Method for the post-treatment of a platinum alloy catalyst material

Abstract

The invention relates to a method for the post-treatment of a platinum alloy catalyst material (6), having the steps of dissolving (100) the platinum alloy catalyst material (6) in a solvent (4), stirring (200) the dissolved platinum alloy catalyst material (6) within a reaction vessel (2), and supplying (300) a first gas (G1) and a second gas (G2) to the platinum alloy catalyst material (6) in the reaction vessel (2), the first and second gas (G1, G2) being alternately added to the dissolved platinum alloy catalyst material (6), and a platinum-containing salt being added.

Description

[0001] Description

[0002] Method for the post-treatment of platinum alloy catalyst material

[0003] The present invention is based on a method according to the preamble of the independent method claim and on a system according to the preamble of the independent system claim.

[0004] State of the art

[0005] Fuel cells are electrochemical energy converters that directly convert the chemical energy stored in a fuel (e.g., hydrogen, methanol) into electrical energy. When hydrogen is used as the energy source, the only byproduct of the conversion is water, which is why fuel cells operated in this way are used for emission-free propulsion in motor vehicles as well as for stationary power generation.

[0006] A widely used design is the polymer electrolyte membrane fuel cell (PEMFC). The PEMFC essentially consists of a membrane electrode assembly (MEA) in which a negative electrode, the anode, and a positive electrode, the cathode, are separated by a polymer electrolyte membrane. In conjunction with bipolar plates for gas supply, cooling, and electrical conductivity, several membrane electrode assemblies can be connected in series to achieve the (high) voltages required for the respective end application.

[0007] The electrodes of a MEA typically consist of a highly porous, carbon-based substrate. Nanometer-sized platinum or platinum alloy particles are deposited on this substrate; these particles, as electrochemically active species, significantly determine the cell's performance. Increased performance can be achieved either by using higher amounts of platinum or by developing more active catalyst materials. The latter allows for a reduction in the total amount of platinum required, which represents a significant cost component of the PEMFC system, as well as enabling the PEMFC system to operate at higher cell voltages, resulting in a higher efficiency in utilizing the hydrogen energy carrier.

[0008] Such more active catalyst materials are, for example, in the form of platinum alloys with the general formula Pt. xM is known, where M corresponds to another transition metal (M = Co, Ni, Fe, Cu, ...). The presence of transition metal atoms in the metallic nanoparticles results in increased catalytic activity for the oxygen reduction reaction due to electronic effects. This enables PEMFC operation at higher cell voltages and thus increases efficiency.

[0009] Unfortunately, catalyst materials are exposed to an electrochemically aggressive local environment, which includes elevated temperatures (80–120°C), voltages and voltage cycles (0–1.0 V), and, most importantly, strongly acidic conditions (pH = 0). The typically reactive transition metals of the alloy (M = Co, Ni, Fe, Cu, ...) are unstable under these conditions with respect to proton oxidation.

[0010] In real-world continuous operation, this leads to a steady dissolution of this transition metal, which remains in cationic form within the PEMFC. This has two particularly serious consequences for the performance of the PEMFC.

[0011] First, the loss of transition metal atoms from the crystal lattice of the platinum alloy leads to a decrease in the desired geometric stress and electronic effects, which is accompanied by a progressive loss of catalytic activity for the oxygen reduction reaction. In the limiting case, this activity is reduced to that of a pure platinum catalyst.

[0012] Secondly, the dissolved transition metal cations bind to the polymer electrolyte, which ensures the proton conductivity essential for cell operation. This is located primarily in the polymer electrolyte membrane, but also as an ionomer binder in the anode and cathode. Due to the generally higher valence of the transition metal cations (Co2+ , Ni 2+ The higher binding affinity of the dissolved transition metal cations (vs. IT) displaces protons from the polymer electrolyte, thus impairing proton conductivity. At high concentrations of dissolved transition metal cations, this leads to a substantially reduced performance, especially at high current densities.

[0013] Prior art provides methods for treating platinum alloy catalysts which, by targeted removal of transition metal atoms from near-surface regions, promote a catalyst structure in which transition metal-depleted surface regions around a Pt x M-alloy core are arranged so that the susceptibility of the transition metal atoms from the crystal lattice to oxidation can be reduced.

[0014] Although the described catalyst structures exhibit a lower tendency for the loss of transition metal atoms from the platinum alloy crystal lattice, the aggressive conditions in fuel cells can still lead to a continuous loss of transition metal atoms from the platinum alloy catalysts. In particular, the electrochemically induced restructurings occurring during fuel cell operation (e.g., through voltage cycling) can also reach the deeper-lying transition metal atoms, so that a complete elimination of the associated contamination effects is not yet possible.

