JP2005222707A - Fuel cell system and operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell power generating device enhancing durability by suppressing deterioration caused by oxidation and dissolution by potential rising of a cathode and an anode at starting stopping, and to provide its operation method. <P>SOLUTION: A fuel cell system is equipped with a fuel cell 5 comprising an electrolyte 1, a pair of electrodes 4a, 4c, and a pair of separators 7a, 7c, and oxidant gas and fuel gas are sealed in the fuel cell 5, and when the operation of the fuel cell is stopped, the potential of the electrode for replacing the oxidant gas and the fuel gas in the sealed part with inert gas is kept low, and thereby, deterioration caused by oxidation and dissolution is suppressed and the durability of the fuel cell system is enhanced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system that uses a small amount of gas and suppresses deterioration of the fuel cell due to start-stop or improves durability, and an operation method thereof.

  The configuration and operation of a conventional general solid polymer electrolyte fuel cell will be described with reference to FIGS. FIG. 1 shows a basic structure of a polymer electrolyte fuel cell (hereinafter referred to as PEFC) among conventional fuel cells. In a fuel cell, a fuel gas such as hydrogen and an oxidant gas containing oxygen such as air are electrochemically reacted by a gas diffusion electrode, and electricity and heat are generated simultaneously. As the electrolyte 1, a polymer electrolyte membrane that selectively transports hydrogen ions is used. A catalyst reaction layer 2 mainly composed of carbon powder carrying a platinum-based metal catalyst is disposed on both surfaces of the electrolyte 1 in close contact with each other. The reaction shown in (Chemical Formula 1) and (Chemical Formula 2) occurs in this catalytic reaction layer, and the reaction shown in (Chemical Formula 3) occurs in the fuel cell as a whole.

少なくとも水素を含む燃料ガスは（化１）に示す反応（以降、アノード反応と称する）し、電解質１を介して移動した水素イオンは、酸化剤ガス（以降、カソードガスと称する）と触媒反応層２で（化２）に示す反応（以降、カソード反応と称する）により、水を生成し、このとき電気と熱を生ずる。燃料電池全体としては（化３）に示すように、水素と酸素が反応し水が発生する際に、電気と熱が利用できるのである。水素などの燃料ガスの関与する側をアノードと呼び、図ではａを付け表し、空気などの酸化剤ガスの関与する側をカソードと呼び、図ではｃを付け表した。さらに触媒反応層２ａと２ｃの外面には、ガス通気性と導電性を兼ね備えた拡散層３ａと３ｃをこれに密着して配置する。この拡散層３ａと３ｃと触媒反応層２ａ、２ｃにより電極４ａと４ｃを構成する。

The fuel gas containing at least hydrogen undergoes the reaction shown in (Chemical Formula 1) (hereinafter referred to as an anode reaction), and the hydrogen ions moved through the electrolyte 1 are converted into an oxidant gas (hereinafter referred to as a cathode gas) and a catalytic reaction layer. 2 generates water by the reaction shown in (Chemical Formula 2) (hereinafter referred to as the cathodic reaction). At this time, electricity and heat are generated. As shown in (Chemical Formula 3), the fuel cell as a whole can use electricity and heat when hydrogen and oxygen react to generate water. The side in which a fuel gas such as hydrogen is involved is called an anode, and a is added in the figure, the side in which an oxidant gas such as air is involved is called a cathode, and c is shown in the figure. Furthermore, diffusion layers 3a and 3c having both gas permeability and conductivity are disposed in close contact with the outer surfaces of the catalyst reaction layers 2a and 2c. The diffusion layers 3a and 3c and the catalyst reaction layers 2a and 2c constitute electrodes 4a and 4c.

  Reference numeral 5 denotes an electrode electrolyte assembly (hereinafter referred to as MEA), which is formed by the electrode 4 and the electrolyte 1. The MEA 5 is used for mechanically fixing the MEA 5 and electrically connecting adjacent MEAs 5 to each other, supplying a reaction gas to the electrodes, and carrying away a gas generated by the reaction and excess gas. A pair of conductive separators 7a and 7c, in which the gas flow paths 6a and 6c are formed on the surface in contact with the MEA 5, are disposed. A basic fuel cell unit (hereinafter referred to as a cell) includes an electrolyte 1, a pair of catalytic reaction layers 2a and 2c, a pair of diffusion layers 3a and 3c, a pair of electrodes 4a and 4c, and a pair of separators 7a and 7c. Form. The separators 7a and 7c are in contact with the separators 7c and 7a of the adjacent cells on the surface opposite to the MEA 5. The cooling water passages 8a and 8c are provided on the side where the separators 7a and 7c are in contact, and the cooling water 9 flows there. The cooling water 9 moves heat so as to adjust the temperature of the MEA 5 through the separators 7a and 7c. The MEA gasket 10 seals the MEA 5 and the separator 7a or 7c, and the separator gasket 11 seals the separators 7a and 7c.

  The electrolyte 1 has a fixed charge, and hydrogen ions exist as counter ions of the fixed charge. The electrolyte 1 is required to have a function of selectively allowing hydrogen ions to permeate. For this purpose, the electrolyte 1 needs to retain moisture. This is because when the electrolyte 1 contains moisture, the fixed charge fixed in the electrolyte 1 is ionized, and hydrogen, which is a counter ion of the fixed charge, is ionized and can move.

  The stack will be described with reference to FIG. Since the voltage of the fuel cell is usually as low as about 0.75 V, a plurality of cells are stacked in series so that the voltage becomes high. The current collecting plate 21 is for taking out current from the stack to the outside, and the insulating plate 22 electrically insulates the cell from the outside. The end plate 23 fastens and stacks a stack of cells.

  The fuel cell system will be described with reference to FIG. A fuel cell system is housed in the outer casing 31. The gas cleaning unit 32 removes substances that adversely affect the fuel cell from the raw material gas, guides the fuel gas from the outside through the raw material gas pipe 33, and guides the gas to the fuel generator 35 through the clean gas pipe 36. The valve 34 controls the flow of the raw material gas. The fuel generator 35 generates a fuel gas containing at least hydrogen from the raw material gas. The fuel gas is guided from the fuel generator 35 to the stack 38 through the fuel gas pipe 37. The blower 39 guides the oxidant gas to the stack 38 through the intake pipe 40. The exhaust pipe 42 discharges the oxidant gas discharged from the stack 38 to the outside of the fuel cell system. The fuel gas that has not been used in the stack 38 flows again into the fuel generator 35 through the off-gas pipe 48. The gas from the off-gas pipe 48 is used for combustion or the like, and is used for an endothermic reaction or the like for generating a fuel gas from the raw material gas. The power circuit unit 43 extracts power from the fuel cell stack 38, and the control unit 44 controls the gas, the power circuit unit, and the like. The pump 45 causes water to flow from the cooling water inlet pipe 46 to the water path of the fuel cell stack 38. The water that has flowed through the fuel cell stack 38 is carried to the outside from the cooling water outlet pipe 47. By flowing water through the stack 38 of the fuel cell, the generated heat can be used outside the fuel cell system while maintaining the heated stack 38 at a constant temperature. The fuel cell system includes a stack 38 composed of fuel cells, a gas cleaning unit 32, a fuel generator 35, a power circuit unit 43, and a control unit 44.

