JPH0656765B2 - Molten carbonate fuel cell - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an internal reforming type molten carbonate fuel cell in which a fuel gas reforming means is provided inside a fuel cell body, and in particular to the modification of the fuel gas. The present invention relates to a molten carbonate fuel cell capable of improving quality efficiency.

[Technical background of the invention and its problems]

A fuel cell has a gas that is easily oxidized, such as hydrogen,
This is to obtain direct current power by reacting with an oxidizing gas such as oxygen through an electrochemical reaction process under an appropriate electrolyte to obtain direct current power. Depending on the electrolyte used, phosphoric acid type, molten carbonate type, solid electrolyte It is roughly divided into types.

Of these fuel cells, the molten carbonate type is the one that is operated at a temperature of about 650 ° C.
The main part is generally constructed as shown in FIG.

That is, the fuel cell main body X is configured by stacking a plurality of unit cells 1 with a bipolar separator 2 described later interposed therebetween.

The unit cell 1 is configured by providing a flat electrolyte layer 5 between a pair of gas diffusion electrode plates made of a nickel alloy porous body, that is, an oxidizer electrode 3 and a fuel electrode 4. The electrolyte layer 5 is formed by holding a carbonate electrolyte such as lithium carbonate or potassium carbonate with a ceramic-based holding material such as lithium aluminate.

The bipolar separator 2 is a separator body 6 made of stainless steel.
Side wall members 7a, 7b, 8a, 8b made of stainless steel are brazed in parallel on both sides of each surface so as to form gas flow paths on both sides of the surface in directions orthogonal to each other. The groove formed by the side wall members 7a, 7b, 8a, 8b and the surface of the separator body 6 is used as the gas flow passage (flow passage for the fuel gas P and flow passage for the oxidant gas Q). Further, corrugated plates 9a and 9b made of stainless steel are fitted in these gas flow passages so as to substantially divide the flowing gas therein. Further, a step portion is provided on each end surface of the side wall members 7a, 7b, 8a, 8b to fit the gas diffusion electrode plates 3 and 4, respectively, and the gas diffusion electrodes 3 and 4 are attached to the step portion. The end portions of the fitted side wall members 7a, 7b, 8a, 8b and the electrolyte layer 5
Are wet-sealed to prevent leakage of gas introduced to the gas supply unit. The wet seal has, for example, an electrolyte of Li ₂ CO ₃ / K ₂ C.
In the case of a two-element eutectic coarse formation from O ₃ , 62/38 molar ratio,
When the battery operating temperature was raised to 650 ° C, the above electrolyte
It is performed by melting at 488 ° C.

By the way, in the molten carbonate fuel cell having such a structure, hydrocarbons such as methane, ethane and propane, or alcohols such as methanol and ethanol are used as the fuel gas supplied to the fuel electrode 4. However, even if these gases are directly supplied to the fuel electrode 4, it is difficult to obtain sufficient electric power for practical use because the reaction speed is slow. Therefore, when using these gases, it is necessary to reform them into a hydrogen-rich gas in advance by a reformer before supplying them to the fuel cell.

Conventionally, such a reformer has been installed outside the fuel cell body. However, in order to carry out the reforming reaction,
Since sufficient heat energy is required, when the reformer is installed outside the fuel cell body in this way, the means for supplying the heat energy required for the reforming reaction must be installed outside the fuel cell. Become. Therefore, recently, an internal reforming type fuel cell has been proposed in which a reformer is installed inside the fuel cell main body in order to effectively utilize the thermal energy inside the fuel cell and to simplify the system. ing.

As shown in FIG. 2 showing the fuel cell main body Y, the reforming type molten carbonate fuel cell is such that the upper and lower sides of a rectangular wave type separating plate 11 are separated from each other, and the fuel gas is provided in the upper recess of the separating plate 11. In addition to filling the catalyst 12 for reforming P, the surface of the fuel electrode 13 adjacent to the separator 11 in the upper part of the drawing, which is in contact with the separator 11, has a fuel gas P in a direction orthogonal to the filling zone of the catalyst 12. The groove 14 serving as the flow path is formed.

