DE102015101249B4 - A method for producing an electrocatalyst for an electrode of an electrochemical cell, an electrochemical reactor and an electrocatalyst for an electrochemical cell - Google Patents

Abstract

Method for producing an electrocatalyst for an electrode of an electrochemical cell (10; 60), in which an active catalyst substance (106, 108) is deposited or applied to a carrier substance (102) by chemical reaction, the active catalyst substance (106, 108) is or contains at least one noble metal from the group of platinum, iridium, ruthenium, gold, silver and palladium, wherein the active catalyst substance (106, 108) is deposited on or applied to the carrier substance (102) by an anhydrous chemical reaction at room temperature, characterized in that the carrier substance (102) and at least one noble metal salt of the at least one noble metal are dissolved in a first solvent and that the active catalyst substance (106, 108) by reducing the at least one noble metal salt by adding a reducing agent dissolved in a second solvent on the Carrier substance (102) deposited or r is applied to this.

Description

The present invention relates to a method for producing an electrocatalyst for an electrode of an electrochemical cell, in which an active catalyst substance is deposited or applied to a carrier substance by chemical reaction, the active catalyst substance at least one noble metal from the group of platinum, iridium, ruthenium, gold , Is or contains silver and palladium, the active catalyst substance being deposited on or applied to the carrier substance by an anhydrous chemical reaction at room temperature.

The present invention further relates to an electrocatalyst for an electrode of an electrochemical cell, wherein a carrier substance and an active catalyst substance deposited by chemical reaction on the carrier substance or applied to it, the active catalyst substance at least one noble metal from the group of platinum, iridium, ruthenium, gold , Is or contains silver and palladium, the active catalyst substance being deposited or applied to the carrier substance by an anhydrous chemical reaction at room temperature.

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

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

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

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

Processes, 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 a wide variety of forms. For example, electrochemical reactors in the form of electrochemical cells, especially highly efficient fuel cells and electrolyzers, are becoming increasingly important due to the energy transition that has been decided in Germany. The main reaction at the anode of a fuel cell is the oxidation of hydrogen (HOR - "Hydrogen Oxidation Reaction") and in an electrolyser the evolution of oxygen (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"). So far, electrocatalysts made of pure noble metal or at least with a very high proportion of noble metal have been used for all of the reactions mentioned. In particular, platinum and iridium are used. The costs of such electrocatalysts are correspondingly high.

From the DE 10 2010 044 288 A1 processes for the production of platinum transition metal catalyst particles are known. A metal oxide / platinum composite catalyst and manufacture thereof are disclosed in US Pat DE 11 2011 105 084 T5 described. The DE 100 37 071 A1 discloses noble metal nanoparticles and methods of making and using them. WO 2008/061 975 A2 deals with electrodes for the production of hydrogen by electrolysis of aqueous ammonia solutions and an electrolyser comprising such electrodes and their use. One method of depositing a platinum group metal is disclosed in US Pat DE 17 71 639 B2 known.

It is therefore an object of the present invention to design processes, electrochemical reactors, catalyst-coated membranes, membrane-electrode assemblies, electrodes and electrocatalysts of the type described at the outset in a more cost-effective manner.

This object is achieved according to the invention in a method of the type described above in that the carrier substance and at least one noble metal salt of the at least one noble metal are dissolved in a first solvent and that the active catalyst substance by reducing the at least one noble metal salt by adding one dissolved in a second solvent Reducing agent is deposited on the carrier substance or applied to it.

The method proposed according to the invention 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 noble metals. This is made possible in particular through the use of one or more carrier substances, through which an active surface of the electrocatalyst is increased, without increasing the amount of precious metals. On the contrary: the carrier substance enables the at least one noble metal to accumulate, so that a comparable catalytic activity can be achieved despite the reduced noble metal content, which is equivalent to an increase in the power density of the noble metal. This is accompanied by a significant reduction in costs, since, for example, when using iridium, compared to electrocatalysts that consist of pure iridium, only a significantly lower proportion of iridium is required to achieve the same catalytic activity. According to the invention, the active catalyst substance is deposited or applied to the carrier substance by an anhydrous chemical reaction at room temperature. Carrying out a chemical reaction at room temperature means, in particular, a significantly lower production effort than, for example, applying a catalyst layer to a carrier plate by means of thermal spraying. The electrocatalyst can be produced in a particularly simple manner in that the 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 that the active catalyst substance is dissolved by reducing the at least one noble metal salt by adding one in a second Solvent dissolved reducing agent is deposited on the carrier substance or applied to this. Sodium borohydride (NaBH ₄ ), for example, can be used as the reducing agent. The described mixing of two solutions represents a simple manufacturing method for the electrocatalyst.

