DE202015106071U1 - Electrochemical cell, electrode and electrocatalyst for an electrochemical cell - Google Patents

Abstract

Electrocatalyst for an electrode (38) of an electrochemical cell (10), which electrocatalyst comprises at least one first active catalyst substance (54), in particular for exciting the evolution of oxygen, characterized by at least one first electrically non-conductive carrier substance (58 ) deposited or applied to this second active catalyst substance (56), in particular for the excitation of the oxidation of hydrogen.

Description

The present invention relates to an electrocatalyst for an electrode of an electrochemical cell, which electrocatalyst comprises at least a first active catalyst substance, in particular for stimulating the evolution of oxygen.

Further, a method for producing an electrocatalyst for an electrode of an electrochemical cell will be described below, wherein a first active catalyst substance, in particular for exciting the development of oxygen, is provided.

In addition, the invention relates to a catalyst-coated membrane comprising an ion exchange membrane which is coated on at least one side, in particular on both sides, with an electrocatalyst.

Moreover, the invention relates to a membrane-electrode assembly comprising an ion exchange membrane which is coated on at least one side, in particular on both sides, with an electrocatalyst.

Furthermore, the present invention relates to an electrode for an electrochemical cell, which electrode comprises at least one catalyst layer.

Finally, the present invention also relates to an electrochemical reactor, in particular in the form of an electrochemical cell, comprising at least two electrodes.

Methods, electrocatalysts, catalyst-coated membranes, membrane-electrode assemblies, electrodes and electrochemical reactors of the type described above are known in many ways. In particular, electrochemical reactors, which are designed to carry out an electrochemical reaction and comprise at least two electrodes, are used in various forms. For example, electrochemical reactors in the form of electrochemical cells, in particular highly efficient fuel cells and electrolysers, are increasingly gaining in importance due to the German energy transition.

The main reaction at the anode of a fuel cell is the oxidation of hydrogen (HOR - "Hydrogen Oxidation Reaction") and in an electrolyzer oxygen evolution (OER - "Oxygen Evolution Reaction"). Oxygen is reduced at the cathode of the fuel cell (ORR - "Oxidation Reduction Reaction") and hydrogen is developed during electrolysis (HER - "Hydrogen Evolution Reaction"). For all of these reactions, electrocatalysts of pure precious metal or at least a very high proportion of noble metal have hitherto been used. In particular, platinum and iridium are used. The cost of such electrocatalysts are correspondingly high.

A particular problem encountered with electrolyzers is the diffusion of molecular hydrogen H ₂ formed at the cathode through an ion exchange membrane separating the cathode from the anode toward the anode. This forms at the anode a mixture of molecular oxygen O ₂ and molecular hydrogen H ₂ , so-called oxyhydrogen, also called oxyhydrogen in English-speaking countries. A reactive mixture is when the hydrogen content of the gas mixture at the anode is at least 4% of the gas volume. It is known to apply an additional layer of platinum on the membrane-electrode assembly or the current collector to prevent an excessive anode-side hydrogen concentration. However, this approach is very expensive, as this much of the rare precious metal is needed.

It is therefore an object of the present invention, electrochemical reactors, catalyst-coated membranes, membrane electrode assemblies, electrodes and electrocatalysts of the type described above in such a way that electrochemical reactors can be operated safely.

For this purpose, it is proposed in a method of the type described above that deposited on at least a first electrically non-conductive carrier substance, a second active catalyst substance for exciting the oxidation of hydrogen or applied thereto and that deposited on the first carrier or applied second active catalyst substance is mixed with the first active catalyst substance.

The second active catalyst substance makes it possible to oxidize molecular hydrogen diffusing through the membrane of the electrochemical reactor so as to prevent the formation of a reactive oxyhydrogen gas mixture at the anode. By using the at least one first electrically nonconductive carrier substance, the second active catalyst substance can be partially substituted, so that a maximum HOR activity can be achieved with minimal loading of the at least one first carrier substance with the second active catalyst substance. In particular, the use of noble metals as a second active catalyst substance, despite efficient Hydrogen conversion can be minimized. Moreover, by oxidizing the hydrogen diffusing to the anode, it is possible to further reduce a thickness of the membrane, whereby the overall efficiency of the electrochemical reactor, particularly an electrolyzer, can be further improved. The at least one first, electrically non-conductive carrier substance prevents in particular that the second active catalyst substance is at potential. Moreover, it is also possible in this way to prevent possible poisoning of the first active catalyst substance for the evolution of oxygen. With the proposed method, the electrocatalyst can be produced in an environmentally friendly manner and, in particular, also allows further efficiency optimization by reducing the membrane thickness. The first carrier may also surround the second active catalyst substance.

The oxidation of the hydrogen can lead to the formation of water, in particular by targeted reaction with oxygen. It is therefore advantageous if the at least one first carrier substance is hydrophobic.

It is advantageous if a first carrier substance having an electrical conductivity of not more than 1 × 10 ^-3 S / m is used in order to ensure the preferably desired insulating property of the at least one first carrier substance, if its electrical conductivity should always be below the specified limit value to safely avoid that the second catalyst substance is at potential.

Furthermore, it is favorable if a first carrier substance is used, which is or contains a ceramic, a polymer, in particular tetrafluoroethylene, (PTFE), and / or a metal oxide. Such a first carrier substance makes it possible in a simple manner to deposit or apply the second active catalyst substance for exciting the oxidation of hydrogen thereon. Furthermore, there are many suitable ceramics or metal oxides that are nonconductive.

It is advantageous if a ceramic or a metal oxide is used which contains titanium. In this way, a first carrier substance can be formed, which is significantly more cost-effective than the second active catalyst substance without carriers, that is to say unsupported, applied to the current collector or the membrane.

The electrocatalyst can be formed particularly cost-effectively if titanium oxide (TIO) or titanium dioxide (TIO ₂ ) is used as the metal oxide.

It is advantageous if the first active catalyst substance is deposited on or applied to at least one second, electrically conductive carrier substance. This development makes it possible in particular to produce electrocatalysts whose catalytic activity is comparable with conventional known electrocatalysts, but which contain a significantly smaller amount of the first active catalyst substance, in particular noble metals. This is made possible in particular by the use of one or more electrically conductive second carrier substances, by means of which an active surface of the electrocatalyst is increased without increasing the amount of the first active catalyst substance. On the contrary, the second carrier substance allows the addition of the first active catalyst substance, so that despite a reduced amount of the same a comparable catalytic activity can be achieved, which is equivalent to an increase in the power density of the first catalyst substance. This is accompanied by a significant cost reduction, since, for example, when using iridium as the active first catalyst substance in comparison to electrocatalysts which consist of pure iridium, only a significantly lower proportion of iridium is required to achieve the same catalytic activity. This also applies to platinum.

