EP3658703A1

EP3658703A1 - Hydrocarbon-selective electrode

Info

Publication number: EP3658703A1
Application number: EP18812075.2A
Authority: EP
Inventors: Nemanja Martic; Christian Reller; Günter Schmid; Bernhard Schmid; David Reinisch
Original assignee: Siemens AG
Current assignee: Siemens Energy Global GmbH and Co KG
Priority date: 2017-11-16
Filing date: 2018-11-16
Publication date: 2020-06-03
Also published as: WO2019096540A1; WO2019096985A1; DE102018212409A1; AU2018367216A1; CN111373076A; US20200385877A1; EP3673099A1; US20210172079A1; US11846031B2; CN111433392A; AU2018369463A1

Abstract

The present invention relates to an electrode, which comprises at least one tetragonally crystallized compound containing at least one element selected from the group of Cu and Ag, the crystal lattice of the compound being of the space group I41/amd type.

Description

description

Hydrocarbon-selective electrode

The present invention relates to an electrode, a

An electrolytic cell, a method for producing a Elekt rode, a method for the electrochemical conversion of CCg and / or CO using an electrode, a use of a compound for the reduction or the electrolysis of CO2 and / or CO, and a use of an electrode to Re production or the electrolysis of CO2 and / or CO.

Currently, about 80% of global energy demand is covered by the burning of fossil fuels, whose combustion processes cause a global emission of about 34,000 million tons of carbon dioxide into the atmosphere each year. Due to this release into the atmosphere, most of the carbon dioxide is disposed of, e.g. for a lignite-fired power plant, up to 50,000 tonnes per day. Carbon dioxide is one of the so-called greenhouse gases, whose negative effects on the atmosphere and the climate are discussed. A technical challenge is to produce value products from CO2. Since carbon dioxide is thermodynamically very low, it can be difficult to reduce to recyclable products, which has left the fact reutilization of carbon dioxide so far in theory or in the academic world.

A natural carbon dioxide degradation takes place beispielswei se by photosynthesis. In this process, carbon dioxide is converted into carbohydrates spatially and spatially into many sub-steps in a time and at a molecular level. This process is not so simply adaptable on an industrial scale. A copy of the natural photosynthesis process with large-scale photocatalysis has not yet been sufficiently efficient. An alternative is the electrochemical reduction of carbon dioxide. Systematic studies of the electrochemical reduction of carbon dioxide are still a relatively recent field of development. Only for a few years has there been an effort to develop an electrochemical system that can reduce an acceptable amount of carbon dioxide. Research on a laboratory scale has shown that it is preferable to use metals as catalysts for the electrolysis of carbon dioxide. For example, from the publication "Electrochemical CCg reduction on metal electrodes by Y. Hori", published in: C. Vayenas, et al. (Eds.), Modern Aspects of Electrochemistry, Springer,

New York, 2008, pp. 89-189, Faraday efficiencies are taken on different metal cathodes, which are shown in the following Table 1, taken from this publication.

Table 1: Faraday efficiencies in the electrolysis of CCg on various electrode materials

The table gives Faraday efficiencies [%] of products resulting from carbon dioxide reduction on various metal electrodes. The values given for a 0.1 M potassium bicarbonate solution as electrolytes and current densities below 10 mA / cm ² .

If carbon dioxide is reduced almost exclusively to carbon monoxide, for example on silver, gold, zinc, palladium and gallium cathodes, a large number of hydrocarbons are formed as reaction products in a copper cathode.

For example, in an aqueous system on a silver cathode predominantly carbon monoxide and little hydrogen would arise. The reactions at the anode and cathode can then be exemplified with the following reaction equations:

Cathode: 2 C0 ₂ + 4 e + 4H ⁺ - 2 CO + 2 H ₂ 0

Anode: 2 H ₂ 0 - 0 ₂ + 4 H ⁺ + 4 e

Of particular economic interest is, for example, the electrochemical production of carbon monoxide,

Ethylene or alcohols.

Examples:

Carbon monoxide: C0 ₂ + 2 e + H ₂ 0 - ^► CO + 2 OH

Ethylene: 2C0 ₂ + 12e + 8H ₂ 0 - ^►C ₂ H ₄ + 12 OH

Methane: C0 ₂ + 8 e + 6 H ₂ 0 - ^► CH ₄ + 8 OH

Ethanol: 2C0 ₂ + 12 e + ^9H ₂ 0 - ^►C ₂ H ₅ OH + 12 OH

Monoethylene glycol 2 C0 ₂ + 10 e + 8 H ₂ 0 - ^► HOC ₂ H ₄ OH + 10 OH

The reaction equations show that for the production of ethylene from C0 _2, for example, 12 electrons need to be transferred.

The stepwise reaction of C0 ₂ proceeds via a variety of surface intermediates (-C0 ₂ , -CO, = CH ₂ , -H, etc.). For Each of these intermediates should preferably be given strong interaction with the catalyst surface (s) so that a surface reaction (or further reaction) between the corresponding adsorbates is made light. The product selectivity is thus directly dependent on the crystal surface or its interaction with the surface species. Thus, for example, by experiments on monocrystalline high-index surfaces of copper (Cu 711, 511) in Journal of Molecular Catalysis A Chemical 199 (1): 39-47, 2003, an increased ethylene selectivity can be shown. Materials which have a high number of crystallographic stages or have surface defects also have increased ethylene selectivities, as described in C. Reller,

R. Krause, E. Volkova, B. Schmid, S. Neubauer, A. Rucki,

M. Schuster, G. Schmid, Adv. Energy Mater. 2017, 1602114 (DOI: 10.1002 /aenm.201602114) and DE 102015203245 Al.

There is thus a close correlation between the nanostructure of the catalyst material and the ethylene selectivity. In addition to the property of selectively forming ethylene, the material should retain its product selectivity even at high conversion rates (current densities) or maintain the advantageous structure of the catalyst centers. Due to a high surface mobility of e.g. Copper, however, the generated defects or nanostructures are not always stable over long periods, so that even after a short time (60 min) a degradation of the electrocatalyst can be observed. The material loses the property of forming ethylene due to the structural change. In addition, with applied voltage on structured surfaces, the potentials vary slightly, so that at certain places in a confined space certain intermediates are formed before given, which then can terreagieren at some other place wei. As our own studies show, potential variations are significantly below 50 mV signifi cant.

The product selectivity with respect to hydrocarbons, eg ethylene, is obvious from both morphology and dependent on the chemical composition of the catalyst. For example, Cu ₂ O-based catalysts show increased Faraday efficiency for ethylene compared to CuO or Cu.

However, the chemical stability of the CU2O is not given under negative potential, in particular it is not stable under operating conditions to the reduction.

So far, no long-term stable catalyst systems are known from the prior art, the high current density

> 100 mA / cm ² CO2 can electrochemically reduce to hydrocarbons, such as ethylene. Technically relevant current densities can be achieved using gas diffusion electrodes (GDEs). This is known from the existing state Tech nik for example for large-scale operated chloralkali electrolyses.

There are already known Cu-based gas diffusion electrodes for the generation of hydrocarbons based on CO2 from the literature. In the work of R. Cook in J.

Electrochem. Soc., Vol. 137, no. 2, 1990, for example, a wet chemical process based on a PTFE 30B (suspension) / Cu (OAc) 2 / Vulkan XC 72 mixture is mentioned. The method describes how, on the basis of three coating cycles, a hydrophobic conductive gas transport layer and, on the basis of three further coatings, a catalyst-containing layer are applied. After each layer, a drying phase (325 ° C) followed by static pressing process (1000-5000 psi). For the obtained electrode, a Faraday efficiency of> 60% and a current density of> 400 mA / cm ^{2 was} specified. Reproduction experiments show that the described static pressing process is not too stable

Leads electrodes. An adverse influence of the mixed volcano XC 72 was also found, so that also no hydrocarbons were obtained.

Therefore, there is still a need for long-term stable, efficient electrodes and electrolysis systems for a manufacturer. development of hydrocarbons, such as ethylene, carbon dioxide and / or carbon monoxide.

An embodiment of the present invention relates to an electrode comprising at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd. In particular, the

Electrode include several of these compounds of different chemical composition.

The inventors have found that tetragonal crystallized compounds containing at least one element selected from Cu and Ag, the crystal lattices of the respective compounds belonging to the space group I4i / amd excellent as long-term stable catalysts for the reduction of Koh dioxide and / or carbon monoxide Hydrocarbons, such as ethylene, are suitable, especially at high current densities (> 200 mA / cm ² ). These tetragonal crystallized compounds are also referred to herein as a catalyst.

Tetragonal crystallized compounds of this kind have never before been used or considered as catalysts for the electrochemical reduction of CO 2 and / or CO. Inso far, the invention also relates to a use of one or more of these compounds as a catalyst for the electrochemical reduction of CO2 and / or CO. Furthermore, one or more of these compounds may also be included in the catalyst material in addition to other constituents. Also Kings nen one or more of these compounds can be used as a pre-catalyst. In the preparation of the Katalysatorat Materi as beyond a dendrite formation of the catalyst is possible, whereby overvoltages can be reduced. In particular, a gas diffusion electrode comprising at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd ge, as an electrode for the C0 ₂ reduction and / or CO reductive tion, which shows a high activity and a high selectivity for hydrocarbons, especially for ethylene. The electrode is also particularly suitable for an elec trochemical reaction in liquid electrolytes.

The ent in the electrode of the above embodiment held at least one tetragonal crystallized compound has a crystal lattice of the space group I4i / amd. The compound can be at least partially crystallized in the space group I4i / amd. There are different oxidation states in the compound, which are stabilized by the lattice structure. Furthermore, in the lattice structure, there are nacular three-dimensional cavities which are substantially parallel to the lattice constants a and b. Oxygen species can be transported through these tunnels. Surprisingly, this lattice structure also remains Sustainer when redox processes take place in the electrochemical reduction of CO2. The inventors were able to ascertain this by measurements with an X-ray diffractometer (PXRD) on electrodes after C0 ₂ electrolysis in which the starting phase of the tetragonally crystallized compound was present.

The inventors have also found that the electrode according to embodiments of the invention, preferably Gasdiffu sion electrodes or layers, preferably with at least 0.5 mg / cm ^{2 of} the catalyst or the catalyst combination, one or more of the following advantages in the electrochemical mix reduction of CO2 and / or CO may have hydrocarbons:

a higher selectivity for hydrocarbons, in particular for ethylene, compared to Ag, Cu, CU2O and / or CuO;

a higher stability in the reaction potential against ei ne reduction of the catalyst material;

a superior activity compared to Ag, Cu, CU2O and / or CuO; a lower overpotential for the reduction of CCg and / or CO to ethylene compared to Ag, Cu, CU2O and / or CuO; and

a high thermal stability of the catalyst up to 300 ° C and beyond.

When the electrode of embodiments, preferably gas diffusion electrodes or layers, preferably with at least 0.5 mg / cm ^{2 of} the catalyst or the Katalysatorat combination, an Ag / Cu mixed catalyst, in particular one of the tetragonal crystallized, both Ag and Cu comprises the compounds, the inventors compared to an Ag catalyst one or more of the following advantageous effects in the electrochemical reduction of CO2 found:

a reduced selectivity for CO;

an increased selectivity for hydrocarbons, in particular for ethylene, with increasing current density;

a reduced ^ production; and

a high activity with lower cathode potential.