[0015] Disclosure of the invention

[0016] The invention relates, according to a first aspect, to a method with the features of the independent method claim, and according to a second aspect, to a system with the features of the independent system claim. Further features and details of the invention become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the system according to the invention, and vice versa, so that the disclosure relating to the individual aspects of the invention always includes, or allows for, reciprocal reference.

[0017] The advantage of the inventive method for the post-treatment of platinum alloy catalyst material lies particularly in the fact that a stable segregated core-shell structure of a platinum alloy catalyst material can be generated in a particularly simple and cost-effective manner, which can reliably counteract the loss of transition metal atoms from the crystal lattice of the platinum alloy. In particular, the formation of a Pt-rich outer shell can be accelerated or enhanced. This ultimately leads to a significant increase in the performance and stability of the platinum alloy catalyst material, which in turn greatly improves the efficiency and longevity of fuel cell systems.

[0018] The inventive method for the post-treatment of platinum alloy catalyst material comprises the steps of dissolving the platinum alloy catalyst material in a solvent, stirring the dissolved platinum alloy catalyst material within a reaction vessel, and supplying a first gas and a second gas to the dissolved platinum alloy catalyst material in the reaction vessel, wherein the first and second gases are supplied to the dissolved platinum alloy catalyst material alternately, and wherein a platinum-containing salt is added during the execution of the method.

[0019] In the context of the invention, a post-treatment can be understood to mean, in particular, a treatment that takes place after the synthesis of the platinum alloy catalyst material, preferably immediately after synthesis. The platinum alloy catalyst material in question can preferably be in the form of a platinum alloy with the general formula Pt xM is formed where M corresponds to another transition metal (M = Co, Ni, Fe, Cu, ...). The transition metal cations can therefore preferably be the cations of the other transition metal (M = Co, Ni, Fe, Cu, ...). The platinum alloy catalyst material can preferably be platinum in nanoparticle form, e.g., with a mean diameter of < 10 nm, in particular a mean diameter of 5 nm. It is understood that dissolving can also include dispersion, suspension, or the like. Alternating feeding can, in particular, be understood as a feeding process in which a first gas and a second gas are fed alternately. A platinum-containing salt can, in particular, be understood as a chemical compound consisting of platinum (Pt) as the central metal atom and various anionic components.These salts can be formed by the reaction of platinum with acids or other reagents, leading to stable ionic compounds. Such salts can contain platinum in various oxidation states, preferably +2 or +4.

[0020] Within the scope of the invention, it has been recognized that the alternating gas atmosphere changes provided here can induce chemical stress cycles that mimic the stress cycles occurring during fuel cell operation. This can then lead, in particular, to a more thorough dissolution of transition metals (other than platinum) from the catalyst particles. Thus, more transition metal can be removed from a platinum alloy catalyst, which would otherwise only be released during fuel cell operation. In particular, the formation of a platinum-rich outer shell can be accelerated or enhanced. The contamination effects occurring in the fuel cell can therefore be reduced, which increases the performance and longevity of the fuel cell system.

[0021] To reduce the amount of transition metal that can be released, the invention advantageously provides that the solvent is an acid, preferably nitric acid and / or sulfuric acid and / or hydrochloric acid and / or acetic acid and / or formic acid. Advantageously, the platinum alloy catalyst can be introduced into the acidic solution in powder form and stirred in the reaction vessel for several hours. The reaction vessel can preferably be in the form of a flask. The head volume of the flask above the acidic solution can be filled with air, hydrogen, or an inert gas (nitrogen, argon). For targeted and effective dissolution of the platinum alloy catalyst material in the solvent, it is further advantageous that the process is carried out at a temperature between 5 °C and 150 °C, preferably between 25 °C and 80 °C.

[0022] In the context of a targeted and controllable supply of a first and second gas into a reaction vessel, it can advantageously be provided that the first and the second gas are introduced into the reaction vessel via a controllable supply unit, wherein the controllable supply unit preferably has a glass frit and a first and second metering valve.

[0023] In order to effectively remove transition metal atoms from deeper layers of the catalyst material, it can advantageously be provided that the first gas and the second gas differ with respect to their standard reduction potentials, wherein the first gas and the second gas preferably differ by at least 0.5 V, in particular by at least 1 V.

