High performance transition metal based nitride catalysts for alkaline water electrolysis

Abstract

Improved electrocatalysts for promoting a hydrogen evolution reaction (HER) or an oxygen evolution reaction (OER) from alkaline fresh water and seawater are disclosed. By incorporating metals, such as tungsten and rare earth elements, into the nickel molybdenum nitride framework, Ni1-xMoxN, the disclosed electrocatalysts demonstrate improved catalytic activity and stability compared to the original Ni&Ni0.2Mo0.8N catalysts, particularly under high-current alkaline conditions, in water electrolysis for hydrogen and oxygen production.

Description

HIGH PERFORMANCE TRANSITION METAL BASED NITRIDE CATALYSTS FOR ALKALINE WATER ELECTROLYSIS TECHNICAL FIELD

[0001] The present disclosure relates generally to water electrolysis, and more particularly, to hydrogen evolution reaction and oxygen evolution reaction catalysts having enhanced catalytic activity and stability for use in water electrolysis. BACKGROUND

[0002] In recent decades, the global energy economy based on hydrocarbons has faced serious constraints from both economic and environmental perspectives. The increasing demand for energy has led to a decline in fossil fuel production capacity, threatening global energy supply and putting immense pressure on the environment. Thus, finding alternatives to hydrocarbon fuels is crucial. Hydrogen, with its high energy density, pollution-free nature, and renewability, is considered a promising alternative to fossil fuels.

[0003] There are three main methods of hydrogen production: gray hydrogen, blue hydrogen, and green hydrogen. Gray hydrogen, the most common method, is produced from fossil fuels like oil, natural gas, and coal. While it is a relatively simple process, it is associated with significant greenhouse gas emissions. Blue hydrogen production is like gray hydrogen but captures and stores CO2during the process. Although more environmentally friendly, it remains a transitional solution dependent on fossil fuel supply. In contrast, green hydrogen is produced through the electrolysis of water using renewable energy sources like wind, hydro, solar, and nuclear power, without emitting CO2or other greenhouse gases, making it the most environmentally friendly method.

[0004] Water electrolysis for hydrogen production, however, is limited by electricity costs, conversion efficiency, and other factors. The main reason for the high electricity consumption in hydrogen production through water electrolysis is the high overpotential required for the catalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at the working electrodes. The efficiency and cost of water electrolysis for hydrogen production are largely determined by the materials catalyzing the reactions at both electrodes, namely the cathode HER catalyst and the anode OER catalyst. One of the critical barriers that keep water splitting from being of practical use is the sluggish reaction kinetics of OER and HER due to high overpotentials,4929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) a measure of the kinetic energy barriers. Therefore, catalysis plays a major role in both OER and HER. Highly effective catalysts are required to minimize the overpotentials for OER and HER towards efficient H2 and O2 production.

[0005] While water electrolysis in an alkaline environment is one of the most promising techniques for large-scale and sustainable hydrogen production, the rate of HER is approximately two orders of magnitude lower in an alkaline environment than in an acidic environment, primarily due to the slower HO-H dissociation reaction. Furthermore, the high affinity of OH−ions towards active sites can lead to their occupation by the final products, thereby blocking subsequent reactions and resulting in a higher HER overpotential. Therefore, developing catalysts with fast water dissociation kinetics is of great importance for efficient alkaline-based water electrolysis.

[0006] NiMo-based nanoscale catalysts have been widely recognized as among the most efficient HER catalysts in an alkaline environment due to their quick water dissociation kinetics. However, the dissolution of Mo (which has been widely recognized as an important active site) in such NiMo-based nanoscale catalysts, followed by their deactivation during long-term stability tests, has significantly limited the application of these catalysts.

[0007] Accordingly, there remains a need in the art for high-activity, stable electrocatalysts for advancing the development of water electrolysis technology. SUMMARY

[0008] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter.

[0009] In some embodiments, a catalyst for promoting a hydrogen evolution reaction or an oxygen evolution reaction is provided, the catalyst having formula (I): Ni1-y(Mo1-xMx)yN (I), wherein M is a metal selected from tungsten (W), yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zirconium (Zr), niobium (Nb), hafnium (Hf), or tantalum (Ta); x is a number from 0.01 to 0.99; and y is a number from 0.01 to 0.99. In one embodiment, M may be selected from W, Y, La, Ce, 24929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) Pr, Nd, Sm, Eu, Gd, or Yb; y is a number from 0.6 to 0.9; and x is a number from 0.05 to 0.3. In another embodiment, M is selected from W or Y; y is a number from 0.8 to 0.9; and x is a number 0.1 to 0.2. In still another embodiment, M is W or Y; y is 0.8; and x is 0.1. In yet another embodiment, the catalyst is configured to achieve a current density of 1,000 mA cm-2at an operating voltage of 1.8 V or less for up to 350 hours.

[0010] In further embodiments, an electrode is provided, the electrode including a substrate; and a catalyst formed on the substrate, the catalyst having formula (I): Ni1-y(Mo1-xMx)yN (I), wherein M is a metal selected from tungsten (W), yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zirconium (Zr), niobium (Nb), hafnium (Hf), or tantalum (Ta); x is a number from 0.01 to 0.99; and y is a number from 0.01 to 0.99. In one embodiment, M may be selected from W, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, or Yb; y is a number from 0.6 to 0.9; and x is a number from 0.05 to 0.3. In another embodiment, M is selected from W or Y; y is a number from 0.8 to 0.9; and x is a number 0.1 to 0.2. In still another embodiment, M is W or Y; y is 0.8; and x is 0.1. In one embodiment, the substrate includes a three-dimensional substrate, such as a metal foam, a metal wire mesh, or carbon cloth paper. For instance, the three-dimensional substrate may be a metal foam including nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), titanium (Ti), or a combination thereof. In one embodiment, the three-dimensional substrate is nickel (Ni) foam.

[0011] In still further embodiments, a method of making a catalyst for a hydrogen evolution reaction (HER) or an oxygen evolution reaction (OER) is provided, the method including exposing a substrate to an aqueous solution including a first metal salt including nickel, a second metal salt including molybdenum, and a third metal salt including tungsten, a rare earth element, titanium, vanadium, chromium, manganese, zirconium, niobium, hafnium, or tantalum, at a temperature and for a period of time sufficient to form a precursor catalyst, and subjecting the precursor catalyst to a source of nitrogen at a temperature and for a period of time sufficient to form a catalyst having formula (I): Ni1-y(Mo1-xMx)yN (I), wherein: M is a metal selected from tungsten, a rare earth element, titanium, vanadium, chromium, manganese, zirconium, niobium, hafnium, or tantalum; x is a number from 0.01 to 0.99; and y is a number from 0.01 to 0.99. 34929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0012] In one embodiment, the exposing step further includes heating the substrate and the aqueous solution to a temperature above the boiling point of water. For example, the substrate and the aqueous solution can be heated to a temperature of about 80°C to about 300°C. The heating step can be performed for at least about two hours. In another embodiment, the source of nitrogen includes a mixture of ammonia and argon gas. In still another embodiment, the subjecting step is carried out at a temperature of about 400°C to about 600°C. In some embodiments, M is a metal selected from tungsten (W), yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), or lutetium (Lu); y is a number from 0.6 to 0.9; and x is a number from 0.05 to 0.3. In another embodiment, M is W or Y; y is 0.8; and x is 0.1. In still another embodiment, the substrate is a metal foam including nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), titanium (Ti), or a combination thereof. In yet another embodiment, the substrate is nickel (Ni) foam.

[0013] In yet further embodiments, a method for producing oxygen and hydrogen is provided, the method including providing an electrochemical cell including an anode and a cathode, the anode and the cathode each including an electrocatalyst having the formula: Ni1-y(Mo1-xMx)yN (I), wherein M is a metal selected from tungsten (W), yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zirconium (Zr), niobium (Nb), hafnium (Hf), or tantalum (Ta), x is a number from 0.01 to 0.99, and y is a number from 0.01 to 0.99; and applying current to the electrochemical cell, wherein hydrogen is produced at the cathode and oxygen is produced at the anode. In one embodiment, M is selected from W, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, or Yb; y is a number from 0.6 to 0.9; and x is a number from 0.05 to 0.3. In another embodiment, M is W or Y; y is 0.8; and x is 0.1. In another embodiment, the electrochemical cell may further include an electrolyte solution in which the anode and the cathode are immersed. For example, the electrolyte solution may include alkaline water, such as alkaline fresh water or alkaline seawater. In some embodiments, the electrocatalyst is formed on a substrate including metallic foam. 44929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) BRIEF DESCRIPTION OF DRAWINGS

[0014] Further features and advantages can be ascertained from the following detailed description that is provided in connection with the drawings described below:

[0015] Figure 1 is a schematic illustration of the synthesis procedure for the tungsten- alloyed Ni&Ni0.2(Mo1-xWx)0.8N catalyst according to one embodiment.

[0016] Figure 2 shows X-ray diffraction (XRD) patterns of Ni(Mo1-xWx)O4 / NF (x = 0, 0.05, 0.10, 0.15, 0.20, and 0.30) catalysts.

[0017] Figures 3A and 3B are scanning electron microscopy (SEM) images of Ni&Ni0.2(Mo0.90W0.10)0.8N at different magnifications.

[0018] Figure 3C is a transmission electron microscopy (TEM) image of a Ni&Ni0.2(Mo0.90W0.10)0.8N nanorod where the inset shows a higher magnification image of the same nanorod.

[0019] Figures 3D and 3E are high-resolution TEM (HRTEM) images of nanoparticles and nanorods, in Ni&Ni0.2(Mo0.90W0.10)0.8N.

[0020] Figure 3F shows a selected-area electron diffraction (SAED) pattern for Ni0.2(Mo0.90W0.10)0.8N.

[0021] Figures 3G-3K show energy-dispersive X-ray spectroscopy (EDS) element mapping for Ni, Mo, W, N, and O, respectively.

[0022] Figure 3L shows an EDS linear scan (top) and corresponding element dispersion (bottom) across a single Ni&Ni0.2(Mo0.90W0.10)0.8N nanorod.

[0023] Figure 3M shows EDS point analysis of a single Ni&Ni0.2(Mo0.90W0.10)0.8N nanorod.

[0024] Figure 4A shows XRD patterns for Ni&Ni0.2(Mo1-xWx)0.8N where x = 0, 0.05, 0.10, 0.15, and 0.20.

[0025] Figures 4B-4F show high-resolution x-ray photoelectron spectroscopy (XPS) spectra of Ni 2p, Mo 3d, W 4f, N 1s, and O 1s, respectively.

[0026] Figures 5A and 5B are graphs showing a comparison of HER performance in 1 M KOH water and ECSA values, respectively, among Ni&Ni0.2(Mo1-xWx)0.8N samples prepared with various tungsten concentrations.

[0027] Figures 6A and 6B are graphs showing a comparison of performance in 1 M KOH and Tafel slope values among different catalysts. 54929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0028] Figure 6C is a graph showing a comparison of HER activity in 1 M KOH with other state-of-the-art NiMo-based catalysts.

[0029] Figure 7 is a graph showing a comparison of HER performance by Ni&Ni0.2(Mo0.90W0.10)0.8N before stability testing and after up to 60,000 cycles CV scans in 1 M KOH water.

[0030] Figure 8A is a graph showing CP testing of Ni&Ni0.2Mo0.8N and Ni&Ni0.2(Mo0.90W0.10)0.8N at 500 mA cm-2(top) and at 1000 mA cm-2(bottom).

[0031] Figure 8B is a graph showing LSV curves for before and after 100 h of testing at 1000 mA cm-2.

[0032] Figure 9A is a diagram showing structure models for H2O adsorption in Ni&Ni0.2(Mo0.90W0.10)0.8N.

[0033] Figures 9B and 9C show H2O adsorption energy and a free energy diagram for H2O dissociation, respectively, for Ni&Ni0.2Mo0.8N and Ni&Ni0.2(Mo0.90W0.10)0.8N.

