Process for the production of hydrogen

Abstract

The present disclosure relates to processes for the production of hydrogen gas involving a metal in contact with a liquid. The present disclosure also relates to use of the metal for production of hydrogen as described herein, and hydrogen produced by the process described herein.

Description

“PROCESS FOR THE PRODUCTION OF HYDROGEN” RELATED APPLICATION

[0001] The present application claims priority from Australian Provisional Patent Application No 2024903696 filed on 12 November 2024, the contents of which are incorporated herein by reference in their entirety.TECHNICAL FIELD

[0002] The present disclosure relates to processes for the production of hydrogen gas involving a metal in contact with a liquid. The present disclosure also relates to use of the metal for production of hydrogen as described herein, and hydrogen produced by the process described herein.BACKGROUND

[0003] Hydrogen is a clean burning fuel that is often considered to be a secondary source of energy, which is one that can be used to store and transport energy produced by other energy sources. When burned in with oxygen, hydrogen produces a source of energy with water vapour being the only byproduct. Because of this, the production of hydrogen from water is of particular interest due to the circular nature of this material lifecycle.

[0004] One of the challenges of producing hydrogen from water is increasing the efficiency of the process to ensure minimal loss of energy and more efficient production of hydrogen. Furthermore, it is desirable that any by-product resulting from processes of producing hydrogen are minimised and / or are easily reused or recycled.

[0005] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.SUMMARY

[0006] In a first aspect, disclosed herein is a process for producing hydrogen, the process comprising:applying electromagnetic radiation to at least one post-transition metal, or optionally at least one post-transition metal alloy, in contact with a liquid comprising at least one oxygen-containing species, thereby causing oxidation of the at least one post-transition metal to produce an oxidised post-transition metal species and hydrogen,wherein optionally the at least one post-transition metal, or the optional post-transition metal alloy, does not comprise aluminium.

[0007] In some embodiments of the first aspect, the at least one post-transition metal, or the optional post-transition metal alloy, does not comprise aluminium.

[0008] In some embodiments of the first aspect, the electromagnetic radiation is visible light. In some embodiments, the source of electromagnetic radiation is sunlight.

[0009] In some embodiments of the first aspect, the at least one post-transition metal, or the optional post-transition metal alloy, is in a liquid state. In some embodiments, the at least one post-transition metal comprises or is gallium. In some embodiments, the oxidised post-transition metal species is a gallium (III) species, preferably gallium oxyhydroxide.

[0010] In some embodiments of the first aspect, the liquid comprising at least one oxygen-containing species comprises or is an aqueous liquid.

[0011] In some embodiments of the first aspect, the process further comprises:reducing the oxidised post-transition metal species, for example by electrolysis, thereby reproducing the at least one post-transition metal, or the optional post-transition metal alloy.

[0012] In some embodiments of the first aspect, the process further comprises dissolving the oxidised post-transition metal species in an acidic, alkaline, or neutral ionic media, preferably an acidic media, prior to the reduction step.

[0013] In a second aspect, disclosed herein is the use of at least one post-transition metal, or optionally at least one post-transition metal alloy, for producing hydrogen in a process according to the first aspect, wherein optionally the at least one post-transition metal, or the optional post-transition metal alloy, does not comprise aluminium.

[0014] In some embodiments of the second aspect, the at least one post-transition metal, or the optional post-transition metal alloy, does not comprise aluminium.

[0015] In some embodiments of the second aspect, the at least one post-transition metal, or the optional post-transition metal alloy, comprises or is gallium.

[0016] In a third aspect, disclosed herein is hydrogen produced by the process according to the first aspect.

[0017] Other aspects and embodiments relating to the present disclosure are described herein. It will be appreciated that each example, aspect and embodiment of the present disclosure described herein is to be applied mutatis mutandis to each and every other example, aspect or embodiment unless specifically stated otherwise. The present disclosure is not to be limited in scope by the specific examples described herein, which are intended for the purpose of exemplification only. Functionally equivalent substituents, compositions, methods and processes are clearly within the scope of the disclosure as described herein.BRIEF DESCRIPTION OF DRAWINGS

[0018] Whilst it will be appreciated that a variety of embodiments disclosed herein may be used, described herein are a number of examples with reference to the following drawings:

[0019] Figure 1: Schematic representation of the experimental set-up of the photo oxidation process

[0020] Figure 2: Photo-current of bulk gallium recorded with and without light irradiation,

[0021] Figure 3: Polarization potential of gallium metal with or without light irradiation.

[0022] Figure 4: Schematic representation of the sonication process used to produce gallium particles, and size distribution of the gallium particles at different sonication times.

[0023] Figure 5: UV-Vis spectra of the gallium particles after sonication.

[0024] Figure 6: Hydrogen yield as a function of time for gallium particles of different sizes under light irradiation.

[0025] Figure 7: Hydrogen yield as a function of time for bulk gallium under light irradiation.

[0026] Figure 8: Hydrogen production rates using bulk and particles of eutectic gallium-indium alloy.

[0027] Figure 9: Hydrogen yield as a function of time for gallium particles under different light irradiation intensities.

[0028] Figure 10: Relationship between power density and temperature of the samples as a function of distance from the light irradiation source.

[0029] Figure 11: Hydrogen yield as a function of time for the 30-minute sonicated gallium particles at various temperatures in the absence of light.

[0030] Figure 12: Hydrogen yield as a function of time for the 30-minute sonicated gallium particles in DI and salt water.

[0031] Figure 13: SEM images of the gallium metal particles (pre-photooxidation) and the gallium oxyhydroxide crystals (post-photooxidation).

[0032] Figure 14: a). XRD patterns of the Ga particles before and after reaction for same sample, and b). Raman spectra of the Ga particles before and after reaction.

[0033] Figure 15: High-resolution XPS spectra of the particles after photo thermal oxidation reaction.

[0034] Figure 16: a) Schematic representation of the 2-electrodes set-up, b) Linear sweep voltammetry of GaOOH in 1 M H2SO4 on glassy carbon electrode (GC) and carbon paper electrode (CP), and c) SEM images of the Ga liquid after recovery on different electrodes (1 and 2: Pt electrode and 3: carbon cloth) in 1 M H2SO4 electrolyte.

[0035] Figure 17: a) and b) Photographs of the carbon paper before and after Ga recovery, respectively, c) SEM image showing Ga deposited on the carbon paper, d) Photograph of Ga deposited on, and detached from, the carbon paper, e) Top-view photograph showing reduced Ga that detached from the carbon paper and accumulated in the electroreduction bath, f) SEM image of the Ga recovered from the bath after detachment from the carbon paper.

[0036] Figure 18: a) XRD pattern of recovered Ga on carbon paper substrate, b) XRD pattern of recovered Ga that detached from the carbon paper during electroreduction.

[0037] Figure 19: Linear sweep voltammetry of Ga(III) in 1.0 M HC1 on carbon paper (CP) electrode substrates.

[0038] Figure 20: SEMZEDX images of the liquid Ga after recovery on carbon paper after electroreduction in 1.0 M HC1 electrolyte.

[0039] Figure 21: Photograph of GaOOH dispersed in various electrolytes: 2 MNaOH, 2 M KOH, and 2 M HC1 (from left to right), after 48 hours of reaction at 90 °C under 400 rpm agitation.

[0040] Figure 22: Hydrogen production yield (% of theoretical) from DI water and recovered Ga particles using a halogen light source.DETAILED DESCRIPTION

[0041] The present disclosure describes the following various non-limiting embodiments, which relate to the present disclosure.Definitions

[0042] In the following description, reference is made, where needed, to any accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments. It is understood that other embodiments may be used, and structural changes may be made without departing from the scope of the present disclosure.

[0043] With regards to the definitions provided herein, unless stated otherwise, or implicit from context, the defined terms and phrases include the provided meanings.Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0044] All publications discussed and / or referenced herein are incorporated herein in their entirety.

[0045] Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.

[0046] Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the examples, steps, features, methods, processes, and compositions, referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

[0047] The term “and / or”, e.g., “X and / or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.

[0048] Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second”item does not require or preclude the existence of lower-numbered item (e.g., a “first” item) and / or a higher-numbered item (e.g., a “third” item).

[0049] As used herein, the phrase “at least one of’, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

[0050] As used herein, the term “about”, unless stated to the contrary, typically refers to a range of up to + / - 10% of the designated value, and includes smaller ranges therein, for example + / - 5% or + / - 1% of the designated value.

[0051] It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination.

[0052] Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4, 4.5, 4.75, and 5, unless where integers are required or implicit from context. This applies regardlessof the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

[0053] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0054] Throughout this specification, the term "consisting essentially of' is intended to exclude elements which would materially affect the properties of the claimed composition, method or process.

[0055] The terms "comprising", "comprise" and "comprises" herein are intended to be optionally substitutable with the terms "consisting essentially of', "consist essentially of', "consists essentially of, "consisting of, "consist of' and "consists of, respectively, in every instance.

[0056] Herein “weight %” may be abbreviated to as “wt%” or “wt.%”. The weight % may be w / w or w / v, unless specifically indicated or clear from context.Specific Terms

[0057] As used herein, the term “post-transition metal” refers to the group 13 to 16 metals in periods 4 to 6, specifically, gallium, indium, thallium, tin, lead, bismuth, and polonium, aluminium, group 12 metals, specifically, zinc, cadmium, and mercury, and copemicium, and the metalloids germanium, arsenic, antimony, and tellurium.

[0058] As used herein, the term “alloy”, refers to mixture of chemical elements if which at least one of the elements is a metal or a metalloid.

[0059] As used herein, the term “eutectic” refers to a homogenous mixture which has a melting point lower than that of its constituents.

[0060] As used herein, the term “transition metals” refers to the elements in groups 4 to 11 of the d-block of the periodic table.

[0061] As used herein, the term “alkali metals” refers to elements in group 1 of the periodic table, excluding hydrogen.

[0062] As used herein, the term “alkaline earth metal” refers to elements in group 2 of the period table.

[0063] As used herein, the term “rare earth element” refers to elements of the lanthanide series, scandium, and yttrium.

[0064] As used herein, the term “noble metal” refers to the group of metals comprising ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.

[0065] As used herein, the term “oxidised post-transition metal species” refers to a compound or ion comprising one or more post-transition metal species having undergone an increase in oxidation state.