  The home fuel cell system includes a fuel cell stack 38 and a fuel generator 35. It is necessary to reduce the performance degradation of the fuel cell system so that the performance can be maintained for a long time. In addition, when using raw gas such as city gas mainly composed of methane for household use, in order to increase the utility cost and CO2 reduction effect, the time period when electricity and heat consumption is low is stopped. An operation method that operates in a time zone where consumption of electricity and heat is large is effective. In general, DSS (Daily Start & Stop or Daily Start-up & Shut-down) operation, which operates in the daytime and stops in the middle of the night, can increase the utility cost and CO2 reduction effect. It is desirable to be able to respond flexibly to driving patterns including starting and stopping. Several reports have been made so far.

  For example, as a solution to these problems, a means for consuming electric power is separately connected in the system until starting the external load connection of the system at the start-up, thereby preventing an open circuit potential (see Patent Document 1). Moreover, the discharge means for suppression of an open circuit voltage was installed in the system (refer patent document 2). Further, in order to keep the ion exchange membrane, which is an electrolyte, in a water retaining state during storage, the humidified inert gas is sealed and stored (see Patent Document 3). In order to prevent oxidation of the oxygen electrode or adhesion of impurities, power generation is performed in a state where the supply of the oxygen-containing gas is stopped, and an oxygen consumption operation is performed to improve durability (see Patent Document 4). Further, hydrogen leaking from the anode to the cathode is used to improve the performance of the cathode electrode (see Patent Document 4).

  In order for the power generation reaction at the electrode of the fuel cell as described above to be performed stably over a long period of time, it is necessary that the interface between the electrolyte and the electrode be stably maintained over a long period of time. The open circuit voltage of a polymer electrolyte fuel cell using hydrogen and oxygen as reactive species is theoretically 1.23V. However, the actual open circuit voltage indicates a mixed potential with impurities and adsorbed species at each of the hydrogen electrode and the oxygen electrode, and a voltage of about 0.93 V to 1.1 V. In addition, some voltage drop occurs due to diffusion of hydrogen and oxygen in the electrolyte. If there is no dissolution of impurities such as extreme metal species, the potential of the hydrogen electrode is greatly influenced by the adsorbed species of the air electrode, and the hybrid potential of the chemical reaction as shown in (Chem. 4) to (Chem. 8). (See Non-Patent Document 1).

Japanese Patent Laid-Open No. 5-251101 JP-A-8-222258 JP-A-6-251788 JP 2002-93448 A JP 2000-260454 A H. Wroblowa, et al., J. Electroanal. Chem., 15, p139-150 (1967), "Adosorption and Kinetics at Platinum Electrodes in The Presence of Oxygen at Zero Net Current"

  However, in the conventional configuration, when the voltage exceeds 0.88 V, as shown in (Chemical Formula 7), oxidation of Pt occurs, and not only the activity of Pt as a catalyst decreases but also dissolution in water occurs. However, there is a problem that flows out.

  Moreover, although the technique which prevents an open circuit is disclosed by the prior art, it does not describe making a voltage into 0.88V or less.

  Further, in the conventional method of purging water or humidified inert gas to the anode or cathode, it is not shown that the potential of each electrode is kept below a certain level, so the inside of the cell is filled with the inert gas. When this is done, the potentials of the anode and cathode are not determined, and gradually enter from the outside, and oxygen shows a voltage of about 0.93 V to 1.1 V at both electrodes, so the electrodes are oxidized or eluted, resulting in reduced performance. There is a problem that will let you. Further, in order to purge, the purge gas needs to be equal to or larger than the purged gas, and there is a problem that consumption of the purge gas is increased.

  Further, in the conventional method of purging water or humidified inert gas, the temperature of the fuel cell stack 38 is lowered at the time of stoppage, condensation occurs inside the fuel cell stack 38, and the volume is reduced. Due to the negative pressure, there are problems such as the inflow of external oxygen, the electrolyte 1 being stressed and broken, and the electrodes 4a and 4c being short-circuited.

  Further, in the conventional method in which the cell is generated with the supply of the oxidant gas stopped and oxygen in the gas dew 6c is consumed and then the inert gas is purged into the gas dew 6a, the gas dew 6c cannot be consumed. There was a problem that the electrode 4c was oxidized and deteriorated due to the influence of residual oxygen or air mixed in due to diffusion or leakage. In addition, since oxygen is forcibly consumed by power generation, the potential of the electrode 4c is not uniform, and the activation state of the cathode is different every time it is stopped, and the battery voltage at startup varies.

  Also, the problem that the cathode electrode performance is improved by hydrogen leaking from the anode to the cathode where air exists is that the potential becomes unstable due to the mixing of oxygen and hydrogen, and the cathode performance varies. There is.

  Moreover, the thing which improves the performance of a cathode electrode by flowing hydrogen to a cathode has the subject that the ratio of the hydrogen which is not used for electric power generation increases, and the electric power generation efficiency per energy falls.

  Further, those using nitrogen gas as an inert gas for purging have a problem that requires a special device such as a nitrogen gas cylinder.

  The present invention solves the above-described conventional problems, and when the fuel cell is stopped, the oxidant gas and the fuel gas are enclosed in the stack and the peripheral path, and the fuel gas or the oxidant gas is not purged by the purge. The amount of inert gas used can also be reduced, and the fuel gas sealed in the fuel cell is diffused through the electrolyte and present on the electrode on the oxidant gas side to prevent oxidation or dissolution of the electrode. By supplying an inert gas from the outside when the volume is reduced, a fuel cell system capable of maintaining a long-term life without applying stress to the electrolyte without reducing the pressure of the enclosing portion, and a method of operating the fuel cell system The purpose is to provide.

  In order to solve the conventional problem, the fuel cell system of the present invention stops the supply of the fuel gas and the oxidant gas when stopped, stops the inflow and discharge of the fuel gas and the oxidant gas by the shutoff valve, The fuel cell system is configured to inject a gas inert to the fuel cell during stoppage into one or both of the fuel gas path and the oxidant gas path.

  As a result, the fuel gas quickly penetrates into the oxidant gas side through the electrolyte, so that the potential of the electrode is lowered and deterioration due to dissolution of platinum or the like can be suppressed. Furthermore, since the fuel gas or the oxidant gas is not purged, the amount of inert gas used can be reduced. Furthermore, since the inert gas can be supplied from the outside when the volume of the encapsulated gas decreases due to a reaction or the like, the pressure of the encapsulated portion does not decrease, the stress or the like is not applied to the electrolyte, and the lifetime can be maintained for a long time. It is possible to realize a highly durable fuel cell system that can suppress deterioration due to start and stop.

  The fuel cell system of the present invention and the operation method thereof include a fuel gas and an oxidant gas enclosed in a path including a stack at the time of stoppage, and a reduction in the volume of the enclosed gas is injected to introduce an inert gas. The amount used can be made small, and even when starting and stopping, deterioration due to oxidation or dissolution of the electrode can be suppressed, and the life of the fuel cell system can be extended.

