EP4713135A1 - Multimetallic alloy electrocatalysts for acidic oxygen evolution reaction - Google Patents

Abstract

Disclosed herein are a catalyst including a multicomponent alloy having a single-phase structure. The multicomponent alloy includes iridium, ruthenium, or a combination thereof in combination with at least four metals, wherein the at least four metals does not include a platinum group metal. Methods of preparing the catalyst are also provided herein.

Description

MULTIMETALLIC ALLOY ELECTROCATALYSTS FOR ACIDIC OXYGEN EVOLUTION REACTION Inventors Peidong Yang Arifin Luthfi Maulana Pengcheng Chen Carlos Lizandara Pueyo Fabian Seeler Rui Zhang Stefan Kotrel Britta Mayerhoefer Sandip De Maximilian Samuel Andreas Springer

Attorney Docket No.39425-352 MULTIMETALLIC ALLOY ELECTROCATALYSTS FOR ACIDIC OXYGEN EVOLUTION REACTION CROSS REFERENCE TO RELATED APPLICATION(S) [0001] The present application claims priority to U.S. Provisional Patent Application No. 63/466,850 filed on May 16, 2023, the entire contents of which are incorporated herein. FIELD OF THE INVENTION [0002] Disclosed herein are a catalyst including a multicomponent alloy, wherein the multicomponent alloy includes iridium (Ir), ruthenium (Ru), or a combination thereof and at least four metals, wherein the multicomponent alloy has a single-phase structure. The catalyst described herein may also be used in a method for performing an oxygen evolution reaction. BACKGROUND [0003] Electrochemical water splitting in acidic media using renewable resources is an important pathway for the decarbonization of large-scale hydrogen (H2) production. As a half- cell reaction of the overall reaction, oxygen evolution reaction (OER) at the anode may impede the wide application of efficient proton-exchange membrane water electrolyzers. This is believed to be because of its sluggish kinetics and harsh reaction environment. To date, IrO₂ and RuO2 catalysts are being used in an acidic OER owing to their high activity. However even with these scarce and costly noble-metal-based catalysts, their stability to perform OER in a long run is still insufficient due to the dissolution of Ir and Ru in the presence of acidic electrolyte and highly oxidative biased condition. [0004] Therefore, to attain a more efficient water splitting process, there is a need to develop a catalyst that has both improved activity and enhanced stability. SUMMARY [0005] Disclosed herein in an embodiment is a catalyst. In an embodiment, the catalyst includes a multicomponent alloy comprising iridium (Ir), ruthenium (Ru), or a combination thereof and at least four metals, wherein the multicomponent alloy has a single-phase structure. [0006] In some embodiments, the catalyst may have a core and a shell. In some embodiments, the core may include the multicomponent alloy. In some embodiments, the shell may be Ir-rich. In other embodiments, the shell may be Ru-rich. In yet another embodiment, Attorney Docket No.39425-352 the shell may be Ir and Ru rich. In some embodiments, the shell may have a thickness of about 0.1 nm to about 20 nm. [0007] In some embodiments, the catalyst may further include at least four metals. The at least four metals may be selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). In some embodiments, the at least four metals does not include a platinum group metal (pgm). [0008] In some embodiments, the catalyst may further include a support. [0009] In some embodiments, the catalyst may be stable for at least about 12 hours. In some embodiments, the catalyst may have a particle size distribution between about 2 nm to about 200 nm. [00010] In some embodiments, the multicomponent alloy may include Ir, then the catalyst may have an atomic ratio between Ir and the at least four metals being equimolar. In some embodiments of the catalyst, Ir and the at least four metals may be included to form a single alloy phase. In other embodiments of the catalyst, Ru and the at least four metals may be included to form single alloy phase. In yet another embodiment of the catalyst, Ru and at least five metals, or at least six metals may be included to form a single alloy phase. [00011] In some embodiments, the multicomponent alloy may include Ir and the at least for metals may be selected from the group consisting of Fe, Co, Ni and Cu, and a ratio of Ir:Fe:Co:Ni:Cu is about 24:16:25:19:15. [00012] In another embodiment of the present disclosure, a method of preparing a catalyst is provided. The method may include performing a microwave-assisted shock synthesis or a colloidal synthesis. [00013] In another embodiment, a method of performing oxygen evolution reaction may including using a catalyst of the present disclosure.

Attorney Docket No.39425-352 BRIEF DESCRIPTION OF THE DRAWINGS [00014] FIG.1A depicts the low resolution HAADF-STEM image of IrFeCoNiCu-HEA dispersed on carbon paper substrate (scale bar, 500 nm) according to an embodiment of the present disclosure; [00015] FIG.1B depicts the high resolution HAADF-STEM image (scale bar, 2 nm) and inset of the corresponding FFT showing a typical FCC structure; [00016] FIG.1C depicts the XRD pattern of IrFeCoNiCu-HEA showing the single-phase FCC structure; [00017] FIG. 1D depicts the homogeneous elemental distribution of IrFeCoNiCu-HEA through individual and overlay STEM-EDS map (scale bar, 50 nm); [00018] FIG. 2 depicts the low-magnification TEM image (scale bar, 200 nm) showing monodispersed IrFeCoNiCu-HEA on carbon paper substrate with varied particle size and histogram of the nanoparticle size distribution; [00019] FIG.3 depicts EDS elemental spectra analyzed from selected region of interest of an IrFeCoNiCu-HEA nanoparticle; [00020] FIG. 4 depicts aberration-corrected HAADF-STEM images of the IrFeCoNiCu- HEA nanoparticle showing random distribution of elements (scale bar, 2 nm); [00021] FIG. 5 depicts aberration-corrected HAADF-STEM images of IrRuFeCoNi-HEA nanoparticles showing random distribution of elements; [00022] FIG.6 depicts the powder X-ray diffraction pattern of IrRuFeCoNi-HEA; [00023] FIG. 7 depicts the STEM-EDS elemental maps of IrRuFeCoNi-HEA showing homogeneous elemental distribution (scale bar, 50 nm); [00024] FIG. 8 depicts EDS elemental spectra analyzed from a selected region of interest of an IrRuFeCoNi-HEA nanoparticle; [00025] FIG. 9A depicts the X-ray diffractogram of Ru_x(Ir,Fe,Co,Ni)_1−x with various x compositions, showing the multi-phase structures at near-equimolar Ru concentrations. [00026] FIG. 9B depicts the HR-STEM image and the corresponding FFT analysis of the major fcc phase in Ru0.20(Ir,Fe,Co,Ni)0.80. [00027] FIG. 9C depicts the HR-STEM image and the corresponding FFT analysis of the minor hcp phase in Ru0.20(Ir,Fe,Co,Ni)0.80. [00028] FIG. 9D depicts a low magnification HAADF-STEM image, showing the dispersion of nanoparticles on a carbon paper substrate. Attorney Docket No.39425-352 [00029] FIG. 9E depicts the HAADF-STEM image and STEM-EDS maps show the homogeneous distribution of all elements. [00030] FIG. 10 depicts the Rietveld refinement analysis of Ru0.08(Ir,Fe,Co,Ni)0.92, Ru_0.12(Ir,Fe,Co,Ni)_0.88, Ru_0.16(Ir,Fe,Co,Ni)_0.84, and Ru_0.20(Ir,Fe,Co,Ni)_0.80. [00031] FIG. 11 depicts the aberration-corrected HAADF-STEM image and the corresponding FFT analysis of as-prepared Ru_0.20(Ir,Fe,Co,Ni)_0.80 confirm the presence of the fcc and hcp phases and as-prepared IrFeCoNi with only fcc phase. [00032] FIG. 12 depicts the HR-TEM images and their corresponding FFT analysis of as-prepared Ru0.20(Ir,Fe,Co,Ni)0.80, confirming the presence of the fcc and hcp phases. [00033] FIG. 13 depicts the histogram of the nanoparticle’s size distribution in Ru0.20(Ir,Fe,Co,Ni)0.80 measured from about 500 particles. The size distribution of other Ru_x(Ir,Fe,Co,Ni)_1−x samples is similar. [00034] FIG. 14 depicts the HAADF-STEM image and STEM-EDS elemental maps, showing the uniform elemental distribution in IrFeCoNi, Ru_0.08(Ir,Fe,Co,Ni)_0.92, Ru0.12(Ir,Fe,Co,Ni)0.88, Ru0.16(Ir,Fe,Co,Ni)0.84 and Ru0.20(Ir,Fe,Co,Ni)0.80. [00035] FIG. 15 depicts the STEM-EDS spectra analyzed from IrFeCoNi, Ru0.08(Ir,Fe,Co,Ni)0.92, Ru0.12(Ir,Fe,Co,Ni)0.88, Ru0.16(Ir,Fe,Co,Ni)0.84, and Ru0.20(Ir,Fe,Co,Ni)0.80. The TEM samples were drop-casted on Au TEM grids with ultrathin carbon film. The Au signals are from the TEM grid. The Cu signals are from the washers and clips used in the TEM holder.  [00036] FIG.16A illustrates OER polarization curve in 0.1 M HClO₄ electrolyte; [00037] FIG.16B depicts the corresponding Tafel slope of FIG.16A; [00038] FIG.16C depicts the Ir-mass-based activity measured at different overpotentials; [00039] FIG. 16D depicts chronopotentiometry measurement at a constant current density of 10 mA cm^-2; [00040] FIG. 17 depicts powder XRD pattern of IrFe, IrCo, and IrNi with similar Ir-mass loading of about 288 µg cm^-2 _geo; [00041] FIG. 18A depicts the OER polarization curves of representative Ru_x(Ir,Fe,Co,Ni)_1−x variations with as prepared monometallic Ir and Ru benchmark catalysts in 0.1 M HClO4 electrolyte (scan rate: 5 mV s⁻¹). [00042] FIG. 18B depicts the corresponding Tafel slopes showing improved OER kinetics in Ru0.20(Ir,Fe,Co,Ni)0.80. Attorney Docket No.39425-352 [00043] FIG. 18C depicts the OER activity normalized to the mass of noble metals (Ir and Ru) measured at different overpotentials. [00044] FIG. 18D depicts the chronopotentiometry curves showing the stability of representative Ru_x(Ir,Fe,Co,Ni)_1−x variations over 24 hours of measurement at a constant current density of 10 mA cm⁻². The inset shows the poor stability of monometallic Ir and Ru benchmark catalysts. [00045] FIG.19 depicts the powder XRD pattern of monometallic Ru and Ir synthesized via microwave-assisted shock synthesis on carbon paper substrates. [00046] FIG. 20 depicts the OER polarization curves of all Rux(Ir,Fe,Co,Ni)1−x variations in 0.1 M HClO₄ electrolyte (scan rate: 5 mV s⁻¹). [00047] FIG. 21 depicts the OER polarization curves of all Rux(Ir,Fe,Co,Ni)1−x variations normalized to the mass loading of all noble metals (Ru and/or Ir) in 0.1 M HClO₄ electrolyte (scan rate: 5 mV s⁻¹). The Ir mass loading of all catalysts is about 288 μg cm⁻²geo, while the equimolar (Ru_0.20(Ir,Fe,Co,Ni)_0.80) Ru mass loading is about 152 μg cm⁻² _geo. [00048] FIG. 22 depicts the ECSA estimation from double layer capacitance (Cdl) measurements in carbon paper substrate, benchmark Ir, benchmark Ru, IrFeCoNi, Ru0.08(Ir,Fe,Co,Ni)0.92, Ru0.12(Ir,Fe,Co,Ni)0.88, Ru0.16(Ir,Fe,Co,Ni)0.84, and Ru0.20(Ir,Fe,Co,Ni)0.80. The scan rate was varied from 20 to 100 mV s⁻¹ at a non-faradaic potential range of +1.0 V_RHE to +1.1 V_RHE. [00049] FIG. 23 depicts the ECSA from the double layer capacitance (Cdl) measurements as estimated from the slope of each curve of all benchmark and Rux(Ir,Fe,Co,Ni)1−x catalysts and the specific activity of all benchmark and Rux(Ir,Fe,Co,Ni)1−x variations in 0.1 M HClO₄ electrolyte (scan rate: 5 mV s⁻¹). [00050] FIG. 24 depicts the chronopotentiometry curves show the stability of Ru_0.08(Ir,Fe,Co,Ni)_0.92, Ru_0.12(Ir,Fe,Co,Ni)_0.88, and Ru_0.16(Ir,Fe,Co,Ni)_0.84 over 24 hours of measurement at a constant current density of 10 mA cm⁻² in 0.1 M HClO4 electrolyte.  [00051] FIG. 25 depicts Ir-mass-based polarization curve of IrFeCoNiCu-HEA and Ir catalysts in 0.1 M HClO4; [00052] FIG.26 depicts ECSA analysis using hydrogen underpotential deposition (HUPD) method of IrFeCoNiCu-HEA and Ir catalysts in 0.1 M HClO4; [00053] FIG. 27 depicts the OER polarization curve between monometallic Ir, Ru, IrFeCoNiCu-HEA, and IrRuFeCoNi-HEA in 0.1 M HClO4; Attorney Docket No.39425-352 [00054] FIG. 28 depicts the chronopotentiometry measurement of IrFeCoNiCu-HEA and IrRuFeCoNi-HEA at a constant current density of 10 mA cm⁻²; [00055] FIG.29A depicts the cyclic voltammogram under HUPD potential range for shock- synthesized and colloidally-synthesized (untreated, air-annealed, and plasma-cleaned) IrFeCoNiCu-HEA samples showing the importance of air annealing to activate the colloidally- synthesized catalyst. [00056] FIG. 29B depicts the cyclic voltammogram under Ir(III)/Ir(IV) redox potential range for shock-synthesized and colloidally-synthesized (untreated, air-annealed, and plasma- cleaned) IrFeCoNiCu-HEA samples showing the importance of air annealing to activate the colloidally-synthesized catalyst. [00057] FIG.29C depicts the linear-sweep voltammogram of pure monometallic Ir, shock- synthesized IrFeCoNiCu-HEA, and colloidally-synthesized (untreated, air-annealed, and plasma-cleaned) IrFeCoNiCu-HEA samples showing the comparable activity of air-annealed sample. [00058] FIG. 29D depicts the Tafel plot of pure monometallic Ir, shock-synthesized IrFeCoNiCu-HEA, and air-annealed IrFeCoNiCu-HEA samples showing the comparable OER kinetics between the shock-synthesized and air-annealed samples. [00059] FIG.30A-D depicts HRTEM images of several region of interests near the surface of IrFeCoNiCu-HEA (A, B) before the OER test showing the presence of encapsulating carbon layers and (C, D) after the OER test showing the disappearance of the carbon layers due to delamination (all scale bar, 5 nm); [00060] FIG. 31A depicts STEM-EDS maps showing the elemental distribution of IrFeCoNiCu-HEA at different timepoints of OER stability test (scale bar, 20 nm); [00061] FIG. 31B depicts TEM-EDS maps showing the elemental distribution near the surface of the evolved IrFeCoNiCu-HEA nanoparticle after 4 hours of chronopotentiometry test showing the Ir-rich shell layer (scale bar, 10 nm); [00062] FIG. 31C depicts the comparison of the (111) diffraction peak from XRD measurement of as-synthesized and post-electrolysis IrFeCoNiCu-HEA. [00063] FIG.31D depicts a high-resolution STEM image showing the distinguishable near- surface structure, showing the metallic HEA core, Ir-rich alloy shell layer, and a thin layer of oxide on the surface of the evolved nanoparticle after undergoing electrochemical activation step (scale bar, 2 nm); Attorney Docket No.39425-352 [00064] FIG. 31E depicts a high-resolution STEM image showing the Ir-rich shell layer mainly decorated by Ir-rich nano-domains (scale bar, 2 nm); [00065] FIG.31F depicts the magnified high-resolution STEM image from a certain region in FIG.31E showing the Ir-rich nano-domains and the corresponding FFT analysis (scale bar, 1 nm); [00066] FIG.31G depicts the magnified high-resolution STEM image from another region of interest in FIG.31E showing the Ir-rich nano-domains and the corresponding FFT analysis (scale bar, 1 nm); [00067] FIG. 32A-B depicts STEM-EDS maps showing the elemental distribution of each component of IrFeCoNiCu-HEA after 4 hours of OER chronopotentiometry test at 10 mA cm- ² (scale bar, 10 nm); [00068] FIG. 33 depicts the concentration of dissolved metals in the HClO₄ electrolyte measured using ICP-OES after the electrochemical activation step, after 4 hours, and after 12 hours of chronopotentiometry test at constant current density of 10 mA cm^-2; [00069] FIG.34 depicts selected region of interest (ROI 1: whole nanoparticle and ROI 2: nanoparticle’s core) and their corresponding EDS elemental spectra of IrFeCoNiCu-HEA nanoparticle after undergoing 4 hours of OER chronopotentiometry test at 10 mA cm^-2 ; [00070] FIG. 35 depicts selected region of interest (ROI 3-5: nanoparticle’s Ir-rich shell layer) and their corresponding EDS elemental spectra of IrFeCoNiCu-HEA nanoparticle after undergoing 4 hours of OER chronopotentiometry test at 10 mA cm^-2 ; [00071] FIG. 36 depicts the powder XRD pattern of as-synthesized and post-electrolysis IrFeCoNiCu-HEA; [00072] FIG.37 depicts HAADF-STEM images of IrFeCoNiCu-HEA after the OER test at different timepoints (after electrochemical activation and after 4 hours of chronopotentiometry test at 10 mA cm^-2); [00073] FIG.38A depicts STEM-EDS maps showing the distribution of Ir and O elements in an evolved IrFeCoNiCu-HEA nanoparticle. [00074] FIG. 38B depicts a line profile of Ir and O elemental distribution based on a line scan depicted in FIG.24a. [00075] FIG. 39 depicts STEM-EELS maps showing the distribution of Ir and O elements in an evolved IrFeCoNiCu-HEA nanoparticle. [00076] FIG. 40 depicts the near-surface structure of evolved IrFeCoNiCu-HEA showing the Ir-rich shell layer and the thin oxide layer. Attorney Docket No.39425-352 [00077] FIG. 41 illustrates the evolution of IrFeCoNiCu-HEA into a structure with Ir-rich shell layer due to leaching process under acidic OER conditions, as well as the delamination of encapsulating carbon layers. [00078] FIG.42 depicts the concentration of dissolved metals in the electrolyte sample of Ru, Ir, and Ru0.20(Ir,Fe,Co,Ni)0.80 was measured using offline ICP-OES after electrochemical activation and after 24 hours of chronopotentiometry test. [00079] FIG. 43A depicts the HAADF-STEM image and STEM-EDS maps of post- electrolyzed Ru_0.20(Ir,Fe,Co,Ni)_0.80 show the homogeneous elemental distribution in the nanoparticle’s core with RuIr-rich shell layer on the evolved surface. The Ir + Ni and Ru + Fe superimposed maps are used as an example to show the depletion of 3d metals near the surface. [00080] FIG.43B depicts the HAADF-STEM image and STEM-EDS maps of a section in FIG. 43A at higher magnification with a dashed line to visualize the surface edge and the depletion of the 3d metals near the surface. [00081] FIG. 43C depicts a line-scan profile from a region of interest in FIG. 43B shows the RuIr-rich shell layer on the evolved surface. [00082] FIG. 43D depicts the HR-STEM image of post-electrolyzed Ru0.20(Ir,Fe,Co,Ni)0.80 shows the structure of evolved nanoparticles with (i) a pristine fcc core and (ii) amorphous features on the shell layer. [00083] FIG.43E depicts the HR-STEM image of Ru_0.20(Ir,Fe,Co,Ni)_0.80 after 24 hours of chronopotentiometry test at a constant current density of 10 mA cm⁻², showing the thickness of the shell layer does not increase significantly. [00084] FIG. 44A-B depicts the HAADF-STEM image and STEM-EDS elemental maps show the distribution of all elements in IrFeCoNi after electrochemical activation and Ru0.20(Ir,Fe,Co,Ni)0.80 after 24 hours of chronopotentiometry test at 10 mA cm⁻². The Ru+Ir and Ir+Ni composite maps are used as examples to show the Ir-rich (in IrFeCoNi) or RuIr-rich (in RuIrFeCoNi) shell layer. [00085] FIG. 45 depicts the aberration-corrected HAADF-STEM images of various Rux(Ir,Fe,Co,Ni)1−x samples taken after the electrochemical activation step or 24 hours of chronopotentiometry test at a constant current density of 10 mA cm⁻². [00086] FIG.46 depicts the high-resolution XPS spectra of Ru 3d, Ir 4f, and O 1s in as- prepared and post-electrolyzed Ru_0.20(Ir,Fe,Co,Ni)_0.80 show a consistent shift in several representative peaks due to an increased contribution from the oxidized species, indicating the oxidation of the catalyst after undergoing OER. Attorney Docket No.39425-352 [00087] FIG.47 depicts the XPS survey spectra and high-resolution XPS spectra of Fe 2p, Co 2p, and Ni 2p of as-prepared and post-electrolyzed Ru_0.20(Ir,Fe,Co,Ni)_0.80. All spectra were calibrated against the C 1s peak at a binding energy of 248.8 eV. [00088] FIG. 48 depicts the powder XRD pattern of as-prepared and post-electrolyzed Ru0.20(Ir,Fe,Co,Ni)0.80 shows no apparent shifts in the diffraction peaks, both from the fcc and hcp phases. The XRD measurements were performed at around the same spot on the sample. [00089] FIG. 49 depicts the powder XRD pattern of as-prepared equimolar RuIrFeCoNiCu-HEA comprising six elements in comparison to RuIrFeCoNi-HEA. [00090] FIG. 50 depicts the powder XRD pattern, HAADF-STEM image, and STEM- EDS elemental maps of as-prepared Ru_0.20(Pt,Fe,Co,Ni)_0.80 and Ru_0.16(Pt,Fe,Co,Ni)_0.84. [00091] FIG. 51 depicts the powder XRD pattern, HAADF-STEM image, and STEM- EDS elemental maps of as-prepared Ru_0.20(Pd,Fe,Co,Ni)_0.80 and Ru_0.16(Pd,Fe,Co,Ni)_0.84. [00092] FIG. 52 depicts the powder XRD pattern, HAADF-STEM image, and STEM- EDS elemental maps of as-prepared Ru_0.20(Cr,Fe,Co,Ni)_0.80 and Ru_0.16(Cr,Fe,Co,Ni)_0.84. [00093] FIG. 53 depicts the powder XRD pattern, HAADF-STEM image, and STEM- EDS elemental maps of as-prepared Ru0.20(Cu,Fe,Co,Ni)0.80. [00094] FIG. 54 depicts the OER polarization curves of shock-synthesized Ru0.20(Pt,Fe,Co,Ni)0.80 and Ru0.20(Cu,Fe,Co,Ni)0.80 in comparison to other benchmark catalysts (scan rate: 5 mV s⁻¹). [00095] FIG. 55 depicts the chronopotentiometry test of air-annealed colloidally- synthesized IrFeCoNiCu-HEA over 24 hours of measurement at a constant current density of 10 mA cm⁻², showing the stability of the catalyst. [00096] FIG. 56 depicts the comparison of the concentration of dissolved metals between shock- and colloidally-synthesized IrFeCoNiCu-HEA after the electrochemical activation step. [00097] FIG.57 depicts the HAADF-STEM image and STEM-EDS elemental maps of air-annealed and post-electrolyzed colloidally-synthesized IrFeCoNiCu-HEA. [00098] FIG.58 depicts the aberration-corrected HAADF-STEM images of as-prepared colloidally-synthesized IrFeCoNiCu-HEA. [00099] FIG. 59 depicts the aberration-corrected HAADF-STEM images of post- electrolyzed colloidally-synthesized IrFeCoNiCu-HEA. Attorney Docket No.39425-352 [000100] FIG. 60 depicts the atomic ratio determination of colloidally-synthesized IrFeCoNiCu-, PtRuFeCoNi-, IrRuFeCoNiCu-, and IrRuFeCoNi-HEA as measured using ICP- OES. [000101] FIG. 61 depicts the OER polarization curves of air-annealed colloidally- synthesized PtRuFeCoNi, IrRuFeCoNi, and IrRuFeCoNiCu-HEA in comparison to other benchmark catalysts (scan rate: 5 mV s⁻¹). [000102] FIG.62 depicts the cyclic voltammetry (CV) curves of air-annealed colloidally- synthesized PtRuFeCoNi and IrRuFeCoNi within the H_UPD and Ir(III)/Ir(IV) redox peak potential regions. [000103] FIG. 63 depicts the atomic ratio determination of colloidally-synthesized equimolar and Cu-rich IrFeCoNiCu-HEA as measured using ICP-OES. [000104] FIG. 64 depicts the OER polarization curves of air-annealed colloidally- synthesized equimolar and Cu-rich IrFeCoNiCu-HEA in comparison to other benchmark catalysts (scan rate: 5 mV s⁻¹).   