In order to improve the use of the electrocatalyst in electrochemical cells or reactors, it is favorable if a highly conductive and / or corrosion-resistant second carrier substance is used. In particular, in acidic electrolyte often used so the life of the electrocatalyst can be significantly extended.

Preferably, a second carrier substance with an electrical conductivity of at least 1 × 10 ⁶ S / m is used. Such a second carrier substance enables the optimum derivation of the electrons produced during the electrolytic splitting of water.

Excellent activities for the oxygen evolution reaction and / or the hydrogen oxidation reaction can be achieved if a first and / or a second active catalyst substance is used, which is or contains a noble metal or a mixture of two or more noble metals. It is therefore possible in particular to use noble metals or mixtures of noble metals which are particularly suitable for the reactions indicated. By using the first or first carrier substance, however, the amount of noble metals to be used in conventional electrocatalysts can be significantly reduced.

It is advantageous if a first and / or a second catalyst substance is used which comprises platinum (Pt), iridium (Ir), ruthenium (Ru), Palladium (Pd), iridium-vanadium (IrV), platinum-iridium (PtIr) or platinum-iridium-vanadium (PtIrV) or a mixture of one or more of these substances. The substances and mixtures mentioned make it possible, in particular, to achieve desired activities for the oxygen evolution reaction and the hydrogen oxidation reaction with the electrocatalyst.

It is advantageous if, to form a supported nanocatalyst, the at least one first active catalyst substance is deposited or applied to the second carrier substance in the form of nanoparticles and / or if the at least one second active catalyst substance is deposited in the form of nanoparticles on the first carrier substance or is applied to this. In particular, the first and / or the second carrier substance can also be provided in the form of nanoparticles, so that overall a significant increase in the active surface of the electrocatalyst can be achieved, without increasing the amount of the first and / or second active catalyst substance.

Preferably, the at least one first active catalyst substance is deposited or applied to the second carrier substance by an anhydrous chemical reaction and / or the at least one second active catalyst substance is deposited or applied to the first carrier substance by an anhydrous chemical reaction. In particular, the chemical reaction is carried out at room temperature and in particular under a protective gas atmosphere. For example, argon can be used as protective gas. To carry out a chemical reaction at room temperature means, in particular, a significantly lower production outlay than, for example, the application of a catalyst layer to a carrier plate by means of thermal spraying.

The electrocatalyst can be produced in a particularly simple manner if the second carrier substance and at least one noble metal salt, in particular a chlorine salt, of the at least one noble metal are dissolved in a first solvent and if the at least one first active catalyst substance is obtained by reducing the at least one noble metal salt by adding a deposited in a second solvent reducing agent deposited on the second carrier substance or is applied thereto and / or when the first carrier substance and at least one noble metal salt, in particular a chlorine salt, of the at least one noble metal are dissolved in a third solvent and if the at least one second active catalyst substance by depositing or depositing onto the first support substance by reduction of the at least one noble metal salt by adding a reducing agent dissolved in a fourth solvent. As a reducing agent, for example, sodium borohydride (NaBH ₄ ) can be used. The described mixing of two solutions represents a simple production method of the electrocatalyst.

Preferably, a hydrocarbon-based solvent, in particular anhydrous ethanol, is used as the first, second, third and / or fourth solvent. Ethanol is an environmentally friendly solvent and is available at low cost. In particular, when both the first and / or the second carrier substance and the at least one noble metal salt are dissolved in the same solvent, the provision of a second, third and fourth solvent can be dispensed with. For example, xylene can also be used as the first, second, third and / or fourth solvent.

In order to improve a surface activity in the reaction, it is favorable if a surfactant, in particular a cationic surfactant, is dissolved in the first and / or third solvent before dissolving the first and / or second carrier substance.

Cetyltrimethylammonium bromide (CTAB) is preferably used as the cationic surfactant. This surfactant is particularly surface-active and prevents nanoparticles of the first and / or second carrier substance from agglomerating during the reaction carried out and thus minimizing a surface for depositing the at least one first and / or second active catalyst substance.

It is advantageous if a first solution is prepared from the second carrier substance and the first solvent, if a second solution is prepared from the at least one noble metal salt and the second solvent and if the first and the second solution are mixed prior to adding the reducing agent, and when a third solution is prepared from the at least one noble metal salt and the fourth solvent and when the third and fourth solutions are mixed prior to adding the reducing agent. In this way, more than a homogeneous mixing of the first and / or the second carrier substance and the noble metal ions in the solution can be achieved before the reduction of the noble metal ions.

In order to improve the performance of the chemical reaction and to achieve the highest possible overall electrochemical surface area of the electrocatalyst, it is advantageous if the first and / or the second carrier substance are used in powder form. In particular, the powder Particles of the first or the second carrier substance in the nanometer range include. Preferably, a size of the nanoparticles of the first and / or the second carrier substance is in a range of about 10 nm to 500 nm, in particular about 50 nm.

Preferably, a second carrier substance is used, which is titanium and / or oxygen and / or iridium and / or antimony and / or tin and / or a metal and / or silicon and / or carbon and / or boron and / or gold and / or a Electroceramics is or contains. Such second carrier substances, in particular also mixtures of the specified substances, are outstandingly suitable for the formation of electrocatalysts with a high catalytic activity, in particular for the oxygen evolution reaction and a low noble metal content. Under an electroceramic is to be understood in particular an electrically conductive ceramic.

It is particularly advantageous if titanium suboxide (Ti ₄ O ₇ ) or iridium in the modification Ir black or antimony tin oxide (ATO) or titanium metal oxide (Ti _{1 -x} M _x O ₂ with M = W , Nb, Mo) or boron-doped silicon carbide (SiC: B) or fluorine-doped tin oxide (SnO ₂ : F) or gold (Au) is used. Titanium suboxide, in particular, has excellent properties that enable the deposition of noble metals on the second support.

In the case of an electrocatalyst of the type described in the introduction, the object stated in the introduction is achieved according to the invention by comprising at least one second active catalyst substance deposited on a first, electrically nonconductive carrier substance or applied thereto to excite the oxidation of hydrogen.

