catalysts

Abstract

A method of producing a catalyst is disclosed. The method comprising: providing precursors dissolved in a solvent, providing a coordinating polymer, combining the coordinating polymer and the precursors dissolved in a solvent and stirring to form a mixture, drying the mixture to from a dried mixture; and calcinating the dried mixture to form agglomerated iridium- ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 – 5 nm thus obtaining the catalyst. Further, a catalyst comprising agglomerated iridium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 nm – 5 nm, an electrode thereof and a use thereof are disclosed.

Description

[0001] CATALYSTS

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to catalysts and to the method of preparation thereof. The present disclosure further relates to an electrode with a catalytic film. The present disclosure further relates to a use of the catalyst or electrode thereof.

[0004] BACKGROUND

[0005] Oxygen evolution reaction (OER) is an electrochemical process involved in energy conversion and storage technologies such as water splitting, rechargeable metal-air batteries, and regenerative fuel cells. OER is the anodic half-reaction in these systems, where water (H2O) is oxidized to oxygen gas (O2). Efficient OER catalysts are essential for improving the energy efficiency of systems reliant on water oxidation. OER catalysts currently on the market are a trade-off between efficiency, stability, scarcity and cost. Noble metal oxide catalysts (such as IrO2or RuO2) are efficient and stable but suffer from high cost and scarcity and cost of the metal. Transition metal oxides, such as those based on Co, Ni, Fe, and Mn, are abundant and cheap but exhibit lower activity and poor stability, especially in acidic conditions. Metal phosphides, sulfides, and nitrides (e. g., Ni2P, CoS2) are efficient catalysts but tend to oxidize under OER conditions, reducing stability. The balance between achieving high efficiency, maintaining stability under operational conditions, and ensuring scalability due to material cost and abundance is a challenge in OER catalyst development.

[0006] SUMMARY

[0007] A method of producing a catalyst is disclosed. The method comprises:a. providing precursors dissolved in a solvent, wherein the precursors are a precursor of iridium ( Ir), a precursor of ruthenium (Ru), and a precursor of tungsten (W);

[0008] b. providing a coordinating polymer;

[0009] c. combining the coordinating polymer and the precursors dissolved in a solvent and stirring to form a mixture;

[0010] d. drying the mixture to from a dried mixture;

[0011] and

[0012] e. calcinating the dried mixture to form agglomerated iridium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 - 5 nm thus obtaining the catalyst.

[0013] Further, a catalyst is disclosed. The catalyst comprises agglomerated iridium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 - 5 nm.

[0014] Further, an electrode is disclosed. The electrode comprises:

[0015] a conductive substrate; and

[0016] a catalytic layer deposited on the conductive substrate comprising the catalyst as disclosed.

[0017] Further, a use is disclosed. The use comprises using the catalyst as disclosed or the electrode thereof for water electrolysis.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

[0020] Figure 1 shows a schematic representation of the method to produce a catalyst.Figure 2 shows TEM images of experimental samples and comparative samples.

[0021] Figure 3 shows electrochemical categorisation of the experimental sample catalysts and comparative s amp les.

[0022] Figure 4 compares the experimental sample catalysts and multiple comparative samples.

[0023] Figure 5 shows a TEM image of an experimental s amp 1 e.

[0024] Figure 6 shows a chronopotentiometric profile of an experimental sample.

[0025] DETAILED DESCRIPTION

[0026] The present disclosure relates to a method of producing a catalyst. The method comprises:

[0027] a. providing precursors dissolved in a solvent, wherein the precursors are a precursor of iridium (Ir), a precursor of ruthenium (Ru), and a precursor of tungsten (W);

[0028] b. providing a coordinating polymer;

[0029] c. combining the coordinating polymer and the precursors dissolved in a solvent and stirring to form a mixture;

[0030] d. drying the mixture to from a dried mixture;

[0031] and

[0032] e. calcinating the dried mixture to form agglomerated iridium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 - 5 nm thus obtaining the catalyst.

[0033] With such a method, a catalyst comprising of agglomerated iridium-ruthenium-tungsten oxide nanoparticles may be produced. The coordinating polymer coordinates and stabilizes the Ir, Ru and W precursors such that agglomerated iridium-ruthenium-tungsten oxide nanoparticles may form after calcination. The coordinating polymer enables a small size of the resultingagglomerated iridium-ruthenium-tungsten oxide nanoparticles, such as in the range of 0.5 - 5 nm. The added benefit of the iridium-ruthenium-tungsten oxide nanoparticles having a small size is increased catalytic surface area, thus the resulting catalyst may have improved catalytic activity and efficiency. The resulting catalyst may be stable in acidic operational conditions. The resulting catalyst may have reduced overpotential to commercially available catalysts. The reduced over-potential may directly make the catalyst more energy efficient as it requires less energy to drive the electrochemical reaction. Further added benefit is that the method allows for a reduced amount of iridium to be used in the catalyst while still producing a catalyst with high catalytic activity, stability and efficiency. Reduced amount of iridium conserves limited natural resources and lowers production cost. This method is a scalable method suitable for large scale production of catalysts.

[0034] In the context of this specification, the term "catalyst" may be understood as referring to a substance that increases the rate of a chemical reaction without being consumed in the process. The catalyst may be a nanocatalyst. The catalyst may be, for example, an electrocatalyst or a photocatalyst. The catalyst may be used in energy conversion and storage, such as fuel cells, batteries, or for hydrogen production, water splitting, or CO2 reduction or O2 reduction. The catalysts disclosed herein may be suitable for water electrolysis. The catalysts disclosed herein may be suitable as catalysts for the oxygen evolution reaction (OER) or oxygen reduction reaction (ORR). The catalysts disclosed herein may be stable in acidic conditions. In the context of this specification, the term "nanocatalyst" may be understood as referring to a catalytic material composed of particles at the nanoscale, such as having a mean diameter below 5 nm. In the context of this specification, theterm "electrocatalyst" may be understood as referring to a catalytic material that facilitates and accelerates electrochemical reactions by lowering the activation energy. An electrocatalyst may be the anode catalyst or cathode in devices such as fuel cells, electrolyzers, and batteries. In the context of this specification, the term "photocatalyst" may be understood as referring to a catalytic material that enables or enhances chemical reactions upon absorption of light.

