JP2924009B2 - How to stop fuel cell power generation - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of stopping a power generation operation including an emergency stop or a long stop of a matrix fuel cell, and more particularly to a method of replacing a reaction gas with an inert gas. .

[Conventional technology]

As is well known, a fuel cell is a cell stack in which a plurality of single cells in which a matrix holding an electrolyte is sandwiched between a pair of fuel electrodes and an oxidant electrode are stacked with a gas impermeable plate interposed on a stacking surface, and A hydrogen-rich fuel gas is supplied to a fuel gas passage defined between the electrode and the gas impermeable plate, and air or oxygen as an oxidant defined between the oxidant electrode and the gas impermeable plate. To generate electric power. In addition, since the fuel cell generates water on the oxidant electrode side due to the power generation reaction, the operating temperature of a cell using highly hygroscopic phosphoric acid as an electrolyte is from 130 ° C to 190 ° C.
Generally, the power generation operation is performed while maintaining the high temperature of about 190 ° C. to facilitate discharge of generated water and maintaining the activity of the electrode catalyst. When the current flowing through the external load circuit is cut off to stop or stop the operation of the fuel cell operated in this way, a high value of a high-temperature open circuit voltage is generated in each cell, and the electrode catalyst particles become coarse. Deterioration (referred to as sintering) in which the electrode surface area is reduced, resulting in reduced power generation performance and reduced service life. Also, as the battery temperature decreases, the phosphoric acid is diluted by adsorbing moisture in the reaction gas,
The volumetric expansion of the phosphoric acid solution excessively seeps out of the matrix toward the electrode, causing a supply failure of the reaction gas. Further, various obstacles occur, such as a decrease in the gas dividing function of the matrix in which the phosphoric acid solution has leaked, causing the reaction gas and fuel gas to come into contact with each other and increasing the risk of generating explosive air.

Therefore, in order to avoid these obstacles and stop the power generation of the fuel cell, the external load circuit is shut off, the supply of the fuel gas and the oxidizing gas is stopped, and the fuel gas formed by the fuel gas passage and its supply / discharge manifold is formed. A dry inert gas such as nitrogen is supplied to each of the compartment and the oxidant compartment including the oxidant passage and its supply / discharge manifold, and the temperature of the fuel cell is lowered while purging the remaining reaction gas (fuel gas or oxidant gas). There are known ways to do this. When the fuel cell is to be stopped for a short period of time, the external load circuit is opened, the fuel gas and air are supplied by natural convection, and the battery is discharged through a discharge resistor provided in parallel with the external load circuit, and the oxidizing agent is discharged. A method of consuming oxygen in the air in a compartment and filling the compartment with nitrogen in the air to stop power generation. In addition, a method is known in which nitrogen generated in an oxidant compartment is supplied to a fuel gas compartment to purge hydrogen and then both gas compartments are sealed, discharge resistance is released, and power generation is stopped for a long time. (See JP-A-55-19713).

[Problems to be solved by the invention]

In the former method, the reaction gas in both compartments can be quickly purged by supplying nitrogen gas from the outside, so that the trouble due to the high-temperature open circuit voltage and the trouble due to the absorption of phosphoric acid are caused. , As well as the danger of reactant gases coming into contact with each other. That is, regarding the high-temperature open circuit voltage, since both the oxidizing electrode and the fuel electrode are purged with nitrogen, the potentials of the two electrodes with respect to, for example, a standard hydrogen potential are substantially equal, and the open circuit voltage of the cell determined by the potential difference is apparent. It has been considered that the temperature is sufficiently low, so that adverse effects such as sintering due to the high-temperature open circuit voltage can be avoided. However, on the oxidant electrode side, there is residual adsorbed oxygen chemically adsorbed on the surface of the electrocatalyst particles, and it is not possible to desorb this residual adsorbed oxygen only by purging with nitrogen gas. Recent studies have shown that high potential is maintained, and the disadvantage that exposure to high potential at high temperatures until the oxidant electrode cools has the disadvantage that the adverse effect on the catalyst layer cannot be avoided. It was revealed.

