WO2019011577A1

WO2019011577A1 - Membrane-coupled cathode for the reduction of carbon dioxide in acid-based electrolytes without mobile cations

Info

Publication number: WO2019011577A1
Application number: PCT/EP2018/065854
Authority: WO
Inventors: Bernhard Schmid; Christian Reller; Günter Schmid
Original assignee: Siemens Aktiengesellschaft
Priority date: 2017-07-12
Filing date: 2018-06-14
Publication date: 2019-01-17
Also published as: DE102017211930A1; CN110914477A; AU2018300589A1; US20210079538A1; EP3622100A1

Abstract

The invention relates to a method for the electrolysis of CO2, wherein the electrolytic cell has a salt bridge space, having a fluid and/or dissolved acid, said electrolytic cell comprising: a cathode chamber having a cathode; a first ion exchanger membrane containing an anion exchanger and/or an anion transporter and adjacent to the cathode chamber, wherein the cathode directly contacts the first ion exchanger membrane; an anode chamber having an anode; and a diaphragm adjacent to the anode chamber; wherein a salt bridge space is also provided, which is arranged between the first ion exchanger membrane and the diaphragm. The invention also relates to an electrolysis system comprising the electrolytic cell, and the use of the electrolytic cell or the system for the electrolysis of CO2.

Description

description

Membrane-coupled cathode for the reduction of carbon dioxide in acid-based electrolytes without mobile cations

The present invention relates to a method for electric ^¬ analysis of CO2, wherein the electrolytic cell comprises a salt bridges ^¬ space that can accommodate a liquid and / or dissolved acid environmentally, an electrolytic cell having a cathode compartment comprising a cathode, a first ion exchange membrane to an anion exchanger and / or anion contains and which is adjacent to the cathode compartment, said cathode contacting the first ion exchange membrane directly adjoins an anode compartment comprising an anode, and a diaphragm wel ^¬ ches to said anode compartment, wherein further a Salzbrü ^¬ ckenraum is present, which is between the first ion exchange membrane and the diaphragm is arranged, a

Electrolysis plant comprising the electrolytic cell and the use of the electrolytic cell of the plant or to the Electric ^¬ analysis of CO2.

State of the art The burning of fossil fuels currently covers about 80% of the global energy demand. As a result of these incineration processes in 2011, worldwide approx

34,032.7 million tons of carbon dioxide (C0 ₂₎ emitted into the At ^¬ phere. This release is the easiest way to dispose of even large amounts of CO2 (lignite-fired power plants over 50,000 t per day).

The discussion about the negative effects of the greenhouse gas CO2 on the climate has led to a reflection on the reuse of CO2. Thermodynamic sailed ^¬ hen is very low CO2, and can therefore hardly be reduced again to useful products. Systematic studies of the electrochemical reduction of carbon dioxide are still a relatively new development ^¬ lung field. Only for a few years has there been an effort to develop an electrochemical system that can reduce an acceptable amount of carbon dioxide. Research in the laboratory scale have shown that metals are to be used as catalysts for the electrolysis of carbon dioxide ^¬ preferred. From the publication Electrochemical CO2 reduction on metal electrodes by Y. Hori, published in: C. Vayenas, et al. (Eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89-189, Faraday efficiencies (FE) are exemplarily taken on different metal cathodes, some of which are shown by way of example in Table 1. Table 1: Faraday efficiencies for the conversion of C02 into different products on different metal electrodes

Electrode CH ₄ C ₂ H ₄ C ₂ H ₅ OH C ₃ H ₇ OH CO HCOO ^" H ₂ Total

Cu 33.3 25.5 5.7 3 0 1.3 9.4 20.5 103.5

Au 0 .0 0.0 0.0 0 0 87.1 0.7 10.2 98.0

Ag 0 .0 0.0 0.0 0 0 81.5 0.8 12.4 94.6

Zn 0 .0 0.0 0.0 0 0 79.4 6.1 9.9 95.4

Pd 2 .9 0.0 0.0 0 0 28.3 2.8 26.2 60.2

Ga 0 .0 0.0 0.0 0 0 23.2 0.0 79.0 102.0

Pb 0 .0 0.0 0.0 0 0 0.0 97.4 5.0 102.4

Hg 0 .0 0.0 0.0 0 0 0.0 99.5 0.0 99.5

In 0 .0 0.0 0.0 0 0 2.1 94.9 3.3 100.3

Sn 0 .0 0.0 0.0 0 0 7.1 88.4 4.6 100.1

Cd 1 .3 0.0 0.0 0 0 13.9 78.4 9.4 103.0

Tl 0 .0 0.0 0.0 0 0 0.0 95.1 6.2 101.3

Ni 1 .8 0.1 0.0 0 0 0.0 1.4 88.9 92.4

Fe 0 .0 0.0 0.0 0 0 0.0 0.0 94.8 94.8

Pt 0 .0 0.0 0.0 0 0 0.0 0.1 95.7 95.8

Ti 0 .0 0.0 0.0 0 0 0.0 0.0 99.7 99.7

Table 1 shows Faraday efficiencies FE (in [%]) of products resulting from carbon dioxide reduction on various metal electrodes. The specified Values are valid for a 0.1 M

Potassium bicarbonate solution as electrolyte.

As can be seen from Table 1, the electrochemical reduction of CO2 on solid-state electrodes in aqueous electrolyte solutions offers a multitude of product possibilities.

Currently, the electrification of the chemical industry is discussed. This means that chemical precursors or fuels are preferably to be produced from CO2 and / or CO and / or H2O while supplying excess electrical energy, preferably from regenerative sources. In the introductory phase of such a technology, the aim is that the economic value of a substance is significantly greater than its calorific value or fuel value in order to achieve economic efficiency at an early stage.

In order to achieve acceptable conversion rates in the CC> 2 electrolysis, is preferably sufficient availability of CO2 to the catalytically active centers of the cathode sicherge ^¬ provides. At current densities above ~ 50mAcm ^{~ 2, however} , this supply via the solubility of CO2 in an electrolyte is difficult. Therefore, the CO 2 is provided di ^¬ rectly as a gas available at high current densities usually. Here, a so-called ^¬ three-phase zone is advantageous, in which the reaction gas CO2, the catalytically active electrode and the electrolyte are available. For this purpose, porous electrodes, so-called gas diffusion electrodes, can be used, which can be realized in various ways.

For example, they can be used as bonded with polymers elekt ^¬ driven conductive catalyst particles, for example, as ex- trudierter or calendered film be present, representing a

Full-catalyst gas diffusion electrode corresponds, or as a porous, catalytically inactive, but conductive electrode, eg in the form of carbon fiber gas diffusion layers impregnated with a small amount of active catalyst particles.

Alternatively, it is also possible to attach a catalyst to a solid electrolyte, which can also be used as a catalyst.

Coated membrane can be called. Here, too, a three-phase zone between the catalyst, the Festelekt ^¬ rolyten and the CO2 can form. With corresponding structures electrochemical re ^¬ production of CO2 to chemically usable products is possible.

For example, US 2017/0037522 A1 discloses a process for producing formic acid in an electrochemical device.

In addition, acids in the anode compartment are also quite common, as for example in J. Shi, F. Shi, N. Song, J-X. Liu, X-K Yang, Y-J Jia, Z-W Xiao, P. Du Journal of Power Sources, 2014, 259, 50-53.

However, there is a need for a simple and effective electrolytic process for reducing CO2 using high current densities while avoiding the formation of CO2 at the anode, for example by protolysis of carbonate-containing electrolytes in aqueous electrolytes. Electrolysis cells in which the CO2 / O2 mixtures are formed at the anode are known, for example, from US 2016 0251755 A1 and US Pat. No. 9,481,939.

Summary of the invention

The inventors have made basic considerations of CO 2 electrolysis to solve the above problem, and have found that, contrary to previous expectations, at sufficiently high current densities, CO 2 is present in the presence of a liquid and / or dissolved acid at one of the casings. thodenraum facing membrane, which has a

Anion exchanger and / or anion transporter contains, for example, in a salt bridge space and / or in the anolyte, effectively CO ₂ can be converted to economically reusable products and the formation of hydrogen can be überra ^¬ sarily suppressed.

The results of these basic considerations for the electrolysis of CO ₂ , which form the basis of the present invention, are further elaborated below. The following explanations are valid for example for the above systems. A La ^¬ charge transport model for the CC basis of these considerations can be created> ₂ electrolysis, as follows:

1) Considerations for salt electrolytes

The cathodic reduction of CO2 to CO in the presence of water can be represented in the simplest approximation by the following equation, whereby analogous equations can also be given correspondingly in the production of hydrocarbons from CO2:

C0 ₂ + H ₂ O + 2e ^" -> CO + 2 OH ^" (1)

Since m is the 3-phase zone usually CO2 is available in excess (which may also be present in a substoichiometric amount, as one can assign the CO2 to any particular catalyst center), the formed OH ^~ ions can react with this to HC0 ₃ ^~ ion ,

OH ^" + C0 ₂ -> HCO3 (2)

It follows:

3C0 ₂ + H ₂ O + 2e ^" -> CO + 2 HC0 ₃ (1 in 2)

This reaction has far-reaching consequences for charge transport within the porous electrode. Since HCC> 3 ^~ unlike OH ^~ is not capable of charge transport through the Grotthuss mechanism, its molar Leitfä ^¬ ability is lower by a multiple.

It should also be noted that the solubility of alkali metal hydrogen carbonate MHCO ₃ (M = Li, Na, K, Rb, Cs) is lower than that of the hydroxides of the alkali metals, which can lead to unwanted crystallization of salts faster.

In CC> 2 electrolysis, however, solutions of alkali metal salts are frequently used as electrolytes. The molar conductivity of HCC> 3 ^~ is only about half that of the alkali metal ions (M ⁺ in the following), which is why in a region of the electrode in which both the M ⁺ ions of the electrolyte and those on the cathode generated HCC> 3 ^~ ions are present, is ge ^¬ carry the bulk of the charge transport of the M ⁺ ions.

Because of their low conductivity, the cathodically produced HCC> 3 ^~ ions occur in this case not from the electrode into the electrolyte. Instead penetrate the more mobile M ⁺ ions in the electrode and form with the HCC> 3 ^~ ion a salt. This salt can then emerge as a solution or permeate at the side of the electrode facing away from the electrolyte. However, is not an efficient dissipation of MHCO ₃ Lö ^¬ sung respected, it can also lead to crystallization of these salts.

Over a longer period of time, this phenomenon leads to an increasing penetration of the electrode with the electrolyte solution. As a result, pores can be irreversibly flooded, which can lead to the collapse of the CO2 supply to the electrode and thus to its failure.

2) Considerations for solid electrolytes _η

Solid electrolytes are in electrolysis cells, for example, membranes from polymers modified with charged functionalities. In particular, the applicability of anion exchange membranes (AEM) for CO2 electrolysis is known from the literature, for example from US 2016 0251755 AI, US 9481939 and US

2017/0037522 AI.

In an AEM the cationic functional groups are stationary. In the absence of other ions of charge trans ^¬ port can only be done by HCC> 3 ^~ ions in this case therefore usually. However, this method can in particular be applied only when the anode is being ^¬ connected directly to the membrane.

The supply of HCC> 3 ^~ ions to the anode, however, is not desirable because there the bound CO2 is released by neutralization again. H ₂ 0 - 2e ^" -> 2 H ⁺ + H 0 ₂

HCO3 ^" + H ⁺ -> H ₂ 0 + C0 ₂

It mixes with the formed at the anode Sau ^¬ erstoff, and there is a hard aufarbeitbares or Near-to useless CO2 / O2 mixture having a CC> 2 content of up to 80 mol%. As a result, up to 67 mol% of the inserted CC> 2 can be lost unused for the CO case.

As described above, the considerations made above also apply in a similar way to other products of CO 2 Redukti ^¬ on. In the case of products derived from CO2 by reduction with more than two electrons, for example, the proportion of CC> 2 used, which is converted into bicarbonate, correspondingly higher. For example, for methane:

9 C0 ₂ + 8e- + 6 H ₂ 0 - »CH ₄ + 8 HC0 ₃ ^"

14 C0 ₂ + 12 e- + 8 H ₂ 0 -> C ₂ H ₄ + 12 HC0 ₃ ^" In this case, for example, up to 89 mol% in the case of CH ₄ or 86 mol% in the case of C2H _{4 of} the CC> 2 used can be lost via the anode.

On the other hand, if a cathode AEM composite is to be coupled to an anodic half cell terminated against HCC> 3 ^~ , again an electrolyte is required. The aforementioned condition of the absence of other ions is then no longer present, and the charge transport is again carried by other ions than the HCC> 3 ^~ ions, for example ^{insbesonde ¬} re M ⁺ ions. Although the fixed cationic functional groups of the AEM can repel the M ⁺ ions, however, M ⁺ ions in the AEM with the HCC> 3 ^~ ions, a counter-ion available.

Therefore, an AEM may occur when, for example, the anionic portion is completely ^~ occupied by HCC> 3, while the occupied cationic see part partly by M ⁺ ion and partly by the kationi ^¬ rule functional groups of the polymer a formal double salt system exist, and in the interior becomes.

