JP2006302551A - Fuel cell system and its operating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system wherein deterioration caused by oxidation and dissolution due to the potential rise of a positive electrode and a negative electrode is suppressed when stopping the system operationally and for a long period of time to enhance its durability, and also to provide its operating method. <P>SOLUTION: During stop of the fuel cell system, a gas passage of a fuel cell stack 38 is filled with water. Thereby, gas is prevented from infiltrating by means of a water seal even when the fuel cell system is stopped for a long period of time, and deterioration caused by oxidation and dissolution of the electrodes is suppressed to enhance durability of the fuel cell system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a fuel cell, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, a power circuit unit that extracts power from the fuel cell, a control unit that controls the gas, the power circuit unit, and the like. The present invention relates to a provided fuel cell system and an operation method thereof.

  The configuration and operation of a conventional general solid polymer electrolyte type fuel cell are the same as those of the fuel cell system used in the fuel cell system according to Embodiments 1 and 2 of the present invention shown in FIGS. 2 will be described with reference to the conventional fuel cell system shown in FIG.

  FIG. 2 shows a basic configuration 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. In this catalytic reaction layer, the reaction of the following chemical formula 1 and the chemical formula 2 shown in the following (chemical formula 2) occurs, and the fuel cell as a whole undergoes the reaction of the chemical formula 3 shown in the following (chemical formula 3). appear.

  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 converted into the oxidant gas (hereinafter referred to as the cathode gas) and the catalytic reaction layer. In the reaction shown in (Chemical Formula 2) (hereinafter referred to as the cathodic reaction), water is produced, and at this time, electricity and heat are produced.

  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 fuel gas such as hydrogen is involved is referred to as an anode, and in the following figure, it is represented by the symbol a, the side in which oxidant gas such as air is involved is referred to as the cathode, and in the following diagram, it is represented by symbol c. did. 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 electrodes 4 a and 4 c and the electrolyte 1. The MEA 5 mechanically fixes the MEA 5 and electrically connects the adjacent MEAs 5 to each other in series. Further, the MEA 5 supplies the reaction gas to the electrodes 4a and 4c, and carries the gas generated by the reaction and excess gas. A pair of conductive separators 7a and 7c, in which gas channels 6a and 6c for leaving are formed on the surface in contact with the MEA 5, are arranged.

  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 constitute a basic fuel cell unit (hereinafter referred to as a cell). Formed). 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 11 seals the MEA 5 and the separator 7a or 7c, and the separator gasket 10 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.

  A fuel cell stack in which the cells shown in FIG. 3 are stacked will be described. 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 plates 21a and 21c are for taking out current from the fuel cell stack, and the insulating plates 22a and 22c electrically insulate the cell from the outside. The end plates 23a and 23c fasten and mechanically hold the fuel cell stack in which the cells are stacked.

  The fuel cell system shown in FIG. 5 will be described. 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 fuel cell stack 38 through the fuel gas pipe 37. The blower 39 guides the oxidant gas to the fuel cell stack 38 through the intake pipe 40. The exhaust pipe 42 discharges the oxidant gas discharged from the fuel cell stack 38 to the outside of the fuel cell system. The fuel gas that has not been used in the fuel cell 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 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 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. When water flows through the fuel cell stack 38, the generated heat can be used outside the fuel cell system while maintaining the heated fuel cell stack 38 at a constant temperature. The fuel cell system includes a fuel cell 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. Reference numerals 37a and 37b denote pressure measuring units, 50 denotes an anode exhaust gas port, and 52 denotes a voltage measuring unit.

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 source gas such as city gas mainly composed of methane is used for household use, it is stopped during periods of low electricity and heat consumption in order to increase the utility cost and CO ₂ reduction effect. 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 CO ₂ reduction effect, and fuel cells. It is desirable that the system can flexibly cope with an operation pattern including start and stop. 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 5). Further, without using nitrogen, the fuel gas was purged with water and stopped while the water was stored to prevent the membrane from drying (see Patent Document 6).

  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 the potential of the hydrogen electrode does not dissolve impurities such as extreme metal species, the potential is greatly influenced by the adsorbed species of the air electrode. From the chemical formula 4 shown in the following (Chemical formula 4), It is thought to be due to the hybrid potential of the chemical reaction as shown in Chemical Formula 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 JP 2003-317771 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, the method of purging the inert gas has a problem that the gas inside the fuel cell stack of the fuel cell is replaced with external air due to diffusion and deteriorates the electrode during a long-term stoppage.

  Further, when the voltage exceeds 0.88 V, as shown in Chemical Formula 7 of (Chemical Formula 7), oxidation of Pt occurs, and not only the activity of Pt as a catalyst decreases but also dissolution in water occurs. 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.

  In addition, 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. When filled with, the remaining air or oxygen that gradually enters from the outside shows a voltage of about 0.93 V to 1.1 V on both electrodes, so that the electrode is oxidized or eluted and the performance is degraded. There is a problem.

  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, the volume is reduced, and the negative pressure is generated. Therefore, there are problems that external oxygen flows in, the electrolyte 1 is stressed and damaged, and the electrodes 4a and 4c are short-circuited.

  Further, in the conventional method of generating power in the state where the supply of the oxidant gas is stopped and consuming oxygen in the gas flow path 6c, the gas flow path 6a is purged with an inert gas. There has been a problem that the electrode 4c is oxidized and deteriorated due to the influence of oxygen remaining without being consumed and air mixed in due to diffusion or leakage. Further, 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 there is a problem in that the battery voltage at startup varies.

  In addition, those that try to improve the performance of the cathode electrode due to hydrogen leaking to the cathode where air exists from the anode, the potential becomes unstable due to the mixing of oxygen and hydrogen, and there is a problem that the performance of the cathode varies. There is.

  Also, there is no indication for measures to improve the performance of the cathode electrode by flowing hydrogen to the cathode, as countermeasures against oxygen entering by gas diffusion during stoppage are shown. There is a problem that the life is shortened.