With such a configuration, the fuel gas P comes into contact with the catalyst 12 in the process of flowing through the groove 14 and is reformed. Since the reforming reaction of the fuel gas by this catalyst is performed at 650 ° C. which is the normal operating temperature of the fuel cell, the reforming reaction proceeds at a sufficiently fast rate. As a result, hydrogen-rich fuel gas can be generated inside the fuel cell main body Y, and the above-described effects can be achieved.

However, in the molten carbon dioxide fuel cell having such a configuration, the fuel gas P flowing through the groove 14 and the catalyst 13 are in contact with each other only at a very small portion, so that the reforming efficiency of the fuel gas is poor. There was a flaw. Therefore, the fuel gas may not be completely reformed, and some unreformed fuel gas may reach the gas discharge side. Moreover, when the fuel cell main body has such a structure, the fuel electrode 13 needs to be grooved, and the fuel gas P and the oxidant gas Q at the end face of the separator 11 are formed.
There was a problem that it was difficult to isolate

[Object of the Invention]

The present invention is based on such a problem,
An object of the invention is to provide a molten carbonate fuel cell of an internal reforming type, which can efficiently reform a fuel gas and can simplify the structure. Especially.

[Outline of Invention]

According to the present invention, an oxidant electrode and a fuel electrode are provided so as to sandwich an electrolyte layer made of a carbonate, and an oxidant gas passage is formed along the outer surface of the oxidant electrode to allow an oxidant gas to flow therethrough. A fuel gas passage for allowing a fuel gas to flow therethrough is provided along the outer surface, and a molten carbonate fuel cell is formed so that an electromotive reaction is caused between both the gas diffused and permeated through the oxidizer electrode and the fuel electrode and the carbonate. A porous plate mounted so as to fill the fuel gas passage that allows the fuel gas to flow along the outer surface of the fuel electrode, and the porous plate formed in the porous plate so as to be orthogonal to the flow direction of the fuel gas. Multiple grooves,
It is characterized by comprising a catalyst substance for reforming the fuel gas filled in these grooves and flowing through the porous plate.

〔The invention's effect〕

According to the present invention, the porous plate is mounted so as to fill the fuel gas passage through which the fuel gas flows along the outer surface of the fuel electrode,
Since a plurality of grooves are provided in this porous plate so as to be orthogonal to the flow direction of the fuel gas, and these grooves are filled with the catalyst layer, the catalyst layer should be present at the position where the gas does not progress. become. If the catalyst layer exists at such a position, the contact area between the catalyst layer and the fuel gas can be significantly increased as compared with the conventional case. In addition, since the fuel gas is turbulently flown by the catalyst layer, the reforming efficiency of the fuel gas can be greatly increased by this.

Further, with the above configuration, the catalyst layers are arranged in the porous plate in a divided manner in the flow direction of the fuel gas, and a sufficient flow passage cross-sectional area can be secured between the catalyst layer rows. Therefore, the pressure loss in the clogged fuel gas passage in the porous plate can be made smaller than in the case where the catalyst is filled without gaps in the fuel gas flow direction.

Furthermore, since it is a reforming reaction, the temperature is locally reduced at the portion where the reforming reaction is concentrated, but as described above, the catalyst layer is divided in the flow direction of the fuel gas inside the porous plate. If they are arranged in such a manner, the reaction does not concentrate on one catalyst, and therefore there is an advantage that the temperature distribution in the plane direction of the fuel cell can be made uniform.

Further, the present invention has a very simple structure in which a porous plate with a catalyst layer is provided so as to fill a fuel gas passage through which the fuel gas flows along the outer surface of the fuel electrode. For this reason,
In particular, since it is not necessary to perform special processing on the fuel electrode, the separator, etc., it is possible to provide an internal reforming type molten carbonate fuel cell without complicating the structure.

