METHOD FOR WATER SPLITTING WITH A PEROVSKITE ELECTRODE

Abstract

An electrode includes a transparent substrate, and a layer of a nanostructured material at least partially covering a surface of the transparent substrate. The nanostructured material includes defective perovskite nanostructures (DPNSs) in the form of nanoplates having an average particle size in a range of 10 to 100 nanometers (nm), an interplanar spacing d(101) of the (101) plane in a range of 0.3 to 0.4 nm, and an interplanar spacing d(104) of the (104) plane in a range of 0.2 to 0.3 nm. A method of making the electrode.

Claims

1. (canceled)

2. The method of claim 19, wherein the transparent substrate is a glass substrate, and wherein the glass substrate is at least one selected from the group consisting of a fluorine doped tin oxide (FTO) glass substrate, a tin doped indium oxide (ITO) glass substrate, an aluminum doped zinc oxide (AZO) glass substrate, a niobium doped titanium dioxide (NTO) glass substrate, an indium doped cadmium oxide (ICO) glass substrate, an indium doped zinc oxide (IZO) glass substrate, a fluorine doped zinc oxide (FZO) glass substrate, a gallium doped zinc oxide (GZO) glass substrate, an antimony doped tin oxide (ATO) glass substrate, a phosphorus doped tin oxide (PTO) glass substrate, a zinc antimonate glass substrate, a zinc oxide glass substrate, a ruthenium oxide glass substrate, a rhenium oxide glass substrate, a silver oxide glass substrate, and a nickel oxide glass substrate.

3. The method of claim 19, wherein the transparent substrate is a glassy carbon substrate.

4. The method of claim 19, wherein the nanostructured material has a formula ATiO.sub.3-x, wherein: A is at least one metal selected from the group consisting of Ba, Co, Ni, Pb, Zn, Sr, and La, and 0<x<3.

5. The method of claim 19, wherein the nanostructured material has a formula CoTiO.sub.3-x, wherein 0<x<3.

6. The method of claim 19, wherein the electrode has an overpotential of 0.2 to 0.5 volts (V) in an acidic medium at a current density of 5 to 20 milliamperes per square centimeter (mA/cm.sup.2).

7. The method of claim 19, wherein the electrode has a double layer capacitance of 200 to 280 microfarads per square centimeter (F/cm.sup.2) in an acidic medium at an overpotential of 0.352 V.sub.RHE.

8. The method of claim 19, wherein the electrode has an active surface area of 4 to 10 square centimeters (cm.sup.2) in an acidic medium at an overpotential of 0.352 V.sub.RHE.

9. The method of claim 19, wherein the electrode has a Tafel slope of 80 to 110 millivolts per decade (mV/decade) in an acidic medium at a scan rate of 5 to 20 millivolts per second (mV/s).

10-18. (canceled)

19. A method for electrochemical water splitting, comprising: applying a potential between a working electrode and a counter electrode in an electrochemical cell containing an electrolyte to form hydrogen and oxygen; wherein the working electrode comprises an electrode having a transparent substrate, and a layer of a nanostructured material at least partially covering a surface of the transparent substrate; wherein the nanostructured material comprises defective perovskite nanostructures (DPNSs) in the form of nanoplates having an average particle size in a range of 10 to 100 nanometers (nm), an interplanar spacing d(101) of the (101) plane in a range of 0.3 to 0.4 nm, and an interplanar spacing d(104) of the (104) plane in a range of 0.2 to 0.3 nm, as determined by X-ray diffraction; and wherein the electrolyte comprising an aqueous solution of an acid having a concentration of 0.001 to 3 molars (M).

20. The method of claim 19, wherein the acid comprises at least one acid selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, boric acid, and citric acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0031] FIG. 1 is a schematic flow diagram of a method of making an electrode, according to certain embodiments;

[0032] FIG. 2 is a schematic flow diagram depicting a method for layering a nanostructured material (NSM) covering a surface of a transparent substrate, according to certain embodiments;

[0033] FIG. 3A shows an X-ray diffraction (XRD) spectrum of pure-titanium oxide (TiO.sub.2), D-TiO.sub.2-x, pure-cobalt titanate (CoTiO.sub.3), and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0034] FIG. 3B shows a magnified XRD spectrum of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0035] FIG. 4A shows a scanning electron microscope (SEM) image of pure-TiO.sub.2, according to certain embodiments;

[0036] FIG. 4B shows an SEM image of D-TiO.sub.2-x, according to certain embodiments;

[0037] FIG. 4C shows an SEM image of pure-CoTiO.sub.3, according to certain embodiments;

[0038] FIG. 4D shows an SEM image of D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0039] FIG. 5A shows a transmission electron microscope (TEM) image of pure-TiO.sub.2, according to certain embodiments;

[0040] FIG. 5B shows a TEM image of D-TiO.sub.2-x, according to certain embodiments;

[0041] FIG. 5C shows a TEM image of pure-CoTiO.sub.3, according to certain embodiments;

[0042] FIG. 5D shows a TEM image of D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0043] FIG. 6A shows a high-resolution transmission electron microscopy (HRTEM) image showing (101) lattice plane of pure-TiO.sub.2, exhibiting a lattice spacing of 0.352 nm, according to certain embodiments;

[0044] FIG. 6B shows a HRTEM image showing (101) lattice plane of D-TiO.sub.2-x NSs, exhibiting a lattice spacing of 0.352 nm, according to certain embodiments;

[0045] FIG. 6C shows a HRTEM image showing (104) lattice plane of pure-CoTiO.sub.3, exhibiting a lattice spacing of 0.273 nm, according to certain embodiments;

[0046] FIG. 6D shows a HRTEM image of D-CoTiO.sub.3-x NSMs showing the (104) lattice plane of D-CoTiO.sub.3-x defective perovskite nanostructures (DPNSs) displaying a lattice spacing of 0.273 nm, according to certain embodiments;

[0047] FIG. 7A shows an energy dispersive X-ray spectroscopy (EDX) of pure-TiO.sub.2, according to certain embodiments;

[0048] FIG. 7B shows an elemental mapping of pure-TiO.sub.2, according to certain embodiments;

[0049] FIG. 7C shows an elemental mapping of Ti in pure-TiO.sub.2, according to certain embodiments;

[0050] FIG. 7D shows an elemental mapping of oxygen (O) in pure-TiO.sub.2, according to certain embodiments;

[0051] FIG. 7E shows an EDX of D-TiO.sub.2-x, according to certain embodiments;

[0052] FIG. 7F shows an elemental mapping of D-TiO.sub.2-x, according to certain embodiments;

[0053] FIG. 7G shows an elemental mapping of Ti in D-TiO.sub.2-x, according to certain embodiments;

[0054] FIG. 7H shows an elemental mapping of O in D-TiO.sub.2-x, according to certain embodiments;

[0055] FIG. 7I shows an EDX of pure-CoTiO.sub.3, according to certain embodiments;

[0056] FIG. 7J shows an elemental mapping of pure-CoTiO.sub.3, according to certain embodiments;

[0057] FIG. 7K shows an elemental mapping of Co in pure-CoTiO.sub.3, according to certain embodiments;

[0058] FIG. 7L shows an elemental mapping of Ti in pure-CoTiO.sub.3, according to certain embodiments;

[0059] FIG. 7M shows an elemental mapping of O in pure-CoTiO.sub.3, according to certain embodiments;

[0060] FIG. 7N shows an EDX of D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0061] FIG. 7O shows an elemental mapping of D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0062] FIG. 7P shows an elemental mapping of Co in D-CoTiO.sub.3-x, according to certain embodiments;

[0063] FIG. 7Q shows an elemental mapping of Ti in D-CoTiO.sub.3-x, according to certain embodiments;

[0064] FIG. 7R shows an elemental mapping of O in D-CoTiO.sub.3-x, according to certain embodiments;

[0065] FIG. 8A illustrates an X-ray photoelectron (XPS) spectrum showing survey plots of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0066] FIG. 8B illustrates an XPS spectrum of Ti 2p showing plots of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0067] FIG. 8C illustrates an XPS spectrum of Co 2p showing plots of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0068] FIG. 8D illustrates an XPS spectrum of O Is showing plots of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0069] FIG. 9A illustrates a deconvoluted high-resolution XPS spectrum of Ti 2p showing a plot of D-TiO.sub.2-x, according to certain embodiments;

[0070] FIG. 9B illustrates a deconvoluted high-resolution XPS spectrum of Ti 2p showing a plot of D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0071] FIG. 10A illustrates a linear sweep voltammetry (LSV) curve of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0072] FIG. 10B illustrates a histogram plot of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0073] FIG. 10C illustrates of a cyclic voltammetry (CV) curve of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0074] FIG. 10D illustrates an electrochemical surface area (ECSA) plots of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0075] FIG. 11A illustrates Tafel plots of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0076] FIG. 11B illustrates a proposed hydrogen evolution process (HEP) Volmer-Heyrovsky (V-H) mechanism of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0077] FIG. 11C illustrates an electrochemical impedance spectroscopy (EIS) curve of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0078] FIG. 11D illustrates stability plots (Cp and Cv) of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, according to certain embodiments;

