JP2008071642A - Solid polymer electrolyte fuel cell system and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve life characteristics as well as demonstrating a stable voltage characteristics for a long period. <P>SOLUTION: A solid polymer electrolyte fuel cell system has a fuel cell stack 201 which is constructed by laminating a membrane electrode assembly arranged so as to interpose a polymer electrolyte membrane by a fuel electrode and an oxidizer electrode and a separator which supplies and exhausts fuel gas to the fuel electrode and supplies and exhausts oxidizer gas to the oxidizer electrode. While performing maintenance and correction of operating condition by setting and monitoring the operating condition by a control part, the fuel gas containing hydrogen is supplied and exhausted by a fuel gas system and the oxidizer gas is supplied and exhausted by an oxidizer gas system, and the power obtained by the fuel cell stack 201 is flowed to an external load. A part of the fuel gas of the fuel gas system is extracted to the fuel cell stack 201 in continuous power generation, and this fuel gas is added to the oxidizer gas to be supplied to the fuel cell stack 201 as a reduction gas containing hydrogen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid polymer electrolyte fuel cell system using a solid polymer having hydrogen ion conductivity as an electrolyte and an operation method thereof.

  In recent years, fuel cells have attracted attention as highly efficient energy conversion devices. This fuel cell is classified into several types according to the difference in electrolyte. Among them, the solid polymer electrolyte fuel cell using a solid polymer having hydrogen ion conductivity as an electrolyte has a compact structure and high output density. In addition, it can be operated with a simple system, and has attracted a great deal of attention as a power source for space, vehicles, and households.

  Recently, a perfluorocarbon sulfonic acid membrane (for example, Nafion: trade name, manufactured by DuPont) or the like has been used as a polymer electrolyte.

  A solid polymer electrolyte fuel cell using such a polymer electrolyte as an electrolyte membrane is usually configured as a battery stack structure having a stacked body in which a plurality of unit cells 101 are stacked as shown in FIG.

  Here, in FIG. 11, the membrane / electrode assembly 102 in the unit cell 101 includes a polymer electrolyte membrane 103, a fuel electrode 104 and an oxidant disposed so as to sandwich both sides of the polymer electrolyte membrane 103. It is composed of poles 105. In the fuel electrode 104 and the oxidant electrode 105, substrates 106 and 107 made of a conductive porous material and gas diffusion layers 108 and 109 containing carbon powder and a water repellent material are formed on the inner surfaces of the substrates 106 and 107, respectively. Has been. Further, the gas diffusion layers 108 and 109 are respectively supported on the inner surfaces thereof by catalyst layers 110 and 111 to which a catalyst and an electrolyte, or further a water repellent material are added.

  In addition, as a method for forming the membrane / electrode assembly 102, a method in which the fuel electrode 104 and the oxidant electrode 105 are bonded to the polymer electrolyte membrane 103 by thermocompression bonding and integrated is performed.

  Further, the unit cell 101 is disposed in contact with the separator fuel electrode surface 112 disposed in contact with the back surface of the fuel electrode 104 and the back surface of the oxidant electrode 105 so as to sandwich the membrane-electrode assembly 102. And a separator oxidant electrode surface 113.

  A fuel gas supply groove 114 is formed on the separator fuel electrode surface 112 as a plurality of gas flow paths for distributing and supplying fuel gas, and a plurality of oxidant gases are distributed and supplied to the separator oxidant electrode surface 113. An oxidant gas supply groove 115 is formed as a gas flow path.

  In many cases, the separator fuel electrode surface 112 and the separator oxidant electrode surface 113 form a separator that is integrated with the front and back, and a plurality of unit cells 101 are stacked while alternately stacking the membrane / electrode assembly 102 and the separator. A battery stack is configured as a laminate.

  In the solid polymer electrolyte fuel cell having such a configuration, as a cell reaction, hydrogen, which is a reaction gas, particularly a fuel gas, diffuses in the fuel electrode side catalyst layer via the fuel electrode side gas diffusion layer, and carries carbon. When it reaches a catalyst such as platinum on the body, it reacts and is separated into hydrogen ions and electrons.

  The separated electrons move from the fuel electrode side through the external circuit to the oxidant electrode, and hydrogen ions move into the electrolyte membrane using the electrolyte approaching the catalyst in the fuel electrode side catalyst layer as a transmission path. Then, it reaches the oxidant electrode and diffuses the electrolyte in the oxidant electrode side catalyst layer as a transmission path, and reacts with oxygen on the catalyst to form product water. This generated water moves through the catalyst layer and the gas diffusion layer or evaporates and is removed to the outside of the gas diffusion layer substrate.

  On the other hand, as a basic configuration of the fuel cell system using the battery stack, a fuel cell stack, a fuel gas system for supplying and discharging a fuel gas containing hydrogen to the fuel cell stack, and an oxidant gas are supplied and discharged. A reaction gas supply unit including an oxidant gas system, a cooling water system that supplies and discharges cooling water, a power circuit unit that obtains electric power by connecting the fuel cell stack and an external load so as to be energized, and It is configured by a control unit that performs operation condition maintenance and correction by setting and monitoring the operating conditions of the accessory devices including the reaction gas supply unit and the power circuit unit.

  FIG. 12 is a configuration diagram showing an example of such a fuel cell system.