As already described above, such electrocatalysts can be produced with relatively little effort and in an environmentally friendly manner. In addition, the cost of such electrocatalysts compared to conventional electrocatalysts, which consist mainly or entirely of precious metals, significantly lower without having to accept a loss of catalytic activity in purchasing. The second active catalyst substance can effectively oxidize hydrogen at the anode with oxygen to water, thereby significantly reducing the risk of an oxyhydrogen gas reaction. The use of a first, electrically non-conductive carrier substance also has the advantage that no large amounts of the second active catalyst substance are needed.

Due to the support of the second catalyst substance of this only a comparatively smaller amount is needed. In particular, a cost-effective material which is not electrically conductive can be used as the first carrier substance. The first carrier may also surround the second active catalyst substance.

Advantageously, the first carrier substance has an electrical conductivity of at most 1 × 10 ^-3 S / m. Such low electrical conductivity prevents the second catalyst substance from being at potential.

In a cost effective manner, the second catalyst substance can be at least partially reduced in the otherwise required amount, if the first carrier substance is or contains a ceramic, a polymer, in particular tetrafluoroethylene (PTFE), and / or a metal oxide.

The electrocatalyst can be produced in a simple manner if the ceramic or the metal oxide contains titanium. In addition, such a first carrier substance compared to a second active catalyst substance, which consists of a noble metal or a mixture of noble metals, can be produced significantly cheaper.

In particular, good properties of the first carrier substance for depositing or applying the second active catalyst substance can be obtained if the metal oxide is titanium oxide (TIO) or titanium dioxide (TIO ₂ ).

It is advantageous if the first active catalyst substance is deposited on or applied to a first, electrically conductive carrier substance. Thus, the electrocatalyst can be formed with the same activity with significantly less precious metal.

In order to optimize the catalytic activity of the electrocatalyst, it is advantageous if the second carrier substance is highly conductive and / or corrosion resistant. Especially when acidic and alkaline electrolytes are used, high corrosion resistance is desirable.

Conveniently, the second carrier substance has an electrical conductivity of at least 1 × 10 ⁶ S / m. Such a conductivity ensures, in particular, that electrons formed in the decomposition of water can be safely removed from the anode.

Preferably, the first and / or the second catalyst substance is a noble metal or a mixture of two or more noble metals. Precious metals or precious metal mixtures are outstandingly suited to stimulate or assist the development of oxygen and / or the oxidation of hydrogen.

According to a preferred embodiment of the invention it can be provided that the first and / or the second catalyst substance platinum (Pt), iridium (Ir), ruthenium (Ru), palladium (Pd), iridium-vanadium (IrV), platinum-iridium ( PtIr) or platinum-iridium-vanadium (PtIrV) or a mixture of one or more of these substances. The specified substances allow an efficient evolution of oxygen and also a good oxidation of hydrogen. To mix transition metals from the fourth subgroup (titanium group) or the fifth subgroup (vanadium group) of the Periodic Table of the Elements with noble metals to catalyst substances makes it possible in particular to produce much cheaper electrocatalysts compared to pure precious metals. In addition, such a mixture also permits the formation of alloys with noble metals, in particular also on the proposed carrier substances, both on metals and metallic alloys and on ceramics, in particular electrically conductive ceramics, or non-conductive carrier substances such as ceramics or non-conductive metal oxides , Transition metals such as titanium, zirconium, hafnium, vanadium, niobium or tantalum are significantly cheaper compared to precious metals and allow an optimal alloy with precious metals and corresponding carrier substances.

It is advantageous if the electrocatalyst is designed in the form of a supported nanocatalyst, in which the first active catalyst substance is deposited in the form of nanoparticles on the second carrier substance or applied thereto and / or in which the second active catalyst substance in the form of nanoparticles on the deposited or applied to the first carrier substance. Such an electrocatalyst has a high active surface area. In particular, the first and / or the second carrier substance in the form of nanoparticles can be used to form the electrocatalyst, whereby an active surface of the electrocatalyst can be further increased. With the same amount of precious metal, such an electrocatalyst has a significantly improved power density, since for a comparable catalytic activity significantly lower amounts of active catalyst substances, in particular precious metals, must be used.

It is advantageous if the at least one first active catalyst substance is deposited on or applied to the second carrier substance by an anhydrous chemical reaction and / or if the at least one second active catalyst substance is deposited on or applied to the first carrier substance by an anhydrous chemical reaction is. Such an electrocatalyst can be produced with relatively low expenditure on equipment and at low cost.

In order to produce the largest possible active surface of the electrocatalyst, it is favorable if the first and / or the second carrier substance are powdery. In particular, the first and / or the second carrier substance may be a powder with particles which have a size in the nanometer range. In particular, the particles may have a size in a range from 10 nm to 800 nm, in particular in a range from 50 nm to about 400 nm.

According to another preferred embodiment of the invention it can be provided that the second carrier substance is titanium and / or oxygen and / or iridium and / or antimony and / or tin and / or a metal and / or silicon and / or carbon and / or boron and / or gold and / or an electroceramics is or contains. In particular, highly conductive and / or corrosion-resistant powders which can be provided with a first active catalyst substance can be produced with the abovementioned substances.

Particularly good catalytic activities can be achieved if the second carrier titanium suboxide (Ti ₄ O ₇ ) or iridium in the modification Ir-black or antimony-tin-oxide (ATO) or titanium metal oxide (Ti _1-x M _x O ₂ with M = W, Nb, Mo) or boron doped silicon carbide (SiC: B) or fluorine doped tin oxide (SnO ₂ : F) or gold (Au). Titanium suboxide, in particular, has excellent properties that enable the deposition of noble metals on the second support.

Further, the use of one of the electrocatalysts described above for the production of catalyst-coated membranes and membrane electrode assemblies for electrochemical cells is proposed, in particular for fuel cells and electrolyzers, more particularly ion exchange membrane fuel cells and ion exchange membrane water electrolyzers.

In particular, high-performance catalyst-coated membranes and membrane-electrode assemblies can be produced inexpensively in this way.

The object stated in the introduction is further achieved according to the invention in the case of a catalyst-coated membrane of the type described in the introduction in that the electrocatalyst is in the form of one of the electrocatalysts described above.

