Ruthenium oxide modified with platinum oxide and electrode for oxygen evolution reaction

Abstract

The present invention relates to a ruthenium oxide modified with a transition metal (M) oxide, where M = Pt, Rh, Pd, Ag and / or Au, in particular a ruthenium oxide modified with a platinum oxide catalyst, for use in polymer electrolyte membrane (PEM) fuel cells, water electrolysis, regenerative fuel cells (RFC) or oxygen generating electrodes in various electrolytic applications.

Description

[0001] Specification

[0002] The present invention relates to ruthenium oxide modified with a transition metal (M) oxide, where M = Pt, Rh, Pd, Ag, and / or Au, in particular ruthenium oxide modified with a platinum oxide catalyst, which is used in polymer electrolyte membrane (PEM) fuel cells, water electrolysis, regenerative fuel cells (RFCs), or oxygen evolution electrodes in various electrolysis applications. The present invention also relates to a method for obtaining a catalyst composition, a catalyst composition obtainable or obtained by said method, an electronic device comprising said catalyst composition, and a catalyst composition for use as a catalyst for the oxygen evolution reaction.

[0003] Hydrogen is a promising clean energy carrier that can be produced by various technologies. High-quality hydrogen can be produced by water electrolysis. As known to those skilled in the art, a water electrolyzer contains at least one half-cell with an anode in which the oxygen evolution reaction (OER) occurs, and at least one half-cell with a cathode in which the hydrogen evolution reaction (HER) occurs. If two or more cells are connected together, a stacked configuration is obtained. Thus, a water electrolyzer with a stacked configuration contains at least two half-cells with an anode and / or at least two half-cells with a cathode.

[0004] Different types of water electrolyzers are known.

[0005] In a PEM water electrolyzer, a solid polymer electrolyte is used, which is responsible for proton transport from the anode to the cathode, while electrically insulating the electrodes from each other and responsible for separating the product gases.

[0006] Due to its complexity, the oxygen evolution reaction has slow kinetics, which is why a significant overpotential is required on the anode side to produce oxygen at a reasonable rate. Typically, PEM water electrolyzers operate at a voltage of about 1.5 V to 2 V. Since the pH is strongly acidic (PEM: pH less than 2) and an overpotential must be applied, the materials present on the anode side of the PEM water electrolyzer need to be very corrosion-resistant.

[0007] Typically, the anode of a water electrolyzer includes a catalyst for the oxygen evolution reaction (OER electrocatalyst). Suitable OER electrocatalysts are known to those skilled in the art and have been described, for example, in “A comprehensive review on PEM water electrolysis” by M. Carmo et al., International Journal of Hydrogen Energy, Vol. 38, 2013, pp. 4901 - 4934; and “The Mechanism of Water Oxidation: From Electrolysis via Homogeneous to Biological Catalysis” by H. Dau et al., ChemCatChem, 2010, 2, pp. 724 - 761.

[0008] Iridium oxide or ruthenium oxide is known to be an effective catalyst for the oxygen evolution reaction (EP 2 608 297 A1, Reier et al. Electrocatalytic Oxygen Evolution Reaction in Acidic Environ - ments—Reaction Mechanisms and Catalysts. Adv. Energy Mater. 2017, 7, 1601275).

[0009] However, iridium resources are scarce and expensive, and ruthenium oxide, either alone or in the form of a Pt - Ru alloy, has relatively low stability. The limited iridium resources will be a major obstacle to the development of PEM electrolysis technology. To expand the use of electrolyzers, anodes made of cheaper and more abundant materials are needed.

[0010] As an alternative form to iridium catalysts, some research has been conducted on platinum metal oxides using +1 / +2 / +3 ions such as Li, Na, Mg, Ca, Zn, Cd, Co, Ni, Mn, Cu, Ag, Bi, In, and Ce, where the +1 / +2 ions are fully suitable for the bronze structure.

[0011] EP 3 581 682 A1 discloses an anode for electrolysis that includes a homogeneous platinum bronze M x Pt3O4, where the metal element M is selected from the group consisting of Mn, Co, Cu, Ag, Bi, and Ce. These anodes are inexpensive and have excellent durability, and thus are a good alternative form to Ir anodes. However, the activity is still lower than that of Ir anodes.

[0012] R.D. Shannon et al., Inorg. Chem., 21, 3372 (1982) discloses a method for synthesizing M x Pt3O4 (M = Li, Na, Mg, Ca, Zn, Cd, Co, and Ni).

[0013] WO 2018 / 110423 A1 describes the synthesis of M x Pt3O4 by mixing platinum(IV) oxide (PtO2) and metal nitrates in a molar ratio of 3:1. As metal nitrates, Co, Ce, Ca, Li, Na, Bi, Ag, Cu, Mn, and In are used.

[0014] Yim et al., International Journal of Hydrogen Energy 30 (2005) 1345 describes a method for preparing a mixed PtRuO x material by physically mixing Pt and RuO x to obtain an electrocatalyst with an appropriate composition. An inorganic Ru precursor is dissolved in deionized water, and then the aqueous solution is dried at 110 °C for 12 hours, followed by calcination in air at 400 °C for 5 hours to form an oxidized phase. However, this material shows poor performance as a catalyst for the oxygen evolution reaction.

