EP1651800B1 - Electrochemical cell - Google Patents

Abstract

The invention describes an electrochemical cell for the electrolysis of an aqueous solution of hydrogen chloride, comprising at least an anode half-cell with an anode, a cathode half-cell with a gas diffusion electrode as cathode and an ion exchange membrane arranged between the anode half-cell and the cathode half-cell, the membrane consisting of at least a perfluorosulfonic acid polymer, wherein the gas diffusion electrode and the ion exchange membrane are adjacent to each other, characterised in that the gas diffusion electrode and the ion exchange membrane, under a pressure of 250 g/cm2 and at a temperature of 60° C., have a contact area of at least 50%, with respect to the geometric area.

Description

The invention relates to an electrochemical cell having a gas diffusion electrode as a cathode, which is particularly suitable for the electrolysis of an aqueous solution of hydrogen chloride.

A method for the electrolysis of an aqueous solution of hydrogen chloride is, for example US Pat. No. 5,770,035 known. An anode compartment with a suitable anode, consisting for example of a substrate of a titanium-palladium alloy, which is coated with a mixed oxide of ruthenium, iridium and titanium, is filled with the aqueous solution of hydrogen chloride. The chlorine formed at the anode escapes from the anode compartment and is fed to a suitable treatment. The anode compartment is separated from a cathode compartment by a commercially available cation exchange membrane. On the cathode side, a gas diffusion electrode is located on the cation exchange membrane. The gas diffusion electrode in turn rests on a power distributor. Gas diffusion electrodes are, for example, oxygen-consuming cathodes (SVK). In the case of an SVK as a gas diffusion electrode, air, oxygen-enriched air or pure oxygen is usually introduced into the cathode space, which is reduced at the SVK.

An electrochemical cell for electrolysis An aqueous solution of hydrogen chloride containing a gas diffusion cathode and an ion exchange membrane which are in close contact is made of EP-A 0 785 294 known .

Commercially available ion exchange membranes have a flat carrier made of a woven fabric, mesh, braid or the like, for example of polytetrafluoroethylene (PTFE), to which on one side a perfluorosulfonic acid polymer, such as Nafion ^® , a commercial product of DuPont, is applied. If such an ion exchange membrane is used in an electrolysis cell with a gas diffusion electrode as an oxygen-consuming cathode for the electrolysis of an aqueous solution of hydrogen chloride, a comparatively high operating voltage in the range from 1.25 to 1.3 V at 5 kA / m ² can be observed.

The object of the present invention is therefore to provide a membrane electrolysis cell with a gas diffusion electrode as the cathode, in particular for the electrolysis of an aqueous solution of hydrogen chloride, which has the lowest possible operating voltage.

The invention relates to an electrochemical cell according to claim 1 for the electrolysis of an aqueous solution of hydrogen chloride, at least consisting of an anode half-cell with an anode, a cathode half-cell with a gas diffusion electrode as the cathode and an arranged between the anode half-cell and cathode half-cell ion exchange membrane, which at least from a Perfluorsulfonsäure- Polymer, wherein the gas diffusion electrode and the ion exchange membrane to each other, characterized in that the gas diffusion electrode and the ion exchange membrane under a pressure of 250 g / cm ² and a temperature of 60 ° C, a contact area of at least 50%, preferably of at least 70%, with respect to the geometric surface.

The contact surface of the invention between the gas diffusion electrode and the Ionenaustauschermembran.unter pressure of 250 g / cm ² and a temperature of 60 ° C can be determined, for example, according to Example 5. The experiment according to Example 5 simulates the conditions of pressure and temperature in the electrochemical cell according to the invention during operation.

The ion exchange membrane consisting of at least one layer of a perfluorosulfonic acid polymer such as Nafion ^®. Other perfluorosulfonic acid polymers which can be used for the electrolysis cell according to the invention are, for example, in EP-A 1 292 634 described. The ion exchange membrane may additionally comprise a carrier or embedded microfibers for mechanical reinforcement.