[0035] In the context of this specification, the term "oxygen evolution reaction (OER) " may be understood as referring to the electrochemical reaction in which water (H2O) is oxidized to form oxygen gas (O2), protons (H+), and electrons (e-), typically occurring in the presence of a catalyst. In the context of this specification, the term "oxygen reduction reaction (ORR) " may be understood as referring to the electrochemical reaction in which oxygen gas (O2) is reduced to water (H2O) or hydroxide ions (OH-), typically occurring in the presence of a catalyst.

[0036] In such a method, the precursor of Iridium ( Ir) is provided. The precursor of Ir may be, for example, iridium ( III ) chloride ( IrCl3), iridium ( III ) chloride hydrate ( IrCl3××H2O), iridium ( IV) chloride hydrate ( IrCl4××H2O), Hydrogen hexachloroiridate ( IV) hydrate (H2Cl6Ir××H2O), iridium acetylacetonate ( Ir (acac)3), or iridium carbonyl ( Ir4(CO)12). In an embodiment the precursor of Iridium ( Ir) may be iridium ( III ) chloride hydrate or Hydrogen hexachloroiridate ( IV) hydrate. Ir, Ru and W are transition metals and may be referred to as metal ions throughout this disclosure.

[0037] In such a method, the precursor of Ruthenium (Ru) is provided. The precursor of Ru may be, for example, ruthenium chloride (RuCl3), ruthenium chloride hydrate (RuCl3××H2O), ruthenium acetylacetonate (Ru (acac)3), or ruthenium carbonyl (Ru3(CO)12). In anembodiment, the precursor of Ruthenium (Ru) may be ruthenium chloride or ruthenium chloride hydrate.

[0038] In such a method, the precursor of Tungsten (W) is provided. The precursor of W may be, for example, tungsten hexachloride (WCl6), ammonium tungstate ((NH4)2WO4), or tungsten hexacarbonyl (W(CO)6) • In an embodiment, the precursor of Tungsten (W) may be tungsten hexachloride.

[0039] In an embodiment, the precursors may be provided at a Irx: Ruy: Wzmolar ratio, where x is 0 < x < 1.5, y is 0 < y ≤ 1, and z is 0 < z ≤ 1.5. This may be understood as the molar ratio of Ir to Ru and W in relation to each other. The expression "0 < x < 1.5" should be understood as the amount of x being greater than 0 or smaller than or equal to 1.5.

[0040] In an embodiment, in the Irx: Ruy: Wzmolar ratio, x may be in the range of 0.40 - 1.5. Such as that x is 0.40 ≤ x ≤ 1.5. In an embodiment, in the Irx: Ruy: Wzmolar ratio, x is in the range of 0.40 - 1.5, or 0.50 - 1.25, or 0.75 - 1. In an embodiment, in the Irx: Ruy: Wzmolar ratio, x may be 1.

[0041] In an embodiment, in the Irx: Ruy: Wzmolar ratio, y may be in the range of 0.10 - 1. Such as that y is 0.10 ≤ y ≤ 1. In an embodiment, in the Irx: Ruy: Wzmolar ratio, y may be in the range of 0.10 - 1, or 0.10 -0.70, or 0.20 - 0. 6, or 0.20 - 0.50, or 0.20 - 0.40. In an embodiment, in the Irx: Ruy: Wzmolar ratio, y may be 0.30.

[0042] In an embodiment, in the Irx: Ruy: Wzmolar ratio, z may be in the range of 0. 05 - 1.5. Such as that y is 0.05 ≤ z ≤ 1.5. In an embodiment, in the Irx: Ruy: Wzmolar ratio, z may be in the range of 0.05 - 1.5, or 0.05 -1, or 0.10 - 1. In an embodiment, in the Irx: Ruy: Wzmolar ratio, z may be 0.10, 0.50, or 1.

[0043] The method of producing a catalyst as disclosed may enable using a reduced amount of iridium or ruthenium to produce a catalyst. Particularly iridium is arare and expensive metal, the reduction of which yields the benefit of being more sustainable and more cost effective. With the method of producing a catalyst it is possible to reduce the amount if iridium in the resulting catalyst without reducing the activity or stability of the catalyst. With the method of producing a catalyst it is possible to reduce the amount if iridium in the resulting catalyst and still improve the activity or stability of the catalyst.

[0044] In the context of this specification, the term "solvent" may be understood as referring to a liquid substance capable of dissolving other substances to form a solution. The solvent may be ethanol, isopropanol, butanol, methanol, propanol, pentanol, ethylene glycol, diethylene glycol, phenol, benzene, chloroform, or a combination or mixture thereof, such as a mixture of at least two of these. In the context of this specification, the term "dissolve" may be understood as referring to the process of incorporating a solute into a solvent to create a solution. The dissolving of the solute into the solvent may comprise agitation, mixing, stirring or blending or other measures to advance dissolution such as heating or adjusting pH of the solvent. The dissolving may happen in room temperature.

[0045] In an embodiment, providing a providing precursors dissolved in a solvent comprises:

[0046] i. providing a precursor of iridium ( Ir), a precursor of ruthenium (Ru), and a precursor of tungsten (W);

[0047] ii. providing a solvent;

[0048] iii. dissolving the provided precursors in the provided solvent to form precursors dissolved in a solvent.

[0049] In such a method, the precursors thereof are previously dissolved precursors. Multiple methods of dissolving precursors exist and are known to the person skilled in the art. Further, the method may comprisedissolving the precursors in a solvent. The dissolving of the precursors in the solvent may happen simultaneously, such as that each precursor is separately diluted in a solvent.

