JPH0850904A - Fuel cell - Google Patents

Abstract

PURPOSE:To take out electric energy at high conversion efficiency by uniformly supplying a fuel gas and an oxidant gas. CONSTITUTION:An electrode protruded part 30, protruded in a manifold for supplying a fuel gas and an oxidant gas from the side surface of a laminated unit cell, is provided on the end parts of gas diffusion electrodes 3a and 3b. The size of the pore diameter of the electrode protruded part 30 is made equal to or larger than the pore diameter of a porous body composing gas diffusion electrodes 3a and 3b to increase gas diffusivity into a cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell, and more particularly to a fuel cell in which a fuel gas and an oxidant gas can be uniformly diffused in each cell.

[0002]

2. Description of the Related Art A fuel cell is known as a device for directly converting the energy of a fuel into electric energy. In this fuel cell, usually, a pair of porous electrodes are arranged with an electrolyte layer sandwiched between them, a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidant gas such as oxygen is contacted with the back surface of the other electrode. The electrodes are brought into contact with each other, and the electrochemical reaction generated at this time is used to extract electric energy from between the electrodes. In the fuel cell configured as described above, as long as the fuel gas and the oxidant gas are supplied, electric energy can be extracted with high conversion efficiency.

A fuel cell using phosphoric acid as an electrolyte will be described below as a typical fuel cell. FIG. 6 shows a structural example of a unit cell in a ribbed electrode type fuel cell using phosphoric acid as an electrolyte based on the above principle. In FIG. 6, the electrolyte layer 1 is obtained by impregnating a matrix with phosphoric acid as an electrolyte, and the anode electrode 3a and the cathode electrode 3 made of a porous carbon material sandwiching the electrolyte layer 1 are used.
b are arranged respectively. Catalyst layers 2a and 2b are coated on the sides of the anode electrode 3a and the cathode electrode 3b which are in contact with the electrolyte layer 1, respectively. A plurality of ribs 4a and 4b are formed on the back side of each of the electrodes 3a and 3b, and flow channels 5a and 5b are formed between the ribs 4a and between the ribs 4b to pass the fuel gas and the oxidant gas, respectively. ing.

Here, the flow groove 5a for flowing the fuel gas
And the flow grooves 5b through which the oxidant gas flows are arranged in directions orthogonal to each other, and a plurality of these flow grooves 5a and 5b are formed in parallel with each other. Such a unit cell is sandwiched between the separators 6 made of dense carbon to form a unit cell stack.

Further, the reaction gas flowing through the flow channels 5a, 5b diffuses in the pores of the porous carbon material of the anode electrode 3a and the cathode electrode 3b, and the catalyst layers 2a, 2b formed between them and the electrolyte layer 1 are formed. So that it can flow up to
The anode electrode 3a and the cathode electrode 3b have a density that does not hinder gas diffusion, and the size of pores is configured in consideration of the strength and gas diffusibility of the members.

Further, as shown in FIG. 7, the unit cell laminated body has a collector plate 7, an insulating plate 8, a tightening plate 9 and a terminal 10 attached to the upper and lower ends thereof, respectively, with an appropriate tightening pressure. It is assembled with it tightened from the top and bottom. A pair of fuel gas supply manifolds 15 and a fuel gas for supplying / discharging the fuel gas 12 and the oxidant gas 13 through the gaskets 11 through the pipes 14 and 14 are provided on the side surfaces of the unit cell stack described above. Exhaust manifold 16, pair of oxidant gas supply manifolds 17
The fuel cell is constructed by disposing the oxidant gas discharge manifold 18 and the oxidant gas discharge manifold 18 so as to face each other and tightening and fixing them at an appropriate pressure.

Therefore, as shown in FIG. 8, the fuel gas 12 flowing from the pipe 14 of the fuel gas supply manifold 15 is introduced.
Flows into the unit cell stack, reaches the fuel gas discharge manifold 16 while causing a chemical reaction and changes the gas composition, and flows into the fuel cell so as to be discharged from the pipe 14 to the outside. The same applies to the oxidant gas 13, so the drawing is omitted. In a fuel cell using phosphoric acid as an electrolyte, a gas containing hydrogen as a main component obtained by improving natural gas is used as the fuel gas 12, and air is used as the oxidant gas.