[0066] As used herein, the term “liquid metal” refers to a metal or alloy that is a liquid at or near room temperature under atmospheric pressure. An example of such a metal is mercury or gallium.

[0067] As used herein, the term “low melting point metal” refers to a metal or alloy that has a melting point below about 330 °C at 1 atm. In one embodiment, at least one “low melting point metal” has a melting point (in °C at 1 atm), of about or less than about: 330, 320, 310, 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, or 30.

[0068] As used herein, the term “particle” refers to a discrete piece of matter with an average diameter of less than about 1 cm.

[0069] As used herein, the term “microparticle” refers to a particle with a diameter between about 0.1 pm and about 100 pm.

[0070] As used herein, the term “nanoparticle” refers to a particle with a diameter between about Inm and about 100 nm.

[0071] As used herein, the term “film” refers to a layer of a material with a thickness ranging single layer of atoms or molecule of the material up to 100 pm. The term “thin film” refers to films with a thickness of less than about 0.1 pm.

[0072] As used herein, the term “radio waves”, refers to electromagnetic radiation with a wavelength greater than about 1 m.

[0073] As used herein, the term “microwaves”, refers to electromagnetic radiation with a wavelength less than about 1 m and greater than about 1 mm.

[0074] As used herein, the term “infrared”, refers to electromagnetic radiation with a wavelength less than about 1 mm and greater than about 750 nm.

[0075] As used herein, the term “visible light”, refers to electromagnetic radiation with a wavelength less than about 750 nm and greater than about 400 nm.

[0076] As used herein, the term “ultraviolet”, refers to electromagnetic radiation with a wavelength less than about 400 nm and greater than about 10 nm.

[0077] As used herein, the term “X-ray”, refers to electromagnetic radiation with a wavelength less than about 10 nm and greater than about 0.1 mm.

[0078] As used herein, the term “gamma ray”, refers to electromagnetic radiation with a wavelength less than about 0.1 nm.

[0079] As used herein, the term “terahertz waves”, refers to electromagnetic radiation with a wavelength less than about 1000 gm and greater than about 100 gm.

[0080] As used herein, the term “near infrared”, refers to electromagnetic radiation with a wavelength less than about 1400 nm and greater than about 750 nm.

[0081] As used herein, the term “short-wavelength infrared”, refers to electromagnetic radiation with a wavelength less than about 3 gm and greater than about 1.4 gm.

[0082] As used herein, the term “mid-wavelength infrared”, refers to electromagnetic radiation with a wavelength less than about 8 gm and greater than about 3 gm.

[0083] As used herein, the term “long-wavelength infrared”, refers to electromagnetic radiation with a wavelength less than about 15 gm and greater than about 8 gm.

[0084] As used herein, the term “far infrared”, refers to electromagnetic radiation with a wavelength less than about 1000 gm and greater than about 15 gm.

[0085] As used herein, the term “ultraviolet A”, refers to electromagnetic radiation with a wavelength less than about 400 nm and greater than about 315 nm.

[0086] As used herein, the term “ultraviolet B”, refers to electromagnetic radiation with a wavelength less than about 315 nm and greater than about 280 nm.

[0087] As used herein, the term “ultraviolet C”, refers to electromagnetic radiation with a wavelength less than about 280 nm and greater than about 100 nm.

[0088] As used herein, the term “vacuum ultraviolet” refers to electromagnetic radiation with a wavelength of less than about 100 nm and more than about 10 nm.

[0089] As used herein, the term “sunlight” refers to electromagnetic radiation from the sun.

[0090] As used herein, the term “aqueous liquid” refers to a liquid solution which substantially comprises water.

[0091] As used herein, the term “organic liquid” refers to a liquid solution which comprises one or more organic solvents.

[0092] As used herein, the term “organic solvent” refers to a solvent is a carbon-based substance that is used to dissolve another substance or substances.

[0093] As used herein, the term “mixed aqueous organic liquid” refers to a liquid which comprises substantial portions of both water and one or more organic solvents.

[0094] As used herein the term “artificially electromagnetic radiation source” refers to a source of electromagnetic radiation other than sunlight.

[0095] As used herein, the term “electrolysis” refers to the use of a direct electric currently to drive an otherwise non-spontaneous chemical reaction.Processes

[0096] Disclosed herein is a process for producing hydrogen. The process comprises: applying electromagnetic radiation to at least one post-transition metal in contact with a liquid comprising at least one oxygen-containing species, thereby causing oxidation of the post-transition metal to produce an oxidised post-transition metal species and hydrogen.

[0097] In the process described herein, the at least one post-transition metal does not comprise aluminium. Advantageously, the process described herein does not require the use of aluminium. For example, as described herein and as shown in the Examples, the present inventors have surprisingly found that the post-transition metal gallium alone canbe used to produce hydrogen in the process described herein. Advantageously, hydrogen was produced in a high theoretical yield of close to about 100%.

[0098] In some embodiments of the process described herein, the oxidation of the at least one post-transition metal does not produce oxygen. Advantageously, as described herein and as shown in the Examples, the process of the present disclosure can generate hydrogen gas without generating other gaseous byproducts, such as oxygen. This can beneficially avoid the need for a separation step and the production of a hazardous explosive mixture of oxygen and hydrogen gases, which can occur in other hydrogen production processes.

[0099] In some embodiments of the process described herein, the process is conducted in the absence of a catalyst. Advantageously, the process of the present disclosure does not require the use of the catalysts typically present in conventional electrolyser technologies for hydrogen production.

[0100] The process may be conducted in any suitable reactor. The reactor may preferably allow for penetration of electromagnetic radiation into the reactor. The reactor may preferably be non-conductive. The reactor may preferably be impervious, for example water-tight, gas-tight, or both. Examples of suitable reactor materials include one or more of glass, quartz, and a ceramic.Electromagnetic radiation

[0101] Herein the electromagnetic radiation can be any of any type suitable for progressing the reaction. It will be appreciated that the wavelength of the electromagnetic radiation can vary. In one embodiment, the electromagnetic radiation may be selected from one or more of extremely low frequency electromagnetic fields, radio waves, microwaves, infrared, thermal radiation (heat), visible light, ultraviolet, X-rays, and gamma rays. The electromagnetic radiation may also be defined by subcategories of these types, including terahertz waves, near infrared, short-wavelength infrared, midwavelength infrared, long wavelength infrared, ultraviolet A, ultraviolet B and ultraviolet C, and vacuum ultraviolet.

[0102] In one embodiment, the electromagnetic radiation may be selected from one or more of extremely low frequency electromagnetic fields, radio waves, microwaves,infrared, visible light, ultraviolet, X-rays, and gamma rays. In one embodiment, the electromagnetic radiation may be selected from one or more of radio waves, microwaves, infrared, visible light, and ultraviolet. In one embodiment, the electromagnetic radiation may be selected from one or more of microwaves, infrared, visible light, and ultraviolet. In one embodiment, the electromagnetic radiation may be selected from one or more of infrared, visible light, and ultraviolet. In one embodiment, the electromagnetic radiation may be one or both of infrared and visible light. In one embodiment, the electromagnetic radiation may be visible light.

[0103] In one embodiment at least one post-transition metal (as described herein), in contact with a liquid comprising at least one oxygen-containing species (as described herein), is exposed to electromagnetic radiation selected from one or more of extremely low frequency electromagnetic fields, radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Optionally heat may also be applied for a period of time, wherein the at least one post-transition metal (as described herein) and / or liquid comprising at least one oxygen-containing species (as described herein), prior to, during and / or after exposure to electromagnetic radiation. The at least one post-transition metal (as described herein) and / or liquid comprising at least one oxygen-containing species (as described herein) may be exposed to a temperature of about, or at least about (in °C) of: 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or in a range of any two of these values, for a period of time prior to, during and / or after exposure to electromagnetic radiation. The period of time may be about, or at least about (in hours of): 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or a range of any two of these values.

[0104] In some embodiments, the electromagnetic radiation comprises or is visible light. Advantageously, as shown in the Examples, the present inventors have demonstrated that visible light can be used to oxidise a post-transition metal according to the process described herein to generate hydrogen. Beneficially, visible light can be derived from natural sources of such as sunlight, which can allow for the green production of hydrogen.

[0105] In one embodiment, the wavelength of the electromagnetic radiation may be about, or at least about:• (in pm): 5, 10, 15, 20, 30, 50, 75, 100; and / or• (in nm): 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 70, 100, 150, 200, 250, 280, 300, 315, 350, 380, 400, 450, 500, 600, 700, 750, 780, 800; and / or• (in pm): 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10, 11, 12, 13, 14, 15, 20, 30, 50, 75, 100, 150, 200, 300, 500, 750; and / or• (in mm): 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.1, 2.4, 2.7, 3.0, 3.3, 3.6, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 10, 11.3, 14, 16.7, 20, 25, 30, 35, 37.5, 50, 75, 100, 125, 150, 200, 300, 350, 375, 500, 750, 1000; and / or• (in m): 1, 10, 100, 1000; and / or• (in km) 10, 100, 1000, 5000, 6000, 10000, or 100000.The wavelength of the electromagnetic radiation may be in a range provided by any two these upper and / or lower values, for example (in nm) between about 380 and about 2500.

[0106] In one embodiment, the wavelength of the electromagnetic radiation may be less than about:• (in pm): 5, 10, 15, 20, 30, 50, 75, 100; and / or• (in nm): 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 70, 100, 150, 200, 250, 280, 300, 315, 350, 380, 400, 450, 500, 600, 700, 750, 780, 800; and / or• (in pm): 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10, 11, 12, 13, 14, 15, 20, 30, 50, 75, 100, 150, 200, 300, 500, 750; and / or• (in mm): 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.1, 2.4, 2.7, 3.0, 3.3, 3.6, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 10, 11.3, 14, 16.7, 20, 25, 30, 35, 37.5, 50, 75, 100, 125, 150, 200, 300, 350, 375, 500, 750, 1000; and / or• (in m): 1, 10, 100, 1000; and / or• (in km) 10, 100, 1000, 5000, 6000, 10000, or 100000.The wavelength of the electromagnetic radiation may be in a range provided by any two these upper and / or lower values, for example (in nm) between about 200 and about 1,000,000,000 or between about 200 and about 2500 or between about 380 and about 2500.