[0015] Kamitaka et al. Catalysts 2018, 8, 258 disclose Co-Pt bronzes for electrocatalysis in acidic media.

[0016] Cherevko et al. compared the activity and stability of metal and oxidized Ir and Ru materials for the oxygen evolution reaction in acidic media in "Oxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability" (Catalysis Today 262 (2016) 170–180). Cherevkov et al. concluded that RuO2 is comparable to conventional Ir and IrO2 in terms of the activity of the oxygen evolution reaction. In terms of durability, Ru-containing catalysts lag behind their Ir counterparts. Cherevkov et al. also found that metals have a dissolution rate that is 2-3 orders of magnitude higher than their corresponding oxides. A high dissolution rate means that the catalyst is unstable under reaction conditions.

[0017] Yi et al. disclose a catalyst with the composition of Ru 0.9 Pt 0.1 O2 deposited on a carbon support in "Effect of Pt introduced on Ru-based electrocatalyst for oxygen evolution activity and stability“ (Electrochemistry Communications 104 (2019) 106469). It is found that this phase has some abnormally high OER activity and remarkable stability. This observation is explained twice. First, Pt dissolves from the catalyst surface to produce a Pt-depleted surface and form an amorphous hydrated surface layer with unsaturated but very active Ru sites. Second, the core of the catalyst remains unchanged and consists of the initial Ru 0.9 Pt 0.1 O2, which has no catalytic activity but provides the necessary stability for the amorphous hydrated and Pt-depleted surface layer. Although this catalyst shows some remarkable activity, its activity stems from the initial loss of expensive Pt from the catalyst surface, which is not economically attractive. The noble metal loss even aggregates through the applied preparation route. Yi et al. synthesized the corresponding Ru 0.9 Pt 0.1 alloy and used a high-temperature calcination process to convert this material into a binary oxide. However, as revealed by XRD analysis, the conversion is not quantitative, and the presence of the metallic Ru component may lead to additional noble metal loss due to the inherently higher dissolution rate of the metal. In addition, relying on the dissolution process to achieve the desired activity makes long-term stability in a commercially relevant electrolyzer system unlikely.

[0018] "Electrochemical analysis of high temperature methanol electro-oxidation at Pt-decorated Ru catalysts" by A.S. Arico et al., Journal of Electroanalytical Chemistry 576 (2005), pages 161 to 169 involves the study of methanol electro-oxidation in situ on a Pt-decorated support-free Ru catalyst with a Pt loading of 0.1 mg / cm 2 at high temperature in a direct methanol fuel cell.

[0019] "A trace of Pt can significantly boost RuO2 for acidic water splitting" by Qing Yao et al., Chinese Journal of Catalysis 43(2022), pp. 1493 - 1501 discloses the activation and stabilization of RuO2-based electrocatalysts for acidic water splitting by trace Pt. Experimental and theoretical analyses reveal that atomically dispersed Pt incorporated into the RuO2 lattice helps increase the concentration of O vacancies, which effectively enhances the interaction with reaction intermediates and thus reduces the energy barrier for forming OOH*.

[0020] The object of the present invention is to provide a composition that is neither based on Ir nor on inherently inactive binary RuPt oxide phases. Additionally, the composition should not rely on the surface dissolution of Pt to obtain the desired gain in activity. The object of the present invention is to determine the stabilizing effect on the high-activity RuO2 structure without changing the bulk morphology and composition of the bulk material.

[0021] The catalyst composition of the present invention comprises ruthenium oxide RuO2 particles having a RuO2 lattice structure, wherein the RuO2 particles have at least one transition metal (M) oxide deposited on the particle surface, where M = Pt, Rh, Pd, Ag, and / or Au, and wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO2 phase in an amount less than 1 wt%.

[0022] Contrary to other platinum-ruthenium oxide catalysts, the Ru oxide phase itself does not contain a significant amount of transition metal (M) oxide, preferably platinum. Preferably, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO2 oxide in an amount less than 0.75 wt%, more preferably less than 0.5 wt%. Thus, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide may be present in the RuO2 oxide in an amount from 0 wt% to less than 1 wt%, preferably from 0 wt% to less than 0.75 wt%, more preferably from 0 wt% to 0.5 wt%.

[0023] Contrary to other platinum ruthenium oxide catalysts, the catalyst composition contains less than 5 wt%, preferably less than 2 wt%, more preferably less than 1 wt%, and even more preferably less than 0.5 wt% of elemental transition metal (M), preferably platinum, relative to the total mass of the catalyst. Thus, relative to the total mass of the catalyst composition, elemental transition metal (M), preferably platinum, may be present in the RuO2 oxide in an amount of 0 wt% to less than 5 wt%, preferably 0 wt% to less than 2 wt%, more preferably 0 wt% to 1 wt%, and even more preferably 0 wt% to 0.5 wt%.

[0024] The transition metal (M) oxide is preferably platinum, rhodium, palladium, silver, and / or gold, more preferably platinum, palladium, and / or rhodium, and even more preferably platinum.

[0025] The elemental transition metal (M) is preferably platinum, rhodium, palladium, silver, and / or gold, more preferably platinum, palladium, and / or rhodium, and even more preferably platinum.