Such a catalyst-coated membrane has the advantages described above in connection with preferred embodiments of electrocatalysts. In particular, it can be compared to conventional membrane electrode Units are designed significantly cheaper.

The object stated in the introduction is also achieved according to the invention in a membrane-electrode assembly of the type described in the introduction in that the electrocatalyst is in the form of one of the electrocatalysts described above.

Such a membrane-electrode assembly has the advantages described above in connection with preferred embodiments of electrocatalysts. In particular, it can be formed much cheaper compared to conventional membrane electrode assemblies.

The object stated in the introduction is further achieved according to the invention in an electrode of the type described in the introduction in that the at least one catalyst layer comprises one of the above-described electrocatalysts or is formed by one of the electrocatalysts described above.

Such an electrode has the advantages described above in connection with preferred embodiments of electrocatalysts. In particular, it can be formed significantly cheaper compared to conventional electrodes.

Preferably, the at least one catalyst layer is in the form of an anodic or cathodic catalyst layer. In particular, catalyst layers of anodes and cathodes of electrochemical cells or reactors can be formed.

In particular, it is favorable if the electrode is designed in the form of an anode for a water electrolyzer. In particular, it may be an ion exchange membrane water electrolyzer, for example in the form of a proton exchange membrane water electrolyzer. With such an electrode, water can be decomposed much more cost-effectively into its constituents water oxygen and oxygen.

Furthermore, it is favorable if the electrode is designed in the form of a cathode for a fuel cell. In particular, it may be an ion exchange membrane fuel cell, for example in the form of a proton exchange membrane fuel cell. Such an electrode proposed according to the invention is significantly cheaper to produce compared to conventional electrodes.

In order to be able to form in particular compact electrochemical cells and reactors, it is advantageous if the electrode comprises an electrode carrier in the form of a bipolar plate. This may for example be formed from a suitable metal and having gas ducts to divert gases formed during use of the electrochemical cell or to direct these supplied gases to the electrocatalysts.

In order to improve a passage of formed gases or the merging thereof in electrochemical reactors and cells, it is advantageous if the electrode comprises a gas diffusion layer applied to the electrode carrier.

In order to improve a reaction of the electrochemical cell, it is advantageous if the at least one catalyst layer is applied to the gas diffusion layer. For example, in an electrochemical cell or electrochemical reactor, two such electrodes may be joined together, separated by a proton exchange membrane. In other words, then catalyst layers can be formed on both sides of a proton exchange membrane, which in turn are each separated by a gas diffusion layer of an electrode carrier.

In the case of an electrochemical reactor of the type described in the introduction, the object stated in the introduction is also achieved according to the invention in that at least one of the two electrodes is designed in the form of one of the advantageous electrodes described above.

Such an electrochemical reactor is significantly cheaper compared to conventional electrochemical cells, since the required amount of noble metals is significantly reduced. It also reduces the risk of a blast gas explosion.

It is favorable if the electrochemical reactor in the form of an ion exchange membrane fuel cell, an ion exchange membrane water electrolyzer, a redox flow battery, an electrochemical reactor for carbon dioxide and nitrogen reduction, an electrochemical reactor for the oxidation and / or reduction of lignin, an electrochemical reactor for Hydrogenation of gases or liquids, an electrochemical cell for electrochemical water treatment, lithium-air battery, metal-air battery or a metal-layer deposition electrolyzer is formed. With all these different uses of electrochemical cells and reactors, it is possible to significantly save costs, especially in the production thereof without reducing the operation and efficiency of the electrochemical reactor or the electrochemical cell.

The following description of preferred embodiments of the invention is used in conjunction with the drawings for further explanation. Show it:

1 FIG. 1 is a schematic sectional view through an ion exchange membrane water electolyser; FIG.

2 Fig. 1 is a schematic representation of an anodic layer of an ion exchange membrane water electrolyzer;

3a FIG. 2 is a schematic sectional view of a first variant of a membrane-electrode assembly of an ion exchange membrane water electrolyzer; FIG.

3b FIG. 2 is a schematic sectional view of a first variant of a membrane-electrode assembly of an ion exchange membrane water electrolyzer; FIG.

3c FIG. 2 is a schematic sectional view of a first variant of a membrane-electrode assembly of an ion exchange membrane water electrolyzer; FIG.

3d FIG. 2 is a schematic sectional view of a first variant of a membrane-electrode assembly of an ion exchange membrane water electrolyzer; FIG.

3e FIG. 2 is a schematic sectional view of a first variant of a membrane-electrode assembly of an ion exchange membrane water electrolyzer; FIG.

4 : a schematic representation of the chemical synthesis of an Ir / Ti ₄ O ₇ catalyst;

5 Comparison of activity measurements of catalytic layers according to the prior art and the invention, wherein the current values were normalized to A mg ^-1 Ir;

6 : Secondary Electron Microscope Image of Ir-Black from Umicore;

7a : Secondary electron micrograph of the electrocatalyst IrV (with Ir-Mohr);

7b : Secondary electron micrograph of the electrocatalyst Pt / Ti ₄ O ₇ ;

7c : Secondary electron micrograph of the electrocatalyst Pt / Ti ₄ O ₇ ;

7d : Secondary electron micrograph of the electrocatalyst Pt ₃ Ir / Ti ₄ O ₇ ;

7e : Secondary electron micrograph of the electrocatalyst PtIr ₃ / Ti ₄ O ₇ ;

7f : Secondary electron micrograph of the electrocatalyst IrV / Ti ₄ O ₇ , heat-treated after synthesis of the electrocatalyst Ir / Ti ₄ O ₇ ;

7g : Secondary electron micrograph of the electrocatalyst Ir / Ti ₄ O ₇ (heat-treated);

8th : Representation of the OER activity of the electrocatalysts IrV / Ti ₄ O ₇ , Ir / Ti ₄ O ₇ , Ir-Mohr (from Umicore) + Ti ₄ O ₇ , Ir-Mohr (from Umicore), IrO ₂ / TiO ₂ aka Elyst Ir75 (by Umicore);

9 Illustration of the ORR and OER activity of the electrocatalysts Pt ₃ Ir / Ti ₄ O ₇ , PtIr ₃ / Ti ₄ O ₇ , PtIr / Ti ₄ O ₇ , Ir-Mohr (ex Umicore), Pt-Mohr (ex Johnson Matthey );

10 : Representation of the OER activity of the electrocatalysts PtIr ₃ / ATO, PtIr ₃ / Ti ₄ O ₇ , Ir-Mohr (ex Umicore); and

11 : a schematic representation of the synthesis of the electrocatalyst PtIr / Ti ₄ O ₇ .