  Further, when the gas path is purged with the fuel gas or the raw material gas at the time of starting, there is a problem that the fuel gas or the raw material gas is discharged to the outside and the energy utilization rate is deteriorated.

  In view of the above-described conventional problems, the problem to be solved by the present invention is to provide a long-life fuel cell system and an operation method thereof for suppressing deterioration and improving durability of the fuel cell when starting and stopping. It is in.

  In order to solve the above problems, the fuel cell system of the present invention stops the supply of the fuel gas and the oxidant gas, detects the voltage of the fuel cell, and at least oxidizes water in the fuel cell when the fuel cell starts and stops. Injected into the agent gas path. As a result, it is possible to prevent the cathode and anode electrodes from becoming a high potential, and at least the cathode electrode is filled with water, so that it is possible to prevent oxygen from entering even during stoppage. A long-life fuel cell system that does not deteriorate and maintains high performance for a long time can be realized.

  Further, the fuel cell system operating method of the present invention stops the supply of the fuel gas and the oxidant gas when the fuel cell is stopped, detects the voltage of the fuel cell, and fuels water when the voltage is 0.88 V or less. This is an operation method in which the battery is injected into at least an oxidizing gas path. As a result, it is possible to prevent oxidation / dissolution of the electrode, further eliminate oxygen in the oxidant gas path, and even if stopped for a long time, it is possible to prevent gas from entering if there is water, including a long-term stoppage. Prevents deterioration due to start / stop and maintains high performance for a long time.

  The fuel cell system and its operation method of the present invention is to put water into one or both of the fuel gas and the oxidant gas after the electrode potential on the oxidant gas side is lowered at the time of stop to prevent electrode deterioration due to acid and dissolution. Thus, even when starting and stopping with a long-term stop, 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 that includes a pair of separators, 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, A power circuit unit that extracts power from the fuel cell; a voltage measurement unit that measures the voltage of the fuel cell; a control unit that controls gas, the power circuit unit, and the like; cooling water that extracts heat generated in the fuel cell; A cooling water tank for storing cooling water. When the fuel cell is stopped, the supply of fuel gas and oxidant gas is stopped, the voltage of the fuel cell is detected, and water is injected into at least the oxidant gas path of the fuel cell. It is a fuel cell system.

  As a result, when the fuel cell is started and stopped, hydrogen in the fuel gas moves to the electrode on the oxidant gas side through the membrane, lowers the potential of the electrode on the oxidant gas side, and can suppress electrode deterioration due to oxidation / dissolution. By injecting water into one or both of the fuel gas and oxidant gas paths, the inflow of oxygen can be suppressed even during a long-term stop, so that deterioration due to start / stop including a long-term stop can be prevented. High performance can be maintained for a long time.

  According to a second aspect of the present invention, there is provided an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and an oxidant gas containing oxygen for the other A fuel cell including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell And a cooling water tank for storing water and cooling water. When the fuel cell is stopped, the supply of fuel gas and oxidant gas is stopped, the voltage of the fuel cell is detected, and water is fueled when the voltage is 0.88 V or less. It is an operating method of a fuel cell system for injecting at least oxidizer gas path pond.

  As a result, when stopping, hydrogen in the fuel gas moves to the electrode on the oxidant gas side through the membrane, lowers the potential of the electrode on the oxidant gas side, and the fuel gas electrode is a hydrogen electrode. .88V or less is that the potential is 0.88V or less in terms of hydrogen electrode ratio, and it is possible to prevent the oxidation of platinum represented by the chemical formula 9 of (Chemical Formula 9), and to oxidize and dissolve the electrode. In addition, by injecting water at least into the oxidant gas path, oxygen in the oxidant gas path can be eliminated, and even if stopped for a long period of time, it can be prevented from entering the gas if there is water. Therefore, it is possible to prevent deterioration due to start-up and stop, including stoppage, and maintain high performance for a long time.

  According to a third aspect of the invention, there is provided an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes, and an oxidant gas containing oxygen for the other A fuel cell including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell A cooling water tank for storing water and cooling water is provided, and when the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, and a sufficient time has passed so that the voltage of the fuel cell becomes 0.88 V or less. A method of operating a fuel cell system for injecting at least oxidizer gas passage of the fuel cell water.

  Thus, by managing the time without measuring the voltage, the potential of each electrode of the fuel cell can be reduced to 0.88 V or less at which the oxidation of platinum represented by the chemical formula 9 of (Chemical Formula 9) occurs with a simple configuration. , Can prevent oxidation / dissolution of the electrode, and at least by injecting water into the oxidant gas path, the oxygen in the oxidant gas path can be eliminated, and even if it is stopped for a long period of time, it can prevent gas from entering Therefore, it is possible to prevent deterioration due to start / stop including long-term stop and maintain high performance for a long time.

  According to a fourth aspect of the present invention, there is provided an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes, and an oxidant gas containing oxygen for the other A fuel cell including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell A cooling water tank for storing water and cooling water. When the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, and water is injected when the pressure of the gas path of the fuel cell is reduced. It is a fuel cell system capable of a force change constant below.

  As a result, when the supply of the fuel gas and the oxidant gas is stopped, hydrogen mainly moves from the anode side to the cathode side through the membrane, reacts with oxygen on the cathode side to become water, and approximately the fuel gas made from the raw material gas 80% is hydrogen, but when air is used as the oxidant gas, oxygen is approximately 20%. Therefore, when hydrogen and oxygen react at a ratio of 2 to 1, hydrogen will eventually remain. Since both electrodes of the battery are at a low potential, deterioration due to oxidation and dissolution can be prevented, and furthermore, an amount of water corresponding to the gas reacting to reduce the volume is injected, so the pressure in each gas path is It is possible to prevent a large change, and since a large stress is not applied to the film, a long life can be obtained without causing a crack due to the stress.

