JP5339473B2 - Reversible cell operation control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve efficient operation by safely and surely carrying out switching over of an operation mode in a reversible cell formed by integrating a solid polymer water electrolysis device and a fuel cell. <P>SOLUTION: In the reversible cell 1 formed by integrating the solid polymer water electrolysis device and the fuel cell, when the operation mode is switched over from water electrolysis device operation to fuel cell operation, inert gas is supplied from an inert gas supply source 31 to a flow passage interior of the reversible cell 1 to dry the interior of the reversible cell 1. A dry situation is determined based on increase in resistance between current supply/current collecting plates 2, 3 by an AC resistance measuring instrument 35, and after a resistance increased value reaches within an appropriate range, a control device 34 stops the supply of gas, and then starts the operation of the fuel cell. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an operation control method for a reversible cell in which a solid polymer water electrolyzer (WE) and a fuel cell (FC) are integrated.

  A solid polymer reversible cell is a device in which the functions of a water electrolysis device and a fuel cell of the same shape are integrated. In Japan, as disclosed in Patent Document 1, research on optimization of components is performed. However, it has not been put into practical use at present. The reason for this is that, on a practical scale, there are technical difficulties in establishing and controlling the opposite physical phenomena of water electrolysis device and fuel cell with the same member.

  That is, there are two cases in which the operation mode is switched: a fuel cell operation → water electrolyzer operation and a reverse water electrolyzer operation → fuel cell operation. Among these, when switching from the former fuel cell operation to the water electrolysis apparatus operation, the switching determination is not particularly necessary. That is, in this case, it is necessary to change the internal base material of the reversible cell that is water-repellent during fuel cell operation, such as the ion exchange membrane and the current supply / current collector, to the hydrophilicity necessary for water electrolysis apparatus operation. This is because these internal base materials can be easily made hydrophilic simply by supplying electrolyzed water to the inside of the cell, and electrolyzed water can be supplied to the electrode surface and the water electrolyzer can be operated.

However, when switching from the latter water electrolyzer operation to the fuel cell operation, an appropriate switching determination is required. This is because, when switching from water electrolyzer operation to fuel cell operation, even if the reaction gas is supplied to the cell internal substrate that has become hydrophilic in the water electrolyzer operation and loses gas permeability, This is because sufficient gas is not supplied to the surface and fuel cell operation is impossible. Further, even if the gas permeability is partially recovered, other portions do not effectively act (react) as electrodes, so that the apparent electrode area is reduced. As a result, the reaction occurs intensively only in the gas permeable portion, resulting in performance degradation. In such a case, depending on the area of the electrode that acts effectively, a sudden drop in the output voltage occurs immediately after the start of the load operation, the ion exchange membrane dries due to the temperature rise accompanying the reaction, etc., and the hydrogen gas is in the H ⁺ (proton) state Rather than permeating to the cathode side in the state of molecules (cross leak), the hydrogen gas that permeates and the oxidant gas supplied to the cathode react on the electrode, causing explosion and other combustion, so the ion exchange membrane There is also a possibility of causing damage.

JP 2004-134134 A

  The present invention has been made in view of the above points, and in a reversible cell in which a solid polymer water electrolyzer (WE) and a fuel cell (FC) are integrated, the operation mode can be switched safely and reliably. It is an object of the present invention to provide a control method for repeatedly realizing efficient operation.

  In order to prevent the phenomenon described above, the gas repellent property of the supply / current collector is recovered by drying the internal base material of the reversible cell until the water repellency is recovered after the operation of the water electrolysis apparatus is completed. It is necessary to return to a state where it can respond effectively. However, it is also necessary to ensure a certain degree of wetness for the ion exchange membrane, which is one of the cell inner substrates.

Therefore, in the present invention, in the polymer electrolyte reversible cell capable of switching the operation mode between the water electrolyzer operation and the fuel cell operation, the water electrolyzer is used for switching the operation mode from the water electrolyzer operation to the fuel cell operation. In a state where the supply of electrolyzed water in operation is stopped, the reversible cell is operated with a water electrolyzer and the inside of the reversible cell is dried.
The operation mode is switched based on the resistance increase value of the ion exchange membrane inside the reversible cell or the activity of the ion exchange membrane surface.

