JPH01128362A - Operating method for fuel cell - Google Patents

Abstract

PURPOSE:To prevent the deterioration of electrode from the electrolytic corrosion and to secure the safety of the plant by making the anode system fuel gas in a condition diluted by an inert gas and purging by the inert gas at only the cathode system side, at the time when the operation of a fuel cell is halted, for example, and, throwing in a resistor at the DC side and opening the resistor at the time when the voltage is reduced less than the e.m.f. of a concentration cell. CONSTITUTION:When the operation of a cell is stopped or at a waiting condition, an adequate amount of gas is let flow while a fuel gas cutoff valve 4 is kept in the open condition, a cathode system nitrogen blow valve 7 is turned from OFF to ON and an air cutoff valve 5 is OFF to blow an inert gas to the cathode system, and the voltage of the cell is reduced. Moreover, a switch 12 is turned on to make the cell input side short-circuited by a resistor 11. As a result, the cell voltage can be reduced rapidly less than the protective level, and the electrolytic corrosion deterioration of the cell can be prevented. Furthermore, at the time when the cell voltage is reduced less than the e.m.f. of a concentration cell which is determined by the H2 density and the like, the said resistor 11 is opened electrically. Consequently, the generation of H2 to the cathode system can be prevented, and the safety is secured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of operating a fuel cell, and in particular, a method for maintaining stable performance of a fuel cell over a long period of time and at the same time maintaining safe operation of the cell. This invention relates to a preferred method of operating a fuel cell.

[Conventional technology]

In conventional fuel cell operation, the system stops from generating electricity.

When transitioning to the storage state, the anode and cathode co-reactant gas was replaced with an inert gas to lower the potential. Furthermore, as described in Japanese Patent Laid-Open No. 61-32362, the time required for potential reduction has been shortened by intermittently connecting a resistor during inert gas purging.

[Problem that the invention seeks to solve]

In the above conventional technology, in the process of stopping from the operating state,
This method purges the anode and cathode systems with inert gas to prevent direct mixing of reactant gases while lowering the cell voltage. The deterioration is large, and even though the battery voltage must be rapidly lowered, it takes a long time to lower it to the battery protection level, which poses a problem that not only catalyst deterioration occurs but also the battery shutdown process becomes long. Furthermore, it is difficult to completely replace the O2 components that remain adsorbed on the cathode or the O2 components that leak to the anode system by only purging with inert gas, and the potential of each electrode cannot be sufficiently reduced, resulting in complete catalyst deterioration. The problem was that it could not be prevented.

According to JP-A No. 61-32362, the battery output side is short-circuited with a resistor, and the short-circuit current that flows at this time rapidly consumes the remaining 02, thereby significantly shortening the time for the battery voltage to drop. The fuel gas is also replaced with an inert gas, and there is a problem that the voltage of each cell becomes unbalanced due to the amount of remaining H0, and cells whose H÷ disappears quickly deteriorate due to an electrolytic corrosion reaction. Ta.

JP-A No. 59-75569 discloses a method of sealing N2 gas containing Hz into the anode and cathode electrodes when stored at room temperature, but since Hz is also mixed into the cathode system, residual 02 and Unfortunately, the direct combustion reaction consumed 02 and caused damage to the electrode catalyst layer. Furthermore, this known example relates to a storage method at room temperature, and if it is applied as it is during fuel cell operation, the temperature will be too high and there is no risk of further safety problems, and it is essentially safe to maintain the electrode potential. The fuel cell plant can be kept safe and stable by minimizing the deterioration in battery performance that occurs during the battery shutdown process, standby, and storage, or by further preventing the generation of Hz to the cathode. The present invention provides a fuel cell operating method that increases operating efficiency.

[Means for solving problems]

The above purpose is to install a resistor on the DC output side of the fuel cell via a switch, and when the fuel cell is stopped or on standby, the anode fuel gas is diluted with the same or appropriate amount of inert gas as used during power generation. By purging only the cathode system with an inert gas and inserting a resistor on the DC output side of the fuel cell (first invention), or in addition to the above means, the cell voltage can be changed to This is achieved by electrically disconnecting the resistor when the electromotive force becomes lower than the concentration battery electromotive force determined by concentration, pressure, temperature, etc. (second invention).

[Effect]

In other words, when the fuel cell is stopped, or when the cell temperature and pressure are the same as during power generation, when the load is temporarily released and standby, the cathode system is blown with inert gas to remove the oxidizing agent, and then By short-circuiting the DC output side of the battery with a suitable resistor, a current according to the remaining electromotive force is caused to flow, and this current attracts and remains on the cathode system. 2 or 02 leaking from outside the system is electrochemically digested to rapidly lower the cathode potential. At this time, since fuel gas or an inert gas partially containing fuel gas is flowed through the anode system, a sufficient amount of charged bodies moving in the electrolyte, such as H+ in a phosphoric acid fuel cell, is supplied. As in the case of simply blowing with an inert gas, it is possible to completely prevent deterioration due to electrolytic corrosion reaction of cells due to non-uniformity of residual H+ among a large number of cells.

