JP4761107B2 - Fuel cell stack - Google Patents

Description

  The present invention relates to a fuel cell stack, and more particularly to a technique effective for improving warm-up performance at the time of starting.

  Fuel cells produce electricity through a reaction that produces water from the reaction of hydrogen and oxygen. Since this reaction is an exothermic reaction, there is almost no temperature drop in continuous operation such as a stationary type, and there is no fear that water vapor condenses and ice is generated. However, in the case of a fuel cell stack for in-vehicle use, there is no problem when traveling, but if the outside air temperature decreases when the vehicle is parked in a parking lot or a garage, water vapor may condense and become ice. In such a case, gas diffusion in the cell is partially blocked, and power generation cannot be performed or performance may be degraded. Further, partial gas shortage due to icing on the fuel electrode side also causes deterioration of the cell itself.

As a countermeasure, the fuel cell stack is warmed up by using thermal energy from combustion using a heater or fuel gas at start-up, or by flowing dry gas or heating with a heater etc. at the time of stoppage, Although it is conceivable to reduce the amount of moisture in the cell that causes the problem, in any case, energy consumption occurs, so that the energy efficiency of the entire fuel cell system is reduced. From such a background, a technique has been proposed in which a latent heat storage material is mixed into cooling water and the fuel cell stack is warmed up by heat generated by the phase change of the latent heat storage material (see, for example, Patent Document 1).
JP 2004-150336 A

  However, the technique described in Patent Document 1 is intended to absorb a large amount of heat more efficiently than the cooling system that absorbs heat from the fuel cell only by sensible heat, in other words, for the purpose of improving the cooling performance of the fuel cell. The amount of heat exchange is increased by changing the phase of a latent heat storage material that maintains fluidity even when solidified by a radiator or the like. For this reason, the latent heat storage material passes through the radiator even at the time of warming up, so that quick warming up cannot be performed. The above problems are not limited to icing, but also occur at low temperature start.

  Accordingly, an object of the present invention is to provide a fuel cell stack with sufficient warm-up performance without causing a decrease in energy efficiency.

  The present invention is a fuel cell stack including a cell stack in which a plurality of cells having a membrane-electrode assembly and separators disposed on both sides thereof are stacked, and holds a latent heat storage material that generates heat by phase change The heat storage material holder to be provided is in contact with the cell.

  In such a configuration, when the latent heat storage material generates heat, the generated heat is directly transferred from the heat storage material holder holding the latent heat storage material to the cell, so that the fuel cell stack can be quickly warmed up. Latent heat storage materials include, for example, sodium acetate trihydrate, disodium hydrogen phosphate decahydrate, sodium sulfate decahydrate, sodium thiosulfate pentahydrate, and calcium chloride hexahydrate. It is a heat storage material that can be supercooled, such as materials, and when the supercooled state is released and a phase change occurs from a liquid (including gel) to a solid, solidification heat is generated during the phase change. .

  The heat storage material holder may be configured to further hold a trigger that promotes a phase change of the latent heat storage material. As a trigger, what can give disturbances, such as a mechanical or electrical vibration and an impact, is employ | adopted with respect to a latent heat storage material.

  The heat storage material holder may be provided at an end portion in the cell stacking direction. With such a configuration, it is possible to selectively warm up the end cell that is most susceptible to the influence of a decrease in outside air temperature.

  The heat storage material holder may be conductive. In such a configuration, the degree of freedom of arrangement increases, and it becomes possible to provide the heat storage material holder inside the cell stack in the stacking direction.

  The heat storage material holder may have an output terminal. In such a configuration, it is possible to take out the total power of the fuel cell stack from the output terminal of the heat storage material holder, and the size of the fuel cell stack is reduced.

The heat storage material holder may have a medium flow path on a side surface thereof through which a part of a heat exchange medium used for heat exchange with the cell is circulated. In such a configuration, since the heat exchange medium heated by the heat generated by the latent heat storage material flows through the cells, it is possible to quickly warm up the cells that do not contact the heat storage material holder.

