JP2526284B2 - Method for operating molten carbonate fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for operating a fuel cell of a type using molten carbonate as an electrolyte, that is, a method for operating a molten carbonate fuel cell, and in particular, the life of the fuel cell. The present invention relates to a method for operating a molten carbonate fuel cell capable of exhibiting high cell performance immediately after restarting power generation after a temporary stop of operation.

[Prior Art] No invention has been found that examined a purge gas for holding a molten carbonate fuel cell at a temperature equal to or higher than the melting point of the electrolyte. However, generally, in a fuel cell of a type that uses gas as a fuel and an oxidant, the inside of the cell is purged with an inert gas when power generation is stopped. Also,
It is also known that without purging the battery with inert gas at all times, the inert gas is used only when the reactive gas is expelled from the battery, and after purging the reactive gas outside the battery, the purging of the inert gas may be stopped. This is a matter. Thus, the role of supplying the inert gas to the battery is that if the reaction gas remains in the battery, the electrochemical reaction (power generation reaction) cannot be completely stopped. For example, in a phosphoric acid fuel cell, if the cell is stored with the reaction gas remaining in the cell, the potential of the electrochemical reaction causes the platinum particles, which are the active components of the catalyst, to become large and the performance to drop. The problem occurs. In addition, storage with a voltage applied may accelerate movement of the electrolyte or cause a risk of handling. Therefore, when the battery is on standby in preparation for the next power generation, purging with an inert gas, especially nitrogen, has been the conventional method. However, according to this method, depending on the type of battery, there is a problem that the performance of the battery cannot be reproduced by the gas to be purged. Particularly, in the molten carbonate fuel cell, the performance at the time of re-power generation may be significantly reduced depending on the composition of the gas to be purged. There have been many unclear points about this cause, and it was thought that it was a completely unique phenomenon.

[Problems to be Solved by the Invention]

The above-mentioned conventional technique is based on the experience so far, and does not elucidate the phenomenon occurring in the battery to prolong the battery life and provide a high-performance battery from the start of power generation. Therefore, as described above, there is a problem that it takes a long time to recover the battery performance, or a problem that the battery life is short.

It is an object of the present invention to provide a method for operating a molten carbonate fuel cell, which can prolong the life of the molten carbonate fuel cell and obtain high-performance cell performance from the start of power generation.

[Means for solving the problem]

In order to achieve the above object, the method for operating a molten carbonate fuel cell of the present invention is to control the type of purge gas supplied to the cell. That is, when the electrolyte is kept above the melting point and when the temperature reaches the melting point of the electrolyte during the temperature rising process, the purge gas having the property of suppressing the movement of the electrolyte is supplied to the anode side and the cathode side of the battery, and the electrolyte is supplied before starting the power generation. Is operated so that the electrode is appropriately wetted with the electrolyte by supplying the purge gas which is easy to move. The purge gas may be the same kind of gas or different kinds of gas on the anode side and the cathode side. As the purge gas for suppressing the movement of the electrolyte, a gas having a low affinity with the molten carbonate as the electrolyte is suitable, and as the purge gas for facilitating the movement, a gas having a high affinity with the molten carbonate is suitable. As a gas with a low affinity for molten carbonate,
A gas comprising at least one type of N ₂ , He and Ar gas, and a gas having a high affinity include at least one type of CO ₂ and O ₂ gas or a gas containing them.
However, gas containing O ₂ gas is not supplied to the anode side.

In addition, if the viewpoint of the method for achieving the above object is changed, when the battery is held above the melting point of the electrolyte, the electrolyte is prevented from migrating to the electrode and the electrolyte is migrating to the electrode by a required amount before the start of power generation. It is what makes me. The reason why the electrolyte is moved to the electrode to a required extent before the start of power generation is to widen the electromotive reaction field of the battery.

The degree of transfer of the electrolyte to the electrode is preferably such that the transfer of the electrolyte to the cathode causes the electrolyte occupancy of the cathode to be 15 to 55%, and the transfer of the electrolyte to the anode causes the anode to move. Electrolyte occupancy is 20 ~
It is about 80%. Then, it is particularly desirable that the electrolyte occupancy ratios of the cathode and the anode are each in the above-mentioned range.

[Work]

The operation of the molten carbonate fuel cell operating method of the present invention is as follows. First, in order to extend the life of the battery, the electrolyte is not moved from the electrolyte substrate.
That is, it prevents the electrolyte from moving to the electrodes (anode and cathode) located on both sides of the electrolyte plate. When the electrolyte moves to the electrode, the electrolyte creeps in the separator plate in contact with the electrode and is consumed by the corrosion reaction of the separator. Therefore, by suppressing the movement to the electrode, the consumption of the electrolyte due to this phenomenon can be prevented. It is a well known fact that when the electrolyte is consumed, the internal resistance of the battery increases and the battery performance deteriorates. On the other hand, in order to more easily cause the electrochemical reaction at the electrode during power generation, it is necessary to widen the reaction area. This is because the reaction field is formed near the three-phase interface where solid, liquid and gas coexist. For this purpose, it is necessary to properly wet the electrode with molten carbonate. The present invention controls these contradictory phenomena depending on the type of gas supplied to the battery.

〔Example〕

 Examples of the present invention will be described below.

