DE1671842C3 - Method for manufacturing a gas diffusion electrode - Google Patents

Description

ao gas exposed electrode surface applied

the electrode surface exposed to the gas has

The present invention relates to a method surface the same property as a surface,

for the production of a gas diffusion electrode from one in which the water-repellent substance in one

porous sintered materials, consisting essentially of nickel, were applied at extremely high concentrations;

standing plate and a water-repellent as therefore owns the film on the exposed to the gas

Layer on the gas side of the plate. Very strong water-repellent properties,

From French patents 1354465 in particular for a limited time after

and 1368 479 and the Belgian patent specification termination of electrode manufacture. This proprietary

644 187 it is known, on porous electrode body shaft of the electrode, however, goes within very

of fuel cells lost a water-repellent layer 30 for a short time when a large discharge

from a plastic film, ζ. B. from Polyfluorkohlen- ßer current density takes place. Such an electrode

to apply hydrogen. Applying one has the advantage that there is very little electrolyte

Such a film on the electrode does not have to be impervious to the service life of this type of electrode

Considerable pressure must be applied in order to achieve sufficient- but even less than in the case of an electrode made with

to achieve adequate adhesive strength. As a result, the 35 is not provided with any such coating. This post

Porosity of the film and possibly also of the parts are based on the following circumstances: Since on

Electrode impaired. If the foil is partially detached from the gas-side electrode surface, a film

from the electrode, the gas collects through the det, the gas is not sufficiently in the reaction

Eiektrode urgent electrolyte, so that the foil zone is fed, thereby deteriorating the

will continue to be replaced. 40 Discharge occurs. Furthermore, since electrodes with

The object of the present invention is to use too little strength

found a porous, water-repellent layer on a thin on the gas-side surface

to apply the gas side of the electrode without the electrode applied film locally in the elec-

while the porosity of the electrode or the layer electrode body a, so that the areas in which

is affected. 45 the film has penetrated, highly water-repellent

The invention solves this problem in that are. When the so-called three-phase zone, according to the invention, the sintered plate is hydrophobized in areas penetrated by itself with progressive development and then jade is achieved, the reactive surface for producing the water-repellent layer on the gas side of the plate becomes powdery polyfluoro due to the strongly water-repellent properties - 50 of these areas decreased. Therefore, hydrocarbon resin is forced to be applied. In the current discharge in these areas with extreme application of the powder, there is no need for a higher pressure of a large current strength, whereby a drop in the kata is exerted on the electrode, so that the lytic activity occurs.
Porosity is not affected. The invention creates a gas-side electrode layer with little resistance to the gas surface with water-repellent property, without opposing it, so that the gas does not have to be supplied under increased pressure that in this case worsen the discharge and a discharge with great properties entry. This is only possible through over-over current strength. At the same time, electrolyte loss is achieved with a fluorocarbon resin powder by seeping out onto a mini electrode surface on the gas side. Diemum reduced. 60 This overdrawing can be done by

Polyfluorocarbon resins, which are applied to the speaking surface of an electrode with the

Gassieitige surface of the highly porous, sintered, rounded upper part of a rod brings into contact

Basically made of nickel plates on which the resin powder is located. Given-

Let brimgen are, for example, Monochlorotrifluor- if the resin powder can be on one of the

Mihylen, Tetrafluoropolyäthylen and a copolymer 65 melting point of the resin lying temperature

made of tetra- and hexafluoropolyethylene. The last to be heated, so that it is applied locally to the electrode

The named copolymer, however, has a particularly good surface when it is melted. Independent before

Adhesion strength on the sintered plate. the type of overcoat keeps the dejected "

Λ 671 842

Fluorocarbon film its original white fig. 6 is a graphical representation of the character

F;. 'Be at and there is no substantial deterioration of this air electrode as a function of the exercise, such as when the resin is heated for its time;

Melting point or higher occurs. The electrode F i g .. 7 is a schematic representation of the elec-

_{In this state, w} ill be used in the trade described above.