  The medium flow path may be configured to have a pressure loss comparable to that of a medium flow path interposed between adjacent cells. In such a configuration, even when the medium supply to the cells and the heat storage material holder is performed in parallel via, for example, a manifold, the heat exchange medium is evenly distributed to the cells and the heat storage material holder. Is possible.

  The heat storage material holder may have a heat insulating property on the surface side not in contact with the cell. In such a configuration, the heat release by the latent heat storage material is effectively suppressed to the outside, and the heat transfer efficiency to the cell is improved.

  The fuel cell stack of the present invention may have a control unit that promotes a phase change of the latent heat storage material by the trigger at the start. With such a configuration, warm-up at start-up that requires ice melting can be reliably performed.

  The controller may be configured to prompt the phase change only when the stack temperature is equal to or lower than a predetermined value. In such a configuration, even at the time of start-up, it is possible to selectively perform warm-up only when truly warm-up is necessary.

  According to the fuel cell stack of the present invention, when the latent heat storage material generates heat, this thermal energy is directly transferred from the heat storage material holder holding the latent heat storage material to the cell. The fuel cell stack can be quickly warmed up without consuming extra energy to remove the internal moisture. Therefore, it is possible to provide a fuel cell stack that does not cause a decrease in energy efficiency and has sufficient warm-up performance.

(First embodiment)
FIG. 1 is a system configuration diagram showing a main part of a fuel cell system including a fuel cell stack according to the first embodiment of the present invention. This fuel cell system is particularly suitable for use in an in-vehicle power generation system of a fuel cell vehicle, but can also be applied to, for example, a stationary power generation system.

  Air as an oxidant gas is supplied to the cathode of the fuel cell stack 10, and the exhaust from the cathode is discharged to the outside. On the other hand, hydrogen as a fuel gas is supplied to the anode of the fuel cell stack 10 and exhaust (off gas) from the anode circulates again through the fuel cell stack 10, but is appropriately discharged to the outside depending on the impurity concentration in the off gas ( Purged).

  In addition to these reaction gases (hydrogen and air), the cooling water (heat exchange medium) is also supplied to the fuel cell stack 10. The cooling water flows through the cooling water system 21 by the pump 20, and is cooled (heat exchange) by the radiator 22 during normal operation, and then supplied to the fuel cell stack 10. Temperature sensors T1 and T2 for detecting the coolant temperature are provided on the fuel cell stack inlet side and outlet side of the coolant system 21.

  The cooling water system 21 is branched into two upstream of the radiator 22, one of which bypasses the radiator 22 and is connected to flow path switching means such as a rotary valve 23 provided downstream of the radiator 22. The bypass pipe 21a is used. With this configuration, in a predetermined case (for example, at the time of starting, etc.), the cooling water flowing out from the fuel cell stack 10 can be supplied to the fuel cell stack 10 as it is without being cooled (heat exchange) by the radiator 22. It has become.

  As shown in FIG. 2, the fuel cell stack 10 includes a cell stack (hereinafter referred to as a cell stack 11) that generates electricity by an electrochemical reaction between hydrogen and oxygen, and both end surfaces of the cell stack 11 (of the fuel cell stack). A heat storage material holding body 13 provided in contact with the end cell 12 of the cell stack 11.

  The heat storage material holder 13 is fastened to the cell stack 11 together with the power generation cells, and is a part of the fuel cell stack 10 in the cell stacking direction (in this embodiment, an end, but other embodiments described later) As well as inside.).

  Each cell has a membrane-electrode assembly (hereinafter referred to as “MEA”) sandwiched on both sides by a separator having a fuel gas (hydrogen etc.) channel and an oxidant gas (oxygen etc.) channel. is there. The MEA was generated at the reaction electrode by diffusing and permeating the fuel gas or the oxidant gas on both sides of the joined body of the electrolyte membrane that does not transmit electrons and permeates ions and the reaction electrode that holds both sides of the electrolyte membrane. It is sandwiched by a diffusion layer that can transmit electrons.