With the supply of electrolyzed water in the water electrolyzer operation stopped in this manner , the reversible cell is operated with the water electrolyzer and the inside of the reversible cell is dried to increase the resistance of the ion exchange membrane inside the reversible cell. Since the switching of the operation mode is performed based on the value or the activity of the ion exchange membrane surface, it is possible to surely switch how much the drying does not cause a performance degradation due to a decrease in the effective electrode area. It is possible to determine whether the safe switching can be performed without causing the above-described cross leak due to excessive drying.

The drying can be performed, for example, by supplying an inert gas to the inside of the cell, for example, the flow path of the fuel gas or the oxidant gas . It is possible to obtain the amount of evaporated water from the inside of the cell by obtaining the saturated water vapor amount at the outlet gas temperature from the supply gas flow rate and the gas pressure inside the flow path.
The supply direction of the inert gas into the reversible cell may be changed as appropriate during the next drying. For example, when supplying from above and discharging from below, supply from below and discharge from above alternately or every appropriate number of times from the next time. Thereby, unevenness of drying can be prevented.

In addition, the determination of the drying condition is performed by obtaining the outlet gas temperature of the reversible cell, and obtaining the saturated water vapor amount at the outlet gas temperature from the supply gas flow rate and the gas pressure inside the flow path at that time, thereby evaporating from the inside of the cell. It is also possible by determining the amount of moisture.

The determination of the drying state can also be made based on the amount of substance discharged from the inside of the reversible cell, for example, the amount of evaporated water, the amount of drained condensed (eg, water).

  Further, the drying may be performed by operating the reversible cell in the operation mode of the water electrolysis apparatus. When the reversible cell is operated as a water electrolysis device, if the valve is closed, the reversible cell is empty, and the water inside the reversible cell can be decomposed into oxygen and hydrogen and dried. In the case where the drying is performed by performing such an empty water electrolyzer operation on the reversible cell, it is based on the gas generated in the operation mode of the water electrolyzer operation, that is, the integrated amount of oxygen and hydrogen. It is possible to determine the dry situation.

  If any one of the above three determination methods is employed, it is possible to appropriately prevent energization and fuel cell operation in an insufficient state. In other words, efficient operation and extension of the device life can be realized.

  It should be noted that in the above-described determination of the drying state, a predetermined value, that is, a value and range suitable for starting the fuel cell operation are obtained in advance, and the fuel cell operation is started when entering this range. do it. By doing so, a general-purpose, automated, and standardized reversible cell or fuel cell can be provided.

  According to the present invention, in a reversible cell in which a solid polymer water electrolyzer and a fuel cell are integrated, the operation mode can be switched safely and reliably, and efficient operation can be repeatedly realized. Is possible.

It is explanatory drawing which showed typically the internal structure of the reversible cell used in embodiment. It is a partial expanded horizontal sectional view of the reversible cell used in the embodiment. It is explanatory drawing which shows the gas distribution condition around the reversible cell at the time of water electrolysis apparatus driving | operation. It is explanatory drawing which shows the gas distribution condition around the reversible cell at the time of fuel cell operation. It is explanatory drawing which shows the gas distribution condition around a reversible cell when supplying inert gas and performing dry operation. It is a graph which shows the output stability of the fuel cell after switching from water electrolyzer operation to fuel cell operation. It is a graph which shows the relationship between the activity of a film | membrane surface, and the resistance increase value between supply and current collecting plates. It is a graph which shows the relationship between the amount of evaporating water inside a reversible cell, and the resistance increase value between supply and current collecting plates. It is a graph which shows the shortest switchable time by inert gas supply conditions. It is explanatory drawing which shows the gas distribution condition around a reversible cell when carrying out the drying operation by heating. It is explanatory drawing which shows the gas distribution condition around a reversible cell when drying operation is carried out by cooling. It is explanatory drawing which shows the gas distribution condition around a reversible cell when performing dry operation by water electrolysis operation.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 schematically shows the inside of the reversible cell 1, and FIG. 2 shows a horizontal cross section of the reversible cell 1. As shown in FIG. 2, the reversible cell 1 has the power supply / collection plates 2, 3 arranged on the outermost sides, and two electrode catalysts at the center between the supply / collection plates 2, 3. An ion exchange membrane 4b made of a solid electrolyte material is placed between the electrode parts 4a and 4a made of layers, and an MEA 4 that is a combined power generation unit is placed. On the outside of each electrode catalyst layer 4a, supply and current collectors 5 and 6 are arranged, respectively. The supply / current collectors 5 and 6 are made of, for example, a porous material. For convenience of drawing and explanation, FIG. 1 shows a single cell, but a reversible cell for practical use has several tens to several hundreds of single cells arranged between the power supply and current collector plates 2 and 3. These are clamped and clamped by end plates (not shown) located outside the power supply / collection plates 2 and 3, respectively.