In 1 is a schematic section through an electrochemical reactor in the form of an electrochemical cell 10 namely by a water electrolyzer 12 which is in the form of a proton exchange membrane water electrolyzer 14 is formed, which is an ion exchange membrane water electrolyzer. It includes a proton exchange membrane ("PEM") 16 For example, perfluorinated sulfuric acid ("PFSA").

The electrochemical cell 10 further comprises a catalyst-coated membrane 18 , A cathode 20 the electrochemical cell 10 includes a cathodic bipolar plate 22 that is a flow field 24 the cathodic bipolar plate 22 defined by a plurality of channels 26 , which is a so-called hydrogen distributor 28 form for deriving the hydrogen formed by the electrolysis.

On the cathodic bipolar plate 22 is a cathodic gas diffusion layer 32 applied to the cathodic bipolar plate 22 a contact surface 30 Are defined.

On the cathodic gas diffusion layer 32 is a cathodic catalyst layer 34 applied through the proton exchange membrane 16 which is adjacent to an anode catalyst layer of an anode 38 the electrochemical cell 10 borders. The anodic catalyst layer 36 which is a current collector 40 defining layer adjacent, adjacent to an anodic bipolar plate 42 and defines with this a contact surface 44 ,

Also in the anodic bipolar plate 42 are to the current collector 40 pointing out several channels 46 formed, which is a flow field 10 the anodic bipolar plate 42 define. The majority of channels 46 defines a water distributor 50 , with which water can be supplied for the electrolysis.

In 2 is an example of the structure of the anodic catalyst layer 36 on the ion exchange membrane 16 shown.

The catalyst layer 36 comprises a second carrier substance 52 , For example in the form of an electrically conductive substrate. On the second vehicle 52 is a first active catalyst substance 54 deposited or applied for exciting the development of oxygen, for example by a wet-chemical reaction described in detail below. In particular, a noble metal or a mixture of two or more noble metals may be used as the first catalyst substance, for example platinum (Pt), iridium (Ir), ruthenium (Ru), palladium (Pd), iridium-vanadium (IrV), platinum-iridium ( PtIr) or platinum-iridium-vanadium (PtIrV) or a mixture of one or more of these substances.

To pass through the ion exchange membrane 16 To oxidize H ₂ molecular hydrogen diffusing, thus forming a reactive oxyhydrogen gas mixture with that at the anode 38 formed molecular oxygen O _{2 is} prevented, includes the anodic catalyst layer 36 further a second active catalyst substance 56 on a first vehicle 58 applied or deposited on this. The second active catalyst substance 56 may be formed from the same materials as the first catalyst substance 54 , However, the first carrier differs 58 from the second vehicle 52 in that it is electrically non-conductive. Preferably, the electrical conductivity of the first carrier substance 58 not larger than 1 × 10 ^-3 S / m. The first vehicle 58 is preferably formed by a ceramic or an electrically non-conductive metal oxide. Both may contain titanium in particular. As the first carrier 58 Titanium oxide or titanium dioxide is preferably used.

The electrical conductivity of the second carrier substance 52 is preferably at least 1 × 10 ⁶ S / m. In addition, a corrosion-resistant second carrier substance is preferred 52 selected.

By the support of the first catalyst substance 54 on the second vehicle 52 and the second catalyst substance 58 For example, precious metal loading can be minimized despite efficient hydrogen oxidation (HOR) reactions. To the migration of the protons formed during the electrolysis through the ion exchange membrane 16 To improve, this can be reduced in thickness. By the second active catalyst substance 56 on the first vehicle 58 effectively prevents the risk of the formation of a reactive oxyhydrogen gas mixture at the anode. The molecular hydrogen becomes through the second catalyst substance 56 reacted with the existing molecular oxygen to water (H ₂ O).

The first catalyst substance 54 primarily serves to aid the oxygen evolution reaction (OER) in the cleavage of H ₂ O.

The chemical reaction equations for the electrolysis of water are given below: 2H ₂ O → 4H ⁺ + e ^- + O ₂ 4H ⁺ + 4e ^- → 2H ₂

The formation of molecular hydrogen occurs at the cathode, depending on the thickness of the ion exchange membrane 16 can not prevent molecular hydrogen H ₂ through the ion exchange membrane 16 to the anode 38 diffused.

In the 3a to 3e are various embodiments for the integration of the electrocatalyst for the hydrogen oxidation reaction in the anodic catalyst layer 36 through the ion exchange membrane 16 and the catalyst layers 34 and 36 defined membrane electrode unit 60 shown schematically.

In 3a includes the membrane-electrode assembly 60 an anodic catalyst layer 36 produced by a mixture of one on the second carrier substance 52 supported first active catalyst substance 54 and one on the first vehicle 58 supported second catalyst substance 56 is formed. The formation of the catalyst layer 36 is realized by physical mixing of the two supported catalyst substances 54 and 56 before application to the ion exchange membrane 16 ,

At the in 3b illustrated variant of the membrane electrode assembly 60 is the catalyst layer 36 segmented trained. Segments with the supported first catalyst substance 54 form so-called HOR segments 62 directed to the ion exchange membrane 16 applied and adjacent to so-called OER segments 64 are arranged. The OER segments 64 are formed by the supported first catalyst substance 54 on the second vehicle 52 , The HOR segments 62 and the OER segments 64 may be striped or checkered on the ion exchange membrane 16 be applied.

As in 3c shown schematically, the membrane-electrode unit 60 also with a two-layer catalyst layer 36 be formed. On the ion exchange membrane 16 is a mixed layer 66 from the on the first vehicle 58 supported second active catalyst substance 56 with perfluorosulfonic acid polymer particles (PFSA). This will be followed by an OER layer 68 covered by the first active catalyst substance 54 is formed on the second vehicle 52 is supported.

In 3d is another variant of the membrane electrode assembly 60 shown. It essentially corresponds to the variant 3c , wherein additionally between the mixed layer 66 and the OER layer 68 another ion exchange membrane layer 70 is introduced. It can also be said here that the ion exchange membrane forming an ion conductor is an internal mixed layer 66 by introducing supported HOR catalyst and PFSA particles into the ion exchange membrane 16 is trained.