The carrier of the ion exchange membrane is preferably a net, woven fabric, braid, knitted fabric, fleece or foam of an elastically or plastically deformable material, more preferably of metal, plastic, carbon and / or glass fibers. As plastics are particularly suitable PTFE, PVC or PVC-HT.

In a preferred embodiment of the ion exchange membrane, the support is embedded in a layer or between at least two layers of perfluorosulfonic acid polymer. The ion exchange membrane is particularly preferably composed of at least two layers of the perfluorosulfonic acid polymer, wherein the carrier of the ion exchange membrane is embedded between the layers or in one of the two layers of perfluorosulfonic acid polymer. This can be done, for example, by applying at least one layer of a perfluorosulfonic acid polymer to both sides of the support. When the support is embedded in a layer or between at least two layers of the perfluorosulfonic acid polymer, the ion exchange membrane has a smoother surface than an ion exchange membrane in which the support has only one side of a layer of a perfluorosulfonic acid polymer. A smoother surface of the ion exchange membrane allows better contact with the gas diffusion electrode. The smoother the surface of the ion exchange membrane, the larger it is the area where the ion exchange membrane contacts the adjacent gas diffusion electrode.

The gas diffusion electrode comprises an electrically conductive support, preferably of a woven, braided, mesh or fleece of carbon, metal or sintered metal. The metal or sintered metal must be resistant to hydrochloric acid. These include e.g. Titanium, hafnium, zirconium, niobium, tantalum and some Hastalloy alloys. The electroconductive support is optionally provided with a coating composition containing an acetylene black polytetrafluoroethylene mixture. This coating composition can be applied, for example, by trowelling onto the electrically conductive support and then sintered at temperatures of about 340 ° C. This coating composition serves as a gas diffusion layer. The gas diffusion layer can be applied to the electrically conductive carrier over the entire surface. It may also be wholly or partly incorporated into the open-pore structure of the wearer, i. a fabric, braid, net or the like. embedded. An electrically conductive carrier made of a carbon nonwoven fabric, which is provided with a gas diffusion layer of an acetylene black polytetrafluoroethylene mixture, is commercially available, for example from the company SGL Carbon Group.

The gas diffusion electrode further comprises a catalyst-containing layer, also referred to as a catalyst layer. The catalysts used for the gas diffusion electrode are: noble metals, eg Pt, Rh, Ir, Re, Pd, noble metal alloys, eg Pt-Ru, compounds containing precious metals, eg noble metal-containing sulfides and oxides, and Chevrel phases, eg Mo ₄ Ru ₂ Se ₈ or Mo ₄ Ru ₂ S ₈ , which may also contain Pt, Rh, Re, Pd etc.

An appropriate for the erfmdungsgemäße electrolysis cell gas diffusion electrode and its preparation is for example WO 04/032263 A known. The electrical contact of the gas diffusion electrode via a power distributor, on which rests the gas diffusion electrode.

In the electrochemical cell according to the invention, the ion exchange membrane and the gas diffusion electrode, which in operation acts as a cathode, lie against one another over the entire area, the ion exchange membrane and the gas diffusion electrode having a contact area of at least 50 under a pressure of 250 g / cm ² and a temperature of 60 ° C. % exhibit. In general, an electrochemical cell of the type according to the invention is operated under a pressure of 0.2 to 0.5 kg / m ² and a temperature of 40 to 65 ° C. For the gas diffusion electrode as smooth as possible surface is desirable because the smoothest possible surface improves contact with the ion exchange membrane. In order to achieve the smoothest possible surface, for example, the gas diffusion layer and / or the catalyst layer can be applied by means of a spray process, wherein the drops of the sprayed dispersion must be as uniform as possible. A suitable spraying method is eg off WO 04/032263 A known. Preferably, an open-pored, electrically conductive carrier is used in which the pores are closed by the gas diffusion layer. The gas diffusion layer and / or catalyst layer may also be applied by rolling or brushing.