  A space S1 is formed between the supply / current collector 5 and the supply / current collector plate 2, and a space S2 is formed between the supply / current collector 6 and the supply / current collector plate 3. . In each of the spaces S1 and S2, separators 7 each having a corrugated cross section are disposed. This reversible cell employs a water-cooling method, and cooling water flow paths 11 and flow paths 12 are alternately formed in the space S1 by the separators 7 disposed in the space S1. On the other hand, the cooling water flow path 13 and the flow path 14 are alternately formed also in the space S2 by the separator 7 arranged in the space S2. 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) provided with a heat pump, and is operated to maintain, for example, 60 ° C. at the entrance of the reversible cell 1.

  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.

  An electrode portion 4a of the cathode (during water electrolysis operation) is formed at the boundary surface between the ion exchange membrane 4b and the supply / current collector 5, and the boundary surface between the ion exchange membrane 4b and the supply / current collector 6 is formed. The electrode part 4a of the anode (at the time of water electrolysis operation) is formed.

  The flow path configuration of fuel gas or the like in the reversible cell 1 is as shown in FIG. That is, these flow paths are constituted by, for example, stainless steel piping, the flow path F1 is connected to the flow port 12a, the flow path F2 is connected to the flow port 14a, and the flow path is connected to the flow port 14b. F3 is connected, and the flow path F4 is connected to the circulation port 12b. Further, branched channels F5 to F8 are connected to the channels F1 to F4, respectively. Each of the flow paths F1 to F8 is provided with valves V1 to V8 that open and close the corresponding flow paths.

And when performing the water electrolysis operation of the reversible cell 1 having such a configuration, as shown in FIG. 3, the valves V1 to V4 are opened (the other valves are closed), and electrolyzed water is supplied from the flow paths F3 and F4. By supplying electric power from the external power source to the power supply / collector plates 2 and 3, the electrolyzed water is electrolyzed to generate pure hydrogen and pure oxygen. Then, pure hydrogen flows from the flow port 12a through the flow path F1 and is discharged from the reversible cell 1, and pure oxygen flows from the flow port 14a through the flow path F2 and is discharged from the reversible cell 1. In FIG. 3, (G) indicates a gaseous state, and (L) indicates a liquid state. The hydrogen gas discharged from the flow path F1 and the oxygen gas discharged from the flow path F2 have a very small amount of H ₂ O used in actual operation (only a few percent are decomposed). Since these gases exist as bubbles in water, they are described as (G, L) for convenience.
Further, it is not always necessary to supply electrolytic water to the flow path F3, and operation is possible if this is supplied only to the flow path F4. That is, the supply gas supply line piping may be one, or each of the flow paths F3 and F4 may be connected to turn on only one.

