DE102017128058A1 - Electrochemical electrode with multinary metal alloy as reduction catalyst - Google Patents

Abstract

The present invention relates to an electrode for an electrochemical device comprising a catalytically active alloy catalyst for catalyzing the reduction of a reducible compound. The invention further relates to an electrochemical device comprising an anode, an electrode according to the invention as a cathode and an electrolyte arranged between the anode and cathode, a method for operating an electrochemical device according to the invention and the use of a multinary alloy as a reduction catalyst. The catalytically active alloy comprises at least four Metals and one of these at least four metals is manganese. None of these at least four metals is present in an amount of ≤5 atomic% and ≥70 atomic% in the alloy, and the content of palladium or platinum in the alloy is ≤10 atomic%.

Description

The present invention relates to an electrode for an electrochemical device comprising a catalyst for catalyzing the reduction of a reducible compound. The invention further relates to an electrochemical device comprising an anode, an electrode according to the invention as a cathode and an electrolyte arranged between the anode and cathode, a method for operating an electrochemical device according to the invention and the use of a multinary alloy as a reduction catalyst.

Fuel cells can generate electrical energy from hydrogen and oxygen. If the energy for the upstream electrolysis of water in hydrogen and oxygen comes from renewable sources, so can build a climate-friendly energy concept.

However, energy losses are associated with the complex four-electron reactions occurring in the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). To minimize these losses catalysts can be used. Here platinum and platinum alloys have been the most widely explored as catalytically active metals. Platinum and palladium alloys are currently the most active and thus most effective catalyst and are therefore used in the industry as state of the art for the ORR. A disadvantage of their use are the high costs associated with such precious metals.

Multinary metal alloys, as one of their features, may have a single-phase structure over several intermetallic phases. Studies are known for the catalysis of multinary, noble metal-containing alloys such as FeCoNiCuAgPt or CuRuOsIrPt in the oxidation of methanol. Regarding the ORR, the publication of J. Li, HS Stein, K. Sliozberg, J. Liu, Y. Liu, G. Sertic, E. Scanley, A. Ludwig, J. Schroers, W. Schuhmann et al., J. Mater. Chem. A 2017, 5, 67 the evaluation of quaternary TiPdAgAu alloys. However, these multinary alloys contain all the precious metals.

CN 106756407 A discloses a CrMnFeCoNiZr "high entropy" alloy and a manufacturing method therefor. The "high entropy" alloy is composed of chromium, manganese, iron, cobalt, nickel and zirconium, and the components are composed of the molar ratio Cr _a Mn _b Fe _c Co _d Ni _e Zr _f where a, b, c, d and e are in the range of 0.7-1.2 and f are in the range of 0.1-2.2.

CN 106374116 relates to a high entropy alloy composite coating on a metal bipolar plate of a fuel cell and a production process of the high entropy alloy composite coating. The highly entropic alloy composite coating is fabricated on the surface of the metallic bipolar plate using a closed-field unsymmetrical magnetron sputtering technique. The composite coating on the surface of a substrate of the metal bipolar plate consists of a high entropy alloy layer, a multi-component alloy carbon transition layer, and an amorphous carbon layer located on the outermost surface.

The publication of G. Laplanche, A. Kostka, OM Horst, G. Eggeler, EP George, Acta Materialia 2016, 118, 152-163 "Microstructure evolution and critical stress for twinning in the CrMnFeCoNi high-entropy alloy" examines the mechanical properties of a CrMnFeCoNi high-performance alloy.

WO 2017/132725 A1 discloses an alloy having a platinum solid solution matrix: 20 to 70 at.%, palladium> 0 to 70 at.%, cobalt:> 0 to 50 at.% and at least one of: nickel to 50 at.%, chromium to 50 at.% and iron up to 50 at.%.

The object of the present invention has been to at least partially overcome the disadvantages of the prior art. In particular, it has the object to provide an electrode for an electrochemical device comprising a catalyst for catalyzing the reduction of a reducible compound which has a reduced content of palladium and platinum with comparable activity.