It is advantageous if, in order to form a supported nanocatalyst, the active catalyst substance is deposited in the form of nanoparticles on the support substance or applied to it. In particular, the carrier substance can also be provided in the form of nano-articles, so that overall a significant increase in the active surface of the electrocatalyst can be achieved without increasing the amount of noble metal used.

The active catalyst substance is preferably deposited or applied to the carrier substance by an anhydrous chemical reaction under a protective gas atmosphere. For example, argon can be used as the protective gas.

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

In order to improve a surface activity during the reaction, it is advantageous if a surfactant, in particular a cationic surfactant, is dissolved in the first solvent before the carrier substance is dissolved.

Cetyltrimethylammonium bromide (CTAB) is preferably used as the cationic surfactant. This surfactant has a particularly surface-active effect and prevents nanoparticles of the carrier substance from agglomerating during the reaction carried out and thus minimizing a surface for the deposition of the at least one noble metal.

It is favorable if a first solution is produced from the carrier substance and the first solvent, if a second solution is produced from the at least one noble metal salt and the second solvent, and if the first and second solutions are mixed before adding the reducing agent. In this way, more than homogeneous mixing of the carrier substance and the noble metal ions in the solution can be achieved before the noble metal ions are reduced.

In order to further reduce the noble metal content in the electrocatalyst, it is advantageous if at least one transition metal is also added to the active catalyst substance. For example, this can take place when the chemical reaction is carried out or after reduction of the at least one noble metal salt. In particular, this can be done by a corresponding treatment with a transition metal salt in an acidic solution, which is mixed with the catalyst substance that has been produced up to this point in time.

It is advantageous if a metal from the 4th subgroup (titanium group) or the 5th subgroup (vanadium group) of the Periodic Table of the Elements is added as the at least one transition metal. Such transition metals are significantly cheaper than noble metals, but can replace them in an electrocatalyst prepared as described without the electrochemical activity of the catalyst substance being reduced.

It is particularly advantageous if titanium, zirconium, hafnium, vanadium, niobium and / or tantalum are added as the at least one transition metal. In this way, with the transition metals mentioned in conjunction with the at least one noble metal used, alloys can be formed which are supported by the carrier substance be carried. In this way, high active surfaces can be generated that are in no way inferior to pure precious metals in terms of their electrochemical activity.

According to a further preferred variant of the method according to the invention it can be provided that iridium (Ir), iridium-vanadium (IrV), platinum-iridium (PtIr) or platinum-iridium-vanadium (PtIrV) is produced as the active catalyst substance. To form the electrocatalyst according to the invention, all of these catalyst substances are deposited on a carrier substance or applied to it.

In order to improve the performance of the chemical reaction and overall to achieve the highest possible electrochemical surface of the electrocatalyst, it is advantageous if the carrier substance is used in powder form. In particular, the powder can comprise particles of the carrier substance in the nanometer range. The size of the nanoparticles of the carrier substance is preferably in a range from approximately 10 nm to 500 nm, in particular approximately 50 nm.

In order to improve the use of the electrocatalyst in electrochemical cells or reactors, it is advantageous if a highly conductive and / or corrosion-resistant carrier substance is used. In particular with acidic electrolytes that are frequently used, the service life of the electrocatalyst can thus be significantly extended.

A carrier substance is preferably 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 an electroceramic is or contains. Such carrier substances, in particular mixtures of the specified substances, are outstandingly suitable for the formation of electrocatalysts with a high catalytic activity and a low noble metal content.

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 precious metals to be deposited on the substrate.

The object set out at the beginning is also achieved according to the invention in an electrocatalyst of the type described at the outset in that the active catalyst substance is deposited on the carrier substance by reducing at least one noble metal salt of the at least one noble metal dissolved in a first solvent with the carrier substance by adding a reducing agent dissolved in a second solvent deposited or applied to them.

As already described above, such electrocatalysts can be produced with relatively little effort and in an environmentally friendly manner. In addition, the costs of such electrocatalysts are significantly lower compared to conventional electrocatalysts, which consist predominantly of noble metals or entirely of noble metals, without having to accept a loss of catalytic activity. It is advantageous that the active catalyst substance is deposited on the carrier substance or applied to it by an anhydrous chemical reaction at room temperature. Such an electrocatalyst can be produced inexpensively and with relatively little expenditure on equipment. The electrocatalyst can be produced in a particularly simple manner in that the active catalyst substance is deposited on or applied to the carrier substance by reducing at least one noble metal salt of the at least one noble metal dissolved with the carrier substance in a first solvent by adding a reducing agent dissolved in a second solvent . Sodium borohydride (NaBH ₄ ), for example, can be used as the reducing agent. The described mixing of two solutions represents a simple manufacturing method for the electrocatalyst.