As described above, the gas composition of the fuel gas 12 and the oxidant gas 13 changes due to a chemical reaction.
In the fuel cell using phosphoric acid as the electrolyte, the gas density after the reaction is higher than the gas density before the reaction due to the change in the gas composition of the fuel gas 12. In the usual case, the increase is about double.

On the other hand, since the oxidant gas 13 contains nitrogen which is not involved in the chemical reaction as a main component, the change in gas density before and after the reaction is small. In the usual case, the gas density after the reaction is lower than the gas density before the reaction of the oxidant gas 13 contrary to the above-mentioned fuel gas 12, but the ratio is about 15%.

By the way, the fuel gas supply manifold 15
And the fuel gas discharge manifold 16, the oxidant gas supply manifold 17, and the oxidant gas discharge manifold 1
The internal pressure change of 8 is a hydrostatic pressure effect generated by the gas density in each manifold, and the gradient of the pressure change that linearly increases from the upper part of the manifold to the lower part of the manifold is proportional to the gas density.

As a result, the fuel gas 12 and the oxidant gas 13
Of the fuel gas supply manifold 15 and the fuel gas discharge manifold 1 due to the density change due to the gas composition change before and after the reaction
The change in internal pressure in the vertical direction of 6 is different. The same applies to the oxidizing gas supply manifold 17 and the oxidizing gas discharge manifold 18.

Further, the reaction gas branch flow to each of the unit cells stacked in the unit cell stack is, for example, in the fuel gas 12, the internal pressure difference between the fuel gas supply manifold 15 and the fuel gas discharge manifold 16 as the starting force. Done.

[0013]

However, the above-mentioned conventional fuel cell has the following problems to be solved. That is, when the density change before and after the reaction is large like the fuel gas 12, the starting force of the branching of the fuel gas 12 is greatly changed in the unit cell stacks in the upper and lower parts of the manifold and in the unit cells located in these parts. However, there is a problem in that the shunt current is not uniform among the unit cells.

FIG. 9 shows the fuel gas supply manifold 15 for the fuel gas 12 and the fuel gas discharge manifold 1 described above.
6 is shown from the point corresponding to the position of the uppermost unit cell position to the position corresponding to the position of the lowermost unit cell.

It should be noted that the pressure of the oxidizing gas supply manifold 17 for the oxidizing gas 13 and the oxidizing gas discharge manifold 18 corresponding to the uppermost unit cell position is used as a reference.
Since the same applies to the portion corresponding to the position of the lowermost unit cell from here, the description thereof will be omitted.

Referring to FIG. 9, the pressure distribution 19a of the fuel gas supply manifold 15 in the unit cell stack is shown.
Of the fuel gas exhaust manifold 16 and the pressure gradient of the pressure distribution 20 of the fuel gas exhaust manifold 16 are different from each other, the pressure difference which is the starting force of the gas branch flow to each unit cell is different.
That is, the pressure difference, which is the motive force of the gas shunt, changes linearly and decreases from the unit cell stacked on the upper side to the unit cell stacked on the lower side. As a result, the latter is smaller than the unit cell of the former. There is a problem in that the gas split flow rate to the unit cell is reduced, and the power generation performance as a battery is also reduced.

In order to increase the output of the unit cell stack, this decreasing tendency tends to increase as the stack height increases when the number of unit cell stacks is increased. Become.

With respect to the oxidant gas 13, the change in gas density before and after the reaction is originally small, and the nonuniformity of the split flow does not occur as much as in the case of the fuel gas 12. In this way, the fuel gas 12 and the oxidant gas 13 supplied to the unit cells from the fuel gas supply manifold 15 and the oxidant gas supply manifold 17 to the unit cell stack are distributed between the unit cells in the vertical direction of the unit cell stack. As a result, the chemical reaction conditions will change, resulting in a situation in which electrical energy cannot be extracted with the high conversion efficiency that was initially expected. Therefore, in the process in which electric energy is generated from the unit cell by the electrochemical reaction, the voltage distribution 21a in the stacking direction is as shown in FIG.

The present invention has been made in consideration of the above circumstances, and provides a fuel cell capable of uniformly supplying a fuel gas and an oxidant gas and extracting electric energy with high conversion efficiency. To aim.

