Continuous process for sustainable hydrogen production

Abstract

The present disclosure provides a method for producing hydrogen. The method includes a thermochemical reaction by contacting a metal or its alloy with steam to produce a metal oxide and / or a metal hydroxide and hydrogen. The method then includes contacting the metal oxide and / or the metal hydroxide produced in the thermochemical reaction with water or an alkaline aqueous solution to produce a solution including metal ions. Finally, the method includes an electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of the cathode contacts the solution including the metal ions to produce hydrogen, oxygen and the metal or its alloy.

Description

[0001] The present invention relates to a method for producing hydrogen. In a particular embodiment of the present invention, the method may be a sustainable cycle process. The present invention also extends to an apparatus for producing hydrogen.

[0002] Hydrogen is an important energy carrier and has the potential to replace hydrocarbon fuels for sustainable development. Current energy issues associated with hydrocarbon fuels, such as air pollution, climate change and resource scarcity are important motivations for exploring hydrogen. As an alternative fuel source, hydrogen has the highest specific energy content of all fuels and can be used for clean power generation in fuel cells with limited or no net atmospheric emissions, and facilitates efficient energy storage. Hydrogen can be used directly as a transportation fuel to produce higher energy efficiency, which is receiving very favorable attention as a technical and political issue.

[0003] Currently, there are several industrial methods for hydrogen production, and these methods are reforming, photoconversion and electrolysis, which have received prominent attention. The advantages and disadvantages of the methods have been discussed. Water electrolysis provides the cleanest solution for hydrogen production. The advantages of water electrolysis are: (i) it produces zero carbon emissions; (ii) it produces pure hydrogen, which affects fuel cell technology, which is severely affected by impurities in the hydrogen feed; (iii) it is independent of hydrocarbon resources; (iv) it can be operated in small plants; and (v) renewable energy sources (such as photovoltaic solar, wind, hydroelectric, etc.) can be easily associated with water electrolysis cells to produce hydrogen.

[0004] The electrolytic process of water splitting is technically simple, and there are many technologies related to water electrolysis processes, such as alkaline electrolysis, polymer electrolyte membrane (PEM) and solid oxide electrolysis cell (SOEC). Involving the growing problems of electrolysis processes are high energy demand, installation costs and low safety, durability and energy efficiency. Some electrolyzers, especially PEM, are highly sensitive to the purity of water and additional water treatment must be applied before electrolysis. Therefore, a large amount of research efforts are devoted to improving operating conditions, including the electrochemical activity of electrodes and electrolytes, and reducing the overall resistance of the electrolytic cell.

[0005] The present invention arises from the work of the inventors in an attempt to overcome the problems associated with the prior art.

[0006] According to a first aspect of the present invention, there is provided a method for generating hydrogen, the method comprising:

[0007] - thermochemical reaction by contacting the metal or its alloy with steam to produce metal oxides and / or metal hydroxides and hydrogen;

[0008] - contacting the metal oxide and / or the metal hydroxide produced in the thermochemical reaction with water or an alkaline aqueous solution to produce a solution comprising metal ions; and

[0009] - performing an electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of the cathode contacts the solution comprising the metal ions, to produce hydrogen, oxygen and the metal or the alloy thereof.

[0010] Advantageously, both the thermochemical reaction and the electrochemical reaction produce hydrogen.

[0011] It will be appreciated that the electrochemical reaction may be performed prior to the thermochemical reaction.

[0012] Therefore, according to a second aspect, there is provided a method for producing hydrogen, the method comprising:

[0013] - contacting the metal oxide and / or metal hydroxide with water or an alkaline aqueous solution to produce a solution comprising metal ions;

[0014] - performing an electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of said cathode contacts said solution comprising said metal ions, to produce hydrogen, oxygen and a metal or an alloy thereof; and

[0015] - a thermochemical reaction is carried out by contacting the metal or the alloy thereof produced in the electrochemical reaction with steam to produce the metal oxide and / or the metal hydroxide and hydrogen.

[0016] The electrochemical reaction may be continuous or repeated. The thermochemical reaction may be continuous or repeated. Contacting the metal oxide and / or metal hydroxide with water or an alkaline aqueous solution to produce a solution comprising metal ions may be continuous or repeated.

[0017] In a preferred embodiment, the electrochemical reaction is carried out continuously. Therefore, the metal or its alloy produced in the electrochemical reaction can be collected while the electrochemical reaction is being carried out. The thermochemical reaction is preferably carried out continuously. Therefore, the metal or its alloy collected from the electrochemical reaction can be fed into the thermochemical reaction while the thermochemical reaction is being carried out. In addition, the metal oxide and / or metal hydroxide produced in the thermochemical reaction can be collected while the thermochemical reaction is being carried out.