This object is achieved by an electrode according to claim 1, an electrochemical device according to claim 9, a method of operating an electrochemical device according to claim 11 and a use according to claim 13. Advantageous developments are specified in the subclaims. They can be combined as desired, provided the context does not clearly result in the opposite.

According to the invention, an electrode for an electrochemical device comprising a catalyst for catalyzing the reduction of a reducible compound, wherein the catalyst comprises an alloy of at least four metals, one of these at least four metals is manganese, none of these at least four metals in a proportion of ≤ 5 atomic% and ≥70 atomic% in the alloy, and the content of palladium or platinum in the alloy is ≤10 atomic%.

It has been found that electrodes according to the invention can be used with such catalysts with reduced contents of palladium or platinum instead of pure or predominantly palladium- or platinum-based electrodes with comparable activity.

The reducible compound is preferably a gas and may be oxygen in particular. Then, the catalyst catalyzes the oxygen reduction reaction (ORR) that may occur in electrochemical devices.

Without being bound by theory, it is believed that the at least quaternary alloy in the catalyst is at least partially present as a so-called high entropy alloy (HEA). Then there is a solid solution of the individual alloy components together.

The electrode according to the invention can be constructed from the catalyst with the alloy. However, it is preferred that the electrode is in the form of a catalyst-coated substrate. A suitable substrate is graphite, for example. The surface of the substrate is preferably covered with the catalyst to ≥90%, more preferably ≥95%, and particularly preferably ≥99%.

The catalyst may contain other constituents in addition to the alloy. However, it is preferred that apart from the alloy there are no further constituents in the catalyst, in particular no separate noble metal such as, for example, palladium or platinum. Exceptions to this are non-alloyed phases of the metals which form the alloy.

According to the invention, it is provided that the alloy is an alloy of at least four metals. There may also be five, six, seven or even more metals in the alloy. It is further contemplated that one of the alloying metals is manganese. Preferably, chromium, cobalt, manganese and nickel and optionally iron are present in the alloy.

In the alloy, none of the at least four metals is present in an amount of ≤5 at% and ≥70 at% in the alloy. It is preferable that none of these at least four metals be present in an amount of ≤10 at% and ≥60 at% in the alloy, more preferably none of these at least four metals in a proportion of ≤15 at% and ≥35 Atomic% in the alloy. The sum of the atomic% statement always amounts to ≤ 100 atomic%.

For example, the alloy may contain chromium, iron, cobalt and nickel as alloying ingredients. Another example is an alloy with chromium, manganese, cobalt and nickel. Preferred is an alloy with chromium, manganese, iron, cobalt and nickel.

Finally, in the alloy, the proportion of palladium or platinum is ≦ 10 atom%. This is to be understood as meaning the sum of the atomic percentages of palladium, platinum or mixtures thereof. In this way, the cost of precious metal content is reduced. The proportion of palladium or platinum is preferably ≦ 5 atom%, more preferably ≦ 1 atom%. It is very particularly preferred if the alloy (apart from technically unavoidable impurities) contains no palladium and no platinum. If the alloy contains palladium and platinum, the above upper limits apply mutatis mutandis to the sum of the atomic percentages of palladium and platinum.

1. 1) Der Katalysator liegt in Form von Nanopartikeln vor, von denen über 50 % einen Durchmesser von ≤ 25 nm aufweisen;
2. 2) Elektrolyt: 0.1 M KOH (unter Luft/keine Sauerstoffsättigung);
3. 3) Spannungsvorschubgeschwindigkeit: 10 mV/s;
4. 4) Subtraktion des an blanker Elektrode gemessenen Stroms vom Strom mit immobilisierten Katalysatornanopartikeln auf entsprechender Elektrode;
5. 5) Es werden im zeitlichen Verlauf stabile Stromkurven betrachtet;
6. 6) Normierung des Differenzstroms durch einen der Sauerstoffreduktion zuzuordnenden Plateaustromwert (Diffusionsgrenzstrom i_ss) mit i_ss = 1.