It is favorable if the electrocatalyst is designed in the form of a supported nanocatalyst, in which the active catalyst substance is deposited on the carrier substance in the form of nanoparticles or applied to it. Such an electrocatalyst has a high active surface. In particular, the carrier substance in the form of nanoparticles can also be used to form the electrocatalyst, whereby an active surface area of the electrocatalyst can be increased further. With the same amount of noble metal, such an electrocatalyst has a significantly improved power density, since significantly smaller amounts of noble metals have to be used for a comparable catalytic activity.

In order to further reduce the amount of noble metal used, it is advantageous if the active catalyst substance also contains at least one transition metal.

The at least one transition metal is preferably a metal from the 4th subgroup (titanium group) or the 5th subgroup (vanadium group) of the Periodic Table of the Elements. Such transition metals are compared to Precious metals are significantly cheaper and allow alloys to be formed with precious metals, in particular also on carrier substances, both on metals and metallic alloys and on ceramics, in particular electroceramics.

It is advantageous if the at least one transition metal is titanium, zirconium, hafnium, vanadium, niobium or tantalum. Such metals are particularly cheap compared to precious metals and enable an optimal alloy with precious metals and corresponding carrier substances.

According to a further preferred embodiment of the invention it can be provided that the active catalyst substance is iridium (Ir), iridium-vanadium (IrV), platinum-iridium (PtIr) or platinum-iridium-vanadium (PtIrV). Such catalyst substances on a corresponding carrier substance make it possible in particular to form an electrocatalyst with a significantly reduced proportion of noble metals, to be precise without significant losses in the catalytic activity.

The electrocatalyst can be manufactured particularly inexpensively if the active catalyst substance is deposited on the carrier substance by a wet chemical reaction at room temperature. A wet chemical reaction, in particular anhydrous, enables simple handling for the production of the electrocatalyst. Furthermore, the absence of water avoids oxidation of the catalyst and agglomeration and reduces reaction kinetics.

In order to generate the largest possible active surface of the electrocatalyst, it is advantageous if the carrier substance is in powder form. In particular, the carrier substance can be a powder with particles which have a size in the nanometer range. In particular, the particles can have a size in a range from 10 nm to 800 nm, in particular in a range from 50 nm to approximately 400 nm.

In order to optimize the catalytic activity of the electrocatalyst, it is advantageous if the carrier substance is highly conductive and / or corrosion-resistant. A high level of corrosion resistance is particularly desirable when using acidic and alkaline electrolytes.

According to a further preferred embodiment of the invention it can be provided that the carrier substance 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 electroceramic is or contains. In particular, highly conductive and / or corrosion-resistant powders, which can be provided with an active catalyst substance, can be produced with the substances mentioned.

Particularly good catalytic activities can be achieved if the carrier substance is 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 precious metals to be deposited on the substrate.

Furthermore, the object set out at the beginning is achieved according to the invention by using one of the electrocatalysts described above for the production of catalyst-coated membranes and membrane-electrode units for electrochemical cells, namely for electrolysers, further in particular ion exchange membrane water electrolysers.

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

The object set at the beginning is also achieved according to the invention in a catalyst-coated membrane of the type described at the outset in that the electrocatalyst is designed 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 made significantly more cost-effective than conventional membrane electrode units.

The object set at the beginning is also achieved according to the invention in a membrane-electrode unit of the type described at the outset in that the electrocatalyst is designed in the form of one of the electrocatalysts described above.

Such a membrane-electrode unit has the advantages described above in connection with preferred embodiments of electrocatalysts. In particular, it can be made significantly more cost-effective than conventional membrane electrode units.

The object set at the beginning is also used in the case of an electrode described type solved according to the invention in that the at least one catalyst layer comprises one of the electrocatalysts described above 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 made significantly more cost-effective than conventional electrodes.

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

It is particularly favorable if the electrode is designed in the form of an anode for a water electrolyzer. In particular, it can be an ion exchange membrane water electrolyser, for example in the form of a proton exchange membrane water electrolyser. With such an electrode, water can be broken down into its constituent parts hydrogen and oxygen much more cost-effectively.

It is also advantageous if the electrode is designed in the form of a cathode for a fuel cell. In particular, it can 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 more cost-effective to produce than conventional electrodes.

In order to be able to form compact electrochemical cells and reactors in particular, it is advantageous if the electrode comprises an electrode carrier in the form of a bipolar plate. This can, for example, be formed from a suitable metal and have gas ducts in order to divert gases formed when the electrochemical cell is used or to conduct gases supplied to the electrocatalysts.

In order to improve the passage of formed gases or the merging of the same 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, two such electrodes can be joined together in an electrochemical cell or an electrochemical reactor, wherein they are separated from one another by a proton exchange membrane. In other words, catalyst layers can then be formed on both sides of a proton exchange membrane, which in turn are each separated from an electrode carrier by a gas diffusion layer.

The object set at the beginning is also achieved according to the invention in an electrochemical reactor of the type described at the beginning 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 more cost-effective than conventional electrochemical cells, since the amount of noble metals required is significantly reduced.