[0018] The metal oxide and / or metal hydroxide collected from the thermochemical reaction can be contacted with water or an alkaline aqueous solution to produce a solution comprising metal ions. The solution comprising metal ions can be fed into an electrochemical cell comprising a cathode when an electrochemical reaction is performed. Alternatively, the metal oxide and / or metal hydroxide collected from the thermochemical reaction can be fed into an electrochemical cell comprising a cathode when an electrochemical reaction is performed. Therefore, the metal oxide and / or metal hydroxide will increase the concentration of the metal ions in the solution comprising the metal ions.

[0019] In a preferred embodiment, the methods of the first and second aspects are repeated. Advantageously, further hydrogen may be generated without the need to provide any further metal, alloy thereof, metal oxide or metal hydroxide.

[0020] Thus, by way of example, the method may include:

[0021] - a first thermochemical reaction is carried out by contacting the metal or its alloy with steam to produce metal oxides and / or metal hydroxides and hydrogen;

[0022] - contacting the metal oxide and / or the metal hydroxide produced in the first thermochemical reaction with water or an alkaline aqueous solution to produce a solution comprising metal ions;

[0023] - performing a first electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of the cathode contacts the solution comprising the metal ions, to produce hydrogen, oxygen and the metal or the alloy thereof;

[0024] - performing a second thermochemical reaction by contacting the metal or the alloy thereof produced in the first electrochemical reaction with steam to produce the metal oxide and / or the metal hydroxide and hydrogen;

[0025] - contacting the metal oxide and / or the metal hydroxide produced in the second thermochemical reaction with water or an alkaline aqueous solution to produce a solution comprising metal ions; and

[0026] - performing a second electrochemical reaction by applying a voltage across the anode and cathode, whereby at least a portion of the cathode contacts the solution comprising the metal ions, to produce hydrogen, oxygen and the metal or the alloy thereof.

[0027] It can be understood that the method of the second aspect can be repeated similarly.

[0028] Preferably, the methods of the first aspect and the second aspect are repeated multiple times.

[0029] Thus, the methods of the first and second aspects may include discrete steps repeated multiple times, or continuous reactions performed in parallel. In either case, the method of generating hydrogen can be viewed as a thermochemical / electrochemical cycle. Fig.14 As shown, the only raw material required for the continuous generation of hydrogen is water. Therefore, once the initial amount of metal, its alloy, metal oxide and / or metal hydroxide has been supplied, it can be continuously recycled in the thermochemical / electrochemical cycle. Therefore, no additional metal / metal oxide / metal hydroxide will be needed. Similarly, in the embodiment using an alkaline solution, it can be supplemented by adding water and contacting it with the metal oxide and / or metal hydroxide produced in the thermochemical reaction. However, no additional alkali is needed.

[0030] The metal or its alloy may be an s-block metal, a p-block metal, a transition metal (i.e., a d-block metal), an f-block metal, or an alloy thereof. Preferably, the metal or its alloy is a transition metal, a p-block metal, or an alloy thereof. The s-block metal or its alloy may be an alkaline earth metal or its alloy. The alkaline earth metal or its alloy may be selected from the group consisting of beryllium, magnesium, calcium, strontium, and barium. The p-block metal or its alloy may be selected from the group consisting of tin, lead, thallium, selenium, and bismuth. Preferably, the p-block metal is lead or tin. In the most preferred embodiment, the p-block metal or its alloy is tin. The transition metal or its alloy may be selected from the group consisting of zinc, copper, iron, nickel, cobalt, manganese, titanium, molybdenum, cadmium, chromium, vanadium, silver, rhodium, platinum, palladium, iridium, osmium, rhenium, ruthenium, lanthanum, and zirconium. Preferably, the transition metal or its alloy is selected from the group consisting of zinc, copper, iron, nickel, cobalt, manganese, chromium, and vanadium. More preferably, the transition metal or its alloy is selected from the group consisting of zinc, iron, nickel, chromium and vanadium. In the most preferred embodiment, the transition metal or its alloy is zinc. The f-block metal or its alloy may be selected from the group consisting of cerium, gadolinium, yttrium, holmium, samarium and terbium.

