JPH0690932B2 - How to operate a fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of operating a fuel cell, and more particularly, to keeping the performance of the fuel cell stable for a long time and at the same time keeping the operation of the cell safe. The present invention relates to a preferable fuel cell operation method.

[Conventional technology]

In the operation of a conventional fuel cell, the anode / cathode system co-reactive gas is replaced with an inert gas to reduce the potential when the power generation state is stopped and the storage state is changed. Further, as described in JP-A-61-32362, by continuously connecting the resistor during the inert gas purge, the time required for lowering the potential has been shortened.

[Problems to be solved by the invention]

The above-mentioned conventional technology, in the process of stopping from the operating state,
The anode and cathode systems are each purged with an inert gas to prevent the reaction gas from being directly mixed, while lowering the battery voltage. In particular, at high temperatures such as operating temperature, the noble metal catalyst used in the electrode There is a problem that it takes a long time to fall to the battery protection level even though the battery is greatly deteriorated and the battery voltage has to be rapidly lowered, and not only the catalyst deterioration but also the battery stopping step becomes long. Furthermore, the only purging with an inert gas it is difficult to completely replace such as O ₂ component that leaks O ₂ component adsorbed remaining in the cathode or to the anode system, the catalyst deterioration can not be sufficiently reduced the potential of each electrode There is a problem in that it cannot be completely prevented.

According to Japanese Patent Laid-Open No. 61-32362, the battery output side is short-circuited by a resistor, and the short-circuit current flowing at this time rapidly consumes the residual O ₂ to significantly reduce the battery voltage drop time. However, the fuel gas is also replaced by an inert gas, and the voltage of each cell becomes unbalanced depending on the amount of remaining H +, and there was a problem that the cell in which H + disappeared quickly deteriorates due to the electrolytic corrosion reaction. .

Japanese Unexamined Patent Publication No. 59-75569 discloses a method of enclosing N ₂ gas containing H ₂ in the anode and cathode electrodes when it is stored at room temperature, but since H ₂ is mixed in the cathode system, it remains. will consume O ₂ by direct combustion reacts with O ₂ to,
There is a problem that the electrode catalyst layer and the like are damaged. Further, this known example relates to a storage method at room temperature, and if it is applied as it is when the fuel cell is operating, there is a great risk that a safety problem will occur as the temperature becomes higher.

An object of the present invention is to reduce the electrode potential in an essentially safe manner in a short time and without deterioration of electrolytic corrosion of the electrode, and to minimize the deterioration of the battery performance that occurs during the battery shutdown process or standby, storage. A method of operating a fuel cell is provided that keeps the fuel cell plant safe and stable to improve the operating efficiency by suppressing or further preventing the generation of H _{2 at} the cathode.

[Means for solving problems]

The purpose of the above is to provide a resistor circuit on the DC output side of the fuel cell through a switch so that when the fuel cell is stopped or in standby, the amount of the anode fuel gas is the same as that during power generation, or an appropriate amount of inert gas. In the diluted state, purging only the cathode system with an inert gas, and turning on the resistor circuit on the DC output side of the fuel cell (first invention), or in addition to the above means, the cell voltage This is achieved by electrically disconnecting the resistor circuit (second invention) when the voltage becomes lower than the electromotive force level for generating hydrogen gas on the cathode side due to the cell action.

[Action]

That is, when the fuel cell is stopped or the temperature and pressure of the fuel cell are the same as those during power generation, the cathode system is blown with an inert gas to remove the oxidizer when the load is temporarily released and waiting. By short-circuiting the DC output side of the battery with an appropriate resistor circuit, flow a current according to the residual electromotive force,
Adsorbed by the current to the cathode system, the O ₂ to leak from the O ₂ or outside the system remaining electrochemically digested, so as rapidly to lower the cathode potential. At this time, a fuel gas or an inert gas containing a part of the fuel gas is allowed to flow in the anode system, so that a charged body moving in the electrolyte, for example, a phosphoric acid fuel cell, is sufficiently supplied with H +. As in the case of blowing only with an inert gas,
It is possible to completely prevent the deterioration of the cells due to the electrolytic corrosion reaction due to the nonuniformity of H + remaining among a large number of cells.