[0079] FIG. 12A shows a SEM image of the D-CoTiO.sub.3-x DPNSs catalyst after stability tests, according to certain embodiments;

[0080] FIG. 12B shows a TEM image of the D-CoTiO.sub.3-x DPNSs catalyst after stability tests, according to certain embodiments;

[0081] FIG. 12C shows an XRD image of the D-CoTiO.sub.3-x DPNSs catalyst after stability tests, according to certain embodiments;

[0082] FIG. 12D shows an EDX image of the D-CoTiO.sub.3-x DPNSs catalyst after stability tests, according to certain embodiments;

[0083] FIG. 12E shows an elemental mapping of the D-CoTiO.sub.3-x DPNSs catalyst, according to certain embodiments;

[0084] FIG. 12F shows an elemental mapping of the D-CoTiO.sub.3-x DPNSs catalyst showing the presence of cobalt, according to certain embodiments;

[0085] FIG. 12G shows an elemental mapping of the D-CoTiO.sub.3-x DPNSs catalyst showing the presence of titanium, according to certain embodiments; and

[0086] FIG. 12H shows an elemental mapping of the D-CoTiO.sub.3-x DPNSs catalyst showing the presence of oxygen, according to certain embodiments.

DETAILED DESCRIPTION

[0087] In the drawings, reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words a, an and the like generally carry a meaning of one or more, unless stated otherwise.

[0088] Furthermore, the terms approximately, approximate, about, and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.

[0089] As used herein, the term electrode refers to an electrical conductor used to contact a non-metallic part of a circuit e.g., a semiconductor, an electrolyte, a vacuum, or air.

[0090] As used herein, the term substrate refers to an underlying layer that supports the primary layer.

[0091] As used herein, the term current density refers to the amount of electric current traveling per unit cross-section area.

[0092] As used herein, the term Tafel slope refers to the relationship between the overpotential and the logarithmic current density.

[0093] As used herein, the term electrochemical cell refers to a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions.

[0094] As used herein, the term water splitting refers to the chemical reaction in which water is broken down into oxygen and hydrogen.

##STR00001##

[0095] Aspects of the present disclosure are directed to a nanostructured material (NSMs)-based electrocatalyst for an electrochemical water-splitting reaction. According to an aspect of the present disclosure, an electrode containing the NSMs-based electrocatalyst is described. The electrode includes a transparent substrate. The transparent substrate is a glass substrate, and wherein the glass substrate is at least one selected from the group consisting of a fluorine doped tin oxide (FTO) glass substrate, a tin doped indium oxide (ITO) glass substrate, an aluminum doped zinc oxide (AZO) glass substrate, a niobium doped titanium dioxide (NTO) glass substrate, an indium doped cadmium oxide (ICO) glass substrate, an indium doped zinc oxide (IZO) glass substrate, a fluorine doped zinc oxide (FZO) glass substrate, a gallium doped zinc oxide (GZO) glass substrate, an antimony doped tin oxide (ATO) glass substrate, a phosphorus doped tin oxide (PTO) glass substrate, a zinc antimonate glass substrate, a zinc oxide glass substrate, a ruthenium oxide glass substrate, a rhenium oxide glass substrate, a silver oxide glass substrate, and a nickel oxide glass substrate. In a preferred embodiment, the transparent substrate is a glassy carbon substrate. Optionally, the transparent substrate may be replaced by a titanium plate or a copper plate. The substrate may be of a single layer or several layers. In an example, the substrate made of glass may optionally be coated with a layer of FTO or PTO, or any other materials as stated above, and then sintered together to provide the substrate.

[0096] In some embodiments, the substrate may have a thickness of less than or equal to about 3 mm, for example, ranging from about 0.1 mm to about 2.5 mm, from about 0.3 mm to about 2 mm, from about 0.7 mm to about 1.5 mm, or from about 1 mm to about 1.2 mm, including all ranges and subranges therebetween. However, it is preferably 0.5 mm to 3 mm from the viewpoint of easiness in handling. Other ranges are also possible.

[0097] The electrode further includes a layer of a nanostructured material (NSMs) at least partially covering the surface of the transparent substrate. The dispersion of the NSMs on the transparent substrate is one of the critical factors that affect the performance of the electrode. The deposition of the NSM on the transparent substrate may be brought about by any of the methods conventionally known in the artfor example: spin coating/drop casting technique. In a preferred embodiment, drop-casting technique was applied to ensure uniform deposition of the NSM on the transparent substrate. In this method, a solution containing the NSM is cast on the transparent substrate, followed by the evaporation of the solventto obtain the electrode. In some embodiments, at least 50% of the surface of the transparent substrate is covered by the nanostructured material based on a total surface area of the transparent substrate, preferably at least 70%, preferably at least 90%, or even more preferably at least 99%, based on the total surface area of the transparent substrate. In another embodiment only one side of the transparent substrate is covered with nanostructured material. Other ranges are also possible.

[0098] The NSM includes defective perovskite nanostructures (DPNSs). Referring to FIGS. 4A to D, the DPNSs are in the form of nanoplates having an average particle size in a range of 10 to 100 nanometers (nm), including 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 and 95 nm. In some embodiments, the geometry of the DPNSs may alternately include, but is not limited to, a circular, polygonal, triangular, and rectangular shape. In some embodiments, the DPNSs have an interplanar spacing d(101) of the (101) plane in a range of 0.3 to 0.4 nm, preferably 0.32 to 0.38 nm, preferably 0.34 to 0.36 nm, or even more preferably about 0.35 nm, as determined by X-ray diffraction. In some further embodiments, the DPNSs have an interplanar spacing d(104) of the (104) plane in a range of 0.2 to 0.3 nm, preferably 0.22 to 0.28 nm, preferably 0.24 to 0.26 nm, or even more preferably about 0.25 nm, as determined by X-ray diffraction. Other ranges are also possible. The d-spacing or the lattice spacing or inter-atomic spacing is the distance between the parallel planes of atoms.

[0099] The nanostructured material has a formula ATiO.sub.3-x, where A is at least one metal selected from the group consisting of barium (Ba), cobalt (Co), nickel (Ni), lead (Pb), zinc (Zn), strontium (Sr), and lanthanum (La), or the like, and two or more elements may be used. In some embodiments, A may be magnesium (Mg), calcium (Ca), strontium (Sr), or the like, and two or more elements may be used. In the formula ATiO.sub.3-x, in which 0<x<3. In a preferred embodiment, Co is used in NSMs. The cobalt may exist in oxidation states of +2 or +3. The nanostructured material has a formula CoTiO.sub.3-x, in which 0<x<3.

[0100] The CoTiO.sub.3-x material includes 10 to 30 wt. %, more preferably 12 to 28 wt. %, more preferably 14 to 26 wt. %, and yet more preferably 16 to 24 wt. % Co; 20 to 40 wt. %, more preferably 22 to 38 wt. %, more preferably 24 to 36 wt. %, and yet more preferably 26 to 32 wt. % Tie; 40 to 60 wt. %, more preferably 42 to 58 wt. %, more preferably 44 to 56 wt. %, and yet more preferably 46 to 52 wt. % O, each wt. % based on the total weight of the CoTiO.sub.3-x material by energy dispersive X-ray (EDX). Other ranges are also possible.

[0101] In an embodiment, the surface of the transparent substrate is deposited partially or wholly with at least one layer of the CoTiO.sub.3-x material in a uniform and continuous manner. In a preferred embodiment, the CoTiO.sub.3-x material forms a continuous layer on at least one surface of the glassy carbon substrate. In an embodiment, particles of the CoTiO.sub.3-x material may form a monolayer on the glassy carbon substrate. In another embodiment, the particles of the CoTiO.sub.3-x material may form more than a single layer on the glassy carbon substrate.

[0102] In a preferred embodiment, the CoTiO.sub.3-x based electrode was evaluated for the electrocatalytic activity that operated in an acidic media consisting of 0.5 molar (M) H.sub.2SO.sub.4. In one embodiment, the synthesized CoTiO.sub.3-x based electrode has an overpotential of 0.2 to 0.5 volts (V), preferably 0.3 to 0.4 V, or even more preferably about 0.35 V, at a current density of 5 to 20 milliamperes per square centimeter (mA/cm.sup.2), or even more preferably about 10 mA/cm.sup.2. In one embodiment, the synthesized CoTiO.sub.3-x based electrode has a double layer capacitance of 200 to 280 microfarads per square centimeter (F/cm.sup.2), preferably 220 to 260 F/cm.sup.2, or even more preferably about 240 F/cm.sup.2 at an overpotential of 0.352 V.sub.RHE. In a preferred embodiment, the synthesized CoTiO.sub.3-x based electrode has an active surface area of 4 to 10 square centimeters (cm.sup.2), preferably 6 to 8 cm.sup.2, or even more preferably about 5 cm.sup.2 at an overpotential of 0.352 V.sub.RHE. In a more preferred embodiment, the synthesized CoTiO.sub.3-x based electrode has a Tafel slope of 80 to 110 millivolts per decade (mV/decade), preferably 90 to 100 mV/decade, or even more preferably about 100 mV/decade, at a scan rate of 5 to 20 millivolts per second (mV/s), or even more preferably about 10 mV/s. Other ranges are also possible.