Next, the above state forms a kind of concentration battery state for each cell, and even after the remaining Oz is completely consumed due to adsorption or leakage, the gas concentration remains at the anode and cathode electrodes. An electromotive force determined by the difference between the two is generated, and the difference between the electromotive forces appears as the battery voltage, and the current continues to flow through the short-circuit resistor. At this time, in electrolyte section 5, H+ flows from the anode to the cathode, and part of this H+ is used to consume the residual 02 and leaked 02 mentioned above, and the rest is recombined and generated as Hz gas on the cathode side. . This phenomenon significantly impairs the safety of the fuel cell when introducing the oxidizing agent the next time the fuel cell is restarted. This will also lead to plant shutdowns, which will impair stable plant operation, and will significantly reduce the operational efficiency of a fuel cell power plant, such as a reduction in availability. In contrast, in the present invention, gas concentration, pressure,
When the electromotive force of the concentration battery is below the theoretical concentration battery electromotive force determined by temperature, etc., the resistor on the battery output side is electrically disconnected by a switch, so after the remaining O2 is consumed, the movement of H+ to the cathode is blocked, and the H2 to the cathode system is The generation of can be completely prevented. Furthermore, if Ox increases in the cathode system due to an increase in 02 leakage from outside the system or some kind of trouble, and the battery voltage causes an electromotive force of the concentration battery, the resistor can be turned on again using the switch. can be consumed again and the cathode potential can always be kept below the battery protection level.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. Reference numerals 1 and 2 show the battery bodies in a simplified manner, and the anode part and the cathode part are stacked with unit batteries constructed by ordinary means, and each has its own gas supply and exhaust device, and the interior of the battery container 3 is shown in FIG. It is stored in.

4.5 and 6.7 are a fuel gas cutoff valve, an air cutoff valve, a nitrogen cutoff valve, and a cathode nitrogen blow valve, respectively;
．． 6 are anode portion 1° and cathode portion 2. A valve 7 is connected to the nitrogen system piping and the cathode system piping in order to supply nitrogen gas to the cathode portion 2 .

8 is an H2 sensor disposed between the anode part 1 and the fuel gas cutoff valve, 9 is a voltmeter that measures the battery voltage, and 10 is a discriminator that calculates a reference voltage based on the signal of the H2 sensor, etc. It has a function to compare and discriminate with the output of 9.

Reference numeral 11 designates the above-described resistor disposed on the DC output side of the battery, 12 a switch for opening and closing the resistor 11, and 13 an inverter for converting the DC output of the battery into AC.

In the above configuration, when the operation of the fuel cell is stopped or temporarily on standby, the fuel gas cutoff valve 4 is left open to allow an appropriate amount of gas to flow, and the cathode nitrogen blow valve is changed from the closed state to the open state and the air Close the shutoff valve and blow inert gas into the cathode system to lower the battery voltage. Furthermore, the switch 12 is set to ○N, and the battery DC output side is connected to the resistor 11.
short circuit. In this case, as described above, the 02 remaining in the cathode system such as the cathode part 2 is consumed by electrochemical reaction, and the cathode potential quickly decreases.
The cathode potential can be kept below the battery protection level.

FIG. 2 is a diagram comparing the attenuation characteristics of battery voltage between the conventional example and this embodiment. In the conventional example, the cell voltage is lowered by nitrogen blowing for both the anode system and the cathode system, but the voltage attenuation characteristic is exponential, and this time constant is determined by the amount of nitrogen that is considered appropriate for a normal fuel cell plant. We have confirmed that it takes approximately 30 minutes to 1 hour. On the other hand, the characteristic shown by the chain line is the case of this embodiment, and the battery voltage can be rapidly reduced by turning on the resistor 11, that is, it can be made below the battery protection level. Compared to the conventional example, the time required to reach the protection level or lower is 1
・Can be significantly shortened from 15 to 1/10 or less,
It was possible to reduce the performance degradation caused by agglomeration of the noble metal catalyst used in the cathode electrode to a level that does not pose a practical problem.

Figure 3 shows the change in battery voltage over time during storage, and in the case of this example shown by the solid line, the performance degradation rate is 0 to 1 mV per 1000%, which is almost no problem in operation. 17 compared to the conventional example.
It has been experimentally confirmed that the ratio is 5 to 1/10.

