USE THEREOF STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

This invention was made with government support under ^' grant no, DE- SC0OI 2575 awarded by the Department of Energy. The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS This PCT application claims priority to U.S. Provisionai Patent

Application Serial No. 62/535 ,267, filed July 21 , 2017, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTIO

Global climate. change and diminishing oil reserves -argue for the global community to move beyond fossil fuels and look for alternative sources of sustainable green energy (Cox et al,. Nature, 2000, 408: 184-187), Hydrogen is one of the most important green, renewable energy sources and shows great promise as the next potential replacement for fossil fuels if .cost effective mass production of the molecule is realized (Gray, Nat. Chem., 2009, 1 :7), In this regard, discovery of economical hydrogen: evolution catalysts made from Earth~ab.und.attt materials plays pivotal role is this realization (Cray, Nat, Chera. ,2009, 1 :7; Bard et at. Ace. Ghent.. Res,, 1995, 28: 1 1 -145), In the context of a hydrogen economy, research across the globe has been interested in developing Earth-abundant catalysts for hydrogen evolution from the electrolysis of water (i.e., water splitting).

Much effort has been dedicated over the years to discover, understand and. optimize cost-efleeti ve e!ecirocatalysts to drive the: hydrogen evolution reaction (HER), which is the reduction half .reactio n the overall water spitting reaction (Morates-Gitio et aL Chem, Soc, Rev., 2014, 3:6555-6569; S et al, Chem. Soc, Rev..2016, 45:1529* 1541 ; Zoo et al, Chem, Soc, Rev,, 2015, 4:51 8-5180), Prior work on HER has shown that transition metal based sulfides, carbides and phosphides are. some of the most effective materials for acidic hydrogen evolution (Zou et ai,, Chern. Soc. Rev., 2015, 44:5148-51.80; Vesborg et a1. ₅ 1 Rhys. Chem. Lett, 2015, 6:951-957). However, to implement HER at the industrial scale, both HER and the oxidation- half reaction, the oxyge evolution reaction (OER), should he efficient in the same medium (Montoya et ai, .Nat. Mater., 2 ! % .1-6:70-81; Thenuwara et ai. ACS CataL, 2016, 6:7739-7743; Thenuwara et ai., Angew. Chem, Int. Ed., 2016, 55: 10381- 10385). Thus, when choosing a solution medium to -split water nd generate

hydrogen, an alkaline medium is preferred, since many inexpensive O.BR catalysts Ml in. acidic medium. (Gong et a!., Mand Res., 2016, 9:28-46). A lmost all of the present commercial methods to carry out the electrolysis of water use expensive precious metal platinum {$ 927 per ounce) ^' as the hydrogen evolving catalyst. Thus, research across the globe has focused on. making an elet rocatalyst. composed of Earth- abundant elements, to generate hydrogen during the electrolysis of wa ter (typically under alkaline conditions) that could compete with die efficiency of platinum. Thus, a ^' cheap inexpensive catalyst is essential to drop the price of hydrogen gas production (from water electrolysis).

Compared with acidic HER electrocatalysis, alkaline HER eleetroeatalysts have attracted limited .research attention and the discover of novel materials is rarely reported (Gong et ai., Natro Res., 2016, :28-46). Currently, commercial alkaline electrolyses use .high surface area: Raney i or its derivatives, but these materials exhibit a considerable- ovetpotentiai and long term stability issues (Birry e a!., J. Appi E!eetrochetn., 2004, 34:735-749; Subbararaan et at, Science, 201 1. 334: 1256). Recent examples Of successful. Earth-abundant metal based alkaline HER electrocatalysts include Chevrel-phase ternary sulfides (ovetpotentiai o -250 mV at 1 aiA cm' ² ) (Jiang et al„ Angew, Chem, int. Ed„ 2016, 55: 15240-15245), Ni doped MoSa nanosheets (over otentiai of --98 mV at 10 niA enr ² ) (Zhang et al., Energy Environ. Set,, 2 1.6, 9:2789-2793) and eiectrodeposited amorphous cobalt- phosphorous-derived (Co-P)/ nickel-phosphorous-derived (Ni-P) ailoys (overpotehtial of -10 ,mV at 10 mA cm" ² ) _. (Jiang et al, Angew. Chem. int. Ed.., 2015, 54, 625 i - 6254; Jiang et al., ChemCatChem., 2016, 8: 16- 112).

There is a need in the- art for novel, inexpensive catalysts made from Earth-abundant materials that can efficientl generate hydrogen from the electrolysis of water. The present invention addresses this unmet need.

7 BRIEF DESCRIPTION OF THE DRAWINGS

The followi ng detailed description of preferred embodiments of the invention will be better understood ^' when read in conjunction with the appended drawings.

Figure 1 depicts a graplv of experimental data _, demonstrating

■polarization corves of eleelrodeposiie Co-Mo phosphorous films on nickel foam (substrate) and Ft wire in a 1 M KOFI solution.

Figure 2, comprising- Figures 2A-2B, depicts experimental data demonstrating the stability investigation of a G.oo.?Moiu-P film. Figure 2A depicts a graph of experimental data demonstrating the stability investigation, with

electrochemical cycles. Figure 2B depicts a graph of experimental data demonstrating chronopotmtiometric measurement at a constant current density of .10 raA cm ^"2 , figure 3 depicts a _. graph of experimental data demonstrating \h evolution from Coo.?Moi -P film, as a function of electroly sis time at constant electric current of 1 1 mA. The inset, shows the detector response from gas eh.romatograph verifying the evolved gas is hydrogen.

Figure 4, comprising Figures 4A-4C, depicts scanning electron microscop (SEM) images of alloys. Figure 4.4 depicts an SEM Image of an Mo-P alloy. Figure 4B depicts an SEM image of a Co-Mo alloy. Figure C depicts an SEM image of a Co-P alloy.

Figure 5* comprising Figures 5A-D, depicts the morphology of Co- Mo-P. Figure 5A depicts an SEM image of Coo.s-Moo,s-P. Figure 58 depicts ao: SEM image tf CMA-MOM-P. Figure 5C depicts an. SEM image of COO.T-MOO P. Figure 5.D

Figure 6 depicts an SEM Image of a Co» Mo¾ P catalyst on copper foil which shows near complete coverage of the rough film.

Figure 7 depicts SEM-Energy dispersive spectroscopy (EDS) elemental maps Of oo.7-Moo.s-P.

Figure 8 depicts an ^' experimental X-ray diffraction (XRD) pattern for Co Moo.3~P catalys Results suggest the structure of the electrocatalyst is amorphous in nature.

