DE2129429A1 - PROCESS FOR GENERATING A CONTINUOUS HYDROPHOBIC CHANGE OVER THE CROSS SECTION OF ELECTRODES - Google Patents

Description

Kombinat VKB galvanic elements

Method for generating a continuous change in hydrophobicity over the Cross section of electrodes

The invention relates to a method for producing a continuous Change in hydrophobicity over the. Cross section of electrodes for galvanic flowers nt θ.

Such electrodes are suitable, preferably for use in fuel elements and hybrid systems

After the method both electrodes or parts thereof, for the Oxygen reduction as well as for the fuel oxidation produced «ground ·

Bs has already been proposed to make hydrophobic carbon electrodes by soaking catalytically highly active coal bodies ax solutions or dispersions of. Water repellants, such as polyethylene, polytetrafluoroethylene, paraffin and others to produce · TJm a uniform distribution of the liquid-repellent To reach substances. " a homogeneously activated carbon must be present This is technologically very difficult and with unsatisfactory reproducibility to reach." A. Another disadvantage of this process is that the hydrophobizing agent layer applied in this way is relatively easy to remove Electrolytes are infiltrated, can

To avoid the disadvantages outlined, use hydrophobic carbon electrodes also by mixing coal powder with hydrophobic binder and then Hot or cold pressing can be produced · In these cases, however, a relatively high proportion of binding agent is required to achieve a sufficient Achieving hydrophobicity, however, with increasing binder content, the catalytic activity and electron conductivity are greatly reduced

It is known to prepress mixtures in which the binder is used at the same time is deposited as a hydrophobic film on the carbon particles prior to compression »

The combination of high performance old good hydrophobicity and tightness of the Electrodes are possible with multilayer electrodes · There are electrodes with graded Hydrophobicity known, whereby the electrolyte is fixed near the electrolyte side

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309829/0544

These electrodes are produced by spraying and sintering Clay polyethylene- and polytetrafluoroethylene-bonded carbon layers on one With Setrafluoroethylene hydrophobized ITickelsinter foil and subsequent compression On the electrolyte side, 3 carbon layers are usually 5, 10 and 15 $ polyethylene » which is dissolved in xylene at 120 ° C., sprayed on. You are on Teflon-bonded Eohle-Graphitschiehten, which the function of the locking of the electrolyte, take over

The spraying of carbon-polyethylene layers or other carbon-binder layers, in which the binder is dissolved or finely dispersed, stubbornly Ojahüllung the carbon grain by a polyethylene film and thus to strengthen. TFex reduction of the electron conductivity and the reduction of the catalytic insulation Activity of coal »

w Starting from the disadvantages mentioned, the purpose of the invention is to provide coal electrodes with high performance "good hydrophobicity and Mnreiehender electronic conductivity · The invention is based on the object. Reasons to use a carbon electrode. create that can be operated for a long time at low operating pressure or atmospheric pressure with high gas conversion efficiency and ir.ob.er power *

According to the invention, the task is accomplished with a carbon electrode containing a support structure solved »whose hydrophobicity is continuously over the slectrode

changes and that the carbon bodies are not completely removed from the binder msMillt · Contains the electrode surface facing the electrolyte the lowest proportion of biochemicals »

Erfi & dBsgsgemäS TEsrdon more carbon layers, for example those dosed with a content aa HiederdruokpolyäthyloEptilver vos 4, 8, 12 and 16 jS _f and afterwards £ @ 3End Leaving angeaintert and compacted "Then, the electrode having a IsösoH ^ is aiaittelj, examples orphan xylene, gaträakt and at appropriate , dried by the solvent as a result of remedies »The binder in the boreholes is preferably dissolved and separated again as a film with the evaporation of the musty substance in the porcelain dissolved © binder partially penetrates into the binder & msEen pores of the llektrsds, whereby a change in hydrophobicity can be achieved according to the concentration gradient. Another variant lies in the fact that the solubility, like anch'dio YeEdampfajagsgesohwindi ^ sit of the solvent, can be controlled by the use of ^ Esisohen, s _a B »I ^ lßi / jseaaol / Sstralsjrdrofureß» -

3 0 9 8 2 9/0544 " ³ "

ORIGlNAL BATHROOM

It has been found that even single-layer electrodes with one over the electrode body Evenly distributed hydrophobicity can be produced by Pressed articles made of activated carbon and binder with a solvent, «ie Soaked in xylene · By subsequent evaporation, the same escapes again, whereby the binder is deposited as a film and increases the hydrophobicity of the electrode body

According to the invention, the solvent can in all cases also contain monomeric xolene hydrogens, how styrene can be added during the process of solvent evaporation polymaking

It was also found that substances with water-repellent properties, such as ζ · Β · paraffins, can also be added to the solvent » which bring about a reinforcement of the hydrophobic effect that can be achieved according to the invention

The invention is to be explained in more detail below using the following exemplary embodiments

Example

1 · An electrode composed of three layers of carbon WDE 0 * 2-1 and the binder pressure-molded polyethylene in the layer arrangement carbon with 5 % binder, carbon with 10 $ binder and carbon with 15 $ binder on a suitable, conductive support structure is treated as follows the JUlektrodenkörper is either heated to 60 ° C and then in xylene or in a vacuum at KOrmaltemperatur impregnated · then 2 Standen is at 130 - heated I50 ⁰ C, whereby a part of the binder read and as a fine film on the surface and in the pores separates. In the subsequent electrochemical measurement, the treated electrodes showed considerably higher hydrophobicity than before

With a loss of activity of $ 15 and an increase in resistance of 20 56, an increase in the service life when working without overpressure was achieved by a factor of 8

2 · The xylene is given a certain amount, preferably before the impregnation process between 1 and 5 # of a low polymerized styrene added During the heating process, the styrene polymerizes completely, which results in an additional increase in hydrophobicity. The decrease in activity was between $ 15 and $ 20 with an increase in resistance from 2o - 25 5S, the service life increased by a factor of 10 »

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3 · This method can be applied · electrodes consisting of coal P 33 i of a layer arrangement carbon and 5 io high-pressure polyethylene) coal with 10 $ IE SD and coal with 20 f> EE-ND on a conductive support structure on high-pressure polyethylene resulted in Treatment according to the invention with a loss of activity of 5 # and an increase in resistance of 10-12 $, an increase in the service life at 50 mA / cm with oxygen at 65 C and the factor 2

309829 / 05U

Claims (1)

Claims. " Process for producing a continuous change in hydrophobicity via the cross-section of electrodes for galvanic elements, characterized in that that the binder particles of the pore surface by soaking. Sweeping layer electrodes with solvents and connect- ^ * ~ the evaporation of the same can be deposited as a hydrophobic film and the hydrophobicity changes continuously over the slectrode cross-section 2 · Method according to claim 1, characterized in that multilayer electrodes Bit of continuously increasing hydrophobicity can be produced by the dissolution capacity as well as the evaporation rate Use of reading mixtures is controlled 3. The method according to claim 1, characterized in that single-layer electrodes of uniform hydrophobicity can also be produced. 4 · The method according to claim 1, characterized in that the solvent may contain an additional water repellent, which is deposited together with the dissolved particles of the binding agent 5 · The method according to claim 1, characterized in that the solvent monomeric hydrocarbons, e.g. styrene, are added, which in the polymerize the process described, whereby an additional increase in hydrophobicity is achieved 309829 / 06U