The tetragonal crystallized compound may also be selected from CU4O3 and a compound which is isomorphous to CU4O3, in particular a compound which is isomorphous to paramelaconite. At least one of the lattice sites corresponding to the Cu ⁺ and the Cu ^{2+ can} contain Cu or Ag or portions of Cu or Ag in the crystal lattice of the isomer of CU4O3 (Cu ⁺ 2Cu ²⁺ 203). In this case, the isomorphic to CU4O3 connec tion can be selected from Ag _0, ssCeSii _, 42, Ag ₂ Cu203, Ag _0, 2sSii _{, 7} 2Yb, Cui, o ₃₅ TeI, CuCr ₂ 0 _4, C ₄ H ₄ CuN ₆ , Ag _{0 , 7} CeSii, 3, Ag ₈ O ₄ S ₂ Si, Ag ₃ CuS ₂ , CuTeCl, Ba ₂ Cs ₂ Cu ₃ Fi 2, CuO ₄ Rh ₂ , CuFe ₂ O ₄ , Ag _0, 3 CeSii, 7, Ag ₆ O ₈ SSi, BaCulnFv, Cuo, 99TeBr, BaCu ₂ 0 ₂ , Cui ₆ 0i _{4, i5} , YBa ₂ Cu ₃ 0 ₆ and

CsAggCl _ö CssNs _. The electrode may comprise any combination of said tetragonal crystallized compounds. By using one or more of these compounds in the electrode, the above-described advantages in the electrochemical reduction of CO 2 and / or CO to hydrocarbons can be achieved particularly comprehensively. The electrode may comprise the at least one tetragonal crystallized compound in an amount of 0.1-100 wt. %, preferably 40-100 wt. %, more preferably 70-100 wt. %, based on the electrode or on a region of the electrode. This amount of the at least one tetragonal crystallized compound promotes the electrochemical reduction of CCg and / or CO to hydrocarbons.

Furthermore, the at least one tetragonal crystallized compound can be applied to a carrier. In this case, the compound can be applied in particular with a mass density of at least 0.5 mg / cm ² . Preferably, the mass consumption can be 1 to 10 mg / cm ² . Furthermore, the electrode may be a gas diffusion electrode. As a result, the advantages explained above can be realized particularly well who the.

Furthermore, the invention relates to an electrolytic cell comprising an electrode according to embodiments, preferably as Katho de.

A further embodiment of the invention relates to a method for producing an electrode, in particular an electrode according to embodiments, comprising

Providing at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I 4i / amd; and

further comprising a step selected from:

Applying the compound to a carrier; and

Forms the connection to an electrode.

The method of the above embodiment enables the production of an electrode according to embodiments of the invention with the previously described advantages in the electrochemical reduction of CO2 and / or CO to hydrocarbons. In the process according to embodiments, the compound may be selected from CU4O3 and a compound which is isomorphic to CU4O3. In this case, in the crystal lattice of CU4O3 (Cu ⁺ 2Cu ²⁺ 203) isomorphic compound of at least one of the lattice sites corresponding to the Cu ⁺ and the Cu ²⁺ , Cu or Ag or portions of Cu or Ag. In this case, the isomorphic to CU4O3 Ver connection can be selected from Ag ₀ , ssCeSii, 42, Ag ₂ Cu203,

YBa ₂ Cu ₃ 0 ₆ and CsAggCl _ö CssNs. In particular, in the process, any combination of said tetragonal crystallized compounds can be provided and processed.

The step of applying the compound to the carrier may be selected from

Applying a mixture or a powder comprising the compound to the carrier and dry rolling the mixture or powder onto the carrier;

Applications of a dispersion comprising the compound on the carrier; and

Contacting the carrier with a gas phase comprising the compound, and applying the compound to the carrier from the gaseous phase.

In this way, an electrode according to preferred Ausfüh tion forms with an existing on the support electrolytically active catalyst layer can be generated. The layer thickness of the generated catalyst layer may be in the range of 10 nm or more, preferably 50 nm to 0.5 mm. In this case, the compound can be applied with a mass coverage of at least 0.5 mg / cm ² . Furthermore, the rolling on at a temperature of 25-100 ° C, preferably 60-80 ° C, take place.

In embodiments of the method in which the compound is applied to a carrier, this may be a Gasdiffu sion electrode, a carrier of a gas diffusion electrode or a gas diffusion layer. In the method according to the above-described embodiment, in which an electrode is formed, the step of molding the compound to an electrode may include rolling out a powder comprising the compound to the electrode. Further, a mixture comprising the compound may be formed into the electrode, which mixture may be powdery or may contain a liquid.

In addition, in the process of embodiments, the electrodes may be made such that the compound is contained in an amount of 0.1-100 wt. %, preferably 40-100 wt. %, further preferably 70-100 wt. %, with respect to the electrode or to a region of the electrode. This amount of at least one tetragonal crystallized compound promotes electrochemical reduction of CCg and / or CO to hydrocarbons.

Furthermore, in the process according to embodiments, the compound can be provided and applied or formed in a mixture comprising at least one binder, preferably also an ionomer. By using a binder, a suitable adjustment of pores or channels of the formed electrode layer or electrode can be achieved, which promote the electrolytic conversion of CO2 and / or CO.

In this case, the at least one binder in an amount of> 0 to 30 wt. %, based on the total weight of the United bond and the at least one binder, be keep ent in the mixture.

Furthermore, an embodiment of the invention relates to a method for the electrochemical conversion of CO2 and / or CO, wherein CO2 and / or CO is introduced into an electrolytic cell comprising an electrode according to embodiments of the invention as a cathode at the cathode and reduced. Furthermore, an embodiment of the invention is directed to a use of at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd, for reduction or in the electrolysis of CO2 and / or CO2 CO.

Another embodiment relates to a use of an electrode according to embodiments for the reduction or the electrolysis of CO2 and / or CO.

Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments, which are explained in more detail in connection with the following drawings.

Description of the figures

The accompanying drawings, taken in conjunction with the description, are particularly illustrative of 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 shown to each other. Same, functionally identical and functionally equivalent elements, features and components are provided in the figures of the drawings, unless otherwise stated, each with the same reference characters. In the drawings show

Fig. 1 is the Pourbaix diagram of copper;

2 shows a measured powder X-ray diffractogram of CU4O3,

FIGS. 3 to 8 each show a simulated powder X-ray

diffractogram of Ag2Cu203, Ag3CuS2,

Ag ₈ 0 ₄ S ₂ Si, Cu0 ₄ Rh ₂ , CuCr ₂ 0 ₄ , and BaCu ₂ 0 ₂ in this order; 9 to 26 exemplary, schematic configurations for a construction of electrolysis cells according to embodiments;

Fig. 27 is an SEM photograph of Example 1;

28a to 28h results of electrochemical Messun conditions with CU4O3 of Example 1;

FIGS. 29 and 30, a powder X-ray diffractogram and a

SEM image of Example 2;

Figs. 31 and 32 are results of electrochemical measurements of Example 2;

33a to 33f results of electrochemical measurements for gaseous products of a C0 ₂ reduction with Ag ₂ Cu ₂ O ₃ according to Example 2;

34a to 34e results of electrochemical Messun conditions for liquid products of a C0 ₂ reduction with Ag ₂ Cu ₂ 0 ₃ according to Example 2; and

Fig. 35a and 35b Faraday efficiencies (FE) for the gasför shaped products ethylene and hydrogen CO reduction with Ag ₂ Cu ₂ 0 ₃ according to Example 2.

Detailed description of the invention

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

An electrode is an electrical conductor that can supply electrical current to a liquid, a gas, a vacuum or a solid body. In particular, an electrode is not Powder or a particle, but may comprise particles and / or a powder or be prepared from a powder. Ei ne cathode is in this case an electrode at which an electrochemical reduction can take place, and an anode, an electrode at which an electrochemical oxidation can take place. In this case, the electrochemical conversion takes place according to certain embodiments in the presence of preferably aqueous electrolytes.

Quantities in the context of the present invention are based on wt. %, unless otherwise stated or obvious from the context. In the material of the catalytic active region, e.g. a layer, an electrode or gas diffusion electrode according to embodiments of the invention, the Gew. % Shares to 100% by weight.

In the context of the present invention, what is meant to be hydrophobic is water-repellent. Hydrophobic pores and / or channels are, according to embodiments of the invention, those which reject water. In particular, hydrophobic properties may be associated with substances or molecules with non-polar groups.

In contrast, the ability to interact with water and other polar substances is understood to be hydrophilic.

In the context of the present invention, the term paramelaconite is used to denote naturally occurring and synthetically produced CU4O3. Preferably, in embodiments of the invention, synthetically produced CU4O3 is used.

Electrode several of these compounds of different chemical Mixer composition include. The compounds are centrosymmetric at room temperature. The tetragonal crystallized compound serves as a catalyst in the electrode and surprisingly leads to one or more of the above-described beneficial effects, especially in the reduction of carbon dioxide and / or carbon monoxide to hydrocarbons, such as ethylene or ethanol.

The tetragonal crystallized compound may be selected from CU ₄ O ₃ and a compound which is isomorphous to CU ₄ O ₃ , in particular a compound which is isomorphous to paramelaconite. In this case, in the crystal lattice of CU ₄ O ₃ (Cu ⁺ ₂ Cu ²⁺ ₂ 0 ₃ ) isomorphic compound of at least one of the lattice sites corresponding to the Cu ⁺ and the Cu ²⁺ , Cu or Ag or portions of Cu or Ag. Here, the isomorphic to Cu ₄ O ₃ compound is ^¬ selects be made of Ag _0, ₅₈ CeSii, _42, Ag ₂ Cu ₂ 0 _3, Ag _{0 28} Sii, ₇₂ Yb, Cui, O ₃ Ştei, CuCr ₂ 0 _4, C ₄ H ₄ CUN ₆ , Ag _{0, 7} CeSii, ₃ , Ag ₈ 0 ₄ S ₂ Si, Ag ₃ CuS ₂ , CuTeCl,

Ba ₂ Cs ₂ Cu ₃ Fi ₂ , CuO ₄ Rh ₂ , CuFe ₂ 0 ₄ , Ag _{0, 3} CeSii, ₇ , AgeCySSi, BaCuInF ₇ , Cuo, ₉₉ TeBr, BaC ^ Cy, Cui ₆ 0i ₄ , i ₅ , YBa ₂ Cu ₃ 0 ₆ and CsAggCleCssNs. The electrode may comprise any combination of said tet ragonally crystallized compounds. By using one or more of these compounds in the electrode, the above-described advantages in the electrochemical reduction of CO ₂ and / or CO to hydrocarbons can be achieved particularly comprehensively.

According to embodiments, in the crystal lattice of the CU4O3 (CU ⁺ 2CU ²⁺ 203) isomorphic compound starting from CU4O3, the Cu ⁺ lattice site may be entirely or partially replaced by another atom. The same can apply alternatively or additionally for the Cu ²⁺ grid position. In this case, the charge of the wholly or partly present at the Cu ⁺ - / Cu ²⁺ lattice site atom may differ from that of the Cu ⁺ or Cu ²⁺ . At least one of the Cu ⁺ and Cu ²⁺ corresponding lattice sites may contain Cu or Ag or portions thereof. Charge compensation can be achieved by monovalent, divalent or trivalent anions. An embodiment of the invention relates to an electrode comprising CU4O3 and / or Ag ₂ Cu203.

In the following, by way of example, the compounds CU4O3, Ag ₂ Cu ₂ 03, Ag ₃ CuS _2, Ag ₈ 0 ₄ S ₂ Si, Cu0 ₄ Rh _2, CuCr ₂ 0 _4, and BaCu ₂ 0 ₂ described with reference to FIGS. 1 to 8 , Figures 1 and 2 relate to CU4O3, wherein Figure 1 represents the Pourbaix diagram for copper and Figure 2 shows a measured powder X-ray diffractogram of CU4O3. FIGS. 3 to 8 each show a simulated powder X-ray diffractogram of Ag ₂ Cu ₂ O 3, Ag ₂ CuS ₂ , AgsCySi, CuCyRhp, CuCr ₂ 04, and BaCu ₂ O ₂ in this order.