Thus, the penetration of M ⁺ in the presence of a salt ^¬ electrolyte, although limited by an AEM, but not completely prevented. Borversuchen at respective La ^¬ - as in Comparative Example 1 below - was observed crystallization of MHCO ₃ on the back electrode side (gas side). The phenomenon is all ^¬ recently greatly attenuated compared to a direct contact between the cathode and electrolyte. Although the proportion of HCC> 3 ^~ at La ^¬ charge transport can be significantly increased as compared to an operation without AEM, and can be determined, for example to -50 mol%, for example by gas chromatographic C02 ~ measurement, but is still limited. The reason for this is the low mobility of bicarbonate anions, as indicated above and from the following Table 2, which is available from Current Separations 18: 3 (1999), Conductance _n

Measurements, Part 1: Theory, Lou Coury, pp. 91-96.

Table 2: Charge mobility of different ions

Cation Λ ° ₊ (S-cm ² / mol) anion A ° _ (S-cm ² / mol)

H ⁺ 349, 6 OH ^" 199, 1

Li ⁺ 38.7 F ^~ 55, 4

Na ⁺ 50.10 Cl ^" 76, 35

K ⁺ 73.50 Br ^" 78.1

Rb ⁺ 77.8 l ^" 76.8

Cs ⁺ 77.2 N0 ₂ ^~ 71.8

Ag ⁺ 61, 9 N0 ₃ ^" 71.46

NH ₄ ⁺ 73.5 C10 ₃ ^" 64, 6

Ethyl ammonium 47.2 CIO4 ^" 67.3

Diethylammonium 42.0 I0 ₄ ^" 54.5

Triethylammonium 34.3 HCO3 ^" 44.5

Tetraethylammonium 32, 6H ₂ PO ₄ ^" 57

Tetra-n-butylammonium 19.5 HSO3 ^" 50

Dimethyl ammonium 51.8 HSO4 ^" 50

Trimethylammonium 47.2 HC2O4 ^" 40.2

Tetramethylammonium 44.9 HCOO ^" 54.6

Piperidinium 37.2 CH ₃ COO ^" 40.9

C ₆ H ₅ COO ^" 32, 4

Be ²⁺ 90

Mg ²⁺ 106, 0 C0 ₃ ^{2 "} 138.6

Ca ²⁺ 119, 0 HPO4 ^{2 "} 66

Sr ²⁺ 118, 9 S0 ₄ ^{2 "} 160, 0

Ba ²⁺ 127.2 C2O4 ^{2 "} 148.2

Fe ²⁺ 108.0

Cu ²⁺ 107.2 P0 ₄ ^{3 "} 207

Zn ²⁺ 105, 6 Fe (CN) ₆ ^{3 "} 302.7

Pb ²⁺ 142, 0

U0 ₂ ²⁺ 64 Fe (CN) ₆ ^{4 "} 442, 0

Al ³⁺ 183

Fe ³⁺ 204

La ³⁺ 209, 1

3) Considerations for acidic electrolytes:

The CO ₂ electrolysis in aqueous electrolytes might not be thermodynamically possible, since the decomposition voltage for the reaction

C0 ₂ -> CO + 0 ₂ 1.32V (3) is higher for the reaction:

H ₂ 0 -> H ₂ + ^ 0 ₂ 1.23V (4)

Nevertheless, the process is possible under suitable conditions because, on the one hand, suitable catalysts have a high overpotential for water decomposition, and on the other hand, at higher current densities, high local pH values can typically form in the immediate vicinity of the electrode. For the latter effect, a diffusion gradient is usually required, in which the OH ^~ 'CC> 3 ^{2 ~} and HCC> 3 ^~ ions formed at the electrode displace the counterions of M ⁺ ions from the electrolyte. In addition, the M ⁺ concentration in the immediate vicinity of the electrode should be increased by attraction of the M ⁺ ions by the electric field. As a result, the water reduction potential can drop, which suppresses the hydrogen evolution. In contrast, the initial step of CO ₂ reduction is not pH dependent, which makes it more dominant. However, if acids are added to the electrolyte, this gradient can not develop in sufficient strength. In acidified electrolytes, therefore, usually only H ₂ / CO mixtures with large H ₂ ~ excess are obtained. In pure acid electrolytes the CO ₂ reduction usually takes place only in the trace range. However, it should be mentioned at this point that the previously described passage of electrolytes through the electrode can not be observed when using pure acid electrolytes, as is also apparent from the following Comparative Example 2. The passage of electrolytes is therefore as before ^¬ discussed by the penetration of cations in the

Caused electrode. Since no cations are pre ^¬ sent in the present Comparative Example 2 as well as in the present embodiment, as described in further detail below, fin det no electrolyte passage instead of more. The previously dis ^¬ cussed models can thus be confirmed.

4) Considerations for a combination of an AEM and pure acid electrolyte

An entirely different situation arises when an AEM is introduced between a pure acid electrolyte (eg H ₂ SO ₄ , as in the embodiment 1). In this case, for example, very good selectivities for CO> 95% can also be achieved in a pure acid electrolyte at high current densities> 100 mAcm ^-2 .

The reason for this lies in a peculiarity of the carbonate acid-base system. Unlike other systems, such as the sulfate system exists in the carbonate equilibrium no neut ^¬ rale acid.

CO3 ^{2 ""} ^■ HCO3 ^"" ^■ C0 ₂ + H ₂ 0 S0 ₄ ^{2 ""} ^■ HSO4 ^"" ^■ H2SO4

Consequently, HCC can> 3 ^~ No act as counter-ion for the single in the electrolyte cations "H ^+". A double salt situation like with alkali metal salt electrolytes therefore can not exist. A presence of "H ^+" ions in the AEM is therefore only possible if the acid anions (eg SC> 4 ^{2 ~} ) of the electrolyte are present in the AEM. Are they produced by a sufficiently high ion current from the AEM? In spite of an acid electrolyte, a high pH can be established in the cathode AEM composite. The only other charge transport pathway is the conduction of OH ^~ via the Grotthuß mechanism by the membrane swollen in H ₂ O, or a hopping transport of HCC> 3 ^~ from localized polymer-bound cation to localized cation.

Since, as already explained, initially the acid anions have to be displaced from the AEM, a minimum current density is required to exploit this effect. In the following embodiment, this was about 50mAcm ^{~ 2} ; below this current density almost exclusively H ₂ evolution was observed. At higher current densities, the selectivity for CO was> 90% and increased steadily with increasing current density, as shown below in the embodiment.

Figures 1 and 2 illustrate this difference in the use of different electrolytes 1, which abut the anion exchange membrane AEM, and which pass as ions to the cathode K. 1 shows the variant of this is with a salt M ⁺ X ^~ shown as the electrolyte 1 by way of example, while shown as Elect ^¬ rolyt 1 ^¬ against the variant in Figure 2 with an acid H ⁺ X ^~. According to a first aspect, the present invention relates to a method for the electrolysis of CO _2, wherein an electrolyzer comprising ^¬ sezelle

a cathode compartment comprising a cathode;

a first ion exchange membrane containing a

Anion exchanger and / or Anionentransporter and which adjoins the cathode compartment, wherein the cathode directly contacts the first ion exchange membrane, wherein the contact according to certain embodiments is also ionic in nature;

an anode compartment comprising an anode;

a first separator membrane; and a salt bridge space, wherein the salt bridge space is arranged between the first ion exchange membrane and the first separator membrane,

is used,

wherein CO _{2 is} reduced at the cathode, wherein the electrolyte in the salt bridge space consists of a liquid acid and / or a solution of an acid.

In addition, in another aspect, the present invention relates to a process for the electrolysis of CO ₂ , comprising an electrolytic cell

a cathode compartment comprising a cathode;

a first ion exchange membrane containing a

Anion exchanger and / or Anionentransporter and which adjoins the cathode compartment, wherein the cathode directly contacts the first ion exchange membrane, wherein the contact according to certain embodiments is also ionic in nature; and

an anode compartment comprising an anode, the anode compartment adjoining the first ion exchange membrane;

is used,

wherein CO _{2 is} reduced at the cathode, wherein the electrolyte in the anode compartment consists of a liquid acid and / or a solution of an acid.

In addition, there is disclosed an electrolytic cell comprising a cathode compartment including a cathode;

a first ion exchange membrane containing a

Anionenaustauscher and / or Anionentransporter contains and which adjoins the cathode compartment, wherein the cathode directly contacts the first ion exchange membrane;

an anode compartment comprising an anode; and

a diaphragm adjacent to the anode compartment;

further comprising a salt bridge space, wherein the salt bridge space between the first ion exchange membrane and the

Diaphragm is arranged, wherein the diaphragm is not ion-conductive. Furthermore, an electrolysis system, which comprises OF INVENTION ^¬ dung modern electrolytic cell and the use of OF INVENTION ^¬ to the invention electrolysis cell or electrolysis system according to the invention for the electrolysis of CO2 disclosed.

Further aspects of the present invention can be found in the dependent claims and the detailed description. Description of the figures

The accompanying drawings are intended to illustrate embodiments of the present invention and to provide a further understanding thereof. In the context of the description, they serve to explain concepts and principles of the invention. Other embodiments and many of the stated advantages will become apparent with reference to the drawings. The elements of the drawings are not necessarily to measure ^¬ scale shown to each other. Identical, functionally identical and identically acting elements, features and components are in the figures of the drawings, unless otherwise stated, each provided with the same reference numerals.

FIGS. 1 and 2 show a graphic representation of the cathodic half-cell of the previously described transport models of ions of salts and acids in an AEM, which is applied to a cathode.

Figure 3 shows schematically an example of a Elektrolyseanla- ge with an electrolytic cell as it is used in a erfindungsge ^¬ MAESSEN method of application.

FIGS. 4 and 5 schematically show further examples of electrolysis cells with which the method according to the invention can be carried out.

FIGS. 6 and 7 schematically show a graphical representation of the different CC> 2 release in a a salt electrolyte (Figure 6) and an acid electrolyte (Figure 7).

FIG. 8 shows schematically an electrolysis plant according to the invention with an AEM diaphragm cell according to the invention in which the process according to the invention can be carried out.

FIG. 9 shows a schematic representation of an AEM bipolar double-membrane cell in which the method according to the invention can likewise be carried out.

Figure 10 schematically shows the experimental setup in fiction, modern ^¬ Example 1. The figure 11 are experimental results of the invention

Example 1, where there is a plot of Faraday efficiency against the applied current density.

Figure 12 schematically shows the experimental setup in the present Comparative Example 1, and 13, the thus obtained test results ^¬, again a plot of the Faraday efficiency is against the applied current density.

In Figure 14, the experimental results of Example 1 (solid lines) to those of the comparative example ^¬ game according to the invention are 1 (dotted lines) juxtaposed for comparison.

Figure 15 shows a schematic representation of the Versuchsauf ^¬ construction in Comparative Example 2, and Figure 16, the thus erhalte- NEN experimental results, again a plot of the Faraday efficiency is against the applied current density.

In Figure 17, the experimental results of Example 1 of the invention (solid lines) are those of the comparative example ^¬ Game 2 (dotted lines) juxtaposed for comparison. In addition, in Figure 18, a comparison of Comparative Example 2 (solid; w / o AEM) and Example 1 (ge ^¬ dashed lines; w / AEM) shown at a current density of 150 mAcm ^-2 he preserved ^¬ gas chromatograms.

FIGS. 19 and 20 each schematically show the experimental setup in Reference Examples 1 and 2, and FIGS. 21 and 22 show the experimental results obtained therein. Detailed description of the invention

definitions

Thus, unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

Gas diffusion electrodes (GDE) in general are electrodes in which liquid, solid and gaseous phases are present, and where in particular a conductive catalyst catalyses an electrochemical reaction between the liquid and the gaseous phase. The embodiments may be of different nature, for example as a porous "solid material catalyst", possibly with auxiliary ^¬ layers to adjust the hydrophobicity, in which case, for example, a membrane GDE composite, eg AEM GDE composite may be prepared, as a conductive porous support having in which a catalyst can be applied in a thin layer, in which case again a membrane-GDE composite, eg AEM-GDE composite, can be produced, or as a composite porous catalyst, optionally with an additive directly on a membrane, eg AEM, can be applied and then form a CCM in the composite.

In the context of the present invention, hydrophobic is understood as meaning water-repellent. Hydrophobic pores and / or channels According to the invention, therefore, those which reject water. In particular, hydrophobic properties are associated according to the invention with substances or molecules with nonpolar groups. In contrast, hydrophilic is understood as the ability to interact with water and other polar substances.

In the application, quantities are by weight. %, unless otherwise stated or obvious from the context.

The normal pressure is 101325 Pa = 1.01325 bar. Electro-osmosis:

Under electro-osmosis is meant an electrodynamic Phenom ^¬ nouns, in which, on the particles in solution with a positive zeta potential, a force towards the cathode and on all of the particles with a negative zeta potential, a force acts to the anode. If a conversion takes place at the electrodes, ie a galvanic current flows, then also a stream of the particles with positive Zeta potential comes to the cathode, independently of whether the species participates in the conversion or not. The same applies to a negative zeta potential and the anode. If the cathode is porous, the medium is also pumped through the electrode. It is also known as an electro-osmotic pump.

