CHROMIUM AND NICKEL CO-DOPED RUTHENIUM OXIDE CATALYST FOR OXYGEN EVOLUTION REACTION IN ACIDIC MEDIA

Abstract

An oxygen evolution reaction (OER) catalyst for reaction in acidic media comprising: a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst, and wherein the chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst comprises a Cr and a Ni co-doped in a ruthenium oxide (RuO2). Methods of preparing the OER catalyst are disclosed.

Description

TECHNICAL FIELD

The present disclosure generally relates to an oxygen evolution reaction (OER) catalyst comprising: a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, and wherein the chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst comprises a Cr and a Ni co-doped in a ruthenium oxide (RuO₂).

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it may be described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor implicitly admitted as prior art against the present technology.

Water electrolysis (WE) using the hydrogen evolution reaction is widely recognized as a promising method for clean and sustainable hydrogen production. Currently, the dominant alkaline-based water electrolysis methods encounter challenges such as high ohmic resistance, limited current density, low efficiency, and poor long-term stability.

Proton exchange membrane (PEM) electrolysis provides efficient proton transfers and can effectively tackle the above challenges. Sluggish oxygen evolution reaction (OER) in acidic media has been a major long-existing obstacle in PEM systems and has therefore attracted great research interest.

IrO₂ (iridium oxide) is currently considered the only practical OER electrocatalyst in PEM electrolysis devices due to its high activity and durability. However, the high cost and low global reserve of Ir limit its large-scale applications. Less-expensive catalysts for acidic OER are in great demand.

RuO₂ (ruthenium oxide) has been recognized as an attractive alternative to IrO₂ for acidic OER due to its lower cost. While RuO₂ presents higher OER activity than IrO₂, its long-term stability remains a big challenge. In recent years, various strategies, i.e., lattice doping, strain effect, and morphology and structure modifications, have been tried to improve the performance of RuO₂ in acidic media.

It would be desirable to improve activity and stability of RuO₂ for acidic oxygen evolution reaction.

SUMMARY

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

In various aspects, the present teachings provide oxygen evolution reaction (OER) catalyst comprising:

• • a chromium (Cr) and a nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, and
  • wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO₂).

In some aspects, the OER catalyst is Ru_0.75Cr_0.125 Ni_0.125O₂.

In yet another aspect of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst increased OER activity as indicated by a decrease in overpotential by about 89 mV at 10 mA/cm² as compared to OER activity of a RuO₂ catalyst not co-doped with the chromium and the nickel.

In yet another aspect of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst is durable for about 2.5 to about 100 hours.

In yet another aspect of the OER catalyst, the chromium is from chromium (II) chloride CrCl₂ precursor.

In another aspect of the OER catalyst, the nickel is from nickel(II) chloride hexahydrate NiCl₂·6H₂O precursor.

In yet another aspect, a proton exchange membrane (PEM) water electrolyzer comprises the OER catalyst.

Yet another aspect is a method of performing OER catalysis in acidic media, the acidic media comprising an OER catalyst, the OER catalyst comprising:

• • a nickel (Ni) and chromium (Cr) co-doped ruthenium oxide (RuO₂) catalyst, and
  • wherein the nickel (Ni) chromium (Cr) co-doped ruthenium oxide (RuO₂) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO₂).

In these different aspects of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst is a solid solution metal oxide. In these different aspects of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst comprises nanoparticles of the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst having a particle size of less than about 10 nm. The OER catalyst comprises a tetragonal rutile-type structure. The OER catalyst is at an anode in a PEM water electrolyzer. In these different aspects, the OER catalyst is applicable for an acidic OER. In some aspects, the acidic media comprises perchloric acid (HClO₄).

Further areas of applicability and various methods of enhancing the above technology will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

The present teachings will become more fully understood from the detailed description and the accompanying drawings wherein:

FIG. 1 illustrates a proton exchange membrane (PEM) water electrolysis reaction.

FIG. 2 provides comparison of X-ray diffraction patterns of synthesized RuO₂, and synthesized Ru_0.75Cr_0.125Ni_0.125O₂, along with peaks from RuO₂ standard (PDF #04-009-8495) provided for comparison.

FIG. 3A provides bright-field scanning transmission electron microscope (STEM) image of commercial RuO₂ (scale bar 20 nm).

FIG. 3B provides bright-field scanning transmission electron microscope (STEM) image of synthesized RuO₂ (scale bar 10 nm).

FIG. 3C provides bright-field scanning transmission electron microscope (STEM) image of synthesized Ru_0.75Cr_0.125Ni_0.125O₂ (scale bar 10 nm).

