Systems for continuous generation of hydrogen gas and value-adding chemicals

Abstract

The technology concerns a process for generating hydrogen gas and chemicals of high value, while preventing water oxidation and generation of oxygen gas.

Description

[0001] SYSTEMS FOR CONTINUOUS GENERATION OF HYDROGEN GAS AND VALUE-ADDING CHEMICALS TECHNOLOGICAL FIELD

[0002] The invention generally contemplates systems for continuous generation of hydrogen gas, as well as various chemicals of industrial value.

[0003] BACKGROUND OF THE INVENTION

[0004] Generation of hydrogen gas by water electrolysis is important for the energy transition and decarbonization of various industrial processes. In water electrolysis, water is decomposed by electricity into oxygen gas at the anode (H2O —> 02 + 4H++ 4e“, E° = +1.23 V at pH 0) and hydrogen gas at the cathode (2H++ 2e“ H2, E° = 0 V at pH 0). The generated hydrogen gas can be used as a fuel for transportation or for energy storage. It may also be used as a feedstock material for industrial chemical processes such as ammonia production. However, oxygen gas is a low value byproduct, and the oxygen evolution reaction has sluggish kinetics, which decreases the electrolytic efficiency with typically 300-500 mV overpotential and results in increasing the cost of hydrogen production by water electrolysis. Another challenge of hydrogen production by water electrolysis is that this process conventionally requires the use of expensive membranes in order to separate the hydrogen gas and oxygen gas for safe operation.

[0005] SUMMARY OF THE INVENTION

[0006] The use of an aqueous halide solution, such as a bromide solution (or chlorine, or an iodide solution), instead of acidic or alkaline water, can replace the oxygen evolution reaction for enhancing kinetics of hydrogen gas production and reducing energy consumption. This is so because the halide solution has a lower driving force when converted to a halogen form, 2Br“ —> Br2 + 2e“ (E° = +1.09 V at pH 0), compared to oxygen evolution (E0= +1.23 V at pH 0). The generation of hydrogen gas coupled to bromine evolution realizes only one product in the gas phase (H2), instead of two gases (H2 and O2) in water electrolysis. Therefore, electrolysis of aqueous halide solutions, instead of acidic or alkaline water electrolysis, ensures high H2 gas purity and safe use of the generated hydrogen gas. The generated bromine, as an exemplary halogen, is a water- soluble liquid and is heavier than water. As a result, the bromine sinks down to the bottom of the cell, whereas the hydrogen gas bubbles rise to the headspace of the cell, where they are separated from the liquid solution. This spontaneous phase separation enables safe operation in undivided or membraneless cells, unlike conventional electrolysis with cells divided by membranes into anodic and cathodic compartments. This membraneless electrolysis has many unique advantages over other electrolyzers.

[0007] The inventors of the technology disclosed herein have developed unique industrially-viable systems and processes for producing hydrogen gas, as the sole gaseous product of the electrolysis, and a variety of value-adding chemicals (herein referred to as VACs) usable in different industries, such as the chemical industry, or as final products, while completely avoiding the production of oxygen gas. The ability to yield VACs, instead of oxygen gas, increases the value proposition above that of water electrolysis. As described below, the energy efficiency is expected to be higher for processes of this invention and the cost of the system is expected to be lower because it has no membranes, resulting in a potential benefit that is even higher than that is predicted by comparing the chemical products and educts alone.

[0008] The uniqueness of processes of the invention resides not only in the generation of VACs or generally reactive materials such as halogen liquids (e.g., bromine or iodine), sodium hydroxide and oxidized halogen forms (such as hypobromous acid (HBrO) or hypoiodous acid (HIO)), but also in the possibility for using these materials for in situ bromination / iodination or oxidation of various organic or inorganic substrates, generating additional VACs at no additional energetic cost.

[0009] In most general terms, the technology concerns processes carried out in a membraneless electrolytic cell (a reactor) comprising an electrode assembly (a cathode and an anode) and a mixture of organic and aqueous components, which may form a biphasic unmixed system or a mixed two-component system. Under the conditions of use, hydrogen gas is generated and halide ions (being bromide ions (Br“) or iodide ions (I-) or chloride ions (Cl-)) present in the solution are converted into the corresponding halogen liquids (bromine (Bn) or iodine (U)), or chlorine (Ch) gas, or into the corresponding oxides (e.g., hypobromous acid (HBrO) or hypoiodous acid (HIO) or hypochi orous acid (HC10)) through a series of spontaneous chemical reactions that occur in the aqueous part of the mixture. The conditions of use are controlled to prevent the production of oxygen gas. Despite the fact the bromide, iodide and chloride solutions may be used in processes and systems of the invention, in some configurations, the halide solution is a bromide solution and not an iodide or not a chloride solution. In other configurations, the halide solution may be an iodide solution.

[0010] In still other configurations, the halide solution may be a bromide or an iodide solution, excluding a chloride solution.

[0011] The halide solution is not a fluoride solution.

[0012] In most general terms, processes of the invention may be used for generating hydrogen gas and VACs, in one or more equivalent ways, including:

[0013] -Production of hydrogen gas (H2) and bromine (Br2), or bromine products, in a biphasic system comprising aqueous electrolyte and immiscible organic solvent; or -Production of hydrogen gas (H2) and iodine (I2), or iodine products, in a biphasic system comprising aqueous electrolyte and immiscible organic solvent; or -Production of hydrogen gas (H2) and chlorine (Ch), or chlorine products, in a biphasic system comprising aqueous electrolyte and immiscible organic solvent; or -Production of hydrogen gas (H2) and epoxides by partial oxidation or epoxidation of alkenes (olefins) or other substrates in a mixed phase system; or

[0014] -Production of hydrogen gas (H2) and bromination, iodination or chlorination products by halogenation of alkenes (olefins) or other substrates in a mixed phase system; or

[0015] -Production of hydrogen gas (H2) and sulfuric acid (H2SO4), or other oxoacids, by electrolysis and chemical looping processes.

[0016] In a first of its aspects, the invention concerns a process for generating hydrogen gas and one or more value-adding chemicals (VACs), the process comprising reacting in a membraneless reactor (or an electrolyzer) operated under electrolytic conditions a combination (homogenous or heterogenous) of an aqueous halide solution and an organic medium (which may be water-insoluble or water soluble), optionally comprising an organic or an inorganic substrate material, to produce halogen products, or to convert said organic or inorganic substrate material (if present) into a corresponding halogenated or oxidized form thereof, wherein the aqueous (e.g., acidic) halide solution comprises halide ions convertible under the electrolytic conditions into said halogen products, namely halogen liquids or gases and / or oxidized halide species, thereby preventing water oxidation and generation of oxygen gas, and wherein the halide ions are selected from bromide ions, iodide ions and chloride ions.

[0017] In some embodiments, the halide solution further comprises an acid.

[0018] In some embodiments, the halide solution is maintained at a pH below 6.5 In some embodiments, the presence of halide ions in the aqueous solution, the acidic electrolysis conditions and optionally the carrying of the process at room temperature or at low temperatures, in general, prevents water oxidation and the generation of oxygen gas.

[0019] In some embodiments, the process is for generating hydrogen gas and VACs, the process comprising reacting in a membraneless reactor operated under electrolytic conditions a heterogenous (phase-separated) mixture of an aqueous halide solution and a water-insoluble organic medium (without an organic or an inorganic substrate material that can covert to VACs during the process), to produce halogen products (being VACs), wherein the aqueous halide solution (e.g., being acidic) comprises halide ions convertible under the electrolytic conditions into the halogen products (being for example halogen liquids and / or oxidized halide species), thereby preventing water oxidation and generating of oxygen gas, and wherein the halide ions are selected from bromide ions, iodide ions and chloride ions.

[0020] The halogen products or oxidized halide products are as disclosed herein. The halide ions are generally ions of Br, I or Cl. The generated aqueous halide solution, as disclosed herein, is responsible for ensuring that oxygen gas is not generated by water oxidation, and that the hydrogen gas generated is the only gaseous product in the electrolytic reaction. It should be noted that while other gaseous products may be formed in step(s) subsequent to the electrolysis steps, such products may be chlorine gas and other oxidation or epoxidation side products, the only product generated during the electrolytic step is hydrogen gas.

[0021] The mixture of the aqueous halide solution (also referred to as an electrolyte solution), which may be a bromide or an iodide or a chloride solution (comprising, for example, Na or K salts of Cl, Br, or I), and the water-insoluble organic medium, which may optionally comprise an organic or an inorganic substrate material, may be allowed to form into a homogeneous mixture by mixing, stirring or turbulent flow (or other flow conditions that mix the two solutions), or may be allowed to separate into a biphasic state (a heterogeneous or inhomogeneous state), wherein the aqueous and the organic components separate into distinct phases. Typically, the water-insoluble organic medium is selected to have a density higher than that of water, to permit the organic phase to occupy the lower volume of the mixture in a biphasic state.

[0022] In some cases, therefore, the mixture is an unstirred or unmixed heterogenous (biphasic) system comprising the aqueous halide solution and the water-insoluble organic medium. In such cases, as demonstrated herein, the conversion of the halide, e.g., bromide ions, in the mixture to bromine liquid, takes place in an unstirred or unmixed biphasic system, wherein the organic medium occupies the lower volume in the system.

[0023] Reaction (1) and (2) depict the overall reactions that result in generation of hydrogen gas and bromine:

[0024] H2SO4+ 2NaBr → H2+ Br2+ 2Na++ SO42−(1)

[0025] 2HBr → H2+ Br2(2).

[0026] The reaction produces hydrogen (H2) at the cathode, and bromine (Br2) or a different halogen liquid, at the anode. The hydrogen evolves at the cathode into the aqueous electrolyte (NaBr or KBr in water) and is eventually separated from the electrolyte into the gas phase and stored in a gas tank or other vessel. The bromine is produced at the anode and sinks down to the bottom of the electrolytic cell where it dissolves into an organic medium that can be easily separated from the aqueous electrolyte solution due to gravity. This spontaneous phase separation lets go of the need for a membrane or diaphragm that divides the electrolytic cell into cathodic and anodic compartments as in conventional water electrolysis, as well as in most decoupled water electrolysis schemes that use soluble redox couples.

[0027] Reaction (1) above produces Na+and OH“ ions, in addition to H2and Br2. Therefore, an acid, e.g., sulfuric acid (H2SO4), must be present to prevent alkalinization of the aqueous electrolyte by neutralizing the OH“ ions.

[0028] A similar reaction sequence results in generation of hydrogen gas and iodine, where Nal or KI is used in the halide or electrolyte solution. A similar reaction sequence results in generation of hydrogen gas and chlorine gas (produced in two separate steps), where NaCl or KC1 is used in the halide or electrolyte solution.

[0029] In some embodiments, the process comprises reacting the mixture of the aqueous halide solution and the water-insoluble organic medium (optionally comprising an organic or an inorganic substrate material), under conditions that cause conversion of the halide ions (chloride ions (Cl“), bromide ions (Br), or iodide ions (I-)) present in the halide solution (originating from the corresponding Na or K salts) into the corresponding halogen liquids (bromine (Bn) or iodine (I2), respectively), or chlorine gas (Ch), which may be collected.

[0030] In some embodiments, the process comprising

[0031] - reacting under electrolytic conditions an unmixed heterogenous (biphasic) mixture of the aqueous halide (bromide or iodide) solution and the water-insoluble organic medium, to generate hydrogen gas and the corresponding halogen liquid (bromine or iodine), under controlled conditions preventing water oxidation and production of oxygen gas; and

[0032] - collecting said hydrogen gas in the headspace of the reactor and said halogen liquid in the organic solvent at the bottom of the reactor.

[0033] In some embodiments, the reactor may comprise an auxiliary chamber configured to collect therein the separated halogen liquid (bromine or iodine).

[0034] In some embodiments, the halogen liquid dissolves into the organic medium and is collected therewith.

[0035] In some embodiments, the organic medium being a water-insoluble organic solvent has a density greater than that of water. In such embodiments, the organic solvent may be selected amongst aprotic solvents such as dichloromethane (DCM), chloroform, carbon tetrachloride, nitromethane, and 1,2-di chloroethane.

[0036] In some embodiments, in cases where the halogen liquid is to be separated from the organic medium (e.g., bromine in DCM), phase separation techniques such as reduced-pressure distillation, azeotropic distillation, fractional crystallization or others may be used.

[0037] The value-adding chemicals (VACs) or compounds are high value products of importance or of commercial value in many of the industries. The products may be of value as reagents, reactants, solvents, intermediates, etc, or as final products that may be used in such industries as the medical, cosmetic, agricultural, or electronic industries. Notwithstanding the potential use of such VACs, the VACs may result from direct chemical conversion of the halide ions (Br or I ions) present in the aqueous halide solution. Such VACs may be halogen liquids (e.g., bromine or iodine liquids, soluble in the organic phase), metal hydroxides (such as sodium and potassium hydroxide) and oxidized halogen forms (such as hypobromous acid (HBrO) and hypoiodous acid (HIO)).

[0038] In some cases, further VACs may form when the VACs generated from direct chemical conversion of the halide ions, as described above, are allowed to react with an organic or an inorganic substrate material. In such cases, the organic medium may comprise an organic or an inorganic substrate material that is susceptible to chemical conversion in presence of a halide ions, halogen liquids (e.g., bromine or iodine liquids, soluble in the organic phase), metal hydroxides (such as sodium and potassium hydroxide) and oxidized halogen forms (such as hypobromous acid (HBrO) and hypoiodous acid (HIO)).

[0039] In some embodiments, the organic medium may comprise an organic substrate that is susceptible to halogenation (i.e., bromination or iodination), or to oxidation (partial or complete oxidation).

[0040] In other embodiments, the organic medium may comprise an inorganic substrate that is susceptible to oxidation (partial or complete oxidation).

[0041] The substrate material (organic or inorganic) may be selected to permit a desired chemical conversion by any oxidative or ion exchange chemical reaction. The chemical conversion reactions may be halogenation, radical halogenation, oxidation, alcohol or aldehyde oxidation, epoxidation, Hoffmann bromamide reactions, and others. In some cases, the organic substrate may be selected from alkanes, alkenes, alkynes, alcohols, carbonyl compounds (such as aldehydes, ketones, and esters), aromatic compounds, and others that are reactive under conditions of the electrolytic conditions to undergo radical halogenation, addition reactions, electrophilic aromatic substitution, a-halogenation reactions, allylic halogenation, and others. In some cases, the inorganic substrate may be selected from metals, metal oxides, metal alloys, non-metal inorganics, elemental materials such as elemental sulfur, elemental phosphorus, sulfides, phosphides, nitrides, carbides and others.