[0034] Figure 10A is a diagram showing structure models for hydrogen adsorption in Ni&Ni0.2(Mo0.90W0.10)0.8N.

[0035] Figures 10B and 10C show a free energy diagram for H adsorption and formation energy for Mo atoms, respectively, in Ni&Ni0.2Mo0.8N and Ni&Ni0.2(Mo0.90W0.10)0.8N.

[0036] Figure 11A is a graph showing performance by Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH for overall water electrolysis.

[0037] Figure 11B show the results of chronopotentiometric (CP) testing for overall water electrolysis in various conditions using 1000 mA cm-2.

[0038] Figures 12A and 12B are graphs showing a comparison of HER performance in 1 M KOH seawater and corresponding Tafel slope values among different catalysts, respectively.

[0039] Figure 13A is a graph showing performance by Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH for overall seawater electrolysis.

[0040] Figure 13B is a graph showing measured and theoretical gaseous products at 500 mA cm-2in 1 M KOH seawater electrolyte.

[0041] Figure 14A shows CP testing of Ni&Ni0.2(Mo0.90W0.10)0.8N.

[0042] Figures 14B and 14C show linear sweep voltammetry (LSV) curves for before and after 100 h at 1000 mA cm-2in 1 M KOH seawater and 300 h 500 mA cm-2in 6 M KOH seawater, respectively. 64929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0043] Figure 15A shows CP testing for overall seawater electrolysis in 6 M KOH seawater at 25 °C using 1000 mA cm-2.

[0044] Figure 15B shows LSV curves for before and after 100 h of CP testing at 1000 mA cm-2in 6 M KOH seawater at 25 °C.

[0045] Figure 16A is a schematic illustration of an AEM electrolyzer used in accordance with the present disclosure.

[0046] Figure 16B is a graph showing the overall water electrolysis performance of 5×5 cm2catalyst test area in the AEM electrolyzer.

[0047] Figure 16C shows CP testing by the 5×5 cm2AEM electrolyzer at 65 °C with a constant current of 25 A.

[0048] Figure 17 is a schematic illustration of the synthesis procedure for the yttrium- alloyed Ni&Ni0.2(Mo1-xYx)0.8N catalyst according to one embodiment.

[0049] Figure 18A is an XRD pattern of Ni(Mo1-xYx)O4 for x = 0, 0.05, 0.10, and 0.15.

[0050] Figure 18B is an XRD pattern of Ni & Ni0.2(Mo1-xYx)0.8N for x = 0, 0.05, 0.10, and 0.15.

[0051] Figures 19A-19D show SEM images of Ni&Ni0.2(Mo1-xYx)0.8N for x = 0, 0.05, 0.10, and 0.15 at different magnifications. Insets show distributions of rod diagonal lengths in each composition.

[0052] Figure 20A is a SEM image of Ni&Ni0.2(Mo0.90Y0.10)0.8N at different magnifications.

[0053] Figures 20B and 20C are higher magnification TEM images of a Ni&Ni0.2(Mo0.90Y0.1)0.8N nanorod.

[0054] Figures 21A and 21B are HRTEM images of nanoparticles and nanorods of Ni&Ni0.2(Mo0.90Y0.10)0.8N.

[0055] Figure 21C is a SAED pattern of Ni&Ni0.2(Mo0.90Y0.10)0.8N.

[0056] Figures 21D-21H show EDS element mapping of Ni&Ni0.2(Mo0.90Y0.10)0.8N for Ni, Mo, Y, N, and O.

[0057] Figure 22A shows XPS survey results for Ni&Ni0.2Mo0.8N and yttrium alloyed Ni&Ni0.2(Mo0.90Y0.10)0.8N catalysts.

[0058] Figures 22B-22F show high-resolution spectra of Ni 2p, Mo 3d, Y 3d, N 1s, and O 1s, respectively, for the Ni&Ni0.2(Mo0.90Y0.10)0.8N catalyst. 74929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0059] Figures 23A and 23B are graphs showing a comparison of HER performance in 1 M KOH water and ECSA values, respectively, among Ni&Ni0.2(Mo1-xYx)0.8N samples prepared with various yttrium concentrations.

[0060] Figures 24A and 24B show the catalytic activity normalized for ECSA and mass among Ni&Ni0.2(Mo1-xYx)0.8N samples prepared with various concentrations.

[0061] Figure 24C is a graph showing a comparison of HER activity with other NiMo- based catalysts.

[0062] Figure 25A is a graph showing CP testing of Ni&Ni0.2(Mo0.90Y0.10)0.8N (top) and Ni&Ni0.2Mo0.8N (bottom).

[0063] Figure 25B shows LSV curves for both before and after 200 h of CP testing at 1000 mA cm-2and 25°C in 1 M KOH.

[0064] Figure 26A is a graph showing CP testing of Ni&Ni0.2(Mo0.90Y0.10)0.8N (top) and Ni&Ni0.2Mo0.8N (bottom).

[0065] Figure 26B shows LSV curves for both before and after 300 h of CP testing at 1000 mA cm-2and 25°C in 6 M KOH.

[0066] Figure 27A is a graph showing CP testing of Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH (top) and Ni&Ni0.2Mo0.8N || NiFe LDH (bottom) at 1,000 mA cm-2and 25°C in 1 M KOH.

[0067] Figure 27B shows LSV curves for both before and after 300 h of CP testing at 1,000 mA cm-2and 25°C in 1 M KOH.

[0068] Figure 28A is a graph showing CP testing of Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH (top) and Ni&Ni0.2Mo0.8N || NiFe LDH (bottom) at 1,000 mA cm-2and 65°C in 6 M KOH.

[0069] Figure 28B shows LSV curves for both before and after 300 h of CP testing at 1,000 mA cm-2and 65°C in 6 M KOH.

[0070] Figure 29 is a graph showing overall water electrolysis performance of a 5×5 cm2AEM electrolyzer using Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH (top line) and Ni&Ni0.2Mo0.8N || NiFe LDH (bottom line) at 65 °C in 1 M KOH.

[0071] Figure 30 is a graph showing the results of performance testing of Ni&Ni0.2(Mo0.9W0.10)0.8N and Ni&Ni0.2(Mo0.9Cr0.1)0.8N when compared to pristine Ni&Ni0.2Mo0.8N and other types of catalysts.

[0072] Figures 31 and 32 are graphs showing the results of performance testing of various rare earth element alloyed Ni&Ni0.2(Mo0.90M0.10)0.8N and Ni&Ni0.2(Mo0.95M0.05)0.8N catalysts. 84929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) DETAILED DESCRIPTION

[0073] It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various illustrative embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. For example, a figure may illustrate an exemplary embodiment with multiple features or combinations of features that are not required in one or more other embodiments and thus a figure may disclose one or more embodiments that have fewer features or a different combination of features than the illustrated embodiment. Embodiments may include some but not all the features illustrated in a figure and some embodiments may combine features illustrated in one figure with features illustrated in another figure. Therefore, combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in the broadest sense and are instead merely to describe particularly representative examples. In addition, the disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not itself dictate a relationship between the various embodiments and / or configurations discussed.

[0074] 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 of this disclosure. 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 specification and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well known functions or constructions may not be described in detail for brevity or clarity.

[0075] The terms “about” and “approximately” shall generally mean an acceptable degree of error or variation for the quantity measured given the nature or precision of the measurements. Numerical quantities given in this description are approximate unless stated otherwise, meaning that the term “about” or “approximately” can be inferred when not expressly stated.

[0076] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural (i.e., “at least one”) forms as well, unless the context clearly indicates otherwise. 94929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0077] It is to be understood that any given element of the disclosed embodiments of the invention may be embodied in a single structure, a single step, a single substance, or the like. Similarly, a given element of the disclosed embodiment may be embodied in multiple structures, steps, substances, or the like.

[0078] The present disclosure provides improved bifunctional electrocatalysts for water electrolysis, and more particularly, electrocatalysts for water splitting, including for promoting a hydrogen evolution reaction (HER) in which hydrogen (H2) is produced via the electrolysis of water (H2O) and / or an oxygen evolution reaction (OER) in which oxygen (O2) is produced. The electrocatalysts can catalyze the HER and / or OER under alkaline conditions, such as in alkaline fresh water and seawater. Through metal alloying, the electrocatalysts of the present disclosure incorporate metals, such as tungsten and rare earth elements, into a nickel molybdenum nitride framework – Ni1-xMoxN. Without being bound by any particular theory, it is believed that, by incorporating tungsten or a rare earth element into Ni1-xMoxN, the electrocatalysts of the present disclosure are able to restrict the dissolution of molybdenum and provide improved catalytic activity, stability, and lower operational voltage for achieving substantial current densities compared to conventional nickel molybdenum nitride catalysts.

[0079] Electrocatalysts

[0080] The present disclosure provides metal-based nickel molybdenum nitride (NiMoN) electrocatalysts. The term, “electrocatalyst,” as used herein refers to a catalyst that increases the rate of oxidation and / or reduction reactions in electrochemical reactions. In one embodiment, the electrocatalyst of the present disclosure is a compound of formula (I): Ni1-y(Mo1-xMx)yN (I), where M is a metal selected from tungsten (W), yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zirconium (Zr), niobium (Nb), hafnium (Hf), or tantalum (Ta); x is a number from 0.01 to 0.99; and y is a number from 0.01 to 0.99.

[0081] In some embodiments, M may be selected from W, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, or Yb. In another embodiment, M may be selected from W or Y. For example, M may be W. In still another embodiment, M may be Y. In some embodiments, the electrocatalysts of the present 104929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) disclosure are free of noble metals. In further embodiments, y may be a number from 0.6 to 0.9. In another embodiment, y may be a number from 0.7 to 0.9. For instance, y may be a number from 0.8 to 0.9. In still further embodiments, x may be a number from 0.05 to 0.3. In another embodiment, x may be a number from 0.1 to 0.25. In still another embodiment, x may be a number from 0.15 to 0.2.

[0082] In another embodiment, the electrocatalyst of the present disclosure is a compound of formula (II): Ni1-y(Mo1-xWx)yN (II), where x is a number from 0.01 to 0.99 and y is a number from 0.01 to 0.99. In one embodiment, y may be a number from 0.8 to 0.9 and x may be a number from 0.05 to 0.3. In another embodiment, y may be 0.8 and x may be 0.05 to 0.2. In still another embodiment, y may be 0.8 and x may be 0.1. In another embodiment, y may be 0.8 and x may be 0.05. In still another embodiment, y may be 0.8 and x may be 0.15. In yet another embodiment, y may be 0.8 and x may be 0.2. In another embodiment, y may be 0.8 and x may be 0.3.

[0083] In still another embodiment, the electrocatalyst of the present disclosure is a compound of formula (III): Ni1-y(Mo1-xYx)yN (III), where x is a number from 0.1 to 0.99 and y is a number from 0.1 to 0.99. In one embodiment, y may be a number from 0.8 to 0.9 and x may be a number from 0.05 to 0.2. For instance, y may be 0.8 and x may be 0.1. In another embodiment, y may be 0.8 and x may be 0.05. In still another embodiment, y may be 0.8 and x may be 0.15. In yet another embodiment, y may be 0.8 and x may be 0.2.