FIG. 4A provides high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) image of nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst for chemical mapping using energy dispersive X-ray spectroscopy (EDS).

FIG. 4B provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of oxygen (O) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst.

FIG. 4C provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of ruthenium (Ru) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst.

FIG. 4D provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of chromium (Cr) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst.

FIG. 4E provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of nickel (Ni) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst.

FIG. 5A provides linear sweep voltammetry (LSV) curves for commercial RuO₂ (broken line), synthesized RuO₂ (unbroken line), and synthesized Ru_0.75Cr_0.125Ni_0.125O₂ (tracked line) in reaction performed in 0.1 M perchloric acid (HClO₄).

FIG. 5B provides chronopotentiometry (CP) stability tests for commercial RuO₂ (broken line), synthesized RuO₂ (unbroken line), and synthesized Ru_0.75Cr_0.125Ni_0.125O₂ (tracked line) in reaction performed in 0.1 M perchloric acid (HClO₄).

It should be noted that the figures set forth herein are intended to exemplify the general characteristics of the methods, algorithms, and devices among those of the present technology, for the purpose of the description of certain aspects. These figures may not precisely reflect the characteristics of any given aspect and are not necessarily intended to define or limit specific examples within the scope of this technology. Further, certain aspects may incorporate features from a combination of figures.

DETAILED DESCRIPTION

The present teachings relate to lattice doping to stabilize RuO₂ crystal structure, therefore improving activity and durability of RuO₂ based catalysts for oxygen evolution reaction in acidic media.

In various aspects, the present teachings provide oxygen evolution reaction (OER) catalyst comprising:

• • a chromium (Cr) and a nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, and
  • wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO₂).

In some aspects, the chromium used for doping can be from chromium (II) chloride CrCl₂ precursor.

In some aspects the nickel can be from nickel(II) chloride hexahydrate NiCl₂·6H₂O precursor.

In some aspects of the OER catalyst, Ru (ruthenium) ranges from about 75.0 at % (atomic percent) to about 33.3 at %, chromium ranges from about 12.5 at % to about 33.3 at %, and nickel ranges from about 12.5% to about 33.3 at %.

In some aspects, the OER catalyst is Ru_0.75Cr_0.125 Ni_0.125O₂.

In yet another aspect of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst increased OER activity as indicated by a decrease in overpotential by about 89 mV at 10 mA/cm² as compared to OER activity of a RuO₂ catalyst not co-doped with the chromium and the nickel.

In yet another aspect of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst is durable for about 100 hours. In some aspects, the disclosed OER catalysts are durable for about 2.5 to about 100 hours.

In yet another aspect, a proton exchange membrane (PEM) water electrolyzer comprises the OER catalyst.

In these different aspects of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst is a solid solution metal oxide.

In these different aspects of the OER catalyst, the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst comprises nanoparticles of the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst having a particle size of less than about 10 nm, about 8 nm, about 6 nm, about 5 nm, or less than about 5 nm.

The OER catalyst comprises a tetragonal rutile-type structure.

The OER catalyst is at an anode in a PEM water electrolyzer. The OER catalyst is applicable for OER reaction in an acidic medium. In some aspects, the acidic media comprises perchloric acid (HClO₄).

The disclosed OER catalysts can increase OER activity by a decrease in overpotential by about 89 mV at 10 mA/cm² as compared to OER activity of catalyst of an RuO₂ not co-doped with the chromium and nickel.

Yet another aspect is a method of performing OER catalysis in acidic media, the acidic media comprising an OER catalyst, the OER catalyst comprising:

• • a nickel (Ni) and chromium (Cr) co-doped ruthenium oxide (RuO₂) catalyst, and
  • wherein the nickel (Ni) chromium (Cr) co-doped ruthenium oxide (RuO₂) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO₂). The acidic media can be perchloric acid (HClO₄).

FIG. 1 illustrates a proton exchange membrane (PEM) water electrolysis reaction. An electrolyzer is an electrochemical device to convert electricity and water into hydrogen and oxygen, these gases can then be used as a means to store energy for later use. Proton exchange membrane (PEM) electrolysis is the electrolysis of water in a PEM water electrolyzer cell equipped with a solid polymer electrolyte that is responsible for the conduction of protons, separation of product gases, and electrical insulation of the electrodes. It involves a proton-exchange membrane.