CU4O3, also called paramelaconite, is a mixed valent oxide with equal proportions of mono- and divalent Cu ions and is therefore sometimes formally called Cu ⁺ ₂ Cu ²⁺ ₂ 03 or Cu ⁺ ₂ 0 · (Cu ²⁺ 0) ₂ worded. The crystal structure (space group J4i / amd) of paramelaconite was identified as tetragonal, consisting of interpenetrating chains of Cu ⁺ -0 and Cu ²⁺ -0. The Cu ²⁺ ions are coordinated with two 0 ^{2 ~} ions, while the Cu ⁺ ions are planarly coordinated with four 0 ^{2 ~} ions. Paramelaconite is thermodynamically stable below 300 ° C, at temperatures above 300 ° C it decomposes into CuO and Cu ₂ 0.

The electrochemical stability of paramelaconite is shown in the Pourbaix diagram of FIG. The graph shows the higher electrochemical stability of CU4O3 over the reduction compared to Cu ₂ 0. As can be seen from the graph, a preferred operating range of electrodes with paramelaconite is at a pH between 6 and 14, preferably between 10 and 14 Powder X-ray diffractograms of CU4O3 are shown in FIG. The powder X-ray diffractograms shown here were taken with a Bruker D2 PHASER diffractometer using CuK radiation at a scan speed of 0.02 ° s ^-1 .

In 2012, Zhao et al. in Zhao, L. et al. , Facile Solvothermal Synthesis of Phase-Pure CU4O3 Microspheres and Their Lithium Storage Properties, Chem. Mater. 2012, 24, pages 1136-1142, the synthesis of phase-pure

Paramelaconite microspheres using a simple solvothermal method. The C 1 -Cg microspheres were obtained by reacting the precursor copper (11) nitrate trihydrate (Cu (NO ₃ ) _{2 '} 3H ₂ O) in a mixed solvent of ethanol and N, N-dimethylformamide (DMF). The reaction was carried out in a 50 mL Teflon-lined stainless steel autoclave at 130 ° C for several hours. As described in the examples, the inventors could synthesize along the route of Zhao et al. increase the reaction volume to 1.1 1 and increase the yield to more than 10 g.

The compound Ag ₂ Cu ₂ C> ₃ whose X-ray diffractogram is shown in Fig. 3 consists of silver (I) and copper (II) ions. The structure contains two different oxygen species (01 and 02) with a ratio of 1: 2. Oxygen species 01 is in the tetrahedral environment of four copper (II) ions. The oxygen species 02 is tetrahedral to give two Ag + ions and two Cu2 + ions. It crystallizes in a tetragonal structure with the space group

141 / amd. The lattice constants are a = b 0.5886 nm and

c = 1.0689 nm (CC = 51672, ICSD). The crystal lattice contains an extensive network of three-dimensional tunnels through which oxygen species and ions can be transported. The transport of oxygen through the tunnels allowed a change in the oxidation states from Agl + to Ag3 + as well as Cu2 + to Cul + without the lattice structure collapsing.

The direct band gap is 2.2eV.

FIG. 4 shows the simulated X-ray diffractogram of FIG

Ag ₃ CuS _2. The mineral Jalpaite with the same sum formula exists at 25 ° C in the space group I4i / amd and has a pronounced ionic conductivity. Fig. 5 shows the Si mulated X-ray diffractogram of Ags0 ₄ S ₂ Si. Fig. 6 illustrates the simulated X-ray diffractogram of Cu0 ₄ Rh _2. The synthesis of Cu0 ₄ Rh ₂ was the fact that Rh ₂ 0 ₃ and CuO and pelleted in an evacuated quartz ampoule at 1073 K annealed for 24 h (according to Ohgushi K., Gotou H., Yagi T., Ueda Y .: High-pressure synthesis and magnetic properties of orthorhombic CuRh ₂ 0 _4; J. Phys. Soc. Jpn. 75 (023707) (2006 )

1-3). FIG. 7 shows the simulated X-ray diffractogram of CuCr ₂ O ₄ . Fig. 8 shows the simulated

X-ray diffractogram of BaCu ₂ 0 ₂ .

The crystal lattices of all tetragonal compounds used in embodiments of the inven tion in space group I4i / amd crystallized compounds each contain an extensive network of three-dimensional tunnels through which oxygen species can be transported. this makes possible

a change in the oxidation state without the lattice collapse. This property is in the view of the inventors one reason why the compounds surprisingly for the use as catalysts, in particular in the electrolysis of C0 ₂ and / or CO, as

have proven extremely beneficial.

In the electrode of embodiments of the invention, the amount of the tetragonal crystallized compound is

Room group I4i / amd not limited. According to certain embodiments, the compound is present in an amount of 0.1-100% by weight, preferably 40-100% by weight. %, more preferably 70-100 wt. %, based on the electrode. According to further embodiments, the compound is present in an amount of 0.1-100% by weight, preferably 40-100% by weight, more preferably 70-100% by weight, based on the catalytically active part of the electrode, for example in one Layer of the electrode, for example, if the electrode is multi-layered, for example with a gas diffusion layer, and / or is designed as a gas diffusion electrode.

According to certain embodiments, the tetragonal crystallized connection of the space group I4i / amd is applied to a carrier, which is not particularly limited, as much in terms of the material as the embodiment. For example, a carrier may have a compact solid body. per, eg in the form of a pencil or strip, eg a metal strip. The compact solid may include, for example, a metal such as Cu or an alloy thereof, or may exist. Further, the support may be a porous structure, for example a sheet, such as a net or a Ge active, or a coated body. The support may also be formed, for example, as a gas diffusion electrode, possibly also with a plurality, for example 2, 3, 4, 5, 6 or more layers, of a suitable material or ge as a gas diffusion layer on a suitable substrate, which is also not particularly limited and may also include multiple layers, eg, 2, 3, 4, 5, 6, or more. As a gas diffusion electrode or gas diffusion layer may also serve a commercially available electrode or layer accordingly. The material of the carrier is preferably conductive and comprises, for example, a metal and / or an alloy thereof, a ceramic such as ITO, an inorganic non-metal conductor such as carbon and / or an ion- or electrically conductive polymer.

Also, the tetragonal crystallized compound of

Space group I4i / amd in the production of

Gas diffusion layers or gas diffusion electrodes are used. Thus, according to certain embodiments, an electrode is a gas diffusion electrode or an electrode comprising a gas diffusion layer, wherein the gas diffusion electrode or the gas diffusion layer contains or even consists of the tetragonal crystallized compound of the space group I4i / amd. When a gas diffusion layer comprises the tetragonal crystallized compound of

Raumgroupppe I4i / amd, this may be applied to a porous or non-porous substrate.

If the tetragonal crystallized compound of space group I4i / amd is applied to a support, it is according to certain embodiments with a mass of at least 0.5 mg / cm ² applied. In this case, the application is preferably not flat in order to produce a larger active surface. to be able to provide. In addition, pores or pores of the carrier are preferably not substantially sealed with the application, so that a gas such as carbon dioxide can easily reach the compound. According to certain embodiments, the compound with a mass coverage of between 0.5 and 20 mg / cm ² , preferably between 0.8 and

15 mg / cm ² , more preferably between 1 and 10 mg / cm ² brought up. On the basis of these values, the amount of the tetra-crystalline compound of the space group I4i / amd can be suitably determined as a catalyst for application to a specific support.

The inventors have found, in particular, that embodiments of the gas diffusion electrode, in particular gas diffusion electrodes or layers, preferably with at least 1 mg / cm ^{2 of} the tetragonal crystallized compound of the space group I4i / amd, have one or more of the following advantages in the electrochemical reduction of CO2 and / or CO to hydrocarbons may have:

a higher stability at the reaction potential against a reduction to Ag or Cu;

a superior activity compared to Ag, Cu, CU2O and / or CuO; and

a lower overpotential for the reduction of CO2 to ethylene compared to Ag, Cu, CU2O and / or CuO.

When the electrode of embodiments, preferably embodiments of gas diffusion electrodes or layers, preferably with at least 0.5 mg / cm ^{2 of} the catalyst or the catalyst combination, an Ag / Cu mixed catalyst, in particular special tetragonal crystallized, both Ag and Cu In comparison with an Ag catalyst, the inventors have, in particular, one or more of the following advantageous effects in the case of chemical reduction of CO2 detected:

a reduced selectivity for CO;

a reduced ^ production; and

a high activity with lower cathode potential.

According to certain embodiments, the electrode is a gas diffusion electrode, which is not particularly limited and single or multi-layered, e.g. with 2, 3, 4, 5, 6 or more layers can be executed. In such a multilayered gas diffusion electrode, for example, the tetragonally crystallized compound of the space group I 4i / amd can then also be present only in one layer or not in all layers, ie for example form one or more gas diffusion layers. Particularly with a gas diffusion electrode, good contact with a gas comprising CO 2 and / or CO or essentially consisting of CO 2 and / or CO is very well possible, so that an efficient electrochemical production of C 2 H 4 can be achieved here. In addition, however, this can also be achieved with an electrode comprising a gas diffusion layer containing or consisting of the tetragonal crystallized compound of the space group

I4i / amd be effected, since here also a large surface Reaktionsflä for such a gas can be offered.

In embodiments, the following parameters and properties of a hydrocarbon-selective gas diffusion electrode or gas diffusion layer, individually or in combination, have proved favorable:

Good wettability of the electrode surface so that an aqueous electrolyte can come into contact with the catalyst.

• High electrical conductivity of the electrode or the catalyst and a homogeneous potential distribution over the entire electrode surface (potential-dependent product selectivity).

• High chemical and mechanical stability during electrolysis (suppression of cracking and corrosion). The ratio between hydrophilic and hydrophobic Po renvolumen is preferably in the range of about (0.01-1): 3, more preferably about in the range of (0.1-0, 5): 3 and preferably at about 0.2: 3rd

• Defined porosity with a suitable ratio between hydrophilic and hydrophobic channels or pores.

Further advantageous in a gas diffusion electrode or a gas diffusion layer according to execution forms average pore sizes in the range of 0.2 to 7 ym, be preferably in the range of 0.4 to 5ym and preferably in the range of Be 0.5 to 2ym.

According to certain embodiments, the electrode contains particles comprising the tetragonal crystallized compound of the space group I4i / amd, such as Cu403_Particles. For example, these particles are used to prepare the electrode of embodiments of the invention, in particular a gas diffusion electrode, or a gas diffusion layer. The particles used or contained in the electrode can have a substantially uniform particle size, for example between 0.01 and 100 μm, for example between 0.05 and 80 μm, preferably 0.08 to 10 μm, more preferably between 0.1 and 5 ym, eg between 0.5 and 1 ym. In addition, the catalyst particles according to certain embodiments further have a suitable electrical conductivity, in particular a high electrical conductivity s of> 10 ³ S / m, preferably 10 ⁴ S / m or more, more preferably 10 ⁵ S / m or more, in particular other 10 ⁶ S / m or more. In this case, if appropriate, suitable additives such as metal particles may be added in order to increase the conductivity of the particles. In addition, according to certain embodiments, the catalyst particles have a low overpotential for the electroreduction of CO2 and / or CO. Furthermore, the catalyst particles according to certain embodiments have a high purity without foreign metal traces. By suitable structuring, possibly with By using promoters and / or additives, high selectivity and long-term stability can be achieved.

For a particularly good catalytic activity, a gas diffusion electrode or an electrode with gas diffusion layer according to embodiments have hydrophilic and hydrophobic Be rich that allow a good three-phase relationship liquid, solid, gaseous. Particularly active catalyst centers are liquid, solid, gaseous in the three-phase region. The gas diffusion electrode of certain embodiments thus has a penetration of the bulk material with hydrophilic and hydrophobic channels in order to obtain as many as possible three-phase areas for active catalyst centers. The same applies to the gas diffusion layer according to embodiments.