[0026] The average layer thickness of the transition metal (M) oxide coating, preferably the platinum coating, is in the range of 1 nm to 5 nm, preferably 1 nm to 3 nm. In addition, it is found that MO x is finely distributed at the grain boundaries / surfaces of the Ru oxide particles. The average layer thickness preferably refers to the median of the layer thickness. The determination of the coating thickness is preferably carried out using transmission electron microscopy (TEM) because TEM provides a means to directly measure the oxide thickness in a quantitative manner. TEM is preferably carried out using a probe-corrected Themis Z 3.1 machine (Thermo-Fisher, Waltham, USA) in different acquisition modes including high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM), integrated differential phase contrast (iDPC)–STEM, bright-field TEM, and electron diffraction.

[0027] Preferably, the grain size of the RuO2 phase measured by XRD is in the range of 2 nm and 60 nm, more preferably in the range of 10 nm and 50 nm, and even more preferably in the range of 20 nm and 40 nm.

[0028] The crystal structure of the transition metal oxide cannot be detected by XRD. If the Pt oxide crystal structure is to form in trace amounts, then the proportion of this platinum oxide phase is less than 0.5 wt%, preferably below 0.25 wt%, and more preferably below 0.1 wt% relative to the total mass of the catalyst composition. Preferably, the transition metal (M) oxide, preferably the Pt oxide phase, does not produce diffraction lines attributable to it.

[0029] Preferably, all the particles of the RuO2 phase have a particle size of less than 200 nm, preferably less than 150 nm, and more preferably less than 100 nm measured by TEM particle size analysis.

[0030] The grain size of the RuO2 phase is preferably on average from 5 nm to 150 nm, more preferably from 10 nm to 80 nm, as characterized by TEM measurement. The shape of the particles is preferably spherical.

[0031] The deposition method of the transition metal (M) oxide, preferably Pt oxide, on RuO2 can be carried out using any preparation technique known to those skilled in the art. Suitable preparation methods can be, for example, incipient wetness impregnation, atomic layer deposition or chemical vapor deposition.

[0032] Another deposition method comprises the steps of: (a) mixing a predetermined amount of Pt oxide with a Ru precursor, (b) subjecting the starting material mixture to a solid-phase reaction, and (c) removing by-products from the resulting reaction product. For this deposition method, the sodium content is preferably kept equal to or below 500 ppm.

[0033] The present invention also provides a catalyst composition comprising ruthenium oxide RuO2 particles containing a RuO2 lattice structure, wherein the RuO2 particles have a transition metal (M) oxide deposited on the surface of the particles, where M = Pt, Rh, Pd, Ag and / or Au,

[0034] wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO2 phase in an amount of less than 1% by weight,

[0035] wherein, relative to the total mass of the catalyst, the catalyst composition contains less than 1% by weight of the elemental transition metal (M).

[0036] The present invention also provides a method for obtaining a catalyst composition, wherein the composition comprises ruthenium oxide RuO2 particles containing a RuO2 lattice structure, wherein the RuO2 particles have a transition metal (M) oxide deposited on the surface of the particles, where M = Pt, Rh, Pd, Ag and / or Au, wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO2 phase in an amount of less than 1% by weight,

[0037] The method comprises the following steps:

[0038] (a) mixing a predetermined amount of Pt oxide with a Ru precursor,

[0039] (b) subjecting the starting material mixture to a solid-phase reaction, and

[0040] (c) removing by-products from the resulting reaction product.

[0041] Furthermore, the present invention provides a catalyst composition obtainable by or obtained by the above method.

[0042] Preferably, relative to the total mass of the catalyst composition, the catalyst composition contains less than 1 wt%, preferably from 0 wt% to less than 1 wt%, more preferably from 0 wt% to 0.5 wt% of the elemental transition metal (M).

[0043] The present invention demonstrates that materials based on ruthenium oxide modified with platinum oxide show surprisingly high catalytic activity towards the oxygen evolution reaction and are very stable under highly corrosive conditions. Ruthenium is available up to 20 times more than iridium. This will also solve the iridium supply problem and allow large-scale PEM electrolysis devices.

[0044] Characterization of the catalyst

[0045] The term "transition metal (M) oxide, preferably ruthenium oxide modified with platinum oxide" means that the catalyst comprises ruthenium oxide particles having a transition metal (M) oxide (preferably platinum oxide) deposited on the particle surface.

[0046] Preferably, the transition metal (M) oxide covers at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and more preferably 100% of the particle surface of the ruthenium oxide particles, e.g., completely covers the particle surface of the ruthenium oxide particles. Analysis of the particle surface is preferably carried out using transmission electron microscopy (TEM). TEM is preferably carried out using a probe-corrected Themis Z 3.1 machine (Thermo-Fisher, Waltham, USA) in different acquisition modes including high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), integral differential phase contrast (iDPC)–STEM, bright-field TEM, and electron diffraction.

[0047] Preferably, relative to the total mass of the catalyst, the total amount of the transition metal (M) oxide (preferably platinum) in the catalyst composition is in the range of 1 wt% to 20 wt%, more preferably 5 wt% to 15 wt%, more preferably 8 wt% to 12 wt%. Preferably, the remaining amount of up to 100 wt% is ruthenium and oxygen. Preferably, relative to the total mass of the catalyst, the total amount of ruthenium in the catalyst composition is in the range of 55 wt% to 75 wt%, more preferably 60 wt% to 70 wt%, more preferably 63 wt% to 67 wt%.