The half reaction taking place on the anode side of a PEM water electrolyzer is referred to as the Oxygen Evolution Reaction (OER). Here the liquid water reactant is supplied to catalyst where the supplied water is oxidized to oxygen, protons and electrons:

The half reaction taking place on the cathode side of a PEM water electrolyzer is the Hydrogen Evolution Reaction (HER), wherein the supplied electrons and the protons that have conducted through the membrane are combined to create gaseous hydrogen:

The total reaction is: H₂O(liquid)→H₂(gas)+½O₂(gas).

FIG. 2 provides comparison of X-ray diffraction patterns of synthesized RuO₂, and synthesized Ru_0.75Cr_0.125Ni_0.125O₂. Intensity is provided in arbitrary units (a. u.). FIG. 2 shows that a pure phase of tetragonal rutile-type structure was obtained in the synthesized Ru_0.75Cr_0.125Ni_0.125O₂. X-ray diffraction (XRD) peaks of synthesized Ru_0.75Cr_0.125Ni_0.125O₂ shifted to higher 2θ (2 theta) as compared with those of RuO₂, indicating the incorporation of Cr and Ni in RuO₂ crystal lattice. Peaks from RuO₂ standard (PDF #04-009-8495) is provided for comparison in FIG. 2.

FIGS. 3A, 3B and 3C provide bright-field scanning transmission electron microscope (STEM) images.

FIG. 3A provides bright-field scanning transmission electron microscope (STEM) image of commercial RuO₂.

FIG. 3B provides bright-field scanning transmission electron microscope (STEM) image of synthesized RuO₂.

FIG. 3C provides bright-field scanning transmission electron microscope (STEM) image of synthesized Ru_0.75Cr_0.125Ni_0.125O₂.

Scanning transmission electron microscope (STEM) images in FIG. 3C showed a crystallite structure of <5 nm (less than 5 nm) particle size for synthesized Ru_0.75Cr_0.125Ni_0.125O₂ as compared with ˜6 nm (about 6 nm) for RuO₂ (FIG. 3B). For comparison, STEM image of commercial RuO₂ is also shown in FIG. 3A. Commercial RuO₂ had much larger particle size of about 20 nm.

Chemical mapping using energy dispersive X-ray spectroscopy (EDS) in STEM showed a uniform distribution of Cr, Ni and Ru in the nanoparticles (FIGS. 4A, 4B, 4C, 4D and 4E), further confirmed the lattice doping of RuO₂ with Cr and Ni.

FIG. 4A provides high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) image of nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst for chemical mapping using energy dispersive X-ray spectroscopy (EDS).

FIG. 4B provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of oxygen (O) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, as shown in green color.

FIG. 4C provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of ruthenium (Ru) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, as shown in orange color.

FIG. 4D provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of chromium (Cr) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, as shown in red color.

FIG. 4E provides chemical mapping using energy dispersive X-ray spectroscopy (EDS) in scanning transmission electron microscope (STEM) of nickel (Ni) in nanoparticles of a chromium (Cr) and nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, as shown in purple color.

Rotating disk electrode (RDE) evaluation results are shown in FIGS. 5A and 5B. FIG. 5A provides linear sweep voltammetry (LSV) curves for commercial RuO₂, synthesized RuO₂, and synthesized Ru_0.75Cr_0.125Ni_0.125O₂ performed in 0.1M perchloric acid. For comparison, commercial RuO₂ were also evaluated using the same conditions. Synthesized RuO₂ showed higher activity than commercial RuO₂. Incorporation of Cr and Ni in RuO₂ as in synthesized Ru_0.75Cr_0.125Ni_0.125O₂ showed increased OER activity than commercial RuO₂. Synthesized Ru_0.75Cr_0.125Ni_0.125O₂ showed increased OER activity than synthesized RuO₂.

FIG. 5B provides chronopotentiometry (CP) stability tests for commercial RuO₂, synthesized RuO₂, and synthesized Ru_0.75Cr_0.125Ni_0.125O₂ performed in 0.1M perchloric acid. Ru_0.75Cr_0.125Ni_0.125O₂ catalyst synthesized by Cr and Ni co-doping of RuO₂ significantly increased the OER durability as compared to commercial RuO₂ or synthesized RuO₂. While commercial and synthesized RuO₂ degraded in less than one and two hours respectively, Ru_0.75Cr_0.125Ni_0.125O₂ lasted about 90 hours.

EXAMPLE

Various aspects of the present disclosure are further illustrated with respect to the following example. It is to be understood that this example is provided to illustrate specific examples of the present disclosure and should not be construed as limiting the scope of the present disclosure in or to any particular aspect.