[0024] With a view to the most effective possible removal of transition metal atoms (other than Pt) from deeper layers of the platinum alloy catalyst material, the invention advantageously provides that the first gas contains oxygen, preferably oxygen as its largest component, and / or the second gas contains hydrogen, preferably hydrogen as its largest component. Preferably, the first gas may contain 0.01 to 100 vol% oxygen, with the remainder of the gas being nitrogen or argon, and / or the second gas may contain 1 to 100 vol% hydrogen, with the remainder of the gas being nitrogen or argon.

[0025] Within the framework of a controlled supply of a first and second gas to a reaction vessel, it can advantageously be provided that the cycle duration in which the first gas and / or the second gas is introduced is from 5 seconds to 24 hours, preferably from 30 seconds to 30 minutes. The transition metal content of a platinum alloy catalyst can be precisely controlled via the duration and number of gas or voltage cycles. A greater number of gas or voltage cycles leads to a higher release of the transition metal.

[0026] With a view to further minimizing the probability of transition metal atoms escaping from a platinum alloy catalyst material during fuel cell operation, it can also be advantageous to implement targeted temperature control of the platinum alloy catalyst material to stimulate a reorganization of its lattice structure. This targeted temperature control can be carried out at a defined

[0027] temperature and / or within a defined temperature range.

[0028] With a view to a simple and quick implementation of the process in question, it can advantageously also be provided according to the invention that the platinum-containing salt is added once, preferably before the introduction of the first gas and the second gas into the reaction vessel.

[0029] Alternatively, with a view to a simple and quick implementation of the process in question, it can also be provided that the platinum-containing salt is added once, preferably during the introduction of the first or second gas into the reaction vessel, in particular during the introduction of the first gas.

[0030] In this context, it can be particularly advantageous to accelerate or enhance the formation of a Pt-rich outer shell if the platinum-containing salt is added during one of the last 1 to 10 gas supply cycles of the first and second gases, preferably during one of the last 1 to 3 gas supply cycles, and especially during the last gas supply cycle of the first and second gases. A gas supply cycle can be defined in particular as the single

[0031] The introduction process of a first and second gas is understood to mean the time period between the start of the introduction of the first gas and the subsequent completion of the introduction of the second gas. The platinum-containing salt is preferably added during the introduction of the first gas or between the introduction of the first gas and the introduction of the second gas, particularly preferably immediately before the introduction of the second gas begins.

[0032] Advantageously, with regard to the introduction of gases, it is also conceivable that pauses are deliberately planned between the gas introductions. Stirring can preferably continue during such a pause. The platinum-containing salt can then advantageously be added during a pause between the addition of a first gas and a second gas. The addition of the platinum salt can then, for example, take place either during the introduction of the first gas (air / oxygen) or during the pause before the introduction of the second gas. It is understood that, alternatively or cumulatively, the platinum salt can also be added during a pause between the introduction of the second and the first gas.

[0033] As an alternative to a single addition of the platinum-containing salt, it can also be provided that the platinum-containing salt is added several times, preferably during the introduction of the first and / or second gas into the reaction vessel, in particular during the introduction of the first gas.

[0034] To further increase the acceleration or enhancement of the formation of a Pt-rich outer shell, it is also conceivable that the dose in which the platinum-containing salt is added is increased continuously or stepwise.

[0035] For the effective formation of a Pt-rich outer shell, it can also be advantageous if the platinum-containing salt is a divalent or tetravalent platinum compound, preferably PtCb, PtCNOsh, PtCk, or a mixture thereof. It is understood that other Pt compounds can also be used, such as chloroplatinic acid (H₂PtCl₆), potassium tetrachloroplatinate (K₂PtCl₄), or sodium hexachloroplatinate (Na₂PtCl₆).

[0036] The invention also relates to a system for the post-treatment of platinum alloy catalyst material, in particular for carrying out a process described above.The system according to the invention comprises a reaction vessel for receiving the platinum alloy catalyst material and the solvent for dissolving the platinum alloy catalyst material, a stirrer for stirring the dissolved platinum alloy catalyst material within the reaction vessel, and a controllable feed unit for supplying a first gas and a second gas to the dissolved platinum alloy catalyst material in the reaction vessel, wherein the first and the second gas can be supplied to the dissolved platinum alloy catalyst material alternately via the controllable feed unit, and wherein a further controllable feed unit is provided for supplying a platinum-containing salt. Thus, the system according to the invention has the same advantages as those already described in detail with regard to the process according to the invention.