[0048] The BET surface area of the catalyst composition of the present invention is 5 m 2 / g to 200 m 2 / g, preferably 20 m 2 / g to 150 m 2 / g, more preferably 30 m 2 / g to 100 m 2 / g.

[0049] Support

[0050] The bulk catalyst may have a limited electrochemically active surface area. To increase the catalytically active surface area, the catalyst composition may also be supported on a suitable support material. The support material is preferably an inorganic oxide, carbide or nitride material such as antimony-doped tin oxide (ATO), substoichiometric titanium oxides (TiO, Ti2O3, Ti3O5 and Ti4O7), TiC, ZrC, HfC, TaC, TiN, ZrN, HfN, TaN, boron carbide, boron-oxygen-carbide or boron carbide containing other elements such as borosilicon carbide oxide, more preferably, TiO2, doped or undoped SnO2.

[0051] The catalyst composition of the present invention may also be used as the support material itself and coated with additional catalytic material, such as coated with iridium.

[0052] The grain size can be determined by X-ray analysis. X-ray diffraction (XRD) measurements can be used to determine the grain size (diameter) and crystal orientation. Preferably, the grain size can be determined from the diffraction pattern of the powder. Preferably, the data can be collected on a Bruker AXSD8 Advance diffractometer that uses a copper anode operating at 40 kV and 40 mA and runs a scan from 2° to 80° (2θ) with a step size of 0.02° (2θ). The data can be analyzed using TOPAS 6. The grain size can be reported using the integral breadth method (LVol-IB) as reported in TOPAS.

[0053] The chemical composition can be analyzed via atomic emission spectroscopy or using energy-dispersive X-ray spectroscopy (EDXS). Preferably, the chemical composition can be analyzed using an integrated SuperX G2 energy-dispersive X-ray spectroscopy (EDXS) detector (Thermo-Fisher, Waltham, USA). EDXS can preferably be used to analyze the grain boundaries / surfaces of Ru particles.

[0054] Transmission electron microscopy (TEM) can be used to analyze the particle surface. In particular, TEM images can be employed to analyze the particle surface of Ru particles. TEM is preferably performed using a probe-corrected Themis Z 3.1 machine (Thermo-Fisher, Waltham, USA) in different acquisition modes including high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM), integral differential phase contrast (iDPC)–STEM, bright-field TEM and electron diffraction.

[0055] The determination of the coating thickness can also be carried out using TEM, as TEM provides a means to directly measure the oxide thickness in a quantitative manner.

[0056] In addition, the particle size can be determined by TEM particle size analysis. Preferably, the particle size analysis can be carried out using the FIJI software tool (Schindelin, J., Arganda-Carreras, I., Frise, E., Kaynig, V., Longair, M., Pietzsch, T., Cardona, A. (2012) Fiji: an open-source platform for biological-image analysis. Nature Methods, 9(7), 676–682. doi:10.1038 / nmeth.2019).

[0057] The diffraction pattern can be evaluated using Prodas software (Proscope, Gangelt, Germany, version: 1.4).

[0058] Advantages

[0059] Contrary to the prior art, the described invention demonstrates that the platinum oxide-modified ruthenium oxide catalytic material has surprisingly high activity and stability for the electrochemical oxygen evolution reaction under acidic conditions (much greater than that of the binary oxides alone). The present invention solves the problem of limited Ir supply by providing an alternative form based on oxides of Ru and Pt, which are elements with significantly higher availability. Contrary to other reported Ru-containing materials, higher stability is achieved. The stability is achieved by depositing platinum oxide on the surface of RuO2 particles rather than by removing platinum from the surface of Ru-containing particles.

[0060] The present invention is further illustrated by the following set of embodiments and combinations of embodiments obtained from the indicated dependencies and cross-references. Specifically, it should be noted that in each case where the scope of an embodiment is mentioned, for example, in the context of a term such as "the catalyst composition according to any one of embodiments 1 to 4", each embodiment within that scope is clearly disclosed to those skilled in the art, i.e., the wording of the term should be understood by those skilled in the art as being synonymous with "the catalyst composition according to any one of embodiments 1, 2, 3, and 4". In addition, it should be clearly stated that the following set of embodiments represents a properly structured part of the general description of the preferred aspects of the present invention and thus appropriately supports but does not represent the claims of the present invention.

[0061] Embodiment 1 :

[0062] A catalyst composition, the catalyst composition comprising ruthenium oxide RuO₂ particles, which contain a RuO₂ lattice structure, wherein the RuO₂ particles have at least one transition metal (M) oxide deposited on the particle surface, where M = Pt, Rh, Pd, Ag, and / or Au, and wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO₂ phase in an amount less than 1 wt%.

[0063] Embodiment 2 :

[0064] The catalyst composition according to embodiment 1, wherein, relative to the total mass of the catalyst composition, the proportion of the lattice structure of the transition metal (M) oxide is less than 0.5 wt%.

[0065] Embodiment 3 :

[0066] The catalyst composition according to embodiment 1 or 2, wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO₂ phase present in the RuO₂ oxide in an amount less than 0.75 wt%, more preferably less than 0.5 wt%; or wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO₂ phase present in the RuO₂ oxide in an amount from 0 wt% to less than 1 wt%, preferably from 0 wt% to less than 0.75 wt%, more preferably from 0 wt% to 0.5 wt%.

