Air-cooled fuel cell system

Abstract

To provide a fuel cell system that can appropriately restore the activity of a cathode catalyst.SOLUTION: An air-cooled fuel cell system is provided. The fuel cell system comprises a fuel cell, a hydrogen system that supplies hydrogen to the fuel cell, a reaction air system that supplies reaction air to the fuel cell, and a cooling air system that supplies cooling air to the fuel cell. The fuel cell has a reaction air path and a cooling air path having independent channel structures of the reaction air and the cooling air. When the activity of a cathode catalyst of the fuel cell is reduced and restoration control of increasing the activity is required, the fuel cell system, as the restoration control, reduces the amount of the reaction air supplied to the fuel cell, while maintaining supply of the hydrogen to the fuel cell and supply of the cooling air to the fuel cell.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to air-cooled fuel cell systems. [Background technology]

[0002] Various technologies have been proposed regarding fuel cells (FCs), such as those disclosed in Patent Documents 1-5. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-216783 A [Patent Document 2] JP 2017-510954 A [Patent Document 3] JP 2022-185251 A [Patent Document 4] JP 2022-185247 A [Patent Document 5] JP 2008-192468 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional open-type air-cooled fuel cells, the inflow of cooling air and reaction air cannot be restricted at the same time, so if the activity of the fuel cell's cathode catalyst decreases, recovery control to increase the activity cannot be performed.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide an air-cooled fuel cell system that can appropriately restore the activity of the cathode catalyst. [Means for solving the problem]

[0006] In a first embodiment of the present disclosure, there is provided an air-cooled fuel cell system, the fuel cell system includes a fuel cell, a hydrogen system that supplies hydrogen to the fuel cell, a reaction air system that supplies reaction air to the fuel cell, and a cooling air system that supplies cooling air to the fuel cell; the fuel cell has a reaction air flow path and a cooling air flow path having an independent flow path structure for the reaction air and the cooling air, The present invention provides a fuel cell system characterized in that, when the activity of the cathode catalyst of the fuel cell decreases and recovery control to increase the activity is required, the fuel cell system reduces the amount of reactant air supplied to the fuel cell while maintaining the supply of hydrogen to the fuel cell and the supply of cooling air to the fuel cell as the recovery control.

[0007] In the second embodiment of the present disclosure, in the first embodiment, the reaction air system has a reaction air blowing means, The cooling air system includes a cooling air blowing means, a hydrogen discharge flow path of the hydrogen system merges with a cooling air discharge flow path of the cooling air system; During the recovery control, the fuel cell system may stop the reaction air blowing means and drive the cooling air blowing means to dilute the hydrogen with the cooling air and discharge the diluted hydrogen to the outside of the fuel cell system.

[0008] In a third embodiment of the present disclosure, in the first embodiment, after the recovery control is started, when at least one of the following conditions is satisfied: the voltage of the fuel cell drops to a predetermined voltage, or a predetermined time has elapsed, the fuel cell system may increase the amount of reactant air supplied to the fuel cell.

[0009] In a fourth embodiment of the present disclosure, the fuel cell system in the first embodiment further comprises an electrical system, the electrical system includes a diode in a power line to the fuel cell; The fuel cell system may connect the fuel cell to the power line during the recovery control.

[0010] In a fifth embodiment of the present disclosure, the fuel cell system in the first embodiment includes an electrical system, the electrical system has a fuel cell relay on a power line to the fuel cell; The fuel cell system may turn off the fuel cell relay during the recovery control. Effect of the Invention

[0011] The fuel cell system of the present disclosure can appropriately restore the activity of the cathode catalyst. [Brief description of the drawings]