The material flows caused by electro-osmosis can also flow in opposite directions to concentration gradients. Diffusion induced currents that the concentration gradient ausglei ^¬ chen can thereby be compensated.

According to a first aspect, the present invention relates to a method for the electrolysis of CO _2, wherein an electrolyzer comprising ^¬ sezelle

a cathode compartment comprising a cathode; a first ion exchange membrane containing a

an anode compartment comprising an anode;

a first separator membrane; and

a salt bridge space, wherein the salt bridge space is arranged between the first ion exchange membrane and the first separator membrane,

is used,

wherein CO ₂ is reduced at the cathode, wherein the Salzbrü ^¬ ckenraum comprises a liquid acid and / or dissolved acid. According to certain embodiments, the electrolyte in the salt bridge space consists of the liquid acid and / or the solution of an acid, for example solid or gaseous acid, for example in water, for example double-distilled or demineralized water.

In a second aspect, the present invention relates to a process for the electrolysis of CO ₂ , comprising an electrolyte cell

a cathode compartment comprising a cathode;

a first ion exchange membrane containing a

Anionenaustauscher and / or Anionentransporter contains and which adjoins the cathode compartment, wherein the cathode directly contacts the first ion exchange membrane; and

an anode compartment comprising an anode, wherein the anode compartment adjoins the first ion exchange membrane;

is used,

wherein CO _{2 is} reduced at the cathode, wherein the anode compartment comprises a liquid and / or dissolved acid. According limited hours ^¬ th embodiments, the electrolyte in the anode chamber from the liquid acid and / or the solution of a - for example, solid or gaseous - acid, for example in water, for example double-distilled or deionized water.

In order to illustrate in advance the inventive similarities and the differences of the methods according to the invention, these will be clarified in advance by means of figures, wherein the Methods are not limited to the embodiments shown in these figures. The individual components of the cells used in the method according to the invention as well as the cell according to the invention in which the method according to the invention can be carried out are then disclosed in detail below.

Exemplary different operating modes of a double-membrane cell and single-membrane cell, with which the inventive method can be carried out are shown in Figures 3 to 5 - in Figure 3, also in conjunction with other components of an electrolysis, also in view of inventive method. In the figures, for example ^¬ way is considered a CC> ₂ reduction to CO. Basically, the process is not limited to this reaction son ^¬ countries can for any other products, such Kohlenwas ^¬ bons, etc., preferably gaseous and / or liquid, ver ^¬ applies to. Fig. 3 shows an example of a 2 membrane assembly for CO ₂ - electric reduction with an acidic anode reaction. Here, in each case the cathode K in the cathode space I and the anode A in the anode space III is provided, between these spaces a salt bridge space II is formed, which is separated from the cathode space I by a first ion exchange membrane, here as AEM, and the anode space III by a first separator. Membrane, here as CEM, for example as a cation and / or proton exchange membrane is separated. To ^¬ went from catholyte k to supply the cathode with a substrate, such as H ₂ 0 gesättiges, gaseous CO _2, electrolyte s in the salt bridge chamber comprising liquid and / or dissolved acid, coupling the half-cells together, and anolyte A are also shown for the supply the anode with substrate, for example HCl and / or H ₂ O, as well as a return R of CO ₂ . The other symbols in FIG. 3 as well as the analogous figures 8, 9, 10, 12, 15, 19 and 20 are common fluidic symbols. In contrast to the use of a salt salt-neutral to weakly basic salt electrolyte, cathodically generated HCC> 3 ^~ can be neutralized at the interface between the anion exchange membrane (AEM) and the salt bridge electrolyte by the present method according to the first aspect , This can prevent that HCC> 3 ^~ can move to the anode and is then lost as unbrauch ^¬ bares CO ₂ / O ₂ mixture. It will thus be according ^¬ voted embodiments salt bridge space nearly pure CO ₂ with only minimal traces of cathodic products freige ^¬ sets that can be directly supplied to the cathode compartment I again.

Figures 4 and 5 show in addition, other structures of an electrolytic cell such as may be used in a method according to the two ^¬ th aspect of the present invention. In the two-chamber design no salt bridge space is provided, so that the anode space III connects directly to the AEM, in which case the anode, as shown in Figures 4 and 5, may be located at any point in the anode compartment III. Corresponding embodiments of the anode space are as shown in Figure 3 is possible in a method with a structure, that is where the anode A is not located on the CEM on ^¬. The electrolytic cell shown in Figures 4 and 5 may also be used in the embodiment shown in Figure 3 Elektrolyseanla ^¬ ge. Also, the various half-cells of Figures 3 to 5, as well as the corresponding arranged components of the electrolysis system, can be combined as desired, as well as with other (not shown) Elektrolysehalbzellen. As can be seen from FIGS. 3 to 5, the methods according to the invention are distinguished by the fact that the cathode K contacts the first ion exchange membrane, which contains an anion exchanger and / or anion transporter, directly, in particular also ionically. In addition, the space adjoining the first ion exchange membrane-either the salt bridge space II in FIG. 3 or the anode space III in FIGS. 4 and 5-contains a liquid and / or dissolved acid. .

The processes according to the invention are distinguished, in particular, by the use of a liquid and / or dissolved acid in the salt bridge space or in the anode space, especially in comparison to strongly acidic ion exchanger packages or similar solid devices:

First of all, gas bubbles produced in the salt bridge space or anode space can be transported away unhindered by the fluid through the medium, which enables a simple mode of operation. In addition, higher flow rates can be selected to ensure better cooling of the system. In addition, of course, even with the use of liquid and / or dissolved acids a simple and inexpensive operation is possible, especially in comparison to ion exchangers. Furthermore, with the use of liquid and / or dissolved acids, an accumulation of metal impurities in parts of the electrolysis cell can be prevented by washing them out with the liquid and / or dissolved acid. Accordingly, an external electrolyte treatment, eg with a cation exchanger, is also possible below. In particular, this represents a major difference to US 2017/0037522 A1, which discloses an empty or ion-exchanged middle chamber. The salt bridge space in the method of the first aspect or the anode compartment in the method of the second aspect are not particularly limited insofar as they connect respectively to the first Io ^¬ nenaustauschermembran. The term salt bridge space is used here in terms of its function to act as a bridge between the anode assembly and cathode assembly and thereby have cations and anions, which, however, do not have to form salts in the present case. Since in the present case a liquid or dissolved acid is present in the salt bridge space, this could also be called an acid bridge space or ion bridge space. However, since this term is not familiar, the space is according to the invention as a salt bridge space be ^¬ draws, even if in the classic sense, no salt must be present. In the salt bridge space, if present, there is an electrolyte in the process according to the invention which can ensure the electrolytic ionic bond between the cathode arrangement and the anode arrangement. This electrolyte is also referred to as salt bridge and has a liquid and / or gelös ^¬ te acid.

The salt bridge thus serves as an electrolyte, preferably with high ionic conductivity, and serves to establish the contact between anode and cathode. According to certain ^embodiments , the salt bridge also enables the dissipation of lost heat. In addition, the salt bridge can serve as the reaction medium for anodically and cathodically generated ions such as proton, hydroxide or hydrogen carbonate ions.

The technical teaching is the construction and the Be ^¬ drove the cathodic half-cell. This consists of a gas-permeable electrically connected catalyst layer, which is in direct contact with an AEM, on the opposite side, an acid-based electrolyte, preferably without Al ^¬ kalimetallkationen, in particular without metal cations, followed. The acid is not particularly limited insofar as it is present as a liquid and / or in solution, so that the acid can flow through the salt bridge space and / or the anode space. According to certain embodiments, the acid is water-soluble and / or is present as a solution in a suitable solvent such as water, alcohols, aldehydes, esters, carbonates, etc. and / or mixtures, in particular water, eg bidistilled or demineralized water.

In certain embodiments, an acid of the

Electrolytes in the salt bridge space a pK _s value of 6 or less, preferably 5 or less, more preferably 3 or less, even more preferably 1 or less, particularly preferably 0 or less, wherein preferably the liquid and / or dissolved acid is selected from dilute or un ^¬ diluted H ₂ SO ₄ , a solution of H ₂ N-SO ₂ -OH, dilute or undiluted HCIO ₄ , a solution of H ₃ PO ₄ , dilute or undiluted CF ₃ -COOH, dilute or undiluted CF ₃ - S O ₂ - OH, a solution of (CF ₃ - S O 2) 2 ^_NH , a solution of HF, dilute or undiluted HCOOH, dilute or undiluted CH ₃ -COOH, a solution of HCl, a solution of HBr, a solution of HI, and / or mixtures thereof.

The acid electrolyte is characterized in accordance with certain exporting ^¬ by the embodiments absence of mobile cations - such as hereinafter defined, in particular metal cations, au ^¬ SSER "H ^+" or "D ^+" of. In the following, instead of H ⁺ or D ^+, only H ⁺ or protons are used. Thus, the electrolyte preferably contains no cations other than mobile "H ^+", especially metal cations. In the inventive execution example sulfuric acid, in particular diluted pivot ^¬ ric acid (H2 _SO4) is used which, because of their low price and their high conductivity as Alternatively, other acids may also be used, as stated above, with strong acids having non-oxidizing anions being preferred, such as H ₂ N-SO ₂ -OH, HC 10 ₄ , H ₃ PO ₄ , CF ₃ -COOH, CF ₃ -SO ₂ -OH, (CF ₃ - SC> 2) 2-NH, etc. Even weak acids can, preferably in higher concentrations, for example greater than 10 wt.% Or 20 wt.%, Eg greater than 30% by weight, or at their respective maximum conductivity, for example HF, HCOOH, CH ₃ -COOH.

This is particularly preferred if this acid is identical to the cathodic product of the CO 2 electrolysis, for example in the case of formic acid or acetic acid. In particular, the acids may be present in a concentration up to 30 wt.%, Preferably to 50 wt.%, More preferably to 70 wt.%, And in particular ^¬ sondere to 100 wt.%, Are present. Also, especially with proven compatibility with the Elektrodenkataly ^¬ sators, other acids can be used, such as dissolved HCl, HBr, HI.

For the purposes of the invention, a salt electrolyte which is usually adjacent to the first ion exchange membrane is added. For example, in the salt bridge space or in the anode space, in particular replaced by an acid.

In the presence of a salt bridge space, the advantage of the CO2-free anode and the partial separation of the CO 2 surplus in the salt bridge space continue to exist, as shown schematically in FIGS. 6 and 7. In contrast to the use of a salt electrolyte 2 in the salt bridge space as shown in Figure 6, the release of the CO2 does not take place but at the interface between CEM and electrolyte, but, as shown in Fi ^¬ gur 7, at the interface between AEM and acid 3. In FIGS. 6 and 7, an acid is also present in the anode compartment. Since in the preferred embodiment shown both for the

Anolyte as well as for the salt bridge acids are used, it is also possible to select these with identical composition. Since no osmotic pressures occur in this case and the release of the CO2 S can take place in front of the salt bridge, in particular in the region of the first ion exchange membrane and thus away from the first separator membrane, if present, wherein the HCC> 3 ^~ the first separator membrane according to In certain embodiments, it is no longer absolutely necessary to use an ion-selective membrane as the first separator membrane, and, for example, a diaphragm can be used to separate CO2 and O2. Accordingly, a diaphragm is also possible as the first separator membrane, as further explained below, and consequently a corresponding electrolysis cell according to the invention, for example an AEM sensor, can also be used.

Diaphragm cell - as further explained below - be used in he ^¬ inventive method.

It should be noted that it is fundamentally possible to pump anolyte and salt bridge from a common reservoir, in which case it is preferable to ensure reliable degassing of the electrolyte so as not to entrain any gases. This is possible due to the low solubility of CO 2 in the especially acid-based electrolytes. According to certain embodiments, the processes according to the invention are therefore preferably carried out at elevated temperatures in the range of 50-120 ° C., preferably between 60-90 ° C., in order to further minimize gas solubility.

Corresponding considerations also apply analogously when a two-chamber structure according to the method of the second aspect verwen ^¬ det is used.

In the inventive method, the acid concentration is preferably selected such that it lies around the Leitfähigkeitsma ^¬ ximum the acid. In this case, the conductivity, in particular ^¬ sondere for sulfuric acid (3 mol / 1 = ~ 30%) to be almost an order of large ^¬ ßenordnung higher than that obtained by similarly high, but lying on the saturation limit salt concentrations (1 - 2 mol / 1) can be achieved. Exemplary Conductive ^¬ possibilities are shown in Tables 3 and 4 for sulfuric acid and phos phoric acid ^¬.

