JPS61118970A - Molten salt fuel cell - Google Patents

Abstract

PURPOSE:To increase the life of a molten salt fuel cell by inhibiting the migration of the electrolyte from the surface of the gas-diffusing electrode to the cell jar wall and pipings by forming a boron nitride layer on the surface of the oxidizing or fuel electrode touching the electrolyte. CONSTITUTION:After a powdery mixture composed of 92pts. nickel carbonyl and 8pts. chromium powder s packed into a core material consisting of a nickel net, the thus formed body is sintered in a hydrogen stream at 950 deg.C to obtain a sintered body principally consisting of nickel. Next, a boron nitride powder is fixed by pressure to the surface touching the electrolyte of the sintered body used as the fuel electrode. On the other hand, after a mixture composed of 100pts. nickel carbonyl and 32pts. lithium carbonate is heated in air and then oxidized, the oxidized mixture is pulverized before the pulverized mixture is pressed and packed into a foamy nickel plate and then the thus formed body is sintered in air to make an oxidizing electrode. Next, a boron nitride powder is fixed by pressure to the surface of the oxidizing electrode touching the electrolyte to form a porous layer between the oxidizing electrode and the electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a molten salt fuel cell operating at about 600 to 700° C. and its electrode.

BACKGROUND OF THE INVENTION The most common conventional molten salt fuel cells are those using molten alkali carbonates. That is, lithium carbonate,
A mixture of sodium carbonate, potassium carbonate, etc. is used as an electrolyte, which is processed into a plate shape along with a molten salt-resistant powder such as lithium aluminate, and this is held between a fuel electrode and an oxidation electrode to form a battery. There is.

As the oxidizing electrode, lithium-doped nickel oxide has been most commonly considered and tested because of the need for molten carbonate resistance in an oxidizing atmosphere. It also has electrical conductivity and catalytic activity, making it a promising candidate for an oxidizing electrode.

On the other hand, among the many conductive materials, Ni-Kel is most commonly used for fuel electrodes because it must withstand molten carbonate in a reducing atmosphere, and it suppresses oversintering during operation. Additives such as chromium are used for this purpose.

That is, the most common battery constituent materials are a combination of a porous oxygen electrode made of lithium-doped nickel oxide, an electrolyte body made of molten alkali carbonate and lithium aluminate, and a porous nickel fuel electrode.

There are still many problems to be solved in order to improve the characteristics, especially the lifespan, of molten salt fuel cells constructed using these components. For example, there are problems caused by the electrolyte, such as long-term maintenance of adhesion between the electrode and the electrolyte body, and electrolyte shortage in the electrolyte holder due to migration of the electrolyte to the container or electrode. These problems are important along with the problem of corrosion resistance of electrodes, etc., and the deterioration of performance due to reduction in electrode porosity due to oversintering.

As a means to maintain long-term adhesion between the electrode and electrolyte and to prevent electrolyte shortages in the electrolyte holding body due to electrolyte movement, attempts have been made to apply extra electrolyte between the electrode and electrolyte body. , has some effect. In other words, by such means, it has become possible to considerably suppress the deterioration in performance due to electrolyte shortage.

Problems to be Solved by the Invention However, in long-term operation, the adhesion between the electrode and the electrolyte body decreases, and electrolyte movement causes a shortage of electrolyte in the electrolyte holding body, resulting in a decrease in performance. I found out that it brings.

The present invention improves the electrodes to inhibit electrolyte migration through the electrodes and provides a long-life molten salt fuel cell.

Means for Solving the Problems The present invention provides a molten salt fuel cell using a fuel mainly composed of hydrogen, an oxidizing agent mainly composed of air, and a molten salt as an electrolyte. A boron nitride layer is formed on the surface in contact with the electrolyte.

Effect: By the above means, it is possible to suppress the movement of the electrolyte from the gas diffusion electrode surface to the wall of the battery case, piping, etc.

Therefore, the shortage of electrolyte in the electrolyte holder can be suppressed, the adhesion between the electrode and the electrolyte body can be maintained for a long period of time, and the life of the molten salt fuel cell can be extended.

The most effective method for forming the boron nitride layer is to rub the powder onto the electrode surface and press it. In addition, as a method for forming a porous layer that is uniform and has excellent adhesion, there is a method of forming boron nitride by sputtering. However, industrially, it is sufficient to use a powder pressure bonding method, which is easy to operate and has almost good uniformity, or a method in which it is applied directly with an adhesive.

When such a porous layer is applied to an oxidation electrode, it may be formed in an amount of about 0.5 to 5++y/c-, for example, on the surface of a lithiated nickel oxide porous body in contact with the electrolyte. Even when other metal oxides are used, the amount added may be the same. Similarly, for the fuel electrode, a sintered body mainly composed of, for example, 2Y Kel is used as the electrode, and boron nitride is formed in an amount of about 0.5 to 5 my/crj on the surface of the electrode that comes into contact with the electrolyte.