The largest possible contact surface is achieved by the appropriate choice of the gas diffusion electrode and the ion exchange membrane. Both must have the smoothest possible surface and at the same time the best possible micro-deformability, i. have a good deformability in the micrometer range.

In a specific embodiment of the electrolysis cell according to the invention, the catalyst layer of the gas diffusion electrode is applied to the ion exchange membrane. The catalyst layer may be applied to the ion exchange membrane by, for example, spraying or by the film casting method known in the art. In this way, the ion exchange membrane and the catalyst layer form a membrane electrode assembly (MEA). In this case, the electrically conductive carrier is attached to the gas diffusion layer on the catalyst layer. The contact area according to the invention of at least 50%, preferably at least 70%, based on the geometric area, under a pressure of 250 g / cm ² and a temperature of 60 ° C lies here between the gas diffusion layer and the catalyst layer of the MEA.

In the electrolysis of an aqueous solution of hydrogen chloride (hydrochloric acid), the electrolysis cell according to the invention has an operating voltage which is lower by 100 to 300 mV.

In a preferred embodiment, the ion exchange membrane is made up of at least two layers, the layers having different equivalent weights. For the purposes of the present invention, the equivalent weight is to be understood as meaning the amount of perfluorosulfonic acid polymer required to neutralize 1 liter of 1N sodium hydroxide solution. The equivalent weight is thus a measure of the concentration of the ion-exchanging sulfonic acid groups. The equivalent weight of the ion exchange membrane is preferably 600 to 2500, more preferably 900 to 2000.

If the ion exchange membrane is composed of several layers with different equivalent weight, then the layers can in principle be arranged arbitrarily to one another. However, preference is given to an ion exchange membrane in which the layer of the ion exchange membrane which faces the gas diffusion electrode, ie bears against the gas diffusion electrode, has a higher equivalent weight than the other layers. For example, if the ion exchange membrane is composed of two layers, the equivalent weight of the anode facing layer is 600 to 1100 and the equivalent weight of the gas diffusion electrode If more than two layers are present, the equivalent weight may increase, for example, from the layer facing the anode in the direction of the layer facing the gas diffusion electrode. However, it is also possible that higher and lower equivalent weight layers are alternately arranged, with the layer adjacent to the gas diffusion electrode having the highest equivalent weight.

By choosing the equivalent weight as well as the choice of layers with different equivalent weights, the chlorine transport through the ion exchange membrane can be reduced. The least possible migration of chlorine through the ion exchange membrane is desirable. Ideally, the migration of chlorine should be completely suppressed, as chlorine in the catalyst layer of the gas diffusion electrode is reduced to chloride and forms dilute hydrochloric acid with the reaction water formed in the cathode half-cell. This can not be reused on the one hand and must therefore be disposed of. On the other hand, the contact of dilute hydrochloric acid with the gas diffusion electrode leads to overvoltages and possibly to corrosive damage to the catalyst contained in the gas diffusion electrode.

Furthermore, in the case of the electrochemical cell according to the invention, the transport of water from the anode half cell through the ion exchange membrane into the cathode half cell is reduced to about one third. This too is advantageous since less dilute hydrochloric acid is formed in the cathode half-cell, which must be disposed of. Another advantage of the lower water transport is that there is less risk of the formation of a water film on the surface of the gas diffusion electrode. This in turn improves the oxygen transport through the gas diffusion electrode.

The anode of the electrochemical cell according to the invention consists of a network; Woven fabric, knitted fabric, braid or the like, preferably made of an expanded metal such as Pd-stabilized titanium, which is provided for example with a coating of Ru-Ti mixed oxide. A suitable anode is for example out WO 03/056065 A known.

Examples example 1

In a laboratory test with a laboratory cell, which had an electrochemically active area of 100 cm ² , gas diffusion electrodes, as they were US 6,402,930 respectively. US 6,149,782 Fumatech having an equivalent weight of 950 tested with a proton-conducting ion exchange membrane of Perfluorsulfonsäuretyps the Fa.