  As shown in FIGS. 3 and 4, the heat storage material holding body 13 has a flat outer shape having a predetermined thickness, and includes a hollow box-shaped main body portion 31 and a plurality of inner space portions of the main body portion 31. A plurality of ribs 32 that are divided into heat storage material filling spaces, and a latent heat storage material 33 that is filled in each heat storage material filling space and generates heat due to a phase change, and a trigger 34 that promotes a phase change of the latent heat storage material 33 Are integrally provided (FIG. 2).

  The rib part 32 is fastened to the cell stack 11 together with the first effect that the cross-sectional area of the heat storage material holder 13 can be increased and the electrical resistance of the heat storage material holder 13 can be reduced. The second effect that the strength to resist the fastening force at the time can be ensured, and the surface area related to the heat exchange with the cell can be increased, and the rapid heat exchange (warming up) can be realized. There is a third effect.

  As for the third effect of the rib portion 32, the main body portion is not necessarily configured to interconnect the plate-like members opposed to each other in the cell stacking direction in the main body portion 31 like the rib portion 32 of the present embodiment. If it is the structure which can make the inner surface of 31 uneven | corrugated (fin shape), for example, it will stand up from one said plate-shaped member, and it will extend to the other plate-shaped member side, but this other plate-shaped member The structure which has not reached (contact | abutted) may be sufficient.

  The main body portion 31 and the rib portion 32 of the heat storage material holder 13 preferably have thermal conductivity and electrical conductivity, such as SUS (stainless steel) or Fe, and more preferably, for example, carbon or titanium. Like a compound, it is preferable to have corrosion resistance (acid resistance) against the latent heat storage material 33 in addition to the thermal conductivity and electrical conductivity. However, this corrosion resistance may be imparted by subjecting the main body portion 31 and the rib portion 32 made of SUS, Fe, or the like to surface treatment.

  Further, by filling the latent heat storage material 33 in a bag made of a corrosion-resistant resin such as polyethylene, the main body portion 31 and the rib portion 32 made of SUS, Fe, etc., and the latent heat storage material 33 may not be in direct contact with each other. Good.

  The latent heat storage material 33 is sodium acetate trihydrate, disodium hydrogen phosphate decahydrate, sodium sulfate decahydrate, sodium thiosulfate pentahydrate, and calcium chloride hexahydrate. For example, when a disturbance such as vibration or shock is given by a trigger 34 due to mechanical or electrical factors, the supercooled state is released and the liquid (including gel) is released. It causes a phase change to a solid and generates heat of solidification during the phase change.

  As the configuration of the trigger 34, for example, a coil, a plunger disposed inside the coil so as to be able to advance and retract, an urging means such as a spring for urging the plunger in the forward direction, and energization to the coil are controlled. It is possible to adopt a configuration including a control means. In this configuration, before the trigger operation, the plunger is retracted in a direction against the urging force of the spring (a direction away from the heat storage material holder 13) by an electromagnetic force generated by energizing the coil, and the coil energization is cut during the trigger operation. By releasing the electromagnetic force, the plunger can be driven in the direction of the urging force of the spring to give a mechanical shock to the heat storage material holder 13.

  The control unit 100 (FIG. 1) is configured by a control computer system, and includes a required load such as an accelerator opening signal of a vehicle (not shown), and sensors (pressure sensors, temperature sensors T1, T2) provided in each part of the fuel cell system. Control information from each device (air compressor, pump 20 etc.), and controls the operation of valves (rotary valve 23 etc.) and motors in each part of the system.

  For example, when the temperature of the fuel cell stack 10 (stack temperature) is equal to or lower than a predetermined temperature at the time of start-up, the control unit 100 operates the trigger 34 to cause mechanical vibration, impact, etc., to the latent heat storage material 33. To promote the phase change (liquid → solid) of the latent heat storage material 33 and generate heat of solidification.