  According to a fifth aspect of the present invention, there is provided an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and an oxidant gas containing oxygen for the other A fuel cell including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell A cooling water tank for storing water and cooling water. When the fuel cell is stopped, the gas supply is stopped when the oxidant gas precedes the fuel gas, and the injection of water into the gas path of the fuel cell is also performed by the oxidant gas. Since the fuel cell system is operated before the fuel gas path, the supply of the oxidant gas is stopped, but the fuel gas is supplied for a certain amount of time. Since the remainder of the reaction and consumed is more hydrogen, the potential of the electrode can be lowered more reliably and the life can be more reliably increased.

  According to a sixth aspect of the present invention, there is provided an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and an oxidant gas containing oxygen for the other A fuel cell including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell And a cooling water tank for storing water and cooling water. When the fuel cell is stopped, the supply of the oxidant gas is stopped. The oxidant gas path injects water and expels the gas, and then stops the fuel gas and stops fuel. By making the gas path a fuel cell system that can inject water when the volume decreases due to temperature change etc., it is possible to prevent the film from being damaged due to volume change during stoppage, so the film will not be damaged, High performance can be maintained for a long time.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, a fuel cell system or a fuel cell system operating method that uses cooling water as water that enters the path of the fuel cell when stopped Thus, since a water that does not adversely affect the fuel cell can be used without providing a new water supply device, a long life can be realized with a simple configuration.

  The eighth invention provides an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas 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 including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell A cooling water tank for storing water and cooling water is provided. Water is injected into one or both of the fuel gas and oxidant gas paths at the time of stoppage and stopped, and one of the fuel gas and oxidant gas paths at the time of start-up is stopped. The both water chased with fuel gas purified in the gas purifying unit, the fuel gas used for purging is a fuel cell system capable of eliminating the leakage of fuel gas is burned in the combustion section.

  This prevents air from entering even when the water held in the fuel cell is expelled at the start-up, prevents the electrode potential from being raised, prevents electrode deterioration, and also causes the fuel gas used for expulsion to fuel. This makes it possible to recover energy as heat, so that energy efficiency is not reduced.

  A ninth invention is a gas 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 including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell It is equipped with a cooling water tank for storing water and cooling water. At the time of stoppage, water is injected into at least the fuel gas path to stop it. At startup, the water in the fuel gas path is expelled with fuel gas and used for expulsion. The fuel gas is a fuel cell system capable of eliminating the leakage of fuel gas is burned in the combustion section.

  This prevents the entry of air even when driving out the water held in the fuel cell at the time of start-up, and further prevents the deterioration of the electrode because the potential of the electrode can be kept low more reliably because hydrogen is supplied, Furthermore, energy can be recovered as heat by fueling the fuel gas used for eviction, so that energy efficiency can be prevented from being reduced.

  A tenth aspect of the invention provides an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas that supplies / discharges a fuel gas containing at least hydrogen to one of the electrodes and supplies / discharges an oxidant gas containing oxygen to the other A fuel cell including a pair of separators having a flow path, a fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, and a gas cleaning unit that removes components that adversely affect the fuel cell from the raw material gas A power circuit unit that extracts power from the fuel cell, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and cooling that extracts heat generated in the fuel cell A cooling water tank for storing water and cooling water. When stopping, inject water into one or both of the fuel gas and oxidant gas passages to stop it. By using the fuel cell system operation method, fuel gas can be flowed even at start-up, and oxidant gas can be flowed while keeping the electrode potential sufficiently low, so that power generation can be started without causing deterioration of the electrode at high potential at start-up. This will extend the service life.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment.

(Embodiment 1)
FIG. 1 is a configuration diagram of a fuel cell system according to Embodiment 1 of the present invention, and FIG. 2 shows a basic configuration of a polymer electrolyte fuel cell employed in the fuel cell system of the present invention. FIG. 3 is a configuration diagram of a fuel cell stack in which fuel cells are stacked. Before describing the fuel cell system of the present invention, the basic structure of the employed polymer electrolyte fuel cell will be described with reference to FIGS.

  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 catalytic reaction layer 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 of (Chemical Formula 1) and Chemical Formula 2 of (Chemical Formula 2) occurs in this catalytic reaction layer. The fuel gas containing at least hydrogen undergoes the reaction shown in Chemical Formula 1 of (Chemical Formula 1) (hereinafter referred to as the anode reaction), and the hydrogen ions moved through the electrolyte 1 are converted into the oxidant gas and the catalytic reaction layer (Chemical Formula 2). By the reaction shown in Chemical Formula 2 (hereinafter referred to as the cathode reaction), water is generated, and at this time, electricity and heat are generated.

  The side in which a fuel gas such as hydrogen is involved is called an anode, and in FIGS. 2 and 3, the side with an oxidant gas such as air is called a cathode, and the side in FIG. 2 and FIG. c is attached. Further, 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) 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. 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 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. 3 shows a fuel cell stack in which the cells described in FIG. 1 are stacked. 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 fuel cell stack 38 from a pair of current collecting plates 21a and 21c, the cell and the outside are electrically insulated by a pair of insulating plates 22a and 22c, and a cell is formed by a pair of end plates 23a and 23c. Are stacked and mechanically held.

  The oxidant gas is provided with an oxidant gas inlet 24in (hereinafter referred to as a cathode inlet) provided at the upper part of the end plate 23c and a cooling water inlet 26in, and a fuel gas outlet 25out (hereinafter referred to as an anode outlet) at the lower part. Is provided). A fuel gas inlet 25in (hereinafter referred to as an anode inlet, not shown) is provided at the upper part of the other end plate 23a forming a pair with the end plate 23c provided with the cathode inlet 24in, and an oxidation is provided at the lower part. An agent gas outlet 24out (hereinafter referred to as a cathode outlet, not shown) and a cooling water outlet 26out (not shown) are provided.