[0050] In an embodiment, a method of producing a catalyst, may comprise:

[0051] a. providing a precursor of iridium ( Ir), a precursor of ruthenium (Ru), and a precursor of tungsten (W);

[0052] b. providing a solvent;

[0053] c. dissolving the provided precursors in the provided solvent to form precursors dissolved in a solvent;

[0054] d. providing a coordinating polymer;

[0055] e. combining the coordinating polymer and the precursors dissolved in a solvent and stirring to form a mixture;

[0056] f. drying the mixture to from a dried mixture;

[0057] and

[0058] g. calcinating the dried mixture to form agglomerated iridium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 - 5 nm thus obtaining the catalyst.

[0059] In such a method, precursors and a solvent are provided. The provided precursors may be dissolved in the solvent to provide dissolved precursors. In an embodiment, dissolving the provided precursors in the provided solvent to form dissolved precursors may further comprise agitation, stirring, mixing, or heating the precursors and the solvent while dissolving.

[0060] In an embodiment, the solvent is water, ethanol, isopropanol, butanol, methanol, propanol, pentanol, ethylene glycol, diethylene glycol, phenol, acetone, benzene, chloroform, or a mixture of at least two of these. The solvent may be an absolute solvent or for example an aqueous solution or a mixture of at least twoof the listed solvents. In an embodiment, the solvent is water, ethanol, isopropanol, butanol, methanol, propanol, pentanol, ethylene glycol, diethylene glycol, phenol, acetone, benzene, or chloroform.

[0061] In the context of this specification, the term "coordinating polymer" may be understood as referring to a polymer containing at least one functional group capable of forming coordination bonds with metal ions, such as a functional group acting as an electron donor, with the metal ions. Such a coordinating polymer may comprise multiple functional groups able to act as electron donors. Such a coordinating polymer may comprise, for example, amines, imines, carboxylate groups, or phosphonate groups. The coordinating polymer may be, for example, polyethyleneimine, poly (acrylic acid), poly (methacrylic acid), or poly ( 4-vinylpyridine ), or a mixture of at least two of these.

[0062] In an embodiment the coordinating polymer may be polyethyleneimine, poly (acrylic acid), poly (methacrylic acid), or poly ( 4-vinylpyridine ), or a mixture of at least two of these. In an embodiment, the coordinating polymer may comprise primary amines, secondary amines and / or tertiary amines. In an embodiment the coordinating polymer may be polyethyleneimine, poly (acrylic acid), poly (methacrylic acid), or poly (4-vinylpyridine ). In an embodiment the coordinating polymer is provided at an amount that is in the range of 5-10 times the total mass of the precursor of iridium ( Ir), the precursor of ruthenium (Ru), and the precursor of tungsten (W) combined. This may be understood as the coordinating polymer being provided at 5-10 times to total mass of the Ir, Ru and W precursors combined, such as at a ratio of 5: 10 to 10: 1 relative to the total mass of the precursors.

[0063] When the coordinating polymer is combined with the dissolved precursors, the coordinating polymer may form coordination bonds with the iridium-ruthenium-tungsten metal ions, which may stabilize the metal ions. This may be understood as that the coordinating polymer may comprise multiple donor atoms (such as nitrogen, oxygen, or phosphorus) that each may donate electrons to metal ions, thus forming coordinating bonds, and thus simultaneously coordinating the metal ion from multiple functional groups on the polymer chain, creating stabilized iridium-ruthenium-tungsten metal ions. An added utility of the coordinating polymer is that the stabilization / coordination of the iridium-ruthenium-tungsten metal ions enables formation of agglomerated iridium-ruthenium-tungsten oxide nanoparticles with a mean diameter in the range of 0.5 - 4 nm, or 0. 6 - 3 nm, or 0.7 - 2 nm, or 0.8 - 1.9 nm, or 0. 9 - 1.8 nm. This may be understood as that coordinating the iridium-ruthenium-tungsten metal ions with the coordinating polymer may enable a smaller size, which provides a larger surface area, which may enhance catalytic activity, efficiency and stability. The enhanced catalytic activity may enable, for example, using reduced amounts of iridium.

[0064] When combining the coordinating polymer and the precursors dissolved in a solvent and stirring to form a mixture, the formed mixture may be homogenous. The stirring may be any form of stirring, agitation or blending known to the person skilled in the art. The stirring may last for 10 - 60 minutes, such as 30 minutes or until the mixture is nearly homogenous or homogenous. In an embodiment, the combining the coordinating polymer and the precursors dissolved in a solvent and stirring forms a homogenous mixture. A nearly homogenous or homogenous mixture may have the added benefit of having evenly mixed metals and polymer that results in effective coordination of the metal ions.

[0065] In the context of this specification, the term "drying" may be understood as referring to the process of removing solvent from a substance. Several methodsof drying mixtures exist, such as heating the mixture to evaporate the solvent, vacuum drying, or air drying. The method of drying may depend on the used solvent. The person skilled in the art may choose varied methods of drying to obtain a dried mixture.

[0066] The drying the mixture may comprise heating the mixture. When drying the mixture to from a dried mixture, the mixture may be dried at 60 - 100 °C for 90 -210 minutes, such as at 60 °C, or 70 °C, or 80 °C, or 90 °C, or 100 °C for about 1.5 hours, or about 2 hours, or about 3 hours, or about 3.5 hours. In an embodiment, drying of the mixture may comprise drying the mixture at 60 - 100 °C for 90 - 210 minutes. In an embodiment, drying of the mixture may comprise drying the mixture at 60 - 100 °C for 1.5 - 3.5 hours. In an embodiment, the solvent is ethanol and the drying of the mixture may comprise drying the mixture at 75 - 90 °C for 160 - 190 minutes.