The ion exchange membrane had as carrier a glass fiber inner support web, ie, the support was embedded in the perfluorosulfonic acid polymer. The ion exchange membrane used is in EP-A 129 26 34 described.

The gas diffusion electrode had the following structure: An electrically conductive carbon fabric support was provided with a gas diffusion layer composed of an acetylene black-polytetrafluoroethylene mixture. On this carrier provided with the gas diffusion layer, a catalyst layer consisting of a catalyst-polytetrafluoroethylene mixture was applied. The rhodium catalyst was present sorbed on carbon black (Vulcan XC72 ^®). Since the gas diffusion electrode was operated in direct contact with an ion exchange membrane, it was additionally provided with a layer made of Nafion ^®, a proton conducting ionomer in order to achieve a better connection to the ion exchange membrane. The oxygen-consuming cathode was almost smooth on its surface except for the typical shrinkage cracks from the manufacturing process. The oxygen-consuming cathodes used are in US 6,149,782 described. The current distributor of the oxygen-consuming cathode was a titanium expanded metal with a Ti / Ru mixed oxide coating.

The anode used was a commercially available titanium-palladium expanded metal anode with a titanium-ruthenium mixed oxide coating.

Under the operating conditions of 5 kA / m ² , 60 ° C, 14% technical hydrochloric acid and a distance of 3 mm between the anode and 200 mbar hydrostatically pressed ion exchange membrane to the cathode, the test cell showed an operating voltage of 1.16 V in a 16- daily continuous operation.

Example 2 (comparative example)

In several comparative experiments under the conditions described in Example 1, the oxygen-consuming ^cathodes described in Example 1 were tested with a proton-conducting ion exchange membrane of the type Nafion® 324 from DuPont.

The oxygen-consuming cathodes were from the same manufacturing batch as the oxygen-consuming cathodes used in Example 1.

In this ion exchange membrane, the carrier was not coated on both sides with the perfluorosulfonic acid polymer, but only on one side, wherein the carrier was in the form of a supporting tissue on the Sauerstoffverzehrkathode. As a result, sufficient surface contact of the oxygen-consuming cathode with the perfluorosulfonic acid polymer of the ion exchange membrane was not possible. The structure of the supporting fabric significantly increases the roughness of the surface.

Operating voltages of 1.31 to 1.33 V were found in the comparative experiments.

Example 3

Tests were carried out with oxygen-consuming cathodes of different surface roughness in the arrangement described in Example 1 and under the operating conditions defined in Example 1.

In a first test, an ion exchange membrane from Fumatech described in Example 1 was tested with an oxygen-consuming cathode, which consisted of a carbon nonwoven, filled with a gas diffusion layer (as described in Example 1) and with a catalyst layer consisting of 30% rhodium sulfide on soot type Vulcan ^® XC72 and Nafion ^® -Ionomerlösung was sprayed. The oxygen-consuming cathode had a surface roughness of about 140 μm, cf. Example 5, on. This electrode showed a stable operating voltage of 1.28 V.

In a second test, this oxygen-consuming ^{cathode was} tested with a ^Nafion® 324 ion exchange membrane from DuPont. A voltage of 1.32 V was found. It has thus been found that both the smoothness of the membrane and the smoothness of the oxygen-consuming cathode are decisive for a large contact area between the ion exchange membrane and the gas diffusion electrode.