  Next, the operation of the fuel cell system having the above configuration will be described. At the start, first, the temperature of the fuel cell stack 10 (stack temperature) is detected. In the present embodiment, the coolant temperature detected by the temperature sensor T2 disposed on the fuel cell stack outlet side of the coolant system 21 is regarded as the stack temperature. In the case of a low temperature start when the stack temperature is equal to or lower than a predetermined temperature (for example, 5 ° C.), the trigger 34 is actuated to give mechanical vibration and impact to the latent heat storage material 33.

  Then, the supercooled state of the latent heat storage material 33 is released, and the latent heat storage material 33 undergoes a phase change from a liquid to a solid, and generates solidification heat along with the phase change. The generated solidification heat is directly transferred to the end cells 12 of the cell stack 11 in contact with the heat storage material holder 13 via the heat storage material holder 13 holding the latent heat storage material 33. That is, the trigger 34 is activated only when the stack temperature is equal to or lower than a predetermined value, and the phase change of the latent heat storage material 33 is promoted, so that it is selected only at the time of start-up and when truly warming up is required. Thus, the warm-up of the fuel cell stack 10 is started.

  Further, in the present embodiment, as shown in the experimental results of FIG. 7, the end cell 12 that is most susceptible to the influence of a decrease in outside air temperature can be selectively warmed up. It is possible to obtain.

  In FIG. 7, the solid line is the first embodiment of the present invention using the heat storage holder 13 shown in FIGS. 3 and 4, and the broken line is a comparative example. In the comparative example (broken line), power generation was first performed until the end cell 12 reached 80 ° C., and after power generation was stopped, the cell was left in a constant temperature bath in a 0 ° C. environment for 4 hours. Next, the current was gradually inserted and fixed at a constant current for 30 seconds, and then the cell voltage of each cell was measured.

  On the other hand, in the first example (solid line), power generation is performed until the end cell 12 reaches 80 ° C., and the process from power generation stop to standing in a thermostatic chamber for 4 hours in a constant temperature bath is the above-described comparative example. However, after that, the trigger 34 is operated to cause a phase change in the latent heat storage material 33. In this example, sodium acetate trihydrate was used as the latent heat storage material 33. Next, as in the comparative example described above, the current was gradually inserted and fixed at a constant current for 30 seconds, and then the cell voltage of each cell was measured.

  As is clear from FIG. 7, in the comparative example (broken line), the cell voltage of the cell located on the left end side and the right end side of the cell stack 11, that is, the left and right end cells 12 and the cells in the vicinity thereof is the cell stack 11. It can be seen that, although it is extremely lower than that of the central portion of the cell and its neighboring cells, it is increased in the first embodiment (solid line). The cell voltage difference between them is a maximum of 15%. That is, according to the fuel cell stack 10 of the first embodiment, it was confirmed that the end cells 12 can be quickly warmed up.

(Second Embodiment)
As shown in FIG. 5, the heat storage material holder 41 according to the present embodiment has a meandering concave groove on one side surface (hereinafter referred to as an inner end surface 41 </ b> A) on the side in contact with the cell stack 11 (inside the cell stacking direction). A refrigerant flow path (medium flow path) 42 is formed. The refrigerant flow path 42 is formed, for example, to have the same form as the separator refrigerant flow path so as to have a pressure loss comparable to a refrigerant flow path (hereinafter referred to as a separator refrigerant flow path) formed in a separator (not shown). Yes.

  Cooling water flowing through the cooling water system 21 is introduced into the fuel cell stack 10 from the inlet side manifold 15, and flows in parallel through each cell of the cell stack 11 and both the heat storage material holders 13, 13, so that the outlet side manifold. 16 is derived from the fuel cell stack 10. At this time, since the refrigerant flow path 42 is formed to have the same pressure loss as the separator refrigerant flow path, the cooling water introduced into the fuel cell stack 10 from the inlet side manifold 15 is supplied to each cell and both heat storage material holders. 13 and 13 are equally distributed.