Table 3: Electrical conductivity of sulfuric acid (and oleum) at 25 ° C (from Conductometry - Conductivity measurement, Peter Bruttel, revised by Dr. Christine Thielen, Dr. Anja Zimmer, Metrohm AG, Switzerland, page 37)

Conductivity% H ₂ S0 ₄ (S0 ₃ ) Conductivity [mS / cm]

H ₂ so ₄ [mS / cm]

3, 93 177 53.5 555

7.00 308 58.4 471

10.0 426 63, 1 380

14.6 586 72.3 223

19.8 717 85.9 124

25.3 796 95, 4 124

29.4 825 98, 0 94, 7

34.3 819 100.0 10.46

39.1 781 101.5 32, 05

43.9 714 103, 8 34.50

48.7 640 105, 1 28.84 M (H ₂ SO ₄ ) = 98, 07 g / mol

M (SO ₃ ) = 80, 06 g / mol

Table 4: Electrical conductivity of phosphoric acid at 25 ° C (from conductometry - conductivity measurement, Peter

Bruttel, revised by Dr. med. Christine Thielen, dr. Anja Zimmer, Metrohm AG, Switzerland, page 37)

M (H ₃ PO ₄ ) = 97, 995 g / mol The individual constituents of an electrolytic cell used in the process according to the invention as well as of the electrolysis cell according to the invention will now be further described and disclosed. The cathode space, the anode space and the possibly existing salt bridge space according to the invention in the methods as well as in the electrolysis cell according to the invention discussed below are not particularly limited in terms of shape, Ma ^¬ material, dimensions, etc., insofar as they the cathode, the anode and the receive first ion exchange membrane and possibly the first separator membrane. The two or three spaces may be, for example, within a common cell ge ^¬ forms, in which case they can be accordingly separated by the first Ionenaustau ^¬ exchange membrane and possibly correspond the first separator membrane. For the individual rooms in this case may be provided corresponding to ^¬ guiding and outlet devices for reactants and products, for example in the form of liquid, gas, solution, suspension, etc. to be carried out depending on the electrolysis, which possibly also each rückge- can be led. Again, there is no limitation, and the individual rooms can be flowed through in parallel streams or in countercurrent. % Said still further CO contained th may, thus for example at least 20 volume CO ₂ contains - - For example, in an electrolysis of CO _2. This to the cathode in solution, as a gas, etc. fed ^¬ the - for example, in countercurrent to an electrolyte flow in the salt bridge space in the three-chamber design or in the anode chamber in a two-chamber design (without first separator membrane). There is no restriction here. Corresponding Zuführmog ^¬ possibilities exist also in the anode compartment and will be explained in more detail below. The respective supply can be provided both continuously and discontinuously, for example pulsed, etc., for which pumps, valves, etc. can be provided in an electrolysis plant according to the invention, as well as cooling and / or heating devices, in order to correspondingly desired reactions to catalyze the anode and / or cathode. The materials of the respective rooms or the electrolysis cell and / or the other constituents of the electrolysis plant can also be appropriately adapted to desired reactions, reactants, products, electrolytes, etc. In addition, of course, at least one power source per electrolytic cell is included. Other device parts which occur in electrolysis cells or electrolysis systems can also be provided in the electrolysis plant or electrolysis cell according to the invention. According to certain embodiments, a stack comprising 2 - 1000, preferably 2 - 200 cells, and whose operating voltage is preferably in the range of 3 - 1500 V, particularly preferably 200 - 600 V, is constructed from these individual cells.

According to certain embodiments, a reactant gas formed in the salt bridge space, for example CO ₂ , which may also contain H ₂ and / or CO, is recycled again in the direction of the cathode space. The cathode according to the invention is not particularly limited and may be adapted to a desired half-reaction in ^¬ play with respect to the reaction products, in that they contact with the first ion exchange membrane directly, at least one location is so with the first ion exchange membrane directly in contact, preferably the cathode in Essentially flat with the first ion exchange membrane is in direct contact. Thus, the cathode is adjacent at ^¬ least in a region directly to the first ion exchange membrane to. For example, a cathode such as Cu, Ag, Au, Zn, Pb, Sn, Bi, Pt, Pd, Ir, Os, Fe, Ni, Co, W, Mo, etc. may be a cathode for reducing CO ₂ and possibly CO. , or mixtures and / or alloys thereof, preferably Cu, Ag, Au, Zn, Pb, Sn, or mixtures and / or alloys thereof, and / or a salt thereof, wherein suitable materials can be adapted to a desired product. The catalyst can thus be selected depending on the desired product. In the case of reduction of CO ₂ to CO, for example the Katalysa ^¬ tor is preferably based on Ag, Au, Zn and / or their compounds such as Ag ₂ T, AgO, AU ₂ O, Au ₂ O _3, ZnO. For the preparation of hydrocarbons Cu or Cu-containing compounds such as CU ₂ O, CuO and / or copper-containing mixed oxides with other metals, etc., are preferred. For preparation of formic acid are in ^¬ game as catalysts based on Pb and / or Cu, in particular Cu possible. Since the formation of hydrogen at high current densities can be completely ^suppressed by the anion transport, it is also possible to use catalysts for CO ₂ reduction which do not have a high overvoltage to hydrogen, for example reduction catalysts such as Pt, Pd, Ir, Os or carbonyl-forming metals such as Fe , Ni, Co, W, Mo. Thus, the mode of operation described in connection with cell design opens up new approaches in CO ₂ reduction chemistry, which do not depend on hydrogen overvoltage.

The cathode is the electrode on which takes place the reductive Halbreak ^¬ tion. It may be one or more parts and, for example, as a gas diffusion electrode, porous Electrode or directly with the AEM in the composite, etc. be ^{ausgebil ¬} det.

The following embodiments are here, for example mög ^¬ Lich:

- Gas diffusion electrode and porous bound Kataly ^¬ sator structure, in accordance with certain embodiments by means of a suitable ionomer, such as egg ^¬ nes anionic ionomer with the first Ionenaustau ^¬ exchange membrane, for example a

Anion exchange membrane (AEM), e.g. can be ion-conducting and / or mechanically bonded;

Gas diffusion electrode or porous bound Kataly ^¬ satorstruktur, which according to certain embodiments may be partially pressed into the first ion exchange membrane, for example an AEM;

porous, conductive, catalytically inactive structure, for example carbon paper GDL or carbon-paper-GDL (gas diffusion layer, gas diffusion layer), coal ^¬ fabric Cloth GDL or Carbon-Cloth-GDL, and / or polymer-bound film granular glassy carbon, which is impregnated with the catalyst of the cathode and optionally an ionomer, that the connection to the first ion exchange membrane, such as an AEM, enables ^¬, wherein the electrode then mechanically to the first ion exchange membrane, such as an AEM pressed or previously compressed with the first ion exchange membrane, for example an AEM, to form a composite; particulate catalyst, which is applied by means of a suitable ionomer to a suitable support, for example a porous conductive support, and according to certain embodiments can abut the first ion exchange membrane, for example an AEM;

- particulate catalyst which is pressed into the einge- the first ion exchange membrane, such as an AEM, or coated on it and is ^¬ play according conductively connected with, wherein this structure may then be pressed onto a conductive, porous electrode, for example as a so-called CCM (catalyst-catalyzed membrane), wherein a catalytic activity of this electrode is basically not required and, for example, carbon-based GDI / s or lattice, for example, titanium, wherein it is not excluded that this electrode contains ionomers and / or contains the active catalyst or consists thereof in large parts;

non-closed sheet, such as a net or an expanded metal, which consists for example of a catalyst or comprises this or is coated with this and according to certain embodiments ^¬ forms on the first ion exchange membrane, such as an AEM, is applied;

polymer-bound unsupported catalyst structure from particulate ^¬ kulärem catalyst containing an ionomer, which allows the attachment to the first ion exchange membrane, such as an AEM, contains or was subsequently impregnated therewith, the electrode then me ^¬ chanically to the first ion exchange membrane, for example an AEM, pressed or previously compressed with the first ion exchange membrane, for example an AEM, to form a composite; porous, conductive carrier impregnated with a suitable catalyst and optionally an ionomer and, according to certain embodiments, being attached to the first ion exchange membrane, for example an AEM;

non-ionic gas diffusion electrode which has been subsequently impregnated with a suitable ionomer, for example an anionic ionomer ionomer and, according to certain embodiments, is attached to the first ion exchange membrane, for example an AEM, or is connected thereto, eg via an ionomer. Also, various combinations of the electrode structures described above are possible as the cathode. The corresponding cathodes may in this case also contain materials customary in cathodes, such as binders, ionomers, for example anionic ionomers, fillers, hydrophilic additives, etc., which are not particularly limited. In addition to the catalyst, according to certain embodiments, therefore, the cathode may comprise at least one ionomer, for example an anion-conducting or anion-transporting ionomer (eg anion exchange resin, anion transport resin), which may for example comprise different ion exchange functional groups, which may be the same or different, for example tertiary amine groups, alkylammonium groups and / or phosphonium groups), a, for example, conductive, substrate (eg, a metal such as titanium), and / or at least one non-metal such as carbon, Si, boron nitride (BN), boron ^¬ doped diamond, etc., and / or at least one conductive oxide such as indium tin oxide (ITO), aluminum zinc oxide (AZO) or fluorinated tin oxide (FTO) - for example, as used to ^produce photoelectrodes, and / or at least one polymer based on polyacetylene,

Polyethoxythiophene, polyaniline or polypyrrole, such as in polymer-based electrodes; nonconductive supports such as e.g. Polymer nets are possible, for example, with sufficient conductivity of the catalyst layer), binders (e.g., hydrophilic and / or hydrophobic polymers, e.g., organic binders, e.g., selected from PTFE

(Polytetrafluoroethylene), PVDF (polyvinylidene difluoride), PFA

(Perfluoroalkoxy polymers), FEP (fluorinated ethylene-propylene copolymers), PFSA (perfluorosulfonic acid polymers), and mixtures thereof, in particular PTFE), conductive fillers (eg carbon), non-conductive fillers (eg glass) and / or hydrophilic additives (eg Al ₂ O _3, MVDC _2, hydrophilic Ma ^¬ terialien such as polysulfones, such as polyphenylsulfones, polyimides, polybenzoxazoles or polyether ketones, or generally in Elect ^¬ rolyten electrochemically stable polymers, polymerized "Io niche liquids ", and / or organic conductors such as

PEDOT: PSS or PANI (champrose sulfonic acid sorted

Polyaniline), which are not particularly limited.

The cathode, in particular in the form of a gas diffusion electric ^¬ de, for example connected to the first ion exchange membrane, or in the form of a CCM includes, in accordance with certain embodiments, ion-conducting components, in particular a anionenleitfähige component.

Other cathode shapes are possible, such as Katho ^¬ the bodies, as they are be ^¬ enrolled in US2016 0251755-A1 and US9481939.

Also, the anode according to the invention is not particularly limited and may be adapted to a desired half-reaction in ^¬ play with respect to the reaction products. At the anode, which is electrically connected to the cathode by means of a current source for the provision of the voltage for the electrolysis, the oxidation of a substance takes place in the anode space. In addition, the material of the anode is not special ^¬ limited and it depends primarily on the desired reaction from. Exemplary electrode materials include platinum or platinum alloys, palladium or palladium alloys and glassy carbon, iron, nickel, etc. More anode Mate ^¬ rials are also conductive oxides such as doped or

undoped Ti0 _2, indium tin oxide (ITO), fluorine-doped tin oxide ^¬ (FTO), aluminum-doped zinc oxide (AZO), iridium oxide, etc. If necessary, For example, these catalytically active compounds can also be superficially applied only in thin-film technology, for example on a titanium and / or carbon support. The anode catalyst is not particularly limited. As Ka ^¬ talysator for 0 ₂ - or Cl ₂ ~ generation for example, IrO get _x (1.5 <x <2) or ₂ Ru0 used. These can be supported (in the form of conductive carbon black, activated carbon, graphite, etc.) as well as a mixed oxide with other metals such as Ti0 _2, vorlie ^¬ gene, and / or on a conductive material such as C. Older- Alternatively, catalysts based on Fe-Ni or Co-Ni can also be used for the generation of C. For this purpose, for example, the structure described below with bipolar membrane or bipolar membrane is suitable.

The anode is the electrode at which the oxidative half reaction takes place. It can also be designed as a gas diffusion electrode, porous electrode or solid electrode or solid electrode, etc.

The following embodiments are possible:

Gas diffusion electrode or porous bound Kataly ^¬ satorstruktur, according to certain embodiments by means of a suitable ionomer, for example ei ^¬ cationic ionomer, with the first separator membrane, if present, for example, a cation exchange membrane (CEM) or a diaphragm, eg ion conducting and / or can be mechanically bonded; Gas diffusion electrode or porous bound Kataly ^¬ satorstruktur, which may be partially pressed into certain embodiments, partially in the first separator membrane, for example, a CEM or a diaphragm ^¬ ;

particulate catalyst, which is applied by means of a suitable ionomer to a suitable support, for example a porous conductive support, and according to certain embodiments, can abut the first separator membrane, for example a CEM or a diaphragm;

particulate catalyst which is pressed into the first separator membrane, for example a CEM or a diaphragm, and for example is connected in accordance with it lei ^¬ tend;

non-closed sheet, such as a net or an expanded metal, for example, consists of a catalyst or comprises this or is coated with this and according to certain embodiments ^¬ forms on the first separator membrane, such as a CEM or a diaphragm abuts; solid electrode, in which case also a gap between the first separator membrane, such as a CEM or a diaphragm, and the anode can best ^¬ hen, but this is not preferred;

- Porous, conductive carrier, with a suitable

Catalyst and possibly an ionomer is impregnated and according to certain embodiments of the first separator membrane, for example a CEM or a diaphragm abuts;

non-ionically conductive gas diffusion electrode which has been subsequently impregnated with a suitable ionomer, for example a cation-conducting ionomer, and according to certain embodiments bears against the first separator membrane, for example a CEM or a diaphragm

any variants of the discussed embodiments, wherein the electrode e.g. contains an anodically stable anionic conductive material and is applied directly to the anion-conducting layer of a bipolar membrane.