  On the other hand, when the reversible cell 1 is operated as a fuel cell, the valves V1, V2, V7, and V8 are opened (the other valves are closed) as shown in FIG. Electric power is generated in the reversible cell 1 by supplying humidified fuel gas (hydrogen gas) to the port 12a and supplying humidified oxidant gas (oxygen) to the flow port 14a. This can be removed from a few and supplied to the load. Regarding the water generated as a result of the reaction, the cathode side flows from the flow port 12b through the flow path F8 and is discharged from the reversible cell 1, and the anode side flows from the flow port 14b through the flow path F7 and is discharged from the reversible cell 1. . Note that the flow paths F3, F4, F5, and F6 serving as a junction pipe or a branch pipe communicate with the humidifying tank.

  Further, an inert gas supply route is added to the flow paths 12 and 14 in the reversible cell 1. That is, as shown in FIG. 1, an inert gas such as nitrogen gas from the inert gas supply source 31 passes through the supply path 36 via the valve 32 and the mass flow controller 33 in the flow paths F5 and F6. It can be supplied.

  The valve 32 and the mass flow controller 33 are controlled by a control device 34. That is, an AC resistance measuring device 35 is connected to the power supply / collection plates 2, 3, and the control device 34 is based on the resistance value of the power supply / collection plates 2, 3 measured by the AC resistance measurement device 35. Controls the valve 32 and the mass flow controller 33. The valve 32 corresponds to the valves V5 and V6 in FIGS.

  The reversible cell 1, the flow path around it, and the main equipment configuration are as described above. When switching from the water electrolysis operation to the fuel cell operation, the inside of the reversible cell 1 is completely wet. Therefore, since the fuel cell operation cannot be performed as it is, it is necessary to dry the inside of the reversible cell 1.

  Therefore, first, after completion of the water electrolysis operation, as shown in FIG. 5, the valves V1 to V4 are closed and the other valves V5 to 8 are opened. As shown in FIG. An inert gas is supplied into the flow paths 12 and 14. Thereby, the water in the flow paths 12 and 14 is drained, and the inside of the reversible cell 1 is dried.

  At this time, the resistance value between the supply / collection plates 2 and 3 of the reversible cell 1 is measured by the AC resistance measuring device 35, and the inert gas is supplied on the basis of the resistance value in a completely wet state inside the cell. From the resulting resistance increase value (= resistance increase value of the ion exchange membrane), the drying state inside the cell is judged.

  If the resistance increase value falls within the specified range, as shown in FIG. 4, the valves V5 and V6 are closed, and then the valves V1 and V2 are opened to humidify the fuel cell operation. The supply of the reacted gas (fuel gas, oxidant gas) is started.

The specific range of the resistance increase value that the inventors have experimented is as shown in FIG. This figure shows that after the water electrolysis operation is completed, the inner base material of the reversible cell 1 is dried with an inert gas, the resistance value of the ion exchange membrane is increased to a certain value, and then the supply of the inert gas is stopped. The result of confirming the stability of the output voltage value when the operation (current density: 0.1 → 0.2 A / cm ² ) is started is shown. The numbers (resistance value per unit area: mΩ · cm ² ) shown in the figure indicate the resistance value of the ion exchange membrane raised by drying, and the solid line indicates the output voltage value during load operation.

From this figure, it can be considered that it is possible to safely switch the range in which the slope does not rise or fall, that is, the resistance rise value is in the range of 50 to 1500 [mΩ · cm ² ]. However, switching is possible in other ranges, but when the resistance increase value is less than 50 [mΩ · cm ² ], the output voltage value decreases with time, so that the internal substrate of the reversible cell 1 is dried. Can be switched in the range of 2000 [mΩ · cm ² ] or more, but the voltage drop immediately after the start of the load operation is large and the ion exchange membrane may be damaged. It is desirable to supply humidified gas within the specified range.

  As a result, the operation mode can be switched from the water electrolysis apparatus operation to the fuel cell operation safely and reliably, and an efficient operation can be realized.

  In the above example, the drying by supplying the inert gas is performed by supplying from the upper side of the flow paths 12 and 14 and discharging from the lower side. However, when this is repeated, the inside of the reversible cell 1 is gradually increased. In the current collectors 5 and 6, only the upper side is easily dried, and even if the resistance increase value as a whole is within an appropriate range, there is a possibility that the lower side is not in an appropriate dry state. . In that case, the efficiency of the fuel cell operation is reduced.