Figure 9, comprising Figures 9A-9B, depicts characterization ofCoo ?- Mot»P. Figure 9A depicts a transmission electron microscopy (Π ) image of Coo.?- Mot»P. Figure 9B depicts a selected area electron diffraction pattern (SAED) for C o ^' 0o.3-P. The lack of dift aetfcm spots in SAED also suggest that the structure of the materia! is amorphous.

Figure 10» comprising Figures- 1 OA- I OC, epicts chemical state characterization of Co-Mo-P. Figure 10A depicts X-ray pliotoeieetron spectroscopy (XPS) spectra: of Co 2 regions fCooj-Mpoj-P before nd after HER. Figure LOB depicts XPS spectra of Mo 3d regions of Coo.--Moo.3-P before and after HER. Figure 1.0C depicts XPS spectra of P Is regions of C6O/?-MOOJ-P before and after HER.

Figure I I , comprising .Figures 1 l.A-1 I D, depicts characterization of Coo MoQ;3-P. Figure 1 1A depicts a scanning transmission electron microscopy (STEM) image f C00.7- 00.3-P. Figure I I B depicts an elemental/map for P. Figure I IB depicts an elemental map for Mo, Figure 1 1 C- depicts an elemental map for Co.

Figure 1.2, comprising Figures 1 A-1.2F, depicts electrochemical ana ly sis of Co-Mo-P along wi th Co- P and Pt w ire for com arison. Figure 12A depicts polarization curves using a standard three electrode configuration, (graphite counter electrode). Figure I2B depicts Ta-fel curves. .Figure- 12C depicts polarization curves recorded from a two electrode- configu tion where- 20%- Ir/C was _. used .as the anode and Pt, Ceo.7-Moe.3~P was used as the cathode. Figure 12D depicts a durability test of Coo.7 ^« Mo(»P using cyclic voltammetry. Figure I.2E depicts long term stability for C0 .7-M00.3-P using chronopotentiemetry at IO- niA cnr ^2' for 24 h. Figure 12 F shows plots of the differences between anodic and caihodie current (ja-jc) at an open circuit potential versus scan rate, which was used to determine the double- layer capacitance of the ekctroeataly sis.

Figure .13 depicts an SEM image of C00.7- M 00.3- catalyst after HER.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to A catalyst of formula I: Cox yP (formula I), wherein: x ranges from about 0,4 to 1.0, and y ranges from about 0, 1 to 0,5. in one embodiment, x ranges from about -0.5. to 0,9, and y ranges ^■ from 0.2 to 0.4. In one. embodiment, x is about 0.7, and y is about .0.3. in one embodiment, the catalyst is a film.. In one embodiment, the film, is applied on a substrate; In one embodiment, the- substrate- is selected from the group consisting of copper foil and nickel foam.

The present invention also relates to an electrode comprising a substrate and a catalyst on at least a portion of the surface of the substrate, wherein the. catalyst is, a catalyst of formula I:· CoMayP ^< (formula 1), wherein: x ranges from about 0.4 to 1.0, and y ranges from about 0.1, to 0.5, In one embodiment, x ranges from about 0.5 to 0.9, and y ranges from 0,2 to 0,4. In one embodiment, is about 0.7, and y is about 0,3, In one embodiment, the substrate is selected from the group consi sti n of copper foil and nickel foam. in. one embodiment, the present i nvention is a device comprising the electrode, in one embodiment, the device is selected from the .group consisting of a s lar cell and a fuel cell

in another aspect, the present invention, relates to a method of preparin a catalyst using eleetrodeposition, wherein the method. comprises the steps of: a, immersing a substrate in an aqueous solution comprising- cobalt, molybdenum, and phosphorous; b. applying a. voltage to the substrate, wherein the catalyst forms a fil m on at leas t a portion of fee surface of the substrate. In one embod iment, the catalyst forms a film on the surface of the substrate. In one embodiment, the molar ratio betwee cobalt and molybdenum ranges from about 0,4:0, ί to 1.0:0.3, in one embodiment, the molar ratio between cobalt and molybdenum is about 0.7:0.3, Irs one embodimen t, the total concentration, of cobalt and molybdenum, in the aqueous solution is about 50 mM. In one embodiment, the voltage ranges from about—1.3 V to -1,6 V, In one embodiment, the voltage is about --1 ,5 V. In one embodiment, the eleetrodeposition is performed for a period of time ranging from about 300 seconds to 900 seconds, in one -embodiment, the eleetrodeposition is performed for a period of time of about 600 seconds.

In a: further aspect, the present invention relates to a method of producing hydrogen, the method includes the. steps of: a, providing a cell comprisin an electrode comprising a catalyst of formula I in. an aqueous solution; and b.

applying a current, to the cell, whereby hydrogen is produced at the electrode, wherein in formula I: CosMoyP (formula I), ranges from about 0,4 to 3,0, and y ranges from about 0, 1 to 0,5, In one embodiment, -the catalyst is a thin film deposited on at least a ^• portion of the surface of the electrode. In one embodiment,, x is about 0.7, and y is about 0,3, in one embodiment, the aqueous solution is an alkaline solution. In one embodiment, the pH of the solution is about 14, In one embodiment, the celt includes one chamber, In one embodiment, the cell further comprises a second electrode, in one embodiment, the cell further comprises a reference electrode.

The present invention also relates to a method of water electrolysis, the method comprising the steps of: a. providing a cell comprising an. electrode comprising- a catalyst of formula 1 in. an aqueous solution; and b, applying a current to the cell whereby water is electrolysed at the electrode, wherein in formula 1:

Co MoyP (formula I), % ranges from about 0.4 to 1.0, and y ranges from about 0,1 to 0.5. In one ^' embodiment, the catalyst is a thin film depositee! on at least a portion of the surface of the electrode, hi one embodiment, x is about 0.7, and y is about 0.3. In one embodiment, the aqueous solution is an alkaline solution, hi. one embodiment, th pH of the solution is about 14, In one embodiment, the cell includes one chamber, in. one embodiment, the cell further comprises a- second electrode, hi one embodiment, the cell further comprises a reference electrode.