[0107] In some embodiments, the electromagnetic radiation has a wavelength of between about 200 nm to about 1 m. In some embodiments, the electromagnetic radiation has a wavelength of between about 200 nm to about 1 mm. In some embodiments, the electromagnetic radiation has a wavelength of between about 200 nm to about 2500 nm. In some embodiments, the electromagnetic radiation has a wavelength of between about 380 nm to about 2500 nm, preferably about 380 nm to about 780 nm.

[0108] In one embodiment one only one wavelength is used in the process as described herein. In another embodiment, a plurality of different wavelengths are used in the process as described herein, for example 2, 3 or 4 different wavelengths.

[0109] The intensity of the electromagnetic radiation can vary. The energy of the electromagnetic radiation can be measured as the luminous flux incident per surface area on the liquid containing the low melting point or liquid post-transition metal. In one embodiment, luminous flux incident per surface area on the liquid containing the low melting point or liquid post-transition metal may be tailored for a specific metal, alloy, and / or mixture thereof. The energy of the electromagnetic radiation can also be measured in power of radiation per surface area on the liquid containing the low melting point or liquid post-transition metal. In one embodiment, power of radiation per surface area on the liquid containing the low melting point or liquid post-transition metal may be tailored for a specific metal, alloy, and / or mixture thereof. In some embodiments, the intensity of the electromagnetic radiation (in milliwatt per square centimetre, mW cm2) may be at least about 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 550, 600, 650, 700, 750, 800, 850, 900, or 1000. In some embodiments, the intensity of the electromagnetic radiation (in watt per square centimetre, W cm2) may be less than about 10.0, 9.5, 9.0, 8.5, 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.5, 3.0, 2.5, 2.0, 1.5, or 1.0. The intensity of the electromagnetic radiation may be in a range provided by any two of these upper and / or lower values, for example between about 1 mW cm2to about 10 W cm2. In one embodiment, the electromagnetic radiation has an intensity of between about 1 mW cm2to about 10,000 mW cm2(equivalent to about 0.01 to about 100 suns). In one embodiment, the electromagnetic radiation has an intensity of between about 100 mWcm2to about 3000 mW cm2(equivalent to about 1 to about 30 suns). In one embodiment, the electromagnetic radiation has an intensity of between about 500 mW cm2to about 3000 mW cm2(equivalent to about 5 to about 30 suns).

[0110] Any suitable source of electromagnetic radiation may be used. The electromagnetic radiation may be from a single source, or from multiple sources of electromagnetic radiation.

[0111] Examples of suitable source of electromagnetic radiation include sunlight, an artificial light source, an electromagnetic field (EMF)-emitting device; a mobile phone; a Wi-Fi device; a terahertz radiation-emitting device; a microwave; an infrared heater; an induction heater; an X-ray device; a gamma source; and mechanical agitation. The artificial radiation source may be one or more of an incandescent light source, or a luminescent light source, such as an electroluminescent source (such as an LED or a laser) or an electric discharge source (such as a xenon arc lamp or a fluorescent light). In one embodiment, the source of the electromagnetic radiation is selected from one or more of sunlight; an artificial light source such as a halogen lamp, a fluorescent lamp or a lightemitting diode; a laser; an electromagnetic field (EMF)-emitting device; a mobile phone; a Wi-Fi device; a terahertz radiation-emitting device; a microwave; an infrared heater; an ultraviolet lamp; an X-ray device; and a gamma source. In one embodiment, the source of the electromagnetic radiation is selected from one or more of sunlight; an artificial light source such as a halogen lamp, a fluorescent lamp or a light-emitting diode; a laser; an infrared heater; and an ultraviolet lamp. In one embodiment, the source of the electromagnetic radiation is selected from one or more of sunlight; an artificial light source such as a halogen lamp, a fluorescent lamp or a light-emitting diode; a laser; an infrared heater; and an ultraviolet lamp.

[0112] In some embodiments, the source of the electromagnetic radiation comprises or is sunlight. Advantageously, as shown in the Examples, the present inventors have demonstrated that sunlight can be used to oxidise a post-transition metal according to the process described herein to generate hydrogen. Beneficially, sunlight is a natural source of electromagnetic radiation, which may allow for the production of green hydrogen.Post-transition metal

[0113] The processes disclosed herein involve applying electromagnetic radiation to at least one post-transition metal. The term “at least one” will be understood to mean “one or more”. For example, the term “at least one post-transition metal” will be understood to mean one or more post-transition metals, that is, one or more species of post-transition metal. As described herein, the at least one transition metal does not comprise aluminium.

[0114] Examples of suitable post-transition metals include, but are not limited to: gallium, indium, thallium, tin, lead, bismuth, polonium, zinc, cadmium, and mercury, copemicium, germanium, arsenic, antimony, tellurium, and mixtures thereof. In one embodiment, the at least one post-transition metal is one or more selected from, but not limited to: gallium, indium, tin, bismuth, zinc, mercury, lead, antimony, and mixtures thereof. In one embodiment, the at least one post-transition metal is one or more selected from, but not limited to: gallium, indium, tin, bismuth, zinc, and mixtures thereof. In one embodiment, the at least one post-transition metal is one or more selected from, but not limited to: gallium, tin, bismuth, zinc, and mixtures thereof. In one embodiment, the at least one post-transition metal is one or more selected from, but not limited to: gallium, indium, and mixtures thereof.

[0115] In some embodiments, the at least one post-transition metal, alloy or mixture, comprises or is gallium. Advantageously, as shown in the Examples, gallium was capable of being oxidised in the process described herein to produce hydrogen, and in high theoretical yield. Beneficially, compared to other types of liquid metals, gallium can be considered non-toxic, which may improve its uptake and useability in hydrogen production processes.

[0116] Accordingly, the present disclosure also provides a process for producing hydrogen, the process comprising:applying electromagnetic radiation to gallium, which may include alloys and mixtures comprising gallium, in contact with a liquid comprising at least one oxygen-containing species, thereby causing oxidation of the gallium to produce a oxidised gallium and hydrogen.

[0117] The at least one post-transition metal (or alloy or mixture) may be in a solid state, a liquid state, or both, during at least part of the process. In some embodiments, the at least one post-transition metal is in a liquid state during at least part of the process. In some embodiments, the at least one post-transition metal is a pure or substantially pure post-transition metal with a melting point below the temperature at which the process is operated and / or at the pressure at which the process, or at least a part thereof, is operated. In one embodiment, the at least one post-transition metal is provided as an alloy with a melting point below the temperature at which the process, or part thereof, is operated and / or at the pressure at which the process, or part thereof, is operated. In one embodiment, the at least one post-transition metal is provided as a eutectic alloy. In one embodiment, the at least one post-transition metal is provided as a eutectic alloy with a melting point below the temperature at which the process, or part thereof, is operated and / or at the pressure at which the process, or part thereof, is operated.

[0118] In one embodiment, the at least one post-transition metal may be pure or substantially pure. It will be appreciated that the term “substantially pure” allows for the presence of minor impurities. In some embodiments, the purity of at least one substantially pure post-transition metal (in wt. %) may be at least about: 90, 91, 92, 93, 94, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99, 99.2, 99.5, 99.7, or 99.9. In some embodiments, the purity of the of at least one substantially pure post-transition metal (in wt. %) may be less than about: 99.9, 99.7, 99.5, 99.2, 99, 98.5, 98, 97.5, 96, 95.5, 95, 94, 93, 92, 91, or 90. The purity of at least one substantially pure post-transition metal (in wt. %) may be in a range provided by any two of these upper and / or lower values, for example between about 90 and about 95. In some embodiments, at least one posttransition metal may have a purity (in wt. %) which is less than 90, for example about or less than about 85, 80, 75, 70, 65, 60, 55 or 50.

[0119] In some embodiments, the at least one post-transition metal may be provided as an alloy or mixture, wherein the alloy or mixture does not comprise aluminium. In some embodiments, the at least one post-transition metal is an alloy or mixture comprising any one or more materials selected from, but not limited to: other post-transition metals (except not aluminium), transition metals, alkali metals, alkaline earth metals, rare earth elements, noble metals, and mixtures thereof.

[0120] In some embodiments, the other post-transition metals in the alloy or mixture are one or more selected from the group comprising, but not limited to: gallium, indium, thallium, tin, lead, bismuth, polonium, zinc, cadmium, mercury, copemicium, germanium, arsenic, antimony, and tellurium. In some embodiments, the other posttransition metals are one or more selected from: gallium, indium, tin, bismuth, mercury, lead, zinc, and antimony. In some embodiments, the at least one post-transition metal is an alloy or mixture comprising, or consisting of, gallium and indium.

[0121] In one embodiment an alloy or mixture may comprise one or more transition metals. In some embodiments, the transition metals in one or more alloys and / or mixtures are one or more selected from, but not limited to: copper, nickel, and iron.

[0122] In some embodiments, the alkali metals in the alloy or mixture are one or more selected from, but not limited to: lithium, sodium, potassium, rubidium, caesium, and francium. In some embodiments, the alkali metals are one or more selected from: lithium, magnesium, calcium, and sodium.

[0123] In some embodiments, the alkaline earth metals in the alloy or mixture are one or more selected from, but not limited to: beryllium, magnesium, calcium, strontium, barium, and radium. In some embodiments, the alkaline earth metals are one or more selected from magnesium and calcium.

[0124] In some embodiments, the rare earth elements in the alloy or mixture are one or more selected from, but not limited to: scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium thulium, ytterbium, and lutetium. In some embodiments, the rare earth element is cerium.

[0125] In some embodiments, the noble metals in the alloy or mixture are one or more selected from, but not limited to: ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold. In some embodiments, the noble metals are one or more selected from: ruthenium, palladium, silver, iridium, platinum, and gold.

[0126] The at least one post-transition metal may be obtained from any suitable source. In some embodiments, the at least one post-transition metal is recycled or is extracted from a source containing the post-transition metal. In some embodiments, the at least onepost-transition metal is recycled or extracted from electronic waste. In embodiments where the at least one post-transition metal comprises or is gallium, the gallium may be recycled or extracted from a source containing gallium, for example recycled or extracted from electronic waste. Examples of suitable gallium sources include natural sources such as bauxite ore and zinc ores, and electronic waste such as LEDs and semiconductors.

