JP2010282768A - Reversible cell operating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize the performance deterioration of a reversible cell with a solid polymer water electrolysis device and a fuel cell which are integrated, when operated for a long period, while eliminating the need for special control, an electrolytic current higher than a rated current, a current supply installation and the sustaining operation of a pump or the like. <P>SOLUTION: During operating the reversible cell 1 with the solid polymer water electrolysis device and the fuel cell integrated to actualize the change-over of an operation mode between the water electrolysis operation and fuel cell operation, the water electrolysis operation and fuel cell operation are alternately carried out. When the operation mode is the water electrolysis operation right before the operation of the reversible cell 1 is stopped for one hour or longer for storage, the finishing-ready fuel cell operation is carried out for a predetermined time and then the operation of the reversible cell 1 is stopped. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention minimizes performance degradation associated with long-term operation in a reversible cell in which a polymer electrolyte water electrolyzer and a fuel cell are integrated (hereinafter, sometimes simply referred to as “reversible cell”). The present invention relates to a method for realizing a long service life while keeping it at a minimum.

  A solid polymer reversible cell in which a water electrolysis cell and a fuel cell that can be configured as a solid polymer electrolyte cell of the same shape are integrated is generally a membrane of a solid electrolyte material (polymer membrane). ) Are sandwiched by electrode catalyst layers from both sides, and a power generation unit (MEA: Electrode Assembly), an oxidant electrode current collector and a fuel electrode current collector joined to the outside thereof, and these oxidant electrode current collectors The main part is comprised by the separator arrange | positioned on each outer side of the body and the anode current collector. Usually, the separator has a corrugated plate shape, and each independent space formed by the separator, the oxidant electrode current collector, and the separator and the fuel electrode current collector includes an oxidant (oxygen gas) and a fuel (hydrogen gas). The reaction gas flow path is configured. The MEA, the oxidant electrode current collector, and the fuel electrode current collector form a cell internal substrate.

  In such a reversible cell, there are a resistance overvoltage, an activation overvoltage, and a diffusion overvoltage as internal resistances (overvoltages) that degrade the performance of water electrolysis and fuel cells. When operated for a long time, gas stays in the reaction site and part of the micropores in the vicinity of the gas during water electrolysis and water stays in the fuel cell. In some cases, wetting occurs at the electrode portions. When this phenomenon occurs, diffusion of water and gas necessary for the reaction to the reaction site is hindered. In addition, contaminants contained in battery components, systems, and fuel (hereinafter sometimes simply referred to as “contamination”) accumulate in the membrane electrode junction. Due to these phenomena, each overvoltage gradually increases, and as a result, the performance of the reversible cell decreases.

  As a conventional technique for recovery of a reaction site, as disclosed in Patent Document 1, a hydrogen-containing gas is supplied to an oxidant electrode when a fuel cell is operated in a power generation stop state, and a power source is connected between the two electrodes. There is a method for a fuel cell in which an electric current is passed from the electrode to the oxidant electrode to eliminate water in the micropores. As a conventional technique for the contamination problem, as disclosed in Patent Document 2, there is a method for a water electrolysis cell in which electrolysis is performed with an electrolytic current exceeding the rating and the contamination is pushed out of the membrane. Furthermore, if water stays in the hydrogen electrode after the water electrolysis operation, contamination from the cell components or the like dissolves in the staying water, and contamination of the electrolyte membrane or catalyst occurs when the electrolyte membrane or catalyst is exposed to this state. The technique described in Patent Document 3 attempts to solve this problem by turning water to both poles for a while after the operation is stopped.

JP 2003-272686 A Japanese Unexamined Patent Publication No. 6-86939 JP 2003-293179 A

  However, according to the technique described in Patent Document 1, it is necessary to strictly monitor a plurality of factors such as a current value applied to the fuel cell from the outside and a hydrogen flow rate to be supplied. A system for supplying hydrogen-containing gas to the electrode is required. Moreover, in the technique described in Patent Document 2, an electrolytic current exceeding the rating is required as a driving force for discharging the contamination that has entered from the oxygen electrode after moving it to the hydrogen electrode through the membrane. Becomes excessive. Furthermore, in the technique of Patent Document 3, it is necessary to operate a pump for flowing water even though the operation is stopped. Considering the case where the operation is not performed for a long period of time, the operation is not only wasteful but also a power failure, etc. It cannot respond to the unexpected situation.

  The present invention has been made in view of such points, and in a reversible cell capable of both water electrolysis and fuel cell operation, special control, electrolytic current exceeding the rating, current supply equipment, continuous operation of the pump, etc. It is not necessary, and the purpose is to realize a long life by minimizing the performance degradation caused by long-term operation.

