DE102017223521A1 - Flow-through anion exchanger fillings for electrolyte gaps in the CO2 electrolysis for better spatial distribution of gas evolution - Google Patents

Abstract

The present invention relates to an electrolysis cell having a multi-chamber structure, wherein a first ion exchange membrane comprising an anion exchanger adjoins a cathode space, with a salt bridge space adjoining this first ion exchange membrane comprising a solid anion exchanger; an electrolysis plant with such an electrolysis cell; and a method of electrolysis of CO using such an electrolytic cell or electrolysis plant.

Description

The present invention relates to an electrolysis cell having a multi-chamber structure, wherein a first ion exchange membrane comprising an anion exchanger adjoins a cathode space, with a salt bridge space adjoining this first ion exchange membrane comprising a solid anion exchanger; an electrolysis plant with such an electrolysis cell; and a method for electrolysis of CO ₂ using such an electrolytic cell or electrolysis plant.

The burning of fossil fuels currently covers about 80% of global energy needs. In 2011, these combustion processes emitted around 34,032.7 million tonnes of carbon dioxide (CO ₂ ) into the atmosphere worldwide. This release is the easiest way to dispose of even large amounts of CO ₂ (lignite power plants over 50000 tons per day).

The discussion about the negative effects of the greenhouse gas CO ₂ on the climate has led to a reflection on the recycling of CO ₂ . Thermodynamically, CO _{2 is} very low and can therefore be reduced back to useful products.

In nature, CO _{2 is} converted into carbohydrates by photosynthesis. This temporally and on a molecular level spatially divided into many sub-steps process is very difficult to copy on an industrial scale. The currently more efficient way compared to pure photocatalysis is the electrochemical reduction of CO _2. A mixed form is light-assisted electrolysis or electrically assisted photocatalysis. Both terms are synonymous to use, depending on the perspective of the viewer.

As with photosynthesis, CO _{2 is transformed} into an energetically higher-value product (such as CO, CH ₄ , C ₂ H ₄ , in this process with the supply of electrical energy (possibly photo-assisted), which can be obtained from regenerative energy sources such as wind or sun, etc.) converted. The amount of energy required in this reduction ideally corresponds to the combustion energy of the fuel and should only come from renewable sources. An overproduction of renewable energies is not continuously available, but currently only at times with strong sunlight and strong wind. However, this will continue to increase in the near future as renewable energy continues to expand.

The electrochemical reduction of CO ₂ to solid-state electrodes offers in aqueous electrolyte solutions a variety of product possibilities, for which exemplary Faraday efficiencies on different metal cathodes in Table 1, taken from "Electrochemical CO ₂ 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, are shown. Table 1: Faraday efficiencies in the electrolysis of CO ₂ on various electrode materials 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

Currently, the electrification of the chemical industry is discussed. This means that chemical precursors or fuels are preferably to be produced from CO ₂ (CO), H ₂ O 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 (calorific value).

Electrolysis processes have evolved significantly in recent decades. For example, the PEM water electrolysis could be optimized to high current densities. Large electrolysers with megawatts of capacity are being launched on the market.

In CO ₂ electrolysis it has been found that coupling of the cathode to an anion exchange membrane (AEM) is associated with significant advantages in terms of selectivity, stability and technical feasibility.

Furthermore, it is known that by the AEM generated at the cathode as a byproduct HCO ₃ ^- can be transported further in the direction of the anode and at a time dependent on cell design location, such as from the anode side formed protons, can be decomposed to CO _2. It has been shown that it may be advantageous to use tri-cell cells in which the CO _{2 is released} separately from the products of the electrodes as this facilitates feedback.

Corresponding cell concepts can, for example, the US 2017037522 A1 , the DE 102017208610.6 , the DE 102017211930.6 be removed.

In these cells, the cathode compartment is usually limited by an AEM. As a result, cathodically generated anions such as HCO ₃ ^- , CO ₃ ^2- , OH ^- can be transported away in the direction of the anode. With respect to the configuration of the anode space and the gap between the anode and cathode space, the sources mentioned vary greatly. Common to them, however, is a region between the AEM, which delimits the cathode space, and the anode, which contains a strongly acidic medium or generates protons in which HCO ₃ ^- , CO ₃ ^2- are decomposed by protonation to CO ₂ . Furthermore, the charge transport in all these cells can be carried in sections by different charge carriers. In contrast to other electrochemical structures, the charge carriers are usually not exchanged between the half cells, but destroyed in the additional gap between them.

In the US 2017037522 A1 and the DE 102017211930.6 the central cleft contains only strongly acidic media. The release of CO ₂ is therefore usually directly on the surface of the AEM, wherein in the US2017037522A1 the medium of the gap is fixed while it is in DE 102017211930.6 is liquid. The surface of the AEM can be heavily loaded with gas bubbles, which can lead to a partial isolation of the membrane and thus to higher electrical losses in the cell. A direct contact strong acid solid media with the AEM should also be avoided because the solid media can not escape the released at this pH limit CO ₂ .

In the DE 102017208610.6 the gap contains a neutral to weakly basic electrolyte, which usually contains carbonates. The CO ₂ release therefore usually takes place on the surface of the second separator membrane, which may also be problematic. In addition, it has been found that the use of salts, in particular with metal cations, can be associated with disadvantages in electrolyte columns.

At present, no solutions to the problem described are known. Its extent can, as in DE 102017208610.6 be reduced by increasing the system pressure. However, excessive pressure increase is undesirable because of the increased solubility of gases in water.

There is thus a need for an improved electrolysis cell or an improved electrolysis system, in which the formation of gas bubbles on a membrane in a multi-chamber system can be effectively avoided.

The inventors have found that with an additional electrolyzer component, in particular cell voltage, operational stability and energy efficiency can be improved. In this case, this component is preferably integrated so that in the resulting entire cell neither salt incrustations of the electrodes nor CO ₂ development in the anode compartment are possible. The present invention represents a significant improvement of already disclosed cell concepts.

This is achieved in particular by filling a salt bridge space in an electrolysis cell with a solid anion exchanger which comprises at least in the vicinity of the cathode / AEM an, for example bicarbonate, carbonate and / or hydroxide conductive, for example strongly basic, anion exchanger. The anion exchanger causes a gas evolution, for example, the CO ₂ evolution in the CO ₂ electrolysis, can be distributed in the salt bridge space in the volume and not only takes place at the AEM salt bridge space interface.

In the following, the terms anion exchanger and anion transporter are used interchangeably. The transport function is characterized in that the anion exchange / anion transport material provides cations that compensate for the charge of the anions. The anion itself is, according to certain embodiments, only so easily bound that a dynamic exchange is made possible, thus providing a transport path for the anion in the electrolyte. At the same time, the cation is immobilized on the polymer back wheel of the anion exchange material so that it itself can not participate in charge transport processes.

• - einen Kathodenraum umfassend eine Kathode;
• - eine erste Ionenaustauschermembran, welche einen Anionenaustauscher enthält und welche an den Kathodenraum angrenzt, wobei die Kathode die erste Ionenaustauschermembran kontaktiert;
• - einen Anodenraum umfassend eine Anode; und
• - einen ersten Separator, welcher an den Anodenraum angrenzt;

weiter umfassend einen Salzbrückenraum, wobei der Salzbrückenraum zwischen der ersten Ionenaustauschermembran und dem ersten Separator angeordnet ist, wobei der Salzbrückenraum einen festen Anionenaustauscher umfasst, welcher zumindest teilweise mit der ersten Ionenaustauschermembran in Kontakt ist.In a first aspect, the present invention relates to an electrolytic cell comprising

• a cathode compartment comprising a cathode;
• a first ion exchange membrane containing an anion exchanger adjacent to the cathode compartment, the cathode contacting the first ion exchange membrane;
• an anode compartment comprising an anode; and
• a first separator adjacent to the anode compartment;

further comprising a salt bridge space, wherein the salt bridge space between the first ion exchange membrane and the first separator is arranged, wherein the salt bridge space comprises a solid anion exchanger, which is at least partially in contact with the first ion exchange membrane.

Further disclosed is an electrolysis plant comprising an electrolysis cell according to the invention.

In addition, the present invention is directed to a method for the electrolysis of CO ₂ , wherein an electrolysis cell according to the invention or an electrolysis plant according to the invention is used, wherein CO _{2 is} reduced at the cathode and formed at the cathode bicarbonate and / or carbonate through the first ion exchange membrane to a Electrolyte migrated in the salt bridge space, wherein the bicarbonate and / or carbonate is also transported by the solid anion exchanger in the salt bridge space away from the first ion exchange membrane.

Yet another aspect of the present invention relates to the use of an electrolysis cell according to the invention or an electrolysis plant according to the invention for the electrolysis of CO ₂ and / or CO.

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

list of figures

• 1 bis 9 zeigen schematisch mögliche Ausgestaltungen einer erfindungsgemäßen Elektrolysezelle.
• In 10 ist beispielhaft schematisch eine erfindungsgemäße Elektrolyseanlage dargestellt.

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 scale. 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.

• 1 to 9 schematically show possible embodiments of an electrolytic cell according to the invention.
• In 10 is an example schematically illustrated an electrolysis plant according to the invention.

Detailed description of the invention

definitions

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

Quantities in the context of the present invention relate to wt.%, Unless otherwise specified or apparent from the context. In the gas diffusion electrode according to the invention, the weight percentages to 100% by weight complement each other.

In the context of the present invention, hydrophobic is understood as meaning water-repellent. Hydrophobic pores and / or channels according to the invention are therefore those which repel 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.