[0127] It will be appreciated that the at least one post-transition metal alloys or mixtures of any of the above embodiments may contain impurities. In some embodiments, the purity of the at least one post-transition metal alloy or mixture (in wt. %) may be at least about: 90, 91, 92, 93, 94, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99, 99.2, 99.5, 99.7, or 99.9. In some embodiments, the purity of the at least one post-transition metal alloy or mixture (in wt. %) may be less than about: 99.9, 99.7, 99.5, 99.2, 99, 98.5, 98, 97.5, 96, 95.5, 95, 94, 93, 92, 91, or 90. The purity of the at least one post-transition metal alloy or mixture (in wt. %) may be in a range provided by any two of these upper and / or lower values, for example between about 90 and about 95. In some embodiments, at least one post-transition metal alloy may have a purity (in wt. %) which is less than 90, for example about or less than about 85, 80, 75, 70, 65, 60, 55 or 50.

[0128] In the processes disclosed herein, the at least one post-transition metal is oxidised to produce an oxidised post-transition metal species. The oxidised posttransition metal species comprises one or more post-transition metal atoms that may each independently be in an oxidation state selected from +1, +2, +3, +4, +5, +6, +7, +8, and +9. Herein, the oxidised post-transition metal species may comprise an oxyhydroxide form of the at least one post-transition metal. In some embodiments, the oxidised posttransition metal species comprises one or more post-transition metal atoms having the same oxidation state. In some embodiments, the process comprises forming only a single oxidised post-transition metal species. In embodiments where the at least one posttransition metal is gallium, the oxidised post-transition metal species may comprise gallium in the +3 oxidation state (that is, a gallium (III) species). In embodiments where the at least one post-transition metal is gallium, the oxidised post-transition metal species may comprise gallium oxyhydroxide.Post-transition metal form

[0129] The at least one post-transition metal may be provided in any suitable form. In one embodiment, the at least one post-transition metal is provided as a bulk material, for example having a cross section of greater than 1 cm in any direction.

[0130] In some embodiments, the at least one post-transition metal is provided in the form of particles. Advantageously, providing the at least one post-transition metal in the form of particles can increase the surface area, for example compared to a bulk form, which may increase the reaction rate. It will be appreciated that at least a portion of the particles may vary in size The size of particles in a sample can be characterised using methods known in the art, for example by determining the D50 value of the sample, which gives the median size of the particles.

[0131] Particles may be measured by an appropriate technique in the art. In one embodiment image analysis software, for example Imaged and / or Photoshop may be used to measure the particle size distribution. Alternative techniques, such as light scattering methods like DLS, could also be used for metal particle size distribution analysis. Due to the soft nature of liquid metal particles, methods applicable to soft materials can also be considered (e.g. one or more of ASTM methods, including, but not limited to: B822, D4464, E2651, and D1921). In one embodiment one or more of the following ASTM standards could be used: ASTM B822-20 (as updated 12 October 2020), ASTM D4464-15 (as updated 3 June 2020), ASTM E2651-19 (as updated 8 April 2019), and / or ASTM DI 921-18 (as updated 18 April 2018).

[0132] . In some embodiments, at least a portion of the particles may comprise one or more of: microparticles, nanoparticles, or mixtures thereof. In some embodiments, at least a portion of the particles may have a D50 particle size (in pm) of less than about: 10000, 7500, 5000, 3000, 2000, 1000, 750, 500, 300, 200, 100, 10, 7.5, 5, 3, 2, 1.5, 1, 0.75, 0.5, 0.3, 0.2, 0.1, 0.075, 0.05, 0.03, 0.02, 0.01, 0.005, or 0.001. In some embodiments, at least a portion of the particles may have a D50 particle size (in pm) of at least about: 0.001, 0.005, 0.01, 0.02, 0.03, 0.05, 0.075, 0.1, 0.2, 0.3, 0.5, 0.75, 1, 1,5, 2, 3, 5, 7.5, 10, 20, 30, 50, 75, 100, 200, 300, 500, 750, 1000, 2000, 3000, 5000, 7500, 10000. The D50 particle size of the particles may be in a range (in pm) provided by any two of these upper and / or lower values, for example between about 0.001 and about 100,between about 0.1 and about 100, between about 0.5 and about 1.5, or between about 0.001 and about 0.1. In one embodiment the particles are measured in accordance with an ASTM standard (e.g. one or more of ASTM methods, including but not limited to: B822, D4464, E2651, and D1921), and optionally: ASTM B822-20 (as updated 12 October 2020), ASTM D4464- 15 (as updated 3 June 2020), ASTM E2651 - 19 (as updated 8 April 2019), and / or ASTM D1921-18 (as updated 18 April 2018).

[0133] The particles may be produced from a bulk material using a variety of methods. The particles may be produced from a bulk material in a solid state or in a liquid state. In some embodiments, at least a portion of the particles may be produced from a bulk material using one or more methods selected from, but not limited to: sonication, mechanical agitation, atomization, emulsification, electro spraying, microfluidics, ball milling, grinding, cutting, mechanical shaping, and wire forming. In one embodiment, at least a portion of the particles are produced from a bulk material by sonication. In some embodiments, at least a portion of the particles may be produced by sonication of the bulk material for a time (in minutes) of less than about: 120, 90, 60, 50, 40, 30, 20, 10, 5, 2, or 1. In some embodiments, at least a portion of the particles may be produced by sonication of the bulk material for a time (in minutes) of at least about: 1, 2, 5, 10, 20, 30, 40, 50, 60, 90, or 120. At least a portion of the particles may be produced by sonication of the bulk material for a time (in minutes) between any two of these upper and / or lower values, for example between about 10 and about 60. In one embodiment, particles are be produced by sonication of the bulk material for a time of about 30 minutes.

[0134] In one embodiment, the at least one post-transition metal may be provided as a film. Advantageously, providing the at least one post-transition metal in the form of a film can increase the surface area, for example compared to a bulk form, which may increase the reaction rate. In some embodiments the film may be a thin film. In some embodiments the film may have a thickness of less than about (in pm): 100, 50, 25, 10, 5, 2.5, 1, 0.5, 0.25, or 0.1, or (in nm) 50, 25, 10, 5, 2.5, 1, 0.5, 0.25, or 0.1. The film may be produced, for example, by painting and / or spray deposition of the at least one posttransition metal on a substrate. In some embodiments, the film can be provided on a solid support, such as particles.Liquid

[0135] The processes disclosed herein involve at least one post-transition metal in contact with a liquid, which comprises at least one oxygen-containing species. The at least one oxygen-containing species may have one or more oxygen atoms that are directly bonded to one or more hydrogen atoms, for example one or more -OH groups.

[0136] The liquid may comprise an aqueous liquid, an organic liquid, and mixtures thereof. In some embodiments, the liquid comprises or is an aqueous liquid. Beneficially, water is an abundant source of hydrogen. In some embodiments, the liquid comprises or is an organic liquid. In some embodiments, the liquid comprises or is a mixed aqueous organic liquid.

[0137] In one embodiment, the liquid may comprise one or more organic solvents. The one or more organic solvents may not be limited, and may be selected based on one or more factors such as the one or more post-transition metals. In one embodiment, the liquid may comprise one or more organic solvents selected from, but not limited to: halogenated hydrocarbons like chlorobenzene, bromobenzene, di chlorobenzene, trifluoro methyl benzene and trichlorobenzene, ethers like diethyl ether, ethyl propyl ether, n-butyl ether, anisole, phenetole, cyclohexyl methyl ether, dimethyl ether, dimethyl glycol, diphenyl ether, dipropyl ether, diisopropyl ether, di-n-butyl ether, diisobutyl ether, diisoamyl ether, ethylene glycol dimethyl ether, isopropyl ethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, di chlorodi ethyl ether, methyltetrahydrofuran, polyethers of ethylene oxide and / or propylene oxide, nitrated hydrocarbons like nitromethane, nitroethane, nitropropane, nitrobenzene, chloronitrobenzene and ethyl benzene), aliphatic, cycloaliphatic or aromatic hydrocarbons like pentane, n-hexane, n-heptane, n-octane, nonane, cymene, petroleum fractions having a boiling range of from about 25 °C to about 350 °C, cyclohexane, methylcyclohexane, petroleum ether, ligroin, octane, benzene toluene, xylene, dimethylbenzene, di ethylbenzene, esters like malonates, n-butyl acetate, methyl acetate, ethyl acetate, isobutyl acetate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate and ethylene carbonate, and aliphatic alcohols like methanol, ethanol, n-propanol, isopropanol, n-butanol and tert-amyl alcohol), mesitylene, diethyl ketone, methyl ethyl ketone, acetonitrile and mixtures thereof

[0138] In some embodiments, the liquid may comprise any one or more of: water, methanol, ethanol, glycerol, ethylene glycol, propylene glycol, dimethyl sulfoxide, toluene, tetradecane, octane, hexane, pentane, hydrofluoroether 7500, methyl tert-butyl ether, acetone, isopropanol, chloroform, 1,2-di chlorobenzene, and mixtures thereof.

[0139] In one embodiment, the liquid comprises an aqueous solution or aqueous solvent. In some embodiments, the water in the liquid is one or more selected from, but not limited to: wastewater, processed wastewater, rainwater, brackish water, sea water, and mixtures thereof. In some embodiments, the liquid comprises or is purified water. The purified water may be purified using methods known in the art, for example by one or more techniques selected from carbon filtration, reverse osmosis, and electrodeionisation. The purity the water may be defined by its resistivity, which can be measured using ASTM DI 125-23. In some embodiments, the resistivity of the water (in Q m) may be less than about: 200000, 180000, 150000, 100000, 80000, 50000, 20000, 15000, 12000, 10000, 7500, 5000, 2500, 1000, 750, 500, 200, 100, 75, 50, 25, 10, 5, 2, 1, 0.8, 0.6, 0.4, 0.2, or 0.1. In some embodiments, the resistivity of the water (in Q m) may be about, or at least about: 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2, 5, 10, 25, 50, 75, 100, 200, 500, 750, 1000, 2500, 5000, 7500, 10000, 12000, 15000, 20000, 50000, 80000, 100000, 150000, 180000, or 200000. The resistivity of the water (in Q m) may be in a range provided by any two of these upper and / or lower values, for example about 100000 to about 200000.