  As shown in FIG. 12, the fuel cell stack 201 includes a fuel gas supply and discharge flow path, an oxidant gas supply and discharge flow path, and a cooling water supply and discharge flow path for a unit cell inside the fuel cell stack. A manifold that distributes or merges fuel gas, oxidant gas, and cooling water is connected to each of the fuel gas system, oxidant gas system, and cooling water system, and the manifold is provided outside the fuel cell stack. A supply port and a discharge port that are connected to each other are installed for each system.

  As for the fuel gas system, purified hydrogen is used, or a raw material gas such as natural gas is introduced into the fuel generator 202, and hydrogen is contained by a reforming reaction utilizing a catalytic action or the like in the fuel generator 202. Used as reformed fuel gas. At this time, a filter or a transformer for removing impurities in the raw material gas or the fuel gas or the fuel cell stack 201 to remove moisture so that the reforming reaction and the cell reaction of the fuel cell stack 201 are not hindered before and after the reforming. In some cases, a humidifier is provided adjacent to the fuel generator.

  Next, after the fuel gas is introduced into the fuel cell stack 201, it is used for the cell reaction in the surface of each unit cell, and the surplus is discharged from the fuel cell stack 201 as a fuel exhaust gas. Further, the fuel exhaust gas is introduced into the combustion unit 203 in the fuel generator 202, reused as the heated fuel for the reforming reaction, and then discharged outside the fuel cell system.

  As for the oxidant gas system, air in the atmosphere as the oxidant gas is introduced into the fuel cell system by the oxidant gas system blower 204 and supplied to the fuel cell stack 201. At this time, a humidifier for humidifying the oxidant gas air may be installed before the fuel cell stack 201 is introduced.

  After the oxidant gas air is supplied to the fuel cell stack 201, it is used for the battery reaction in each unit cell surface, and the surplus is discharged from the fuel cell stack 201 as the oxidant exhaust gas.

  As for the cooling water system, the cooling water is introduced from the outside of the fuel cell system by the cooling water pump 205 or is recirculated through a cooling water tank installed in the fuel cell system and supplied to the fuel cell stack 201. The supplied cooling water is heated by a heater to keep the fuel cell stack 201 at a set temperature, collect heat generated in the fuel cell stack 201, and adjust the stack temperature. Furthermore, in order to humidify each cell in the fuel cell stack 201, when a supply path of humidified water from the cooling water system to each cell is installed, a part of the cooling water is used as the humidifying water.

  After the cooling water is supplied to the fuel cell stack 201, it is collected in a cooling water tank via a heat exchanger, an ion exchanger, etc. and reused as cooling water or discharged outside the fuel cell system.

  The fuel gas supply valve 206 and the discharge valve 207 for controlling and shutting off the flow rate are provided before and after each device constituting the fuel gas system, the oxidant gas system, and the cooling water system communicating with the fuel cell stack 201 as described above. A gas supply valve 208 and a discharge valve 209, and a cooling water supply valve 210 and a discharge valve 211 are installed.

  Next, an operation method of the conventional solid polymer electrolyte fuel cell system will be described.

  As a state before starting the fuel cell system, the source gas supply valve 212, the fuel gas supply valve 206 and the discharge valve 207, the oxidant gas supply valve 208 and the discharge valve 209, and the cooling water supply valve 210 and the discharge valve 211 are closed. ing.

  When starting up, first, the coolant supply valve 210 and the discharge valve 211 are opened, and the coolant is supplied to the fuel cell stack 201 by the coolant pump 205 while the temperature of the coolant is raised by the heater.

  When the temperature of the fuel cell stack 201 reaches a predetermined value, the raw material gas supply valve 212 such as natural gas is opened, and the raw material gas is supplied to the fuel generator 202. When the fuel generator 202 generates fuel gas that satisfies a predetermined composition standard, the fuel gas supply valve 206 and the discharge valve 207 are opened, and the fuel gas is supplied to the fuel cell stack 201. Further, when purified hydrogen is used as the fuel gas, it may be supplied directly to the fuel cell stack 201.

  Further, as for the oxidant gas, the oxidant gas supply valve 208 and the discharge valve 209 are opened, and air in the atmosphere is supplied to the fuel cell stack 201 by the oxidant gas system blower 204. At this time, the humidifier is heated to a predetermined temperature immediately before the fuel cell stack 201, and oxidant gas air containing water vapor may be supplied to the fuel cell stack 201.

  Thus, when oxidant gas air is supplied to the fuel cell stack 201 following the fuel gas, the cell voltage of each unit cell in the fuel cell stack 201 rises. Further, when the control unit determines that the flow rate or supply time of the fuel gas, the oxidant gas air, or the cell voltage has reached a predetermined state, the power circuit unit connects the fuel cell stack to an external load for energization. Start.

  In addition, the control unit adjusts the current value or the voltage value flowing through the fuel cell stack so that a predetermined output is obtained upon energization, and continuously maintains the set condition. Further, when the control unit continuously generates power, the state of the flow rate, composition, temperature, and the like is set so that the fuel gas, the oxidant gas, and the cooling water are stably supplied according to a predetermined output value. Management control is performed while monitoring with the sensor attached to the valve.

  When the fuel cell system is stopped, in order to reduce the output to the external load, the power circuit unit is turned off or cut off to be in a no-load state. Next, each supply valve and discharge valve of the fuel gas system and oxidant gas system are closed, and system devices such as the fuel generator 202, the oxidant gas system blower 204, the cooling water pump 205, and the heater are sequentially stopped. Then, the temperature of the fuel cell stack and attached devices is lowered to shift to the heat retaining state and the stop is completed.