[0042] Non-limiting examples of substrate materials include elemental sulfur, elemental phosphorus, ethene, propene, 1-butene, 1-hexene, isobutylene, 1,3-butadiene, isoprene, cyclohexene, cyclopentene, norbornene (bicyclo[2.2.1]hept-2-ene), styrene, a-methyl styrene, 1-octene, 1-decene, limonene, acetylene, phenyl acetylene, 1-butyne, propargyl alcohol, 2-butyne, benzene, toluene, ethylbenzene, cumene, o-xylene, m-xylene, p-xylene, anisole, phenol, aniline, nitrobenzene, chlorobenzene, bromobenzene, naphthalene, anthracene, phenanthrene, biphenyl, mesitylene, 1,3,5-trimethoxybenzene, catechol, hydroquinone, resorcinol, salicylic acid, benzoic acid, benzaldehyde, acetophenone, p-anisidine, phenylacetic acid, 4-nitrotoluene, p-cresol, acetone, cyclohexanone, cyclopentanone, acetaldehyde, propanal, ethyl acetoacetate, methyl acetoacetate, acetyl acetone, propiophenone, 1-phenyl-2-propanone, methyl ethyl ketone, 2-pentanone, chalcone, pyrrole, indole, furan, thiophene, pyridine, imidazole, pyrimidine, quinoline, isoquinoline, indazole, carbazole, benzothiophene, benzofuran, oxazole, thiazole, benzyl alcohol, allyl alcohol, thiophenol, benzyl mercaptan, thioanisole, N, N-dimethylaniline, cholesterol, estrone, tyrosine, tryptophan, serotonin, dopamine, adenine, guanine, thymine, uracil, and others.

[0043] In some non-limiting exemplary embodiments, the organic substrate is cyclohexene (for example undergoing bromination to 1,2-dibromohexane).

[0044] When organic or inorganic substrates are present, the overall VACs generated by processes of the invention may include halogen liquids (such as bromine or iodine liquids), metal hydroxides (such as sodium and potassium hydroxide), oxidized halogen compounds (such as hypobromous acid (HBrO) and hypoiodous acid (HIO)), sulfuric acid, oxidized organic compounds, mono- or multi -halogenated organic compounds, mono- or multi -halogenated aromatic compounds, products of radical halogenation, products of addition reactions, products of electrophilic aromatic substitution, products of a-halogenation reactions, products of allylic halogenation, and others. As a person versed in the art would appreciate, the type and selection of VACs may depend on the organic or inorganic substrate material used, which is not limited by molecular weight and chemical composition.

[0045] In some embodiments, the aqueous solution may contain a buffer such as borate, phosphate, acetate, carbonate or another buffer.

[0046] In some embodiments, the aqueous solution may contain other additives such as wetting agents, leaching agents, surfactants, chelating agents, or ionic compounds (e.g., NaCl, NaSO4, NaNO3, etc.). In some embodiments, the aqueous solution may contain sodium dichromate (Na2Cr2O7), typically in milligrams to grams per liter. In some cases, where the chemical conversion of the organic or inorganic substrate may require a catalyst, a photo-initiator, a chemical initiator, metal complexes, or any other reagent, may be added to or generally may be present in the organic medium. In some embodiments, the chemical conversion may involve radical halogenation. In such or other cases, the process may comprise illuminating or irradiating the solution, either in its biphasic state (heterogenous mixture) or the mixed state (homogenous mixture), as disclosed herein, with a UV light or sunlight (concentrated or unconcentrated sunlight).

[0047] In cases where the process is a continuous process, or at least a partially continuous process, the organic medium comprising the VAC (e.g., resulting from chemical conversion of the inorganic or organic substrate materials), the process may comprise replacing the organic medium containing the VAC with an organic medium that is free of said VAC and which may further comprise an amount of the inorganic or organic substrate materials or additives.

[0048] As noted herein, processes of the invention are carried out in a reactor or an electrolyzer operating under ^electrolytic conditions”. These conditions comprise maintaining the mixture in said reactor or electrolyzer, having a pair of electrodes (or an electrode assembly) immersed in the aqueous medium of said mixture, operating at a current density of 100 mA / cm2or above (normalized by the anode geometric area). Typically, the aqueous medium is maintained at a pH below 6.5 and at a temperature near or at room temperature (e.g., at a temperature between 20-33 °C) or at an elevated temperature not exceeding 90°C. The reactor may be operated at an internal pressure not exceeding 10 bars. The aqueous medium may comprise a metal halide such as a sodium halide, e.g., sodium bromide (NaBr) or sodium iodide (Nal), or a potassium halide, e.g., potassium bromide (KBr) or potassium iodide (KI), or other metal halides as disclosed herein. In some cases, the medium may further comprise a hydrogen halide acid, e.g., hydrobromic acid (HBr) or hydroiodic acid (HI). In some cases, the medium may comprise a natural halide source, e.g., seawater (e.g., from the Dead Sea), concentrated seawater from chemical industries, or concentrate seawater from desalination plants. Notwithstanding the composition or source of the aqueous medium used, it should have an oxidative potential that is smaller than that required for oxidation of water and production of oxygen gas. Typically, the oxidation potential may be E0= 1.09 V for a Br-based solution, or E0= 0.54 V for an I-based solution, when maintained at a pH below 6.5.

[0049] In some cases, where the “pH is below 6.5”, the pH may be between zero and 6.5, or between 2 and 6.5, or between 3 and 6.5 or between 5 and 6.5, or between zero and 3, or between zero and 5, or between 3 and 5. In other words, the pH may be any value between zero and 6.5, inclusive.

[0050] In some embodiments, the process comprises of anode and cathode in an aqueous phase comprising of sodium bromide (> 1 M) and sulfuric acid (> 0.5 M) at current density of 100 mA / cm2or above, at near or at room temperature (between 20 and 33 °C), 1 atm, pH below 6.5, or at a pH as selected herein.

[0051] In some embodiments, the process comprises of anode and cathode in an aqueous phase comprising of sodium bromide (> 1 M), borate buffer (> 0.2 M) at current density of 100 mA / cm2or above, at near or at room temperature (between 20 and 33 °C), 1 atm, below pH 6.5, as selected herein.

[0052] In certain configurations, the controlled conditions used for generating hydrogen gas and the VACs, while preventing the production of oxygen gas, may comprise stirring or mixing the aqueous solution (water with NaBr or KBr or Nal or KI and possibly other additives) such that phase separation between the aqueous and halogen liquids is not maintained. In the mixed phase (a homogenous mixture of the aqueous and organic solutions), the halogen liquid (e.g., bromine or iodine) is not separated from the aqueous solution and some or all of the halogen liquid reacts with water and converts into hydrobromic acid (HBr) and hypobromous acid (HBrO), or hydroiodic acid (HI) and hypoiodous acid (HIO), through spontaneous chemical reactions within water, following reactions (3) or (4):

[0053] Br2+ H2O → HBr + HBrO (3)

[0054]

[0055] I2+ H2O → HI + HIO (4).

[0056] The generation of HBr and HBrO (or HI and HIO) may drive oxidation (partial or complete) of organic substrates present in the organic medium or in the mixed solution, converting them into VACs. Thus, in some embodiments, the process comprises permitting said HBrO (or HIO) to oxidize an organic or an inorganic substrate material present in the organic medium.

[0057] The invention further provides a process for generating brominated or iodinated or partially-oxidized or oxidized organic compounds (as VACs), the process comprising reacting in a membraneless reactor operated under electrolytic conditions a mixture of an aqueous halide solution and a water-insoluble organic medium optionally comprising an organic or an inorganic substrate material, causing conversion of halide ions in said halide solution into the corresponding halogen liquids (i.e., Br2or I2) and optionally further into the oxidized halide forms thereof (i.e., HBrO or HIO), and permitting said halogen liquids, and / or said oxidized halide forms to react with the organic substrate (if present), thereby preventing water oxidation and oxygen gas generation, wherein the aqueous halide solution is a bromide or an iodide solution.

[0058] The invention further provides a process for generating hydrogen gas and sulfuric acid (or other oxoacids) as the VAC, the process comprising in a closed-loop system having (i) a membraneless electrolytic cell (or reactor) comprising an electrode pair or an electrode assembly implemented in an halide aqueous solution of a hydrogen halide (e.g., hydrobromic acid (HBr) or hydroiodic acid (HI)), and (ii) a chemical cell comprising a mixture of water and a sulfur source:

[0059] -electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid (e.g., Br2or I2);

[0060] -transferring (or permit flowing of) said halogen liquid to the chemical cell, to cause transformation of said sulfur source into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions that react with protons (H+, from the water) to form (or regenerate) hydrogen halide (e.g., hydrobromic acid (HBr) or hydroiodic acid (HI)); and

[0061] -feeding the formed or generated hydrogen halide back into the electrolytic cell. The process is repeated in a closed-loop fashion to permit continuous generation of sulfur-based products.

[0062] The sulfur source may be elemental sulfur (sulfur powder) or SO2gas, or any other sulfur containing material that can be transformed, under the conditions of the process into sulfuric acid.

[0063] In some embodiments, the sulfur source is elemental sulfur (sulfur powder) and the chemical cell comprises a heated water solution of the elemental sulfur. In such embodiments, the process comprising:

[0064] in a closed-loop system having (i) a membraneless electrolytic cell (or reactor) comprising an electrode pair or an electrode assembly implemented in an halide aqueous solution of a hydrogen halide (e.g., hydrobromic acid (HBr) or hydroiodic acid (HI)), and (ii) a chemical cell comprising a heated mixture of water and elemental sulfur: -electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid (e.g., Br2or I2);

[0065] -transferring (or permit flowing of) said halogen liquid to the chemical cell, to cause oxidation of the elemental sulfur into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions that react with protons (H+, from the water) to form (or regenerate) hydrogen halide (e.g., hydrobromic acid (HBr) or hydroiodic acid (HI)); and

[0066] -feeding the formed or generated hydrogen halide back into the electrolytic cell. In some embodiments, the temperature of the heated mixture of water and elemental sulfur (comprising also the halogen liquid) in the chemical cell may be between 70 and 110 °C or may be heated to or maintained at a temperature between 70 and 110 °C.

[0067] In some embodiments, the sulfur source is SO2gas and the chemical cell comprises a water solution (not heated, typically at a temperature between 20 and 33°C) into which SO2gas is bubbled or added by other means. In such embodiments, the process comprising:

[0068] in a closed-loop system having (i) a membraneless electrolytic cell (or reactor) comprising an electrode pair or an electrode assembly implemented in an halide aqueous solution of a hydrogen halide (e.g., hydrobromic acid (HBr) or hydroiodic acid (HI)), and (ii) a chemical cell comprising a mixture of water and SO2:

[0069] -electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid (e.g., Br2or I2);

[0070] -transferring (or permit flowing of) said halogen liquid to the chemical cell, to cause transformation of the SO2into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions that react with protons (H+, from the water) to form (or regenerate) hydrogen halide (e.g., hydrobromic acid (HBr) or hydroiodic acid (HI)); and

[0071] -feeding the formed or generated hydrogen halide back into the electrolytic cell. In some embodiments, the halogen liquid (Br2or I2) is converted to hydrogen halide (HBr or HI) and sulfuric acid in presence of the heated water and elemental sulfur (S). In some embodiments, the halogen liquid (Br2or I2) is converted to hydrogen halide (HBr or HI) and sulfuric acid in presence of water, at room temperature, and sulfur dioxide (SO2).

[0072] In some embodiments, the process comprises separating the mixed solution comprising the hydrogen halide (HBr or HI) and sulfuric acid (or other oxoacids), and feeding the hydrogen halide back into the electrolytic cell.

[0073] In some embodiments, the process comprises separating said sulfuric acid.

[0074] In some embodiments, the halide solution is an acidic solution comprising an acid such as hydrobromic acid (HBr) solution, or sodium bromide (NaBr) with sulfuric acid (H2SO4) solution, having a pH between -2 and 3.

[0075] In some embodiments, the transferring of said halogen liquid to the chemical cell comprises use of a pump.

[0076] In some embodiments, the transferring of said halogen liquid to the chemical cell comprises use of air-blowing method.

[0077] In some embodiments, the transferring of said halogen liquid to the chemical cell comprises use of tetrabutylammonium bromide (TBAB).

[0078] In some embodiments, the separation of said hydrogen halide and sulfuric acid produced in the chemical cell comprises use of distillation.

[0079] In some embodiments, the electrolytic conditions comprise of hydrobromic acid, or sodium bromide with sulfuric acid, at current density of 0.1 A / cm2or above at temperature near room temperature (20-33 °C) and 1 atm in the electrolytic cell. In some embodiments, the current density is changed periodically during electrolysis between low and high values. Low values can be 0 to 0.1 A / cm2and high values can be 0.5 to 5 A / cm2.

[0080] In some embodiments, the chemical cell comprises element sulfur powder.

[0081] In some embodiments, the chemical cell comprises sulfur dioxide gas.

[0082] In some embodiments, the electrolytic cell is configured to receive an aqueous solution of hydrogen halide that is separated from the hydrogen halide and sulfuric acid mixture in the chemical cell and is fed back into the electrolytic cell; and the chemical cell is configured to receive halogen solution from the electrolytic cell, together with water and elemental sulfur or sulfur dioxide.

[0083] In some embodiments, other inorganic substrate material, such as phosphorus or phosphorus pentoxide may be used as reagents instead of sulfur or sulfur dioxide. The invention further provides a system for generating hydrogen gas and VAC such as epoxides, in a mixed-phase organic-inorganic (aqueous) solution, the system comprising one (or more) membraneless electrolytic cell (referred to as reactor) including an electrode assembly (a cathode and an anode), the reactor being configured to receive a mixed-phase solution comprising an aqueous halide solution (a bromide or an iodide solution) and a water-soluble organic medium optionally containing organic substrate materials, the system being equipped with stirring or other mixing mechanism configured and operable to stir or mix or cause turbulation in the solution; wherein the halide solution is maintained at a neutral pH or a pH above 6, at a temperature near room temperature (20-33 °C) or at elevated temperatures not exceeding 90°C, and under ambient pressure or a pressure not exceeding 10 bars; and wherein the system is operated at a current density of 0.1 A / cm2or above (normalized by the anode geometric area).

[0084] In some embodiments, the system comprising a water-soluble mixture containing organic substrate materials, water-soluble organic solvent, and an aqueous bromide (or iodide) solution, at current density of 10 mA / cm2or above, at 20°C or a temperature not exceeding 90°C, and a pressure up to 10 bars.

[0085] Non-limiting examples of the organic substrate materials include ethene, propene, 1-butene, 1-hexene, isobutylene, 1,3-butadiene, isoprene, cyclohexene, cyclopentene, norbornene (bicyclo[2.2.1]hept-2-ene), styrene, α-methylstyrene, 1-octene, 1-decene, limonene, acetylene, phenylacetylene, 1-butyne, propargyl alcohol, 2-butyne, benzene, toluene, ethylbenzene, cumene, o-xylene, m-xylene, p-xylene, anisole, phenol, aniline, nitrobenzene, chlorobenzene, bromobenzene, naphthalene, anthracene, phenanthrene, biphenyl, mesitylene, 1,3,5-trimethoxybenzene, catechol, hydroquinone, resorcinol, salicylic acid, benzoic acid, benzaldehyde, acetophenone, p-anisidine, phenylacetic acid, 4-nitrotoluene, p-cresol, acetone, cyclohexanone, cyclopentanone, acetaldehyde, propanal, ethyl acetoacetate, methyl acetoacetate, acetyl acetone, propiophenone, 1-phenyl-2-propanone, methyl ethyl ketone, 2-pentanone, chalcone, pyrrole, indole, furan, thiophene, pyridine, imidazole, pyrimidine, quinoline, isoquinoline, indazole, carbazole, benzothiophene, benzofuran, oxazole, thiazole, benzyl alcohol, allyl alcohol, thiophenol, benzyl mercaptan, thioanisole, N, N-dimethylaniline, cholesterol, estrone, tyrosine, tryptophan, serotonin, dopamine, adenine, guanine, thymine, uracil, and others.

