JPH04179060A - Fuel cell - Google Patents

Abstract

PURPOSE:Toi provide a fuel cell capable of long time service by forming a low temp. region at the reaction gas outgoing side end of a porous electrode with a catalyst layer or cooling plate interposed, using phosphoric acid as electrolyte, and reducing its being brought to outside cell. CONSTITUTION:The evaporation amount of phosphoric acid as electrolyte increases with rise oif the temperature. When phosphoric acid vapor evaporated once in the gaseous phase is led to an atmosphere at a temp erature lower than at the time of evaporation, a phosphoric acid vapor partial pressure in the gaseous phase due to this temp. is obtained, and the phosphoric acid vapor is brought to outside the unitary cell from the reaction gas outgoing side. If therefore a low temp. region is formed at the reaction gas outgoing side end of a porous electrode, the phosphoric acid vapor corresponding to the temp erature difference from the high temp. region can be condensed and collected in this low temp erature region. Thereby bringing-out of the phosphoric acid as electrolyte to outside fuel cell is reduced, and a fuel cell capable of long time service is accomplished.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a fuel cell, and in particular to a method for reducing the amount of phosphoric acid taken out of the cell in a phosphoric acid fuel cell. It's about configuration.

(Prior Art) As is well known, a fuel cell is a device that directly converts energy contained in fuel into electrical energy. This fuel cell usually has a pair of porous electrodes with a catalyst layer supported on the surface sandwiching a matrix layer that holds an electrolyte, and a fuel gas such as hydrogen gas is brought into contact with the back surface of one electrode. At the same time, an oxidizing gas such as air is brought into contact with the back surface of the other electrode, and the electrochemical reaction that occurs at this time is used to extract electrical energy from between the pair of electrodes. .

FIG. 11 is a partial cross-sectional view showing the structure of this type of fuel cell. 1 is a stacked cell, with a matrix layer holding phosphoric acid as an electrolyte, and a catalyst on one side in contact with the matrix layer. A unit cell is made up of a stack of layers, a fuel gas or oxidizing gas supply channel (concave groove) on the other side, and a pair of porous electrodes made of carbon material that enable gas diffusion. It is constructed by laminating a plurality of cells, and a cooling plate 2 is inserted and installed in each laminated cell 1 to heat it from room temperature to operating temperature during startup and to remove excess heat during operation. In addition, the upper and lower sides of a stacked cell group formed by stacking a plurality of stacked cells 1 vertically are sandwiched between current collector plates 3, 3, and are tightened in the stacking direction via clamping fittings 4.4 disposed above and below, respectively. There is.

Further, a manifold 5 is disposed on the side surface of the stacked cell group in order to collectively supply and exhaust the oxidant gas and fuel gas for each unit cell. This manifold 5 is
It is fixed via a fluorine-swelled sealing material 6 that is in close contact with the current collector plate 3 and a molded fluororubber backing 7 that is placed outside of the sealing material 6 .

The unit cell described above allows the oxidant gas and fuel gas to flow from one side to the other, but there is also a unit cell that allows the oxidant gas and fuel gas to flow in two directions, turning from the other side and returning to one side. be.

FIG. 12 is a perspective view showing this example.

In the figure, 8 is a matrix layer holding phosphoric acid as an electrolyte, 9 is an anode electrode, and 10 is a cathode electrode. Here, the anode electrode 9 is formed of a carbon-based material into a porous plate shape having gas permeability, and includes an anode electrode substrate 11 provided with a plurality of grooves serving as fuel gas supply paths on the negative side surface; It is composed of an anode side catalyst layer 12 supported in layers on the other side of this anode electrode substrate II. Further, the cathode electrode 10 is similarly formed in the shape of a porous plate having gas permeability using a carbon-based material, and a cathode electrode substrate 13 is provided with a plurality of grooves that serve as supply paths for the oxidant gas on the negative side surface. and a cathode-side catalyst layer 14 supported on the other surface of the cathode electrode substrate 13 in a layered manner. In addition, the code|symbol 15 shows a separator.

By the way, the above-described fuel cell is normally operated at a high temperature of around 21) 0°C. At this time, phosphoric acid (P2O3°), which is an electrolytic solution held in the matrix layer, is carried out of the unit cell together with fuel gas and oxidizing gas by evaporation and scattering, and as time passes, the retention material gradually disappears. It will continue to decrease.