  In order to achieve the above object, the present invention is an operation method of a reversible cell in which a solid polymer water electrolysis device and a fuel cell are integrated and the operation mode can be switched between a water electrolysis operation and a fuel cell operation. When the water electrolysis operation and the fuel cell operation are alternately performed and when the operation of the reversible cell is stopped for one hour or more, if the operation mode before the stop is the water electrolysis operation, After the electrolysis operation, the completion preparation fuel cell operation is performed for a predetermined time, and then the operation of the reversible cell is stopped.

  Immediately after the start of water electrolysis operation, the gas generated by water electrolysis stays in the electrode catalyst layer and current collector that constitute the electrode part that is originally filled with water, especially in a very small part of the micropores of the electrode catalyst layer. As a result, the water supply to the reaction site is hindered and the portion does not contribute to the reaction. Therefore, the performance decreases (input voltage increases) while this phenomenon occurs. The performance is stabilized when the transient phenomenon converges and becomes a steady state. In the case of water electrolysis, this phenomenon is observed particularly immediately after the start of operation, and even after the performance has stabilized, there is a possibility that it may proceed at a very small rate locally. Since the gas remaining in the micropores is in the dense electrode catalyst layer, it is difficult to discharge even if the water electrolysis operation is stopped and the circulating water is continuously supplied. In addition, if the water electrolysis operation is stopped and left unattended, a cross leak occurs between the two electrodes, so that some gas reacts on the catalyst, but it does not completely consume but also accompanies the cross leak. There is also a risk of membrane breakage. In particular, when an electrode with poor gas release properties is used, the transient phenomenon lasts for a long time, and in extreme cases, it may lead to local decomposition and breakage of the membrane, and the function as an electrode may be completely lost. is there. Therefore, as the continuous operation time of the water electrolysis operation becomes longer, and even if the operation is performed for a short time, the number of gas retention sites increases every time the water electrolysis operation is performed, and the performance decreases accordingly.

  In this respect, according to the present invention, the water electrolysis operation and the fuel cell operation are alternately performed, so that the gas retained in the electrode micropores during the water electrolysis operation can be reliably consumed by the fuel cell operation. Therefore, the reaction site of water electrolysis can be reliably recovered without incurring the risk as described above, and the performance when performing the water electrolysis operation again can be recovered to the maximum. In addition, as a cause of deterioration associated with long-term operation common to both modes, there is a performance decrease caused by a decrease in ion exchange performance due to contamination, but also against this, operation in the opposite mode alternately as in the present invention. Since the movement direction of protons is reversed, the contamination mixed during operation in each mode can be easily swept away in the direction in which it enters. At this time, since the contamination at the end portion can be easily removed, it is effective to perform the operation in the opposite mode alternately as in the present invention.

  Further, in the present invention, when the operation of the reversible cell itself is stopped for 1 hour or longer, if the operation mode before the stop is the water electrolysis operation, the end preparation fuel cell operation is performed for a predetermined time after the water electrolysis operation. Then, the operation of the reversible cell is stopped. Thereby, when resuming the operation of the reversible cell after stopping the operation for a long time, the resumption can be started immediately regardless of whether the resumption is a water electrolysis operation or a fuel cell operation.

  That is, when the water electrolysis operation is stopped (stored) for a long time, the water electrolysis operation is completed, and all the cells inside the cell are completely wet. (Especially on the hydrogen side) can cause performance degradation during storage, which makes recovery difficult. If the cell electrolysis operation is completed and the cell internal substrate is in a wet state, when the operation mode at the next start-up is the fuel cell operation, the inside of the cell needs to be dried before the start-up. The saturated water vapor partial pressure of the drying gas decreases with decreasing temperature. This means that the lower the temperature, the smaller the amount of moisture that can be taken away (vaporized) by the dry gas. Therefore, the lower the cell temperature, the longer it takes to dry to a specified state (the dry gas vaporizes a certain amount of water from the inside of the cell). Here, since a practically dry gas (for example, outside air) always contains a very small amount of a contamination component (impurities in the outside air, such as Ca), the contamination component accumulates in the reaction film as the drying time increases. This causes performance degradation. Also, for practical use, it is very inconvenient if it cannot be started immediately when it is desired to start it.

In this regard, in the present invention, after the water electrolysis operation before stopping for a long time, the operation of the reversible cell is stopped after the “end preparation fuel cell operation” is once performed for a predetermined time. (Especially on the hydrogen side) is basically wet-free and there is no residual water inside the cell that causes performance degradation, so performance degradation can be greatly suppressed compared to when the storage is terminated after water electrolysis. . It should be noted that there is no particular problem when the fuel cell is stored after the operation is finished.
In addition, the end preparation fuel cell operation is used for convenience in order to distinguish it from the fuel cell operation for power generation according to the load on the normal demand side. Same as battery operation. However, the operation for a predetermined time, for example, about 5 to 10 minutes is sufficient, and an extremely short time is required as compared with the normal fuel cell operation.