  As an operation method of such a conventional solid polymer electrolyte fuel cell system, there are the following problems.

  That is, at the stage where the fuel gas and the oxidant gas are supplied to the fuel cell stack in the no-load connection state before starting energization or at the time of shutting off at the time of starting or stopping the fuel cell, each cell undergoes a potential change and becomes a high potential. Transition to open circuit state.

  The potential of the oxidizer electrode in the open circuit state is theoretically 1.23 V due to the reaction of hydrogen and oxygen. However, during actual start-up and stop, the activity decreases due to the influence of reactive species such as impurities, A mixed potential of 1.23 V or less is exhibited due to a voltage drop due to inhibition of diffusion of the reaction gas.

  For this reason, when the oxidant electrode is exposed to an open circuit state in an oxidant gas atmosphere and becomes a high potential near 1 V, the Pt catalyst particles in the catalyst layer are gradually oxidized and eluted.

In the initial stage of supplying hydrogen to the fuel electrode in the presence of air at the oxidant electrode at the start-up, a reaction similar to that in the normal operation occurs in the region where the hydrogen of the fuel electrode has reached, and the oxidant electrode is reduced to 0. 0. While an electric potential of 8 V or more is generated, in the region where hydrogen has not reached in the fuel electrode, the fuel gas is insufficient due to uneven local reaction gas distribution in the cell plane,
A reaction of C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ occurs at the oxidizer electrode,
A reaction of O ₂ + 4H ⁺ + 4e ⁻ → H ₂ O occurs at the fuel electrode. By these reactions, carbon corrosion such as a carbon carrier supporting a catalyst such as Pt in the catalyst layer of the oxidant electrode is generated. As a result, the catalyst-carrying carbon support is worn out, which promotes dissolution and dropping of Pt particles and induces a decrease in activity.

  In addition, impurities in the reaction gas of the fuel gas and oxidant gas are mixed in the cell, or the eluate of the base material in the cell and the fuel cell system enters the electrode and adheres to the catalyst surface to cause a catalytic reaction. There is concern that the battery reaction may be hindered by reducing the activity, or by adsorbing metal ions or the like by substituting the functional group of the electrolyte membrane to reduce the ionic conductivity.

  Furthermore, even during continuous power generation where a predetermined potential is shifted from the high potential state at the time of start-up, the Pt oxide remains formed on the surface of the Pt catalyst particles along with the history of the high potential state, and the catalytic activity There is a concern that it may be a factor that hinders this.

  Therefore, recently, in order to solve the above-mentioned problems, it is possible to remove impurities such as oxides deposited on the electrode due to a high potential state during start-up or stop of the battery, or performance deterioration due to oxidation or dissolution of the catalyst. The following methods have been proposed as a method for suppressing the above-described problem.

(1) A method of eluting and removing impurities such as oxides attached to the electrode by lowering the electrode potential at the start of operation (for example, Patent Document 1).

(2) In order to suppress deterioration of the oxidant electrode at the time of startup, supply of hydrogen gas to the oxidant gas channel is started at least before the hydrogen gas reaches the fuel gas channel at the time of system startup, and at least the fuel A method of switching to supply of oxidant gas to the oxidant gas flow channel after hydrogen gas has spread to the gas flow channel (for example, Patent Document 2).

(3) A method of replacing the reaction gas of the fuel electrode and the oxidant electrode with an inert gas during the stop (for example, Patent Document 3).

(4) A method of controlling the potentials of the fuel electrode and the oxidant electrode in a stopped and stored state (for example, Patent Document 4).

(5) As a method for recovering cell characteristics during operation and maintenance, oxidation is performed in order to prevent impurity ions such as metal ions from lowering the ionic conductivity and water content of the electrolyte membrane and degrading the catalytic activity. A method in which carbon dioxide is mixed into an agent gas to make the oxidizer electrode in an acidic atmosphere for a predetermined time (for example, Patent Document 5).
JP 2005-085662 A Japanese Patent Laid-Open No. 2005-149838 JP 2005-222707 A JP 2005-251434 A JP 2002-042849 A

  However, the solid polymer electrolyte fuel cell system operating method as described above has the following problems.

  There is a problem that the cell voltage characteristics are lowered when a solid polymer electrolyte fuel cell generates power over a long period of time, and as a cause, there is a concern about deterioration of the carbon carrier catalyst containing Pt of the catalyst layer which is a cell electrode member. As a cause of this deterioration, it is considered that impurities and Pt oxide are adsorbed and coated on the surface of the Pt catalyst particles by use during continuous power generation, and the Pt surface area is reduced to lower the catalytic activity.

  On the other hand, in the countermeasures such as the start / stop operation method disclosed in Patent Document 1 to Patent Document 5 described above, the Pt catalyst activity is removed temporarily by removing Pt oxide on the Pt surface. It was.

  However, as described above, with respect to the operation method of the conventional solid polymer electrolyte fuel cell system, a part of the Pt catalyst particles are dissolved during the operation of removing impurities and Pt oxide attached to the catalyst, Furthermore, when power generation is continued, Pt oxide or the like covering the surface of the Pt catalyst particles is formed again, and there is a problem that the catalyst particles are worn every time the operation of removing impurities and Pt oxide is repeated.

  In addition, even at a predetermined potential during continuous power generation, there is a possibility that the formation of Pt oxide on the surface of the Pt catalyst particles gradually proceeds in the catalyst layer of the oxidant electrode due to the influence of the mixed potential. Therefore, it is necessary to remove the oxide adhering to the catalyst, but each time the catalyst particles are worn out, there is a concern that the Pt reaction surface area is reduced, the activity is lowered, and the cell characteristics are lowered.