[0037] In the context of a controlled supply of a first and second gas into a reaction vessel, it is advantageously provided that the controllable supply unit comprises a glass frit and a first and second metering valve. The metering valves can preferably be controlled via a microcontroller and a first and second relay. Furthermore, the system can include a flow controller for regulating the inflow to the reaction vessel.

[0038] Advantages described in detail in relation to the method for the post-treatment of platinum alloy catalyst material according to the first aspect of the invention apply equally to the system for the post-treatment of platinum alloy catalyst material and vice versa.

[0039] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can be essential to the invention individually or in any combination.

[0040] Figure 1 schematically shows a representation of the individual steps of a process according to the invention for the post-treatment of platinum alloy catalyst material.

[0041] Figure 2 shows a representation of a system according to the invention for the post-treatment of platinum alloy catalyst material,

[0042] Figure 3 shows a plot of the chemical potential against time during the alternating supply of a first and second gas.

[0043] Figure 4 shows a plot of normalized transition metal release for a post-treated compound according to the invention.

[0044] Platinum alloy catalyst material and an untreated platinum alloy catalyst material

[0045] (left) as well as a plot of the current-voltage characteristics for a fuel cell with a post-treated unit according to the invention.

[0046] Platinum alloy catalyst material and for a fuel cell with an untreated

[0047] Platinum alloy catalyst material (right),

[0048] Figure 5 shows the change of a particle of a platinum alloy catalyst material as a result of carrying out a known method for the post-treatment of platinum alloy catalyst material (top) and a method according to the invention for the post-treatment of platinum alloy catalyst material (bottom), and

[0049] Figure 6 shows a representation of the process flow of a method according to the invention for the post-treatment of platinum alloy catalyst material.

[0050] Fig. 1 shows a schematic representation of the individual steps of a process according to the invention for the post-treatment of platinum alloy catalyst material 6. The process according to the invention comprises the steps of dissolving 100 the platinum alloy catalyst material 6 in a solvent 4, stirring 200 the dissolved platinum alloy catalyst material 6 within a reaction vessel 2, and supplying 300 a first gas G1 and a second gas G2 to the dissolved platinum alloy catalyst material 6 in the reaction vessel 2, wherein the first and second gas G1, G2 are supplied alternately to the dissolved platinum alloy catalyst material 6, and wherein a platinum-containing salt is added.

[0051] The solvent may advantageously be an acid, preferably nitric acid and / or sulfuric acid and / or hydrochloric acid and / or acetic acid and / or formic acid.

[0052] Furthermore, the process can be carried out at a temperature between 5 °C and 150 °C, preferably between 25 °C and 80 °C.

[0053] The first and second gas G1, G2 can be introduced into the reaction vessel 2 via a controllable feed unit 8, which preferably has a glass frit 8a and a first and second metering valve 10a, 10b.

[0054] The first gas G1 and the second gas G2 differ in their standard reduction potentials, preferably by at least 0.5 V, and in particular by at least 1 V.

[0055] The first gas G1 can contain oxygen as the largest component by quantity, and the second gas hydrogen.

[0056] The cycle duration during which the first gas G1 and / or the second gas G2 is introduced can range from 5 seconds to 24 hours, preferably from 30 seconds to 30 minutes. The platinum-containing salt can be added once, preferably before the introduction of the first gas G1 and the second gas G2 into the reaction vessel 2.

[0057] Alternatively, the platinum-containing salt can be added once during the introduction of 300 of the first or second gas G1, G2 into the reaction vessel 2, in particular during the introduction of 300 of the first gas G2.

[0058] The platinum-containing salt can be added during one of the last 1 to 10 gas supply cycles of the first and second gas G1, G2, preferably during one of the last 1 to 3 gas supply cycles, particularly during the last gas supply cycle.

[0059] Alternatively, it can also be provided that the platinum-containing salt is added several times, preferably during the supply of 300 of the first and / or second gas G1 , G2 into the reaction vessel 2, in particular during the supply of 300 of the first gas G2.

[0060] It may also be provided that the dose in which the platinum-containing salt is added is increased continuously or gradually.

[0061] The platinum-containing salt can advantageously be a divalent or tetravalent platinum compound, preferably PtCb, PtCNOsh, PtCL or a mixture thereof.

[0062] Fig. 2 shows a schematic representation of a system 1 according to the invention for the post-treatment of platinum alloy catalyst material 6.