Before the completion of preparation fuel cell operation, the electrolyzed water remaining in the flow path of the reversible cell is discharged from the inside of the cell, and air is supplied only to the reaction gas flow path on the side that becomes the oxidant electrode during fuel cell operation. And you may make it implement the drying process which dries a cell internal base material. As a result, the end preparation fuel cell operation can be started promptly, and as a result, the total time until the reversible cell itself stops can be shortened. According to the knowledge of the inventors, when air is supplied only to the reaction gas channel on the side serving as the oxidant electrode, the moisture on the oxidant electrode side is transferred from the oxidant electrode current collector to the air, and It is discharged out of the system by air. On the other hand, the moisture on the fuel electrode side is first transmitted from the fuel electrode current collector to the MEA and the oxidant side current collector, finally transmitted to the air, and discharged outside the system by the air. Therefore, the cell internal substrate can be suitably dried without supplying an inert gas such as nitrogen gas to the reaction gas passages on both the oxidant electrode side and the fuel electrode side. As the air used in the present invention, air in the atmosphere can of course be used as it is, and air that has been subjected to dehumidification treatment by a normal air conditioner may be used. Preferably, the dew point temperature is 20 ° C or lower.
When discharging the electrolyzed water remaining in the flow path from the inside of the cell, supply gas to the reaction gas flow path inside the reversible cell so that the electrolyzed water remaining in the flow path is discharged from the inside of the cell. Also good.

  At the start of the drying step, the temperature of the reversible cell is preferably set to 70 ° C. or higher. This is because the saturated water vapor partial pressure rises rapidly from around 70 ° C. Here, the temperature of the reversible cell being 70 ° C. or higher means that the temperature of the current collector in the reversible cell is 70 ° C. or higher. However, since it is actually difficult to measure the temperature of the current collector, the channel inlet temperature on the oxygen electrode side where the electrolyzed water flows during water electrolysis operation is measured, and the channel inlet temperature is 70 ° C. or higher. It only has to be. This is because the temperature of the current collector is higher than the temperature of the flow path inlet.

  Thus, by setting the temperature of the reversible cell to 70 ° C. or higher at the start of the drying process, the time required for the drying process can be dramatically shortened. The temperature of the reversible cell can be increased to 70 ° C. or higher by, for example, setting the operating temperature of the water electrolysis operation to 70 ° C. or higher. However, if the operating temperature of the water electrolysis operation cannot be increased to 70 ° C. or higher due to the device environment, load conditions, or device characteristics, for example, the water electrolysis operation is passed to the reversible cell before the end of the water electrolysis operation before the reversible cell stops. Reduce the flow rate of cooling water to flow, increase the temperature of the cooling water, or control both, etc., before resuming the operation of the water electrolyzer before stopping the reversible cell The current density supplied to the battery may be increased to increase the amount of heat generated by the reversible cell itself.

The above-described completion preparation fuel cell operation is preferably performed under the following conditions. That is,
Saturated water vapor amount at reversible cell temperature of hydrogen side supply gas: MH _{2 -SAT} [mol / s]
Saturated water vapor amount at reversible cell temperature of oxygen side supply gas: M _O2-SAT [mol / s]
Amount of water vapor in hydrogen-side supply gas: MH ₂ [mol / s]
Amount of water vapor in oxygen-side supply gas: M _O2 [mol / s]
When the amount of reaction product water is _{MH 2 O} [mol / s],
It is preferable to operate the end preparation fuel cell in the range of (M _{H2 -SAT} + M _{O2 -SAT} ) − (M _H2 + M _O2 + M _H2O ) ≦ 0. Thereby, deterioration due to excessive drying of the film of the reversible cell or the current collector can be suppressed.
In addition, the reversible cell temperature here is specifically the inlet temperature of the cooling water in the reversible cell.

  Further, after the end preparation fuel cell operation is finished, before the reversible cell is stopped, the inside of the reversible cell may be pressurized, and then the flow path leading to the reversible cell may be closed. Thereby, it is possible to prevent external air from entering the reversible cell as the temperature drops.

  According to the present invention, in a reversible cell capable of both water electrolysis and fuel cell operation, long-term operation is not required without special control, electrolytic current exceeding the rating, current supply equipment, continuous operation of the pump, etc. In addition, when the reversible cell is restarted after a long-time operation stop, the operation mode after the restart is the water electrolysis operation, the fuel cell, or the like. Any of the driving can be started immediately.