[0140] The at least one post-transition metal and the liquid may be present in any suitable amount or ratio. The ratio may be suitably selected based on any one of the following: the electromagnetic radiation, the liquid, the reactor, the reactor design, the at least one post-transition metal (which may be an alloy or mixture as described herein), and the form or size of the at least one post-transition metal.

[0141] In some embodiments, the amount of the at least one post-transition metal (or post-transition metal alloy or mixture) in the liquid (in % v / v) may be about, or at least about: 0.001, 0.002, 0.005, 0.008, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1, 0.2, 0.3, 0.5, 0.7, 1, 2.5, 5, 7.5, 10, 15, or 20. In one embodiment, the amount of the post- transition metal or post-transition metal alloy in the liquid (in % v / v) may be less than about: 20, 15, 10, 7.5, 5, 2.5, 1, 0.7, 0.5, 0.3, 0.2, 0.1, 0.07, 0.05, 0.03, 0.01, 0.008, 0.005, 0.002, or 0.001. Theamount of the post- transition metal or post-transition metal alloy in the liquid (in % v / v) may be in an amount provided by any two of these upper and / or lower values, for example between about 0.008 and about 0.08, or between about 0.02 to about 0.08. In one embodiment, the amount of the at least one post-transition metal in the liquid is about 0.02% v / v.

[0142] In some embodiments, the amount of the at least one post-transition metal (or post-transition metal alloy or mixture) in the liquid (in %w / v) may be about, or at least about, 0.06, 0.12, 0.3, 0.5, 0.6, 1.2, 3, 5, 6, 12, 30, 50, 60, or 120. In one embodiment, the amount of the post- transition metal or post-transition metal alloy in the liquid (in % w / v) may be less than about: 120, 60, 50, 30, 12, 6, 5, 3, 1.2, 0.6, 0.5, 0.3, 0.12, or 0.06. The amount of the post- transition metal or post-transition metal alloy in the liquid (in % w / v) may be in an amount provided by any two of these upper and / or lower values, for example between about 0.05 to about 0.5, or between about 0.12 and about 0.5. In one embodiment, the amount of the at least one post-transition metal in the liquid is about 0.12% w / v.Oxidation Process Conditions

[0143] The temperature of the liquid in which the process occurs can vary. The temperature of the liquid may be close to the boiling point of the liquid. The temperature of the liquid may be above the melting point of the at least one post-transition metal, which may advantageously provide (or maintain) the at least one post-transition metal in a liquid state. In some embodiments, the temperature of the liquid (in °C), for at least part of the process, may be about, or less than about 500, 450, 400, 350, 300, 275, 250, 225, 200, 175, 150, 125, 110, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 8, 6, 4, 2, or 1. In some embodiments, the temperature of the liquid (in °C), for at least part of the process, may be more than about: 1, 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 125, 150, 175, 200, 225, 250, 275, 300, 350, 400, 450, or 500. The temperature of the liquid (in °C) may be in a range provided by any two of these upper and / or lower values, for example, between about 2 and about 500, between about 2 and 300, or between about 4 and 100. Over the course of the process the temperature may be changed once or a plurality of times.

[0144] The vapor pressure exerted by liquid or one more solvents dispersed in the liquid may vary. In some embodiments, optionally where the liquid comprises or substantially comprises water, at least part of the process may be conducted such that the water exerts a vapor pressure (in kPa) of less than about: 20000, 17500, 15000, 12500, 10000, 7500, 5000, 3000, 2000, 1000, 750, 500, 300, 200, 150, 125, 101.3, 100, 75, 50, 40, 30, 20, 10, 5, 2, 1, or 0.5. In some embodiments, optionally where the liquid comprises or substantially comprises water, at least part of the process may be conducted such that the water exerts a vapor pressure (in kPa) of about, or at least about: 0.5, 1, 2, 5, 10, 20, 30, 40 ,50, 75, 100, 101.3, 125, 150, 200, 300, 500, 750, 1000, 2000, 3000, 5000, 7500, 10000, 12500, 15000, 17500, or 20000. At least part of the process may be conducted such that solvent substantially comprising water exerts a vapour pressure in a range provided by any two of these upper and / or lower values, for example between about 0.5 and 101.3.

[0145] The pressure under which the process is conducted can vary. In some embodiments, at least part of the process may be conducted at a pressure (in kPa) of about, or less than about: 20000, 17500, 15000, 12500, 10000, 7500, 5000, 3000, 2000, 1000, 750, 500, 300, 200, 150, 125, or 101.3. In some embodiments, at least part of the process may be conducted at a pressure (in kPa) of at least about: 101.3, 125, 150, 200, 300, 500, 750, 1000, 2000, 3000, 5000, 7500, 10000, 12500, 15000, 17500, or 20000. At least part of the process may be conducted under a pressure (in kPa) in a range provided by any two of these upper and / or lower values, for example, between about 101.3 and about 500. In one embodiment, the process is conducted at a pressure of about 101.3 kPa. In some embodiment, the process is conducted at substantially atmospheric pressure.

[0146] It will be appreciated that the oxidation process conditions may be selected depending on the at least one post-transition metal being used.Time

[0147] In one embodiment there is no time limit on the application of electromagnetic radiation to at least one post-transition metal, or alloy or mixture thereof, in contact with a liquid comprising at least one oxygen-containing species, as described herein. For a method or process or use as described herein, the application of the electromagnetic radiation may be applied until a sufficient or required amount of hydrogen has evolvedand / or there is a plateau in the evolution of hydrogen, which may be followed by the reduction of any oxidised post-transition metal species. In one embodiment, for a method or process or use as described herein, electromagnetic radiation is applied to at least one post-transition metal, or alloy or mixture thereof, for a period of about, or at least about (in minutes): of 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60. The timing may be affected by a number of factors including, but not limited to the type and / or intensity of the electromagnetic radiation, varying the temperature and / or the concentration of the at least one post-transition metal, or alloy or mixture thereof.Solid support

[0148] The at least one post-transition metal may be provided on a solid support, which is optionally a porous solid support. In some embodiments, the solid support is conductive. In some embodiments, the solid support may be a metallic or carbon support. The solid support may be suitably selected to improve the efficiency of the oxidation reaction and / or the reduction reaction.

[0149] The solid support may be one or more selected from, but not limited to: metal oxides, ceramics, carbon materials, metals, and polymeric materials. In some embodiments, the solid support may be one or more selected from aluminium oxide, silicon dioxide, titanium dioxide, zeolites, mesoporous silica, zirconia, magnesium oxide, glass fibre, activated carbon, carbon black, carbon nanotubes, graphene, carbon paper, carbon cloth, carbon fibre, stainless steel, nickel, polystyrene, polyethylene glycol, polymethyl methacrylate, polyacrylate, poly vinylidene difluoride, polyethylene terephthalate, and polycarbonate.

[0150] The solid support may be added at any suitable time during the process. For example, in embodiments where the at least one post-transition metal is provided in the form of particles, the solid support may be added during fabrication of the at least one post-transition metal particles, to provide the solid supported post-transition metal particles. In another embodiment, the solid support may be added to particles of the at least one post-transition metal (i.e., after fabrication of the at least one post-transition metal particles), to provide the solid supported post-transition metal particles.

[0151] Herein the size of one or more solid support is not limited, but may be tailored for a specific reaction or set of conditions, for example the size of a reactor being used for one or more reactions. In one embodiment, one or more solid supports may be on the macro-scale. In another embodiment, one or more solid supports may be selected from, but not limited to: carbon fiber cloth, carbon paper, woven or non-woven metal sheets, plain metal sheets, polymer-based sheets, or mixtures thereof. In another embodiment, porous and gel-like supports, such as hydrogels and aerogels made from organic or inorganic materials, may also be used as a solid support. The size of one or more solid supports may be on the scale of millimetres to centimetres or even meter-sized sheet supports.Reduction process

[0152] The process of the present disclosure may further comprise a step of reducing the at least one oxidised post-transition metal species to produce the at least one posttransition metal.

[0153] In one embodiment one or more of the at least one oxidised post-transition metal species may be reduced via electrolysis to regenerate at least one post-transition metal, or alloy, or mixture thereof, can be electrolytically reduced, allowing metal regeneration.

[0154] The reduction step may be conducted in an appropriate media, for example in acidic, alkaline, or neutral ionic media. Appropriate types and concentrations of electrolytes (e.g. KC1), may be present.

[0155] The reduction step may be tailored by varying one or more parameters, selected from, but not limited to: presence and / or selection of electrolyte composition, pH, current density and potential of the cells, and mixtures thereof.

[0156] Advantageously, as described herein and as shown in the Examples, the oxidised post-transition metal species can be subjected to reduction in order to reproduce the post-transition metal, which can then undergo further oxidation to produce hydrogen in a circular process. This can beneficially avoid the need for continuous addition of the at least one post-transition metal, which may lower operational costs and resource consumption. Further, as shown in the Examples, reduction of the oxidised post-transition metal was achieved with a high theoretical round-trip efficiency of above about 50%.

[0157] Accordingly, the present disclosure also provides a circular process for producing hydrogen, the process comprising:(a) applying electromagnetic radiation to a least one post-transition metal in contact with a liquid comprising at least one oxygen-containing species, thereby causing oxidation of the at least one post-transition metal to produce an oxidised post-transition metal species and hydrogen,(b) reducing the oxidised post-transition metal species to reproduce the at least one post-transition metal, and(c) optionally repeating steps (a) and (b)

[0158] The reduction step of the at least one oxidised post-transition metal species may be conducted by an appropriate method in the art. For example, a method as described in US3966568A or Illes et al., J. Environ. Chem. Eng. 11 (2023) 110391, the contents of which are incorporated by reference.

[0159] The at least one oxidised post-transition metal species may dissolved, or dissociated, in an acidic, alkaline, or neutral ionic media, prior to the reduction step. This may assist in converting the at least one oxidised post-transition metal species to a soluble species (e.g. a soluble Ga(III) species), which can allow the reduction step to proceed in the same medium. Examples of suitable alkaline media include, but are not limited to, sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution, and combinations thereof. Examples of suitable acidic media include, but are not limited to, hydrochloric acid (HC1) solution, sulfuric acid (H2SO4) solution, nitric acid (HNO3) solution, and combinations thereof, solutions. Examples of suitable neutral ionic media include sodium chloride (NaCl) solution.