[0086] In some embodiments, the water-soluble organic solvent comprises of acetonitrile, dimethyl sulfoxide, dimethylformamide, and others. In some embodiments, the aqueous bromide solution comprises of sodium bromide, potassium bromide, lithium bromide, and others.

[0087] The invention further provides:

[0088] A process for generating hydrogen gas and value-adding chemicals (VACs), the process comprising reacting in a membraneless electrolytic cell, operated under electrolytic conditions, a mixture of an aqueous halide solution and an organic medium, optionally comprising an organic or an inorganic substrate material, to produce halogen products or to convert said organic or inorganic substrate material, if present, into a corresponding halogenated or oxidized form thereof, wherein the electrolytic conditions comprise:

[0089] -maintaining the aqueous halide solution at a pH below 3 (or optionally at a neutral pH or a pH between 6 to 8 when a substrate material is present);

[0090] -operating at a current density of at least 100 mA / cm2;

[0091] to thereby prevent water oxidation and oxygen gas generation,

[0092] wherein the halogen products are halogen liquids, chlorine gas and / or oxidized halide compounds; and

[0093] wherein the aqueous halide solution is not a fluoride solution.

[0094] In some configurations of processes of the invention, the halide solution is a bromide solution and the halogen products are bromine and / or oxidized bromine compounds.

[0095] In some configurations of processes of the invention, the halide solution is an iodide solution and the halogen products are iodine and / or oxidized iodine compounds.

[0096] In some configurations of processes of the invention, the halide solution is a chloride solution and the halogen products are chlorine gas and / or oxidized chlorine compounds.

[0097] In some configurations of processes of the invention, the halide solution is not a chloride solution.

[0098] In some configurations of processes of the invention, the organic medium is water soluble.

[0099] In some configurations of processes of the invention, the organic medium is water-insoluble.

[0100] In some configurations of processes of the invention, the aqueous halide solution comprises a metal halide, or a hydrogen halide. In some configurations of processes of the invention, the metal halide is selected from a lithium, a sodium, a calcium, a magnesium and a potassium halide.

[0101] In some configurations of processes of the invention, the mixture is an unstirred or unmixed biphasic system (heterogenous mixture) comprising the aqueous halide solution and a water-insoluble organic medium.

[0102] In some configurations of processes of the invention, the organic medium is a water-insoluble organic medium having a higher density than water.

[0103] In some configurations of processes of the invention, the organic medium is free of organic or inorganic substrate materials.

[0104] In some configurations of processes of the invention, the halide solution comprises halide ions that are converted into a corresponding halogen liquid, and corresponding oxidized halide forms, and wherein the halogen liquid is separated.

[0105] In some configurations of processes of the invention, the process comprising: - reacting under electrolytic conditions an unstirred biphasic system (heterogenous mixture) of the aqueous halide solution and water-insoluble organic medium, to generate hydrogen gas and the corresponding halogen liquid, under the conditions preventing production of oxygen gas; and

[0106] - collecting said hydrogen gas and said halogen liquid separately from each other.

[0107] In some configurations of processes of the invention, the VAC is one or more products resulting from direct chemical conversion of halide ions present in the aqueous halide solution.

[0108] In some configurations of processes of the invention, the VAC is selected from halogen liquids, metal hydroxides and oxidized halide forms.

[0109] In some configurations of processes of the invention, the oxidized halide forms include hypobromous acid (HBrO) and hypoiodous acid (HIO).

[0110] In some configurations of processes of the invention, the mixture is a stirred or a mixed mixture (homogenous mixture) comprising the aqueous halide solution and the organic medium.

[0111] In some configurations of processes of the invention, the organic medium comprises an organic or an inorganic substrate material susceptible to chemical conversion in presence of a halide ions, halogen liquids, metal hydroxides and oxidized halide forms. In some configurations of processes of the invention, the organic substrate material is susceptible to bromination or iodination, or to oxidation.

[0112] In some configurations of processes of the invention, the inorganic substrate material is an inorganic material susceptible to oxidation.

[0113] In some configurations of processes of the invention, the organic substrate material is selected from alkanes, alkenes, alkynes, alcohols, carbonyl compounds, and aromatic compounds, reactive under the electrolytic conditions to undergo radical halogenation, addition reactions, electrophilic aromatic substitution, α-halogenation reactions, or allylic halogenation.

[0114] In some configurations of processes of the invention, the inorganic substrate is selected from metals, metal and non-metal oxides, metal alloys, non-metal inorganics, elemental materials, elemental phosphorus, sulfides, phosphides, nitrides, and carbides.

[0115] In some configurations of processes of the invention, the organic substrate material is an olefin, or a compound comprising one or more double or triple bonds.

[0116] In some configurations of processes of the invention, the inorganic substrate material is elemental sulfur, sulfur dioxide, nitrous acid, phosphorus, silicon, or boron.

[0117] In some configurations of processes of the invention, the VAC is selected halogen liquids, metal hydroxides, oxidized halogen forms, sulfuric acid, oxidized organic compounds, mono- or multi-halogenated organic compounds, mono- or multihalogenated aromatic compounds, products of oxidation, radical halogenation, products of addition reactions, products of electrophilic aromatic substitution, products of α-halogenation reactions, and products of allylic halogenation.

[0118] In some configurations of processes of the invention, the organic medium comprises an organic substrate material, and optionally an amount of one or more reactive materials selected to permit radical halogenation of the organic substrate material under exposure to UV light or sunlight.

[0119] In some configurations of processes of the invention, the electrolytic conditions comprise maintaining the mixture at a temperature between 20 and 33°C or at a temperature not exceeding 90°C.

[0120] In some configurations of processes of the invention, the electrolytic conditions comprise maintaining the mixture at a pressure below 10 bars.

[0121] In some configurations of processes of the invention, the pressure is 1 atm. In some configurations of processes of the invention, the electrolytic conditions comprise maintaining the halide solution at a pH between zero and 3.

[0122] In some configurations of processes of the invention, each of the VAC products is separated from the organic medium.

[0123] In some configurations of processes of the invention, the process is a continuous process, generating hydrogen gas and one or more VACs, wherein the process comprises replenishing the organic or inorganic substrate material in the organic medium to thereby continuously generate said VACs.

[0124] In some configurations of processes of the invention, the process is operated in a batch-wise fashion.

[0125] A process is further provided for generating hydrogen gas and sulfuric acid, the process comprising in a closed-loop system having (i) a membraneless electrolytic cell comprising an electrode pair implemented in an halide aqueous solution comprising a hydrogen halide, and (ii) a chemical cell comprising a mixture of water and a sulfur source:

[0126] -electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid;

[0127] -transferring or permit flowing of said halogen liquid to the chemical cell, to cause transformation of said sulfur source into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions to regenerate the hydrogen halide; and -feeding the formed or regenerated hydrogen halide back into the electrolytic cell. In some configurations of processes of the invention, the process is repeated in a closed-loop fashion to permit continuous generation of sulfur-based products.

[0128] In some configurations of processes of the invention, the sulfur source is elemental sulfur (sulfur powder) or SO2gas, or any other sulfur containing material transformable, under the conditions of the process into sulfuric acid.

[0129] In some configurations of processes of the invention, the sulfur source is elemental sulfur (sulfur powder) and the chemical cell comprises a heated water solution of the elemental sulfur.

[0130] In some configurations of processes of the invention, the process comprising: in a closed-loop system having (i) a membraneless electrolytic cell comprising an electrode pair or an electrode assembly implemented in an halide aqueous solution comprising a hydrogen halide, and (ii) a chemical cell comprising a heated mixture of water and elemental sulfur:

[0131] -electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid;

[0132] -transferring or permit flowing of said halogen liquid to the chemical cell, to cause oxidation of the elemental sulfur into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions to form or regenerate the hydrogen halide; and -feeding the formed or generated hydrogen halide back into the electrolytic cell. In some configurations of processes of the invention, the temperature of the heated mixture of water and elemental sulfur in the chemical cell is between 70 and 110 °C.

[0133] In some configurations of processes of the invention, the sulfur source is SO2gas and the chemical cell comprises a water solution into which SO2gas is bubbled or added by other means.

[0134] In some configurations of processes of the invention, the process comprising: in a closed-loop system having (i) a membraneless electrolytic cell comprising an electrode pair or an electrode assembly implemented in an halide aqueous solution comprising a hydrogen halide, and (ii) a chemical cell comprising a mixture of water and SO2:

[0135] -electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid;

[0136] -transferring or permit flowing of said halogen liquid to the chemical cell, to cause transformation of the SO2 into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions to form or regenerate the hydrogen halide; and -feeding the formed or regenerated hydrogen halide back into the electrolytic cell. In some configurations of processes of the invention, the process comprising separating the hydrogen halide and sulfuric acid, and feeding the hydrogen halide back into the electrolytic cell.

[0137] In some configurations of processes of the invention, the process comprising separating said sulfuric acid.

[0138] In some configurations of processes of the invention, the halide solution is an acidic solution comprising an acid such as hydrobromic acid (HBr) solution, or sodium bromide (NaBr) with sulfuric acid (H2SO4) solution, and having a pH between -2 and 3. In some configurations of processes of the invention, the transferring of said halogen liquid to the chemical cell comprises use of a pump, or use of air-blowing method.

[0139] In some configurations of processes of the invention, the electrolytic conditions comprise use of hydrobromic acid, or sodium bromide with sulfuric acid, at a current density of 0.1 A / cm2or above, at a temperature between 20 and 33 °C, and 1 atm in the electrolytic cell.

[0140] In some configurations of processes of the invention, the current density is changed periodically during electrolysis between 0 to 0.1 A / cm2and 0.5 to 5 A / cm2.

[0141] In some configurations of processes of the invention, the process operated in a constant current or a changing current mode.

[0142] A system is provided for generating hydrogen gas and value-adding chemicals (VACs), the system comprising one or more membraneless reactors, each reactor including an electrode assembly and is configured to receive a mixed solution comprising an aqueous halide solution and an organic medium, the system being equipped with a stirring or a mixing mechanism configured and operable to stir or mix or cause turbulation to the solution; wherein the halide solution is maintained at a pH below 3 or neutral pH between 6 and 8, at a temperature between 20 and 33 °C, or at a temperature not exceeding 90°C, and under a pressure not exceeding 10 bars; wherein the system is operated at a current density of 100 mA / cm2or above (normalized by an anode area).

[0143] BRIEF DESCRIPTION OF THE DRAWINGS

[0144] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0145] Figs. 1A-G- Hybrid water and bromide electrolysis. (A) Schematic illustration of the hybrid electrolysis (step 1) and subsequent bromination process (step 2). (B) Picture of a membraneless cell before electrolysis begins. (C) Picture of the same cell during electrolysis at a constant current of 1 A. (D) Anodic current density versus potential curves (IR corrected) in different NaBr concentrations ((1) to (7): 1.50 M to 0.00 M of NaBr) and a constant concentration (0.5 M) of H2SO4(pH ≈ 0), obtained by linear sweep voltammetry (LSV) measurements with a potential scan rate of 5 mV / s. (E) Tafel slope versus concentration of bromide, [Br“], data extracted from LSV measurements. (F) Cathodic current density versus potential curves (IR corrected) in 0 M and 1.5 M NaBr ( (1) and (2) curves, respectively) with a constant concentration (0.5 M) of H2SO4(pH ≈ 0), obtained by LSV measurements with a potential scan rate of 5 mV / s. Insert zooms in between -0.1 and 0 VRHE. (G) Cell voltage (IR corrected) vs. steady-state cathodic (top x-axis) or anodic (bottom x-axis) current density, obtained by galvanostatic measurements at different currents ranging from 10 to 2000 mA in 1.5 M NaBr + 0.5 M H2SO4electrolyte. The error bars present the standard deviation of three repeated measurements under the same conditions. The red asterisks represent results obtained in 1.5 M HBr electrolyte. All the measurements were done in ambient conditions (room temperature and atmospheric pressure).

[0146] Figs.2A-B- depict the various mechanisms for producing VAC according to some embodiments of the invention.

[0147] Figs. 3A-C- Pictures of the electrolytic cell before (A) and after (B) 30 minutes of electrolysis at a constant current density of 300 mA / cm2in 1.5M NaBr aqueous electrolyte with 0.3M borate buffer, and organic solvent (dichloromethane, DCM) that sinks to the bottom of the cell. The cell voltage during electrolysis is shown in (C). The DCM turns red by the bromine (Bn) that is produced at the anode and sinks down to the bottom of the cell.

[0148] Figs. 4A-D- (A) Bromination of cyclohexene and bromine at ambient conditions.

[0149] (B) Radical bromination of toluene with bromine under sunlight; (C) and (D) snapshots of both reactions show that the red color (of bromine) completely disappears in a few seconds once the reactions terminate.

[0150] Fig. 5-1H-NMR analysis of the reaction products in the organic solvent (DCM) with cyclohexane in the proof-of-concept experiment presented in Fig. 4A.

[0151] Fig. 6-1H-NMR analysis of the reaction products in the organic solvent (DCM) in the modified proof-of-concept experiment with co-generation of hydrogen and 1,2-dibromohexane.

[0152] Fig- 7- General depiction of a process according to some embodiments of the invention.

[0153] Figs. 8A-B- Hybrid electrosynthesis. (A) Schematic illustration of the hybrid electrosynthesis process in a mixed phase solution of aqueous NaBr electrolyte mixed with organic solvent containing an olefin that is converted to epoxide. (B) Anodic (top) and cathodic (bottom) current density versus potential (IR corrected) polarization curves in a water-acetonitrile mixed phase solution (1:1 v:v ratio) containing 0.3M NaBr in the aqueous phase and 0.02M styrene in the organic phase ((1) curves), 0.3M NaBr (pH ~ 7, (2) curves), 0.3M NaNO3(pH ~ 7, (3) curves), and 0.3M NaBr with 0.5M H2SO4 (pH ~ 0, (4) curves). The measurements were carried out by chronoamperometry measurements at constant potentials, applied for 30 seconds, under stirring (350 rpm), except for a complementary measurement in 0.3M NaBr without stirring ((5) curve). All the measurements were carried out in room temperature using freshly prepared solutions.