Example 4

• Nafion^® 117: einlagig mit einem Äquivalentgewicht von 1100; ohne Stützgewebe
• Nafion^® 324: zweilagig mit einem Äquivalentgewicht von 1100 bzw. 1500; mit einem der Sauerstoffverzehrkathode zugewandten außenliegenden Stützgewebe, d.h. der Träger war nicht in das Perfluorsulfonsäure-Polymer eingebettet
• Ionenaustauschermembran der Fa. Fumatech, einlagig mit einem Äquivalentgewicht von 950 und innenliegendem Stützgewebe, d.h. der Träger war in das Perfluorsulfonsäure-Polymer eingebettet (nachfolgend als Fumatech-Membran 950 bezeichnet)

Chlorine diffusion through different ion exchange membrane types was investigated. This manifests itself in connection with the water transport number under operating conditions in a different hydrochloric acid concentration of the catholyte. The following membranes were tested under standstill conditions in the de-energized state:

• Nafion ^® 117: a single layer having an equivalent weight of 1100; without supporting tissue
• Nafion ^® 324: two layers having an equivalent weight of 1100 or 1500; with an outer support fabric facing the oxygen-consuming cathode, ie the support was not embedded in the perfluorosulfonic acid polymer
• Fumatech ion exchange membrane, single-ply 950 equivalent weight and internal support fabric, ie the support was embedded in the perfluorosulfonic acid polymer (hereinafter referred to as Fumatech 950 membrane).

• Nafion^® 117: 3511 mg Chlor
• Nafion^® 324: 503 mg Chlor
• Fumatech-Membran 950: 1144 mg Chlor

The following behavior with regard to chlorine diffusion was observed in a 7-hour test:

• Nafion ^® 117: 3511 mg Chlorine
• Nafion ^® 324: 503 mg of chloroauric
• Fumatech membrane 950: 1144 mg of chlorine

Moreover, it was found that, under comparable operation of the three types of membranes, the Nafion ^® membranes under the stated conditions of Example 1 a water transport value of about 1 (ie, 1 mol H ₂ O per mole of photons through the membrane) exhibited, while the Fumatech- Membrane only a water transport number of 0.37, ie about a third, had.

It was found that the single-layer membrane Nafion ^® 117 and the Fumatech membrane 950 have different by more than a factor of 3 chlorine diffusion, the advantages were with the Fumatech membrane despite the low equivalent weight.

On the other hand, the double layers of the Nafion ^® 324 brought in connection with the higher equivalent weight of the cathode-side layer, a reduction of the chlorine transportation to approximately 1/7 compared to the Nafion ^® 117 or to about half compared to the Fumatech membrane 950th

In view of the low chlorine diffusion, an ion exchange membrane having a combination of two or more layers of different equivalent weights is preferred, with the equivalent weight increasing toward the oxygen-consuming cathode. In this way, a significant reduction of the chlorine diffusion, possibly to zero, can be achieved. The water transport number of the Fumatech membrane, which is about 1/3 of that of the Nafion ^® membranes, allows the oxygen-consuming cathode to be operated in a damp state, ie not wet. Operation in wet condition is known by all Nafion ^® membranes.

Example 5

With the help of the following laboratory experiment, the contact surface between gas diffusion electrode (GDE) and ion exchange membrane was determined by simulating the conditions prevailing in an electrolytic cell.

A strip of an ion exchange membrane of about 3 × 7 cm ² was impregnated on one side with 30 μl of a fluorescence solution. The fluorescence solution was prepared from a glycerol-water mixture. For this, the fluorescein powder was dissolved in water and added to glycerol. The ratio of water: glycerol was 1: 1 (80 mg fluorescein, 4.7 g water, 4.7 g glycerol).

The unilaterally impregnated ion exchange membrane was stretched over a neoprene fine foam pad so that the impregnated surface was supported on the fine foam pad. This the fine foam cushion facing surface is hereinafter also referred to as the bottom. The neoprene foam pad had a size of 2.2 x 2.2 cm ² .

The top of the ion exchange membrane was also wetted with 30 μl of the fluorescence solution. Subsequently, the surface was covered with a glass plate and pressed with a weight of about 200 g. As a result, the fluorescence solution on the top and bottom of the ion exchange membrane spread evenly over both surfaces.