[0160] Accordingly, in some embodiments, the method further comprises a step of dissolving, or dissociating, the oxidised post-transition metal species in an acidic, alkaline, or neutral ionic media, prior to the reduction step. In some embodiments, theoxidised post-transition metal species is dissolved, or dissociated, in an acidic or alkaline media, prior to the reduction step.

[0161] In some embodiments, the oxidised post-transition metal species is dissolved, or dissociated, in an acidic medium, prior to the reduction step. Advantageously, as shown in the Examples, the dissolution of GaOOH was found to be more favourable in acidic (HC1) solution over alkaline (NaOH, KOH) solution. The acidic medium may further comprise a salt, such as a chloride containing salt (e.g. NaCl), which can further promote the dissociation reaction.

[0162] In some embodiments, the acidic medium is hydrochloric acid solution. Advantageously, the present inventors have found that hydrochloric acid solution may exhibit higher efficiency for dissociation of GaOOH over other acid media such as sulfuric acid solution. Any suitable concentration of hydrochloric acid solution may be used. For example, the concentration of the hydrochloric acid solution (in M) may be about, or more than about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, or a range provided by any two of these values, for example, between 2 and 12. In some embodiments, the concentration of the hydrochloric acid solution is about, or more than about, 2 M.

[0163] The dissolving step may be performed at elevated temperature, which can further promote the dissociation reaction. For example, the temperature of the media (in °C), for at least part of the dissolving step, may be about, or more than about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, or 110, or a range provided by any two of these values, for example, between 80 to 110. In some embodiments, the dissolving step is performed at about, or more than about, 90 °C. The dissolving step may be conducted at temperatures above the boiling point of the media, with the media maintained under pressure in a sealed reactor, such as an autoclave.

[0164] The dissolving step may additionally, or alternatively, be performed with mechanical agitation (e.g. stirring) and / or sonication, which can further promote the dissociation reaction.

[0165] In one embodiment, the reduction of the at least one post-transition metal oxide is performed via electrolysis. Advantageously, as shown in the Examples, the reduction of oxidised post-transition metal via electrolysis can be conducted at low voltage, whichmay allow for a circular process for producing hydrogen with low energy consumption. The electrolysis may be performed in an acidic, alkaline, or neutral ionic media, which may be the acidic, alkaline, or neutral ionic media of the dissolving step described herein. In some embodiments, the electrolysis is performed in an acidic media, which may be an acidic media as described in relation to the dissolving step. In some embodiments, the electrolysis is performed in aqueous hydrochloric acid (HC1). The concentration of the hydrochloric acid solution (in M) may be about, or more than about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, or a range provided by any two of these values, for example, between 2 and 12. In some embodiments, the concentration of the hydrochloric acid solution is about, or more than about, 2 M.

[0166] The reduction step may be conducted using renewable energy sources, such as solar or wind. This may beneficially allow for a circular process for producing green hydrogen.Additional embodiments

[0167] The present disclosure also provides one or more post-transition metals when used in any of the processes according to the present disclosure, wherein the at least one post-transition metal does not comprise aluminium. The present disclosure also provides the use of at least one post-transition metal for producing hydrogen in a process according to the present disclosure, wherein the at least one post-transition metal does not comprise aluminium. In some embodiments, the at least one post-transition metal comprises or is gallium.

[0168] The present disclosure also provides hydrogen produced by any of the processes according to the present disclosure.EXAMPLE EMBODIMENTS

[0169] The present disclosure may be described by one or more of the following example embodiments.1. A process for producing hydrogen, the process comprising:applying electromagnetic radiation to at least one post-transition metal in contact with a liquid comprising at least one oxygen-containing species, thereby causing oxidation of the at least one post-transition metal to produce an oxidised post-transition metal species and hydrogen,wherein the at least one post-transition metal does not comprise aluminium.2. The process according to example embodiment 1, wherein the electromagnetic radiation is selected from any one or more of extremely low frequency electromagnetic fields, radio waves, microwaves, infrared , thermal radiation (heat), visible light, ultraviolet, X-rays, and gamma rays, preferably one or more of extremely low frequency electromagnetic fields, radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.3. The process according to example embodiment 1 or example embodiment 2, wherein the electromagnetic radiation has a wavelength of about 200 nm to about 2500 nm, preferably about 380 nm to about 2500 nm, more preferably about 380 nm to about 780 nm.4. The process according to any one of the preceding example embodiments, wherein the source of the electromagnetic radiation is selected from one or more of sunlight; an artificial light source such as a halogen lamp, a fluorescent lamp or a lightemitting diode; a laser; an electromagnetic field (EMF)-emitting device; a mobile phone; a Wi-Fi device; a terahertz radiation-emitting device; a microwave; an infrared heater; an induction heater; an ultraviolet lamp; an X-ray device; a gamma source; and mechanical agitation.5. The process according to any one of the preceding example embodiments, wherein the at least one post-transition metal is in a liquid state.6. The process according to any one of the preceding example embodiments, wherein the at least one post-transition metal is selected from any one or more of gallium, indium, tin, bismuth, mercury, lead, and antimony.7. The process according to any one of the preceding example embodiments, wherein the at least one post-transition metal comprises or is gallium.8. The process according to example embodiment 7, wherein the oxidised posttransition metal species comprises or is a gallium (III) species, preferably gallium oxyhydroxide.9. The process according to any one of the preceding example embodiments, wherein the at least one post-transition metal is provided as a pure metal, or a substantially pure metal.10. The process according to any one of the preceding example embodiments, wherein the at least one post-transition metal is provided as an alloy or mixture, wherein the alloy or mixture does not comprise aluminium.11. The process according to example embodiment 10, wherein the at least one post-transition metal is provided as an alloy or mixture with any one or more of a posttransition metal, a transition metal, an alkali metal, a rare earth element, and a noble metal.12. The process according to any one of the preceding example embodiments, wherein the at least one post-transition metal is provided in the form of particles, preferably wherein at least a portion of the particles have a particle size of less than about 1 cm, or less than about 1 mm, or less than about 100 pm, or less than about 10 pm, or less than about 1 pm.13. The process according to any one of example embodiments 1 to 11, wherein the at least one post-transition metal is provided in the form of a film, such as a thin film.14. The process according to any one of the preceding example embodiments, wherein the liquid comprising at least one oxygen-containing species is selected from an aqueous liquid, an organic liquid, and mixtures thereof.15. The process according to any one of the preceding example embodiments, wherein the liquid comprising at least one oxygen-containing species comprises one or more of: water, methanol, ethanol, glycerol, ethylene glycol, propylene glycol, dimethyl sulfoxide, toluene, tetradecane, octane, hexane, pentane, hydrofluoroether 7500, methyl tert-butyl ether, acetone, isopropanol, chloroform, 1,2-di chlorobenzene,and mixtures thereof such as a water methanol mixture, a water ethanol mixture, and a water glycerol mixture.16. The process according to any one of the preceding example embodiments, wherein the liquid comprising at least one oxygen-containing species comprises or is an aqueous liquid.17. The process according to example embodiment 16, wherein the aqueous liquid is or comprises one or more of: wastewater, processed wastewater, rainwater, brackish water, sea water, and mixtures thereof.18. The process according to example embodiment 16 or example embodiment 17, wherein for at least part of the process, the process is conducted such that the temperature of the aqueous liquid is from about 4 °C to about 100 °C.19. The process according to any one of example embodiments 16 to 18, wherein for at least part of the process, the process is conducted such that the aqueous liquid has a vapour pressure from about 3 kPa to about 16500 kPa, preferably from about 3 kPa to about 101 kPa.20. The process according to any one of the preceding example embodiments, wherein for at least part of the process, the process is conducted at substantially atmospheric pressure.21. The process according to any one of the preceding example embodiments, wherein the at least one post-transition metal, preferably gallium, is disposed on a solid support, optionally a porous solid support.22. The process according to example embodiment 21, wherein the solid support comprises or consists of one or more materials selected from metal oxides, ceramics, carbon materials, metals, polymeric materials, and mixtures thereof.23. The process according to example embodiment 21 or example embodiment 22, wherein the solid support comprises or consists of one or more materials selected from aluminium oxide, silicon dioxide, titanium dioxide, zeolites, mesoporous silica, zirconia, magnesium oxide, glass fibre, activated carbon, carbon black, carbon nanotubes, graphene, carbon paper, carbon cloth, carbon fibre, stainless steel, nickel,polystyrene, polyethylene glycol, polymethyl methacrylate, polyacrylate, polyethylene terephthalate, and polycarbonate, and mixtures thereof.24. The process according to any one of the preceding example embodiments, wherein the process further comprises:reducing the oxidised post-transition metal species, thereby reproducing the at least one post-transition metal.25. The process according to example embodiment 24, wherein the oxidised posttransition metal species is reduced via electrolysis.26. The process according to claim 24 or claim 25, wherein the process further comprises dissolving the oxidised post-transition metal species in an acidic, alkaline, or neutral ionic media, preferably an acidic media, prior to the reduction step.27. Use of at least one post-transition metal for producing hydrogen in a process according to any one of example embodiments 1 to 26, wherein the at least one posttransition metal does not comprise aluminium.28. The use according to example embodiment 27, wherein the at least one posttransition metal is recycled or is extracted from a source comprising the at least one post-transition metal.29. The use according to example embodiment 27 or example embodiment 28, wherein the at least one post- transition metal comprises or is gallium.30. Hydrogen produced by the process according to any one of example embodiments 1 to 26.EXAMPLESMaterials

[0170] Gallium beads (99.999% purity) and indium (99.999% purity) were purchased from Indium Corporation (USA) and ethanol absolute (99.5% purity) was purchased from Merck Australia. Mili-Q water, resistivity 18.2 MQ cm @ 25 °C; total organic carbon (TOC) < 5 ppb was used for the oxidation reactions. Simulated seawater solutions were prepared with a sodium chloride concentration of 0.18 M (NaCl, >99%, ChemSupply, Australia). A seawater sample was collected from nearshore waters at the beach face in the eastern suburbs of Sydney, Australia, and filtered through a 0.45 pm syringe filter prior to use.Analytical methods

[0171] A Nexis GC-2030 gas chromatograph (Shimadzu, Japan) was used to analyze the gas composition and quantify evolved products during the hydrogen production experiments. The instrument is equipped with a thermal conductivity detector (TCD) and a high-precision column suitable for detecting hydrogen (IL).