[0067] In the context of this specification, the term "calcinating" may be understood as referring to the process of heating a substance to high temperatures, such as 300 - 900 °C, for a time period, such as 3 - 5 hours, in the absence or limited presence of air or an oxygen containing gas to effect thermal decomposition or phase transition.

[0068] The calcinating the dried mixture may comprise contacting the dried mixture with an atmosphere of an oxygen containing gas at a temperature of 300-900 °C for 3-5 hours. In an embodiment, calcinating the dried mixture may comprise contacting the dried mixture with an atmosphere of an oxygen containing gas at a temperature of 300-900 °C for 3-5 hours. In an embodiment, the calcinating the dried mixture ay comprise contacting the dried mixture with an atmosphere of an oxygen containing gas at a temperature of 350 - 400 °C for 3-7 hours or 350-370 °C for 4-6 hours. The calcinating the dried mixture may produce agglomerated metal oxidenanoparticles. The calcinating the dried mixture may result in the thermal decomposition of the coordinating polymer. The calcinating the dried mixture may produce agglomerated iridium-ruthenium-tungsten oxide nanoparticles. After calcinating the dried mixture, trace carbon and / or nitrogen may remain in the final product. The calcinating the dried mixture may produce a powder. In the context of this specification, the term "agglomerated" may be understood as referring to the clustering or gathering of particles into a mass or aggregate. In the context of this specification, the term "nanoparticles" may be understood as referring to particles with dimensions measured in nanometers, such as those with a mean diameter of below 5 nm. In the context of this specification, the term "agglomerated iridium-ruthenium-tungsten oxide nanoparticles" may be understood as agglomerates or aggregates or conglomerates or clusters of iridium-ruthenium-tungsten oxide nanoparticles. Agglomerated iridium-ruthenium-tungsten oxide nanoparticles may form as result of calcination of the dried mixture in the method as disclosed.

[0069] The size or mean diameter of the nanoparticles may be measured by imaging using a transmission electron microscope (TEM). The TEM might be a Jeol JEM-1400 TEM JEOL field emission gun microscope, or other suitable TEM. First, TEM images are captures, then individual nanoparticles are identified in the TEM images comprising the use of imaging processing software. Then the diameter of each nanoparticle is measured. A dataset is created from the measured diameters of a sufficient number of nanoparticles to ensure statistical significance. The mean diameter may be calculated as the average of the measured diameters. A standard deviation may be calculated for the diameter. As such, the mean diameter may be understood as the average of the diameters measured from a representative subset of the nanoparticles. In a non-limiting example, while the measured mean diameterin the sample may be in the range of 1 - 5 nm, the nanoparticles may vary in size such as between 1 - 15 nm, 1 - 20 nm, or 1 - 25 nm, or 1 - 30 nm, such that despite the variation in size, the mean diameter is in the range of 1 - 5 nm.

[0070] The agglomerated iridium-ruthenium-tungsten oxide nanoparticles may have a mean diameter between 0 - 5 nm, such as a mean diameter that is greater than 1 nm, or 0.5 nm, or 0. 6 nm, or 0.7 nm, or 0.8 nm, or 0.9 nm and less than or equal to 4 nm, or 3 nm, or 2.5 nm, or 2 nm, or 1.9 nm, or 1.8 nm, or 1.7 nm, or 1. 6 nm. In an embodiment, the agglomerated iridium-ruthenium-tung-sten oxide nanoparticles have a mean diameter in the range of 0.5 - 4 nm, or 0. 6 - 3 nm, or 0.7 - 2 nm, or 0.8 - 1.9 nm, or 0.9 - 1.8 nm. In an embodiment, the agglomerated iridium-ruthenium-tungsten oxide nanoparticles have a mean diameter in the range of 1. 6 - 5 nm, or 1.5 - 4 nm, or 1.4 - 3 nm, or 1.3 - 2 nm, or 1.2 -1.9 nm, or 1.1 - 1.8 nm. The added utility of a small size of the agglomerated iridium-ruthenium-tungsten oxide nanoparticles, such as the mean diameter below or equal to 5 nm, may be increased surface area. The added utility of a very small size of the agglomerated iridium-ruthenium-tungsten oxide nanoparticles, such as the mean diameter below or equal to 2 nm, may be a further increased surface area. The increased surface area may directly translate to an increase electrochemical surface area and thus enable higher catalytic activity. The increased surface area may further affect other catalytic features, such as catalytic efficiency such that a lower energy input is needed to activate the catalyst, or catalytic stability such that the catalyst does not degrade, or reaction kinetics such that the catalyst has a small transfer resistance.

[0071] The agglomerated iridium-ruthenium-tungsten oxide nanoparticles may have an electrochemical surface area (ECSA) in the range of 250 - 700 as measured bycyclic voltammetry. Specifically, measuring ECSA may be done using the double-layer capacitance (Cdi) values, extracted from cyclic voltammetry measurements. The Cdi may be calculated from the slope of the linear relationship between the average current density (Δj) and the scan rate. In an embodiment, the agglomerated irid-ium-ruthenium-tungsten oxide nanoparticles may have an electrochemical surface area (ECSA) in the range of 250 - 600 as measured by calculating the double-layer capacitance (Cdi) values from cyclic voltammetry measurements. In an embodiment, the agglomerated iridium-ru-thenium-tungsten oxide nanoparticles may have an electrochemical surface area (ECSA) in the range of 250 -700, or 300 - 650, or 400 - 625, or 500 - 600 as measured by calculating the double-layer capacitance (Cdi) values from cyclic voltammetry measurements.