FIG. 4 shows the results of a further microscopic examination of the battery voltage characteristics of this example. If the resistor 11 is kept in the ON state even after the voltage drops below the battery protection level, the battery voltage will reach the predetermined voltage. The electromotive force of a concentration battery is determined as the difference in electromotive force between each electrode, which is determined by the fact that the electrolyte exhibits a constant voltage.If the electrolyte is phosphoric acid, for example, Hz acts on each electrode, causing an electrochemical reaction based on the concentration difference. A predetermined electromotive force is generated in the battery according to Nernst's theorem from the difference between the two. At this time, since the remaining 02 has already been completely consumed in the region (2) where the electromotive force of the concentration battery is lower than that shown in Fig. 4, H is passed through the electrolyte from the anode to the cathode.
+ will move and produce Hz in the cathode part 2. Such a state greatly impairs safety when introducing an oxidizing agent when restarting the battery, and the movement of 0FFL and H+ must be prevented by the resistor 11 and switch 12 shown in this embodiment. . Furthermore, if the battery voltage exceeds the electromotive force of the concentration battery due to the incorporation of glue Q2 from outside the system, the resistor 11 may be turned on again to consume 02 through an electrochemical reaction.

FIG. 5 shows the results of investigating the relationship between the electromotive force of the concentration cell and the H2 concentration. If the horizontal axis is arranged as a logarithm, the electromotive force of the concentration cell corresponds to the H2 concentration of the fuel gas introduced into the anode system, and the electromotive force of the concentration cell can be determined by monitoring the H2 concentration with the Hz sensor 8. By comparing the voltage level with the battery voltage measured by the voltmeter 9 by the discriminator 10, the resistor 11 is turned on.
.

OFF, and safe operation without Hz generation at the cathode can be maintained.

〔Effect of the invention〕

According to the present invention, the resistor provided on the DC output side of the battery is inserted into the anode system without cutting off the fuel gas, and the fuel gas is adsorbed and remains in the cathode system. 2 can be electrochemically consumed to rapidly lower the cell voltage below the protection level, thus preventing the agglomeration of the precious metal catalyst due to the high cathode potential, and
It is possible to simultaneously prevent electrolytic corrosion deterioration of the battery due to the lack of +.Furthermore, if the system is configured to open the resistor below the electromotive force of the concentration battery determined by the H2 concentration, the generation of Hz in the cathode system can be prevented. It has the effect of providing an extremely safe method of operating fuel cells.6

[Brief explanation of the drawing]

Fig. 1 is a piping system diagram of the main body of a fuel cell showing an embodiment of the present invention, Fig. 2 is a comparison diagram of battery voltage attenuation characteristics, Fig. 3 is a comparison diagram of battery voltage drop characteristics due to storage, FIG. 4 is a diagram showing the characteristics of the electromotive force of the concentration battery, and FIG. 5 is a diagram showing the dependence of the electromotive force of the concentration battery on H2 concentration. 1... Anode part, 2... Cathode part, 3...
-Battery container, 4...Fuel gas cutoff valve, 5...Air cutoff valve, 6...Nitrogen gas cutoff valve, 7...Cathode system nitrogen blow valve. 8... H2 sensor, 9... Voltmeter, 10... Discriminator.

Claims (1)

[Claims] 1. A gas diffusion electrode including a pair of gas diffusion electrodes, an electrolyte layer sandwiched between these electrodes, and a supply/discharge device for supplying and discharging an oxidizing gas and a fuel gas to each electrode, and an electrochemical reaction between the electrodes. In a fuel cell that obtains electrical energy by
The anode system is characterized by flowing fuel gas equivalent to that used during power generation or mixed with an appropriate inert gas, and lowering the cathode potential by short-circuiting the DC output side of the fuel cell with an appropriate resistance. How to operate a fuel cell. 2. A fuel that includes a pair of gas diffusion electrodes, an electrolyte layer sandwiched between these electrodes, and a supply/discharge device for supplying and discharging oxidizing gas and fuel gas to each electrode, and obtains electrical energy through an electrochemical reaction between the electrodes. In batteries, when stopping fuel cell operation or temporarily removing the load and waiting, only the cathode oxidizing gas is switched to an inert gas and purged.
In the anode system, fuel gas equivalent to that used during power generation or mixed with an appropriate inert gas is flowed, and the cathode potential is lowered by short-circuiting the DC output side of the fuel cell with an appropriate resistance. A fuel cell operating method characterized by electrically disconnecting a resistor provided on the DC output side of the fuel cell when the cell voltage drops due to the concentration cell electromotive force determined by gas concentration, pressure, temperature, etc. 3. The method of operating a fuel cell according to claim 2, characterized in that the electromotive force of the concentration cell is determined by monitoring the H_2 concentration with an H_2 sensor.