  In order to prevent this, the supply direction of the inert gas into the reversible cell 1 is reversed from the previous time, that is, from the lower side to the upper side of the flow paths 12, 14. They may be alternately supplied or supplied from the opposite direction at an appropriate number of times. In such a case, for example, a bypass flow path (not shown) connected to the flow path F8 is provided on the upstream side of the valve V5 of the flow path F5 used as the inert gas supply path, and the inert gas supply path is also provided. By providing a bypass flow path (not shown) connected to the flow path F7 on the upstream side of the valve V6 of the used flow path F6, closing the valves V5 and V8 and opening the valves V6 and V7, respectively. It is possible to supply an inert gas from below to above the flow paths 12 and 14.

  Since the resistance value of the ion exchange membrane and the activity of the surface of the ion exchange membrane have a correlation, as shown in FIG. 7, the range of resistance increase of the ion exchange membrane capable of safe switching operation is ion exchanged. It can also be expressed in terms of the activity range of the film surface. According to this, the preferable activity value for switching the operation mode from the water electrolysis apparatus operation to the fuel cell operation is 0.12 to 0.83. Therefore, the activity of the surface of the ion exchange membrane is calculated from the resistance value of the ion exchange membrane by an appropriate personal computer, and the dry state is judged based on the obtained ion activity or the inert gas is controlled. It may be.

  In the above example, the increase in the resistance value of the ion exchange membrane 4b is used as a criterion for drying. Instead, the outlet gas temperature of the reversible cell 1 is obtained, and the supply gas flow rate and the pressure in the flow path at that time are obtained. From the above, the amount of water vapor evaporated from the inside of the cell may be obtained by obtaining the saturated water vapor amount at the outlet gas temperature.

That is, FIG. 8 shows the amount of evaporated water due to mass transfer and the supply / collector plate 2 of the reversible cell 1 when the drying conditions (flow rate: m _PG , reversible cell 1 main body temperature: T _PG ) with an inert gas are changed. 3 shows a resistance increase value between 3 and 3 (standard when fully wet). From this figure, regardless of the drying conditions, the amount of evaporated water and the resistance increase value between the supply and current collecting plates 2 and 3 of the reversible cell 1 are shown. Shows that there is a correlation. The amount of evaporated water that begins to increase the resistance between the supply and current collecting plates 2 and 3 of the reversible cell 1 matches the amount of water held by the supply and current collectors 5 and 6 when completely wetted, and is described above. As can be seen, the increase in resistance between the power supply and current collecting plates 2 and 3 represents the increase in resistance of the ion exchange membrane 4b. In FIG. 8, _PPG is the pressure in the flow path.

  Therefore, as described above, instead of measuring the increase in resistance of the ion exchange membrane 4b, the outlet gas temperature of the reversible cell 1, that is, the temperature of the flow ports 12b and 14b and the flow paths 12 and 14 in the example of FIG. The amount of evaporated water from the inside of the reversible cell 1 may be obtained by obtaining the pressure of

The amount of evaporated water depends on the relationship between the supply temperature of the inert gas and its flow rate, the gas pressure in the flow path, and the temperature of the main body of the reversible cell 1 at that time. The gas temperature at the flow ports 12b and 14b is obtained from the equation (constant wall temperature), the saturated water vapor pressure and gas partial pressure at that temperature, and the amount of saturated water vapor are obtained from the inert gas supply flow rate. It can be an amount. That is, when switching operation,
Gas pressure inside the cell: P ₀ [Pa]
Gas temperature at cell outlet: T _OUT [° C]
Saturated water vapor pressure at T _OUT : P _{H2O, TOUT} [Pa]
Flow rate of inert gas: M _PG [mol / s]
Evaporated water content: _{MH 2 O} [mol / s]
Then, the amount of evaporated water: _{MH 2 O} is expressed by the following equation.
M _H2O = {P _{H2O, TOUT} / (P ₀ -P _{H2O, TOUT} )} × M _PG

"Formula of laminar heat transfer in the run-up section of pipe flow (constant wall temperature)"
When the distance from the heating start point is x, the diameter of the circular tube is d, and the fluid temperature at the circular tube inlet is Tin, the mixing average temperature Tm (x +) is obtained by the following equation.