  Furthermore, it is necessary to take measures to prevent the catalyst performance from deteriorating without going through a complicated operation procedure against the deterioration of the cell characteristics over time during continuous operation.

  The present invention has been made to solve the above-described problems, and provides a solid polymer electrolyte fuel cell system capable of exhibiting stable voltage characteristics over a long period of time and improving life characteristics, and an operating method thereof. The purpose is to do.

  In order to achieve the above object, the present invention constitutes and operates a solid polymer electrolyte fuel cell system by the following means and methods.

(1) Fuel gas is supplied to and discharged from the membrane / electrode assembly and the fuel electrode arranged so as to sandwich the polymer electrolyte membrane between the fuel electrode and the oxidant electrode, and oxidant gas is supplied to the oxidant electrode. A fuel cell stack configured by stacking separators to be discharged, a fuel gas system for supplying and discharging a fuel gas containing hydrogen to the fuel cell stack, and an oxidant gas for supplying and discharging an oxidant gas Operating conditions of a reaction gas supply unit including a system, a power circuit unit that obtains power by connecting the fuel cell stack and an external load so as to be energized, and operating conditions of the accessory device including the reaction gas supply unit and the power circuit unit A solid polymer electrolyte fuel cell system including a control unit that maintains and corrects the operating state by setting and monitoring of the fuel cell, and a reduction gas is added to the oxidant gas supplied to the fuel cell stack. It is provided with a sexually gas addition means.

(2) Fuel gas is supplied to and discharged from the membrane / electrode assembly and the fuel electrode arranged so as to sandwich the polymer electrolyte membrane between the fuel electrode and the oxidant electrode, and the oxidant gas is supplied to the oxidant electrode. A fuel cell stack configured by stacking separators to be discharged, a fuel gas system for supplying and discharging a fuel gas containing hydrogen to the fuel cell stack, and an oxidant gas for supplying and discharging an oxidant gas Operating conditions of a reaction gas supply unit including a system, a power circuit unit that obtains power by connecting the fuel cell stack and an external load so as to be energized, and operating conditions of the accessory device including the reaction gas supply unit and the power circuit unit A solid polymer electrolyte fuel cell system having a control unit that maintains and corrects the operating state by setting and monitoring the fuel cell stack during continuous power generation, the oxidation of the oxidant gas system Characterized by operation contain a reducing gas containing hydrogen that is added continuously from the pipe for the reducing gas added to the oxidizing gas supplied through the gas supply pipe.

(3) Fuel gas is supplied to and discharged from the membrane / electrode assembly and the fuel electrode arranged so as to sandwich the polymer electrolyte membrane between the fuel electrode and the oxidant electrode, and oxidant gas is supplied to the oxidant electrode. A fuel cell stack configured by stacking separators to be discharged, a fuel gas system for supplying and discharging a fuel gas containing hydrogen to the fuel cell stack, and an oxidant gas for supplying and discharging an oxidant gas Operating conditions of a reaction gas supply unit including a system, a power circuit unit that obtains power by connecting the fuel cell stack and an external load so as to be energized, and operating conditions of the accessory device including the reaction gas supply unit and the power circuit unit A solid polymer electrolyte fuel cell system comprising a controller for maintaining and correcting the operating state by setting and monitoring of the fuel cell stack, and a cell performance recovery operation of the fuel cell stack during startup and shutdown When the fuel gas containing hydrogen is supplied from the fuel supply system to the oxidant gas system, the humidified oxidant gas passes through the junction where the fuel gas containing hydrogen merges. To do.

  According to the present invention, it is possible to prevent deterioration of the activity of the electrode catalyst and to obtain stable activity over a long period of time, so that the battery characteristics are stabilized and the life can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a first embodiment of a solid polymer electrolyte fuel cell system according to the present invention. In FIG. 1, the same parts as those in FIG. State.

  In the first embodiment, as shown in FIG. 1, the fuel gas discharge side pipe 302 for discharging the fuel gas from the fuel cell stack 201 is branched to supply a part of the fuel gas and the oxidant gas to the fuel cell stack 201. The oxidant gas supply side pipe 301 is refluxed.

  That is, as shown in FIG. 1, one end of a reducing gas addition pipe 304 is connected to a branch point 303 provided in a fuel gas discharge side pipe 302 downstream from the fuel gas discharge valve 207 to oxidize the fuel cell stack 201. The other end of the reducing gas addition pipe 304 is connected to a junction 305 provided upstream of the oxidizing gas supply valve 208 of the oxidizing gas supply side pipe 301 for supplying the oxidizing gas. In the middle of this reducing gas addition pipe 304, there are provided a check valve 306 for preventing the back flow of the oxidizing gas and a reducing gas addition valve 307 for controlling the flow rate.

  In this case, when purified hydrogen or reformed gas is used as the fuel gas discharged from the fuel cell stack 201, the CO concentration in the exhaust gas may increase due to fuel consumption in the fuel cell stack 201. The reformed gas containing hydrogen supplied via the CO removing device is used as the reducing gas. Furthermore, by controlling the flow rate with the reducing gas addition valve 307, it is possible to supply the reducing cell containing hydrogen to the oxidant gas so that the reducing gas containing hydrogen is always included in the fuel cell stack during continuous power generation. In addition, the concentration of hydrogen added as the reducing gas in the oxidizing gas can be controlled to 4% or less.