The anode may be attached to the acid electrolyte or directly on the first ion exchange membrane, e.g. AEM, for example in the form of a sheet (e.g., a fine mesh coated mesh), if no salt bridge space is present, but the latter is not preferred. Again, various combinations of different anode structures are possible. According to certain embodiments, the cathode is contacted via the liquid acid, for example in the salt bridge space or in the anode space, e.g. in the salt bridge space, coupled to the anodic half-cell.

The corresponding anodes can also contain materials customary in anodes such as binders, ionomers, for example cation-conducting ionomers, for example containing sulfonic acid and / or phosphonic acid groups, fillers, hydrophilic additives, etc., which are not particularly limited For example, also described above with respect to the cathodes.

In an electrolysis cell according to the invention as well as in the methods according to the invention, the electrodes mentioned above by way of example can be combined with one another as desired.

In addition, electrolytes may also be present in the anode space and / or cathode space, which are also referred to as anolyte or catholyte, but it is not excluded according to the invention that no electrolytes are present in the two spaces and correspondingly, for example, only ^gases for conversion into These are supplied, for example, only CO2, if necessary, as a mixture with, for example, CO and / or H2O, which may also be liquid, for example as an aerosol, but before ^¬ admits gaseous H2O to the cathode and / or water or HCl to the anode. According to certain embodiments, an anolyte is present, which extends from the salt bridge, so the electrolyte of the salt bridge chamber having a liquid and / or dissolved acid - etc. under failed ^¬ may or may correspond to this, for example in terms contained solvents, acids - as available If no salt bridge is present, the anolyte comprises a liquid and / or dissolved acid.

A catholyte in this case is the electrolyte flow around the cathode and, according to certain embodiments, serves to supply the cathode with substrate or educt. The following exporting ^¬ insurance forms are possible, for example. The catholyte may be, for example, as a solution of the substrate (C0 ₂₎ in a liquid Trä ^¬ gerphase (eg water) and / or as a mixture of the substrate with other gases (eg CO + CO2; steam + CO2) vorlie ^¬ gene also may be prepared by a. Return recycled Ga ^¬ se as CO and / or H2 may be present. Also, as described above, the substrate may be present as a pure phase, eg CO2.

Arise Kings ^¬ nen these are washed from the catholyte in responding uncharged liquid products and can also be separated in the presence circuit according optional. An anolyte is an electrolyte flow around the anode or at the anode and, according to certain embodiments, serves to supply the anode with substrate or starting material and, if appropriate, the removal of anode products. The following embodiments are possible, for example. The anolyte can be used as a solution of the substrate (eg hydrochloric acid = HCl _aq ) in a liquid carrier phase (eg water), optionally with conductive salts, which are not restricted - in particular when using a

Bipolar membrane as the first separator membrane, wherein the anolyte may also be basic here and may also contain cations, as described below, or as a mixture of the substrate with other gases (eg hydrochloric acid = HCl _g + H ₂ O, SO ₂ , etc.) available. As with the catholyte, however, the substrate can also be present as a pure phase, for example in the form of hydrogen chloride gas = HCl _g .

According to certain embodiments of the anode compartment comprises an anolyte that includes a liquid and / or dissolved acid, preferably wherein the anolyte and / or the acid salt ^¬ bridge space and the electrolyte in the salt bridge space no mobile cations other than protons and / or deuterons in particular no metal cations. According to certain embodiments, the acid in the salt bridge space does not comprise any mobile cations other than protons and / or deuterons, in particular no metal cations. According to certain embodiments, the anolyte does not comprise mobile cations except protons and / or deuterons, especially no metal cations. Mobile cations are here cations which are not bound by a chemical bond to a carrier, and / or in particular an ion mobility of more than

1 × 10 ^-8 m ² / (s-V), in particular more than 1 × 10 ^-10 m ² / (s-V). According to certain embodiments, in the anodic half-reaction no mobile cations other than "D ⁺ , H ⁺ ", in particular no metal cations, are released or ^generated, In such a case, for example, for the special case of O ₂ evolution at the anode Water (especially in the case CCM anode) or acids with not oxidizable anions as anolyte or reagent in question. For halogen generation at the anode are suitable in particular for this case, the halogen-hydrogen acids HCl, HBr or HI, wherein halide salts may not be suitable when using a diaphragm as a first separator membrane, but when using a bipolar membrane as first separator membrane can be used. Also, the use of SO2 in the anolyte for the preparation of Schwefelsäu ^¬ acid, or for the production of H2O H2O2, etc., is possible.

According to certain embodiments, the anolyte is an aqueous electrolyte, it being possible if appropriate for the corresponding anolyte to be added to the anolyte, which are reacted at the anode. The educt addition is not particularly limited here.

Likewise, the educt addition in the supply to the cathode space is not limited. For example, CO2 can be added outside the cathode compartment to water, or can also be added through a gas diffusion electrode, or can be supplied only as a gas to the cathode compartment. Corresponding considerations are possible analogously for the anode compartment, depending on the starting material used, e.g. Water, HCl, etc., and desired product.

The first ion exchange membrane, which has a

Anion exchanger and / or anion transporter or a

Anionentransportmaterial contains and which is adjacent to the cathode ^¬ space, the invention is not particularly be ^¬ limits. It separates the cathode from the salt bridge space in the process of the first aspect as well as in the electrolysis cell according to the invention or in the process of the second aspect separates the cathode from the anode space, so that from the direction of the cathode space comprising CO2 in the direction of the electrolyte the order cathode / first Ionenaustauschermemb ^¬ ran / salt bridge space (first aspect) or cathode / first ion exchange membrane / anode space result. It contains in particular according to certain embodiments, an anion exchanger or consists of this, which in the currentless state in the form of an acid-anion salt, preferably according to the acid the salt bridge, is present, and more preferably passes from a minimum current density in the bicarbonate / carbonate form. According to certain embodiments, the first ion exchange membrane is an anion exchange membrane and / or anion transporter membrane. According to certain embodiments, the first ion exchange membrane may be a hydrophobic one

Have layer, for example, on the cathode side for better gas contacting. Preferably, the

Anion exchange membrane and / anion-transporter membrane also as cationic (though for example trace), especially proton, blocker. Specially an anion exchanger and / or

Anion transporter with tightly bound cations can constitute a blockade for mobile cations due to Coulomb repulsion, which can additionally counteract salt precipitation, in particular within the cathode. The reason for this is probably the formation of

Hydrogencarbonationen during the electrolysis and the resulting formation of bicarbonate salts from the transported through the membrane cations, if they are present. Without liquid electrolyte or sufficient active anion transport, these or their salts can usually not be removed.

Particularly in the case of a membrane electrode assembly (MEA), the accumulation of the electrolyte cations in the region of the interface is usually due to the electroosmosis. In this case, a concentration gradient can not simply be broken down on the electrode side, since a catalyst-based cathode, which is designed as described above, eg a gas diffusion electrode or a CCM, usually has only a very poor anion conductivity. Through the In ^¬ tegration anions conductive components, the anion conductivity can be improved significantly here. In the process described here, the electrolyte contains only protons. These are such as metal cations also contemplated by the electric field towards the cathode, but they will contact Kgs ^¬ NEN / hydrocarbonate not as such by the AEM in the carbo ^¬ nat because they contain therein with the Hydrogen carbonate ions abreact. The fundamental difference to the use of salt electrolytes is that charge transport at the AEM electrolyte boundary does not take place by migration of one charge carrier, but rather by destruction of two oppositely charged charge carriers.

To improve the operational stability, ion transporters, in particular anion transport resins, can be used as binder material or additive in the electrode itself

and / or can be reduced in an anion exchange layer, which lies against the cathode in order to derive, for example, resulting OH ^~ ions quickly or partially buffering, so that the Re ^¬ action with CO ₂ and the associated formation of hydrogen- carbonates or

Aniontransfer resins HCC> 3 ^~ conduct self. In principle, an anion transport can be carried out by anion exchangers. Furthermore, especially an integrated anion exchanger again provides a blockade for cations, eg also

Metallkationspuren, which can additionally counteract salt precipitation and contamination of the electrode. In the case of protons, hydrogen formation can be suppressed.

The first ion exchange membrane, for example from the cathode side adjacent to the salt bridge in the process of the first aspect, can thus contain, for example, an anion exchanger and / or anion and / or anion transporter in the form of an anion exchanger and / or transporter layer, in which case further layers such as hydrophobic layers Improvement of contact with a gas, such as CO ₂ , may be included. According to certain embodiments, the first ion exchange membrane is an anion exchange membrane and / or

Anionentransportermembran, so for example an ion-conductive membrane (or in a broader sense, a membrane with an anion exchange layer and / or

Anionentransportschicht) with positively charged Funktionalsie ^¬ of the pump which is not particularly limited. A Favor ^¬ ter charge transport takes place in the anion exchange and / or Anionentransporterschicht or a

Anionenaustauschermenbran and / or Anionentransportermembran held by anions. In particular, the first Ionenaus ^¬ exchange membrane and in particular serves

Anionenaustauscherschicht and / or Anionentransporterschicht or an anion exchange membrane and / or

Anion transporter membrane for providing a

Anion transport along fixed fixed positive charges. In particular, the penetration of an electrolyte, for example proton-containing electrolyte, into the cathode promoted by electro-osmotic forces can be reduced or completely avoided. The ion exchanger contained in the membrane can, according to certain embodiments, be converted in particular into the carbonate / bicarbonate form during operation and thereby suppress the passage of protons through the membrane to the cathode.

A suitable first ion exchange membrane, for example anion exchange membrane and / or anion transporter membrane, exhibits good performance according to certain embodiments

Wettability by means of water and / or acids, in particular aqueous acids, a high ionic conductivity, and / or a tolerance of the functional groups contained therein to high pH values, in particular, shows no Hoffmann elimination. An exemplary AEM according to the present invention is the A201-CE membrane marketed by Tokuyama, the "Sustainion" marketed by Dioxide Materials, or an anion exchange membrane sold by Fumatech, such as Fumasep FAS-PET or Fumasep FAD-PET.

Moreover, the first separator membrane is not particularly limited if it is present, that is, for example, in the method according to the first aspect of the present invention. According to certain embodiments, the first separator membrane (as viewed from the anode side adjacent to the Salzbrü ^¬ CKE) is selected from an ion exchange membrane which contains a cation exchanger, a bipolar membrane, WO is at at the bipolar membrane is preferably the cation layer toward the cathode and oriented towards the anions lei ^¬ tend layer towards the anode, and a diaphragm. A suitable first separator membrane, for example a cation exchange membrane or a bipolar membrane, contains, for example, a cation exchanger which can be in contact with the electrolyte in the salt bridge space. It may, for example, contain a cation exchanger in the form of a cation exchange layer, in which case further layers, such as hydrophobicizing layers, may be contained. It may also be designed as a bipolar membrane or as a cation exchange membrane (CEM). The cation exchange membrane or cation exchange layer is, for example, an ion-conductive membrane or ion-conducting layer with negatively charged functionalizations. An exemplary charge transport into the salt bridge takes place in such a first separator membrane by cations. For example, commercially available Nafion® membranes are suitable as CEM, or the product marketed by Fumatech fumapem-F membranes vertiebene Aciplex by Asahi Kasei, or Vertrie AGC ^¬ surrounded Flemionmembranen. In principle, however, other with strongly acidic groups (groups such as sulfonic acid,

Phosphonic acid) modified polymer membranes are used. According to certain embodiments, the first separator membrane prevents the passage of anions, in particular HCC> 3 ^~ , into the anode space.

In addition, in the present process as in of the inventive electrolytic cell the first separator membrane, rendering the cell less com plex ^¬ and can be made cheaper may be formed as a diaphragm. According to certain embodiments, the diaphragm essentially separates the anode space and the salt bridge space, for example more than 70%, 80% or 90%, based on the interface between anode space and salt bridge space, or separates the anode space and the salt bridge space, that is to say 100%, based on the interface between anode compartment and salt bridge space. In particular can be prevented by the use of liquid acid in the salt bridge space that HCC> 3 ^~ ions reach the anode compartment. In this respect, it is thus possible to dispense with a cation exchanger layer in the first separator membrane. The slide is phragma this is not particularly limited and may for example ^¬ game based on a ceramic (eg ZrÜ ₂ or ₃ Zr (PC> 4) 3) and / or a swellable functionalized polymer, such as PTFE, to be. Also binders (eg hydrophilic and / or hydrophobic polymers, eg organic binders, eg selected from PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PFA

(Perfluoroalkoxy polymers), FEP (fluorinated ethylene-propylene copolymers), PFSA (perfluorosulfonic acid polymers), and mixtures thereof, in particular PTFE), conductive fillers (eg carbon), non-conductive fillers (eg glass) and / or hydrophilic additives (eg Al ₂ O _3, MVDC _2, hydrophilic Ma ^¬ terialien such as polysulfones, such as polyphenylsulfones (PPSU), polyimides, polybenzoxazoles or polyether ketones or general ^¬ my electrochemically stable in the electrolyte polymers may be present. in certain embodiments, the diaphragm is porous and Since it is not itself ionic, it should preferably be able to swell in the acid electrolyte used, and it is a physical barrier to gases and can not be penetrated by gas bubbles a porous polymeric structure, wherein the Gundpolymer is hydro ^¬ phil (eg PPSU). In contrast to the CEM or bipolar membrane umfass the polymer does not have charged functionalities. May further include the diaphragm more preferably hydro ^¬ hydrophilic structure-imparting components such as metal oxides (eg, ZrC> ₂₎ or ceramics as set forth above.