  The oxidant gas and the fuel gas are supplied to the fuel cell stack through the cathode inlet 24in and the anode inlet 25in, and are supplied to all the single cells through the manifold arranged at the top. In each single cell, the gas flow paths 6a and 6c have various shapes such as a meandering shape (so-called serpentine shape), but as a whole flow from the top to the bottom, and then the oxidant gas and the fuel gas are Collected from each single cell and discharged from cathode outlet 24out and anode outlet 25out, respectively.

  Further, the cooling water enters the fuel cell stack from the cooling water inlet 26in and is supplied to all the single cells through the manifold arranged at the upper part. In the single cell, the cooling water path 8 has various shapes such as a straight shape and a meandering shape, but as a whole, water flows from the upper part toward the lower part. Therefore, the temperature of the cooling water during power generation and heat generation of the fuel cell tends to be higher at the cooling water outlet 26out than at the cooling water inlet 26in, and in each single cell, the temperature tends to be higher in the lower part than in the upper part.

  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. A valve 34 is provided in the path of the raw material gas pipe 33 and is opened when the flow of the raw material gas is controlled and the gas is allowed to flow to the fuel generator 35. The fuel generator 35 generates a fuel gas containing at least hydrogen from the raw material gas.

  Reference numeral 38 denotes a fuel cell stack, which is a fuel cell stack in which a plurality of single cells of a fuel cell whose details are shown in FIGS. 1 and 2 are stacked. Fuel gas is led from the fuel generator 35 to the fuel cell stack 38 through the fuel gas pipe 37 from the anode inlet 25in. The fuel gas that has not been used in the fuel cell stack 38 flows again into the fuel generator 35 through the off-gas pipe 48 in which the auto drain 70 is disposed from the anode outlet 25out. The auto drain 70 reduces moisture in the gas flowing into the off-gas pipe 48 by condensation or the like.

  The gas whose moisture has been reduced by the auto drain 70 and is easily combusted is used for combustion or the like by a burner (not shown) provided in the fuel generator 35 or the like, and an endothermic reaction for generating fuel gas from the raw material gas. Used for etc. Exhaust gas such as combustion is discharged to the outside through the anode exhaust port 50. An anode pressure gauge 91 is disposed in the fuel gas pipe 37 and measures the pressure of the gas path 6 a in the fuel cell stack 38 communicating with the fuel gas pipe 37.

  The air as the oxidant gas is led from the outside to the first humidifier 41 by the blower 39 through the intake pipe 40 and then humidified by the second humidifier 42, and then the cathode inlet through the secondary out pipe 51. The fuel cell stack 38 is led from 24 inches. The oxidant gas that has not been used in the fuel cell stack 38 passes through the cathode off-gas pipe 62 from the cathode outlet 24out and flows into the primary path of moisture and heat of the first humidifier, and then flows from the exhaust pipe 63 to the outside of the fuel cell system. To be discharged.

  The voltage of the fuel cell stack 38 is measured by the voltage measuring unit 52, the electric power of the fuel cell stack 38 is taken out by the power circuit unit 43, and the gas and the power circuit unit 43 are controlled by the control unit 44. Cooling water that takes heat away from the fuel cell stack 38 is stored in the cooling water tank 60. The cooling water in the cooling water tank 60 is caused to flow from the cooling water inlet pipe 46 through the cooling water inlet 26in to the water path of the fuel cell stack 38 by the cooling water circulation pump 45, and the water flowing through the fuel cell 38 is cooled. After flowing from the water outlet 26out to the second humidifier 42 through the cooling water outlet pipe 47 and acting as a primary fluid for exchanging heat with water in the second humidifier 42, the hot outlet is connected via the hot water primary outlet pipe 54. It flows into the three-way valve 55.

  The three-way valve 55 controls the ratio of the cooling water flowing through the connected cooling water return pipe 56 and the heat exchange pipe 57. If the temperature sensor 61 disposed in the cooling water tank 60 causes the temperature of the cooling water in the cooling water tank 60 to be high, the three-way valve 55 increases the ratio of the cooling water flowing through the heat exchange pipe 57 to increase the cooling water in the cooling water tank 60. If the temperature of the cooling water is low, the three-way valve 55 increases the ratio of the cooling water flowing through the cooling water return pipe 56. The cooling water that has flowed through the heat exchanger pipe 57 flows into the heat exchanger 58.

  The heat exchanger 58 moves heat using the cooling water as a primary fluid for heat exchange, and the cooling water that has passed through the heat exchanger 58 returns to the cooling water tank 60 via the heat exchange return pipe 59. A secondary inlet pipe 65 and a secondary outlet pipe 66 are connected to the secondary side of the heat exchanger 58, and the heat exchanged from the cooling water in the heat exchanger 58 is stored in an external hot water storage or the like. In the fuel cell stack 38, hydrogen in the fuel gas and oxygen in the oxidant gas react to generate a reaction represented by Chemical Formula 1 of (Chemical Formula 1) and Chemical Formula 2 of (Chemical Formula 2). ) Occurs as shown in Chemical Formula 3.

  In the fuel cell stack 38, hydrogen and oxygen react to generate water, and at this time, electricity and heat are generated. Since the oxidant gas, the fuel gas, and the cooling water flow from the upper part to the lower part of the fuel cell stack 38, the hydrogen gas partial pressure in the fuel gas and the oxygen partial pressure in the oxidant gas are lower in the lower part than in the upper part. High moisture content and temperature. Since the reaction amount is determined by the current taken out from the fuel cell stack 38, the calorific value can be substantially determined. Therefore, the temperature condition of the fuel cell stack 38 can be kept almost constant by controlling the temperature and speed of the cooling water flowing into the fuel cell stack 38.

  The cathode water purge three-way valve 75 is disposed in the path of the cathode off-gas pipe 62, and the cathode water purge three-way valve 75 is connected to the cooling water tank 60 by the cathode water purge pipe 76. A cathode pressure gauge 92 is arranged between the fuel cell stack 38 and measures the pressure of the gas path 6c in the fuel cell stack 38 in communication therewith. The fuel gas purge pipe 71 connects the cooling water tank 60 and the fuel gas pipe 37, and controls the inflow of the cooling water into the fuel gas pipe 37 by opening and closing the fuel gas purge valve 72.

