JP5591315B2 - Operation method of fuel cell - Google Patents

Description

  The present invention provides an operation of a fuel cell having an electrolyte / electrode structure in which electrodes are disposed on both sides of an electrolyte, and a separator, and a fuel gas channel and an oxidant gas channel set in a counterflow are formed. Regarding the method.

  For example, a solid polymer fuel cell employs a solid polymer electrolyte membrane made of a polymer ion exchange membrane. This fuel cell has an electrolyte membrane / electrode structure (MEA) in which an anode electrode and a cathode electrode each having an electrode catalyst (electrode catalyst layer) and porous carbon (gas diffusion layer) are disposed on both sides of the electrolyte membrane. A power generation cell sandwiched between separators (bipolar plates) is formed. Usually, a predetermined number of power generation cells are stacked to be used as, for example, an in-vehicle fuel cell stack.

  In a fuel cell, a fuel gas flow channel (hereinafter also referred to as a reaction gas flow channel) for flowing fuel gas to the anode electrode with an MEA sandwiched in the plane of the separator and an oxidant gas for flowing the cathode electrode to the cathode electrode An oxidant gas channel (hereinafter also referred to as a reaction gas channel) is provided. Further, for each power generation cell or each of the plurality of power generation cells, a cooling medium flow path for flowing a cooling medium is provided along the electrode surface direction between adjacent separators.

  In this type of fuel cell, it is necessary to moisturize the electrolyte membrane in order to ensure good ion conductivity. For this reason, a method is employed in which an oxidizing gas (for example, air) or a fuel gas (for example, hydrogen gas), which is a reactive gas, is humidified and supplied to the fuel cell.

  At this time, moisture for humidification may be liquefied without being absorbed by the electrolyte membrane and stay in the reaction gas flow path. On the other hand, in the fuel cell, generated water is generated at the cathode electrode by a power generation reaction, and the generated water is back-diffused through the electrolyte membrane in the anode electrode. For this reason, moisture tends to condense and stay in the reaction gas channel, and flooding due to condensed water may occur.

  Thus, for example, a method for humidifying a solid polymer electrolyte fuel cell disclosed in Patent Document 1 is known. In this humidification method, an anode gas and a cathode gas as reaction gases are made to flow opposite to each other, and a solid polymer electrolyte membrane is passed from one of the reaction gases flowing opposite to the other in the upstream and downstream portions of the reaction gas channel. It is characterized in that the solid polymer electrolyte membrane is humidified by the fuel cell reaction product water by moving the water through the water.

  For this reason, the fuel cell reaction product water enables self-humidification without supplying water from the outside, which is rational and simple as a humidification system.

JP 2002-25584 A

  However, in a fuel cell that employs a counter flow of reaction gas, the moisture content distribution during power generation tends to increase at the power generation surface center side while drying at both ends of the power generation surface where reaction gas inlets are provided. ing. Further, this tendency is not affected by a change in the humidified state of the reaction gas that is humidified in advance (increase / decrease in input humidity).

  Accordingly, there is a problem that the water content increases and condensation occurs on the power generation surface center side, and stagnant water is generated. On the other hand, at both ends of the power generation surface, there is a problem that the water content is reduced and the electrolyte membrane is dried.

  The present invention solves this type of problem, and it is possible to make the water distribution in the power generation surface uniform by a simple process and to maintain a good power generation performance. The purpose is to provide.

  The present invention has an electrolyte membrane / electrode structure in which electrodes are disposed on both sides of an electrolyte membrane, and a separator, and fuel gas is circulated along the power generation surface between the one electrode and the separator. A fuel gas flow path is formed, and an oxidant gas flow path for flowing an oxidant gas along the power generation surface is formed between the other electrode and the separator, and the fuel gas flow path The oxidant gas flow path relates to a method of operating a fuel cell in which the respective flow directions are set to counterflows opposite to each other.

  In this operation method, the supply amount of the fuel gas supplied to the fuel gas passage is repeatedly increased and decreased, while the supply amount of the oxidant gas supplied to the oxidant gas passage is repeatedly increased and decreased. At this time, the increase in the supply amount of the fuel gas and the increase in the supply amount of the oxidant gas are performed alternately.