[0084] The electrocatalysts of the present disclosure can function at electrode surfaces or as the electrode itself. In one embodiment, the electrocatalyst is the electrode. For example, the electrocatalysts of the present disclosure can function as a combination of the catalyst and the electrode. In some embodiments, the electrocatalysts of the present disclosure are self-supported. The term, “self-supported,” as used herein, refers to an electrocatalyst in which the catalytically active material is directly grown on a conductive substrate to provide an electrode for use in an electrochemical system for catalyzing an electrochemical reaction. The conductive substrate may include any suitable conductive scaffold. In one embodiment, the conductive substrate is a three- dimensional substrate. Examples of suitable conductive substrates include, but are not limited to, 114929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) carbon felt paper (CFP), carbon cloth (CC), graphite plates, metallic foams, metal wire meshes, metal foils (such as titanium plates and copper plates), and conductive glass (such as FTO and ITO). In one embodiment, the substrate is a metallic foam. For example, the metallic foam may include nickel (Ni) foam, copper (Cu) foam, iron (Fe) foam, cobalt (Co) foam, titanium (Ti) foam, or a combination thereof. In one embodiment, the substrate is nickel (Ni) foam. The foam of the substrate can have any suitable thickness. For example, in some embodiments, the foam has a thickness in the range of from about 1 mm to about 3 mm. In another embodiment, the foam may have a thickness of about 1 mm to about 2 mm. In further embodiments, the foam may have a purity of at least 99 percent. In still further embodiments, the foam can have a porosity of greater than or equal to about 95, 96, or 97 percent, or in the range of from about 95 to about 97 percent, and may include from about 80 to about 110 pores per inch, and / or average pore diameters in the range of from about 0.2 to about 0.6 mm.

[0085] In further embodiments, the self-supported electrocatalysts of the present disclosure are nanostructured. In one embodiment, the electrocatalysts are in the form of nanorods. Nanorods are rod-like structures having an average diameter in the range of from about 1 nm to about 100 nm. This includes average diameters in the range of from about 20 nm to about 80 nm, and from about 30 nm to about 60 nm. It is noted, however, the term “diameter” is not meant to connote a perfectly spherical cross-section; irregular, elliptical, circular, square, or rectangular cross-sections may be used with the nanorods. In another embodiment, the electrocatalysts are in the form of nanosheets. Nanosheets are two-dimensional nanostructures with a thickness ranging from about 1 nm to about 100 nm.

[0086] The electrocatalysts of the present disclosure demonstrate excellent catalytic activity as hydrogen evolution reaction (HER) electrocatalysts at a high current density. For example, in some embodiments, when operated in a 1M alkaline solution, the electrocatalysts can achieve a current density of 1,000 mA cm-2at operating voltages of 1.8 V or less. In another embodiment, the electrocatalysts can achieve a current density of 1,000 mA cm-2at operating voltages of 1.75 V or less. In still another embodiment, the electrocatalysts can achieve a current density of 1,000 mA cm-2at operating voltages of 1.7 V or less. In yet another embodiment, the electrocatalysts can achieve a current density of 1,000 mA cm-2at operating voltages of 1.6 V or less. In another embodiment, the electrocatalysts can achieve a current density of 1,000 mA cm-2at operating voltages of 1.55 V or less. 124929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0087] The electrocatalysts of the present disclosure also demonstrate enhanced stability. In one embodiment, the electrocatalysts maintain stability at a current density of 1,000 mA cm-2for up to 200 hours. In another embodiment, the electrocatalysts maintain stability at a current density of 1,000 mA cm-2for up to 250 hours. In still another embodiment, the electrocatalysts maintain stability at a current density of 1,000 mA cm-2for up to 300 hours. In yet another embodiment, he electrocatalysts of the present disclosure maintain stability at a current density of 1,000 mA cm-2for up to 350 hours.

[0088] Moreover, in 1 M KOH water, the electrocatalysts of the present disclosure required an overpotential of 115 mV or less to deliver a current density of 1000 mA cm-2. In another embodiment, the electrocatalysts of the present disclosure required an overpotential of 114 mV or less to deliver a current density of 1000 mA cm-2. In another embodiment, the electrocatalysts of the present disclosure required an overpotential of 110 mV or less to deliver a current density of 1000 mA cm-2. In still another embodiment, the electrocatalysts of the present disclosure required an overpotential of 105 mV or less to deliver a current density of 1000 mA cm-2.

[0089] Methods of Making Electrocatalysts

[0090] The present disclosure also provides methods of making the electrocatalysts described herein. For example, the present disclosure provides methods of making the electrocatalysts for a hydrogen evolution reaction (HER) at a cathode in water splitting. The electrocatalysts of the present disclosure may be used on their own, combined with other additives (for example, binders such ionomers, and fillers such as conductive carbon), and / or “self- supported” in which the catalytically active material is disposed on an underlying substrate to provide an electrode for use in an electrochemical system for catalyzing an electrochemical reaction, as discussed above.

[0091] In one embodiment, for forming the self-supported electrocatalysts described herein, the methods of the present disclosure include growing the electrocatalyst on any of the three-dimensional substrates discussed above. This step may be done via a hydrothermal reaction A hydrothermal reaction generally involves mixing metal salts and precipitants into a solvent and treating the solution at a specified temperature above the boiling point of water. In one embodiment, the methods of the present disclosure include exposing any of the substrates described above to an aqueous solution, including a source of nickel, a source of molybdenum, 134929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) and a source of tungsten or rare earth element, dissolved in a solvent, such as deionized water (DI water).

[0092] In one embodiment, the sources of each component of the electrocatalyst may be a salt of the desired metal. For example, the source of nickel may be a nickel salt, such as nickel (II) nitrate hexahydrate. In another embodiment, the source of molybdenum may be a molybdenum salt, such as ammonium molybdate tetrahydrate. In still another embodiment, the source of tungsten may be a tungsten salt, such as an ammonium tungsten oxide hydrate. In yet another embodiment, the source of rare earth element may be a salt of the desired rare earth element, such as, for example, yttrium(III) nitrate hexahydrate, lanthanum(III) nitrate hexahydrate, cerium(III) nitrate hexahydrate, praseodymium(III) nitrate hexahydrate, neodymium(III) nitrate hexahydrate, samarium(III) nitrate hexahydrate, europium(III) nitrate pentahydrate, gadolinium(III) nitrate hexahydrate, or ytterbium(III) nitrate pentahydrate.

[0093] The substrate may be exposed to the aqueous solution at a temperature and for a period of time sufficient to form a precursor catalyst including nickel, molybdenum, and tungsten or the rare earth element supported on the substrate. In one embodiment, the mixture of the substrate and aqueous solution is heated at a temperature above the boiling point of water. For example, the mixture of the substrate and aqueous solution can be heated at a temperature of about 80°C to about 300°C. In another embodiment, the mixture of the substrate and aqueous solution can be heated at a temperature of about 120°C to about 180°C. In another embodiment, the mixture of the substrate and aqueous solution can be heated at a temperature of about 130°C to about 170°C. In still another embodiment, the mixture of the substrate and aqueous solution can be heated at a temperature of about 140°C to about 160°C. In yet another embodiment, the mixture of the substrate and aqueous solution can be heated at a temperature of about 145°C to about 155°C. The temperature may be maintained for at least about two hours. For instance, the temperature may be maintained from about two hours to about sixteen hours. In further embodiments, the step of exposing the substrate to the aqueous solution can be performed at a pressure less than 15.5 atmospheres (atm). In one embodiment, the step is performed at a pressure ranging from 0.1 atm to 10 atm. In another embodiment, the step is performed at a pressure ranging from 0.5 atm to 2 atm. In some embodiments, the mixture can be transferred to a hydrothermal reactor and then placed in an oven for heating. 144929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0094] The precursor catalyst may be subjected to thermal nitridation. A thermal nitridation reaction exposes the precursor catalyst to a high temperature environment with nitrogen gas to introduce nitrogen atoms into the material, converting it into a nitride compound. In this embodiment, the precursor catalyst is subjected to a source of nitrogen at a temperature and for a period of time sufficient to form a catalyst having formula (I) described above. In one embodiment, the source of nitrogen is in the form of a gas. The gas may be, for example, ammonia (NH3) or a gas mixture of ammonia (NH3) and argon (Ar). The precursor catalyst may be subjected to the source of nitrogen in a tube furnace. In some embodiments, the thermal nitridation reaction may be carried out at a temperature of about 300°C to about 800°C. In another embodiment, the thermal nitridation reaction may be carried out at a temperature of about 400°C to about 600°C. The temperature may be maintained for at least about one hour. For instance, the temperature should be maintained for at least about two hours. While the use of hydrothermal and thermal nitridation reactions have been exemplified herein, those skilled in the art would readily appreciate that other methods for preparing self-supporting electrodes, such as electrochemical deposition, vapor deposition, vacuum filtration, and freeze-drying, may also be used.

[0095] Methods and Systems for Water Electrolysis

[0096] Electrocatalytic systems including the disclosed electrocatalysts (or electrodes formed thereof) are also provided. The electrocatalytic systems can be used in the water electrolysis process, for instance, during the hydrogen evolution reaction (HER), for producing hydrogen. The system may include an electrochemical cell configured to contain a fluid including an electrochemical reactant (for example, a species to be oxidized to form an oxidation product, a species to be reduced to form a reduction product, or both); a cathode in contact with the fluid, where the cathode includes any of the disclosed electrocatalysts supported thereon; and an anode. The selection of fluid depends upon the particular electrochemical reaction to be catalyzed. For HER, the fluid may be an electrolyte solution (for instance, a solution of water and a water-soluble electrolyte). In one embodiment, the electrolyte solution is an alkaline medium. For instance, the electrolyte may be alkaline water, such as alkaline fresh water or alkaline seawater. Various materials for the anode may be used. In one embodiment, the anode may be an oxygen evolution reaction catalyst. For example, the anode may be a NiFe-layered double hydroxide (LDH)-based electrocatalyst. 154929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0097] The electrodes, for instance, the cathode and anode, may be immersed in the fluid and may be in electrical communication with one another. The electrocatalytic system may further include a power source in electrical communication with the electrodes, the power source configured to apply an electrical potential across the electrodes. Other components may be included in the systems of the present disclosure, for example, a membrane separating the electrodes, a collection cell configured to collect the oxidation / reduction product(s) from the electrochemical cell, etc.

[0098] Methods of using the disclosed electrocatalysts (or electrodes or electrocatalytic systems including the electrocatalysts) to catalyze an electrochemical reaction are also provided. In some embodiments, the electrocatalysts are used to produce hydrogen from alkaline water, such as alkaline fresh water or alkaline seawater. As explained above, by applying a certain voltage across the anode and cathode of the electrolysis cell, water undergoes an oxidation reaction at the anode to produce oxygen, while protons combine with electrons at the cathode to undergo a reduction reaction to produce hydrogen. In this aspect, the methods of the present disclosure include exposing any of the disclosed electrocatalysts (which are supported on the cathode) to a fluid including an electrochemical reactant. The exposure results in the reduction of another electrochemical reactant (for example, hydrogen ions) at the electrocatalytic material-fluid interface to produce a reduction product (for instance, hydrogen (H2)), which may also be separated from the fluid and collected.

[0099] EXAMPLES

[0100] The following non-limiting examples demonstrate catalysts that may be made in accordance with the present disclosure. The examples are merely illustrative of the preferred embodiments of the present disclosure and are not to be construed as limiting the disclosure, the scope of which is defined by the appended claims.

[0101] Example 1: Tungsten-alloyed Ni&Ni0.2Mo0.8N Catalysts

[0102] Overview

[0103] Tungsten-alloyed Ni&Ni0.2Mo0.8N (Ni& Ni1-y(Mo1-xWx)yN]) nanorod arrays were synthesized on the surface of Ni foam via a hydrothermal method followed by high-temperature nitridation. The resulting Ni&Ni1-y(Mo1-xWx)yN catalyst showed highly efficient alkaline HER activity, delivering a current density of 1000 mA cm-2at an overpotential of 114 mV and exhibiting a Tafel slope of 33.6 mV dec-1, which are superior to the corresponding overpotential and Tafel 164929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) slope values of 149 mV and 38.6 mV dec-1, respectively, for pristine Ni&Ni0.2Mo0.8N. Additionally, Ni&Ni1-y(Mo1-xWx)yN (for example, Ni0.2(Mo0.90W0.10)0.8N) exhibited excellent stability throughout 300 h of operation in 1 M KOH water at a current density of 500 mA cm-2, significantly outperforming pristine Ni&Ni0.2Mo0.8N under the same conditions, as well as during 60,000 cyclic voltammetry (CV) scans in 1 M KOH water. DFT analyses showed that tungsten- alloying further decreased the energy barrier to water dissociation and lowered the formation energy for Mo sites on Ni&Ni1-y(Mo1-xWx)yN. Finally, the Ni&Ni1-y(Mo1-xWx)yN catalyst was employed as a cathode to pair with the benchmark non-noble-metal oxygen evolution reaction (OER) catalyst NiFe LDH in an anion exchange membrane water electrolyzer (AEMWE) with an active working area of 25 cm2. The AEMWE delivered a current of 25 A (current density of 1000 mA cm-2) at 1.752 V in 1 M KOH water at 65 °C and remained stable over 350 h of operation. Therefore, tungsten-alloyed Ni&Ni1-y(Mo1-xWx)yN can significantly promote the catalytic activity of Mo in Ni&Ni1-y(Mo1-xWx)yN and stabilize the active Mo sites on this catalyst.