In addition, if the porous plate is formed of an electron conductive member, it can simultaneously have a current collecting function for each unit battery, and if the porous plate has a predetermined mechanical strength, each unit battery can be It can also have a function as a support.

Example of Invention

Hereinafter, the details of the present invention will be described based on the illustrated embodiments.
In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals. Therefore, detailed description of the overlapping parts will be omitted.

Example 1 FIG. 3 is a view showing a main structure of a molten carbonate fuel cell according to Example 1, that is, a fuel cell main body Z.

The fuel cell body Z is different from the conventional fuel cell body X shown in FIG. 1 in the configuration of the bipolar separator 21. The bipolar separator 21 according to the present embodiment has a new gas reformer instead of the corrugated plate 9a conventionally fitted in the groove formed by the side wall members 7a and 7b and the upper surface of the separator body 6 in the figure. The plate 22 is fitted.

As shown in FIG. 4, the gas reforming plate 22 has a plurality of V grooves 24 extending in a direction orthogonal to the flow direction of the fuel gas P on both surfaces of a porous plate 23 made of a porous body. The V grooves 24 are formed alternately and are filled with the catalyst 25.

In this embodiment, the porous plate 23 has a thickness of 2 mm.
The nickel porous body (porosity 90%) was cut into a size of 200 × 180 mm and used. V-grooves 24 having a depth of 1 mm are formed alternately on both sides of the porous plate 23 at a pitch of 5 mm, and the alumina-magnesia-supported nickel catalyst 25 (specific surface area 32 m ² / g) and ethanol are formed in the V-grooves 24. A slurry formed by mixing and was filled. After the ethanol was volatilized, the obtained gas reforming plate 22 was incorporated into the fuel cell main body Z shown in FIG. The fuel cell main body Z was composed of unit cells 1 of three layers, and a stainless steel plate was used as the corrugated plate 9b provided in the flow path of the oxidant gas of the fuel cell main body Z.

A fuel cell was assembled by assembling a reaction gas manifold, an end plate, a tightening bar and the like (not shown) to the fuel cell main body Z thus obtained. Then, the fuel cell was housed in a muffle furnace and operated at a temperature of 650 ° C.
In this operation experiment, as the fuel gas P and the oxidant gas Q to be supplied to the fuel cell, the fuel gas was methane (CH ₄ ) + water (H ₂ O); s / c = 2.5, the oxidant gas was 70 Air / CO ₂ fuel. Gas ... Methanol (CH ₃ OH) + water (H ₂ O); s / c = 2.5 Oxidant gas ... 70 Air / CO ₂ were used.

Example 2 A similar experiment was conducted by replacing only the porous plate 23 of Example 1 with a porous foam of stainless steel 316L (porosity 92%).

Example 3 A similar experiment was conducted by replacing only the catalyst 25 of Example 1 with the nickel catalyst containing lithium aluminate.

Comparative Example The concave portion of the rectangular wave type separator 11 shown in FIG. 2 on the fuel electrode 13 side was filled with an alumina-magnesia support nickel catalyst, and the conventional fuel cell main body Y shown in FIG. Similar experiments were conducted.

When the cell voltage of each unit cell with respect to the current density in the above Examples 1 to 4 and the conventional example was measured, the result shown in FIG. 5 was obtained when methane was used as the fuel gas, and The results shown in FIG. 6 were obtained when methanol was used.

As is clear from this figure, the cell characteristics (A, B, C, D) of the fuel cells of Examples 1 to 4 can be improved as compared with the cell characteristics (E) of the fuel cells of Comparative Example. It could be confirmed.

Further, the conversion efficiency of the fuel gas reforming in each experiment was measured, and the results shown in the table below were obtained.

As is clear from this table, it was confirmed that the fuel cells according to Examples 1 to 4 had better conversion efficiency of fuel gas reforming than the comparative examples.