[0012] [Figure 1] 1 is an exploded perspective view showing an example of a single cell of a fuel cell provided in a fuel cell system according to the present disclosure; [Diagram 2] 1 is a schematic perspective view showing an example of a fuel cell stack provided in a fuel cell system according to the present disclosure. [Diagram 3] 1 is a system configuration diagram showing an example of a fuel cell system according to the present disclosure. [Figure 4] 2 is a circuit diagram showing an example of an electrical system provided in the fuel cell system of the present disclosure. FIG. [Diagram 5] 4 is a flowchart showing an example of control of the fuel cell system of the present disclosure. [Figure 6] 6 is a flowchart showing another example of the control of the fuel cell system according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described. Note that matters other than those specifically mentioned in this specification and necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a fuel cell system that does not characterize the present disclosure) can be understood as design matters of a person skilled in the art based on the prior art in the field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. In the present disclosure, the gas supplied to the anode of the fuel cell is a fuel gas (anode gas), and the gas supplied to the cathode of the fuel cell is an oxidant gas (cathode gas). The fuel gas is a gas that mainly contains hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be oxygen, air, etc. In the present disclosure, air as the oxidant gas is referred to as reaction air, and air as the cooling gas is referred to as cooling air.

[0014] The present disclosure provides an air-cooled fuel cell system, comprising: the fuel cell system includes a fuel cell, a hydrogen system that supplies hydrogen to the fuel cell, a reaction air system that supplies reaction air to the fuel cell, and a cooling air system that supplies cooling air to the fuel cell; the fuel cell has a reaction air flow path and a cooling air flow path having an independent flow path structure for the reaction air and the cooling air, The present invention provides a fuel cell system characterized in that, when the activity of the cathode catalyst of the fuel cell decreases and recovery control to increase the activity is required, the fuel cell system reduces the amount of reactant air supplied to the fuel cell while maintaining the supply of hydrogen to the fuel cell and the supply of cooling air to the fuel cell as the recovery control.

[0015] This disclosure relates to improving the performance of air-cooled fuel cells, and in a system with independent flow paths for reaction air and cooling air, the reaction air system is controlled and the voltage is reduced to achieve a refreshing effect on the cathode catalyst.

[0016] In an air-cooled fuel cell, the volume of the fluid used for cooling is larger than in a water-cooled fuel cell, and the flow path structure for passing the fluid is also larger. For example, to cool 4kW, the amount of cooling water required is about 5L / min, whereas more than 10,000L / min of air is required. When a fuel cell continues to generate electricity, the catalytic activity decreases due to the accumulation of oxides on the cathode catalyst surface, and the power generation efficiency drops. At that time, the power generation efficiency can be restored by performing a refresh process. To perform the refresh process, it is necessary to make the cathode oxygen-deficient and lower the cell potential. In addition, since the power supply decreases during the refresh process, it is necessary to perform the process as quickly as possible. In open-type air-cooled fuel cells, the reaction air system cannot be sealed, so the potential cannot be lowered when not generating electricity, or if the sealed space is large, it takes a long time to lower the potential. In addition, if the potential is lowered while generating electricity, complex control such as balancing the current and air flow rate is required. In an open-type air-cooled fuel cell, since it has only one air blowing means, the air blowing means cannot be stopped in order to dilute the exhaust hydrogen. Therefore, if the potential is to be lowered, complex control must be performed while generating electricity, or additional equipment such as a bypass valve must be installed. Therefore, in an open-type air-cooled fuel cell, it is structurally difficult to seal the air system, and even if it can be sealed, the sealed volume is quite large, making it difficult to lower the potential in a short period of time to perform a refresh process.

[0017] The fuel cell system includes a fuel cell that generates electricity by reacting hydrogen with air, a hydrogen system that supplies the hydrogen needed to generate electricity to the fuel cell, a reaction air system that supplies reaction air to the fuel cell, and a cooling air system that supplies cooling air to the fuel cell to cool the heat generated by power generation.

[0018] The fuel cell may have only one unit cell (cell) of the fuel cell, or may be a fuel cell stack (stack) which is a laminate of a plurality of cells. In this disclosure, both cells and fuel cell stacks may be referred to as fuel cells. The number of cells stacked in the fuel cell stack is not particularly limited, and may be, for example, from 2 to several hundred. The fuel cell stack may have wavy cooling fins on each cell to provide cooling air flow paths. The fuel cell stack may have current collector plates, pressure plates, etc. at the ends in the stacking direction.

