JP2010153218A - Operation switching method of reversible cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a short-time and easy switching method of operation modes for a reversible cell integrating a solid polymer type water electrolysis device and a fuel cell. <P>SOLUTION: In the reversible cell 1 integrating the solid polymer type water electrolysis device and the fuel cell, when the operation mode is switched over from the water electrolysis device operation to the fuel cell operation, electrolyte water remaining in a channel is drained from inside the cell by supplying gas into a reaction gas channel inside the reversible cell 1 after finishing the water electrolysis operation and before starting the fuel cell operation. Afterwards, an interior substrate of the cell is dried by supplying air only to the reaction gas channel 14 on an oxidant electrode side when the fuel cell is in operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching method for switching operation from a water electrolysis operation to a fuel cell operation in a reversible cell in which a solid polymer water electrolysis device and a fuel cell are integrated.

  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.

  Since the reversible cell having such a structure is a device in which the functions of water electrolysis and a fuel cell are integrated, operation mode switching operation occurs. There are two types of switching: water electrolysis operation → fuel cell operation and fuel cell operation → water electrolysis operation. Among these, in switching from water electrolysis operation to fuel cell operation, since the cell internal substrate is completely wet in the water electrolysis operation, the reaction gas is supplied to start the fuel cell operation in that state. However, the gas supply to the reaction field is hindered by the wetting of the base material, and as a result, the fuel cell operation becomes impossible. In order to freely switch the operation of the reversible cell, in the operation switching from water electrolysis operation to fuel cell operation, wetting of the substrate after water electrolysis operation is appropriately controlled, and the reaction gas is smoothly supplied to the reaction field It is necessary to secure a state that can be done quickly.

  In this regard, for example, as a conventionally proposed technique, there is one that uses an inert gas in order to dry a cell internal substrate completely wetted by water electrolysis (Patent Document 1). This is because the inert gas is supplied to the reaction gas passages on both the oxidizer electrode side and the fuel electrode side, and the cell internal substrate is completely dried once for the purpose of restoring the water repellency of the cell internal substrate. That's it. The dry state inside the cell is judged by the resistance increase value of the polymer membrane having proton conductivity. And after supplying the inert gas and drying in that way, the humidified reaction gas is supplied and the excessively dried polymer film is brought into an appropriate wet state, and then a load is applied (starting fuel cell operation) )

  In addition, in a stack in which single cells (minimum unit electrolysis / power generation units) are stacked, the residual water inside the cells, which is the cause of uneven drying between the cells, can be supplied by supplying a certain amount or more of inert gas. A technique has also been proposed in which the cell base material is uniformly dried by blowing off (Patent Document 2).

JP 2006-127807 A JP 2007-115588 A

  The technique described in Patent Document 1 can be switched safely and reliably, but requires an inert gas facility. If the number of stacked cells increases, an amount of inert gas proportional to the number of cells will be required, so that the inert gas supply equipment will become larger and the initial cost and running cost will increase as the output of the reversible cell increases. I could not deny it. Furthermore, for the purpose of restoring the water repellency of the cell internal substrate, the polymer film is once dried to the specified value, and then the polymer film is moistened with a reaction humidifying gas. There was room. The technique described in Patent Document 2 also requires an inert gas facility, and the drainage capacity when discharging the residual electrolyzed water remaining in the channel depends on gravity and gas pressure. All of them require a large amount of inert gas (for example, nitrogen gas).

  The present invention has been made in view of the above points, and it is intended to perform operation switching from a water electrolysis operation to a fuel cell operation in a short time and in a simple manner without requiring an inert gas and its supply equipment. Yes.

  In order to achieve the above object, the present invention provides a reversible cell in which a solid polymer water electrolyzer and a fuel cell are integrated, and the operation mode can be switched between water electrolyzer operation and fuel cell operation. In the method of switching the operation mode from the device operation to the fuel cell operation, after the water electrolysis device operation is completed and before the fuel cell operation is performed, gas is supplied to the reaction gas flow channel inside the reversible cell, The remaining electrolyzed water 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 operation of the fuel cell to dry the cell internal substrate.

  According to the knowledge of the inventors, when air is supplied only to the reaction gas channel on the side that becomes the oxidant electrode, the moisture on the oxidant electrode side is transferred from the oxidant electrode current collector to the air, and the air Is discharged outside the system. 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. Accordingly, the substrate inside the cell 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 in the prior art. Of course, as the air used in the present invention, air in the atmosphere can be used as it is, or 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.