The soaked and applied to a fine foam pad ion exchange membrane was stored in a desiccator at 100% humidity and at room temperature for 3 hours. The membrane was completely saturated. After storage in the desiccator, the two surfaces of the ion exchange membrane were freed from the remaining liquid film.

The gas diffusion electrode having an area of 2.2 × 2.2 cm ² was placed on the ion exchange membrane (the surface facing the ion exchange membrane will hereinafter also be referred to as a surface). On the back, ie the ion exchange membrane facing away from the surface of the gas diffusion electrode, the power distributor was placed. Then the appropriate weight was provided, which ensures the pressure of 250 g / cm ² . This overall structure was stored in a desiccator at 100% humidity and 60 ° C, 19 h in a drying oven.

After storage, the gas diffusion electrode was removed and fixed on a microscope slide for microscopic evaluation.

• Von der GDE-Oberfläche wurde eine Übersichtsaufnahme im Rückstreu- und Fluoreszenzkontrast aufgenommen. Der Bildausschnitt betrug 6,250 x 6,250 mm². Die Photomultiplier-Verstärkung des Rückstreukanals wurde bei voller Laserleistung (ca. 22 mW, Laserausgang) auf 322 Volt festgelegt. Die Photomultiplierspannung des Fluoreszenzkanals betrug 1000 Volt. Die Bilder wurden im Modus 488 / > 590 nm aufgenommen. Bei dieser Einstellung wurde mit der Wellenlänge 488 nm des Ar⁺ - Lasers beleuchtet. Das Rückstreubild wurde bei der gleichen Wellenlänge aufgezeichnet. Das Bild im Fluoreszenzkanal wurde vom Fluoreszenzlicht der Probenoberfläche, welches langwelliger als 590 nm ist, erstellt.

Evaluation in Confocal Laser Scanning Microscope Leica TCS NT:

• From the GDE surface, a survey was taken in the backscatter and fluorescence contrast. The image section was 6.250 x 6.250 mm ² . The photomultiplier gain of the Backscattering channel was set to 322 volts at full laser power (about 22 mW, laser output). The photomultiplier voltage of the fluorescence channel was 1000 volts. The pictures were taken in 488 /> 590 nm mode. At this setting, the 488 nm wavelength of the Ar ⁺ laser was illuminated. The backscatter image was recorded at the same wavelength. The image in the fluorescence channel was created by the fluorescence light of the sample surface, which is longer than 590 nm.

The images for evaluation of the pressure surface were taken with the objective x 10 / 0.3 air. The image section was then 1.0 × 1.0 mm ² . For statistical verification, 8 image sections were taken. Since the surfaces have clear topographical structures, cross-sectional series were taken. In the case of the gas diffusion electrode according to example 1 (carbon cloth electrode), the height difference to be overcome was about 70 μm, for the carbon nonwoven electrode about 140 μm. Images were also recorded in 488 /> 590 nm mode. In the case of the carbon cloth electrode, a sectional image series of 72.9 μm was taken in each case with 63 individual sections. The gain at the backscatter channel was 231 volts, the gain at the fluorescence channel was 672 volts.

In the case of the carbon nonwoven electrode, a sectional image series of 143 μm was recorded with 127 individual sections. The gain at the backscatter channel was 266 volts, the gain at the fluorescence channel was 672 volts.

From the image data set of the backscatter canal, a topography image was created. From the image data set of the fluorescence channel, a projection image was generated. In this projection image, only the brightest point from the cross-section series running in the z direction was shown for each xy coordinate. This image was used for further image analysis of area occupation. '

A histogram was taken in a set image frame with an enclosed area of 261632 pixels. In this histogram, the frequencies that have occurred were determined for each intensity (0 - 255) (see Table 1).