The present invention relates in part to a method of producin hydrogen, the method comprising the steps of: a, immersing a substrate in an aqueous solution comprising cobalt.- ^' molybdenum, and phosphorous; and b, applying a voltage to the substrate, wherein a catalyst of formula 1 forms a f lm on at least a portion of the surface of the substrate; c. removing the first aqueous solution; d, adding an alkaline solution.; and e. applying" a current to the substrate, whereby hydrogen is produced, wherein in. formula 1: C sMo P (formula I), x ranges from about 0,4 to 1.0. and y ranges from about 0,1 to 0.5. In one embodiment, x is about 0.7, and y is about 0,3. In one embodiment the pH of the solution is about 14.

in- another aspect, the invention, relates to a method of water

electrolysis, the method comprising- the steps of: a. immersing a substrate in. an.

aqueous solution comprising cobalt, molybdenum, and phosphorous; and b, applying a voltage t the substrate* a catalyst of formula I forms a film on at least a portion of me surface, of the substrate; c. removing the aqueous solution; d. adding an. alkaline solution; and e. applying a current to the substrate, whereby water is electrolysed, wherein in formula k C x oy (formula 1), x ranges from about 0.4 to 1 .0, and y ranges from about 0.1 to 0.3. In one embodiment, x is about 0.7,. and y Is about 0,3. In one embodiment, the pH of the sol ution is abou t 1.4,

In another aspect, the inventor relates to a method of producing hydrogen, the method comprising the steps of a. immersing a substrate; in an. aqueous .solution comprising cobalt, molybdenum, -and phosphorous; and b. applying a voltage to- the substrate, wherein a catalyst of formula I forms a film on at least a portion of the surface of the substrate; c, removing the substrate from the aqueous solution; d. immersing the -substrate in ^' an alkaline solution;, and e. applying a current to the substrate, whereb hydrogen is produced, wherein in formula I: CXkMoyP (formula I), x ranges from about 0.4 to 1.0, and y ranges from about 0.1 to 0,5. In one

embodiment, x is about 0.7, and y is about 0.3. in one embodiment, the pH of the solution is about 14.

The present invention relates, in part, to a method of water electrolysis, the method comprising the steps of: a. immersing a substrate i an aqueous solution comprising c bal molybdenum, and phosphorous; and b, applying a voltage to the substrate, wherein a catalyst of formula I forms a film on at least portion of the surface of the substrate; c. .removing the substrate from the a ueous solution; d.

immersing the substrate in an alkaline solution; and e, applying a current to the substrate, whereby water is electrolysed, wherein in formula Ϊ: Cox o P (ibrraola 1), x ra ges from about 04 to 1.0, and y ranges from about 0. i to 0.5. In one

embodiment, x Is about <);?. and y is about 0.3. In one embodiment, the pH of the solution is about 14.

The present invention further relates, in part, to a system for producing hydrogen, the. system comprising: a ceil for generating electricity, wherein the ceil comprises an. electrode comprising a catalyst of formula I, _, wherein t he electricity electrolyzes water at the electrode to produce hydrogen, wherein in formula 1 ^*

CoxMojfP (formula 1), x ranges from about 0.4 to 1.0, and y ranges from about 0.1 ^' to 0.5. In one embodiment, x is about 0.7, and y is about 0,3. In one embodiment, the cell is a solar cell.

DETAILED DESCRIPTION

The present invention relates to the unexpected discovery that multi- metal, catalysts comprising certain molar ratios of cobalt to molybdenum (present along with phosphorous) exhibit improved properties over known catalysts for generating hydrogen From the electrolysis of water. For example, th catalysts of the present invention exhibit exceptional catalytic properties for the hydrogen evolution reaction (HER), a key reaction in water splittin technology to produce hydrogen gas, in one embodiment, the catalysts of the present invention, are composed of Earth- abundant elements, and exhibit catalytic, properties that improve significantly upon the properties of known HER catalysts, such as i and cobalt phosphides. The catalysts of the invention also exhibit superior stability in alkaline solutions.

The present invention also relates to the discovery of a novel method for the electrolysis of water, which utilizes the catalysts described herein. The present invention also relates to methods of preparing the catalysis of the invention.

The present invention also relates to electrodes nd devices comprising catalysts of the invention,

Unless defined otherwise, all technical nd scientific terms used herein have t e: same .meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used m the practice or testing of the present Invention, the preferred methods and materials are described.

As used herein, each of the followi g terms has the .meaning associated with it in this section.

The articles " " and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than, one element.

"About" as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%, ±10%, ±3%, ±1%, and ±0.1% from the specified value, as such variations are appropriate.

As-used herein, the term "overpotentiai" refers to the potential or oxidation potential and the potential at which the event is experimentally observed.

Ranges: throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not he construed a an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically discloseti ail the possible subranges as well as individual numerical values within that range. For example, description of a range such as from I to 6 should be considered to have specifically disclosed

^• subranges such as from 1 to 3. from 1 to 4, from I to 3, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, S , and 6. This applies regardless of the breadth of the range. .Description

The present nvention relates to the unexpected discovery that muHi- mefcd catalysts comprising certain molar ^' atios of cobalt to molybdenum exhibit improved properties over known Earth-abundant catalysts for generating hydrogen from the electrolysis of water. For example,- the catalysts of the present invention exhibit exceptional catalytic properties for the hydrogen evolution reaction (HER), a key reaction in water splitting technology to produce hydrogen gas, in one

embodimen t, the catalysts of the present in vention are composed, of Earth-abundant elements, and exhibit catalytic properties that significantly improve upon the properties of known HER catalysts, such as those made from Earth-abundant catalysts (see Table 1 ) . The cataly sts of the invention were also found to exhibit superior stability in alkaline solutions, in which water electroly sis is typically carried out.

The prese t in ention al s relates to methods of preparing the cataly sts of the invention, in one embodiment, the catalysts are prepared using

electTodeposition methods.

The present invention also relates to the discovery of a novel method for the preparation of hydrogen gas, which utilizes the catalysts described herein.

The present invention also relates to the discovery of a novel method for the electrolysis of water, which utilises the catalysis described herein.

The ability ^' to generate hydrogen gas for use as a fuel source using green methods is important for developing renewable energy sources. For example, electricit can be generated with a solar cell using only solar radiation, and the electricit can be used t carry ut hy drogen: gas production via water electrolysis. Therefore, it is desirable to have solar cells that Include catalysts that can efficiently electrolyse water to produce hydrogen gas, such as the catalysts of the present invention. Thus, the present invention als includes devices comprising electrodes and/or catalysts of the present invention, such as fuel cells and solar cells.

Catalysts of the Invention

The present invention includes novel multi-metal catalysts, in one embodiment, the catalysts are useful for the hydrogen evolution reaction (H ER), The catalysts may be prepared ftora Earth -abundant metals, which are relatively inexpensive compared to other known HER catalysis, such as platinum. In addition, the catalysis of the present invention were found to exhibit an overpoienttal of about 25-30 T»V at a current density of 10 mA cm ^'2 . In one embodiment, the catalyst includes cobalt (Co), molybdenum (Mo), and phosphorus (P).

in one embodiment, the catalyst is a catalyst of formula I:

CosMbyP (formula 1),

wherein:

ranges from about 0,4 to 1 ), and

y ranges from about 0,1 to 0.5.