[0020]

In order to solve the above-mentioned problems, the first aspect of the present invention is to arrange a pair of gas diffusion electrodes made of a porous body with an electrolyte layer in which a matrix is impregnated with an electrolyte sandwiched therebetween. In a fuel cell in which a plurality of unit cells each having the above structure are stacked, and a manifold for supplying and discharging a fuel gas and an oxidant gas is provided on the side of the unit cell, An electrode protrusion protruding into the manifold is provided at the end of the gas diffusion electrode, and the size of the pore diameter of the electrode protrusion is set to be larger than that of the porous body forming the gas diffusion electrode. Characterize.

According to a second aspect of the present invention, in the fuel gas and oxidant gas supply / discharge manifold according to the first aspect, an inert gas other than that is introduced into the fuel gas and the oxidant gas during partial load operation. It is characterized by

A third aspect of the present invention is characterized in that the inert gas introducing pipe for introducing the inert gas according to the second aspect is provided for each battery block.

A fourth aspect of the present invention is characterized in that the amount of the inert gas introduced from the inert gas introducing pipe according to the third aspect is variable for each unit cell.

A fifth aspect of the invention is characterized in that the inert gas introducing pipe according to the fourth aspect is provided with a plurality of gas introducing branch pipes at positions corresponding to the respective unit cells.

[0025]

According to the first aspect of the present invention, the electrode protrusion protruding from the side surface of the stacked unit cells into the fuel gas and oxidant gas supply manifold is provided at the end of the gas diffusion electrode, and the pore diameter of the electrode protrusion is increased. By making the size of the porous body larger than that of the gas diffusion electrode,
The fuel gas and the oxidant gas supplied from the outside are received by the electrode protruding portion, and the gas pressure with the larger pore diameter is higher, so that the gas diffusibility into the cell can be improved.

According to a second aspect of the present invention, the fuel gas and oxidant gas supply / discharge manifold according to the first aspect introduces an inert gas other than that into the fuel gas and the oxidant gas during partial load operation. By doing so, it is possible to increase the gas flow rate and ensure the gas flow rate supply to the entire fuel cell.

In the third aspect, the inert gas introducing pipe for introducing the inert gas according to the second aspect is provided for each battery block, thereby preventing excess and deficiency of gas flow rate supply for each battery block. The necessary and sufficient amount can be supplied.

In the fourth aspect, the amount of the inert gas introduced from the inert gas introducing pipe according to the third aspect is changed for each unit cell, thereby preventing excess and deficiency of the gas flow rate supply per each unit cell. A necessary and sufficient amount can be supplied.

According to a fifth aspect of the present invention, a plurality of gas introduction branch pipes are provided at positions corresponding to the unit cells of the inert gas introduction pipe according to the fourth aspect, so that the gas flow rate is reliably supplied to each cell. Can be

[0030]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show each embodiment of the fuel cell according to the present invention. In each of these embodiments, the same members as those of the conventional structure will be described with the same reference numerals as those in FIGS. 6 to 10.

<First Embodiment> FIG. 1 is a perspective view showing a main part of a first embodiment of a fuel cell according to the present invention. As shown in FIG. 1, the fuel gas supply manifold 15 and the oxidant gas supply manifold 17 are provided on the side where the flow channels 5a and 5b, which are the reaction gas flow paths of the anode electrode 3a and the cathode electrode 3b, which are gas diffusion electrodes, are formed. So that it projects inside
An electrode protrusion 30 composed of a porous body is provided. The electrode protrusion 30 is made of carbon fiber or the like, and has a pore diameter equal to or larger than the pore diameter of the porous body forming the anode electrode 3a and the cathode electrode 3b.

Next, the operation of this embodiment will be described.

In the fuel cell of this embodiment having such a structure, the fuel gas 12 is produced as described below.
And the oxidant gas 13 is supplied. That is, these supplied reaction gases are received in the electrode protrusions 30, and the pressure of the gas having the larger pore diameter is higher, so that the reaction gas diffuses through the electrode protrusions 30 and contacts the electrode protrusions 30. It extends to the electrode 3a and the cathode electrode 3b. The reaction gas that has come into contact with the anode electrode 3a and the cathode electrode 3b in this manner is taken into the anode electrode 3a and the cathode electrode 3b having the small pore diameters from the electrode protrusion 30 due to the pressure difference between the gas having the pore diameters.

Further, as shown in FIG. 2, the internal pressure distribution 19b of the fuel gas supply manifold 15 and the internal pressure distribution 20 of the fuel gas discharge manifold 16 increase the fuel gas flow rate, resulting in an increase in pressure loss. The pressure difference between the fuel gas supply manifold 15 and the fuel gas discharge manifold 16 can be made uniform over the entire cell stack height direction. As a result, it is possible to make the gas partial flow uniform to each unit cell that flows using this pressure difference as a starting force.