[0103] The crystalline structures of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs may be characterized by X-ray diffraction (XRD), respectively. In some embodiments, the XRD patterns are collected in a Powder X-ray diffraction (XRD, Bruker D8 Advance diffractometer) equipped with a Cu-K radiation source (=0.15406 nm) for a 2 range extending between 5 and 80, preferably 15 and 70, further preferably 30 and 60 at an angular rate of 0.005 to 0.04 s.sup.1, preferably 0.01 to 0.03 s.sup.1, or even preferably 0.02 s.sup.1.

[0104] In some embodiments, the pure-TiO.sub.2 (302) has a first intense peak with a 2 theta (0) value in a range of 22 to 28 in an X-ray diffraction (XRD) spectrum, or preferably about 25, as depicted in FIG. 3A. In some further embodiments, the pure-TiO.sub.2 (302) has at least a second intense peak with a 2 value in a range of 30 to 36, or even more preferably about 33, at least a third intense peak with a 2 value in a range of 42 to 48, or even more preferably about 45, at least a fourth intense peak with a 2 value in a range of 52 to 58, or even more preferably about 55, at least a fifth intense peak with a 2 value in a range of 59 to 65, or even more preferably about 62, at least a sixth intense peak with a 2 value in a range of 65 to 75, as depicted in FIG. 3A. In some embodiments, the D-TiO.sub.2-x has at least a first intense peak with a 2 value in a range of 22 to 28, at least a second intense peak with a 2 value in a range of 30 to 36, at least a third intense peak with a 2 value in a range of 42 to 48, at least a fourth intense peak with a 2 value in a range of 52 to 58, at least a fifth intense peak with a 2 value in a range of 59 to 65, and at least a sixth intense peak with a 2 value in a range of 65 to 75, as depicted in FIG. 3A. In some further embodiments, the pure-CoTiO.sub.3 has at least a first intense peak with a 2 value in a range of 22 to 28, or even more preferably about 25, at least a second intense peak with a 2 value in a range of 30 to 38, or even more preferably 32 to 36, at least a third intense peak with a 20 value in a range of 38 to 44, or even more preferably about 41, at least a fourth intense peak with a 2 value in a range of 46 to 52, or even more preferably about 49, at least a fifth intense peak with a 2 value in a range of 52 to 56, or even more preferably about 54, at least a sixth intense peak with a 2 value in a range of 59 to 68, or even more preferably about 62 to 66, as depicted in FIG. 3A. In some, ore preferred embodiments, the D-CoTiO.sub.3x has at least a first intense peak with a 2 value in a range of 22 to 28, or even more preferably about 25, at least a second intense peak with a 2 value in a range of 30 to 38, or even more preferably 32 to 36, at least a third intense peak with a 2 value in a range of 38 to 44, or even more preferably about 41, at least a fourth intense peak with a 2 value in a range of 46 to 52, or even more preferably about 49, at least a fifth intense peak with a 2 value in a range of 52 to 56, or even more preferably about 54, at least a sixth intense peak with a 2 value in a range of 59 to 68, or even more preferably about 62 to 66, as depicted in FIG. 3A. Other ranges are also possible.

[0105] In an exemplary embodiment, a method of making the electrode is described. Referring to FIG. 1, a schematic flow diagram of a method of making the electrode is illustrated. The order in which the method 50 is described is not intended to be construed as a limitation, and any number of the described method steps may be combined in any order to implement the method 50. Additionally, individual steps may be removed or skipped from the method 50 without departing from the spirit and scope of the present disclosure.

[0106] At step 52, the method 50 includes preparing the nanostructured material having defective perovskite nanostructures by mixing titanium salt, an alkaline earth metal base, and water to form a precipitate in a first mixture. The titanium salt includes one or more of titanium tetrachloride, titanium trichloride, titanium potassium fluoride, titanium potassium oxalate, titanium sulfate, titanium tetra iodide, and/or its hydrate. In a preferred embodiment, the titanium salt is TiCl.sub.4. The alkaline earth metal base may include alkaline earth metal carbonate and/or an alkaline earth metal hydroxide. The alkaline earth metals are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Suitable examples of the alkaline earth metal base include sodium hydroxide, calcium hydroxide, sodium carbonate, calcium oxide, potassium hydroxide, potassium carbonate, potassium bicarbonate, sodium bicarbonate, etc. In some embodiments, the alkaline earth metal base is sodium hydroxide. The molar concentration of the alkaline earth hydroxide is in a range of 1 to 5 M, preferably 2 to 4 M, more preferably about 2.5 M. The first mixture may be further subjected to an ultrasonication for a time range of 45 to 75 minutes, preferably 60 minutes. Other ranges are also possible. As used herein, the term sonication refers to the process in which sound waves are used to agitate particles in a solution. In some embodiments, other modes of agitation known to those of ordinary skill in the art, for example, via stirring, swirling, mixing, or a combination thereof may be employed to form the resultant mixture. During sonication, a reaction occurs between the titanium salt and the alkaline earth metal hydroxide to yield a precipitate.

[0107] At step 54, the method 50 includes removing the precipitate from the first mixture, drying, and calcining at a temperature of at least 600 degrees centigrade (C) to form a TiO.sub.2 nanocomposite. The precipitates were rinsed using DIW to eliminate impurities, and salts such as, the residual chloride ions (Cl.sup.). Further, the precipitate was dried at a temperature range of 60-100 C., preferably 75-90 C., more preferably to about 80 C., for 12-36 hours, preferably 20-30 hours, more preferably 24 hours. Other ranges are also possible. The drying may be carried out in an oven. After drying, calcination was carried out by heating the precipitate to a high temperature, under a restricted supply of ambient oxygen. This is performed to remove impurities or volatile substances and to incur thermal decomposition. In some embodiments, the calcination is carried out in a furnace preferably equipped with a temperature control system, which may provide a heating rate of up to 50 C./min, preferably up to 40 C./min, preferably up to 30 C./min, preferably up to 20 C./min, preferably up to 10 C./min, preferably up to 5 C./min. In preferred embodiments, the first mixture is heated with a heating rate in the range of 4 to 8 C./min, preferably 4.5 to 7.5 C./min, preferably 5 C./min to a temperature range of 600 to 800 C., preferably 620 to 780 C., preferably 700 C. for 3 to 5 hours, more preferably 3 to 4.5 hours, and yet more preferably 3 hours, to form the TiO.sub.2 composite. Other ranges are also possible.

[0108] At step 56, the method 50 includes mixing the TiO.sub.2 nanocomposite and a borohydride-reducing agent to form a second mixture. The weight ratio of the TiO.sub.2 nanocomposite to the borohydride-reducing agent is in a range of 1:5 to 5:1, preferably 1:3 to 3:1, more preferably 1:2 to 2:1, and yet more preferably 1:2. Suitable examples of borohydride reducing agents include sodium borohydride, calcium borohydride, lithium borohydride, cyanoborohydride, or a combination thereof. In a preferred embodiment, the borohydride reducing agent is sodium borohydride. The Ti.sup.4+ in the TiO.sub.2 nanocomposite is reduced to Ti.sup.3+ in the presence of NaBH.sub.4. Optionally, peroxides, such as hydrogen peroxide may be used instead of borohydride reducing agent to reduce Ti.sup.4+ in the TiO.sub.2 nanocomposite.

[0109] At step 58, the method 50 includes calcining the second mixture at a temperature of at least 600 C. to form a defective nanocomposite of formula TiO.sub.2-x where 0<x<2. In some embodiments, the calcination is carried out in a furnace preferably equipped with a temperature control system, which may provide a heating rate of up to 50 C./min, preferably up to 40 C./min, preferably up to 30 C./min, preferably up to 20 C./min, preferably up to 10 C./min, preferably up to 5 C./min. In preferred embodiments, the second mixture is heated with a heating rate in the range of 4 to 8 C./min, preferably 4.5 to 7.5 C./min, preferably 5 C./min to a temperature range of 600 to 800 C., preferably 620 to 780 C., preferably 700 C. for 3 to 5 hours, more preferably 3 to 4.5 hours, and yet more preferably 3 hours, followed by natural cooling down to the room temperature to form the defective nanocomposite. Other ranges are also possible. The defective nanocomposite is referred to as D-TiO.sub.2-x NSs.