A particularly simple variant of the membrane-electrode unit 60 is in 3e shown schematically. Here are HOR catalyst particles 72 in through the ion exchange membrane 16 formed ion conductor introduced directly.

In 4 schematically shows the chemical synthesis of the electrocatalyst for the hydrogen oxidation reaction, namely platinum on titanium dioxide (Pt / TiO ₂ ), in which TiO _{2 forms} the first carrier substance and platinum (Pt) the active second catalyst substance.

First, cetyltrimethylammonium bromide (CTAB), which acts as a surfactant, is dissolved in anhydrous ethanol, for example, it may then be placed in a three-necked flask. The addition of CTAB on the one hand promotes distortion on the support material, on the other hand it serves to form nanoparticles.

Subsequently, the carrier material TiO _{2 is} added. For better mixing, the solution can be placed in an ultrasonic bath.

Further, platinum (IV) chloride (PtCl ₄ ) is dissolved in anhydrous ethanol and then supplied to the mixture contained in the three-necked flask. The entire mixture is treated again for several minutes in an ultrasonic bath. Then argon is added and the rotation is switched on.

After a few hours, the temperature of the mixture, which took place at room temperature, is cooled by means of an ice bath and the rotation is increased.

The reducing agent sodium borohydride (NaBH ₄ ) is dissolved in anhydrous ethanol and added dropwise. The low temperature, which reduces the reaction rate, the increased rotation and the slow dropwise addition of NaBH ₄ guarantees both a good distribution of the catalytically active substance on the carrier material and the agglomeration of catalyst material into large particles.

After the mixture has been mixed with the magnetic stirrer for several hours, the argon supply is turned off and the rotation of the magnetic stirrer is switched off.

Using a Woulff bottle, the mixture is filtered through a paper filter and washed several times with ethanol. Thereafter, the filtrate, ie the obtained HOR electrocatalyst Pt / TiO ₂ , dried in an oven at 65 ° C.

Alternatively, the electrocatalyst can be prepared by means of a centrifuge. Several washes with water, ethanol or, alternatively, H ₂ SO ₄ solution purify the electrocatalyst of CTAB impurities and salts formed during the synthesis. For this purpose, the catalyst powder is alternately dispersed in the respective washing solution and then separated again by means of a centrifuge.

Optionally, the HOR electrocatalyst Pt / TiO ₂ can be treated with a transition metal, for example with vanadium. For vanadium treatment, vanadyl sulfate (VOSO ₄ ) is dissolved in sulfuric acid (H ₂ SO ₄ ) and the purified and dried electrocatalyst Pt / TiO ₂ is added. The solution is thoroughly mixed and the water contained in the mixture is subsequently evaporated. The remainder of the mixture is dried in an oven at 500 ° C. under a hydrogen atmosphere. Thus, the catalyst PtV / TiO _{2 is} produced.

In the synthesis described, only the environmentally friendly ethanol is used as the solvent. Titanium dioxide (TiO ₂ ) is used as a carrier material. In order to additionally reduce the amount of platinum used as the second active catalyst substance, as described, the HOR electrocatalyst can optionally be modified by adding vanadium. As a result, a platinum loading of the catalyst can be significantly reduced compared to pure platinum and controlled to a desired value. The cost of producing such a supported catalyst is significantly lower when compared to pure platinum, considering current precious metal prices.

The preparation of the OER electrocatalyst is for example in the German Patent Application 10 2015 101 249.9 described.

Forming the anodic catalyst layer 36 as shown schematically in 3a as shown by mixing a supported OER catalyst and a supported HOR catalyst in the ratio 9: 1, as shown in activity measurements that in 5 arithmetically normalized to current values per milligram iridium, that the OER catalyst is not poisoned by the HOR catalyst. Rather, there is no reduction in activity. In the 5 The measured values recorded were recorded under argon-saturated 0.5 molar H ₂ SO ₄ solution at 24 ° Celsius and at a rotational speed of 2300 revolutions per minute. The recording rate was 5mV. The voltage was measured relative to a reversible hydrogen electrode (RHE). For comparison are in 5 Activity measurements with a standard OER catalyst shown in dashed lines and solid with a supported OER catalyst.

In 6 is a secondary electron micrograph of the electrocatalyst Iridium-Black Company Umicore shown.

For comparison shows 7a at a somewhat double magnification, a secondary electron microscope photograph of the electrocatalyst IrV, wherein the iridium used is iridium-Mohr. IrV is formed from the configuration Iridium Black by the vanadium treatment described above using vanadyl sulfate.

In 7b is a secondary electron micrograph of a supported Pt / Ti ₄ O ₇ type electrocatalyst shown with one compared to 7a about fifty times smaller magnification. This electrocatalyst is used as an OER catalyst.

7c shows a secondary electron micrograph of the electrocatalyst Pt / Ti ₄ O ₇ . The magnification corresponds approximately to the increase in the recording of 6 ,

7d shows by way of example a secondary electron micrograph of the electrocatalyst Pt ₃ Ir ₁ / Ti ₄ O ₇ with an enlargement approximately corresponding to the increase in the uptake of the 7a equivalent. This electrocatalyst is also used as an OER catalyst.

The 7e shows a secondary electron micrograph of the electrocatalyst PtIr ₃ / Ti ₄ O ₇ with a resolution comparable to that in 7d shown recording. An example of a synthesis of this electrocatalyst will be given in more detail below. This electrocatalyst is also used as an OER catalyst.

The 7f shows a secondary electron micrograph of the electrocatalyst IrV / Ti ₄ O ₇ . This electrocatalyst is prepared by heat-treating the synthesized electrocatalyst Ir / Ti ₄ O ₇ as described above. The resolution of the representation in 7f corresponds to something of half the resolution of the representation of 7e , This electrocatalyst is also used as an OER catalyst.

7g Finally, a secondary electron micrograph of the electrocatalyst Ir / Ti ₄ O ₇ as obtained by the above-described chemical reaction is shown. It is therefore the electrocatalyst, which by treatment with vanadium in the in 7f represented electrocatalyst IrV / Ti ₄ O ₇ can be transferred. This electrocatalyst is also used as an OER catalyst.

