JP2009187883A - Cell characteristic recovery operation method for fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cell characteristic recovery operation method for a fuel cell system, which can recover cell characteristics without decreasing the durability of a fuel cell. <P>SOLUTION: The cell characteristic recovery operation method includes: a fuel cell 2 formed by stacking unit cells; a fuel gas supply means 3 for supplying fuel gas to a fuel electrode 2a; and an oxidant gas supply means 4 for supplying oxidant gas to an oxidant electrode 2b, wherein the method recovers cell characteristics by temporarily more decreasing the cell voltage of the fuel cell 2 than that in the normal power generation. When cell voltage is lowered below the previously set value in normal power generation, operation is changed to the condition in which the cell voltage of the unit cell is lower than that in the normal operation, and no hydrogen is generated in proton reduction reaction in the oxidant electrode 2b. The operation condition is returned to that in the normal power generation before the cell voltage of the unit cell is lowered below 0.1 V. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for recovering cell characteristics of a fuel cell system suitable for a fuel cell system using, for example, a polymer electrolyte fuel cell.

  As is well known, a fuel cell system supplies a fuel gas such as hydrogen reformed and generated by a fuel reformer and an oxidant gas such as air to the fuel cell, and combines the combined energy of hydrogen and oxygen in the fuel cell. This is a power generation device that directly converts to electric energy and takes it out. Since this fuel cell system is a power generation based on a chemical reaction, it has a high power generation efficiency despite its relatively small size, and is excellent in environmental performance with less pollutant emission and noise. Furthermore, the fuel cell system can be applied as a cogeneration system by recovering the heat generated and generated as a result of power generation along with the supply of electric power as hot water or steam, so factories, hospitals, stores, etc. It is expected to be used in a wide range of applications such as commercial use, general household use, and automobile use.

  As a fuel cell used in such a fuel cell system, for example, there is a solid polymer fuel cell, which includes a membrane electrode assembly in which a fuel electrode and an oxidant electrode are bonded on both sides of a polymer electrolyte membrane, on both sides thereof. A separator having a fuel gas channel and an oxidant gas channel is provided and sandwiched. The catalyst layer constituting part of the fuel electrode and the oxidant electrode is composed of a composite of a carbon support carrying a metal catalyst such as platinum or a platinum alloy and a polymer electrolyte. A fuel cell is generally composed of a stack formed by stacking a large number of unit cells having such a structure.

  However, in such a fuel cell system, there is a phenomenon in which the cell characteristics of the fuel cell gradually deteriorate due to continuous power generation for a long time. The phenomenon in which the battery characteristics are deteriorated includes those in which the battery characteristics can be recovered and those in which the battery characteristics cannot be recovered.

  One of the recoverable characteristic degradation is characteristic degradation due to platinum oxidation in the oxidizer electrode. As a method of recovering the characteristic deterioration in this case, the cell voltage of the fuel cell during power generation is temporarily reduced to 0.6 V or less, preferably 0.1 V or less, thereby shifting the oxidant electrode potential to the base. In this method, the platinum oxide contained in the oxidizer electrode is reduced to platinum, the catalytic activity is recovered, and the deterioration of battery characteristics is recovered (for example, see Patent Document 1).

However, in such a method, when the battery voltage of the fuel cell during power generation is temporarily reduced, if the battery voltage is excessively reduced, a proton reduction reaction may occur at the oxidant electrode and hydrogen may be generated. When the generation of hydrogen is an oxidant electrode, a direct combustion reaction of hydrogen and oxygen occurs on the platinum catalyst, and there is a possibility that a portion that is locally hot is generated. It is conceivable that when the temperature is locally increased by the combustion reaction, the deterioration of the electrolyte membrane is accelerated, and the durability of the fuel cell is lowered due to the deterioration of the electrolyte membrane.
Special table 2003-536232 gazette

  The present invention has been made in view of the above situation, and the object of the present invention is to recover the battery characteristics without accelerating the deterioration of the electrolyte membrane of the fuel cell, and to recover the battery characteristics. It is an object of the present invention to provide a method for recovering the cell characteristics of a fuel cell system that does not cause a decrease in the durability of the fuel cell when performed.

  A method for recovering battery characteristics of a fuel cell system according to the present invention includes a fuel cell formed by stacking unit cells, a fuel gas supply means for supplying fuel gas to a fuel electrode of the fuel cell, and an oxidant electrode of the fuel cell. And an oxidant gas supply means for supplying an oxidant gas to the fuel cell, wherein the battery voltage is restored by temporarily lowering the battery voltage of the fuel cell from that during normal power generation. A method for recovering battery characteristics of a system, wherein when the battery voltage falls below a preset value during normal power generation, the battery voltage of the unit cell is lower than during normal power generation, and is caused by a proton reduction reaction at the oxidant electrode. The operation condition is changed so that the voltage is such that hydrogen generation does not occur, power generation is continued for a predetermined time, and the operation condition is returned to the operation condition at the time of normal power generation before the battery voltage of the unit cell falls below 0.1V. A method characterized by Unisuru.