Table 1 below gives the thus determined contact area in% and the mean square deviation over 8 measurements for different combinations of ion exchange membranes and gas diffusion electrodes. As the carbon diffusion electrodes were used: carbon cloth electrodes according to Example 1 (hereinafter also referred to as Type A), carbon nonwoven electrodes according to Example 3, wherein the carbon web was filled with a gas diffusion layer and sprayed with a rhodium sulfide catalyst layer and a Nafion ^® ionomer solution (hereinafter also referred to as type B) and carbon nonwoven electrodes, which with a gas diffusion layer open-pore coated and sprayed with a rhodium sulfide catalyst layer and a Nafion ^® ionomer solution (hereinafter also referred to as Type C). Under an open-pored coating is here to be understood a coating which the pores of the carbon fabric or the like. does not close. An open-pored coating can be achieved, for example, by impregnating the carrier, for example the carbon nonwoven, while in a closed-pored, ie filled, coating, the gas diffusion layer is applied to the carrier, for example, whereby the pores of the carrier are filled.

Fumatech with an internal, ie embedded, carrier according to Example 1 (referred to as Fumatech 950), ion exchange membranes of the perfluorosulfonic acid type of the company. DuPont with an overlying, ie not embedded, support according to Example 2 (designated ^Nafion® 324) and ion exchange membranes of the perfluorosulfonic acid type from DuPont without carrier (designated ^Nafion® 105).

The voltage was measured at 5 kA / m ² and 60 ° C.

The results in Table 1 show that a large contact area between ion exchange membrane and gas diffusion electrode is associated with a lower cell voltage than a small contact area. <b><u> Table 1 </ u></b> ion exchange membrane Gas diffusion electrode Contact area [%] mean square deviation Voltage [V] Fumatech 950 Type A 76.5 2.8 1.16 Nafion ^® 105 Type A 74.4 2.3 1.17 Fumatech 950 Type B 18.0 3.0 1.28 Nafion ^® 324 Type B 8.3 1.5 1.32 Fumatech 950 Type C 75.3 4.1 1.22 Nafion ^® 324 Type C 6.5 1.6 1.31

Claims (9)

1. Electrochemical cell for the electrolysis of an aqueous solution of hydrogen chloride, which consists at least of an node half cell having an anode, a cathode half cell having a gas diffusion electrode as cathode and an ion-exchange membrane which consists at least of a perfluorosulphonic acid polymer and is arranged between anode half cell and cathode half cell, where the gas diffusion electrode and the ion-exchange membrane rest against one another, characterized in that the gas diffusion electrode and the ion-exchange membrane have a contact area of at least 50%, based on the geometric area, measured outside the cell under a pressure of 250 g/cm² and a temperature of 60°C.
2. Electrochemical cell according to Claim 1, characterized in that the contact area is at least 70%.
3. Electrochemical cell according to either of Claims 1-2, characterized in that the ion-exchange membrane has a layer of a perfluorosulphonic acid polymer and a support is embedded in the layer of the perfluorosulphonic acid polymer.
4. Electrochemical cell according to either of Claims 1-2, characterized in that the ion-exchange membrane has at least two layers of a perfluorosulphonic acid polymer and a support is embedded between two layers or in one of the two layers of the perfluorosulphonic acid polymer.
5. Electrochemical cell according to Claim 4, characterized in that the ion-exchange membrane has at least two layers, where the layers have different equivalent weights.
6. Electrochemical cell according to any of Claims 1-5, characterized in that the layers of the perfluorosulphonic acid polymer have an equivalent weight of from 600 to 2500, preferably from 900 to 2000.
7. Electrochemical cell according to either Claim 5 or 6, characterized in that the layer facing the gas diffusion electrode has a higher equivalent weight than the other layers.
8. Electrochemical cell according to any of Claims 1-7, characterized in that the catalyst layer of the gas diffusion electrode is applied to the ion-exchange membrane.
9. Electrochemical cell according to any of Claims 1-8, characterized in that the ion-exchange membrane has a support composed of a mesh, woven fabric, braid, knitted fabric, nonwoven or foam composed of a plastically or elastically deformable material, preferably metal, plastic, carbon and/or glass fibres.