  Here, at the junction 305 for mixing the reducing gas with the oxidant gas and supplying it to the fuel cell stack 201, the reducing gas addition pipe 304 is supplied with the oxidant gas system as shown in FIG. It is inserted so as to be orthogonal to the side pipe 301. In addition, the reducing gas addition pipe 304 has a nozzle at a substantially central portion of the supply pipe 301 of the oxidant gas system so that the reducing gas added at a smaller flow rate than the oxidant gas does not stay. The shape is provided with a supply port 308 having a shape.

  FIG. 1 shows a branch of a fuel gas discharge side pipe 302 that discharges fuel gas from the fuel cell stack 201, and a part of the fuel gas is supplied to an oxidant gas supply side pipe 301 that supplies oxidant gas to the fuel cell stack 201. Although the configuration for recirculation is shown, when the fuel cell stack is operated under the condition that the discharged fuel gas is small, the fuel gas supply side pipe 309 for supplying the fuel gas to the fuel cell stack 201 as shown in FIG. One end of a reducing gas addition pipe 311 is connected to a branching point 310 provided upstream of the fuel gas supply valve 206 of the gas, and oxidation of an oxidant gas supply side pipe 301 for supplying an oxidant gas to the fuel cell stack 201 is performed. The other end of the reducing gas addition pipe 311 may be connected to a confluence 305 provided upstream of the agent gas supply valve 208. In this case, a check valve 306 for preventing the oxidant gas from flowing backward and a reducing gas addition valve 307 for controlling the flow rate are provided in the middle of the reducing gas addition pipe 311 as in FIG. It is done.

  Next, the operation of the solid polymer electrolyte fuel cell system configured as described above will be described.

  In the first embodiment, hydrogen contained in the fuel gas is added to the oxidant gas as a reducing gas and supplied to the fuel cell stack 201.

  FIG. 4 shows cell voltage / current characteristics under power generation conditions when hydrogen is added as a reducing gas to the oxidant gas and when hydrogen is not added.

  As can be seen from this characteristic, the cell voltage on the low current side and in the no-load state tends to decrease as the amount of hydrogen added increases. In this case, since the cell voltage is detected as a potential difference between the oxidizer electrode and the fuel electrode, the potential of the oxidizer electrode is lowered by the addition of hydrogen, and the high potential state is relaxed. By relaxing the high potential state of the oxidizer electrode under no-load conditions, the generation of Pt oxide formed on the Pt catalyst surface is suppressed in the high potential state, and elution of Pt oxide accompanying the potential change is prevented. To prevent.

  FIG. 5 shows a cyclic voltammogram of an oxidizer electrode having a catalyst layer using a Pt catalyst for a single cell of a solid polymer electrolyte fuel cell.

  When the potential rises in the presence of hydrogen, hydrogen is adsorbed on the Pt catalyst, and an oxidation current is detected. Further, when the potential is increased, Pt oxide is generated. A single cell in a fuel cell stack at the time of power generation is often used in a state where the potential of the oxidizer electrode is usually in the vicinity of 0.5 to 1 V. Hydrogen adsorbed on the Pt catalyst surface, Pt oxide, etc. Are considered to coexist and form a mixed potential.

  In this state, as shown in the present invention, when hydrogen or a reducing gas having the same adsorption characteristics as hydrogen is added to the oxidant gas, a part of the Pt catalyst particle surface of the oxidant electrode is charged with hydrogen. The progress of the generation of Pt oxide on the surface of the Pt catalyst particles is suppressed by the action of the reducing gas to be adsorbed and coated.

  Therefore, by starting the supply of the reducing gas from the start of power generation, it is possible to suppress the oxidant electrode from being in a high potential state, and further by continuously supplying the reducing gas even during continuous power generation, Since a state in which a reducing gas containing hydrogen is adsorbed and covered on a part of the Pt catalyst surface is maintained, it is possible to reduce the formation and dissolution of oxides on the surface of the Pt catalyst and to suppress deterioration of the catalyst. Become.

FIG. 6 shows the difference in cell voltage between the case where hydrogen is added to the oxidant gas as a reducing gas and the case where hydrogen is not added at the rated set current value (for example, 0.2 A / cm ² ) in FIG. The hydrogen concentration of each is tabulated as a parameter.

  While maintaining the operation as described above, it is possible to suitably obtain a predetermined output under a condition where the hydrogen concentration is 4% or less as a condition that the cell output characteristics do not deteriorate at the same rated set current value as in the past. ing. Further, by setting the hydrogen concentration contained in the oxidant gas to 4% or less, safety can be ensured at or below the explosion concentration limit.

  In addition, when the reducing gas is added, by using the fuel gas containing hydrogen used in the fuel cell system, the installation of the reducing gas cylinder or the like can be omitted, and the supply of the reducing gas can be omitted. The structure can be simplified.

  Furthermore, the reducing gas addition pipe is a nozzle-shaped supply port, and is located at the center of the oxidant gas system supply side pipe to prevent the added reducing gas from staying and mix uniformly. It becomes possible.

  As described above, according to the first embodiment of the present invention, the Pt oxide covering the surface of the Pt catalyst of the oxidant electrode, which is concerned as a factor for reducing the cell voltage, is applied to the operation method of the solid polymer electrolyte fuel cell. It is possible to suppress the formation of reaction inhibition products, and to prevent the Pt surface area from being reduced due to wear or sintering of Pt particles accompanying dissolution of Pt oxide due to potential fluctuations such as when starting and stopping.