[0172] SEM, SEMZEDX, and size distribution measurements were performed using a Thermo Scientific Phenom XL SEM with Integrated EDS system and thermoelectrically cooled silicon drift detector for imaging and elemental mapping at an accelerating voltage of 15.0 kV. Particle size distributions were estimated from SEM images. Image analysis was performed using Photoshop or ImageJ

[0173] Raman spectroscopy was performed using a Renishaw Raman in Via Qontor with upright microscope instrument using a 532 nm laser source (50 mW). Exposure time was 10 s at 10% laser power.

[0174] XPS elemental analysis and valence band analysis were conducted using a Thermo Scientific ESCALAB 250 Xi, mono-chromated Al Ka X-ray spectrometer.

[0175] XRD patterns were obtained using a Rigaku-Smart lab-SE instrument with a scanning range of 10° to 120° for the sonicated nanoparticle before reaction and scanning range of 10° to 90° for the particle post reaction at a scan rate of 1.09 min-1 ( = 1.5418 A, Cu-Ka radiation).

[0176] The Ga concentrations were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES, PerkinElmer, USA).

[0177] Electroreduction electrochemical experiments were performed using an electrochemical station (CHI650E, CH Instruments Inc., USA), with a three-electrode cell using platinum as working electrode, saturated calomel electrode as the reference electrode, and graphite as the counter-electrode.

[0178] Further electrochemical characterization and electro-reduction experiments were performed using an electrochemical workstation (CHI650E, CH Instruments Inc., USA), a three-electrode cell using carbon paper (MGL280, AMS, USA) as working electrodes, a saturated calomel electrode as the reference electrode, and a graphite rod as the counter-electrode. Linear sweep voltammetry curves and chronoamperometry were carried out in N2-saturated 1.0 M HC1 electrolyte. The linear sweep voltammetry was performed at a scan rate of lOmVs"1. All polarization curves were automatically adjusted to account for the iR contribution from the cell. The recorded potential was converted to a reversible hydrogen electrode (RHE) according to the Nemst equation: ERHE=ESCE + 0.241+0.059 pH.

[0179] Prior to electro-recovery, GaOOH was treated with 2 M HC1 at 90 °C for 6 hours to convert it into a soluble Ga3+species via acid-mediated leaching.

[0180] To quantify Ga recovery, the carbon paper electrode was weighed in its dried state both before and after the electro-recovery process. In addition to the Ga deposited on the carbon paper, any Ga droplets that detached during electroreduction and accumulated in the electrolyte bath were also collected, dried, and weighed. The total recovered mass was calculated as the sum of Ga retained on the carbon paper and Ga collected from the bath.

[0181] Electrochemical measurements were conducted in a controlled laboratory environment at an average room temperature of 21°C. Photocurrents and polarization potentials were recorded using a liquid Ga drop as the working electrode connected to a gold wire within a glass capillary.

[0182] UV-vis spectroscopy was performed to obtain the optical absorption spectra and bandgaps of the composites using a Shimazu UV-3600i Plus Shimazu.Example 1: Evaluating the effect of photoirradiation on gallium metal

[0183] The effect of photoirradiation of bulk gallium metal on the polarization potential of the gallium metal and the photocurrent was evaluated by performing measurements of open circuit potentials using the setup in shown in Figure lb. The current across the cell was measured over a duration of 300 seconds, during which the gallium metal was exposed to periodic cycles of visible light irradiation and darkness. It was observed that the current across the cell increased when irradiation occurred and decreased when visible light irradiation ceased. This response was observed for all instances of the visible light irradiation / darkness cycle (Figure 2). The polarization potential of the gallium metal was also measured and was shown to increase when the gallium metal was irradiated with visible light (Figure 3).Example 2: Synthesis and characterisation of gallium particles

[0184] To prepare gallium metal particles, gallium metal (0.2 g) was placed into a borosilicate glass vial (21 mL) and the vial placed onto a hot plate set at 70 °C for 15 minutes to melt of the gallium metal. Following the melting process, ethanol (10 mL) was added to the borosilicate glass vial and the mixture was immediately subjected to ultrasonication at room temperature using a 1 / 8” sonication probe (SONICS VCX750, 750W set at 40% amplitude and 20 kHz) inside a closed isolation cabinet. Ethanol was used to avoid excessive preliminary oxidation of the liquid gallium metal. After sonication, the ethanol was allowed to evaporate at room temperature to obtain the gallium metal particles. Milli-Q water (10 mL) was added to the dried gallium metal particles and the mixture was subjected to bath sonication for 2 minutes to disperse the particles.

[0185] By varying the time of the ultrasonication step the size of the gallium metal particles could be controlled. Samples were sonicated for durations of 5, 10, 20, or 30 min to produce samples of particles with varying size (Figure 4). Particle size was measured by SEM analysis using image processing software and was estimated to be 1.3 pm, 990 nm, 720 nm, and 640 nm for the 5 min, 10 min, 20 min, and 30 minultrasonication samples, respectively. The visible light absorption of the various samples was measured using UV-Vis spectroscopy (Figure 5). Particle size did not appear to directly correlate with the overall light absorption of the samples.

[0186] Eutectic gallium-indium alloy (EGain, 75.5 wt% Ga and 24.5 wt% In) was prepared by melting the two metals on a hot plate for 2 hours. EGain particles were then produced by sonication, following a procedure similar to that used for synthesizing Ga metal particles.Example 3: Hydrogen production using gallium particles

[0187] Tests were performed to determine the effect of various reaction parameters on the ability of gallium metal particles produced in Example 2 to produce hydrogen gas. The hydrogen produced during the test reactions was quantified and stored using the water displacement technique, wherein hydrogen gas was collected in a 250 ml graduated glass column (collection vessel) by filling it with water and submerging it open side down in a vessel filled with water. The reaction vessel was connected to the collection vessel via a tube. As hydrogen gas was generated in the reaction vessel it displaced water from the collection vessel. The volume of gas collected was measured by observing the change in water level in the graduated glass column (collection vessel), providing quantification via the graduated markings on the column. The following test were performed to assess reaction parameters:Effect of particle size on hydrogen production

[0188] Hydrogen gas production using gallium metal of different particle sizes, produced from the different sonication durations, was measured. A photo reactor was set up with gallium particles (0.2 g) placed in 10 ml of water and exposed to a commercial halogen lamp (600 W / cm2irradiation, emitting visible light in the 400 to 800 nm range). It was observed that smaller particles facilitated faster hydrogen production and a greater total yield of hydrogen for a given intensity of light irradiation (Figure 6).

[0189] A comparative experiment using bulk (un- sonicated) gallium metal was also performed with irradiation at 600 W / cm2. The bulk gallium metal was found to be far less effective in producing hydrogen than any of the sonicated particles (Figure 7).Hydrogen production using gallium-indium alloyHydrogen gas production using a eutectic alloy of gallium and indium (EGain) was measured with irradiation at 600 mW / cm2. The reaction rates were lower for the EGain systems, as compared to pure Ga. The use of particulate EGain (average particle size 400 nm) achieved a production rate of -76.5 mL g'1h'1, whereas the rate was much lower using bulk EGain (Figure 8). The yields, which were calculated based on the theoretical amount of Ga in the alloy, reached 21% after 36 h and 90% after 4.25 h for the bulk and particulate EGain, respectively .Effect of light intensity on hydrogen production

[0190] A series of measurements were conducted to evaluate the effect of light intensity on hydrogen production. A photo reactor was set up with 640 nm Ga particles (0.2 g) placed in 10 ml of water and exposed to a commercial halogen lamp (50W, emitting visible light in the 400 to 800 nm range). The reactor was positioned at varying distances (0.2 cm, 2 cm, 4 cm, and 5 cm) from the lamp to achieve different energy absorption levels. Experiments were conducted for 5 hours.

[0191] Calculations showed that at 0.2 cm, the energy density was 600 W / cm2, approximately equivalent to 6 Suns. The energy densities at other distances were 450 W / cm2at 2 cm, 270 W / cm2at 4 cm, and 230 W / cm2at 5 cm. The system provided both visible light and heat to the samples. Maximum hydrogen output was achieved at 600 W / cm2, with complete hydrogen production of approximately 100 mL of hydrogen and complete gallium oxidation occurring after 90 minutes of irradiation at this intensity. As light intensity decreased, hydrogen production also diminished. At 270 W / cm2, production was minimal, while at 300 W / cm2and 350 W / cm2, hydrogen production reached 38 mL and 56 mL by the maximum time of 5 hours, respectively (Figure 9). Temperature measurements showed that the light irradiation intensity caused heating of the liquid containing Ga particles, with temperatures ranging from 93 °C at 600 W / cm2to 51 °C at 230 W / cm2(Figure 10).Effect of temperature in absence of light on hydrogen production

[0192] In order to determine the effect of temperature in absence of light on hydrogen production, measurements were conducted in which the 30-minute sonicated (640 nm) gallium metal particles in water were heated without exposure to light. Vials were placed on top of hotplates with temperatures adjusted to bring the 10 ml of DI water inside ofthe vials to temperatures ranging from 40 to 90°C. For the samples with temperatures of 0 °C and 20 °C the vials were placed inside of a container filled up with ice or left on top of an OFF hotplate, respectively. The vials were kept in the dark with no-exposure to light and the hydrogen gas production measured. The experiments were conducted for 5 hours.

[0193] In the absence of light, complete hydrogen production was not possible within the measured time period. The samples not exposed to light consistently produced less hydrogen and at a slower rate than their light irradiated counterparts (Figure 11). Even when heated to 90°C, hydrogen production in darkness reached a total of only 42 mL after 90 minutes, less than half the amount produced at a comparable temperature when irradiated with visible light. The samples at 0 °C and 20 °C produced a negligible amount of hydrogen.Effect of water salinity

[0194] The effect of the salinity of the water on the production of hydrogen was evaluated. Samples were made using 0.2 g of 620 nm gallium particles in 10 mL of Milli-Q water or salt water (25 g / L NaCl in Milli-Q water). The samples were irradiated with visible light at an intensity of 600 W / cm2and the hydrogen production measured. The experiments were conducted until hydrogen gas production ceased.

[0195] As shown in Figure 12, the use of saltwater in place of DI water had an insignificant effect on the rate of hydrogen production and minimal effect on the total hydrogen produced by the system. This indicates the relative insensitivity of the gallium metal particle system to the salinity of the water.Example 4: Characterisation of the photooxidation product and regeneration of gallium metal.

