JPH0646568B2 - Molten salt fuel cell - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a fuel cell using a molten salt such as a molten carbonate as an electrolyte and a gaseous active material.

Configuration of Conventional Example and Problems Thereof FIG. 4 shows a conventional example of the configuration of a molten carbonate fuel cell representing a fuel cell using a molten salt as an electrolyte. Mixed carbonates such as potassium carbonate and lithium carbonate (Li ₂ CO ₃ : K
₂ CO ₃ = 62: 38) was mixed with fine powder of lithium aluminate and hot-pressed, and an electrolyte body 1 (55% by weight of lithium aluminate) was used as a fuel electrode (negative electrode) 2 made of a nickel sintered body and lithium nickel. The gas chambers 4 and 5 are sandwiched between the oxide electrodes (positive electrodes) 3 of oxides, and current collectors 6 and 7 are disposed in the gas chambers 4 and 5 for both collecting current and fixing the electrodes. The active material gas is supplied from the gas chamber inlets 8 and 9, and the exhaust gas is discharged from the gas chamber outlets 10 and 11. 12 is a bipolar plate.

The oxidant gas used in this molten carbonate fuel cell is a mixed gas of air and carbon dioxide, and carbonate ions generated by reducing this gas at the positive electrode are released into the molten salt. On the other hand, in the negative electrode, hydrogen gas supplied as a fuel reacts with carbonate ions to generate water and carbon dioxide. At that time, the electric current in the electrolyte is carried by the movement of carbonate ions. As described above, the electrolyte body 1 has a role as a partition plate for preventing the mixing of the fuel gas and the oxidant gas, and a role for promptly transporting carbonate ions generated by the positive electrode reaction to the reaction site on the negative electrode.

However, if the operation of the conventional fuel cell shown in FIG. 4 is continued, the amount of the molten carbonate electrolyte in the electrolyte body decreases, and these important roles are hindered. That is, due to the drying and cracking of the electrolyte, mixing of the oxidant gas and the fuel gas may occur, or the internal resistance of the battery may increase.

FIG. 5 shows the result of the life test of the conventional battery to concretely show how the electrolytic mass decreases. When the operation is continued at a constant current of 150mA / cm ² , the battery output voltage begins to drop about 1000 hours after the start of operation and then 0.025 every 1000 hours.
The output voltage decreased at the rate of V, and after about 5000 hours, it decreased to 0.15V, which is 0.1V lower than that at the start of the operation, to 0.65V. Meanwhile, the internal resistance indicated by the black circle in the figure is 0.6Ω / cm ² to 1.2.
It rose to Ω / cm ² . This increase in internal resistance is apparently due to the dissipation of the electrolyte in the electrolyte body. The operating temperature is 650 ° C.

In order to prevent the deterioration of battery performance due to the dissipation and drying of the electrolyte during battery operation, we are also considering ways to keep excess carbonate in the electrolyte beforehand or to add carbonate directly during operation. However, it is difficult to control the amount of carbonate, the driving operation becomes complicated, etc.
He had various problems. In addition, these methods have two main causes of the reduction of carbonates: 1) leaching into other battery constituent materials such as electrodes, current collectors, and bipolar plates, 2) evaporation into active material gas, Of these, the former was effective, but the latter was not a fundamental solution.

As described above, the conventional battery cannot fundamentally prevent the evaporation and drying of the electrolyte, which is a major obstacle to extending the life, which is essential for practical use.

OBJECT OF THE INVENTION It is an object of the present invention to provide a molten salt fuel cell with an electrolyte that can be replenished and at the same time control the amount of the electrolyte, thereby prolonging the life of the cell.

Structure of the Invention The present invention is characterized in that a molten salt bubbler is provided in the upstream side of the active material gas supply side, and the gas passing through the bubbler is introduced into the battery.

Description of Examples Molten carbonate has a larger contact angle in nickel used in the negative electrode than in lithium nickel oxide, which is the positive electrode material,
As a result, in general, the negative electrode side is more likely to be in a state of electrolyte shortage. Therefore, as an embodiment of the present invention, an example in which a molten salt bubbler is provided before the negative gas supply is shown. FIG. 1 shows a battery system according to the present invention, and FIG. 2 shows a structural diagram of a molten salt bubbler. Reference numeral 13 denotes a fuel cell main body having the structure as shown in FIG. 4, in which a fuel supply passage 14 and a gas discharge passage 15 are provided in a gas chamber on the negative electrode side, and an oxidant gas supply passage is provided in a gas chamber on the positive electrode side. 16 and the gas discharge path 17 are connected. Reference numeral 18 is a molten salt bubbler provided in a bypass passage of the fuel supply passage 14. The fuel cell body 13 and the molten salt bubbler 18 are the electric furnace 1.
It is installed in 9.