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 design may be of a different nature, for example, as a porous "bulk catalyst" with optional adjuvants to adjust the hydrophobicity, then, for example, a membrane-GDE composite, e.g. AEM-GDE composite, can be produced; as a conductive porous support to which a catalyst can be applied in a thin layer, in which case again a membrane-GDE composite, e.g. AEM-GDE composite, can be produced; or as a composite porous catalyst, optionally with additive directly on a membrane, e.g. AEM, can be applied and then in combination can form a catalyst coated membrane (CCM).

The normal pressure is 101325 Pa = 1.01325 bar.

Electro-osmosis:

Electro-osmosis is an electrodynamic phenomenon in which a force towards the cathode acts on particles in solution with a positive zeta potential, and a force acts on the anode on all particles with a negative zeta potential. If conversion takes place at the electrodes, i. If a galvanic current flows, a stream of the particles with a positive zeta potential also flows to the cathode, irrespective of whether the species participates in the reaction 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-related currents that balance the concentration gradients can thereby be overcompensated.

• - einen Kathodenraum umfassend eine Kathode;
• - eine erste Ionenaustauschermembran, welche einen Anionenaustauscher enthält und welche an den Kathodenraum angrenzt, wobei die Kathode die erste Ionenaustauschermembran kontaktiert;
• - einen Anodenraum umfassend eine Anode; und
• - einen ersten Separator, welcher an den Anodenraum angrenzt;

weiter umfassend einen Salzbrückenraum, wobei der Salzbrückenraum zwischen der ersten Ionenaustauschermembran und dem ersten Separator angeordnet ist, wobei der Salzbrückenraum einen festen Anionenaustauscher umfasst, welcher zumindest teilweise mit der ersten Ionenaustauschermembran in Kontakt ist.In a first aspect, the present invention relates to an electrolytic cell comprising

• a cathode compartment comprising a cathode;
• a first ion exchange membrane containing an anion exchanger adjacent to the cathode compartment, the cathode contacting the first ion exchange membrane;
• an anode compartment comprising an anode; and
• a first separator adjacent to the anode compartment;

further comprising a salt bridge space, wherein the salt bridge space between the first ion exchange membrane and the first separator is arranged, wherein the salt bridge space comprises a solid anion exchanger, which is at least partially in contact with the first ion exchange membrane.

The salt bridge space is not particularly limited insofar as it correspondingly adjoins the first ion exchange membrane at least partially, in particular mechanically and / or ionically, so that the solid anion exchanger in it can at least partially be in contact with the first ion exchange membrane. According to certain embodiments, the solid anion exchanger is in contact with the first ion exchange membrane at least substantially in a region where the cathode contacts the first ion exchange membrane on an opposite side of that membrane or in a region that is larger. In this way, a good transfer of anions, which are generated in the cathode and passed through the first ion exchange membrane, can be ensured. The term "in contact with the first ion exchange membrane" here does not exclude that the contact is not full-surface, but according to certain embodiments such that a flow of fluids, ie liquids and / or gases, through the solid anion exchanger is possible.

The term salt bridge space is here used 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 at least one ion exchanger is present in the salt bridge space, this could also be called an ion bridge space. However, since this term is not familiar, the space is referred to as salt bridge space according to the invention, even if in the classic sense, no salt must be present.

The dimensions of the salt bridge space are also not particularly limited, and may be used as a space or a gap, e.g. be formed between the first ion exchange membrane and the first separator, which are arranged for example parallel to each other.

The salt bridge space does not necessarily have to be in contact with the first separator which adjoins the anode space, ie more than three chambers may also be present in an electrolysis cell according to the invention. Thus, the term "interposed between the first ion exchange membrane and the first separator" means that the salt bridge space may be located anywhere between the first ion exchange membrane and the first separator insofar as it comprises a solid anion exchanger which is at least partially bound to the first ion exchange membrane in FIG Contact is. In this respect, the salt bridge space adjoins the first ion exchange membrane, which does not exclude, however, that a second separator or even further separators and / or further cell spaces are present in addition to the first separator. According to certain embodiments, the salt bridge space is in contact with the first separator. In this respect, the electrolysis cell according to the invention can be constructed, for example, as a multi-chamber cell, for example a three-chamber cell, as described in US Pat US 2017037522 A1 . DE 102017208610.6 , and DE 102017211930.6 and to which reference is made for such cells. Thus, for example, there may be a three-compartment cell in which there are three chambers (I, II, III). Thus, the electrolytic contacting between the cathode space and the anode space can be effected and / or facilitated with the salt bridge space.

The cathode space, the anode space and the salt bridge space are not particularly limited in the electrolytic cell of the present invention in terms of shape, material, dimensions, etc. insofar as they can accommodate the cathode, the anode and the first ion exchange membrane and the first separator. The three spaces are formed in the electrolysis cell according to the invention, in which case they can then be correspondingly separated, for example, by the first ion exchange membrane and the first separator, for example with the first separator between the salt bridge space and the anode space.

Depending on the electrolysis to be carried out, corresponding supply and discharge devices for educts and products, for example in the form of liquid, gas, solution, suspension, etc., may be provided for the individual spaces, and these may possibly also be recycled in each case. Again, there is no limitation, and the individual rooms can be flowed through in parallel streams or in countercurrent. For example, in an electrolysis of CO ₂ - which may still contain CO, that is, for example, at least 20 vol.% CO ₂ contains - this to the cathode in solution, as a gas, etc. are supplied - for example, in countercurrent to an electrolyte flow in the salt bridge space in a three-chamber design. There is no restriction here.

Corresponding feed options also exist in the anode compartment and are also described 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 - which will also be discussed below, as well as cooling and / or heating devices, to be able to catalyze corresponding desired reactions at 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 gas formed in the salt bridge space, which corresponds, for example, to the educt gas, for example CO ₂ , which may also contain traces of, H ₂ and / or CO, is returned to the cathode space, for which an appropriate electrolysis plant according to the invention Return device can be provided.

According to the invention, the cathode is not particularly limited and may be adapted to a desired half reaction, for example with respect to the reaction products insofar as it contacts the first ion exchange membrane directly, ie it is in direct contact with the first ion exchange membrane at at least one point, preferably with the surface being substantially flat is in direct contact with the first ion exchange membrane. Thus, at least in one area, the cathode directly adjoins the first ion exchange membrane. 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 the reduction of CO ₂ to CO, for example, the catalyst is preferably based on Ag, Au, Zn and / or their compounds such as Ag ₂ O, 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 the production of formic acid, for example, catalysts based on Pb, Sn and / or Cu, in particular Pb, Sn, are possible. Since the formation of hydrogen at high current densities can be completely suppressed by the anion transport according to certain embodiments, 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 avenues in CO ₂ reduction chemistry, which do not depend on hydrogen overvoltage.

• - Gasdiffusionselektrode bzw. poröse gebundene Katalysatorstruktur, die gemäß bestimmten Ausführungsformen mittels eines geeigneten Ionomers, beispielsweise eines anionischen Ionomers, mit der ersten Ionenaustauschermembran, beispielsweise einer Anionenaustauschermembran (AEM), z.B. ionenleitend und/oder mechanisch verklebt sein kann;
• - Gasdiffusionselektrode bzw. poröse gebundene Katalysatorstruktur, die gemäß bestimmten Ausführungsformen partiell in die erste Ionenaustauschermembran, beispielsweise eine AEM, gepresst sein kann;
• - poröse, leitfähige, katalytisch inaktiven Struktur, z.B. Kohlenstoff-Papier-GDL bzw. Carbon-Paper-GDL (gas diffusion layer, Gasdiffusionsschicht), Kohlenstoff-Tuch-GDL bzw. Carbon-Cloth-GDL, und/oder polymergebundener Film aus granularem Glaskohlenstoff, der mit dem Katalysator der Kathode und ggf. einem Ionomer, dass die Anbindung an die erste Ionenaustauschermembran, beispielsweise eine AEM, ermöglicht, imprägniert ist, wobei die Elektrode dann mechanisch auf die erste Ionenaustauschermembran, beispielsweise eine AEM, gepresst oder vorher mit der ersten Ionenaustauschermembran, beispielsweise einer AEM, verpresst sein kann, um einen Verbund zu bilden;
• - partikulärer Katalysator, der mittels eines geeigneten Ionomers auf einen geeigneten Träger, beispielsweise einen porösen leitfähigen Träger, aufgebracht ist und gemäß bestimmten Ausführungsformen an der ersten Ionenaustauschermembran, beispielsweise einer AEM, anliegen kann;
• - partikulärer Katalysator, der in die die erste Ionenaustauschermembran, beispielsweise eine AEM, eingepresst ist oder auf diese beschichtet ist und beispielsweise entsprechend leitend verbunden ist, wobei diese Struktur dann beispielsweise als sogenannte CCM (Catalyst-Caoted-Membrane; katalysator-beschichtete Membran) dann auf eine leitfähige, poröse Elektrode gepresst sein kann, wobei eine katalytische Aktivität dieser Elektrode grundsätzlich nicht erforderlich ist und beispielsweise Kohlenstoff basierte GDL's oder Gitter, beispielsweise aus Titan, verwendet werden können, wobei hierbei nicht ausgeschlossen ist, dass diese Elektrode Ionomere enthält und/oder den aktiven Katalysator enthält oder in großen Teilen daraus besteht;
• - nicht geschlossenes Flächengebilde, z.B. ein Netz oder ein Streckmetall, das beispielsweise aus einem Katalysator besteht bzw. diesen umfasst oder mit diesem beschichtet ist und gemäß bestimmten Ausführungsformen an der ersten Ionenaustauschermembran, beispielsweise einer AEM, anliegt;
• - polymergebundene Vollkatalysator-Struktur aus partikulärem Katalysator, die ein Ionomer, das die Anbindung an die erste Ionenaustauschermembran, beispielsweise eine AEM, ermöglicht, enthält oder nachträglich damit imprägniert wurde, wobei die Elektrode dann mechanisch auf die erste Ionenaustauschermembran, beispielsweise eine AEM, gepresst oder vorher mit der ersten Ionenaustauschermembran, beispielsweise einer AEM, verpresst sein kann, um einen Verbund zu bilden;
• - poröser, leitfähiger Träger, der mit einem geeigneten Katalysator und ggf. einem Ionomer imprägniert ist und gemäß bestimmten Ausführungsformen an der ersten Ionenaustauschermembran, beispielsweise einer AEM, anliegt;
• - nicht ionenleitfähige Gasdiffusionselektrode, die nachträglich mit einem geeigneten Ionomer, beispielsweise einem anionleitfähigen Ionomer, imprägniert wurde und gemäß bestimmten Ausführungsformen an der ersten Ionenaustauschermembran, beispielsweise einer AEM, anliegt oder mit dieser, z.B. über ein Ionomer, verbunden ist.