It is favorable if the electrochemical reactor is in the form of 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 the hydrogenation of gases or liquids , an electrochemical cell for electrochemical water treatment, lithium-air battery, metal-air battery or a metal layer deposition electrolyzer. With all these different uses of electrochemical cells and reactors, it is possible to save significant costs, in particular in the manufacture of the same, without reducing the mode of operation and efficiency of the electrochemical reactor or the electrochemical cell.

• 1: eine schematische Schnittansicht durch einen Ionenaustauschmembran- Wasserelektrolyseur;
• 2: eine schematische Schnittansicht durch eine Ionenaustauschmembran- Brennstoffzelle;
• 3: eine schematische Schnittansicht einer Membran-Elektroden-Einheit eines Ionenaustauschmembran-Wasserelektrolyseurs;
• 3b: eine schematische Schnittansicht einer Membran-Elektroden-Einheit einer Ionenaustauschmembran-Brennstoffzelle;
• 4: eine schematische Darstellung einer anodischen Schicht eines Ionenaustauschmembran- Wasserelektrolyseurs;
• 5: eine schematische Darstellung der chemischen Synthese eines Ir/ Ti407-Katalysators;
• 6: Sekundärelektronenmikroskop-Aufnahme von Ir-Black der Firma Umicore;
• 7a: Sekundärelektronenmikroskop-Aufnahme des Elektrokatalysators IrV (mit Ir-Mohr);
• 7b: Sekundärelektronenmikroskop-Aufnahme des Elektrokatalysators Pt/Ti₄O₇;
• 7c: Sekundärelektronenmikroskop-Aufnahme des Elektrokatalysators Pt/ Ti₄O₇;
• 7d: Sekundärelektronenmikroskop-Aufnahme des Elektrokatalysators Pt₃Ir/Ti₄O₇;
• 7e: Sekundärelektronenmikroskop-Aufnahme des Elektrokatalysators PtIr_3/Ti₄O₇;
• 7f: Sekundärelektronenmikroskop-Aufnahme des Elektrokatalysators IrV/Ti₄O₇, wärmebehandelt nach Synthese des Elektrokatalysators Ir/Ti407;
• 7g: Sekundärelektronenmikroskop-Aufnahme des Elektrokatalysators Ir/Ti₄O₇ (hitzebehandelt);
• 8: Darstellung der OER-Aktivität der Elektrokatalysatoren IrV/Ti₄O₇, Ir/Ti407, Ir-Mohr (von Umicore) + Ti₄O₇, Ir-Mohr (von Umicore), IrO_2/TiO₂ aka Elyst Ir75 (von Umicore);
• 9: Darstellung der ORR- und OER-Aktivität der Elektrokatalysatoren Pt3lr/Ti407, PtIr_3/Ti₄O₇, PtIr/Ti407, Ir-Mohr (von Umicore), Pt-Mohr (von Johnson Matthey);
• 10: Darstellung der OER-Aktivität der Elektrokatalysatoren PtIr₃/ATO, PtIr_3/Ti₄O₇, Ir-Mohr (von Umicore); und
• 11: eine schematische Darstellung der Synthese des Elektrokatalysators PtIr/Ti407.

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

• 1 : a schematic sectional view through an ion exchange membrane water electrolyzer;
• 2 : a schematic sectional view through an ion exchange membrane fuel cell;
• 3 : a schematic sectional view of a membrane electrode unit of an ion exchange membrane water electrolyser;
• 3b : a schematic sectional view of a membrane electrode unit of an ion exchange membrane fuel cell;
• 4th : a schematic representation of an anodic layer of an ion exchange membrane water electrolyzer;
• 5 : a schematic representation of the chemical synthesis of an Ir / Ti407 catalyst;
• 6th : Secondary electron microscope image of Ir-Black from Umicore;
• 7a : Secondary electron microscope picture of the electrocatalyst IrV (with Ir-Mohr);
• 7b : Secondary electron microscope picture of the electrocatalyst Pt / Ti ₄ O ₇ ;
• 7c : Secondary electron microscope picture of the electrocatalyst Pt / Ti ₄ O ₇ ;
• 7d : Secondary electron microscope picture of the electrocatalyst Pt ₃ Ir / Ti ₄ O ₇ ;
• 7e : Secondary electron microscope picture of the electrocatalyst PtIr _{3 /} Ti ₄ O ₇ ;
• 7f : Secondary electron microscope picture of the electrocatalyst IrV / Ti ₄ O ₇ , heat-treated after synthesis of the electrocatalyst Ir / Ti407;
• 7g : Secondary electron microscope picture 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 / Ti407, Ir-Mohr (from Umicore) + Ti ₄ O ₇ , Ir-Mohr (from Umicore), IrO _{2 /} TiO ₂ aka Elyst Ir75 (from Umicore);
• 9 : Representation of the ORR and OER activity of the electrocatalysts Pt3lr / Ti407, PtIr _{3 /} Ti ₄ O ₇ , PtIr / Ti407, Ir-Mohr (from Umicore), Pt-Mohr (from Johnson Matthey);
• 10 : Representation of the OER activity of the electrocatalysts PtIr ₃ / ATO, PtIr _{3 /} Ti ₄ O ₇ , Ir-Mohr (from Umicore); and
• 11 : a schematic representation of the synthesis of the electrocatalyst PtIr / Ti407.