[0067] Embodiment 4 :

[0068] The catalyst composition according to at least one of embodiments 1 to 3, wherein, relative to the total mass of the catalyst, the catalyst composition contains less than 5 wt%, preferably less than 2 wt%, more preferably less than 1 wt%, more preferably less than 0.5 wt% of elemental transition metal (M), preferably platinum; or wherein, relative to the total mass of the catalyst composition, the catalyst composition contains from 0 wt% to less than 5 wt%, preferably from 0 wt% to less than 2 wt%, more preferably from 0 wt% to 1 wt%, more preferably from 0 wt% to less than 1 wt%, more preferably from 0 wt% to 0.5 wt%, more preferably from 0 wt% to less than 0.5 wt% of elemental transition metal (M).

[0069] Embodiment 5 :

[0070] The catalyst composition according to at least one of Embodiments 1 to 4, wherein the transition metal (M) oxide is platinum, rhodium, palladium, silver, and / or gold, preferably platinum, palladium, and / or rhodium, more preferably platinum; and / or

[0071] wherein the elemental transition metal (M) is platinum, rhodium, palladium, silver, and / or gold, preferably platinum, palladium, and / or rhodium, more preferably platinum.

[0072] Embodiment 6 :

[0073] The catalyst composition according to at least one of Embodiments 1 to 5, wherein the average layer thickness of the transition metal (M) oxide coating, preferably the platinum coating, is in the range of 1 nm to 5 nm, preferably 1 nm to 3 nm.

[0074] Embodiment 7 :

[0075] The catalyst composition according to at least one of Embodiments 1 to 6, wherein the grain size of the RuO2 phase measured by XRD is in the range of 2 nm and 60 nm, preferably in the range of 10 nm and 50 nm, more preferably in the range of 20 nm and 40 nm.

[0076] Embodiment 8 :

[0077] The catalyst composition according to at least one of Embodiments 1 to 7, wherein, if the Pt oxide crystal structure should form in trace amounts, the proportion of the platinum oxide phase is less than 0.5 wt%, preferably less than 0.25 wt%, more preferably less than 0.1 wt% relative to the total mass of the catalyst composition.

[0078] Embodiment 9 :

[0079] The catalyst composition according to at least one of Embodiments 1 to 8, wherein all the particles of the RuO2 phase have a particle size of less than 200 nm, preferably less than 150 nm, more preferably less than 100 nm measured by TEM particle size analysis.

[0080] Embodiment 10 :

[0081] The catalyst composition according to at least one of Embodiments 1 to 9, wherein the particle size of the RuO2 phase averages from 5 nm to 150 nm, preferably 10 nm to 80 nm.

[0082] Embodiment 11 :

[0083] The catalyst composition according to at least one of embodiments 1 to 10, wherein, based on the total mass of the catalyst, the total amount of transition metal (M) oxide, preferably platinum, in the catalyst composition is in the range of 1 wt% to 20 wt%, preferably 5 wt% to 15 wt%, preferably 8 wt% to 12 wt%; and / or

[0084] wherein the remaining amount of up to 100 wt% is ruthenium and oxygen; and / or

[0085] wherein, based on the total mass of the catalyst, the total amount of ruthenium in the catalyst composition is in the range of 55 wt% to 75 wt%, preferably 60 wt% to 70 wt%, more preferably 63 wt% to 67 wt%.

[0086] Embodiment 12 :

[0087] The catalyst composition according to at least one of embodiments 1 to 11, wherein the BET surface area of the catalyst composition is 5 m 2 / g to 200 m 2 / g, preferably 20 m 2 / g to 150 m 2 / g, more preferably 30 m 2 / g to 100 m 2 / g.

[0088] Embodiment 13 :

[0089] The catalyst composition according to at least one of embodiments 1 to 12, wherein the catalyst composition is supported on a support material, and the support material is preferably an inorganic oxide, carbide or nitride material.

[0090] Embodiment 14 :

[0091] The catalyst composition according to at least one of embodiments 1 to 12, wherein the catalyst composition itself is used as a support material, preferably wherein the catalyst composition is coated with an additional catalytic material, which is preferably iridium.

[0092] Embodiment 15 :

[0093] The catalyst composition according to at least one of embodiments 1 to 14, wherein, based on the total mass of the catalyst, the catalyst composition contains less than 2 wt% of elemental transition metal (M).

[0094] Embodiment 16 :

[0095] The catalyst composition according to at least one of embodiments 1 to 15, wherein the average layer thickness of the transition metal (M) oxide coating is in the range of 1 nm to 5 nm.

[0096] Embodiment 17 :

[0097] The catalyst composition according to at least one of embodiments 1 to 16, wherein the grain size of the RuO2 phase measured by XRD is in the range of 2 nm and 60 nm.

[0098] Embodiment 18 :

[0099] The catalyst composition according to at least one of embodiments 1 to 17, wherein the particle size of the RuO2 phase has an average of 5 nm to 150 nm, as characterized by TEM measurement.

[0100] Embodiment 19 :

[0101] The catalyst composition according to at least one of embodiments 1 to 18, wherein relative to the total mass of the catalyst, the catalyst composition contains 1 wt% to 20 wt% of transition metal (M) oxide, 55 wt% to 75 wt% of ruthenium, and up to 100 wt% of the remaining amount of oxygen.