[0019] A fuel cell has a reactant air flow path (oxidant gas flow path) and a cooling air flow path (cooling gas flow path) with independent flow path structures for the reactant air and the cooling air, and may further have a hydrogen gas flow path (fuel gas flow path). A flow path structure in which the reaction air and the cooling air are separate means that there is no sharing of air between the flow paths from the supply of air to the fuel cell to the exhaust of air from the fuel cell. Note that the flow path for exhausting the air exhausted from the fuel cell to the outside of the fuel cell system may or may not be separate.

[0020] The cell may have a flow path structure for passing the reaction air and the cooling air such that the flow of the cooling air and the flow of the reaction air cross each other in a plan view. The flow of the cooling air and the flow of the reaction air may cross each other or be perpendicular to each other. The cell may have a power generation portion. The power generating section may have a rectangular shape in a plan view. The power generating section may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes. The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include a fluorine-based electrolyte membrane such as a thin film of perfluorosulfonic acid containing water, and a hydrocarbon-based electrolyte membrane. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont). The two electrodes are the anode (fuel electrode or hydrogen electrode) and the cathode (oxygen electrode or air electrode). The electrodes include a catalyst layer and may include a gas diffusion layer as necessary, and the power generating portion may be a membrane electrode gas diffusion layer assembly (MEGA). The catalyst layer includes a catalyst, and the catalyst may include a catalytic metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity. Examples of the catalytic metal that can be used include platinum (Pt) and alloys of Pt with other metals (e.g., Pt alloys mixed with cobalt and nickel, etc.) The catalytic metal used as the cathode catalyst and the catalytic metal used as the anode catalyst may be the same or different. The electrolyte may be a fluorine-based resin, etc. As the fluorine-based resin, for example, a Nafion solution, etc. may be used. The catalytic metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalytic metal (catalyst-supporting carrier) and the electrolyte may be mixed. The support for supporting the catalytic metal may be, for example, a carbon material such as carbon that is generally available commercially. The gas diffusion layer may be a conductive member having air holes. Examples of the conductive member include porous carbon materials such as carbon cloth and carbon paper, and porous metal members such as metal mesh and foamed metal. The fuel cell may include a separator. The separators collect the electric current generated by power generation and function as partition walls. In a fuel cell, the separators are usually arranged on both sides of the power generation section in the stacking direction so that the power generation section is sandwiched between a pair of separators. One of the pair of separators is an anode separator and the other is a cathode separator. The anode separator may have grooves that serve as hydrogen gas flow paths on the surface facing the power generation section. The cathode separator may have grooves that serve as reaction air channels on the surface facing the power generation section. The separator may have holes forming manifolds such as supply holes and discharge holes for circulating a fluid in the stacking direction of the cells. The separator may be made of, for example, dense carbon obtained by compressing carbon to make it gas impermeable, or a press-molded metal (for example, iron, titanium, stainless steel, etc.). The cell may include an insulating resin frame disposed on the outer side (periphery) of the membrane electrode assembly in the planar direction between the anode separator and the cathode separator. The resin frame is molded into a plate-like and frame-like shape using a thermoplastic resin, and seals the gap between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. For the resin frame, for example, a resin such as PE, PP, PET, or PEN can be used. The resin frame may be a three-layer sheet composed of three layers with an adhesive layer disposed on the surface layer.

[0021] The fuel cell system may include a control device. The control device may control the reaction air system, the hydrogen system, the cooling air system, etc., and may control the entire fuel cell system. The control device physically has, for example, a processing device such as a CPU (central processing unit), a ROM (read-only memory) that stores control programs and control data processed by the CPU, a storage device such as a RAM (random access memory) that is mainly used as various working areas for control processing, and an input / output interface, and may be an ECU (electronic control unit), etc.