In 1 is a schematic section through an electrochemical reactor in the form of an electrochemical cell 10 namely through a water electrolyzer 12 , which is in the form of a proton exchange membrane water electrolyzer 14th which forms an ion exchange membrane water electrolyzer. It comprises a proton exchange membrane (“PEM”) 16, for example made of perfluorinated sulfuric acid (“PFSA”).

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

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

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

Also in the anodic bipolar plate 42 are to the current collector 40 indicating several channels 46 formed which a flow field 48 the anodic bipolar plate 42 define. The majority of channels 46 defines a water distributor 50 with which water can be supplied for electrolysis.

2 shows schematically another electrochemical cell 60 in the form of a fuel cell 62 , which is designed in the form of a proton exchange membrane fuel cell.

The fuel cell 62 comprises a proton exchange membrane 66 and a catalyst coated membrane 68 .

An anode 70 the electrochemical cell 60 includes an anodic bipolar plate 72 which have a plurality of channels 76 which includes a flow field 74 the anodic bipolar plate 72 define. The majority of channels 76 forms a hydrogen distributor 78 to the fuel cell 62 To supply hydrogen. Between the anodic bipolar plate 72 and an anodic gas diffusion layer 82 is a contact surface 80 educated.

The anodic gas diffusion layer 82 is with an anodic catalyst layer 84 covered by a cathodic catalyst layer 86 through the proton exchange membrane 66 is separated.

The cathodic catalyst layer 86 forms part of a cathode 88 the electrochemical cell 60 , which with a cathodic gas diffusion layer 90 is covered.

The cathodic gas diffusion layer 90 is flat on a cathodic bipolar plate 92 on, with between the cathodic gas diffusion layer 90 and the cathodic bipolar plate 92 a contact surface 94 is defined.

The cathodic bipolar plate 92 has a plurality of channels 96 on facing towards the anodic bipolar plate 72 indicating are open and a flow field 98 define to form an oxygen distributor 100 .

3a FIG. 13 shows an enlarged partial sectional view of the electrochemical cell from FIG 1 , namely the catalyst-coated membrane 18th . The proton exchange membrane 16 the same is on the one hand covered by the anodic catalyst layer 36 and on the other hand through the cathodic catalyst layer 34 .

The peculiarity of the electrochemical cell 10 consists in the structure of the anodic catalyst layer, which is described in more detail below. The anodic catalyst layer serves to improve the oxygen evolution reaction (OER).

3b shows schematically an enlarged partial sectional view of the electrochemical cell 60 out 2 , namely the catalyst-coated membrane 68 . The proton exchange membrane 66 is on the one hand through the cathodic catalyst layer 86 covered and on the other hand by the anodic catalyst layer 84 .

The cathodic catalyst layer 86 serves to improve the oxygen reduction reaction (ORR) and represents the specialty of the electrochemical cell 60 represent.

In 4th is an example of the structure of the anodic catalyst layer 36 on the proton exchange membrane 16 shown schematically.

The catalyst layer comprises a carrier substance 102 , for example in the form of a conductive ceramic carrier 104 , which is in the form of nanoparticles.

On the carrier substance 102 are nanoparticles of a catalyst substance 106 upset. With the catalyst substance 106 it can in particular be a noble metal from the group of platinum, iridium, ruthenium, gold, silver and palladium and / or an alloy, for example IrV.

The carrier 104 can for example be Ti ₄ O ₇ .

At the anodic catalyst layer, the oxygen evolution reaction (OER) is supported in the splitting of H ₂ O.

In 5 the chemical synthesis of the electrocatalyst Ir / Ti ₄ O ₇ is shown schematically, in which Ti ₄ O _{7 forms} the carrier substance and iridium (Ir) the active catalyst substance.

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

Then the support material Ti ₄ O _{7 is} added. For better mixing, the solution can be placed in an ultrasonic bath.

Furthermore, iridium (III) chloride (IrCl ₃ ) is dissolved in anhydrous ethanol and then added to the mixture contained in the three-necked flask. The entire mixture is treated again in the ultrasonic bath for several minutes. Then argon is flown in and the rotation is switched on.