It is explanatory drawing which showed typically the longitudinal cross-section structure of the reversible cell used in embodiment. It is explanatory drawing which showed typically the horizontal cross-section structure of the reversible cell of FIG. It is explanatory drawing which showed typically the system | strain of the reversible cell of FIG. It is a graph which shows the change of the input voltage at the time of implementing repeatedly the reversible cell of FIG. 1 in the single operation mode of water electrolysis operation. It is a graph which shows the change of the output voltage at the time of implementing repeatedly the reversible cell of FIG. 1 in the single operation mode of fuel cell operation. 2 is a graph illustrating changes in input voltage and output voltage when water electrolysis operation and fuel cell operation are alternately performed in the reversible cell of FIG. 1. 2 is a graph showing changes based on the number of operations of an input voltage and an output voltage when water electrolysis operation and fuel cell operation are alternately performed in the reversible cell of FIG. 1. In the reversible cell of FIG. 1, it is a graph which shows the input voltage at the time of starting the operation mode before storage, and the water electrolysis operation after storage.

  Embodiments of the present invention will be described below. FIG. 1 schematically shows the inside of the reversible cell 1, and FIG. 2 shows a horizontal cross section of the reversible cell 1. In addition, this reversible cell 1 has shown the single cell which is the minimum unit of an electric power generation and electrolysis unit. As shown in FIG. 2, the reversible cell 1 has power supply / collection plates 2 and 3 arranged on the outermost sides. An ion exchange membrane 4c made of a solid electrolyte material is arranged between the two electrode portions 4a and 4b made of an electrode catalyst layer at the center between the power supply and current collecting plates 2 and 3 to form a composite. The MEA 4 that is the generated power unit is configured. For example, current collectors 5 and 6 made of, for example, a porous material are disposed outside the electrode portions 4a and 4b. In the present embodiment, the MEA 4 and the current collectors 5 and 6 constitute a cell internal substrate. The electrode portion 4a serves as a cathode during the water electrolysis operation, and the electrode portion 4b serves as an anode during the water electrolysis operation.

A space S ₁ is formed between the current collector 5 and the supply / current collection plate 2, and a space S ₂ is formed between the current collector 6 and the supply / current collection plate 3. In each of the spaces S ₁ and S ₂ , a corrugated separator 7 is disposed. The reversible cell 1 has adopted the cooling method by water cooling, by the separator 7 disposed in the space S _1, the space S _1, the cooling water passage 11 and the passage 12 are formed alternately. On the other hand, by the separator 7 disposed in the space S _2, in the space S _2, the cooling water passage 13 and the passage 14 are formed alternately. The cooling water is circulated through the cooling water passage 11 and a constant temperature water tank (not shown) and a cooling tower (not shown) with a heat pump, and is operated so as to maintain, for example, 60 ° C. to 80 ° C. at the entrance of the reversible cell 1. Is done.

  Returning again to FIG. 1, further description will be made. Flow ports 12 a and 12 b are formed at both ends of the flow channel 12, and flow ports 14 a and 14 b are formed at both ends of the flow channel 14.

  Next, the gas system, discharge system, etc. of the reversible cell 1 having such a configuration will be described. As shown in FIG. 3, the flow channel 31 is connected to the flow port 12a, the flow channel 41 is connected to the flow port 14a, the flow channel 51 is connected to the flow port 14b, and the flow port 12b. Each is connected to a flow path 61. Each flow path 31, 41, 51, 61 and a bypass flow path 45 described later are constituted by, for example, stainless steel piping.

  Channels 33 and 34 are connected to the channel 31 via a tank 32 that serves as a pure water storage tank during water electrolysis operation. The flow paths 33 and 34 are provided with valves 33a and 34a, respectively.

  Flow paths 43 and 44 are connected to the flow path 41 via a tank 42 that serves as a pure water storage tank during water electrolysis operation. Valves 43a and 44a are provided in the flow paths 43 and 44, respectively. Further, a bypass channel 45 that bypasses the tank 42 is connected between the channel 41 and the channel 43, and a valve 45 a is provided in the bypass channel 45. A blower 46 is provided at the end of the flow path 43 to supply air that is purge gas and also acts as an oxidant when switching from water electrolysis operation to fuel cell operation.

  A valve 51 a is provided in the flow path 51, a flow path 52 is connected between the flow path 51 and the tank 42, and a pump 53 and a valve 52 a are provided in the flow path 52. The pump 53 supplies pure water stored in the tank 42 to the reversible cell 1 during the water electrolysis operation.

  The flow path 61 is provided with a valve 61a. A flow path (not shown) may be provided between the flow path 61 and the tank 32, and a pump and a valve (both not shown) may be provided in the flow path. By this, in the event that water on the fuel electrode side is not sufficient at the time of water electrolysis operation, by appropriately supplying water to the fuel electrode side using these pumps and valves (both not shown), It is possible to prevent the membrane from being damaged and prevent the membrane from being damaged.