  Further, in this operation method, when it is determined that water is retained in the fuel gas channel or the oxidant gas channel, or when it is determined that the electrolyte membrane is dry, the supply amount of the fuel gas It is preferable to repeat the increase and decrease and the increase and decrease in the supply amount of the oxidant gas, respectively.

  Further, in this operation method, the total stoichiometric ratio of the oxidant gas and the fuel gas is preferably the same as that during normal operation.

  According to the present invention, when the supply amount of the fuel gas is increased, the supply amount of the oxidant gas is decreased, while when the supply amount of the oxidant gas is increased, the supply amount of the fuel gas is decreased. Has been. For this reason, the area | region where required water content is obtained can be increased over the whole electric power generation surface. In addition, since the amount of stagnant water is reduced, the power generation stability is improved, and the elution components from the MEA or the separator are reduced to improve the durability.

  As a result, the water distribution in the power generation surface can be made uniform by a simple process, and good power generation performance can be maintained.

1 is an explanatory diagram of a schematic configuration of a fuel cell system to which an operation method according to an embodiment of the present invention is applied. It is a disassembled perspective explanatory drawing of the fuel cell which comprises the said fuel cell system. It is a flowchart explaining the said driving | running method. It is a timing chart explaining flow control of fuel gas and oxidant gas. It is explanatory drawing of the moisture content at the time of oxidant gas flow amount being increased, and fuel gas flow rate being reduced. It is explanatory drawing of the moisture content at the time of the said oxidant gas flow rate being reduced while the said fuel gas flow rate is increased. It is explanatory drawing of the moisture content of the electric power generation surface whole surface by performing flow control. It is a timing chart explaining other flow control of fuel gas and oxidant gas. It is explanatory drawing of stoichiometry at the time of applying to normal driving | operation.

  As shown in FIG. 1, a fuel cell system 10 to which an operation method according to an embodiment of the present invention is applied is mounted on a fuel cell vehicle (not shown) such as a fuel cell electric vehicle, for example.

  The fuel cell system 10 includes a fuel cell stack 12, an oxidant gas supply device 14 for supplying an oxidant gas to the fuel cell stack 12, a fuel gas supply device 16 for supplying a fuel gas to the fuel cell stack 12, And a controller (control device) 18 that controls the entire fuel cell system 10. Although not shown, the fuel cell stack 12 is connected to a cooling medium supply device for circulatingly supplying the cooling medium.

  The fuel cell stack 12 is configured by stacking a plurality of fuel cells 20. As shown in FIG. 2, each fuel cell 20 includes an electrolyte membrane / electrode structure 22, and a first metal separator 24 and a second metal separator 26 that sandwich the electrolyte membrane / electrode structure 22. The first metal separator 24 and the second metal separator 26 are formed by, for example, pressing a corrugated metal sheet, a stainless steel sheet, an aluminum sheet, a plated steel sheet, or a thin metal sheet having a surface treatment for corrosion prevention on the metal surface thereof. However, for example, a carbon separator may be used.

  The electrolyte membrane / electrode structure 22 includes, for example, a solid polymer electrolyte membrane 28 in which a perfluorosulfonic acid thin film is impregnated with water, and an anode electrode 30 and a cathode electrode 32 sandwiching the solid polymer electrolyte membrane 28. Prepare. The solid polymer electrolyte membrane 28 has a larger planar dimension than the anode electrode 30 and the cathode electrode 32.

  The electrolyte membrane / electrode structure 22 may constitute a step MEA in which the anode electrode 30 and the cathode electrode 32 are set to have different plane dimensions.

  The anode electrode 30 and the cathode electrode 32 are formed by uniformly applying a gas diffusion layer (not shown) made of carbon paper or the like and porous carbon particles carrying a platinum alloy on the surface thereof to the surface of the gas diffusion layer. And an electrode catalyst layer (not shown) to be formed. The electrode catalyst layers are formed on both surfaces of the solid polymer electrolyte membrane 28, and a power generation surface is formed in a region where the pair of electrode catalyst layers overlap.