  Here, the wet state of the current collector in the air serving as the dry gas varies depending on the air flow direction, that is, the supply direction. Therefore, when air is supplied from only one direction and drying is performed, there is a possibility that a state where the upstream is dry but the downstream is not yet dried may occur. In this case, it is necessary to continuously supply air in order to dry the downstream side. However, if air is continuously supplied even though the upstream side is dry, the MEA on the upstream side, particularly the polymer membrane, may be excessively dried, and the membrane may be damaged.

  In order to cope with such a case, when supplying air and drying the cell internal substrate, the supply direction of air supplied to the reaction gas flow path may be reversed during the drying. This not only maximizes the amount of moisture transferred in the portion that is most desired to be dried, but also increases the amount of moisture in the air flow direction, so downstream after the reverse rotation (upstream before the reverse rotation) In this case, the MEA can be appropriately humidified to protect it, and as a result, the entire cell inner substrate can be uniformly dried.

  The amount of water vapor transferred from the cell internal substrate to be transmitted to the supplied air is calculated in advance, and the air is supplied until the residual moisture content of the cell internal substrate reaches a predetermined value based on the result. It may be.

  In this case, as described above, in the present invention, moisture (substance) transmission is performed by the difference in moisture concentration between the air and the cell internal substrate, and the moisture transmission path is the oxidant electrode current collector on the oxidant electrode side. Air from the body is the air, and the fuel electrode side first transmits the MEA and the oxidant side current collector from the fuel electrode current collector, and is finally transmitted to the air and discharged out of the system. Therefore, when the amount of water vapor movement is calculated in advance, strictly speaking, the diffusion coefficient of the bipolar current collector and the film in the substrate lamination direction is obtained, and the wet state in the thickness direction of the substrate is calculated for each member according to Fick's law. In addition, it is necessary to calculate the wet state of the bipolar current collector by determining the mass transfer rate between the surface of the oxidant electrode current collector and the air dry gas. However, since the thickness of the bipolar current collector and the MEA in the stacking direction is as thin as only 1 mm or less, there is no need to calculate the wet state in the base material internal stacking direction from a practical viewpoint. Therefore, the oxidant electrode current collector can be regarded as one substrate. In this way, by performing mass transfer calculation between the current collector regarded as one substrate and air, the amount of moisture movement in the air flow direction can be calculated, and based on that, the amount of residual moisture in the substrate inside the cell Since it is possible to obtain the time until the temperature reaches a predetermined value (dryness), it is easy to control the air supply time.

  In this way, the air is supplied before the time when the residual moisture content of the cell internal substrate reaches a predetermined value, and after that, the supply of air remains as it is, and the humidified or non-humidified gas is not supplied to the reaction gas channel on the fuel electrode side. A humidified fuel gas may be supplied to perform low load fuel cell operation lower than the rated value. That is, a fuel cell operation with a low load (low current density) lower than the rating may be performed during the drying. Thereafter, the current density may be gradually increased to approach the rated operation. As a result, although it is a low load operation at the initial operation, it is possible to gradually carry out a normal rated operation, shortening the dry operation time without power generation, and as a result efficient fuel cell operation as a whole. Can be implemented. Here, the low-humidified and non-humidified fuel gas means one having a dew point temperature of, for example, 30 ° C. or less.

  To supply the air until the residual moisture content of the cell internal substrate reaches a predetermined value based on the result of calculation in advance of the amount of water vapor transferred from the cell internal substrate transmitted to the supplied air. Instead, the open circuit voltage of the reversible cell may be measured, and the air may be supplied until the measurement result reaches a predetermined value. The open circuit voltage is a voltage in a state where no load is applied. The polymer membrane in the reversible cell has a high open circuit voltage when wet, but the open circuit voltage decreases as it dries. It may be considered that the operation has been switched.

  If the air containing a lot of moisture discharged from the reversible cell is dehumidified, and the air whose humidity has been lowered is used again as the air supplied to the reaction gas flow path on the oxidizer electrode side, it can be used for switching. There is no need to secure the air to be provided separately, and the necessary air and oxygen can be saved by adding a mechanism for storing or circulating the air.

  By performing a hydrophilic treatment on the current collector in the reversible cell to reduce the surface tension of the base material, it is possible to reduce the water retention capacity of the current collector itself and enhance the drainage effect of residual water due to the weight of the water. In this way, by increasing the effective rate of natural drainage due to its own weight, the amount of water discharged during drying due to the transfer of substances (moisture) between current collectors can be drastically reduced, and the time required for switching can be shortened. This leads to a reduction in the power required for switching, such as the blower power of the blower.