  Although the supply source of hydrogen is not clearly shown in this figure, supply sources such as those obtained by storing hydrogen obtained by water electrolysis operation in a high-pressure tank or hydrogen storage alloy, or those obtained by reforming fossil fuels It can be installed separately.

  Each of the above-described valves 33a, 34a, 43a, 44a, 45a, 51a, 52a, 61a is controlled by the control device 71. The control device 71 also controls a power supply facility 72 that supplies current for electrolyzing water to the reversible cell 1 during water electrolysis operation and supplies power to the demand side during fuel cell operation.

Next, an operation method of the reversible cell 1 having such a main configuration will be described.
(During fuel cell operation)
The valves 33a, 43a, 51a, 61a are opened, and the valves 34a, 44a, 45a, 52a are closed. Then, fuel (hydrogen gas) is introduced into the flow path 33, humidified in the tank 32, and then introduced into the reversible cell 1 through the flow path 31 and the circulation port 12 a. Further, an oxidant (oxygen gas or air) is introduced into the flow path 43, humidified in the tank 42, and then introduced into the reversible cell 1 through the flow port 14 a. As a result, a power generation reaction occurs in the cell internal substrate of the reversible cell 1, and electrons flow from the electrode portion 4 a to the electrode portion 4 b through the power supply facility 72, thereby generating a current.

  In the power generation reaction, an amount of gas corresponding to the external load is consumed, and surplus fuel (hydrogen gas) is discharged through the circulation port 12b and the flow path 61, and surplus oxidant (oxygen gas or air). Is discharged through the circulation port 14 b and the flow path 51. The thick arrows in FIG. 1 indicate the flow of the reaction gas in that case.

(During water electrolysis operation)
The valves 33a, 43a, 51a, 45a, 61a are closed and the valves 34a, 44a, 52a are opened. The pure water stored in the tank 42 is sucked by the pump 53 and introduced into the reversible cell 1 through the flow path 51 and the flow port 14b. On the other hand, a current applied to the current collectors 5 and 6 is supplied from the power supply facility 72 (electrons flow from the current collector 6 → the power supply facility 72 → the current collector 5), and the current in the flow path 14 shown in FIG. The water is electrolyzed to generate oxygen and hydrogen in amounts corresponding to the supplied current.

  The hydrogen generated in the water electrolysis operation flows from the flow path 31 to the tank 32 through the flow port 12a, and after performing a gas-liquid separation process in the tank 32, the hydrogen is discharged to the outside through the flow path 34. On the other hand, oxygen generated in the water electrolysis operation flows from the flow path 41 to the tank 42 via the flow port 14a, and after gas-liquid separation processing is performed in the tank 42, the oxygen is discharged to the outside through the flow path 44. The pure hydrogen and pure oxygen after these gas-liquid separation processes are stored in a separate fuel storage facility and oxidant storage facility (both not shown), so that the next fuel cell operation is possible. It can be used as a fuel and an oxidant.

  In the reversible cell 1 having the above-described configuration, it is necessary to make the base material of the electrode portion 4b, which serves as an oxidant electrode in a fuel cell, to withstand the operation state of water electrolysis, for example, Japanese Patent Application Laid-Open No. 2004-134134. As disclosed in Japanese Patent Application Laid-Open No. 2007-12315, a small amount of iridium is mixed in the platinum electrode catalyst to adjust the water repellency of the substrate, and the current collector and the separator are plated with Pt. .

  The reversible cell 1 described above can arbitrarily perform both the water electrolysis operation and the fuel cell operation in this way. Accordingly, for example, water electrolysis operation → water electrolysis operation → water electrolysis operation can be performed intermittently, and conversely, fuel cell operation → fuel cell operation → fuel cell operation, etc. It is also possible to carry out only the fuel cell operation intermittently at intervals. However, if only a single mode operation is performed in this manner, the performance degradation becomes increasingly noticeable as described above.

When the inventor actually verified, for example, when only the water electrolysis operation was intermittently performed, a result as shown in FIG. 4 was obtained. FIG. 4 shows changes with time in performance when the water electrolysis operation is repeated in a single mode, the horizontal axis shows the operation time, and the vertical axis shows the input voltage (v) required for water electrolysis. The current density is 1.0 A / cm ² . According to this, the performance deteriorates to some extent in the initial stage of operation (that is, the input voltage becomes high), and then gradually decreases. Then, once the operation is stopped and the operation is restarted, the performance is recovered to some extent, but the initial performance is not recovered, and the performance gradually decreases with each operation. Here, when an electrode structure with good gas / water drainage is adopted, the performance hardly deteriorates after the performance deteriorates in the initial stage of operation, and the same time-dependent change is shown every time. descend.