Next, in the above state, by forming a kind of concentration cell state for each cell, even if the residual O ₂ is completely consumed due to adsorption or leakage, the gas concentration at the anode and cathode electrodes is increased. An electromotive force that is determined by the difference between the two is generated, and the difference between the two electromotive forces appears as a battery voltage, and the current continues to flow through the short-circuit resistance. At this time, in the electrolyte part, H + flows from the anode to the cathode, a part of this H + is used for consumption of the above-mentioned residual O ₂ and leak O ₂ , and the rest is recombined to the cathode side as H ₂ gas. Is generated. This phenomenon significantly impairs the safety of the fuel cell when the oxidant is introduced when the fuel cell is restarted next time, and is caused by the operation of various safety devices equipped in the fuel cell plant. The operation efficiency of the fuel cell power generation plant will be significantly reduced, such as the interruption of the plant, the impaired stable operation of the plant, and the lowered operation rate. On the other hand, in the present invention, since the resistor circuit on the battery output side is electrically disconnected by the switch below the theoretical concentration battery electromotive force determined by the gas concentration, pressure, temperature, etc., after consumption of residual O ₂ The transfer of H + to the cathode is blocked, and H ₂ generation in the cathode system can be completely prevented. Furthermore, due to an increase in O ₂ leakage from the outside of the system or some trouble,
When O ₂ increases and the battery voltage exceeds the electromotive force of the concentration battery, by turning on the resistor with the switch again,
O ₂ can be consumed again to keep the cathode potential below the cell protection level at all times.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. 1 and 2 show the battery main body in a simplified manner, but the anode part and the cathode part are respectively laminated with unit batteries constituted by a normal means, and each has a gas supply / discharge device and inside the battery container 3. It is stored in.

4, 5, 6 and 7 are a fuel gas cutoff valve, an air cutoff valve, a nitrogen cutoff valve, and a cathode nitrogen blow valve, respectively, and 4, 5 and 6 are respectively connected to the anode part 1, the caustic part 2 and the battery container 3. Reference numeral 7 is a valve connected to the nitrogen system pipe and the cathode system pipe for supplying nitrogen gas to the cathode portion 2.

8 is disposed between the anode part 1 and the fuel gas cutoff valve
H ₂ sensor, 9 is a voltmeter that measures the battery voltage, 10 is a discriminator, which calculates the reference voltage from the signal of the H ₂ sensor,
It has a function of comparing with the output of the voltmeter 9.

Reference numeral 11 is the above-described resistor circuit arranged on the DC output side of the battery, 12 is a switch for opening and closing the resistor circuit 11, and 13 is 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 stands by, the fuel gas cutoff valve 4 is allowed to flow an appropriate amount of gas while being in the open state, and the cathode nitrogen blow valve is in the open state to the open state. The shut-off valve is closed and the cathode system is blown with an inert gas to lower the battery voltage. Further, the switch 12 is turned on and the battery DC output side is connected to the resistor circuit 11
Short circuit. By doing so, as described above, the O ₂ remaining in the cathode system such as the cathode portion 2 is consumed by the electrochemical reaction, the cathode potential is rapidly lowered, and the cathode potential can be kept below the battery protection level.

FIG. 2 is a diagram comparing the attenuation characteristics of the battery voltage between the conventional example and the present embodiment. The conventional example is a case where both the anode system and the cathode system lower the cell voltage by nitrogen blowing, but the voltage decay characteristic is exponential, and this time constant is the nitrogen amount considered to be appropriate in a normal fuel cell plant. We have confirmed that the order is about 30 minutes to 1 hour. On the other hand, the characteristic indicated by the chain line is the case of this embodiment, and the battery voltage can be rapidly lowered by turning on the resistor circuit 11, that is, the battery protection level or less. Compared with the conventional example, the time required to be below the protection level is
It was able to be greatly shortened from 1/5 to 1/10 or less, and the performance deterioration due to the aggregation of the noble metal catalyst used for the cathode electrode could be reduced to such an extent that it would not be a practical problem.

FIG. 3 is a diagram showing the change with time of the battery voltage during storage. In the case of this example shown by the solid line, the performance deterioration rate is 1000 ha.
It has been experimentally confirmed that it can be suppressed to a level of 0 to 1 mV per operation, which is not a problem in operation, and is 1/5 to 1/10 that of the conventional example.

