DE1671482A1 - Catalyst electrode - Google Patents

Description

SIGRI ELBKTROGRAPHIiD GMBH Meitingen, the -6th FfB. 1968

'pa 68/3602

The present invention "relates to a catalyst electrode for electrochemical processes ». especially for

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Fuel cells, with a conductive carrier, u aiii , the Katulyaator and carbon particles are applied in. ? _v

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It is known as electrodes for fuel cells to use made of porous carbon. However, this is difficult in the required small thickness and large area to produce the desired high performance. In particular there is no such thing pure carbon electrodes the necessary mechanical strength. '

There are therefore already known electrodes that are made using corrosion-resistant plastics in Combination with finely divided carbon or graphite as The catalyst, carrier and conductor circumvent these difficulties. This essentially consists of mixtures electrolyte-repellent plastics, mostly polytetrafluoroethylene, as binders and coal particles - as such are all varieties and mixtures from coal to graphite meant - very, - ends. The coal particles serve here either as a catalyst or as a catalyst carrier, as well as a current conductor. The production of a highly active and resilient electrode in such a small one Strength to avoid diffusion polarization, from such a mixture makes high demands on the procedural skills of the manufacturer and rarely leads to the goal.

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It is also known the mechanical strength of such To increase electrodes by using thin polytetrafluoroethylene plates as embossers or foils or thin plates of sintered nickel can be used. The usage a nickel carrier also has the advantage of good power line. If non-conductive supports are used, separate collectors in the form of nickel nets or the like are required. ^ pressed onto the catalytic converter side. However, this can reduce the conditions for the formation of the three-phase boundary are changed in an uncontrolled manner or an impermissibly high contact resistance occurs.

Efforts were also made without reducing the mechanical Strength of the electrodes the proportion of the Kunststoffändemittols decrease in order to obtain better conductivity. This was achieved by using staple graphite fibers, which in a mixture with the catalyst support "j | matted. Even with such electrodes, however, a support layer made of expanded metal was required in order to achieve the required mechanical strength "

However, the use of metallic carriers brings considerable benefits Trouble with yourself. The production of thin sintered bodies or finely perforated sheets is namely, extremely difficult. In addition, such materials are very expensive. Eventually such increase

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metallic support in the electrode the weight of the whole Battery considerable. Achieving the lowest possible weight is in the case of batteries, which are intended for portable installations are of the utmost importance.

The present invention is therefore based on the object to find a catalyst electrode for electrochemical processes, especially for fuel cells, which on the one hand has sufficient mechanical strength, on the other hand it is lighter, easier to manufacture and cheaper than the known electrodes, which contain a metallic carrier. To solve this problem, the invention proposes a catalyst electrode of the type mentioned at the outset, in which, according to the invention, the carrier consists of a graphite fabric.

A graphite fabric is corrosion-resistant, elastic, has sufficient mechanical strength and is electrical good conductors. Such tissue is made according to known methods by. Coking obtained from natural or synthetic fibers

When manufacturing the electrode is expedient on the graphite fabric a plastic layer that repels the electrolyte, preferably polytetrafluoroethylene, applied and then applied the catalyst layer.

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With respect to any small irregularities of the plastic layer, it is expedient ¹ ,, hydrophobe the tissue. * This is particularly suitable, an aqueous dispersion of polytetrafluoroethylene, which is sprayed or dipped into the tissue. If the polytetrafluoroethylene is then sintered in, the fabric treated with it is completely water-repellent, but very permeable to air. '

In the plastic layer applied to the fabric expediently stored carbon or graphite oak, to increase the electrical conductivity. This layer has the task of the electrode for the electrolyte to make impermeable. The Catalyst layer applied, for the binding of which a plastic is also expediently used, but it does not have to be completely hydrophobic because the electrolyte a three-phase boundary should form in the vicinity of the catalyst and therefore something must penetrate. The applied Polytetrafluoroethylene layers must be sintered, whatever for the respective layer or individually expediently for all together under the application of pressure he follows. .

It is possible to build up the plastic layer from several layers that differ in the ratio of plastic to

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proportion: differentiate the proportion of the conductive filler. It a part of the catalyst can also be introduced into these layers. The application of the layers can be done by spraying, dipping or brushing.