[0072] The agglomerated iridium-ruthenium-tungsten oxide nanoparticles may be the catalyst. When collecting the catalyst, it may be beneficial to perform washing steps, such as washing the catalyst with an aqueous solution 1 - 5 times, wherein the aqueous solution is water or a solvent mixed with water. In an embodiment, the method further comprises washing the catalyst with an aqueous solution, wherein the aqueous solution is water or a solvent mixed with water. In an embodiment, the method further comprises washing the catalyst 1 - 5 times with an aqueous solution, wherein the aqueous solution is water or a solvent mixed with water. The washing may remove carbon and / or nitrogen and / or other ions released in the calcination and result in a pure catalyst that is more catalytically active. The solvent mixed with water may be 1: 1 (v / v) or 2: 1 (v / v) or 1: 2 (v / v) water and solvent.

[0073] When collected, the catalyst may be in the form of a powder. The catalyst may be used in the form of a powder. The catalyst may be further processed into other usable forms, such as inks to make thin films, thinfilms, or for example pressed into pellets. In an embodiment, the method further comprises applying a film of the catalyst on a conductive substrate or applying the catalyst as a layer in a membrane electrode assembly.

[0074] In an embodiment, the catalyst comprising agglomerated iridium- ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 - 5 nm is produced by the method of producing a catalyst as disclosed. The produced catalyst may have a reduced overpotential compared to commercially available catalysts. The reduced overpotential may enable improved energy efficiency in electrochemical processes compared to commercially available catalysts.

[0075] The present disclosure further relates to a catalyst comprising agglomerated iridium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 - 5 nm.

[0076] Such a catalyst may have a small particle size and thus a large electrochemical surface area. As a result, the catalyst may have increased catalytic activity and reduced overpotential compared to commercially available catalysts. The catalyst may efficient and provide faster reaction rates. The catalyst may be stable even in acidic operating conditions. The catalyst may have a reduced overpotential, making the catalyst more energy efficient. The catalyst may comprise of a reduced amount of iridium compared to commercially available catalysts, which saves limited natural resources and costs.

[0077] In such a catalyst the agglomerated iridium-ruthenium-tungsten oxide nanoparticles have a mean diameter greater than 0 nm and less than or equal to 4 nm, or 3 nm, or 2.5 nm, or 2 nm, or 1.9 nm, or 1.8 nm. In an embodiment, the agglomerated iridium-ruthenium-tung-sten oxide nanoparticles have a mean diameter 0.5 - 4 nm, or 0. 6 - 3 nm, or 0.7 - 2 nm, or 0.8 - 1.9 nm, or0.9 - 1.8 nm. In an embodiment, the agglomerated irid-ium-ruthenium-tungsten oxide nanoparticles have a mean diameter in the range of 1. 6 - 5 nm, or 1.5 - 4 nm, or 1.4 - 3 nm, or 1.3 - 2 nm, or 1.2 - 1.9 nm, or 1.1 -1.8 nm. As a result of the small size of the agglomerated iridium-ruthenium-tungsten oxide nanoparticles in the catalyst, the total electrochemical surface area of the catalyst may be increased. The increased electrochemical surface area may affect features of the catalyst, such as catalytic efficiency such that a lower energy input is needed to activate the catalyst, or catalytic stability such that the catalyst does not degrade, or reaction kinetics such that the catalyst has a small transfer resistance. The catalyst may have reduced over-potential compared to commercially available catalysts, which enables improved energy efficiency. As a result of the catalytic improvements the catalyst may comprise less iridium that commercially available catalysts.

[0078] In an embodiment, the agglomerated iridium-ruthenium-tungsten oxide nanoparticles may have an electrochemical surface area (ECSA) in the range of 250 -600 as measured by calculating the double-layer capacitance (Cdi) values from cyclic voltammetry measurements. In an embodiment, the agglomerated iridium-ruthenium-tungsten oxide nanoparticles may have an electrochemical surface area (ECSA) in the range of 250 -700, or 300 - 650, or 400 - 625, or 500 - 600 as measured by calculating the double-layer capacitance (Cdi) values from cyclic voltammetry measurements.

[0079] In an embodiment, the catalyst has a general formula of IrxRuyWzOn, where x is 0 < x < 1.5, y is 0 < y ≤ 1, and z is 0 < z ≤ 1.5.

[0080] In an embodiment, in the general formula of IrxRuyWzOn, x may be in the range of 0.40 - 1.5. This may be understood as the molar ratio of Ir to Ru and W. In an embodiment, in the general formula of IrxRuyWzOn, x is in the range of 0.40 - 1.5, or 0.50 - 1, or 0.75 - 1.In an embodiment, in the general formula of IrxRuyWzOn, x may be 1. The n may be understood as the variable amount of oxygen present in the iridium-ruthenium-tung-sten oxide nanoparticles. The person skilled in the art understands that the amount of oxygen present in the catalyst varies based on the molar ratios of metal oxides. In an embodiment, in the general formula of IrxRuyWzOn, n may be 0 < n < 4.5. In an embodiment, in the general formula of IrxRuyWzOn, n may be in the range of 1 - 4.5, or 2 - 4, or 3 - 4, such as 2.5, or 3.1, or 3.5, or 4.

[0081] In an embodiment, in the general formula of IrxRuyWzOn, y may be in the range of 0.10 - 1. In an embodiment, in the general formula of IrxRuyWzOn, y may be in the range of 0.10 - 1, or 0.10 - 0. 60, or 0.20 -0.50, or 0.20 - 0.50, or 0.20 - 0.40. In an embodiment, in the general formula of IrxRuyWzOn, y may be 0.3.

[0082] In an embodiment, in the Irx: Ruy: Wzmolar ratio, z may be in the range of 0.05 - 1.5. In an embodiment, in the general formula of IrxRuyWzOn, z may be in the range of 0.05 - 1.5, or 0.05 - 1, or 0.10 - 1. In an embodiment, in the general formula of IrxRuyWzOn, z may be 0.10, 0.50, or 1.

[0083] The catalyst may be in the form of a powder. The catalyst may be used in the form of a powder. The catalyst may further be in the form of film, a layer, or a composite material. The catalyst may also be used in the form of film, a layer, or a composite material. In an embodiment, the catalyst may be in the form of a powder, a film, a layer, a composite material.