  From the above, it can be seen that drying inside the reversible cell 1 is divided into the following two steps. One is a drying step of the power supply / current collectors 5 and 6, and at this time, the resistance of the ion exchange membrane 4b does not increase yet. The other is an ion exchange membrane 4b drying step, and when the ion exchange membrane 4b starts to dry, the resistance of the ion exchange membrane 4b increases. Here, paying attention to the amount of evaporated water in each drying, the supply and current collectors 5 and 6 are measured before the moisture content held by the supply and current collectors 5 and 6 in a completely wet state is incorporated into the reversible cell 1. By doing so, the amount of evaporated water until the resistance of the ion exchange membrane 4b starts to increase can be known.

Further, regarding the ion exchange membrane 4b, the amount of evaporated water for setting the increase in membrane resistance to a predetermined value is known from the correlation between the amount of evaporated water and the resistance increase value of the ion exchange membrane 4b. From the sum of the amount of evaporated water and the drying conditions (inert gas supply temperature and flow rate, gas pressure in the flow path (because the water vapor partial pressure changes as the pressure changes), the temperature of the reversible cell 1) Based on the method for calculating the amount of evaporated water, the time required for switching from the water electrolyzer operation to the fuel cell operation can be calculated. That is, the time required for switching the reversible cell 1 from the water electrolyzer operation to the fuel cell operation can be known in advance.
That is, in the operation switching condition when the amount of evaporated water described above is obtained,
Evaporated water content for making membrane resistance a predetermined value: M [mol]
Time required for operation switching: t [s]
Then, the operation required time: t is expressed by the following equation.
t = M / M _H2O

  If this is utilized, it becomes possible to arbitrarily operate the time required for switching by changing the main body temperature of the reversible cell 1 at the time of operation switching and the supply temperature, flow rate, and pressure of the inert gas. Conversely, when the required switching time is specified, it is also possible to derive a switching condition for completing the switching within that time.

When the inventor actually changes the flow rate of the inert gas when the temperature of the reversible cell 1 is 60 ° C., 70 ° C., and 78 ° C. using the reversible cell 1 of FIGS. When the shortest switchable time was examined, a result as shown in FIG. 9 was obtained.
As can be seen, it is possible to control the switchable time by changing the main body temperature of the reversible cell 1 and the flow rate of the inert gas, and the same result can be obtained by changing the temperature of the inert gas. It can be inferred that

  In the above-described example, the inside of the reversible cell 1 is dried by supplying an inert gas to the inside of the reversible cell 1, but instead, the reversible cell 1 may be heated or cooled.

  In order to heat and cool the reversible cell 1, for example, the temperature of the cooling water flowing in the cooling water flow paths 11 and 13 may be raised and lowered. By raising the temperature of the cooling water, for example, by raising the temperature by 10 ° C. to 20 ° C. compared to that during normal operation (for example, 60 ° C. → 70 ° C. to 80 ° C.), the temperature of the entire reversible cell 1 rises. As shown in FIG. 10, it evaporates and is discharged from the reversible cell 1 to the outside through the flow port 12a, the flow channel F1, the flow port 14a, and the flow channel F2. Further, by lowering the temperature of the cooling water (for example, 60 ° C. → 40 ° C.), the temperature of the entire reversible cell 1 is reduced, and the water inside the reversible cell 1 is condensed, as shown in FIG. 12b, the flow path F8, the circulation port 14b, and the flow path F7 are discharged | emitted from the reversible cell 1 outside. Thereby, the inside of the reversible cell 1 can be dried. In these cases, in order to efficiently and quickly discharge water, the above-described supply of inert gas may be used in combination. Furthermore, the supply of cooling water may be stopped, and heat exchanged with normal temperature water (for example, tap water) or cold water for air conditioning may be used instead.