The cathode is the electrode at which the reductive half-reaction takes place. It can be embodied in one or more parts and be formed, for example, as a gas diffusion electrode, porous electrode or directly with the AEM in a composite, etc.
The following embodiments are possible, for example:

• Gas diffusion electrode or porous bonded catalyst structure, which according to certain embodiments by means of a suitable ionomer, for example an anionic ionomer, with the first ion exchange membrane, such as an anion exchange membrane (AEM), for example ion-conducting and / or mechanically bonded;
• - Gas diffusion electrode or porous bonded catalyst structure, which according to certain embodiments may be partially pressed into the first ion exchange membrane, such as an AEM;
• porous, conductive, catalytically inactive structure, eg carbon-paper-GDL or carbon-paper-GDL (gas diffusion layer), carbon-cloth-GDL or carbon-cloth-GDL, and / or polymer-bonded film of granular Glassy carbon which is impregnated with the catalyst of the cathode and, if appropriate, an ionomer which makes possible the attachment to the first ion exchange membrane, for example an AEM, the said electrode then being mechanically applied 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;
• 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, in which the first ion exchange membrane, for example an AEM, is pressed or coated onto it and, for example, correspondingly conductively connected, this structure then being known, for example, as CCM (Catalyst-Caoted membrane, catalyst-coated membrane) may be pressed onto a conductive, porous electrode, wherein a catalytic activity of this electrode is basically not required and, for example, carbon-based GDL's or gratings, for example made of titanium, can be used, whereby it is not excluded that this electrode contains ionomers and / or contains or consists in large part of the active catalyst;
• non-closed sheet material, eg a net or an expanded metal, which for example consists of, comprises or is coated with a catalyst and according to certain embodiments bears against the first ion exchange membrane, for example an AEM;
• polymer-bonded unsupported catalyst structure comprising particulate catalyst containing or subsequently impregnated with an ionomer which allows attachment to the first ion exchange membrane, for example an AEM, the electrode then being mechanically pressed onto the first ion exchange membrane, for example an AEM previously compressed with the first ion exchange membrane, such as an AEM, to form a composite;
• porous conductive carrier impregnated with a suitable catalyst and optionally an ionomer and, according to certain embodiments, being applied to the first ion exchange membrane, for example an AEM;
• non-ion-conductive gas diffusion electrode, which was subsequently impregnated with a suitable ionomer, for example an anionic ionomer, and according to certain embodiments is applied 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. Thus, according to certain embodiments, besides the catalyst, the cathode may comprise at least one ionomer, for example an anionic ionomer (eg, anion exchange resin, anion transport resin) which may include, for example, various ion exchange functional groups, which may be the same or different, for example, tertiary amine groups, alkyl ammonium groups and / or phosphonium groups), for example a conductive carrier material (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 one Oxide such as indium tin oxide (ITO), aluminum zinc oxide (AZO) or fluorinated tin oxide (FTO) - for example as used to make photoelectrodes, and / or at least one polymer based on polyacetylene, polyethoxythiophene, polyaniline or polypyrrole, such as in polymer based electrodes; non-conductive supports such as polymer nets are possible, for example, with sufficient conductivity of the catalyst layer), binders (eg hydrophilic and / or hydrophobic polymers, eg organic binders, eg selected from PTFE (polytetrafluoroethylene), PVDF (polyvinylidifluoride), 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 , MgO ₂ , hydrophilic materials such as polysulfones, for example polyphenylsulfones, polyimides, polybenzoxazoles or polyether ketones or in the electrolyte generally electrochemically stable polymers, polymerized "ionic liquids", and / or organic conductors such as PEDOT: PSS or PANI (champhersulfonsäuredortierte polyaniline) containing are not particularly limited.

The cathode, especially in the form of a gas diffusion electrode, e.g. bonded to the first ion exchange membrane, or contained in the form of a CCM, according to certain embodiments, contains ionically conductive components, in particular an anionic conductive component.

Other cathode forms are possible, for example, cathode structures, as in US 20160251755 A1 and US 9481939 are described.

Also, the anode according to the invention is not particularly limited and may be adapted to a desired half reaction, for example with respect to the reaction products. At the anode, which is electrically connected to the cathode by means of a current source for providing the voltage for the electrolysis, the oxidation of a substance takes place in the anode space. Moreover, the material of the anode is not particularly limited and depends primarily on the desired reaction. Exemplary anode materials include platinum alloys, palladium and glassy carbon, iron, nickel, etc. Other anode materials are also conductive oxides such as doped TiO 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 a catalyst for O ₂ or Cl ₂ generation, for example, IrO _x (1.5 <x <2) or RuO ₂ are used. These may also be present as a mixed oxide with other metals, eg TiO ₂ , and / or be supported on a conductive material such as C (in the form of carbon black, activated carbon, graphite, etc.). Alternatively, catalysts based on Fe-Ni or Co-Ni can also be used for O ₂ production. For this purpose, for example, the structure described below with bipolar membrane or bipolar membrane is suitable.

• - Gasdiffusionselektrode bzw. poröse gebundene Katalysatorstruktur, die gemäß bestimmten Ausführungsformen mittels eines geeigneten Ionomers, beispielsweise eines kationischen Ionomers, mit dem ersten Separator, beispielsweise einer Kationenaustauschermembran (CEM) oder einem Diaphragma, z.B. ionenleitend und/oder mechanisch verklebt sein kann;
• - Gasdiffusionselektrode bzw. poröse gebundene Katalysatorstruktur, die gemäß bestimmten Ausführungsformen partiell in den ersten Separator, beispielsweise eine CEM oder ein Diaphragma, gepresst sein kann;
• - partikulärer Katalysator, der mittels eines geeigneten Ionomers auf einen geeigneten Träger, beispielsweise einen porösen leitfähigen Träger, aufgebracht ist und gemäß bestimmten Ausführungsformen am ersten Separator, beispielsweise einer CEM oder einem Diaphragma, anliegen kann;
• - partikulärer Katalysator, der in den ersten Separator, beispielsweise eine CEM oder ein Diaphragma, eingepresst ist und beispielsweise entsprechend leitend verbunden ist;
• - nicht geschlossenes Flächengebilde, z.B. ein Netz oder ein Streckmetall, das beispielsweise aus einem Katalysator besteht bzw. diesen umfasst oder mit diesem beschichtet ist und gemäß bestimmten Ausführungsformen am ersten Separator, beispielsweise einer CEM oder einem Diaphragma, anliegt;
• - solide Elektrode, wobei in diesem Fall auch ein Spalt zwischen dem ersten Separator, beispielsweise einer CEM oder einem Diaphragma, und der Anode bestehen kann;
• - poröser, leitfähiger Träger, der mit einem geeigneten Katalysator und ggf. einem Ionomer imprägniert ist und gemäß bestimmten Ausführungsformen am ersten Separator, beispielsweise einer CEM oder einem Diaphragma, anliegt;
• - nicht ionenleitfähige Gasdiffusionselektrode, die nachträglich mit einem geeigneten Ionomer, beispielsweise einem kationleitfähigen Ionomer, imprägniert wurde und gemäß bestimmten Ausführungsformen am ersten Separator, beispielsweise einer CEM oder einem Diaphragma, anliegt;
• - beliebige Varianten der diskutierten Ausführungsformen, wobei die Elektrode z.B. ein anodisch stabiles anionenleitfähiges Material enthält und direkt an der anionenleitenden Schicht einer Bipolarmembran anliegt.