[0154] Fig. 9- Comparison with previous studies. Cell voltage (IR corrected) vs. steady-state current density results obtained by galvanostatic measurements at different current densities ranging from 5 to 500 mA cm-2((1) circles). The error bars present the standard deviation of four repeated measurements under the same conditions. For comparison, results of previous studies on hybrid electrosynthesis are presented by (2) and (3) colors for membrane and membraneless cells, respectively, and circles, squares, and triangles for bromide-, chloride-, and ROS-mediated epoxidation reactions, respectively.

[0155] Fig. 10- Epoxide yield and Faradaic efficiency. Epoxide yields (left, red) and Faradaic efficiency (right, blue) values versus cathodic (up) and anodic (bottom) current density. Electrolysis was carried out in a water-acetonitrile mixed-phase solution (50 mL, 1:1 v:v ratio) containing 0.3M NaBr in the aqueous phase and 0.02M styrene in the organic phase, except for the highest current test (marked with *) that was carried out with a 10 times larger volume of 500 mL. The left insert presents a photograph of the membraneless cell before electrolysis, and the right insert shows the same cell during electrolysis at a constant current of 200 mA.

[0156] Fig. 11-1H-NMR spectrum of the crude product from epoxidation in the electrolytic cell with 9.6 mmol styrene as organic substrate and 14.0 mmol of accumulated electron transfer (i.e., 7.0 mmol of HBrO assuming Faradaic efficiency of 100%), produced by electrosynthesis at a constant current of 500 mA (current density of 250 mA cm-2on anode) for 2800 s in water-acetonitrile mixed solution (1:1 v:v ratio) containing 0.3M NaBr in the aqueous phase at a larger scale with a total volume of 0.5 L.1H NMR (500 MHz, CDCl3) 8 6.68-6.62 (dd, 0.30H), 5 5.72-5.67 (dd, 0.31H), 5 5.18-5.16 (d, 0.32H), 5 3.79-3.77 (t, 1.00H), 5 3.07-3.06 (m, 1.03H), 5 2.73-2.72 (dd, 1.04H). *The integration of the NMR signals is the ratio between residue reactant and produced products. Figs. 12A-C- Durability test. (A) Electrolysis setup for measuring the volume of H2 gas that evolved during the durability test. (B) Amount of H2 gas evolved during ten consecutive one-hour long electrolysis tests (colored curves) at a constant current (100 mA), in comparison to the amount predicted by the charge (current x time product) assuming two electrons per H2 molecule (black curves). (C) IR corrected cell voltage (colored curve, left y-axis) versus time during the same electrolysis tests as in panel (B), and cathodic Faradaic efficiency values (diamond symbols, right y-axis) for each segment of electrolysis test. The electrolysis test was carried out in a sealed three-neck flask (100 mL) with a water-acetonitrile mixed phase solution containing a mixture (1:1 v:v ratio) of 0.3M NaBr aqueous electrolyte and 0.02M styrene in acetonitrile, using a DSA anode (1 cm2) and a Pt foil cathode (1 cm2). Each one-hour segment of the test was carried out with a fresh electrolyte.

[0157] Figs. 13A-E- Electrode stability. SEM micrographs and EDS elemental maps of Ti and Ru (magenta and green, respectively) of the DSA anode before (A) and after (B) the durability test. (C) Raman spectra of the DSA anode before (top curve) and after (bottom curve) the durability test, using mapping mode scanning of the selected areas marked in the optical micrographs in panel (D). The optical micrographs framed with black and red frames in panel (D) represent the anode before and after the durability test, respectively. (E) XRD diffractograms of the DSA anode before (top) and after (middle) the durability test. The intensity difference (A) between them is presented by the bottom curve.

[0158] Fig. 14- Benchmark radar chart. Comparison of anodic and cathodic Faradaic efficiencies, product selectivity, and cell voltages at 100 and 300 mA / cm2. The shape and color of the data points are consistent the other results presented herein, where circles mark with (1) correspond to this work, (2) and (3) symbols represent membrane and membraneless systems, squares and circles represent chloride- and bromide-mediated processes, respectively.

[0159] Fig. 15- Process diagram. Schematic illustration of the overall process with electrolytic cell producing gaseous hydrogen (EE) and liquid bromine (Bn) in hydrobromic acid (HBr) electrolyte, chemical cell producing sulfuric acid (H2SO4) and recovering the HBr by chemical looping of Bn with water (H2O) and sulfur (S), and a distiller separating the HBr (that returns to the electrolytic cell) and H2SO4.

[0160] Figs. 16A-G- Electrochemical measurements. (A) Schematic illustration of an undivided (membraneless) electrolytic cell with spontaneous biphasic separation of the hydrogen gas produced at the cathode and liquid bromine produced at the anode. (B) and (C) Photographs of an electrolytic cell before electrolysis begins (B) and during electrolysis at a constant current of 1 A (C). (D) Anodic current density versus anodic potential curves (IR corrected) in different HBr concentrations ((1) to (7) represent 0.0 to 2.0 M of HBr, pH ~ 0), obtained by linear sweep voltammetry (LSV) measurements. (E) Tafel slope of the anodic LSV measurements at different bromide concentrations, [Br−].

[0161] (F) Cathodic current density versus potential curves (IR corrected) in 1.5M NaBr (1) and 1.5M HNO3 (2) (pH ~ 0), respectively, obtained by LSV measurements.. All the LSV measurements were conducted with a potential scan rate of 5 mV / s. (G) Cell voltage (IR corrected) vs. steady-state current density results obtained by galvanostatic measurements at different currents ranging from 5 to 2500 mA. The error bars present the standard deviation of at least two repeated measurements under the same conditions. (1)-(5) points present this work and the results in alkaline electrolyzer (AEL), anion exchange membrane electrolyzer (AEMEL), proton exchange membrane electrolyzer (PEMEL), solid oxide electrolysis cell (SOEC), respectively, reported in literature.

[0162] Figs. 17A-D- Durability test. (A) Photograph of custom-made electrolyzer for the electrolytic process. (B) A close-up view of the electrolyte and electrodes within the electrolyzer during electrolysis. (C) IR-corrected cell voltage (top), amount of EE evolved (bottom, (1)) versus time during a 45-minute electrolysis test at a constant current density of 1 A / cm2, compared with the theoretical amount predicted from the charge (current x time), assuming two electrons per EE molecule ((2) curve). (D) IR-corrected cell voltage (top, left y-axis), voltage efficiency (top, right y-axis), amount of EE evolved (bottom, left y-axis) compared with the theoretical amount (dash curves) versus time during ten segments of electrolysis tests (colored curves) at a constant current of 0.5 A / cm2, and cathodic Faradaic efficiency values (star symbols, bottom, right y-axis) for each segment of test. The 1stand 7thsegments used freshly prepared electrolyte; the 2nd, 3rd, 4th, 8th, and 9thsegments used the electrolyte after distillation; the 5thand 10thsegments used the electrolyte after air-blowing; and the 6thsegment used the electrolyte after the addition of TBAB and filtration. Distillation, air-blowing, and the addition of TBAB were applied for separating the produced bromine from the HBr electrolyte. The electrolysis tests were carried out in the custom-made electrolyzer (A, B) with 1.5 M HBr electrolyte (0.75 L), using a DSA anode (1 cm2) and Pt foil cathode (1 cm2).

[0163] Fig. 18- Air-blowing method was used to remove the produced bromine (Bn) from the reddish-brown HBr electrolyte after electrolysis. The separated bromine was separated with the air-flow and collected in aqueous tetrabutylammounium bromide (TBAB) solution, where the yellow precipitate is the formed liquid tetrabutylammounium tribromide (TBATB).

[0164] Fig. 19- Electrolysis in mixed mode after chemical looping. (Top) IR-corrected cell voltage versus time during electrolysis using a mixed mode, 1 A cm-2for 20 seconds and 0 A cm-2for 10 seconds in a cycle, for 300 cycles. The experiment used DSA (1 cm2) anode and Pt foil (1 cm2) cathode in the custom-built flow electrolyzer, containing the solution after chemical looping (2 g of sulfur, 10 mL of bromine, and 260 mL of water that makes the final HBr concentration as 1.5 M). (Bottom) A zoom-in view of the cell voltage versus time curve between 4000 and 5000 seconds.

[0165] DETAILED DESCRIPTION OF EMBODIMENTS SYSTEM I - Production of hydrogen (H2) and bromine (B ), or bromine products, in a biphasic system comprising aqueous electrolyte and immiscible organic solvent Fig. 1A illustrates a general hybrid electrolysis process that produces gaseous hydrogen, H2(), and liquid bromine, Br2(), in the first step (step 1), and separate the produced bromine into a storage vessel or use it further for bromination processes that involve di-bromination or radical bromination reactions in the second step (step 2). A biphasic electrolytic cell is used in step 1 (Fig. IB), with an aqueous phase containing water as solvent, sodium bromide (NaBr) as bromide (Br“) source and sulfuric acid (H2SO4) for maintaining acidic conditions that prevent the hydrolysis of bromine (which occurs at pH > 7), and an organic phase comprising an immiscible and high-density organic solvent such as dichloromethane (DCM), chloroform or carbon tetrachloride. The organic phase is heavier (p = 1.33 g / cm3for dichloromethane, 1.49 g / cm3for chloroform and 1.59 g / cm3for carbon tetrachloride) than the aqueous phase (p = 1.13 g / cm3for 1,5M NaBr in water), therefore it sinks down to the bottom of the cell and spontaneous phase separation is achieved without effort. To maintain the phases separated, the electrolytic process is carried out without stirring. Upon applying a constant current to the electrodes in the upper part of the electrolytic cell (Fig. IB), the cathode produces hydrogen by the hydrogen evolution reaction (HER) while the anode produces bromine (Bn) by the bromine evolution reaction (BER). The overall reaction produces hydrogen bubbles that purge out of the electrolyte to the headspace of the cell (and from there the hydrogen can flow to a storage vessel), and liquid bromine (p = 3.12 g / cm3) that sinks down to the bottom of the cell where it dissolves into the organic phase, turning its color from transparent (Fig. IB) to dark red as electrolysis proceeds (Fig. 1C). Some bromine remains in the upper part of the cell, turning its color from transparent (Fig. IB) to orange (Fig. 1C). The brominerich organic phase can be readily drained out from the bottom of the electrolytic cell and transferred to another vessel in order to store the bromine or, alternatively, use it further for bromination reactions such as mono-bromination under sunlight radiation or heat, dibromination, alcohol oxidation or other reactions that produce high-value chemicals.

[0166] Cathode: H2SO4 + 2e“ — > H2 + SCU2' (rxn. 1)

[0167] Anode: 2NaBr Bn + 2e“ + 2Na+(rxn. 2)

[0168] Overall: H2SO4+ 2NaBr → H2+ Br2+ 2Na++ SO42−(rxn. 3)

[0169] The hybrid electrolytic process was examined in a biphasic system with an aqueous electrolyte of NaBr at different concentration (0 to 1.5 M) and 0.5 M H2SO4 to maintain acidic conditions (pH ~ 0) in order to prevent bromine hydrolysis, and an organic solvent DCM that collects the bromine produced at the anode and separates it from the aqueous electrolyte (Fig. IB). Since it was aimed to demonstrate membraneless electrolysis, the electrolytic cell was not divided into cathodic and anodic compartments. The anode, a commercial RuO2–TiO2 / Ti dimensionally stable anode (DSA), was immersed deeper into the electrolyte (2 cm) than the Pt cathode (1 cm, Fig. IB) to reduce crossover of the bromine from the anode to the cathode where it can be reduced, which would result in a Faradic loss. Therefore, the cathodic current density, Jc= I / Acwhere I is the current and Acis the geometric cathode area (1 cm2), is twofold higher than the anodic current density, Ja= I / Aawhere Aais the geometric anode area (2 cm2). Some measurements were carried out in a three-electrode configuration using an Hg / Hg2SO4 reference electrode to record the anode and cathode potentials (Figs. ID and IF), whereas other measurements were carried out in a two-electrode configuration that measures the overall voltage between the anode and cathode, aka the cell voltage, Vcell(Fig. 1G). In keeping with the conventional practice in water electrolysis, Vcellwas corrected by reducing the current (I) x resistance (R) product from the voltage applied by the potentiostat (Vapp), Vcell= Vapp− IR. R, the series resistance, was measured by the current interruption method.

[0170] Fig. ID shows that the anodic current density increases, at a given potential, and the anode potential decreases, at a given current density, with increasing NaBr concentrations. Thus, a high NaBr concentration is constructive for achieving fast bromine evolution and low overpotential (high efficiency), while suppressing competing oxygen evolution that occurs at high anodic potential (> 1.5 V vs. RHE, see black curve measured without NaBr). At low NaBr concentrations (< 0.2 M) the current is limited by the bromide concentration, [Br], giving rise to a current plateau at high potentials (1.4 - 1.5 V vs. RHE) due to mass transport limitations. At high concentrations (> 0.5 M) these limitations are mitigated and the current density increases exponentially with the potential, typically to polarized electrodes. At the highest NaBr concentration (1.5 M, red curve), the anodic current density reaches 0.5 A / cm2at a potential of 1.33 V vs. RHE, far below the onset of oxygen evolution (1.5 V vs. RHE, black curve). Tafel analysis of the anodic current density versus overpotential curves, assuming a logarithmic relationship J = J0exp(η ln(10) / A) where η = E − Erevis the overpotential, E is the applied potential (IR-corrected), Erevis the reversible potential (aka the Nernst potential) and A is the Tafel slope. Stable Tafel slopes were found in all the LSV measurements (at different bromide concentrations) at overpotentials ranging between 20 and 150 mV, increasing linearly from 70 to 85 mV / dec with increasing bromide concentrations from 0.05 to 1.5 M (Fig. IE). This observation implies that the rate-determining step reaction depends on the bromide concentration. Furthermore, the linear dependence of the Tafel slope A on the bromide concentration [Br] implies a first-order reaction. Among the different BER mechanisms, the Volmer-Heyrovsky mechanism seems most plausible, where both steps are first-order reactions. Thus, the reaction order has no change in spite of a plausible shift of the rate-determining step from the Volmer step to the Heyrovsky step with increasing bromide concentrations, as suggested by the Tafel analysis. The exchange current density Jowas found to increase 30-fold from 0.1 to 3.4 mA / cm2with increasing bromide concentrations from 0.05 to 1.5 M, demonstrating faster kinetics of bromide oxidation at high [Br ]. Fig. IF shows that the cathodic current density has a small overpotential of ~60 mV at 100 mA / cm2, and it hardly changes with NaBr (1.5 M) and without it (0 M). This is attributed to the addition of H2SO4 (0.5 M) that provides an acidic environment (pH ~ 0) that facilitates the HER by providing plenty of protons for the reaction. This is an important advantage of the hybrid electrolysis process over tests carried out at nearneutral pH and presented a cathodic overpotential of over 200 mV at half the current density value (50 mA / cm2), despite using the same cathode (Pt foil). Operation in acidic electrolyte reduces the cathodic polarization loss and increases the energy efficiency for the production of hydrogen.