  Also, a fuel cell formed by stacking unit cells, fuel gas supply means for supplying fuel gas to the fuel electrode of the fuel cell, and oxidant gas supply means for supplying oxidant gas to the oxidant electrode of the fuel cell A battery characteristic recovery operation method for a fuel cell system, wherein the battery voltage is recovered by temporarily lowering the battery voltage of the fuel cell from the battery voltage during normal power generation, Every time the power generation time of the fuel cell system passes a predetermined time, the battery voltage of the unit cell is lower than that during normal power generation, and the oxidant electrode is operated so as not to generate hydrogen by proton reduction reaction. The method is characterized in that an operation for changing the condition is performed to continue power generation for a predetermined time, and the operating condition is returned to the operating condition at the time of normal power generation before the battery voltage of the unit cell falls below 0.1V. .

Furthermore, the operation for changing the operating conditions is an operation for increasing or decreasing the supply flow rate of the oxidant gas to the oxidant electrode,
Further, the operation for changing the operating condition is an operation for increasing or decreasing the amount of current taken out from the fuel cell as compared with that during normal power generation,
Furthermore, the operation for changing the operating condition is performed after the supply flow rate of the fuel gas to the fuel electrode is increased from the previous supply amount.

  According to the present invention, since the battery voltage is recovered by setting the battery voltage at a voltage at which no hydrogen is generated by the proton reduction reaction at the oxidizer electrode and lower than that during normal power generation, the fuel cell is recovered by the combustion reaction of the generated hydrogen. The electrolyte membrane does not reach a high temperature locally, battery characteristics can be recovered without accelerating the deterioration of the electrolyte membrane, and there is no risk of reducing the durability of the fuel cell at that time, etc. The effect of.

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

  First, a first embodiment will be described with reference to FIGS. FIG. 1 is a block diagram showing a schematic configuration of a fuel cell system, FIG. 2 is a flowchart showing a process for recovering cell characteristics, and FIG. FIG. 4 is a diagram showing the dependency of the amount of hydrogen peroxide generated on the oxidant electrode of the fuel cell on the oxidant electrode potential.

  In FIG. 1, a fuel cell system 1 includes, for example, a solid polymer fuel cell 2 and a fuel electrode 2a of the fuel cell 2 that reforms a hydrocarbon-based raw fuel to obtain a hydrogen-rich gas to produce a hydrogen gas. A fuel gas supply means 3 such as a fuel reforming device, an oxidant gas supply means 4 for supplying air from the outside to the oxidant electrode 2b of the fuel cell 2 and supplying oxygen gas of the oxidant gas, and a fuel cell 2, and a controller 5 that controls the operation of the fuel cell system 1 while controlling the amount of oxidant gas supplied to the oxidant electrode 2 b of the fuel cell 2. 6a is a fuel gas supply pipe, and 7a is an oxidant gas supply pipe. Reference numeral 6b denotes a fuel electrode gas discharge pipe, and reference numeral 7b denotes an oxidant electrode gas discharge pipe.

  Although not shown, the fuel cell 2 is composed of a stack formed by stacking a large number of single cells. The fuel electrode 2a and the oxidant electrode 2b partially carry a metal catalyst such as platinum or a platinum alloy. In this structure, an electrolyte membrane 2c made of a polymer electrolyte is sandwiched between the two electrodes 2a and 2b. The fuel cell 2 includes the hydrogen rich gas supplied to the fuel electrode 2a through the fuel gas supply pipe 6a from the fuel reformer of the fuel gas supply means 3 and the oxidant gas supply means 4 to the oxidant electrode 2b. Electricity is generated by directly converting oxygen binding energy of air supplied through the oxidant gas supply pipe 7a into electric energy.

  In the fuel cell system 1 configured as described above, the battery characteristics of the fuel cell 2 gradually deteriorate due to continuous power generation over a long period of time. For this reason, in order to recover the deterioration of the battery characteristics caused by the platinum oxidation in the recoverable oxidant electrode 2b, the battery voltage is set in advance during normal continuous power generation under the control of the control device 5. When the voltage value falls below the voltage value, an operation for changing the operating condition for performing the battery characteristic recovery operation is started and executed.