Wise used This means that the originally _ · _Βη : _β ι ι

^{very large p} present in the sintered plate

Pores adjusted to an appropriate size. This example concerns binary gas diffusion elec-

In addition, the resin does not penetrate when using an oxygen-hydrogen fuel cell. into the electrode body so that the: Gas ίο First, the oxygen electrode is described, supply is not hindered and no deterioration - To a quantity of commercially available nickel carbon

tion of the discharge properties occurs. The electron yl _n of class A with a purity of 99.9 ° / o and trodenoberfläche that with the resin coated an apparent specific gravity of 2.1 wurwurde, is more water-repellent than any to 2.5 percent by weight acetylene black, and furthermore Mebekannte , coated electrode. 15 thylaikohol is added and from this a sludge-even if the pressure of the mixture similar to the elec- tricity on the gas side is produced. B. when dried with stirring. The methyl alcohol of this electrode is not absolutely necessary in this mixing stage under difficult conditions, especially in contact with Hch, but its admixture is preferred in order to obtain the atmosphere for use in the air so a uniform mixture. The oxygen found, the gas-side electrode is mixed powder is 1: 5 minutes in the water surface not moist and the air diffuses smoothly hydrogen atmosphere at 900 ⁰ C, one sintered into the electrode body without a substantial electrode plate with a thickness of 0, 9 mm ago deterioration of the discharge capability occurs. was asked. Before sintering was a nickel screen

In conventional electrodes not behan- as _w ith an aperture of 0.833 mm in the Delter gas side surface occurs nut powder charged mold introduced a strong Einsik-. After the core of the electrolyte when used as an air electrode on the sintered plate by spot welding a lead electrode at atmospheric pressure, so that this electrode was attached to conduct current, electrodes soon became unusable; on the other hand, silver is used as a catalyst on the basis of a series of lier electrodes with a film on their gas side - process steps, such as impregnation with silver nitrate, on the surface as the discharge progresses all- reducing with a solution of caustic alkali and gradually their water-repellent properties of formalin, Washing with water and drying a gas side surface. Placed at the after inventions, wherein a silver content of 40 mg / cm * grounding method according electrodes produced was aimed. Before the addition of the porosity, it was found that, even if the electrolyte was silver, about 82% and afterwards about 78%. Something that penetrates, the surface on the gas side of the standing block is never wetted with a commercially available penetrating liquid and the fluorocarbon resin emulsion (diluted to liquid runs off in drops. There is an 8% solution) impregnated. Then, the recognized that such a result loading with only one block for one hour in a hydrogen atmosphere at from sintered material having a large porosity 40,340 ⁰ C was heated and made watertight. Then standing electrode is obtained. In one known, a commercially available copolymer of polythene electrode with low porosity is almost tetra- and polyhexafluoroethylene in powder form with a considerably large current discharge density with a particle diameter of several microns at atmospheric pressure. -Learning occurs at an amount of about 5 mg / cm ² applied. Which has a very strong polarization. 45 on the basis of the above-mentioned process steps

The invention will now be presented using the following electrodes as oxygen-electro-examples and the accompanying drawings. the used.

The drawings give the characteristic weight percent nickel carbonyl of good A.

Shafts of by the method according to the invention with 40 percent by weight of a product was the The gas diffusion electrodes provided here are of grade B with an apparent specific weight application in fuel cells again. of about 1.0 and further 3 percent by weight

Fig. 1 is a graph of the current of commercial alumina mixed and the Ge-D voltage properties of an oxygen electrode mixed thoroughly. The mixture and a hydrogen electrode when used in was then 15 minutes at 920 ^° C. in the hydrogen of an oxygen-hydrogen fuel cell; 55 electricity sintered together with a nickel mesh. F ie 2 is a graphic representation of the life Then platinum was added to the standing sintered duration of an oxygen and a hydrogen electrolyte plate in a manner known per se, so that ^a platinum content of 10 mg / cm * was achieved. The Fig. 3 is a graphical representation of the current-sintered block had a porosity of about 79 * clamping rings when the electrode was applied before the platinum was added