FIG. 6 shows changes with time in performance when the fuel cell is operated repeatedly in a single mode, and the horizontal axis shows the operation time and the output voltage (v) of the fuel cell. The current density is 0.6 A / cm ² . Also in this case, it can be seen that the performance deteriorates to some extent at the beginning of the operation, and then gradually decreases. Then, once the operation is stopped and the operation is restarted, the performance is recovered to some extent, but is not recovered to the initial performance, and the performance gradually decreases with each operation. Here again, when an electrode structure with good gas / water drainage is adopted, the performance hardly deteriorates after the performance deteriorates at the initial stage of operation, and the same time-dependent change is shown every time. Decrease gradually.

  According to the present invention, when the reversible cell 1 having such a configuration is operated, the water electrolysis operation and the fuel cell operation are alternately performed. As a result, the performance degradation as seen in FIGS. 4 and 5 can be suppressed. When the inventor actually verified, the result shown in FIG. 6 was obtained.

FIG. 6 shows the water electrolysis input voltage (v) and the output voltage (v of the fuel cell) when the water electrolysis operation and the fuel cell operation are alternately performed (hereinafter simply referred to as “alternate operation”). ), The left vertical axis represents the water electrolysis input voltage, the right vertical axis represents the fuel cell output voltage, and in the graph of FIG. 6, the upper half represents the water electrolysis input voltage and the lower half represents the fuel cell output. Each change of voltage over time is described. The current density during water electrolysis operation is 1.0 A / cm ² , and the current density during fuel cell operation is 0.6 A / cm ² .

  In addition, when alternately performing the water electrolysis operation and the fuel cell operation in such a manner, the fuel cell operation with a low current value is operated for a longer time so that the total load of the fuel cell operation and the water electrolysis operation is made equal. It is desirable.

  As shown in FIG. 6, by alternately performing the water electrolysis operation and the fuel cell operation, the performance degradation that occurs every time the operation is performed as seen in the single mode operation is eliminated, and the electrode with poor gas / water drainability is eliminated. Even when the structure was adopted, it was confirmed that the vicinity of the initial performance was maintained for a long time.

  Further, FIG. 7 shows the results of summarizing the performance change when the alternate operation is repeated. In the graph, the upper graph shows the water electrolysis input voltage, the lower graph shows the fuel cell output voltage, and the number of operations is shown. These changes are shown when repeated. According to the inventor's knowledge, by performing the alternating operation, in this example, the performance degradation speed was reduced by 35% or more than in the single mode. However, the effect ratio shown here is an example, and as described above, if the operation is alternate, the direction of proton movement will be reversed, and the contamination mixed during operation in each mode will be in the direction in which it entered. As the operation time becomes longer and the number of times of switching increases, a further effect can be expected from the effect of reducing the performance degradation for the single mode.

  One of the causes of deterioration is a reduction in the thickness of the electrode catalyst layer. As a countermeasure, a method of ensuring durability by increasing the thickness of the electrode catalyst layer is conceivable. In such a case, in the single mode operation, the gas / water removal property is deteriorated, so that the reaction site is reduced, that is, the performance is significantly reduced (the same tendency as in FIGS. 4 and 5 occurs). However, by performing the alternating operation as in the present invention, it is possible to keep the reduction of effective reaction sites limited and temporary, and the durability can be improved.

  By alternately operating the reversible cells 1 in this way, the performance of water electrolysis and fuel cells can be maintained over a long period of time. The ideal use / operation form that can maximize the use of this effect is a reversible cell that switches between water electrolysis operation and fuel cell operation with a single unit, and performs normal operation (switching operation periodically). This alone can prevent major deterioration acceleration factors and maintain the performance in the vicinity of the initial stage for a long time. Further, the shorter the switching cycle, the more effective and the switching up to the day unit is recommended. However, the present invention can be implemented even with the switching unit in the circumferential unit. As a concrete method of use, introduction to a system premised on operation between both modes is optimal. For example, it is proposed to apply to a power load leveling system in which hydrogen is produced by water electrolysis operation using nighttime electricity and stored, and fuel cell operation is performed using hydrogen stored at the peak of daytime power demand. it can. In addition, when water electrolysis is performed using electricity derived from natural energy (for example, solar cells, wind power generation, etc.) and the amount of power generated by natural energy is insufficient, fuel cell operation is performed within the range where the total load in both operation modes is the same. The method of operating to compensate for the shortage by switching to.

  By the way, when the water electrolysis operation and the fuel cell operation are alternately performed in this way, and the operation is stopped for a period longer than the normal switching interval, for example, 1 hour or more (hereinafter, simply referred to as “storage”), When the last operation is a water electrolysis operation, after the water electrolysis operation, it is preferable to stop the operation of the reversible cell after performing the end preparation fuel cell operation for a predetermined time. As a result, there is no performance degradation regardless of which mode is activated next time.