As demonstrated by the experimental data described herein, certain molar ratios of cobalt to molybdenum (Co:Mo) were unexpectedly found to exhibit improved properties over other catalysts, in one embodiment, x ranges torn, about 0,4 to L0, and y ranges from about 0, 1 to 0,5, wherein x and y represent the moiar ratio of Co and Mb, respectively . In another embodiment, x ranges front about 0.5 to 0,9, and y ran es fr m 0,2 to OA in one embodiment, is about 0,7, and y is about 0.3.

in some embodiments, the catalysts of the invention are catalyst films, The films may he deposited onto substrates or supports, as would be understood by one of ordinary skill in. the art. in one embodiment, the substrate or support is an electrically conductin substrate or support, .Non- Hmiting examples of substrates and supports include JTO (indium-tin oxide), FT O (fluorine doped tin oxide), carbon, steel, stainless steel, copper, titanium, and nickel Textured substrates can also he used, for example, nickel foam. In one embodiment, the substrate is a Copper foil in another embodiment, the substrate is nickel foam.

The present in vention also includes methods of preparing the catalysts described herein, in one embodiment, the catalysts of the invention are prepared using methods of deposition, as would be understood by one of ordinary skill in the art. Non-li mi ting exam ples of deposit ion inc lude painting a slurry carried in organic or inorganic media, slurry spraying onto a hot or cold substrate, spray pyrolysis onto a hot substrate, flame spraying, solution spraying, dipping the substrate into the sol and heating, screen printing, electrolytic deposition, eleeirodeposition, including electrophoretie deposition, electroplating, and underpoteritial deposition, physical or chemical evaporation, sputtering, electrostatic spraying, plasma spraying, chemical vapor deposition, molecular beam -epitaxy, and laser techniques,

in one aspect, the present invention includes a method of preparing a catalyst, wherein the catalyst is applied to the surface of a substrate usi ng a method of deposi tion. In one embodiment, the method of deposition is eleeirodeposi tion, as would he understood by one of ordinary .skill in the art. .Using _, electrodepqsition methods, the inventive catalysts can he prepared in situ preparation of the inventive catalysts at the prescribed ratio, and can he prepared in minutes, as opposed to other methods which can take hours or days. Moreover, the ease with which

eleetrodeposition can he used to prepare the catalysts .results in a scalable; production method, which can be easily adapted for preparation on an industrial scale. Use of eleetrodeposition also permits control over the concentration of metals in the catalyst following deposition.

Eleetrodeposition of the catalysis of the invention may be carried out by any of a number of processes known to those skilled in the art. As would be understood by one of ordinary skill in the art, using eleetrodeposition, the catalyst forms a film r coat ing on the surface of the substrate..

In one embodiment, ^' the method.- of preparing a .catalyst using e ^' ieetrodeposltion comprises the steps oft

a, immersing a substrate in an aqueous solution comprising cobalt, molybdenum, and phosphorous; and

h, applying a voltage to the substrate, wherein the catalyst forms a film on at least a portion of the surface of the substrate.

molybdenum, -and- phosphorus may be prepared by adding appropriate amounts of compounds comprising each of the respective elements.. . on-limiting examples of suitable compounds comprising molybdenum include Mods, NaaMoO^

(NH4¼M 7024, (N.H4&M0G4, and the like., in one embodiment, the compound is MoCk Non-limiting examples of suitable compounds comprising cobalt include CoNCh, C0SO4, and the like, in one embodiment, the compound is CoNOs. A non- limiting exampl e of a suitable compound comprising phosphorous Is Na%P(¼. I n one embodiment, the aqueous solution is an electrolyte solution. The electrolytes are the electrical, conductor which carries the current and completes an electric -circuit between two electrodes.

Th aqueous soluiion may comprise additional components which may be adjusted to modify the deposition rate and/or the composition of the catalysis following deposition, as would be understood by one of ordinary skill in the art. Examples of additional components include N ^' aOAc, citrates such as sodium citrate, dtraie^w nomuffi-eiecttO!ytes.s.uch.as triamraomum citrate, ajSO*, and ammonia.

The molar ratio between cobalt and moly bdenum in the aqueous Solution .may be ^' adjusted as necessary in order to control, the molar ratio of cobalt and molybdenum in the catalyst after deposition, hi one embodiment, the molar ratio between cobalt and molybdenum ranges from about 0.4:0.1 to 1.0:0.5. In another embodiment, the molar ratio between cobalt and molybdenum ranges from about 0.5:0.2 to 0.9:0.4. In another embodiment, the molar ratio between cobalt and molybdenum is about 0.7:0.3.

The total concentration of coba.it and molybdenum in the aqueous solution can be adjusted as necessary. In one embodiment, the total concentration of cobalt and molybdenum ranges from about 1 mM to about 100 mM. in another embodiment the total concentration of cobalt and. molybden um ranges from about 1.0 mM to about 60 mM, In one embodiment, the total concentration of cobal and moly bdenum is about 50 mM.

The total concentration, of cobalt, molybdenum, and phosphorous in the aqueous solution can ^' be adjusted as necessary, in one embodiment, the total concentration of -cobalt, molybdenum, and phosphorous ranges from about 1 mM to about 100 mM. In another embodiment,, the total concentration of cobalt, molybdenum, and phosphorous ranges ^" from about .10 mM to about 60 raM. in one embodiment, the total concentration of cobalt, molybdenum, and phosphorous is- about S raM.

The voltage may be adjusted to achieve the desired rate of deposition on the substrate, as would be- understood by one of ordinary skill in the art, in one embodiment, -the voltage ranges from about -0,50 V to -2.5 V. In one embodiment, the voltage ranges from about -.1.0 V to -2.0 V. h one embodiment, the voltage ranges from about -1.3 V to -1.6 V. in one embodiment, the voltage ranges from about -1.4 V to -1 ,5 V. in one embodiment, the voltage is about - 1.5 V.

The electrodeposition may be performed ^' for an appropriate period of time, in one embodiment, the electrodeposition is performed for a period of time ranging from about 30. seconds to 6000 seconds. In one embodiment, the

electrodeposition is performed for a period of time ranging from about 60 seconds to 3000 seconds. In one embodiment, the -electrodeposition is performed for a period of time ranging from about 120 seconds to 1500 seconds, in one embodiment, the ^■ electrode-position, is performed for a period of time ran ing from about 300 seconds: to 900 seconds, in one embodiment, the elect«)dep siti n. is performed for a period of time of about 600 seconds.