Thus, the hydrocarbon selective gas diffusion electrodes and gas diffusion layers of embodiments may have multiple intrinsic properties. There may be a close interplay between the electrocatalyst and the electrode.

The electrode of embodiments may comprise, in addition to the tetragonal crystallized compound of space group I4i / amd, further components such as promoters, conductivity additives, cocatalysts and / or binders / binders. The Be handles binders and binders are in the present invention as synonymous words with the same meaning be. Thus, for example, as indicated above, additives can be added to increase the conductivity in order to enable good electrical and / or ionic contacting of the tetragonally crystallized compound of the space group I4i / amd. For example, cocatalysts may optionally catalyze the formation of further products from ethylene and / or also the formation of intermediates in the electrochemical reduction of CO2 to ethylene. However, the co-catalysts may also catalyze completely different reactions, for example, if a starting material other than CO2 in a electrochemical reaction, eg an electrolysis, is used.

In the electrode of embodiments, in particular in a gas diffusion electrode or a gas diffusion layer, at least one binder may be contained, which is not particularly limited. It is also possible to use two or more different binders, even in different layers of the electrode. The binder for the gas diffusion electrode, if present, is not particularly limited, and includes, for example, a hydrophilic and / or hydrophobic polymer, for example, a hydrophobic polymer. In this way, a suitable adjustment of the predominantly hydrophobic pores or channels can be achieved. According to certain embodiments, the at least one binder is an organic binder, e.g. selected from PTFE

(Polytetrafluoroethylene), PVDF (polyvinylidene difluoride), PFA (perfluoroalkoxy polymers), FEP (fluorinated ethylene-propylene copolymers), PFSA (perfluorosulfonic acid polymers), and mixtures thereof, especially PTFE. To adjust the hydrophilicity, hydrophilic materials such as polysulfones, i. Polyphenylsulfones, polyimides, polybenzoxazoles or

Polyether ketones or generally in the electrolyte electrochemically stable polymers, as well as, for example, polymerized "Ioni cal liquids", or organic conductors such as PEDOT: PSS or PANI (champhersulfonsäuredorted polyaniline) are set .This allows a suitable adjustment of the hydrophobic pores or channels In particular, for the preparation of the gas diffusion electrode PTFE Parti angle with a particle diameter between 0.01 and 95 ym, preferably between 0.05 and 70 ym, more preferably between 0.1 and 40 ym, for example 0.3 to 20 ym, for example Suitable PTFE powders include, for example, Dyneon® TF 9205 and Dyneon TF 1750. Suitable binder particles, for example PTFE particles, may for example be approximately spherical, for example spherical, and For example, they can be prepared by emulsion polymerization the binder particles are free of surface-active substances. The particle size can be determined, for example, according to ISO 13321 or D4894-98a and can correspond, for example, to the manufacturer's instructions (eg TF 9205: medium

Particle size 8ym according to ISO 13321; TF 1750: medium

Particle size 25ym according to ASTM D4894-98a).

The binder may, for example, in a proportion of 0.1 to 50 wt. %, for example when using a hydrophilic ion transport material, e.g. 0.1 to 30 wt. %, preferably from 0.1 to 25 wt. %, e.g. From 0.1 to 20% by weight, more preferably from 3 to 20% by weight, more preferably from 3 to 10% by weight, even more preferably from 5 to 10% by weight, based on the electrode, in particular based on the gas diffusion electrode, or on the catalytically active area, eg a layer containing electro de. According to certain embodiments, the binder has a pronounced shear thinning behavior such that fiber formation occurs during the mixing process. Ion transport materials may, for example, be mixed in at higher contents if they contain hydrophobic or hydrophobicizing structural units, in particular containing F, or fluorinated alkyl or aryl units. It can fibers formed in the manufacture fibers around the particles wrap without completely enclose the surface. The optimum mixing time can be determined, for example, by direct visualization of the fiber formation in the scanning electron microscope.

Also, an ion transport material may find application in the electrode of embodiments, which is not particularly limited. The ion transport material, for example an ion exchange material, may be, for example, an ion transport resin, for example an ion exchange resin, but also another ion transport material, for example an ion exchange material such as a zeolite, etc. According to certain embodiments, the ion transport material is an ion exchange resin. This is not particularly limited. According to certain embodiments, the ionic transport material an anion transport material, beispielsewei an anion exchange resin. According to certain embodiments, the anion transport material or material is

Anionic transporters an anion exchange material, e.g. an anion exchange resin. In certain embodiments, the ion transport material also has a

Kationenblockerfunktion, so can prevent penetration of Katio NEN in the electrode, in particular a Gasdiffusionselektro or an electrode with gas diffusion layer, or at least reduce. Especially an integrated

Anionene transporter or an anion transport material with tightly bound cations can represent a blockade for mobile cations by Coulomb repulsion, which a salt excretion, especially within a gas diffusion electrode or a gas diffusion layer, in addition can counteract entge. It is irrelevant whether the Gasdiffusi onselektrode is completely set with the anion transporter. Anion-conducting additives can additionally increase the power of the electrode, in particular during a reduction. In this case, an ionomer, such as e.g. 20 Gew.iige alcoholi cal suspension or a 5 wt.% Suspension of a

Anion exchange ionomer (e.g., AS 4 Tokuyama). Also, e.g. the use of Type 1 (typically trialkyl ammonium functionalized resins) and Type 2 (typically alkyl hydroxyalkyl functionalized resins)

Anion exchange resins possible.

Another embodiment relates to an electrolytic cell comprising the electrode of embodiments. The electrode can be used as a compact solid, as a porous electrode, e.g. Gas diffusion electrode, or as a coated body, e.g. with a gas diffusion layer, be formed. Here are embodiments as a gas diffusion electrode or electrode with gas diffusion layer comprising or consisting of the tetragonal crystallized compound of the Raumgrupppe

I4i / amd preferred. In the electrolysis cell, the electrode of embodiments is preferably the cathode in order to reduce the on, for example, the reduction of a gas comprising or consisting of CCg and / or CO.

The other components of the electrolysis cell are not particularly limited, and it includes those which are commonly used in electrolysis cells, e.g. a counter electrode.

In the electrolytic cell, the electrode of execution forms a cathode, so be connected as a cathode. According to certain embodiments, the electrolysis cell further comprises an anode and at least one membrane and / or at least one diaphragm between the cathode and anode, for example at least one anion exchange membrane.

The other components of the electrolytic cell, such as the counter electrode, e.g. the anode, possibly a membrane and / or a diaphragm, supply line (s) and discharge (s), the voltage source voltage, etc., and other optional devices such as cooling or heating devices are not particularly limited. The same applies to anolytes and / or catholytes used in such an electrolysis cell, wherein the electrolytic cell according to certain embodiments on Kathodensei te for the reduction of carbon dioxide and / or CO is used. As part of the invention, the design of the Ano denraums and the cathode compartment is also not particularly limited.

Likewise, an electrolysis cell of embodiments in an electrolysis plant find application. Thus, an electrolytic system is also disclosed, comprising the electrode or the electrolysis cell of embodiments.

A suitable electrolytic cell for the use of the Elekt rode of embodiments of the invention, for example, a Gasdif fusion electrode comprises, for example, the electrode as Ka method with a not further limited anode. The electrochemical reaction at the anode / counter electrode is also not particularly limited. The cell is preferred by the Electrode as a gas diffusion electrode or as an electrode with gas diffusion layer divided into at least two chambers, of which the counter electrode facing away from the chamber (behind the GDE) acts as a gas chamber. The remainder of the cell may be traversed by one or more electrolytes. The cell may further comprise one or more separators, so that the cell may also comprise, for example, 3 or 4 chambers. These separators can be not only in trinsically ion-conducting gas separators (diaphragm) as well as ion-selective membranes (anion exchangers Memb ran, cation exchange membrane, proton exchange membrane) or bipolar membranes, which are not particularly be are limited. These separators can be flowed around by one or more electrolytes from both sides as well as, if you own one for this operation, directly against one of the electrodes. Thus, for example, both the cathode and the anode be designed as a half-membrane electrode composite, wherein in the case of the cathode, the electrode of embodiments, in particular as a gas diffusion electrode or as an electrode with gas diffusion layer, preferably part of this composite. The counter electrode may also be performed, for example, as a catalyst-coated membrane. In a two-chamber cell, both electrodes can also abut directly on a common membrane.

If the electrode of embodiments as a gas diffusion electrode is not applied directly to a separator membrane, both a "flow through" operation, in which the electrode is flowed through by the feed gas, as well as a "flow-by" operation is possible, wherein the feed gas is passed past the side facing the electrolyte abge. If the gas diffusion electrode is directly connected to the separator or one of the separators, only "flow-by" operation is possible, especially when more than 95% by volume, preferably more than 98% by volume, of the product gases is used over the gas side of the

Electrode be discharged.

Exemplary embodiments for a structure of electrolyte cells according to embodiments of the invention - also in a Sound with the above statements - as well as anode and Ka thodenräumen are shown in Figures 9 to 26 schematically Darge, wherein in Figures 24 to 26 further components of an electrolysis system are shown schematically. In the fol lowing concepts of electrolysis cells will be explained, which are compatible with the method of embodiments of the invention for the electrochemical conversion of carbon dioxide and / or carbon monoxide and can be used in embodiments of the proceedings.

The following abbreviations are used in FIGS. 9 to 26: I-IV: spaces in the electrolysis cell, as described below in each case

K: cathode

M: membrane

A: anode

AEM: anion exchange membrane

CEM: cation / proton exchange membrane

DF: Diaphragm

k: catholyte

a: anolyte

GC: gas chromatograph

GH: gas humidification

P: permeate

The other symbols in the diagrams are usual calibrate Fluidic- switching _Z.

In Figures 9 to 26 exemplary structures are shown with ver different membranes, which, however, do not limit the cells shown. Thus, instead of a membrane, for example, a diaphragm may be provided. Also, FIGS. 9 to 26 show on the cathode side a reduction of a gas, for example comprising or consisting essentially of CO.sub.2, wherein the electrolysis cells are not limited thereto and correspondingly reactions on the cathode side in the liquid phase or solution, etc. are possible , In this regard too, the figures limit the electrolytes Not a cell of embodiments. Likewise, in the various constructions, anolyte, catholyte and optionally electrolyte may be the same or different in a space and are not particularly limited.

9 shows an arrangement in which both the cathode K and the anode A rest against a membrane M and behind the cathode K a reaction gas flows past in the cathode space I.

On the anode side, there is the anode space II. In FIG. 10, no membrane is found in comparison with FIG. 9, and the cathode K and the anode A are separated by the space II. The structure in Figure 11 corresponds in construction substantially to that of Fi gur 10, in which case the cathode K is flowed through.

FIG. 12 shows a two-membrane arrangement, wherein between two membranes M a bridge space II is provided which electrolytically couples the cathode K and the anode A. The cathode space I corresponds to that of FIG. 9, and the anode space III to the anode space II of FIG. 9. The arrangement in FIG. 13 differs from that of FIG. 12 in that the anode A does not bear against the second membrane M on the right.