  One end edge of the fuel cell 20 in the direction of arrow B (the horizontal direction in FIG. 2) communicates with each other in the direction of arrow A, which is the stacking direction, and oxidant gas, for example, oxygen-containing gas (hereinafter also referred to as air). ) For supplying an oxidant gas supply passage 34a for supplying a cooling medium, a cooling medium supply passage 36a for supplying a cooling medium, and a fuel gas, for example, a hydrogen-containing gas (hereinafter also referred to as hydrogen gas). The fuel gas discharge communication holes 38b are arranged in the arrow C direction (vertical direction).

  The other end edge of the fuel cell 20 in the direction of arrow B communicates with each other in the direction of arrow A, a fuel gas supply communication hole 38a for supplying fuel gas, and a cooling medium discharge communication hole for discharging the cooling medium. 36 b and an oxidant gas discharge communication hole 34 b for discharging the oxidant gas are arranged in the arrow C direction.

  On the surface 24 a of the first metal separator 24 facing the electrolyte membrane / electrode structure 22, for example, a linear (or wavy) fuel gas passage 40 extending in the direction of arrow B is formed. The fuel gas flow path 40 communicates with the fuel gas supply communication hole 38a and the fuel gas discharge communication hole 38b.

  On the surface 26 a of the second metal separator 26 facing the electrolyte membrane / electrode structure 22, for example, a linear (or wavy) oxidant gas flow path 42 extending in the direction of arrow B is provided. The oxidant gas passage 42 communicates with the oxidant gas supply communication hole 34a and the oxidant gas discharge communication hole 34b. The fuel gas flow path 40 and the oxidant gas flow path 42 are set to counterflows in which the flow directions are opposite to each other.

  A cooling medium flow path 44 communicating with the cooling medium supply communication hole 36a and the cooling medium discharge communication hole 36b is formed between the surface 24b of the first metal separator 24 and the surface 26b of the second metal separator 26 adjacent to each other. Is done. The cooling medium flow path 44 is formed by overlapping the back surface shape of the fuel gas flow path 40 and the back surface shape of the oxidant gas flow path 42. The cooling medium flow direction of the cooling medium flow path 44 is set to the same direction as the oxidant gas flow direction of the oxidant gas flow path 42.

  The first seal member 48 is integrated with the surfaces 24 a and 24 b of the first metal separator 24 around the outer peripheral end of the first metal separator 24. The second seal member 50 is integrated with the surfaces 26 a and 26 b of the second metal separator 26 around the outer peripheral end of the second metal separator 26.

  The first seal member 48 and the second seal member 50 include, for example, EPDM, NBR, fluorine rubber, silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber, styrene rubber, chloroprene or acrylic rubber, and cushioning materials. Alternatively, an elastic seal member such as a packing material is used.

  As shown in FIG. 1, in the fuel cell stack 12, end plates 52a and 52b are arranged at both ends of the plurality of fuel cells 20 in the stacking direction. Although not shown, a tightening load is applied between the end plates 52a and 52b in the stacking direction via a tie rod or a casing including the end plates 52a and 52b.

  The end plate 52a is provided with an oxidant gas inlet manifold 54a for supplying an oxidant gas and an oxidant gas outlet manifold 54b for discharging the oxidant gas, which communicate with each other in the stacking direction of the fuel cells 20.

  The end plate 52b is provided with a fuel gas inlet manifold 56a for supplying a fuel gas and a fuel gas outlet manifold 56b for discharging the fuel gas, which communicate with each other in the stacking direction of the fuel cells 20.

  The oxidant gas supply device 14 includes an air pump 60 that compresses and supplies air from the atmosphere, and the air pump 60 is disposed in an air supply channel (oxidant gas supply channel) 62. The air supply flow path 62 communicates with the oxidant gas inlet manifold 54 a of the fuel cell stack 12.