Detailed Description [000105] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. [000106] As used herein, “a” or “an” entity refers to one or more of that entity, e.g., “a compound” refers to one or more compounds or at least one compound unless stated otherwise. As such, the terms “a” (or “an”), “one or more”, and “at least one” are used interchangeably herein. [000107] As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Additionally, as used herein, “or” means “and/or.” [000108] As used herein, the term “multicomponent” refers to a composition including more than one element, or metal. [000109] A multicomponent alloy, such as a high entropy alloy (HEA), nanoparticles are an emerging class of nanomaterials that may be used in a variety of different fields, including Attorney Docket No.39425-352 catalysis. It has been found that by incorporating five or more elements or metals in a single particle generates a considerable configurational entropy. This configurational entropy can dominate the particle’s thermodynamic behavior, can stabilize the alloyed structure, and/or can mitigate any structural in an acidic environment. Additionally, a multicomponent alloy may manifest a mixing effect where a synergistic response arising from the mutual electronic interactions between its constituent elements is observed. It has further been found that the availability of multi-element active sites on the surface of HEA nanoparticles make HEA a suitable platform to facilitate a catalyst reaction, such as OER. The present disclosure relates to a multicomponent alloy, such as a high entropy alloy, that is Ir- based, Ru-based or a combination thereof with additional elements/metals. The catalyst described herein has been found to demonstrate excellent performed when used for acidic OER. Additionally, the catalysis including a multicomponent alloy may be synthesized using microwave-assisted shock synthesis or colloidal synthesis, which produced catalysis having better activity and stability when compared to a monometallic counterpart or other Ir/Ru based alloys. [000110] In an embodiment of the present disclosure, a catalyst including a multicomponent alloy is provided. The multicomponent alloy may include a nanoparticle including iridium (Ir), ruthenium (Ru), or a combination thereof and at least four metals. The multicomponent alloy may have a single phase structure. In some embodiments, the multicomponent alloy may include Ir and at least four metals. In other embodiments, the multicomponent alloy may include Ru and at least four metals. In yet another embodiments, the multicomponent alloy may include Ir, Ru and at least four metals. [000111] In some embodiments, the catalyst may have a core and a shell. In such embodiments, it has been found that an Ir-rich, Ru-rich, or Ir and Ru-rich shell structure may form on the nanoparticle, while maintaining a homogeneous elemental distribution characteristic of the multicomponent alloy. [000112]  Disclosed herein in an embodiment is a catalyst. In an embodiment, the catalyst includes a multicomponent alloy comprising iridium (Ir), and at least four metals, wherein the multicomponent alloy has a single-phase structure. In some embodiments, the multicomponent alloy may be a nanoparticle. [000113] In some embodiments, the catalyst may have a core and a shell. In some embodiments, the core may include the multicomponent alloy. In some embodiments, the shell may be Ir-rich. In some embodiments, the shell may have a thickness of about 0.1 nm to about 20 nm. In other embodiments, the thickness of the shell may be about 0.3 nm to about 18 nm, Attorney Docket No.39425-352 about 0.5 nm to about 16 nm, about 1 nm to about 14 nm, about 2 nm to about 12 nm, about 3 nm to about 10 nm, about 4 nm to about 8 nm, or about 5 nm to about 7 nm, or any range herein. In yet other embodiments, the thickness of the shell may be about 0.1 nm, about 0.5 nm, about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, or about 20 nm. [000114] In some embodiments, the catalyst may include at least four metals. The at least four metals may be selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). In other embodiments, the at least four metals may be selected from the group consisting of chromium (Cr), manganese (Mn), molybdenum (Mo), hafnium (Hf), titanium (Ti), zirconium (Zr), aluminum (Al), gallium (Ga), germanium (Ge), tin (Sn), zinc (Zn), vanadium (V), scandium (Sc), yttrium (Y), tungsten (W), Platinum (Pt), Fe, Co, Ni, and Cu. In some embodiments, the at least four metals does not include a platinum group metal (pgm). As used herein, a “platinum group metal” or “pgm” refers to iridium, osmium, palladium, platinum, rhodium, or ruthenium. [000115] In some embodiments, the catalyst may further include a support. The support may be any suitable carrier material as known in the art. In some embodiments, the support may include an inorganic oxide, carbide or nitride material. For example, the support may be antimony doped tin oxide (ATO), titanium suboxides (TiO, Ti₂O₃, Ti₃O₅, and Ti₄O₇),TiC, ZrC, HfC, TaC, TiN, ZrN, HfN, TaN, boron carbide, boron-oxy-carbide, or boron carbides, containing further elements such as boron silicon oxycarbide, TiO₂, or doped or undoped SnO₂. [000116] In some embodiments, the catalyst may be stable for at least about 12 hours. In some embodiments, the catalyst may be stable for about 12 hours, about 13 hours, about 14 hours, about 15 hours, about 16 hours, about 17 hours, about 18 hours, about 20 hours, about 21 hours, about 22 hours, about 23 hours, about 24 hours, about 28 hours, about 32 hours, or about 36 hours. [000117] In some embodiments, the catalyst may have a particle size distribution between about 2 nm to about 200 nm. In other embodiments, the particle size distribution may be between about 2 nm to about 190 nm, about 5 nm to about 180 nm, about 10 nm to about 170 nm, about 20 nm to about 160 nm, about 30 nm to about 150 nm, about 40 nm to about 140 nm, about 50 nm to about 130 nm, about 60 nm to about 120 nm, about 70 nm to about 110 nm, or about 80 nm to about 100 nm. In other embodiments, the particle size distribution may be about 2 nm, about 5 nm, about 10 nm, about 15 nm, about 25 nm, about 40 nm, about 50 Attorney Docket No.39425-352 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 110 nm, about 120 nm, about 130 nm, about 140 nm, about 150 nm, about 160 nm, about 170 nm, about 180 nm, about 190 nm, or about 200 nm. [000118] In some embodiments, the multicomponent alloy may have an atomic ratio between Ir and the at least four metals being equimolar. In some embodiments of the catalyst, Ir and the at least four metals may be included to form a single alloy phase. [000119] In some embodiments, the multicomponent alloy may include Ir and the at least for metals may be selected from the group consisting of Fe, Co, Ni and Cu, and a ratio of Ir:Fe:Co:Ni:Cu is about 24:16:25:19:15. [000120] In another embodiment of the present disclosure, a method of preparing a catalyst is provided. The method may include performing a microwave-assisted shock synthesis or a colloidal synthesis. [000121] In another embodiment, a method of performing oxygen evolution reaction may including using a catalyst of the present disclosure. [000122] In another embodiment, a catalyst may include a multicomponent alloy comprising ruthenium (Ru), and at least four metals, wherein the multicomponent alloy has a single-phase structure. In some embodiments, the multicomponent alloy may be a nanoparticle. [000123] In some embodiments, the catalyst may have a core and a shell. In some embodiments, the core may include the multicomponent alloy. In some embodiments, the shell may be Ru-rich. In some embodiments, the shell may have a thickness of about 0.1 nm to about 20 nm. In other embodiments, the thickness of the shell may be about 0.3 nm to about 18 nm, about 0.5 nm to about 16 nm, about 1 nm to about 14 nm, about 2 nm to about 12 nm, about 3 nm to about 10 nm, about 4 nm to about 8 nm, or about 5 nm to about 7 nm, or any range herein. In yet other embodiments, the thickness of the shell may be about 0.1 nm, about 0.5 nm, about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, or about 20 nm. [000124] In some embodiments, the at least four metals may be selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu), and Platinum (Pt) . In other embodiments, the at least four metals may be selected from the group consisting of chromium (Cr), manganese (Mn), molybdenum (Mo), hafnium (Hf), titanium (Ti), zirconium (Zr), aluminum (Al), gallium (Ga), germanium (Ge), tin (Sn), zinc (Zn), vanadium (V), scandium Attorney Docket No.39425-352 (Sc), yttrium (Y), tungsten (W), Fe, Co, Ni, Cu, and Pt. In some embodiments, the at least four metals does not include a platinum group metal (pgm). [000125] In some embodiments, the catalyst may further include a support. The support may be any suitable carrier material as known in the art. In some embodiments, the support may include an inorganic oxide, carbide or nitride material. For example, the support may be antimony doped tin oxide (ATO), titanium suboxides (TiO, Ti₂O₃, Ti₃O₅, and Ti₄O₇),TiC, ZrC, HfC, TaC, TiN, ZrN, HfN, TaN, boron carbide, boron-oxy-carbide, or boron carbides, containing further elements such as boron silicon oxycarbide, TiO₂, or doped or undoped SnO₂. [000126] In some embodiments, the catalyst may be stable for at least about 12 hours. In some embodiments, the catalyst may be stable for about 12 hours, about 13 hours, about 14 hours, about 15 hours, about 16 hours, about 17 hours, about 18 hours, about 20 hours, about 21 hours, about 22 hours, about 23 hours, about 24 hours, about 28 hours, about 32 hours, or about 36 hours. [000127] In some embodiments, the catalyst may have a particle size distribution between about 2 nm to about 200 nm. In other embodiments, the particle size distribution may be between about 2 nm to about 190 nm, about 5 nm to about 180 nm, about 10 nm to about 170 nm, about 20 nm to about 160 nm, about 30 nm to about 150 nm, about 40 nm to about 140 nm, about 50 nm to about 130 nm, about 60 nm to about 120 nm, about 70 nm to about 110 nm, or about 80 nm to about 100 nm. In other embodiments, the particle size distribution may be about 2 nm, about 5 nm, about 10 nm, about 15 nm, about 25 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 110 nm, about 120 nm, about 130 nm, about 140 nm, about 150 nm, about 160 nm, about 170 nm, about 180 nm, about 190 nm, or about 200 nm. [000128] In some embodiments, the multicomponent alloy may have an atomic ratio between Ru and the at least four metals being equimolar. In some embodiments of the catalyst, Ru and the at least four metals may be included to form a single alloy phase. [000129] In another embodiment, a catalyst may include a multicomponent alloy comprising Ir, Ru, and at least four metals, wherein the multicomponent alloy has a single-phase structure. In some embodiments, the multicomponent alloy may be a nanoparticle. [000130] In some embodiments, the catalyst may have a core and a shell. In some embodiments, the core may include the multicomponent alloy. In some embodiments, the shell may be Ir and Ru-rich. In some embodiments, the shell may have a thickness of about 0.1 nm to about 20 nm. In other embodiments, the thickness of the shell may be about 0.3 nm to about Attorney Docket No.39425-352 18 nm, about 0.5 nm to about 16 nm, about 1 nm to about 14 nm, about 2 nm to about 12 nm, about 3 nm to about 10 nm, about 4 nm to about 8 nm, or about 5 nm to about 7 nm, or any range herein. In yet other embodiments, the thickness of the shell may be about 0.1 nm, about 0.5 nm, about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, or about 20 nm. [000131] In some embodiments, the at least four metals may be selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). In other embodiments, the at least four metals may be selected from the group consisting of chromium (Cr), manganese (Mn), molybdenum (Mo), hafnium (Hf), titanium (Ti), zirconium (Zr), aluminum (Al), gallium (Ga), germanium (Ge), tin (Sn), zinc (Zn), vanadium (V), scandium (Sc), yttrium (Y), tungsten (W), Platinum (Pt), Fe, Co, Ni, and Cu. In some embodiments, the at least four metals does not include a platinum