  A cathode switching three-way valve 80 is disposed in the secondary out pipe 51, and gas supplied to the fuel cell stack 38 is oxidant gas that has passed through the humidifier or fuel gas that has passed through the fuel gas pipe 37. Switch between. A cathode off-gas three-way valve 81 is disposed in the cathode off-gas pipe 62, and switches whether gas or water passing through the cathode off-gas pipe 62 flows to the first humidifier 41 side or the cathode drain pipe 82 side. .

  The cathode drain pipe 82 is connected to an anode off-gas three-way valve 83 provided in the path of the off-gas pipe 48. The anode offgas three-way valve 83 switches the fuel gas after passing through the fuel cell stack 38 and the fluid such as water after passing through the cathode drain pipe 82 to the auto drain 70 provided in the path of the offgas pipe 48. The exhaust pipe 85 discharges oxidant gas exhaust gas to the outside.

  The basic operation of the fuel cell system during power generation will be described below. 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 and 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 unit 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.

  In the fuel generator 35, hydrogen and carbon dioxide are generated by the reaction shown in the following chemical formula 9 (chemical formula 9). The carbon monoxide generated simultaneously is 10 ppm or less by the shift reaction as shown in the following chemical formula 10 and the carbon monoxide selective oxidation reaction as shown in the following chemical formula 11. To be removed.

  Here, when water is added in a minimum amount necessary for the reaction, a fuel gas containing hydrogen and moisture can be produced. The fuel gas purge valve 72 is closed, the cathode switching three-way valve 80 is a path between the second humidifier 42 and the fuel cell stack 38, and the cathode offgas three-way valve 81 is a path between the fuel cell stack 38 and the first humidifier 41. The anode off-gas three-way valve 83 is set to be a path between the fuel cell stack 38 and the auto drain 70, and the fuel gas flows into the fuel cell stack 38 of the fuel cell via the fuel gas pipe 37.

  The oxidant gas passes through the first humidifier 41 and the second humidifier 42 by the blower 39 and then flows into the fuel cell stack 38. Electricity is generated here, and heat is also generated. The exhaust gas of the oxidant gas is discharged to the outside through the exhaust pipe 85. As the 1st humidifier 41, what flows oxidant gas into warm water, what blows water in oxidant gas, etc. can be used, but the flat membrane type total heat exchange type was used in this embodiment. In this case, when water and heat in the exhaust gas pass through the first humidifier 41, they are transferred from the intake pipe 40 into the oxidant gas that is 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, then passes through the second humidifier 42 from the cooling water outlet pipe 47, and is led to the three-way valve 55. . As the second humidifier 42, one that flows an oxidant gas into warm water, one that blows water into the oxidant gas, or the like can be used, but in this embodiment, the water and heat in the cooling water are the first in the flat membrane type. When passing through the second humidifier 42, it is moved into the oxidant gas flowing from the first humidifier 41.

  If the temperature of the controlled cooling water tank 60 is low so that the temperature of the cooling water in the cooling water tank 60 becomes constant, the three-way valve 55 reduces the amount of water flowing through the cooling water return pipe 56. Conversely, if the temperature of the cooling water tank 60 is high, the amount of water flowing through the heat exchange pipe 57 is increased. The water that has passed through the heat exchange pipe 57 is used as a heat supply source to the secondary side as a primary side of heat in the heat exchanger 58. A secondary inlet pipe 65 and a secondary outlet pipe 66 are connected to the secondary side of the heat exchanger 58, and the heat exchanged from the cooling water in the heat exchanger 58 is stored in an external hot water storage or the like.

  The cooling water that has been heated by the heat exchanger 58 and has fallen in temperature returns to the cooling water tank 60 through the cooling water inlet pipe 46, so that the temperature in the cooling water tank 60 becomes low. As a result, the heat generated in the fuel cell stack 38 of the fuel cell can be taken out and used for hot water supply or the like. In the power generation in the fuel cell stack 38, the voltage is measured by the voltage measurement unit 52, and if the voltage value is higher than a certain value, the control unit 44 determines that the power generation is sufficiently performed, and the power circuit unit 43 extracts the power. It is. In the power circuit unit 43, direct current power taken out from the fuel cell stack 38 is converted into alternating current, 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 fuel cell 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 in 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, the oxygen-containing gas and the fuel gas react around the MEA 5 to generate water, and electrons flow. Further, heat is generated during the reaction, and the temperature of MEA 5 rises. For this reason, the heat generated by 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, if there is too much water, 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. (Hereafter, this state is referred to as flatting).

  Hereinafter, the operation after the reaction in the fuel cell will be described with reference to FIG. The 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 is reduced in the moisture contained in the off gas by the auto drain, and then 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 in the fuel generator 35.

  Since the reaction for generating the fuel gas from the raw material gas is an endothermic reaction as represented by Chemical Formula 9 in (Chemical Formula 9), it is used as heat necessary for the reaction. The water accumulated in the auto drain 70 is discharged to the outside through a route not shown. The power circuit 43 serves to draw DC power from the fuel cell stack 38 after the fuel cell starts power generation. 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 MEA 5 electrolyte 1 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.

  Next, a method for stopping the operation of the fuel cell will be described. The blower 39 is stopped and the supply of the oxidant gas to the fuel cell stack 38 is stopped. Next, the cathode water purge three-way valve 75 is switched to a path where the fuel cell stack 38 and the cooling water tank 60 are connected, and the cooling water is guided to the gas path 6c of the fuel cell stack 38 and the remaining air is expelled to the outside. At this time, hydrogen in the gas path 6 a diffuses to the electrode 4 c through the electrolyte 1.