Example 1

Synthesis and Testing of Ru_0.75Cr_0.125Ni_0.125O₂

0.1736 g of RuCl₃, 0.0171 g of CrCl₂ and 0.0331 g of NiCl₂·6H₂O (Ru, Cr, and Ni at a molar ratio of 3:0.5:0.5) were added in 150 ml of 1 M HCl and sonicated for 2 hours. 0.4 g of Carbon black was then added and dispersed by stirring for 20 hours under room temperature. The mixture was dried by using a rotary evaporator and the remaining powder was collected. The powder was annealed in a flowing Ar/H₂ (7% H₂) atmosphere at 900° C. for 4 hours and then annealed in air at 550° C. for 4 hours.

Synthesis of RuO₂

For synthesis of RuO₂ (referred to as synthesized RuO₂), no CrCl₂ and NiCl₂·6H₂O were added as described above for the synthesis of Ru_0.75Cr_0.125 Ni_0.125O₂, and the rest of the procedure remained the same as described above.

Ink and Electrode Preparation for Electrochemical Measurements 20 mg of catalyst powder was added to a mixture of 1 ml of isopropyl alcohol, 4 ml of DI water, and 100 μl of NAFION® Dispersion D520 and sonicated for 1 h to obtain a well-dispersed catalyst ink. For electrode preparation, 20 μl of catalyst ink was drop-cast on a 5.0-mm-diameter glassy carbon electrode, resulting in a catalyst loading of 400 g/cm². The electrode was mounted to a rotator (Pine Instrument rotator upside down) and was rotated at a speed of 200 rpm and dried.

Electrochemical Measurement

The electrochemical experiments were conducted using a Pine Instrument rotating disk electrode (RDE) workstation. A three-electrode system, consisting of the catalyst film-coated glassy carbon working electrode, a platinum wire counter electrode, and a home-made Pt reference electrode (with fresh H₂ from water electrolysis for each test), were used for all electrochemical measurements. The electrolyte used was 0.1 M HClO₄.

Linear sweep voltammetry (LSV) test was performed at a scan rate of 1 mV/s; RDE rotating speed 1600 rpm; in O₂ saturated 0.1 M HClO₄. Results are provided in FIG. 5A.

Chronopotentiometry (CP) test was performed at 10 mV/cm². Results are provided in FIG. 5B.

Further, the disclosure comprises additional notes and examples as detailed below.

Clauses

Clause 1. An oxygen evolution reaction (OER) catalyst comprising:

• • a chromium (Cr) and a nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst, and
  • wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO₂).

Clause 2. The OER catalyst of clause 1, wherein Ru (ruthenium) ranges from about 75.0 at % to about 33.3 at %, chromium ranges from about 12.5 at % to about 33.3 at %, nickel ranges from about 12.5% to about 33.3 at %.

Clause 3. The OER catalyst of clause 1, wherein the OER catalyst is Ru_0.75Cr_0.125 NiO_0.125O₂.

Clause 4. The OER catalyst of clause 1, wherein a chromium for doping the ruthenium oxide (RuO₂) is from chromium (II) chloride CrCl₂ precursor.

Clause 5. The OER catalyst of clause 1, wherein a nickel for doping the ruthenium oxide (RuO₂) is from nickel(II) chloride hexahydrate NiCl₂·6H₂O precursor.

Clause 6. The OER catalyst of clause 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst is a solid solution metal oxide.

Clause 7. The OER catalyst of clause 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst comprises nanoparticles of the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst.

Clause 8. The OER catalyst of clause 1, wherein the OER catalyst has a particle size of less than about 10 nm.

Clause 9. The OER catalyst of clause 1, wherein the OER catalyst comprises a tetragonal rutile-type structure.

Clause 10. The OER catalyst of clause 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst is at an anode of a proton exchange membrane (PEM) water electrolyzer.

Clause 11. The OER catalyst of clause 1, wherein the OER catalyst is applicable for an acidic OER.

Clause 12. The OER catalyst of clause 1, wherein OER activity is performed in an acidic media, wherein the acidic media is perchloric acid.

Clause 13. The OER catalyst of clause 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst increased OER activity as indicated by a decrease in overpotential by about 89 MV at 10 mA/cm² as compared to OER activity of a RuO₂ catalyst not co-doped with the chromium and nickel.

Clause 14. The OER catalyst of clause 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO₂) catalyst is durable for about 2.5 to about 100 hours.

Clause 15. A proton exchange membrane (PEM) water electrolyzer comprising the OER catalyst of clause 1.