  As a result of the above-described action, the time-dependent characteristics of the cell voltage in the continuous power generation state as shown in FIG. 7 are compared with the case where hydrogen is added to the oxidant gas as a reducing gas and the case where hydrogen is added. There was little tendency to decrease the cell voltage, and more stable aging characteristics were shown.

  As a result, the deterioration of the activity of the electrode catalyst can be prevented and a stable activity can be obtained over a long period of time, so that the battery characteristics can be stabilized and the life can be improved.

  FIG. 8 is a block diagram showing a second embodiment of the solid polymer electrolyte fuel cell system according to the present invention. The same parts as those in FIGS. 12 and 1 are denoted by the same reference numerals, and description thereof is omitted. Describe the differences.

  In the second embodiment, as shown in FIG. 8, the fuel gas discharge valve 207 provided in the fuel gas discharge side pipe 302 for discharging the fuel gas from the fuel cell stack 201 and the fuel gas discharge valve 207 are provided downstream. A fuel gas recycle blower 401 is provided in the pipe between the branch point 303 and a part of the fuel gas is passed from the branch point 303 through the reducing gas addition pipe 304 to the oxidant gas supply side pipe 301 of the fuel cell stack 201. A humidifier 402 is provided between the merging point 305 to be refluxed and the oxidant gas system blower 204, and a part of the fuel gas is mixed with the oxidant gas humidified by the humidifier 402 to oxidize the fuel cell stack 201. The gas is supplied through the agent gas supply valve 208.

  Even in such a configuration, in addition to obtaining the same operation and effect as in the first embodiment, the vicinity of the junction 305 can be made a high humidity atmosphere with humidified water vapor, so that impurities are contained in the oxidant gas. Fuel gas containing hydrogen added as a reducing gas, which can prevent the occurrence of direct combustion reaction between the oxidant gas and the fuel gas starting from the reaction of the impurity fine particles, which is a concern when fine particles are mixed Can be prevented from being consumed.

  FIG. 9 is a block diagram showing a third embodiment of a solid polymer electrolyte fuel cell system according to the present invention. The same parts as those in FIGS. 12 and 1 are denoted by the same reference numerals, and description thereof is omitted. Describe the differences.

  In the third embodiment, as shown in FIG. 9, the fuel gas discharge valve 207 provided in the fuel gas discharge side pipe 302 for discharging the fuel gas from the fuel cell stack 201 and the fuel gas discharge valve 207 are provided downstream. A fuel gas recycle blower 501 is provided in the pipe between the branch point 303 and a part of the fuel gas from the branch point 303 through the reducing gas addition pipe 304 and the oxidant gas supply side pipe 301 of the fuel cell stack 201. In this configuration, each piping portion that becomes the junction 503 to be refluxed is inserted into the humidifier 502.

  FIG. 10 shows the internal structure of the humidifier 502.

  In FIG. 10, humidified water 505 is stored in a container 504, and in this container 504, an oxidant gas supply side pipe 301 that supplies an oxidant gas to the pipe fuel cell stack 201 is separated and one of the pipes is separated. The oxidant gas supply port 506 and the supply port 507 of the reducing gas addition pipe 304 are inserted into the humidified water 505 and the other separated oxidant gas supply side pipe 301 is connected to the humidified water 505 in the container 504. The mixed gas of the oxidant gas and the reducing gas can be supplied to the fuel cell stack 201 by being inserted into the upper space portion.

  Therefore, in the humidifier 502 configured as described above, the oxidizing gas supply side pipe 301 and the supply ports 506 and 507 of the reducing gas addition pipe 304 are not in contact with each other through the humidifying water 505. A reducing gas can be mixed.

  Even with such a configuration, in addition to the same operations and effects as those of the first embodiment and the second embodiment, the following operations and effects can be obtained.

  As described above, each pipe portion that becomes the junction point 503 for returning a part of the fuel gas to the oxidant gas supply side pipe 301 of the fuel cell stack 201 through the reducing gas addition pipe 304 is inserted into the humidifier 502. By adopting a configuration, it is possible to remove the impurity fine particles that may be mixed into the oxidant gas by trapping with humidified water in the humidifier, and to further remove the impurity fine particles by making the atmosphere humid with humidified water vapor. Since it is possible to prevent the direct combustion reaction between the oxidant gas and the fuel gas as the starting point of the reaction, the reduction in the effect of the present invention due to the consumption of the fuel gas containing hydrogen added as the reducing gas is suppressed. can do. In this case, accumulation of impurities can be eliminated by periodically replacing the humidified water in the humidifier.

  The second embodiment or the third embodiment described above is a case in which a decrease in cell voltage during continuous power generation of the fuel cell stack is suppressed. However, the present invention is not limited to this, and the fuel cell system is started or stopped. It can also be applied to cell characteristic deterioration prevention operation and characteristic recovery operation at the time. That is, when the supply of hydrogen gas to the oxidant gas passage is started as disclosed in Japanese Patent Application Laid-Open No. 2005-149838, etc., the hydrogen gas supply port to the oxidant gas passage is started. Can be realized by providing a portion through which the humidified oxidant gas passes or inside the humidifier.

  In this way, in addition to obtaining the same operational effects as those of the second and third embodiments, the oxidant can be safely used in the conventional cell characteristic deterioration prevention operation and characteristic recovery operation. Hydrogen gas can be supplied to the gas flow path.