[0104] Materials and Methods

[0105] Synthesis of Catalysts

[0106] Chemicals. Nickel (II) nitrate hexahydrate (Ni(NO3)2 6H2O, ≥97 %, Sigma- Aldrich), ammonium molybdate tetrahydrate ((NH4)6Mo7O244H2O, 81.0-83.0 % MoO3basis, Sigma-Aldrich), ammonium tungsten oxide hydrate ((NH4)6W12O39 xH2O, Alfa Aesar), iron (III) nitrate hexahydrate (Fe(NO3)3 9H2O, 98 %, Sigma-Aldrich), urea (Promega Corporation), ammoniumfluoride (NH4F, 96 %, Alfa Aesar), Pt / C (platium, nominally 20 % on carbon black, Alfa Aesar), Nafion (117 solution, 5 wt.%, Sigma-Aldrich), potassium hydroxide (KOH, 85 %, pellets, ACS regent, Acros Organics), ethanol (C2H5OH, Decon Labs, Inc.), and hydrochloric acid (HCl, 36.5 %–38.0 % w / w, Fisher Chemical) were used without further purification. Ni foam (NF, thickness: 1.6 mm, porosity: ~95 %) was used as the substrate for the preparation of all catalysts. NF was cleaned with 3 M HCl, ethanol, and deionized (DI) water several times before use. DI water was used to prepare solutions unless otherwise specified. Seawater was collected from Galveston Bay, Galveston, Texas, USA (29.303° N, 94.772° W), and was left standing for one week to allow the visible impurities to settle, after which the supernatant was collected before use. The white precipitates (mainly Ca(OH)2 and Mg(OH)2) produced during the preparation of alkaline natural seawater were removed by centrifugation at 7200 rpm for 5 min before use. 174929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0107] Ni(Mo1-xWx)O4 catalyst synthesis. The Ni(Mo1-xWx)O4catalyst was synthesized on NF using a conventional hydrothermal method. Pieces of NF (2 × 5 cm2) were initially cleaned with HCl solution, ethanol, and DI water. Subsequently, 40 mmol of Ni(NO3)26H2O, 10 (1-x) (x = 0, 0.05, 0.10, 0.15, 0.20, 0.30, or 1.00) mmol of (NH4)6Mo7O244H2O, and 10x (x = 0, 0.05, 0.10, 0.15, 0.20, 0.30, or 1.00) mmol of (NH4)6W12O39xH2O were dissolved in 60 ml of DI water. Once fully dissolved, each mixture was transferred to a 100 ml hydrothermal reactor along with a piece of the cleaned NF. The reactor was then placed in an oven and maintained at 150 °C for 6 h. After each reaction, the product was rinsed with DI water and air-dried to obtain the Ni(Mo1-xWx)O4catalyst.

[0108] Ni&Ni0.2(Mo1-xWx)0.8N catalyst synthesis. The as-prepared Ni(Mo1-xWx)O4 catalysts were then subjected to thermal nitridation in a tube furnace. Specifically, each sample was transferred to a tube furnace with a gas mixture of NH3and Ar flowing at 120 standard cubic centimeters per minute (SCCM) and 30 SCCM, respectively. Each thermal nitridation reaction was carried out at 400 °C for 2 h. Once cooled to room temperature, the resulting product was a Ni&Ni0.2(Mo1-xWx)0.8N catalyst.

[0109] NiFe LDH catalyst synthesis. The NiFe LDH catalyst was synthesized using the same hydrothermal method as for Ni(Mo1-xWx)O4. A piece of NF (2 × 5 cm2) was initially cleaned with HCl solution, ethanol, and DI water. Subsequently, 10 mmol of Ni(NO3)26H2O, 10 mmol of Fe(NO3)39H2O, 60 mmol urea, and 75 mmol of NH4F were dissolved in 60 ml of DI water. Once fully dissolved, the mixture was transferred to a 100 ml hydrothermal reactor along with the cleaned NF. The reactor was then placed in an oven and maintained at 150 °C for 6 h. After the reaction, the product was rinsed with DI water and air-dried to obtain the NiFe LDH catalyst.

[0110] Preparation of Pt / C catalyst on NF. To prepare a Pt / C electrode for comparison, 40 mg of Pt / C and 60 µl of Nafion were dispersed in 540 µl of ethanol and 400 µl of DI water. The mixture was then sonicated for 30 min. Afterward, the NF substrate was immersed in the solution for several hours, and then removed and left to air dry overnight to obtain the Pt / C catalyst.

[0111] Characterizations

[0112] Materials characterization. The morphology and nanostructure of the samples were determined by scanning electron microscopy (SEM, LEO 1525) and transmission electron microscopy (TEM, JEOL 2010F) coupled with energy-dispersive X-ray spectroscopy (EDS). The phase composition of the samples was characterized by X-ray diffraction (PANalytical X’pert 184929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) PRO diffractometer with a Cu Kα radiation source) and by X-ray photoelectron spectroscopy (XPS, PHI Quantera SXM scanning X-ray microprobe).

[0113] Electrochemical measurements. Electrochemical measurements were performed on a Gamry Reference 600 electrochemical workstation. The HER measurements were conducted using a three-electrode configuration, with the prepared sample (~0.5 cm2), a graphite electrode, and a Hg / HgO electrode serving as the working electrode, counter electrode, and reference electrode, respectively. Cyclic voltammetry (CV) measurements were performed at a scan rate of 2 mV s-1with iR compensation using the current-interrupt (CI) mode. The potential of the reference electrode was converted to the potential of the reversible hydrogen electrode (RHE) using the following equation: ERHE = EHg / HgO+0.098+0.0591×pH. The pH values of 1 M KOH and 1 M KOH seawater are both approximately 14, while the pH value of 6 M KOH seawater is 14.83.

[0114] The electrochemically active surface area (ECSA) can be determined using the following equation: ECSA=Cdl / Cs. The double-layer capacitance (Cdl) is calculated from the non- Faradaic region of CV measurements in 1 M KOH, with scan rates varying from 1 to 3 mV s-1. The specific capacitance (Cs) value, typically in the range of 20-60 µF cm-2for a flat surface, is used in this calculation. Here, a Csvalue of 40 µF cm-2is chosen to estimate the ECSA.

[0115] DFT calculations. Density functional theory (DFT) calculations were carried out using the Vienna ab initio simulation package (VASP, version 6.4.2) code. The core electrons were treated using the projector augmented-wave (PAW) pseudopotential. Meanwhile, the electron interactions were described using the revised Perdew-Burke-Ernzerhof (RPBE) exchange- correlation functional of the generalized gradient approximation (GGA), which has proven to be more accurate than the Perdew-Burke-Ernzerhof (PBE) functional. The plane wave pseudopotential with a kinetic cutoff energy of 500eV and the Gaussian smearing method with an electronic temperature of kBT = 0.05 eV were used in all our DFT calculations. During the system relaxing process, the total electronic energies were converged to 10-6eV and the residual forces on the atoms were converged to 0.02 eV Å-1.

[0116] Mo-and Ni-exposed Ni&Ni0.2Mo0.8N substrate models were modulated using a 5- layer slab with a 3×2 surface cell, and a 15-Å-thick vacuum space was introduced into the surface models to avoid the interlayer interactions. In the practical calculations, only the top 2 layers were allowed to relax in the geometrical optimization. The Brillouin-zone integration was conducted using a 5×5×1 Monkhorst-Pack grid. 194929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0117] The formation energy of Mo atoms is calculated as: ∆Eform= Etot- Esub- µMo, where Etotand Esubare the total energy of the optimized substrate with Mo atoms and without Mo atoms, respectively, both of which can be directly obtained from DFT calculations, and µMo is the chemical potential of Mo, which can be calculated from the bulk phase. The free energy (EG) of the adsorbed species is calculated as: EG = Eele + ZPE – TS, where Eele is the electronic energy, ZPE is the zero point energy, T is the temperature (20 °C in the calculations), and S is the vibrational entropy. ZPE and S can be estimated according to the vibrational frequencies.

[0118] Faradaic efficiency measurements. Faradaic efficiency (FE) for overall seawater electrolysis was determined using a drainage method at room temperature. Briefly, the Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH pair worked at a constant current density of 500 mA cm-2in 1 M KOH seawater and the volume (V) of each gas product was recorded every 5 min. FE was calculated based on the equation: FE = V / [Vm×i×t / (n×F)] × 100 %, where V is the volume of a particular gas product (L), Vm is the standard molar volume (24.4 L mol-1), i is the current (A), t is the time (s), n is the number of electrons involved in generating one molecule of a gas product (2 for hydrogen gas and 4 for oxygen gas), and F is the Faraday constant (96485.3 C mol-1).

[0119] AEM electrolyzer fabrication and testing. An anion exchange membrane (AEM) electrolyzer was assembled using an anode (25 cm2), a cathode (25 cm2), and an anion exchange membrane (Sustainion® X37-50 Grade RT, Dioxide Materials). NF, cleaned beforehand, served as the gas diffusion layer, while a Teflon polytetrafluoroethylene (PTFE) film was utilized as a gasket. Ni&Ni0.2(Mo0.90W0.10)0.8N and NiFe LDH catalysts, integrated onto NF, were directly employed as the monolithic cathode and anode, respectively, to construct the Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH AEM electrolyzer. Polarization and stability tests were carried out using a VOLTEQ HY7530EX power source in constant-current mode, with voltages recorded using a Keithley 2400-C SourceMeter. Water electrolysis performance measurements in the AEM electrolyzer, encompassing I-V plots and stability assessments, were conducted under steady-state conditions.

[0120] Results

[0121] As schematically shown in Figure 1, a two-step method, hydrothermal synthesis followed by thermal nitridation, was employed to synthesize Ni & Ni1-x(Mo1-yWy)xN catalysts where x represents the W concentration in the hydrothermal synthesis step. There was a gradual color change in Ni(Mo1-xWx)O4with increasing x from 0.05 to 0.20, which strongly indicates the 204929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) uniform incorporation of W into NiMoO4. The Ni(Mo0.70W0.30)O4sample exhibited a sudden color change to dark green, suggesting the formation of new species. X-ray diffraction (XRD) results in Figure 2 show that the Ni(Mo1-xWx)O4 (x = 0, 0.05, and 0.10) samples exhibited the typical NiMoO4∙0.7H2O (PDF#97-024-7435) pattern, while the Ni4W6O21(OH)2∙4H2O (PDF#47-0143) pattern appeared for x > 0.1 and became dominant for Ni(Mo0.7W0.3)O4. The XRD results, thus, indicate that W alloying in NiMoO4 has its limits despite the similar atomic radii of W and Mo. When an excessive W source is employed during the hydrothermal process, Ni4W6O21(OH)2∙4H2O is formed and the formation of NiMoO4 is significantly impeded. Subsequent to the hydrothermal synthesis step, each Ni(Mo1-xWx)O4 sample underwent thermal nitridation to yield the final Ni&Ni0.2(Mo1-xWx)0.8N catalysts.