group metal (pgm). [000132] In some embodiments, the catalyst may further include a support. The support may be any suitable carrier material as known in the art. In some embodiments, the support may include an inorganic oxide, carbide or nitride material. For example, the support may be antimony doped tin oxide (ATO), titanium suboxides (TiO, Ti2O3, Ti3O5, and Ti4O7),TiC, ZrC, HfC, TaC, TiN, ZrN, HfN, TaN, boron carbide, boron-oxy-carbide, or boron carbides, containing further elements such as boron silicon oxycarbide, TiO₂, or doped or undoped SnO₂. [000133] In some embodiments, the catalyst may be stable for at least about 12 hours. In some embodiments, the catalyst may be stable for about 12 hours, about 13 hours, about 14 hours, about 15 hours, about 16 hours, about 17 hours, about 18 hours, about 20 hours, about 21 hours, about 22 hours, about 23 hours, about 24 hours, about 28 hours, about 32 hours, or about 36 hours. [000134] In some embodiments, the catalyst may have a particle size distribution between about 2 nm to about 200 nm. In other embodiments, the particle size distribution may be between about 2 nm to about 190 nm, about 5 nm to about 180 nm, about 10 nm to about 170 nm, about 20 nm to about 160 nm, about 30 nm to about 150 nm, about 40 nm to about 140 nm, about 50 nm to about 130 nm, about 60 nm to about 120 nm, about 70 nm to about 110 nm, or about 80 nm to about 100 nm. In other embodiments, the particle size distribution may be about 2 nm, about 5 nm, about 10 nm, about 15 nm, about 25 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 110 nm, about Attorney Docket No.39425-352 120 nm, about 130 nm, about 140 nm, about 150 nm, about 160 nm, about 170 nm, about 180 nm, about 190 nm, or about 200 nm. [000135] In some embodiments, the multicomponent alloy may have an atomic ratio between Ir, Ru and the at least four metals being equimolar. In some embodiments of the catalyst, Ir, Ru and the at least four metals may be included to form a single alloy phase. [000136] In some embodiments, a method of preparing the catalysts is provided. The method may include using colloidal synthesis, or top-down synthesis using pulsed laser ablation (PLAL) to prepare a catalyst as described herein. [000137] Claims or descriptions that include “or” or “and/or” between at least one members of a group are considered satisfied if one, more than one, or all of the group members are present in, employed in, or otherwise relevant to a given product or process unless indicated to the contrary or otherwise evident from the context. The disclosure includes embodiments in which exactly one member of the group is present in, employed in, or otherwise relevant to a given product or process. The disclosure includes embodiments in which more than one, or all the group members are present in, employed in, or otherwise relevant to a given product or process. [000138] Furthermore, the disclosure encompasses all variations, combinations, and permutations in which at least one limitation, element, clause, and descriptive term from at least one of the listed claims is introduced into another claim. For example, any claim that is dependent on another claim can be modified to include at least one limitation found in any other claim that is dependent on the same base claim. Where elements are presented as lists, such as, e.g., in Markush group format, each subgroup of the elements is also disclosed, and any element(s) can be removed from the group. It should be understood that, in general, where the disclosure, or aspects of the disclosure, is/are referred to as comprising particular elements and/or features, embodiments of the disclosure or aspects of the disclosure consist, or consist essentially of, such elements and/or features. For purposes of simplicity, those embodiments have not been specifically set forth in haec verba herein. Where ranges are given (such as, e.g., from [X] to [Y]), endpoints (such as, e.g., [X] and [Y] in the phrase “from [X] to [Y]”) are included unless otherwise indicated. Furthermore, unless otherwise indicated or otherwise evident from the context and understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value or sub-range within the stated ranges in different embodiments of the disclosure, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. Attorney Docket No.39425-352 [000139] Those of ordinary skill in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the disclosure described herein. Such equivalents are intended to be encompassed by the following claims. EXAMPLES [000140] The following examples are intended to be illustrative and are not meant in any way to limit the scope of the disclosure. [000141] A variety of comparative examples of different iridium catalysts were prepared along with a catalyst including a HEA of the present disclosure. Chemicals for Preparation of Catalysts [000142] Iridium(IV) chloride hydrate (IrCl₄ ^H₂O, ≥99.9% trace metals basis), ruthenium (III) chloride hydrate (RuCl3 ^H2O, 99.98% trace metals basis), chloroplatinic acid hexahydrate (H₂PtCl₆ ^6H₂O), palladium (II) chloride (PdCl₂), iron(III) chloride hexahydrate (FeCl₃ ^6H₂O, ≥98% trace metals basis), cobalt(II) chloride hexahydrate (CoCl3 ^6H2O, ≥97% trace metal basis), nickel(II) chloride hexahydrate (NiCl2 ^6H2O, ≥99.9% trace metal basis), copper(II) chloride dihydrate (CuCl2 ^2H2O, ≥99.999% trace metals basis), chromium (III) chloride hydrate (CrCl3 ^6H2O), perchloric acid (HClO470%, 99.999% trace metal basis), and ethanol (C₂H₅OH ≥99.5%) were purchased from Sigma Aldrich, Inc. and used without further purification. Carbon papers (Sigracet, 29AA and 39AA) and proton-exchange membranes (Nafion 115) were purchased from Fuel Cell Store, Inc. Titanium TEM grids with a 15-25 nm carbon support film and gold TEM grid with ultrathin carbon film (< 3 nm in thickness) on lacey support film were purchased form Ted Pella, Inc. Deionized water (18.2 MΩ ^cm, < 5 ppb TOC) was obtained from a Millipore Milli-Q IQ 7000 Ultrapure Water System. Characterization of the Samples [000143] Transmission electron microscopy (TEM) study was carried out using Hitachi H- 7650. High-resolution TEM (HR-TEM) images were obtained using FEI Tecnai F20 at an accelerating voltage of 300 kV. High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and energy dispersive X-ray spectroscopy (EDS) mapping analysis were performed with Thermo Fisher Scientific TitanX 60-300 with accelerating voltage of 300 kV. Aberration-corrected HAADF-STEM images were acquired using Transmission Electron Aberration-corrected Microscope (TEAM) 0.5 with accelerating Attorney Docket No.39425-352 voltage of 300 kV. X-ray photoelectron spectroscopy (XPS) spectra were recorded using Thermo Scientific K-Alpha Plus X-ray Photoelectron Spectroscope with a monochromatic Al- Ka source. Powder X-ray Diffraction (XRD) pattern was obtained using Bruker AXS D8 Advance diffractometer with a monochromatic Cu-Ka source. Inductively coupled plasma optical emission spectroscopy (ICP-OES) measurement was performed using PerkinElmer Optima 7000 DV. Synthesis of Ir Catalysts [000144] IrCl4 ^H2O was dissolved in ethanol with concentration of 0.5 mol L^-1. 3 µL of the solution was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was sealed in a 20 mL glass vial and occupied with Ar with the help of an Ar-purged glovebox (MBRAUN Unilab Pro). The vial was then transferred into a microwave oven (Panasonic NN-SN686S, 1200 W). The vial was irradiated at 1200 watts (W) for 10-11 seconds (s) and naturally cooled down to room temperature. The resulting Ir-loaded carbon paper has a theoretical Ir loading of ~288 µgIrcm^-2. Synthesis of IrFe, IrCo, and IrNi Catalysts [000145] To prepare IrFe bimetallic catalysts, IrCl4 ^H2O and FeCl3 ^6H2O were dissolved in ethanol with a total salt concentration of 0.5 mol L^-1.6 µL of the solution was drop-casted onto a carbon paper with the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave with a similar manner to the syntheses of Ir catalysts as previously described. IrCo and IrNi bimetallic catalysts were prepared in a similar manner using CoCl₃ ^6H₂O and NiCl₂ ^6H₂O, respectively. The resulting IrM-loaded carbon paper has a theoretical loading of ~288 µgIrcm^-2. Synthesis of IrFeCoNiCu High-entropy Alloy (HEA) Catalysts of the present disclosure [000146] To prepare IrFeCoNiCu-HEA, IrCl₄ ^H₂O, FeCl₃ ^6H₂O, CoCl₃ ^6H₂O, NiCl₂ ^6H₂O, and CuCl2 ^2H2O were dissolved in ethanol with a total salt concentration of 0.5 mol L^-1. 15 µL of the solution was drop-casted onto a carbon paper within the area of 1 cm². The salt- loaded carbon paper was then sealed and irradiated in a microwave with a similar manner to the synthesis of Ir catalysts as previously described. The resulting IrFeCoNiCu-loaded carbon paper has a theoretical loading of ~288 µgIrcm^-2. Attorney Docket No.39425-352 [000147] The sample of IrFeCoNiCu-HEA was kept in a small vial under Ar atmosphere and transferred to a household microwave for microwave shock synthesis. By using this method, rapid heating and rapid quenching from the microwave irradiation was able to synthesize single-phase alloyed structures at nanoscale. Localized heating induced by the microwave radiation absorption at the carbon substrate defects provide sufficient heat for the thermal decomposition of the metal salts. After high-temperature reduction, rapid quenching helps the solidification of the liquid metal mixture to yield a homogenous elemental distribution in the solid nanoparticle state and avoid any phase separation. [000148] It was found that the IrFeCoNiCu-HEA nanoparticles can be dispersed on the carbon paper substrate with nanoparticles size distributed between 20 to 200 nm. (See FIG. 1A and FIG. 2). The vast particle size distribution is largely caused by the inhomogeneity of carbon paper substrate and different heating conditions delivered by the microwave setup for every synthesis. HAADF-STEM and XRD studies were conducted to elucidate the structure of the synthesized HEA. The results of HAADF-STEM image are shown in FIG. 1B, while the XRD pattern is in FIG. 1C. The XRD pattern confirmed that the IrFeCoNiCu-HEA nanoparticles have a dominant single-phase structure without any other additional phases. Compared to the XRD pattern of each individual component, it is clear that the XRD peaks of IrFeCoNiCu-HEA do not belong to any of the monometallic elements indicating a homogenous mixing between the constituting elements. The average lattice constant calculated from XRD measurements was 0.364 nm. With an assumption of equimolar concentration (20 at.