  In the first to third embodiments, one of the fuel gas discharge side pipe 302 or the fuel gas supply side pipe 309 of the fuel gas system for supplying and discharging the fuel gas containing hydrogen to the fuel cell stack 201 is branched, Between this branch point and the oxidant gas-based oxidant gas supply side pipe 301 for supplying and discharging the oxidant gas to and from the fuel cell stack 201, a reducing gas addition pipe 311 connects the fuel to the oxidant gas. Although a part of the gas is added as a reducing gas containing hydrogen, as another embodiment, one end of the reducing gas addition pipe 311 is connected to the oxidizing gas supply side pipe 301 of the oxidizing gas system, A reducing gas supply source, for example, a hydrogen supply source is connected to the other end of the reducing gas addition pipe 311, and the reducing property is supplied from the hydrogen supply source via the check valve 306 and the reducing gas addition valve 307. Also hydrogen as scan to be contained in the oxidant gas can be obtained the same effects as the embodiments described above.

  The present invention is not limited to the embodiment described above and shown in the drawings, and various modifications can be made without departing from the scope of the invention.

The block diagram which shows 1st Embodiment of the solid polymer electrolyte fuel cell system by this invention. Sectional drawing which shows the confluence | merging part of the piping for reducing gas addition in the same embodiment, and the supply side piping of oxidizing gas system. The block diagram which shows the other connection example of piping for reducing gas addition in the same embodiment. The figure which shows the cell voltage and electric current characteristic in the electric power generation conditions in the case where hydrogen is added to oxidizing agent gas as reducing gas, and not adding in the same embodiment. The figure which shows the cyclic voltammogram of the oxidant electrode which has the catalyst layer using the Pt catalyst similarly about the single cell of a solid polymer electrolyte type fuel cell. FIG. 5 is also a graph showing the cell voltage difference when hydrogen is added to the oxidant gas as a reducing gas and the concentration of hydrogen in the oxidant gas as a parameter at the rated set current value of FIG. 4. The figure which shows the time-dependent characteristic of the cell voltage similarly in a continuous electric power generation state. The block diagram which shows 2nd Embodiment of the solid polymer electrolyte fuel cell system by this invention. The block diagram which shows 3rd Embodiment of the solid polymer electrolyte fuel cell system by this invention. Sectional drawing which shows the structure inside the humidifier in the embodiment. Sectional drawing which shows the structure of the conventional solid polymer electrolyte type fuel cell. The block diagram which shows the conventional solid polymer electrolyte type fuel cell system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Unit cell, 102 ... Membrane electrode assembly, 103 ... Polymer electrolyte membrane, 104 ... Fuel electrode, 105 ... Oxidant electrode, 106 ... Fuel electrode substrate, 107 ... Oxidant electrode substrate, 108 ... Fuel electrode gas diffusion , 109 ... oxidant electrode gas diffusion layer, 110 ... fuel electrode catalyst layer, 111 ... oxidant electrode catalyst layer, 112 ... separator fuel electrode surface, 113 ... separator oxidant electrode surface, 114 ... fuel gas supply groove, 115 ... Oxidant gas supply groove, 201 ... fuel cell stack, 202 ... fuel generator, 203 ... combustion unit, 204 ... oxidant gas system blower, 205 ... cooling water pump, 206 ... fuel gas supply valve, 207 ... fuel gas discharge valve 208 ... Oxidant gas supply valve, 209 ... Oxidant gas discharge valve, 210 ... Cooling water supply valve, 211 ... Cooling water discharge valve, 212 ... Raw material gas supply valve, 301 ... Agent gas supply side pipe, 302 ... Fuel gas discharge side pipe, 303, 310 ... Branch point, 304, 311 ... Pipe for reducing gas addition, 305, 503 ... Confluence, 306 ... Check valve, 307 ... Reduction Reactive gas addition valve, 308 ... nozzle-shaped supply port, 309 ... fuel gas supply side piping, 401, 501 ... fuel gas recycle blower, 402 ... humidifier, 502 ... humidifier, 504 ... container, 505 ... humidified water, 506 ... Oxidant gas supply port, 507 ... Pipe supply port for reducing gas addition

Claims (17)