[0084] The present disclosure further relates to an electrode. The electrode comprises:

[0085] a conductive substrate; and

[0086] a catalytic layer deposited on the conductive substrate comprising the catalyst as disclosed.

[0087] In an embodiment, the electrode may be a part of a membrane electrode assembly. In such a membraneelectrode assembly, the membrane electrode assembly comprises: a catalytic layer deposited on the conductive substrate comprising the catalyst as disclosed. The conductive substrate may be an ion conductive substrate, such as an electrolyte membrane. The conductive substrate may be an electronically conductive substrate, such as a porous transport layer. In such a membrane electrode assembly, the catalyst as disclosed may act as the anode catalyst.

[0088] Further, a use is disclosed. The use comprises using the catalyst as disclosed or the electrode thereof for water electrolysis or as a catalyst for the oxygen evolution reaction (OER). In an embodiment, the catalyst as disclosed is used for water electrolysis. In an embodiment, the catalyst as disclosed is used in the oxygen evolution reaction (OER).

[0089] EXAMPLE

[0090] Figure 1 shows a schematic representation of the method of producing a catalyst. Precursors of Ir, Ru, and W previously dissolved in a solvent are mixed with a coordinating polymer, followed by stirring to ensure homogeneity. In an example embodiment, the precursors are dissolved in absolute ethanol and the coordinating polymer is polyethylenimine. In an example embodiment the mixture is stirred for 30 minutes to provide a homogenous mixture. The resulting homogenous mixture is dried to remove the solvent through evaporation. In an example embodiment, the drying comprises a temperature of 90 °C for 180 minutes. The resulting dried mixture is then calcined in a furnace at high temperatures to produce the catalyst, as shown in the rightmost image. In an example embodiment, the catalyst is in a powder form and further comprises trace nitrogen and carbon. In an example embodiment, the catalyst is washed with an aqueous solution of ethanol three times, such as to remove the trace elements.Example 1 - Ternary oxide catalysts

[0091] A precursor of Ir was provided in the form of IrCl3hydrate. A precursor of Ru was provided in the form of RUCI3 hydrate. A precursor of W was provided in the form of WC16.

[0092] The precursors were provided in three different molar ratios of Ir, Ru and W:

[0093] Sample 1: IriRuo.3Wi

[0094] Sample 2: IriRuo.3Wo.5

[0095] Sample 3: IriRuo.3Wo.i

[0096] The precursors were then dissolved in absolute ethanol. After the dissolution, the coordinating polymer poly-ethylenimine (PEI ) is added to stabilize the metal ions. The coordinating polymer was provided in an amount of 10 times ( 1000 g) the total mass of the of the precursors ( 100 g). The precursors dissolved in ethanol and PEI were then stirred to generate a viscous and homogenous mixture. The mixture was then dried at 90 °C for 180 minutes, followed by a calcination process at 400 °C for 4 hours. In the final step, the resultant black powder was washed four times with ethanol: water ( 1: 1 v / v) solution and collected by centrifugation.

[0097] Final catalyst samples are denoted as: Sample 1: IriRuo.3WiOx

[0098] Sample 2: IriRuo.3Wo.5Ox

[0099] Sample 3: IriRu0.3W0.iOx

[0100] Figure 2. Transmission Electron Microscopy (TEM) images of experimental catalysts and comparative samples, (a-e) TEM micrographs showing the morphology of the samples at different regions with a uniform scale bar of 100 nm. Size analysis of Sample 1 (a) mean diameter 2.8 ± 1.2 nm and Sample 2 (b) mean diameter 1.8 ± 0. 3 nm.

[0101] Samples 1-3 were then imaged using a transmission electron microscope (TEM) (Fig. 2 ). TEM imageswere obtained on a Jeol JEM-1400 TEM JEOL field emission gun microscope, operating at an accelerating voltage of 120 kV. TEM samples were prepared by dispersing the nanoparticle suspension in ethanol and drop casting onto carbon-coated copper grids. The TEM images revelated that Sample 2 was composed of agglomerated nanoparticles with a mean diameter of 1.85 ± 0.3 nm (Fig. 2b, Table 1 ). Comparative samples IriRuo.30xand IrOxwere also imaged (Fig. 2, d-e). As seen in the TEM images, Samples 1 and 2 show a small and evenly dispersed material.

[0102] Electrochemical characterization

[0103] Figure 3: Electrochemical characterisation, a) linear sweep voltammograms of Samples 1-3 and two comparative samples ( IriRuo.30xand IrOx) pointer shape denotes the sample, b) overpotential measured at 10 mA cur2(orange, horizontal lines) and 50 mA cur2(blue, vertical lines) of the experimental and comparative samples, c) Tafel plot of the experimental and comparative samples, log of current density (x-axis) to overpotential in volts (y-axis), d) Nyquist plot ( impedance) at 1.5 V, e) electrochemical surface area (ECSA) for Samples 1-3 and two comparative samples ( IriRuo.30xand IrOx), f ) a stability plot measuring the potential vs. reversible hydrogen electrode (RHE) in volts (y-axis) over time (x-axis) of Sample 2 ( IriRuo.sWo.s).