On the other hand, in the latter two conventional methods, the apparatus can be simplified because supply of an inert gas such as nitrogen is not required.However, while supplying a reaction gas by natural diffusion, oxygen and air in the air are discharged by a small current discharge. Since the hydrogen in the fuel gas is slowly consumed, the time during which the electrode is exposed to a state close to the high-temperature open circuit voltage is longer than in the former case, and during this time, deterioration of the electrode catalyst cannot be avoided. In addition, since the oxygen concentration in the oxidant compartment is reduced and the hydrogen concentration in the fuel gas compartment is also reduced, the remaining adsorbed oxygen of the oxidant electrode is not sufficiently consumed or it takes time to consume. However, the problem remains that the oxidant electrode is exposed to a high potential during this time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for shutting down an operation in which the residual adsorbed oxygen of an oxidant electrode can be consumed almost completely by shifting the purge timing of a reactive gas by an inert gas by a predetermined time between both compartments.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, air as an oxidant is supplied from an oxidant compartment to an oxidant electrode sandwiching a matrix holding an electrolyte, and hydrogen-rich is supplied from a fuel gas compartment to a fuel cell. When stopping the power generation of the fuel cell that supplies the fuel gas and generates power, the external load circuit of the fuel cell is opened, the air is switched to the inert gas, and the gas in the oxidant compartment is replaced,
The supply of the fuel gas is stopped to fill the fuel gas into the fuel gas compartment, the oxidant electrode and the fuel electrode are connected to a discharge resistor, and a current generated by an electromotive reaction flows as a discharge current. Disconnecting the connection to the discharge resistor after the current has become equal to or less than the predetermined value, or opening the external load circuit of the fuel cell, switching the air to an inert gas and replacing the gas in the oxidant compartment,
The supply of the fuel gas is stopped to fill the fuel gas into the fuel gas compartment, and then an inert gas is supplied into the fuel gas compartment to oxidize the fuel gas filled in the fuel gas compartment. Introduced to the agent compartment, the residual adsorbed oxygen is consumed by the catalytic combustion reaction of the oxidant electrode, or the external load circuit of the fuel cell is opened, the air is switched to inert gas, and the oxidant compartment is opened. Gas replacement,
The supply of the fuel gas is stopped to fill the fuel gas into the fuel gas compartment, the oxidant electrode and the fuel electrode are connected to a discharge resistor, and a current generated by an electromotive reaction flows as a discharge current. After the current becomes equal to or less than a predetermined value, the gas supply side of the fuel gas compartment is opened to the air, and the remaining fuel gas and air in the fuel gas compartment are mixed by natural convection, and the catalytic fuel reaction of the fuel electrode is performed. By this, the hydrogen in the remaining fuel gas is burned, and the inside of the combustion gas compartment is replaced with an inert gas.

[Action]

In the above means, after shutting off the external load circuit, first, an inert gas is supplied to the oxidant compartment to purge the oxidant gas, the fuel gas is sealed in the fuel gas compartment, and the fuel gas is enclosed in parallel with the external load circuit. The discharge resistor is turned on to form a low-current discharge circuit, so that the oxidizer electrode is supplied with abundant hydrogen ions and charges generated by the electrode reaction of the fuel electrode through the electrolyte and the short circuit. Then, the residual adsorbed oxygen is consumed by an electrode reaction with the residual adsorbed oxygen chemically adsorbed on the oxidant electrode, so that the potential of the oxidant electrode is greatly reduced. Since the decrease in the electrode potential can be detected by monitoring the decrease in the discharge current, after confirming the decrease in the discharge current, the inert gas is supplied to the fuel gas section chamber to purge the fuel gas, and the discharge circuit is opened. As a result, the reaction gas containing the residual adsorbed oxygen is purged or consumed almost completely and quickly, and a function of almost completely avoiding deterioration of the electrode catalyst, absorption of phosphoric acid, or contact of the reaction gas is obtained.

If hydrogen molecules diffusing and permeating the matrix are brought into contact with the residual adsorbed oxygen on the surface of the oxidant electrode to perform catalytic combustion, the residual adsorbed oxygen is eliminated without using discharge resistance, and the potential of the oxidant electrode is reduced. The function of lowering is obtained.