In FIGS. 14 to 18, in turn, arrangements with only one membrane can be seen. In Figure 14, as in Figure 9, the cathode K flows behind in the space I, wherein on the other side of a cathode chamber II II is adjacent to the membrane M. The membrane M is in turn separated from the anode A by the anode compartment III. The structure in Figure 15 corresponds to that in Figure 14, wherein the cathode K is flowed through here. In Figures 16 and 17, the membrane M is directly adjacent to the anode A, so that the Ano denraum III on the side facing away from the membrane M of the anode A is located, otherwise they each show the back-flowed and flow-through variant of Figures 14 and 15. FIG 18 shows a back-flow variant in which the membrane M abuts the cathode, the space II makes the electrolytic contact to the anode A and space III is located on the gegenüberlie ing side of the anode A. Figures 19 to 23 show further variants of two-membrane arrangements, with backflowed Varian th at the cathode in Figures 19, 21 and 23, and flows through th variants in Figures 20 and 22. In Figures 19 and 20 is a membrane (Right) at the anode, so that the Ano denraum IV joins the right to the anode and a Kopp ment to the cathode compartment II on the bridge space III stattfin det. Likewise, such a coupling takes place in FIGS. 21 and 22, the anode space IV between membrane M and anode A lying here. In Figure 23 in turn is a membrane M (left) to the cathode K, so that a coupling to the anode room III is provided on the bridge space II, wherein on the right of the anode A, a further space IV is provided, in which, for example, another reactant gas for the oxidation at the anode A can be supplied.

Figures 24 to 26 show cell variants in which a reduction of CO2 at the cathode K after supply to the room I and an oxidation of water at the anode A - which is supplied to the anode space III with the anolyte a - is shown to oxygen at play These reactions do not restrict the demonstrated electrolytic cells and electrolysis systems. FIGS. 24 and 25 also show that the CO2 can be humidified in a gas humidification GH in order to facilitate the ionic contacting with the cathode K. Besides, as shown in Figs. 24 to 26, the product gas of the reduction can be analyzed with a gas chromatograph GC. The same applies, as shown in Figures 24 and 25, after separation of a permeate p for the

Reactant gas. In the example of FIG. 24, a catholyte k is supplied to the bridge space II, which allows electrolytic coupling between cathode K and anode A, the cathode K abutting an anion exchange membrane AEM and the anode A on a cation exchange membrane CEM. In the example of FIG. 25, only one cation exchange membrane CEM is present, otherwise the structure corresponds to that of FIG. 24, wherein the space II directly contacts the cathode K, ie does not constitute a bridge space. In the cell structure of FIG. 26 In comparison to FIG. 25, the cation exchange membrane CEM is not present at the anode.

In addition, cell variants are also possible, as already described in DE 10 2015 209 509 A1, DE 10 2015 212 504 A1,

DE 10 2015 201 132 Al, DE 102017208610.6, DE 102017211930.6, US 2017037522 Al or US 9481939 B2 are described and in which an electrode of embodiments of the invention may also find application.

As can be seen from the above, arise with the front lying electrode a variety of possible Zellanordnun conditions.

The following description refers to methods according to embodiments of the invention for producing a Elekt rode. In particular, the method can be used to produce an electrode of embodiments, so that explanations of specific constituents of the electrode can also be applied to the methods.

The present invention also relates to a method for producing an electrode, in particular an electrode ge according to one of the embodiments of the invention, comprising

Providing at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd; and

further comprising a step selected from:

Applying the compound to a carrier; and

Forms the connection to an electrode.

In embodiments of the method, the tetragonal crystallized compound may be further selected from CU4O3 and a compound which is isomorphous to CU4O3, in particular a compound which is isomorphous to paramelaconite. In this case, in the Kris tallgitter to CU4O3 (Cu ⁺ 2Cu ²⁺ 203) isomorphous compound minutes least one of the lattice sites, the Cu ⁺ and Cu ²⁺ corresponds speak Cu or Ag or parts of Cu or Ag. In this case, the isomorphic to CU4O3 compound can be selected from Ag _0.58 CeSii, ₄₂ , Ag ₂ Cu ₂ 0 ₃ , Ag _{0 28} Sii, ₇₂ Yb, Cui, ₀ 3sTeI, CuCr ₂ 0 _4, C ₄ H ₄ CUN ₆ , Ag _{0, 7} CeSii _, 3, Ag ₈ 0 ₄ S ₂ Si, Ag ₃ CuS ₂ , CuTeCl, Ba ₂ Cs ₂ Cu ₈ Fi ₂ , Cu0 ₄ Rh ₂ , CuFe ₂ 0 ₄ , Ag _0, 3CeSii _, 7, Ag ₆ 0 ₈ SSi, BaCuInF ₇ , Cuo _, 99TeBr, BaCu ₂ 0 ₂ , Cui ₆ 0i _{4, i5} , YBa ₂ Cu ₈ 0 ₆ and C ₈ Ag9Cl6Cs ₅ N _8. In particular, any combination of said tetragonal crystalline compounds can be used become. The explanations given above for the crystal lattice to CU4O3 (Cu ⁺ ₂ Cu ² ₂ 0 ₈₎ iso morph compound apply accordingly.

The step of providing the compound may include preparing the tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd. This is especially true when the compound is provided in a mixture. The preparation of a mixture comprising the compound and optionally e.g. At least one binder is not particularly limited in this case and can be done in a suitable manner. For example, mixing may be done with a knife mill, but is not limited thereto. In a knife mill, a preferred mixing time is in the range of 60-200 s, preferably between 90-150 s. For other mixers, other mixing durations may result accordingly. However, according to certain embodiments, the preparation of the mixture comprises mixing for 60-200 seconds, preferably 90-150 seconds.

In further embodiments of the method, the step of applying the compound to the carrier may be selected

Applications of a dispersion comprising the compound on the carrier; and Contacting the carrier with a gas phase comprising the compound, and applying the compound to the carrier from the gaseous phase.

The thickness of the layer of the compound applied to the support may be in the range of 10 nm or more, preferably 50 nm to 0.5 mm. The compound can be brought to the carrier depending Weil with a mass density of at least 0.5 mg / cm ² .

For processing a mixture, for example a powder mixture, or a powder, into an electrode, in particular a gas diffusion electrode or an electrode with a gas diffusion layer, dry calendering, for example the dry calendering process described in DE 102015215309.6 or WO 2017/025285, can be used. As far as the application step in which dry calendering can be carried out, reference is also made to the said applications. The same applies to embodiments of the method in which the connection to a

Electrode is formed, which may also include a dry calendering.

The orders of the mixture or the powder on a, for example, copper-containing carrier, preferably in the form of a sheet, is also not particularly limited, and can be, for example, by applying in powder form suc conditions. The carrier is not particularly limited and can the above with respect on the electrode described ent, where it can be designed here, for example, as a grid, grid, etc.

Also, the dry rolling of the mixture or the powder on the carrier is not particularly limited, and can be done, for example, with a roller. In certain embodiments, rolling is carried out at a temperature of 25-100 ° C, preferably 60-80 ° C. It is also possible to apply and coat several layers together on a carrier by this method, for example a hydrophobic layer which can produce better contact with a gas comprising CCg and thus improve gas transport to the catalyst.

Further, the tetragonal crystallized compound containing tend at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd, are screened onto an existing electrode without an additional binder. The base layer may then be made, for example, from powder mixtures of a Cu powder, e.g. with a grain size of 100-160 ym, with a binder, e.g. 10-15% by weight of PTFE Dyneon TF 1750 or 7-10% by weight of Dyneon TF 2021.

The step of applying the compound may be further carried out by applying a dispersion comprising the compound as indicated above. The dispersion can be a suspension. Such application of the compound can be carried out as follows:

Applying a suspension comprising the compound and optionally at least one binder to the carrier, and

Drying the suspension; or

Orders of the compound or a mixture comprising the compound on the support from the gas phase.

In this way, in particular gas diffusion layers can be produced. For this example, a Sus pension wet deposition or a vapor deposition can be used. Furthermore, thin layers of, for example

Paramelaconite can be generated based on laser ablation, electron microscopy, DC Reactive Sputtering or Chemical Vapor Deposition (CVD).

In the methods of embodiments in which the compound is applied to a support, a support may be provided. The provision of the carrier is not particularly limited, and it can be used, for example, in the Rah men of the electrode discussed carrier, for example, a support of a gas diffusion electrode, a gas diffusion electrode or a gas diffusion layer, eg on a suitable substrate. Further, in Ausfüh tion forms of the method, the orders of the suspension is not particularly limited, and may, for example, by

Dripping, dipping, etc. done. Thus, for example, the material may be applied as a suspension to a commercially available GDL (e.g., Freudenberg C2, Sigracet 35 BC). It is preferred, if in this case also an ionomer, such as e.g. 20 Gew.iige alcoholic suspension or a 5 wt.% Suspension of a Anionenaustauscherionomer (eg AS 4 Tukuyama) is used, and / or other additives, Bindemit tel, etc., which in the context of the electrode of Ausführungsfor men of the invention were discussed. For example, the use of Type 1 (typically trialkyl ammonium functionalized resins) and Type 2 (typically

Alkylhydroxyalkyl-functionalized resins)

Anion exchange resins possible.

The drying of the suspension is likewise not restricted and can be carried out, for example, by solidification by evaporation or precipitation with removal of the solvent or solvent mixture of the suspension, which are not particularly limited.

In the alternative embodiment of applying the compound or a mixture comprising the compound from the gaseous phase, the provision of a carrier is likewise not particularly limited, and can be carried out as above. Also, the application of the compound or the mixture comprising the compound from the gas phase is not particularly limited and may be carried out based on physical vapor deposition methods such as laser ablation or chemical vapor deposition (CVD). As a result, thin films comprising, for example, paramelaconite or its isomorphs and mixtures thereof can be obtained. According to certain embodiments, the carrier is a gas diffusion electrode, a carrier of a gas diffusion electrode or a gas diffusion layer.

As discussed above, in an alternative embodiment of the method, after providing the at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd, a form of the compound becomes one Electrode performed. For example, the method may include preparing a powder comprising the compound and rolling out the powder to form an electrode. The preparation of the powder is not particularly limited here, nor is the rolling out to a powder, e.g. with a roller. The rolling can be e.g. at a temperature of 15 to 300 ° C, e.g. 20 to

250 ° C, e.g. 22 to 200 ° C, preferably 25-150 ° C, further before given to 60-80 ° C, take place. With respect to the powder can also be referenced as in the comments above versions of the electrode of Ausfüh. Further, a mixture may be formed by molding the compound to the electrode, which mixture may be powdery or may contain a liquid.

In the above-mentioned methods, in which besides the tetra gonal in the space group I4i / amd crystallized compound containing at least one element selected from Cu and Ag, other constituents may also be present in a mixture or suspension, according to certain embodiments, the at least one Binder contained in the mixture or the Suspensi on, wherein the at least one binder preferably comprises an ionomer. According to certain embodiments, the at least one binder is in an amount of> 0 to 30 wt. %, based on the total weight of the compound and at least one binder, in the mixture or suspension. By the method of embodiments of the invention, the electrode can be made such that the compound is contained in an amount of 0.1-100 wt. %, preferably 40-100 wt. %, more preferably 70-100 wt. %, based on the electrode, in particular based on the gas diffusion electrode, or on the catalytically active region, for example a layer of

Electrode, is included.

A further embodiment of the present invention is directed to a process for the electrochemical conversion of CCg and / or CO (carbon dioxide and / or carbon monoxide), wherein CO2 and / or CO introduced and reduced in an electrolytic cell comprising an electrode of embodiments as a cathode at the cathode becomes.

Thus, the present invention also relates to a method and an electrolysis system for electrochemical carbon dioxide utilization. Carbon dioxide (CO2) is introduced into an electrolytic cell and applied to a cathode by means of an electrode of embodiments, e.g. a gas diffusion electrode (GDE), reduced on the cathode side. GDEs are electrodes in which liquid, solid and gaseous phase are present and in which the conductive catalyst catalyses the electrochemical reaction between the liquid and the gaseous phase.

The introduction of the carbon dioxide and / or carbon monoxide, if necessary, at the cathode is not particularly limited in this case, and can e.g. from the gas phase or from a solution.