  That is, as shown in FIG. 2, the operation for recovering the battery characteristics is performed in the first stage S1, when the normal continuous power generation is performed, the unit cell voltage of the fuel cell 2 is preset by the control device 5. It continues to monitor whether or not it falls below a predetermined voltage lower than the normal generated voltage. And it starts when the control apparatus 5 detects that the cell voltage has fallen below the predetermined voltage set beforehand.

  By detecting that the unit cell voltage has fallen below the predetermined voltage, the control device 5 is operated so as to reduce the flow rate of the oxidant gas supplied from the oxidant gas supply means 4 to the fuel cell 2 in the subsequent second stage S2. Control to change the condition. At this time, control is performed so that the generated voltage of the unit cell is lower than the normal generated voltage by reducing the flow rate of the oxidant gas supply, and is preferably 0.6 V or less.

  Further, in the third step S3, the operation is continued for a predetermined time in a state where the unit cell voltage is lower than the normal power generation voltage while being monitored by the control device 5, and before the unit cell voltage falls below 0.1V, the oxidant Control is performed to change the operating condition so that the flow rate of the oxidant gas supplied from the gas supply means 4 to the fuel cell 2 is returned to the flow rate before starting the operation for restoring the battery characteristics. At this time, the oxidant gas supply amount may be adjusted to be increased or decreased so that the unit cell voltage is lower than the normal power generation voltage that does not fall below 0.1 V until a predetermined time elapses. Thus, by operating so that the unit cell voltage becomes a voltage lower than the normal power generation voltage not lower than 0.1 V, the platinum oxide contained in the oxidant electrode 2b is reduced, and the battery characteristics are recovered.

  Then, after the battery characteristics are recovered, the normal power generation operation of the fuel cell 2 is resumed by setting the unit cell voltage to a normal power generation voltage.

  The operation for recovering the battery characteristics is based on the fact that the potential of the oxidant electrode 2b is shifted to the base by reducing the oxidant gas supply flow rate, and the platinum oxide contained in the oxidant electrode 2b is reduced. As shown in FIG. 3, the horizontal axis represents the oxidant electrode potential and the vertical axis represents the hydrogen generation amount, and when the potential of the oxidant electrode 2b falls below 0.1 V, the hydrogen generation amount rapidly increases to 0.1 V. Thus, hydrogen generation does not occur. From this, before the cell voltage falls below 0.1 V, the oxidant gas supply flow rate is returned to a value higher than the flow rate before starting the battery characteristic recovery operation, so that the oxidant electrode 2b generates hydrogen by proton reduction reaction. It can be prevented from occurring.

  In addition, since there is no generation of hydrogen at the oxidant electrode 2b during the recovery operation, there is no possibility of direct combustion reaction on the platinum catalyst by oxygen supplied to the oxidant electrode 2b, which is compared with the electrochemical reaction. In addition, since there is no possibility of local high temperature generated by the direct combustion reaction having a large calorific value, the deterioration of the electrolyte membrane 2c can be prevented.

  On the other hand, oxygen supplied to the oxidant electrode 2b of the fuel cell 2 causes an oxygen reduction reaction at the oxidant electrode 2b, and hydrogen peroxide is generated as a byproduct. It is known that hydrogen peroxide generated as a by-product of the reaction in this way greatly affects the acceleration of deterioration of the electrolyte membrane 2c.

  Therefore, when measuring the hydrogen peroxide generated when the battery characteristic recovery operation is performed, as shown in FIG. 4, the horizontal axis represents the oxidant electrode potential and the vertical axis represents the hydrogen peroxide generation amount. The amount of hydrogen peroxide generated depends on the potential of the oxidant electrode 2b, and the amount of hydrogen peroxide generated increases rapidly when the potential of the oxidant electrode 2b falls below 0.1V. From this, it is possible to prevent the rapid generation of hydrogen peroxide in the oxidizer electrode 2b by preventing the cell voltage from falling below 0.1V, and to suppress the acceleration of the deterioration of the electrolyte membrane 2c. it can.

  As a result, when performing the operation of changing the battery characteristics by changing the operating conditions, hydrogen generation at the oxidant electrode 2b is suppressed by preventing the potential of the oxidant electrode 2b from falling below 0.1V, There is no risk of a direct combustion reaction due to hydrogen and oxygen at the oxidant electrode 2b, and a rapid increase in the amount of hydrogen peroxide produced at the oxidant electrode 2b is suppressed. Thereby, the battery characteristics can be recovered in a state where there is no possibility that the durability of the fuel cell 2 is lowered.