In one embodiment of the electrode, at a current of -0.5 on the normalized scale, the catalyst has an overvoltage for the oxygen reduction reaction of ≦ 800 mV (preferably ≦ 700 mV, more preferably ≦ 600 mV). This current on the normalized scale is measured under the following conditions:

1. 1) The catalyst is in the form of nanoparticles, of which more than 50% have a diameter of ≤ 25 nm;
2. 2) Electrolyte: 0.1 M KOH (under air / no oxygen saturation);
3. 3) voltage feed rate: 10 mV / s;
4. 4) subtracting the current measured on the bare electrode from the current with immobilized catalyst nanoparticles on a corresponding electrode;
5. 5) stable current curves are considered over time;
6. 6) Normalization of the differential current by a plateau _{flux value} to be assigned to the oxygen reduction (diffusion limiting current i _ss ) with i _ss = 1.

An overvoltage of 800 mV for the oxygen reduction reaction corresponds to 429 mV against RHE (reversible hydrogen electrode). Therefore, it can also be expressed that the catalyst under the above measurement conditions at a current of -0.5 on the normalized scale, a potential against RHE of ≥ 429 mV, preferably ≥ 430 mV to ≤ 700 mV and more preferably ≥ 550 mV to ≤ 750 mV having.

In a further embodiment of the electrode, the catalyst is present at least partially in the form of nanoparticles. In particular, the alloy may be present at least partially in the form of nanoparticles. For the purposes of the present invention, nanoparticles are understood as meaning particles having a dimension of at least one spatial direction of ≦ 1000 nm, preferably ≦ 500 nm, more preferably ≦ 100 nm and particularly preferably ≦ 10 nm.

wobei die Reste R₁ bis R₄ unabhängig voneinander für C₁-C₂₀-Alkyl oder C₂-C₂₀-Alkylether stehen. Geeignete Anionen sind beispielsweise [BF₄]^-, [B(CN)₄]^-, [CF₃BF₃]^-, [C₂F₅BF₃]^-, [n-C₃F₇BF₃]^-, [n-C₄F₉BF₃]^-, [(C₂F₅)₃PF₃]^-, [CF₃CO₂]^-, [CF₃SO₃]^-, [N(COCF₃)(SO₂CF₃)]^-, [N(SO₂CF₃)₂]^-, [EtOSO₃]^-, [N(CN)₂]^-, [C(CN)₃]^-, [SCN]^-, [SeCN]^-, [CuCl₂]^-, [AlCl₄]^-, [ZnCl₄]^2- oder [F(HF)₂₃]^-. Bevorzugt ist [BMim][N(Tf)₂] (1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imid).In a further embodiment of the electrode, the nanoparticles are obtained by co-sputtering into an ionic liquid, by chemical synthesis, chemical vapor deposition or by laser ablation. Suitable cations in the ionic liquid are, for example:

where the radicals R ₁ to R ₄ independently of one another are C ₁ -C ₂₀ -alkyl or C ₂ -C ₂₀ -alkyl ethers. Examples of suitable anions are [BF ₄ ] ^- , [B (CN) ₄ ] ^- , [CF ₃ BF ₃ ] ^- , [C ₂ F ₅ BF ₃ ] ^- , [nC ₃ F ₇ BF ₃ ] ^- , [nC ₄ F ₉ BF ₃ ] ^- , [(C ₂ F ₅ ) ₃ PF ₃ ] ^- , [CF ₃ CO ₂ ] ^- , [CF ₃ SO ₃ ] ^- , [N (COCF ₃ ) (SO ₂ CF ₃ )] ^- , [N (SO ₂ CF ₃ ) ₂ ] ^- , [EtOSO ₃ ] ^- , [N (CN) ₂ ] ^- , [C (CN) ₃ ] ^- , [SCN] ^- , [SeCN] ^- , [CuCl ₂ ] ^- , [AlCl ₄ ] ^- , [ZnCl ₄ ] ^2- or [F (HF) ₂₃ ] ^- . Preferred is [BMim] [N (Tf) ₂ ] (1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide).

In a further embodiment of the electrode, the catalyst is present as solid material or nanostructured solid material. In particular, the alloy may be present at least partially in the form of a nanostructured solid material. In the context of the present invention, nanostructures are understood to mean structures which have a dimension of at least one spatial direction of ≦ 1000 nm, preferably ≦ 500 nm, more preferably ≦ 100 nm and particularly preferably ≦ 10 nm.