[0022] The reaction air system supplies reaction air to the fuel cell as an oxidant gas and adjusts the flow rate of the reaction air. The reaction air system may include a reaction air pipe and the like. The hydrogen system supplies hydrogen as a fuel gas to the fuel cell and adjusts the flow rate of the hydrogen, and may include a hydrogen tank, a hydrogen inlet valve, an injector, a gas-liquid separator, a hydrogen purge valve, an ejector for hydrogen circulation, a hydrogen pump for hydrogen circulation, and hydrogen piping. The cooling air system supplies cooling air as a cooling gas to the fuel cell and adjusts the flow rate of the cooling air.

[0023] The reaction air system may have an inlet-side sealing valve at the reaction air inlet of the fuel cell, and an outlet-side sealing valve at the reaction air outlet of the fuel cell. In the present disclosure, the fuel cell has a flow path structure in which the reaction air and the cooling air are independent, and valves (an inlet-side sealing valve and an outlet-side sealing valve) are installed in the reaction air system at the inlet and outlet of the reaction air of the fuel cell, so that the fuel cell cathode can be sealed in a smaller volume than when the fuel cell has a flow path structure in which the reaction air and the cooling air are common. During power generation by the fuel cell, when the activity of the cathode catalyst of the fuel cell decreases and recovery control is required to increase the activity, the valves at the inlet and outlet of the reaction air are sealed, so that the small amount of oxygen that is sealed is quickly consumed, and the potential of the fuel cell can be reduced in a short time. At that time, hydrogen from the anode is consumed, so hydrogen supply is continued to suppress catalyst deterioration associated with the generation of abnormal potential due to hydrogen shortage.

[0024] When the activity of the cathode catalyst of the fuel cell decreases and recovery control to increase the activity is necessary, the fuel cell system performs the recovery control by reducing the amount of the reactant air supplied to the fuel cell while maintaining the supply of the hydrogen to the fuel cell and the supply of the cooling air to the fuel cell. During recovery control (refresh process), the supply of hydrogen to the fuel cell is maintained to prevent abnormal potential. During recovery control (refresh process), at least the amount of reactant air supplied to the fuel cell is reduced, and if necessary, the supply of reactant air to the fuel cell is stopped. In addition, the inlet and outlet valves of the reactant air system (the inlet and outlet sealing valves) are closed, and the cathode of the fuel cell is sealed. The voltage of the fuel cell is then lowered to a specified voltage. When the fuel cell reaches the specified voltage, the inlet and outlet valves of the reactant air system (the inlet and outlet sealing valves) are opened. Recovery control may be determined to be necessary when at least one of the following conditions is met: when the fuel cell voltage deviates from the expected voltage, when continuous power generation operation has been performed for a certain period of time or more, when the fuel cell has been left without generating power for a certain period of time or more. In other words, when at least one of these conditions is met, it may be considered that the activity of the cathode catalyst has decreased.

[0025] In the present disclosure, after the recovery control is started, when at least one of the following conditions is satisfied: the voltage of the fuel cell drops to a predetermined voltage, or a predetermined time has elapsed, the fuel cell system may increase the amount of reactant air supplied to the fuel cell. The decision as to whether or not to end recovery control may be made by any one of the following, or a combination of the following: Voltage sensors may be installed at both ends of the fuel cell stack to detect the total voltage, and the end of recovery control may be determined when the total voltage value drops to a predetermined voltage. Voltage sensors may be installed in all or some of the cells, and the end of recovery control may be determined when the voltage value of at least one of the cells drops to a predetermined voltage. The time it takes for the voltage to drop to a predetermined voltage may be recorded in advance, and the end of recovery control may be determined when the predetermined time has elapsed.