  In the present embodiment, the operation for recovering the battery characteristics is started when the control device 5 detects that the value is lower than a preset voltage value. However, this is not necessarily the case. The battery characteristic recovery operation may be started every preset time. In that case, it is not necessary to monitor the battery voltage during normal power generation, thereby simplifying the system. Further, each cell voltage may not be directly measured, but may be calculated as an average value from the voltage of a stack formed by stacking unit cells.

  A second embodiment will be described with reference to FIGS. 5 and 6 and with reference to FIGS. FIG. 5 is a block diagram showing a schematic configuration of the fuel cell system, and FIG. 6 is a flowchart showing a process for recovering battery characteristics. In addition, the same code | symbol is attached | subjected to the same part as 1st Embodiment, description is abbreviate | omitted, and the structure of this embodiment different from 1st Embodiment is demonstrated.

  In FIG. 5, the fuel cell system 11 includes, for example, a polymer electrolyte fuel cell 2, a fuel gas supply means 3 for supplying hydrogen gas as fuel gas to the fuel electrode 2 a of the fuel cell 2, and an oxidation of the fuel cell 2. The oxidant gas supply means 4 for supplying oxygen gas of the oxidant gas to the agent electrode 2b and the battery voltage of the fuel cell 2 are monitored, and the operation of the fuel cell system 11 is controlled while controlling the amount of current taken from the fuel cell 2. A control device 12 for controlling is provided.

  In the fuel cell system 11 configured as described above, in the fuel cell 2, the hydrogen rich gas supplied to the fuel electrode 2a from the fuel gas supply means 3 such as a fuel reformer via the fuel gas supply pipe 6a and the oxidation Electricity is generated by directly converting the oxygen binding energy of the air supplied from the oxidant gas supply means 4 to the agent electrode 2b through the oxidant gas supply pipe 7a into electric energy.

  And the battery characteristic of the fuel cell 2 gradually deteriorates by continuously generating power for a long time. Therefore, in order to recover the deterioration of the battery characteristics caused by the platinum oxidation in the recoverable oxidizer electrode 2b, the battery voltage is set in advance during normal continuous power generation under the control of the control device 12. When the voltage value falls below the voltage value, an operation for changing the operating condition for performing the battery characteristic recovery operation is started and executed.

  That is, as shown in FIG. 6, the operation for recovering the battery characteristics is performed in the first stage S11 when the normal continuous power generation is performed, and the unit cell voltage of the fuel cell 2 is preset by the control device 12. It continues to monitor whether or not it falls below a predetermined voltage lower than the normal generated voltage. And it starts when the control apparatus 12 detects that the cell voltage has fallen below the predetermined voltage set beforehand.

  By detecting that the unit cell voltage has fallen below the predetermined voltage, in the subsequent second stage S12, the control device 12 increases the amount of current that is larger than the amount of current extracted from the fuel cell 2 in the normal power generation at that time. Control is performed to change the operating conditions so that is extracted to the outside. At this time, the control is performed so that the generated voltage of the single cell is lower than the normal generated voltage by increasing the amount of current taken out from the fuel cell 2, preferably 0.6 V or less. Further, preferably, before changing the operating condition so as to increase the amount of current taken from the fuel cell 2, the fuel gas supply means 3 is controlled to change the fuel gas supply flow rate so that the current amount can be increased. Increase the fuel gas supply flow rate up to. Desirably, when the current amount is increased after the operating condition is changed, the fuel gas supply amount is increased beyond the consumed fuel gas flow rate calculated from the current amount.

  Further, in the third step S13, the operation is continued for a predetermined time while the unit cell voltage is lower than the normal power generation voltage while being monitored by the control device 12, and before the unit cell voltage falls below 0.1V, the fuel cell Control is performed to change the operating condition so that the amount of current taken out from 2 is returned to the amount of current taken out before the start of the battery characteristic recovery operation. At this time, the current amount may be adjusted to increase or decrease so that the unit cell voltage is lower than the normal power generation voltage that does not fall below 0.1 V until a predetermined time elapses. By operating the cell voltage so that the cell voltage does not fall below 0.1V and lower than the normal power generation voltage, platinum oxide contained in the oxidizer electrode 2b is reduced, and the battery characteristics are recovered. To do.

  Then, after the battery characteristics are recovered, the normal power generation operation of the fuel cell 2 is resumed by setting the unit cell voltage to a normal power generation voltage.