  A first invention is a gas flow path for supplying and discharging an electrolyte, a pair of electrodes sandwiching the electrolyte, and a fuel gas containing at least hydrogen on one of the electrodes, and an oxidant gas containing oxygen on the other A fuel cell comprising a pair of separators, a shutoff valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied to the fuel cell from a raw material gas, Controls a gas cleaning unit that removes components that adversely affect the fuel cell from the source gas, a power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, and a gas and power circuit unit In a fuel cell system having a control unit, when the fuel cell is stopped, the supply of fuel gas and oxidant gas is stopped, the shutoff valve is closed, and the inflow and discharge of fuel gas and oxidant gas are stopped. In addition, since the fuel cell system injects a gas inert to the fuel cell during stoppage into one or both of the fuel gas path and the oxidant gas path, the oxidant gas and the fuel gas are sealed. Since the gas quickly diffuses to the oxidant gas side, the potential of the electrode on the oxidant gas side can be lowered quickly, so that the electrode having catalytic action such as platinum is not deteriorated by dissolution, etc. As the inert gas is injected in an amount corresponding to the volume reduced in step (b), the amount of inert gas used is small and does not become negative pressure. Therefore, excessive stress can be prevented from being applied to the electrolyte, etc. It can be maintained.

  According to the second invention, in particular, the electrode potential of the first invention is lowered. The volume of the space of the oxidant gas path sealed by the shutoff valve is equal to the volume of the space of the fuel gas path sealed by the shutoff valve. It is surely performed by setting the volume not to exceed twice. When the fuel gas is generated from the raw material gas by the fuel generator, the reaction is as shown in (Chemical Formula 9), and carbon dioxide is generated with respect to the hydrogen 4.

よって、水素の含有量は約８０％である。一方、最も多く用いられる酸素含有ガスは空気であるが、この酸素含有率は約２０％である。水素と酸素は２対１の割合で反応するため、酸化剤ガス経路の空間の体積が燃料ガス経路の空間の体積の２倍を超えない体積とすると、反応後には酸素はなく、水素が残るので電極の電位を長期間確実に下げることができ、長期間高性能が維持できる燃料電池システムが実現できるのである。

Therefore, the hydrogen content is about 80%. On the other hand, the most frequently used oxygen-containing gas is air, but this oxygen content is about 20%. Since hydrogen and oxygen react at a ratio of 2 to 1, if the volume of the oxidant gas path space does not exceed twice the volume of the fuel gas path space, there will be no oxygen after the reaction and hydrogen will remain As a result, the potential of the electrode can be reliably lowered for a long period of time, and a fuel cell system capable of maintaining high performance for a long period of time can be realized.

  The third invention relates to a change in volume due to dew condensation during a long-term stop in the fuel cell system of the first invention or the second invention, and the dew point of the gas inert to the fuel cell is 0 ° C. or less. Even if the temperature of the stack drops during a long-term stop, if the dew point of the inert gas is 0 ° C or less, there is no condensation in the inert gas up to 0 ° C. Since no extra stress is applied to the gas path and the electrolyte membrane, a fuel cell system capable of maintaining high performance for a long time can be realized.

  A fourth invention provides an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying / discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying / discharging an oxidant gas containing oxygen to the other A fuel cell comprising a pair of separators, a shutoff valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied to the fuel cell from a raw material gas, Controls a gas cleaning unit that removes components that adversely affect the fuel cell from the source gas, a power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, and a gas and power circuit unit In a fuel cell system having a control unit, when the fuel cell is stopped, the supply of fuel gas and oxidant gas is stopped, the shutoff valve of the oxidant gas flow path is closed, and the inflow and discharge of the oxidant gas are stopped. After, by a method of operating a fuel cell to close the shut-off valve of the fuel gas flow passage, in the inflow and outflow the absence of the oxidizing gas, and so that the condition exists where there is a flow of the fuel gas. At this time, even if hydrogen in the fuel gas diffuses through the electrolyte, the fuel gas flows in, so the hydrogen is replenished, but the oxidant gas is enclosed, so the amount of oxygen etc. decreases. is there. Therefore, by using the fuel cell operation method of the present invention, the potential of the electrode on the oxidant gas side can be reliably lowered, so that deterioration can be suppressed and high performance can be maintained for a long time.

  A fifth invention provides an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidant gas containing oxygen to the other A fuel cell comprising a pair of separators, a shutoff valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied to the fuel cell from a raw material gas, Controls a gas cleaning unit that removes components that adversely affect the fuel cell from the source gas, a power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, and a gas and power circuit unit In the fuel cell system having the control unit, when the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, the shutoff valve of the oxidant gas channel and the fuel gas channel is closed, and the gas inflow and By reducing the potential of the electrode quickly by adopting a fuel cell system operation method in which inert gas is injected into one or both of the oxidant gas flow path and the fuel gas flow path at regular intervals after stopping the discharge. Not only can it prevent dissolution of the electrode with catalytic action and suppress deterioration, but also it can reduce the pressure change of the enclosing path including the stopped stack with a simple configuration, thus preventing large stress on the electrolyte etc. Therefore, breakage and the like can be prevented, and high performance can be maintained for a long time.

  A sixth invention provides an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying / discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying / discharging an oxidant gas containing oxygen to the other A fuel cell comprising a pair of separators, a shutoff valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied to the fuel cell from a raw material gas, A gas cleaning unit that removes components that adversely affect the fuel cell from the source gas, a power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, and temperature detection that detects the temperature of the fuel cell And a control unit that controls the gas, the power circuit unit, etc., when the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, and the oxidant gas flow path and the fuel cell are stopped. After shutting off the gas flow shut-off valve and stopping gas inflow and exhaust, when the stack temperature changes by more than a certain level from the temperature detector, an inert gas is introduced into one or both of the oxidant gas flow path and the fuel gas flow path. By operating the fuel cell system to be injected, the potential of the electrode can be quickly lowered to prevent the dissolution of the catalytic electrode and suppress degradation, and the volume of the enclosed gas can be reduced due to condensation caused by the temperature drop. Since it can be kept below a certain level, it is possible to prevent a large stress from being applied to the electrolyte and the like, and to maintain high performance for a long period of time.

  A seventh aspect of the invention provides an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying / discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying / discharging an oxidant gas containing oxygen to the other A fuel cell comprising a pair of separators, a shutoff valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied to the fuel cell from a raw material gas, A gas cleaning unit that removes components that adversely affect the fuel cell from the source gas, a power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, an oxidant gas path of the fuel cell, and fuel In a fuel cell system having a pressure detection unit that detects the pressure of a gas path and a control unit that controls a gas, a power circuit unit, etc., supply of fuel gas and oxidant gas when the fuel cell is stopped After stopping the oxidant gas flow path and the fuel gas flow path shutoff valve and stopping the inflow and discharge of gas, the oxidant gas flow path is changed when the pressure of the gas flow path of the stack changes from the pressure detection unit over a certain level. By using a fuel cell system operation method that injects inert gas into one or both of the fuel gas flow path, it is possible to prevent degradation of the electrode having catalytic action by rapidly lowering the electrode potential and to suppress deterioration. In addition, since the inert gas is injected based on the pressure change detected by the pressure detector, the stress applied to the electrolyte and the like can be further reduced, so that high performance can be maintained for a long time.