[0122] Scanning electron microscopy (SEM) analysis revealed that the Ni&Ni0.2(Mo0.90W0.10)0.8N catalyst on Ni foam, as shown in Figures 3A and 3B, maintains a rod- like structure similar to that of its precursor, Ni(Mo0.90W0.10)O4. This similarity suggests that there are minimal morphological changes in the catalysts following thermal nitridation treatment. SEM images of Ni&Ni0.2(Mo1-xWx)0.8N samples with different W concentrations showed that, from 0 ≤ x ≤ 0.10, the average nanorod size increased with increasing x, while it decreased with increasing x for x > 0.10. It can, therefore, be concluded that the successful alloying of W can enlarge the size of Ni&Ni1-x(Mo1-yWy)xN nanorods, but when excessive W is added during the hydrothermal process, the Ni4W6O21(OH)2∙4H2O will be produced and the formation of NiMoO4 will be restricted, which can lead to a decrease in Ni&Ni1-x(Mo1-yWy)xN nanorod size. For Ni&Ni0.2(Mo0.70W0.30)0.8N, large amounts of NiWN microscale particles can be observed, which strongly confirms the above conclusion.

[0123] Transmission electron microscopy (TEM) was employed to analyze the morphology and crystal structure of Ni&Ni0.2(Mo0.90W0.10)0.8N. Figure 3C and its inset revealed that numerous nanoparticles were embedded on its surface nanorods. High-resolution TEM (HRTEM) images in Figures 3D and 3E, respectively, showed lattice spacing of 0.203 nm for Ni(111) on the nanoparticles and 0.246 nm for Ni0.2Mo0.8N(100) on the nanorod. The selected- area electron diffraction (SAED) pattern for Ni&Ni0.2(Mo0.90W0.10)0.8N in Figure 3F displayed diffraction rings corresponding to Ni(200), Ni(111), Ni0.2Mo0.8N(110), and Ni0.2Mo0.8N(100), consistent with the HRTEM findings. Energy-dispersive X-ray spectroscopy (EDS) mapping (Figures 3G-3K) and line analysis (Figure 3L) confirmed uniform elemental distribution across 214929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) each nanorod. Additionally, point analysis of an individual nanorod, as shown in Figure 3M, revealed that the atomic percentages of Ni, Mo, and W were 42.37%, 39.13%, and 4.03%, respectively, with a Mo:W atomic ratio close to 0.9:0.1.

[0124] The Ni&Ni0.2(Mo1-xWx)0.8N crystal structures were further analyzed using XRD measurements of selected powder samples. As shown in Figure 4A, the main peaks in the XRD pattern for the pristine Ni&Ni0.2Mo0.8N powder align with those for metallic nickel (PDF#04- 0850) and Ni0.2Mo0.8N (PDF#29-0931). The XRD patterns of the alloyed Ni&Ni0.2(Mo1-xWx)0.8N samples with x ≤ 0.20 closely resemble that of pristine Ni&Ni0.2Mo0.8N, with no significant shifts in their characteristic peaks. This observation confirms that low-level W-alloying does not induce noticeable changes in the crystal structure after thermal nitridation.

[0125] X-ray photoelectron spectroscopy (XPS) was utilized to investigate the surface chemical states of elements in the Ni&Ni0.2(Mo0.90W0.10)0.8N catalyst. As shown in Figures 4B-4F, high-resolution XPS spectra provide detailed insights into the surface chemistry of Ni&Ni0.2(Mo0.90W0.10)0.8N. In Figure 4B, the peaks at 853.4 eV and 870.7 eV are assigned to Ni02p3 / 2 and Ni02p1 / 2, respectively, while peaks at 855.8 eV and 873.4 eV, indicative of Ni2+2p3 / 2 and Ni2+2p1 / 2, respectively, suggest slight surface oxidation. Accompanying satellite peaks are located at 861.1 eV and 878.9 eV. The Mo 3d spectrum (Figure 4C) exhibited peaks at 229.6 eV and 232.7 eV, respectively, corresponding to Mo3+3d5 / 2 and Mo3+3d3 / 2, that are attributed to Mo- N bonds, while peaks at 230.4 eV and 235.1 eV arise from minor oxidation. The overlap in energy levels between Mo 4p and W 4f in Ni&Ni0.2(Mo0.90W0.10)0.8N complicated their XPS analysis. However, the Mo 4p peaks in Figure 4D are discerned to be located at 36.9 eV and 39.7 eV, corresponding to Mo 4p3 / 2 and Mo 4p1 / 2, respectively, while weaker peaks at 33.5 eV and 35.1 eV are identified as W4+4f7 / 2 and W4+4f5 / 2, respectively, reflecting the low W concentration. The N 1s spectrum (Figure 4E) revealed a metal-N bond at 397.3 eV, a N-H peak resulting from adsorbed NH3 at 399.5 eV, and a peak at 395.2 eV corresponding to Mo 2p3 / 2. The O 1s spectrum (Figure 4F) displayed peaks at 530.0 eV, 530.7 eV, and 531.5 eV, attributed to Ni-O, Mo-O, and W-O bonds, respectively. By comparing the high-resolution XPS spectra of Ni&Ni0.2(Mo0.90W0.10)0.8N with those of pristine Ni&Ni0.2Mo0.8N, it can be seen that tungsten-alloying did not cause valence changes in the other elements, which is consistent with the XRD results and indicates that the alloying process is stable and effective. 224929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0126] To investigate the impact of W-alloying on the hydrogen evolution reaction (HER) performance of Ni&Ni0.2Mo0.8N, the HER activity of Ni&Ni1-x(Mo1-yWy)xN was assessed using a three-electrode system in 1 M KOH water electrolyte at room temperature. Figure 5A shows that optimal W concentration was achieved for Ni&Ni0.2(Mo0.90W0.10)0.8N. The HER performance of Ni&Ni0.2(Mo0.95W0.05)0.8N showed no significant enhancement compared to that of pristine Ni&Ni0.2Mo0.8N. However, at x = 0.10, the performance significantly improved; Ni&Ni0.2(Mo0.90W0.10)0.8N delivered a current density of 1000 mA cm-2at an overpotential of only 114 mV, a notable enhancement over the pristine Ni&Ni0.2Mo0.8N. Further increasing W, though, led to an increasing decline in HER performance. To gain insight into the intrinsic activity of the Ni&Ni0.2(Mo1-xWx)0.8N catalysts, their electrochemically active surface area per unit of geometric area (ECSA / geo) values were quantified. This measurement, conducted through cyclic voltammetry (CV) at varying scan rates, helps in determining each material’s catalytic efficiency. Despite the lower ECSA / geo value for Ni&Ni0.2(Mo0.90W0.10)0.8N compared to that of pristine Ni&Ni0.2Mo0.8N (Figure 5B), it exhibited better HER performance normalized for ECSA. This indicates that, even with a smaller active surface area per unit of geometric area, Ni&Ni0.2(Mo0.90W0.10)0.8N may have higher intrinsic activity, with each of its active sites being more effective than those on pristine Ni&Ni0.2Mo0.8N.

[0127] Ni&Ni0.2(Mo0.90W0.10)0.8N also demonstrated better HER performance results when compared with Pt / C and bare Ni foam. As detailed in Figure 6A, Ni&Ni0.2(Mo0.90W0.10)0.8N achieved current densities of 100, 500, and 1000 mA cm-2at the respective overpotentials of 22, 75, and 114 mV, significantly outperforming Pt / C, which required overpotentials of 45, 167, and 250 mV for the same current densities. Notably, as shown in Figure 6B, NiWN and Pt / C were found to have relatively large Tafel slope values of 135.4 mV dec-1and 88.3 mV dec-1, respectively, while Ni&Ni0.2(Mo0.90W0.10)0.8N and Ni&Ni0.2Mo0.8N exhibited closer values of 33.6 mV dec-1and 38.6 mV dec-1, respectively. This indicates that Ni&Ni0.2(Mo0.90W0.10)0.8N follows the Volmer-Tafel mechanism, with the Tafel step being the rate-determining step. When compared with other state-of-the-art NiMo-based HER catalysts, Ni&Ni0.2(Mo0.90W0.10)0.8N is among the best performers in terms of overpotential required to deliver a current density of 500 mA cm-2and its Tafel slope value, as demonstrated in Figure 6C.

[0128] In addition to high activity, the long-term stability of a catalyst during hydrogen production is crucial. Therefore, a systematic study on the stability of Ni&Ni0.2(Mo0.90W0.10)0.8N 234929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) was conducted. First, its stability was assessed through repeated CV scans (0 to 0.15 V vs. RHE), and the results are shown in Figure 7. Notably, the linear sweep voltammetry (LSV) curves for Ni&Ni0.2(Mo0.90W0.10)0.8N showed no obvious decay even after 60,000 CV scans, indicating its remarkable stability.

[0129] Furthermore, chronopotentiometric (CP) results (Figure 8A) revealed that the Ni&Ni0.2(Mo0.90W0.10)0.8N catalyst maintained its performance at a current density of 500 mA cm-2for 300 h and at 1000 mA cm-2for 100 h without significant decay. For comparison, a CP test of the pristine Ni&Ni0.2Mo0.8N was conducted at a current density of 500 mA cm-2. The results showed that its performance can only be maintained at this current density for about 100 h before it begins to decay. To further analyze the crystal structure and morphology of the Ni&Ni0.2(Mo0.90W0.10)0.8N catalyst after long-term operation, TEM analysis was performed after 300 h of CP testing at a current density of 500 mA cm-2. The results showed that, in agreement with previous measurements, a large number of nanoparticles remained embedded in the nanorods, and the lattice spacing for both the nanoparticles and nanorods, as well as the diffraction rings in the SAED, remained unchanged. EDS mapping and line analysis verified that uniform distribution of the elements in the Ni&Ni0.2(Mo0.90W0.10)0.8N nanorods was maintained after long-term operation, and corresponding point analysis showed that the Ni:Mo atomic ratio remained approximately 1:0.9. For comparison, TEM analysis was performed on Ni&Ni0.2Mo0.8N after testing under the same conditions as for Ni&Ni0.2(Mo0.90W0.10)0.8N, and the results showed that its elemental distribution and ratios changed significantly, such that the atomic ratio of Ni to Mo became approximately 3:1 and a large amount of Mo was lost, which led to the attenuation of the catalyst's activity and its destabilization. In contrast, tungsten-alloying kept the Ni&Ni0.2Mo0.8N elemental ratios stable, and the activity and stability of Ni&Ni0.2(Mo0.90W0.10)0.8N could be maintained. In addition, XPS analysis was performed on Ni&Ni0.2(Mo0.90W0.10)0.8N after 300 h of CP testing at a current density of 500 mA cm-2to further confirm its stability. The XPS spectra showed that the characteristic peaks for each element remained unchanged and, in particular, nickel and molybdenum retained the same respective valence states as before long-term operation. This indicates that tungsten-alloying enhances the catalyst’s activity and significantly bolsters its stability. Figure 8B shows a comparison of LSV curves for Ni&Ni0.2(Mo0.90W0.10)0.8N before and after continuous operation at a high industrial-level current density of 1000 mA cm-2for 100 h, further affirming its high stability and sustained activity of under demanding conditions. 244929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0130] Density Functional Theory (DFT) calculations were employed to elucidate the HER active sites on Ni&Ni0.2(Mo0.90W0.10)0.8N and to assess its stability. A pristine Ni&Ni0.2Mo0.8N model, comprising Ni metal clusters and Ni0.2Mo0.8N (202), was initially established. Subsequently, a Ni&Ni0.2(Mo0.90W0.10)0.8N model was constructed by substituting a tungsten atom for that of molybdenum.

[0131] In comparison to pristine Ni&Ni0.2Mo0.8N, the tungsten-alloyed Ni&Ni0.2(Mo0.90W0.10)0.8N exhibited lower H2O adsorption energy (Figures 9A and 9B), indicating its better H2O adsorption capacity, which promotes the H2O dissociation process. The corresponding free energy diagram shown in Figure 9C revealed that the energy barriers for water dissociation in pristine Ni&Ni0.2Mo0.8N and Ni&Ni0.2(Mo0.90W0.10)0.8N are 0.54 eV and 0.42 eV, respectively. This suggests that W-alloying enhances the H2O dissociation kinetics in Ni&Ni0.2(Mo0.90W0.10)0.8N.