  On the other hand, by performing a hydrophilic treatment on the surface of the separator that forms the reaction gas flow path in the reversible cell, a purge for discharging the remaining water in the flow path at the initial stage of switching becomes unnecessary.

  In addition, by increasing the porosity and opening ratio of the current collector in the cell internal substrate, the drainage effect can be further enhanced by securing a drain flow path in the vertical direction inside the current collector, and through the current collector The mass transfer efficiency can be improved and the drying time can be shortened.

  According to the present invention, in a reversible cell in which a solid polymer type water electrolysis device and a fuel cell are integrated, an operation from a water electrolysis operation to a fuel cell operation without requiring an inert gas and its supply equipment is required. Switching can be performed in a short time and simply.

  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 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) 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.

  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 later-described bypass flow paths 45, 47 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. Further, a bypass channel 47 different from the channel 52 is connected between the channel 41 and the channel 51, and a valve 47 a is provided in the bypass channel 47.

  A valve 61 a is provided in the flow path 61, a flow path 62 is connected between the flow path 61 and the tank 32, and a pump 63 and a valve 62 a are provided in the flow path 62. The pump 63 supplies the pure water stored in the tank 32 to the reversible cell 1 during the water electrolysis operation. In addition, since it is not necessary to supply pure water into the flow path 12 during the water electrolysis operation, the pump 63 and the valve 62a are not necessarily installed, but in the event of an emergency. In this embodiment, the pump 63 and the valve 62a are provided in order to prevent the membrane from drying and to flush out the generated hydrogen with water. In particular, in the case of an emergency, the membrane may be dried and damaged during water electrolysis operation if the water on the fuel electrode side is insufficient, causing the membrane to dry locally and break. In view of this point, even during the water electrolysis operation, such a situation can be prevented by supplying water appropriately to the fuel electrode side using the pump 63 and the valve 62a.

  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, 47a, 51a, 52a, 61a, 62a is controlled by the control device 71. Further, the control device 71 includes a calculation unit (not shown) that executes calculation for a specified time, which will be described later, and further supplies a current for electrolyzing water to the reversible cell 1 during water electrolysis operation, It also controls the power supply facility 72 that supplies power to the demand side during battery 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, 47a, 52a, 62a 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, 47a, 61a are closed, and the valves 34a, 44a, 52a, 62a are opened. The pure water stored in the tank 32 is sucked in by the pump 63 and introduced into the reversible cell 1 through the flow path 61 and the flow port 12b, and the pure water stored in the tank 42 is sucked in by the pump 53 and flows in the flow path 51, flow. It is introduced into the reversible cell 1 through the mouth 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.

  When switching from such water electrolyzer operation to fuel cell operation, the switching operation is performed according to the flow shown in FIG.

  That is, when the operation of the water electrolysis apparatus is completed (step P1), only the valves 33a, 43a, 51a, 61a are first opened and all other valves are closed (step P2). 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 (step P3). 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.

  Next, the valves 33a and 43a are closed, the valve 45a is opened, the blower 46 is activated, and the internal substrate of the reversible cell 1 is dried only from the oxidant electrode side (step P4). 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 from the mass transfer rate between the cell internal substrate and air supplied by the blower 46 and the drying conditions at that time. The time required for drying (specified time) is calculated (step P5).

  Then, after drying for the required drying time (step P6), the valve 45a is closed and the valves 33a and 43a are opened to supply the reaction gas (fuel, oxidant) to the reversible cell 1 (step P7). The fuel cell operation is started (step P8). When switching from the fuel cell operation to the water electrolysis apparatus operation, no special control is required as disclosed in Japanese Patent Application Laid-Open No. 2006-127807.

Next, the calculation of the drying time in step P5 will be described in detail. First, the current collectors 5 and 6 and the flow paths 12 and 14 are divided into meshes in the gas flow direction, and a water vapor movement amount (= local water vapor movement amount) m _H2O (dif) [mol / s] in each mesh is calculated. The mass transfer rate: h _DH2O [m / s] between the wetted surfaces (the surface portions of the current collectors 5 and 6) and air (dry gas) at this time is experimentally determined in consideration of various states of the flow.

Next, regarding the dry state of each mesh, the local water vapor transfer amount m _H2O (dif) is integrated with the drying time to obtain the total water vapor transfer amount at each time. By subtracting this value from the residual water amount held by the current collectors 5 and 6 at the beginning of switching: m _H2ORI [mol], the residual water amount at that time is obtained. Here, m _H2ORI is the maximum value that the _current collectors 5 and 6 can hold, and this value can be experimentally measured in advance.