The present invention also includes- electrodes comprising the catalysts of the inven tion. In one embodiment, the electrode includes a substrate and the catalyst, wherein the catalyst is deposited on the surface of the substrate. In one embodiment, the catalyst is deposited on at. least a portion of the surface of the substrate. Any .high surface area electrically conducting material is contemplated .as a substrate i the present invention., in one embodiment, the substrate or support is an electrically conducting substrate or support. Non-limiting examples of substrates and supports include ΠΌ (indium-tin oxide), PTO (fluorine doped tin oxide), carbon, steel, stainless steel, copper, titanium, and .nicke Textured ^' substrates -can also be used, for example, nickel foam, to one embodiment, the substrate is a copper foil In another embodiment, ^■ the substrate is nickel foam..

The present invention also includes devices comprising catalysts and/or electrodes of the present invention. Non-limiting examples of devices include ceils such as electrochemical cells, fuel cells (which includes both a non-rechargeable fuel eel! and a rechargeable fuel cell), solar cells, direct methanol fuel cells and metal/air rechargeable celis such as Za/air cells, batteries, solar panels, and redox, flow batteries. In one embodiment, the device is a ceil, in one embodiment, the device is selected f om the group consisting of a fuel cell and. a solar cell.

Methods of ^' Use.

The present invention includes methods of performing electrochemical processes using the catalysts invention. Non-limiting examples of electrochemical processes include electrolysis of water (water splitting), hydrogen evolution reaction (HER), electroplating. Oxidative treatment of Organic pollutants, electro-flotation, salt splitting, electrochemical synthesis of organic species, electro-dialysis, metal recovery, metal refining, electrochemical synthesis of pure elements, oxygen reduction as cathodic process, and die oxidation of water to oxygen as an anodic process. In one embodiment, the catalysts of the invention are useful in the hydrogen evolution reaction.

In one aspect , the presen t in v ention inc l udes a method of producing hydrogen., in one embodiment, the hydrogen production takes place in a ceil o an. electrode comprising a catalyst of the invention. In one embodiment, the method includes the steps of:

a. providing a eel! comprising an electrode comprising a catalyst of the kvention in an aqueous solution; and

b. applying a current to the cell, whereby hydrogen is produced at the electrode.

in another aspect, the present invention includes a method of ater ^' electrolysis:. In one embodiment, the electrolysis takes place m a cell on an electrode comprising a catalyst of the invention, in one embodiment, the method includes the steps of:

a. providing a ceil comprising an electrode comprising a catalyst of the invention in an aqueous solution; and

b. applying a current, to the cell, whereby water is electrolysed at the electrode. As would he understood by one of ordinary skill, in the art, the electrolysis o f water us ing t he methods of the in vention results i n th e production of hydrogen gas .

As described, herein, the ease with which the catalysts can be deposited on a substrate In combination with the superior activity of the catalysts in producing hydrogen gas demonstrates the co mmercial viability of the catalysis of the invention. Therefore, the present invention also includes novel methods for producing hydrogen wh ich combine methods of producing the catalysts with previously described methods for producing hydrogen or methods of water electrolysis. In a non-l uniting, example,, after the catalyst is deposited on the substrate, the aqueous solution comprising cobalt, molybdenum, and phosphorus can be replaced with -a alkaline solution in order to carry out water electrolysis.

In one aspect, the present invention includes a. method of producing hydrogen. The method includes the steps of:

a. immersin ^' a substrate in an aqueous sol utio comprising cobal t , molybdenum, and phosphorous; and

b. applying a voltage to the substrate, w herein a catalyst of the i vention forms a -film on at least portion of the surface o f the substrate ;

c. removing the first aqueous solution;

d. adding an alkaline solution; and

e. applying current to the substrate, whereby hydrogen is produced.

34 in one aspect, the present invention, also includes a method of water electrolysis. The method includes the steps of:

a. immersing a substrate in an aqueous solution comprising cobalt

molybdenum, and phosphorous; and

k applying a voltage to the substrate, wherein a catalyst of the invention forms a film on at least a portion of the surface of the substrate;

c. removing the aqueous solution;

d. adding an alkaline solution; and

e. applyin a current to the substrate, whereby water is electrolyzed.

In another non-limiting example, after the catalyst is deposited on tbe substrate, the substrate can be removed from the aqueous solution comprising cobalt; molybdenum, and phosphorous, and immersed in "an. alkaline solution in order to carry out water electrolysis.

In one. aspect the present Invention includes a method of producing hydrogen. The method includes tbe steps of;

a. immersing a substrate in. an. aqueous solution comprising cobalt

molybdenum, and phosphorous; and

b. applying a voltage to the substrate, wherein a catalyst of the invention forms a fil m on at least a portion of the surface of the substrate;

e. removing the substrate from the aqueous solution;

d. immersing the substrate in an alkaline solution; and

e. appl ing a current to the substrate, whereby hydrogen is produced.

In one aspect, the present invention also includes a method of water .electrolysis. The method includes the steps of:

a, immersing a substrate in an aqueous solution comprising cobalt, molybdenum, and phosphorous; and

b. applying a voltage to the substrate, wherein a catalyst of the invention forms a film on at least a portion of the surface of the substrate;.

o, removing tbe ^■ substrate from tbe aqueous solution;

d. immersing the substrate in an alkaline solution; and

e, applying a current to tbe substrate, whereby water is electro Sy zed.

in one embodiment, the catalyst is a thin film deposited on at least a portion of the surface of tbe electrode.

In one embodiment, the electrode is a cathode. In one embodiment, the cell is a solar cell. In one embodiment, he cell fa a fuel ceil.

In one embodiment, the current ranges from about 0.10 mA car ² to 100 mA em ^"2 , in one embodiment, the current ranges from about 1 tnA emr' to 50 mA cm ^{~ 2} . In one embodtmeni, the current ranges- from about 5 mA enr ² to 25 m A cnT ² . in one embodiment, the current is about 10 mA cm ² .

In one embodiment, the aqueous solution is an electrolyte solution, in one embodiment, the aqueous solution is an alkaline solution, in one embodiment,, the elecirode is immersed in the aqueous solution. The pH of the alkaline solution may be adjusted accordingly in order to attain the desired rate of hydrogen production, in one embodiment, the pE of the alkaline solution is about 8 or greater . In one embodiment the pH of the alkaline solution is about 10 or greater, in one ^' embodiment, the pH of ■the alkaline solution is about 12 or greater, in one embodiment, th pH of the alkaline solution is about 14 or greater. In one embodiment, the pH of the alkaline solution is about 1 ,

In one embodiment, the cell includes one chamber. In. one embodiment, the cell further includes a second electrode. In one embodiment, the cell further comprises a reference electrode.