[0132] Based on structure models for H adsorption (Figure 10A) and the corresponding free energy diagram (Figure 10B), the alloyed Ni&Ni0.2(Mo0.90W0.10)0.8N and pristine Ni&Ni0.2Mo0.8N exhibited similar H adsorption / desorption, which indicates that this does not have a significant effect on the difference in their intrinsic activity. Therefore, the promoted H2O adsorption ability of alloyed Ni&Ni0.2(Mo0.90W0.10)0.8N and its lower energy barrier for water dissociation together result in its better intrinsic activity in comparison to Ni&Ni0.2Mo0.8N. Regarding the stability of these catalysts, since Mo is a key active site and prone to detachment, the formation energy required for Mo in each was explored. The results shown in Figure 10C revealed that Ni&Ni0.2(Mo0.90W0.10)0.8N exhibited a lower formation energy of −6.1 eV in comparison to –5.3 eV for Ni&Ni0.2Mo0.8N, which suggests that Mo is less likely to detach in the tungsten-alloyed catalyst, in agreement with the experimental findings. The DFT calculations thus confirmed that tungsten-alloying can significantly enhance the HER activity of Ni&Ni0.2(Mo0.90W0.10)0.8N by improving its dissociation capabilities and by stabilizing the Mo sites on the catalyst via lower formation energy.

[0133] To thoroughly evaluate the performance of Ni&Ni0.2(Mo0.90W0.10)0.8N under industrial conditions, comprehensive testing for overall water electrolysis was conducted. The benchmark NiFe LDH was employed as the oxygen evolution reaction (OER) catalyst to pair with Ni&Ni0.2(Mo0.90W0.10)0.8N in a two-electrode setup, which was subsequently tested under different environments. As shown in Figure 11A, the two-electrode setup required voltages of only 1.511 254929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) V, 1.604 V, and 1.669 V to reach current densities of 100 mA cm-2, 500 mA cm-2, and 1000 mA cm-2, respectively, in 1 M KOH at 25 °C. At the elevated temperature of 65 °C, achieving a current density of 1000 mA cm-2necessitated a voltage of only 1.540 V. In 6 M KOH, the required voltages remained low with only 1.590 V and 1.544 V needed to attain a current density of 1000 mA cm-2at 25 °C and at 65 °C, respectively. These results demonstrated the efficient performance of Ni&Ni0.2(Mo0.90W0.10)0.8N in varied conditions, highlighting its potential for practical applications in water electrolysis on an industrial scale.

[0134] Stability testing for overall water electrolysis using both pristine Ni&Ni0.2Mo0.8N and tungsten-alloyed Ni&Ni0.2(Mo0.90W0.10)0.8N for comparison was conducted. It was observed that the Ni&Ni0.2Mo0.8N || NiFe LDH pair could not maintain long-term stability in 6 M KOH at 65 °C, with a noticeable decay in performance after 200 h confirmed by LSV results obtained before and after CP testing. On the other hand, the Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH system underwent stability testing for overall water electrolysis in 1 M KOH at 25 °C and in 6 M KOH at 65 °C and maintained good stability in both conditions, as shown in Figure 11B. Corresponding LSV curves revealed that the catalytic activity of Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH remained consistent after CP testing for 150 h in 1 M KOH at 25 °C and for 200 h in 6 M KOH at 65 °C. Additionally, it was found that Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH requireed a lower voltage (1.544 V) than Ni&Ni0.2Mo0.8N || NiFe LDH (1.574 V) to achieve the same current density of 1000 mA cm-2before stability testing. This demonstrates that the tungsten-alloyed Ni&Ni0.2(Mo0.90W0.10)0.8N exhibits greater stability and better electrochemical performance for overall water electrolysis.

[0135] Moreover, a comprehensive activity and stability assessment of Ni&Ni0.2(Mo0.90W0.10)0.8N for HER, as well as for overall seawater electrolysis when paired with NiFe LDH, was conducted. When using treated seawater in an alkaline environment of 1 M KOH, Ni&Ni0.2(Mo0.90W0.10)0.8N achieved current densities of 100, 500, and 1000 mA cm-2at overpotentials of 26, 83, and 126 mV, respectively, as shown in Figure 12A. Compared to deionized water, treated seawater exhibited only a minor impact on the catalyst’s performance. The only noticeable change was a slight increase in the Tafel slope value for Ni&Ni0.2(Mo0.90W0.10)0.8N (Figure 12B), suggesting slightly worse reaction kinetics for the catalyst caused by the poisoning effects of seawater impurities. 264929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0136] Similarly, the use of NiFe LDH as an OER catalyst paired with Ni&Ni0.2(Mo0.90W0.10)0.8N in a two-electrode setup was tested in different environments (as shown in Figure 13A), the two-electrode setup required voltages of only 1.535 V, 1.627 V, and 1.696 V to achieve current densities of 100 mA cm-2,500 mA cm-2,1000 mA cm-2, respectively, in 1 M KOH seawater solution at 25 °C. In 6 M KOH seawater, the required voltages of only 1.687 V and 1.548 V were needed to attain a current density of 1000 mA cm-2at 25 °C and 65 °C, respectively. Due to the existence of Cl–in the seawater electrolyte, the chlorine evolution reaction (CER) is a potential side reaction at the anode side during overall seawater electrolysis. To study the Faradaic efficiency (FE) of the Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH pair, a well-discussed drainage method was employed. FE testing was conducted at a current density of 500 mA cm-2in 1 M KOH seawater using the two-electrode setup with a working area of 0.5 cm2. The results in Figure 13N demonstrate a close alignment between theoretical and experimental production for both H2 and O2, indicating a FE close to 100% for both HER and OER.

[0137] The stability of the Ni&Ni0.2(Mo0.90W0.10)0.8N catalyst in treated seawater was assessed through CP testing under various conditions and by comparing the LSV curves obtained before and after testing (Figures 14A-14C). Ni&Ni0.2(Mo0.90W0.10)0.8N was found to remain stable under an industrial-level current density of 1000 mA cm-2over 100 h in 1 M KOH seawater at 25 °C, as well as under a high current density of 500 mA cm-2over 300 h in 6 M KOH seawater at 65 °C.

[0138] Furthermore, the overall stability of the Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH pair during overall seawater electrolysis was examined. As shown in Figures 15A and 15B, Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH remained stable in 6 M KOH seawater at 25 °C for 100 h under an industrial-grade current density of 1000 mA cm-2, reinforcing the premise that Ni&Ni0.2(Mo0.90W0.10)0.8N can maintain relative stability in seawater electrolytes.

[0139] To assess the practical applicability of Ni&Ni0.2(Mo0.90W0.10)0.8N for industrial use, a 5×5 cm2membrane electrode assembly (MEA), as schematically illustrated in Figure 16A, was constructed. Polarization measurements (Figure 16B) revealed that, in 1 M KOH water at 65 °C, the MEA can deliver an absolute current of 25 A at a voltage of 1.752 V, corresponding to a current density of 1000 mA cm-2. In comparison with other MEAs using state-of-the-art non-precious- metal catalysts, the one incorporating Ni&Ni0.2(Mo0.90W0.10)0.8N and NiFe LDH studied here was found to be among the best performers due to the lower overpotential required for its high-current- 274929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) density HER. During long-term stability testing of this MEA, a noticeable increase in cell voltage was observed after 300 h (Figure 16C). However, upon replacing only the anion exchange membrane (AEM) and the gas diffusion layers, there was a substantial recovery in voltage, and the system maintained stability for an additional 50 h. Polarization measurements taken after 350 h of testing further confirmed the exceptional stability of the system.

[0140] Figure 30 shows the results of additional performance testing for the Ni&Ni0.2(Mo0.90W0.10)0.8N catalyst as well as Ni&Ni0.2(Mo0.90Cr0.10)0.8N when compared to pristine Ni&Ni0.2Mo0.8N and other types of catalysts. The performance results of each catalyst (for example, the voltage required to reach a current density of 1,000 mA cm-2) are shown in Table 1 below. Table 1: Performance Results of Ni&Ni0.2(Mo0.90W0.10)0.8N, Ni&Ni0.2(Mo0.90Cr0.10)0.8N, and Other Catalysts Catalyst Name Performance @1000 mA cm-2

[0141] As shown in Figure 30 and in Table 1, the results demonstrate that the catalysts alloyed with tungsten and chromium outperformed the original catalyst, Ni & Ni0.2Mo0.8N, and the other types of catalysts. Indeed, the catalysts alloyed with tungsten and chromium required lower voltages than Ni & Ni0.2Mo0.8N and the other catalysts to reach a current density of 1,000 mA cm-2.

[0142] In summary, a highly stable high-performance tungsten-alloyed Ni&Ni0.2(Mo0.90W0.10)0.8N catalyst was synthesized. A series of experimental characterizations revealed that the tungsten-alloying can significantly enhance the HER activity and stability of 284929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) Ni&Ni0.2(Mo0.90W0.10)0.8N. Further DFT calculations showed that tungsten-alloying facilitates the water dissociation ability of Ni&Ni0.2(Mo0.90W0.10)0.8N and lowers the formation energy of Mo sites on the catalyst, thus enhancing its activity and stability, respectively. When coupled with NiFe LDH for overall water electrolysis, the Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH two-electrode setup required a voltage of only 1.544 V to deliver a current density of 1000 mA cm-2in 6 M KOH at 65 °C and maintained its activity throughout 200 h of operation under the same conditions. Additionally, the highly efficient and robust HER performance by Ni&Ni0.2(Mo0.90W0.10)0.8N remained evident in alkaline seawater electrolytes. The Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH pair was assembled in an AEM electrolyzer that demonstrated high activity (1.752 V at 1000 mA cm-2) and remarkable stability (1000 mA cm-2over 350 h) in 1 M KOH at 65 °C, indicating its high potential for industrial application. This example thus provides a solution to the fundamental instability issue for the highly active Ni&Ni0.2Mo0.8N via tungsten-alloying and a path toward industrial application of the noble-metal-free Ni&Ni0.2(Mo0.90W0.10)0.8N for both alkaline fresh water and seawater hydrogen production.

[0143] Example 2: Yttrium & Other Rare Earth Element Alloyed Ni&Ni0.2(Mo0.90M0.10)0.8N and Ni&Ni0.2(Mo0.95M0.05)0.8N Catalysts

[0144] Overview

[0145] Alloys of certain rare earth elements and NiMoN were synthesized, discovering a highly active and stable catalyst, Ni&Ni0.2(Mo0.90Y0.10)0.8N. Experimental data demonstrate that this catalyst required only 100 mV overpotential to achieve a current density of 1000 mA cm-2, making it one of the best NiMo-based HER catalysts reported so far. Paired with NiFe LDH in a two-electrode setup, the catalyst operated at an exceptionally low voltage of 1.538 V in 6 M KOH at 65 °C, delivering a current density of 1000 mA cm-2while maintaining activity for up to 300 hours. Assembled in a large-area 25 cm2AEM electrolyzer, it exhibited high activity under the same conditions of 1M KOH at 65 °C. Through alloying with rare earth elements, such as yttrium, the activity and stability of NiMoN can be enhanced, providing a new approach for the industrial application of the non-precious metal catalyst Ni&Ni0.2(Mo0.90Y0.10)0.8N in producing hydrogen from alkaline fresh water.

