive holding current density” indicating the degree of elution is also 20 μA / cm ² or less.

When stainless steel is used as a separator for a polymer electrolyte fuel cell, it is needless to say that the passive state holding current density is desirably as low as possible. It is important to take a stable low value,
Less than 10 μA / cm ² is most desirable, then 10-20
μA / cm ² is desirable.

The passive current density of the comparative example is 30 to 80 μm.
A / cm ² , which can be said to be suppressed, but indicates that relatively large elution has occurred from the separator.

The present inventors have determined that the passive state holding current density> 50 based on the relationship with the performance characteristics of an actual single cell battery as a criterion for judging the applicability as a fuel cell separator material.
It was determined that the performance was insufficient at μA / cm ² . In the case of a material having a passivation holding current density of 50 μA / cm ² or less, even a real single cell evaluation test has not been able to confirm the problematic continuous deterioration of the performance, which is extremely suitable as a rapid simulation environment evaluation condition. Is determined to be. Also in the present results, in the case of the invention example, it is at the same level as the gold plating material (test steel 27) which is one of the most desirable metal materials in the polymer electrolyte fuel cell environment. It was determined that it could be secured.

Next, as an evaluation of characteristics in a state where the battery was loaded as a separator inside an actual solid polymer type single cell battery,
One hour after the flow of the fuel gas into the battery, the voltage of the single cell battery was measured and compared with the initial voltage to determine the rate of voltage decrease. The rate of decrease was determined by 1− (voltage V after one hour has elapsed / initial voltage v).

The polymer electrolyte fuel cell used in the evaluation was a modified battery cell FC50 manufactured by Electrochem, USA.

The gas for fuel on the anode side is 99.9.
999% hydrogen gas was used, and air was used as the cathode electrode side gas. The entire body of the battery was kept at 78 ± 2 ° C., and the humidity control inside the battery was adjusted on the entry side based on the measurement of the exhaust gas moisture concentration on the cell exit side. The pressure inside the battery is
1 atm. The introduction gas pressure of hydrogen gas and air into the battery was adjusted at 0.04 to 0.20 bar. The cell performance evaluation was continuously performed from a state where 500 mA / cm ² −0.62 V was confirmed at a single cell voltage.

As a single cell performance measuring system, a modified fuel cell measuring system based on the 890 series manufactured by Scribner, USA was used. It is expected that the characteristics will change depending on the battery operating state, but this is a comparative evaluation under the same conditions.

The results are shown in Table 2.

As is evident from Table 2, in the examples of the present invention, the voltage drop rates were all 0.05 or less, which was equivalent to the No. 27 expensive and highly corrosion-resistant gold-plated separator. Moreover, in the comparative example which deviated from the chemical composition specified in the present invention, the voltage reduction rate was extremely large, 0.3 to 0.8.

Some of the test pieces were evaluated by performing a long-term test, and the results obtained were close to the short-term test results shown in Table 2 and correlated.

The toughness of stainless steel at room temperature is generally inferior to ferritic stainless steel as compared to austenitic stainless steel. However, as is clear from the Charpy test results in Table 2, the series of examples of the present invention having lower C and N contents are much superior to the comparative examples having higher C and N contents in steel. It has high toughness. In general, the room temperature toughness is apparently improved as the sheet thickness becomes thinner, so that there is no practical problem at the level of the present invention. That is, it can be said that the normal temperature toughness of the hot-rolled coil, which is a problem when producing a high-purity ferritic stainless steel, is good. In general, the room temperature toughness is apparently improved as the sheet thickness is reduced, and therefore there is no practical problem at the level of the steel of the present invention.

[0076]

The polymer electrolyte fuel cell of the present invention can be manufactured at a low cost because the separator is made of ferritic stainless steel and does not require expensive gold plating.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a polymer electrolyte fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Solid molecular electrolyte membrane 3 Fuel electrode membrane 4 Oxidizer electrode membrane 5a, 5b Separator

Continuation of the front page (56) References JP-A-6-146006 (JP, A) JP-A-8-188853 (JP, A) JP-A-8-311620 (JP, A) JP-A-9-157801 (JP) JP-A 9-241809 (JP, A) JP-A 10-280103 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8/02 H01M 8/10 C22C 38/00 302 C22C 38/46 C22C 38/50

Claims (4)

(57) [Claims] 1. A laminate in which a plurality of unit cells in which a fuel electrode membrane and an oxidant electrode membrane are overlapped with a solid polymer electrolyte membrane in the center, and a separator is interposed between the unit cells,
A polymer electrolyte fuel cell for supplying a fuel gas and an oxidant gas to generate DC power, wherein the separator is made of a ferritic stainless steel having the following chemical composition. % By weight, S: 0.005% or less, P: 0.025% or less, V: 0.2% or less, Ni: 0.2% or less, Cu: 0.2% or less, Cr: 10.5 or more 35%, Mo: 0 to 6%, Rare earth element: 0 to 0.1%, and (Cr + 3Mo) is in the range of 10.5 to 43% 2. The ferrite stainless steel contains Si and Mn in a weight percentage of not more than 0.3% and Mn of not more than 0.3%.
The polymer electrolyte fuel cell according to claim 1, wherein the content is 4% or less. 3. The amount of C and N in the ferritic stainless steel is expressed in% by weight,
C: 0.018% or less, N: 0.018% or less, and C
And the total content of N and N is 0.025% or less.
Or the polymer electrolyte fuel cell according to 2. 4. A ferritic stainless steel comprising Ti and Nb.
One or two of the following, and Ti is not more than 0.2% by weight%, and 6 (C% + N%) to 25 (C% +
Nb) and Nb is 0.3% or less and 6C
The polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the concentration is in the range of 25% to 25C%.