  An eighth invention provides an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying / discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying / discharging an oxidant gas containing oxygen to the other A fuel cell having a pair of separators, a shutoff valve provided in a supply path and a discharge path for fuel gas and oxidant gas, and an inert gas for supplying an inert gas in a path enclosed by the shutoff valve A supply valve, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas, and a power circuit unit that extracts electric power from the fuel cell; Supplying a fuel gas and an oxidant gas when the fuel cell is stopped in a fuel cell system having a voltage measuring unit for measuring a voltage of the fuel cell and a control unit for controlling a gas, a power circuit unit, etc. After stopping and closing the shutoff valves of the oxidant gas flow path and the fuel gas flow path to stop the inflow and discharge of the gas, the inert gas supply valve is opened and the fuel cell system that always supplies the inert gas at a constant pressure By adopting the operation method, it is possible not only to prevent the electrode having a catalytic action from being dissolved by quickly lowering the potential of the electrode and to suppress the deterioration, but also because a constant pressure is always applied to the enclosing path. Even if the volume of the gas or the oxidant gas changes, the pressure applied to the electrolyte or the like is constant, so that the damage due to the stress change and the like can be reduced, so that high performance can be maintained for a long time.

  In the ninth aspect of the invention, in particular, a fuel that is an inert gas with respect to the fuel cell system of any one of the first to eighth aspects is used as a raw material gas that is removed by a component gas cleaning unit that adversely affects the fuel cell. By using the operation method of the battery system or the fuel cell system, high performance can be easily maintained for a long period of time without using a special device such as a nitrogen cylinder.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
FIG. 1 shows a basic configuration of a polymer electrolyte fuel cell among the fuel cell systems according to Embodiment 1 of the present invention. In a fuel cell, a fuel gas containing at least hydrogen and an oxidant gas containing oxygen such as air are electrochemically reacted by a gas diffusion electrode, and electricity and heat are generated simultaneously. The electrolyte 1 is used by a polymer electrolyte membrane that selectively transports hydrogen ions. A catalyst reaction layer 2 mainly composed of carbon powder carrying a platinum-based metal catalyst is disposed on both surfaces of the electrolyte 1 in close contact with each other. Reactions shown in (Chemical Formula 1) and (Chemical Formula 2) occur in the catalytic reaction layers 2a and 2c. The fuel gas containing at least hydrogen undergoes the reaction shown in (Chemical Formula 1) (hereinafter referred to as the anode reaction), and the hydrogen ions moved through the electrolyte 1 are expressed in (Chemical Formula 2) in the oxidant gas and the catalytic reaction layer 2. The reaction (hereinafter referred to as the cathodic reaction) produces water, which generates electricity and heat. The side in which a fuel gas such as hydrogen is involved is called an anode, and a is added in the figure, the side in which an oxidant gas such as air is involved is called a cathode, and c is shown in the figure. Furthermore, diffusion layers 3a and 3c having both gas permeability and conductivity are arranged in close contact with the outer surfaces of the catalyst reaction layers 2a and 2c, respectively. The diffusion layer 3a and the catalyst reaction layer 2a constitute an electrode 4a, and the diffusion layer 3c and the catalyst reaction layer 2c constitute an electrode 4c.

  An electrode electrolyte assembly (hereinafter referred to as MEA) 5 is formed of electrodes 4 a and 4 c and electrolyte 1. The MEA 5 is used for mechanically fixing the MEA 5 and electrically connecting adjacent MEAs 5 to each other, supplying a reaction gas to the electrodes, and carrying away a gas generated by the reaction and excess gas. A pair of conductive separators 7a and 7c, in which the gas flow paths 6a and 6c are formed on the surface in contact with the MEA 5, are disposed. A basic fuel cell (hereinafter referred to as a cell) comprising an electrolyte 1, a pair of catalytic reaction layers 2a and 2c, a pair of diffusion layers 3a and 3c, a pair of electrodes 4a and 4c, and a pair of separators 7a and 7c. Form. The separators 7a and 7c are in contact with the separators 7c and 7a of the adjacent cells on the surface opposite to the MEA 5. A cooling water passage 8 is provided on the side where the separators 7a and 7c are in contact, and the cooling water 9 flows there. The cooling water 9 moves heat so as to adjust the temperature of the MEA 5 through the separators 7a and 7c. The MEA 5 and the separator 7 a or 7 c are sealed with the MEA gasket 11, and the separators 7 a and 7 c are sealed with the separator gasket 10.

  The electrolyte 1 has a fixed charge, and hydrogen ions exist as counter ions of the fixed charge. The electrolyte 1 is required to have a function of selectively allowing hydrogen ions to permeate. For this purpose, the electrolyte 1 needs to retain moisture. This is because when the electrolyte 1 contains moisture, the fixed charge fixed in the electrolyte 1 is ionized, and hydrogen, which is a counter ion of the fixed charge, is ionized and can move.

  FIG. 2 is a stack of cells and is called a stack. Since the voltage of the fuel battery cell is usually as low as about 0.75 V, a plurality of cells are stacked in series so as to obtain a high voltage. A current is taken out from the pair of current collecting plates 21 to the outside from the stack, the cell and the outside are electrically insulated by the pair of insulating plates 22, and the stack of the cells stacked is fastened by the pair of end plates 23. Retained.

  FIG. 3 is a configuration diagram of the fuel cell system. The fuel cell system is housed in the outer casing 31. The raw material gas taken in from the raw material gas pipe 33 from the outside is purified by the gas cleaning unit 32 that removes substances that adversely affect the fuel cell, and then guided to the fuel generator 35 through the clean gas pipe 36. The clean gas pipe 36 is provided with a valve 61 and is opened when gas is supplied to the fuel generator 35. A valve 34 is provided in the path of the raw material gas pipe 33 to control the flow of the raw material gas. The fuel generator 35 generates a fuel gas containing at least hydrogen from the raw material gas. Reference numeral 38 denotes a stack, which is a fuel cell and a stack whose details are shown in FIGS. Fuel gas is led from the fuel generator 35 to the stack 38 via the fuel gas pipe 37.

  Air as the oxidant gas is led from the outside to the stack 38 through the intake pipe 40 by the blower 39. The oxidant gas that has not been used in the stack 38 is discharged out of the fuel cell system through the exhaust pipe 42. Since the fuel cell needs moisture, the oxidant gas flowing into the stack 38 is humidified by the humidifier 41. The fuel gas that has not been used in the stack 38 flows again into the fuel generator 35 through the off-gas pipe 48. The gas from the off-gas pipe 48 is used for combustion or the like, and is used for an endothermic reaction or the like for generating a fuel gas from the raw material gas.

  A bypass pipe 55 is branched from the clean gas pipe 36. A shutoff valve 49 is provided in the fuel gas pipe 37 to shut off the gas flow in the fuel gas supply path of the stack 38. The off gas pipe 48 is provided with a shutoff valve 51 for shutting off the gas flow in the fuel gas discharge path of the stack 38. The shut-off valve 57 is provided in the oxidant gas supply path from the humidifier 41 to the stack 38, and blocks the gas flow in the oxidant gas supply path of the stack 38. The shut-off valve 58 is provided in the oxidant gas discharge path from the stack 38 and blocks the gas flow in the oxidant gas discharge path of the stack 38.

  A pressure gauge 59 is provided in the shutoff valve 49 and the fuel gas supply path of the stack 38, and the pressures of the fuel gas supply path and the fuel gas path in the stack 38 are measured. A pressure gauge 60 is provided in the oxidant gas supply path of the shut-off valve 57 and the stack 38, and the pressure in the oxidant gas supply path and the oxidant gas path in the stack 38 is measured.

  A branch valve 63 is provided in the fuel gas pipe 37. The bypass pipe 55 is branched, and one of the bypass pipes 55 is connected to the branch valve 63 via the check valve 62. The other branch of the bypass pipe 55 is connected to the branch valve 64 via a check valve 65. The branch valve 64 is provided in the shutoff valve 57 and the oxidant gas supply path of the stack 38. The voltage of the fuel cell stack 38 is measured by the voltage measuring unit 52, the electric power is taken out by the power circuit unit 43, and the gas and the power circuit unit are controlled by the control unit 44.