[0063] The system 1 according to the invention comprises a reaction vessel 2 for receiving the platinum alloy catalyst material 6 and the solvent 4 for dissolving the platinum alloy catalyst material 6, a stirrer 16 for stirring 200 of the dissolved platinum alloy catalyst material 6 within the reaction vessel 2, and a controllable feed unit 8 for supplying 300 of a first gas G1 and a second gas G2 into the reaction vessel 2 to the dissolved platinum alloy catalyst material 6, wherein the first and the second gas G1, G2 can be supplied alternately to the dissolved platinum alloy catalyst material 6 via the controllable feed unit 8, and a further controllable feed unit 8' is provided for supplying a platinum-containing salt.

[0064] The adjustable feed unit 8 includes a glass frit 8a (not shown) and a first and second metering valve 10a, 10b, which are controlled by a microcontroller 14 and a first and second relay R1, R2. Furthermore, the system 1 includes a flow controller 12 for regulating the flow of gases G1, G2 to the reaction vessel 2.

[0065] Fig. 3 shows a plot of the chemical potential Pot. against time t during the alternating supply of a first and second gas G1 and G2 in the form of oxygen - O2 and hydrogen - H2. The alternating gas atmosphere changes can induce chemical stress cycles that can replicate the stress cycles occurring in fuel cell operation, leading in particular to a deeper dissolution of transition metals from the catalyst particles.

[0066] Fig. 4 shows a plot of a normalized transition metal release for a platinum alloy catalyst material 6 treated according to the invention and an untreated platinum alloy catalyst material 6R. S f (left) as well as a plot of the current-voltage characteristics for a fuel cell with a platinum alloy catalyst material 6 treated according to the invention and for a fuel cell with an untreated platinum alloy catalyst material 6R e f (right).

[0067] As can be seen in Fig. 4, the transition metal release for a platinum alloy catalyst material 6 treated according to the invention is significantly greater than for the untreated platinum alloy catalyst material 6R. e f.

[0068] The plot of the current-voltage characteristic curves shows the performance of the catalyst materials 6 treated according to the invention. The higher the cell potential at a defined current density, the more efficient the cell. As can be seen from the current-voltage characteristic curves in Fig. 4 (right), the achieved cell voltage is in the range of low current densities (< 500 mA / cm²). 2 ) for the catalyst 6 treated according to the invention slightly lower than for the reference platinum alloy catalyst 6R e f. This reflects the lower transition metal content of the treated catalyst compared to the starting material, resulting in a slightly reduced catalytic activity for the oxygen reduction reaction. In the range of higher current densities (> 1000 mA / cm²) 2Effects of transition metal contamination (e.g., proton conductivity limitation) become apparent, particularly at low relative humidity. Here, the material 6 treated according to the invention achieves significantly higher cell voltage and thus a higher conversion efficiency of the hydrogen used. The lower transition metal content of the catalyst material 6 treated according to the invention results in lower transition metal release under the operating conditions of the fuel cell, which ultimately leads to reduced contamination effects. The catalyst treated according to the invention is therefore clearly more efficient.

[0069] Fig. 5 shows a schematic representation of the change of a particle of a platinum alloy catalyst material 6 as a result of carrying out a known method for the post-treatment of platinum alloy catalyst material 6 (above) and a method according to the invention for the post-treatment of platinum alloy catalyst material 6 (below).

[0070] As can be seen in Fig. 5, by applying the inventive method for the post-treatment of platinum alloy catalyst material 6 (below) a higher PG content of Pt can be achieved thanks to the additional addition of a (here divalent) platinum-containing salt. 2+ - ions around the platinum alloy catalyst material 6 are obtained, such that after the oxidation of Pt atoms and metal atoms from the platinum alloy catalyst material 6 (left side) in the reduction step (right side) Pt 2+-ions (reduced to Pt atoms) attach to the outer surfaces of the platinum alloy catalyst material 6 and thus a significantly thicker shell 6b of Pt atoms can be formed around the core 6a of the platinum alloy catalyst material 6 than in the known method for the post-treatment of platinum alloy catalyst material 6.

[0071] Fig. 6 shows a schematic representation of the process flow of a method according to the invention for the post-treatment of

[0072] Platinum alloy catalyst material 6.

[0073] As can be seen in Fig. 6, a platinum-containing salt can be added once to a dissolved platinum alloy catalyst material 6 (Ex. a) or several times during an oxidation step (with the addition of

[0074] Oxygen - e.g. b) and / or during a reduction step (with the addition of hydrogen - e.g. c).

[0075] Advantageously, a platinum-containing salt can also be added during a pause between an oxidation step and a reduction step, i.e., between b and c in Fig. 6.