%) of each component, the estimated lattice constant predicted using ideal Vegard’s law was 0.366 nm, which was consistent with the calculated value from XRD measurements. [000149] The single-phase solid solution alloy structure of the IrFeCoNiCu-HEA was further confirmed by energy dispersive spectroscopy (EDS) elemental mapping (See FIG.1D). The elemental distribution maps of FIG. 1D showed a homogeneous distribution of each individual components without any significant phase separation or elemental segregation. A selected region of interest was chosen for the EDS spectra which is shown in FIG.3. From the EDS spectra, the typical atomic ratio between Ir:Fe:Co:Ni:Cu was calculated to be 24:16:25:19:15, which is consistent with definition of a high-entropy alloy at bulk level. In addition, the homogeneous distribution and random mixing of the elements was also confirmed from the Z-contrast in the HAADF-STEM images of the sample at a higher magnification as shown in FIG. 1B and FIG. 4, in which Ir atoms had the highest atomic number showed the brightest contrast. - Attorney Docket No.39425-352 Synthesis of IrFeCoNiCu High-entropy Alloy (HEA) Catalysts via colloidal synthesis [000150] Preparation of IrFeCoNiCu-HEA via colloidal synthesis was prepared using the procedure described in patent application PCT/EP2023/059220, WO 2023198617. Activation of Colloidally-synthesized IrFeCoNiCu High-entropy Alloy (HEA) Catalysts [000151] Colloidally-synthesized IrFeCoNiCu-HEA samples may need to be activated before being used as an OER catalyst. [000152] The activation process includes air annealing (using a box furnace at 500°C for 60 s under a still-air atmosphere) or O₂ plasma cleaning (using plasma cleaner at 100-200 mTorr for about 2-10 minutes). [000153] The colloidally-synthesized IrFeCoNiCu-HEA was first washed with ~10 mL hexane + ~15 mL ethanol and then centrifuged for 10 minutes at 12,000 rpm to remove the organic ligands. The washing process was repeated about 3 times. [000154] Washed IrFeCoNiCu-HEA was then dispersed in ethanol. The ethanol dispersion was then drop-casted onto carbon paper with desired Ir-mass-based loading. This sample was described to be untreated and regarded as a control sample. [000155] For the air annealing process, the HEA-loaded carbon paper was first transferred to an uncapped vial. It was then put into a box furnace that has been heated to 500°C. The annealing process can last for about 60 s. After that, the vial was immediately taken out and cooled down. [000156] For the plasma cleaning process, the HEA-loaded carbon paper was first transferred to a glass slide. It was then put into a plasma cleaner. The plasma cleaner was vacuumed to a base pressure of about 100-200 mTorr. After base pressure was achieved, oxygen was slowly purged into the plasma cleaner chamber for about 2-10 minutes. The plasma cleaner chamber was then brought back to atmospheric pressure and the glass slide can now be safely taken out. Synthesis of IrRuFeCoNi High-entropy Alloy (HEA) Catalysts of the present disclosure [000157] To prepare IrRuFeCoNi-HEA, IrCl₄ ^H₂O, RuCl₃ ^H₂O, FeCl₃ ^6H₂O, CoCl₃ ^6H₂O, and NiCl2 ^6H2O were dissolved in ethanol with a total salt concentration of 0.5 mol L^-1. 15 µL of the solution was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave with a similar manner to the Attorney Docket No.39425-352 synthesis of Ir catalysts as previously described. The resulting IrRuFeCoNi-loaded carbon paper had a theoretical loading of ~288 µg_Ircm^-2. [000158] The sample of IrRuFeCoNi-HEA was kept in a small vial under Ar atmosphere and transferred to a household microwave for microwave shock synthesis. By using this method, rapid heating and rapid quenching from the microwave irradiation was able to synthesize single-phase alloyed structures at nanoscale. Localized heating induced by the microwave radiation absorption at the carbon substrate defects provide sufficient heat for the thermal decomposition of the metal salts. After high-temperature reduction, rapid quenching helps the solidification of the liquid metal mixture to yield a homogenous elemental distribution in the solid nanoparticle state and avoid any phase separation. [000159] It was found that the IrRuFeCoNi-HEA nanoparticles can be dispersed on the carbon paper substrate with nanoparticles size distributed between 20 to 200 nm. The vast particle size distribution was largely caused by the inhomogeneity of carbon paper substrate and different heating conditions delivered by the microwave setup for every synthesis. HAADF-STEM and XRD studies were conducted to elucidate the structure of the synthesized HEA. The results of HAADF-STEM image are shown in FIG.5, while the XRD pattern is in FIG.6. The XRD pattern confirmed that the IrRuFeCoNi-HEA nanoparticles have a dominant single-phase structure with an additional phase. [000160] The solid solution alloy structure of the IrRuFeCoNi-HEA was further confirmed by energy dispersive spectroscopy (EDS) elemental mapping (See FIG. 7). The elemental distribution maps of FIG.7 showed a homogeneous distribution of each individual components without any significant phase separation or elemental segregation. A selected region of interest was chosen for the EDS spectra which is shown in FIG. 8. From the EDS spectra, the typical atomic ratio between Ir:Ru:Fe:Co:Ni was calculated to be 29:14:27:16:14, which is consistent with definition of a high-entropy alloy at bulk level. Synthesis of Ru Catalysts [000161] RuCl3 ^H2O was dissolved in ethanol with a total salt concentration of 0.5 mol L^-1. 3 µL of the solution was drop-casted onto a carbon paper with an area of 1 cm². The salt- loaded carbon paper was then sealed and irradiated in a microwave in a similar manner to the syntheses of Ir catalysts as previously described. The resulting Ru-loaded carbon paper has a theoretical loading of ~151 µgRucm^-2. Attorney Docket No.39425-352 Synthesis of Ru_x(Ir,Fe,Co,Ni)_1-x Alloy Catalysts of the present disclosure [000162] To prepare IrFeCoNi, IrCl₄∙H₂O, FeCl₃∙6H₂O, CoCl₂∙6H₂O, and NiCl₂∙6H₂O were dissolved in ethanol with a total salt concentration of 0.5 mol L⁻¹. 12 μL of the solution was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave, similar to the synthesis of Ir and Ru catalysts. [000163] To prepare Ru_x(Ir,Fe,Co,Ni)_1−x, RuCl₃∙H₂O, IrCl₄∙H₂O, FeCl₃∙6H₂O, CoCl₂∙6H₂O, and NiCl2∙6H2O were dissolved in ethanol with a total salt concentration of 0.5 mol L⁻¹. The volume of Ru precursor was varied from 0.75, 1.50, 2.25, to 3.00 μL and mixed with 12 μL of (Ir,Fe,Co,Ni) salt precursor (3.00 μL each). The mixed solution with various total salt volumes was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave, similar to the synthesis of Ir catalysts. In Ru_0.20(Ir,Fe,Co,Ni)_0.80, the resulting catalyst-loaded carbon paper has a theoretical Ir+Ru loading of ~439 μgIr+Ru cm⁻². [000164] FIG. 9A depicts the powder X-ray diffraction (XRD) patterns of all Rux(Ir,Fe,Co,Ni)1−x variations. IrFeCoNi assumed a typical fcc crystal structure with an average lattice constant of 0.365 nm. As Ru was gradually incorporated with increasing concentration (x = 0.08 and 0.12 at.%), the crystal structures remained to assume a single-phase fcc structure. However, when the Ru ratio was increased to x = 0.16 and 0.20 at.%, a secondary phase appeared, while the fcc structure still accounted for the primary phase. From Rietveld's refinement analysis (FIG. 10), the secondary structure was identified to be most likely an hcp phase. The hcp phase fraction at concentration x = 0.16 at.% was calculated to be about 16% and grew to be about 23% at x = 0.20 at.% (equimolar), with the rest being the primary fcc phase. The average lattice constant for equimolar Ru_0.20(Ir,Fe,Co,Ni)_0.80 was measured to be about afcc = 0.368 nm for the fcc phase and about ahcp = 0.262 nm and chcp = 0.424 nm for the hcp phase with c/a ≈ 1.617. [000165] The multi-phase structures were also confirmed locally through atomic-resolution high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) analysis. FIG. 9B depicts the lattice structure and the corresponding fast Fourier transform _{(FFT) analysis of the fcc phase in Ru0.20(Ir,Fe,Co,Ni)0.80 as seen from the fcc [1} ^ത _{11] zone axis.} The random distribution of the elements can also be scrutinized qualitatively from the Z- contrast. The lattice structure and FFT analysis in FIG. 9C confirm the presence of the hcp _{phase in Ru0.20(Ir,Fe,Co,Ni)0.80 as seen from the hcp [12} ^ത ₁₃ ^ത _{] zone axis. FIG. 11 and FIG. 12} show additional lattice structure analysis from HAADF-STEM and high-resolution TEM (HR- Attorney Docket No.39425-352 TEM) images of as-prepared Ru0.20(Ir,Fe,Co,Ni)0.80, respectively, further confirming the presence of the multi-phase structures. The synthesized nanoparticles from all variations could be well dispersed on the carbon paper substrate with size distribution ranging from about 5 to 150 nm (FIG.9D and FIG.13). [000166] The homogeneous distribution of the solid solution structure of all composition variations was verified through elemental mapping analysis via STEM energy dispersive spectroscopy (STEM-EDS). FIG. 9E depicts the STEM-EDS maps of each element in Ru_0.20(Ir,Fe,Co,Ni)_0.80, showing the homogeneity of the synthesized nanoparticles without apparent phase separation. At lower magnifications, numerous STEM-EDS analyses also show uniform distribution at multiple particle levels (FIG.14). The atomic ratio of all variations was evaluated to be close to the nominal value, as determined by STEM-EDS (local) and inductively coupled plasma optical emission spectroscopy (ICP-OES, whole sample information) (FIG.15, Table 1, Table 2). Table 1. The atomic ratio of as-prepared Rux(Ir,Fe,Co,Ni)1−x samples as measured using ICP- OES (whole sample information). Atomic Percentage (at.%) from ICP-OES Sample Table 2. The atomic ratio of as-prepared Ru_x(Ir,Fe,Co,Ni)_1−x samples as measured using STEM-EDS (local ensemble information) spectral analysis. The spectra were taken from FIG. 15. The quantification of each element was determined using the Cliff-Lorimer method. Atomic Percentage (at.%) from STEM-EDS Sample Attorney Docket No.39425-352 Electrochemical Measurements for OER using catalysis of present disclosure [000167] Electrochemical OER measurements were performed using the HEA sample according to the present disclosure to evaluate its electrocatalytic activity and stability. The measurements were carried out using a three-electrode system in an H-cell using 0.1 M ClO₄ electrolyte. [000168] The electrochemical measurements for acidic OER were performed in a two- compartment conventional H-cell using a three-electrode setup connected to a Biologic VSP potentiostat at room temperature. Each compartment was filled with 35 mL of 0.1 M HClO₄ electrolyte that was prepared from HClO470% stock solution. The two compartments were separated by a proton-exchange membrane (Nafion 115). A saturated Ag/AgCl electrode (saturated in 3 M KCl) and a graphite rod were used as the reference and counter electrodes, respectively. The catalyst-loaded carbon papers were used as the working electrode. Prior to electrochemical measurements, the working electrode compartment was purged and bubbled with Ar gas of ultrahigh purity for about 30 minutes. During the electrochemical measurements, the compartment was also continuously purged with Ar. [000169] Cyclic voltammetry (CV) scans between +0.05 VRHE and +0.80 VRHE for 5 cycles with a scan rate of 50 mV s⁻¹ were performed to underpotentially deposit hydrogen (HUPD) for electrochemically active surface area (ECSA) calculations after the capacitance current has been subtracted. The ECSA was determined from the hydrogen desorption (anodic scan) with a conversion factor of 218 μC cm⁻². [000170] CV scans between +0.40 VRHE and +1.40 VRHE for 5 cycles with a scan rate of 50 mV s⁻¹ were carried out to estimate the number of accessible active sites based on the integration of the Ir(III)/Ir(IV) oxidation peak after the capacitance current has been subtracted. [000171] Electrochemical activation between +1.0 VRHE and +1.80 VRHE for 5 CV cycles with a scan rate of 50 mV s⁻¹ was applied to obtain a stable CV curve. After a series of voltammetry scans, the OER activity was measured by linear-sweep voltammetry (LSV) between +1.0 VRHE and +1.80 VRHE with a scan rate of 5 mV s⁻¹. The iR-drop was compensated at 85% using the Biologic VSP potentiostat. The catalytic stability tests were performed using chronopotetiometry measurement at a constant current density of 10 mA cm⁻² using a similar experimental setup. Attorney Docket No.39425-352 [000172] FIG. 16A depicts the OER polarization curve of a blank carbon paper, monometallic Ir as the benchmark, IrM (M= Fe, Co, Ni) bimetallic alloys, and IrFeCoNiCu- HEA samples. Compared to the pure Ir counterpart with similar Ir-mass loading (~288 μgIr cm⁻² _geo.), IrFeCoNiCu-HEA exhibited an enhanced activity with an overpotential measured of about 302 mV at 10 mA cm⁻², while the overpotential of pure Ir catalyst is about 352 mV. As an additional activity comparison, the inventors also performed OER test to IrFe, IrCo, and IrNi catalysts. These catalysts have been widely reported to exhibit excellent OER performance in acidic media compared to pure Ir and the state-of-the- art IrO₂ catalyst. These bimetallic catalysts were prepared in a similar fashion to that of IrFeCoNiCu-HEA with similar Ir-mass loading (See Figure 17). Compared to these catalysts, IrFeCoNiCu-HEA showed better OER activity, further signifying the excellent performance of this HEA. The OER kinetics on IrFeCoNiCu-HEA nanoparticles were also improved, showed by the Tafel slope of about 58.0 mV dec⁻¹ for the IrFeCoNiCu-HEA, which is lower than that of pure Ir (about 75.8 mV dec⁻¹) and other IrM bimetallic systems, as presented in Figure 9B. [000173] From the polarization curves shown in FIG.18A, the average overpotential for benchmark monometallic Ir and Ru catalysts (FIG.19) at 10 mA cm⁻² was measured to be 352 mV and 257 mV, respectively. IrFeCoNi exhibits decent OER activity with an overpotential of ~315 mV, suggesting the activity enhancement caused by multi-elemental mixing compared to benchmark Ir. [000174] With the addition of Ru, the OER overpotential decreased as Ru concentration gradually increased (FIG. 20), with equimolar Ru_0.20(Ir,Fe,Co,Ni)_0.80 having the lowest overpotential of ~237 mV (FIG. 18A), which is ~78 mV lower than that of IrFeCoNi. As the best-performing Ru-containing catalyst, we focus more on the performance of equimolar Ru0.20(Ir,Fe,Co,Ni)0.80. From the Tafel slope analysis shown in FIG. 18B, the addition of Ru improves the OER kinetics with a measured slope of about 49 mV dec⁻¹. The overall activity and kinetic enhancement demonstrate the effect of introducing and uniformly mixing Ru in the IrFeCoNi multi-component alloy matrix. [000175] As shown in FIG. 18C, FIG. 21, FIG. 22, and FIG. 23, Ru0.20(Ir,Fe,Co,Ni)0.80 exhibits a high mass-activity of ~92 A g⁻¹ _Ir+Ru and specific activity of ~0.096 mA cm⁻² _ECSA, both measured at 300 mV of overpotential. In comparison, IrFeCoNi shows mass activity of ~16 A g⁻¹ _Ir and specific activity of ~0.023 mA cm⁻² _ECSA at the same overpotential. [000176] The OER stability of the catalysts was evaluated through chronopotentiometry measurement at a constant current density of 10 mA cm⁻². Over 24 hours of operation, Attorney Docket No.39425-352 Ru0.20(Ir,Fe,Co,Ni)0.80 shows enhanced OER stability with relatively low activity degradation of ~1.1 mV h⁻¹ (FIG. 24), while IrFeCoNi also demonstrates a stable OER operation with a slightly higher degradation rate (~1.4 mV h⁻¹) as seen in FIG. 18D. In comparison, monometallic Ir and Ru counterparts exhibit poor stability, as obviously seen in FIG.18D inset. Here, we particularly remark on shock-synthesized Ru nanoparticles as a classic example of activity-stability trade-off in OER. While initially being very active with low overpotential and high intrinsic catalytic activity, its stability only lasted for less than an hour of operation. In a multi-component alloy structure, the presence of Ru could be exploited to enhance its overall activity while simultaneously improving its OER stability due to the stabilized mixing of Ru in such an entropy-stabilized structure. [000177] Activity comparison between an HEA catalyst with one of its monometallic components or with the state-of-the-art catalyst of interest has always been a challenge, primarily due to the substantially different number of elements involved in the catalyst. To address this issue, the activity of IrFeCoNiCu-HEA and monometallic Ir was compared by normalizing the current density with Ir-mass loading and electrochemically active surface area (ECSA) measured using hydrogen underpotential deposition (HUPD). With similar Ir-mass loading, IrFeCoNiCu-HEA demonstrated a better Ir-mass-based activity compared to pure Ir catalyst (Figure 16C and 25). At 300 mV overpotential, the activity of IrFeCoNiCu-HEA (34.67 A g⁻¹Ir) is about 2.2 times better than that of pure Ir (15.76 A g⁻¹Ir). The ECSA for both IrFeCoNiCu-HEA and pure Ir was measured to be about 6.68 m2 g⁻¹Ir and 5.51 m2 g⁻¹Ir, respectively. When normalized to the ECSA, IrFeCoNiCu-HEA exhibited activity 1.8 times better compared to that of pure Ir catalyst at 300 mV overpotential (See Figure 26). Since the two catalysts had a relatively comparable ECSA, it was confirmed that the OER activity enhancement did not arise from an increase in surface area of the catalyst. The OER stability of the catalysts was also evaluated using chronopotentiometry tests at constant current density of 10 mA cm⁻² up to 12 hours of measurement. As indicated in Figure 16D, IrFeCoNiCu-HEA sustained a better OER stability compared to pure Ir. After 12 hours, the overpotential increase measured from chronopotentiometry test for IrFeCoNiCu-HEA is <60 mV, while for pure Ir is up to 120 mV. [000178] FIG.27 depicts the OER polarization curve of IrRuFeCoNi, IrFeCoNiCu, pure monometallic Ir, and pure monometallic Ru. IrRuFeCoNi exhibits an excellent OER performance with overpotential ~231 mV. FIG. 28 illustrates the stability of IrRuFeCoNi compared to IrFeCoNiCu under chronopotentiometry measurements with constant current Attorney Docket No.39425-352 density held at 10 mA cm⁻². IrRuFeCoNi shows a remarkable stability without any significant activity degradation. [000179] FIG.29A shows the cyclic voltammetry under HUPD potential range between shock-synthesized and colloidally-synthesized (untreated, air-annealed, and plasma-cleaned) IrFeCoNiCu-HEA samples. Air annealing was shown to be able to activate the catalyst presumably due to the decomposition of all ligands that cap the pre-treated catalyst nanoparticles, thus exposing the catalytic active sites. This is indicated by the characteristic HUPD peaks of Ir sites that can only be seen in the shock-synthesized and air-annealed samples. The loading of Ir in all samples is expected to be about 50-80 μgIr cm⁻²geo. [000180] FIG. 29B shows the cyclic voltammetry under Ir(III)/Ir redox peaks between shock-synthesized and colloidally-synthesized (untreated, air- and plasma- cleaned) IrFeCoNiCu-HEA samples. Again, air annealed shows the characteristic Ir(III)/Ir(IV) redox peak that can only be seen in the shock-synthesized sample. [000181] FIG. 29C shows the linear sweeping voltammetry curve between shock- synthesized and colloidally-synthesized (untreated, air-annealed, and plasma-cleaned) IrFeCoNiCu-HEA samples. The air-annealed sample is shown to have a comparable activity with the shock-synthesized sample, highlighting the importance of thermal activation in colloidally-synthesized samples. FIG. 29D depicts the Tafel plot between pure monometallic Ir, shock-synthesized, and air-annealed IrFeCoNiCu-HEA. The two HEA samples show a similar value of the Tafel slope, indicating similar OER kinetics between the two. This further validates the HEA-like structure of the colloidally-synthesized IrFeCoNiCu-HEA. [000182] During the synthesis process, the existence of carbon layers was observed encapsulating the HEA nanoparticles with thickness of about 5 nm (Figure 30A). The encapsulating layers have been reported to be formed on typical processes that involves heat treatment on different types of carbon substrates. The presence of encapsulating carbon layers have been widely debated for its effect in enhancing the activity and durability of Pt-based nanomaterials for oxygen reduction reaction (ORR) as it actually blocks the active Pt sites. However, in the case of our synthesized IrFeCoNiCu-HEA, we observed that the carbon layers were eventually delaminated after undergoing OER experiment (Figure 30B). Therefore, the inventors do not believe that the carbon layers will influence the activity and stability of the catalyst. [000183] After evaluating the activity and stability of the catalysts, the structural evolution of IrFeCoNiCu-HEA before and after OER experiments were then analyzed. Here, Attorney Docket No.39425-352 the inventors have shown evidence of structural evolution in IrFeCoNiCu-HEA under acidic OER conditions. FIG. 31A depicts the ex-situ STEM-EDS maps of each element, a superimposed map between Ir and Ni, and the overlay map of all elements of different IrFeCoNiCu-HEA samples collected from different treatments. The purpose of superimposing Ir and Ni elemental maps was to simply provide an example of better color contrast to evaluate the elemental distribution more thoroughly. The top row lists the elemental maps of as- synthesized IrFeCoNiCu-HEA before undergoing OER experiments. The homogeneous distribution and random mixing of all incorporated elements were verified. The middle row of FIG.31A shows the maps of an IrFeCoNiCu-HEA nanoparticle after undergoing initial cyclic voltammetry (CV) for electrochemical activation and linear-sweep voltammetry (LSV) for activity measurement. From the superimposed Ir + Ni and the overlay map, an Ir-rich shell layer was detected to form on the surface of the nanoparticles with a measured average thickness of about 2-6 nm. Meanwhile, the core of the nanoparticles was found to still preserve the characteristic homogeneous elemental distribution of the HEA without any phase separation or elemental segregation. The average thickness of the Ir-rich shell is found to not increase significantly in samples collected after undergoing 4 hours (FIG.32A), 8 hours (FIG. 32B), and 12 hours of chronopotentiometry test at 10 mA cm⁻² (bottom row of FIG.31A). This suggests that the evolved structure is relatively stable and does not undergo any further dramatic structural decay. [000184] To further elucidate the driving force of this structural evolution phenomenon and to obtain ensemble information, the concentration of the dissolved metals in the electrolyte was measured and collected from different time points using inductively coupled plasma optical emission spectroscopy (ICP-OES) through ex-situ offline measurements (FIG.33). The result indicates that the dissolution process had already taken place immediately after the initial electrochemical activation step. The dissolved 3d metals were detected to have a much higher concentration than Ir due to their lower oxidation potential. This leads to the conclusion that the 3d metals and a small portion of Ir atoms occupying near the surface of the nanoparticles were leached away into the electrolyte, thus forming the Ir-rich shell layer. The concentration of the dissolved metals was found to not increase significantly after the initial dissolution process, as indicated by the similar concentration measured after 4 hours of chronopotentiometry measurement. There was a slight increase in the concentration of dissolved metals after 12 hours of enduring the stability test. However, the concentration increase was much less significant than the dissolution at the initial step. This implies that the Attorney Docket No.39425-352 dissolution process occurs primarily during the electrochemical activation step and the dissolution during the stability test is relatively negligible. It also corroborated the finding that the average thickness of the Ir-rich shell layer does not increase significantly, even after 12 hours of the stability test. [000185] FIG.31B displays a high-resolution view of the Ir-rich shell layer from a sample taken after undergoing 4 hours of chronopotentiometry test. From the individual elemental map, the shell layer was not completely absent from the existence of the 3d metals. The elemental distribution of Ir was noticed to remain homogeneous, both in the core and around the edge or the surface of the nanoparticle. However, the elemental distribution for the 3d metals was seen to be more diffuse approaching the surface of the nanoparticle (illustrated by the dashed lines), implying that the core and the near-surface structure have different elemental compositions. The 3d metals concentration was depleted near the surface layer, leaving mostly Ir atoms with much higher concentration. Using this map, the composition of the skin layer was further resolved by measuring the atomic ratio at different regions of interest through STEM-EDS elemental analysis (FIG.34 and 35, Table 3). At the level of the whole region, Ir largely dominated the overall composition (~31.9 at.