JP2001351666A - Fuel cell system using phosphoric acid and stopping method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent an outflow of phosphoric acid caused by the water generated as a reaction product, and to enable to efficiently keep an electric power generating property. SOLUTION: The fuel cell system comprises a fuel cell stack 12, an oxidant gas flow path 44 connected to an oxidant gas flow path 32 inside the fuel cell stack 12, a fuel gas flow path 46 connected to a fuel gas flow path 34 inside the fuel cell stack 12, and the first and the second connection paths 48a, 48b enabled to connect the oxidant gas flow path 44 with the fuel gas flow path 46.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of power generators having a joined body composed of an electrolyte impregnated with phosphoric acid sandwiched between an anode electrode and a cathode electrode, and the joined body sandwiched between separators. The present invention relates to a phosphoric acid type fuel cell system including a fuel cell stack in which cells are stacked and a method for stopping the same.

[0002]

2. Description of the Related Art A fuel cell, for example, a phosphoric acid type fuel cell (PAFC) is provided on both sides of an electrolyte in which porous phosphoric acid (matrix) is impregnated with concentrated phosphoric acid. A power generation cell is provided by sandwiching a joined body (MEA) having a pair of cathode electrodes with a separator (bipolar plate). Usually, a predetermined number of the power generation cells are stacked. Used as a fuel cell stack.

In the above fuel cell stack, a fuel gas (reactive gas) supplied to the anode electrode, for example,
In a gas mainly containing hydrogen (hydrogen-containing gas), hydrogen is ionized on the catalyst electrode, and moves toward the cathode side electrode through the electrolyte. The electrons generated during that time are taken out to an external circuit and used as DC electric energy.

On the other hand, an oxidizing gas (reactive gas), for example, a gas mainly containing oxygen or air (oxygen-containing gas) is supplied to the cathode side electrode. Ions, electrons and oxygen react to produce water.

Generally, in a phosphoric acid type fuel cell, since the operating temperature is set to a relatively high temperature (around 140 ° C. to 200 ° C.), water generated during operation is vaporized and discharged to the outside. Have been. However, when the temperature is lowered, for example, when the operation is stopped, the generated water is present as liquid water, and liquid water exceeding the amount that can be stored in the electrolyte layer and the electrode is introduced into the reaction gas flow path. .

However, the phosphoric acid constituting the electrolyte has a very high hydrophilicity and flows out of the electrolyte layer and the electrode together with the liquid water introduced into the reaction gas flow path. As a result, there is a problem that the power generation performance of the power generation cell is reduced and the life of the fuel cell itself is shortened.

In order to prevent a decrease in the concentration of phosphoric acid during shutdown, a fuel cell system disclosed in, for example, Japanese Patent Application Laid-Open No. 3-93166 is known. In this conventional technique, after the supply of fuel gas is stopped, the air is heated and dried and supplied to the electrode, and the supply / discharge valve of the electrode is closed while the gas space in the electrode is filled with dry air. I have.

[0008]

However, in the above-mentioned prior art, a heat exchanger must be used for heating and drying the air, which complicates the structure. Moreover,
In the above-described conventional technology, the reaction water is supplied only to the supply / discharge path of the reaction air supplied / discharged to / from the air electrode. However, actually, generated water is also generated on the hydrogen electrode side. For this reason, it has been pointed out that the generated water exists as liquid water on the hydrogen electrode side as the temperature decreases, and the phosphoric acid concentration decreases due to the outflow of phosphoric acid.

[0009]

In the phosphoric acid type fuel cell system according to the first and fourth aspects of the present invention and the method for stopping the same, the oxidizing gas or the fuel gas is supplied to the first flow path in the fuel cell stack. Is supplied, and the other reaction gas is supplied to the second flow passage in the fuel cell stack, thereby generating power. When the power generation of the fuel cell stack ends, supply and discharge of the other reaction gas are stopped, and only one reaction gas is supplied to the first and second flow paths in the fuel cell stack. You.

Thus, in the first and second flow paths,
The reaction is not caused, and the water present in the first and second flow paths can be reliably removed under the flow of only one reaction gas. Therefore, when the power generation of the fuel cell stack is stopped, there is no liquid water in the first and second flow paths, and the outflow of phosphoric acid can be reliably prevented with a simple configuration and steps, and the desired power generation performance can be obtained. Can be maintained effectively, and a reduction in the life can be avoided.