Τ ig. 4 is a paphic ^^ 9 £ a, -Emulsion ^ ines J * »* ^^^ this electrode depending on the

this E & gg ^ ^ tsÄ ^ ÄiÄS ^

Fig. 13 is a current-voltage diagram for an anti-tetrafluoroethylene resin of several sizes

s ' 6

Sphere further heated to 150 ⁰ C. After heating the binary gas diffusion according to the invention

the fluorocarbon resin had the same white ion electrodes will be described in detail.

The same color as it was before the heating and had a different color

better adhesion. In this way, powders used were made not only of grade A, but

Obtain hydrogen electrodes. S can also be made from a mixture of quality A and B

Mh these two types of gas electrodes would be one. Made in view of mechanical strength, oxygen water fuel cell. 40% of potassium hydroxide solution is used as the electrode. In the case of quality B, this is preferably 30 percent by weight or less discharge with various current wires. The proportion of added acetylene-containing potentials are shown in FIG. 1 shown. As for carbon black, it should preferably be 4 percent by weight or, for comparison purposes, electrodes from known materials were used. The optimum sintering temperature lies in sintered nickel plates with porosities of between 850 and 95O ⁰ C. The proportion of the silver produced as catalyst and added in the sator is the same amount as above in the Sauer method 10 mg / cm ² or less. In the Erfinstoffelektroden silver and in the dung Wasserstoffelektro- i _5, however, the suitable proportion is introduced between the platinum. There were then cells below 20 and 70 mg / cm ² . For the above-mentioned Nickelelek use of these electrodes made and with trode, the optimal amount is 40 mg / cm-. A similar experiment was carried out there. The polyvinyl clearly the water-repellent properties, the potentials of the respective electrodes were as po- Fluorkohlential already described in this example, against a mercury Over-2-oxide-EJektrode as encryption _ao hydrocarbon resin emulsion measured with respect to a möggleichselektrode. From the graphic perspective, long life is most expedient. The position clearly shows that the above three emulsions are used as a 3 to 20% solution. Electrodes even with a gas supply at an increased The optimal concentration is between 5 and pressure properties that are poorer than those according to the invention. The amount of applied fluorocarbons according to electrodes, such as hydrogen resin, with which permanent adhesion

In Fig. 1 means curve A the voltage (below can be achieved is between 1 and

a gas pressure of 10 mm Hg above atmospheric 10 mg / cm ² . Applying a larger amount

pressure for oxygen and hydrogen) of the cell can lead to a detachment of the resin; From the-

when using the electrodes according to the invention. For this reason, the optimal quantity range lies between

Curve A gives the potential of the oxygen electrode 30 see 2 and 6 mg / cm ² .

again. Curve A _n shows the potential of the hydrogen electrode. This is sufficient for the hydrogen electrode. Curves B, C and D give the above-described oxygen electrode potentials used by cells when using hand-sintered substrate to meet the requirements. In the case of the usual electrodes made from sintered nickel plates, however, an example will be described with porosities of 40, 50 and 60 ° / c for a gas in which alumina was used. The aldruck von Oxygen and Hydrogen, in each case only slight use of grade A nickel, causes 70, 55 and 40 mm Hg above atmospheric pressure an undesirable one, below the lower according to the invention. The curves B ₀ , C ₀ and D ₀ give the respective limit (70%) lying porosity. This gene potentials of the oxygen electrodes again. The disadvantage can be avoided by using curves B _n , C _n and D _{n together to} give the potentials of 40 with grade B nickel. The optimal hydrogen electrodes again. Then an amount of grade B was between 30 and continuous discharge using 60 percent by weight. The optimal proportion of the binary gas diffusion-giving alumina produced according to the invention is between 3 and 7 weight electrodes and binary gas diffusion electrodes with percent. Platinum is added in an amount of 1 to a coating of a copolymer of poly-45 15 mg / cm ² as a catalyst. However, in order to develop the tetra- and polyhexafluoroethylene on the gas side full catalytic activity of platinum. To surface and melt this coating, an amount of 10 mg / cm ^s heating in a nitrogen atmosphere for one hour was used in this example. With regard to the selection of the water-350 ° C, with a current density of 30 mA / cm ² and repellent substance and the method used-80 mA / cm *. The results are shown in FIG. In this figure, A _{denotes 0} and repulsive, the potentials of the oxygen substance electrode according to the invention can be found in the case of the water A _{n in} the same way as in the case of the production and hydrogen electrodes. B ₀ and B _n mean the development of the oxygen electrode proceed. Potentials of the latter oxygen or water