[0171] Steady state galvanostatic measurements were carried out in 1.5 M NaBr and 0.5 M H2SO4 electrolyte at different current densities ranging from 5 mA / cm2to 1 A / cm2for the anode and from 10 mA / cm2to 2 A / cm2for the (smaller) cathode. The measurements were repeated three times, resulting in reproducible results. The average cell voltage (Vcell) and standard deviation extracted from these measurements are presented in Fig.

[0172] 1G, displaying Vcellas a function of the anodic current density on the primary x-axis (bottom) or the cathodic current density on the secondary x-axis (top). A cell voltage of only 1.14+0.03 V (IR corrected) is needed to drive hydrogen evolution at the cathode and bromine evolution at the anode at a low current density of 10 and 5 mA / cm2, respectably. This result corresponds to a low overvoltage of only 54+30 mV close to the onset of these reactions. In contrast, the OER alone gives rise to a minimum overpotential of 200-400 mV in water electrolysis, due to the four charge transfer steps that are required to generate an O2 molecule which strain the bonds with different reaction intermediates. This difficult reaction is replaced here by the BER that involves two charge transfer steps instead of four in the OER. At the highest current density, 2 A / cm2at the cathode and 1 A / cm2at the anode, the cell voltage reaches 1.76+0.06 V (IR corrected), on par with state-of-the-art PEM electrolyzers. To compare with water electrolysis, the voltage efficiency was defined with regards to the higher heating value (HHV) of the hydrogen produced at the cathode, 1.48 V / Vcell. The cell voltage and voltage efficiency values at different current densities are presented in Table 1. The voltage efficiency of the process exceeds other decoupled water electrolysis processes, and is on par with the best electrolyzers reported to date.

[0173] Besides the volage efficiency, the current (i.e., Faradaic) efficiency is another important benchmark in electrolysis. To examine the Faradaic efficiency of our process, chronopotentiometry measurements at constant currents of 0.5, 1.0, and 2.0 A were carried out for 1, 0.5 and 0.25 h, respectively, passing a constant charge of 1800 C between the electrodes. The amount of bromine produced during these measurements was analyzed by iodometric titration. Since part of the bromine remained in the electrolyte while the most dissolved in the organic solvent (Fig. 1C), the bromine content in each phase was measured by iodometric titration of aliquots of the respective phases. The sum of bromine in both phases was converted to a Faradaic charge, QF, by assigning two electrons per Bn molecule and the Faradaic efficiency was calculated by dividing QF by 1800 C. The results are presented in Table 1. First, the effect of electrolyte composition on Faradaic efficiency was examined. The baseline electrolyte comprised 1.5 M NaBr and 0.5 M H2SO4 in deionized water, without additives. This electrolyte yielded Faradaic efficiency above 85% at cathodic current densities of 0.5 and 1 A / cm2, dropping slightly to 81±4% at 2 A / cm2. About three quarters (-75%) of the bromine was in the organic solvent, and one quarter remained in the aqueous electrolyte. This remainer can be readily extracted from the electrolyte by distillation or adding tetrabutylammonium bromide to it to produce tetrabutyl ammonium tribromide precipitates, [(CH3CH2CH2CH2)4N]+Br~ + Br2-> [ CH3CH2CH2CH2)4N]+Br3~ f. This reaction converted the electrolyte from an orange solution (Fig. 1C) to a colorless solution, indicating that no bromine remained in it. In a continuous process, the bromine-rich organic solvent (DCM) would be constantly replaced by a fresh solvent. This would increase the concentration gradient and the driving force for bromine to dissolve in the organic solvent (in comparison to the batch process demonstrated in this work), reducing the amount of bromine that remains in the aqueous electrolyte.

[0174] In the batch experiments, the bromine that remained in the electrolyte could reach the cathode and be reduced back to bromide. This backward reaction, the so-called redox shuttling, results in a Faradic loss of nearly 13% at cathodic current densities of 0.5 and 1 A / cm2, increasing to -19% at 2 A / cm2. Without the organic solvent, the Faradaic efficiency dropped from 86±5% to 69±1% (at 1 A / cm2), demonstrating the advantage of using an organic solvent to collect the bromine produced at the anode and separate it from the electrolyte where it can be reduced at the cathode. Increasing the distance between the electrodes from 0.5 to 2 cm had little effect on the Faradaic efficiency, but it increased the cell voltage from 2.23±0.2 V to 3.43±0.5 V (at 1 A / cm2, without IR correction) by increasing the series resistance in the electrolyte. Adding Na2Cr2O7(1 g / L) to the electrolyte increased the Faradic efficiency from 86±5% to 93±5% (at 1 A / cm2), with a small change in the cell voltage that increased from 2.7±0.2 V to 2.9±0.4 V (without IR correction). Both effects are assigned to a chromium hydroxide (Cr(OH)3) thin layer that coated the cathode by cathodic deposition of chromium ions during the electrolysis process, as reported elsewhere. On the one hand this layer prevents the reduction of bromine at the cathode, increasing the Faradaic efficiency, but on the other hand it increases the series resistance (R), decreasing the voltage efficiency. The Na2Cr2O7additive yields toxic and carcinogenic Cr(VI) ions in the electrolyte, and its use has been restricted in Europe, USA and other countries. Adding the organic solvent (DCM) reduces the Faradaic loss, enabling membraneless electrolysis without using Na2Cr2O7.

[0175] The effects of NaBr concentration and H2SO4 were also examined. Reducing the concentration of NaBr from 1.5 M to 1 M was found to have a counter-productive effect, reducing the Faradic efficiency from 86±5% to 78±3% (at 1 A / cm2). Increasing it to 3 M had a negligible influence on the Faradaic efficiency. Likewise, removing H2SO4 from the electrolyte had a negligible influence on the apparent Faradic efficiency, but it led to a steep increase in the cell voltage to 3.71 V (IR corrected, at 1 A / cm2). It should be noted that without H2SO4 the electrolyte was no longer acidic and the pH increased from 7 up to 12 during electrolysis. Under these conditions, bromine (Bn) is unstable in the electrolyte and it converts to BrCU and BrO", as was confirmed by UV-vis spectroscopy.

[0176] Current Average Faradaic Bn in Bn in organic Electrolyte additional density voltage3efficiency aqueous solvent conditions (anodic; and voltage (%) electrolyte

[0177] cathodic) efficiency

[0178] 1.5 M NaBr / 0.25;0.5 1.43 V, 87±3 2.2±0.1 mmol 5.8±0.2 mmol O.5 M H2SO4 A / cm2103±2% (27%) (73%) 1.5 M NaBr / 0.5; 1 A / cm21.47V, 86±5 1.9±0.2 mmol 6.1±0.3 O.5 M H2SO4 101±10% (23%) mmol (77%) 1.5 M NaBr / 1; 2 A / cm21.76 V, 81±4 2.4±0.1 mmol 5.1±0.3 O.5 M H2SO4 84±5% (32%) mmol

[0179] (68%)

[0180]

[0181] 1.5 M NaBr without DCM 0.5; 1 A / cm21.53V, 69±1 6.4±0.1 mmol / O.5 MH2SO4 97±6% (100%)

[0182] 1.5 M NaBr 2 cm distance 0.5; 1 A / cm22.32V, 84±3 2.2±0.1 mmol 5.6±0.2 O.5 MH2SO4 47±12% (28%) mmol (78%) 1.5 M NaBr lg / L 0.5; 1 A / cm21.60 V, 93±5 3.3±0.3 mmol 5.4±0.2 O.5 MH2SO4 Na2Cr2O793±15% (37%) mmol (63%) 1.0 M NaBr / 0.5; 1 A / cm21.49V, 78±3 2.8±0.1 mmol 4.5±0.2 O.5 MH2SO4 99±11% (38%) mmol (62%) 3.0 M NaBr / 0.5; 1 A / cm21.55V, 86±6 2.7±0.1 mmol 5.3±0.5 O.5 MH2SO4 95±12% (34%) mmol (66%) 1.5 M NaBr 2 cm distance; 0.5; 1 A / cm23.71V, 88±4b5.2±0.2 mmol 3.1±.2 mmol (without pH from 7 to 40% (61%) (39%) H2SO4) 12

[0183]

[0184] Table 1. Voltage efficiency, Faradaic efficiency and the distribution of the produced bromine in the aqueous electrolyte and organic solvent phases at various experimental conditions, a: The cell voltage values were IR corrected, b: Without H2SO4 the electrolyte was mildly alkaline (pH 12) and the Bn was converted to BrCh' and BrO" in the electrolyte.

[0185] Bromination reactions

[0186] The bromine produced in the first step (step 1) can be further used to convert low-value chemicals into high-value chemicals, as demonstrated in the following examples.

[0187] Example 1: Electrolysis of a biphasic water / DCM system was carried out at a constant current density of 300 mA / cm2in 1.5M NaBr aqueous electrolyte with 0.3M borate buffer, and organic solvent (dichloromethane, DCM) forming a bottom phase of the cell. A depiction of the cell is illustrated in Fig. 2A and Fig. 3.

[0188] Following the electrolysis, the bromine-rich DCM was transferred to a different cell and 0.0028 mol of cyclohexene was added to it. This quantity corresponds to the amount of bromine (0.0028 mol) produced from 0.0056 mol of electron transferred during electrolysis, calculated based on the current x time (= charge) with 2 electrons per Bn molecule. The solution was stirred and it quickly turned transparent after adding the

[0189] cyclohexane to it, indicating the bromination reaction,

[0190]

[0191] , was complete as shown in Figs. 4A, 4C. The composition of the transparent solution was analyzed by 'H-NMR and gas chromatography, showing about 87%-90% conversion to 1,2-dibromohexane, as shown in Fig. 5.

[0192] Similar to the mentioned bromination with cyclohexene, an example of radical halogenation is shown in Figs. 4B, 4D, where the bromine-rich DCM was transferred to a different cell and 0.0028 mol of toluene was added to it. The solution did not have any change until it was exposed under sunlight where it quickly turned white from red color,

[0193] indicating the photo-initiated radical halogenation reaction,

[0194]

[0195] was complete. The composition of the resulted solution was analyzed by 'H-NMR and gas chromatography, showing about 87-92% conversion to benzyl bromide.

[0196] Example 2: A process modification was demonstrated by introducing the cyclohexane to the DCM solvent prior to the beginning of the electrolysis experiment, while other electrolysis setting remains the same as example 1. During electrolysis, the bromine sinks to the bottom of the cell where it reacts with cyclohexane and converts it to 1,2-dibromohexane, as illustrated in Fig. 2B. As a result, the DCM stays transparent during electrolysis. The reaction products in the organic solvent (DCM) were analyzed by 'H-NMR and gas chromatography, yielding similar results to the batch process in the first proof-of-concept, with a yield of 77%-82% for 1,2-dibromohexane and a yield of 12% for 2-bromocyclohexanol, as shown in Fig. 6.

[0197] The examples disclosed herein demonstrate hydrogen production combined with organic synthesis using bromine or, alternatively, hypobromous acid. The general process scheme is depicted in Fig. 7.

[0198] This route (System I) aims at producing bromine, storing it in an organic solvent that is phase-separated from the aqueous electrolyte in which the hydrogen is produced (Fig. 2A and 2B) The bromine-rich organic solvent can be used to drive bromination

[0199] reactions such as cyclohexane to 1,2-dibromohexane (^

[0200]

[0201] ) as was demonstrated in example 2. This route applies essentially to any unsaturated organic molecules with carbon-carbon double bonds (C=C) and triple bonds (C=C). In addition, employing UV light or even sunlight can induce radical bromination with vast types of organic molecules, producing mono-Br-substituted products, such as converting low- > value toluene to a value-adding chemical benzyl bromide

[0202]

[0203] ( ) as was demonstrated in example 1. Alternatively, the bromine can be extracted from the organic solvent and be used as a feedstock for the bromine industry, with applications ranging from producing pesticides such as bromomethane (commonly called methyl bromide) to flame retardants and many other products.

[0204] Herein, it is worth noting that this route for the production and collection of bromine via electrolysis in a biphasic system such as the ones illustrated in Figs.2A and 2B can be also applied in a similar fashion for the purpose of iodine production. Replacing aqueous bromide by aqueous iodide can lead an anodic reaction that oxidizes iodide ions to iodine,

[0205]

[0206] 21" h + 2e" with low potential of E° = +0.54 V at pH 0, where the generated iodine is insoluble in water but dissolves in organic medium, such as dichloromethane (58.6 g / L).

[0207] SYSTEM II - Production of hydrogen (H2) and epoxides by partial epoxidation of alkenes (olefins) in a mixed phase system

[0208] In this part, a path forward is presented for achieving substantial and additional benchmarks in a membraneless electrolytic cell that separates the hydrogen produced at the cathode and the epoxide produced in the solution without dividing the cell into separated compartments. The inventors present here a new process that produces hydrogen and epoxide by adding organic solvent (acetonitrile) mixed with olefin (styrene) to an aqueous NaBr electrolyte. Instead of splitting water into hydrogen and oxygen, this bromide-mediated electrolysis produces hydrogen and replaces the anodic oxygen evolution with partial oxidation of olefins to produce high-value epoxides.

[0209] The overall process in System II comprises of electrochemical and chemical reactions that generate gaseous hydrogen and liquid bromine at the anode, whereby the bromine reacts with olefins in the mixed-phase (homogenous) solution, which are subsequently converted to epoxides by reaction with hydroxide ions. The overall reaction consumes water and olefin (and electrical energy) and produces hydrogen and epoxide, as illustrated in Fig. 8A. Electrochemical reactions

[0210] Cathode: H2O + 2e“ — H2 + OH“ (rxn. 1)

[0211] Anode: Br“ -*■ Bn + 2e“ (rxn. 2)

[0212] The process begins by presenting cathodic and anodic chronoamperometry and linear sweep voltammetry (LSV) measurements that were carried out in a three-electrode configuration using an Ag / AgCl reference electrode to record the corresponding potentials, followed by electrolysis measurements in a two-electrode configuration that measures the overall cell voltage. All the electrolytic measurements were carried out in undivided electrolytic cells with water and acetonitrile mixed phase solution (1:1 v:v ratio) with 0.3 M NaBr in the aqueous phase (pH 7), unless otherwise specified. In keeping with the conventional practice in water electrolysis, the IR-corrected cell voltage, cathodic and anodic potentials, are presented corrected by subtracting the current (I) x resistance (R) product from the voltage (potential) applied by the potentiostat.