Further, in the phosphoric acid type fuel cell system according to claim 2 of the present invention, the first supply / discharge of one reaction gas is performed.
First and second communication paths are provided so as to be able to communicate with the reaction gas path and the second reaction gas path for supplying and discharging the other reaction gas. The first and second reaction gas paths are provided with first and second inlet-side on-off valves and first and second outlet-side on-off valves, while the first and second communication paths are
A third inlet side on-off valve and a third outlet side on-off valve are provided.

Therefore, by closing the second inlet-side on-off valve and the second outlet-side on-off valve, the first and third inlet-side on-off valves and the first and third outlet-side on-off valves are opened. The first reaction gas can be smoothly supplied to the first and second flow paths in the fuel cell stack. Thus, with a simple configuration, the supply and stop of the first and second reaction gases and the change of the supply path are easily and reliably performed.

Further, in the phosphoric acid type fuel cell system according to the third and sixth aspects of the present invention and the method for stopping the same, the electrolyte includes an electrolyte layer in which polybenzimidazole holds phosphoric acid. Therefore, the weight and size of the entire fuel cell stack can be easily reduced.

Further, in the method for shutting down the phosphoric acid type fuel cell system according to the fifth aspect of the present invention, one reaction may be caused to flow into the second flow path outside the combustion range when the oxidizing gas and the fuel gas are mixed. Gas is introduced. For this reason, the combustion by the oxidizing gas and the fuel gas is not performed in the second flow path, and only the original purpose of removing moisture is reliably performed.

[0015]

FIG. 1 is a schematic diagram illustrating a phosphoric acid fuel cell system 10 according to an embodiment of the present invention.

The phosphoric acid type fuel cell system 10 includes a fuel cell stack 12.
A predetermined number of power generation cells 14 are stacked in the direction of arrow A, and end plates 16a and 16b are arranged at both ends in the stacking direction. End plate 16
A plurality of power generation cells 14 are integrally tightened and held in the direction of arrow A by tightening a and 16b with the tightening bolts 18 and the nuts 20.

The power generation cell 14 includes a cathode electrode 24 and an anode electrode 26 sandwiching an electrolyte layer 22 made of porous silicon carbide or a basic polymer, for example, polybenzimidazole impregnated with phosphoric acid. The cathode electrode 24 and the anode electrode 26 are provided with a gas diffusion layer made of, for example, porous carbon paper, which is a porous layer. The power generation cell 14 is configured by disposing a pair of separators 30 as bipolar plates on both sides of the joined body 28.

An oxidizing gas flow path (first flow path) 32 for supplying an oxidizing gas, which is one reactive gas, is formed on the surface of the separator 30 facing the cathode-side electrode 24. A fuel gas flow path (second flow path) 34 for supplying a fuel gas, which is the other reaction gas, is formed on the surface facing the anode-side electrode 26.

The end plate 16a is provided with an oxidizing gas inlet (reaction gas inlet) 36 and a fuel gas inlet (reaction gas inlet) 38.
In b, an oxidizing gas outlet (reaction gas outlet) 40 and a fuel gas outlet (reaction gas outlet) 42 are provided.

The phosphoric acid type fuel cell system 10 includes a fuel cell stack 12 configured as described above, and an oxidant gas flow path of the fuel cell stack 12 through an oxidant gas inlet 36 and an oxidant gas outlet 40. An oxidizing gas passage (first reaction gas passage) 44 communicating with the fuel gas inlet 3;
A fuel gas passage (second reaction gas passage) 46 communicating with the fuel gas flow path 34 of the fuel cell stack 12 via the fuel gas stack 8 and the fuel gas outlet 42; A first communication path 48a that allows communication between the gas path 44 and the fuel gas path 46; and a first communication path 48a that allows communication between the oxidizing gas path 44 and the fuel gas path 46 on the reaction gas outlet side of the fuel cell stack 12. And a two-way passage 48b.

The oxidizing gas passage 44 is provided outside the portion where the first and second communication passages 48a and 48b communicate with each other, and is provided with a first inlet side opening / closing valve 50 and a first outlet side opening / closing valve 52. On the other hand, the fuel gas passage 46 has a second inlet-side opening / closing valve 54 and a second outlet-side opening / closing valve 56 located outside a portion where the first and second communication passages 48a and 48b communicate. . A pump 60 is provided on the upstream side of the oxidizing gas path 44. First and second communication paths 48a, 48b
Is provided with a third inlet-side opening / closing valve 62 and a third outlet-side opening / closing valve 64 capable of communicating with and shutting off the oxidizing gas passage 44 and the fuel gas passage 46.