The combustion gas split into the cell stack constructed by using the unit cell as described above is orthogonal to the combustion gas and flows into the cell stack. Reach the gas exhaust manifold 16. The voltage distribution 21b in the stacking direction is as shown in FIG. 3 in the process in which electric energy is generated from the unit cell by the electrochemical reaction that occurs at this time.

That is, in the present embodiment, the fuel gas 12 that has flowed into the fuel gas supply manifold 15 is divided into each unit cell and reaches the inside of the fuel gas discharge manifold 16 through the flow grooves 5a and 5b. The flow rate of the fuel gas flowing into each unit cell is equal to the pressure difference between the fuel gas supply manifold 15 and the fuel gas discharge manifold 16.

Therefore, if the flow rate of the fuel gas passing through the flow grooves 5a and 5b is increased to increase the generated pressure loss, the fuel gas density before the reaction inside the fuel gas supply manifold 15 and the inside of the fuel gas discharge manifold 16 are increased. Even if there is a large pressure difference due to the hydrostatic effect of the fuel gas density after the reaction, the pressure difference that becomes the starting force of the fuel gas branch flow between each unit cell located at the top of the cell stack and each unit cell located at the bottom of the cell stack. Can greatly exceed the hydrostatic pressure difference, and the fuel gas branch flow rate to each unit cell can be made uniform.

On the other hand, since the air used as the oxidant gas is mainly composed of nitrogen gas that does not participate in the reaction, there is no great difference between the gas density inside the air supply manifold and the gas density inside the air discharge manifold, and therefore the hydrostatic pressure action is exerted. Effects are almost equal. However, in order to obtain the amount of oxygen necessary for the reaction, the flow rate is increased to increase the pressure loss generated in the flow groove of the oxidant gas 13, and the oxidant gas branch flow rate to each unit cell is made uniform. be able to.

By the way, in the present embodiment, during partial load operation, as shown in FIG. 1, an inert gas 31 other than the fuel gas and the oxidant gas is introduced into the fuel gas 12 and the oxidant gas 13 to produce a gas. By increasing the flow rate and diffusing the gas at the electrode protrusion (gas diffusion electrode end) 30, the pressure loss increases. As a result, the internal pressure distribution of the fuel gas supply manifold 15 and the fuel gas discharge manifold 16 is The pressure difference between the fuel gas supply manifold 15 and the fuel gas discharge manifold 16 can be made uniform over the entire cell stack height direction. During the process in which electric energy is generated from the unit cell by the electrochemical reaction, the voltage distribution in the stacking direction is as shown in FIGS.

Further, in this embodiment, during the partial load operation, by providing the inert gas introducing pipe 60 for each cell block as shown in FIG.
1 is reliably supplied, and nonuniformity of the gas split flow rate of the fuel cell due to a decrease in gas flow rate is prevented in advance, and stable operation is enabled.

<Second Embodiment> FIG. 4 is a sectional view showing a second embodiment of the fuel cell according to the present invention. The same parts as those in the first embodiment will be described with the same reference numerals. The same applies to the following examples. In the present embodiment, during the partial load operation, as shown in FIG. 4, in the inert gas introducing pipe 32 for each unit cell, the inert gas branch pipe 3 is provided.
It has an inert gas introducing pipe 32 whose supply amount can be changed by changing the number of 3 and the inner diameter. Therefore, according to this embodiment, the amount of the inert gas 31 supplied to the electrode protrusions 20 of the unit cell can be adjusted, and the inert gas 3 can be adjusted.
It is possible to prevent excess and deficiency of the supply amount of No. 1 and to supply a necessary and sufficient amount. The other structure and operation are the same as those of the first embodiment, and the description thereof will be omitted.

<Third Embodiment> FIG. 5 is a perspective view of a main portion of a third embodiment of the fuel cell according to the present invention. In the present embodiment, during partial load operation, a plurality of inert gas branch pipes 33 are provided at positions corresponding to the unit cells formed in a stepwise manner on the inert gas introduction pipe 32 as shown in FIG. By doing so, the supply of the inert gas 31 to each cell can be ensured. The other structure and operation are the same as those of the first embodiment, and the description thereof will be omitted.