[0110] At step 60, the method 50 includes mixing and sonicating the defective nanocomposite, a cobalt salt, and a solvent to form a suspension. The cobalt salt includes cobalt sulfate, cobalt acetate, cobalt citrate, cobalt iodide, cobalt chloride, cobalt perchlorate, cobalt nitrate, cobalt phosphate, cobalt triflate, cobalt bis(trifluoromethanesulfonyl)imide, cobalt tetrafluoroborate, cobalt bromide, and/or its hydrate. In the preferred embodiment, the cobalt salt is (Co(NO.sub.3).sub.2). The solvent is at least one selected from the group consisting of a ketone solvent, an ester solvent, an alcohol solvent, an amide solvent, and an ether solvent. Suitable examples of the alcohol solvent include, tert-amyl alcohol, benzyl alcohol, 1,4-butanediol, 1,2,4-butanetriol, butanol, diethylene glycol, ethanol, ethylene glycol, 2-ethylhexanol, furfuryl alcohol, glycerol, isobutanol, isopropyl alcohol, methanol, pentyl alcohol, propanol, or a combination thereof. Suitable examples of the ester solvents are ethyl acetate, benzyl benzoate, butyl acetate, diethyl carbonate, dimethyl adipate, ethyl acetoacetate, ethyl butyrate, ethyl lactate, ethylene carbonate, hexyl acetate, isobutyl acetate, isopropyl acetate, methyl acetate, propyl acetate, propylene carbonate, triacetin, or a combination thereof. Suitable examples of ketone solvent include acetone, cyclohexanone, diacetone, methyl ethyl ketone and methyl isobutyl ketone. Suitable examples of amide solvents include 1,3-dimethyl-2-imidazolidinone, dimethylacetamide, dimethylformamide, etc. Suitable examples of ether solvents include diethyl ether, dimethyl ether, dipropyl ether etc. In a preferred embodiment, the solvent is an alcohol solvent; the alcohol solvent includes ethylene glycol. The sonication can be performed ultrasonically for a time range of 45 to 75 minutes, more preferably 60 minutes. In some embodiments, other modes of agitation known to those of ordinary skill in the art, for example, via stirring, swirling, mixing, or a combination thereof may be employed to form the resultant mixture. The sonication process enables the cobalt ion adsorption and transmission into the defective nanocomposite.

[0111] At step 62, the method 50 includes generating a pulsed laser using a laser device and projecting the pulsed laser onto the suspension to form an ablated nanocomposite in the suspension. In a preferred embodiment, the pulsed laser has a wavelength of 500 to 560 nm, preferably 510-550 nm, more preferably 20-540 nm, more preferably to about 532 nm; and a pulse energy of 300 to 400 millijoules (mJ) for about 15 to 25 minutes, more preferably 18 to 22 minutes, and yet more preferably 20 minutes; pulse duration was in a range of 5-10 ns, preferably 6-9 ns, and more preferably to about 8 ns; the pulse width was in a range of 8-10 ns, preferably 9 ns, at a frequency of 8-15 Hz, preferably 10 Hz to form the ablated nanocomposite. Other ranges are also possible.

[0112] At step 64, the method 50 includes removing the ablated nanocomposite from the second suspension, washing, and drying to form a nanostructured material precursor. In the preferred embodiment, the obtained product was centrifuged and washed repeatedly using EA followed by drying at a temperature range of 60-80 C., preferably 70 C. The drying may be carried out in an oven. Other ranges are also possible.

[0113] At step 66, the method 50 includes calcining the nanostructured material precursor at a temperature of at least 600 C. to form the nanostructured material. In the preferred embodiment, the nanostructured material precursor is calcined by heating it to a high temperature, under a restricted supply of ambient oxygen. This is performed to remove impurities or volatile substances and to incur thermal decomposition. In some embodiments, the calcination is carried out in a furnace preferably equipped with a temperature control system, which may provide a heating rate of up to 50 C./min, preferably up to 40 C./min, preferably up to 30 C./min, preferably up to 20 C./min, preferably up to 10 C./min, preferably up to 5 C./min. In preferred embodiments, the first mixture is heated with a heating rate in the range of 4 to 8 C./min, preferably 4.5 to 7.5 C./min, preferably 5 C./min to a temperature range of 600 to 800 C., preferably 620 to 780 C., preferably 700 C. for 3 to 5 hours, more preferably 3 to 4.5 hours, and yet more preferably 3 hours, to form the nanostructured material (DPNSs). Other ranges are also possible.

[0114] Referring to FIG. 2, a method for the layering of the nanostructured material (NSM) at least partially covering a surface of the glass substrate is illustrated. The order in which the method 150 is described is not intended to be construed as a limitation, and any number of the described method steps may be combined in any order to implement the method 150. Additionally, individual steps may be removed or skipped from the method 150 without departing from the spirit and scope of the present disclosure.

[0115] At step 152, the method 150 includes coating the transparent substrate by mixing the NSM, a sulfonated polymer and a solvent mixture to form a third mixture. The sulfonated polymer includes at least one of nafion, sulfonated poly(ether ether ketone)(SPEEK), sulfonated polyimide, sulfonated poly(phenylene oxide) (PPO), sulfonated poly(arylene ether sulfone), and sulfonated poly(4-phenoxybenzoyl-1,4-phenylene). The solvent mixture includes an alcohol solvent and an ester solvent. Suitable examples of the alcohol solvent include, tert-amyl alcohol, benzyl alcohol, 1,4-butanediol, 1,2,4-butanetriol, butanol, diethylene glycol, ethanol, ethylene glycol, 2-ethylhexanol, furfuryl alcohol, glycerol, isobutanol, isopropyl alcohol, methanol, pentyl alcohol, propanol, or a combination thereof. Suitable examples of the ester solvents are ethyl acetate, benzyl benzoate, butyl acetate, diethyl carbonate, dimethyl adipate, ethyl acetoacetate, ethyl butyrate, ethyl lactate, ethylene carbonate, hexyl acetate, isobutyl acetate, isopropyl acetate, methyl acetate, propyl acetate, propylene carbonate, triacetin, or a combination thereof. A volume ratio of the alcohol solvent and the ester solvent is in a range of 1:50 to 1:10, preferably 1:40 to 1:20, or even more preferably about 1:30. Other ranges are also possible.

[0116] At step 154, the method 150 includes sonicating the third mixture to form a coating composition. The mixture was subjected to ultrasonication for at least 1 hour, preferably at least 3 hours, or even more preferably at least 6 hours to enable cobalt ion adsorption and transmission into the surfaces of the TiO.sub.2-x. The ultrasonication may be carried out in a sonication bath or a probe.

[0117] At step 156, the method 150 includes drop casting the coating composition onto a surface of the transparent substrate and drying to form the electrode having the layer of the nanostructured material at least partially covered on the surface of the transparent substrate. In a preferred embodiment, at least 70%, preferably 80%, more preferably 90%, and yet more preferably 95% of the outer surface area of the glass substrate is covered with a layer of the coating composition.

[0118] During the drop casting method, the solvent may be evaporated by drying/heating the transparent substrate at a temperature range of 30-150 C., preferably 50-120 C. The drying may be performed in a vacuum, microwave, etc. Various parameters such as concentration of the NSM in the third mixture, deposition time, temperature, can be varied to obtain the electrode with desired properties. Such variations are obvious to a person skilled in the art.

[0119] The electrode of the present disclosure has an overpotential of 0.2 to 0.5 volts (V) in an acidic medium at a current density of 5 to 20 milliamperes per square centimeter (mA/cm.sup.2). The electrode has a double-layer capacitance of 200 to 280 microfarads per square centimeter (F/cm.sup.2) in an acidic medium at an overpotential of 0.352 volts reversible hydrogen electrode (V.sub.RHE). The electrode has an active surface area of 4 to 10 square centimeters (cm.sup.2) in an acidic medium at an overpotential of 0.352 V.sub.RHE. The Tafel slope shows how efficiently an electrode can produce current in response to a change in applied potential. Therefore, a low Tafel slope suggests that less overpotential is required to get a high current. The electrode has a Tafel slope of 80 to 110 millivolts per decade (mV/decade) in an acidic medium at a scan rate of 5 to 20 millivolts per second (mV/s).

[0120] The defective perovskite nanostructures (DPNSs) of D-cobalt titanate (CoTiO.sub.3-x) prepared from cobalt nitrate and black-titanium oxide (TiO.sub.2-x) (D-TiO.sub.2-x) by advanced pulse laser ablation in liquid (PLAL) method were characterized, and its hydroelectric (HE) activity was evaluated to determine their electrocatalytic potential and efficiency improvement. The DPNSs-based working electrode shows improved electrochemical performance due to its low over-potential (0.352 volts (V)), reduced Tafel slope (94.7 millivolts per decade (mV/dec)), high double layer capacitance (235.3 microfarads per square centimeter (F/cm.sup.2)), large electrochemically active surface area (6.72 square centimeters (cm.sup.2)) and exceptional long-term stability.

[0121] The improvement in the HE efficiency was ascribed to the metal-support interaction of DPNSs that yielded high conductivity, high exposure of abundant active sites, wide active surface area, improved kinetics, and fast charge transport. Furthermore, Volmer-Heyrovsky (V-H) reaction mechanism was responsible for hydrogen (H.sub.2) generation by the proposed DPNSs-based electrode. The systematic approach for fabricating DPNSs-based electrodes to produce H.sub.2 from water splitting may be helpful for green energy generation, solving future environmental problems and energy crises.