[0102] Embodiment 20 :

[0103] The catalyst composition according to at least one of embodiments 1 to 19, wherein the transition metal (M) oxide is platinum, rhodium, and / or palladium, preferably wherein the transition metal (M) oxide is platinum.

[0104] Embodiment 21 :

[0105] A catalyst composition, the catalyst composition comprising ruthenium oxide RuO2 particles, which contain a RuO2 lattice structure, wherein the RuO2 particles have a transition metal (M) oxide deposited on the surface of the particles, wherein M = Pt, Rh, Pd, Ag, and / or Au,

[0106] wherein calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO2 phase in an amount less than 1 wt%,

[0107] wherein relative to the total mass of the catalyst, the catalyst composition contains less than 1 wt% of elemental transition metal (M).

[0108] Embodiment 22 :

[0109] Method for obtaining a catalyst composition, wherein the composition comprises ruthenium oxide RuO₂ particles containing a RuO₂ lattice structure, wherein the RuO₂ particles have a transition metal (M) oxide deposited on their particle surface, where M = Pt, Rh, Pd, Ag and / or Au,

[0110] wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO₂ phase in an amount less than 1% by weight,

[0111] The method comprises the following steps:

[0112] (a) Mixing a predetermined amount of Pt oxide with a Ru precursor,

[0113] (b) Subjecting the starting mixture to a solid-phase reaction, and

[0114] (c) Removing by-products from the resulting reaction product.

[0115] Embodiment 23 :

[0116] A catalyst composition obtainable by or obtained by the method according to embodiment 22.

[0117] Embodiment 24 :

[0118] The catalyst composition according to embodiment 23, wherein the catalyst composition comprises less than 1% by weight of elemental transition metal (M) relative to the total mass of the catalyst.

[0119] Embodiment 25 :

[0120] An electrochemical device comprising the catalyst composition according to any one of the preceding embodiments.

[0121] Embodiment 26 :

[0122] Use of the catalyst composition according to any one of the preceding embodiments as a catalyst for the oxygen evolution reaction. Examples

[0123] Experimental procedure

[0124] 1. X-ray diffraction pattern of the powder

[0125] The sample was homogenized in a mortar, flattened into the sample holder, and data were collected on a Bruker AXS D8 Advance diffractometer using a copper anode operating at 40 kV and 40 mA. Scanning was performed from 2° to 80° (2θ) with a step size of 0.02° (2θ). TOPAS 6 (1) was used to analyze the data. The grain size was reported using the integral breadth method (LVol-IB) as reported in TOPAS.

[0126] Literature

[0127] (1) TOPAS 6 User Manual, 2017, Bruker AXS GmbH, Karlsruhe, Germany

[0128] 2. TEM images and EDS distribution

[0129] The powder sample was dispersed in ethanol and applied to an ultrathin carbon-coated grid by the drop-on-grid method. The sample was imaged by transmission electron microscopy (TEM) in different acquisition modes including high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM), integral differential phase contrast (iDPC)–STEM, bright-field TEM, and electron diffraction using a probe-corrected Themis Z 3.1 machine (Thermo-Fisher, Waltham, USA). The chemical composition was analyzed using an integrated SuperX G2 energy-dispersive X-ray spectroscopy (EDXS) detector (Thermo-Fisher, Waltham, USA). The data were analyzed using Velox 2.1x software (Thermo-Fisher, Waltham, USA). Particle size analysis was performed using the FIJI software tool (Schindelin, J., Arganda-Carreras, I., Frise, E., Kaynig, V., Longair, M., Pietzsch, T., Cardona, A. (2012)). Fiji: An open-source platform for biological-image analysis. Nature Methods, 9(7), 676–682. doi:10.1038 / nmeth.2019). The diffraction patterns were evaluated using Prodas software (Proscope, Gangelt, Germany, version: 1.4).

[0130] 3. Electrochemical measurements

[0131] Experiments were conducted at room temperature and under an argon atmosphere in 0.5 M H2SO4 electrolyte. The catalyst was dispersed at 1 wt% into H2O / IPA 10 / 1 to obtain an ink by sonication, and the ink was drop-cast onto a gold electrode. All catalysts were deposited to achieve the same total mass loading on the electrode as the thin film. The electrode was immersed in the electrolyte and the activity was measured by linear sweep voltammetry in the potential range of 1.2 V to 1.7 V versus the reversible hydrogen electrode (RHE).

[0132] Preparation of the examples

[0133] Samples of the present invention

[0134] Platinum oxide-modified ruthenium oxide was prepared according to the following method. The Ru(NO)NO3 solution with 18.8 wt% Ru from BASF Italia (batch number: 9002401825) was dropped onto the PtO2 precursor by completely covering / wetting the solid precursor, and mixing was carried out. The atomic platinum to ruthenium ratio of this precursor was 3:1. PtO2 with 500 ppm Na content (model 40402) from Sigma Aldrich was used.

[0135] Then the PtO2 impregnated with the Ru-containing solution was ground into a fine powder. Then the powder was dried and heat-treated using the following protocol.