[0196] Characterization of the gallium particles before and after photooxidation was performed using SEM imaging, X-ray diffraction, and Raman spectroscopy. SEM images (Figure 13) showed the progressive conversion of pure gallium metal droplets into crystalline gallium oxyhydroxide (GaOOH) as photooxidation progressed. X-ray diffraction (XRD) and Raman spectroscopy analysis confirmed the transformation of gallium metal to gallium oxyhydroxide after the photooxidation process (Figure 14).Furthermore, X-ray photoelectron spectroscopy (XPS) analysis indicated that after the complete consumption of gallium metal no residual liquid gallium remained and all material had been converted to gallium oxyhydroxide (Figure 15).

[0197] Regeneration efficiency of the gallium metal from the gallium oxyhydroxide was evaluated using a 2-electrode setup (shown in figure 16a). Samples were dissolved in IM H2SO4 and linear sweep voltammetry of the gallium oxyhydroxide was performed using a glassy carbon electrode and a carbon paper electrode. The results showed that reduction of gallium oxyhydroxide can be a low-energy -intensive process (Figure 16b). The presence of metallic gallium post reduction was confirmed by SEM with integrated EDS (Figure 16c), verifying the effectiveness of the reduction of gallium oxyhydroxide to regenerate the gallium metal.Example 5: Further characterisation of the photooxidation product and regeneration of gallium metal.

[0198] Following H2 generation, Ga was successfully recovered from the photothermal reactor via electrochemical reduction, with a recovery efficiency of approximately 95% by weight relative to the initial Ga used (Figure 17). XRD analysis of both the Ga recovered on the carbon substrate and the detached Ga after a reaction cycle revealed the characteristic broad peak of amorphous Ga, with no detectable gallium oxide crystalline by-products or alloying phases (Figure 18), confirming that the Ga remained chemically unaltered during the reaction.

[0199] A standard electrochemical reduction setup was used in an acidic electrolyte at a low concentration (1.0 M HC1), as schematically presented in Figure 15a. The Ga electrode reaction (GER) was observed simultaneously with the hydrogen evolution reaction (HER) as seen in Figure 19 on carbon paper (CP) electrode substrates. In the potential region of -0.8 to -1.5 V, reduction currents begin at -0.095 V for Ga(III) on CP. The potential at 10 mA / cm2is -1.017 V vs RHE for the electroreduction of Ga(III) on CP. The initial cathodic current reflects the initiation of GER and HER, while the subsequent steady-state current sustained HER activity, highlighting the reducibility of Ga(III). No O is seen in the Ga droplets and Ga is formed in a fully reduced metallic state. The presence of metallic Ga post-reduction is confirmed by the observedmorphology and EDS analysis verifying the elemental composition, demonstrating a successful reduction process into metallic Ga (Figure 20).

[0200] While GaOOH has been rarely studied as a precursor for reduction to metallic Ga, we propose that the ability of GaOOH to dissociate into Ga(III) species in an ionic form such as Ga3+ions in acidic environments may advantageously enable a more efficient reduction reaction.

[0201] Prior to electro-recovery, GaOOH was dissociated in 2 M HC1 at 90 °C for 6 h to convert it into a soluble Ga3+species via acid-mediated leaching, allowing electroreduction to proceed in the same reaction medium. While alkaline pathways are often employed for Ga electro-recovery, the dissolution of GaOOH in bases such as NaOH and KOH was found to be less favourable, with GaOOH remaining stable over several days (shown in Figure 21). The 2M HC1 solution became visibly clear after 6 hours, indicating complete dissolution of GaOOH, whereas the alkaline solutions retained suspended solid phases.

[0202] Dissociation of GaOOH to Ga3+was found to be preferred in HC1 at concentrations above 2 M and at temperatures at or above 90 °C. For example, at higher concentrations of 12 M HC1, the dissociation reaction proceeded within a few minutes at 90 °C under agitation.

[0203] After electroreduction of the soluble Ga(III), the recovered Ga was processed into particles following the same sonication procedure and reintroduced into the photothermal oxidation reactor. The H2 yield using the recovered Ga was 99.4% (Figure 22).

[0204] Other possibilities for circular recovery involve the dissolution of GaOOH into Ga(III) ions in sodium hydroxide, followed by electrodeposition onto other metal electrodes.

[0205] In addition, due to the liquid state of Ga under operating conditions inside the photothermal reactor, the regenerated metal avoids crystallographic trapping, ensuring sustained oxyhydroxidation reactivity upon recycling

[0206] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS1. A process for producing hydrogen, the process comprising:applying electromagnetic radiation to at least one post-transition metal in contact with a liquid comprising at least one oxygen-containing species, thereby causing oxidation of the at least one post-transition metal to produce an oxidised post-transition metal species and hydrogen,wherein the at least one post-transition metal does not comprise aluminium.

2. The process according to claim 1, wherein the electromagnetic radiation is selected from any one or more of extremely low frequency electromagnetic fields, radio waves, microwaves, infrared , thermal radiation (heat), visible light, ultraviolet, X-rays, and gamma rays.

3. The process according to claim 1 or claim 2, wherein the electromagnetic radiation has a wavelength of about 380 nm to about 2500 nm, preferably about 380 nm to about 780 nm.

4. The process according to any one of the preceding claims, wherein the source of the electromagnetic radiation is selected from one or more of sunlight; an artificial light source such as a halogen lamp, a fluorescent lamp or a light-emitting diode; a laser; an electromagnetic field (EMF)-emitting device; a mobile phone; a Wi-Fi device; a terahertz radiation-emitting device; a microwave; an infrared heater; an induction heater; an ultraviolet lamp; an X-ray device; a gamma source; and mechanical agitation.

5. The process according to any one of the preceding claims, wherein the at least one post-transition metal is in a liquid state.

6. The process according to any one of the preceding claims, wherein the at least one post-transition metal is selected from any one or more of gallium, indium, tin, bismuth, zinc, mercury, lead, and antimony.

7. The process according to any one of the preceding claims, wherein the at least one post-transition metal comprises or is gallium.

8. The process according to claim 7, wherein the oxidised post-transition metal species comprises or is a gallium (III) species, preferably gallium oxyhydroxide.

9. The process according to any one of the preceding claims, wherein the at least one post-transition metal is provided as a pure metal, or a substantially pure metal.

10. The process according to any one of the preceding claims, wherein the at least one post-transition metal is provided as an alloy or mixture, wherein the alloy or mixture does not comprise aluminium.

11. The process according to claim 10, wherein the at least one post-transition metal is provided as an alloy or mixture with any one or more of a post-transition metal, a transition metal, an alkali metal, a rare earth element, and a noble metal.

12. The process according to any one of the preceding claims, wherein the at least one post-transition metal is provided in the form of particles, preferably wherein at least a portion of the particles have a particle size of less than about 1 cm, or less than about 1 mm, or less than about 100 pm, or less than about 10 pm, or less than about 1 pm.

13. The process according to any one of claims 1 to 11, wherein the at least one post-transition metal is provided in the form of a film, such as a thin film.

14. The process according to any one of the preceding claims, wherein the liquid comprising at least one oxygen-containing species is selected from an aqueous liquid, an organic liquid, and mixtures thereof.

15. The process according to any one of the preceding claims, wherein the liquid comprising at least one oxygen-containing species comprises one or more of: water, methanol, ethanol, glycerol, ethylene glycol, propylene glycol, dimethyl sulfoxide,toluene, tetradecane, octane, hexane, pentane, hydrofluoroether 7500, methyl tert-butyl ether, acetone, isopropanol, chloroform, 1,2-di chlorobenzene, and mixtures thereof such as a water methanol mixture, a water ethanol mixture, and a water glycerol mixture.

16. The process according to any one of the preceding claims, wherein the liquid comprising at least one oxygen-containing species comprises or is an aqueous liquid.

17. The process according to claim 16, wherein the aqueous liquid is or comprises one or more of: wastewater, processed wastewater, rainwater, brackish water, sea water, and mixtures thereof.

18. The process according to claim 16 or claim 17, wherein for at least part of the process, the process is conducted such that the temperature of the aqueous liquid is from about 4 °C to about 100 °C.

19. The process according to any one of claims 16 to 18, wherein for at least part of the process, the process is conducted such that the aqueous liquid has a vapour pressure from about 3 kPa to about 16500 kPa, preferably from about 3 kPa to about 101 kPa.

20. The process according to any one of the preceding claims, wherein for at least part of the process, the process is conducted at substantially atmospheric pressure.

21. The process according to any one of the preceding claims, wherein the at least one post-transition metal is disposed on a solid support, optionally a porous solid support.

22. The process according to claim 21, wherein the solid support comprises or consists of one or more materials selected from metal oxides, ceramics, carbon materials, metals, polymeric materials, and mixtures thereof.

23. The process according to claim 21 or claim 22, wherein the solid support comprises or consists of one or more materials selected from aluminium oxide, silicon dioxide, titanium dioxide, zeolites, mesoporous silica, zirconia, magnesium oxide, glass fibre, activated carbon, carbon black, carbon nanotubes, graphene, carbon paper, carbon cloth, carbon fibre, stainless steel, nickel, polystyrene, polyethylene glycol, polymethyl methacrylate, polyacrylate, polyethylene terephthalate, and polycarbonate, and mixtures thereof.

24. The process according to any one of the preceding claims, wherein the process further comprises:reducing the oxidised post-transition metal species, thereby reproducing the at least one post-transition metal.

25. The process according to claim 24, wherein the oxidised post-transition metal species is reduced via electrolysis.

26. The process according to claim 24 or claim 25, wherein the process further comprises dissolving the oxidised post-transition metal species in an acidic, alkaline, or neutral ionic media, preferably an acidic media, prior to the reduction step.

27. Use of at least one post-transition metal for producing hydrogen in a process according to any one of claims 1 to 26, wherein the at least one post-transition metal does not comprise aluminium.

28. The use according to claim 27, wherein the at least one post-transition metal is recycled or is extracted from a source comprising the at least one post-transition metal.

29. The use according to claim 27 or claim 28, wherein the at least one posttransition metal comprises or is gallium.

30. Hydrogen produced by the process according to any one of claims 1 to 26.

Images