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 bonded catalyst structure, which may be according to certain embodiments by means of a suitable ionomer, such as a cationic ionomer, with the first separator, such as a cation exchange membrane (CEM) or a diaphragm, for example ion-conducting and / or mechanically bonded;
• A gas diffusion electrode or porous bonded catalyst structure which, according to certain embodiments, may be partially pressed into the first separator, for example a CEM or a diaphragm;
• particulate catalyst applied to a suitable support, for example a porous conductive support, by means of a suitable ionomer and, according to certain embodiments, abutting the first separator, for example a CEM or a diaphragm;
• particulate catalyst which is pressed into the first separator, for example a CEM or a diaphragm, and for example is correspondingly conductively connected;
• non-closed sheet material, eg a net or an expanded metal, which for example consists of, comprises or is coated with a catalyst and, according to certain embodiments, bears against the first separator, for example a CEM or a diaphragm;
• solid electrode, in which case there may also be a gap between the first separator, for example a CEM or a diaphragm, and the anode;
• porous conductive carrier impregnated with a suitable catalyst and optionally an ionomer and, according to certain embodiments, abutting the first separator, for example a CEM or a diaphragm;
• non-ionic gas diffusion electrode which has been subsequently impregnated with a suitable ionomer, for example a cationic ionomer, and according to certain embodiments is applied to the first separator, for example a CEM or a diaphragm;
• - Any variants of the discussed embodiments, wherein the electrode, for example, contains an anodically stable anion conductive material and is applied directly to the anion-conducting layer of a bipolar membrane.

Again, various combinations of different anode structures are possible.

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

According to certain embodiments, the cathode and / or the anode is 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 formed as a non-closed sheet. According to certain embodiments, the cathode is a gas diffusion electrode, a porous bonded catalyst structure, a particulate supported catalyst, a particulate catalyst coating on the first and / or second ion exchange membrane, a porous conductive support in which a catalyst is impregnated, and / or is formed as a non-closed sheet containing (r / s) an anion exchange material and / or anion transport material. According to certain embodiments, the anode is a gas diffusion electrode, a porous bound catalyst structure, a particulate supported catalyst, a particulate catalyst coating on the first and / or second ion exchange membrane, a porous conductive support in which a catalyst is impregnated, and / or is formed as a non-closed sheet which contains (r / s) a cation exchange material and / or is coupled and / or bound to a bipolar membrane.

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 is not particularly limited here. The anode and / or the cathode are therefore contacted in accordance with certain embodiments of the salt bridge opposite side by conductive structures. These are not particularly limited. These may be, for example, coal flows, metal foams, metal knits, expanded metals, graphite structures or metal structures.

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 this supplied be, for example, only CO ₂ , possibly also as a mixture with, for example CO and / or H ₂ O, which may also be liquid, for example as an aerosol, but preferably gaseous H ₂ O to the cathode and / or water or HCl to the anode. According to certain embodiments, an anolyte is present which may differ from or correspond to an electrolyte of the salt bridge space, for example with respect to contained solvents, acids, etc.

A catholyte in this case is the electrolyte flow around the cathode or at the cathode and, according to certain embodiments, serves to supply the cathode with substrate or educt. The following embodiments are possible, for example. The catholyte can be used, for example, as a solution of the substrate (CO ₂ ) in a liquid carrier phase (eg water) and / or as a mixture of the substrate with other gases (eg CO + CO ₂ , water vapor + CO ₂ , N ₂ and / or certain proportions O ₂ , SO ₂ , SO ₃ , etc.). Also, recycle gases such as CO and / or H ₂ may be present through recycle. The substrate can also be in the form of a pure phase, for example CO ₂ . If uncharged liquid products are formed during the reaction, they can be washed out by the catholyte and can then be optionally separated afterwards.

An anolyte is an electrolyte stream 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 limited - in particular when using a bipolar membrane as the first separator membrane, wherein the anolyte here also basic may be 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.) are present. 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, the anolyte is an aqueous electrolyte, it being possible where 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, CO ₂ may be added to water outside the cathode compartment, or may also be added through a gas diffusion electrode, or may be supplied only as a gas to the cathode compartment. Corresponding considerations are possible analogously for the anode compartment, depending on the educt used, for example water, HCl, NaCl, KCl, etc., and the desired product.

The first ion exchange membrane containing an anion exchanger and / or anion transporter or an anion transport material and which adjoins the cathode compartment is not particularly limited in the present invention. It separates the cathode from the salt bridge space in the electrolysis cell according to the invention as well as in the process according to the invention, so that the cathode / first ion exchange membrane / salt bridge space sequence results from the direction of the cathode space in the direction of the electrolyte. In particular according to certain embodiments, it contains an anion exchanger or consists of this, which is present in the form of an acid-anion salt in the electroless state, preferably according to an acid which is present in the salt bridge space and which more preferably from a minimum current density into the bicarbonate / carbonate ion. Shape passes over. 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 comprise a hydrophobic layer, for example, on the cathode side for better gas contacting. The anion exchange membrane and / or anion transporter membrane preferably also acts as cation (albeit in trace), in particular proton, blocker. Specifically, an anion exchanger and / or anion transporter with tightly bound cations can represent a blockade for mobile cations by Coulombabstoßung, which can additionally counteract salt precipitation, in particular within the cathode.

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. A concentration gradient can not be easily degraded on the electrode side, since a catalyst-based cathode, which is designed as set out above, e.g. a gas diffusion electrode or a CCM, optionally only has a very poor Anionenleitfähigkeit, depending on the anion and a selected electrolyte. By integrating anions of conductive components, the anion conductivity can be significantly improved.

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 in an anion exchange layer which is applied to the cathode, for example, to rapidly dissipate or partially buffer the resulting OH ^- ions, so that the Reaction with CO ₂ and the associated formation of bicarbonates and / or carbonates can be reduced or the Anionentransportharze HCO ₃ ^- or CO ₃ ^2- conduct itself. In principle, an anion transport can take place by anion exchangers. Furthermore, in particular, an integrated anion exchanger in turn represents a blockade for cations, for example metal traces of catalysis, which can additionally counteract salt precipitation and contamination of the electrode. In the case of protons, for example, the formation of hydrogen can be suppressed.

The first ion exchange membrane may thus contain, for example, an anion exchanger and / or anion transporter in the form of an anion exchanger and / or transporter layer, in which case further layers such as hydrophobicizing layers may be included to improve the contact with a gas, eg CO ₂ . According to certain embodiments, the first ion exchange membrane is an anion exchange membrane and / or anion transporter membrane, ie for example an ion-conductive membrane (or in a broader sense a membrane with an anion exchange layer and / or Anionentransporterschicht) with positively charged Funktionsalsierungen, which is not particularly limited. A preferred charge transport takes place in the anion exchanger layer and / or Anionenentransporterschicht or an anion exchange membrane and / or Anionentransportermembran by anions. In particular, the first ion exchange membrane and / or therein in particular an anion exchange layer and / or Anionentransporterschicht or an anion exchange membrane and / or Anionentransportermembran serves to provide an 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 be converted in accordance with certain embodiments, in particular in operation in the carbonate / bicarbonate form 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, according to certain embodiments, exhibits good wettability by water and / or acids, especially aqueous acids, 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, e.g. Fumasep FAS-PET or Fumasep FAD-PET.

In addition, the first separator is not particularly limited.

According to certain embodiments, the first separator, for example, according to certain embodiments, seen from the anode side adjacent to the salt bridge space, selected from an ion exchange membrane containing a cation exchanger, a bipolar membrane, wherein in the bipolar membrane preferably the cation conductive layer is oriented towards the cathode and the anion-conducting layer towards the anode, and a diaphragm. According to certain embodiments, the first separator is a cation exchange membrane, a bipolar membrane or a diaphragm.

A suitable first separator, for example a cation exchange membrane or a bipolar membrane, contains, for example, a cation exchanger which can be in contact with the salt bridge space. It may, for example, contain a cation exchanger in the form of a cation exchanger layer, in which case further layers, such as hydrophobicizing layers, may be contained. It can 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-conducting membrane or ion-conducting layer with negatively charged functionalizations. An exemplary charge transport into the salt bridge space takes place in such a first separator by cations. For example, commercially available Nafion® membranes are suitable as CEM, or the Fumapem-F membranes sold by Fumatech, the Aciplex marketed by Asahi Kasei, or the Flemion membranes marketed by AGC. In principle, however, it is also possible to use other polymer membranes modified with strongly acidic groups (groups such as sulfonic acid, phosphonic acid). According to certain embodiments, the first separator prevents the passage of anions, in particular HCO ₃ ^- , into the anode space.

In addition, in the electrolysis cell according to the invention, as well as in the method according to the invention, the first separator can be formed as a diaphragm, whereby the cell can be made less complex and less expensive. 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. The same applies to other first separators. Particular preference is given to embodiments which bring about gas separation, for example the CO ₂ in the salt bridge space and the O ₂ in the anode space.

The diaphragm is not particularly limited in this case and may for example be based on a ceramic (eg ZrO ₂ or Zr ₃ (PO ₄ ) ₃ ) and / or a swellable functionalized polymer, eg PTFE. Also binders (eg hydrophilic and / or hydrophobic polymers, for example organic binders, for example selected from PTFE (polytetrafluoroethylene), PVDF (polyvinylidifluoride), 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 , MgO ₂ , hydrophilic materials such as polysulfones, eg polyphenylsulfones (PPSU), Polyimides, polybenzoxazoles or polyether ketones or electrochemically stable polymers generally in the electrolyte may be present.

According to certain embodiments, the diaphragm is porous and / or hydrophilic. Since it is not ion-conductive itself, it should preferably be able to swell in an electrolyte, such as an acid. Furthermore, it is a physical barrier to gases and can not be penetrated by gas bubbles. For example, it is a porous polymer structure wherein the base polymer is hydrophilic (eg PPSU). Unlike the CEM or bipolar membrane, the polymer does not contain charged functionalities. Further, the diaphragm may further preferably include hydrophilic structuring components such as metal oxides (eg, ZrO ₂ and / or other materials such as particles over the surface thereof) or ceramics as set forth above.