Further, regarding the dry state of the reversible cell 1, the total water vapor transfer amount M _H2O (dif) [mol / s] is obtained by integrating the local water vapor transfer amount m _H2O (dif) in the air flow direction. The value is integrated with the drying time, and the residual water amount at that time is obtained by subtracting from the total residual water amount held by the current collectors 5 and 6: _MH2ORI [mol]. The following formulas (1) to (5) were used for calculating each value. Here, c _SH2O [mol / m ³ ] is the water vapor concentration of the _current collectors 5 and 6, and c _CH2O [mol / m ³ ] is the water vapor concentration of the flow channels 12 and 14.

According to the above calculation, if the air is supplied to the oxidizer electrode side (flow path 14) until the time when _MH2OR becomes 0 (= specified time), the remaining water inside the current collectors 5 and 6 is completely _removed. Drained and a diffusion route from the flow path of the reaction gas (fuel, oxidant) to the reaction field, that is, a route crossing the current collectors 5 and 6 toward the MEA 4 side is secured, and fuel cell operation becomes possible. In this method, the mass transfer rate between the wetted surface (current collectors 5 and 6 surfaces) and the air to be supplied, and the maximum value that the current collectors 5 and 6 can hold are determined in advance. The present invention is also applicable when the shape of the internal base material or the base material specification of the reversible cell 1 changes.

  In the above example, the supply direction of the air supplied by the blower 46 is the direction from the flow port 14a to the flow port 14b, according to FIG. 1, but the air is supplied from only one direction and dried. In this case, there is a possibility that the upstream side (side near the circulation port 14a) is dried, but the downstream side (side near the circulation port 14b) is not yet dried. If air is supplied as it is, the upstream MEA, particularly the ion exchange membrane 4c, which is a polymer membrane, may be excessively dried and damaged.

  In order to prevent such a situation, for example, the valves 47a and 44a are opened, the other valves are closed, and the air supplied by the blower 46 is supplied from the flow port 14b to the flow path 14 in the reversible cell 1. The air supply direction may be reversed. This not only maximizes the amount of moisture transferred in the portion that is most desired to be dried, but also increases the amount of moisture in the air flow direction. Therefore, after the reverse rotation, the downstream side (the side closer to the circulation port 14a) ), The MEA 4 can be appropriately humidified to protect it, and as a result, the entire cell inner substrate can be uniformly dried.

  Further, in the flow shown in FIG. 4 described above, air is supplied for a specified time calculated by the calculation unit of the control device 71, but the reaction gas flow path on the fuel electrode side during the specified time. The low-humidity or non-humidified fuel gas may be supplied to the flow path 12 to perform a low-load fuel cell operation lower than the rating. As a result, although it is a low-load operation in the initial stage, the normal rated operation can be gradually performed, and the time for the dry operation without power generation is shortened, resulting in an efficient fuel cell as a whole. Driving can be carried out.

  In the example described above, the amount of water vapor transferred from the cell internal substrate to be transmitted to the supplied air is calculated in advance, and the residual moisture content of the cell internal substrate reaches a predetermined value based on the result. Although the drying time is calculated, the open circuit voltage of the reversible cell 1 may be measured, and the air may be supplied until the measurement result reaches a predetermined value. For the measurement of the open circuit voltage, a publicly known one used when judging deterioration of the catalyst can be used.

  By the way, the drying time of the base material inside the cell by the supply of air as described above for switching from the water electrolyzer operation to the fuel cell operation, that is, the time required for switching is based on the water held by the current collectors 5 and 6. Depends on the time to discharge outside. Therefore, the following method is effective for further shortening such switching time.

  First, by reducing the thickness of the current collectors 5 and 6, the amount of water that the current collectors 5 and 6 can hold is reduced, and the absolute amount to be discharged is reduced. By reducing the thickness of the MEA 4 and the current collectors 5 and 6, the diffusion rate of water from the fuel electrode side to the oxidant electrode side can be increased. FIG. 5 shows the difference in time required for drying when the thickness of the current collectors 5 and 6 is changed in the reversible cell having the same electrode area.

  In addition, the cross-sectional area of the flow paths 12 and 14 is reduced to increase the gas flow rate, or the rib portions of the flow paths 12 and 14 (portions where the separator 7 presses the current collectors 5 and 6) are minimized to directly connect with the air. The amount of moisture transferred to the air is maximized by increasing the area (current collector surface area) of the wetted part in contact. FIG. 5 shows the difference in drying time when the contact area between air and current collectors 5 and 6 is changed in a reversible cell having the same electrode area.