[0104] Electrochemical measurements were performed using an Autolab PGSTAT128N potentiostat in a standard three-electrode cell configuration. A 4.0 mm diameter L-shaped glassy carbon electrode (geometric area: 0.1257 cm2) served as the working electrode, a graphite rod as the counter electrode, and a reversible hydrogen electrode (RHE) as the reference electrode. Catalyst inks were prepared by dispersing 5. 0 mg of catalyst in 1 ml of an ethanol: water: Nation® 5% (7: 2. 9: 0.1 v / v / v) solution and sonicating for 60 min to obtain a homogeneous mixture. Subsequently, 3.15 µL of the ink was drop-casted onto the glassy carbon electrode and dried at 50 °C, resulting in a catalyst loading of 250 μg cm-2. The catalytic activity of the samples was analyzed by linear sweep voltammetry (Fig. 3) together with comparative samples. Sample 2 had the highest current density at the lowest applied potential (Fig. 3). Tafel slope (mV dec-1) comparing overpotential to the logarithm of the current density (log j (mA cm-2) ) is shown in Fig. 3a. Over-potential measurement at current density of 10 mA cm-2(Fig. 3b) showed that Sample 2 had the lowest overpotential of all the studied samples. Sample 1 also showed a lower overpotential than the comparative samples.

[0105] Electrochemical impedance spectroscopy (EIS) measured at 1.5 V from 100 kHz to 10 Hz and amplitude of 10 mV demonstrates that Sample 2 has the smallest charge transfer resistance (approx. 7.5 Q) (Fig. 3d). Also, the electrochemical surface area (ECSA) was determined using the double-layer capacitance (Cdi) values, extracted from cyclic voltammetry measurements (Fig. 3e). Specifically, Cdi was calculated from the slope of the linear relationship between the average current density (Δj) and the scan rate (Fig. 3e). Sample 2 had the largest surface area ( 542 cm2). All electrochemical characterisation measurements were carried out in 0.5 mol L-1H2SO4solution.

[0106] Table 1. Size distribution and electrochemical characterization

[0107] S amp 1 e Mean diameter (nm) ECSA H (mV) Tafel cm2at 10 (mV mA dec-1) cm-2

[0108] S amp 1 e 1 2.7 ± 2.3 277 284 52. 3 S amp 1 e 2 1.8 ± 0.3 542 240 51. 5

[0109]

[0110] S amp 1 e 3 2.8 ± 1.2 327 270 54. 6The results show that Sample 2 had the smallest size and thus the largest surface area provide enhanced catalytic abilities, demonstrated by the electrochemical characterization. Sample 2 was the most efficient among the synthesized samples and exhibited the smallest overpotential, the smallest charge transfer resistance, and is especially suited for OER.

[0111] Figure 4. Comparative analysis of the literature reported values (Tafel (mV dec-1), y-axis) and over-potential (mV) at 10 mA cm-2in acidic medium (x-axis) of known Ir-based catalyst comparative samples. Sample 2 ( Ir1Ru0.3W0.5) is shown as a green star.

[0112] Sample 2 is among the best materials for OER, showing a reduced overpotential and charge transfer resistance compared to the known Ir-based catalysts (Fig.

[0113] 4 ). Further, the Sample 2 overpotential increases at a slower rate as the current density increases, showing that the catalyst is highly efficient.

[0114] Therefore, as disclosed and exemplified above, the method of producing a catalyst may be easily scalable and cost effective. The method may enable the production of catalysts that have a low overpotential. The method may produce a catalyst that may be efficient and stable even in acidic conditions. The method may enable the production of a catalyst comprising of nanoscale agglomerated iridium-ruthenium-tungsten oxide nanoparticles that have a large electrochemical surface area. The method further may enable that less iridium is used in the production of the catalyst, sparing limited and rare natural resources.

[0115] The catalyst comprises of agglomerated iridium-ruthenium-tungsten oxide nanoparticles that have a small size and a large surface area. The catalyst may have a low over potential and require less activation energy to catalyse the reaction. The catalyst may be efficient and stable. The catalyst may comprise lessiridium and as such be more sustainable than commer-cially available options.

[0116] Example 2 - Quaternary metal oxide catalysts

[0117] The precursors were provided in four different molar ratios of Ru, Ir, W, and Ta:

[0118] Quaternary sample 1: Ru0.6Ir0.2W0.1Ta0.1Quaternary sample 2: Ru0.5Ir0.2W0.2Ta0.1Quaternary sample 3: Ru0.6Ir0.1W0.2Ta0.1Quaternary sample 4: Ru0.5Ir0.1W0.3Ta0.1

[0119] Ruthenium (Ru) is now the primary component. The concentrations of Iridium ( Ir) and Tungsten (W) were decreased to optimize cost and performance. Tantalum (Ta) was introduced as a stabilizing element to enhance catalytic stability.

[0120] Tantalum precursor used was TaCls.

[0121] The method of production follows the method as disclosed in the first example, however, the temperature of the calcination step was refined to a range of 350-370 °C and duration of 6 hours.

[0122] Table 2. Experimental samples

[0123] Experimental Overpotential Tafel

[0124] ECSA

[0125] sample at 10 mA cm-2mV dec-1

[0126] Ru0.6Ir0.2W0.1Ta0.1256 60.3 461

[0127] Ru0.5Ir0.2W0.2Ta0.1245 60.4 610

[0128] Ru0.6Ir0.1W0.2Ta0.1230 47.3 843

[0129] Ru0.5Ir0.1W0.3Ta0.1219 49.5 956Morphological analysis showed that the quaternary experimental samples were morphologically similar to ternary experimental samples, exhibiting small particles (2-3 nm) and occasional larger rod-shaped structures (Figure 5).

[0130] Figure 5. The TEM image for Ru0.6Ir0.2W0.1Ta0.1illustrates the distribution of particles small and occasional larger rod-shaped structures.

[0131] The electrochemical stability of Ru0.6Ir0.2W0.1Ta0.1was evaluated in a single-cell PEM water electrolyzer using a Nafion 115 membrane and shown in Figure 6.

[0132] Figure 6. The electrochemical stability of Ru0.6Ir0.2W0.1Ta0.1was measured. Operating at a constant current density of 1 A cm-2 for 300 h, the chronopoten-tiometric profile (shown below) indicated a minimal deactivation rate of only 0.04 mV h-1, demonstrating the robust durability of the quaternary catalyst.

[0133] It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above, instead they may vary within the scope of the claims.