A suitable first separator, for example a cation exchange membrane, a bipolar membrane and / or a diaphragm, exhibits, according to certain embodiments, good wettability by water and / or acids, high ionic conductivity, stability towards reactive species that can be generated at the anode ( for example given for perfluorinated polymers), and / or a stability in the required pH regimes, for example towards an acid in salt bridge space.

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

Also, for some of the electrochemical reactions on the catalyst electrodes, the presence of water is advantageous.
eg 3 CO ₂ + H ₂ O + 2e ^- → CO + 2 HCO ₃ ^-
or depending on the pH: 2CO ₂ + 2e ^- → CO + CO ₃ ^2-

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

• - Ein Diaphragma wird bevorzugt verwendet, wenn die Salzbrücke (der Elektrolyt im Salzbrückenraum) und der Anolyt eine identische, bevorzugt inerte, Säure aufweisen oder aus dieser bestehen, wobei hier dann das Diaphragma dazu dient, Gase getrennt zu halten, sodass Kohlendioxid nicht in den Anodenraum übertritt, und/oder wenn an der Anode O₂ produziert wird, insbesondere um Kosten zu sparen.
• - Eine Kationenaustauschermembran oder eine Membran mit einer Kationenaustauscherschicht werden insbesondere verwendet, wenn ein Elektrolyt im Salzbrückenraum - auch im Rahmen der Erfindung als „Salzbrücke“ bezeichnet, und der Anolyt nicht identisch sind, und/oder insbesondere wenn der Anolyt HCl, HBr und/oder HI enthält, und/oder wenn eine Chlorproduktion an der Anode erfolgt. Da die Kationenaustauschermembran den Übertritt von Anionen aus dem Anolyten in die Salzbrücke verhindert und im Unterschied zum Diaphragma keine offene Porosität aufweist, kann die Anode freier gestaltet werden. Im Prinzip ist in solch einer Ausführungsform für die Anodenreaktion nur bevorzugt, dass sie keine mobilen Kationen, außer Protonen, freisetzt, die durch die CEM in die Salzbrücke übertreten können.
• - Eine bipolare Membran bzw. Bipolar-Membran, wobei bevorzugt eine Anionenaustauscherschicht und/oder Anionentransporterschicht der bipolaren Membran zum Anodenraum hin gerichtet ist und eine Kationenaustauscherschicht und/oder Kationentransporterschicht der bipolaren Membran zum Salzbrückenraum hin gerichtet ist, wird insbesondere verwendet, wenn die Salzbrücke, also der Elektrolyt im Salzbrückenraum, und der Anolyt nicht identisch sind, und/oder der Anolyt insbesondere Basen und oder Salze enthält, und/oder bei Verwendung wässriger Elektrolyte. Insbesondere bei der Verwendung von bipolaren Membranen als erster Separator kann der Anodenraum unabhängig von der Salzbrücke und dem Kathodenraum gestaltet werden, was eine Vielzahl an Anodenreaktionen mit gewünschten Produkten erlaubt, und insbesondere bei der Verwendung von Basen können auch billigere Anoden bzw. Anodenkatalysatoren, beispielsweise Nickel oder Eisen basierte Anodenkatalysatoren für eine Sauerstoffentwicklung, verwendet werden.

In particular, according to certain embodiments, at least one of the following first separators is used:

• - A diaphragm is preferably used when the salt bridge (the electrolyte in the salt bridge space) and the anolyte have an identical, preferably inert, acid or consist of this, in which case the diaphragm serves to keep gases separated so that carbon dioxide is not in the Anodenraum exceeds, and / or if at the anode O _{2 is} produced, in particular to save costs.
• A cation exchange membrane or a membrane with a cation exchange layer are used in particular if an electrolyte in the salt bridge space - also referred to in the context of the invention as "salt bridge", and the anolyte are not identical, and / or in particular if the anolyte HCl, HBr and / or HI contains, and / or if a chlorine production takes place at the anode. Since the cation exchange membrane prevents the passage of 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, for the anode reaction, it is only preferred that it release no mobile cations, other than protons, which can cross into the salt bridge through the CEM.
• A bipolar membrane or bipolar membrane, wherein preferably an anion exchanger layer and / or anion transport layer of the bipolar membrane is directed towards the anode space and a cation exchanger layer and / or cation transport layer of the bipolar membrane is directed towards the salt bridge space, is used in particular when the salt bridge, Thus, the electrolyte in the salt bridge space, and the anolyte are not identical, and / or the anolyte contains in particular bases and or salts, and / or when using aqueous electrolytes. Particularly in the case of the use of bipolar membranes as the first separator, the anode compartment can be designed independently of the salt bridge and the cathode compartment, which allows a multiplicity of anode reactions with desired products, and in particular when using bases, cheaper anodes or anode catalysts, for example nickel, can also be used or iron based anode catalysts for oxygen evolution.

A bipolar membrane may, for example, be designed as a sandwich of a CEM and an AEM. In this case, but usually not two superimposed membranes are present, but it is a membrane with at least two layers. 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.

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.

As a result, it is also possible to realize a construction for a basic anode reaction which manages without constant tracking and removal of salts or anode products. This is otherwise possible only with the use of anolyte based on acids with electrochemically inactive anions such as H ₂ SO ₄ . When using a bipolar membrane can also hydroxide electrolyte such as KOH or NaOH as Anolyte can be used. High pH values thermodynamically favor the water oxidation and allow the use of much cheaper anode catalysts, for example based on iron-nickel, which would not be stable in acids or neutrals.

Thus, for the purposes of the invention, when using a bipolar membrane as the first separator membrane, the use of bases, e.g. a hydroxide base, as anolyte when an acid is used in the salt bridge.

It is not excluded according to the invention that further membranes and / or diaphragms are provided in addition to the first ion exchange membrane and the first separator.

According to certain embodiments, the anode contacts the first separator, as already described above by way of example. This makes a good connection to the salt bridge space 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 support structures between the anode and the first separator so.

The solid anion exchanger, which is at least partially in contact with the first ion exchange membrane and is included in the salt bridge space is not particularly limited according to the invention, if it is present as a solid - that is not in solution, can exchange anions, and at least partially in contact with the first ion exchange membrane is. Preferably, the solid anion exchanger is hydrophilic.

As already explained above, it is preferred that the solid anion exchanger, at least in the region of the cathode on the opposite side of the first ion exchange membrane, is substantially in contact therewith, ie for example more than 50% of the area of the first ion exchange membrane, preferably more than 60%, more preferably more than 70%, in particular more than 80%, are in contact with the solid anion exchanger - that is, touching it, based on the area of the first ion exchange membrane which is in contact with the cathode.

In certain embodiments, the solid anion exchanger is not in full contact with the first ion exchange membrane, particularly not in the region where the cathode on the opposite side of the first ion exchange membrane contacts it to provide fluid transport between the first anion exchange membrane and the solid anion exchanger , It is thus also preferred according to certain embodiments that the solid anion exchanger at least in the region of the cathode on the opposite side of the first ion exchange membrane with this with 99% or less of the area of the first ion exchange membrane, preferably 97% or less, more preferably 95% or less , in particular 92% or less, is in contact with the solid anion exchanger based on the area of the first ion exchange membrane which is in contact with the cathode.

The further mechanical design of the solid anion exchanger, which can also be understood as a filling medium is not particularly limited, and it may, for example, as a bed of solid anion exchange particles, which are not particularly limited, as a porous structure, such as spongy, and / or than, for example be formed regularly, porous self-supporting structure. If the solid anion exchanger is present as a bed of solid anion exchange particles, the particles preferably have a particle size between 5 μm and 2 mm, more preferably between 100 μm and 1 mm, it being possible to determine the particle size for example with sieve analysis. According to certain embodiments, the particles are adapted to the size of the cell and / or to the corresponding flow regime. According to certain embodiments, the solid anion exchanger is present as a bed and / or a porous structure. According to certain embodiments, the solid anion exchanger, optionally with other solid components, e.g. neutral particles or cation exchangers, in salt bridge space, a filling.

• - eine komprimierte Schüttung aus, z.B. pelletierten, Anionenaustauscherpartikeln
• - ein schwammartiges poröses Gebilde
• - ein regelmäßig poröses selbstragendes Gebilde, wie es beispielsweise durch Umgießen von Polymer-Kugeln mit einer Lösung des Anionenaustauschermaterials des festen Anionenaustauschers und anschließendem Auflösen der Templat-Kugeln erhalten werden kann. Die Struktur sollte jedoch zumindest teilweise offen bzw. offen sein, um einen Elektrolyt- und Gasfluss gewährleisten zu können.

Examples of the mechanical design of the solid anion exchanger are, for example

• - A compressed bed of, for example, pelleted, anion exchange particles
• - a spongy porous structure
• - A regularly porous self-supporting structure, as can be obtained, for example, by casting around polymer beads with a solution of the anion exchange material of the solid anion exchanger and subsequent dissolution of the template beads. However, the structure should be at least partially open or open in order to ensure an electrolyte and gas flow can.

In addition, porous carrier beats (latex beads) can be impregnated with an anion exchange ionomer and thus function as anion exchange particles. The bonding of a particle bed of any, eg neutral and / or uncharged, eg polymeric, particles with an anion exchange ionomer is preferred according to certain embodiments. The advantage of this method is a higher number of exchanger groups available for the transport of anions.