  The oxidant gas supply device 14 includes an air discharge passage (oxidant gas discharge passage) 64 communicating with the oxidant gas outlet manifold 54b. The air discharge channel 64 is provided with a back pressure control valve 66 with an adjustable opening for adjusting the pressure of air supplied from the air pump 60 through the air supply channel 62 to the fuel cell stack 12.

  The fuel gas supply device 16 includes a hydrogen tank 70 that stores high-pressure hydrogen. The hydrogen tank 70 communicates with the fuel gas inlet manifold 56 a of the fuel cell stack 12 through a hydrogen supply channel (fuel gas supply pipe) 72.

  In the hydrogen supply flow path 72, a pressure reducing valve 74, a shutoff valve 76, and an ejector 78 are provided. The ejector 78 supplies the hydrogen gas supplied from the hydrogen tank 70 to the fuel cell stack 12 through the hydrogen supply flow path 72 and exhaust gas containing unused hydrogen gas that has not been used in the fuel cell stack 12. Then, the gas is sucked from the hydrogen circulation path 80 and supplied again as fuel gas to the fuel cell stack 12.

  An off gas passage 82 communicates with the fuel gas outlet manifold 56b. A hydrogen circulation path 80 communicates with the off gas flow path 82, and a purge valve (for example, an on-off valve) 84 is connected to the off gas flow path 82.

  The controller 18 detects that the staying water detector 86 for detecting that water is staying in at least one of the fuel gas passage 40 or the oxidant gas passage 42 and the solid polymer electrolyte membrane 28 are dry. And a film dryness detection unit 88 for detection. The staying water detection unit 86 detects, for example, at least one of the pressure loss of the fuel gas passage 40 or the pressure loss of the oxidant gas passage 42, and determines whether or not the generated water has stayed based on the detected pressure loss. to decide. Specifically, when the generated water stays, the pressure loss increases. The membrane dry detection unit 88 determines whether or not the solid polymer electrolyte membrane 28 is dry, for example, by measuring the impedance of the fuel cell stack 12. Specifically, when the solid polymer electrolyte membrane 28 is dried, the impedance increases.

  The operation of the fuel cell system 10 configured as described above will be described below.

  First, the case where the fuel cell system 10 is normally operated will be described. In the normal operation, the amount of the reaction gas obtained by multiplying the amount of the oxidant gas and the amount of the fuel gas required based on the current value taken out from the fuel cell stack 12 by a predetermined stoichiometric ratio is set. Driving under conditions.

  Therefore, air is sent to the air supply flow path 62 via the air pump 60 constituting the oxidant gas supply device 14. Air is supplied to the oxidant gas inlet manifold 54 a of the fuel cell stack 12. As shown in FIG. 2, this air is introduced into the oxidant gas flow path 42 of the second metal separator 26 from the oxidant gas supply communication hole 34a. The air moves in the direction of arrow B and is supplied to the cathode electrode 32 of the electrolyte membrane / electrode structure 22.

  On the other hand, as shown in FIG. 1, in the fuel gas supply device 16, the hydrogen gas decompressed by the pressure reducing valve 74 from the hydrogen tank 70 is supplied to the hydrogen supply flow path 72 by opening the shutoff valve 76. . This hydrogen gas is supplied to the fuel gas inlet manifold 56 a of the fuel cell stack 12 through the hydrogen supply flow path 72.

  As shown in FIG. 2, the hydrogen gas supplied into the fuel cell stack 12 is introduced into the fuel gas flow path 40 of the first metal separator 24 through the fuel gas supply communication hole 38a. The hydrogen gas moves in the direction of arrow B (counterflow with air) and is supplied to the anode electrode 30 of the electrolyte membrane / electrode structure 22.

  Therefore, in each electrolyte membrane / electrode structure 22, the oxidant gas (air) supplied to the cathode electrode 32 and the fuel gas (hydrogen gas) supplied to the anode electrode 30 are electrochemically generated in the electrode catalyst layer. It is consumed by the reaction to generate electricity.