The operation of the thus constructed phosphoric acid fuel cell system 10 will be described below.

During operation of the fuel cell stack 12, FIG.
As shown in the figure, the first and second inlet-side on-off valves 50, 54
And the first and second outlet-side on-off valves 52 and 56 are arranged at the communicating position (open position), while the third inlet-side on-off valve 6
The second and third outlet side opening / closing valves 64 are arranged in the closed position. Therefore, the oxidizing gas, which is air or an oxygen-containing gas, is supplied from the oxidizing gas passage 44 to the oxidizing gas inlet 36 of the end plate 16a, while the fuel gas passage 46 is provided.
A fuel gas such as a hydrogen-containing gas is supplied to the fuel gas inlet 38 of the end plate 16a.

In the fuel cell stack 12, the oxidizing gas is supplied to the cathode 24 through the oxidizing gas flow path 32 of the separator 30, and the fuel gas flows through the fuel gas flow path 34 of the separator 30. And supplied to the anode 26. Thus, power is generated in each power generation cell 14, and power is supplied to a load such as a motor.

Next, a method of stopping the fuel cell stack 12 operating as described above will be described.

As shown in FIG. 2, the second inlet-side on-off valve 54
In addition, the second outlet opening / closing valve 56 is closed, and supply and discharge of the fuel gas from the fuel gas path 46 to the fuel cell stack 12 are stopped. On the other hand, the third inlet side on-off valve 62 and the third outlet side on-off valve 64 are opened. Therefore, the oxidizing gas supplied to the oxidizing gas passage 44 via the pump 60 is supplied to the oxidizing gas passage 32 via the oxidizing gas inlet 36 of the fuel cell stack 12 and the first communication passage The fuel gas is supplied to the fuel gas flow path 34 from the fuel gas inlet 38 of the fuel cell stack 12 through 48a.

As a result, in each of the power generation cells 14, only the oxidizing gas is supplied along the cathode 24 and the anode 26. Moisture (water vapor) remaining in the flow path 32 and the fuel gas flow path 34 is generated by the oxidizing gas outlet 40 and the fuel gas outlet 4 of the fuel cell stack 12.
Exhausted from 2. A part of the oxidizing gas containing moisture is discharged to the oxidizing gas path 44 via the second communication path 48b, while the remaining part is directly discharged to the oxidizing gas path 44.

At this time, the oxidizing gas is introduced into the fuel gas flow path 34 outside the combustion range when the oxidizing gas and the fuel gas are mixed, for example, when the oxidizing gas is air and the fuel gas is hydrogen. In some cases, the mixing is performed at a hydrogen concentration other than 4% to 75%. That is, this is to prevent combustion from occurring in the fuel gas flow path 34.

As described above, the flow of the oxidizing gas to the oxidizing gas flow path 32 and the fuel gas flow path 34
Even when the temperature of the fuel cell 4 drops to the outside air temperature, the process is performed until the water vapor in the fuel cell stack 12 does not condense into excess liquid water.

Next, as shown in FIG. 3, the first and third inlet side opening / closing valves 50, 62 and the first and third outlet side opening / closing valves 52, 64 are closed. Accordingly, the supply and discharge of the oxidizing gas to and from the fuel cell stack 12 are stopped, and the oxidizing gas is sealed in the fuel cell stack 12.

As described above, in this embodiment, when the power generation of the fuel cell stack 12 is stopped, the oxidizing gas passage 3
2 and the water produced by the reaction in the fuel gas flow path 34 do not exist as liquid water, and the phosphoric acid held in the electrolyte layer 22 can be reliably prevented from flowing out together with the liquid water. become. As a result, the power generation performance of each power generation cell 14 can be effectively maintained, and a reduction in battery life can be avoided.

In the present embodiment, the oxidizing gas passage 4
It is only necessary to provide the first and second communication passages 48a and 48b at the reaction gas inlet side and the reaction gas outlet side of the fuel cell stack 12 in the fuel gas stack 4 and the fuel gas path 46, respectively. Therefore, there is an advantage that the entire configuration of the phosphoric acid type fuel cell system 10 is effectively simplified and economical.

Further, in the present embodiment, the electrolyte layer 22
Is composed of an electrolyte layer in which phosphoric acid is held in a matrix of a basic polymer, particularly polybenzimidazole. For this reason, there is an advantage that the weight and size of the entire fuel cell stack 12 can be easily reduced.