After a few hours, the temperature of the mixture, which took place at room temperature, is cooled with the aid 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 slows the reaction rate, the increased rotation and the slow dropping of NaBH ₄ both guarantee good distribution of the catalytically active substance on the support material and prevent 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 switched 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. The filtrate, ie the resulting Ir / Ti ₄ O ₇ electrocatalyst, is then dried in an oven at 65 ° C.

Optionally, the Ir / Ti ₄ O ₇ electrocatalyst can be treated with a transition metal, such as vanadium. For a vanadium treatment, vanadyl sulfate (VOSO ₄ ) is dissolved in sulfuric acid (H ₂ SO ₄ ) and the cleaned and dried electrocatalyst Ir / Ti ₄ O ₇ is added. The solution is mixed well and the water contained in the mixture is then evaporated. The remainder of the mixture is in the oven at 500 ° C dried under a hydrogen atmosphere. This is how the IrV / Ti ₄ O ₇ electrocatalyst is made.

Alternatively, the electrocatalyst, especially Ir / Ti ₄ O ₇ , can be treated with a transition metal, for example vanadium, also by ball milling, the polyethylene glycol method (polyethylne glycol method) or the Adams fusion method ("Adams fusion method") ) respectively.

Vanadium can be introduced into Ir / Ti ₄ O ₇ by chemical reaction in two ways in particular. On the one hand, vanadium can be added to the lattice or in clusters of iridium nanoparticles using a soluble vanadium precursor ("V precursor") in ethanol and incorporating the dissolved vanadium precursor in an initial step of the synthesis, as above for iridium (III) -Chloride. On the other hand, as described above in connection with the vanadium treatment using vanadyl sulfate, VO _{x can be used} to modify the surface of iridium nanoparticle agglomerates that have already formed.

In the synthesis described, only the environmentally friendly ethanol is used as a solvent. Titanium suboxide (Ti ₄ O ₇ ) is used as the carrier material. In order to additionally reduce the amount of iridium used, the electrocatalyst can optionally be modified by adding vanadium, as described. As a result, the iridium loading of the electrocatalyst can be significantly reduced compared to pure iridium and controlled to a desired value. Taking into account current precious metal prices, the costs for the production of such a supported electrocatalyst are significantly lower compared to pure iridium.

In 6th a secondary electron microscope image of the electrocatalyst Iridium-Black from Umicore is shown.

For comparison shows 7a at about twice the magnification, a secondary electron microscope image shows the electrocatalyst IrV, whereby the iridium used is iridium black. IrV is formed from the Iridium Black configuration by the vanadium treatment described above using vanadyl sulfate.

In 7b is a secondary electron microscope image of an electrocatalyst of the Pt / Ti ₄ O _{7 type} shown with a compared to 7a about fifty times smaller magnification.

7c shows a secondary electron microscope picture of the electrocatalyst Pt / Ti ₄ O ₇ . The magnification corresponds roughly to the magnification of the recording of the 6th .

7d shows an example of a secondary electron microscope image of the electrocatalyst Pt ₃ Ir ₁ / Ti ₄ O ₇ with a magnification that is approximately the magnification of the image of 7a corresponds.

The 7e shows a secondary electron microscope image of the PtIr ₃ / Ti ₄ O ₇ electrocatalyst with a resolution comparable to that in FIG 7d shown recording. An example of a synthesis of this electrocatalyst is given in more detail below.

The 7f shows a secondary electron microscope picture of the electrocatalyst IrV / Ti ₄ O ₇ . This electrocatalyst is produced by heat treating the synthesized Ir / Ti ₄ O ₇ electrocatalyst as described above. The resolution of the representation in 7f corresponds to about half the resolution of the representation of 7e .

7g finally shows a secondary electron microscope picture of the electrocatalyst Ir / Ti ₄ O ₇ as it is obtained by the chemical reaction described above. So it is about the electrocatalyst, which by treatment with vanadium in the in 7f illustrated electrocatalyst IrV / Ti ₄ O ₇ can be converted.

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 of the Umicore company. As the measured dependence of the voltage based on the reversible hydrogen electrode (RHE) on the current shows, the activity of the specified electrocatalysts increases continuously starting from iridium oxide on TiO ₂ to 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 , Pt3lri / Ti407, Pt ₁ Ir ₃ / Ti ₄ O ₇ , Ir-Mohr (UC = Umicore) and Pt-Mohr (JM = Johnson Matthey). Here, too, it can be seen that by mixing platinum and iridium and applying this mixture to Ti ₄ O ₇ , compared to pure iridium, significantly higher current densities are achieved at significantly lower potentials. Even pure platinum is surpassed by at least Pt3lri / Ti407 and Pt ₁ Ir ₃ / Ti ₄ O ₇ .