(Problem to be Solved by the Invention) Therefore, various measures have been taken to retain the electrolyte in the matrix layer.
For electrolyte self-retaining fuel cells, the porous electrode substrate is hydrophilized, impregnated with electrolyte and stored, and the porous electrode substrate It is known that the battery life is extended by replenishing the electrolyte from the battery. However, in this type of electrolyte self-retaining type, there is a limit to the amount of electrolyte stored in the fuel cell, and there is no means for replenishing the electrolyte from the outside, so even if the battery element is healthy, the electrolyte will not be present. If it disappears, operation cannot continue, and there is a limit to how long the operation time can be extended.

On the other hand, as another measure, a method is known in which an electrolytic solution is externally replenished during operation to extend the operating time of the battery (see Japanese Patent Application Laid-open No. 74265/1983). However, with this type of electrolyte replenishment type, it is difficult to know when to replenish the electrolyte, the structure is complicated, and the manufacturing process is significantly increased.

Therefore, an object of the present invention is to reduce the amount of phosphoric acid, which is an electrolytic solution, being taken out of the fuel cell while simplifying the configuration.
The purpose of the present invention is to provide a fuel cell that enables long-time operation and has improved reliability.

[Structure of the Invention] (Means for Solving the Problems) The present invention comprises a matrix layer holding an electrolytic solution, a catalyst layer supported in layers on the surface in contact with the matrix layer, and a reactive gas supported on the opposite surface. In a fuel cell in which a unit cell is composed of a pair of porous electrodes provided with a plurality of concave grooves that serve as supply channels for gas, and a plurality of these unit cells are stacked and a cooling plate is inserted, the reaction gas outlet of the porous electrode A low temperature region is formed at the side end via a catalyst layer or a cooling plate.

(Function) The amount of evaporation of phosphoric acid, which becomes the electrolyte, increases as the temperature rises. When the phosphoric acid vapor that has evaporated once in the gas phase is introduced into an atmosphere at a lower temperature than that at the time of evaporation, the partial pressure of the phosphoric acid vapor in the gas phase becomes due to the temperature. Furthermore, phosphoric acid vapor is carried out of the unit cell from the outlet side of the reaction gas. therefore,
When a low-temperature region is formed at the end of the porous electrode on the reaction gas outlet side, phosphoric acid vapor corresponding to the temperature difference from the high-temperature region can be condensed and recovered in this low-temperature region, reducing the amount of phosphoric acid vapor carried out of the unit cell. can.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a front view showing essential parts of an embodiment of the present invention;
FIG. 2 is a sectional view taken along line A--A in FIG. 1.

In FIGS. 1 and 2, the cooling plate 20 includes a cooling plate body 2j made of a material with good thermal conductivity, such as copper material, and a cooling plate body 21 embedded in the cooling plate body 21, which includes a plurality of U
A cooling pipe 22 formed in a state in which shaped parts are arranged and connected, and a cooling pipe 23 formed in a U shape, which is embedded in the cooling plate main body 21 and is arranged independently and parallel to the cooling pipe 22. It consists of

The cooling plate 20 is inserted and installed in each stacked cell 1 in which a plurality of unit cells are stacked, and the cooling plate 20 is arranged so that the side where the cooling pipe 23 is buried is the outlet side of the reaction gas.

Further, cooling water is supplied to the cooling pipes 22 and 23 independently from the cooling water system.

Next, the operation of the embodiment configured as above will be explained. The amount of phosphoric acid that evaporates into the gas phase depends on the temperature, as shown in FIG. 3, and the amount of evaporation increases as the temperature increases.

A gas phase equilibrium relationship is established between the partial pressure of phosphoric acid vapor in the gas phase and the liquid phase, and if phosphoric acid that has been evaporated once in the gas phase is placed in an atmosphere with a lower temperature than that at the time of evaporation, the temperature in the gas phase will change due to the temperature. The partial pressure of phosphoric acid vapor becomes.

That is, when phosphoric acid vapor evaporated at a high temperature is exposed to a low temperature, phosphorus vapor corresponding to the temperature difference is condensed and recovered into the liquid phase again.

On the other hand, in the cooling plate 20, the cooling pipe 22
3. Therefore, if cooling water is supplied independently to the cooling pipes 22 and 23, the heat dissipation effect of the part where the cooling pipe 22 is buried will be better than that of the other parts.

As a result, the temperature distribution in the planar direction of the electrode plate is lower on the reaction gas outlet side than on other parts, as shown in FIG. Therefore, when phosphoric acid evaporated in a relatively high temperature range on the electrode plate is exposed to a low temperature range on the electrode plate,
The amount of evaporated phosphoric acid corresponding to the temperature difference can be condensed and recovered into the liquid phase again in the low temperature range of the electrode plate, and the amount of phosphoric acid taken out of the cell can be reduced.