  If the flow path in the rotary valve 23 is switched in advance so that the cooling water circulates on the bypass pipe 21a side, in other words, bypasses the radiator 22, the refrigerant flow path of the heat storage material holder 13 is circulated. Since the cooling water heated in the meantime is supplied to each cell of the fuel cell stack 10 via the inlet side manifold 15 without being cooled by the radiator 22, as shown in FIG. It is possible to quickly warm up the cells not in contact with 33, that is, the cells on the inner side of the end cells 12 in the cell stacking direction.

  In FIG. 8, a solid line is the second embodiment of the present invention using the heat storage material holder 41 shown in FIG. 5, and a broken line is a comparative example. In the comparative example (broken line), power generation was first performed until the end cell 12 reached 80 ° C., and after power generation was stopped, the cell was left in a constant temperature bath in a 0 ° C. environment for 4 hours. Next, the current was gradually inserted and fixed at a constant current for 30 seconds, and then the cell voltage of each cell was measured.

  On the other hand, in the second embodiment (solid line), power generation is performed until the end cell 12 reaches 80 ° C., and the process from power generation stop to standing in a constant temperature bath for 4 hours in the constant temperature bath is the above-described comparative example. However, after that, the trigger is operated to cause a phase change in the latent heat storage material 33. In this example, sodium acetate trihydrate was used as the latent heat storage material 33. Next, as in the comparative example described above, the current was gradually inserted and fixed at a constant current for 30 seconds, and then the cell voltage of each cell was measured.

  As is clear from FIG. 8, in the comparative example (broken line), the cell voltage of the cells located on the left end side and the right end side of the cell stack 11, that is, the left and right end cells 12 and the cells in the vicinity thereof is It can be seen that, although it is extremely lower than that of the central portion of the cell and its neighboring cells, it is increased in the second embodiment (solid line). The cell voltage difference between them is a maximum of 9%. That is, in the second embodiment of the present invention, performance degradation due to the low temperature in the end cell 12 is suppressed.

  Furthermore, in the second embodiment, the cell voltage also rises for the cells closer to the center than the end cells 12. That is, according to the fuel cell stack 10 of the second embodiment, it was confirmed that not only the end cells 12 but also the cells inside the end cells 12 can be quickly warmed up.

(Third embodiment)
In addition to the configuration of the second embodiment shown in FIG. 5, the heat storage material holding body 51 according to the present embodiment has another side surface (hereinafter referred to as the cell stacking direction outer side) opposite to the inner end surface 41 </ b> A having the refrigerant flow path 42 (hereinafter, cell stacking direction). The output terminal 52 is provided on the outer end surface. The output terminal 52 protrudes in a direction orthogonal to the cell stacking direction (upward along the outer end surface in FIG. 6). According to such a configuration, since the total power of the fuel cell stack 10 can be taken out from the output terminal 52 of the heat storage material holder 51, the size of the fuel cell stack 11 can be reduced.

(Other embodiments)
The present invention can be applied with various modifications other than the above embodiment. For example, in addition to the above-described configuration, the trigger may include a vibrator such as a piezo element, a voltage applying unit that applies a voltage to the vibrator, and a control unit that controls the applied voltage. In this configuration, a potential difference is applied to the vibrator, and mechanical vibration can be continuously applied to the latent heat storage material 33 by the vibrating vibrator.

  Further, the trigger may be configured to include an electrode disposed in the latent heat storage material 33 and a control unit that controls energization to the electrode. In this configuration, an electrical shock can be applied to the latent heat storage material 33 by energizing the electrodes.

  The heat storage material holders 13... Are provided by providing heat insulating materials on the outer peripheral surface and outer end surface of the heat storage material holders 13, or inside the outer peripheral wall part and outer end wall part of the heat storage material holders 13. It is good also as a structure provided with heat insulation in the surface side which does not contact the cell laminated body (cell) 11 by forming a some void | hole part. According to such a configuration, since the heat generated by the latent heat storage material 33 is effectively suppressed from being released to the outside, the heat transfer efficiency to the cell is improved, and warm-up can be performed in a shorter time.