[0146] Materials and Methods

[0147] Synthesis of Catalysts 294929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)

[0148] Chemicals. Nickel (II) nitrate hexahydrate (Ni(NO3)26H2O, ≥97 %, Sigma- Aldrich), ammonium molybdate tetrahydrate ((NH4)6Mo7O24 4H2O, 81.0-83.0 % MoO3 basis, Sigma-Aldrich), Yttrium(III) nitrate hexahydrate (Y(NO3)3 6H2O, 99.8% trace metals basis, Sigma-Aldrich), Lanthanum(III) nitrate hexahydrate (La(NO3)36H2O, 99.999% trace metals basis, Sigma-Aldrich), Cerium(III) nitrate hexahydrate (Ce(NO3)36H2O, 99% trace metals basis, Sigma- Aldrich), Praseodymium(III) nitrate hexahydrate (Pr(NO3)3 6H2O, 99.9% trace metals basis, Sigma-Aldrich), Neodymium(III) nitrate hexahydrate (Nd(NO3)36H2O, 99.9% trace metals basis, Sigma-Aldrich), Samarium(III) nitrate hexahydrate (Sm(NO3)36H2O, 99.9% trace metals basis, Sigma-Aldrich), Europium(III) nitrate pentahydrate (Eu(NO3)3 5H2O, 99.9% trace metals basis, Sigma-Aldrich), Gadolinium(III) nitrate hexahydrate (Gd(NO3)36H2O, 99.99% trace metals basis, Sigma-Aldrich), Ytterbium(III) nitrate pentahydrate (Yb(NO3)35H2O, 99.9% trace metals basis, Sigma-Aldrich), iron (III) nitrate hexahydrate (Fe(NO3)3 9H2O, 98 %, Sigma-Aldrich), urea (Promega Corporation), ammoniumfluoride (NH4F, 96 %, Alfa Aesar), Pt / C (platinum, nominally 20 % on carbon black, Alfa Aesar), Nafion (117 solution, 5 wt.%, Sigma-Aldrich), potassium hydroxide (KOH, 85 %, pellets, ACS regent, Acros Organics), ethanol (C2H5OH, Decon Labs, Inc.), and hydrochloric acid (HCl, 36.5 %–38.0 % w / w, Fisher Chemical) were used without further purification. Ni foam (NF, thickness: 1.6 mm, porosity: ~95 %) was used as the substrate for the preparation of all catalysts. NF was cleaned with 3 M HCl, ethanol, and deionized (DI) water several times before use. DI water was used to prepare solutions unless otherwise specified. Seawater was collected from Galveston Bay, Galveston, Texas, USA (29.303° N, 94.772° W), and was left standing for one week to allow the visible impurities to settle, after which the supernatant was collected before use. The white precipitates [mainly Ca(OH)2 and Mg(OH)2] produced during the preparation of alkaline natural seawater were removed by centrifugation at 7200 rpm for 5 min before use.

[0149] Ni(Mo1-xYx)O4 catalyst synthesis. The Ni(Mo1-xWx)O4 catalyst was synthesized on NF using a conventional hydrothermal method. Pieces of NF (2 × 5 cm2) were initially cleaned with HCl solution, ethanol, and DI water. Subsequently, 40 mmol of Ni(NO3)26H2O, 10 (1-x) (x = 0, 0.05, 0.10, 0.15) mmol of (NH4)6Mo7O244H2O, and 10x (x = 0, 0.05, 0.10, 0.15) mmol of Y(NO3)36H2O were dissolved in 60 ml of DI water. Once fully dissolved, each mixture was transferred to a 100 ml hydrothermal reactor along with a piece of the cleaned NF. The reactor was 304929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) then placed in an oven and maintained at 150 °C for 6 h. After each reaction, the product was rinsed with DI water and air-dried to obtain the Ni(Mo1-xYx)O4 catalyst.

[0150] Ni&Ni0.2(Mo1-xYx)0.8N catalyst synthesis. The as-prepared Ni(Mo1-xYx)O4 catalysts were then subjected to thermal nitridation in a tube furnace. Specifically, each sample was transferred to a tube furnace with a gas mixture of NH3 and Ar flowing at 120 standard cubic centimeters per minute (SCCM) and 30 SCCM, respectively. Each thermal nitridation reaction was carried out at 400 °C for 2 h. Once cooled to room temperature, the resulting product was a Ni&Ni0.2(Mo1-xYx)0.8N catalyst.

[0151] NiFe LDH catalyst synthesis. The NiFe LDH catalyst was synthesized using the same hydrothermal method as for Ni(Mo1-xYx)O4. A piece of NF (2 × 5 cm2) was initially cleaned with HCl solution, ethanol, and DI water. Subsequently, 10 mmol of Ni(NO3)26H2O, 10 mmol of Fe(NO3)39H2O, 60 mmol urea, and 75 mmol of NH4F were dissolved in 60 ml of DI water. Once fully dissolved, the mixture was transferred to a 100 ml hydrothermal reactor along with the cleaned NF. The reactor was then placed in an oven and maintained at 150 °C for 6 h. After the reaction, the product was rinsed with DI water and air-dried to obtain the NiFe LDH catalyst.

[0152] Preparation of Pt / C catalyst on NF. To prepare a Pt / C electrode for comparison, 40 mg of Pt / C and 60 µl of Nafion were dispersed in 540 µl of ethanol and 400 µl of DI water. The mixture was then sonicated for 30 min. Afterward, the NF substrate was immersed in the solution for several hours, and then removed and left to air dry overnight to obtain the Pt / C catalyst.

[0153] Characterizations

[0154] Materials characterization. The morphology and nanostructure of the samples were determined by scanning electron microscopy (SEM, LEO 1525) and transmission electron microscopy (TEM, JEOL 2010F) coupled with energy-dispersive X-ray spectroscopy (EDS). Inductively coupled plasma optical emission spectroscopy (ICP-OES) was obtained using an AGILENT 725 ICP-OES. The phase composition of the samples was characterized by X-ray diffraction (PANalytical X’pert PRO diffractometer with a Cu Kα radiation source) and by X-ray photoelectron spectroscopy (XPS, PHI Quantera SXM scanning X-ray microprobe).

[0155] Electrochemical measurements. Electrochemical measurements were performed on a Gamry Reference 3000 electrochemical workstation. The HER measurements were conducted using a three-electrode configuration, with the prepared sample (~0.5 cm2), a graphite electrode, and a Hg / HgO electrode serving as the working electrode, counter electrode, and reference 314929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) electrode, respectively. Cyclic voltammetry (CV) measurements were performed at a scan rate of 2 mV s-1with iR compensation using the current-interrupt (CI) mode. The potential of the reference electrode was converted to the potential of the reversible hydrogen electrode (RHE) using the following equation: ERHE = EHg / HgO+0.098+0.0591×pH. The pH values of 1 M KOH is both approximately 13.7, while the pH value of 6 M KOH is 14.83.

[0156] AEM electrolyzer fabrication and testing. An anion exchange membrane (AEM) electrolyzer was assembled using an anode (25 cm2), a cathode (25 cm2), and an anion exchange membrane (Sustainion® X37-50 Grade RT, Dioxide Materials). NF, cleaned beforehand, served as the gas diffusion layer, while a Teflon polytetrafluoroethylene (PTFE) film was utilized as a gasket. Ni&Ni0.2(Mo0.90Y0.10)0.8N and NiFe LDH catalysts, integrated onto NF, were directly employed as the monolithic cathode and anode, respectively, to construct the Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH AEM electrolyzer. Polarization and stability tests were carried out using a VOLTEQ HY7530EX power source in constant-current mode, with voltages recorded using a Keithley 2400-C SourceMeter. Water electrolysis performance measurements in the AEM electrolyzer, encompassing I-V plots and stability assessments, were conducted under steady-state conditions.

[0157] Results

[0158] For the synthesis of rare earth elements alloyed with Ni & Ni0.2Mo0.8N, the two- step method involving hydrothermal synthesis of precursors followed by thermal nitridation was employed. Since there are 17 rare earth elements, this study only selected 9 of them for screening, with the same preparation method and alloying ratio. Figure 17 shows the schematic diagram of the yttrium alloying process where “x” represents the concentration of Y in the hydrothermal synthesis process. The addition of yttrium caused a noticeable color change in the samples, indicating the formation of new species with the introduction of yttrium. The XRD results, as shown in Figures 18A and 18B, display that the Ni(Mo1-xYx)O4 (x=0, 0.05, 0.10, 0.15) samples exhibit the typical pattern of NiMoO4·0.7H2O (PDF#97-024-7435). With the gradual increase in yttrium concentration, the peaks at lower angles become stronger and new peaks appear, indicating that the addition of yttrium leads to lattice distortion in the host material.

[0159] Following the hydrothermal synthesis step, each precursor sample was subjected to thermal nitridation to obtain the final Ni&Ni0.2(Mo1-xYx)0.8N catalyst. Similar to the tungsten 324929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) alloyed Ni&Ni0.2(Mo1-xWx)0.8N, the XRD patterns after thermal nitridation treatment mainly show two peaks, corresponding to Ni & Ni0.2Mo0.8N and metallic Ni, respectively. The characteristic peaks do not shift significantly, indicating that the catalyst did not undergo noticeable changes due to the addition of a small amount of yttrium after thermal nitridation treatment.

[0160] The SEM image analysis of yttrium at different concentrations is shown in Figures 19A-19D. The SEM images revealed that the addition of yttrium correspondingly increases the average size of the nanorods towards the right.

[0161] Figure 20A and its inset show that the addition of yttrium to Ni & Ni0.2Mo0.8N results in a significant morphological change. The nanorods attached to the nickel foam become more numerous and denser, making it difficult to discern the surface of the substrate. The increase in both the average size of the nanorods and their quantity indicates a significant increase in the catalyst loading per unit area of the nickel foam, which is highly beneficial for the catalyst. The TEM analysis was employed to examine the morphology and crystal structure of Ni&Ni0.2(Mo0.90Y0.10)0.8N. As shown in Figures 20B and 20C, it was discovered that the yttrium- alloyed Ni&Ni0.2(Mo0.90Y0.10)0.8N, along with the previously discussed Ni&Ni0.2(Mo0.90Y0.10)0.8N and the original Ni & Ni0.2Mo0.8N, all exhibit a nano-rod and nano-particle structure with high surface roughness.

[0162] High-resolution transmission electron microscopy (HRTEM), as depicted in Figures 21A and 21B allowed for the determination of the lattice spacing of the nanoparticles Ni(111) as 0.203 nm and the nano-rods Ni0.2(Mo0.90Y0.10)0.8N as 0.246 nm. The selected area electron diffraction (SAED) patterns shown in Figure 21C displayed diffraction rings corresponding to Ni(200), Ni(111), Ni0.2(Mo0.90Y0.10)0.8N (100), and Ni0.2(Mo0.90Y0.10)0.8N (110), consistent with the HRTEM results. Energy-dispersive X-ray spectroscopy (EDS) mapping demonstrated uniform elemental distribution along each nanorod shown in Figures 21D-21H. Inductively coupled plasma (ICP) analysis of the sample powder revealed the weight percentages of Ni, Mo, and Y to be 29.23%, 44.98%, and 4.32% respectively, resulting in a Mo:Y atomic ratio of about 1:0.104, or Mo:Y ratio of 90.6:9.4, approximately 9:1.