  The pump 45 causes water to flow from the cooling water inlet pipe 46 to the water path of the fuel cell stack 38, and the water that has flowed through the fuel cell 38 is carried from the cooling water outlet pipe 47 to the outside. The cooling water inlet pipe 46 is provided with a temperature detection unit 67 and the cooling water outlet pipe 47 is provided with a temperature detection unit 66. The temperature of the inflow and outflow of water flowing through the stack 38 of the fuel cell is kept constant, thereby generating heat. The generated heat can be utilized outside the fuel cell system while keeping the stack 38 at a constant temperature. The fuel cell system includes a stack 38 composed of fuel cells, a gas cleaning unit 32, a fuel generator 35, a power circuit unit 43, and a control unit 44.

  The basic operation will be described. In FIG. 3, the valve 34 is opened, and the source gas flows from the source gas pipe 33 into the gas cleaning unit 32. Although hydrocarbon gas such as natural gas or propane gas can be used as the source gas, 13A of city gas which is a mixed gas of methane, ethane, propane and butane gas is used in this embodiment. As the gas cleaning part 32, a member for removing a gas odorant such as TBM (tertiary butyl mercaptan), DMS (dimethyl sulfide), THT (tetrahydrothiofin) is used. This is because sulfur compounds such as odorants are adsorbed on the catalyst of the fuel cell to become a catalyst poison and inhibit the reaction. The fuel generator 35 generates hydrogen and carbon dioxide by the reaction shown in (Chemical Formula 9). The simultaneously generated carbon monoxide is removed so as to be 10 ppm or less by a shift reaction as shown in (Chemical Formula 10) and a carbon monoxide selective oxidation reaction as shown in (Chemical Formula 11).

ここで、水を反応に必要な最低限量以上を入れると、水素と水分を含む燃料ガスが作成できる。遮断弁４９と５１を開き、分岐弁６３を燃料生成器３５とスタック３８の経路となるよう設定させており、燃料ガスは燃料ガス配管３７を介して燃料電池のスタック３８に流れ込む。遮断弁５７と５８を開き、分岐弁６４をブロワー３９とスタック３９の経路となるよう設定させておくと、酸化剤ガスはブロワー３９により加湿器４１を通った後、スタック３８に流れ込む。酸化剤ガスの排ガスは排気管４２により外部に排出される。加湿器４１として、温水に酸化剤ガスを流すものや、酸化剤ガス中に水を吹き込むもの等が使用できるが、本実施の形態では平膜式の全熱交換型を使用した。これは、排ガス中の水と熱が加湿器４１を通過する際に、吸気管４０から運ばれ原料となる酸化剤ガス中に移動させるものである。

Here, when water is added in a minimum amount necessary for the reaction, a fuel gas containing hydrogen and moisture can be produced. The shut-off valves 49 and 51 are opened, and the branch valve 63 is set to be a path between the fuel generator 35 and the stack 38, and the fuel gas flows into the fuel cell stack 38 via the fuel gas pipe 37. When the shutoff valves 57 and 58 are opened and the branch valve 64 is set to be a path between the blower 39 and the stack 39, the oxidant gas passes through the humidifier 41 by the blower 39 and then flows into the stack 38. The exhaust gas of the oxidant gas is discharged to the outside through the exhaust pipe 42. As the humidifier 41, one that flows an oxidant gas into warm water or one that blows water into the oxidant gas can be used. In this embodiment, a flat membrane type total heat exchange type is used. In this case, when water and heat in the exhaust gas pass through the humidifier 41, they are carried from the intake pipe 40 and moved into the oxidant gas as the raw material.

  The cooling water flows from the cooling water inlet pipe 46 to the water path of the fuel cell stack 38 from the pump 45, and then the water is carried to the outside from the cooling water outlet pipe 47. Although not shown in the figure, the cooling water inlet pipe 45 and the cooling water outlet are connected to the transfer pipe 47, such as a device for accumulating or using heat such as a normal water heater. The heat generated in the fuel cell stack 38 is taken out and can be used for hot water supply or the like. In the power generation in the stack 38, the voltage is measured by the voltage measuring unit 52, and when the voltage value indicates a certain voltage value or more, the control unit 44 determines that the power generation is sufficiently performed, and the power circuit unit 43 extracts the power. The power circuit unit 43 converts the DC power extracted from the stack 38 into AC, and is connected to a power line used at home or the like by so-called system linkage.

  The operation of the fuel cell in the stack 38 will be described with reference to FIG. An oxygen-containing gas such as air is flowed through the gas flow path 6c, and a fuel gas containing hydrogen is flowed through the gas flow path 6a. Hydrogen in the fuel gas diffuses through the diffusion layer 3a and reaches the catalytic reaction layer 2a. In the catalytic reaction layer 2a, hydrogen is divided into hydrogen ions and electrons. The electrons are moved to the cathode side through an external circuit. The hydrogen ions permeate the electrolyte 1 and move to the cathode side and reach the catalytic reaction layer 2c. Oxygen in the oxidant gas such as air diffuses through the diffusion layer 3c and reaches the catalytic reaction layer 2c. In the catalyst reaction layer 2c, oxygen reacts with electrons to form oxygen ions, and the oxygen ions react with hydrogen ions to generate water. That is, oxygen-containing gas and fuel gas react around MEA 5 to generate water, and electrons flow. Further, heat is generated during the reaction, and the temperature of MEA 5 rises. Therefore, the heat generated in the reaction is carried out by water by flowing water or the like through the cooling water paths 8a and 8c. That is, heat and current (electricity) are generated. At this time, it is important to control the humidity of the introduced gas and the amount of water generated by the reaction. When there is little moisture, the electrolyte 1 is dried and the ionization of the fixed charge is reduced, so that the movement of hydrogen is reduced, so that the generation of heat and electricity is reduced. On the other hand, when there is too much moisture, water accumulates around the MEA 5 or around the catalyst reaction layers 2a and 2c, and the gas supply is inhibited and the reaction is suppressed, so that the generation of heat and electricity is reduced ( Hereinafter, this state is referred to as flatting).

  The operation after reacting in the fuel cell will be described with reference to FIG. Exhaust gas in which the oxidant gas is not used is transferred to the oxidant gas sent from the blower 39 through the humidifier 41 and then discharged to the outside. The off gas that has not been used for the fuel gas flows again into the fuel generator 35 through the off gas pipe 48. The gas from the off gas pipe 48 is used for combustion in the fuel generator 35. Since the reaction for generating the fuel gas from the raw material gas is an endothermic reaction as shown in (Chemical Formula 9), it is used as heat necessary for the reaction. The power circuit 43 serves to draw DC power from the stack 38 after the fuel cell starts generating power. The controller 44 controls the other parts of the fuel cell system so as to keep the control optimal. In the present embodiment, in FIG. 1, the MEA 5 is created as follows.

  Carbon powder acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd., particle size 35 nm) was mixed with an aqueous dispersion of polytetrafluoroethylene (PTFE) (D1 manufactured by Daikin Industries, Ltd.) and dried. A water repellent ink containing 20% by weight of PTFE was prepared. This ink is applied and impregnated on carbon paper (TGPH060H manufactured by Toray Industries, Inc.) serving as a base material for the gas diffusion layer, heat treated at 300 ° C. using a hot air dryer, and the gas diffusion layer (about 200 μm). ) Was formed.