[0026] The reaction air system may have a reaction air blowing means, the cooling air system may have a cooling air blowing means, and the hydrogen exhaust flow path of the hydrogen system may merge with the cooling air exhaust flow path of the cooling air system. The hydrogen exhaust flow path of the hydrogen system may further have a junction part that can merge with the reaction air exhaust flow path of the reaction air system. By having independent blowing means for the reaction air system and the cooling air system, and by having the hydrogen exhaust flow path merge with the cooling air exhaust flow path, during recovery control, the fuel cell system can stop the reaction air blowing means and drive the cooling air blowing means, thereby diluting the hydrogen with cooling air and discharging it outside the fuel cell system, and can perform temperature control. The reaction air blowing means and the cooling air blowing means may be an air compressor, an air pump, an air blower, an air fan, or the like, respectively. The reaction air system may have a reaction air intake port for taking in reaction air from outside the fuel cell system, and the reaction air intake port may be provided with a pressure loss body such as an air filter. The cooling air system may have a cooling air intake port through which cooling air is taken in from outside the fuel cell system, and the cooling air intake port may be provided with a pressure loss body such as an air filter.

[0027] The fuel cell system may include an electrical system. The electrical system may have a diode on the power line to the fuel cell, and may or may not have a fuel cell relay. By having a diode, it is possible to prevent the occurrence of reverse current from the power line to the fuel cell. The fuel cell system may connect the fuel cell to the power line during recovery control. By performing recovery control while the fuel cell is connected to the power line, oxygen consumption in the reaction air system is completed quickly, and the recovery control time is shortened. Also, if the fuel cell is disconnected from the power line during recovery control and the fuel cell is in an open circuit state, if oxygen is present in the cathode and hydrogen in the anode, the cell voltage will rise to a high potential (around 1.0 V), oxidation of the catalyst will progress, and the performance degradation of the catalyst layer will progress, but by performing recovery control while the fuel cell is connected to the power line, the fuel cell voltage is suppressed to fuel cell voltage V1 ≦ power line voltage V2, so it is possible to prevent the cell from reaching a high potential during recovery control.

[0028] The electrical system may include a fuel cell relay in the power line to the fuel cell, and may or may not include a diode. If the electrical system of the fuel cell system has a fuel cell relay on the power line and does not have a diode, the fuel cell system may turn off the fuel cell relay during recovery control. If diodes are not installed on the electrical power lines due to the cost or size of the fuel cell system, the cells will temporarily reach a high potential, but recovery control can be performed after disconnecting the relay to prevent reverse current from the power lines.

[0029] FIG. 1 is an exploded perspective view showing an example of a single cell of a fuel cell provided in a fuel cell system of the present disclosure. 1 includes cooling fins (cooling air flow paths) 2 that serve as flow paths for cooling air (cooling gas) 7, a reaction air inlet 3, a reaction air outlet 4, a hydrogen gas inlet 5, a hydrogen gas outlet 6, two separators 11, and an MEA and a resin frame 12 sandwiched between the two separators 11. As shown in FIG. 1, the fuel cell 1 has a flow path structure in which the reaction air 9 and the cooling air 7 are independent of each other.

[0030] FIG. 2 is a schematic perspective view showing an example of a fuel cell stack included in the fuel cell system of the present disclosure. The fuel cell stack 10 shown in FIG. 2 is a stack of a plurality of cells 1.

[0031] FIG. 3 is a system configuration diagram showing an example of a fuel cell system according to the present disclosure. The fuel cell system shown in Fig. 3 includes a fuel cell stack 10, a reaction air system 20, a cooling air system 30, and a hydrogen system 40. The reaction air system 20 includes a reaction air intake port 21, an air blower 22, an inlet side sealing valve 23, and an outlet side sealing valve 24. The cooling air system 30 includes a cooling fan 31. The hydrogen system 40 includes a hydrogen tank 41, a hydrogen inlet valve 42, a gas-liquid separator 43, a hydrogen purge valve 44, and a hydrogen pump 45. The fuel cell system shown in Fig. 3 includes sealing valves 23, 24 at the inlet and outlet of the reaction air system 20, and includes independent blowing means 22, 31 for the reaction air system 20 and the cooling air system 30.

[0032] FIG. 4 is a circuit diagram showing an example of an electrical system included in the fuel cell system of the present disclosure. The electrical system 50 shown in FIG. 4 includes a power line 51, a diode 52, a relay 53, a power consumption absorbing means 54 such as a battery / capacitor, auxiliary equipment 55, and a power consumption device 56. By installing a diode 52 on the power line 51 and connecting the fuel cell stack 10 to the power line 51 during recovery control, it is possible to shorten the recovery control time while avoiding the occurrence of reverse current from the power line 51 to the fuel cell stack 10.