Experiment (1) First, the amount of molten carbonate transferred to the electrode depending on the type of gas was examined. FIG. 1 shows an example of the results of studying the movement of molten carbonate using a porous nickel electrode having a porosity of about 70% and an average pore diameter of 7 μm. Carbonate powder (Li ₂ O ₃ : K ₂ CO ₃ = 62 mol: 38 mol, mixed carbonate) was placed on the electrode, the temperature was set to 650 ° C., the carbonate was melted, and gas pressure was applied from one side, The pressure is measured and evaluated on the other side. That is, the pressure difference is generated in a shorter time as the atmosphere in which the molten carbonate as the electrolyte is more easily moved. In FIG. 1, the symbol A shows the results under the CO ₂ gas atmosphere, the symbol B shows the results under the air atmosphere, and the symbol C shows the results under the N ₂ gas atmosphere. is there. It can be seen from Fig. 1 that the movement of the electrolyte is very large in the CO ₂ gas atmosphere. On the contrary, it was found to be very small in the N ₂ gas atmosphere. It is considered that this is due to the affinity for molten carbonate, that is, the solubility of gas.

Experiment (2) With respect to the pore volume of the cathode, the extent to which the performance was high when molten carbonate was present was examined. FIG. 2 summarizes the occupancy ratio of the electrolyte with respect to the cathode polarization. From FIG. 2, it can be said that the electrolytic mass in the cathode is preferably about 15 to 55%, particularly 20 to 50% in terms of pore occupancy.

Experiment (3) Similar to Experiment 2, the occupation rate of the electrode material with respect to the anode polarization was examined. FIG. 3 shows the results. From Fig. 3, it was found that the performance of the anode is excellent in a wide range of 20 to 80%.

From the results of Experiments (1), (2), and (3) described above, hold the battery at a temperature equal to or higher than the melting point of the electrolyte, that is, stand by for power generation, and then, as the holding condition when starting power generation next, In order to prevent the migration of the electrolyte, N ₂ gas was supplied to the anode side and cathode side of the cell, and it was decided to mix CO ₂ gas with 50% of N ₂ before the start of power generation. The time to start supplying CO ₂ was selected 1 hour before the start of power generation. At the start of power generation, the supply gas is switched again, and the reaction gas is supplied to the anode side and the cathode side to generate power. Incorporating this operating condition, usually indicated by the symbol d the voltage performance of the conventional molten carbonate fuel cell having an electrode area 100 cm ^2, which was operated at a current density of 150 mA / cm ² by supplying a reaction gas to Figure 4. FIG. 4 shows the performance of a battery in which N ₂ gas was supplied to the battery, which is a conventionally known method, when power generation was stopped, and reaction gas was immediately supplied at the start of power generation, without using the conditions according to the present invention. Indicated for. In FIG. 4, temporary operation was stopped after 1500 hours and 2600 hours, and power was regenerated under each condition. As is clear from FIG. 4, it was found that the battery according to the present invention can always obtain stable performance for a long time without deterioration in performance.

Although only CO ₂ gas, N ₂ gas and air were described in the above-mentioned examples, O ₂ gas has a property close to that of CO ₂ gas. However, O ₂ gas is not supplied to the anode side in order to avoid oxidation of the anode. He or Ar gas can be cited as a material having a property close to that of N ₂ gas. Needless to say, the present invention may use these other gases or a combination of these gases. Also, before starting power generation, the electrolyte is switched to a gas that is easy to move or is mixed, but this time and mixing ratio differ depending on the shape of the battery, the electrodes used, the physical properties of the electrolyte plate, etc. It is possible to choose.

〔The invention's effect〕

According to the present invention, as shown in FIG. 4, the battery performance can be maintained at high performance for a long time.

[Brief description of drawings]

FIG. 1 shows the types of gas and the amount of movement of the electrolyte according to the present invention, FIG. 2 shows the electrolyte occupancy and cathode polarization, FIG. 3 shows the electrolyte occupancy and anode polarization, and FIG. 4 shows the present invention. FIG. 6 is a diagram showing a comparison of long-term characteristics of a battery operated by the above operating method and a battery operated by a conventional method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasutaka Komatsu 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Shigeyoshi Kobayashi 502 Jinmachi, Tsuchiura-shi, Ibaraki Shares Company Hitachi, Ltd. Mechanical Research Laboratory (56) Reference JP-A-63-276879 (JP, A) JP-A-63-298974 (JP, A)

Claims (3)

(57) [Claims] 1. A method for operating a molten carbonate fuel cell using molten carbonate as an electrolyte, wherein when the cell is held at a temperature equal to or higher than the melting point of the electrolyte, a purge gas having a small affinity with the molten carbonate is supplied to the anode side of the cell. Of the molten carbonate fuel cell, wherein the purge gas supplied to both the cathode side and the cathode side and switched to the purge gas supplied to the anode side and the cathode side a predetermined time before the start of power generation is switched to a purge gas having a high affinity for the molten carbonate. Method of operation. 2. A purge gas having a low affinity for molten carbonate is at least one of N ₂ , He and Ar gas,
The method for operating a molten carbonate fuel cell according to claim 1, wherein the purge gas having a high affinity with the molten carbonate is CO ₂ gas or a gas containing CO ₂ . 3. The supply of the purge gas having a high affinity with the molten carbonate performed a predetermined time before the start of power generation is melted with the flow of the purge gas having a low affinity with the molten carbonate being supplied to the anode side and the cathode side. 3. The method for operating a molten carbonate fuel cell according to claim 1, wherein the method is performed by mixing a purge gas having a high affinity with carbonate.