  On the other hand, 66 parts by weight of a catalyst body (50 wt% Pt) obtained by supporting a Pt catalyst on Ketjen Black (Ketjen Black EC, Ketjen Black International Co., Ltd., particle size 30 nm), which is carbon powder. Is mixed with 33 parts by weight (polymer dry weight) of perfluorocarbon sulfonic acid ionomer (5% by weight Nafion dispersion manufactured by Aldrich, USA) which is a hydrogen ion conductive material and a binder, and the resulting mixture is molded. Thus, a catalyst layer (10 to 20 μm) was formed.

  The gas diffusion layer and the catalyst layer obtained as described above were bonded to both surfaces of a polymer electrolyte membrane (Nafion 112 membrane manufactured by DuPont, USA) to produce MEA5.

  Next, a rubber gasket plate was joined to the outer periphery of the electrolyte 1 of the MEA 5 produced as described above, and manifold holes for circulating cooling water, fuel gas, and oxidant gas were formed.

  On the other hand, a conductive separator plate 7 made of a graphite plate impregnated with a phenol resin, having an outer dimension of 20 cm × 32 cm × 1.3 mm and having a gas flow path and a cooling water flow path having a depth of 0.5 mm. Using.

  Details of the present embodiment and a flowchart of the operation method will be described with reference to FIG. In the present embodiment, the raw material gas cleaned by the gas cleaning unit 32 is used as the inert gas. Since the main component of the source gas is methane gas, the polymer electrolyte fuel cell used in the present embodiment has almost no reactivity and can be treated as an inert gas.

  First, the fuel cell system shown in FIG. 3 generates power and generates heat (operation process). In (operation process), 13A gas of city gas was used as the source gas, and air was used as the oxidant gas. As for the temperature of the fuel cell stack 38, the temperature of cooling water (water in the cooling water inlet pipe 46) entering the stack is 61 ° C., and the temperature of water coming out of the stack (water in the cooling water outlet pipe 47) is 69 ° C. The pump 45 was operated in response to the signals from the temperature detectors 66 and 67. The conditions were 64 ° C., fuel gas utilization rate (Uf) of 70%, and oxygen utilization rate (Uo) of 40%. The fuel gas and air were humidified so as to have a dew point of 64 ° C., respectively, and a current of a certain voltage was taken out from the power circuit unit 43 as power. The current was adjusted to a current density of 0.2 A / cm @ 2 with respect to the apparent area of the electrode. Although not shown in the cooling water inlet pipe 46 and the cooling water outlet pipe 47, a hot water storage tank is attached.

  The (operation process) was followed by (stop process 1). In (stop process 1), first, the valves 34 and 57 and the shutoff valves 49 and 64 are closed, the blower 39 is stopped, and the supply of fuel gas and oxidant gas to the stack 38 is stopped. Next, the shut-off valves 51 and 58 are closed, and the fuel gas path and oxidant gas path of the stack are sealed. Further, the power circuit unit 43 is controlled with a predetermined voltage. In the present embodiment, when the voltage per unit cell of the stack 38 is 0.5 V or higher, the current is controlled by the power circuit unit 43, and when the voltage is lower than 0.5 V, the current is not extracted. As a result, it is possible to prevent the electrode potential from becoming high, and thus it is possible to prevent deterioration such as dissolution of the electrode.

  In the present invention, the volume of the oxidant gas path to be sealed is about 1.5 liters, and the volume of the fuel gas path is about 1 liter. Therefore, the volume of the oxidant gas path is the same as that of the fuel gas path. Since the volume is approximately 1.5 times, the amount of hydrogen to be encapsulated is more than twice the amount of oxygen. At this time, hydrogen in the fuel gas diffuses through the electrolyte 1 and reaches the electrode on the oxidant gas side. Since the oxidant gas is sealed so that there is no inflow or outflow, the diffused hydrogen drifts near the electrode, the electrode potential on the oxidant gas side shows the potential of hydrogen, and the electrode potential drops quickly. . At this time, the oxide or the like attached to the electrode is reduced and removed, so that the activity of the electrode is restored. As a result, the fuel cell can be maintained with high performance.

  Next, the process proceeds to (stop process 2). Since hydrogen further diffuses to the oxidant gas side, it reacts with oxygen contained in the oxidant gas to generate water. Since the stack temperature is 100 ° C. or less, the generated water exists as a liquid. Therefore, hydrogen diffuses on the fuel gas side to reduce the gas amount, and oxygen reacts on the oxidant gas side to generate liquid water, thereby reducing the gas amount.

  In addition, since these reactions depend on the rate at which hydrogen diffuses in the electrolyte 1, the reaction rate can be predicted. Therefore, in (stop stroke 2), when a certain time elapses, the valve 34 is opened and the branch valve 63 is connected to the stack 38 and the check valve 62, and the branch valve 64 is connected to the check valve 65 and the stack 38. Act to form. Check valves 62 and 65 can only flow in the direction of stack 38. As a result, the raw material gas flows into the fuel gas and oxidant gas enclosing portion, and compensates for the reduction of the gas in each path and prevents a large stress on the electrolyte 1 and the MEA gasket 11, thereby damaging the electrolyte 1 and the like. There is no. In addition, even if the reaction proceeds, hydrogen does not disappear, so the electrode can always be kept at a low potential, so that dissolution of the electrode containing the catalyst can be suppressed, so that high performance can be maintained for a long time. .

  In the present embodiment, the raw material gas cleaned by the gas cleaning unit 32 is used as the inert gas. Since the dew point of the moisture in the source gas is 0 ° C. or lower, even if the temperature of the stack 38 is lowered, the moisture in the injected gas is not condensed and the volume change is small, so that the electrolyte 1 and the like are damaged. And high performance can be maintained for a long time. Further, since the amount of the inert gas used in one stop is less than or equal to the enclosed volume of the oxidant gas passage and the fuel gas passage, the amount used is very small and there is no waste. The same effect can be obtained even when nitrogen gas, helium, argon, or the like is used as the inert gas.

  When the fuel cell system is started, power generation can be performed by setting each component such as a valve so as to be again (operation stroke).

(Embodiment 2)
A flowchart of the operation method of the second embodiment will be described with reference to FIG. The basic configuration and operation are the same as those in the first embodiment. (Operation process) and (Stop process 1) are the same as those in the first embodiment.

  Next, the process proceeds to (stop process 2). Hydrogen diffuses to the oxidant gas side and reacts with oxygen contained in the oxidant gas to produce water. When all of the enclosed oxygen has reacted, the reaction to produce water is complete. When the operation is further stopped, the stack temperature decreases from about 64 ° C. (the operation process). As a result, water vapor contained in the sealed gas causes condensation, and the volume of the gas decreases.

  In (stop process 2), the pump 45 is operated intermittently, and the temperature of the stack 38 is measured by the temperature detectors 66 and 67. When the temperature of the stack changes more than a certain level, it is determined that the pressure drop due to condensation is large, and the valve 34 is opened to form a path connecting the branch valve 63 to the stack 38 and the check valve 62, and the branch valve 64 is connected to the check valve 65. It operates so as to form a path connecting the stacks 38, feeds the raw material gas into the encapsulating portion of the fuel gas and the oxidant gas, compensates for the reduction of the gas in each path, and prevents a large stress on the electrolyte 1 and the MEA gasket 11. Thereby, it can further prevent that the electrolyte 1 etc. are damaged. In addition, even if the reaction proceeds, hydrogen does not disappear, so the electrode can always be kept at a low potential, so that dissolution of the electrode containing the catalyst can be suppressed, so that high performance can be maintained for a long time. .

