JPS60221594A - Air electrode for electrolyzing alkali chloride - Google Patents

Abstract

PURPOSE:To prolong the life of an air electrode by using powder having a prescribed specific surface area obtd. by graphitizing furnace black as the constituent material of the air electrode. CONSTITUTION:The air electrode for electrolyzing alkali chloride is made of graphite powder having <=95m<2>/g specific surface area obtd. by graphitizing furnace black. The air electrode has superior resistance to corrosion by an electrolytic soln. contg. alkali chloride, so the life of the electrode is prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air electrode for alkali chloride electrolysis, and its purpose is to obtain a specific surface area by treating furnace black with graphite as a constituent material of the air electrode. By using a graphite powder bed of 95 m / f or less,
The purpose is to keep the air electrode floating for a longer period of time.

Conventionally, in alkali chloride electrolytic cells that have been put into practical use, extruded metal made of mild steel is usually used as a cathode. The cathodic reaction in this case is 21i2(J +2
e-+ R2↑+20H-'(11,' fl h-
Water damage occurs from the roaring eggplant - rjf horse τ fuel K M
When a so-called air electrode is used as a cathode, the cathode reaction is Ow -1-2Kt (J + 4e-→4on-(2)
Therefore, the cathode potential is theoretically 1.28 V when compared with the reaction of the above-mentioned formula (1). When the voltage is changed to 8, the sliding voltage decreases by 1.28V. Even in an actual electrolytic cell, it is 0.9~
1. It is possible to reduce the burden of OV. For these reasons, in recent years, the use of air electrodes instead of mild steel has been attracting attention as a hidden aspect of salt electrolyzers.

Carbon powder is used as a carrier for the catalyst or catalyst metal in the air electrode. Carbon powder is roughly divided into activated carbon,
It can be classified into carbon black and graphite. Activated carbon is produced by carbonizing wood or coal as a starting material and at the same time subjecting it to activation treatment. Carbon bra! Furnace black is a general term for materials obtained by incomplete combustion or thermal decomposition of carbonized carbon, and is a furnace black obtained by incomplete combustion of hydrocarbons in a furnace, natural gas flame,
Channel brawak manufactured by channel steel,
Thermal black is produced by thermally decomposing natural gas.It is a single layer of thermal black, and it is made by exothermic decomposition of acetylene.Thermal black is produced by putting hydrocarbons into a shallow open pot and then burning them. The resulting lamp blur can be categorized as follows.

Graphite is classified into natural graphite and artificial graphite. Artificial graphite powder is made by mixing coke-based carbon powder with a binder that easily carbonizes, such as tar or pitch, forming it into a block, then graphitizing it, and finally crushing it. Recently, activated carbon or carbon black is being considered as a powder that can be processed along the river. Although these graphitized carbon powders are also a type of artificial graphite, they are distinguished from the so-called artificial graphite described above.

Among these various carbon powders, fuel 7K rllA
The material being considered for electrodes has a specific surface area of 20
Various activated carbons of 0 to 2000 m/V, specific surface area of 100
Furnace black and graphitized furnace black of m/g or more, acetylene black with a specific surface area of about 60 In2/f/, natural graphite with a specific 1thI product of 1001n2/f or more, and artificial graphite with a specific surface area of 70 m2/f or less. be. And as carbon powder for fuel cells, 100m/
Furnace black, what is the product of ratio table [II] over f?
Natural graphite or graphitized fur unsubstituted wax is said to be suitable.

However, the knowledge obtained in the field of fuel 1r and ponds cannot necessarily be directly applied to the field of alkali chloride electrolysis. In particular, it has recently been found that the life of the air electrode is extremely short when it is applied to the air electrode of fuel 1H,m and immediately applied to the solution of nr=carbonaceous powdered alkali. This is because fuel cells and alkaline electrolysis use the same air electrode, but the type of electrolyte.

Electrolyte D degree 9 operating temperature or made iic! The flow density and the operating conditions are different. 1. In other words, alkaline fuel? ! In a, the electrolyte is usually a 30% potassium hydroxide water bath solution, the operating temperature is in the range from room temperature to 60"C, and the operating current density is about 100 mA/
It is d. On the other hand, in alkaline chloride electrolysis, the electrolyte (cathode electrolyte) used is a 40-50% potassium hydroxide water bath solution or a 30-40% sodium hydroxide aqueous solution, and the operating temperature is 80-95%. The operating current density is 3o.

~4 Q Q mA/Cd.

′! j! The lifespan of carbon is closely related to the corrosion of carbon.According to a study by Genmeisha et al., corrosion of carbon is caused by a high concentration of alkaline hydroxide bath solution.
1. The higher the operating temperature, the more progress is made, and if the corrosion resistance of carbon is the same, the operating DC -2
The larger the degree of i'L is, the shorter the life of the air electrode will be.In other words, if the same carbon is used, under the operating conditions of the above-mentioned correct fuel '11', , the corrosion of carbon does not progress that much and its life is long enough, whereas with alkali chloride IJ7, the corrosion of carbon progresses more, and the lifespan of air (V's life is short).

