DE2005394A1 - Process for the production of gas-permeable, electrolyte-impermeable foils for electrochemical cells, in particular fuel cells - Google Patents

Description

R. 9750

Pf / Hi 01/26/70

System for. Patent application

ROBERT BOSCH GfJBH, 7 Stuttgart T, Breitscheidstrasse 4

Process for the production of gas- permeable, electrolyte- :. impermeable pollen for electrochemical cells, especially fuel cells'

The invention relates to a method for producing gas-permeable, hydrophobic films made of polytetrafluoroethylene (PTi ¹ E) or other fluorine-containing polymers for electrochemical cells, in particular fuel cells.

It is known that porous polytetrafluoroethylene films are less Thickness can be made by using polytetrafluoroethylene with porcine formers and suitable liquids to one Processed dough that is rolled out into foils and then sintered

will. .

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109835/1351
^A ORIGINAL

Robert Boson GmbH R. 9750 Pf / Ri

Stuttgart;

The object of the present invention is to develop a manufacturing method for gas-permeable foils, which is easy to carry out and in which the losses can be kept small; the method should also enable the production of foils which are still impermeable to electrolytes even under relatively high hydrostatic pressure.

This object is achieved according to the invention in that suspended Poly te trafluorethylene particles or suspended particles other fluorine-containing polymer electrophoretically on auxiliary electrodes deposited in the desired shape and sintered the deposited layer after evaporation of the suspending agent will.

Should the cehicht also with higher hydrostatic pressures (p> 100 cm WB) be electrolyte impermeable, it becomes after rolled after sintering.

In some cases it is beneficial to re-sinter the layer after the '.'Fold; This is especially the case when the hydrostatic pressures at which the layer should still be electrolyte-tight go well beyond TjO cm WS, in which case the gas permeability then naturally also becomes smaller. When using PTFE sintering processes are carried out at temperatures of 330-400 ⁰ C.

The suspension liquids used in the electrophoretic Separation mainly of chloroform, carbon tetrachloride, Trichlorethylene or water is used.

The invention is explained in more detail in the following examples;

109835/1351 BAD ORlQiNAL

Robert Bosch GmbH / * 9750

Stuttgart

Example 1;

200 g of PTFE powder are finely divided in 4 l of carbon tetrachloride with the aid of a suspension stirrer. Two round auxiliary electrodes with a diameter of 10 cm made of stainless steel sheet are immersed in this suspension. The electrodes facing each other are 5 cm apart. The voltage between the electrodes is 20 kV, the deposition time approx. Five seconds. The suspension is gently stirred during the deposition: The anode with the deposited layer is sintered after evaporation of the main fraction of the carbon tetrachloride (for five minutes at Raumtenperatur) at 370 ⁰ C for 45 minutes in the heat air oven. The PTFE film, which has a thickness of approx. 150 μm at the chosen deposition time, now easily detaches from the auxiliary electrode. This film is alzdruck rolled at a V / of about 100 kg / cm into a film roll and then again sintered for 30 minutes at 380 ⁰ C. At a hydrostatic pressure of 190 cm water generated by a 1.5 m high 6 N KOH solution, the film is impermeable to electrolytes over the entire duration of the test of five days.

Example 2:

100 g of PTFE powder suspended in 4 l of trichlorethylene. A 2 mm thick, 100 cm large plate made of ceramic material serves as the anode, on the back of which a metallic conductor is attached. The voltage between the electrodes located 5 cm apart is approx. TO kV, the deposition time again approx. Five seconds. Ceramic plate and deposited layer are ^{sintered at 360 °} C. for 30 minutes and then quenched in cold water. This gives a very tough and flexible film, which is then rolled in a film roller with a rolling pressure of approx. 100 kg / cm. The thus obtained

1093 25/13 51;

Robert Bosch OmbII. Γι. 9750. Pf / Ri

Stuttgart

Int film at a high of a 1.2 m 4, generated hydrostatic pressure from 170 cm V ₁ ¹ S '] except elektrolyturidurchlässig in-HgSO, solution over the entire test of five days.

The method according to the invention makes it possible in a simple manner and with practically no loss of output; sinat er ial foils Polytetrafluoroethylene or other fluorine-containing polymers to produce, despite practically any, through the auxiliary electrode certain shapes have great uniformity in their thickness. The films are mechanical with good flexibility very stable, porous, gas-permeable, but electrolyte-impermeable: at an overpressure of 0.5 at, the air-

2 - 1

permeability 80 ml cm min, while the electrolyte impermeability up to a hydrostatic pressure of approx. 200 cm water column is guaranteed. Those are the qualities you are looking for right now required for so-called self-breathing gas diffusion electrodes in fuel cells, which is why they are preferred on this Area find use.

109835/1351

Claims (4)

Robert Bosch Π-inbH β. 975 Q ■ F £ / Bi Stuttgart. ., ^: ' \ Claims - ■ / 1 .J Process for the production of porous, gas-permeable hydrophobic EoIieη made of polytetrafluoroethylene or other fluorine-containing polymers for electrochemical cells / insber Special fuel cells, characterized in that suspended polytetrafluoroethylene particles or suspended particles Another fluorine-containing polymer electrophoresed: 'oh, up | Auxiliary electrodes of the desired Porm deposited and the deposited layer is sintered after evaporation of the suspending agent. . 2. The method according to claim 1, characterized in that the Layer is rolled after sintering. 3. The method according to claim 2, characterized in that the layer is optionally sintered again after the V / alzen. > 4. The method according to claim 1, characterized in that chloroform, carbon tetrachloride, trichlorethylene or water is used as the suspension liquid. % BATH