  When the fuel cell system is started, power generation can be performed by setting each component such as a valve so as to be again (operation stroke).

(Embodiment 3)
A flowchart of the operation method according to the third embodiment will be described with reference to FIG. The basic configuration and operation are the same as those in the first embodiment. (Operation process) is the same as in the first embodiment.

  Next, (stop process 1) is performed. In (stop step 1), first, the valve 57 is closed, the blower 39 is stopped, and the supply of the oxidant gas to the stack 38 is stopped. The shut-off valve 58 is then closed and the oxidant gas path of the stack is sealed. By closing the shut-off valve on the gas inlet side and then closing the shut-off valve on the outlet side, it is possible to prevent the sealed gas path including the stack 38 from being abnormally pressurized. At this time, hydrogen in the fuel gas diffuses through the electrolyte 1 and reaches the electrode on the oxidant gas side. Since the oxidant gas is sealed so that there is no inflow or outflow, the diffused hydrogen drifts near the electrode, the electrode potential on the oxidant gas side shows the potential of hydrogen, and the electrode potential drops quickly. . At this time, the oxide or the like attached to the electrode is reduced and removed, so that the activity of the electrode is restored. As a result, the fuel cell can be maintained with high performance.

  Further, the power circuit unit 43 is controlled with a predetermined voltage. In the present embodiment, when the voltage per unit cell of the stack 38 is 0.5 V or higher, the current is controlled by the power circuit unit 43, and when the voltage is lower than 0.5 V, the current is not extracted. As a result, it is possible to prevent the electrode potential from becoming high, and thus it is possible to prevent deterioration such as dissolution of the electrode. Furthermore, since hydrogen diffuses to the oxidant gas side, it reacts with oxygen contained in the oxidant gas to produce water. On the fuel gas side, hydrogen is supplied as a fuel gas, but on the oxidant gas side, oxygen reacts and the concentration decreases. The volume of the oxidant gas to be sealed is more than twice the volume of the fuel gas when sealed, or the electrode potential on the oxidant gas side is sufficiently lowered to completely remove oxides etc. adhering to the electrode surface In this case, (stop process 1) can be maintained for a sufficiently long time, oxygen can be consumed, and performance degradation due to oxygen can be sufficiently prevented.

  Further, when oxygen in the enclosed oxidant gas is consumed by the reaction, the pressure in the oxidant gas path decreases. When the pressure measuring unit 60 detects a pressure drop in the oxidant gas path, the branch valve 64 is opened, and the raw material gas purified by the gas cleaning unit 34 is caused to flow into the oxidant gas path. As a result, stress due to decompression of the enclosing path can be prevented, and high performance can be maintained for a long time.

  Next, the process proceeds to (stop process 2). In (stop process 2), the valve 34 is closed and the valve 61 and the shut-off valve 49 are closed except when the source gas is flowing through the sealing path. Next, by closing the shut-off valve 51, an abnormal pressure change in the fuel gas sealing path can be prevented. When the pressure measuring unit 59 detects that the pressure of the sealed fuel gas path has decreased due to hydrogen diffusion or the like, the valve 34 is opened, and the raw material gas is caused to flow into the fuel gas path sealed by the branch valve 63. As a result, the pressure change is almost eliminated and the stress change to the electrolyte 1 or the like can be prevented, so that high performance can be maintained for a long time.

  According to the present embodiment, since the oxygen gas and fuel gas enclosing path can be made in a state where there is no oxygen and hydrogen is present, only the oxide on the surface of the two electrodes is removed to increase the activity. In addition, since the potential can be kept low, deterioration due to dissolution or the like can be prevented, so that high performance can be maintained for a long time.

  When the fuel cell system is started, power generation can be performed by setting each component such as a valve so as to be again (operation stroke).

(Embodiment 4)
A flowchart of the operation method of the fourth embodiment will be described with reference to FIG. The basic configuration and operation are the same as those in the third embodiment. (Operation process) is the same as in the third embodiment.

  Next, (stop process 1) is performed. In (stop step 1), first, the valve 57 is closed, the blower 39 is stopped, and the supply of the oxidant gas to the stack 38 is stopped. Next, the shutoff valve 58 is closed, the oxidant gas path of the stack is sealed, the branch valve 64 is opened, and a path through which the source gas purified by the gas cleaning unit 34 can flow into the oxidant gas path is created. The oxidizing gas sealing path is pushed by the pressure of the raw material gas. Usually, since the pressure of city gas etc. is 5 kPa or less, it is very slight.

  Further, the oxidant gas does not flow back into the raw material gas by the function of the check valve 65. At this time, hydrogen in the fuel gas diffuses through the electrolyte 1 and reaches the electrode on the oxidant gas side. Since the oxidant gas is sealed so that there is no inflow or outflow, the diffused hydrogen drifts near the electrode, the electrode potential on the oxidant gas side shows the potential of hydrogen, and the electrode potential drops quickly. . At this time, the oxide or the like attached to the electrode is reduced and removed, so that the activity of the electrode is restored. As a result, the fuel cell can be maintained with high performance.

  Further, the power circuit unit 43 is controlled with a predetermined voltage. In the present embodiment, when the voltage per unit cell of the stack 38 is 0.5 V or higher, the current is controlled by the power circuit unit 43, and when the voltage is lower than 0.5 V, the current is not extracted. As a result, it is possible to prevent the electrode potential from becoming high, and thus it is possible to prevent deterioration such as dissolution of the electrode. Furthermore, since hydrogen diffuses to the oxidant gas side, it reacts with oxygen contained in the oxidant gas to produce water. On the fuel gas side, hydrogen is supplied as a fuel gas, but on the oxidant gas side, oxygen reacts and the concentration decreases. The volume of the oxidant gas to be sealed is more than twice the volume of the fuel gas when sealed, or the electrode potential on the oxidant gas side is sufficiently lowered to completely remove oxides etc. adhering to the electrode surface In this case, (stop process 1) can be maintained for a sufficiently long time, oxygen can be consumed, and performance degradation due to oxygen can be sufficiently prevented. Further, when the oxygen in the enclosed oxidant gas is consumed by the reaction, the pressure of the oxidant gas path decreases, so that the raw material gas purified by the gas cleaning unit 34 flows into the oxidant gas path. Thereby, the stress by the pressure change of an enclosure path | route can be prevented, and high performance can be maintained for a long period of time.

  Next, the process proceeds to (stop process 2). In (stop step 2), after closing the valve 61 and the shutoff valve 49, the shutoff valve 51 is closed and the fuel gas path is sealed. Further, the branch valve 62 is opened to create a path through which the raw material gas purified by the gas cleaning unit 34 can flow into the fuel gas path. The fuel gas sealing path is pushed by the pressure of the raw material gas, and the pressure difference through the electrolyte 1 is eliminated. Usually, since the pressure of city gas etc. is 5 kPa or less, it is very slight. Due to the function of the check valve 62, the fuel gas does not flow into the raw material gas. When the pressure of the fuel gas path enclosed by hydrogen diffusion or the like decreases, the raw material gas flows in, so there is almost no pressure change and it is possible to prevent stress changes to the electrolyte 1 etc., so that high performance is maintained for a long time. It can be done.