  When hydrogen begins to arrive at the electrode 4c, the potential of the electrode 4c decreases from the potential of oxygen until then to the potential of hydrogen, so that the voltage of the cell decreases and the voltage of the fuel cell stack 38 in which the cells are stacked also decreases. I will do it. After the voltage of the fuel cell stack is measured by the voltage measuring unit 52 and it can be determined that the cell voltage has become 0.88 V or less, the valve 34 is closed, the fuel generator 35 is stopped, and the supply of fuel gas is stopped. As a result, the electrodes 4a and 4c do not have a potential exceeding 0.88V, and deterioration due to platinum oxidation and dissolution according to the chemical formula 7 shown in (Chemical Formula 7) can be prevented.

  Since the stopped fuel cell stack 38 does not generate heat, the temperature decreases, the volume of the gas and water in the gas flow paths 6a and 6c decreases due to condensation and contraction, and the pressure in the gas paths 6a and 6c decreases. At this time, the cooling water is added to the gas path 6c by the operation of the cathode water purge three-way valve 75 to prevent the pressure from decreasing. With respect to the gas path 6a, the fuel gas purge valve 72 is opened and cooling water is supplied, so that a pressure drop is prevented.

  In this embodiment, cooling water is used as the water supplied to the gas paths 6a and 6c. Since the cooling water passes through the cooling water paths 8a and 8c in the fuel cell stack 38, cleanliness such as low electrical conductivity is required and maintained, so that it is suitable for supplying to the gas path. Since no device or the like is added, the deterioration due to the start and stop of the fuel cell can be prevented easily.

  During the stop, since the gas path 6a is filled with water, air does not enter through the MEA gasket 11, so that the electrode 4c is always kept at a low potential, so that almost no deterioration occurs. The gas path 6a is filled with water and fuel gas, but since there is no water seal in the fuel gas portion, there is slight diffusion of fuel gas and oxygen intrusion. When the fuel gas goes out, water is additionally injected because the internal pressure drops.

  When oxygen enters, it reacts with hydrogen to become water and the pressure drops, so water is also injected. Eventually, since the gas path 4a is also filled with water, a water seal is formed, so that intrusion of oxygen and the like is eliminated, and the electrode 4a is hardly deteriorated even if it is stopped for a long period of time. By using this fuel cell operation method without deterioration, a fuel cell system having a long life can be realized.

  Next, a method for starting the fuel cell system will be described. The valve 34 is opened and the fuel generator 35 is operated. The fuel gas purge valve 72 is closed and the fuel gas is caused to flow through the fuel gas pipe 37. The water in the gas path 6 a of the fuel cell stack 38 is pushed out by the fuel gas and reaches the anode off-gas three-way valve 83. At this time, the anode off-gas three-way valve 83 connects the fuel cell stack 38 and the auto drain 70, and water is transported to the auto drain 70, where the water is removed and the extruded fuel gas is generated through the off gas pipe 48. It returns to the container 35 and is used for combustion.

  As a result, the electrode 4a becomes a hydrogen potential, and a low potential is maintained. Next, the cathode switching three-way valve 80 operates to connect the fuel gas pipe 37 and the fuel cell stack 38, and the cathode water purge three-way valve 75 operates to connect the fuel cell stack 38 and the cathode off-gas three-way valve 81. The cathode off-gas three-way valve 81 operates to connect the cathode off-gas pipe 62 and the anode off-gas three-way valve 83, and the anode off-gas three-way valve 83 operates to connect the cathode drain pipe 82 and the auto drain 70.

  Thus, the fuel gas supplied from the fuel generator 35 flows out the water accumulated in the gas path 6 c of the fuel cell stack 38 via the cathode switching three-way valve 80. The fuel gas and the water expelled by the fuel gas pass through the cathode offgas pipe 62 and are led to the auto drain 70 through the cathode offgas three-way valve 81 and the anode offgas three-way valve 83. Here, water is removed and the fuel gas is used again for combustion in the fuel generator 35. As a result, the electrode 6c is also at a hydrogen potential, and a low potential is maintained.

  Thereafter, the cathode switching three-way valve 80 is a path connecting the second humidifier 42 and the fuel cell stack 38, and the cathode offgas three-way valve 81 is a path connecting the fuel cell stack 38 and the first humidifier 41, anode offgas The path is again switched to the path connecting the three-way valve 83, the fuel cell stack 38, and the auto drain 70. The fuel gas flows through the gas path 6a of the fuel cell stack 38 and then returns to the fuel generator 35. Next, the blower 39 operates and the humidified oxidant gas flows into the gas path 6 c of the fuel cell stack 38. At this time, power generation starts and voltage is generated, but before the cell voltage reaches the fuel cell stack voltage equivalent to 0.88V, the power circuit unit 43 starts to take current, so the cell voltage should be less than 0.88V. maintain.

  As a result, it is possible to eliminate almost no deterioration due to dissolution of the electrode even at the time of start-up, so that a long-life fuel cell system can be realized by using this fuel cell operation method. In this embodiment, during the stoppage, water is stored in the gas path of the fuel cell stack 38 so that the electrode is hardly deteriorated, the fuel gas is used to expel the water, and the fuel gas is used for the combustion of the fuel generator 35 and is wasted. This is a highly efficient fuel cell system and a method for operating the fuel cell system.

(Embodiment 2)
The fuel cell system of Embodiment 2 and its operation method will be described with reference to FIG. Reference numerals 1 to 92 shown in FIG. 4 are the same as the constituent elements shown by reference numerals 1 to 92 attached to FIGS. 1 to 3 in the first embodiment, so detailed description will be omitted and different points will be mainly described. . The source gas bypass three-way valve 95 is disposed in the fuel gas pipe 37 and is connected to the clean gas pipe 36 by a source gas bypass pipe 96.