%), surmounting the other 3d metals due to their dissolution after undergoing OER. The core composition of Ir and other 3d metals was consistent with the typical atomic ratio of IrFeCoNiCu-HEA as previously described, suggesting that the core maintained the original HEA structure. On the skin layer region, the composition of Ir was measured to reach a staggering 65-75 at.%, while the rest of the composition was divided unevenly between the 3d metals. This denotes that the near-surface layers lost the ability to retain the typical HEA structure with homogeneous elemental distribution when exposed to harsh acidic OER conditions. The XRD pattern of an IrFeCoNiCu-HEA sample after enduring the OER experiment was then compared to that of the as-synthesized fresh sample (FIG. 31C and 36). From a more detailed inspection of the (111) diffraction peak, the peak of the post-electrolysis sample shifts to a lower diffraction angle corresponding to a larger lattice constant. This was primarily caused by the depletion of the 3d metals and leaving Ir, having the largest lattice constant, to dominate the composition of the nanoparticle. Table 3: The atomic ratio between Ir:Fe:Co:Ni:Cu in the nanoparticle after undergoing 4 hours of OER chronopotentiometry test at 10 mA cm-2 measured using EDS elemental analysis. The Attorney Docket No.39425-352 selected regions of interest are taken from FIG. 26. The quantification of each element was determined using the Cliff-Lorimer method. R_{egion of Interest} ^{Composition (at.-%)} I_{r Fe Co Ni Cu} [000186] Using aberration-corrected HAADF-STEM, the morphology of the near- surface structure for samples that have undergone the electrochemical activation treatment were studied (FIG.31D and 37). The distinction between the HEA core and the shell layer can be clearly seen here. In certain particles, the thickness of the Ir-rich shell varied from one region to another, implying that the dissolution of the metals at different parts of the nanoparticle might occur at different rates. The core of the nanoparticle was observed to still preserve the metallic HEA structure. In the shell layer, the lattice fringes can be easily recognized, indicating that this layer has the typical alloy structure instead of disordered structures. Additionally, a thin oxide layer was detected to form on the surface of the nanoparticles, as designated by the white arrows. The oxide layer was found to be unevenly distributed throughout the surface of the evolved nanoparticle. STEM-EDX analysis near the surface of the nanoparticle was then carried out to resolve the thickness of the oxide layer. FIG. 38A shows the elemental distribution of the nanoparticle, including the O K-edge. From the line scan profile (FIG.38B), the measured average thickness of this oxide layer was about 1 nm and was consistent with the observation from the HAADF-STEM image. Electron energy-loss spectroscopy (EELS) mapping and analysis were also carried out to resolve the formation of oxide structure in the post-electrolysis samples. EELS elemental maps (FIG. 39) confirmed the presence of oxygen at an appreciable concentration near the surface of the nanoparticle. However, oxygen was not only detected on the surface but also in the Ir-rich shell layer. This implies that we cannot rule out the possibility that a trace amount of oxide structures might also form in the shell layer. Further investigation of the near-surface structure (FIG.31E and 40) demonstrates the presence of Ir nano-domains populating the shell layer and surface of the evolved nanoparticles. FIG. 31F and 31G showed that the Ir domains have different in-plane rotational angles located near Attorney Docket No.39425-352 the surface of the nanoparticle. FFT analysis of the corresponding images confirmed that these structures are mainly domains consisting of Ir. [000187] FIG. 41 summarizes the general picture of the structural evolution illustrating the delamination of the encapsulating carbon layers and the dissolution of the mostly 3d metal atoms from the surface of the nanoparticle, leaving an Ir-rich shell layer. From the structural evolution study demonstrated by this work, it is now understood that high-entropy alloy nanoparticles are also susceptible to a structural change of the nanoparticles’ surface after being exposed to harsh electrocatalytic environments (i.e., highly oxidative-biased and acidic conditions). This suggests that the entropic stabilization effect near the surface of the HEA catalysts is less enhanced compared to the electrochemical redox that occurs on the surface leading to a certain degree of surface reconstruction. [000188] The concentration of dissolved metals in the electrolyte of benchmark Ir, Ru, and Ru0.20(Ir,Fe,Co,Ni)0.80 catalysts was measured using ex situ ICP-OES after the OER activity and stability (post 24 hours) measurements, as summarized in FIG. 42. As predicted, the dissolution had already occurred during the initial electrochemical activation step. The dissolved metals concentration in Ru0.20(Ir,Fe,Co,Ni)0.80 after 24 hours of stability testing was measured not to increase significantly, as expected from the stable OER activity (FIG. 18D). The amount of dissolved Ir and Ru is quite insignificant compared to the other 3d metal components. The extreme dissolution of the monometallic Ru benchmark catalyst after the electrochemical activation step is responsible for its activity degradation. The leaching of Ru in Ru_0.20(Ir,Fe,Co,Ni)_0.80 alloy was significantly suppressed compared to the monometallic Ru, further confirming the stabilization of Ru in the multi-component alloy matrix structure.  [000189] From STEM-EDS elemental and composite maps displayed in FIG. 43A, the dissolution of the 3d metals induces the development of a thin RuIr-rich shell layer near the surface of the evolved nanoparticles while the core maintains the homogeneous distribution of all five elements. In IrFeCoNi, an Ir-rich shell structure was also observed (FIG. 44A). However, in Ru_0.20(Ir,Fe,Co,Ni)_0.80, Ru was not exhaustively depleted within the evolved region, as seen in FIG. 43B, even after 24 hours of operation (FIG. 44B). The observation is consistent with the relatively similar and low amount of dissolved Ir and Ru detected in the ICP-OES analysis compared to the 3d metals. The RuIr-rich shell layer was measured to be ~1–2 nm in thickness, as measured from the line scan profile depicted in FIG.43C. [000190] FIG. 43D and FIG. 45 show the thin shell layer formed on the surface of the evolved nanoparticles after the electrochemical activation step. The average thickness of the Attorney Docket No.39425-352 shell layer was also measured to be ~1–2 nm, consistent with the STEM-EDS line profile analysis. In FIG.43D, the post-electrolyzed nanoparticle’s core and shell, which differ greatly in structure from each other, were probed. Position (i) marks the core where the pristine structure of as-prepared Ru_0.20(Ir,Fe,Co,Ni)_0.80 can still be maintained. The corresponding FFT analysis shows that the structure assumes the original fcc lattice. Position (ii) shows an amorphous region of the evolved surface, which might be composed of mainly IrOx, RuOx, or the combination thereof since the two are the only elements detected at higher concentrations on the shell layer (FIG. 43A, FIG. 43B, FIG. 43C). Surface amorphization and oxidation of OER catalysts are widely known to occur under OER-relevant potential to remove unstable species, exposing only the sites that can durably facilitate OER. The surface reconstruction leads to the formation of amorphous oxide, which is considered to be the OER active species. While highly active amorphous structures with abundant undercoordinated sites are unstable, polycrystalline IrOx or RuOx that are less active but more stable can also develop in addition to the amorphous counterparts. Although the exact OER-active sites remain unclear and need to be probed under in situ operating conditions, we speculate that the developed RuIr-rich amorphous or polycrystalline oxide layer is the OER active species. After 24 hours of stability measurement, the evolved structure showed no different structural transformation trend, and the shell layer showed no significant increase in thickness (FIG. 43E and FIG.45), indicating a stable shell layer during the galvanostatic testing. [000191] Ex situ X-ray photoelectron spectroscopy (XPS) measurements were conducted to identify the oxidation state of the as-prepared and post-electrolyzed Ru_0.20(Ir,Fe,Co,Ni)_0.80 catalyst and to confirm the presence of lattice oxide structure. FIG.46 show the high-resolution XPS spectra of Ru 3d, Ir 4f, and O 1s. In addition, FIG.47 depicts the spectra for Fe, Co, and Ni. With respect to the as-prepared sample, the post-electrolyzed catalyst shows consistent positive shifts due to the increased spectral contribution of the species with higher oxidation states, indicating the oxidation of the catalyst after undergoing OER, as demonstrated by Ru 3d5/2 and Ru 3d3/2 peaks (FIG.46A), as well as Ir 4f7/2 and Ir 4f5/2 peaks (FIG.46B). From the survey spectra in FIG. 47, the O 1s peak appears substantially on the post-electrolyzed sample. The spectral assignment analysis in FIG. 46C confirms the significant contribution from lattice oxygen (~532.0 eV) and hydroxyl (~533.0 eV), further providing evidence of an oxidized shell layer that can be attributed to IrO_x- and/or RuO_x-rich oxide layer. [000192] From bulk analysis using XRD, the Bragg peaks between the as-prepared and post-electrolyzed nanoparticles do not show any apparent shift in the diffraction angle (FIG. Attorney Docket No.39425-352 48), although the surface reconstruction is apparent. This is largely due to the formed RuIr-rich oxide shell layer being very thin in thickness that cannot be captured by bulk-sensitive