In a further embodiment of this electrode, the catalyst is obtained in layers by co-sputtering, by chemical synthesis or by laser ablation.

In a further embodiment of the electrode, the electrochemical device is a fuel cell or a metal-air accumulator. Suitable fuel cells or accumulators are, for example, the alkaline fuel cell (AFC), the polymer electrolyte fuel cell (PEMFC), the direct methanol fuel cell (DMFC), the formic acid fuel cell, the phosphoric acid fuel cell (PAFC), the molten carbonate fuel cell (MCFC). , the Solid Oxide Fuel Cell (SOFC), the Direct Carbon Fuel Cell (SOFC, MCFC), the Magnesium Air Accumulator, the Zinc-Air Accumulator, and the Lithium-Air Accumulator. Preferred fuel cells convert hydrogen at the anode and oxygen at the cathode.

In a further embodiment of the electrode, the catalyst catalyzes the reduction of oxygen to water, hydrogen peroxide, metal oxide or metal peroxide. The metal mentioned is preferably magnesium, zinc or lithium.

In a further embodiment of the electrode, the alloy contains the following metals in the stated proportions: chrome ≥ 5 at% to ≤ 70 at% manganese ≥ 5 at% to ≤ 70 at% iron ≥ 0 atom% to ≤ 70 atom% cobalt ≥ 0 atom% to ≤ 70 atom% nickel ≥ 5 atom% to ≤ 70 atom%, where iron and cobalt are not simultaneously present at 0 atomic% and the sum of the atomic percentages is ≤ 100 atomic%.

The following composition is preferred: chrome ≥ 15 at% to ≤ 35 at% manganese ≥ 15 at% to ≤ 35 at% iron ≥ 15 at% to ≤ 35 at% cobalt ≥ 15 at% to ≤ 35 at% nickel ≥ 15 atomic% to ≤ 35 atomic%, where the sum of the atomic percentages is 100 atomic%.

Particularly preferred is the following composition: chrome ≥ 19 at% to ≤ 21 at% manganese ≥ 19 at% to ≤ 21 at% iron ≥ 19 at% to ≤ 21 at% cobalt ≥ 19 at% to ≤ 21 at% nickel ≥ 19 at% to ≤ 21 at% where the sum of the atomic percentages is 100 atomic%.

The invention further relates to an electrochemical device comprising an anode, a cathode and an electrolyte arranged between anode and cathode, wherein the cathode is an electrode according to the invention. Suitable devices include, for example, the alkaline fuel cell (AFC), the polymer electrolyte fuel cell (PEMFC), the direct methanol fuel cell (DMFC), the formic acid fuel cell, the phosphoric acid fuel cell (PAFC), the molten carbonate fuel cell (MCFC), the solid oxide Fuel Cell (SOFC), the Direct Carbon Fuel Cell (SOFC, MCFC), the Magnesium Air Accumulator, Zinc Air Accumulator and the Lithium Air Accumulator. Preferred fuel cells convert hydrogen at the anode and oxygen at the cathode. The electrolyte between anode and cathode may be, for example, KOH, a polymer membrane, phosphoric acid, an alkali-carbonate melt or an oxide-conducting ceramic.

In one embodiment of the device, the anode is arranged to oxidize hydrogen or a metal (preferably magnesium, zinc or lithium) and the cathode to reduce oxygen.

• Bereitstellen einer erfindungsgemäßen elektrochemischen Vorrichtung
• und
• gleichzeitiges Kontaktieren der Anode mit einer oxidierbaren Verbindung und der Kathode mit einer reduzierbaren Verbindung.

Another aspect of the invention is a method of operating an electrochemical device, the method comprising the steps of:

• Provision of an electrochemical device according to the invention
• and
• simultaneously contacting the anode with an oxidizable compound and the cathode with a reducible compound.

In one embodiment of the process, the oxidizable compound is hydrogen or a metal (preferably magnesium, zinc or lithium) and the reducible compound is oxygen.