[0043]

As described above, according to the first aspect of the present invention.
According to the above, an electrode protrusion protruding from the side surface of the stacked unit cells into the manifold is provided at the end of the gas diffusion electrode, and the size of the pore diameter of the electrode protrusion is set to a porous body forming the gas diffusion electrode. By providing the above size, by improving the gas diffusivity of the fuel gas and oxidant gas supplied from the outside, it is possible to provide a highly accurate fuel cell that makes it possible to evenly divide the flow into each unit cell. can do.
Therefore, by increasing the flow rates of the fuel gas and the oxidant gas to each unit cell, the performance of the fuel cell can be improved and electric energy can be obtained with high conversion efficiency.

According to a second aspect of the present invention, the fuel gas and oxidant gas supply / discharge manifold according to the first aspect contains the other inert gas in the fuel gas and the oxidant gas during the partial load operation. By introducing the gas, the gas flow rate can be increased and the gas flow rate can be reliably supplied to the entire fuel cell.

According to the third aspect, since the inert gas introducing pipe for introducing the inert gas according to the second aspect is provided for each battery block, excess or deficiency of gas flow rate supply for each battery block can be prevented. It can prevent and supply necessary and sufficient amount.

According to the fourth aspect, the amount of the inert gas introduced from the inert gas introducing pipe according to the third aspect is changed for each unit cell, so that excess or deficiency of gas flow rate supply for each unit cell is prevented. The necessary and sufficient amount can be supplied.

According to the fifth aspect, the inert gas introducing pipe according to the fourth aspect is provided with a plurality of gas introducing branch pipes at positions corresponding to the respective unit cells, so that the gas flow rate is supplied to each cell. You can be sure.

[Brief description of drawings]

FIG. 1 is a perspective view of essential parts showing a first embodiment of a fuel cell according to the present invention.

FIG. 2 is a pressure distribution diagram of the fuel gas manifold according to the first embodiment.

FIG. 3 is a voltage distribution diagram showing a stacking direction voltage of the fuel cell of the first embodiment.

FIG. 4 is a sectional view showing a second embodiment of the fuel cell according to the present invention.

FIG. 5 is a perspective view of a main part showing a third embodiment of the fuel cell according to the present invention.

FIG. 6 is an explanatory diagram showing a configuration of a general fuel cell.

FIG. 7 is a perspective view showing a conventional fuel cell.

8 is a vertical cross-sectional view of FIG.

FIG. 9 is a pressure distribution diagram of a fuel gas manifold in a conventional fuel cell.

FIG. 10 is a voltage distribution diagram showing a stacking direction voltage of a conventional fuel cell.

[Explanation of symbols]

 1 Electrolyte Layer 3a Anode Electrode (Gas Diffusion Electrode) 3b Cathode Electrode (Gas Diffusion Electrode) 5a Flow Channel 5b Flow Channel 12 Fuel Gas 13 Oxidizer Gas 15 Fuel Gas Supply Manifold 16 Fuel Gas Discharge Manifold 17 Oxidant Gas Supply Manifold 18 Oxidation Agent gas discharge manifold 30 Electrode protrusion 31 Inert gas 32 Inert gas introduction pipe 33 Inert gas branch pipe

Claims (5)

[Claims] 1. A plurality of unit cells each having a pair of gas diffusion electrodes made of a porous body disposed with a matrix sandwiching an electrolyte layer impregnated with an electrolyte, and a fuel gas and an oxidant gas being provided on the sides thereof. In a fuel cell provided with a supply / discharge manifold, an electrode protrusion protruding from the side surface of the stacked unit cells into the fuel gas and oxidant gas supply manifold is provided at an end of the gas diffusion electrode, and The fuel cell is characterized in that the electrode projection has a pore size larger than that of the porous body forming the gas diffusion electrode. 2. The fuel gas and oxidant gas supply manifold introduces an inert gas other than that into the fuel gas and the oxidant gas during partial load operation. Fuel cell. 3. The fuel cell according to claim 2, wherein an inert gas introducing pipe for introducing an inert gas is provided for each cell block. 4. The amount of inert gas introduced from the inert gas introduction pipe is variable for each unit cell.
The fuel cell described. 5. The fuel cell according to claim 4, wherein the inert gas introducing pipe is provided with a plurality of gas introducing branch pipes at positions corresponding to the respective unit cells.