A membrane / electrode assembly arranged to sandwich a polymer electrolyte membrane between a fuel electrode and an oxidant electrode, and a separator for supplying and discharging fuel gas to and from the fuel electrode and supplying and discharging oxidant gas to the oxidant electrode A fuel cell stack configured by stacking, a fuel gas system for supplying and discharging a fuel gas containing hydrogen to the fuel cell stack, and an oxidant gas system for supplying and discharging an oxidant gas A reaction gas supply unit, a power circuit unit that obtains electric power by connecting the fuel cell stack and an external load so as to be energized, and setting of operating conditions of an accessory device including the reaction gas supply unit and the power circuit unit, A solid polymer electrolyte fuel cell system including a control unit for maintaining and correcting the operating state by monitoring;
A solid polymer electrolyte fuel cell system comprising reducing gas addition means for adding a reducing gas to an oxidant gas supplied to the fuel cell stack. The solid polymer electrolyte fuel cell system according to claim 1, wherein
The reducing gas addition means is configured to connect a reducing gas addition pipe to an oxidizing gas supply side pipe of an oxidant gas system and add the reducing gas to the oxidant gas from a reducing gas supply source. Solid polymer electrolyte fuel cell system. The solid polymer electrolyte fuel cell system according to claim 2,
A solid polymer electrolyte fuel cell system, wherein hydrogen is added as a reducing gas to an oxidant gas from the reducing gas supply source. The solid polymer electrolyte fuel cell system according to claim 1, wherein
The reducing gas adding means branches one of a fuel gas discharge side pipe and a fuel gas supply side pipe of a fuel gas system for supplying and discharging a fuel gas containing hydrogen to and from the fuel cell stack. A part of the fuel gas is supplied to the oxidant gas by connecting the oxidant gas-based oxidant gas supply side pipe for supplying and discharging the oxidant gas to the fuel cell stack with a reducing gas addition pipe. A solid polymer electrolyte fuel cell system which is added as a reducing gas containing In the polymer electrolyte fuel cell system according to claim 4,
The solid polymer electrolytic fuel cell system, wherein the reducing gas containing hydrogen added to the oxidant gas is a reformed gas obtained by reforming the fuel gas in the fuel gas system.   6. The solid polymer electrolysis fuel cell system according to claim 5, wherein the reformed gas added as the reducing gas is supplied via a CO removing device. The solid polymer electrolyte fuel cell system according to any one of claims 4 to 6,
2. The solid polymer electrolyte fuel cell system according to claim 1, wherein the reducing gas addition pipe has a nozzle-like shape at a joint portion with the oxidant gas-based oxidant gas supply side pipe. The solid polymer electrolyte fuel cell system according to any one of claims 4 to 7,
A humidifier is provided on the upstream side of the merging portion of the oxidant gas supply side piping and the reducing gas addition piping so that the humidified oxidant gas passes through the merging portion to which the reducing gas is added. A solid polymer electrolyte fuel cell system. The solid polymer electrolyte fuel cell system according to any one of claims 4 to 7,
Each pipe part of the merging part of the oxidant gas supply side pipe and the reducing gas addition pipe is provided in a humidifier, and the oxidant gas and the reductive property are supplied via humidified water without contacting the supply port of each pipe part. A solid polymer electrolyte fuel cell system characterized in that gas is mixed. A membrane / electrode assembly arranged to sandwich a polymer electrolyte membrane between a fuel electrode and an oxidant electrode, and a separator for supplying and discharging fuel gas to and from the fuel electrode and supplying and discharging oxidant gas to the oxidant electrode A fuel cell stack configured by stacking, a fuel gas system for supplying and discharging a fuel gas containing hydrogen to the fuel cell stack, and an oxidant gas system for supplying and discharging an oxidant gas A reaction gas supply unit, a power circuit unit that obtains electric power by connecting the fuel cell stack and an external load so as to be energized, and setting of operating conditions of an accessory device including the reaction gas supply unit and the power circuit unit, In the operation method of the solid polymer electrolyte fuel cell system including a control unit that performs maintenance and correction of the operation state by monitoring,
An operation method for a solid polymer electrolyte fuel cell system, characterized in that a reducing gas is always contained in an oxidant gas supplied to the fuel cell stack during continuous power generation. In the operation method of the solid polymer electrolyte fuel cell system according to claim 10,
A method for operating a solid polymer electrolyte fuel cell system, wherein hydrogen is added as a reducing gas. In the operation method of the solid polymer electrolyte fuel cell system according to claim 10,
A method of operating a solid polymer electrolyte fuel cell system, wherein the fuel gas of the fuel gas system is used as a reducing gas containing hydrogen, and the fuel gas is hydrogen or a reformed gas. In the operation method of the solid polymer electrolyte fuel cell system according to claim 12,
A method of operating a solid polymer electrolyte fuel cell system, characterized in that a humidified oxidant gas passes through a joining portion where a reducing gas containing hydrogen is added to an oxidant gas. In the operation method of the solid polymer electrolyte fuel cell system according to claim 12,
A method for operating a solid polymer electrolyte fuel cell system, characterized by humidifying an oxidant gas in a humidifier provided at a junction where a reducing gas containing hydrogen is added to the oxidant gas. In the operation method of the solid polymer electrolyte fuel cell system according to any one of claims 11 to 14,
A method for operating a solid polymer electrolytic fuel cell system, wherein the concentration of hydrogen added as a reducing gas in an oxidant gas is 4% or less. A membrane / electrode assembly arranged to sandwich a polymer electrolyte membrane between a fuel electrode and an oxidant electrode, and a separator for supplying and discharging fuel gas to and from the fuel electrode and supplying and discharging oxidant gas to the oxidant electrode A fuel cell stack configured by stacking, a fuel gas system for supplying and discharging a fuel gas containing hydrogen to the fuel cell stack, and an oxidant gas system for supplying and discharging an oxidant gas A reaction gas supply unit, a power circuit unit that obtains electric power by connecting the fuel cell stack and an external load so as to be energized, and setting of operating conditions of an accessory device including the reaction gas supply unit and the power circuit unit, In the operation method of the solid polymer electrolyte fuel cell system including a control unit that performs maintenance and correction of the operation state by monitoring,
As an operation for recovering the cell performance of the fuel cell stack during start and stop, when a fuel gas containing hydrogen is supplied from the fuel supply system to the oxidant gas system, a merging portion that joins the fuel gas containing hydrogen is humidified. A method for operating a solid polymer electrolyte fuel cell system, characterized in that an oxidizing gas passes therethrough. The operation method of the solid polymer electrolyte fuel cell system according to claim 16,
A method of operating a solid polymer electrolyte fuel cell system, characterized by humidifying an oxidant gas in a humidifier provided at a junction of an oxidant gas that merges with a hydrogen-containing fuel gas.

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