You will get even better results if you instead a hydrophobized fabric a non-hydrophobic

Abated G-ewobe used and then unilaterally for the better Bond applies a thin layer of plastic. This then becomes the catalyst layer, its hydrophobicity 'Little demands are made, and on top of it a completely hydrophobic top layer, which is completely made of plastic. With this structure the last applied plastic! top layer very tight are pressed and therefore also be correspondingly thin. Sweep the small amount of plastic required, the electrode is very thin, light and also has the advantage "

™ part of an extraordinarily good contact.

Another possibility is to apply an electrolyte-impermeable synthetic ' to apply a layer of fabric. On the other side of the fabric if the catalyst is applied, the catalyst either being bound with plastic or being incorporated directly into the fabric, the catalyst becomes Mib plastic bound, the fabric is hydrophobic so as not to avoid any layer of liquid inhibiting the gas

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To further explain the invention, the im
The following specified exemplary embodiments and the attached FIGS. 1 and 2 are used.

A commercially available polytotrafluoroethylene dispersion is applied to a carbon fabric 1 with a size of 72 × 143 mm and a thickness of 0.45 in. A layer 2 aμs 14> 5mg /

cm of a mixture with a mixing ratio of 1 j 1, based on the solids, of coke powder << 60 jxx and the polytetrafluoroethylene dispersion. Hach drying at 105 ⁰ C ( '' 2 *, 2 '', 2 ') are applied to a wäiSrigen slurry of polytetrafluoroethylene powder and Kokspulvor three sub-layers. These layers of rope can be sprayed or trowelled Averden. The first (2x) consists of 15.5mg / cm with the weight yerh. Coke ϊ Polytftrafluoräthylen = 1 si, the second (2 ^I! ) From 2.9mg / cm with the weight ratio. Coke ι Pols'-tetrafluoroethylene ~ 3 s 1
and the last (2 ^lfl ) from 15.6mg / cm with the Gev /.- Rat. of coke: polytetrafluoroethylene Catalyst: 3: 1: ■ 3 · vmrde ^v used thermally from his oalaen reduced silver as a catalyst. Finally, a layer (3) was applied at 35 mg / em, which consisted of one part of polytetrafluoroethylene and 9 parts of catalyst. the

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Plate was sintered at 38O ⁰ C under a pressure of 4KP / cm for ten minutes. An electrode with a diameter of 56 mm was cut from the very flexible plate. As Lufthalbzclle in 6 N KOH they gave hei / a load

of 2raA / cm a potential against the calom electrode of -10QmV for one "month. (Fig. 1)

After preparation like (2,2 '), the ingot at 380 ⁰ O under a pressure of 20 kp / cm for ten minutes sintered in the above example, and the application of the first two layers. Thereafter, a slurry in toluene of coke and polyethylene in a ratio of 3: 1 was sprayed on to produce a further layer (2 ^11). The amount was 1.9 mg / cm. This was followed by a layer (2 ¹¹¹ ) with 19.4 mg / cm ² consisting of 1 part of polyethylene, 1.5 ropes of coke and 4 parts of catalyst. The last layer (3) with 35.9 mg / cm ² consists of 1 rope of polyethylene and 9 parts of catalyst. The plate is at 120 ⁰ C and

sintered at a pressure of 40kp / cm for 5 minutes.

An electrode is cut out of the plate from the pass-through teaser 56mm. As an air half-cell in 6 N KOH, it gave a potential against the calomary at a load of 2 mA / cm. * electrode of ^ HOmV for one month. (Fig. 1)

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Implementation example_3

A polytetrafluoroethylene dispersion (5) is sprayed onto one side of a carbon fabric (4) of size 72 χ 143nnfl and thickness 0.45mm. The amount "is below 1 mg / cm. An aqueous dispersion (6) with a weight percentage of coke: polytetrafluoroethylene catalyst -3 : T: 3 is sprayed onto it until the dry residue is 40 mg / cm. As a top layer (7). then one carries a coarser polytetrafluoroethylene dispersion to a residue of 14,5mg / cm reaches .The plate is sintered while minutes at 380 ⁰ G under a pressure of 5KP / cm. from the sheet by cutting an electrode 'with the Diameter 56mm. As an air half-cell, with the tissue side against the electrolyte (6 W KOH), it gave a potential against the calom electrode of -105mΩ at a load of 5mA / cm. (Mg. 2)