Systems

The present invention also includes systems for producing hydrogen, in one embodiment, the system includes a cell for generating electricity. In one embodiment, the cell includes an electrode comprisin a catalyst of the invention. In one embodiment, the electricity eleetrolyzes water at the electrode to produce hydrogen. In one- embodiment, the ceil is a solar cell.

EXPERIMENTAL EXAMPLES

The. invention is further described m detail b reference to the following experimental examples. These examples are: provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, .the invention- should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

36 Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the catalysts of the invention and practice the claimed methods. The following - working examples therefore, specifically point out the preferred

embodiments. of the ^' present invention, and are not to be construed as limiting in any way the remainder of the disclosure.

Ex ample J : Preparation of rnu Iti-meial phosphorous films Method of preparation of mutii-raetai phosphorous films

Catalysts films were prepared by electrodeposition on copper foils/nickel foam. Prior to _. the elecfeodeposition, a polished copper foil with a 5 mm diameter was prepared and pasted on to a glassy carbon electrode. Catalysts were also prepared- on commercially bought i foam. In this case, the l foam was cut into 5 mm x 5 mm pieces and one- side was covered with insulating epoxy so that exposed geometric surface area was - 0.25 cm ² . Deposition of the novel eleetrocatalyst on. either substrate was carried out at -1.4 V vs. standard Ag/AgCI for 600 seconds using a standard three electrode configuration. A carbon counter electrode was used and Ag AgCI (sat Cl) electrode was used as the reference electrode. A series of deposition baths (with variable metal molar ratios Co:Mo) were prepared by adding of 50 m of metal (various Co Os and MoCIs masses), 0.5 Na¾PQ¾ and 0.1 M NaOAc in distilled water.

Results and Discussion

The catalytic performance of the eleetodeposited multi-metal finis was investigated in 1 M KOtt solution. For comparison, the hydrogen evolution reaction (HER) performance of Ft wire was also measured under the same test conditions. As shown in Figure 1 , the Co-Mo phosphorous catalyst- film synthesized, with molar ratio of 0.70:0.3 of Co:Mo (Co¾¾ «&3~P) shows a O mV onset

overpotential versus the reversible hydrogen electrode (RHE), which is similar to the precious metal platinum (the ^gold-standard" of HE R catalysis),

Moreover, Coo.?eMoo. P exhibits an overpoteritial of about 25-30 mV at a current density of 10 mA cm ^"2 , which makes this material the roost active non- precious metal based, alkaline e!etrocatalyst reported to date (Table I). As

3 7 demonstrated by the data of Table 1, Coa.?()Moe P was f ound to exhibit the lowest overpotential when directly compared to other non-precioas metal catalysts.

Table 1 ; Comparative data between Coo oM r -P and known catalysts.

Furthermore, Coa.7oMoo,3-P shows excellent stability with continuous operation for 24 hours at 1,0 mA. cm ^'2 also shows no significant performance degradation over 10000 electrochemical cycles (Figure 2). Addstiorislly, catalyst selectivity towards HER was evaluated using a faradaic efficiency determination an Coo.7iH Joi>.3-P showed a 99%. catalytic efficiency {Figure 3), meaning that 99% of the "electricity" went into making hydrogen gas. Example 2: Co-Μά-Ρ based electrocatalyst for superior alkaline \hydrogen evolution reacfon

Methods

Preparation of Co-Mo~P _? Co-P ant! Mo~P films

The catalyst films were prepared by e!eetrodepositkm on nickel foam/copper foil. Commercial bought ΝΪ foam/copper foil was cat into 5 mm ^¾ 5 mm _. pieces and one ^' side was covered with insulating epoxy so that the exposed geometric surface area was 0.25 cm ² . .Deposition was carried out at constant potential of -1 A Y vs standard Ag AgCl for 600 seconds using a standard three electrode

configuration. The counter electrode used was carbon and a Ag AgCl. (sat. KCI) electrode was used as the reference electrode, A series of deposition baths (with variable metal molar ratios Co:.Mo) were prepared: by adding of 50 inM of metal (various C0N-O3 and MoCls masses), 0.5 M NaJtePQa, and 0.1. M NaOAc in distilled water (Table 2), An -example of the- labelin scheme used was that for the catalyst resulting from the electrodepos ion from a bath- comprised of 23 mM Co^ and 25 mM M ^' o ^5* was labeled Coo.s-Moo.s-P. For the preparation of Co~P catalyst, the deposition, bat was prepared by -adding 50 mM C0NO3 solution. 0.5 M MaHaPOi, and 0,1 M NaOAc in distilled water. The deposition bath for Mo-P film was prepared by adding 50 mM aaMoO-i solution, 0.5 M N-aJ PC% and 0.1 M NaOAc in distilled water.

Table 2: Concentration of Co ^1" and. Μ · ' salt solutions used to prepare C0-M0-P and Co-P catal sts

Preparation of Co-Mo alloy films The deposition hath, fox the Co- Mo alloy was prepared by adding 0, 1 M C0NO3, 0.2 M K¾CVf¾0?, and 0,005 N&2M0O solution. The eleetrodepositioii was carried out at: constant potential of -1 ,4 V vs standard Ag AgCl for 600 seconds using ^' a ^' statklard three electrode configuration.

Materials characterizations

SEM images were obtained using a FBI Quanta 450 PEG microscope operated at 30 kV (see SEM images of Mo-P, Co-Mo, and Co-P alloys in Figure 4A- C). EDS analysis was performed with an. Oxford systems .natto-anaiysi EDS system attached to a FEl Quanta 450 FEG-SE microscope operating at 30 kV, XRD measurements were carried out by using a Bruker D8 X*ray diftractoraeter with Cu Ka radiation (λ ·- Ο.ί 5406 ήηι). XPS analysis of the catal st was carried out using a VG Scientific 100 mm hemispherical analyzer and. a Physical Electronics Mg K« X- ray source- operating at 300 W. Elemental analysis was performed using a Thermo Scientific iCAP 7000 Series inductively Coupled Plasma, with an Optical Emission Spectrometer (ICP-OES), Competitions of different catalysis are summarized in Tables 3 and 4.

Table 3: Atomic percentages of Co-Mo-P catalysts before and after alkaline HER.