[0213] The electrolytic process comprises cathodic HER and anodic bromine evolution reaction (BER). Cathodic and anodic polarization curves are shown in Fig. 8B. In still electrolyte (without stirring), the cathodic polarization presents a typical exponential Tafel curve with an onset potential of -1.14 VAg / Agciat 10 mA cm'2(Fig. 8B, blue curve). Hydrogen bubbles evolved at the cathode, and the solution turned yellowish at the anode, indicating bromine evolution. The yellow liquid sank down to the bottom of the cell. The onset potential of the anodic reaction was 0.87 VAg / AgCl at 10 mA cm'2. Unlike the cathodic curve, the anodic curve presents a shoulder at 40 mA cm'2(blue curve), indicating mass transport limitation. No gas bubbles evolved at the anode. These observations, especially the shoulder at 40 mA cm'2, indicate that the anodic reaction was BER rather than water oxidation, since water is prevalent which excludes mass transport limitations at this current density. To confirm this, a control experiment with 0.3 M NaNCE instead of NaBr was carried out (Fig. 8B, orange curve). The onset potential of the anodic reaction, at 10 mA cm'2, increased from 0.87 VAg / AgciinNaBrto 1.45 VAg / Agci in NaNCE, corresponding to bromine and oxygen evolution reactions, respectively. Thus, under these conditions, the overpotential for (the onset of) bromine evolution is lower by 0.58 V than for oxygen evolution, showcasing one of the advantages of replacing OER by BER. When stirring the electrolyte (Fig.8B, red curve), the cathodic curve (dashed line) shifted anodically by about 0.1 V and the shoulder at the anodic curve (solid line) disappeared. Thus, stirring reduces both cathodic and anodic overpotential losses at current densities above 30 mA cm'2. However, the IR-corrected cell voltage, i.e., the difference between the anodic and cathodic potentials, was still high, reaching 1.80 V at 10 mA cm'2, corresponding to an overvoltage of 0.71 V with respect to the reversible cell voltage, 1.09 VSHE - 0 VSHE = 1.09 V. Clearly, under these conditions, almost all the overpotential is caused by the cathodic reaction. This demonstrates the difficulty of evolving hydrogen in near neutral-pH electrolytes, a well-known challenge in seawater and mild alkaline water electrolysis. To examine the performance limits, in terms of cathodic polarization, of our system, we added 0.5M sulfuric acid to the mixed-phase electrolyte (Fig. 8B, green curve) to create favorable low-pH conditions for hydrogen evolution. Consequently, the cathodic curve shifted anodically by -0.80 V, reaching 10 mA cm'2at -0.23 VAg / AgCi, whereas the anodic curve (solid line) shifted slightly to higher overpotentials. The remarkable reduction in the cathodic polarization loss suggests that there is large room for improvement by facilitating water dissociation (H-OH bond cleavage), and / or promoting H20* / 0H* intermediates at the electrode / electrolyte interface, as reported elsewhere. The increase in the anodic overpotential can be assigned to the competition between sulfate and bromide anions absorption.

[0214] Fig. 8B present cathodic and anodic potentiostatic and LSV measurements (black curves) in the baseline mixed phase solution with 0.3M NaBr aqueous electrolyte mixed (1:1 v:v ratio) with acetonitrile containing 0.02M styrene. Adding the styrene gives rise to a small anodic shift in both the cathodic and anodic polarization curves (0.05 and 0.10 V, respectively). Both shifts are assigned to styrene adsorption at the respective electrodes. Styrene adsorption at the cathode enhances the HER activity by modifying the binding energy of protons on the Pt surface, whereas styrene adsorption at the anode competes with the BER by occupying active sites at the surface. The latter explanation is consistent with bromide-mediated oxidation, otherwise the anodic overpotential decreases as styrene is directly oxidized by the anode with low selectivity and yield. Thus, the decrease in the cathodic polarization partially cancels out the increase in the anodic polarization. A cell voltage (IR-corrected) of 2.18±0.04 V is obtained from the difference between the anodic and cathodic potentials at a current density of 50 mA cm'2, nearly the same as without styrene (2.12±0.05V). Steady-state galvanostatic measurements were carried out in water-acetonitrile mixed phase solution with 0.3M NaBr in the aqueous phase and 0.02M in the organic phase, over a broad range of current densities, from 5 to 500 mA cm-2. Fig.9 presents the IR-corrected cell voltage as a function of current density, along with data from previous reports on hybrid electrosynthesis for the co-production of hydrogen and epoxides. The previous reports are divided into membrane and membraneless electrolysis categories (blue triangles and green squares, respectively). The previous results are quite scattered, and our results outperform all of them except for one report that employed diaphragm electrolysis cell and achieved a product selectivity of 75%, considerably lower than in our case (99%). A cell voltage of 1.89 V was achieved at 10 mA cm'2, 2.34 V at 100 mA cm'2and 3.27 V at 500 mA cm-2. These voltage values are higher than state-of-the-art PEM and alkaline water electrolyzers that typically operate at 1.8-2 V at current densities of 1-3 A cm'2and 0.5-0.8 A cm'2, respectively. The voltage gap is most likely due to the difficult HER in our neutral-pH mixed-phase solution. However, the difference is not drastic, and advances in electrode design and process optimization could further lower voltage and enhance efficiency. Overall, the results outperform previous reports on hybrid electrosynthesis and are within reach of competitive voltage values for water electrolysis.

[0215] Chemical reactions

[0216] Bromide-mediated epoxidation proceeds by a sequence of electrochemical and chemical reactions. Electrolysis yields hydrogen gas at the cathode and liquid bromine at the anode. The hydrogen evolves into the gas phase, whereas the bromine is hydrolyzed by water in the bulk solution, producing hypobromous acid (HBrO), as confirmed by UV-vis spectroscopy. The electrophilic HBrO undergoes bromohydroxylation with the olefin substrate, resulting in the formation of a bromohydrin intermediate. Finally, the bromohydrin is dehydrated by the hydroxide ions (OH ) produced at the cathode, yielding the corresponding epoxide as the end product. Overall, the pairing of the electrochemical reactions and the epoxidation reactions consumes only water and olefin to produce hydrogen and epoxide, as illustrated in Fig. 8A.

[0217] Br2 + H2O HBrO + HBr (rxn.3)

[0218] RCH=CH2+ HBrO R(OH)CHCH2Br (rxn. 4)

[0219] R(OH)CHCH2Br + OH“ RCHCH2O + H2O + Br (rxn. 5) H20 + RCH=CH2RCHCH2O + H2(rxn. 6)

[0220] The hybrid electrosynthesis of hydrogen and epoxide was examined at currents ranging from 50 to 500 mA, using a 1 cm2Pt foil cathode and a 2 cm2DSA anode. Cathodic current density values of hundreds of mA per cm2are practical for hydrogen production. At first, the electrolysis was examined at the lowest current, 50 mA. The water-acetonitrile mixed phase solution containing 0.3M NaBr in the aqueous electrolyte was clear and colorless until the electrolysis began, and once the electrodes were polarized hydrogen bubbles began to evolve (Fig. 10). 'H-NMR analysis of the electrolyte after 50 minutes of electrolysis at 50 mA revealed high yield of epoxide production (96±2% of the loaded styrene), and the anodic Faradaic efficiency was 100±2%. These results show that no backwards reactions due to redox shutting of Br2, HBrO and epoxide took place, despite the fact that the cell was undivided into cathodic and anodic compartments. This also implies that the cathode functioned entirely toward hydrogen evolution, as confirmed by hydrogen evolution measurements.

[0221] Subsequent tests at higher currents of 100, 200, and 400 mA maintained high epoxide yield and anodic Faradaic efficiency values above 80% and 93%, respectively. The small drop in comparison to the first test at 50 mA was mainly due to the limited capacity of the electrolyte (50 mL). Therefore, the final test at the highest current, 500 mA, was carried out in a larger cell with electrolyte volume of 500 mL, under the same concentration of NaBr (0.3M) and styrene (0.02M), achieving high epoxide yield of 98±2% (Fig. ll)and high anodic Faradaic efficiency of 99±1%. These results demonstrate the ideal pairing of hydrogen evolution and epoxidation reactions in our system, without using membrane to divide the cell into cathodic and anodic compartments. The selection of NaBr electrolyte and water-acetonitrile mixed phase solution in our system was proved to be successful for hydrogen production and epoxidation at high rate (500 mA / cm2at the cathode), high Faradaic efficiency (-100%) and high epoxide yield (-100%).

[0222] Hydrogen evolution and durability tests

[0223] The durability of our system was examined during 10 hours electrolysis in which the cathodic Faradaic efficiency (hydrogen evolution) was monitored by measuring the volume of hydrogen gas that was vented out of the cell and dividing by the charge (current x time) that passed through the electrodes during the test. The gas volume was measured by the water-displacement method using a sealed three-neck flask (100 mL) as a membraneless electrolytic cell with undivided Pt foil cathode and DSA anode (Fig. 12A).

[0224] Galvanostatic electrolysis was carried out at a constant current density of 100 mA / cm2 for both anode and cathode (having the same area). Due to the limited cell capacity (100 mL) and small solubility of styrene in the water-acetonitrile mixed phase solution, the solution, containing a mixture (1:1 v:v ratio) of 0.3M NaBr aqueous electrolyte and 0.02M styrene in acetonitrile, was refreshed every hour, diving the 10-hour test into ten one-hour segments, Fig. 12B. The average cathodic Faradaic efficiency was 101±5% for all the tests (Fig. 12C), showing no signs of drift from one test to another. The high cathodic Faradaic efficiency value is commensurate with the high anodic Faradaic efficiency (97±2%) that was quantified by 'H-NMR analysis. Like the stable Faradaic measurements, the cell voltage remained stable throughout the ten one-hour segments of the electrolysis test (Fig. 12C), drifting slightly from 2.43 V at the beginning to 2.54 V at the end of the 10 hours test, corresponding to an average drift rate of 11 mV / h. The voltage drift started on the 6th and stopped on the 9th segment, whereas the other segments were quite stable.

[0225] The electrode stability was examined by SEM, EDS, XRD, XPS, and Raman spectroscopy measurements of the DSA anode (the more sensitive of the two electrodes) before and after the 10-hour durability test. No observable changes in electrode morphology, chemical and phase composition were detected (Fig. 13), as well as in the oxidation states of Ti and Ru, demonstrating electrode stability during this test.

[0226] Discussion

[0227] The hybrid electrosynthesis tests presented high Faradaic efficiency for both the cathodic (102±l%) and anodic reactions (99±1%), reaching high current densities (up to 500 mA cm-2) and low cell voltage (1.89 V at 10 mA cm'2, 2.34 V at 100 mA cm'2and 3.27 V at 500 mA cm-2, IR corrected). Likewise, high product selectivity (up to 99%) was achieved for the epoxidation of styrene to styrene oxide. These benchmarks outperform previous studies on bromine- and chlorine-mediated epoxidation in both membrane and membraneless cells, as shown in Fig. 14 The durability of our system was demonstrated in ten-hour electrolysis test (divided into ten one-hour segments), displaying high Faradaic efficiency (Fig. 12B) and a small drift in cell voltage that was observed only in four out of the ten segments (Fig. 12C) and is therefore suspected to result from an experimental artifact. These promising results were achieved using commercially available DSA and Pt foil electrodes, and low-cost NaBr electrolyte. Additionally, the process was carried out in a membraneless electrolytic cell without division to cathodic and anodic compartments, offering flexibility and simplicity in system architecture and operation, and avoiding membrane stability challenges that are particularly difficult in halide solutions.

[0228] Although demonstrated here using a liquid olefin (styrene) that was partially oxidized to a liquid epoxide (styrene oxide), the system can be adapted to operate with gaseous olefins such as ethylene and propylene, and convert them to gaseous epoxides such as ethylene oxide and propylene oxide, respectively. Upon the introduction of a gaseous olefin, the bromine in the solution would react with the olefin to form bromohydrin intermediate, which would then be dehydrated by hydroxide anion from the cathodic HER to produce the corresponding epoxide. By this way, the active mediator, HBrO, will maximize its efficacy and react homogeneously with the gaseous olefin in the electrolyte, like in the industrial HPPO process. Given their relatively low boiling points (10.7 °C for ethylene oxide and 35 °C for propylene oxide), the dissolved epoxide products can be efficiently volatilized to the gas phase by gentle heating. The same principle also allows straightforward product separation from hydrogen by cooling below the boiling point of the produced epoxide. The overall reaction consumes only olefin and water, thereby enabling low-maintenance operation that primarily involves refilling these two feedstocks.

[0229] SYSTEM III- Production of hydrogen (H2) and sulfuric acid (H2SO4), or other oxoacids, by electrolysis and chemical looping processes.

[0230] The process in System III of the invention is a two-step cycle comprising of electrolysis and chemical looping reactions that are carried out in separate electrolytic and chemical cells, as illustrated Fig. 15. In the electrochemical cell, the anodic reaction produces liquid bromine (Ee= 1.09 VSHE), which is highly selective under acidic conditions and more favorable than oxygen evolution in water electrolysis (2H2O

[0231]

[0232] O2 + 4H++ 4e“, Ee= 1.23 VSHE), in a cold HBr electrolyte at room temperature. Concurrently, hydrogen gas is produced at the cathode (Ee= 0 VSHE) by using protons that are prevalent in the acidic electrolyte, thereby skipping the rate-limiting water dissociation reaction (H2O — H++ OH“) in our previous process. The overall electrochemical reaction is described below. The hydrogen gas vents out of the electrolyte to the headspace of the cell whereas the liquid bromine (p = 3.12 g / cm3) sinks down to the bottom of the cell where it is drained and pumped or blown to the chemical cell for the chemical looping process. In the chemical cell, the liquid bromine is used for producing sulfuric acid and hydrobromic acid with added water and sulfur. This chemical looping reaction oxidizes sulfur by bromine forming sulfur dibromide that reacts with water to produce protons and sulfate ions. The protons combine with the sulfate ions and with the recovered bromide ions (from the sulfur dibromide) to form sulfuric acid, H2SO4, and hydrobromic acid, HBr, respectively. The chemical reaction is exothermic (zlT / 6= -132 kJ / mol), but the solution is heated to 70°C to accelerate the reaction. The solution containing high concentration of HBr after chemical looping can be switched to the electrolytic cell directly for further electrolysis, as the accumulated H2SO4 in this solution further accelerates the hydrogen evolution. The used electrolyte with remained dilute HBr is used in the chemical cell for further chemical looping.

[0233] The HBr is isolated from the solution by distillation, collected and transferred back to the electrolytic cell. The distillation of HBr requires much lower temperature than that of H2SO4 because the boiling point of its azeotrope mixture (48%) with water, 124 °C, is much lower than that of H2SO4, 337 °C. This is an important advantage of our process with respect to the conventional process for producing sulfuric acid. The remainder of the distilled solution, i.e., sulfuric acid, can be transferred for further purification to produce pure product of high commercial value and high demand. Overall, the proposed process consumes 1 equiv. of sulfur and 4 equiv. of water and produces 3 equiv. of hydrogen and 1 equiv. of sulfuric acid.

[0234] Electrochemical step:

[0235] Anodic: 2

[0236]

[0237] Br“ Br2 + 2e“ (rxn. 1)

[0238] Cathodic: 2

[0239]

[0240] H++ 2e“ H2 (rxn. 2)

[0241] Overall: 2

[0242]

[0243] HBr Br2 + H2 (rxn. 3)

[0244] Chemical step:

[0245] S + 3Br2+ 4H2O 6HBr + H2SO4(rxn. 4) Overall process:

[0246] S

[0247]

[0248] + 4H2O 3H2+ H2SO4(rxn. 5)

[0249] The global demand for sulfuric acid was about 261 million Mt (metric tons) in 2024. Given the reaction stoichiometry and the molecular weight of H2SO4and H2, 1 Mt of H2SO4produced in our process comes with 61 kg of H2produced (1:16.3 ratio). Therefore, the proposed process can, in principle, account for a large portion (16%) of the global demand for hydrogen (100 million Mt). Furthermore, this portion can be enlarged by increasing the demand to for sulfuric acid by converting it to other oxoacid products using natural resources such as phosphate rock acidification to produce phosphoric acid, seawater acidification to produce hydrochloric acid with global demand of about 98 and 20 million Mt per year, respectively. Taking together the global markets for sulfuric acid, phosphoric acid, and hydrochloric acid, our process could match as much as -32% of the demand for hydrogen.