A battery is constructed using the oxidation electrode and fuel electrode thus manufactured. Although it is most effective to extend the life of the battery by using an electrode in which such a porous layer of boron nitride is formed at both electrodes, the same effect can be obtained even if it is used only at one of the electrodes.

In addition, regarding the amount of boron nitride, 0.5 to 6 K/cM
The degree is appropriate.

EXAMPLES Hereinafter, the present invention will be explained using examples in which the present invention is applied to a fuel electrode and an oxidation electrode.

Carbonyl nickel 92 parts by weight (hereinafter simply expressed in parts)
Using a mixed powder of 8 parts of chromium powder, the wire diameter was 0.18 m.
, 16-a-menu nickel net is used as a core material, and is sintered at 950° C. in a hydrogen stream by a known method to obtain a sintered body mainly made of nickel with a porosity of 76% and a thickness of about 0.7=. This is used as a fuel electrode, and boron nitride powder is applied to the surface in contact with the electrolyte.
．． Apply light pressure to approximately 5mf/cni.

On the other hand, 32 parts of lithium carbonate is added to 10 parts of carbonyl nickel.
of water and heated in air at 900°C for 1 hour.

After oxidation and pulverization, the porosity is 95% and the thickness is approximately 1.2
A foamed nickel plate with an average pore diameter of 150 mμ was processed into an optical fiber, the thickness was adjusted to 0.9 rrvn K by pressure, and then sintered in air at 98° C. for 2 hours to obtain an oxidizing electrode. The porosity is approximately 78%. A porous layer is formed by pressing boron nitride powder in an amount of about 0.91n9/c- on the surface of this electrode that is in contact with the electrolyte.

As the electrolyte and its holder, a paste type consisting of 52% by weight of a mixed salt of lithium carbonate and potassium carbonate and 48% by weight of lithium aluminate powder, with a thickness of 1.1 mm obtained by hot pressing, was used. there was.

A battery was constructed using these and a stainless steel battery case. This molten carbonate fuel cell is designated as (5), and a battery in which a porous layer of boron nitride is formed only on the fuel electrode is designated as (B).
9 batteries with a porous layer of boron nitride formed only on the oxidation electrode.
Toshida. In contrast to these batteries of the present invention, a battery in which no boron nitride layer was formed on either electrode was used as a comparative example.

Each cell was kept at 650°C, and hydrogen containing 20% carbon dioxide (by volume) was supplied as a fuel, and air containing 30% carbon dioxide was supplied as an oxidizer, twice and three times the theoretical value, respectively. I activated it.

Since the present invention is very effective in improving the lifespan, the lifespan characteristics of each battery will be described. The diagram shows each battery at 100
This is the time-voltage relationship during continuous discharge at a current density of mA/crtl. Electrolyte was added at 30oO hours. After 5000 hours of operation time, batteries (8), (to), (q
In this case, the voltage drop was smaller than in Comparative Example q, and in particular, (3
) clearly maintains the best voltage. The reason for this is that in the battery of the present invention, the porous layer of boron nitride provided on the surface of the electrode in contact with the electrolyte acts as if it were a fluororesin waterproofing agent for the gas diffusion electrode that is operated with an electrolyte at room temperature. This is because it has the effect of suppressing the movement of molten carbonate through the battery to other parts such as the battery case. That is, by suppressing such movement, shortage of electrolyte in the electrolyte body is suppressed.

This reduces the drop in battery voltage.

Also, since it is not added in such a large amount, there is little deterioration in initial performance due to this layer. Therefore, the battery (8) with a porous layer of boron nitride on both electrodes has the least voltage drop during discharge, and the battery with the oxidized electrode, which is easily wetted by molten carbonate, has the lowest voltage drop (q) and the following ( B
) and q increase in order.

In the example, a porous layer of boron nitride was formed only on the surface of the electrode in contact with the electrolyte, but it is also possible to impregnate the inside of the electrode with boron nitride or form it on the gas side of the electrode in order to extend the life of the electrode. It is effective for

Effects of the Invention As described above, the present invention makes it possible to extend the life of a molten salt fuel cell.

[Brief explanation of the drawing]

The figure is a diagram showing changes in voltage over time during continuous discharge of a molten salt fuel cell.

Claims (3)

[Claims] (1) A molten salt fuel cell comprising a molten salt electrolyte, an oxidation electrode and a fuel electrode in contact with the electrolyte, and a layer of boron nitride is formed on at least one surface of the electrode in contact with the electrolyte. (2) The molten salt fuel cell according to claim 1, wherein the boron nitride layer comprises a coated layer of boron nitride powder. (3) The molten salt fuel cell of claim 1, wherein said electrode also contains boron nitride.