The solid anion exchanger serves as an open extension of the first ion exchange membrane, for example an AEM, into the volume of the salt bridge space (for example referred to as the gap volume if the salt bridge space is formed as a gap). As a result, the surface of anion-conducting constituents of the electrolysis cell, for example of bicarbonate and / or carbonate-conducting constituents of the electrolysis cell in the case of a CO ₂ -electrolyte, can be greatly increased. A gas such as CO ₂ released by protons from the anode thus covers a smaller part of the surface of the first ion exchange membrane and therefore does not lead to ionic isolation. Furthermore, the solid anion exchanger has an intrinsic ion conductivity, which can create an additional conduction path through the salt bridge space by only solid electrolytes. In the area of the first separator, in the solid ion exchanger, for example, not only HCO ₃ ^- and / or CO ₃ ^2-, but also or only an anion of the electrolyte used in the salt bridge space, such as an acid to be used, serve as mobile carriers. When diluted, for example, in the salt bridge space H ₂ SO ₄ is used as electrolyte, the solid anion exchanger should preferably be selected such that it in addition to good HCO ₃ ^- also a good SO ₄ ^2- comprising conductance and / or CO ₃ ^2-. Accordingly, the material of the solid anion exchanger can be adapted not only to an anion such as HCO ₃ ^- and / or CO ₃ ^2- , which is produced cathodically, but also to other anions, for example in the salt bridge space.

The material of the solid anion exchanger is not limited insofar as it is suitably adapted to the first ion exchange membrane and / or an electrolyte in the salt bridge space, except that it is capable of anion exchange and / or anion transport. For example, the solid anion exchanger may comprise an anion exchange resin containing cations, preferably alkali and / or alkaline earth metal cations, e.g. by complex formation, and / or ammonium ions and / or derivatized ammonium ions such as quaternary ammonium ions, more preferably alkali metal cations and / or ammonium ions and / or derivatized ammonium ions such as quaternary ammonium ions are immobilized. Furthermore, it is also possible for example to bind phosphonium, pyridinium, piperidinium, guanidinium, imidazolium, pyrrazolium and / or sulfonium ions to a support of the solid anion exchanger.

According to certain embodiments, the solid anion exchanger in the salt bridge space comprises cations which are immobilized in a polymeric backbone, the cations in particular being able to exchange bicarbonate ions and / or carbonate ions, these hydrogencarbonate ions and / or carbonate ions preferably being transportable through the solid anion exchanger, to be suitable Provide conductivity in the salt bridge space.

Anion exchangers are usually in acidic (eg in the HSO ₄ ^- form, where they may also be present as solid acids), neutral (eg as TFO or Cl salt) or basic form (eg HCO ₃ ^- form weakly basic, OH ^- form strongly basic) in solid form. In the present invention, depending on the mode of operation, various such anion exchangers may be present side by side in a cell according to the invention, basic anion exchangers preferably being used in the vicinity and / or on the first ion exchange membrane.

According to certain embodiments, the solid anion exchanger is basic, preferably strongly basic. According to certain embodiments, the immobilized cations of the anion exchanger are such that an ion pair formed by them is always completely dissociated, which can be controlled, for example, by the pH. According to certain embodiments, the solid anion exchanger bicarbonate, carbonate and / or OH ^- ions and / or anions of the electrolyte used in the electrolyte of the salt bridge space, for example an acid, to as counterions. This can improve the transport of bicarbonate and / or carbonate from the first ion exchange membrane by means of ion hopping (as opposed to "tunneling" as in the Grotthus mechanism).

In theory, it would also be possible in general to realize a corresponding continuation of the action of the first ion exchange membrane with a solid, eg acid ion exchanger and a basic liquid electrolyte in salt bridge space. In the special case of CO ₂ electrolysis, however, this is not possible because basic solutions are converted by the present CO ₂ in neutral carbonate solutions. For the purposes of this invention, basic media are considered to be anionic conductors, acidic media are used as proton conductors. Ladder. Since in neutral (eg alkali) carbonates the cation transport predominates, a corresponding carbonate solution that is produced does not correspond to an extension of the first ion exchange membrane into the salt bridge space.

In certain embodiments, the solid anion exchanger is hydrophilic. As a result, it is more wettable with an aqueous medium, so that in the salt bridge space, an aqueous medium such as an aqueous acid can be used. In addition, the water can also serve as an additional starting material in the reduction of carbon dioxide, as stated above, and allow a good conductivity.

In addition, the first anion exchanger and / or a filling comprising the solid anion exchanger, optionally with further solid constituents, e.g. neutral particles or cation exchangers, in salt bridge space also for supporting separators and / or membranes, e.g. the first ion exchange membrane and the first separator, against each other. Since this filling has its own ionic conductivity, this form of support does not lead to the isolation of electrode areas. When assembling a cell stack or cell stack, the bed can also be used for power transmission (adhesion) through the entire stack or total stack.

As already discussed, the filling contains at least in the region of the cathode / AEM a solid, eg strongly basic, anion exchanger. The filling may also consist entirely of a solid, eg strongly basic, anion exchanger.
It is advantageous in this case if the chemical nature of the solid anion exchanger is as similar as possible to that of the first ion exchange membrane, for example an AEM. Both components can also be constructed, for example, on the same polymer base, but for example, the chain length and / or the degree of crosslinking may differ.

Exemplary embodiments in which the salt bridge space comprises only one solid anion exchanger are schematically shown in FIG 1 to 3 shown. In the figures, the first separator is shown in contact with the anode. However, according to the invention, this is not absolutely necessary, and the separator can also be present separately from the anode, so that an anode space can also be formed, for example, between the separator and the anode and, if appropriate, the anode also has a space for the anode on an opposite side of such an anode space Supply of substrate, such as a gas, may have.

In 1 is the solid anion exchanger 4 , For example, a strongly basic anion exchanger, in the salt bridge space II which is located between an anion exchange membrane AEM as a first ion exchange membrane based on, for example, strongly basic, anion exchange material 1 and a cation exchange membrane CEM as the first separator based on, for example, strongly acidic, cation exchange material 3 located. To the AEM closes the cathode K and the cathode compartment I, and to the CEM the anode A and the anode compartment III , As shown in the figure, the solid anion exchanger 4 be penetrated by fluids such as gases and / or electrolytes. For all three rooms I . II . III In each case a supply and a discharge are provided.

An alternative embodiment can be found in 2 , wherein the electrolytic cell largely of the 1 matches, except that the CEM by a diaphragm D, for example in the form of a hydrophilic gas separator 5 , was replaced. Another alternative embodiment can be found in 3 , which also largely the embodiment of the 1 corresponds, where the CEM was replaced by a bipolar membrane BPM, in which a cation exchange layer based on a, for example, strongly acidic cation exchange material 3 to the salt bridge room II directed, while an anion exchange layer based on a, for example, strongly basic, anion exchange material 1 directed towards the anode.

In addition to the solid anion exchanger but also other ingredients in the filling in salt bridge space are possible, which can support the release of the recorded and / or transported in the solid anion exchanger bicarbonate.

Thus, the filling may comprise, for example, in addition to one, for example, strongly basic and / or weakly basic, anion exchangers, nonionic ion exchangers, for example poly-alcohols, and / or cation exchangers, for example, weak and / or strong, acidic cation exchangers, which are not particularly limited , For example, in the examples in DE 102017211930.6 found that per flowed electron less than one equivalent of CO ₂ through the first ion exchange membrane, eg a AEM , goes into a central salt bridge room. This indicates besides HCO ₃ ^- also on a transport of CO ₃ ^2- and / or OH ^- out. Acid additions in the solid anion exchangers, such as cation exchangers, can be used, for example, for Conversion of CO ₃ ^2- in HCO ₃ ^- serve. Monovalent ions are usually more mobile in ion exchange media, while in solution multivalent ions are more mobile. By such a corresponding addition, an optimal highly conductive conduction path is created for each type of ion.

4 schematically shows an exemplary embodiment in which such a filling in salt bridge space II with a mixed ion exchange material 2 containing, for example, strongly basic, anion exchange material, which may for example be homogeneously mixed, is provided. The further embodiment of the cell in 4 corresponds to the 1 ,

A comparison of these two cell concepts with, for example, strongly basic, anion exchange material 4 ( 5 ) and mixed ion exchange material 2 containing an eg strongly basic, anion exchange material ( 6 ) is also in 5 and 6 with a generic separator S from a generic material 6 , which may be single or multi-layered, shown. The further structure corresponds to the in 1

According to certain embodiments, the solid salt bridge space further comprises non-ionic and / or unfunctionalized particles, nonionic ion exchangers and / or cation exchangers, preferably the non-ionic and / or unfunctionalized particles, nonionic ion exchangers and / or cation exchangers, more preferably not ion-conducting and / or unfunctionalized particles and / or nonionic ion exchangers, in a region adjacent to the first ion exchange membrane in an amount of up to 20% by volume, preferably up to 17% by volume, more preferably up to 14% by volume, still further preferably up to 10% by volume or up to 5% by volume, based on the total amount of solid anion exchanger and uncharged particles, nonionic ion exchanger and / or cation exchanger. The mixture of the solid anion exchanger with the uncharged particles, the nonionic ion exchanger and / or the cation exchanger is hereby not particularly limited, and may be homogeneous or heterogeneous, e.g. in the form of layers, etc. The uncharged particles, nonionic ion exchangers and / or cation exchangers are not particularly limited. If the filling is constructed in the form of layers, these layers are preferably parallel to the first ion exchange membrane and / or the first separator, wherein the layer adjacent to the first ion exchange membrane contains the uncharged particles, nonionic ion exchangers and / or cation exchangers in an amount of up to to 20% by volume, preferably up to 17% by volume, more preferably up to 14% by volume, even more preferably up to 10% by volume or up to 5% by volume, based on the layer, or only the includes solid anion exchanger or contains.