Claims

Claims 1. Method for the post-treatment of platinum alloy catalyst material (6), comprising the steps: - Dissolving (100) the platinum alloy catalyst material (6) in a solvent (4), - Stirring (200) of the dissolved platinum alloy catalyst material (6) within a reaction vessel (2), - Supplying (300) a first gas (G1) and a second gas (G2) into the reaction vessel (2) to the dissolved platinum alloy catalyst material (6), wherein the first and the second gas (G1 , G2) are supplied alternately to the dissolved platinum alloy catalyst material (6), characterized in that a platinum-containing salt is added.

2. Method according to claim 1, characterized in that the solvent is an acid, wherein the acid preferably comprises nitric acid and / or sulfuric acid and / or hydrochloric acid and / or acetic acid and / or formic acid.

3. Method according to claim 1 or 2, characterized in that the method is carried out at a temperature between 5 °C and 150 °C, preferably between 25 °C and 80 °C.

4. Method according to one of the preceding claims, characterized in that the first and the second gas (G1 , G2) are introduced into the reaction vessel (2) via a controllable feed unit (8), wherein the controllable feed unit (8) preferably comprises a glass frit (8a) and a first and second metering valve (10a, 10b).

5. Method according to one of the preceding claims, characterized in that the first gas (G1) and the second gas (G2) differ with respect to their standard reduction potentials, wherein the first gas (G1) and the second gas (G2) preferably differ by at least 0.5 V, in particular by at least 1 V, with respect to their standard reduction potentials.

6. Method according to one of the preceding claims, characterized in that the first gas (G1) comprises oxygen, preferably comprising oxygen as its largest component, and / or the second gas (G2) comprises hydrogen, preferably comprising hydrogen as its largest component.

7. Method according to one of the preceding claims, characterized in that the cycle duration in which the first gas (G1) and / or the second gas (G2) is introduced is 5 seconds to 24 hours, preferably 30 seconds to 30 minutes.

8. Method according to one of the preceding claims, characterized in that targeted temperature control of the platinum alloy catalyst material (6) is provided to stimulate a reorganization of a lattice structure of the platinum alloy catalyst material (6).

9. Method according to one of the preceding claims, characterized in that the platinum-containing salt is added once, preferably before the introduction (300) of the first gas (G1) and the second gas (G2) into the reaction vessel (2).

10. Method according to one of the preceding claims, characterized in that the platinum-containing salt is added once, preferably during the supply (300) of the first or second gas (G1 , G2) to the reaction vessel (2), in particular during the supply (300) of the first gas (G2).

11. Method according to claim 10, characterized in that the platinum-containing salt is added during one of the last 1 to 10 gas supply cycles of the first and second gas (G1 , G2), preferably during one of the last 1 to 3 gas supply cycles, in particular during the last gas supply cycle.

12. Method according to one of the preceding claims, characterized in that the platinum-containing salt is added during a pause between the addition of a first gas (G1) and a second gas (G2).

13. Method according to one of the preceding claims, characterized in that the platinum-containing salt is added several times, preferably during the supply (300) of the first and / or second gas (G1 , G2) to the reaction vessel (2), in particular during the supply (300) of the first gas (G2).

14. Method according to claim 13, characterized in that the dose in which the platinum-containing salt is added is increased continuously or stepwise.

15. Method according to one of the preceding claims, characterized in that that the platinum-containing salt is a divalent or tetravalent platinum compound, preferably PtCb, Pt(NOs)2, PtCk or a mixture thereof.

16. System (1) for the post-treatment of platinum alloy catalyst material (6), in particular for carrying out a process according to one of claims 1 to 15, comprising: - a reaction vessel (2) for receiving the platinum alloy catalyst material (6) and the solvent (4) for dissolving the platinum alloy catalyst material (6), - a stirrer (16) for stirring (200) the dissolved platinum alloy catalyst material (6) within the reaction vessel (2), - a controllable feed unit (8) for supplying (300) a first gas (G1) and a second gas (G2) into the reaction vessel (2) to the dissolved platinum alloy catalyst material (6), wherein the first and the second gas (G1 , G2) can be supplied alternately to the dissolved platinum alloy catalyst material (6) via the controllable feed unit (8), characterized in that a further controllable feed unit (8') is provided for supplying a platinum-containing salt.

17. System (1) according to claim 16, characterized in that the adjustable feed unit (8) has a glass frit (8a) and a first and second metering valve (10a, 10b).

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