In this case, as the operation condition of the end preparation fuel cell operation, a saturated humidification operation at a high current density is preferable in order to bring the ion exchange membrane 4c into a moderately wet state and flush out contaminants from the ion exchange membrane 4c. According to the inventor's knowledge, this problem can be suppressed by performing a saturated humidification operation for 5 to 10 minutes at a current density of 0.6 A / cm ² or more, and as shown in FIG. It was confirmed that can be maintained. In the figure, WE represents a water electrolysis operation, and FC represents a fuel cell operation.

  Note that if the low humidification operation is performed during the completion preparation fuel cell operation, further drying of the ion exchange membrane 4c and the effect of discharging contaminants from the reaction product water cannot be expected. Here, the low humidification operation refers to an operation state in which the reaction gas supplied to the hydrogen side and the oxygen side of the reversible cell 1 during the fuel cell operation completely vaporizes the generated water generated by the fuel cell power generation. For simplicity, it can be determined by calculating the following values.

Saturated water vapor amount at cell temperature of hydrogen-side supply gas (inlet temperature of flow path 11 in FIG. 2): MH _{2 -SAT} [mol / s]
Saturated water vapor amount at the cell temperature of the oxygen-side supply gas (inlet temperature of the flow path 13 in FIG. 2): M _O2-SAT [mol / s]
Amount of water vapor in hydrogen-side supply gas: MH ₂ [mol / s]
Amount of water vapor in oxygen-side supply gas: M _O2 [mol / s]
Reaction product water amount: _{MH 2 O} [mol / s]
When the following inequality is satisfied, the operation is a low humidification operation. (Normally, the cooling water supplied to the flow paths 11 and 13 is supplied from the same cooling water source. Inlet temperature = the inlet temperature of the flow path 13).
(M _H2−SAT + M _O2−SAT ) − (M _H2 + M _O2 + M _H2O )> 0
Therefore, it is preferable to perform the end preparation fuel cell operation under a condition that does not satisfy the above inequality. That is,
It is preferable to perform the end preparation fuel cell operation in a range satisfying (M _{H2 -SAT} + M _{O2 -SAT} ) − (M _H2 + M _O2 + M _H2O ) ≦ 0. Thereby, deterioration due to excessive drying of the MEA 4 and the current collectors 5 and 6 including the ion exchange membrane 4c can be suppressed.

  By the way, when the operation mode immediately before the end is the water electrolysis operation, it is preferable to perform the end preparation fuel cell operation, but the operation content itself is not different from the fuel cell operation even in the end preparation fuel cell operation. From the situation where the electrode unit 4a, 4b of the MEA 4 constituting the base material inside the reversible cell 1 and the current collectors 5 and 6, especially the current collectors 5 and 6 are still wet, the completion preparation fuel cell operation cannot be performed immediately. Can also be assumed. Therefore, after the end of the water electrolysis operation and before the start of the end preparation fuel cell operation, gas is supplied to the reaction gas flow path inside the reversible cell 1, and the electrolyzed water remaining in the flow path is discharged from the inside of the cell. You may make it implement the drying process which supplies air only to the reaction gas flow path of the side used as an oxidizer electrode at the time of battery operation, and dries a cell internal base material.

  Specifically, when the water electrolysis operation is ended, only the valves 33a, 43a, 51a, 61a are opened, and all other valves are closed. Then, in order to discharge water remaining in the reversible cell 1 with the circuit of the power supply facility 72 cut off, fuel (hydrogen gas) is introduced into the reversible cell 1 from the flow path 31 through the flow port 12a, and an oxidant or Air is introduced into the reversible cell 1 from the flow path 41 through the circulation port 14a. That is, the water in the flow path is discharged by pushing it out of the system by the pressure difference due to these gases. This time is about several seconds, and the flow rate at that time may be determined by adopting, for example, a method disclosed in Japanese Patent Application Laid-Open No. 2007-115588. After the above discharge is completed, the circuit of the power supply facility 72 is released. Note that such a purge operation is not necessarily a process that must be performed, and the process may be omitted and drying may be performed by the operation of a blower 46 described later. Switching to fuel cell operation is performed more smoothly.

  Next, the valves 33a and 43a are closed, the valve 45a is opened, the blower 46 is activated, and the inner substrate of the reversible cell 1 is dried only from the oxidant electrode side. The drying time is the time during which the amount of water transferred from the cell internal substrate to the purge gas becomes a predetermined value (= the amount of water until the cell internal substrate reaches a dry state where the fuel cell can be operated). Is calculated by the calculation unit of the control device 71. The calculation unit (not shown) of the control device 71 calculates the mass transfer inside the cell based on the mass transfer rate between the cell internal substrate and air supplied by the blower 46 and the drying conditions at that time. And calculate the time required for drying (specified time).