FIG. 4 shows the result of further microscopic examination of the battery voltage characteristic of this embodiment. When the resistor circuit 11 is kept in the ON state even after the battery protection level is reached, the predetermined battery voltage is reached. After that, a constant voltage is shown. This voltage level is the electromotive force of the concentration battery which is determined as the difference in the electromotive force of each electrode determined by the inflowing gas component and concentration in the anode part 1 and the cathode part 2, and when the electrolyte is phosphoric acid, for example, H ₂ is A predetermined electromotive force is generated in the battery according to Nernst's theorem from the difference in the electrochemical reaction acting on each electrode based on the concentration difference. At this time, in the region II below the electromotive force of the concentration battery shown in FIG. 4, the remaining O ₂ is completely consumed, so that H + moves in the electrolyte from the anode to the cathode, H ₂ will be generated in part 2. Such a state extremely impairs safety when introducing an oxidizer when the battery is restarted, and the resistor circuit 11 shown in this embodiment is used.
Switch 12 must be turned off to prevent H + from moving. Furthermore, when the battery voltage exceeds the electromotive force of the concentration battery due to leakage O ₂ from the outside of the system, the resistor circuit 11 may be turned on again to consume O ₂ by an electrochemical reaction.

Fig. 5 shows the results of examining the relationship between the electromotive force of the concentration cell and the H ₂ concentration. To summarize the horizontal axis as logarithmic electromotive force of the concentration cell corresponds in H ₂ concentration of the fuel gas introduced into the anode system, cause concentration cell by monitoring the concentration of H ₂ with H ₂ sensor -8 The power can be determined, and the resistor circuit 11 is turned on and off by comparing the voltage level with the battery voltage measured by the discriminator 10 and the voltmeter 9.
It is possible to maintain safe operation without H ₂ production at the cathode.

〔The invention's effect〕

According to the present invention, a resistor circuit provided on the DC output side of a cell is turned on without shutting off fuel gas to the anode system to electrochemically consume O ₂ remaining adsorbed on the cathode system to protect the cell voltage. You can quickly drop below the level,
It is possible to prevent the aggregation of the noble metal catalyst due to the high potential of the cathode, and to prevent it at the same time as the electrolytic corrosion deterioration of the battery due to the deficiency of H +. Furthermore, open the resistor circuit below the electromotive force of the concentration battery determined by the H ₂ concentration. When used as a system, it is possible to prevent the generation of H _{2 in} the cathode system and to provide an extremely safe fuel cell operation method.

[Brief description of drawings]

FIG. 1 is a piping system diagram of a fuel cell body showing an embodiment of the present invention, FIG. 2 is a comparison diagram of attenuation characteristics of cell voltage, FIG. 3 is a comparison diagram of reduction characteristics of cell voltage due to storage, FIG. FIG. 4 is a diagram showing the characteristics of the electromotive force of the concentration cell, and FIG. 5 is a diagram showing the H ₂ concentration dependence of the electromotive force of the concentration cell. 1 ... Anode part, 2 ... Cathode part, 3 ... Battery container, 4 ... Fuel gas shutoff valve, 5 ... Air shutoff valve, 6 ...
… Nitrogen gas shutoff valve, 7 …… Cathode nitrogen blow valve, 8
...... H ₂ sensor, 9 ...... voltmeter, 10 ...... discriminator, 11 ......
Resistor, 12 ... Switch, 13 ... Inverter.

Claims (2)

[Claims] 1. A pair of gas diffusion electrodes, an electrolyte layer sandwiched between these electrodes, and a supply / discharge device for supplying / discharging an oxidant gas and a fuel gas to / from each electrode, and electric energy is generated by an electrochemical reaction between the electrodes. On the DC output side of the fuel cell,
In a method of operating a fuel cell having a configuration in which a resistor circuit equipped with a switch is connected in parallel, when the operation of the fuel cell is stopped or the load is temporarily released and waiting, only the cathode oxidant gas is supplied. After switching to an inert gas and purging, the anode system is made to flow the same amount of fuel gas as when generating power, or a fuel gas mixed with an appropriate inert gas is made to flow, and the cathode potential is lowered by turning on the switch of the resistor circuit. A method of operating a fuel cell characterized by: 2. A pair of gas diffusion electrodes, an electrolyte layer sandwiched between these electrodes, and a supply / discharge device for supplying / discharging an oxidant gas and a fuel gas to / from each electrode, wherein electric energy is generated by an electrochemical reaction between the electrodes. On the DC output side of the fuel cell,
In a method of operating a fuel cell having a configuration in which a resistor circuit equipped with a switch is connected in parallel, when the operation of the fuel cell is stopped or the load is temporarily released and waiting, only the cathode oxidant gas is supplied. After switching to an inert gas and purging, the anode system is made to flow the same amount of fuel gas as when generating power, or a fuel gas mixed with an appropriate inert gas is made to flow, and the cathode potential is lowered by turning on the switch of the resistor circuit. And then electrically disconnecting the resistor circuit provided on the DC output side of the fuel cell when the cell voltage becomes lower than the electromotive force level for generating hydrogen gas on the cathode side due to the action of the concentration cell. Fuel cell operation method