A suitable first separator membrane, for example a cation exchange membrane, a bipolar membrane and / or a diaphragm, exhibits a high wettability by water and / or acids, according to certain embodiments

Ion conductivity, stability to reactive Spe ^¬ zies that can be generated at the anode (beispielswei ^¬ se given for perfluorinated polymers), and / or a Stability the necessary pH regimes, in particular with respect to the liquid acid in the salt bridge space.

According to certain embodiments, the first ion exchange membrane and / or the first separator membrane are hydrophobic if they form a CCM with the electrodes, at least on the side facing the electrodes, so that the reactants of the electrodes are gaseous. According to certain embodiments, the anode and / or cathode is at least partially ^¬ hydrophilic. According to certain embodiments, the first ion exchange membrane and / or the first separator membrane are wettable with water. In order to ensure good ionic conductivity of the ionomers, preference is given to swelling with water. The experiment has shown that poorly wettable membranes can lead to a significant deterioration of the ionic bonding of the electrodes.

Also for some of the electrochemical reactions at the electrodes Ka talysator the presence of water is advantageous for example 3 C0 ₂ + H ₂ 0 + 2e ^"~> CO + 2 HC0 _^3"

Therefore, according to certain embodiments, the anode and / or cathode also have sufficient hydrophilicity. Possibly. This can be adjusted by hydrophilic additives such as T1O ₂ , Al ₂ O ₃ , or other electrochemically inert metal oxides, etc.

In particular, according to certain embodiments, Minim ^¬ least used one of the following first separator membranes. - A diaphragm is preferably used when the salt ^¬ bridge (of the electrolyte in the salt bridge space) and the anolyte ei ^¬ ne identical, preferably inert, have acid or consisting of, in which case then the diaphragm serves to keep them separated gases, so that Carbon dioxide does not pass into the anode compartment, and / or if at the anode O _{2 is} produ ^¬ ed, in particular to save costs. A corresponding construction of an exemplary electrolysis system with diaphragm DF is shown in FIG. 8, with the other system components corresponding to those of FIG. 3 here. - A cation exchange membrane or a membrane having a cation exchange layer are particularly USAGE ^¬ det when the salt bridge and anolyte are not identical, and / or especially when the anolyte HCl, HBr and / or HI containing, and / or if a chlorine production at the anode he follows. Since the cation exchange membrane is the transfer of

Prevents anions from the anolyte into the salt bridge and unlike the diaphragm has no open porosity, the anode can be made more free. In principle, in such an embodiment, the anodic reaction is limited only in that it does not release mobile cations, except protons, that can cross into the salt bridge through the CEM.

A bipolar membrane, preferably a

Anionenaustauscherschicht and / or Anionenentransporterschicht the bipolar membrane is directed towards the anode space and a cation exchange layer and / or cation transport layer of the bipolar membrane directed towards the salt bridge space, is particularly used when the salt bridge and the anolyte are not identical, and / or the anolyte includes in particular ^¬ sondere bases and or salts, and / or use of aqueous electrolytes. Particularly when bipolar membranes are used as the first separator membrane, the anode compartment can be designed independently of the salt bridge and the cathode compartment, which allows a large number of anode reactions with desired products, and in particular when using bases, cheaper anodes or anode catalysts can also be used. For example, nickel-based Anodenkatalysato ^¬ ren for an oxygen evolution, can be used.

An exemplary special construction with a bipolar membrane is shown in FIG. 9, which shows by way of example a 2-membrane structure for CC> 2 electro-reduction with AEM on the cathode side and bipolar membrane. Larem membrane (CEM / AEM) on the anode side shows, here as well as in Figure 1 to 3, the supply of catholyte k, electrolyte s with liquid and / or dissolved acid (electrolyte for the salt bridge space) and anolyte a, as well as a return R of CO ₂ , is shown and on the anode side example ei ^¬ ne oxidation of water. The other reference numerals correspond to those in FIG. 3.

A bipolar membrane may, for example, be designed as a sandwich of a CEM and an AEM. In this case are übli ^¬ cherweise but not two superposed membranes from ^¬ handen, but is a membrane having at least two layers. The illustration in FIG. 9 with AEM and CEM serves only to illustrate the preferred orientation of the layers. The AEM or

Anion exchanger layer shows to the anode, the CEM or cation exchange layer to the cathode. These membranes are almost impassable for both anions and cations. The conductivity of a bipolar membrane is therefore not based on the transportability of ions. Instead, ion transport usually occurs by acid-base dissociation of water in the middle of the membrane. As a result, two oppositely charged charge carriers are generated, which are transported away by the E field.

The generative OH ^~ ions can be passed through the AEM part of the bipolar membrane to the anode, where they are oxidized

40H ^" -> 0 ₂ + 2H ₂ 0 + 4e ^~

and the "H ^+" ions by the CEM-part of the bipolar membrane into the salt bridge or the salt bridge chamber II, where it can be neutralized by the cathodically generated HCC> 3 ^~ ions.

HCO3 ^" + H ⁺ -> C0 ₂ + H ₂ 0

Since the conductivity of the bipolar membrane is based on the separation of charges in the membrane, however, is usually expected with a higher voltage drop. The advantage of such a structure lies in the decoupling of the electrolyte circuits, since, as already mentioned, the bipolar membrane is almost impermeable to all ions.

In this way a structure can be realized for a basic anode reaction that does not require constant updating and from ^¬ leadership of salts or anode products. Otherwise, this is only possible with the use of anions based on acids with electrochemically inactive anions, such as H ₂ SO ₄ . When using a bipolar membrane, hydroxide electrolytes such as KOH or NaOH may also be used as the anolyte. High pH values thermodynamically promote water oxidation and allow the use of much cheaper anode catalysts, eg based on iron-nickel, which would not be stable in acidic form.

Thus, in the context of the invention, when using a bipolar membrane as the first separator membrane, the use of bases, for example a hydroxide base, as the anolyte when an acid is used in the salt bridge. The preferences for certain anolytes listed above do not apply to this special case. The advantage here is that in ba ^¬ sischem anolyte much cheaper anode catalysts, for example, based on Ni / Fe, can be used.

According to the invention, it is not excluded that, in addition to the first ion exchange membrane and possibly the first separator membrane, further membranes and / or diaphragms are provided.

Besides, according to certain embodiments, the anode and / or cathode have sufficient hydrophilicity. Possibly. This can be adjusted by hydrophilic additives such as T1O ₂ , Al ₂ O ₃ , or other electrochemically inert metal oxides, etc.

According to certain embodiments, the cathode and / or the anode is a gas diffusion electrode, as a porous bonded Catalyst structure, as a particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second ion exchange membrane, as a porous conductive support, in which a catalyst is impregnated, and / or as non-closed sheet ^¬ forms. According to certain embodiments, the cathode is a gas diffusion electrode as a porous tethered catalyst ^¬ structure as particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second ion exchange membrane as a porous conductive support, in which a catalyst is impregnated, and or formed as a non-closed sheet, which (r / s) an anion exchange material and / or

Anionentransportmaterial contains. Approximately forms according to certain execution is the anode gas diffusion electrode, as po ^¬ Röse-bound catalyst structure as particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second Ionenaustau ^¬ exchange membrane, a porous conductive support, in which a Ka - talysator is impregnated and / or formed as a non closed sheets which (r / s) is a cation exchanger ^¬ shear material contains and / or gekop ^¬ pelt to a bipolar membrane and / or is bound. The various embodiments of the cathode and anode can be combined with one another as desired.

According to certain embodiments, the anode contacts the first separator membrane, as already described by way of example be ^¬ . This makes a good connection to the salt bridge area possible. In addition, no charge transport through the anolyte is necessary in this case and the charge transport path is shortened. Also electrical shading effects can be bypassed by supporting structures between the anode and the first separator membrane so.

According to certain embodiments, the anode and / or the cathode are contacted with a conductive structure on the side facing away from the salt bridge space. The conductive structure tur is not particularly limited here. The anode

and / or the cathode are thus contacted in accordance with certain embodiments of the side facing away from the salt bridge by conductive structures. These are not particularly limited. These may, for example, be coal flows, metal foams, metal knits, expanded metals, graphite structures or metal structures.

According to certain embodiments, the electrolysis is carried out at a current density of more than 50 mAcm ^-2 , preferably more than 100 mAcm ^-2 , more preferably 150 mAcm ^-2 or more, even more preferably 170 mAcm ^-2 or more or 200 mAcm ^-2 or more, in particular of 250 mAcm ^-2 or more, eg 300 mAcm ^-2 or more, 400 mAcm ^-2 or more, or 600 mAcm ^-2 or more. As stated above, the Faraday yield can be improved, contrary to expectation.

Another advantage of the method according to the invention is the comparatively low demands on the chemical stability of the first ion exchange membrane, eg an AEM. The stability and applicability of particular AEM's is currently limited primarily by two Degradationsme ^¬ mechanisms, on the one hand by the frequent lack of stability ^¬ formality of the functional groups to concentrated Ba sen such as KOH (Hoffmann elimination of quaternary ammonium ions, on the other hand by the destruction of the polymer backbone by anodic oxidation. Since only acid electrolytes are used in the imported here electrolysis systems in contact with the ers ^¬ th ion exchange membrane, the first ion exchange membrane, for example, is exposed to an AEM never concentrated bases. In addition, the anode is preferably not directly attached to the first ion exchange membrane, eg an AEM, which also precludes the anodic damage of this membrane.

By the present electrolysis process, various products can be recovered from CO ₂ , such as CO and / or Hydrocarbons. Also formate can be produced from CO ₂ electrochemical ^¬ mixed.

2 C0 ₂ + H ₂ 0 + 2 e ^" -» HCOO ^" + HC0 ₃ ^" (5)

5 HCOO ^" + H ₂ O ± + OH ^" + HCOOH

Conventionally used carbonate-buffered salt electrolytes as salt bridges usually occur

Deprotonation of formic acid. The actual product is 10 thus formate salts.

HCOOH + MHCO 3 "> HCOOM + H ₂ O + C0 ₂ (6)

The cleavage of formate salts in formic acid is technically difficult and costly, which has hitherto limited the applicability of

C0 ₂ electrolyte has limited to formic acid.

In the system introduced here, this deprotonation does not take place because the electrolyte is an acidic electrolyte,

20 especially pure acid is used. To further Ver ^¬ simplification can for example also in the salt bridge formic ^¬ sensäure such as dilute formic acid, as an electrolyte USAGE ^¬ be det, which can be concentrated by the electrolysis, which through an appropriate electrical conductivity

25 of the formic acid is favored, as shown in Table 5 ersicht ^¬ lich.

Formic acid conductivity [mS / cm] acetic acid conductivity [mS / cm] [wt.%] [Wt.%]

5 6, 22 5 1.36

10 8.26 10 1.76

15 9, 86 15 1, 82

20 11,1 20 1, 82

25 11.4 25 1, 71

30 11,8 30 1, 58

40 11.1 40 1, 23

50 9, 78 50 0.840 7, 92 60 0, 521

5, 92 70 0.270

3, 92 80 0, 093

1, 95

0, 32

Table 5: Conductivity of organic acids at 25 ° C

M (HCOOH) = 46.026 g / mol

M (CH ₃ COOH) = 60.052 g / mol In operation, according to Table 5, for example, a 10% by weight of formic acid is introduced, which is concentrated during operation to, for example, 60-70% by weight. The electrolyte is then stripped down to a residue which is used to restore the starting concentration of 10% by weight. Continuously operating systems in a narrower concentration range are also conceivable. For formic acid, ^electrolytes can preferably be used as based on or from tin or lead. The apparent HCC> 3 ^~ proves transportation that there is a high pH in the range ^¬ Be the cathode. Since formic acid has a lower pK _s value than CO ₂ , this is present in the region of the cathode as formate. These anions are then, for example, also transported away by the first Ionenaustau ^¬ shear membrane, eg AEM, in the salt bridge (first aspect) or the anolyte (second aspect) and re-protonated by the local acid. The latter is regenerated by the protons which pass from the anodic half-cell or are present in the anolyte. A leakage of formic acid on the side facing away from the salt bridge space of the electrode, if any, is not expected.

For the CO ₂ to CO electrolysis, for example, a first ion exchange membrane, for example AEM diaphragm cell ^¬ advantageous, since the components are cheaper and the electrical resistance of the cell is lower.