Further, as a gas replacement method for burning the residual adsorbed oxygen by the catalytic reaction of the oxidant electrode, it is also possible to introduce the residual fuel gas in the fuel gas compartment into the oxidant compartment.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a schematic structural view of a fuel cell for carrying out the method of the present invention. In the figure, reference numeral 1 denotes a cell stack as a fuel cell shown in a simplified manner. Each of a plurality of cells has electrode catalyst layers 3A and 4A on the matrix side with a matrix 2 holding, for example, phosphoric acid as an electrolyte interposed therebetween. A supported oxidant electrode 3 and a fuel electrode 4 are provided, and an oxidant compartment 5 and a fuel gas compartment 6 are defined on the opposite side of the matrix. A three-way valve 11 is provided on the inlet side of the oxidant compartment 5 so as to be switchable between a supply system for air 10 as an oxidant and a supply system for nitrogen 40 as an inert gas. An outlet valve 12 is provided. On the other hand, on the inlet side of the fuel gas compartment 6, a three-way valve 21 is provided with a fuel gas 20 supply system and nitrogen 40 as an inert gas.
Is provided so as to be switchable, and an outlet valve 22 is provided on the outlet side thereof. Further, an external load 31 is connected to the output side of the fuel cell 1 via a circuit breaker 32, and a discharge circuit in which a switch 34, a discharge resistor 33, and a current detector 35 are connected in series is connected to an external load circuit 30. Are connected in parallel.

The power generation operation of the fuel cell configured as described above is performed by the outlet valve.
12 and 22 are opened, and the three-way valves 11 and 21 are connected to the oxidant supply system and the fuel gas supply system, respectively.
This is performed by supplying air 10 to the oxidant compartment 5 and fuel gas 20 to the fuel gas compartment 6 and closing the circuit breaker 32 of the external load circuit 30 to supply power to the external load 31. 1 The temperature of each cell is rated operating temperature,
For example, it is kept at 190 ° C.

In such power generation operation, the electrode catalyst layer 4A of the fuel cell 4
In this case, an electrode reaction (H ₂ → 2H ⁺ + 2e) in which hydrogen H ₂ is decomposed into hydrogen ions H ⁺ and electrons e are released is caused. In the electrode catalyst layer 3A of the oxidant electrode 3, oxygen and hydrogen ions Reacts with water to produce water {(1/2) O ₂ + 2H ⁺ + 2e → H ₂ O}
Becomes an electromotive reaction, and as a whole reaction, an electromotive reaction for generating water by generating water from hydrogen and oxygen is performed. Also,
The hydrogen ions H ⁺ generated at the electrode 4 are transported to the oxidant electrode 3 through phosphoric acid as an electrolyte in the matrix 2,
The generated charge e is carried to the oxidant electrode 3 through the external load circuit 30, and reacts with oxygen contained in the air 10 in the electrode catalyst layer 3A to generate water.