In contrast, a layer adjoining the first separator can, for example, contain the solid anion exchanger in an amount of up to 20% by volume, preferably up to 17% by volume, more preferably up to 14% by volume, even more preferably up to 10% by volume. or up to 5% by volume, based on the layer, and according to certain embodiments, the balance may be a solid cation exchanger. A layer adjacent to the first separator may also comprise only or contain only the solid cation exchanger. According to certain embodiments, the salt bridge space further comprises a solid cation exchanger which is at least partially in contact with the first separator.

As already stated above for the solid anion exchanger, it is preferred in this case for the solid cation exchanger to be in contact, at least in the region of the anode on the opposite side of the first separator, ie for example more than 50% of the area of the first separator, preferably more than 60%, more preferably more than 70%, in particular more than 80%, that touch this, based on the area of the first separator, which is in contact with the anode.

According to certain embodiments, the solid cation exchanger is not in full contact with the first separator, in particular not in the region in which the anode on the opposite side of the first separator contacts it in order to be able to ensure fluid transport between the first separator and the solid cation exchanger , It is thus also preferred according to certain embodiments that the solid cation exchanger at least in the region of the anode on the opposite side of the first separator with this with 99% or less of the area of the first separator, preferably 97% or less, more preferably 95% or less , in particular 92% or less, is in contact with the solid cation exchanger with respect to the area of the first separator which is in contact with the anode.

It is also true for the multilayered configurations of the salt bridge space that solid ion exchangers containing no, eg strongly basic, anion exchange materials and / or no solid ones Anion exchangers are preferably not in contact with the first ion exchange membrane, eg an AEM, to avoid gas release at the point of contact.

According to certain embodiments, the composition of the filling must in particular be e.g. not homogeneous along the cathode-anode junction. Thus, the filling may also be layered, for example with a, e.g. strongly basic, solid anion exchanger or a mixture comprising the solid anion exchanger in the region of the cathode and the first ion exchange membrane, e.g. an AEM, and a, e.g. strong-acid, solid cation exchanger or a mixture comprising the solid cation exchanger in the region of the anode and the first separator.

It is not specified how many different layers can be used, nor their sequences, as long as they meet the requirement that the first ion exchange membrane, e.g. an AEM, adjoining material, e.g. contains strongly basic, anion exchangers.

For example, in such a multi-layered structure of the filling, two or more layers may be present as in FIG 7 to 9 is shown by way of example for two layers.

The cell structure with cathode K , Anode A . AEM and separator S and the cathode compartment I and anode compartment III this corresponds to the 5 , and only the construction of the filling in salt bridge space II is different. In 7 Adjacent to the AEM a layer with one, for example, strongly basic, anion exchange material 4 while to the separator S a layer with a mixed ion exchange material 2 containing, for example, strongly basic, anion exchange material adjacent. In 8th is this mixed ion exchange material 2 containing, for example, strongly basic, anion exchange material of 7 by, for example, acidic or strongly acidic, cation exchange material 3 replaced. In 9 is again compared to 8th that at the AEM attached material by a mixed ion exchange material 2 containing, for example, strongly basic, anion exchange material has been replaced.

According to certain embodiments, the filling, even if it consists only of the solid anion exchanger, is not closed, so that it can be flowed through by an electrolyte and / or a liquid-gas bubble mixture, thus, e.g. Pores or structured open spaces.

Another aspect of the present invention relates to an electrolysis plant comprising an electrolysis cell according to the invention. The corresponding embodiments of the electrolysis cell as well as further exemplary components of an electrolysis plant according to the invention have already been discussed above and are therefore also applicable to the electrolysis plant according to the invention. According to certain embodiments, an electrolysis plant according to the invention comprises a multiplicity of electrolysis cells according to the invention, wherein it is not excluded that there are also other electrolysis cells in addition.

According to certain embodiments, the electrolysis plant according to the invention further comprises a recycling device, which is connected to a discharge of the salt bridge space and a supply of the cathode space, which is adapted to lead a reactant of the cathode reaction, which can be formed in the salt bridge space again in the cathode space.

An electrolytic cell according to the invention is exemplified in 10 shown, in which case the electrolytic cell with the cathode compartment I , the salt bridge room II and the anode compartment III , the anode A, the separator S, the cathode K and the first ion exchange membrane as AEM for example, according to the structure in 5 or 6 can be constructed. To the cathode space CO _{2 is} supplied and remaining from the cathode space CO ₂ , product P and possibly water removed, the water is separated. CO ₂ generated in the salt bridge space and possibly CO ₂ that has passed into the salt bridge space can be recycled via a return to the cathode space after electrolyte j is separated from the salt bridge space, which can also be recycled. On the anode side becomes an anolyte A to the anode room III an example of anodic conversion of H ₂ O and / or HCl to O ₂ and / or Cl _{2 is} shown, wherein the half-cell reaction does not limit the invention. The other symbols in 10 are common fluidic symbols.

According to certain embodiments, the electrolysis plant according to the invention 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, gases such as CO ₂ or To remove O ₂ , and thus to allow a return of anolyte and / or the electrolyte in the salt bridge space. This is particularly advantageous when both come from a be pumped common reservoir, so there is only a common anolyte / electrolyte for salt bridge reservoir space, so the anolyte and the electrolyte in the salt bridge space are identical.

According to certain embodiments, the electrolysis plant according to the invention comprises two separate circuits for anolyte and electrolyte in the salt bridge space, which may optionally have separate devices for electrolyte treatment, in particular devices for removing dissolved gases from an acid, or wherein only the circuit for the electrolyte in Salt bridge space has a corresponding device.

In a still further aspect, the present invention relates to the use of an electrolysis cell or an electrolysis plant according to the invention, which may also comprise a plurality of electrolysis cells according to the invention, for the electrolysis of CO ₂ and / or CO.

In addition, disclosed is a method for the electrolysis of CO ₂ , wherein an electrolysis cell according to the invention or an electrolysis plant according to the invention is used, wherein CO _{2 is} reduced at the cathode and formed at the cathode bicarbonate and / or carbonate migrates through the first ion exchange membrane to an electrolyte in the salt bridge space wherein the bicarbonate and / or carbonate is also transported away from the first ion exchange membrane by the solid anion exchanger in the salt bridge space.

In addition to hydrogen carbonate and / or carbonate, it is not excluded that formate and / or acetate and / or further anions which form migrate through the first ion exchange membrane into the electrolyte of the salt bridge space.

The process according to the invention is carried out with the electrolysis cell according to the invention or the electrolysis plant according to the invention. Consequently, all features discussed with regard to the electrolysis cell according to the invention and the electrolysis system according to the invention can also be used in the method according to the invention. In particular, the cathode compartment, the cathode, the first ion exchange membrane, the anode compartment, the anode, the separator, the salt bridge compartment and the solid anion exchanger, as well as further components, have already been discussed with regard to the electrolysis cell according to the invention and the electrolysis unit according to the invention. The corresponding features can thus be carried out according to the method of the invention. Conversely, the inventive method is also carried out with the electrolysis cell according to the invention or the electrolysis plant, so that embodiments or aspects of the inventive method for the electrolysis of CO ₂ can find in this application, for example, with respect to an electrolyte in the salt bridge space and associated embodiments of the components of Electrolysis cell, such as the first separator.

The process according to the invention CO _{2 is} electrolyzed, although it is not excluded that on the cathode side in addition to CO ₂ another reactant such as CO is present, which can also be electrolyzed, ie a mixture is present, the CO ₂ comprises, and for example CO. For example, an educt on the cathode side contains at least 20 vol.% CO ₂ , for example at least 50 or at least 70 vol.% CO ₂ , and in particular the educt on the cathode side to 100 vol.% CO ₂ . In principle, the electrolysis cell according to the invention can also convert pure CO, in which case, however, no CO _{2 is} released in the salt bridge space.

In the process according to the invention, the filling comprising the solid anion exchanger or consisting of the solid anion exchanger is passed through by an electrolyte, ie a liquid medium. The electrolyte is not particularly limited in this case, but is according to certain embodiments, aqueous. Thus, according to certain embodiments, the salt bridge space comprises an aqueous electrolyte. It may correspond to or be different from the anolyte and / or catholyte, if present.

According to certain embodiments, the electrolyte of the salt bridge space comprises an acid, preferably a water-soluble or water-miscible acid. According to certain embodiments, the electrolyte contains at least 10 ^-6 mol / l H ⁺ and / or its hydrated variants, preferably at least 10 ^-4 mol / l, more preferably at least 10 ^-3 mol / l, even more preferably at least 10 ^-2 mol / l. According to certain embodiments, the electrolyte of the salt bridge space comprises substantially no mobile cations other than H ⁺ and / or its hydrated variants. Preferably, according to certain embodiments, the electrolyte in this case does not comprise any mobile cations except protons, apart from mobile cations in one Amount of common impurities. The electrolyte serves to discharge the CO ₂ 's and keep the filling moist.