10 shows an example of the activity of three electrocatalysts in the oxygen evolution reaction (OER activity) in comparison. The measured current densities are shown in Dependence of the voltage related to the hydrogen reference electrode (RHE). Here, too, there is a significantly increased 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 an electrocatalyst according to the invention is shown schematically in FIG 11 shown. It forms the basis for the production of the PtIrV / Ti ₄ O ₇ electrocatalyst. The electrocatalyst PtIr / Ti ₄ O ₇ with a noble metal content of 30 percent by weight is first produced by means of reduction at room temperature using a wet chemical synthesis process. The treatment of this electrocatalyst with vanadium is optionally carried out in a subsequent step.

To synthesize PtIr / Ti ₄ O _7, 1.17 g of cetyltrimethylammonium bromide (CTAB, VWR Chemicals), a cationic surfactant that reduces the interfacial tension between two phases, is dissolved in 120 ml of anhydrous ethanol with a maximum water content of 0.01% and placed in a three-necked flask. The addition of CTAB on the one hand promotes the dispersion of the noble metals on the carrier material and on the other hand it serves to completely reduce the metallic starting materials and the deposition on the carrier material, the so-called nanoparticle formation.

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

Furthermore, argon is flowed to the solution in order to create an inert gas phase.
53 mg of the red-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%, IrCl3 from Alfa Aesar) , a strongly hygroscopic salt, dissolved in 50 ml of anhydrous ethanol and, after thirty minutes, also added to the three-necked flask.

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 , are dissolved in 20 ml of anhydrous ethanol and added quickly to the mixture.

The speed of the magnetic stirrer is increased to 1100 revolutions / min and the solution is mixed for a further four hours at room temperature in order to achieve a complete reduction.

Then the mixture is filtered with the help of a Woulff bottle and two blue band filter papers, which are suitable for very fine precipitates, and washed several times with pure ethanol (99.0%) so that by-products and CTAB are removed.

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

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

As already noted, the individual synthesis steps are in 11 compiled.

Following the synthesis, the PtIr / Ti ₄ O ₇ electrocatalyst 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. The electrocatalyst is then added and the mixture is treated in an ultrasonic bath for a further thirty minutes. After the solution has been mixed well, 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 an 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 area of low to medium temperature electrochemical applications and techniques. These are, in particular, catalyst layers in membrane electrode units as well as catalyst-coated membranes, polymer electrolyte membrane electrolysers (PEM electrolysers), reversible fuel cells (RBZ), polymer electrolyte fuel cells (PEBZ), oxygen electrodes for various electrolysis applications , Satellite drives, 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 symbols

10

electrochemical cell

12

Water electrolyzer

14th

Ion exchange membrane water electrolyzer

16

Ion exchange membrane

18th

Catalyst-coated membrane

20th

cathode

22nd

cathodic bipolar plate

24

Flow field of the cathodic bipolar plate

26th

channel

28

Hydrogen diffuser / anodic gas diffusion layer

30th

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

60

electrochemical cell

62

Fuel cell

64

Ion exchange membrane fuel cell

66

Ion exchange membrane

68

Catalyst-coated membrane

70

anode

72

anodic bipolar plate

74

Flow field of the anodic bipolar plate

76

channel

78

Hydrogen distributor

80

Contact surface

82

anodic gas diffusion layer

84

anodic catalyst layer

86

cathodic catalyst layer

88

cathode

90

cathodic gas diffusion layer

92

cathodic bipolar plate

94

Contact surface

96

channel

98

Flow field

100

Oxygen distributor

102

Carrier substance

104

carrier

106

Catalyst substance

108

Catalyst substance

120

Catalyst-coated membrane unit

122

Membrane electrode assembly

124

Catalyst-coated membrane unit

126

Membrane electrode assembly

Claims (20)