[0033] FIG. 5 is a flowchart showing an example of control of the fuel cell system of the present disclosure. First, the fuel cell system determines whether recovery control is necessary. If it is determined that recovery control is necessary, the fuel cell system closes the inlet and outlet valves of the reaction air system and starts recovery control. The fuel cell system then determines whether the voltage of the fuel cell has dropped to a predetermined determination threshold. If it is determined that the voltage of the fuel cell has dropped to the predetermined determination threshold, the fuel cell system opens the inlet and outlet valves of the reaction air system and ends the recovery control.

[0034] FIG. 6 is a flowchart showing another example of the control of the fuel cell system of the present disclosure. First, the fuel cell system determines whether recovery control is necessary. If it is determined that recovery control is necessary, the fuel cell system closes the inlet and outlet valves of the reaction air system and starts recovery control. Then, the fuel cell system determines whether a predetermined time has elapsed since the recovery control was performed. If it is determined that the predetermined time has elapsed since the recovery control was performed, the fuel cell system opens the inlet and outlet valves of the reaction air system and ends the recovery control. [Explanation of symbols]

[0035] 1. Cell 2. Cooling fins (cooling air flow path) 3.Reaction air inlet 4.Reaction air outlet 5. Hydrogen gas inlet 6. Hydrogen gas outlet 7. Cooling air (cooling gas) 8. Hydrogen gas 9.Reaction air 10. Fuel Cell Stack 11. Separator 12.MEA, resin frame 20.Reaction air system 21.Reaction air intake 22. Air Blower 23. Inlet side sealing valve 24.Outlet side sealing valve 30. Cooling air system 31. Cooling fan 40. Hydrogen 41. Hydrogen tank 42. Hydrogen inlet valve 43. Gas-liquid separator 44. Hydrogen purge valve 45. Hydrogen pump 50. Electrical system 51. Power Lines 52. Diode 53. Relay 54. Means of absorbing power consumption 55. Auxiliary equipment 56.Power consumption equipment

Claims

1. An air-cooled fuel cell system, the fuel cell system includes a fuel cell, a hydrogen system that supplies hydrogen to the fuel cell, a reaction air system that supplies reaction air to the fuel cell, and a cooling air system that supplies cooling air to the fuel cell; the fuel cell has a reaction air flow path and a cooling air flow path having an independent flow path structure for the reaction air and the cooling air, When the activity of the cathode catalyst of the fuel cell decreases and recovery control to increase the activity is required, the fuel cell system reduces the amount of reactant air supplied to the fuel cell while maintaining the supply of hydrogen to the fuel cell and the supply of cooling air to the fuel cell, as the recovery control.

2. The reaction air system has a reaction air blowing means, The cooling air system includes a cooling air blowing means, a hydrogen discharge flow path of the hydrogen system merges with a cooling air discharge flow path of the cooling air system; 2. The fuel cell system according to claim 1, wherein during the recovery control, the fuel cell system stops the reaction air blowing means and drives the cooling air blowing means to dilute the hydrogen with the cooling air and discharge the diluted hydrogen to the outside of the fuel cell system.

3. 2. The fuel cell system of claim 1, wherein after the start of the recovery control, when at least one of the following conditions is met: the voltage of the fuel cell drops to a predetermined voltage, or a predetermined time has elapsed, the fuel cell system increases the amount of reactant air supplied to the fuel cell.

4. The fuel cell system includes an electrical system; the electrical system includes a diode in a power line to the fuel cell; The fuel cell system according to claim 1 , wherein the fuel cell system connects the fuel cell to the power line during the recovery control.

5. The fuel cell system includes an electrical system; the electrical system has a fuel cell relay on a power line to the fuel cell; The fuel cell system according to claim 1 , wherein the fuel cell system turns off the fuel cell relay during the recovery control.

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