An acid-salt bridge double membrane cell is also advantageous for those applications where there is an exchange of anions between salt bridge and anolyte should be avoided, eg

if anolyte and saline are not identical;

in the co-electrolysis of CO2 and HCl to simultaneously produce a CC> 2 reduction product, eg CO, and Cl ₂ ; in the preparation of formic acid described above, to avoid re-oxidation of the formic acid at the anode;

the use of copper-based cathodes producing alkenes, alkanes, alcohols, and liquid oxygenates; at any combination of these points

With the inventive method, CO2 is electrolyzed, is however not excluded that a further reactant such as CO is on the cathode side in addition to CO2 still present, wel ^¬ ches can be electrolyzed also, so a mixture is present which comprises CO2, and for example, CO. In ^¬ game as a starting material on the cathode side contains at least 20 vol.% CO2, for example at least 50 or at least 70 vol.% CO2, and in particular, the starting material is on the cathode side to 100 vol.% C0. ₂

In a further aspect, the present invention relates to an electrolytic cell comprising

a cathode compartment comprising a cathode;

a first ion exchange membrane containing a

Anionenaustauscher and / or Anionentransporter contains and which adjoins the cathode compartment, wherein the cathode, the first ion exchange membrane directly, preferably also ionically contacted;

an anode compartment comprising an anode; and

a diaphragm adjacent to the anode compartment;

further comprising a salt bridge space, wherein the salt bridge space between the first ion exchange membrane and the diaphragm is arranged.

With this electrolytic cell of the invention procedural ^¬ ren can transit according to the first aspect of the present invention be guided. Consequently, all features discussed with regard to the inventive method are also applicable to the electrolysis cell according to the invention. In particular, the cathode compartment, the cathode, the first ion exchange membrane, the anode compartment, the anode, the diaphragm and the Salzbrü ^¬ ckenraum have already been discussed with regard to the inventive method. The corresponding features can thus correspondingly discussed above in the invention ^shown SEN electrolysis cell to be executed. So the electrolysis cell of the invention or the electrolysis system according to the invention are used in particular in the novel process for the electrolysis of CO ₂ application, which is why aspects that in to ^¬ connexion discussed with these in advance and subsequently ^¬ to, the electrolysis cell of the invention or the electrolysis system according to the invention affect. According Kings ^¬ nen also in conjunction with the electrolysis cell of the invention and / or electrolysis system concerning inventive procedural ^¬ ren that. Also described is an electrolytic cell comprising

a cathode compartment comprising a cathode;

a first ion exchange membrane containing a

an anode compartment comprising an anode; and

a first separator membrane adjacent to the anode compartment;

further comprising a salt bridge chamber, wherein the salt bridge the space between the first ion-exchange membrane and said first separator membrane is disposed, wherein the Salzbrü ^¬ ckenraum comprises a liquid and / or dissolved acid. The method according to the invention according to the first aspect can also be carried out with this cell, so that the features described therein can also be used correspondingly here. According to certain embodiments, the anode contacts the diaphragm. According to certain embodiments, the anode and / or the cathode are contacted with a conductive structure on the side facing away from the salt bridge space.

According to certain embodiments, the cathode and / or the anode are impregnated as a gas diffusion electrode, as a porous bound catalyst structure, as a particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second ion exchange membrane, as a porous conductive support into which a catalyst is impregnated is, and / or forms as non-closed sheet ^¬ forms. According to certain embodiments, the cathode gas ^¬ diffusion electrode as a porous tethered catalyst structural ^¬ tur, as particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second ion exchange membrane as a porous conductibility higer carrier in which a catalyst is impregnated, and / or formed as a non-closed sheet, which (r / s) an anion exchange material and / or

Anionentransportmaterial contains, and / or is the anode as a gas diffusion electrode, as a porous bound catalyst structure, as a particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second ion exchange membrane, as a porous conductive support in which a catalyst impregnated is, and / or formed as a non-closed sheet containing (r / s) a cation exchange material.

According to certain embodiments, the first ion exchange membrane and / or the diaphragm are hydrophilic. According to certain embodiments, the salt bridge space comprises a liquid and / or dissolved acid, wherein preferably an acid of the liquid and / or dissolved acid in the salt bridge space has a pK _s value of 6 or less, preferably 5 or less, more preferably 3 or less, still more preferably 1 or less, particularly preferably 0 or less, which is whereby further preferably selected the liquid and / or Geloes ^¬ te acid from diluted or undiluted H2 _SO4, a solution of H ₂ N- S O2-OH, dilute or undiluted HCIO ₄ , a solution of H ₃ PO ₄ , dilute or undiluted CF ₃ -COOH, dilute or undiluted CF ₃ - S O ₂ -OH, a solution of (CF ₃ - S O ₂ ) 2- NH, a solution of HF, dilute or undiluted HCOOH, dilute or neat CH ₃ -COOH, a solution of HCl, a solution of HBr, a solution of HI, and / or mixtures thereof. According to certain embodiments, the electrolyte in the salt bridge space consists of a liquid and / or dissolved acid and possibly unavoidable impurities.

According to certain embodiments of the anode compartment contains an acid which is preferably identical with the electrolyte in the Salzbrü ^¬ blocks, in particular if the second membrane is designed as a diaphragm.

In a further aspect, the present invention relates to an electrolysis installation comprising the inventive Elect ^¬ rolysezelle. The respective embodiments of the electrolysis cell as well as other exemplary components of an electrolysis system according to the invention have already been dis ^¬ cussed above and are therefore also applicable to the inventive electric ^¬ lyseanlage. According to certain embodiments, an electrolysis plant according to the invention comprises a multiplicity of electrolysis cells according to the invention, although it is not excluded that there are also other electrolysis cells in addition.

According to certain embodiments, the erfindungsge ^¬ Permitted electrolysis system further comprises a feedback device which is connected to a discharge of the salt bridge chamber and a supply of the cathode compartment, which is adapted to a starting material of the cathode reaction, which can be formed again in the salt bridge chamber, in particular a gaseous or with the electrolyte immiscible starting material, to lead back into the cathode space, such as CO ₂ , which may also contain CO and / or H ₂ .. According to certain embodiments, the erfindungsge ^¬ Permitted electrolysis plant further comprises an external device for electrolyte treatment in particular a device for removing dissolved gases from an acid, with which in particular the anolyte and / or the electrolyte are treated in the salt bridge space, for example to remove gases such as CO ₂ or O ₂ , and thus a return of anolyte and / or the To allow electrolyte in the salt bridge space. This is particularly advantageous when both are pumped from a common reservoir, so only a common

Anolyte / electrolyte for salt bridge space reservoir is present, al ^¬ so the anolyte and the electrolyte in the salt bridge space are identical.

According to certain embodiments, the erfindungsge- Permitted electrolysis plant comprising two separate circuits for anolyte and the electrolyte in the salt bridge space, which may optionally separate a ^¬ directions for electrolytic treatment, may comprise particular devices for removing dissolved gases from an acid, or with only the circuit for the elec- rolyt in the salt bridge space a corresponding device on ^¬ has.

In yet another aspect, the present OF INVENTION ^¬ dung relates to the use of an electrolytic cell of the invention or an electrolysis system according to the invention for the electrolyzer ^¬ se of CO _2, which may also comprise a plurality of electrolytic cells according to the invention.

The above embodiments, configurations and further training can be combined with each other, if appropriate. Further possible refinements, developments and implementations of the invention also include not explicitly mentioned combinations of before or below with respect to the embodiments described features of the invention. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

The invention will be further explained in detail with reference to various examples thereof. However, the invention is not limited to these examples. Examples

Example 1 :

The structure of the electrolyzer in Example 1 is similar to the structure shown in FIG. 3 and is shown schematically in FIG.

In this embodiment, a three-compartment cell was used. The cathode used was a carbon-GDL ^coated with silver particles: Freundenberg HL 23. The particles were precipitated by means of NaBH ₄ from AgNC> 3 in ethanol as follows. AGNC> 3 (3.4g, 20 mmol) was dissolved in ethanol ge ^¬ (250ml). NaBH ₄ (3g, 80mmol) was dissolved in NaOH saturated methanol (100ml) and this solution added dropwise. After all silver was precipitated (no blackening at the drop in site), the addition was stopped. The precipitate was transferred to a frit (P4) and washed 4x with 50 ml of ethanol each time and 1 × with 50 ml of diethyl ether. Subsequently, the powder was dried in vacuo. Yield: 2.88 g of borate stabilized particles. From the particles (90 mg) was a dispersion with the

Ionomer AS-4 (anion exchanger, Tokuyama) (180 mg 5% solution in n-PrOH (n-propanol)) in n-PrOH (2.8g). Three layers of this dispersion were applied to a 60 cm ² piece of GDL.

A 10cm ² piece of this cathode was mechanically pressed on an AEM A201-CE (Tokuyama) and the cathode contacted by a Ti ^¬ tan frame. The anode used was an IrÜ _2- coated Ti expanded metal with a mesh size of 1x2 mm. As CEM, a Nafion N115 membrane was used which was pressed directly onto the plug metal.

To ensure sufficient mechanical pressure, five polymer meshes with a mesh size of 0.5mm were integrated into the cell. As the electrolyte, 0. IM H ₂ SO _{4 was} used in the salt bridge space II and in the anode space III. CO ₂ was passed through a gas humidifier GH with water to ^¬. The CO ₂ flux was chosen for the current densities 50, 100, & 150 mAcm ^-2 so that a threefold excess is available (λ = 4). For a first measurement at 10 mAcm ^-2 , the same gas feed was selected for metrological reasons as for 50 mAcm-2 (λ = 20). At the anode oxygen ^¬ was produced, and a product gas from the cathode compartment K was examined after passage through a bubbler (bubbler) B with a gas chromatograph GC. Similarly, a gas separated in the salt bridge space was analyzed by GC.

At the beginning of the experiment, the cell was run at 4V for 20 min. Subsequently, the cell was retracted for 30 minutes at 10 mAcm ^-2 . Subsequently, at 10, 50, 100 and 150mAcm ^{~ 2} both the amount and the composition of the gases in slit I and slit 2 were determined.

Observations:

At the lowest current density lOmAcm ^-2 , no gas evolution was observed in salt bridge space II. At the higher current densities 50, 100 and 150mAcm ^{~ 2} , gas evolution was observed in salt bridge space II. Gas chromatographic analysis of this gas showed that it is pure CO ₂ > 98 vol.%. The proportion of CO in this gas was less than 1 vol. Vo. The highest H ₂ content resulted in about 1.5 vol.%. A direct return of this gas in the cathode feed is therefore possible. Throughout the experiment, no significant electrolyte penetration was observed on the back of the cathode. When disassembling the cell, neither liquid nor salt crystallites were found on the back of the electrode. A final pH measurement of the bubbler B's fill solution revealed a pH ~ 5, which definitively precludes passage of the acid electrolyte.

The test results of Example 1 are shown in FIG. 11, in which the Faraday efficiency FE is plotted against the applied current density J.

The Faraday efficiency for CO increases steadily in this cell with the current density. The reason for this is the transport model described above. Due to the integrated spacer he ^¬ the electrolyte in the cell-heated to ~ 60 ° C, which all ^¬ recently had no negative influence on the selectivity.

Comparative Example 1

The experimental setup used in Comparative Example 1 is shown in Fig. 12 and corresponds substantially to that of the case ^¬ Game 1 and is identical in terms of device components, except that the acid was replaced in the salt bridge chamber II through a _KHCO3 salt electrolyte.

For current densities of 50 and 100 mAcm ^-2 , IM KHCO _{3 was} used as the electrolyte in the salt bridge space. For 150mAcm ^{~ 2, it} had to be changed to a 2M KHCO ₃ for technical reasons (maximum voltage of the potentiostat).

At all current densities, a triple CO 2 excess was used.

Observations:

At all current densities, gas evolution was observed in salt bridge space II. There was no observed increased electrolyte penetration. However, in the Zerle ^¬ supply of the cell fluid and Salzkristallite were found on the Elect ^¬ clearing back of the cathode. The test results of Comparative ^Example 1 are shown in FIG. 13, in which again the Faraday efficiency FE against the applied current density J is plotted.

As can be seen in Figure 13, the selectivity decreases with increasing current density. This is due to the increased passage of alkali metal cations through the electrode and the associated partial flooding of the electrode.

In a comparison between Comparative ^Example 1 ( ^dotted lines) and the exemplary embodiment (solid lines) in FIG. 14, the advantages of the method according to the invention at elevated current densities are shown in comparison to conventional salt electrolytes.

Comparative Example 2:

A schematic representation of the experimental setup in Comparative Example 2 is shown in FIG. 15. In this example the same Ver ^¬ AEM was allowed ^¬ away in comparison to Example 1, to show that this is essential, the further experimental setup corresponds to that of Example. 1 It should be noted that the cathode still contains an anion exchange ionomer corresponding to the polymer base of the AEM.

Observations:

At all measured current densities, gas evolution was observed in salt bridge space II. The analysis of this gas shows, however, that this gas, in contrast to the embodiment mainly H ₂ is (81 vol.% H ₂ , 18 vol.% CO ₂ ) · It was also observed no liquid through ^¬ passes through the cathode. 60 vol.% Of the hydrogen was observed in the cathode compartment I.

The test results of Comparative ^Example 2 are shown in FIG. 16, in which again the Faraday efficiency FE is shown. the applied current density J is applied. This shows the preferred production of hydrogen.