Method for producing an electrocatalyst for an electrode of an electrochemical cell (10; 60), in which an active catalyst substance (106, 108) is deposited or applied to a carrier substance (102) by chemical reaction, the active catalyst substance (106, 108) is or contains at least one noble metal from the group of platinum, iridium, ruthenium, gold, silver and palladium, wherein the active catalyst substance (106, 108) is deposited on or applied to the carrier substance (102) by an anhydrous chemical reaction at room temperature, characterized in that the carrier substance (102) and at least one noble metal salt of the at least one noble metal are dissolved in a first solvent and that the active catalyst substance (106, 108) by reducing the at least one noble metal salt by adding a reducing agent dissolved in a second solvent on the Carrier substance (102) deposited or he is applied to this. Procedure according to Claim 1 , characterized in that, in order to form a supported nanocatalyst, the active catalyst substance (106, 108) is deposited in the form of nanoparticles on the carrier substance (102) or applied to it. Procedure according to Claim 1 or 2 , characterized in that the active catalyst substance (106, 108) is deposited on or applied to the carrier substance (102) by an anhydrous chemical reaction under a protective gas atmosphere. Method according to one of the preceding claims, characterized in that a chlorine salt is used as the at least one noble metal salt. Method according to one of the preceding claims, characterized in that a hydrocarbon-based solvent, in particular anhydrous ethanol, is used as the first and / or second solvent and / or that a surfactant, in particular a surfactant, is used in the first solvent before the carrier substance (102) is dissolved a cationic surfactant, is dissolved. Method according to one of the preceding claims, characterized in that at least one transition metal is also admixed with the active catalyst substance (106, 108). Procedure according to Claim 6 , characterized in that a metal from the 4th subgroup (titanium group) or the 5th subgroup (vanadium group) of the Periodic Table of the Elements is admixed as the at least one transition metal, in particular as the at least one transition metal titanium, zirconium, hafnium, vanadium, Niobium and / or tantalum is added. Method according to one of the preceding claims, characterized in that iridium (Ir), iridium-vanadium (IrV), platinum-iridium (PtIr) or platinum-iridium-vanadium (PtIrV) is produced as the active catalyst substance (106, 108). Method according to one of the preceding claims, characterized in that the carrier substance (102) is used in powder form. Method according to one of the preceding claims, characterized in that a highly conductive and / or corrosion-resistant carrier substance (102) is used. Method according to one of the preceding claims, characterized in that a carrier substance (102) is used which contains a) titanium and / or b) oxygen and / or c) iridium and / or d) antimony and / or e) tin and / or f) is or contains a metal and / or g) silicon and / or h) carbon and / or i) boron and / or j) gold and / or k) an electroceramic, with 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. Electrocatalyst for an electrode (20, 38; 70, 88) of an electrochemical cell (10; 60), wherein a carrier substance (102) and an active catalyst substance (106, 108) deposited by chemical reaction on the carrier substance (102) or applied to it ), wherein the active catalyst substance (106, 108) is or contains at least one noble metal from the group of platinum, iridium, ruthenium, gold, silver and palladium, wherein the active catalyst substance (106, 108) by an anhydrous chemical reaction at room temperature on the Carrier substance (102) is deposited or applied to this, characterized in that the active catalyst substance (106, 108) is reduced by reducing at least one noble metal salt of the at least one noble metal dissolved in a first solvent with the carrier substance (102) by adding one in a second solvent dissolved reducing agent is deposited on the carrier substance (102) or applied to this. Electrocatalyst after Claim 12 , characterized in that it is designed in the form of a supported nanocatalyst, in which the active catalyst substance (106, 108) is deposited in the form of nanoparticles on the carrier substance (102) or applied to it and / or that the active catalyst substance (106, 108) also contains at least one transition metal. Using an electrocatalyst after Claim 12 or 13 for the production of catalyst-coated membranes (16; 66; 120; 124) and membrane-electrode units (16; 66; 122; 126) for electrochemical cells, namely for electrolysers (12), further in particular ion exchange membrane water electrolysers. Catalyst-coated membrane (120; 124) comprising an ion exchange membrane (16; 66) which is coated at least on one side, in particular on both sides, with an electrocatalyst (34, 36; 84, 86), characterized in that the electrocatalyst (34, 36 ; 84, 86) in the form of an electrocatalyst Claim 12 or 13 is trained. Membrane-electrode unit (122; 126) comprising an ion exchange membrane (16; 66) which is coated at least on one side, in particular on both sides, with an electrocatalyst (34, 36; 84, 86), characterized in that the electrocatalyst (34, 36; 84, 86) in the form of an electrocatalyst Claim 12 or 13 is trained. Electrode (20; 38; 70; 88) for an electrochemical cell, which electrode (20; 38; 70; 88) comprises at least one catalyst layer (34, 36; 84, 86), characterized in that the at least one catalyst layer (34 , 36; 84, 86) after an electrocatalyst Claim 12 or 13 includes or by an electrocatalyst Claim 12 or 13 is formed. Electrode after Claim 17 , characterized in that the at least one catalyst layer (34, 36; 84, 86) is in the form of an anodic or cathodic catalyst layer (34, 36; 84, 86). Electrode after Claim 17 or 18th , characterized in that the at least one catalyst layer (34, 36; 84, 86) is applied to a gas diffusion layer (32; 40; 82; 90). Electrochemical reactor, in particular in the form of an electrochemical cell (10), comprising at least two electrodes (20; 38; 70; 88), characterized in that at least one of the two electrodes (20; 38; 70; 88) in the form of an electrode ( 20; 38; 70; 88) according to one of the Claims 17 to 19th is designed, the electrochemical reactor in particular in the form of a) an ion exchange membrane water electrolyzer (14) or b) a redox flow battery or c) an electrochemical reactor for carbon dioxide and nitrogen reduction or d) an electrochemical reactor for the oxidation and / or reduction of Lignin or e) an electrochemical reactor for hydrogenation of gases or liquids or f) an electrochemical cell for electrochemical water treatment or g) a lithium-air battery or h) a metal-air battery or i) a metal layer deposition electrolyzer.

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