Clause 16. A method of performing OER catalysis in acidic media, the method comprising an OER catalysis reaction in acidic media, the acidic media comprising an OER catalyst, the OER catalyst comprising:

• • a nickel (Ni) and chromium (Cr) co-doped ruthenium oxide (RuO₂) catalyst, and
  • wherein the nickel (Ni) chromium (Cr) co-doped ruthenium oxide (RuO₂) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO₂).

The preceding description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical “or.” It should be understood that the various steps within a method may be executed in different order without altering the principles of the present disclosure. Disclosure of ranges includes disclosure of all ranges and subdivided ranges within the entire range.

The headings (such as “Background” and “Summary”) and sub-headings used herein are intended only for general organization of topics within the present disclosure and are not intended to limit the disclosure of the technology or any aspect thereof. The recitation of multiple examples having stated features is not intended to exclude other embodiments having additional features, or other examples incorporating different combinations of the stated features.

As used herein, the terms “comprise” and “include” and their variants are intended to be non-limiting, such that recitation of items in succession or a list is not to the exclusion of other like items that may also be useful in the devices and methods of this technology. Similarly, the terms “can” and “may” and their variants are intended to be non-limiting, such that recitation that an example can or may comprise certain elements or features does not exclude other examples of the present technology that do not contain those elements or features.

As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means +/−5% of the stated value, more typically +/−4% of the stated value, more typically +/−3% of the stated value, more typically, +/−2% of the stated value, even more typically +/−1% of the stated value, and even more typically +/−0.5% of the stated value.

The broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the specification and the following claims. Reference herein to one aspect, or various aspects means that a particular feature, structure, or characteristic described in connection with an embodiment or particular system is included in at least one embodiment or aspect. The appearances of the phrase “in one aspect” (or variations thereof) are not necessarily referring to the same aspect or embodiment. It should be also understood that the various method steps discussed herein do not have to be carried out in the same order as depicted, and not each method step is required in each aspect or embodiment.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations should not be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

1. An oxygen evolution reaction (OER) catalyst comprising:

a chromium (Cr) and a nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst, and

wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO2).

2. The OER catalyst of claim 1, wherein Ru (ruthenium) ranges from about 75.0 at % to about 33.3 at %, chromium ranges from about 12.5 at % to about 33.3 at %, and nickel ranges from about 12.5% to about 33.3 at %.

3. The OER catalyst of claim 1, wherein the OER catalyst is Ru0.75Cr0.125Ni0.125O2.

4. The OER catalyst of claim 1, wherein the chromium for doping the ruthenium oxide (RuO2) is from chromium (II) chloride (CrCl2) precursor.

5. The OER catalyst of claim 1, wherein the nickel for doping the ruthenium oxide (RuO2) is from nickel(II) chloride hexahydrate (NiCl2·6H2O) precursor.

6. The OER catalyst of claim 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst is a solid solution metal oxide.

7. The OER catalyst of claim 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst comprises nanoparticles of the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst.

8. The OER catalyst of claim 1, wherein the OER catalyst has a particle size of less than about 10 nm.

9. The OER catalyst of claim 1, wherein the OER catalyst comprises a tetragonal rutile-type structure.

10. The OER catalyst of claim 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst is at an anode of a proton exchange membrane (PEM) water electrolyzer.

11. The OER catalyst of claim 1, wherein the OER catalyst is applicable for an acidic OER.

12. The OER catalyst of claim 1, wherein OER activity is performed in an acidic media, wherein the acidic media is perchloric acid.

13. The OER catalyst of claim 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst increased OER activity as indicated by a decrease in overpotential by about 89 mV at 10 mA/cm2 as compared to OER activity of a RuO2 catalyst not co-doped with the chromium and nickel.

14. The OER catalyst of claim 1, wherein the chromium (Cr) and the nickel (Ni) co-doped ruthenium oxide (RuO2) catalyst is durable for about 2.5 to about 100 hours.

15. A proton exchange membrane (PEM) water electrolyzer comprising the OER catalyst of claim 1.

16. A method of performing OER catalysis in acidic media, the method comprising an OER catalysis reaction in acidic media, the acidic media comprising an OER catalyst, the OER catalyst comprising:

a nickel (Ni) and chromium (Cr) co-doped ruthenium oxide (RuO2) catalyst, and wherein the nickel (Ni) chromium (Cr) co-doped ruthenium oxide (RuO2) catalyst comprises a Ni and a Cr co-doped in a ruthenium oxide (RuO2).