diffraction experiments. Both the fcc and hcp phases of Ru0.20(Ir,Fe,Co,Ni)0.80 were present after electrolysis, indicating the structural stability of the two phases. Synthesis, Characterization and Measurements of Other Ru-based HEA [000193] To prepare RuIrFeCoNiCu, RuCl₃∙H₂O, IrCl₄∙H₂O, FeCl₃∙6H₂O, CoCl₂∙6H₂O, NiCl2∙6H2O, and CuCl2 ^2H2O were dissolved in ethanol with a total salt concentration of 0.5 mol L⁻¹.18 μL of the solution was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave, similar to the synthesis of Ir catalysts. [000194] FIG.49 depicts the XRD pattern of equimolar RuIrFeCoNi and RuIrFeCoNiCu, showing the successful synthesis of a six-element HEA system with a similar crystal structure to that of RuIrFeCoNi. The shifts of the peak towards the lower Bragg diffraction angle indicate an increase in lattice parameters in RuIrFeCoNiCu due to the addition of the Cu element. [000195] Apart from Ir- and RuIr-based HEA systems, HEA combinations without the inclusion of Ir were also synthesized. [000196] To prepare Ru_x(Pt,Fe,Co,Ni)_1−x, RuCl₃∙H₂O, H₂PtCl₆∙6H₂O, FeCl₃∙6H₂O, CoCl2∙6H2O, and NiCl2∙6H2O were dissolved in ethanol with a total salt concentration of 0.5 mol L⁻¹. The volume of Ru precursor was varied to 2.25 and 3.00 μL and mixed with 12 μL of (Pt,Fe,Co,Ni) salt precursor (3.00 μL each). The mixed solution was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave, similar to the synthesis of Ir catalysts. [000197] FIG. 50 depicts the XRD pattern of Ru_0.20(Pt,Fe,Co,Ni)_0.80 and Ru0.16(Pt,Fe,Co,Ni)0.84, showing the major fcc and minor hcp phases. In the equimolar system, the fraction of the hcp phase was observed to increase. FIG.50 also depicts the HAADF-STEM images and STEM-EDS maps of Ru0.16(Pt,Fe,Co,Ni)0.84, showing the homogeneous distribution of all elements with a few cases of apparent phase separation. [000198] To prepare Rux(Pd,Fe,Co,Ni)1−x, RuCl3∙H2O, PdCl2, FeCl3∙6H2O, CoCl2∙6H2O, and NiCl₂∙6H₂O were dissolved in ethanol with a total salt concentration of 0.5 mol L⁻¹. The volume of Ru precursor was varied to 2.25 and 3.00 μL and mixed with 12 μL of (Pd,Fe,Co,Ni) salt precursor (3.00 μL each). The mixed solution was drop-casted onto a carbon paper within Attorney Docket No.39425-352 the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave, similar to the synthesis of Ir catalysts. [000199] FIG. 51 depicts the XRD pattern of Ru0.20(Pd,Fe,Co,Ni)0.80 and Ru_0.16(Pd,Fe,Co,Ni)_0.84, showing the major fcc and minor hcp phases. In the equimolar system, the fraction of the hcp phase was observed to increase. FIG.51 also depicts the HAADF-STEM images and STEM-EDS maps of Ru_0.16(Pd,Fe,Co,Ni)_0.84, showing the homogeneous distribution of all elements with a few cases of apparent phase separation. [000200] To prepare Ru_x(Cr,Fe,Co,Ni)_1−x, RuCl₃∙H₂O, CrCl₃∙6H₂O, FeCl₃∙6H₂O, CoCl2∙6H2O, and NiCl2∙6H2O were dissolved in ethanol with a total salt concentration of 0.5 mol L⁻¹. The volume of Ru precursor was varied to 2.25 and 3.00 μL and mixed with 12 μL of (Pd,Fe,Co,Ni) salt precursor (3.00 μL each). The mixed solution was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave, similar to the synthesis of Ir catalysts. [000201] FIG. 52 depicts the XRD pattern of Ru_0.20(Cr,Fe,Co,Ni)_0.80 and Ru0.16(Cr,Fe,Co,Ni)0.84, showing the major fcc phase. FIG.52 also depicts the HAADF-STEM images and STEM-EDS maps of Ru0.16(Cr,Fe,Co,Ni)0.84, showing the homogeneous distribution of all elements with a few cases of apparent phase separation. [000202] To prepare Ru0.20(Cu,Fe,Co,Ni)0.80, RuCl3∙H2O, CuCl2 ^2H2O, FeCl3∙6H2O, CoCl₂∙6H₂O, and NiCl₂∙6H₂O were dissolved in ethanol with a total salt concentration of 0.5 mol L⁻¹.15 μL of the mixed solution was drop-casted onto a carbon paper within the area of 1 cm². The salt-loaded carbon paper was then sealed and irradiated in a microwave, similar to the synthesis of Ir catalysts. [000203] FIG.53 depicts the XRD pattern of Ru_0.20(Cu,Fe,Co,Ni)_0.80, showing the major fcc and minor hcp phases. FIG. 53 also depicts the HAADF-STEM images and STEM-EDS maps of Ru_0.20(Cu,Fe,Co,Ni)_0.80, showing the homogeneous distribution of all elements with a few cases of apparent phase separation. [000204] FIG. 54 depicts the OER polarization curves of Ru_0.20(Pt,Fe,Co,Ni)_0.80 and Ru0.20(Cu,Fe,Co,Ni)0.80 with other benchmark catalysts (scan rate: 5 mV s⁻¹). The RuPt- and RuCu-HEA systems show lower OER activities compared to the RuIr-HEA system. However, the RuPt-HEA system demonstrates better stability compared to the RuCu-HEA system during the initial electrochemical activation steps. Characterization and Measurements of Colloidally-synthesized HEAs Attorney Docket No.39425-352 [000205] FIG. 55 depicts the chronopotentiometry curve of air-annealed colloidally- synthesized IrFeCoNiCu-HEA over 24 hours of measurement at a constant current density of 10 mA cm⁻², showing the stability of the catalysts. The initial decrease in overpotential might indicate that the activation process was not complete. After the first 4 hours of stability testing, the catalyst was fully activated and demonstrated stable activity until the end of operation. [000206] FIG. 56 depicts the concentration of dissolved metals comparison between shock-synthesized and air-annealed colloidally-synthesized IrFeCoNiCu-HEA after the electrochemical activation process, showing a similar trend in dissolution, where Fe, Co, Ni, and Cu were dissolved at a faster rate and higher concentration than Ir. [000207] FIG. 57 depicts the HAADF-STEM images and STEM-EDS maps of as- prepared and post-electrolyzed air-annealed colloidally-synthesized IrFeCoNiCu-HEA sample, showing many cases of inhomogeneous elemental distribution between all elements. [000208] FIG.58 depicts the aberration-corrected HAADF-STEM images of air-annealed colloidally-synthesized IrFeCoNiCu-HEA, showing the distribution of the small particles and possible segregation of Ir-rich phases as indicated by the white contrast. [000209] FIG. 59 depicts the aberration-corrected HAADF-STEM images of post- electrolyzed air-annealed colloidally-synthesized IrFeCoNiCu-HEA, showing the relatively dissimilar trend of structural evolution compared to the shock-synthesized counterpart. The evolved nanoparticles were observed to maintain their crystallinity without an apparent Ir-rich shell layer. [000210] FIG. 60 depicts the atomic ratio of colloidally synthesized IrFeCoNiCu-, PtRuFeCoNi-, IrRuFeCoNiCu-, and IrRuFeCoNi-HEA as measured using ICP-OES. The measured atomic ratio matches quite well with the intended nominal ratio. [000211] FIG. 61 depicts the OER polarization curves of air-annealed colloidally- synthesized PtRuFeCoNi-, IrRuFeCoNi-, and IrRuFeCoNiCu-HEA with other benchmark catalysts (scan rate: 5 mV s⁻¹). Colloidally-synthesized PtRuFeCoNi-HEA demonstrates a similar trend with the shock-synthesized counterpart. IrRuFeCoNi- and IrRuFeCoNiCu-HEA show active OER trends initially but suffer from degradation at a higher applied potential. [000212] FIG. 62 depicts the cyclic voltammetry (CV) scans comparing air-annealed colloidally-synthesized PtRuFeCoNi- and IrRuFeCoNi-HEA. PtRuFeCoNi-HEA shows clear redox peaks under the HUPD and metal redox region, most of which could be assigned to Pt redox behavior. On the other hand, IrRuFeCoNi-HEA shows unclear redox peaks.

Claims

Attorney Docket No.39425-352 [000213] FIG. 63 depicts the atomic ratio of equimolar and Cu-rich IrFeCoNiCu-HEA, showing that the measured ratio is close to the intended nominal ratio. [000214] FIG. 64 depicts the OER polarization curves of equimolar and Cu-rich air- annealed colloidally-synthesized IrFeCoNiCu-HEA, showing a slight increase in activity of the Cu-rich system (scan rate: 5 mV s⁻¹). Conclusion of Results [000215] The synthesized IrFeCoNiCu-HEA nanoparticles demonstrated a promising performance to be used as a OER catalysts. The formation of single- phase solid solution alloy of IrFeCoNiCu-HEA was successfully realized using microwave- assisted shock synthesis and was confirmed using various electron microscopy and X-ray diffraction techniques. IrFeCoNiCu-HEA exhibited an enhanced OER activity and stability compared to the monometallic Ir counterpart and other more active Ir-based bimetallic alloys. The inventors discovered that when undergoing OER experiment, IrFeCoNiCu-HEA nanoparticles evolved into a structure where Ir-rich shell layer was formed on the surface of the particle, while the core preserved the homogeneous single-phase HEA structure. The main driving force for this to take place is the dissolution of mainly the 3d metals (Fe, Co, Ni, and Cu) from the surface of the nanoparticle, leaving Ir to populate the surface. From this study, the work illustrated the fact that HEA-based catalysts can sustain excellent stability.

Attorney Docket No.39425-352 What is claimed is: 1. A catalyst comprising: a multicomponent alloy comprising iridium (Ir), and at least four metals, and wherein the multicomponent alloy has a single-phase structure. 2. The catalyst of claim 1, wherein the catalyst has a core and a shell. 3. The catalyst of claim 2, wherein the core includes the multicomponent alloy. 4. The catalyst of any one of claims 1 to 3, wherein the at least four metals is selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). 5. The catalyst of any one of claims 1 to 3, wherein the at least four metals does not include a metal belonging to a platinum group metal (pgm). 6. The catalyst of claim 2, wherein the shell is Ir-rich. 7. The catalyst of any one of the preceding claims, further comprising a support. 8. The catalyst of claim 7, wherein the support includes an inorganic oxide, carbide or nitride material. 9. The catalyst of any of the preceding claims, wherein the catalyst is stable for at least about 12 hours. 10. The catalyst of any of the preceding claims, wherein the catalyst has a particle size distribution between about 2 nm to about 200 nm. 11. The catalyst of claim 1, wherein the at least four metals does not include a metal belonging to a pgm and includes a support. Attorney Docket No.39425-352 12. The catalyst of claim 1, wherein the catalyst has an atomic ratio between Ir and the at least four metals is equimolar. 13. The catalyst of claim 1, wherein Ir and the at least four metals are included to form a single alloy phase. 14. The catalyst of claim 1, wherein the at least four metals is selected from the group consisting of Fe, Co, Ni, Cu, and a ratio of Ir:Fe:Co:Ni:Cu is about 24:16:25:19:15. 15. The catalyst of claim 6, wherein the shell has a thickness of about 0.1 nm to about 20 nm. 16. A method for preparing a catalyst of any one of claims 1 to 15, comprising performing a microwave-assisted shock synthesis or a colloidal synthesis. 17. A method of performing oxygen evolution reaction using a catalyst according to any one of claims 1 to 15. 18. A catalyst comprising: a multicomponent alloy comprising ruthenium (Ru) and iridium (Ir) and at least four metals, wherein the multicomponent alloy has a single phase structure. 19. The catalyst of claim 18, wherein the catalyst has a core and a shell. 20. The catalyst of claim 19, wherein the core includes the multicomponent alloy. 21. The catalyst of claim 20, wherein the shell is Ru-rich, Ir-rich, or a combination thereof. 22. The catalyst of any one of claims 18 to 21, further comprising a support. 23. The catalyst of any one of claims 18 to 22, wherein the at least four metals does not include a pgm.