  The used air (exhaust air) is discharged from the oxidant gas outlet manifold 54b to the air discharge passage 64. This discharged air is discharged through the back pressure control valve 66. The used hydrogen gas is sucked into the ejector 78 from the fuel gas outlet manifold 56b through the hydrogen circulation path 80, and supplied again to the fuel cell stack 12 as fuel gas.

  In the cooling medium supply device (not shown), the cooling medium is supplied to the cooling medium supply communication hole 36a of each fuel cell 20 of the fuel cell stack 12, as shown in FIG. This cooling medium is introduced into a cooling medium flow path 44 formed between the fuel cells 20. The cooling medium moves in the direction of arrow B (the same direction as the flow direction of the oxidant gas) to cool the fuel cell 20, and is then discharged into the cooling medium discharge communication hole 36b.

  Next, an operation method according to an embodiment of the present invention will be described below along the flowchart shown in FIG. In the present embodiment, the total stoichiometric ratio may be the same as that in the normal operation.

  When the operation of the fuel cell system 10 is started (step S1), the process proceeds to step S2, where detection by the stagnant water detection unit 86 and the membrane drying detection unit 88 is performed. The staying water detection unit 86 detects at least one of the pressure loss of the fuel gas passage 40 or the pressure loss of the oxidant gas passage 42. In the fuel gas flow channel 40 and the oxidant gas flow channel 42, when the generated water is retained and the retained water is generated, the accumulated water causes clogging of the flow channel and the pressure loss increases. Therefore, based on the detected pressure loss, it is determined whether or not the generated water has accumulated.

  The membrane dry detection unit 88 detects the humidity of the solid polymer electrolyte membrane 28 by, for example, measuring the impedance of the fuel cell stack 12. Then, based on the detected humidity, it is determined whether or not the solid polymer electrolyte membrane 28 is dry.

  In step S2, if at least retention of generated water (excessive water generated) is detected, or if drying of the solid polymer electrolyte membrane 28 (membrane drying) is detected (YES in step S2), the process proceeds to step S3. The gas flow rate control is performed. This gas flow rate control is performed along the timing shown in FIG.

  Specifically, in the fuel gas supply device 16, by adjusting the opening of the pressure reducing valve 74, the supply amount of the fuel gas supplied to the fuel gas flow path 40 (both supply pressure and supply flow rate, or both) Increase and decrease may be repeated in a substantially pulsed (or wavy) manner. As shown in FIG. 4, the fuel gas is increased from time T1 to time T2, time T3 to time T4, and time T5 to time T6, that is, the stoichiometry is increased. On the other hand, the fuel gas is reduced from time T2 to time T3 and from time T4 to time T5, that is, the stoichiometry is lowered.

  Note that the reduced stoichiometry ensures the stoichiometry (fuel gas flow rate) necessary for the fuel cell stack 12 to generate power. The time during which the fuel gas is increased (time T3 to time T4, etc.) and the time during which the fuel gas is decreased (time T2 to time T3, etc.) may be the same or different. May be.

  Furthermore, in the oxidant gas supply device 14, the back pressure control valve 66 or the air pump 60 is operated, whereby the supply amount of the oxidant gas supplied to the oxidant gas flow path 42 (both supply pressure and supply flow rate or Any increase or decrease may be repeated in a substantially pulse shape (or wave shape). At this time, the increase in the supply amount of the fuel gas and the increase in the supply amount of the oxidant gas are alternately performed with the phases reversed.

  Here, from time T2 to time T3, the oxidant gas flow rate is increased while the fuel gas flow rate is decreased. Therefore, as shown in FIG. 5, the moisture content at the end of the oxidant gas supply communication hole 34a side (cathode inlet side) becomes lower and the fuel gas supply communication hole 38a side (anode inlet side) in the power generation plane. The amount of moisture at the end increases.

  Further, from time T3 to time T4, the fuel gas flow rate is increased while the oxidant gas flow rate is decreased. Therefore, as shown in FIG. 6, in the power generation surface, the moisture amount on the fuel gas supply communication hole 38 a side becomes lower and the moisture amount on the oxidant gas supply communication hole 34 a side becomes higher.