A polytetrafluoroethylene dispersion is sprayed onto one side of a carbon felt 8 of the size 72 3 143 mm and a thickness of 1.00 mm. The amount is less than 10 mg / cm. A coarser polytetrafluoroethylene dispersion is then applied until a residue of 9 before 16.2 mg / cm is reached. The plate is at 380 ⁰ O under a pressure of 5kp /

cm sintered for 15 minutes. On the irrelevant Mushroom becomes a solution of silver nitrate

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brings, "big a residue 10 remains, the 20mg me-

t aiii shine silver per cm; is equivalent to. The silver nitrate is thermally decomposed ^{between 150 and 200 0 G.} An electrode with a diameter of 56mm is cut from the plate. As air half-inches in 6 M KOH, there is a potential of -13SmV for one month with a load of imA / eia. (Pig. 3)

stung imA / eia a potential against the cable electrode

A polytetrafluoroethylene layer 12 is applied to all sides of a carbon fabric 11 of the size 72 × 143 mm and a thickness of 0.45 mm. This can be done by dipping or spraying. The amount is 7.8mg / cm. A coarser Polytetrafluoräthylsn-Uispersion 12 is applied to one side until a residue of 14.4 mg / cm is reached. The plate vi rd at 380 ⁰ G under a pressure of 5KP / cm for 10 minutes sintered. A slurry 14 in toluene of coke and polyethylene in a ratio of 4: 1 is then sprayed onto the other side of the fabric. The amount was 2.2 mg / cm. A layer 15 made of 1 part polyethylene and 9 parts catalyst (24mg / em) is then folded. The disk is sintered at 120 ⁰ C and a pressure of 40kp / cm for 5 minutes.

An electrode with the diameter is cut from the plate 56mra. As a half-cell in 6 M KOH it yielded a load of 2mA / cra a potential against the calom electrode of -120mV for one month, (Fig. 4)

Claims -11-

BATH

Claims (11)

PA 9/462/304 -11- T. catalyst electrode for electrochemical processes,
especially for fuel cells with a conductive support on which the catalyst and carbon particles are in
Plastic bond are applied, 'characterized in that the carrier consists of a carbon or graphite fiber material. 2. Catalyst electrode according to claim 1, characterized in that a plastic layer repelling the electrolyte on the graphite fabric
and a catalyst layer is applied to this » 3 · catalyst electrode according to claim!, Characterized ge
ke η η ζ ei ο Ja-η e t that on one side of the
Graphite fabric has a plastic layer repelling the sheet metal and a catalyst layer is applied to the other. Is bydrophobiert 4 · catalyst electrode according to claim 2 barren 3, characterized in that UAE graphite fabric, preferably lytetrafluoräthylen using P _o. ν ■ -1.2-. ' ^: _; 10 ^ 818/1292 I. ΒΑ0 ORIGINAL, f 167U82 PA 9/462/304 -12- 5. catalyst electrode according to one of claims 2 to 4, characterized in that in the plastic layer contains carbon particles aind. 6. Catalyst electrode according to one or more of the claims 2 to 5, characterized that the. Catalyst layer a plastic as a binding agent contains. 7. Hktalysatorelectrode according to claim 2 or 5> characterized in that the plastic layer consists of polytotrafluoroethylene. 8. catalyst electrode according to claim 6, characterized ge indicates that the binder is made Polytetrafluoroethylene consists. . 9 · catalyst electrode according to claim 2, characterized ge Iren η records that on the catalyst layer another layer of plastic that repels the electrolyte is applied. 10. catalyst electrode according to claim 9> thereby ge indicates that the further plastic layer consists of polytetrafluoroethylene without further inclusions. 109838/1292 PA 9/462/304 -13- 11. A method for producing an electrode according to a or more of claims 1 to 1Q, characterized ge indicates that the various Layers applied to the graphite fabric and then be sintered under pressure. 109838/1292 BADORiGtNAL «Sas Blank page