[0136] 1. Dry at 80 °C for 12 hours

[0137] 2. Heat to 650 °C at 5 K / min

[0138] 3. Hold at 650 °C for 6 hours

[0139] 4. Cool (10 k / min)

[0140] After heat treatment, the sample was treated with aqua regia at 80 °C for 30 minutes. Then the aqua regia-treated sample was dried again at 80 °C for 12 hours. The composition of the obtained material was examined by atomic emission spectroscopy. One sample, BRZ-12, was prepared according to this process. The sample contained 8.9 wt% platinum.

[0141] Comparative examples

[0142] For the comparative example, samples containing PtO2 and RuO2 were prepared similarly to the samples of the present invention, but platinum and ruthenium were dried and calcined respectively. PtO2 (model 206032) with a Na content of 1.6% by weight from Sigma Aldrich was used as a material containing Pt. A Ru (NO) NO3 solution (as used in the embodiments of the present invention) with a Ru content of 18.8% by weight from BASF Italia (batch number: 9002401825) was used as an inorganic Ru precursor. The Ru aqueous solution was dried and heat treated separately in the absence of other metal precursors. The following scheme is as follows:

[0143] 1. Dry at 80°C (dry in a vacuum drying oven and continue drying until the solution becomes dry powder)

[0144] 2. Heating at 5K / min to 650°C

[0145] 3. Maintain at 650℃ for 6 hours

[0146] 4. Cooling (10k / min)

[0147] The individually heat treated samples were then physically mixed and ground into a fine powder. A portion of this material was subjected to the same aqua regia treatment as described in the examples of the present invention. Two samples were prepared according to this process. Samples H2-PEM-192-2 and H2-PEM-194-2 contained 45 wt % and 58 wt % platinum, respectively.

[0148] Comparison between the inventive examples and the comparative examples

[0149] TEM

[0150] Fehler! Verweisquelle konnte nicht gefunden werden. Figure 1 Depicted are the TEM images and elemental distribution EDXS of the samples of the present invention. The TEM images reveal that the core of the particles consists of RuO2, and Pt is only detectable on the surface of the particles. In addition, PtOx is found to be finely distributed at the grain boundaries / surfaces of the Ru particles.

[0151] Figure 2 TEM images of comparative samples after AR treatment are shown. Compared with the samples of the present invention, in the comparative samples (H2-PEM-192, Figure 2 ) are clearly visible in the Ru- and Pt-rich particles. The Pt particles of the comparative sample have a distinct cubic shape.

[0152] XRD

[0153] Figure 3The diffraction pattern of the sample of the present invention is shown. The reflections of the sample originate only from the tetragonal RuO2 lattice. The grain size of RuO2 is calculated to be 25 nm. XRD measurements confirm that the material consists mainly of the RuO2 lattice structure.

[0154] Figure 4 The diffraction pattern of the comparative sample is shown. The reflections of the sample originate from tetragonal RuO2, and the elemental Pt and Pt3O4 lattices can be detected. The grain sizes are 70 nm, 47 nm, and 39 nm, respectively.

[0155] Electrochemical activity of the inventive examples and the comparative examples

[0156] a) Electrochemical cycling to cyclic stability

[0157] Using the method described in a (see Figure 5 ), the sample of the present invention (BRZ-12) was compared with RuO2 (Alfa Aesar), showing that although the conventional RuO2 has very high initial activity, when the material was cycled multiple times between 1.2 V and 1.7 V with respect to the RHE, the activity rapidly decreased and completely disappeared after 30 cycles (see Figure 5 a), while the activity of the sample of the present invention was completely retained (see Figure 5 b). Experiments were carried out at room temperature and in an argon atmosphere in 0.5 M H2SO4 electrolyte. The catalyst was dispersed at 1 wt% into H2O / IPA 10 / 1 to obtain an ink by sonication, and the ink was drop-cast onto a gold electrode. All the catalysts were deposited to achieve the same total mass loading on the electrode as that of the thin film. The electrode was immersed in the electrolyte and the activity was measured by linear sweep voltammetry in the potential range from 1.2 V to 1.7 V with respect to the reversible hydrogen electrode (RHE).

[0158] b) Electrochemical activity

[0159] The comparison of the sample of the present invention (BRZ-12) with the non-inventive comparative example (H2-PEM-192-1) (see Figure 6 ) shows that significantly higher activity was obtained by the examples of the present invention. Experiments were carried out at room temperature and in an argon atmosphere in 0.5 M H2SO4 electrolyte. The catalyst was dispersed at 1 wt% into H2O / IPA 10 / 1 to obtain an ink by sonication, and the ink was drop-cast onto a gold electrode. All the catalysts were deposited to achieve the same total mass loading on the electrode as that of the thin film. The electrode was immersed in the electrolyte and the activity was measured by linear sweep voltammetry in the potential range from 1.2 V to 1.7 V with respect to the reversible hydrogen electrode (RHE).

[0160] The catalyst of the present invention is stable and active for the acidic oxygen evolution reaction.

[0161] Drawings

[0162] Figure 1 : TEM images and elemental distributions of the samples of the present invention

[0163] Figure 2 : TEM images and elemental distributions of the comparative samples

[0164] Figure 3 : Diffraction patterns of the samples of the present invention

[0165] Figure 4 : Diffraction patterns of the comparative samples.