When the operation of the fuel cell during power generation is to be stopped or stopped in this way, in the method of the embodiment, first, the circuit breaker 32 is opened to cut off the load current flowing to the external load 31, and the three-way valve 11 is opened.
Is switched to the inert gas supply system side, and nitrogen 40 as an inert gas is fed into the oxidant compartment 5, and the oxidant 10 in the compartment 5 is purged through the outlet valve 12. By this operation, the oxygen partial pressure in the oxidizing agent compartment 5 is quickly reduced, but it is not possible to purge even the oxygen chemically adsorbed on the electrode catalyst layer 3A of the oxidizing agent electrode 3, and accordingly, the oxidizing agent electrode 3 The potential rises.
Then, the three-way valve 21 and the outlet valve 22 are closed, and the switch 34 is closed in a state where the fuel gas 20 is sealed in the fuel gas compartment 6,
An operation is performed so that a small discharge current i determined by the resistance value of the discharge resistor 33 flows. At this time, the electrode catalyst layer 4A of the fuel electrode 4
Then, an electrode reaction (H ₂ → 2H ² + 2e) for decomposing hydrogen in the fuel gas 20 to generate electric charge e is continuously performed, and the phosphoric acid in the matrix 2 is provided on the electrode catalyst layer 3A of the oxidant electrode 3. hydrogen ions H ⁺ is fed through, and discharge since electrons e are carried by the current i, the electrode reaction {(1/2) of the electrode catalyst layer 3A residual adsorbed oxygen to produce the reduced water O ₂ ⁺ 2H + + 2e
→ H ₂ O｝ is performed. Since the air in the oxidant compartment 5 is purged and there is no replenishment of oxygen in the electrode reaction (electromotive reaction), the reaction is accompanied by consumption of the residual adsorbed oxygen as O ₂ in the above formula. The potential of the electrode 3 is greatly reduced. The decrease in the electrode potential can be known by monitoring the discharge current i approaching zero with the current detector 35. Thus, when the discharge current i approaches zero, the three-way valve 21 is switched to the nitrogen 40 supply system side to purge the fuel gas 20 in the fuel gas compartment 6 and to open and close the switch 34.
And shut off the discharge current i. If the outlet valves 12 and 22 are closed when the fuel gas 20 is purged and the generated water in both compartments is discharged, both compartments are filled with nitrogen gas 40 of the same pressure, and moisture from the outside is removed. Since the intrusion is prevented and both leaks of the nitrogen gas 40 are replenished through the three-way valves 11 and 21, the phosphoric acid as the electrolyte does not absorb moisture even at the axial point where the temperature of the fuel cell 1 has decreased, and The power generation operation of the fuel cell can be stopped or stopped in a state where the contact of the reaction gas is completely avoided.

Further, in the method of the embodiment described above, the example in which the discharge circuit is provided on the output side of the fuel cell has been described. However, the residual adsorbed oxygen can be consumed without providing the discharge circuit.
That is, when the external load 31 is cut off, the heat generated by the power generation reaction decreases, and the temperature of each cell starts to decrease due to the cooling action of the nitrogen gas supplied to the oxidizing compartment, the volume of the electrolytic solution decreases with the decrease in temperature. Is reduced and the amount of hydrogen H ₂ that diffuses and permeates the matrix 2 toward the oxidant electrode 3 increases, so that the catalytic action of the electrode catalyst layer 3A causes the permeated hydrogen and residual adsorbed oxygen to come into direct contact and burn. Action occurs,
Thereby, residual adsorbed oxygen can be consumed. However, it goes without saying that the time required for consuming the residual adsorbed oxygen due to the catalytic combustion is much longer than the time required for consuming the adsorbed oxygen due to the electromotive reaction.

FIG. 2 is a gas flow diagram of a fuel cell power generator for explaining another embodiment of the present invention. When an output power stop command is issued, an external load is shut off, and the three-way valve 11 is set to an inert gas. Switching to the 40 side, the oxidant compartment 5 is replaced with an inert gas, and the three-way valve 21 and the outlet valve 22 are closed to fill the fuel gas 20 into the fuel gas compartment 6. Thereafter, the three-way valve 21 is switched to the inert gas 40 side, and at the same time, the bypass valve 41 is opened to introduce the purge gas containing the fuel gas 20 in the fuel gas compartment 6 to the inlet side of the oxidant compartment. At this time, the oxidant compartment 5 may be kept in a state where the gas replacement by the inert gas 40 is continued, and the three-way valve 11 is closed to remove the inert gas.
The supply of 40 may be stopped. Oxidant compartment 5
The hydrogen contained in the purge gas introduced into the oxidizing agent 3 catalytically combusts with the residual adsorbed oxygen on the oxidant electrode 3, and the residual adsorbed oxygen is consumed, whereby the potential of the oxidant electrode 3 decreases. Further, the off-gas in the oxidant compartment 5 is diluted by the inert gas 40 and discharged through the outlet valve 12 without generating explosion. Therefore, when the outlet valve 12 is closed, the power generation operation can be stopped in a state where both the gas compartments 5 and 6 are replaced with the inert gas.