[0250] Electrolytic process

[0251] The electrolytic and chemical sub-processes were examined and their operational benchmarks were assessed and compared with those of water electrolysis and sulfuric acid production, respectively. First, the electrolytic process was examined in an undivided electrochemical cell with an aqueous HBr electrolyte and an organic solvent that collects the bromine produced at the anode and separates it from the aqueous electrolyte, as illustrated in Fig. 16A. This spontaneous biphasic separation prevents redox shuttling without membrane cell division or using toxic Na2Cr2O? additive as in our bromate-mediated DWE. Using immiscible and high-density organic solvent such as dichloromethane (DCM, p = 1.33 g / cm3), chloroform (1.49 g / cm3), or carbon tetrachloride (1.59 g / cm3) heavier than the aqueous phase (p = 1.12 g / cm3for 1.5M HBr in water), the organic solvent sinks down to the bottom of the cell and spontaneous phase separation is achieved without effort. To maintain the phases separated, the electrolytic process is carried out without stirring.

[0252] Upon applying a constant current to the electrodes in the upper part of the electrolytic cell, the reaction produces gaseous hydrogen that vents out of the electrolyte to the headspace of the cell, and liquid bromine that sinks down to the organic phase at the bottom of the cell, turning its color from transparent (Fig. 16B) to dark red as electrolysis proceeds (Fig. 16C). Some bromine remains in the upper part of the cell, turning its color from transparent to orange (Fig. 16C). Electrochemical measurements were carried out in three-electrode configuration using a commercial RuCb-TiCb / Ti dimensionally stable anode (DSA), Pt foil cathode, and an Hg / Hg2SO4 reference electrode to record the anode and cathode potentials (Figs. 16D, 16E and 16F), and in two-electrode configuration that measures the cell voltage, Vceii, between the anode and cathode (Fig.

[0253] 16G). In keeping with the conventional practice in water electrolysis, Vcen was corrected by reducing the current (I) x resistance (R) product from the voltage applied by the potentiostat (Vapp), Vcell= Vapp− IR. R, the series resistance, was measured by the current interruption method. The electrochemical measurements were carried out in aqueous electrolyte of HBr at different concentrations ranging from 0 to 2M, at room temperature.

[0254] Fig. 16D shows that the anodic current density increases, at a given potential, and the anode potential decreases, at a given current density, with increasing HBr concentrations. Thus, a high HBr concentration is constructive for achieving fast bromine evolution and low overpotential (high efficiency), while suppressing competing oxygen evolution that occurs at high anodic potential (> 1.5 V vs. RHE, see black curve measured without bromide). At low HBr concentrations (< 0.2 M) the current is limited by the bromide concentration, [Br], giving rise to a current plateau at high potentials (1.3 - 1.5 V vs. RHE) due to mass transport limitations. At high concentrations (> 0.5 M) these limitations are mitigated and the current density increases exponentially with the potential, typically to polarized electrodes. At 1.5 M (red curve), the anodic current density reaches 0.5 A / cm2at a potential of 1.41 V vs. RHE, far below the onset of oxygen evolution (1.59 V vs. RHE at 10 mA / cm2, black curve).

[0255] Tafel analysis of the anodic current density versus overpotential curves, assuming a logarithmic relationship J = Joexp(r] n (10) / i4) where r] = E-Erevis the overpotential, E is the applied potential (IR-corrected), Erevis the reversible potential (aka the Nernst potential) and A is the Tafel slope. Reliable Tafel slopes were found in the LSV measurements at high bromide concentrations (> 0.5 M), at low overpotentials ranging between 0 and 50 mV, increasing linearly from 65 to 85 mV / dec with increasing bromide concentrations from 0.5 to 2.0 M (Fig. 16E). This observation implies that the ratedetermining step of the reaction depends on the bromide concentration. Furthermore, the logarithmic dependence of the anodic current density on the bromide concentration implies a first-order reaction, in accordance with previous report. This reaction order remains unchanged from 1.09 to 1.30 VRHE, which differs from the increase of Tafel slope at high overpotential. The Volmer-Heyrovsky mechanism seems most plausible, where both steps are first-order reactions. Thus, the reaction order has no change in spite of a plausible shift of the rate-determining step from the Heyrovsky step to the Volmer step with increasing bromide concentrations, as suggested by the Tafel analysis. The exchange current density Jowas found to increase 2-fold from 3.7 to 6.3 mA / cm2with increasing bromide concentrations from 0.1 to 1.5 M, demonstrating faster kinetics of bromide oxidation at high [Br], These electrochemical experiments were also conducted in electrolyte compositions of different concentrations of NaBr (0.1 M to 1.5 M) and constant 0.5 M H2SO4, to maintain constantly high ion strength especially at low [Br], Under these conditions, the results come to the same conclusion as using HBr electrolyte that high bromide concentrations mitigate mass transport limitations and enhance the kinetics of bromide oxidation.

[0256] Fig. 16F shows that the cathodic current density has a small overpotential of ~75 mV at 100 mA / cm2, and it hardly changes with bromide (1.5 M HBr) and without it (1.5 M HNO3). This is attributed to the acidic enviornment (pH ~ 0) of HBr that facilitates the HER by providing plenty of protons for the reaction. This is an important advanatge of the electrolytic process over our previous study that was carried out at near-neutral pH and presented a cathodic overpotential of over 200 mV at half the current density value (50 mA / cm2), despite using the same cathode (Pt foil). Operation in acidic electrolyte reduces the cathodic polarization loss and increases the energy efficiency for the production of hydrogen.

[0257] Steady state galvanostatic measurements were carried out in 1.5 M HBr electrolyte at different current densities ranging from 5 mA / cm2to 2.5 A / cm2, where the Pt cathode and DSA anode were placed with the same geometric area (1 cm2) for consistency. The measurements were repeated 3 times, resulting in reproducible results. The average cell voltage (Vcell) and standard deviation extracted from these measurements are presented in Fig. 16G, displaying Vcellas a function of the current density. A cell voltage of only 1.10+0.01 V (IR corrected) drived hydrogen evolution at the cathode and bromine evolution at the anode at a low current density of 5 mA / cm2. This result corresponds to a low overvoltage of only 22+10 mV close to the onset of these reactions. In contrast, the OER alone gives rise to a minimum overpotential of 200-400 mV in water electrolysis, due to the four charge transfer steps that are required to generate an O2 molecule which strain the bonds with different intermediates. This difficult reaction is replaced by the BER that involves two electron transfer steps without protons instead of four proton-coupled electron transfer (PCET) steps in the OER. At the highest current density of 2.5 A / cm2, the cell voltage reaches 1.47+0.10 V (IR corrected), which is about 100%HHV for water electrolysis, competitive with state-of-the-art PEM electrolysis, as well as other reported studies mostly at low temperature (60-80°C). Only solid oxide electrolyzer cell (SOEC) results in higher efficiency than our study but with external heating up to 750-900 °C.

[0258] Besides the voltage, the current (i.e., Faradaic) efficiency is another important benchmark in electrolysis. It was first examined in the membraneless biphasic electrolyzer, resulting in Faradaic efficiency 83+2% at constant current densities between 1 to 2 A / cm2. The separation of produced bromine from the cathode, where the backward reaction (redox shuttling) occurs, is found to enhance the Faradaic efficiency, concluded by comparing adding an organic (DCM) phase, sodium dichromate (ISfeCUO?), and without any additives. Adding ISfeCUO? (1 g / L) to the electrolyte maximizes the Faradic efficiency up to 93+5% at 1 A / cm2, which is assigned to a chromium hydroxide (Cr(OH)3) thin layer that coats the cathode by cathodic deposition of chromium ions during the electrolysis. The ISfeCUO? additive yields toxic and carcinogenic Cr(VI) ions in the electrolyte, and its use has been restricted in Europe, USA and other countries.

[0259] A custom-built membraneless flow electrolyzer was developed to enhance the current efficiency of electrolytic process. Fig. 17A shows a photograph of the electrolyzer, which comprises a glass cell housing cathode and anode positioned within an electrolyte channel and a reservoir located above it. During operation, the inlet at the top of the reservoir is sealed, allowing the produced hydrogen gas to rise and displaces the electrolyte containing the descended bromine through the outlet at the bottom of the channel. The displaced electrolyte is collected in a container and weighed by a scale. The electrolyte volume (Vol electrolyte = mmeaSured> ^electrolyte) thus equals the volume of the produced hydrogen gas as determined by air-pressure equilibrium. In addition, most of the produced bromine descended with the flowing electrolyte, remaining spatially separated from the cathode and thereby suppressing redox shuttling. A closer view of the electrode configuration is shown in Fig. 17B, where the electrolyte flows past the electrodes, naturally separating the evolved hydrogen gas (rising bubbles) and bromine (yellow phase) without extra effort. Herein, electrolysis was performed using identical electrodes - a dimentionally stable anode (DSA, 1 cm2) and Pt cathode (1 cm2) in 1.5 M HBr electrolyte at current density of 1 A / cm2. The reaction proceeded for 45 minutes, terminating when the electrolyte level dropped to the height of the electrodes. A Faradaic efficiency of 99.6% was achieved for HER as determined by the ratio of measured and theoretical volumed of evolved hydrogen in Fig. 17C, which is comparable to the Faradaic efficiency of 93±2% for BER measured by iodometric titration.12In addition, the cell voltage (IR corrected) remained stable at 1,28±0.20 V, corresponding to a voltage efficiency of 116±9%. These results confirmed our design rationale that isolating the produced bromine through the flow configuration enables nearly complete current efficiency. Under these operating conditions, the rate of producing hydrogen was determined as 0.373 kgH2 / (m2»h).

[0260] Fig. 17D illustrates high stability of the custom-made electrolyzer employing the DSA and Pt electrodes. Due to the limited electrolyte volume, electrolysis was divided into 10 sequential segments, each performed at a constant current density of 0.5 A / cm2for about 2 (1stand 2nd) or 2.5 (3rdto 10thexcept for 6th) hours. The produced bromine (0.019-0.023 mol Bn) was isolated from the 1.5 M HBr electrolyte (0.75 L, 1.125 mol HBr) to allow reuse of the electrolyte for subsequent electrolysis. Fresh DSA and Pt electrodes together with freshly prepared 1.5 M HBr electrolyte were applied in the 1stsegment, yielding a Faradaic efficiency of 102% for HER and a stable cell voltage of 1.31±0.08 V over 2 hours. The produced Bn in the HBr electrolyte were separated via distillation; the electrolyte color changed from reddish-brown to colorless, and the isolated bromine was suitable for further chemical looping. The HBr electrolyte was readjusted to 1.5 M and reused for the 2ndsegment, which exhibited similar performance with a Faradaic efficiency of 101% for HER and a stable cell voltage of 1.29±0.06 V for 2 hours. Electrolyte treatment was repeated for the 3rdand 4thsegments, resulting in Faradaic efficiencies of 103% and 101% and maintaining cell voltages at 1.26±0.06 and 1.30±0.04 V, respectively. After the 4thsegment, we evaluated an air-blow method for bromine isolation to eliminate the external heat requirement of distillation. As shown in Fig. 18, air with room temperature was introduced into the electrolyzer, and the outlet gas was bubbled through an aqueous tetrabutylammonium bromide (TBAB) solution, forming tetrabutylammonium tribromide (TBATB) as a precipitate. Upon air introduction, the TBAB solution immediately turned from colorless to yellow, and a precipitate formed. Although the HBr electrolyte remained slightly yellow after about half an hour of air-blowing (i.e., partial bromine remained in the electrolyte with the equilibrium Bn + Br“ Bn-), the collected TBATB precipitate indicated that 82% of the produced bromine was removed from the electrolyte. The slightly yellow HBr electrolyte was readjusted to about 1.5 M and reused for the 5thelectrolysis segment, achieving a Faradaic efficiency of 102% and cell voltage of 1.30±0.08 V, comparable to the results obtained using distillation. This finding demonstrates that the heat input for bromine isolation can be minimized, and air-blow at room temperature effectively separates bromine with minimal energy demand. After the 5thsegment, we attempted direct addition of TBAB to the electrolyte to form TBATB precipitate. However, it caused a sharp voltage increase (marked with “ A”) during the 6thsegment, indicating that residual TBAB adversely affected the electrolysis, leading to slight Faradaic efficiency decrease (95%) and unstable operated voltage, 1.56±0.32 V. Consequently, a fresh 1.5 M HBr electrolyte was used for the 7thsegment without replacing the electrodes, restoring stable performance, 1.31±0.02 V for 2.5 hours. The used DSA and Pt electrodes thus maintained stability despite prior TBAB exposure. Distillation was reapplied before 8thand 9thsegments of electrolysis, and the air-blow method was again employed before the 10thsegment of electrolysis. Throughout the entire operation, the Faradaic efficiency and cell voltage remained 102±l% and between 1.20 and 1.40 V over 22 hours, respectively, except for the 6thsegment with TBAB exposure, consistently exceeding 100%HHV relative to conventional water electrolysis.

[0261] Chemical looping step

[0262] As the electrolytic process produces hydrogen and bromine, the hydrogen is isolated and collected in gas phase, while the bromine is transferred to another cell for the subsequent chemical reaction described in rxn. 4. It has been examined and come out high yield of 97% over almost a century. To conduct this reaction, we simply followed the previous study, adding 1 g of sulfur, 5 mL of the produced bromine that is distilled and collected from the acidic electrolyte, and 50 mL of water to the chemical cell. After about 30 minutes at 70 °C (or about 20 minutes at 90 °C), the reaction completed when the reddish-brown solution turned to colorless as all the bromine was consumed. The colorless solution was then distilled and obtained HBr as the azeotrope mixture (48 wt%) with water at its boiling point of 124±1°C, with a yield of 95±1%. This is close to the previous study, demonstrating the fast rate and high yield of the chemical looping, converting S to H2SO4 while recovering HBr from Bn.