The invention likewise relates to the use of an alloy as a reduction catalyst, wherein the alloy comprises at least four metals, one of which is at least four metals manganese, none of these at least four metals in a proportion of ≤ 5 atom% and ≥ 70 atom% in the Alloy is present and the proportion of palladium or platinum in the alloy ≤ 10 atom%. For details on this alloy, reference is made to the above statements to avoid repetition.

In one embodiment of the use, the alloy becomes a catalyst for the reduction of oxygen to water, hydrogen peroxide, metal oxide or metal peroxide. The metal mentioned is preferably magnesium, zinc or lithium.

1. 1) Die Legierung liegt in Form von Nanopartikeln vor, von denen über 50 % einen Durchmesser von ≤ 25 nm aufweisen;
2. 2) Elektrolyt: 0.1 M KOH (unter Luft/keine Sauerstoffsättigung);
3. 3) Spannungsvorschubgeschwindigkeit: 10 mV/s;
4. 4) Subtraktion des an blanker Elektrode gemessenen Stroms vom Strom mit immobilisierten Legierungsnanopartikeln auf entsprechender Elektrode;
5. 5) Es werden im zeitlichen Verlauf stabile Stromkurven betrachtet;
6. 6) Normierung des Differenzstroms durch einen der Sauerstoffreduktion zuzuordnenden Plateaustromwert (Diffusionsgrenzstrom i_ss) mit i_ss = 1.

In another embodiment of the use, at a current of -0.5 on the normalized scale, the alloy has an overvoltage for the oxygen reduction reaction of ≦ 800 mV (preferably ≦ 700 mV, more preferably ≦ 600 mV). This current on the normalized scale is measured under the following conditions:

1. 1) The alloy is in the form of nanoparticles, of which more than 50% have a diameter of ≤ 25 nm;
2. 2) Electrolyte: 0.1 M KOH (under air / no oxygen saturation);
3. 3) voltage feed rate: 10 mV / s;
4. 4) subtracting the current measured on the bare electrode from the current with immobilized alloy nanoparticles on a corresponding electrode;
5. 5) stable current curves are considered over time;
6. 6) Normalization of the differential current by a plateau _{flux value} to be assigned to the oxygen reduction (diffusion limiting current i _ss ) with i _ss = 1.

An overvoltage of 800 mV for the oxygen reduction reaction corresponds to 429 mV against RHE (reversible hydrogen electrode). Therefore, it can also be expressed that the alloy under the above measuring conditions at a current of -0.5 on the normalized scale has a potential against RHE of ≥ 429 mV, preferably ≥ 430 mV to ≤ 700 mV and more preferably ≥ 550 mV to ≤ 650 mV having.

In another embodiment of the use, the alloy contains the following metals in the proportions indicated: chrome ≥ 5 at% to ≤ 70 at% manganese ≥ 5 at% to ≤ 70 at% iron ≥ 0 atom% to ≤ 70 atom% cobalt ≥ 0 atom% to ≤ 70 atom% nickel ≥ 5 atom% to ≤ 70 atom%, where iron and cobalt are not simultaneously present at 0 atomic% and the sum of the atomic percentages is ≤ 100 atomic%.

The following composition is preferred: chrome ≥ 15 at% to ≤ 35 at% manganese ≥ 15 at% to ≤ 35 at% iron ≥ 15 at% to ≤ 35 at% cobalt ≥ 15 at% to ≤ 35 at% nickel ≥ 15 atomic% to ≤ 35 atomic%, where the sum of the atomic percentages is 100 atomic%.

Particularly preferred is the following composition: chrome ≥ 19 at% to ≤ 21 at% manganese ≥ 19 at% to ≤ 21 at% iron ≥ 19 at% to ≤ 21 at% cobalt ≥ 19 at% to ≤ 21 at% nickel ≥ 19 at% to ≤ 21 at% where the sum of the atomic percentages is 100 atomic%.

The invention will be explained in more detail with reference to the following examples and figures, but without being limited thereto.