[0122] The performance of the electrode described in this disclosure was evaluated for its ability to facilitate water-splitting reactions. In some embodiments, the electrode may also be used in the field of batteries, fuel cells, photochemical cells, water splitting cells, electronics, water purification, hydrogen sensors, semiconductors (such as field-effect transistors), magnetic semiconductors, capacitors, data storage devices, biosensors (such as redox protein sensors), photovoltaics, liquid crystal screens, plasma screens, touch screens, OLEDs, antistatic deposits, optical coatings, reflective coverings, anti-reflection coatings, and/or reaction catalysis.

[0123] According to the present disclosure, a method for electrochemical water splitting, is described. The electrochemical water splitting may be performed in a Teflon-made 3-electrode electrochemical cell equipped with a Potentiostat (AutoLab PGSTAT302N) for evaluating the performance of the electrode. In some embodiments, the cell may also include an Ag/AgCl (KCl solution of 3.0 M) reference electrode, a Pt counter electrode, and a working electrode. In some embodiments, the working electrode may be a glassy carbon (GC), and a DPNSs coated glassy carbon prepared according to the method 150. In some further embodiment, the DPNSs material may be dispersed in an electrolyte as a catalyst for water splitting. In some preferred embodiments, a linear sweep voltammetry test may be performed at a scan rate of 10 mV/s. In some further preferred embodiments, the electrochemical impedance spectroscopy (EIS) measurement may be performed at AC voltage of 10 mV and frequency in the range of 0.1 to 105 Hz.

[0124] In some more preferred embodiments, the method includes contacting a working electrode (electrode of the present disclosure) and a counter electrode with the water, and further applying a potential of 0.001 to 1.0 V to the working electrode and a counter electrode immersed in the aqueous electrolyte solution. The electrode forms the working electrode, while the counter electrode forms the auxiliary electrode. The outer surface of the counter electrode includes an inert, electrically conducting chemical substance, such as platinum, gold, or carbon. The carbon may be in the form of graphite or glassy carbon. In one embodiment, the counter electrode may be a wire, a rod, a cylinder, a tube, a scroll, a sheet, a piece of foil, a woven mesh, a perforated sheet, or a brush. The counter electrode material should thus be sufficiently inert to withstand the chemical conditions in the electrolyte solution, such as acidic or basic pH values, without substantially degrading during the electrochemical reaction. The counter electrode preferably should not leach out any chemical substance that interferes with the electrochemical reaction or might lead to undesirable contamination of either electrode. The aqueous electrolyte solution includes an aqueous solution of an acid (acid and an aqueous solution). The electrolyte includes an aqueous solution of an acid having a concentration of 0.001 to 3 M, preferably 0.01 to 2.5 M, preferably 0.1 to 2 M, preferably 0.2 to 1.5 M, preferably 0.4 to 1 M, and yet more preferably about 0.5 M. The acid includes at least one acid selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, boric acid, and citric acid. In a preferred embodiment, the electrolyte is sulfuric acid.

[0125] In some embodiments, the working electrode and the counter-electrode are connected to each other by way of electrical interconnects that allow for the passage of current between the electrodes, when a potential is applied between them. In a preferred embodiment, the electrocatalyst (which forms the working electrode) and the counter electrode are at least partially submerged in the water and are not in physical contact with each other. In an embodiment, the working electrode and the counter-electrode can have the same or different dimensions. In certain embodiments, the working electrode has a cross-section diameter of 1.68 mm, and the counter-electrode as a cross-section diameter of 0.2 mm. The working electrode and the counter-electrode may be arranged as obvious to a person of ordinary skill in the art.

[0126] The electrode of the present disclosure preferably has a current density of 10 to 100 mA/cm.sup.2, more preferably 30 to 80 mA/cm.sup.2, and yet more preferably 50 to 60 mA/cm.sup.2 in an acidic medium at a scan rate of 5 to 20 millivolts per second (mV/s), more preferably 10 to 18 mV/s, and yet more preferably 12 to 16 mV/s. Other ranges are also possible. As used herein, the term current density refers to the amount of current traveling per unit cross-section area. The electrode further has an overpotential of 0.2 to 0.5 V, more preferably 0.3 to 0.4, and yet more preferably about 0.35 V in an acidic medium at a scan rate of 5 to 20 mV/s, more preferably 10 to 18 mV/s, and yet more preferably 12 to 16 mV/s. Other ranges are also possible. As used herein, the term overpotential is referred to as the difference between the equilibrium potential for a given reaction (also called the thermodynamic potential) and the potential at which a catalyst operates at a specific current under specific conditions. The electrode further has a Tafel slope of 80 to 110 millivolts per decade (mV/decade), more preferably 90 to 100 m V/decade, and yet more preferably about 100 mV/decade in an acidic medium at a scan rate of 5 to 20 mV/s, more preferably 10 to 18 mV/s, and yet more preferably 12 to 16 mV/s. The electrode further has a double layer capacitance of 200 to 280 microfarads per square centimeter (F/cm.sup.2), preferably 220 to 260 F/cm.sup.2, or even more preferably about 240 F/cm.sup.2, in an acidic medium at an overpotential of 0.352 V.sub.RHE. The electrode further has an active surface area of 4 to 10 square centimeters (cm.sup.2), preferably 6 to 8 cm.sup.2, or even more preferably about 7 cm.sup.2, in an acidic medium at an overpotential of 0.352 V.sub.RHE. Other ranges are also possible.

Examples

[0127] The following examples demonstrate the catalytic activity of an electrocatalyst, including nanostructured material layering on an electrode, for electrochemical water splitting, as described herein. The examples are provided solely for illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without departing from the spirit and scope of the present disclosure.

Example 1: Materials Required

[0128] Analytical grade (high purity) chemical reagents, including ethylene glycol (EG), sodium hydroxide (NaOH), titanium tetrachloride (TiCl.sub.4), ethyl alcohol (EA), sulfuric acid (H.sub.2SO.sub.4), and sodium borohydride (NaBH.sub.4) were procured from Sigma Aldrich (USA) and used without any additional treatment. The DPNSs were prepared in de-ionized water (DIW).

Example 2: Preparation of Pure-TiO.SUB.2 .NSs

[0129] In preparing pure-TiO.sub.2 NSs, about 1.0 g of TiCl.sub.4 was first dissolved into 50 milliliters (mL) of DIW and then ultrasonicated for 1 hour. Next, the TiO.sub.2 precipitates were formed by adding NaOH (2.5 M) into the Ti(OH).sub.4 solution. Next, the precipitate was carefully rinsed using DIW to eliminate the residual chloride ions, followed by oven drying at 80 C. for 24 hours. Finally, the dried powder was crushed and calcined at 700 C. for 3 hours to obtain pure-TiO.sub.2 NSs.

Example 3: Synthesis of D-TiO.SUB.2-x .NSs

[0130] To prepare the proposed D-TiO.sub.2-x NSs, about 2.0 g of the pure-TiO.sub.2 NSs and about 4.0 g of NaBH.sub.4 were mixed and aggressively mashed for 30 minutes to homogenize. The mixture was then calcined for 3 hours at 700 C., followed by natural cooling to room temperature to get D-TiO.sub.2-x NSs. In the present process, Ti.sup.3+ species were formed from Ti.sup.4+ due to the reduction of pure-TiO.sub.2 NSs in the presence of NaBH.sub.4, converting TiO.sub.2 of white color into black. These Ti.sup.3+ species produced on the D-TiO.sub.2-x NSs surface or subsurface might have altered the environment of chemical bonds on the TiO.sub.2 surface.

Example 4: Synthesis of Pure-CoTiO.SUB.3 .NSs and D-CoTiO.SUB.3-x .DPNSs

[0131] To prepare the pure-CoTiO.sub.3 NSs and D-CoTiO.sub.3-x DPNSs via the PLAL process, about 0.1 g of D-TiO.sub.2-x NSs and about 1.85 g of cobalt nitrate (Co(NO.sub.3).sub.2) were dissolved in 20 mL of EG and subjected to ultrasonication for 1 hour to enable Cobalt ion adsorption and transmission into the D-TiO.sub.2-x surfaces. After 30 minutes, the resultant suspension was subjected to the PLAL process. The obtained product was centrifuged and washed repeatedly using EA, followed by oven drying at 70 C. Later, the dried specimen was then calcined at 700 C. for 3 hours to get powder of D-CoTiO.sub.3-x DPNSs.