[0166] Figure 5 : b) Electrochemical cycle-to-cycle stability of RuO2 relative to a) the samples of the present invention

[0167] Figure 6 : Electrochemical activity of the samples of the present invention compared to the comparative samples

[0168] Cited literature

[0169] - M. Carmo et al., "A comprehensive review on PEM water electroly - sis", International Journal of Hydrogen Energy, Vol. 38, 2013, pp. 4901 - 4934

[0170] - H. Dau et al., "The Mechanism of Water Oxidation: From Electrolysis via Homogeneous to Biological Catalysis", ChemCatChem, 2010, 2, pp. 724 - 761

[0171] - EP 2 608 297 A1

[0172] - Reier et al., "Electrocatalytic Oxygen Evolution Reaction in Acidic Environments—Reaction Mechanisms and Catalysts" Adv. Energy Mater. 2017, 7, 1601275 EP 3 581 682 A1

[0173] - R. D. Shannon et al., Inorg. Chem., 21, 3372 (1982)

[0174] -WO 2018 / 110423 A1

[0175] -Yim et al., International Journal of Hydrogen Energy 30(2005)1345

[0176] -Kamitaka et al., Catalysts 2018, 8, 258

[0177] -Cherevko et al., “Oxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability”, Catalysis Today 262(2016)170–180

[0178] -Yi et al., “Effect of Pt introduced on Ru-based electrocatalyst for oxygen evolution activity and stability”, Electrochemistry Communications 104(2019)106469)

[0179] -A.S. Arico et al., “Electrochemical analysis of high temperature methanol electro-oxidation at Pt-decorated Ru catalysts”, Journal of Electroanalytical Chemistry 576(2005), pp. 161-169

[0180] -Qing Yao et al., “A trace of Pt can significantly boost RuO2 for acidic water splitting”, Chinese Journal of Catalysis 43(2022), pp. 1493-501

Claims

1. A catalyst composition, the catalyst composition comprising ruthenium oxide RuO₂ particles containing a RuO₂ lattice structure, wherein the RuO₂ particles have at least one transition metal (M) oxide deposited on the particle surface, where M = Pt, Rh, Pd, Ag, and / or Au, and wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO₂ phase in an amount less than 1 wt%.

2. The catalyst composition according to claim 1, wherein, relative to the total mass of the catalyst composition, the proportion of the lattice structure of the transition metal (M) oxide is less than 0.5 wt%.

3. The catalyst composition according to claim 1 or 2, wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO₂ phase in an amount less than 0.5 wt%.

4. The catalyst composition according to at least one of claims 1 to 3, wherein, relative to the total mass of the catalyst, the catalyst composition contains less than 2 wt% of elemental transition metal (M) oxide.

5. The catalyst composition according to at least one of claims 1 to 4, wherein the average layer thickness of the transition metal (M) oxide coating is in the range of 1 nm to 5 nm.

6. The catalyst composition according to at least one of claims 1 to 5, wherein the grain size of the RuO₂ phase measured by XRD is in the range of 2 nm and 60 nm.

7. The catalyst composition according to at least one of claims 1 to 6, wherein the particle size of the RuO₂ phase averages from 5 nm to 150 nm, as characterized by TEM measurement.

8. The catalyst composition according to at least one of claims 1 to 7, wherein, relative to the total mass of the catalyst, the catalyst composition contains 1 wt% to 20 wt% of transition metal (M) oxide, 55 wt% to 75 wt% of ruthenium, and up to 100 wt% of the balance of oxygen.

9. The catalyst composition according to at least one of claims 1 to 8, wherein the transition metal (M) oxide is platinum, rhodium, and / or palladium, preferably wherein the transition metal (M) oxide is platinum.

10. A catalyst composition, the catalyst composition comprising ruthenium oxide RuO₂ particles containing a RuO₂ lattice structure, wherein the RuO₂ particles have a transition metal (M) oxide deposited on their particle surface, where M = Pt, Rh, Pd, Ag, and / or Au, wherein, calculated as element M and relative to the total mass of the catalyst composition, the transition metal (M) oxide is present in the RuO₂ phase in an amount less than 1 wt%, wherein, relative to the total mass of the catalyst, the catalyst composition contains less than 1 wt% of elemental transition metal (M).

11. A method for obtaining a catalyst composition, wherein the composition comprises ruthenium oxide RuO₂ particles containing a RuO₂ lattice structure, wherein the RuO₂ particles have a transition metal (M) oxide deposited on the surface of the particles, where M = Pt, Rh, Pd, Ag, and / or Au, and wherein the transition metal (M) oxide is present in the RuO₂ phase in an amount less than 1 wt% calculated as element M and relative to the total mass of the catalyst composition, the method comprising the steps of: (a) mixing a predetermined amount of Pt oxide with a Ru precursor, (b) subjecting the starting material mixture to a solid-state reaction, and (c) removing by-products from the resulting reaction product.

12. A catalyst composition obtainable by or obtained by the method according to claim 11.

13. The catalyst composition according to claim 12, wherein the catalyst composition comprises less than 1 wt% of the elemental transition metal (M) relative to the total mass of the catalyst.

14. An electrochemical device comprising the catalyst composition according to any one of claims 1 to 9, or comprising the catalyst composition according to claims 10, 12, or 13.

15. Use of the catalyst composition according to any one of claims 1 to 9 or according to claims 10, 12, or 13 as a catalyst for the oxygen evolution reaction.

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