Table 4: Atomic percentages of Co~P, Mt>P and Co-Mo alloy catalysis by EDS and ICP-OES

Electrochemical tests

Eleetrocatalytic analysis was carried out using a CHI 6608 poteotiostai operating in a standard three-electrode configuration at ambient temperature (22 2 °C) in I M KQH, All the potentials were measured with respect to a standard calomel (SCE) reference electrode (CM instritnients) and a graphite electrode was used as the counter electrode. The potential, measured against a SCE electrode, was converted to the potential versus the reversible hydrogen electrode (RHE) according to,

ERHK ^ ESCE ÷ E ae 0.059xpH

All the polarization curves were recorded at 0.5 m ^' Vs ^* ' sca rate. For all the catalysts tested here, -polarization curves were replicated at least 5 times. The overpotentia! (η, at a current density of 10 mA. cur ² ) reported are based on an analysis of these data. For Tafe.1 analysis, the HER acti vity of catalyst was evaluated by collecting stead -state .current ^■ -density ) as a Junction of applied potential (E) during hydrogen evolution. The eiirrent density - overpotentia). data were plotted in the form of log j versus η to construc t Tafei plots.

The double laye capacitance measurement was carried out using non- aqueous aprotic electrolyte (0, 15 M KPFWCH3CN) at open, circuit potential. For each capacitive m asttremeot cyclic voltaramefcry scans spanning- ±50 mV of the open, circuit potential was recorded at various scan rates (5, 10, 20, 30, 40, 50 and 60 niVs ^' '), The difference between, anodic current and eaihodie current (ja-jc) at open circuit potential was used t extract the capacitive current

Results and Discussion Alloying or doping different metals into materials which are alread catalytically active is a well-known strateg to control the binding and transformation kinetscs of key reaction intermediates hi catalysis (Bajdich et a!., J. Am, Chem. Soc., 2013, .135:13521 - 13530; Seh et al, Science,.2017, 355), Recent examples of such doping induced catal tic activity modulation, include the doping of ^T iOs/N.i(C)i:f}j with Fe (Fnebel et al„ J- Am. Chem. Soc, 2015, 137:1305-1313), NiFe layered double hydroxide with Co {Thenuwara et aL J. Fhys, Chem, B, 2018, 12.2:847-854},. and CoFeOs w ili W (Zhang et a!.. Science, 2016, 352:333) for OBR, and the doping of CoF iP systems wit Fe and M.n for HER (Liu et al, ACS Catal., 2017, 7:98- 102; Xing et a!., J, Mat. Chem. A, 2016, 4:1386643873). Density functional theory DFT) based theoretical investigations of these systems suggest that such

doping alloying can effectively tune the energetics of the reaction kitermediates; in. GBR, binding of GDH ^* ,OH ^* and O ^* and: in HER, binding of H* or H2O (Seh et at,. Science, 2017, 355; Zhang et ah, Science, 2016, 352:333), The reaction kinetics in alkaline HER takes place via electron-coupled water dissociation (the Volmer step), followed by the reaction between adsorbed hydrogen or between adsorbed, hydrogen and water to form molecular hydrogen (Tqfel or the Heymvsky step). (Subbaraman et al., Science, 201 1, 334: I 256), Thus, the HER activity can be limited by the initial Volmer step or subsequent T fidlHeyrovsky step depending on the active site. For example. Pi shows optimal proton binding {TqfelJHeyrovsly step), however, it shows a poor water dissociative capability (Volmer step) (Markovica et al,. J, Chem. Soe. Faraday Trans., 1996, 92:3719-3725), In the FlsNi hybrid system, the alloying between Pt and .i (a metal which is good at breaking the H-OR bond) influences the energetics of the water dissociative step such that the hybrid sy stem exhibits excellent catalytic-performance (Wang et al, Angew. Chem. tot Bd,, 2016, 128: 13051 -13055; Yu et al, ACS Energy Lett, 201.8 _» 3:237-244). in this regard, substitution of molybdenum (a metal which, shows excellent -hydrogen binding) (Zhang et al.. Energ Environ, Sei., 2016, :2789-2793; Zhang et al, Nat Commu ., 2 17, 8: 15437) with cobalt (an active water dissociation center) (Subbaraman et al, Nat, Mater., 2012, ! 1 :550-557) in amorphous- Co-P should lead to improved alkaline HER performance as a. close proximity of Co and Mo centers would alter the reaction kinetics to enhance the HER. Motivated by this hypothesis, highly HER active Co-P alloy was doped with molybdenum using 0CJ5 as the Mo precursor. The catalyst was synthesized usin room temperature eS.eetrodeposition ^• on Mi foam/copper toil (geometric surface area--0.25 cm ² ) where the eieettodeposMon bath consisted of NaHhPO¾ Co(NC¾) _> MoCls, and CaHLu aG. (see methods section for more detailed information). By varying the Co t Mo precursor ratio, the degree of Mo doping in the eobaii-rriolybdenuiTi-phosp!iorous-derived (Co-Mo-P) alloy was controlled (Table 2), As m example of the labeling of the different samples, the.

catalytic film resulting when the eieetrodepositlon bath contained a Co to Mo molar ratio of 7:3 was labeled as COQ.?-MO<U-P (and the rest were labeled accordingly). Scanning electron microscopy (SEM) analysis of the catalyst alloys with different Co to Mo ratios .showed rough film morphologies with near complete coverage (Figure 5A-C & Figure 6) on the supporting copper foil and Ni foara. Elemental analysis using energy dispersive spectroscopy (EDS) and inducti vely coupled plasma optical emission" s e trometr (ICP-OES) confirmed the presence .of cobalt, molybdenum and. phosphorus, with -90% of the alloy consisting of metals (Co and Mo) and 10% of phosphorous. (Figure 7, Table 3), The absence of well-defined X-ray diffraction

(XR ^' P) peaks (Figure 8), the presence of diffuse rings and the absence of well-defined diffraction spots in the selected area electron diffraction (SAE ^' D) pattern (Figure 9A- B) obtained from transmission electron microscopy (TE ) are experimental

observations that suggest that the electrodeposiied Co-Mo-P films are amorphous in nature. X-ray photoeSeetron spectroscopy (XPS) was employed to investigate the electronic structure of the Co-Mo-P catalyst The Co 2p region showed, two distinct peaks at 778,2 eV (Co 2p ) and 793. eV (Co 2p which is similar to Co 2p XPS of cobalt hound ^' to phosphorous (F igure 10A) (Grosvenor et aL l.norg, Ch ^' em., 2005, 44:8988-8998). The Mo 3d region showed peaks at 228,9 eV (Mo 3d ^sn ) and 231.9 eV (Mo3i/ ^x -} which are assigned to .molybdenum bound to phosphorous (Xiao et aL Energy Environ. ScL 2014, 7:2624-2629) ( Figure Ί0Β). The peak at 130.2 eV for the P 2p region can he assigned to metal (Co and Mo) bound phosphorous i the form of metal phosphide (Grosvenor et at, Inorg, Chem. 2003, 44:8988-8998; Ma et aL Energy Environ. Sci., 2017, 10:788-798) (Figure I OC). To get more insight into the cataiysi structure, the distribution of elements (Co, M and P) in the Co-Mo-P ^' catalyst was determined with scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS). The STEM- EOS elemental maps showed a relatively uniform distribution of Co, Mo and P. (Figure 1 1 A-D). The HER performance of Co- o-P was investigated in a I M KOU solution (pH 14) using linear sweep voitamrnetry at a scan rate of 0.5 mV s" ¹ (see methods section for details) with a standard three electrode configuration. This low sca rate was chosen to maximize the contribution from faradase current and