[0132] An identical procedure was used to make the pure-CoTiO.sub.3 NSs catalyst using pure-TiO.sub.2 powder. The PLAL process was carried out using an Nd:YAG second harmonic laser of wavelength 532 nm, pulse energy of 350 millijoules (mJ), pulse duration of 8 nanoseconds (ns), a pulse width of 9 ns, and repetition rate of 10 hertz (Hz) [M. J. S. Mohamed, M. A. Gondal, M. Hassan, A. Z. Khan, A. M. Surrati, M. A. Almessiere, Exceptional co-catalysts free SrTiO3 perovskite coupled CdSe nanohybrid catalyst by green pulsed laser ablation for electrochemical hydrogen evolution reaction, Chemical Engineering Journal Advances. 11 (2022).sub.100344; and M. Hassan, M. A. Gondal, E. Cevik, T. F. Qahtan, A. Bozkurt, M. A. Dastageer, High performance pliable supercapacitor fabricated using activated carbon nanospheres intercalated into boron nitride nanoplates by pulsed laser ablation technique, Arabian Journal of Chemistry. 13 (2020) 6696-6707, each incorporated herein by reference in their entirety]. Initially, the laser was focused for almost 30 minutes on the cobalt nitrate/D-TiO.sub.2-x NSs mixture dispersed in EG medium to produce adequate laser fluence. The interaction between the incident laser pulse and solid target could ablate the material, creating a plasma plume that chemically reacted (photocatalytic reduction) with the solid target material and liquid to produce the colloidal suspension. These plasma plumes grew, ruptured, and produced the desired NSs in the liquid suspension. This process lacked any chemical reagents or catalysts, thereby obviating the need for additional cleaning of the products after synthesis to achieve high-purity D-CoTiO.sub.3-x DPNSs.

Example 5: Characterizations

[0133] The crystalline structures and phases of the obtained specimens were determined using Powder X-ray diffraction (XRD, Bruker D8 Advance diffractometer; manufactured by Bruker, 40 Manning Road Billerica, MA 01821 United States of America) analysis that used Cu-K line of wavelength ()1.5406 angstroms () as a radiation source. The morphologies of the pure-CoTiO.sub.3 NSs and D-CoTiO.sub.3-x DPNSs catalysts were imaged by scanning electron microscopy (SEM, Hitachi S-4800; manufactured by Hitachi, Chiyoda, Nippon Seimei Marunouchi Building, 1-6-6, Marunouchi, Japan Chiyoda, Nippon Seimei Marunouchi Building, 1-6-6, Marunouchi, Japan) and transmission electron microscopy (TEM, JEM-2100, JEOL, 156 Nakagami-cho, Akishima, Tokyo, 196-0022, Japan). The X-ray photoelectron spectra (XPS) of the specimens were recorded by a Kratos-AXIS DLD spectrometer (manufactured by Kratos, 10680 Treena Street, 6th Floor, San Diego, United States of America) that used Al-K radiation of wavelength 1486.6 eV. The C Is line with binding energy (BE) of 284.6 electronvolts (eV) from the adventitious carbon was used as a reference point.

Example 6: Electrochemical Measurements

[0134] The room temperature electrochemical properties of the prepared catalysts were evaluated using the standard 3 electrodes setup controlled by an Auto-Lab potentiostat electrochemical workstation. The working, reference, and counter electrodes were the glassy carbon (GC), Ag/AgCl, and Pt wire, respectively. The Nernst relation was used to convert the values of the measured potential to a reversible hydrogen electrode (RHE) given by:

[00001]$\begin{array}{cc}{E}_{\mathrm{RHE}}=E_{\mathrm{Agp}}+0.059\mathrm{pH}+E_{\mathrm{Ag}/\mathrm{AgCl}}0.197V& \left(1\right)\end{array}$

[0135] The working electrodes were fabricated using the following procedure. First, 1.0 mg of catalysts powders were mixed with 50 L of 5.0 weight percentage (wt. %) Nafion and 950 microliters (L) of EA. Next, the mixture was subjected to sonication for 30 minutes, achieving a homogeneous ink. Then, 40 L of the as-prepared ink was poured over the GC electrode surface with a loading level of 0.19 milligrams per square centimeters (mg/cm.sup.2), followed by drying at 60 C. Polarization curves were recorded by a linear sweep voltammeter (LSV at a scan rate of 10 mV/s), where 0.5 mol/L of sulfuric acid (H.sub.2SO.sub.4) electrolyte solution was used. The complex impedance of the samples in the frequency range of 10 kilohertz (kHz) and 0.01 Hz (at 5 mV) was measured using an electrochemical impedance spectrometer (EIS). Finally, the mechanism and kinetic properties of the chemical reactions of the catalysts were measured at a constant current using chronopotentiometry (CP).

Example 7: Structural Properties

[0136] FIGS. 3A-3B display the XRD profiles of the produced powder samples, indicating their purity and phases. XRD patterns of pure-TiO.sub.2 (302), D-TiO.sub.2-x (304), pure-CoTiO.sub.3 (306), and D-CoTiO.sub.3-x NSMs (308) (FIG. 3A) showed several significant peaks at 25.28, 36.96, 37.80, 38.56, 48.08, 53.96, 55.08, 62.68, 68.76, 70.28, and 75.16 corresponding to the Bragg's diffraction from the crystal planes of (101), (103), (004), (112), (200), (105), (211), (204), (116), (220), and (215) of the anatase TiO.sub.2 that matched with an International Centre for Diffraction Data (ICDD) no. 21-1272 [G. Zhou, T. Zhao, R. Qian, X. Xia, S. Dai, A. Alsaedi, T. Hayat, J. H. Pan, Decorating (001) dominant anatase TiO.sub.2 nanoflakes array with uniform WO3 clusters for enhanced photoelectrochemical water decontamination, Catal Today. 335 (2019).sub.365-371, incorporated herein by reference in its entirety]. In addition, D-TiO.sub.2-x (304) showed its pure-TiO.sub.2 (302) crystal phase even after the treatment with NaBH.sub.4, demonstrating an insignificant influence of NaBH.sub.4 on the crystal phase. Pure-CoTiO.sub.3 (306) showed intense crystalline reflections at 23.92, 32.84, 35.40, 40.48, 49.0, 53.48, 61.88, and 63.58 due to the diffraction from (012), (104), (110), (113), (024), (116), (214), and (300) lattice planes that agreed with the standard of ICDD no. 15-0866 [M. Mousavi, J. B. Ghasemi, Novel visible-light-responsive Black-TiO.sub.2/CoTiO.sub.3 Z-scheme heterojunction photocatalyst with efficient photocatalytic performance for the degradation of different organic dyes and tetracycline, J Taiwan Inst Chem Eng. 121 (2021).sub.168-183, incorporated herein by reference in its entirety]. The D-CoTiO.sub.3-x DPNSs revealed the same unique diffraction peaks as pure-CoTiO.sub.3. The XRD patterns of pure-TiO.sub.2 (352), D-TiO.sub.2-x (354), pure-CoTiO.sub.3 (356), and D-CoTiO.sub.3-x NSs (358) were magnified (FIG. 3B). The sharp XRD peaks at 25.28 and 32.84 shown by the pure-TiO.sub.2 (352) and pure-CoTiO.sub.3 NSs (356) were slightly shifted to a higher diffraction angle corresponding to D-TiO.sub.2-x (354) and D-CoTiO.sub.3-x NSs (358). This shift can be ascribed to the creation of O.sub.2 vacancies, indicating the induction of lattice disorder and defects in D-TiO.sub.2-x NSs [X. Pan, M.-Q. Yang, X. Fu, N. Zhang, Y.-J. Xu, Defective TiO.sub.2 with oxygen vacancies: synthesis, properties and photocatalytic applications, Nanoscale. 5 (2013) 3601-3614, incorporated herein by reference in its entirety]. In addition, the complete absence of other impurity peaks confirmed the high quality of the pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs.

Example 8: Morphological Properties

[0137] FIG. 4 displays the SEM images of the corresponding pure-TiO.sub.2 (FIG. 4A), D-TiO.sub.2-x (FIG. 4B), pure-CoTiO.sub.3 (FIG. 4C), and D-CoTiO.sub.3-x NMSs (FIG. 4D), indicating the well-defined morphologies and microstructures with strong crystallinity and overlaps, supporting the XRD results. Essentially, the viscous gel-like particle formation observed throughout the synthesis process might be responsible for the nucleation of nanocrystals on the material surface.

[0138] FIG. 5 shows the TEM images of corresponding pure-TiO.sub.2 (FIG. 5A), D-TiO.sub.2-x (FIG. 5B), pure-CoTiO.sub.3 (FIG. 5C), and D-CoTiO.sub.3-x NMSs (FIG. 5D) where all samples showed nanoplates-like morphology in size range of 20-80 nm. FIG. 6 illustrates the HRTEM images of the pure-TiO.sub.2 (FIG. 6A), D-TiO.sub.2-x (FIG. 6B), pure-CoTiO.sub.3 (FIG. 6C), and D-CoTiO.sub.3-x NMSs (FIG. 6D), respectively. The (101) lattice plane of pure-TiO.sub.2 and D-TiO.sub.2-x NSs clearly exhibited a lattice spacing of 0.352 nm. Furthermore, the (104) lattice plane of pure-CoTiO.sub.3 and D-CoTiO.sub.3-x DPNSs displayed a lattice spacing of 0.273 nm.