As described above, according to these embodiments, the fuel gas reforming can be performed simply by simply replacing the corrugated plate provided in the fuel gas flow path of the fuel cell having the conventional structure with the gas reforming plate. The conversion efficiency can be increased. Further, since the porous plate 23 of these examples is made of a porous body of nickel or stainless, it has both a current collecting function and a supporting function for each unit battery.

The present invention is not limited to the above embodiment. For example, as shown in FIG. 7, the groove 32 formed in the porous plate 31 may be rectangular or trapezoidal, and the groove 32 is formed only on one surface of the porous plate 31. It may be formed in. These grooves can be formed by various methods such as machining and pressing. The catalyst to be filled in the groove is, in addition to the above-mentioned one, a carrier comprising at least one selected from alumina, calcia-alumina, alumina-zirconia, lithium zirconate, strontium titanate, lithium titanate or boron nitrite. You may use what added the nickel or nickel alloy catalyst to. These catalysts are not limited to those packed in a slurry state.

Further, the porous plate may be a nickel alloy.

In short, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a main part of a conventional thin metal plate type molten carbonate fuel cell, and FIG. 2 is a structure of a main part of a conventionally proposed internal reforming type molten carbonate fuel cell. FIG. 3 is an exploded perspective view showing the first embodiment of the present invention.
4 is an exploded perspective view showing the configuration of the main part of an internal reforming molten carbonate fuel cell according to the embodiment of FIG. 4, FIG. 4 is a perspective view showing a gas reforming plate in the fuel cell, FIG. 5 and FIG. FIG. 7 is a characteristic diagram for explaining the cell characteristics of the fuel cells according to the first to fourth embodiments in comparison with a comparative example, and FIG. 7 is a gas reforming in a fuel cell according to another embodiment of the present invention. It is a perspective view which shows a board. 1 ... Unit battery, 2, 21 ... Bipolar separator, 3 ... Oxidizer electrode, 4, 13 ... Fuel electrode, 5 ... Electrolyte plate, 6 ...
Separator body, 7a, 7b, 8a, 8b ... Side wall member, 9a, 9b ...
Corrugated plate, 11 ... Separator, 12, 25, 33 ... Catalyst, 22 ... Gas reforming plate, 23, 31 ... Porous plate, X, Y, Z ... Fuel cell body, P ... Fuel Gas, Q ... Oxidizer gas.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-58-10374 (JP, A) JP-A-58-129780 (JP, A) JP-A-60-32255 (JP, A)

Claims (3)

[Claims] 1. An oxidant electrode and a fuel electrode are provided so as to sandwich an electrolyte layer made of a carbonate, and an oxidant gas passage is provided along the outer surface of the oxidant electrode to circulate the oxidant gas. A fuel gas passage for allowing a fuel gas to flow therethrough is provided along the outer surface, and a molten carbonate fuel in which an electromotive reaction is caused between both the gas diffused and permeated through the oxidizer electrode and the fuel electrode and the carbonate. In the cell, a porous plate mounted so as to fill the fuel gas passage that allows the fuel gas to flow along the outer surface of the fuel electrode, and a porous plate formed in the porous plate so as to be orthogonal to the flow direction of the fuel gas. 2. A molten carbonate fuel cell, comprising: a plurality of grooves; and a catalyst layer which is filled in the grooves and reforms a fuel gas flowing in the porous plate. 2. The catalyst layer comprises alumina, alumina-magnesia, calcia-alumina, alumina-zirconia,
Patents characterized in that a nickel catalyst or a nickel alloy catalyst is provided on a support comprising at least one selected from lithium aluminate, lithium zirconate, strontium titanate, lithium titanate or boron nitride. The molten carbonate fuel cell according to claim 1. 3. The molten carbonate fuel cell according to claim 1, wherein the porous plate is made of stainless steel, nickel or a nickel alloy.