  As described above, the fuel gas and the oxidant gas are repeatedly increased and decreased in different phases. Thereby, the moisture content is substantially uniform over the entire power generation surface. FIG. 7 shows the state of moisture on the entire power generation surface obtained by alternately performing the state of moisture in FIG. 5 and the state of moisture in FIG.

  For this reason, in this embodiment, the area | region where required water content is obtained can be increased over the whole electric power generation surface. In addition, since the amount of stagnant water is reduced, the power generation stability is improved, and the eluted components are reduced to improve the durability. For this reason, the moisture distribution in the power generation surface can be made uniform by a simple process, and the effect that it becomes possible to maintain good power generation performance is obtained.

  By the way, in step S3, gas flow rate control is performed, and if it returns to step S2 and it is judged that it is not a stay water excess and it is not film | membrane drying (in step S2 NO), it will progress to step S4. In step S4, the fuel cell system 10 shifts to a normal operation mode.

  The increase / decrease in the fuel gas flow rate and the oxidant gas flow rate is not limited to the present embodiment. For example, the fuel gas and the oxidant gas are directly supplied to the fuel gas path and the oxidation gas by an injector (not shown). You may supply to an agent gas path.

  Moreover, although the fuel gas flow path 40 and the oxidant gas flow path 42 are comprised by the linear flow path, it is not limited to this. The fuel gas flow channel 40 and the oxidant gas flow channel 42 only need to form a counter flow, and for example, a meandering flow channel (serpentine flow channel) can be adopted. Further, the gas flow rate control may be performed as shown in FIG. 8 instead of the pulse shape shown in FIG.

  Furthermore, when excessive retained water or membrane drying does not disappear in step S3, it is possible to cope with this by increasing the flow rate difference L shown in FIG. Also, the present embodiment can be applied in the normal operation mode. At that time, as shown in FIG. 9, the stoichiometry may be set larger than that during normal operation.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell stack 14 ... Oxidant gas supply device 16 ... Fuel gas supply device 18 ... Controller 20 ... Fuel cell 22 ... Electrolyte membrane and electrode structure 24, 26 ... Metal separator 28 ... Solid polymer electrolyte Membrane 30 ... Anode electrode 32 ... Cathode electrode 34a ... Oxidant gas supply communication hole 34b ... Oxidant gas discharge communication hole 36a ... Cooling medium supply communication hole 36b ... Cooling medium discharge communication hole 38a ... Fuel gas supply communication hole 38b ... Fuel gas Discharge communication hole 40 ... Fuel gas flow path 42 ... Oxidant gas flow path 44 ... Cooling medium flow path 60 ... Air pump 66 ... Back pressure control valve 70 ... Hydrogen tank 74 ... Pressure reducing valve 76 ... Shut-off valve 78 ... Ejector 86 ... Retained water Detector 88 ... Membrane dryness detector

Claims (3)

A fuel gas flow having an electrolyte membrane / electrode structure in which electrodes are disposed on both sides of the electrolyte membrane and a separator, and a fuel gas flowing between the one electrode and the separator along the power generation surface A path is formed, and an oxidant gas flow path for flowing an oxidant gas along the power generation surface is formed between the other electrode and the separator, and the fuel gas flow path and the oxidant The gas flow path is a method of operating a fuel cell in which the respective flow directions are set to counterflows opposite to each other,
While repeatedly increasing and decreasing the supply amount of the fuel gas supplied to the fuel gas flow path, repeatedly increasing and decreasing the supply amount of the oxidant gas supplied to the oxidant gas flow path,
The fuel cell operating method is characterized in that the increase in the supply amount of the fuel gas and the increase in the supply amount of the oxidant gas are performed alternately.   In the operation method according to claim 1, when it is determined that water is retained in the fuel gas channel or the oxidant gas channel, or when it is determined that the electrolyte membrane is dry, An operation method of a fuel cell, characterized by repeating the increase and decrease of the supply amount of the fuel gas and the increase and decrease of the supply amount of the oxidant gas, respectively.   3. The operation method according to claim 1, wherein a total stoichiometric ratio of the oxidant gas and the fuel gas is the same as that during normal operation.

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