  In addition, the current collectors 5 and 6 are superhydrophilic processed to reduce the surface tension of the base material, thereby reducing the water retention capacity of the current collectors 5 and 6 themselves, and the drainage effect of residual water due to the weight of the water itself. Increase. At this time, in the case where a dense porous body made of, for example, titanium or carbon fiber is used for the current collectors 5 and 6, the current collector internal vertical direction is increased by a method such as increasing the porosity of the current collectors 5 and 6 themselves. The drainage effect can be further enhanced by securing the drainage channel. Preferably, the porosity of the current collectors 5 and 6 is 75% or more. Moreover, when using what formed the fine through-hole by the fine hole process in the titanium plate for the material of the electrical power collectors 5 and 6, an aperture ratio is good to be 50% or more. Thus, by increasing the effect ratio of natural drainage by its own weight, the amount of water discharged by mass transfer can be drastically reduced. As a result, the required switching time is greatly shortened and the required switching power such as the blower power of the blower 46 is reduced.

  Furthermore, the surface of the separator that forms the flow paths 12 and 14 is also superhydrophilic processed, thereby eliminating the need for purging for discharging residual water in the flow path portion at the initial switching time and further reducing the time required for switching. it can. In order to make full use of the drainage effect due to its own weight, the channels 12 and 14 as drainage routes should be vertically downward and unidirectional parallel flow, and the supply direction of air to be supplied should also flow vertically. Is the best.

  The present invention is useful when switching from water electrolysis operation to fuel cell operation in a reversible cell in which a solid polymer water electrolysis device and a fuel cell are integrated.

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 flowchart of switching operation of an embodiment. It is a graph which shows the time required for drying when the thickness of the current collector is made thinner than before and the contact area is increased.

Explanation of symbols

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, 47a, 51a, 52a, 61a, 62a Valve 53, 63 Pump 71 Controller 71 Power supply equipment

Claims (10)

By integrating the polymer electrolyte water electrolyzer and the fuel cell, a reversible cell that can be switched between water electrolyzer operation and fuel cell operation is switched from water electrolyzer operation to fuel cell operation. In the switching method,
After the operation of the water electrolysis apparatus, before performing the fuel cell operation, supply gas to the reaction gas flow path inside the reversible cell, and discharge the electrolyzed water remaining in the flow path from the inside of the cell,
Thereafter, air is supplied only to the reaction gas flow path on the side that becomes the oxidant electrode during operation of the fuel cell, and the cell internal substrate is dried. The method for switching operation of a reversible cell according to claim 1, wherein when air is supplied and the substrate inside the cell is dried, the supply direction of the air supplied to the reaction gas flow path is reversed during drying. . The amount of water vapor transferred from the cell internal substrate transmitted to the supplied air is calculated in advance, and the air is supplied until the residual moisture content of the cell internal substrate reaches a predetermined value based on the result. The operation switching method of the reversible cell according to claim 1 or 2, characterized in that. The amount of water vapor transferred from the cell internal substrate to be transferred to the supplied air is calculated in advance, and based on the result, the amount of water remaining in the cell internal substrate reaches a predetermined value before the fuel is reached. The reversible cell operation switching method according to claim 1 or 2, wherein a fuel gas is supplied to the reaction gas flow path on the pole side to perform a low-load fuel cell operation lower than the rated value. The method for switching operation of a reversible cell according to claim 1 or 2, wherein the open circuit voltage of the reversible cell is measured and the air is supplied until the result reaches a predetermined value. The air supplied to the reaction gas channel on the side serving as the oxidant electrode is exhausted from the reversible cell, and then dehumidified and used as the air supplied to the reaction gas channel on the side serving as the oxidant electrode. The operation switching method of the reversible cell according to any one of claims 1 to 5. The reversible cell operation switching method according to claim 1, wherein the current collector in the reversible cell is subjected to a hydrophilic treatment. The method for switching operation of a reversible cell according to any one of claims 1 to 7, wherein the surface of the separator forming the reaction gas flow path in the reversible cell is subjected to a hydrophilic treatment. The reversible cell operation switching method according to any one of claims 1 to 8, wherein the current collector in the cell internal substrate is constituted by a porous body, and the porosity thereof is 75% or more. The method of switching operation of a reversible cell according to any one of claims 1 to 8, wherein the current collector in the cell internal substrate is composed of a porous plate, and the aperture ratio is 50% or more.

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