hydrogen electrodes. The gas pressure was 55 at the beginning

each 10 mm above atmospheric pressure for This example relates to an air electrode zui

Oxygen and hydrogen. The arrows indicate the use in an air-methanol fuel cell

the point in time at which the pressure was restored in each case. The same gas diffusion gas electrode wk

the oxygen electrode described in Example 1 increases to 10 mm above atmospheric pressure Hg.

became. The deterioration of the discharge intrinsic 60 produced, except that 60 mg / cm * SU

shafts of the latter electrodes were added up to as catalyst; the methanol

to a certain extent by increasing the gas pressure electrode consisted of a known porous Nik-

as the discharge progressed, a kelelectrode was used in which platinum was incorporated as a catalyst

found that possibly the discharge potential was brought. These electrodes have always been used

last-mentioned electrodes made in a large gas-air-methanol fuel cell. For ver

pressure somewhat worse than that of the same according to the invention, air electrodes were wi <in the same way

manufactured electrodes. in Example 1 from sintered nickel plates with Po

In the following, the conditions for the rosities of 40, 50 and 60% with the addition of voi

1 842

: Silver produced as a catalyst, this elec- tric 10 mm Hg above atmospheric pressure. As elec-

A 30% potassium hydroxide solution was trodden with the emulsion of the fluorocarbon trolyte.

· ■ resin has been made water-repellent. This air hold of 20 percent by volume methanol is used. the

j electrodes were used as a comparison at the current temperature was 38 + 3 ⁰ C.

\ Voltage test used. 5 In this example, the cell was created using

'B e ^- they 1 3 formation of a partition made between the

P Air electrode and the hydrazine electrode inserted This example relates to an air electrode for was; the partition wall was designed so that it could be used in air-hydrazine fuel cells. Passage of hydrazine practically prevented . A sintered plate with a thickness of 0.8 mm was. Under these conditions, the air was tested for properties from a mixture of grade A nickel electrodes. the

■ and activated charcoal, with the partition wall made of polyvinyl chloride

■ Part of the charcoal 9 percent by weight of the nickel-containing cloth, which is impregnated with polyvinyl alcohol; amount fraud. The plate was gnawed in the same way. A hydrazine electrode was used