Example 1 Evaluation of the Catalyst by Normalization to the (Mass Transport Limited) Diffusion Limit Current i _ss (steady state current)

The successful immobilization of CrMnFeCoNi nanoparticles suspended in the ionic liquid [BMim] [N (Tf) ₂ ] on a carbon electrode was demonstrated by significantly increased currents for the ORR compared to a bare electrode. 1 shows the increased current for the ORR after immobilization of CrMnFeCoNi nanoparticles from ionic liquid compared to the bare electrode linear sweep response in 0.1 M KOH.

By applying this method to the nanoparticle samples of the present invention, an electrochemical response of the carbon of the carbon electrode was subtracted and the current obtained thereby on the oxygen reduction on the nanoparticles was divided by the diffusion limiting current. The voltammogram was obtained on a linear sweep for the normalized i _SS . An exponential increase of the current in the kinetically limited potential range is followed by a mass diffusion limited plateau.

The activities obtained here can be compared with the overvoltage to reach a specific current on the current scale normalized against i _SS - analogous to what is often used in the literature - -1 mA / cm ² , but with the advantage that a scale is available which is related to the intrinsic activity and not the geometric surface of the electrode. In order to obtain stable conditions, neither easily fluctuating oxygen saturation was carried out nor induced additional convection. Although this may make the activity of all samples appear smaller, it results in a more accurate comparison of evaluated with this method catalysts.

Example 2: Comparison of inventive catalysts with Pt and MnNi, CoNi and MnCo

The results of this comparison are in 2 displayed. Measurement conditions: potential-assisted immobilization from ionic liquid [BMim] [N (Tf) ₂ ], subtraction of the carbon stream (reduction current at the uncoated carbon electrode) and normalization against the mass-transport-limited steady-state current i _SS ; linear sweep voltammetry in 0.1 M KOH and voltage feed rate of 10 mV / s.

The bimetallic alloys MnNi, CoNi and MnCo showed a comparatively low catalytic activity for the ORR. This was to be expected due to the known low activity of elemental transition metals.

Furthermore, CrMnFeCoNi alloys prepared by combinatorial co-sputtering into [BMim] [N (Tf) ₂ ] were investigated with, as far as technically possible, equiatomic composition. These nanoparticles showed a high catalytic activity for the ORR. These samples are labeled CrMnFeCoNi (I) and CrMnFeCoNi (II) in 2 characterized.

Furthermore, Pt nanoparticles were prepared by sputtering in [BMim] [N (Tf) ₂ ]. These samples are Pt (I) and Pt (II) in 3 characterized. The high activity of CrMnFeCoNi nanoparticles is comparable to that of Pt nanoparticles. This is determined by an approximate overlap of the linear sweep curves (carbon current subtraction and normalized against i _SS ) 2 demonstrated.

To check the results, in particular the reproducibility, CrMnFeCoNi nanoparticles were again prepared in an ionic liquid. This sample is with CrMnFeCoNi (new) in 3 characterized. All CrMnFeCoNi nanoparticle results are consistent within narrow limits.

Example 3 Evaluation of Catalysts by Scanning Droplet Cell (Scatter Droplet Cell, SDC)

Thin film libraries of multinear alloys with CrMnFeCoNi, CrMnCoNi, CrFeCoNi, ZrHfCuNiTi were prepared in varying proportions by means of a concentration gradient of the alloying metals deposited on the substrate. A total of 358 individual alloys per library were made. As a reference, a Pt thin film was further prepared. As a descriptor for the catalytic activity in the ORR, both before and after conditioning, a potential was selected that was located in the kinetically limited region of the respective library. Often this was -175 mV against Ag / AgCl (3 M KCl), but also -1000 mV for ZrHfNiTiCu against Ag / AgCl (3 M KCl).

The individual members of the ZrHfCuNiTi library and the CrFeCoNi library generally showed low activity. As a trend it could be further stated that the activity was also higher for the other alloy samples with increasing content of Mn and Cr.

For comparison with a sputtered Pt surface, the linear sweep voltammograms of alloy samples with a largely equiatomic composition are 3 and 4 shown. 3 shows the voltammograms (10 mV / s) before and 4 after a conditioning cycle at 40 mV / s in 0.1 M KOH in a scanning droplet cell.