In the comparison between the comparative example 2 (dashed lines) and the exemplary embodiment (solid lines) shown in FIG. 17, the advantageous embodiment in example 1 shows with increased selectivity for CO. This is also known from the state shown in Fig. 18 Comparison of the gas chromatograms of Comparative Example 2 (solid line) and the exemplary example (dashed line) at J = 150mAcm ^{~ 2} he ^¬ clearly, in which case the measurement without AEM (w / o AEM ) is shown as a solid line and AEM (w / AEM) as dashed Li ^¬ never. In Example 1 and in Comparative Example 2 it is described that with the use of acid electrolyte no liquid penetrates through the cathode on the side facing away from the electrolyte. Over long operating periods, however, leakage of liquid from the GDE would in principle be conceivable.

By design, these are then not a concentrated carbonate solution, but almost pure What ^¬ ser, in particular no salt solutions - as in the case of metal ^¬ cation-containing electrolytes. This circumstance brings advantages in the construction of the cell as well as in the design of the entire electrolyte system. It could be observed that, for example, titanium contacts in contact with through

Electrode salt solutions can corrode due to the strong negative potential. As a consequence, the permeate turns blue (Ti3 ⁺ ). The titanium corrosion is confirmed here as the cause of the blue coloration by means of chromotropic acid, and the cathodic corrosion detected in control experiments. The permeate liquids (if any) are not or little electrically conductive in the inventive arrangement presented here or in the inventive method. Although the contacts are still exposed to a strong negative potential, but not contacted ionic. Consequently, such corrosion phenomena do not occur or severely limited. As it may be at one The liquid occurring at the back of the electrode is water, this contains no ions, which must be recycled to the electrolyte ^¬ . This liquid can therefore be a ^¬ times discarded. Possibly occurring Korrosionspro- products of the contacts are not in accordance with the electric ^¬ LYTEN washed.

Reference Examples 1 and 2 In Reference Examples 1 and 2, the effects of low anode pH on cell voltage were examined.

According to the Nernst equation, the potential of oxidation of water to oxygen depends on the pH of the electrolyte.

RT

E = 12V - Ξ.3Χ- xpH In order to keep the cell voltage as low as possible, it is therefore advisable to have the highest possible pH value in the anode region. However, this can be maintained according to the invention under the Rahmenbe ^¬ dingung a C0 ₂ -free anode only by using a bi-polar membrane.

With a cation exchange membrane or a diaphragm, the cations would be removed from the anode compartment, which would lead to a lowering of the pH. An anion-exchange membrane at the anode would result in the penetration of HCC> 3 ^~ into the anode space, which would lead to the unwanted mixing of the anodically-generated oxygen with CO ₂ .

To allow for constant operation, an acid is chosen as the anolyte (except when using a bipolar membrane). This initially seems to be of little benefit from the point of view of the cell voltage, since this procedure leads to a high water oxidation rate. DZ

ons potential leads. However Experiments have shown ^¬ to that thermodynamic considerations (after

Nernst equation) only for the "onset" range (ie the range of minimum current densities) At higher current densities, the same cell voltage was observed for an acidic anode and a pH-neutral to slightly basic anode.

For this purpose, a simple comparative experiment was carried out. First of all, the UI characteristic was recorded by a simple construction with acid-anolyte and neutral-buffered salt bridge, FIG. 19, with the corresponding components from Example 1 and Comparative Example 1. Subsequently ^¬ SEN the periphery as shown in FIG. 20 has been converted, so that now the anode with the neutral-buffered electrolyte was supplied. No changes were made to the cell. Moreover, it is at the anode which is applied directly to the membrane to a "cement ro Gap" -Anode. The Leitfä ^¬ ability of the anolyte thus plays the voltage no Rol ^¬ le. The electrolyte in the salt bridge is identical in both cases All changes of the voltage are therefore due to the different pH of the anolyte, and then a UI characteristic was recorded again.The structure in Fig. 19 represents an adaptation of an alkaline electrolysis cell for CO ₂ electrolysis ^{The ion} exchange membrane in a diaphragm was omitted for reasons of comparability.

It should be noted here that the anolyte in the structure of FIG. 20 does not contain anions of stable acids. Therefore, the expression of a locally low pH values, as for example in the case of Na ₂ SC would be possible> 4, here also be ^¬ closed.

FIGS. 21 and 22 show the comparison of the UI characteristics with the measurements with the structure of FIG. 19 with filled squares and the measurements with the structure of FIG. 20 with open circles, FIG. 21 showing the "onset" region of the characteristic - line (in particular the left and FIG. 22, the full line shows characteristic ^¬ to 200 mAcm ^-2.

As is apparent from Fig. 21, in the case of the acid anolyte, the electrolysis starts about 480 mV later. This matches well with the expected value of 460 mV expected for a pH difference of 7. However, it can be seen from Fig. 22 that this effect is valid only in the "onset" range, above a current density of 100 mAcm ^-2 the characteristics coincide.

This clearly shows that for a productive electrolysis system operated at high current densities, the use of acids as the anolyte does not cause any disadvantages with respect to the cell voltage.

Effects of CO ₂ release on cell voltage:

In the two constructions of the reference examples, CC> ₂ release from HCC> 3 ^{~ occurs} in the cell. In the case of the construction according to FIG. 19, this takes place in the salt bridge, in the case of

Structure according to Fig. 20 in the anode compartment. In both cases, the fourfold volume of CO _{2 is} released compared to the anodically generated oxygen. In the case of the construction according to FIG. 19, this occurs before the CEM in the space of the salt bridge. In the case of Fig. 20, this happens in the immediate vicinity of the anode. The resulting gas bubbles are, however, transported away behind the anode. They are thus not in the current path, which explains the smoother curve for this construction (filled squares) in FIG. From the figure, however, also shows that the total voltage does not increase due to the load of the salt bridge.

For the purposes of the present invention, it is further considered in particular not to use a bare cathode, but a cathode AEM composite. For these constructions, a transport number for CO ₂ ^ 0.55 was experimentally obser ^¬ tet. The gas load of a salt bridge space is therefore only Wa half as large as in the present comparative example. Accordingly, in comparable structures, a drastic increase in the voltage through these gas bubbles can not be expected up to a current density of 400mAcm ^{~ 2} .

The situation is different with the anode. This is by the

Transition from an acid anolyte to a carbonate-containing, neutral-buffered electrolyte charged with five times the amount of resulting gases. As a result, parts of the anode can be isolated and cut off from the electrolyte, which simultaneously represents the substrate. In the range of 150-200mAcm ^{~ 2} , the voltage for the acid anolyte is even lower, not least due to the high gas load of the anode (in both cases a non-closed area with catalyst coating).

The present invention is characterized by liquid and / or dissolved acids, in particular pure acids as

Use electrolytes for CO ₂ electrolysis at high current densities and high Faraday efficiency. In addition, was introduced with a three-chamber construction with the first Ionenaus ^¬ exchange membrane and diaphragm, such as an AEM diaphragm Doppelseparator cell, a new cell type. Among other things, there are the following advantages over previous embodiments:

No CC> ₂ release at the anode, only O ₂ or other anodic products

CO ₂ is released in a separate chamber and can be recycled.

No salt excretion

Faraday efficiency of CO generation increases with increasing current density

No or very little permeate into the gas space of the cathode space

When using the same acid in the anode compartment and in the salt bridge, a diaphragm is sufficient to separate anode gas and CO2. Also applicable to the preparation of other CO ₂ Redukti ^¬ modulation products (for example, formic acid)

In addition, a C0 ₂ ~ free anode is not obtained by the construction of the anodic half cell, but by that of the cathodic half cell. This result is totally unexpected and is based on the mechanism of charge anionbasierten Trans ^¬ ports, offset by fixed positive charges.

Claims

claims

1. A method for the electrolysis of CO ₂ , comprising an electrolysis ^¬ cell

a cathode compartment comprising a cathode;

a first ion exchange membrane comprising an anion exchanger and / or anion, and which is adjacent to the cathode compartment, wherein the Ka ^¬ Thode advantage the first ion exchange membrane directly kontak-;

an anode compartment comprising an anode;

a first separator membrane; and

is used,

2. A method for the electrolysis of CO ₂ , comprising an electrolyte ^¬ sezelle

a cathode compartment comprising a cathode; a first ion exchange membrane comprising an anion exchanger and / or anion, and which is adjacent to the cathode compartment, wherein the Ka ^¬ Thode contacting the first ion exchange membrane directly; and

is used,

3. The method of claim 1, wherein the second Ionenaustau ^¬ shear membrane is selected from an Ionenaustauschermemb- ran, which contains a cation exchanger, a bipolar membrane and a diaphragm.

4. The method of claim 1 or 3, wherein the anode compartment comprises an anolyte, which is a liquid and / or dissolved

Acid, preferably wherein the anolyte and / or the acid in the salt bridge space, no mobile cations except protons and / or deuterons, in particular no metal cations comprises.

5. The method of claim 2, wherein the anode is applied to the first ion exchange membrane.

6. The method according to any one of the preceding claims, wherein the electrolysis with a current density of more than 50 mAcm ^-2 , preferably ^¬ be more than 100 mAcm ^-2 , more preferably from 150 mAcm ^-2 or more, even more preferably 170 mAcm ^-2 or more, especially 250 mAcm ^-2 or more, eg 400 mAcm ^-2 or more, or 600 mAcm ^-2 or more.

7. The method according to claim 1, wherein an acid of the electrolyte in the salt bridge space has a pK _s value of 6 or less, preferably 5 or less, more preferably 3 or less, even more preferably 1 or less, in particular preferably 0 or less, preferably wherein the liquid and / or dissolved acid is selected from dilute or undiluted H ₂ SO ₄ , a solution of H ₂ N-SO ₂ -OH, dilute or undiluted HCIO ₄ , a solution of H ₃ PO ₄ , dilute or undiluted CF ₃ -COOH, dilute or undiluted CF ₃ -SO ₂ -OH, a solution of (CF ₃ -SO ₂ ) ₂ -NH, a solution of HF, dilute or undiluted HCOOH, dilute or undiluted CH ₃ -COOH , a solution of HCl, a solution of HBr, a solution of HI, and / or mixtures thereof.

8. electrolytic cell comprising

a cathode compartment comprising a cathode;

a first ion exchange membrane containing a

Contains anion exchanger and / or anion transporter and which is adjacent to the cathode compartment, the cathode directly contacting the first ion exchange membrane;

an anode compartment comprising an anode; and

a diaphragm adjacent to the anode compartment;

further comprising a salt bridge space, wherein the salt bridge space between the first ion exchange membrane and the diaphragm is arranged, wherein the diaphragm is not ion-conductive.

9. An electrolytic cell according to claim 8, wherein the anode is the

Diaphragm contacted, and / or wherein the anode and / or the cathode are contacted on the side remote from the salt bridge space with a conductive structure.

10. The electrolytic cell according to claim 8 or 9, wherein the Ka ^¬ method and / or the anode as a gas diffusion electrode, as ^¬ po ^¬ bound bonded catalyst structure, as a particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second Ionenaustau- shear membrane, as a porous conductive support, in which a catalyst is impregnated, and / or is formed as a non-closed sheet.

11. The electrolytic cell according to claim 10, wherein the cathode as a gas diffusion electrode, as a porous bound catalyst ^¬ structure, as a particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second ion exchange membrane, as a porous conductive support in which a catalyst is impregnated, and / or is formed as a non-closed sheet which contains (r / s) an anion exchange material and / or Anionentransportermaterial, and / or wherein the anode as a gas diffusion electrode, as a porous bound catalyst ^¬ structure, as a particulate catalyst on a support, as a coating of a particulate catalyst on the first and / or second ion exchange membrane, as a porous conductive support in which a catalyst is impregnated, and / or is formed as a non-closed sheet containing (r / s) a cation exchange material.

12. An electrolytic cell according to any one of claims 8 to 11, wherein the first ion exchange membrane and / or the diaphragm are hydrophilic.

13. An electrolytic cell according to any one of claims 8 to 12, where ^¬ in the electrolyte in the salt bridge space consists of a liquid acid and / or a solution of an acid, preferably wherein an acid of the electrolyte in the salt bridge space a pK _s value of 6 or less , preferably 5 or less, more preferably 3 or less, still more preferably 1 or less, particularly preferably 0 or less, more preferably comprising the liquid and / or dissolved acid is selected from diluted or undiluted H2 _SO4, a Solution of H ₂ N-S O ₂ -OH, diluted or undiluted HCIO ₄ , a solution of H ₃ PO ₄ , dilute or undiluted CF ₃ -COOH, dilute or undiluted CF ₃ -SO ₂ -OH, a solution of (CF ₃ - S O2) 2 - NH, a solution of HF, dilute or undiluted HCOOH, dilute or neat CH ₃ -COOH, a solution of HCl, a solution of HBr, a solution of HI, and / or mixtures thereof.

14. electrolysis plant comprising an electrolytic cell according to any one of claims 8 to 13.

15. An electrolysis system according to claim 14, further comprising ei ^¬ ne feedback device, which is connected to a discharge of the salt bridge space and a supply of the cathode space, which is adapted to a reactant of the cathode re ^¬ action, which can be formed in the salt bridge space, again to lead into the cathode compartment.

16. Use of an electrolytic cell according to one of Ansprü ^¬ che 8 to 13 or an electrolysis system according to claim 14 or 15 for the electrolysis of CO ₂ .