  Moreover, when the heat storage material holders 13 are conductive as in the above-described embodiment, the arrangement of the heat storage material holders 13 is a position in contact with the end cell 12, that is, a cell of the cell stack 11. Without being limited to the end portion in the stacking direction, it can be provided inside the cell stack 11 (in the cell stacking direction). That is, there is no restriction on arrangement, and the heat storage material holder 13 can be arranged at a desired position.

  Furthermore, instead of the configuration in which the cooling water supplied to the fuel cell stack 10 is introduced in parallel to each cell of the cell stack 11 and the two heat storage material holders 13, 13. The cooling water may be introduced only into 13, 13... And the cooling water derived from the heat storage holders 13, 13... May be introduced into each cell in parallel. According to such a configuration, since each cell is warmed up from the first cooling water circulation, it is possible to warm up in a shorter time.

  In the above-described embodiment, the refrigerant flow path (separator refrigerant flow path) formed in the separator constituting a part of the cell is illustrated as the medium flow path interposed between the cells adjacent to each other. For example, a medium flow path formed in a plate-like body (cooling plate) provided between cells without forming a part of the cells, in other words, may be provided separately from the cells that generate power.

(Fuel cell vehicle)
According to the fuel cell vehicle equipped with the fuel cell stack 10 of any one of the above embodiments, even if the outside air temperature decreases when the vehicle is parked in a parking lot or a garage, it is possible to warm up without using a heater or fuel gas. Therefore, it is not necessary to consume extra electric power at the time of starting, and a decrease in energy efficiency can be suppressed. In addition, since starting from an icing state can be avoided, it is possible to prevent cell deterioration due to power generation failure, power generation failure, and lack of gas.

The system block diagram which shows the principal part of the fuel cell system provided with the fuel cell stack which concerns on 1st Embodiment of this invention. The front view of the fuel cell stack shown in FIG. The perspective view of the thermal storage material holding body shown in FIG. The longitudinal cross-sectional view of the thermal storage material holding body. The perspective view of the thermal storage material holding body in the fuel cell stack which concerns on 2nd Embodiment of this invention. The perspective view of the thermal storage material holding body in the fuel cell stack which concerns on 3rd Embodiment of this invention. The cell voltage measurement result which shows the effect of 1st Example of this invention. The cell voltage measurement result which shows the effect of 2nd Example of this invention.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 10 ... Fuel cell stack, 11 ... Cell laminated body, 12 ... End cell, 13, 41, 51 ... Heat storage material holder, 33 ... Latent heat storage material, 34 ... Trigger, 42 ... Refrigerant flow path (medium flow path), 52 ... Output terminal, 100 ... Control unit, T1, T2 ... Temperature sensor

Claims (8)

A fuel cell stack including a cell stack in which a plurality of cells having a membrane-electrode assembly and separators disposed on both sides thereof are stacked,
A heat storage material holding body that holds a latent heat storage material that generates heat due to a phase change is provided in contact with the cell,
The heat storage material holding body has a medium flow path through which a part of a heat exchange medium used for heat exchange with the cell is circulated, and the heat exchange medium is connected to the heat storage material holding body and the cell. Can be supplied in parallel,
The fuel cell stack , wherein the medium flow path is formed to have a pressure loss comparable to a medium flow path interposed between adjacent cells .   The fuel cell stack according to claim 1, wherein the heat storage material holder further holds a trigger that promotes a phase change of the latent heat storage material.   The fuel cell stack according to claim 1 or 2, wherein the heat storage material holder is provided at an end portion in a cell stacking direction.   The fuel cell stack according to claim 1, wherein the heat storage material holder has conductivity.   The fuel cell stack according to claim 1, wherein the heat storage material holder has an output terminal. The fuel cell stack according to any one of claims 1 to 5 , wherein the heat storage material holder has a heat insulating property on a surface side not in contact with the cell. The fuel cell stack according to any one of claims 1 to 6 , further comprising a control unit that promotes a phase change of the latent heat storage material by a trigger at the start. The fuel cell stack according to claim 7 , wherein the control unit prompts a phase change only when the stack temperature is equal to or lower than a predetermined value.

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