Example 4: Chronoamperometric Measurements

To prove that the observed current increase is indeed based on the ORR and not merely on the reduction of the previously oxidized sample, chronoamperometric measurements were carried out on a CrMnCoNi sample for 10 minutes at four potentials as a control experiment. The results are in 5 shown. Potentials are related to Ag / AgCl (3 M KCl). To reduce the catalyst, a complete drop in the current is expected once complete reduction is achieved. However, the current remained constant and its magnitude increased with increasing overpotential, which was expected for the ORR with reduction of dissolved species.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• CN 106756407 A [0005]
• CN 106374116 [0006]
• WO 2017/132725 A1 [0008]

Cited non-patent literature

• J. Li, H.S. Stein, K. Sliozberg, J. Liu, Y. Liu, G. Sertic, E. Scanley, A. Ludwig, J. Schroers, W. Schuhmann et al., J. Mater. Chem. A 2017, 5, 67 [0004]
• G. Laplanche, A. Kostka, O.M. Horst, G. Eggeler, E.P. George, Acta Materialia 2016, 118, 152-163 [0007]

Claims (15)

Electrode for an electrochemical device comprising a catalyst for catalyzing the reduction of a reducible compound, characterized in that the catalyst comprises an alloy of at least four metals, one of which is at least four metals manganese, none of these at least four metals in a proportion of ≤ 5 Atomic% and ≥70 at% in the alloy, and the proportion of palladium or platinum in the alloy is ≤10 at%. Electrode according to Claim 1 wherein the catalyst at a current of -0.5 on the normalized scale has an overvoltage for the oxygen reduction reaction of ≤ 800 mV. Electrode according to Claim 1 or 2 , wherein the catalyst is present at least partially in the form of nanoparticles. Electrode according to Claim 3 wherein the nanoparticles are obtained by co-sputtering into an ionic liquid, by chemical synthesis, chemical vapor deposition or by laser ablation. Electrode according to Claim 1 or 2 , wherein the catalyst is present as a solid material or nanostructured solid material. Electrode according to one of Claims 1 to 5 wherein the electrochemical device is a fuel cell or a metal-air battery. Electrode according to one of Claims 1 to 6 wherein the catalyst catalyzes the reduction of oxygen to water, hydrogen peroxide, metal oxide or metal peroxide. Electrode according to one of Claims 1 to 7 in which the alloy contains the following metals in the proportions indicated: chrome ≥ 5 at% to ≤ 70 at% manganese ≥ 5 at% to ≤ 70 at% iron ≥ 0 atom% to ≤ 70 atom% cobalt ≥ 0 atom% to ≤ 70 atom% nickel ≥ 5 atom% to ≤ 70 atom%, where iron and cobalt are not simultaneously present at 0 atomic% and the sum of the atomic percentages is ≤ 100 atomic%. An electrochemical device comprising an anode, a cathode and an electrolyte arranged between the anode and the cathode, characterized in that the cathode has an electrode according to one of the Claims 1 to 8th is. Device according to Claim 9 , wherein the anode is arranged for the oxidation of hydrogen or a metal and the cathode for the reduction of oxygen. A method of operating an electrochemical device, characterized in that the method comprises the steps of: providing an electrochemical device according to Claim 9 or 10 and simultaneously contacting the anode with an oxidizable compound and the cathode with a reducible compound. Method according to Claim 11 wherein the oxidizable compound is hydrogen or a metal and the reducible compound is oxygen. Use of an alloy as a reduction catalyst, characterized in that the alloy comprises at least four metals, one of these at least four metals is manganese, none of these at least four metals in a proportion of ≤ 5 atom% and ≥ 70 atom% is present in the alloy and the proportion of palladium or platinum in the alloy is ≤ 10 at%. Use according to Claim 13 wherein the alloy is used as a catalyst for the reduction of oxygen to water, hydrogen peroxide, metal oxide or metal peroxide. Use according to Claim 13 or 14 wherein the alloy has an overvoltage for the oxygen reduction reaction of ≤800 mV at a current of -0.5 on the normalized scale.

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