In order to ensure a sufficiently high conductivity in the cathode space, an aqueous electrolyte in contact with the electrode used as the cathode, according to certain embodiments, contains a dissolved "conducting salt", which is not particularly limited. The electrocatalyst used in embodiments causes high Faraday efficiency at high current density for a corresponding target product and is beyond long-term stable. For the selective production of the product carbon monoxide pure silver catalysts are already available, which meet industrial requirements. For the selective electroreduction of CCg to get ethylene or Alko, however, no catalysts are currently known that meet these requirements. The Syn thesekonzept described here using an electrode of Ausfüh tion forms of the invention enables the production of electrocatalysts with a low overvoltage and an increased selectivity for hydrocarbons, in particular for ethylene, and alcohols such as ethanol and / or propanol.

According to certain embodiments, the electrochemical reaction takes place, for example an electrolysis, at a current density of 100 mA / cm ² or more, preferably 200 mA / cm ² or more, more preferably 300 mA / cm ² or more, even more preferably 350 mA / cm ² or more, in particular at more than 400 mA / cm ² . Preferably, the electrochemical reaction takes place at the cathode at a pH of pH = 6-14, preferably at a pH between 10 and 14.

In particular, the reduction at the cathode can also

Ethylene can be obtained. Thus, the method according to embodiments of the electrochemical reaction of CCg and / or CO is also a process for producing ethylene.

Moreover, the invention also relates to a use of a tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the Kris tallgitter the compound belongs to the space group I4i / amd, for the reduction of CO2, or in the electrolysis of CO2. Fer ner is in a further embodiment of the invention, a use of an electrode of embodiments for Redukti on or in the electrolysis of CO2 and / or CO indicated. In the uses of embodiments, the tetragonal crystallized compound may be selected from CU4O3 and a compound that is isomorphous to CU4O3. Here, in the crystal grid to the CU4O3 (Cu ⁺ 2Cu ²⁺ 203) isomorphous compound Minim least one of the lattice sites that contain the Cu ⁺ and Cu ²⁺ entspre Chen, Cu or Ag or units of Cu or Ag. In this case, the isomorphic to CU4O3 compound can be selected from

BaCu202, Cui60i4, i5, YBa2Cu306 and CsAggCleCssNs. In particular, any combination of said tetragonal crystallized compounds can be used. The explanations given above about the crystal lattice of CU4O3

(CU ⁺ 2CU ²⁺ 203) isomorphic compound apply accordingly.

The above embodiments, embodiments and Weitererbil applications can, if appropriate, combine with each other. 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.

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

Examples

Example 1 (CU4O3)

The synthesis of CU4O3 was confirmed by a study published by Zhao et al. (Zhao et al., Chem. Mater. 2012, 24,

Pp. 1136-1142) was inspired by the synthetic route (mg range) described.

The synthesis involved a dissolution of 50 mM Cu (NO 3) 2 '3H 2 O in 1.1 l of mixed solvent of ethanol-DMF (the volume ratio of ethanol to DMF is 1: 2). The solution was stirred for 10 minutes and then transferred to a 1.5 1 Glasein rate, which was then placed in a stainless steel autoclave (high pressure reactor BR-1500, Berghof). The autoclave was closed and the reaction mixture kept at 130 ° C for 24 h inside. After 24 h, the glass insert with the reaction mixture was removed from the autoclave and cooled to room temperature by means of an ice bath. The product of the reaction precipitated in the glass insert. After cooling, the supernatant was removed from the glass insert and the remaining solid product was collected by centrifugation and washed three times with ethanol. The recovered powder was first dried under a stream of argon and then dried in vacuo ge. Finally, the powder was stored in a glove box under inert atmosphere.

An X-ray diffractometric (XRD) analysis of the prepared powder showed the presence of the following phases as shown in Figure 2: CU4O3 (reference number 13), CU2O (reference number 11) and Cu (reference number 12). Plotted in FIG. 2 is the angle 2Q (coupled 2 theta / theta,

WL = 1, 54060 angstroms) against the number of pulses I. A quantitative phase analysis was performed. Approximately 40 wt.% Of the powder obtained were CU4O3, the remainder was CU2O with copper traces. An SEM photograph of the obtained powder is shown in FIG. 27.

A gas diffusion electrode (GDE) containing CU4O3 as a catalyst for the C02 electro-reduction was prepared as follows. The previously synthesized powder containing CU4O3 was poured onto a gas diffusion layer (GDL; Freudenberg H23C2 GDL) from solution as follows. The binder used was an ionomer, AS4 from Tokuyama. The ionomer solution is added to the powder containing Cu403 catalyst particles, which was previously dispersed in 1-propanol. The amount of catalyst powder used depends on the desired catalyst loading, but is typically used for mass segregation on the gas diffusion layer 1 mg / cm ² and 10 mg / cm ² , for example, 3.3 mg / cm ² , for example, which was determined by weighing before and after the application of the suspension. The dispersion was then left in an ultrasonic bath for 30 minutes whereupon a uniform catalyst ink was formed. After the ultrasonic treatment, the catalyst ink was poured and dried in an inert atmosphere (argon).

Electrochemical tests of CU4O3 as a catalyst

The electrochemical performance of the GDE containing CU4O3 as catalyst was tested in the electrolytes described below. For this purpose, a stacked three-chamber flow cell was used. The first chamber used as the gas supply chamber was separated from the second chamber by the GDE. The second and third chambers contained a catholyte and anolyte, respectively, and were separated by a Nafion 117 membrane. The electrolytes were pumped through the cell in two separate cycles. The anode compartment was filled with 2.5 M KOH and had an IrO 2 -containing anode. For the cathode space, the GDE was used as the cathode and 0.5 M K2SO4 as the electrolyte with a pH range varying to pH 7. As the counter electrode, a solid, IrO 2 -coated Ti plate was used. The cell was equipped with an Ag / AgCl / 3M KCl reference electrode. For

potentiostatic measurements, the cathode was connected as working electrode.

To demonstrate the activity and selectivity to ethylene, the GDE prepared above was tested with CU4O3. In the potentiostatic electrolysis mode, the cell potential was kept constant during the experiment. Other experiments were performed in the chronoamperometric mode, ie the current was kept constant while the potential of the cell and the potential of the electrode were monitored over time. The experiments were carried out at different current densities (calculated by dividing the delivered total current through which the first chamber of the second Chamber separating GDE surface (here also called active geometric surface of the GDE).

Analysis of gaseous and liquid products

The gaseous products were taken every 15 minutes using gas sampling bags and analyzed with a Thermo Scientific Trace 1310 Gas Chromatograph (GC) equipped with two thermal conductivity detector (TCD) channels. In the case of chronoamperometric long-term electrolysis, the product gas from the flow reactor was passed directly to the GC. The hydrocarbons were separated with a micro-packed GC column (Shincarbon (TM), Restek, Bellefonte, PA, USA) with He as the carrier gas. Water was measured on a packed 5 Å molecular sieve column (Res te, Bellefonte, PY, USA) with Ar as the carrier gas.

The liquid products were analyzed as follows:

After the electrochemical measurements were complete, 1 ml of the catholyte was removed and analyzed by nuclear magnetic resonance to detect liquid products. ^X NMR spectra were recorded on a 400 MHz Bruker Avance 400 spectrometer equipped with a 5 mm Ag ³¹ P autotune BBO sample probe, a pulsed field gradient unit and a gradient control unit. NMR samples were generated as follows: 250mΐ D2O and 50mΐ of an internal standard stock solution with 0.06M potassium fumarate in water was added to 300mΐ of electrolyte.

The Faraday efficiencies (FE) of the liquid and gaseous products were obtained by the equation: with F as the Faraday constant, I as the current, Q as the charge, e as the number of electrons transferred, t as the electrolysis time, and n as the amount of product in moles. C0 ₂ reduction experiments using CU4O3 as catalyst

The result of the electrochemical measurement is shown in Fig. 28a as Faraday efficiency as a function of the time (t) Darge presents. As can be seen therefrom, the CU4O3 showed contained GDE tends excellent maximum selectivity of 40.5% Faraday efficiency (FE) to ethylene at 1.05 V (vs. Ag / AgCl) and 100 mA / cm ² current density J.

Other detected gaseous products were: CO, CH ₄ , C ₂ H 6 and H ₂ .

Chronoamperometric C0 ₂ reduction experiments using CU4O3 as catalyst

The results of the chronoamperometric experiments with CU4O3 as catalyst are shown in FIGS. 28b to 28h, whereby liquid products were detected in addition to gaseous products. Figures 28b through 28g give the combined results of three different experiments, i. performed at three different current densities, again. Fig. 28h shows a long-term stability experiment over 24 hours.

In detail, FIG. 28b shows a time-dependent course of the Faraday efficiencies during electrolysis at different current densities. Fig. 28c shows the time-dependent course of the cathode potentials at different current densities.

Fig. 28d illustrates Faraday efficiencies for all of the Ci products (products with only one C atom) and C2 ₊ products (products with two and more C atoms) and H2 at different current densities calculated for a time after two hours the electrolysis. FIG. 28e to 28g to give the individual Faraday efficiencies of all detected products again, the conditions with CU4O3 as a catalyst under chronoamperometric Bedin at 100 mA / cm ² (Fig. 28e), 200 mA / cm ² (Fig. 28f) and 300 mA / cm ² (FIG. 28g) after two hours of electrolysis. were holding. 28h shows a time-dependent course of the Faraday efficiencies of all detected gas products during a 24-hour electrolysis at a constant current density of 200 mA / cm ² .

The current densities of these experiments were 100 to 300 mA / cm ² . The Faraday efficiency (FE) of ethylene using the C ^ Cy catalyst varied as a function of the applied current density, since increasing the current density shifted the cathode potentials to more negative values. An increase of the current density by 100 mA / cm ² correlated with a shift of the cathode potential by approximately 165 mV (FIGS. 28b and 28c). The results obtained show that at all investigated current densities the C ^ Cy selectivity for ethylene formation remained stable after a run-in phase even after two hours. Surprisingly, as the current densities increase, the FE values for ethylene also increase (FIG. 28b). The highest value (FE for ethylene of 43% at -0.64 V against reversible hydrogen electrode RHE) was achieved at the highest current density investigated (300 mA / cm ² ). For the other current densities tested, namely 100 mA / cm ² and 200 mA / cm ² , FE's of 24% and 31%, respectively, were achieved for ethylene Faraday efficiencies.

When all detected products of the CCg reduction reaction of the experiments shown in Figures 28b to 28e are considered, it can be seen that the product distribution changes significantly with the applied current density (Figures 28d to 28g). The main products of the reduction reaction after two hours in the experiment at -0.31 V vs. RHE (100 mA / cm ² ) were Ci products (products with only one C atom, FE _ci 32.3%), predominantly formate (FE 23.4%). The increase in current density led to a decrease in the selectivity for Ci products, with a FE _ci of 26.4% at -0.47 V vs. RHE (200 mA / cm ² ) and only a FE _ci of 12.9% at -0.64 V vs. RHE (300 mA / cm ² ) were enough. The methane formation was suppressed or reduced (FE 0.2%) and only at -0.64V vs. RHE observed. C2 ₊ production (ie products with two or more carbon atoms) atoms) in turn increased when the current density was increased. The detected C2 ₊ products were ethylene, acetate, ethanol and n-propanol (Figures 28e to 28g). In all experiments, the major C2 ₊ product was ethylene. The lowest selectivity for C2 ₊ products was a FE _C 2 ₊ of 30% at -0.31 V vs. RHE

(100 mA / cm ² ) followed by FE _C 2 ₊ of 44.6% at -0.47 V vs. RHE (200 mA / cm ² ). At -0.64 V vs. RHE reached the Faraday efficiency for C2 ₊ products at their peak value of FE _C 2 ₊ 61.7%, with a corresponding partial current density of jc 2 ₊ = -185 mA / cm ² , and a high C2 ₊ / Ci product ratio of 4.8. In addition to ethylene, a noticeable Faraday efficiency for ethanol (FE 13.4%) at -0.64 V vs. RHE measured. The FE value of H2 was 30% at all current densities tested.