  According to the present embodiment, since the oxygen gas and fuel gas enclosing path can be made in a state where there is no oxygen and hydrogen is present, only the oxide on the surface of the two electrodes is removed to increase the activity. In addition, since the potential can be kept low, deterioration due to dissolution or the like can be prevented, so that high performance can be maintained for a long time.

  When the fuel cell system is started, power generation can be performed by setting each component such as a valve so as to be again (operation stroke).

  INDUSTRIAL APPLICABILITY The fuel cell system and the operation method of the present invention have an effect of suppressing deterioration due to start / stop or improving durability, and are useful for power generation apparatuses and devices using a polymer electrolyte membrane.

  Further, since a source gas such as city gas is used as the inert gas, it is useful for a stationary fuel cell cogeneration system.

Structure diagram showing a part of a unit cell of a fuel cell in Embodiments 1 to 4 of the present invention Structure diagram of stack in which fuel cells according to Embodiments 1 to 4 of the present invention are stacked The block diagram which shows the fuel cell system in Embodiment 1-4 of this invention 1 is a flowchart showing a method for operating a fuel cell system according to Embodiment 1 of the present invention. Flowchart showing the operation method of the fuel cell system in Embodiment 2 of the present invention. Flowchart showing the operation method of the fuel cell system in Embodiment 3 of the present invention. Flowchart showing the operation method of the fuel cell system in Embodiment 4 of the present invention. Configuration diagram showing a conventional fuel cell system

Explanation of symbols

1 Electrolyte 2a Catalytic reaction layer (anode side)
2c Catalytic reaction layer (cathode side)
3a Diffusion layer (anode side)
3c Diffusion layer (cathode side)
4a Electrode (Anode side)
4c electrode (cathode side)
7a Separator (Anode side)
7c Separator (cathode side)
32 Gas cleaning unit 35 Fuel generator 43 Power circuit unit 44 Control unit 52 Voltage measurement unit 49, 51, 57, 58 Shut-off valve 59, 60 Pressure measurement unit 66, 67 Temperature detection unit

Claims (9)

A pair of separators having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidant gas containing oxygen to the other A fuel cell comprising: a fuel gas and an oxidant gas supply path and a discharge valve; a fuel generator for generating fuel gas to be supplied from the source gas to the fuel cell; and a fuel cell A gas purifier that removes the components to be supplied from the raw material gas, a power circuit that extracts power from the fuel cell, a voltage measuring unit that measures the voltage of the fuel cell, and a controller that controls the gas and the power circuit In the fuel cell system, when the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, the shutoff valve is closed, the inflow and the discharge of the fuel gas and the oxidant gas are stopped, and the fuel cell system is stopped. Fuel cell system the fuel cells to inert gas in injected into one or both of the oxidant gas passage and the fuel gas passage. 2. The fuel cell system according to claim 1, wherein the volume of the space of the oxidant gas path sealed by the shut-off valve is a volume not exceeding twice the volume of the space of the fuel gas path sealed by the shut-off valve. The fuel cell system according to claim 1 or 2, wherein the dew point of the gas inert to the fuel cell is 0 ° C or lower. A pair of separators having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidant gas containing oxygen to the other A fuel cell comprising: a fuel gas and an oxidant gas supply path and a discharge valve; a fuel generator for generating fuel gas to be supplied from the source gas to the fuel cell; and a fuel cell A gas purifier that removes the components to be supplied from the raw material gas, a power circuit that extracts power from the fuel cell, a voltage measuring unit that measures the voltage of the fuel cell, and a controller that controls the gas and the power circuit In the fuel cell system, when the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, the shutoff valve of the oxidant gas flow path is closed, and the inflow and discharge of the oxidant gas are stopped. After, the method of operating a fuel cell system for closing the shutoff valve in the fuel gas passage. A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidant gas containing oxygen to the other A fuel cell including a separator, a shut-off valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied from the raw material gas to the fuel cell, and an adverse effect on the fuel cell A gas purifier that removes the components that give the gas from the source gas, a power circuit that extracts power from the fuel cell, a voltage measuring unit that measures the voltage of the fuel cell, and a controller that controls the gas and power circuit, etc. When the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, the shutoff valve of the oxidant gas channel and the fuel gas channel is closed, and the inflow of gas After stopping the output, the one or both of the oxidant gas flow path the fuel gas flow path, a method of operating a fuel cell system for inert gas injection at regular intervals. A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidant gas containing oxygen to the other A fuel cell including a separator, a shut-off valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied from the raw material gas to the fuel cell, and an adverse effect on the fuel cell A gas purifier that removes the components that give off from the source gas, a power circuit that extracts power from the fuel cell, a voltage measuring unit that measures the voltage of the fuel cell, a temperature detector that detects the temperature of the fuel cell, and a gas In the fuel cell system having a control unit that controls the power circuit unit and the like, when the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, and the oxidant gas flow path and the After closing the shutoff valve of the fuel gas flow path and stopping the inflow and discharge of gas, when the temperature of the stack changes by a certain temperature or more from the temperature detector, one of the oxidant gas flow path and the fuel gas flow path or A method of operating a fuel cell system in which an inert gas is injected into both. A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidant gas containing oxygen to the other A fuel cell including a separator, a shut-off valve provided in a supply path and a discharge path for fuel gas and oxidant gas, a fuel generator for generating fuel gas to be supplied from the raw material gas to the fuel cell, and an adverse effect on the fuel cell A gas cleaning unit that removes the components that give the gas from the source gas, a power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, and the pressure of the oxidant gas path and the fuel gas path of the fuel cell In a fuel cell system having a pressure detection unit for detecting gas and a control unit for controlling the gas and power circuit unit, the supply of fuel gas and oxidant gas is stopped when the fuel cell is stopped. After the shutoff valves of the oxidant gas flow path and the fuel gas flow path are closed and gas inflow and discharge are stopped, the oxidant gas flow path changes when the pressure of the gas flow path of the stack changes by a certain level or more from the pressure detection unit. And a method of operating a fuel cell system in which an inert gas is injected into one or both of the fuel gas flow paths. A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidant gas containing oxygen to the other A fuel cell including a separator, a shutoff valve provided in a supply path and a discharge path for fuel gas and oxidant gas, and an inert gas supply valve for supplying an inert gas into a path enclosed by the shutoff valve; A fuel generator for generating fuel gas to be supplied from the source gas to the fuel cell, a gas cleaning unit for removing components that adversely affect the fuel cell from the source gas, a power circuit unit for extracting power from the fuel cell, and a fuel cell In a fuel cell system having a voltage measuring unit for measuring the voltage of the fuel cell and a control unit for controlling the gas and power circuit unit, the fuel gas and the oxidant gas are supplied when the fuel cell is stopped. After stopping the shut-off valves of the oxidant gas flow path and the fuel gas flow path and stopping the inflow and discharge of the gas, the fuel cell is opened and the inert gas supply valve is opened to always supply an inert gas at a constant pressure. How to operate the system. 9. The fuel cell system or the operation of the fuel cell system according to any one of claims 1 to 8, wherein a raw material gas removed by a component gas cleaning unit that adversely affects the fuel cell is used as the gas inert to the fuel cell. Method.

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