According to this embodiment, since the fuel gas in the fuel gas compartment is introduced into the oxidant compartment and catalytically combusted, there is no need for a discharge resistance, the auxiliary device for stopping the operation can be simplified, and the catalytic combustion can be performed. Can be freely controlled by adjusting the bypass valve 41, and the fuel cell is not exposed to an excessively high temperature, so that the advantage that the power generation operation can be safely stopped is obtained.

FIG. 3 is a gas flow diagram showing another embodiment of the present invention. When the power generation operation is to be stopped, first, the external load is shut off, and the three-way valve 11 is switched to the inert gas 40 side to change the oxidizing agent. The air in the compartment 5 is purged, and at the same time, the valves 51 and 22 are closed to fill the fuel gas in the fuel gas compartment 6. If the discharge resistance switch 34 is closed in this state, the residual adsorbed oxygen of the oxidant electrode 3 is consumed by the electromotive reaction of the pair of electrodes, and the electrode potential can be reduced. When the decrease in the electrode potential is detected by the current detector 35 and the outlet valve 12 is closed, the oxidant compartment 5 is filled with an inert gas. In this embodiment, the fuel gas contained in the fuel gas compartment 6 is mixed with the air 50 introduced through the valve 52 by natural convection in the fuel gas compartment 6, and hydrogen and oxygen are catalyzed on the fuel electrode 4. The present embodiment differs from the above embodiments in that the fuel gas compartment 6 is replaced by the remaining inert off-gas (nitrogen in air and carbon dioxide in fuel gas).
In this embodiment, the rate of catalytic combustion reaction can be controlled by adjusting the valve since air 50 is supplied via valve 52 in proportion to the amount of hydrogen and oxygen consumed in fuel gas compartment 6. The advantage is obtained that the power generation operation can be stopped without exposing the fuel cell to an abnormally high temperature.

〔The invention's effect〕

As described above, the present invention provides a time difference between the start time of the oxidant purge of the oxidant compartment by the inert gas and the fuel gas purge of the fuel gas compartment after the external load circuit is shut off. Only the oxidant compartment was purged, and a small discharge current was supplied to the discharge circuit with the fuel gas sealed in the fuel gas compartment. as a result,
The remaining adsorbed oxygen of the oxidant electrode-side catalyst layer, which could not be removed only by gas purging of the oxidant compartment, is consumed by the electromotive reaction between the pair of electrodes, and the potential increase of the oxidant electrode can be prevented. The conventional technique of purging the chamber almost simultaneously with an inert gas can avoid a potential increase of the oxidant electrode caused by the inability to remove the residual adsorbed oxygen and a deterioration of the oxidant electrode caused by the same, and also diffusely supply the reaction gas. Problem with the conventional method of producing and supplying inert gas
It is also possible to avoid the problem that the high-temperature open-circuit voltage and the potential rise are prolonged and the electrode is deteriorated due to prolonged rise, so that the power generation operation can be stopped or stopped immediately without adversely affecting the power generation performance of the fuel cell. A stopping method can be provided.

In addition, since the above-mentioned electromotive reaction is performed in a state where fuel gas is sealed in the fuel gas compartment, when hydrogen in the sealed fuel gas is consumed by the electromotive reaction, carbon dioxide gas is mainly contained in the fuel gas compartment. Therefore, there is an advantage that the gas replacement operation of the fuel gas compartment can be omitted.

In order to completely replace the gas in the fuel gas compartment, air is introduced into the fuel gas compartment, mixed with the remaining fuel gas using natural convection, and catalytically combusted on the fuel electrode. It is possible to consume
Since the carbon dioxide gas in the fuel gas and the nitrogen in the air remain in the fuel gas compartment, the fuel gas compartment can be replaced with an inert gas without supplying an inert gas.

On the other hand, hydrogen permeating from the combustion gas compartment to the oxidant electrode side of the unit cell and residual adsorbed oxygen of the oxidant electrode can be catalytically burned on the oxidant electrode to reduce the electrode potential. In this case, no discharge resistor is required, and an advantage that the configuration of the device can be simplified can be obtained.