[0263] The substantial energy demand associated with separating the two produced acids after chemical looping process, where HBr serves as the electrolyte for continuous electrolysis and H2SO4 is collected as the anodic product, was calculated. The voltage results shown in Fig. 16 and 17 represent only the electric energy consumption during the electrolytic step, which is conducted at room temperature (25 °C) without external heating (thereotical H°rxn = +242 kJ / molm). To accelerate the subsequent chemical looping reaction (rxn. 4), the mixture of S, H2O, and Bn is heated to about 70 °C ( H°rXn = +41 kJ / molm), allowing the reaction to complete within about 30 minutes. As illustrated in Fig. 15, the products, HBr and H2SO4, are separated by distillation at the azeotropic boiling point of 48 wt% HBr (124+1 °C in water; H°rxn = +407 kJ / molm). From the initial materials (S, H2O, and HBr) to the final separated products (H2, H2SO4, and regenerated HBr), the total input energy consists of electrical energy of +242 kJ / molm ( H°rxn1') and heat energy of +445

[0264]

[0265] kJ / molm ( \HCJrxn2+ \HCJrxn'i). In practical implementation, the solution after chemical looping can be directly switched for electrolysis (Fig. 15) instead of immediate distillation. That is, H°rxn3can be decreased to +407 / X kJ / molH2, where X is the turns of switching the solution between electrolytic and chemical cells. An example of electrolysis using the solution after chemical looping is shown in Fig. 19 with a mixed mode, 1 A cm-2for 20 seconds and 0 A cm-2for 10 seconds in a cycle, for 300 cycles. The cell voltage increases about 0.2 V compared to pure 1.5 M HBr electrolyte, due to the coexistence of sulfuric acid. By this method, the cell voltage was stable with A Fee / / of 70 mV for 2.5 hours because it is more efficient for mass transport. Furthermore, the heat demand can be supplied by waste heat available from industrial processes that already consume hydrogen or produce high-temperature gases, such as petroleum refining (approximately -200 kJ released per mol consumed H2), steelmaking (from coke combustion and molten metal), and ammonia synthesis (from high-temperature reactions and gas compression). Besides, the instinct exothermicity of the looping reaction (rxn. 4, \HQ,-x,i4= -132 kJ / molm) along with heat exchange during distillation ( H°rxn5and H°rxn6, -490 kJ / molm), can offset much of the required heat H°rxn2+ H°rxn3+ HQ>-xn ). Therefore, the net external energy is effectively limited to electrical energy of electrolysis (AT / / = +242 kJ / molm). In practice, our result at 1 A / cm2shows the energy of 249 kJ / molm, equivalent to 34.3 kWh / kgH2. This strategy, utilizing waste heat to drive chemical looping reactions rather than relying solely on electrical energy, is conceptually analogous to SOEC, which operates at elevated temperatures (above 700 °C) with superheated water steam to enhance voltage efficiency.

[0266] After chemical looping, the produced sulfuric acid can be easily characterized by adding barium nitrate, forming barium sulfate precipitate. Further applications of the product obtained from this looping reaction, sulfuric acid, are found across a wide range of industries. In the fertilizer sector, sulfuric acid is used to produce phosphoric acid and calcium sulfate, as well as ammonium sulfate. It also serves as an important reagent in the chemical manufacturing, for example in the production of hydrochloric acid; in petroleum refining; in metal processing; in batteries, among others.

[0267] Alternative processes

[0268] An alternative chemical looping route for the proposed process involves the oxidation of sulfur dioxide (SO2) by bromine, rather than the oxidation of elemental sulfur (S). This approach (rxn. 6) enables the looping reaction to proceed at room temperature without external heating. The solution from the looping step can also flow back to the electrolyzer, having similar performance to the proposed process with sulfur powder, which has high voltage efficiency in mixed mode rather than constant current density. The H2SO4 product remaining in the electrolyte not only serve as the co-electrolyte with HBr but can also be withdrawn periodically, depending on its concentration buildup and the efficiency of the electrolysis process. This method also offers potential advantages for the post-treatment of SO2 waste / pollutant from industrial exhaust streams. Combining with the same electrolytic step, 1 equiv. of SO2 and 2 equiv. of H2O produce 1 equiv. of hydrogen gas and 1 equiv. of sulfuric acid (rxn. 7).

[0269] S

[0270]

[0271] O2(Sr) + Br2(aq) + 2H2O(l) 2HBr(aq) + H2SO4(aq) (rxn 6.) SO2(g) + 2H2O (Z) ~^H2(g) + H2SO4(aq) (rxn 7.)

Claims

CLAIMS:

1. A process for generating hydrogen gas and value-adding chemicals (VACs), the process comprising reacting in a membraneless electrolytic cell, operated under electrolytic conditions, a mixture of an aqueous halide solution and an organic medium, optionally comprising an organic or an inorganic substrate material, to produce halogen products or to convert said organic or inorganic substrate material, if present, into a corresponding halogenated or oxidized form thereof, wherein the electrolytic conditions comprise:-maintaining the aqueous halide solution at a pH below 3 (or optionally at a neutral pH or a pH between 6 to 8 when a substrate material is present);-operating at a current density of at least 100 mA / cm2;to thereby prevent water oxidation and oxygen gas generation,wherein the halogen products are halogen liquids, chlorine gas and / or oxidized halide compounds; andwherein the aqueous halide solution is not a fluoride solution.

2. The process according to claim 1, wherein the halide solution is a bromide solution and the halogen products are bromine and / or oxidized bromine compounds.

3. The process according to claim 1, wherein the halide solution is an iodide solution and the halogen products are iodine and / or oxidized iodine compounds.

4. The process according to claim 1, wherein the halide solution is a chloride solution and the halogen products are chlorine gas and / or oxidized chlorine compounds.

5. The process according to claim 1, wherein the halide solution is not a chloride solution.

6. The process according to any one of the preceding claims, wherein the organic medium is water soluble.

7. The process accoridng to any one of claims 1 to 5, wherein the organic medium is water-insoluble.

8. The process according to any one of the preceding claims, wherein the aqueous halide solution comprises a metal halide, or a hydrogen halide.

9. The process according to claim 8, wherein the metal halide is selected from a lithium, a sodium, a calcium, a magnesium and a potassium halide.

10. The process according to claim 1, wherein the mixture is an unstirred or unmixed biphasic system (heterogenous mixture) comprising the aqueous halide solution and a water-insoluble organic medium.

11. The process according to any one of the preceding claims, wherein the organic medium is a water-insoluble organic medium having a higher density than water.

12. The process according to any one of the preceding claims, wherein the organic medium is free of organic or inorganic substrate materials.

13. The process according to any one of the preceding claims, wherein the halide solution comprises halide ions that are converted into a corresponding halogen liquid, and corresponding oxidized halide forms, and wherein the halogen liquid is separated.

14. The process according to claim 1, the process comprising:- reacting under electrolytic conditions an unstirred biphasic system (heterogenous mixture) of the aqueous halide solution and water-insoluble organic medium, to generate hydrogen gas and the corresponding halogen liquid, under the conditions preventing production of oxygen gas; and- collecting said hydrogen gas and said halogen liquid separately from each other.

15. The process according to any one of the preceding claims, wherein the VAC is one or more products resulting from direct chemical conversion of halide ions present in the aqueous halide solution.

16. The process according to claim 15, wherein the VAC is selected from halogen liquids, metal hydroxides and oxidized halide forms.

17. The process according to claim 16, wherein the oxidized halide forms include hypobromous acid (HBrO) and hypoiodous acid (HIO).

18. The process according to claim 1, wherein the mixture is a stirred or a mixed mixture (homogenous mixture) comprising the aqueous halide solution and the organic medium.

19. The process according to claim 18, wherein the organic medium comprises an organic or an inorganic substrate material susceptible to chemical conversion in presence of a halide ions, halogen liquids, metal hydroxides and oxidized halide forms.

20. The process according to claim 19, wherein the organic substrate material is susceptible to bromination or iodination, or to oxidation.

21. The process according to claim 19, wherein the inorganic substrate material is an inorganic material susceptible to oxidation.

22. The process according to any one of the preceding claims, wherein the organic substrate material is selected from alkanes, alkenes, alkynes, alcohols, carbonyl compounds, and aromatic compounds, reactive under the electrolytic conditions to undergo radical halogenation, addition reactions, electrophilic aromatic substitution, α-halogenation reactions, or allylic halogenation.

23. The process according to any one of claims 1 to 21, wherein the inorganic substrate is selected from metals, metal and non-metal oxides, metal alloys, non-metal inorganics, elemental materials, elemental phosphorus, sulfides, phosphides, nitrides, and carbides.

24. The process according to any one of claims 1 to 22, wherein the organic substrate material is an olefin, or a compound comprising one or more double or triple bonds.

25. The process according to claim 23, wherein the inorganic substrate material is elemental sulfur, sulfur dioxide, nitrous acid, phosphorus, silicon, or boron.

26. The process according to any one of the preceding claims, wherein the VAC is selected halogen liquids, metal hydroxides, oxidized halogen forms, sulfuric acid, oxidized organic compounds, mono- or multi-halogenated organic compounds, mono- or multi -halogenated aromatic compounds, products of oxidation, radical halogenation, products of addition reactions, products of electrophilic aromatic substitution, products of α-halogenation reactions, and products of allylic halogenation.

27. The process according to claim 1, wherein the organic medium comprises an organic substrate material, and optionally an amount of one or more reactive materials selected to permit radical halogenation of the organic substrate material under exposure to UV light or sunlight.

28. The process according to any one of the preceding claims, wherein the electrolytic conditions comprise maintaining the mixture at a temperature between 20 and 33°C or at a temperature not exceeding 90°C.

29. The process according to any one of the preceding claims, wherein the electrolytic conditions comprise maintaining the mixture at a pressure below 10 bars.

30. The process according to claim 29, wherein the pressure is 1 atm.

31. The process according to any one of the preceding claims, wherein the electrolytic conditions comprise maintaining the halide solution at a pH between zero and 3.

32. The process according to any one of the preceding claims, wherein each of the VACs is separated from the organic medium.

33. The process according to any one of the preceding claims, wherein the process is a continuous process, generating hydrogen gas and one or more VACs, wherein the process comprises replenishing the organic or inorganic substrate material in the organic medium to thereby continuously generate said VACs.

34. The process according to any one of claims 1 to 33, wherein the process is operated in a batch-wise fashion.

35. A process for generating hydrogen gas and sulfuric acid, the process comprising in a closed-loop system having (i) a membraneless electrolytic cell comprising an electrode pair implemented in an halide aqueous solution comprising a hydrogen halide, and (ii) a chemical cell comprising a mixture of water and a sulfur source:-electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid;-transferring or permit flowing of said halogen liquid to the chemical cell, to cause transformation of said sulfur source into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions to regenerate the hydrogen halide; and -feeding the formed or regenerated hydrogen halide back into the electrolytic cell.

36. The process according to claim 35, repeated in a closed-loop fashion to permit continuous generation of sulfur-based products.

37. The process according to claim 35 or 36, wherein the sulfur source is elemental sulfur (sulfur powder) or SO2gas, or any other sulfur containing material transformable, under the conditions of the process into sulfuric acid.

38. The process according to anyone of claims 35 to 37, wherein the sulfur source is elemental sulfur (sulfur powder) and the chemical cell comprises a heated water solution of the elemental sulfur.

39. The process according to claim 38, the process comprising:in a closed-loop system having (i) a membraneless electrolytic cell comprising an electrode pair or an electrode assembly implemented in an halide aqueous solution comprising a hydrogen halide, and (ii) a chemical cell comprising a heated mixture of water and elemental sulfur:-electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid;-transferring or permit flowing of said halogen liquid to the chemical cell, to cause oxidation of the elemental sulfur into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions to form or regenerate the hydrogen halide; and -feeding the formed or generated hydrogen halide back into the electrolytic cell.

40. The process according to claim 38 or 39, wherein the temperature of the heated mixture of water and elemental sulfur in the chemical cell is between 70 and 110 °C.

41. The process according to any one of claims 35 to 37, wherein the sulfur source is SO2gas and the chemical cell comprises a water solution into which SO2gas is bubbled or added by other means.

42. The process according to claim 41, the process comprising:in a closed-loop system having (i) a membraneless electrolytic cell comprising an electrode pair or an electrode assembly implemented in an halide aqueous solution comprising a hydrogen halide, and (ii) a chemical cell comprising a mixture of water and SO2:-electrolytically transforming halide ions in said halide aqueous solution into a corresponding halogen liquid;-transferring or permit flowing of said halogen liquid to the chemical cell, to cause transformation of the SO2 into sulfuric acid (H2SO4) and reduction of the halogen liquid into the corresponding halide ions to form or regenerate the hydrogen halide; and -feeding the formed or regenerated hydrogen halide back into the electrolytic cell.

43. The process according to any one of claims 35 to 42, the process comprising separating the hydrogen halide and sulfuric acid, and feeding the hydrogen halide back into the electrolytic cell.

44. The process according to any one of claims 35 to 41, the process comprising separating said sulfuric acid.

45. The process according to claim 35, wherein the halide solution is an acidic solution comprising an acid such as hydrobromic acid (HBr) solution, or sodium bromide (NaBr) with sulfuric acid (H2SO4) solution, and having a pH between -2 and 3.

46. The process according to claim 35, wherein the transferring of said halogen liquid to the chemical cell comprises use of a pump, or use of air-blowing method.

47. The process according to claim 35, wherein the electrolytic conditions comprise use of hydrobromic acid, or sodium bromide with sulfuric acid, at a current density of 0.1 A / cm2or above, at a temperature between 20 and 33 °C, and 1 atm in the electrolytic cell.

48. The process according to claim 47, wherein the current density is changed periodically during electrolysis between 0 to 0.1 A / cm2and 0.5 to 5 A / cm2.

49. The process according to any one of the preceding claims, the process operated in a constant current or a changing current mode.

50. A process for generating hydrogen gas and bromine-based value-adding chemicals (VACs), the process comprising reacting in a membraneless electrolytic cell, operated under electrolytic conditions, a mixture of an aqueous bromide solution and an organic medium, optionally comprising an organic or an inorganic substrate material, to produce bromine products or to convert said organic or inorganic substrate material, if present, into a corresponding brominated or oxidized form thereof, wherein the electrolytic conditions comprise:-maintaining the aqueous bromide solution at a pH below 3 (or optionally at a neutral pH or a pH between 6 to 8 when a substrate material is present);-operating at a current density of at least 100 mA / cm2;to thereby prevent water oxidation and oxygen gas generation,wherein the bromine products are bromine liquid and / or oxidized bromide compounds.

51. The process according to claim 50, wherein the aqueous bromide solution comprises Na or K salts of Br, and the organic medium is a water-insoluble organic medium, optionally comprising an organic or an inorganic substrate material.

52. The process according to claim 50, wherein the mixture is a homogeneous mixture formed by continuous mixing, stirring or turbulent flow, or a biphasic mixture.

53. A system for generating hydrogen gas and value-adding chemicals (VACs), the system comprising one or more membraneless reactors, each reactor including an electrode assembly and is configured to receive a mixed solution comprising an aqueous halide solution and an organic medium, the system being equipped with a stirring or a mixing mechanism configured and operable to stir or mix or cause turbulation to the solution; wherein the halide solution is maintained at a pH below 3 or neutral pH between 6 and 8, at a temperature between 20 and 33 °C, or at a temperature not exceeding 90°C, and under a pressure not exceeding 10 bars; wherein the system is operated at a current density of 100 mA / cm2or above (normalized by an anode area).

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