Note that the present invention is not limited to the above-described embodiment (hereinafter referred to as the first embodiment), and various modifications can be made.

FIG. 5 is a front view showing essential parts of another embodiment of the present invention (hereinafter referred to as the second embodiment), and FIG. 6 is a sectional view taken along the line A--A in FIG. 5.

In FIGS. 5 and 6, the cooling plate 25 includes a cooling plate main body 21 and a cooling pipe 26 embedded in the cooling plate main body 21 and formed in a state in which a plurality of U-shaped portions are arranged and connected.
It consists of Here, the cooling pipe 26 has two parts with different diameters, and the small diameter part is the small diameter part 2.
6a, the large diameter portion is defined as the large diameter portion 26.

This cooling plate 25 is also inserted and installed in each laminated cell 1 as in the first embodiment, but the large diameter portion 26b of the cooling pipe 26
Install it so that the side where it is buried is the outlet side of the reaction gas.

In this cooling plate 25, since the surface area of the large diameter part 26b is larger than that of the small diameter part 26a, when cooling water is supplied to the cooling pipe 26, the part where the large diameter part 26b is buried is larger than the small diameter part 26a.
The heat dissipation effect is better than that in the part where 6a is buried. As a result, the temperature distribution in the planar direction of the electrode plate also becomes as shown in FIG. 4, and the same effects as in the first embodiment can be obtained.

FIG. 7 is a perspective view showing a main part of yet another embodiment (hereinafter referred to as the third embodiment) of the present invention. In addition,
This third embodiment focuses on a fuel cell configured such that fuel gas and oxidizing gas flow through a unit cell in two directions, and the boundary between the two directions of flow is separated by a sealing material. In the figure, 8 is a matrix layer, 3o is an anode electrode, and 31 is a cathode electrode. Here, the anode electrode 30 includes an anode electrode substrate 11 and an anode side catalyst layer 3 supported on the other side of the anode electrode substrate 11 in a layered manner.
It consists of 2. Further, the cathode electrode 31 is composed of a cathode electrode substrate 13 and a cathode side catalyst layer 33 supported in layers on the other surface of the cathode electrode substrate I3.

Therefore, the anode side catalyst layer 32 is formed at the corner of the anode side catalyst layer substrate 34 and the anode side catalyst layer substrate 34 corresponding to the outlet side of the oxidizing gas, and extends in a direction perpendicular to the flow of the oxidizing gas. It consists of a long rectangular non-reactive part 35. Further, the cathode side catalyst layer 33 is formed at the corner of the cathode side catalyst layer substrate 36 and the cathode side catalyst layer substrate 36 corresponding to the outlet side of the oxidizing gas, and is elongated in the direction orthogonal to the flow of the oxidizing gas. It is composed of a rectangular non-reactive part 37. Here, the non-reactive part 35.37
has the same composition as the matrix layer 8, the same position in the plane, and no catalyst is supported.

Next, the operation of the third embodiment will be explained. The amount of evaporation of phosphoric acid is proportional to the vapor pressure of phosphoric acid in that part.

Further, regarding the physical properties of phosphoric acid, as shown in FIG. 8, when the concentration of phosphoric acid is constant, the vapor pressure of phosphoric acid increases as the temperature rises. Therefore, by forming non-reacting N35.37 on the oxidant gas outlet side of the anode-side catalyst layer 32 and the cathode-side catalyst layer 33, no chemical reaction occurs in the non-reactive portions 35.37. There is no reaction heat generated accompanying the chemical reaction, and as shown in Figure 9, the temperature of the non-reactive part 35, 37 is lower than other parts, and the evaporated phosphoric acid contained in the reaction gas is removed from the non-reacting part. It can be collected in the non-reacting region formed by portions 35 and 37.

FIG. 10 shows still another embodiment of the present invention (hereinafter referred to as
FIG. 4 is a plan view showing the main parts of a fourth embodiment. In the figure, reference numeral 40 indicates an anode-side catalyst layer supported in layers on an anode electrode (not shown).