[0163] X-ray photoelectron spectroscopy (XPS) was employed to study the surface chemical states of the elements within the Ni&Ni0.2(Mo0.90Y0.10)0.8N catalyst. Figure 22A displays the measured spectra for Ni&Ni0.2(Mo0.90Y0.10)0.8N and the original Ni & Ni0.2Mo0.8N, showing peaks corresponding to Ni 2p, Mo 3d, Y 3d, N1s, and O 1s. Notably, peaks corresponding to 334929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) yttrium were only observed in the spectrum of Ni&Ni0.2(Mo0.90Y0.10)0.8N. Detailed analysis of the fine peaks through high-resolution spectra revealed that the peaks at 853.3 eV and 870.6 eV could be attributed to Ni02p3 / 2 and Ni02p1 / 2, respectively. Peaks at 855.3 eV and 873.7 eV correspond to Ni2+2p3 / 2 and Ni2+2p1 / 2, indicating mild surface oxidation, with two satellite peaks observed at 860.7 eV and 880.1 eV in Figure 22B. The Mo 3d spectrum in Figure 22C shows peaks at 229.7 eV and 232.8 eV, corresponding to Mo3+3d5 / 2 and Mo3+3d3 / 2, contributed by Mo-N bonds, while peaks at 230.5 eV and 235.5 eV arise from mild oxidation of the sample. In Figure 22D, peaks at 157.9 eV and 159.8 eV correspond to Y3+3d5 / 2 and Y3+3d3 / 2, respectively. The N 1s spectrum shown in Figure 22E exhibits a metal-N bond peak at 397.3 eV, a N-H peak at 399.1 eV contributed by adsorbed NH3, and a peak at 395.5 eV corresponding to Mo 2p3 / 2. The presence of O 1s peaks, caused by unavoidable mild surface oxidation, is illustrated in Figure 22F, where peaks at 530.1 eV, 530.6 eV, and 531.4 eV correspond to Ni-O, Mo-O, and Y-O, respectively. Compared to the XPS spectra of the original Ni & Ni0.2Mo0.8N, the addition of yttrium did not induce changes in the valence states of the other elements.

[0164] To investigate the effect of yttrium alloying on the catalytic performance of the original Ni & Ni0.2Mo0.8N, hydrogen evolution reaction (HER) activity tests were first conducted. These tests were measured in a three-electrode system at 25 °C in 1M KOH electrolyte. The optimal ratio of yttrium in Ni&Ni0.2(Mo1-xYx)0.8N was studied, as shown in Figure 23A, where the addition of yttrium significantly improved the performance of the original Ni & Ni0.2Mo0.8N, with the greatest enhancement observed at x=0.10. At this concentration, only 100 mV of overpotential was required to reach a current density of 1000 mA cm-2, an improvement of 31.5 %. Compared to Ni&Ni0.2(Mo0.90W0.10)0.8N, the activity further increased by 12.3 %. To explore the intrinsic activity of Ni&Ni0.2(Mo1-xYx)0.8N, their double-layer capacitance (Cdl) values were calculated at different scan rates using cyclic voltammetry (CV), and their electrochemical active surface area (ECSA) was qualitatively determined, as illustrated in Figure 23B. Under unit area, the ECSA values of catalysts at different concentrations were higher than that of the original catalyst, with Ni&Ni0.2(Mo0.90Y0.10)0.8N having the highest ECSA.

[0165] When combining the ECSA values with HER activity, as shown in Figure 24A, at an overpotential of 100 mV per unit ECSA, the activity at x=0.10 was the best, showing an increase of nearly 63 % compared to the original activity. However, considering the increased loading due to the addition of yttrium, it was necessary to analyze the reasons for the improved activity. Thus, 344929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) by comparing the mass activity, as depicted in Figure 24B, at an overpotential of 100 mV per unit mass, the activity at x=0.10 was found to significantly improve by nearly 40 %. Comparing per unit mass and unit area, it is clear that the intrinsic activity of Ni&Ni0.2(Mo0.90Y0.10)0.8N significantly improved compared to the original.

[0166] The Tafel slope of Ni&Ni0.2(Mo0.90Y0.10)0.8N was calculated from the linear sweep voltammetry (LSV) data to be 24.8 mV dec-1, indicating that the Volmer-Tafel mechanism is followed, and the Tafel step (i.e., the combination of two adsorbed protons) is the rate-determining step. Compared with other current advanced NiMo-based HER catalysts in terms of overpotential at a current density of 500 mA cm-2and Tafel slope, as shown in Figure 24C, the yttrium-alloyed Ni&Ni0.2(Mo0.90Y0.10)0.8N ranks among the best-performing catalysts currently reported. Furthermore, as seen from the inset, catalysts alloyed with other rare earth elements also rank among the top in NiMo-based catalysts.

[0167] For the stability tests, chronoamperometry (CP) was employed to evaluate the stability. As shown in Figure 25A, the 200 hours HER stability tests for Ni&Ni0.2(Mo0.90Y0.10)0.8N and Ni & Ni0.2Mo0.8N catalysts were conducted in 1M KOH at 25 °C. Figure 25B presents the linear sweep voltammetry (LSV) curves of the two catalysts before and after the test under these conditions, clearly demonstrating that Ni&Ni0.2(Mo0.90Y0.10)0.8N not only exhibits excellent HER activity in 1M KOH at 25 °C but also maintains stability at a current density of 1000 mA cm-2for up to 200 hours. In contrast, the original catalyst, Ni & Ni0.2Mo0.8N, showed a noticeable decay.

[0168] Similarly, as can be seen in Figures 26A and 26B, Ni&Ni0.2(Mo0.90Y0.10)0.8N requires only 73 mV of overpotential to reach a current density of 1000 mA cm-2in 6M KOH at 25 °C and can maintain stability for 300 hours. This indicates that Ni&Ni0.2(Mo0.90Y0.10)0.8N can be considered as one of the potential industrial grade HER catalysts.

[0169] To determine the optimal combination for overall water splitting, NiFe-layered double hydroxide (LDH) was still utilized as the oxygen evolution reaction (OER) electrode in different environments. Figure 27A shows the 300 hours stability tests for both Ni&Ni0.2(Mo0.90Y0.10)0.8N and the original Ni & Ni0.2Mo0.8N paired with NiFe LDH in a two- electrode setup at a current density of 1000 mA cm-2in 1M KOH at 25 °C. From Figure 27B, it is evident that Ni&Ni0.2(Mo0.90Y0.10)0.8N can maintain high current density for over 200 hours. In the two-electrode setup, Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH only required voltages of 1.509 V, 1.594 V, and 1.651 V to reach current densities of 100 mA cm-2, 500 mA cm-2, and 1000 mA cm- 354929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029)2, respectively. As compared with the previously reported Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH, the pairing of Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH requires lower voltages and achieves longer stability.

[0170] Under more stringent conditions, in 6M KOH at 65 °C, as shown in Figures 28A and 28B, Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH was able to operate stably for over 300 hours. The table summary clearly indicates that compared to the original two-electrode pairing of Ni & Ni0.2Mo0.8N with NiFe LDH, Ni&Ni0.2(Mo0.90Y0.10)0.8N || NiFe LDH can achieve a current density of 1000 mA cm-2at significantly lower voltages, showcasing its potential as an effective combination for industrial-scale water splitting applications.

[0171] Considering its exceptionally high stability under large current loads and superior activity, a 5x5 cm2membrane electrode assembly was constructed and subjected to performance measurements. This approach is crucial for transitioning from laboratory-scale research to industrial applications, as it involves scaling up the catalyst and testing it under conditions that mimic real-application operational environments. The performance of the membrane electrode assembly not only provides insight into the efficiency and durability of the catalyst on a larger scale but also assesses its potential for integration into existing or future water electrolysis systems. This step is vital for evaluating the feasibility of deploying such advanced materials in commercial electrolyzers, where factors such as the ease of manufacturing, the stability of the catalyst under prolonged operational conditions, and the overall cost-effectiveness of the system are assessed. In a 1M KOH solution at a temperature of 65 °C, this electrode assembly required only 1.722 V to achieve an actual current of 25 A (equivalent to a current density of 1000 mA cm-2), as shown in Figure 29. Compared to the previous Ni&Ni0.2(Mo0.90W0.10)0.8N || NiFe LDH and Ni&Ni0.2Mo0.8N || NiFe LDH, this new combination scheme further reduces the required operating voltage, demonstrating superior performance.

[0172] Figures 31 and 32 show the results of additional performance testing for other rare earth element alloyed Ni&Ni0.2(Mo0.90M0.10)0.8N and Ni&Ni0.2(Mo0.95M0.05)0.8N catalysts. The tests were conducted in 1M KOH at 25 °C. Each of the catalysts listed in the table below were tested. The performance results of each catalyst (for example, the voltage required to reach a current density of 1,000 mA cm-2) are also shown in Table 2 below. 364929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) Table 2: Performance Results of Rare Earth Element Alloyed Ni&Ni0.2(Mo0.90M0.10)0.8N and Ni&Ni0.2(Mo0.95M0.05)0.8N Catalysts Catalyst Name Performance Catalyst Name Performance -2 -2 @1000 mA cm @1000 mA cm

[0173] As shown in Figures 31 and 32 and in Table 2, the results demonstrate that the catalysts alloyed with the rare earth elements, such as yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, and ytterbium, outperformed the original catalyst, Ni & Ni0.2Mo0.8N. Indeed, the catalysts alloyed with the rare earth elements required lower voltages than Ni & Ni0.2Mo0.8N to reach a current density of 1,000 mA cm-2.

[0174] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure and that they may make 374929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) various changes, substitutions, and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. 384929-5318-2991.1

Claims

Attorney Docket: 300318-401003 (UHID# 2024-029) WHAT IS CLAIMED IS:

1. A catalyst for promoting a hydrogen evolution reaction or an oxygen evolution reaction, having formula (I): Ni1-y(Mo1-xMx)yN (I), wherein: M is a metal selected from tungsten (W), yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zirconium (Zr), niobium (Nb), hafnium (Hf), or tantalum (Ta); x is a number from 0.01 to 0.99; and y is a number from 0.01 to 0.

99.

2. The catalyst of claim 1, wherein M is selected from W, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, or Yb; y is a number from 0.6 to 0.9; and x is a number from 0.05 to 0.

3.

3. The catalyst of any preceding claim, wherein M is selected from W and Y; y is a number from 0.8 to 0.9; and x is a number 0.1 to 0.

2.

4. The catalyst of any preceding claim, wherein M is W or Y; y is 0.8; and x is 0.

1.

5. The catalyst of any preceding claim, configured to achieve a current density of 1,000 mA cm-2at an operating voltage of 1.8 V or less for up to 350 hours.

6. An electrode, comprising: a substrate; and a catalyst according to any of claims 1 to 5 formed on the substrate. 394929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) 7. The electrode of claim 6, wherein the substrate comprises a metal foam, a metal wire mesh, or a carbon cloth paper.

8. The electrode of claims 6 or 7, wherein the substrate is a metal foam comprising nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), titanium (Ti), or a combination thereof.

9. A method of making a catalyst for a hydrogen evolution reaction (HER) or an oxygen evolution reaction (OER), comprising: exposing a substrate to an aqueous solution comprising a first metal salt comprising nickel, a second metal salt comprising molybdenum, and a third metal salt comprising tungsten, a rare earth element, titanium, vanadium, chromium, manganese, zirconium, niobium, hafnium, or tantalum, at a temperature and for a period of time sufficient to form a precursor catalyst; and subjecting the precursor catalyst to a source of nitrogen at a temperature and for a period of time sufficient to form a catalyst having formula (I): Ni1-y(Mo1-xMx)yN (I), wherein: M is a metal selected from tungsten, a rare earth element, titanium, vanadium, chromium, manganese, zirconium, niobium, hafnium, or tantalum; x is a number from 0.01 to 0.99; and y is a number from 0.01 to 0.

99.

10. The method of claim 9, further comprising heating the substrate and the aqueous solution to a temperature of about 80°C to about 300°C.

11. The method of claim 10, wherein the heating step is performed for at least about two hours.

12. The method of any of claims 9 to 11, wherein the source of nitrogen comprises a mixture of ammonia and argon gas.

13. A method for producing oxygen or hydrogen, comprising: 404929-5318-2991.1Attorney Docket: 300318-401003 (UHID# 2024-029) providing an electrochemical cell comprising an anode and a cathode, the anode and the cathode each comprising a catalyst according to any of claims 1 to 5 or the electrode according to any of claims 6 to 8; and applying current to the electrochemical cell, wherein hydrogen is produced at the cathode and oxygen is produced at the anode.

14. The method of claim 13, wherein the electrochemical cell further comprises an electrolyte solution in which the anode and the cathode are immersed.

15. The method of claim 14, wherein the electrolyte solution comprises alkaline fresh water or alkaline seawater. 414929-5318-2991.1

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