  In addition, in order to heat and cool the reversible cell 1, other means, for example, hot air or cold air may be supplied from the outside to the reversible cell 1. In such a case, it is preferable to provide an appropriate fin for the separator 7.

  Even when the inside of the reversible cell 1 as described above is dried by heating and cooling, the determination of the drying state may be made based on the resistance increase value or activity of the ion exchange membrane 4b described above. The amount of evaporating water or condensed water discharged during drying may be measured and judged. That is, as described above, since the moisture content of the supply and current collectors 5 and 6 in the completely wet state and the evaporated moisture content of the ion exchange membrane are correlated with the resistance increase value of the ion exchange membrane, The main body of the reversible cell 1 when the range of the evaporated water amount corresponding to the range in which the resistance increase of the membrane corresponds to “a range where safe switching is possible” is obtained and the amount of water discharged from the reversible cell 1 is within that range. The temperature may be changed to fuel cell operation. In such a case, by measuring both the resistance increase value of the ion exchange membrane 4b and the amount of moisture discharged from the reversible cell 1, it is possible to more reliably determine the drying state. Further, regarding the calculation of the required switching time, it is possible to calculate the required time with higher accuracy by using both values together.

  Furthermore, as a method of drying the inside of the reversible cell 1, the reversible cell 1 may be carried out in the operation mode of the water electrolysis apparatus operation. That is, after the operation of the water electrolysis apparatus, as shown in FIG. 12, the supply of the electrolyzed water is stopped by closing the valves V3 and 4, and the electrolyzed water inside the reversible cell 1 is drained by opening the valves V7 and 8. . Thereafter, the operation of the water electrolysis apparatus is started again, and the inside of the reversible cell 1 is dried by decomposing and discharging the electrolyzed water remaining on the base material inside the cell into pure hydrogen / pure oxygen gas.

  As described above, the resistance increase value of the ion exchange membrane 4b and the amount of evaporated water have a correlation, but this amount of evaporated water is the water decomposed during the operation of the water electrolysis apparatus performed for the purpose of drying described above. Since it corresponds to the amount of water, it is possible to determine the drying status by measuring the integrated amount of pure hydrogen / pure oxygen gas, which is a purified gas generated by water electrolyzer operation. It is. Moreover, if the amount of evaporated water corresponding to the “range in which safe operation is possible” is obtained, the amount can be electrolyzed. Therefore, it is possible to arbitrarily select the required switching time by adjusting the applied power. Is possible. Of course, you may use together with the resistance rise value of the ion exchange membrane 4b by the alternating current resistance measuring device 35. FIG.

  By the way, in the polymer electrolyte fuel cell, when the water supplied with the reaction gas inside the operating cell and the reaction product water are not smoothly discharged outside the cell, the base material inside the cell gets wet (flooding). Arise. When this phenomenon occurs, the reaction gas is not supplied to the reaction surface, resulting in a decrease in the output voltage. If this further proceeds, it becomes impossible to continue the operation.

  The present invention can cope with such flooding. In other words, flooding is caused by a decrease in gas flow rate that accompanies a high utilization rate of reaction gas and an increase in reaction product water that accompanies operation in a high current density region. If the explanation is made according to the reversible cell 1 described above, the water / current collectors 5 and 6 may be wetted or flowed due to the fact that water etc.) is not smoothly discharged to the outside of the cell but stagnates inside the cell. It is a phenomenon that blocks the road. When flooding occurs, the ion exchange membrane 4b and the supply / current collectors 5 and 6 that are the cell inner base material at that portion become hydrophilic and lose gas permeability.

  At this time, even if the reaction gas is supplied to the cell internal substrate in that state, the gas is not supplied to the electrode portions 15 and 16, and therefore the portion that has lost the gas permeability effectively acts (reacts) as an electrode. As a result, the apparent electrode area was reduced, leading to a decrease in output voltage, and eventually crossing in the same manner as in the case of an inappropriate drying state that occurred when switching from water electrolyzer operation to fuel cell operation. There is also a possibility of causing leakage or damage of the ion exchange membrane.