In 8th is the activity of the oxygen evolution reaction (OER activity) of the electrocatalysts IrV / Ti ₄ O ₇ , Ir / Ti ₄ O ₇ , Ir-Mohr from Umicore with Ti ₄ O ₇ , pure Mohr from Umicore and iridium oxide on TiO ₂ catalyst Ir75 represented by Umicore. As the measured dependence of the voltage relative to the reversible hydrogen electrode (RHE) on the current shows, the activity of the specified electrocatalysts increases continuously from iridium oxide to TiO ₂ towards the electrocatalyst IrV / Ti ₄ O ₇ .

The activity of electrocatalysts in the oxygen reduction reaction (ORR) are exemplified in 9 for the electrocatalysts Pt ₁ Ir ₁ / Ti ₄ O ₇ , Pt ₃ Ir ₁ / Ti ₄ O ₇ , Pt ₁ Ir ₃ / Ti ₄ O ₇ , Ir-Mohr (UC = Umicore) and Pt-Mohr (JM = Johnson Matthey ) shown schematically. Again, it can be seen that by mixing platinum and iridium and applying this mixture to Ti ₄ O ₇ in comparison to pure iridium significantly higher current densities are achieved at significantly lower potentials. Even pure Platinum is surpassed by at least Pt ₃ Ir ₁ / Ti ₄ O ₇ and Pt ₁ Ir ₃ / Ti ₄ O ₇ .

10 exemplifies the activity of three electrocatalysts in the oxygen evolution reaction (OER activity) in comparison. Shown are the measured current densities as a function of the voltage with respect to the hydrogen reference electrode (RHE). Again, there is a marked increase in the activity of Pt ₁ Ir ₃ / ATO and Pt ₁ Ir ₃ / Ti ₄ O ₇ compared to pure iridium.

Another example of the production of, in particular, an OER electrocatalyst is shown schematically in FIG 11 shown. It forms the basis for the preparation of the electrocatalyst PtIrV / Ti ₄ O ₇ . By means of a wet-chemical synthesis process, the electrocatalyst PtIr / Ti ₄ O ₇ with a noble metal content of 30% by weight is first prepared by reduction at room temperature. The treatment of this electrocatalyst with vanadium is optionally carried out in a subsequent step.

First, for the synthesis of PtIr / Ti ₄ O _7, 1.17 g of cetyltrimethylammonium bromide (CTAB, VWR Chemicals), a cationic surfactant which reduces the interfacial tension between two phases, is dissolved in 120 ml of anhydrous ethanol having a maximum water content of 0.01% and put in a three-necked flask. The addition of CTAB on the one hand promotes the dispersion of the noble metals on the support material and on the other hand it serves for the complete reduction of the metallic starting materials and the deposition on the support material, the so-called nanoparticle formation.

Subsequently, 0.15 g of the support material Ti ₄ O _{7 are} added to the three-necked flask and stirred for better mixing by means of a magnetic stirrer at 500 revolutions / min.

Further, argon is added to the solution to create an inert gas phase.

53 mg of the reddish-brown, crystalline and hygroscopic salt platinum (IV) chloride (99.9%, PtCl ₄ from Alfa Aesar) are mixed with 47 mg iridium (III) chloride (99.9%, IrCl ₃ from Alfa Aesar ), a highly hygroscopic salt, dissolved in 50 ml of anhydrous ethanol and also fed to the three-necked flask after thirty minutes.

After four hours, 152 mg of the reducing agent sodium borohydride (NaBH ₄ from Merck Millipore), a complex salt consisting of a sodium cation Na ⁺ and a complex tetrahydridoborate anion BH ₄ ^- dissolved in 20 ml of anhydrous ethanol and added quickly to the mixture.

The speed of the magnetic stirrer is increased to 1100 rpm and the solution mixed for another four hours at room temperature to achieve complete reduction.

The mixture is then filtered using a Woulff bottle and two blue-band filter papers suitable for very fine precipitates and washed several times with pure ethanol (99.0%) to remove by-products as well as CTAB.

The filtrate, the resulting electrocatalyst PtIr / Ti ₄ O ₇ , dried in an oven at 40˚C and then ground with a mortar.

In order to completely clean the electrocatalyst of CTAB, it is optionally subjected to a heat treatment or washed with ethanol until CTAB is no longer detectable in the mother liquor. In the heat treatment, the electrocatalyst is heated in a gaseous atmosphere of 5% hydrogen and 95% argon at 250 ° C. for two hours. The starting temperature is 30˚C with a temperature ramp of 5˚C / min and a flow rate of the cleaning gas of 30 ml / min.

The individual synthesis steps are as already noted in FIG 11 compiled.

Following the synthesis, the OER electrocatalyst PtIr / Ti ₄ O ₇ can optionally be treated with vanadium. For this purpose, vanadyl sulfate (VOSO ₄ ) from Alfa Aesar is dissolved in demineralized water and added to the ultrasonic bath for better mixing. Subsequently, the electrocatalyst is added and the mixture is treated for an additional thirty minutes in an ultrasonic bath. After the solution has been well mixed, it is heated in an oven at 40 ° C. to evaporate the water. The dried powder is then subjected to a heat treatment at 550 ° C. in air atmosphere for two hours. At the end of this treatment process, the electrocatalyst PtIrV / Ti ₄ O _{7 is obtained} .

The electrocatalysts described above can be used for numerous commercial applications in the field of low-to-medium temperature electrochemical applications and techniques. These are in particular catalyst layers in membrane-electrode assemblies and catalyst-coated membranes, polymer electrolyte membrane electrolyzers (PEM electrolysers), reversible fuel cells (RBZ), polymer electrolyte fuel cells (PEBZ), oxygen electrodes for various electrolysis applications , Satellite propulsion, water treatment and electrochemical membrane reactors for CO ₂ and N ₂ reduction of biomass and also lithium-air batteries and metal-air batteries.