This anode side catalyst layer 40 has an anode side catalyst layer substrate 4
1, a rectangular non-reactive part 42 formed at a corner of the anode side catalyst layer substrate 41 corresponding to the outlet side of the oxidizing gas and elongated in the direction perpendicular to the flow of the oxidizing gas, and a fuel gas It is formed at a corner of the anode-side catalyst layer substrate 41 that reacts on the outlet side of the fuel gas, and consists of a rectangular non-reactive part 43 that is elongated in the direction perpendicular to the flow of fuel gas. here,
The non-reactive portions 42.43 are the non-reactive portions 35. 37
Similarly, it has the same composition as the matrix layer and no catalyst is supported. In addition, the cathode side catalyst layer is also the anode side catalyst layer 4.
0, the code 44 is a cathode side catalyst layer,
Reference numeral 45 indicates a cathode side catalyst layer substrate, reference numeral 46 indicates a non-reactive portion corresponding to the above-described non-reactive portion 42, and reference numeral 47 indicates a non-reactive portion corresponding to the above-described non-reactive portion 43.

The anode electrode and cathode electrode in this example also include:
A boundary portion where the flow directions of the fuel gas and the oxidizer differ is defined by a sealing material (indicated by a broken line in the figure).

As described above, the non-reactive parts 42, 46 and 43° 47 are formed in the anode-side catalyst layer 40 and the cathode-side catalyst layer 44 on the oxidant gas outlet side and the fuel gas outlet side, respectively, so that the non-reactive parts The unit area is further increased, and the amount of phosphoric acid taken out of the unit cell can be reduced.

Furthermore, with respect to the third embodiment and the fourth embodiment, when the oxidant gas and the fuel gas flow in one direction through the unit cell, as in the first embodiment and the second embodiment, their outlet A non-reactive portion may be formed in the cathode side catalyst layer and the cathode side catalyst layer corresponding to the side. Further, in the first embodiment and the second embodiment, the oxidant gas and the fuel gas were applied to a fuel cell in which the oxidizing gas and the fuel gas flowed in one direction through the unit cell, but the third embodiment and the fourth embodiment It can also be applied to fuel cells that allow flow in two directions.

[Effects of the Invention] As explained above, according to the present invention, the cooling plate inserted and installed between the stacked cells is configured to have an excellent cooling effect on the outlet side end of the oxidizing gas, or the anode electrode Since a non-reactive part is formed at the outlet side end of the oxidant gas of the catalyst layer layered and supported on the cathode electrode, the structure is simple, and the temperature associated with the electrochemical reaction between the fuel gas and the oxidant gas can be reduced. It is possible to provide a fuel cell that can be operated for a long time and has improved reliability by reducing the increase in the amount of phosphoric acid that is an electrolyte compared to other parts and reducing the amount of phosphoric acid that is an electrolyte taken out of the cell.

[Brief explanation of the drawing]

Figure 1 is a front view showing essential parts of an embodiment of the present invention, Figure 2 is a sectional view taken along line A-A in Figure 1, and Figure 3 is the relationship between phosphoric acid vapor pressure and temperature related to the present invention. FIG. 4 is an explanatory diagram showing the operation of one embodiment of the present invention, FIG. 5 is a front view showing main parts of another embodiment of the present invention, and FIG. - A sectional view, FIG. 7 is a perspective view showing the main part of yet another embodiment of the present invention, FIG. 8 is a diagram showing the relationship between phosphoric acid concentration and vapor pressure related to the present invention, and FIG. FIG. 9 is an explanatory diagram showing the operation of still another embodiment of the present invention, FIG. 10 is a plan view showing the main part of still another embodiment of the present invention, and FIG.
The figure is a partial sectional view showing the structure of a conventional fuel cell, and FIG. 12 is a perspective view showing an example of the structure of a unit cell of the conventional fuel cell. 1... Laminated cell 8... Matrix layer II... Anode electrode substrate 13... Cathode electrode substrate 20... Cooling plate 22.23...
・Cooling pipe 30...Anode electrode 31...
・Cathode electrode 32...Anode side catalyst layer 33・
...Cathode side catalyst layer 35, 37...non-reactive part? Ω Kaya 1 Figure Kaya 2 [ Captive Atonement → No. 31! I Kaya 4 Figure 5 Figure 1 Figure 6 Figure 7 (mrnHg + phosphorus # variable concentration Figure Z

Claims (1)

[Claims] It consists of a pair of porous electrodes that have a matrix layer that holds an electrolyte, a catalyst layer supported on the surface in contact with the matrix layer, and a plurality of grooves that serve as reaction gas supply channels on the opposite surface. In a fuel cell that constitutes a unit cell, a plurality of these unit cells are stacked and a cooling plate is inserted, and a low temperature is applied to the reactant gas outlet side end of the porous electrode through the catalyst layer or the cooling plate. 1. A fuel cell characterized by forming a region.