The at least one acid in the electrolyte in the salt bridge space is not particularly limited here, but is preferably a water-soluble and / or water-miscible acid, such as HCl, HBr, HI, H ₂ SO ₄ , H ₃ PO ₄ , HTfO (trifluoromethanesulfonic acid), etc. By using at least one acid in the electrolyte, the CO ₂ release from bicarbonate and / or carbonate in the solid anion exchanger, for example a basic or strongly basic ion exchanger, is favored. The release of the CO ₂ preferably takes place in the volume of the salt bridge space and not at the contact surface between the filling comprising the solid anion exchanger or the solid anion exchanger and the separator, since this would also be associated with high voltage losses.

According to certain embodiments, improved gas release in the salt bridge space can be achieved through the use of multilayer fillings as described above. It is of course also possible to construct an electrolyte gradient in the salt bridge space in order to achieve preferential release in the salt bridge space and not at separators such as the first ion exchange membrane, the first separator and optionally further separators and / or ion exchange membranes, for example with multiple electrolyte feeds to the salt bridge space or Layers of fillings, where laminar flows may also be possible to create such electrolyte gradients.

In certain embodiments, the fill comprising the solid anion exchanger or consisting of the solid anion exchanger is preferably ionically conductive to enhance charge transport through the electrolyte.

It is not excluded in the process of the invention to use only water as the electrolyte in the salt bridge space. For this purpose, however, the first separator is preferably designed as an ion exchange membrane comprising a cation exchanger, for example as a cation exchange membrane (CEM), or as a bipolar membrane (BPM). Preferably, the solid filling in addition to the solid anion exchanger then also contains acidic components, e.g. Cation exchanger. Because of the conductivity, however, the use of an acid solution is preferred.

If the first separator is designed as a diaphragm, the electrolyte in the salt bridge space comprises at least one acid, since the diaphragm is not intrinsically ion-conducting. The electrolyte of the salt bridge space may in this case correspond to the anolyte, for example, but also be different.

A particularly preferred embodiment in the process according to the invention results from the use of the solid anion exchanger, if appropriate in a mixture with further constituents in the filling of the salt bridge space, in combination with an acidic electrolyte. As a result, in comparison to the prior art, the contact area between the anion exchanger of the first ion exchange membrane and acidic media can be greatly increased. In solutions according to the prior art, for example in the US 2017037522 A1 and DE 102017208610.6 , the surface of the first ion exchange membrane is always the transition to the acidic medium. This transition is inventively shifted in the volume of the salt bridge space and thereby increases the surface massively. As a result, the insulating effect of gas bubbles formed during CO ₂ electrolysis has less negative effects on the cell voltage. The effect of the anion exchanger / transporter contained in the first ion exchange membrane as a transporter for anions can be continued by the filling in the salt bridge space.

According to certain embodiments, the anode compartment comprises an anolyte which comprises a liquid and / or dissolved acid, preferably wherein the anolyte and / or the acid in the salt bridge space or the electrolyte in the salt bridge space no mobile cations except protons and / or deuterons, in particular no metal ions. Cations, includes. According to certain embodiments, an acid in the salt bridge space does not comprise mobile cations except protons and / or deuterons, especially 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 ^-1 m ² / (s · V), in particular of 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 ⁺ ", especially 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 (in particular in the case of CCM anode) or acids with non-oxidizable anions can be used as the anolyte or reagent. For a halogen generation at the According to this example, the halogen-hydrogen acids HCl, HBr and / or HI are suitable for the anode, for example halide salts are not suitable when using a diaphragm as the first separator membrane, but when using a bipolar membrane as the first separator Membrane can be used. The use of SO ₂ in the anolyte for the production of sulfuric acid, or H ₂ O for the production of H ₂ O ₂ , etc., is possible.

An exemplary method according to the invention will subsequently be described with reference to a specific embodiment of the electrolysis cell 5 explained, which is further discussed below. The statements here relate to a special embodiment of the electrolysis cell 5 so that the following explanations are not in the 5 shown embodiment described above. In such an exemplary method is the cathode space I from the salt bridge room II by a composite of a CO ₂ reducing cathode K and one AEM separated. The cathode compartment I is traversed by, for example moistened, CO ₂ , which is reduced, for example, to CO, C ₂ H ₄ . The moistened CO ₂ stream represents the substrate supply of the cathode. In the sense of a classic three-chamber cell, it represents the catholyte.

The salt bridge room II is from the anode compartment III through the first separator S (eg diaphragm, bipolar membrane, cation-conducting membrane) in combination with the anode A separated, wherein - as stated above, it is also possible that the anode space III directly connected to the first separator. The salt bridge room II is packed with a flowable solid filling containing one, for example, strongly basic, anion exchanger, and is flowed through by an electrolyte flow, which may include an acid as well as water.

The first separator can be selected freely from, for example, a cation exchange membrane (CEM), a non-intrinsically ion-conducting hydrophilic gas separator (diaphragm) or a bipolar membrane (BPM), in which the anion-conducting layer is preferably oriented toward the anode. When using a diaphragm, the electrolyte in the anode compartment III and the liquid electrolyte in the salt bridge compartment are preferred II identical and conductive.

The anode compartment III is the anolyte, eg aqueous HCl, aqueous H ₂ SO ₄ , H ₂ O, etc., flows through, which is the anode A can supply with substrate. If the electrolyte of the salt bridge space and the anolyte have been selected to be identical, they can also be obtained from a common reservoir, but in particular suitable devices are present to avoid carryover of dissolved gases (degassing), for example when the electrolyte is returned.

As indicated above, different from 5 the anode compartment III also between the anode A and the first separator S are located. In such a case, however, the anolyte must be conductive.

The cathode compartment I and the anode compartment III In addition, for example, electrically conductive, eg not closed, structures may include, which serve to contact the electrodes. If the anode is not on the first separator, the requirement of conductivity can be omitted here. Preferably, the anolyte contains only salts and thus mobile "non H ⁺ " cations, when the first separator is a bipolar membrane.

The electrochemical conversion at the anode is not further restricted, wherein it preferably leads to the transfer of H ⁺ from (bipolar membrane) or through (diaphragm or CEM) the first separator in the electrolyte of the salt bridge space.

The above embodiments, refinements and developments can, if appropriate, be combined with one another as desired. Further possible refinements, developments and implementations of the invention also include combinations of features of the invention which have not been explicitly mentioned above or described below with regard to the exemplary embodiments. 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.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2017037522 A1 [0011, 0013, 0039, 0134]
• DE 102017208610 [0011, 0014, 0015, 0134]
• DE 102017211930 [0011, 0013, 0039, 0104]
• DE 102017208610.6 [0039]
• US 20160251755 A1 [0050]
• US 9481939 [0050]

Claims (15)

Electrolytic cell comprising a cathode compartment comprising a cathode; a first ion exchange membrane containing an anion exchanger adjacent to the cathode compartment, the cathode contacting the first ion exchange membrane; an anode compartment comprising an anode; and a first separator adjacent to the anode compartment; further comprising a salt bridge space, wherein the salt bridge space between the first ion exchange membrane and the first separator is arranged, wherein the salt bridge space comprises a solid anion exchanger, which is at least partially in contact with the first ion exchange membrane. Electrolysis cell after Claim 1 wherein the solid anion exchanger in the salt bridge space comprises cations which are immobilized in a polymeric backbone, which cations in particular can exchange hydrogencarbonate and / or carbonate ions. Electrolysis cell after Claim 1 or 2 , wherein the solid anion exchanger is present as a bed and / or porous structure. An electrolytic cell according to any one of the preceding claims, wherein the solid salt bridge space further comprises uncharged particles, nonionic ion exchangers and / or cation exchangers, preferably the uncharged particles, nonionic ion exchangers and / or cation exchangers, more preferably the uncharged particles and / or non ionic ion exchangers, in an area adjacent to the first ion exchange membrane in an amount of up to 20% by volume, based on the total amount of solid anion exchanger and uncharged particles, of nonionic ion exchanger and / or cation exchanger. An electrolytic cell according to any one of the preceding claims, wherein the first separator is a cation exchange membrane, a bipolar membrane or a diaphragm. Electrolysis cell according to one of the preceding claims, wherein the solid anion exchanger is basic, preferably strongly basic. An electrolytic cell according to any one of the preceding claims, wherein the solid anion exchanger is hydrophilic. An electrolytic cell according to any one of the preceding claims, wherein the salt bridge space further comprises a solid cation exchanger which is at least partially in contact with the first separator. Electrolysis plant, comprising an electrolytic cell according to one of Claims 1 to 8th , Electrolysis system after Claim 9 , further comprising a recirculation device, which is connected to a discharge of the salt bridge space and a supply of the cathode space, which is adapted to lead a reactant of the cathode reaction, which can be formed in the salt bridge space, back into the cathode space. Process for the electrolysis of CO ₂ , wherein an electrolytic cell according to one of Claims 1 to 8th or an electrolysis system Claim 9 or 10 is used, wherein CO _{2 is} reduced at the cathode and formed at the cathode bicarbonate and / or carbonate through the first ion exchange membrane to an electrolyte in the salt bridge space, wherein the bicarbonate and / or carbonate also by the solid anion exchanger in the salt bridge space of the first ion exchange membrane is transported away. Method according to Claim 11 wherein the salt bridge space comprises an aqueous electrolyte. Method according to Claim 11 or 12 wherein the electrolyte of the salt bridge space comprises an acid, preferably a water-soluble or water-miscible acid. Method according to one of Claims 11 to 13 wherein the electrolyte of the salt bridge space comprises substantially no mobile cations other than H ⁺ and / or its hydrated variants. Use of an electrolytic cell according to one of Claims 1 to 8th or an electrolysis system Claim 9 or 10 for the electrolysis of CO ₂ and / or CO.

Images