  In order to appropriately cope with this phenomenon, the fuel cell operation is stopped when flooding occurs, and the gas permeability of the current collectors 5 and 6 is decreased by once drying the cell internal substrate until the water repellency is restored. It is necessary to restore the state in which all electrode surfaces can react effectively. However, at the same time, the ion exchange membrane 4b, which is one of the inner substrates of the reversible cell 1, needs to have a certain wet state. Therefore, a criterion for determining whether or not the cell internal substrate is in a state where the fuel cell can be operated is still necessary.

  Therefore, the resistance increase value of the ion exchange membrane 4b, which is a method for determining the dry state adopted when the inert gas supplied to the inside of the reversible cell 1 when switching the operation from the water electrolyzer operation to the fuel cell operation described above, is obtained. It may be determined based on. Note that, as a reference at this time, the resistance increase value may be measured based on the occurrence of flooding.

More specifically, as shown in FIG. 5, when flooding occurs, the valves V <b> 1 to V <b> 4 are closed to stop the reaction gas supply, and the inert gas is supplied from the inert gas supply source 31 to the flow paths 12 and 14. Supply in. Thereby, the water in the flow paths 12 and 14 is drained, and the inside of the reversible cell 1 is dried. Thereafter, when the resistance increase value of the ion exchange membrane 4b measured by the AC resistance measuring device 35 falls within the predetermined appropriate range described above, the supply of the inert gas is stopped, and the fuel cell operation is performed again thereafter. Good.
Note that such a technique adopted for flooding can be applied to not only the above-described reversible cell but also a solid molecular fuel cell.

1 Reversible cell 2, 3 Supply / collection plate 4 MEA
4a Electrode catalyst layer 4b Ion exchange membrane 5, 6 Supply / collector 11, 13 Cooling water flow path 12, 14 Flow path 12a, 12b, 14a, 14b Flow port 31 Inert gas supply source 33 Mass flow controller 34 Control device 35 AC Resistance measuring instrument F1-F8 flow path V1-V8 valve

Claims (4)

In a polymer electrolyte reversible cell capable of switching between the water electrolyzer operation and the fuel cell operation mode,
When switching the operation mode from water electrolyzer operation to fuel cell operation,
With the supply of electrolyzed water in the water electrolyzer operation stopped, the reversible cell is operated with the water electrolyzer, and the inside of the reversible cell is dried.
An operation control method for a reversible cell, wherein the operation mode is switched based on a resistance increase value of an ion exchange membrane inside the reversible cell or an activity on the surface of the ion exchange membrane. In a polymer electrolyte reversible cell capable of switching between the water electrolyzer operation and the fuel cell operation mode,
In switching the operation mode from water electrolyzer operation to fuel cell operation, the inside of the reversible cell is dried by supplying an inert gas inside the reversible cell,
The determination of the drying condition is performed by determining the outlet gas temperature of the reversible cell and determining the amount of saturated water vapor at the outlet gas temperature from the supply gas flow rate at that time and the gas pressure in the flow path, thereby evaporating moisture from the inside of the cell. Do by asking for quantity,
An operation control method for a reversible cell, wherein the operation mode is switched based on the drying state. In a polymer electrolyte reversible cell capable of switching between the water electrolyzer operation and the fuel cell operation mode,
When switching the operation mode from water electrolyzer operation to fuel cell operation,
With the supply of electrolyzed water in the water electrolyzer operation stopped, the reversible cell is operated with the water electrolyzer, and the inside of the reversible cell is dried.
The determination of the drying state is made based on the integrated amount of gas purified in the operation mode of the water electrolysis apparatus operation performed for the purpose of drying,
An operation control method for a reversible cell, wherein the operation mode is switched based on the drying state. ^2. The reversible cell according to claim 1, wherein when the resistance increase value is 50 to 1500 [mΩ · cm ² ], the operation mode is switched from the water electrolysis apparatus operation to the fuel cell operation. Operation control method.

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