During normal operation, the cock 20 is closed and the cock 21 is opened. However, when operating while adding the electrolyte in the battery or preventing the dissipation of the electrolyte, open the cock 20 and close the cock 21 to release hydrogen gas. It is supplied to the battery main body 14 via the molten salt bubbler 18 provided in the electric furnace. In the molten salt bubbler shown in FIG. 2, the hydrogen gas supplied from the hydrogen gas supply pipe 22 is blown into the electrolyte molten salt stored in the molten salt reserve chamber from the tip of the gas blowing pipe to form bubbles. Splashes generated when the generated bubbles burst on the liquid surface become mist of molten salt and mix into hydrogen gas, and the exhaust pipe 2
It is put in the battery from 4. In this example, the molten salt bubbler was placed in the same electric furnace as the molten salt fuel cell so that the temperature was up to the melting point of the molten salt (up to 650 ° C).

The capacity and operating conditions of the molten salt bubbler vary depending on the size and configuration of the molten salt fuel cell used, but for a single cell with an electrode area of about 25 cm ² used as an example,
80 ml of molten salt is used in the reserve chamber, and when supplying electrolyte, hydrogen gas is blown in and the supply gas flow rate is 80 to 200 ml.
It was / min. When the flow rate of the supplied gas for blowing was too high, the gas flow path was blocked by the molten salt, and conversely, when the flow rate was low, the effect of replenishing the electrolyte was low.

On the other hand, inside the battery, the mist of the molten carbonate in the hydrogen gas adheres to the surface of the battery constituent material, in particular, the surface of the negative electrode or the electrolyte holder having a high specific surface area, and is liquefied. The molten carbonate thus liquefied is absorbed and held by the electrolyte holding body, and functions as an electrolyte.

A method using a bubbler as a means for replenishing a solvent that dissolves the electrolyte has already been tried in an alkaline aqueous solution type fuel cell or the like, but the method according to the present invention directly atomizes the electrolyte itself such as molten carbonate and the like. It is something that is replenished and obviously different. Further, as compared with the replenishment of the electrolyte gas by the gas as being considered in the phosphoric acid fuel cell, it is possible to dramatically replenish the gas. Therefore, according to the present invention,
It became easier to control the electrolytic mass during battery operation.

FIG. 3 shows the results of battery life tests carried out using the molten salt bubbler of the present invention. Operation start 2 shown by white circles in the figure
After the hydrogen gas was supplied through the molten salt bubbler after 00 hours, the performance was not deteriorated even after 5500 hours. In addition, the one using the molten salt bubbler, which is indicated by a black circle from 3000 hours to 3800 hours after the start of operation, shows that the performance rapidly recovers by the replacement fluid and that the performance gradually decreases due to evaporation when the replacement fluid is stopped. ing.

EFFECTS OF THE INVENTION As described above, according to the present invention, the electrolyte can be easily added to the molten salt fuel cell, and the amount of the electrolyte can be controlled. Therefore, the life of the fuel cell is dramatically longer than that of the conventional cell.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a battery system according to the invention,
FIG. 2 is a vertical cross-sectional view showing a constitutional example of a molten salt bubbler, and FIG.
FIG. 4 is a view showing a life test result of a molten carbonate fuel cell according to the present invention, FIG. 4 is a longitudinal sectional view of a main part of the molten carbonate fuel cell, and FIG. 5 is a result of a life test of a conventional fuel cell. FIG. 1 ... Electrolyte body, 2 ... Negative electrode, 3 ... Positive electrode, 4,5 ...
Gas chamber, 6, 7 ... Current collector, 8, 9 ... Gas chamber inlet, 1
0,11 …… Gas chamber outlet, 13 …… Battery body, 14 ……
Fuel gas supply path, 16 ... Oxidant gas supply path, 18 ...
Molten salt bubbler, 23 ... Molten carbonate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Iwaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-264055 (JP, A)

Claims (2)

[Claims] 1. An electrolyte body having a molten salt as a constituent element, a pair of electrodes sandwiching the electrolyte body, a gas chamber having separate wall surfaces on the negative electrode side and the positive electrode side of the electrode, and the electrode. Supplying fuel gas and oxidant gas to a conductive current collector arranged in the gas chamber so as to make electrical contact, and to the gas chamber having the negative electrode side wall surface and the positive electrode side wall surface of the electrode ,
Alternatively, in a single molten salt fuel cell having a gas supply pipe for discharging a reaction gas and a discharge pipe, or a laminated molten salt fuel cell in which a plurality of the single molten salt fuel cells are electrically stacked in series, A molten salt fuel cell, characterized in that at least one of supply pipes for fuel gas or oxidant gas is provided with an atomization device for molten electrolyte. 2. A reserve chamber in which an atomizing device stores a molten electrolyte molten salt, and a pipe for blowing a fuel gas or an oxidant gas into the electrolytic molten salt in the form of bubbles,
2. A bubbler comprising a pipe for supplying and exhausting those gases from outside the device, and a bubbler having a void at the top of the reserve chamber for popping the generated bubbles. Molten salt fuel cell.