minimize capatitive curren To determine the optimum Mo concentration, various catalytic alloy films were eleetrodeposited with variable Co to Mo ratios. For comparison, the HER performance of Co-P, Mo-P, Co-Mo alloy and platinum wire were also measured under the same test conditions. As shown in figure ⁷ 12A the best catalyst .formulation, Coo,T-M. iB-P, showed a negligible, ~ 0 V, onset potential versus the reversible hydrogen electrode (RH ^' E). This onset overpotential associated with Coi»Mo<i P was smaller than that associated with Co-P, Mo-P, Co-Mo alloy, Co .g- M00.2-P, Cos).&-Moo. -P _.; Coo.5-Mort.5-P, and other alkaline HER catalysts reported to date. Additionally, Coe.?~Mo j~P exhibits the smallest overpotential (25 m at a current density of .10 mA cm" ² ) and the value is similar to highly actively platinum based HER eSecirocatalysis (Figure 12 A). The presence- of Mo with Co and P results in an overpoienilal reduction, of .about - 100 mV relative to a. Co-P film, emphasizing the synergy between Mo, Co, and P in the Mo-Co-P HER catalyst. The Tate! slope associated with the Co-M o-P is 42 rrsV decade ^{" 3} , which is slightly greater than that of platinum (35m V decade ^"1 ,. Figure 1.26). it is important to mention thai the overpotential associated with the amorphous Mo-Co-P catalyst is significantly lower than conipositionaily similar crystalline electrocataiysts that have been studied in prior research. For ex m l , prior studies show that a Co-Mo-F nanocrystal coated by a few-layer N-doped carbon shell exhibited an overpotential of 83 .mV at 1.0 mA. cm ^*2 , in I M KOH (Ma et al, Energy Environ, Set, ,2017, 10:788-789) and Mo doped CoP (Fang et at. Royal Soc. Open Sci,, 2017, ) nanoparticles exhibited an overpotential of -550 mV at 10 mA enr% in 0,5 M &SO . This amorphous versus crystalline structural issue is addressed below.

Figure 12B shows the polarization curve acquired for eleetrodepositecl Coo 7-M00.3-P in a two-electrode configuration., in this configuration Coe> Moo P was used, as the -reducing -electrode (0,5 mg cm" ² mass loading) and the .commercially available 20% Ir C was used as the- oxidizing _. electrode. As a control, a Pt/C electrode with the same catalyst loading (0.5 mg cm ^'2 ) was used.. The results show thai Co-Mo- P catalyst shows similar activity to Pt/C, where overall water splitting current of 10 mA cm ^*3 was obtained at an overpotential of 290 mV, The majority of this 290 raV overpoteniial arises from, the ,20 % Ir/G catalyst, as Co-M.o-P shows a uch smaller HER verpotential.

The stability of the Mo-Co-P catalyst was tested, using long term electtocatalytic cycling with cyclic voitarametry (CV) at a sears .rate of 50 raV s ^" ', Figure 12D shows the obtained polarisation plots far Co¾.?-Moe.j-P after performing 1000 and 10000 CVs, The results show a very small increase in overpoteniial (~ 7 mV) after 10000 cycles suggesting an excellent stability towards alkaline HER.

Furthermore, -the stability .measurements were complemented by

chronopoteniiometry, where in this electrochemical mode a constant current of 10 niA cm was passed through the catalyst electrode and the overpoteniial was measured as a function of time. Figure 12E shows the resulting chroRopotentiometric curve for Coo.?« o(»P, showing that there was only a negligible increase in overpoteniiai over a rime of 24 hours. The selectivity of Co-Mo-P towards alkaline HER was evaluated by performing a faradaie efficiency measurement which resulted in value of 99%. (Figure 3). For the faradaie efficiency calculation, controlled electrolysis was carried out using .an air tight H-iype eel! at 30 mV overpoteniiai and th evol ed gas (i i was verified with gas chromatography, The double layer capacitance (Ga> of the samples was measured to estimate the electrochemical active surface area using cyclic voltammetry in non -aqueous med i u m. The u se of the non-aqueous mediu : ensured that the current response resulted only from .capacKive charging uon~faradaic) (Yoon et at, I Am, Chem, Soc. ₅ 2018, 140:2397-2400). Gs values for the Co-Mo-F

materials ranged from 0,83- 1.13 rnP while Co-Mo, Co-P and Mo-P samples were associated with Cdj values. of 0.69, showing that the Co-M.o-P system contained an increased number of reactive sites relative to Co-P, o-P and Co-Mo. Moreover, XPS , EDS and SEM mvestigations were perf rmed on the Coo.-- Moo> catal st after the HER stability test to determine whether there were any morphological and/or chemical changes. SEM ^' micrographs obtained after the -stability test showed no change relative to the as-prepared catalyst (Figure 13). However, EDS analysis showed minor decreases in Mo and P content with respect to cobalt (Table 3). Finally, XPS analysis verified that there was no change in the oxidation state of the constituent metals during HER catalysis (Figure 10A-C),

in su mmary , it .has been sho wn that the doping of Co-P with Mo is an effecti ve strategy to tune the catalytic activity of Co-P. The best Mo~Co-P catalyst exhibited an overpoteniiai for HER at a current density of 10 mA cm" ² thai was 100 mV lower than Co-P. Results show thai the .introduction of Mo to the Co-P system effectively tunes the energetics of both water dissociation and proton binding in alkaline HER leading to enhancement in the- catalytic activity (i.e., lowering of the ovefpotential). Overall, the Mo doped Co-P catalyst is active ( ^■ -- 30-35 iaV overpotential at 10 mA. em ^'2 }, stable (retains activity for over 24 hours) and selective (99%, faradaie efficiency for fb) for alkaline eleetroc.atal.ytic HER. Furthermore, the use of Earth-abundant -metals and easy fabrication make Co- o-P a potential replacement for the precious platinum metal catalyst in commercial alkaline electroiyzers.

The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention ma be devised by others skilled in the art without departing from, the true spirit and scope of the invention. The appended claims are intended to he construed to include all such embodiments and equivalent variations.