LIST OF REFERENCE NUMBERS

10

 electrochemical cell

12

 water electrolyser

14

 Ion exchange membrane water electrolyzer

16

 Ion exchange membrane

18

 Catalyst-coated membrane

20

 cathode

22

 cathodic bipolar plate

24

 Flow field of the cathodic bipolar plate

26

 channel

28

 Hydrogen Distributor / Anodic Gas Diffusion Layer

30

 contact surface

32

 cathodic gas diffusion layer

34

 cathodic catalyst layer

36

 anodic catalyst layer

38

 anode

40

 current collector

42

 Anodic bipolar plate

44

 contact surface

46

 channel

48

 flow field

50

 water distributor

52

 second carrier substance

54

 first catalyst substance

56

 second catalyst substance

58

 first carrier substance

60

 Membrane electrode assembly

62

 HOR segment

64

 OER segment

66

 mixed layer

68

 OER layer

70

 Ion-exchange membrane layer

72

 HOR catalyst particles

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102015101249 [0119]

Claims (26)

Electrocatalyst for an electrode ( 38 ) an electrochemical cell ( 10 ), which electrocatalyst has at least one first active catalyst substance ( 54 ), in particular for exciting the development of oxygen, characterized by at least one on a first, electrically non-conductive carrier substance ( 58 ) deposited or applied to this second active catalyst substance ( 56 ), in particular for exciting the oxidation of hydrogen. Electrocatalyst according to Claim 1, characterized in that the first carrier substance ( 58 ) has an electrical conductivity of at most 1 × 10 ^-3 S / m. Electrocatalyst according to Claim 1 or 2, characterized in that the first carrier substance ( 58 ) is or contains a ceramic, a polymer, in particular tetrafluoroethylene (PTFE) and / or a metal oxide. Electrocatalyst according to claim 3, characterized in that the ceramic or the metal oxide contains titanium. Electrocatalyst according to claim 3 or 4, characterized in that the metal oxide is titanium oxide (TiO) or titanium dioxide (TiO ₂ ). Electrocatalyst according to one of Claims 1 to 5, characterized in that the first active catalyst substance ( 54 ) on a first, electrically conductive carrier substance ( 52 ) is deposited or applied to this. Electrocatalyst according to claim 6, characterized in that the second carrier substance ( 52 ) is highly conductive and / or corrosion resistant. Electrocatalyst according to claim 7, characterized in that the second carrier substance ( 52 ) has an electrical conductivity of at least 1 × 10 ⁶ S / m. Electrocatalyst according to one of claims 1 to 8, characterized in that the first and / or the second catalyst substance ( 54 . 56 ) is a noble metal or a mixture of two or more precious metals. Electrocatalyst according to one of claims 1 to 9, characterized in that the first and / or the second catalyst substance ( 54 . 56 ) Platinum (Pt), iridium (Ir), ruthenium (Ru), palladium (Pd), iridium-vanadium (IrV), platinum-iridium (PtIr) or platinum-iridium-vanadium (PtIrV) or a mixture of one or more of these substances is. Electrocatalyst according to one of Claims 1 to 10, characterized in that it is in the form of a supported nanocatalyst in which the at least one first active catalyst substance ( 54 ) in the form of nanoparticles on the second carrier substance ( 52 ) or deposited on it and / or in which the at least one second active catalyst substance ( 56 ) in the form of nanoparticles on the first carrier ( 58 ) is deposited or applied to this. Electrocatalyst according to one of Claims 1 to 11, characterized in that the at least one first active catalyst substance ( 54 ) by an anhydrous chemical reaction on the second carrier substance ( 52 ) or deposited on it and / or that the at least one second active catalyst substance ( 56 ) by an anhydrous chemical reaction on the first carrier ( 58 ) is deposited or applied to this. Electrocatalyst according to one of claims 1 to 12, characterized in that the first and / or the second carrier substance ( 52 . 58 ) are powdery. Electrocatalyst according to one of Claims 1 to 13, characterized in that the second carrier substance ( 52 ) Titanium and / or oxygen and / or iridium and / or antimony and / or tin and / or a metal and / or silicon and / or carbon and / or boron and / or gold and / or a ceramic is or contains. Electrocatalyst according to claim 14, characterized in that the second carrier substance ( 52 ) Titanium suboxide (Ti ₄ O ₇ ) or iridium in the modification Ir-black or antimony-tin oxide (ATO) or titanium metal oxide (Ti _1-x M _x O ₂ with M = W, Nb, Mo) or boron doped Silicon carbide (SiC: B) or gold (Au) is. Catalyst-coated membrane ( 18 ) comprising an ion exchange membrane ( 16 ), which at least one side, in particular on both sides, with an electrocatalyst ( 34 . 36 ), characterized in that the electrocatalyst ( 34 . 36 ) is formed in the form of an electrocatalyst according to one of claims 1 to 15. Membrane electrode unit ( 60 ) comprising an ion exchange membrane ( 16 ), which at least one side, in particular on both sides, with an electrocatalyst ( 34 . 36 ), characterized in that the electrocatalyst ( 34 . 36 ) is formed in the form of an electrocatalyst according to one of claims 1 to 15. Electrode ( 20 . 38 ) for an electrochemical cell ( 10 ), which electrode ( 20 . 38 ) at least one catalyst layer ( 34 . 36 ), characterized in that the at least one catalyst layer ( 34 . 36 ) comprises an electrocatalyst according to any one of claims 1 to 15 or is formed by an electrocatalyst according to any one of claims 1 to 15. Electrode according to Claim 18, characterized in that the at least one catalyst layer ( 34 . 36 ) in the form of an anodic or cathodic catalyst layer ( 34 . 36 ) is trained. An electrode according to claim 18 or 19, characterized in that the electrode ( 38 ) in the form of an anode ( 38 ) for a water electrolyzer ( 12 ), in particular an ion exchange membrane water electrolyzer is formed. An electrode according to claim 18 or 19, characterized in that the electrode ( 20 ) in the form of a cathode ( 20 ) is designed for a fuel cell, in particular an ion exchange membrane fuel cell. Electrode according to one of Claims 18 to 21, characterized by an electrode carrier in the form of a bipolar plate ( 22 . 42 ). An electrode according to claim 22, characterized by a gas diffusion layer applied to the electrode carrier. An electrode according to claim 23, characterized in that the at least one catalyst layer on the gas diffusion layer ( 28 . 32 ) is applied. Electrochemical reactor, in particular in the form of an electrochemical cell ( 10 ) comprising at least two electrodes ( 20 . 38 ), characterized in that at least one of the two electrodes ( 20 . 38 ) in the form of an electrode ( 20 . 38 ) is designed according to one of claims 18 to 24. Electrochemical reactor according to Claim 25, characterized in that the electrochemical reactor is in the form of an ion exchange membrane fuel cell, an ion exchange membrane water electrolyzer ( 14 ), a redox flow battery, an electrochemical reactor for carbon dioxide and nitrogen reduction, an electrochemical reactor for oxidation and / or reduction of lignin, an electrochemical reactor for hydrogenating gases or liquids, an electrochemical cell for electrochemical water treatment or a metal-layer deposition electrolyzer is.

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