As illustrated in FIG. 28h, over a period of 24 hours, maximum ethylene production was achieved with a FE value of 35% at a constant current density of

200 mA / cm ² measured. After 17 hours, a slight decrease in ethylene selectivity was noted, reaching a FE value for ethylene of 33% after 24 hours. This experiment demonstrates the long-term stability of CU4O3 in ethylene production.

Example 2 (Ag ₂ Cu ₂ O 3)

The synthesis of Ag 2 <Su 2 O 3 was based on the synthesis instructions published in the publication Inorganic Chemistry, Vol. 41, No. 25, 2002.

In a 50ml three-necked round bottom flask with magnetic stirrer and

4 ml of 4M NaOH and 2 ml of a salt solution of Cu (NO ₃ ) ₂ * 3H _{2 <} D (0.77 g, 3.2 mmol) (Merck, pa99.5%) and AgNO 3 (0.52 g, 3.1 mmol) (Panreac, pa,

99.98%) with vigorous stirring. After the addition ent stood an olive green precipitate consisting of amorphous Cu (OH) 2 and Ag ₂ 0 was. The batch was stirred for six hours at room temperature and after two hours 40ml Deionized water was added. There was a color change from olive green to black, which was caused by the formation of Ag2Cu2C> 3. After six hours, the black precipitate was filtered off and washed with a Nutsche neutralge. The black Ag2Cu2C> 3 is isotypic to the paramelaconite CU4O3. A proof of the compound and a proof of the phase purity of the produced Ag2Cu2C> 3 were carried out with PXRD. FIGS. 29 and 30 show the associated powder diffractogram (coupled 2 theta / theta, WL = 1, 54060 angstroms) and an SEM image of the generated Ag ₂ Cu ₂ O 3.

Example 2a): Production of an Ag 2 Cu 2 O 3 Gas Diffusion Electrode (GDE) with Cation Exchanger Ionomer

First, a catalyst binder dispersion has been prepared. For this purpose, a suspension of 60 mg of Ag2Cu203 catalyst powder of maximum size dso <5 μm in 2 ml of isopropanol was prepared in a snap-cap rolled-edge glass. To the suspension was added 30 mg of a 20% Nafion dispersion (Nafion DE 2021). The mixture was treated for 15 minutes in ultraplosal bath with occasional shaking.

Subsequently, a gas diffusion layer (GDL) (Freuden berg C2, Sigracet 25BC) with an area of 4 cm × 10 cm was coated. For this purpose, the GDL was fixed with Capton tape on the back of a Pet rischale. In the case of a stable catalyst-binder suspension, this was applied by brush or with an airbrush. In the case of an unstable suspension, the entire contents of the Schnappde ckel rollrandglases was poured over the GDL and evenly distributed. After about 30 minutes of drying time, the process was repeated. In total, 4 steps were needed to produce a catalyst loading of 6 mg / cm ² . Final he followed a drying over 12 hours with an argon gas stream.

Example 2b): Preparation of an Ag2Cu2C> 3-GDE with

Anionenaustauseher ionomer In a 4 ml snap-top vial, 60 mg of catalyst powder and 120 mg of a 5% dispersion of Tokuyama AS4 ionomer were weighed as a binder and diluted with 2 ml of n-propanol. As an alternative ionomer, Sustanion XA9 can be used in ethanol. The mixture was homogenized for 15 minutes in an ultrasonic bath. The dispersion prepared was applied to a gas diffusion layer GDL Freudenberg C2 (4 cm × 10 cm) and dried in an argon stream, and the process was repeated three times. The electrode was dried in argon stream for 12 hours prior to use. The Kata lysatorbeladung was set to 4.5 mg / cm ² .

Example 2c) Preparation of an AgCuC> -GDE with

Anion exchange ionomer

A gas diffusion layer (GDL) (Freudenberg C2) having a microporous carbon black layer and a fiber-based PTFE bonded base was used as a catalyst support. A catalyst ink was prepared by dispersing 90 mg of catalyst powder in 3 ml of 1-propanol. In addition, 25 mΐ of Sustanion XA-9 ionomer (Dioxide Materi als) was added to the catalyst ink. The mixture was then sonicated for 20 minutes. Thereafter, the GDE was prepared by airbrushing the prepared catalyst ink onto the GDL. After bringing the GDE was net overnight at room temperature. The GDL was weighed before and after application of the catalyst to determine catalyst loading. The catalyst loading was 1.5 mg / cm ² (± 0.2). During the spray coating about 50 wt.% Of the catalyst material was lost.

Electrochemical tests of AgCuC as a catalyst

The electrochemical performance of GDE, which contains AgCuC as a catalyst, in C0 ₂ reduction and CO reduction was tested in the electrolysis assemblies described below.

For the CCg reduction, a stacked three-cell flow cell (Micro Flow Cell from ElektroCell) was used. The first chamber, which was used as the CCg gas feed chamber, was separated from the second chamber by the GDE, which served as the cathode. The GDE surface separating the first chamber from the second chamber (here also called active geometric surface) was approximately 10 cm ² . The second and third chambers contained a catholyte and an anolyte, respectively, and were separated by a Nafion 117 membrane (cation exchange membrane). The structure of the stacked three-chamber flow cell is the same as that shown schematically in FIG. The electrolytes were pumped through the cell in two separate cycles. The anode compartment was filled with 2.5 M KOH and had an Ir0 ₂ -containing anode. For the cathode compartment, the GDE was used as the cathode and 0.5 MK ₂ SO ₄ as the electrolyte with a pH range varying by pH 7. All electrolytes were made with ultrapure water (18.2 MΏ cm, MilliQ Millipore System). The

Electrolyte flow was controlled using a peristaltic pump (Ismatec ECOLINE VC-MS / CA8-6) which kept the flow constant at 40 ml / min. CCg gas (Air Liquide, 99.995%) was used without further purification. The gas was continuously in the flow cell

(Gas (feed) chamber) at atmospheric pressure at a constant flow rate of 100 ml / min initiated. The gas flow was monitored with a mass flow monitor (Bronkhorst). Unreacted CO ₂ and formed gas products were evacuated from the gas chamber through a gas outlet on the back of the gas chamber. The cell was equipped with an Ag / AgCl / 3M KCl reference electrode. The pH of the catholyte was monitored during the experiments using a pH electrode (Metrohm). The counterelectrode used was a solid, IrCg <Ir-MMO, iridium-metal mixed oxide) coated Ti plate from ElectroCell. All electrochemical Measurements were performed with a Metrohm Autolab PGSTAT302N potentiostat galvanostat.

For potentiostatic measurements, the cathode was connected as a working electrode. There were too

chronoamperometric measurements performed, i. the current was kept constant while the potential of the cell and the potential of the electrode were monitored over time. The experiments were carried out at different current densities (calculated by dividing the supplied total current by the active geometric surface of the GDE).

For the CO reduction, the same electrolysis structure and the same procedure as for C0 ₂ reduction were used, with the following differences:

- CO was used as gas instead of CO2

- 1 M CSHCO ₃ was used as the catholyte instead of 0.5 MK ₂ SO ₄

- 1 M CSHCO ₃ was used as the anolyte instead of 2.5 M KOH

An anion exchange membrane (Fumatech, FAB-PK-130) was used instead of the cation exchange membrane.

Analysis of gaseous and liquid products

The gaseous products were taken every 15 minutes using gas sampling bags and analyzed with a Thermo Scientific Trace 1310 Gas Chromatograph (GC) equipped with two thermal conductivity detector (TCD) channels. In the case of long-term chronoamperometric electrolysis, the product gas from the flow reactor was passed directly to the GC. The hydrocarbons were separated with a micro-packed GC column (Shincarbon (TM), Restek, Bellefonte, PA, USA) with He as the carrier gas. Water was measured on a packed 5 Å molecular sieve column (Res te, Bellefonte, PY, USA) with Ar as the carrier gas. The liquid products were analyzed as follows:

After the electrochemical measurements were complete, 1 ml of the catholyte was removed and analyzed by nuclear magnetic resonance to detect liquid products. ¹ NMR spectra were recorded on a 400 MHz Bruker Avance 400 spectrometer equipped with a 5 mm Ag ³¹ P autotune BBO sample probe, a pulsed field gradient unit and a gradient control unit. NMR samples were generated as follows: 250mΐ D2O and 50mΐ of an internal standard stock solution with 0.06M potassium fumarate in water was added to 300mΐ of electrolyte.

The Faraday efficiencies (FE) of the liquid and gaseous products were obtained by the equation: with F as the Faraday constant, I as the current, Q as the charge, e as the number of electrons transferred, t as the electrolysis time, and n as the amount of product in moles.

Potentiostatic C0 ₂ reduction experiments using Ag ₂ Cu ₂ O ₃ as catalyst

To demonstrate the activity and selectivity for hydrocarbons, especially for ethylene, an example of a GDE containing Ag ₂ Cu ₂ O 3 was tested. The experiments were carried out in the potentiostatic electrolysis mode, ie the cell potential was kept constant during the experiment. Gaseous products were analyzed with a Thermo Scientific Trace 1310 Gas Chromatograph.

The results of the electrochemical measurements of CO2 reduction are shown in FIG. The following gas products were monitored: C ₂ H ₄ , CO, CH ₄ , C ₂ H ₆ and H ₂ . As can be seen from FIG. 31, CO was found to be the main product in the tested potentials (U) at -0.95 V vs. Ag / AgCl had a maximum of over 80%. On the other hand, at this potential, the formation of hydrocarbons is reduced. However, with more negative potentials, the production of CO decreases and hydrocarbons are increasingly formed (see, for example, the values at -1.1 V vs. Ag / AgCl in FIG. 31), in particular ethylene and methane. The product selectivity is thus very easily controllable over the set potential.

Chronoamperometric C0 ₂ reduction experiments using Ag ₂ Cu ₂ O ₃ as catalyst

Results of chronoamperometric measurements for CO ₂ reduction with an exemplary GDE containing Ag ₂ Cu ₂ O ₃ are shown in FIGS. 33 and 34. Figures 33a to 33f show the results for gas products, while Figures 34a to 34e illustrate the results for C0 ₂ reduction liquid products.

Figures 33a and 33b show detailed results for the gaseous product C ₂ H ₄ . It was measured at various current densities (J), namely 100, 300, 400 and 500 mA / cm ² . At high current densities, high Faraday efficiencies (FE) could be achieved with the GDE. It turned out that high current densities result in high Faraday efficiencies, with a maximum Faraday efficiency at 400 mA / cm ² (FIG. 33 a), even after one hour of electrolysis (FIG. 33 b). Fig. 33c shows corresponding working potentials (U) as a function of time (t). As can be seen, the respective work potentials at the selected current densities remained stable over time. The Ag ₂ Cu _{2 <} D ₃ contained in the GDE thus has high Faraday efficiencies at high current densities for the reduction of CO ₂ to ethylene and is also long-term stable.

For the gas products CO, CH ₄ and H ₂ , the electrochemical measurements are shown in FIGS. 33 d to 33 f. In each case, the Faraday efficiencies at different current densities, namely 100, 300, 400 and 500 mA / cm ² , after one hour of of the GDE. For the products CH ₄ and Pb, an increase of the Faraday efficiencies can be observed in each case with increasing current densities, while for CO with increasing current density a decrease of the Faraday efficiency occurs. For CH ₄ and fh, therefore, an increase in the selectivity of the GDE containing Ag 2 Cu 2 O 3 can be seen with increasing current density.