[0139] FIGS. 7A-7R shows the EDX spectra of the pure-TiO.sub.2 (FIG. 7A), D-TiO.sub.2-x (FIG. 7E), pure-CoTiO.sub.3 (FIG. 7I), and D-CoTiO.sub.3-x NMSs (FIG. 7N), respectively, detecting their right chemical elemental compositions. The well-defined peaks in the EDX spectra indicated the presence of elements like Ti, O, and Co in the proposed NSs, confirming their high purity. FIG. 7B shows an elemental mapping of pure-TiO.sub.2. FIG. 7C shows an elemental mapping of Ti in pure-TiO.sub.2 distributed equally and uniformly throughout the surfaces. FIG. 7D shows an elemental mapping of oxygen (O) in pure-TiO.sub.2 distributed equally and uniformly throughout the surfaces. FIG. 7F shows an elemental mapping of D-TiO.sub.2-x. FIG. 7G shows an elemental mapping of Ti in D-TiO.sub.2-x distributed equally and uniformly throughout the surfaces. FIG. 7H shows an elemental mapping of O in D-TiO.sub.2-x distributed equally and uniformly throughout the surfaces. FIG. 7J shows an elemental mapping of pure-CoTiO.sub.3. FIG. 7K shows an elemental mapping of Co in pure-CoTiO.sub.3 distributed equally and uniformly throughout the surfaces. FIG. 7L shows an elemental mapping of Ti in pure-CoTiO.sub.3 distributed equally and uniformly throughout the surfaces. FIG. 7M shows an elemental mapping of O in pure-CoTiO.sub.3 distributed equally and uniformly throughout the surfaces. FIG. 7O shows an elemental mapping of D-CoTiO.sub.3-x NSMs. FIG. 7P shows an elemental mapping of Co in D-CoTiO.sub.3-x distributed equally and uniformly throughout the surfaces. FIG. 7Q shows an elemental mapping of Ti in D-CoTiO.sub.3-x distributed equally and uniformly throughout the surfaces. FIG. 7R shows an elemental mapping of O in D-CoTiO.sub.3-x distributed equally and uniformly throughout the surfaces. The Au signals arise due to the Au grid used in sample preparation. Furthermore, the EDX elemental mapping shows that all elements are distributed equally and uniformly throughout the surfaces. Because of the superior elemental distribution, the separation of electrons and holes might be increased, leading to an increase in catalytic activity. The defective D-CoTiO.sub.3-x NSPMs structure is attractive for electrocatalysis due to its high efficiency.

Example 9: XPS Analyses

[0140] FIGS. 8A-8D show the XPS spectra of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs, providing their surface valence state distributions and catalytic surface compositions. FIG. 8A shows the surveys of XPS spectra of all prepared NSs revealed the presence of Co, Ti, and O elements, pure-TiO.sub.2 (802), D-TiO.sub.2-x (804), pure-CoTiO.sub.3 (806), and D-CoTiO.sub.3-x NSMs (808). FIG. 8B shows the results of the high-resolution XPS profiles of pure-TiO.sub.2 (822), D-TiO.sub.2-x (824), pure-CoTiO.sub.3 (826), and D-CoTiO.sub.3-x NSMs (828), Co 2p, Ti 2p, and O 1 s displaying that Co 2p was composed of different peaks at 779.19 eV and 794.09 eV corresponding to Co 2p.sub.3/2 and Co 2p.sub.1/2 which indicated the existence of the oxidation states like Co.sup.2+ and Co.sup.3+ [M. A. Gabal, S. A. Hameed, A. Y. Obaid, CoTiO.sub.3 via cobalt oxalate-TiO.sub.2 precursor. Synthesis and characterization, Mater Charact. 71 (2012).sub.87-94, incorporated herein by reference in its entirety]. FIG. 8C shows two peaks of pure-CoTiO.sub.3 (852) and D-CoTiO.sub.3-x (854), the Ti 2p spectrum with two peaks at 458.49 eV and 464.59 eV due to the presence of Ti 2p.sub.3/2 and Ti 2p.sub.1/2, respectively thereby indicating the presence of the Ti.sup.3+ and Ti.sup.4+ oxidation states of (the deconvoluted spectrum of Ti 2p is presented in FIGS. 9A-9B) [Q. Wu, F. Huang, M. Zhao, J. Xu, J. Zhou, Y. Wang, Ultra-small yellow defective TiO.sub.2 nanoparticles for co-catalyst free photocatalytic hydrogen production, Nano Energy. 24 (2016).sub.63-71, incorporated herein by reference in its entirety]. FIG. 8D shows the cores level O 1 s spectra displayed a peak at the lower BE of 531.67 eV compared to the distinct O 1 s peak at 529.37 eV related to O.sub.2 lattice defects, pure-TiO.sub.2 (872), D-TiO.sub.2-x (874), pure-CoTiO.sub.3 (876), and D-CoTiO.sub.3-x NSMs (878). The observed additional peak at 531.67 eV can be ascribed to the existence of the OH group in the sample [G. Ketteler, S. Yamamoto, H. Bluhm, K. Andersson, D. E. Starr, D. F. Ogletree, H. Ogasawara, A. Nilsson, M. Salmeron, The Nature of Water Nucleation Sites on TiO.sub.2 (110) Surfaces Revealed by Ambient Pressure X-ray Photoelectron Spectroscopy, The Journal of Physical Chemistry C. 111 (2007).sub.8278-8282, incorporated herein by reference in its entirety]. There has been a noticeable increase in the number of species adsorbed on the surface, especially the OH group in the D-CoTiO.sub.3-x DPNSs, indicating the promotion of charges separation and their migration tendency towards the sample surface rather than the inter-phase, thus encouraging the molecular adsorptions and redox reaction.

[0141] Compared to pure-CoTiO.sub.3, the BE of Co 2p, Ti 2p, and O 1 s in D-CoTiO.sub.3-x NSs were changed considerably to the low energy level, while pure-TiO.sub.2 has a higher BE of Ti 2p and O 1 s than D-TiO.sub.2-x NSMs, possibly due to the Ti.sup.3+ species. FIGS. 9A-9B illustrates the deconvoluted Ti 2p spectra showed one peak of Ti.sup.3+ positioned at 460.12 eV and two peaks of Ti.sup.4+ at 458.49 eV and 464.59 eV of D-TiO.sub.2-x (FIG. 9A), and D-CoTiO.sub.3-x NSMs (FIG. 9B). Furthermore, the BE difference between Ti2p.sub.1/2 and Ti2p.sub.3/2 was very high (6.1 eV) compared to the pure Ti.sup.4+ state (5.8 eV). The observed shift of Ti2p.sub.1/2 and Ti2p.sub.3/2 peaks indicated a reduction of Ti electronic states from Ti.sup.4+ to Ti.sup.3+. The difference in the synthesis of CoTiO.sub.3 between D-TiO.sub.2-x and pure-TiO.sub.2 was reflected in the change in their binding energies. Including NaBH.sub.4 in the preparation process enabled the conversion of pure-TiO.sub.2 to D-TiO.sub.2-x NSs, mainly responsible for the variation in the experimental results. Because the surface layer was exposed to the NaBH.sub.4 treatment, TiO.sub.2 may be partially reduced, resulting in Ti.sup.3+ species rather than Ti.sup.4+ species in bulk. Consequently, the Ti.sup.3+ on the surface has been demonstrated to oxidize in the air, making it consume Ti.sup.3+ rapidly in the defective D-TiO.sub.2-x NSMs [Y. v Larichev, O. v Netskina, O. v Komova, V. I. Simagina, Comparative XPS study of Rh/Al.sub.2O.sub.3 and Rh/TiO.sub.2 as catalysts for NaBH.sub.4 hydrolysis, Int J Hydrogen Energy. 35 (2010).sub.6501-6507, incorporated herein by reference in its entirety]. Therefore, the unique structural properties of D-CoTiO.sub.3-x DPNSs in the presence of surface elements like Co, Ti, and O helped enhance HEP activity.

Example 10: Hydrogen Evolution Performance

[0142] FIG. 10A shows the linear sweep voltammetry (LSV) curves of bare GC (1010), pure-TiO.sub.2 (1008), D-TiO.sub.2-x (1006), pure-CoTiO.sub.3 (1004), and D-CoTiO.sub.3-x NMSs (1002). The HEP over-potential of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NMSs measured at .sub.10=10 mA/cm.sup.2 corresponded to 0.572, 0.503, 0.450, and 0.352 V. For this measurement; a three-electrode assembly device was used with water electrolysis HEP activity of 0.5 M of H.sub.2SO.sub.4 electrolyte. FIG. 10B compares the HEP electrocatalytic performance of pure-TiO.sub.2 (1022), D-TiO.sub.2-x (1024), pure-CoTiO.sub.3 (1026), and D-CoTiO.sub.3-x NMSs (1028) in terms of various parameters. The electrode made of D-CoTiO.sub.3-x DPNSs showed slightly lower onset potential (0.281 V) and superior catalytic activity at 0.5 mA/cm.sup.2 compared to pure-TiO.sub.2 (0.351 V), D-TiO.sub.2-x (0.342 V), and pure-CoTiO.sub.3 (0.294 V) NSs. Evidently, D-CoTiO.sub.3-x DPNSs exhibited substantial catalytic activity for HEP since an overpotential of 0.6 V was needed to reach the current density (J) of 62.09 mA/cm.sup.2. Because of their high catalytic activity, D-CoTiO.sub.3-x NSPMs catalysts might be used in realistic commercial water-splitting HEP under dark conditions.