  The basic operation of the fuel cell system during power generation will be described below. In FIG. 4, the raw material gas bypass three-way valve 95 becomes a path connecting the fuel generator 35 and the fuel cell stack 38, and the valve 34 is opened. After the source gas is purified from the source gas pipe 33 by the gas cleaning unit 32, the fuel gas is produced by the fuel generator 35. The functions of the gas cleaning unit 32 and the fuel generator 35 are the same as those in the first embodiment. The fuel gas purge valve 72 is closed, the cathode switching three-way valve 80 is a path between the second humidifier 42 and the fuel cell stack 38, and the cathode offgas three-way valve 81 is a path between the fuel cell stack 38 and the first humidifier 41. The anode off-gas three-way valve 83 is set to be a path between the fuel cell stack 38 and the auto drain 70, and the fuel gas flows into the fuel cell stack 38 of the fuel cell via the fuel gas pipe 37.

  The oxidant gas passes through the first humidifier 41 and the second humidifier 42 by the blower 39 and then flows into the fuel cell stack 38. Electricity is generated here and heat is also generated. The exhaust gas of the oxidant gas is discharged to the outside through the exhaust pipe 85. The first humidifier 41 and the second humidifier 42 have the same function as in the first embodiment. The cooling water has the same functions of the heat exchanger 58, the fuel cell stack 38, the voltage measurement unit 52, and the power circuit unit 43 as in the first embodiment.

  Next, a method for stopping the operation of the fuel cell system will be described. The blower 39 is stopped, and supply of the oxidant gas to the fuel cell stack 38 is stopped. Next, the cathode water purge three-way valve 75 is switched to a path where the fuel cell stack 38 and the cooling water tank 60 are connected, and the cooling water is guided to the gas path 6c of the fuel cell stack 38 and the remaining air is expelled to the outside. At this time, hydrogen in the gas path 6 a diffuses to the electrode 4 c through the electrolyte 1. When hydrogen begins to arrive at the electrode 4c, the potential of the electrode 4c decreases from the potential of oxygen until then to the potential of hydrogen, so that the voltage of the cell decreases, and the voltage of the fuel cell stack 38 in which a plurality of cells are stacked is also reduced. It will decline.

  The time from the stop of the blower 39 is calculated by the control unit 44, and after sufficient time has passed for the cell voltage to become 0.88V or less, the valve 34 is closed, the fuel generator 35 is stopped, and the fuel gas Stop supplying. As a result, the electrodes 4a and 4c have a simple configuration without measuring voltage or pressure, and the potentials of both electrodes 4a and 4c do not exceed 0.88V. It can be prevented.

  The time required for the cell voltage to become 0.88 V or less is determined by experiments or the like when the fuel cell stack 38 is designed. The rate of hydrogen permeation is determined by the electrolyte 1 used. As a result, the rate at which oxygen and hydrogen react at the electrode 4c is determined, and the time for which oxygen runs out can be calculated. By setting this time as the time necessary for the voltage to become 0.88 V or less and setting the time until the fuel generator 35 stops longer than this time, the electrode can be deteriorated with a simple configuration of only time measurement. It can be suppressed.

  Next, the fuel gas purge valve 72 is opened, and the fuel gas in the gas path 6a is expelled by the cooling water and filled with the cooling water. As a result, since the gas paths 6c and 6a are both filled with water, even if they are held for a long time, there is no ingress of gas such as air from the outside, and the electrodes 4c and 4a are not dissolved or deteriorated for a long time. It is possible to provide a fuel cell system that hardly deteriorates even when the operation is performed and its operation method.

  Next, a method for starting the fuel cell system will be described. The valve 34 is opened and the fuel generator 35 is activated. Further, the fuel gas purge valve 72 is closed, and the raw material gas bypass three-way valve 95 operates so as to connect the clean gas pipe 36 and the fuel gas pipe 37. As a result, the normalized source gas flows into the fuel gas pipe 37 simultaneously with the fuel generator 35. Water in the gas path 6 a of the fuel cell stack 38 is pushed out by the raw material gas and reaches the anode off-gas three-way valve 83.

  At this time, the anode off-gas three-way valve 83 connects the fuel cell stack 38 and the auto drain 70, and water is transported to the auto drain 70, where water is removed and the extruded raw material gas is fed through the off gas pipe 48 to the fuel generator. It returns to 35 and is used for combustion. As a result, the electrode 4a becomes a hydrogen potential, and a low potential is maintained. Next, the cathode switching three-way valve 80 operates to connect the fuel gas pipe 37 and the fuel cell stack 38, the cathode water purge three-way valve 75 operates to connect the fuel cell stack 38 and the cathode off-gas three-way valve 81, The cathode off-gas three-way valve 81 operates to connect the cathode off-gas pipe 62 and the anode off-gas three-way valve 83, and the anode off-gas three-way valve 83 operates to connect the cathode drain pipe 82 and the auto drain 70.

  As a result, the raw material gas supplied from the fuel gas pipe 37 through the raw material gas bypass three-way valve 95 flows out the water accumulated in the gas path 6 c of the fuel cell stack 38 via the cathode switching three-way valve 80. The source gas and the water expelled by the source gas pass through the cathode offgas pipe 62 and are led to the auto drain 70 via the cathode offgas three-way valve 81 and the anode offgas three-way valve 83. Here, the water is removed and the raw material gas is used again for combustion or the like in the fuel generator 35.

  It is necessary for the fuel generator 35 to correctly perform the reactions shown in Chemical Formula 9 of (Chemical Formula 9), Chemical Formula 10 of (Chemical Formula 10), and Chemical Formula 11 of (Chemical Formula 11). For this purpose, the temperature of the catalyst is adjusted. It takes a certain time to obtain fuel gas. In the present embodiment, the raw material gas is used instead of the fuel gas as the gas for expelling the water accumulated in the gas paths 6c and 6a of the fuel cell stack 38. Thus, the fuel cell system can be activated without waiting for the fuel generator 35 to generate fuel.

  When the fuel gas can be supplied from the fuel generator 35, the cathode switching three-way valve 80 operates to connect the second humidifier 42 and the fuel cell stack 38, and the cathode offgas three-way valve 81 is connected to the cathode offgas pipe 62. And the first humidifier 41, and the anode offgas three-way valve 83 operates to connect the fuel cell stack 38 and the auto drain 70.