Figs. 34a to 34e illustrate the electrochemical measurements for the liquid products formate (34a), acetate (34b), allyl alcohol (34c), ethanol (34d) and n-propanol (34e) after one hour of electrolysis Traces of Metha nol and acetone detected. As can be clearly seen, the Faraday efficiencies increased with increasing current densities of 100, 300, 400 and 500 mA / cm ² for the products formate, acetate, allyl alcohol and ethanol. On the other hand, n-propanol showed FE maxima both at 100 mA / cm ² and at 500 mA / cm ² , but also a tendency of increasing Faraday efficiency with increasing current density from 300 mA / cm ² . For the liquid hydrocarbon products monitored during C0 ₂ reduction, an increase in the selectivity of the GDE containing Ag 2 Cu 2 C> 3 is therefore also evident with increasing current density.

In view of the data of Figs. 33a to 33f and 34a to 34e, it can be seen that CO is the major product (maximum FE of 80% at 100 mA / cm ² ) of C0 ₂ reduction using

Ag ₂ Cu ₂ O 3 as catalyst. It has been observed that the selectivity for CO decreases with increasing current density (Figure 33d). In addition to CO, three other gas products were detected: ethylene, methane and hydrogen. Ethylene reached a maximum FE of 17% at 400 mA / cm ² (Figure 33b) and thus represents the second major product. At higher current densities, the FE began to fall for ethylene. Methane was only added

Current densities greater than 300 mA / cm ² detected, with a maximum FE of 4.5% at 500 mA / cm ² (Fig. 33e). On the other hand, five different liquid products were detected: ethanol, n-propanol, acetate, formate and allyl alcohol. Traces of methanol and acetone (FE <0.05%) were also measured. After CO and ethylene, ethanol represents the third Major product in CCp reduction, with a maximum FE of 11% (Figure 34d). The FE for the other alcohol, namely n-propanol, was below 1% for all current densities tested (Figure 34e). The formation of formate and acetate increased with increasing current densities, with a maximum FE of 4.4% and 2.4%, respectively. Allyl alcohol was detected in traces (Figure 34c).

Comparative CCg reduction experiments using Ag and Ag2 <Su203 as catalysts

Comparative experiments of a GDE with Ag as catalyst, i. containing only Ag as the catalytically active metal, and the GDE used for the measurements of FIG. 31 with Ag2Cu2C> 3 carried out as a catalyst. The respective experimental setup corresponded to that of the abovementioned electrochemical measurements for the Ag2Cu2C> 3-GDE. Ag-GDE was prepared analogously to Ag2Cu2C> 3-GDE using Ag nanoparticles (50-60 nm, 99.9%, iolitec).

The Faraday efficiencies (FE) and the working potentials (U) of the two GDEs were determined as a function of the current density. The associated results are shown in Fig. 32 Darge. Diagrams a and b of Fig. 32 show the Faraday efficiencies at different current densities. The graph a represents the FE results for the Ag catalyst, while the graph b represents those for the Ag2Cu203 catalyst. It can be clearly seen that CO is the only carbonaceous gas product when Ag is used as a catalyst for C0 ₂ reduction. The Ag catalyst gave high Faraday efficiencies for CO at low current densities. With increasing current density, the Faraday efficiencies for CO decreased, while the evolution of hydrogen (HER hydrogen evolution reaction) increased. HER is a side reaction to CO2 electro-reduction that should be suppressed as much as possible. As can be seen from the diagram b, in contrast to the Ag catalyst, the Ag2Cu203 catalyst is able to convert CO2 to valuable hydrocarbons such as methane (CH ₄₎ and To reduce ethylene (C2H4). The predominantly developed gas is still CO, but, as can be seen from diagram b of Fig. 32, the selectivity for CO decreases with increasing current densities. This decrease can be interpreted as an increased selectivity for ethylene with increasing current density. CO is a precursor to ethylene formation during CO 2 reduction, so that higher CO densities are used more efficiently for the production of ethylene. Furthermore, interestingly, the hydrogen evolution HER is greatly reduced when Ag2Cu203 is used as the electrocatalyst. At all current densities tested, the Faraday efficiency of the unwanted HER was below 5%.

The diagram of FIG. 32, which shows the working potentials of the cathode as a function of the current density, also clearly shows that the Ag 2 Cu 2 O 3 catalyst operates at considerably lower potentials than the Ag catalyst. This is important in terms of economic aspects. This makes it possible to operate the C02 electrolysis systems at much lower overall voltages, thereby reducing the energy costs for the use of the electrolysis systems.

Chronoamperometric CO reduction experiments using Ag2Cu203 as catalyst

The results of chrono-amperometric measurements of CO reduction with an exemplary GDE are shown in Figures 35a and 35b. The following gaseous or liquid products were monitored: ethylene (C ₂ H ₄₎ , methane (CH ₄₎ , ethanol (EtOH), acetate (CH 3 COO-), n-propanol, acetone, allyl alcohol (AllylOH, A10H), Methanol (MeOH) and hydrogen (H ₂₎ .

Figures 35a and 35b show the Faraday efficiencies (FE) at current densities of 100 mA / cm ² and 200 mA / cm ² versus time (t) for the gaseous products ethylene and hydrogen. Methane was detected in traces. The Faraday efficiencies for ethylene range between 24 and 29%, while for H2 only Faraday efficiencies between 5 and 29 are found and 10% were detected. Over a period of 120 minutes, the Faraday efficiencies for ethylene remained stable at the current densities tested.

After one hour (h) of electrolysis, the following proportions of liquid products were determined at current densities of 100 mA / cm ² and 200 mA / cm ² on the basis of the Faraday efficiencies (methanol was found only in traces): n-

Ethanol Acetate A10H Propanol Acetone

100 mA / cm ² 39.05% 16.86% 2.12% 6.92% 0.34%

200 mA / cm ² 40.92% 15.49% 1.99% 6.23% 0.30%

It turns out that the formation of hydrogen, methane

(<0.5%) and methanol is suppressed or reduced. This allows Faraday efficiencies of greater than 90% at 100 mA / cm ² and greater than 93% at 200 mA / cm ² for C2 ₊ products, ie products having two or more carbon atoms, to be achieved.

Figures 35a and 35b and the table above illustrate the results when using CO ₂ instead of CO ₂ as the gas in the electrolysis with the Ag ₂ Cu ₂ O 3 -GDE. There were three gas products: ethylene, hydrogen and traces of methane (<0.5% FE). From Fig. 35a, it can be seen that the FE for ethylene remained stable over time for the two current densities, demonstrating the stable catalytic performance of

Ag ₂ Cu203 demonstrated. As the current density increased, so did the FE for ethylene. On the other hand, the FE for hydrogen decreased with increasing current density as well as over time (Figure 35b). As liquid products, six different compounds were detected: ethanol, n-propanol, acetate, acetone, allyl alcohol and traces of methanol (see table above). It turns out that the calculated FE for liquid products do not make much difference at the two different current densities. Common to both tested current densities is that ethanol is the major product, followed by ethylene and acetate. The results for CO reduction using the GDE containing Ag2Cu2C> 3 therefore show that Ag2Cu2C> 3 is a highly active, more selective for hydrocarbon products and / or oxygenate products not only for the reduction of CCg but also for the reduction of CO long-term stable electrocatalyst.

Under aqueous conditions, known catalysts for CO2 and CO reduction (eg, copper-based catalysts) produce a mixture of Ci reduction products (ie products with only one carbon atom) and C2 ₊ reduction products (ie products with two or three carbon atoms) more carbon atoms). C2 ₊ hydrocarbon and oxygenate products are more desirable compared to Ci products. In the case of the C2 ₊ products, this is due to their higher energy densities, easy storage and easy transport as liquids (especially for alcohols). For this reason, it is of great importance to tailor the selectivity of catalysts towards longer and more energetically denser molecules, opening up opportunities for the production of renewable fuels from CO and CO2. With Ag 2 Cu 2 O 3 as a catalyst for CO reduction, the formation of undesired C 1 products and hydrogen was suppressed or reduced, and C 2 ₊ products were produced with Faraday efficiencies greater than 90% at 100 mA / cm ² and greater than 93%. at 200 mA / cm ² (measured after one hour from the beginning of the experiment).

Claims

claims

An electrode comprising at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I 4i / amd.

The electrode of claim 1, wherein said compound is selected from CU4O3 and a compound which is isomorphous to CU4O3.

3. electrode according to claim 2,

wherein in the crystal lattice, the compound of at least one of the lattice sites corresponding to Cu ⁺ and Cu ²⁺ , which is isomorphous to CU4O3 (Cu ⁺ 2Cu ²⁺ 203), contains Cu or Ag or portions of Cu or Ag; and or

wherein the compound isomorphic to CU4O3 is selected from Ago, ssCeSii, 42,

C ₄ H ₄ CUN ₆ , Ag _{0, 7}

CuO ₄ Rh ₂ , CuFe ₂

BaCu202, Cui60i4, i5, YBa2Cu306 and CsAggCleCssNs.

4. An electrode according to any one of the preceding claims, wherein the compound in an amount of 0.1-100 wt. % , prefers

40-100 wt. %, more preferably 70-100 wt. %, based on the electrode or on a portion of the electrode is included; and or

wherein the compound is applied to a support, in particular special with a mass density of at least 0.5 mg / cm ² .

5. An electrode according to any one of the preceding claims, wherein the electrode is a gas diffusion electrode.

6. An electrolytic cell comprising an electrode according to any one of the preceding claims.

7. A process for producing an electrode, in particular an electrode according to one of claims 1 to 5, comprising Providing at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd; and

further comprising a step selected from:

Applying the compound to a carrier; and

Forms the connection to an electrode.

8. The method according to claim 7,

wherein the compound is selected from CU4O3 and a compound which is isomorphous to CU4O3.

9. The method according to claim 8,

wherein the compound isomorphic to CU4O3 is selected from Ago, ssCeSii, 42,

C ₄ H ₄ CUN ₆ , Ag _{0, 7}

CuO ₄ Rh ₂ , CuFe ₂

BaCu202, Cui60i4, i5, YBa2Cu306 and CsAggCleCssNs.

10. The method according to any one of the preceding claims 7 to 9, wherein the step of applying the compound is selected on the Trä ger

Applications of a dispersion comprising the compound on the carrier; and

11. The method according to claim 10,

wherein the compound is applied with a mass coverage of at least 0.5 mg / cm ² ; and or wherein the rolling at a temperature of 25-100 ° C, before given to 60-80 ° C, takes place.

12. The method according to any one of claims 7 to 11, wherein the carrier is a gas diffusion electrode, a carrier of a Gasdif fusion electrode or a gas diffusion layer.

13. The method of claim 7, wherein the step of forming the compound to an electrode comprises rolling out a powder comprising the compound to the electrode.

14. The method according to any one of the preceding claims 7 to 13, wherein the electrode is prepared such that the connec tion in an amount of 0.1-100 wt. % , prefers

wherein the compound is provided and applied or formed in a mixture comprising at least one binder, preferably an ionomer.

15. The method according to claim 14,

wherein the at least one binder in an amount of> 0 to 30 wt. %, based on the total weight of the compound and the at least one binder, is contained in the mixture.

16. Process for the electrochemical conversion of CO2

and / or CO, wherein CO2 and / or CO introduced into an electrolytic cell comprising an electrode according to one of claims 1 to 5 as a cathode at the cathode and reduced.

17. Use of at least one tetragonal crystallized compound containing at least one element selected from Cu and Ag, wherein the crystal lattice of the compound belongs to the space group I4i / amd, for the reduction or in the Elekt rolyse of CO2 and / or CO.

18. Use of an electrode according to one of claims 1 to 5 for the reduction or in the electrolysis of CCg and / or CO.