as in Example 1 with an emulsion of polyfluoro-15 conventional sintered nickel plate, which made 1.5 mg / cm ² hydrocarbon resin water-repellent and contains platinum as a catalyst,
it was in an analogous manner a powder from a It goes without saying that in this case the in; Copolymer of polytetrafluoroethylene and polyhexafluoroethylene electrodes described in Examples 1 and 2 as glued to the surface on the gas side. In this air electrode can be used. In the previous case, however, the activated carbon introduced acts as a catalyst in the case in question, based on an example, so that no additional carbon, which was also used as a single catalyst, is used. When an oxygen ionization catalyst is used, extremely active fuels, such as hydrazine, are shown to have an electrode still in place; aldehyde or sodium borohydride is used, as far as the invention is concerned, with the fluorocarbon: this is decomposed by the catalyst of the air electrode »5 resin on the gas-side surface of a sintered Nik or even by the sintered substrate. In kelplatte with a porosity of 70 ¹ Vo or more in this case, it was found that the decomposition occurs to a lesser extent when applied and / or thereafter heated to a temperature of carbon as a catalyst well below the melting point of the resin al? The discharge properties of this electrode are catalysts such as silver, platinum and palladium; 30 is shown in FIG. 5, while the current density is therefore expediently used as a function of carbon as a function of time in FIG. 6 is shown. substance as a catalyst for the air electrode (this applies in FIG. 5, of course, the potential of the inventive air electrode is also shown for the case that oxygen alone is used. In FIG. 6, these are used). Especially when hydrazine is shown on the shaft as a function of time. 35 The air pressure was 13 mm Hg above atmo- ^; the mixed potential of these two spherical pressure occurs. Potassium hydroxide solution has become a substance, and the polarization of the air electrode with a specific gravity of 1.3 and one becomes undesirably large. In the invention, each forms a content of 1%> hydrazine is used. The temperature but the sintered nickel the basic component of the door was 40 ± 3 ° C.

Electrodes and thereby the hydrazine is through 40 ■ This electrode is intended to decompose this nickel in the following. Because nickel is not written as a catalyst. As Sauerstoffionisationskatalysator affects the Sauerstoffionisierung, there is gate is activated carbon over graphite preferably, from this the advantage that the polymerization due to the appropriate mixing proportion is 5 to 13 overall '- occurrence of the mixed potential at the loading weight percent. The optimal range is between written electrode which is quite weak. The 45 8 and 10 percent by weight. The porosity fluctuates

■ Reduction in the utilization of the fuel as a result of the amount of activated carbon added. By doing of hydrazine consumption, which is another disadvantage of the range from 8 to 10 percent by weight, however, it is not avoided. In this case rosity when using grade A nickel between

; it is, when using an active fuel, see 80 and 83%. The treatment for water removal

> Hydrazine, required, a special process to make pushing 50 and the application of the fluorocarbon

j operation to carry out the diminution of the hydrogen resin on the gas side surface

J Fuel utilization as far as the air electrode is done in the same way as in Example 1.

concerns to prevent; this is a feature that FIG. 7 illustrates one according to the invention

■■ differs from an electrode in other systems. Electrode manufactured according to the method in Fora

• In Fig. 3, curve A _{0 means} the potential of an enlarged section from a cross section

air electrode manufactured according to the invention. B _a , C ₀ through the electrode; with 2 the sintered plate is be

'. and D ₀ mean the potentials of the conventional draws, in which a nickel screen '

Air electrodes made of sintered nickel plates with Po- is embedded: with 3 is according to the invention

rosities of 40, 50 and 60% respectively. The appropriate process produced water-repellent sliding

applied air pressure was designated 60 for all electrodes.

For this purpose 2 sheets of drawings

Claims (2)

Patent claims, for example, are suitable as hydrophobic agents: polyethylene, polystyrene or a polyfluorocarbon. hydrogen emulsion. 1. Method for producing a gas diffusion The water-repellent treatment of the gas «Ipnelectrode made of a porous, sintered, in the 5 exposed electrode surface using essential from nod! existing sheet and materials, such as polyethylene, paraffin and fluorine Hydrophobic water-repellent layer on the gas side is already known the plate, characterized in that known water-repellent making process the sintered plate in a manner known per se is based on the fact that when using polyhydrophobing and then to produce ethylene or paraffin this is dissolved in benzene and aui generation of the water-repellent layer on the gas side of the electrode surface exposed to the gas brings powdered polyfluorocarbon to the plate; if an emulsion of a fluorocarbon resin is applied. Resins & is used, this is first applied to the 2. The method as claimed in claim 1, wherein the desired area is applied, and which is characterized in such a way that that the area applied to the plate is then drawn to a temperature pu ^ deformed resin heated to a temperature below the melting point of the resin the melting point of the resin is heated. Both known processes result in the formation of one Fiims on the electrode surface exposed to the gas. If a film is produced in the above way on the dem