  Next, since the raw material gas bypass three-way valve 95 operates so as to connect the fuel generator 35 and the fuel cell stack 38, the fuel gas enters the gas path 6a of the fuel cell stack 38, so that the potential of the electrode 4a becomes low. Moreover, since hydrogen diffuses also into the electrode 4c through the electrolyte 1, the potential of the electrode 4c can be kept low. Next, the blower 39 operates and the humidified oxidant gas flows into the gas path 6 c of the fuel cell stack 38. At this time, power generation starts and a voltage is generated. However, before the cell voltage reaches the fuel cell stack voltage corresponding to 0.88V, the power circuit unit 43 starts to take current, so the cell voltage is maintained at 0.88V or less. .

  As a result, deterioration due to electrode dissolution or the like can be almost eliminated even at the time of start-up, so that a fuel cell system having a long life can be realized by using the operation method of the fuel cell system. In the present embodiment, during stoppage, water is accumulated in the gas path of the fuel cell stack 38, the electrode is hardly deteriorated, the fuel gas is used to expel the water, the fuel gas is used for the combustion of the fuel generator 35, and is wasted. A highly efficient fuel cell system and a method of operating the fuel cell system.

  INDUSTRIAL APPLICABILITY The fuel cell system and its operation method of the present invention have the effect of suppressing deterioration due to start and stop and long-term stop or improving durability, and are useful for power generation apparatuses and devices using polymer electrolyte membranes. Further, since cooling water is used as the purge medium, it is useful for a stationary fuel cell cogeneration system.

1 is a configuration diagram showing a fuel cell system according to Embodiment 1 of the present invention. Structure diagram showing a part of a unit cell of a fuel cell in Embodiments 1 and 2 of the present invention Structure diagram of fuel cell stack in which fuel cells according to Embodiments 1 and 2 of the present invention are stacked The block diagram which shows the fuel cell system in Embodiment 2 of this 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)
32 Gas Cleaner 35 Fuel Generator 38 Fuel Cell Stack 39 Blower 43 Power Circuit Unit 44 Control Unit 31 Outer Housing 32 Cleaner 70 Auto Drain 52 Voltage Measurement Unit 60 Cooling Water Tank 58 Heat Exchanger 75 Cathode Water Purge 3-way Valve 72 Fuel gas purge valve 80 Cathode switching three-way valve 81 Cathode off-gas three-way valve 91 Anode pressure gauge 92 Cathode pressure gauge

Claims (10)

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 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 the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored A cooling water tank is provided, and when the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, the voltage of the fuel cell is detected, and water is injected into at least the oxidant gas path of the fuel cell. Fuel cell system. 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 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 the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored Provided with a cooling water tank, when the fuel cell is stopped, the supply of fuel gas and oxidant gas is stopped, the voltage of the fuel cell is detected, and when the voltage is 0.88 V or less, water is supplied to the fuel cell. The method of operating a fuel cell system to be injected into the path of the oxidant gas. 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 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 the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored Provided with a cooling water tank. When the fuel cell is stopped, the supply of fuel gas and oxidant gas is stopped, and after sufficient time has passed for the fuel cell voltage to be 0.88 V or less, water is supplied to the fuel cell. The method of operating a fuel cell system to be injected into the path of at least the oxidant gas. 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 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 the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored A cooling water tank is provided, and when the fuel cell is stopped, the supply of fuel gas and oxidant gas is stopped, and when the pressure of the fuel cell gas path drops, water is injected to keep the pressure change of the gas path constant. Fuel cell system can be down. 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 fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, a gas purifier that removes components that adversely affect the fuel cell from the raw material gas, and the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored A cooling water tank, and when the fuel cell is stopped, the gas supply is stopped when the oxidant gas is ahead of the fuel gas, and when the water is injected into the gas path of the fuel cell, the oxidant gas path is also the fuel gas. The method of operating a fuel cell system is later than the road. 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 fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, a gas purifier that removes components that adversely affect the fuel cell from the raw material gas, and the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored A cooling water tank is provided, and when the fuel cell is stopped, the supply of the oxidant gas is stopped. The oxidant gas path injects water and expels the gas, and then the fuel gas is stopped. The fuel cell system capable of injecting water when the volume by the change or the like is reduced. 7. The fuel cell system or the fuel cell system operating method according to claim 1, wherein the water that enters the fuel cell path at the time of stoppage is cooling water. 8. 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 fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, a gas purifier that removes components that adversely affect the fuel cell from the raw material gas, and the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored A cooling water tank is provided to stop water by injecting water into one or both of the fuel gas and oxidant gas paths at the time of shutdown and to supply water from one or both of the fuel gas and oxidant gas paths at the time of startup. Expelling the fuel gas purified in scan clean unit, the fuel cell system the fuel gas which is to eliminate the leakage of fuel gas is burned in the combustion section utilizing the eviction. 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 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 the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored A cooling water tank is provided, and water is injected into one or both of the fuel gas and oxidant gas paths at the time of stoppage to stop it, and means for draining water before the temperature of the fuel cell falls below freezing point during stoppage is provided. Fuel cell system. 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 fuel generator that generates fuel gas to be supplied from the raw material gas to the fuel cell, a gas purifier that removes components that adversely affect the fuel cell from the raw material gas, and the fuel cell A power circuit unit that extracts electric power, a voltage measurement unit that measures the voltage of the fuel cell, a control unit that controls a gas, a power circuit unit, and the like, and a cooling water and a cooling water that extract heat generated in the fuel cell are stored A cooling water tank is provided, and water is injected into one or both of the fuel gas and oxidant gas paths at the time of stoppage to stop it, and after start-up, the fuel gas is allowed to flow before the oxidant gas is allowed to flow. Method of operating a fuel cell system.