  Note that the battery characteristic recovery operation is performed so that the potential of the oxidizer electrode 2b does not fall below 0.1 V when the battery characteristic recovery operation is performed under different operating conditions, as in the first embodiment. As shown in FIG. 3, generation of hydrogen at the oxidant electrode 2b is suppressed, and there is no possibility of direct combustion reaction on the platinum catalyst due to oxygen at the oxidant electrode 2b. Since there is no possibility of the occurrence, deterioration of the electrolyte membrane 2c can be prevented. Furthermore, as shown in FIG. 4, since the rapid generation of hydrogen peroxide at the oxidant electrode 2b can be prevented, acceleration of deterioration of the electrolyte membrane 2c can be suppressed. As a result, the battery characteristics can be recovered in a state where there is no risk of reducing the durability of the fuel cell 2.

  Further, in the battery characteristic recovery operation performed so as to increase the amount of electricity taken out from the fuel cell 2 as compared with before, the responsiveness of the battery voltage is determined by the supply of the oxidant gas in the first embodiment. The battery characteristic recovery operation can be performed in a shorter time than the battery voltage response in the recovery operation for controlling the flow rate.

  In the present embodiment, the operation for restoring the battery characteristics is started when the control device 12 detects that the value is lower than a preset voltage value. However, this is not necessarily the case. The battery characteristic recovery operation may be started every preset time. In that case, it is not necessary to monitor the battery voltage during normal power generation, thereby simplifying the system. Further, each cell voltage may not be directly measured, but may be calculated as an average value from the voltage of a stack formed by stacking unit cells.

It is a block diagram which shows schematic structure of the fuel cell system in the 1st Embodiment of this invention. 3 is a flowchart illustrating a battery characteristic recovery operation process in the first embodiment of the present invention. It is a figure which shows the oxidizing agent electrode potential dependence of the hydrogen generation amount in the oxidizing agent electrode of the fuel cell which concerns on the 1st Embodiment of this invention. It is a figure which shows the oxidizing agent electrode potential dependence of the hydrogen peroxide production amount in the oxidizing agent electrode of the fuel cell which concerns on the 1st Embodiment of this invention. It is a block diagram which shows schematic structure of the fuel cell system in the 2nd Embodiment of this invention. 6 is a flowchart illustrating a battery characteristic recovery operation process according to a second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 ... Fuel cell system 2 ... Fuel cell 2a ... Fuel electrode 2b ... Oxidant electrode 3 ... Fuel gas supply means 4 ... Oxidant gas supply means 5, 12 ... Control device

Claims (5)

A fuel cell formed by stacking unit cells; fuel gas supply means for supplying fuel gas to the fuel electrode of the fuel cell; and oxidant gas supply means for supplying oxidant gas to the oxidant electrode of the fuel cell. A battery characteristic recovery operation method for a fuel cell system, wherein the battery voltage is recovered by temporarily lowering the battery voltage of the fuel cell from that during normal power generation,
Operating conditions so that when the battery voltage falls below a preset value during normal power generation, the battery voltage of the unit cell is lower than that during normal power generation and does not cause hydrogen generation by proton reduction reaction at the oxidant electrode. The fuel cell system is characterized in that power generation is continued for a predetermined time by changing the operating condition, and the operating condition is returned to the operating condition during normal power generation before the battery voltage of the unit cell falls below 0.1V. Battery characteristics recovery operation method. A fuel cell formed by stacking unit cells; fuel gas supply means for supplying fuel gas to the fuel electrode of the fuel cell; and oxidant gas supply means for supplying oxidant gas to the oxidant electrode of the fuel cell. A battery characteristic recovery operation method for a fuel cell system, wherein the battery voltage is recovered by temporarily lowering the battery voltage of the fuel cell from that during normal power generation,
Each time the power generation time of the fuel cell system exceeds a predetermined time, the cell voltage of the unit cell is lower than that during normal power generation, and the oxidant electrode has a voltage at which hydrogen generation due to proton reduction reaction does not occur. A fuel cell characterized in that an operation for changing the operating condition is performed to continue power generation for a predetermined time, and the operating condition is returned to the operating condition during normal power generation before the battery voltage of the unit cell falls below 0.1V. System battery characteristics recovery operation method.   3. The method for recovering battery characteristics of a fuel cell system according to claim 1, wherein the operation for changing the operating condition is an operation for increasing or decreasing a supply flow rate of the oxidant gas to the oxidant electrode.   3. The operation for recovering battery characteristics of a fuel cell system according to claim 1, wherein the operation for changing the operating condition is an operation for increasing / decreasing an amount of current taken out from the fuel cell more than that during normal power generation. Method.   5. The battery characteristic recovery of a fuel cell system according to claim 4, wherein the operation for changing the operating condition is performed after the supply flow rate of the fuel gas to the fuel electrode is increased from the supply amount so far. Method of operation.

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