In this embodiment, when the fuel cell stack 12 is stopped, the oxidizing gas is supplied to the oxidizing gas passage 32 and the fuel gas passage 34 to remove moisture. And the fuel gas is supplied to the oxidizing gas passage
2 and to the fuel gas flow path 34,
It is also possible to remove water.

[0035]

According to the phosphoric acid type fuel cell system and the method for stopping the same according to the present invention, when the power generation of the fuel cell stack is completed, the oxidizing gas and the fuel gas for supplying the oxidizing gas and the fuel gas in the fuel cell stack are reduced. Only one reaction gas is supplied to the first and second flow paths, and the water remaining in the first and second flow paths is reliably removed. Therefore, when the temperature of the fuel cell stack is reduced due to the shutdown, the generated water does not cause the phosphoric acid held in the electrolyte to flow out as liquid water, and the desired power generation performance is effectively maintained. In addition, it is possible to reliably prevent a decrease in battery life.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a phosphoric acid fuel cell system according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram when the phosphoric acid type fuel cell system is stopped.

FIG. 3 is an explanatory diagram when the phosphoric acid type fuel cell system is completely stopped.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Phosphoric acid type fuel cell system 12 ... Fuel cell stack 14 ... Power generation cell 16a, 16b ... End plate 18 ... Tightening bolt 20 ... Nut 22 ... Electrolyte layer 24 ... Cathode side electrode 26 ... Anode side electrode 28 ... Joint body 30 ... Separator 32 ... Oxidizing gas flow path 34 ... Fuel gas flow path 36 ... Oxidizing gas inlet 38 ... Fuel gas inlet 40 ... Oxidizing gas outlet 42 ... Fuel gas outlet 44 ... Oxidizing gas path 46 ... Fuel gas path 48a, 48b ... Communication passages 50, 52, 54, 56, 62, 64 ... On-off valve 60 ... Pump

Claims (6)

[Claims] 1. A fuel comprising a joined body comprising an electrolyte impregnated with phosphoric acid sandwiched between an anode electrode and a cathode electrode, and a plurality of power generation cells having the joined body sandwiched between separators. A cell stack; a first reaction gas path for supplying and discharging one reaction gas, which is an oxidant gas or a fuel gas, to and from a first flow path in the fuel cell stack; A second reaction gas path for supplying and discharging to and from a second flow path in the stack; and a first communication path capable of communicating the first and second reaction gas paths on a reaction gas inlet side of the fuel cell stack. A second communication path that can communicate the first and second reaction gas paths at a reaction gas outlet side of the fuel cell stack, wherein the second communication path is used when the power generation of the fuel cell stack ends.
While blocking the reaction gas path, the first and second
A phosphoric acid-type fuel cell system, wherein the one reaction gas is supplied from the first reaction gas path to the first and second flow paths in the fuel cell stack by opening a communication path. 2. The phosphoric acid type fuel cell system according to claim 1, wherein said first and second reaction gas paths are located outside a portion where both ends of said first and second communication paths communicate with each other. While the first and second inlet-side on-off valves and the first and second outlet-side on-off valves are provided, the first and second communication passages include a third inlet-side on-off valve, a third outlet-side on-off valve, The phosphoric acid type fuel cell system characterized by disposing. 3. The phosphoric acid type fuel cell system according to claim 1, wherein said electrolyte comprises an electrolyte layer in which polybenzimidazole holds phosphoric acid. 4. A fuel comprising a joined body comprising an electrolyte impregnated with phosphoric acid sandwiched between an anode-side electrode and a cathode-side electrode, wherein a plurality of power generation cells having the joined body sandwiched by separators are stacked. A method for stopping a phosphoric acid type fuel cell system including a cell stack, comprising supplying one reaction gas, which is an oxidizing gas or a fuel gas, to a first flow path in the fuel cell stack and the other reaction gas. Supplying power to the second flow path in the fuel cell stack to generate power; and stopping power supply and discharge of the other reactant gas when the power generation of the fuel cell stack is completed. Removing only water from the fuel cell stack by supplying only the one reaction gas to the first and second flow passages in the stack. The method of stopping acid fuel cell system. 5. The stopping method according to claim 4, wherein said one reaction gas is introduced into said second flow path outside a combustion range when said oxidizing gas and said fuel gas are mixed. Method for stopping a phosphoric acid type fuel cell system. 6. The method for stopping a phosphoric acid type fuel cell system according to claim 4, wherein said electrolyte is an electrolyte layer in which phosphoric acid is retained on polybenzimidazole.