Claims

CLAIMS1. A method of producing a catalyst, comprising:a. providing precursors dissolved in a solvent, wherein the precursors are a precursor of iridium (Ir), a precursor of ruthenium (Ru), and a precursor of tungsten (W);b. providing a coordinating polymer;c. combining the coordinating polymer and the precursors dissolved in a solvent and stirring to form a mixture;d. drying the mixture to from a dried mixture;ande. calcinating the dried mixture to form agglomerated iridium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 - 5 nm thus obtaining the catalyst.

2. The method of claim 1, wherein the precursors are provided at a Irx: Ruy: Wzmolar ratio, where x is 0 < x < 1.5, y is 0 < y ≤ 1, and z is 0 < z ≤ 1.5.

3. The method of claim 2, wherein in the Irx: Ruy: Wzmolar ratio, x is in the range of 0.40 – 1.5, or 0.50 – 1.25, or 0.75 – 1.

4. The method of any one of claim 2 or 3, wherein in the Irx: Ruy: Wzmolar ratio, y is in the range of 0.10 - 1, or 0.10 - 0.70, or 0.20 - 0. 6, or 0.20 -0.50, or 0.20 - 0.40.

5. The method of any one of claims 2-4, wherein in the Irx: Ruy: Wzmolar ratio, z is in the range of 0.05 - 1.5, or 0.05 - 1, or 0.10 - 1.

6. The method of any one of the claims 2-5, wherein the Irx: Ruy: Wzmolar ratio x is in the range if 0.4-1. 5, y is in the range of 0.1 - 1, and z is 0.50 or7. The method of any of the preceding claims, wherein providing precursors dissolved in a solvent comprises:i. providing a precursor of iridium ( Ir), a precursor of ruthenium (Ru), and a precursor of tungsten (W);ii. providing a solvent; andiii. dissolving the provided precursors in the provided solvent to form precursors dissolved in a solvent.

8. The method of any one of the preceding claims, wherein the solvent is ethanol, isopropanol, butanol, methanol, propanol, pentanol, ethylene glycol, diethylene glycol, phenol, benzene, chloroform, or a mixture of at least two of these.

9. The method of any one of the preceding claims, wherein the coordinating polymer is polyethyleneimine, poly (acrylic acid), poly (methacrylic acid), or poly ( 4-vinylpyridine ), or a mixture of at least two of these.

10. The method of any one of the preceding claims, wherein drying of the mixture comprises drying the mixture at 60 - 100 °C for 90 - 210 minutes.

11. The method of any one of the preceding claims, wherein calcinating the dried mixture comprises contacting the dried mixture with an atmosphere of an oxygen containing gas at a temperature of 300-900 °C for 3-5 hours.

12. The method of any one of the preceding claims, wherein the agglomerated iridium-ruthenium-tungsten oxide nanoparticles have a mean diameter in the range of 0.5 - 4 nm, or 0. 6 - 3 nm, or 0.7 - 2 nm, or 0.8 - 1.9 nm, or 0.9 - 1.8 nm.

13. The method of any one of the preceding claims, wherein the agglomerated iridium-ruthenium-tungsten oxide nanoparticles have an electrochemical surface area (ECSA) in the range of 250 - 600 as measuredby calculating the double-layer capacitance (Cdi) values from cyclic voltammetry measurements.

14. The method of any one of the preceding claims, wherein the method further comprises washing the catalyst with an aqueous solution, wherein the aqueous solution is water or a solvent mixed with water.

15. The method of any one of the preceding claims, wherein the coordinating polymer is provided at an amount that is in the range of 5-10 times the total mass of the precursor of iridium ( Ir), the precursor of ruthenium (Ru), and the precursor of tungsten (W) combined.

16. A catalyst comprising agglomerated irid-ium-ruthenium-tungsten oxide nanoparticles having a mean diameter in the range of 0.5 nm - 5 nm.

17. The catalyst of claim 16, wherein the agglomerated iridium- ruthenium-tungsten oxide nanoparticles have a mean diameter in the range of 0.5 - 4 nm, or 0. 6 - 3 nm, or 0.7 - 2 nm, or 0.8 - 1.9 nm, or 0.9 -1.8 nm.

18. The catalyst of claims 16 or 17, wherein the agglomerated iridium-ruthenium-tungsten oxide nanoparticles have an electrochemical surface area (ECSA) in the range of 250 - 600 as measured by calculating the double-layer capacitance (Cdi) values from cyclic voltammetry measurements.

19. The catalyst of any of claims 16-18, wherein the catalyst has a general formula of IrxRuyWzOn, where x is 0 < x < 1.5, y is 0 < y ≤ 1, and z is 0 < z ≤ 1.5.

20. The catalyst of claim 19, wherein in the general formula of IrxRuyWzOn, x is in the range of 0.40 - 1.5, or 0.50 - 1.25, or 0.75 - 1.

21. The catalyst of claims 19 or 20, wherein in the general formula of IrxRuyWzOn, y is in the range of 0.10 - 1, or 0.10 - 0.70, or 0.20 - 0. 6, or 0.20 -0.50, or 0.20 - 0.40.

22. The catalyst of any of claims 19-21, wherein in the general formula of IrxRuyWzOn, z is in the range of 0.05 - 1.5, or 0.05 - 1, or 0.10 - 1.

23. The catalyst of any of claims 19-22, wherein the general formula of IrxRuyWzOn, x is in the range if 0.4-1. 5, y is in the range of 0.1 - 1, and z is 0.50 or 1.

24. An electrode comprising:a conductive substrate; anda catalytic layer deposited on the conductive substrate comprising the catalyst produced by the method of any one of claims 1- 15 or the catalyst of any one of claims 16- 23.

25. Use of the catalyst produced by the method of any one of claims 1-15, or the catalyst of any one of claims 16-23, or the electrode of claim 24 for water electrolysis.

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