After the oxidant compartment is replaced with an inert gas, an inert gas is introduced into the fuel gas compartment, and the fuel gas in the fuel gas compartment is introduced into the oxidant compartment to cause catalytic combustion on the oxidant electrode. Even with such a configuration, it is possible to reduce the electrode potential by consuming the residual adsorbed oxygen. In this case, by controlling the rate at which the fuel gas is introduced into the oxidant compartment,
This has the advantage that damage to the battery due to an excessive temperature rise can be avoided, and the consumption of residual adsorbed oxygen and the gas replacement in both gas compartments can be quickly performed by utilizing gas replacement in the oxidant compartment.

[Brief description of the drawings]

FIG. 1 is a gas flow chart showing a method of stopping power generation of a fuel cell according to an embodiment of the present invention, FIG. 2 is a gas flow chart showing a different embodiment of the present invention, and FIG. 3 is another embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 1 ... Fuel cell (cell stack), 2 ... Matrix, 3 ... Oxidant electrode, 4 ... Fuel electrode, 5 ... Oxidant compartment, 6 ... Fuel gas compartment, 11, 21 ... Three directions Valve, 12,
22 ... outlet valve, 30 ... external load circuit, 33 ... discharge resistance,
34… Discharge resistance switch, 35… Current detector, 41… Bypass valve, 51,52… Valve, 10… Oxidant (air), 20…
... fuel gas, 40 ... inert gas, 50 ... air, i ... discharge current.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 8/00-8/24

Claims (3)

(57) [Claims] 1. An oxidant compartment containing a matrix holding an electrolyte is supplied with air as an oxidant from an oxidant compartment to an oxidant electrode, and a hydrogen-rich fuel gas is supplied to a fuel electrode from a fuel gas compartment to generate power. When the power generation of the fuel cell to be performed is stopped, the external load circuit of the fuel cell is opened, the air is switched to an inert gas to replace the gas in the oxidant compartment, and the supply of the fuel gas is stopped to stop the supply of the fuel gas. The fuel gas is sealed in the fuel gas compartment, the oxidizer electrode and the fuel electrode are connected to a discharge resistor, and a current generated by an electromotive reaction flows as a discharge current. A method for stopping power generation of a fuel cell, comprising disconnecting a connection to a resistor. 2. An air as an oxidant is supplied from an oxidant compartment to an oxidant electrode sandwiching a matrix holding an electrolyte, and a hydrogen-rich fuel gas is supplied from a fuel gas compartment to a fuel electrode to generate power. When the power generation of the fuel cell to be performed is stopped, the external load circuit of the fuel cell is opened, the air is switched to an inert gas to replace the gas in the oxidant compartment, and the supply of the fuel gas is stopped to stop the supply of the fuel gas. A fuel gas is sealed in the fuel gas compartment, and then an inert gas is supplied into the fuel gas compartment to introduce the fuel gas sealed in the fuel gas compartment into the oxidant compartment, A method for stopping power generation of a fuel cell, comprising consuming residual adsorbed oxygen by a catalytic combustion reaction of an electrode. 3. An oxidant electrode, which sandwiches a matrix holding an electrolyte, is supplied with air as an oxidant from an oxidant compartment, and a hydrogen-rich fuel gas is supplied from a fuel gas compartment to a fuel electrode to generate power. When the power generation of the fuel cell to be performed is stopped, the external load circuit of the fuel cell is opened, the air is switched to an inert gas to replace the gas in the oxidant compartment, and the supply of the fuel gas is stopped to stop the supply of the fuel gas. A fuel gas is sealed in the fuel gas compartment, and the oxidizer electrode and the fuel electrode are connected to a discharge resistor to flow a current generated by an electromotive reaction as a discharge current. The gas supply side of the fuel gas compartment is opened to the air, the remaining fuel gas in the fuel gas compartment and the air are mixed by natural convection, and the hydrogen in the remaining fuel gas is removed by the catalytic combustion reaction of the fuel electrode. A method for stopping power generation of a fuel cell, comprising burning and replacing the fuel gas compartment with an inert gas.