For these reasons, we determined that the carbon used in the air electrode for alkali chloride electrolysis must be even more corrosion resistant than the carbon used in fuel cells, and after extensive study, we found that: γ that leads to non-invention.

The invention is characterized in that furnace black is blackened and its specific surface area is 95 m/f or more and one piece is used as the carbon powder material for the air electrode for alkali chloride electrolysis.

It has been found that by using such carbon powder, the life of the air electrode for alkali chloride electrolysis is decisively extended.
Even if the same graphitized furnace black is used, the life of the air electrode is decisively different when the specific surface area is 100 m/f or more as in the conventional case and when it is 95 m/f or less as in the present invention. Although it is difficult to say that this has been fully elucidated, the following explanation can be provided.

According to the research of the present inventors, corrosion of carbon at the air electrode is caused by using carbon or a catalyst supported on carbon, with the site where oxygen is adsorbed as the cathode, and the site on the carbon where oxygen is not adsorbed as the anode. It is now clear that this is mostly due to the local to phenomenon.

Well, carbon corrosion occurs at sites that absorb oxygen! The thicker the short-circuit current between the site and the site where the element is not adsorbed, the faster the short-circuit current will advance. The larger the difference between the potential of the site where oxygen is not adsorbed, or in other words, the redox potential of the carbon itself where oxygen is not involved, the larger the difference.
Electrolytic reduction of oxygen K at sites where oxygen is adsorbed
When the position bs - is positive, the redox potential of carbon sites where oxygen is not adsorbed varies depending on the type of carbon, and the more base the potential, the more corrosion of the carbon progresses. The oxidation-reduction potential of carbon can be determined by immersing an air electrode made of carbon in an electrolyte and measuring the potential.

When measured using this method, even if the same graphitized furnace black is used, when the specific surface area is IC95m2/g or less as in the present invention, the oxidation-reduction potential is more responsible than when it is 100 In2/9 or more as in the conventional case. This makes it less susceptible to corrosion.

On the other hand, when the air electrode is operated at 800 to 40 QmA/d, the actual potential is determined by the electrolytic reduction potential of oxygen at the site where oxygen is adsorbed. However, using graphitized furnace black with a specific surface area of 100 m/f or more, the potential of the electrode is approximately 100 mV higher than the potential of the air electrode. Therefore, in the latter case, the difference between the redox potential of carbon sites where oxygen is not adsorbed and the electrolytic reduction potential of oxygen at sites where oxygen is adsorbed is smaller. That is, carbon corrosion is less likely to occur.In other words, if you want to extend the life of the air electrode under harsh operating conditions such as alkaline chloride electrolysis, you will have to sacrifice some degree of potential.

An embodiment of the present invention will be described in detail below.

Embodiment: FIG. 1 shows a cross-sectional structure of an air electrode according to an embodiment of the present invention. The air electrode consists of a porous nickel layer (11) as a current collector and a polarizing matrix, a graphitized furnace black powder bed with a specific surface area of 80 m/f, and poly 4 as a binder.
] Soot layers (2) and 4 consisting of a mixture with ethylene chloride
Finated ethylene-hexafluorinated propylene copolymer and 4
Porous bonding layer (3) consisting of a mixture of fluorinated ethylene/-ethylene copolymer and electrolyte 91 to prevent leakage 1
It consists of a four-layer structure with a porous poly(tetrafluoroethylene) membrane layer (4).

A half cell was assembled using this air electrode TAl as a cathode, the second fuel plate as an anode, and 30% sodium hydroxide as an electrolyte, and the operating temperature was set to 80°C.
While removing carbon dioxide and sending air to the air electrode,
Operate at a density of 800 mA/lri and examine the change in potential at this time. child.

First of all, graphitized carbon black with a specific surface area of 120 m/y was used as a conventional air electrode (uniformly obtained using humans as the starting material). Using activated carbon at 1200 m/f, the conventional air f value (
Even if there was only one C+ vt, similar tests were attempted and the results are shown in Figure 2. In other words, according to the present invention, the air electrode of a car pump with a specific surface area of 80 m"/y has a relatively hard surface and a stable performance over a long period of time. It can be seen that this shows that

As detailed above, Kishiromei supplies air electrodes for alkali chloride electrolysis, and the industrial project III!
It is extremely large.

[Brief explanation of the drawing]

Figure 1 shows a cross-section 6i of an air electrode according to an embodiment of the present invention. Figure 2 shows the change over time in the potential of the air solid according to the first example of the present invention in comparison with a conventional air electrode (uniform, 1+). 2... Melting medium layer. 3... Porous bond; acupuncture needles. 4... Porous polyethylene film layer.

Claims (1)

[Claims] An air electrode for alkali chloride electrolysis, which is a graphite powder bed obtained by graphitizing furnace black and has a specific surface area of 95 m/2 or less.