[0143] FIG. 10C illustrates the cyclic voltammetry (CV) curves of the prepared D-CoTiO.sub.3-x at various scan speeds like 10 mV (1052), 20 mV (1054), 40 mV (1056), 60 mV (1058), 80 mV (1060), 100 mV (1062) and 120 mV (1064). The obtained results clearly indicated the significant effects of the samples' electrochemically active surface area (ECSA) on the HEP activity of the catalysts.

[0144] The slope of the linear fit was used to get the double-layer capacitance (DLC) values by plotting the value of J=Ja-Jc as a function of scan speed (mV/s). FIG. 10D shows the plot based on the DLC values, the calculated values of ECSA for pure-TiO.sub.2 (1072), D-TiO.sub.2-x (1074), pure-CoTiO.sub.3 (1076), and D-CoTiO.sub.3-x NSMs (1078) catalysts were found to be 1.56, 2.67, 3.50, and 6.72 cm.sup.2, respectively. Within the same potential range, D-CoTiO.sub.3-x NSPMs electrocatalysts showed a substantially higher DLC of 235.3 F/cm.sup.2 than pure CoTiO.sub.3 (122.4 F/cm.sup.2) NSs. This affirmed that a larger electrochemical surface area of D-TiO.sub.2-x NSs enabled the significant improvement of HEP in D-CoTiO.sub.3-x DPNSs.

[0145] FIG. 11C displays the EIS results for pure-TiO.sub.2 (1152), D-TiO.sub.2-x (1154), pure-CoTiO.sub.3 (1156), and D-CoTiO.sub.3-x NSMs (1158) catalysts. The EIS spectra were recorded to determine the behavior of charge transfers in the studied NSs. The semicircles in the Nyquist plot represent the resistance of the charge transfers for the proposed catalysts. Generally, a sample with a larger semicircle radius on the plot is more resistant to charge carrier transfer [M. Arshad, H. Du, M. S. Javed, A. Maqsood, I. Ashraf, S. Hussain, W. Ma, H. Ran, Fabrication, structure, and frequency-dependent electrical and dielectric properties of Sr-doped BaTiO.sub.3 ceramics, Ceram Int. 46 (2020) 2238-2246, incorporated herein by reference in its entirety]. It can be seen that the radius of the D-CoTiO.sub.3-x DPNSs semicircle is much smaller than that of pure-TiO.sub.2, D-TiO.sub.2-x, and pure-CoTiO.sub.3 NSMs, confirming an excellent charge transfer capacity of the NSs during the electrochemical HEP.

[0146] Tafel plots were also generated wherein an acidic solution was used to evaluate the catalytic mechanism of D-CoTiO.sub.3-x DPNSs against HEP. According to the HEP mechanism, which consists of numerous step reactions that can be summarized as follows, the Volmer reaction is the first step in the HEP. In this primary discharge step, the initial electron (e.sup.) transfer has occurred. After that, the proton (H.sup.+) receives one e.sup. and thus adsorbs hydrogen on the surface (H*) of electrocatalysts, which is followed by the desorption step, the Heyrovsky reaction happens, in which the H* atom requires a H.sup.+ from the electrolyte to produce H.sub.2 gas, and the recombination step (Tafel reaction), in which two H* atoms combine to produce H.sub.2 gas [A. Lasia, Mechanism and kinetics of the hydrogen evolution reaction, Int J Hydrogen Energy. 44 (2019).sub.19484-19518, incorporated herein by reference in its entirety].

The Volmer-Heyrovsky (V-H) mechanism can be described by:

##STR00002##

The Volmer-Tafel (V-T) mechanism is composed of the following:

##STR00003##

[0147] FIG. 11A illustrates the Tafel plots of the prepared pure-TiO.sub.2 (1108), D-TiO.sub.2-x (1106), pure-CoTiO.sub.3 (1104), and D-CoTiO.sub.3-x NSMs (1102). The rate-limiting (R-L) steps of the electrocatalyst, being an inherent property, could cause the Tafel slopes. Due to the slower progress of the Volmer reaction, the Tafel slope was 120 mV/Dec, suggesting the occurrence of the discharge process is the R-L step. When the Heyrovsky reaction became the R-L step, the Tafel slope was 40 mV/dec. Also, the Tafel slope was 30 mV/Dec when the response limited the progression of HEP. Thus, the linear parts of the Tafel curves were fitted to the relation =b log(J)+a (where , J, b, and a are the overpotential, current density, Tafel slope, and a constant, respectively) to determine the catalysts' reaction mechanism [M. J. S. Mohamed, High bifunctional electrocatalytic activity of FeWO.sub.4/Fe.sub.3O.sub.4@NrGO nanocomposites towards electrolyser and fuel cell technologies, Journal of Electroanalytical Chemistry. 897 (2021).sub.115587, incorporated herein by reference in its entirety]. The values of the Tafel slopes for pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs catalysts were discerned to be 168, 130, 115, and 97 m V/dec, respectively. The smaller value of the Tafel slope for D-CoTiO.sub.3-x DPNSs compared to other HEP catalysts indicates the predominance of V-H reaction throughout the evolution of hydrogen and dominance of Heyrovsky reaction in the desorption process during the R-L step. FIG. 11B shows the V-H reaction mechanism of HEP for D-CoTiO.sub.3-x DPNSs, which is obtained based on the observations. In the proposed mechanism, the HEP V-H reaction was caused by the charge carriers' transfer, allowing the adsorption of water molecules on the surface of catalysts and the formation of H* ions, which eventually combined with electrons to produce H.sub.2.

[0148] Stability being an important evaluating factor for electrocatalysts, continuous CV and CP measurements were performed to establish stability. The CP was measured for 30 hours at 10 mA/cm.sup.2. FIG. 11D shows that the potential fluctuated slightly, which may be due to the bubbles' absorption and release during the HEP, demonstrating excellent stability in an acidic solution of the catalyst made of D-CoTiO.sub.3-x DPNSs. Furthermore, the consistent CV readings performed before and after 1000 cycles help to establish stability even further. Inset of FIG. 11D depicts the polarization plots of the specimens after 1000 cycles, essentially identical to the initial cycle. In short, the high catalytic activity and stability of the D-CoTiO.sub.3-x DPNSs catalyst indicated its potential for practical applications.

[0149] FIGS. 12A-12E show the structures and morphology of D-CoTiO.sub.3-x DPNSs catalyst were re-evaluated after the stability tests. Elemental mapping of the D-CoTiO.sub.3-x DPNSs catalyst shows the presence of Co (FIG. 12F), Ti (FIG. 12G), and oxygen (FIG. 12H), with no significant change in the morphology, structure, and composition was observed, indicating excellent stability of the proposed product. Based on the results, it can be asserted that D-CoTiO.sub.3-x DPNSs catalysts can be a promising material for H.sub.2 fuel cells in the future. In addition, the microscopic size, very uniform distribution, and defective nature of D-CoTiO.sub.2-x DPNSs enabled an efficient charge transfer in the electrolytes, thus increasing the number of catalytic edge sites and improving the HEP performance.

[0150] A new type of nanostructured materials consisting of pure-TiO.sub.2, D-TiO.sub.2-x, pure-CoTiO.sub.3, and D-CoTiO.sub.3-x NSMs were synthesized using the unified sonication and PLAL technique. The prepared samples were characterized using several analytical tools to determine their structures, morphologies, and electrochemical performances. The D-CoTiO.sub.3x DPNSs catalyst showed a higher electrocatalytic efficiency, low over-potential (0.352 V) at 10 mA/cm.sup.2, smaller Tafel slope (94.7 mV/Dec), higher DLC (235.3 F/cm.sup.2), higher ECSA (6.72 cm.sup.2) and long-term stability in HEP than other catalysts. The V-H reaction mechanism was dominant in the R-L stage, which produces H.sub.2. The improved electrochemical efficiency of HEP activity was ascribed to the induced synergetic SMSI effect of the D-CoTiO.sub.3-x DPNSs in offering good conductivity and surface activity. The simultaneous loading of defective D-TiO.sub.2-x NSs with an abundance of many active sites, a large active surface area, improved kinetics, and rapid charge transfer were responsible for the observed enhanced HEP performance. It is established that the proposed D-CoTiO.sub.3-x DPNSs can be an effective catalyst for the HEP from water electrolysis. The defective D-TiO.sub.2-x based NSs are useful for environmental remediation and sustainable energy applications 5 in H.sub.2 fuel economy.

[0151] Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.