  Then, after drying for the required drying time, the valve 45a is closed and the valves 33a and 43a are opened, so that the reaction gas (fuel, oxidant) is supplied to the reversible cell 1 and the end preparation fuel cell operation is started. . By performing the end preparation fuel cell operation through such a process, it is possible to reduce the time from the water electrolysis operation just before the end to the end preparation fuel cell operation until the storage.

  At the start of the drying process, the temperature of the reversible cell 1 is preferably set to 70 ° C. or higher. Speaking of this in accordance with FIG. 1, it is essential that at least the current collector 6 is at least 70 ° C. or higher. However, since it is difficult in practice to measure the temperature of the current collector 6, it is sufficient that the temperature of the circulation port 14 b is 70 ° C. or higher. Further, when the temperature of the reversible cell 1 (the temperature of the circulation port 14b) is set to 70 ° C. or higher, the cooling water flowing through the reversible cell 1 before the end of the water electrolysis operation before the reversible cell 1 is stopped, that is, the cooling water flow You may implement | achieve by controlling the flow volume of the water which flows through the path | routes 11 and 13. FIG. If the flow rate is reduced, the temperature of the reversible cell 1 rises. Of course, the temperature of the water flowing through the cooling water passages 11 and 13 may be controlled. Further, before the end of the water electrolysis operation before the reversible cell 1 is stopped, the current density from the power supply equipment 72 supplied to the reversible cell 1 may be increased to increase the heat generation amount of the reversible cell 1 itself.

  After completion of the fuel cell operation, the system is pressurized with a blower 46 or a fan (not shown), and then the air valves 33a, 61a, 43a, 51a are closed to bring the system to room temperature. Depressurization in the system when the temperature drops can be prevented, thereby preventing external air from entering the reversible cell as the temperature drops.

  The present invention is useful for a reversible cell in which a solid polymer water electrolyzer and a fuel cell are integrated.

1 Reversible cell 2, 3 Supply / collection plate 4 MEA
4a, 4b Electrode portion 4c Ion exchange membrane 5, 6 Current collector 7 Separator 11, 13 Cooling water flow path 12, 14 Flow path (in reversible cell)
12a, 12b, 14a, 14b Flow port 31, 41, 51, 61 Flow path (outside reversible cell)
32, 42 Tank 33a, 34a, 43a, 44a, 45a, 51a, 52a, 61a Valve

Claims (7)

An operation method of a reversible cell in which a solid polymer water electrolyzer and a fuel cell are integrated, and the operation mode can be switched between a water electrolysis operation and a fuel cell operation,
While performing water electrolysis operation and fuel cell operation alternately,
When the operation of the reversible cell itself is stopped for 1 hour or longer, if the operation mode before the stop is a water electrolysis operation, after the water electrolysis operation, the end preparation fuel cell operation is performed for a predetermined time. A method for operating a reversible cell, characterized by stopping the operation of the reversible cell. Before carrying out the end preparation fuel cell operation, the electrolyzed water remaining in the flow path is discharged from the inside of the cell, and then air is supplied only to the reaction gas flow path on the side that becomes the oxidant electrode during the fuel cell operation, The method for operating a reversible cell according to claim 1, wherein a drying step of drying the cell internal substrate is performed. The method of operating a reversible cell according to claim 2, wherein the discharging is performed by supplying a gas to a reaction gas flow path inside the reversible cell. Before the end of the water electrolysis operation before stopping the reversible cell, at least the flow rate or temperature of the cooling water passing through the reversible cell is controlled so that the temperature of the reversible cell is set to 70 ° C. or higher at the start of the drying process. The method of operating a reversible cell according to claim 2 or 3, characterized by comprising: Before the end of the water electrolysis operation before stopping the reversible cell, the current density supplied to the reversible cell is increased to increase the calorific value of the reversible cell itself. At the start of the drying step, the temperature of the reversible cell is set to 70. The method of operating a reversible cell according to claim 2 or 3, wherein the temperature is set to at least ° C. The reversible cell operating method according to any one of claims 1 to 5, wherein the completion preparatory fuel cell operation is performed under the following conditions.
Saturated water vapor amount at reversible cell temperature of hydrogen side supply gas: MH _{2 -SAT} [mol / s]
Saturated water vapor amount at reversible cell temperature of oxygen side supply gas: M _O2-SAT [mol / s]
Amount of water vapor in hydrogen-side supply gas: MH ₂ [mol / s]
Amount of water vapor in oxygen-side supply gas: M _O2 [mol / s]
When the amount of reaction product water is _{MH 2 O} [mol / s],
(M _H2-SAT + M _O2-SAT ) − (M _H2 + M _O2 + M _H2O ) ≦ 0 After the completion preparation fuel cell operation, before the reversible cell is stopped, the inside of the reversible cell is pressurized, and then the flow path leading to the reversible cell is closed. A method of operating the reversible cell as described.

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