[0031] It is understood that metal oxide and / or metal hydroxide can be an oxide and / or hydroxide of one of the metals listed above. For example, if the metal is a transition metal or its alloy, the metal oxide and / or metal hydroxide can be a transition metal oxide and / or transition metal hydroxide. Similarly, transition metal oxide and / or transition metal hydroxide can be selected from the group consisting of zinc oxide (e.g., ZnO), zinc hydroxide, copper oxide, copper hydroxide, iron oxide, iron hydroxide, nickel oxide, nickel hydroxide, cobalt oxide, cobalt hydroxide, manganese oxide, manganese hydroxide, titanium oxide, titanium hydroxide, molybdenum oxide, molybdenum hydroxide, cadmium oxide, cadmium hydroxide, chromium oxide, chromium hydroxide, vanadium oxide, vanadium hydroxide, silver oxide, silver hydroxide, rhodium oxide, rhodium hydroxide, platinum oxide, platinum hydroxide, palladium oxide, palladium hydroxide, iridium oxide, iridium hydroxide, osmium oxide, osmium hydroxide, rhenium oxide, rhenium hydroxide, ruthenium oxide, ruthenium hydroxide, lanthanum oxide, lanthanum hydroxide, zirconium oxide and zirconium hydroxide.

[0032] Alternatively, if the metal is a p-block metal or an alloy thereof, the metal oxide and / or metal hydroxide may be a p-block metal oxide and / or a p-block metal hydroxide. Similarly, the p-block metal oxide and / or p-block metal hydroxide may be selected from the group consisting of tin oxide (e.g., tin dioxide (SnO2) or stannate (SnO3 2- )), tin hydroxide (such as tin (IV) hydroxide), lead oxide, lead hydroxide, thallium oxide, thallium hydroxide, selenium oxide, selenium hydroxide, bismuth oxide and bismuth hydroxide.

[0033] Further alternatively, if the metal is an f-block metal or an alloy thereof, the metal oxide and / or metal hydroxide may be an f-block metal oxide and / or an f-block metal hydroxide. Similarly, the f-block metal oxide and / or f-block metal hydroxide may be selected from the group consisting of cerium oxide, cerium hydroxide, gadolinium oxide, gadolinium hydroxide, yttrium oxide, yttrium hydroxide, holmium oxide, holmium hydroxide, samarium oxide, samarium hydroxide, terbium oxide, and terbium hydroxide.

[0034] In embodiments where the metal oxide and / or metal hydroxide include anions (e.g., stannate), the anions may be provided with counterions. The counterions may be alkali metal ions or alkaline earth metal ions, such as lithium ions, sodium ions, potassium ions, rubidium ions, beryllium ions, magnesium ions, calcium ions, or strontium ions. In some embodiments, the ions are sodium ions. Therefore, the metal oxide and / or metal hydroxide may be sodium stannate (Na2SnO3) or sodium stannate trihydrate (Na2[Sn(OH)6]).

[0035] The metal or its alloy may be contacted with steam wherein the steam flows through the hydrogen at a rate of at least 0.01 standard cubic meters per hour, more preferably wherein the steam flows through the hydrogen at a rate of at least 0.05, at least 0.1, at least 0.15, at least 0.2, or at least 0.25 standard cubic meters per hour and most preferably wherein the steam flows through the hydrogen at a rate of at least 0.3 or at least 0.31 standard cubic meters per hour. The metal or its alloy may be contacted with steam wherein the steam flows through the hydrogen at a rate of less than 5 standard cubic meters per hour, more preferably wherein the steam flows through the hydrogen at a rate of less than 2, less than 1.75, less than 1.5, less than 1.25, or less than 1 standard cubic meters per hour and most preferably wherein the steam flows through the hydrogen at a rate of less than 0.8 or less than 0.78 standard cubic meters per hour. The metal or alloy thereof may be contacted with steam wherein the steam flows through the hydrogen at a rate between 0.01 and 5 standard cubic meters per hour, more preferably wherein the steam flows through the hydrogen at a rate between 0.05 and 2 standard cubic meters per hour, between 0.1 and 1.75 standard cubic meters per hour, between 0.15 and 1.5 standard cubic meters per hour, between 0.2 and 1.25 standard cubic meters per hour or between 0.25 and 1 standard cubic meter per hour and most preferably wherein the steam flows through the hydrogen at a rate between 0.3 and 0.8 standard cubic meters per hour or between 0.31 and 0.78 standard cubic meters per hour.

[0036] Preferably, the metal or its alloy is contacted with steam at a temperature of at least 100°C, more preferably at a temperature of at least 150°C, at least 200°C or at least 250°C and most preferably at a temperature of at least 300°C or at least 350°C. Preferably, the metal or its alloy is contacted with steam at a temperature of less than 700°C, more preferably at a temperature of less than 650°C, less than 600°C or less than 550°C and most preferably at a temperature of less than 500°C or less than 450°C. Preferably, the metal or its alloy is contacted with steam at a temperature between 100°C and 700°C, more preferably at a temperature between 150°C and 650°C, between 200°C and 600°C or between 250°C and 550°C and most preferably at a temperature between 300°C and 500°C or between 350°C and 450°C. Advantageously, at higher temperatures, hydrogen is produced faster.

[0037] Preferably, the metal or its alloy is contacted with steam at a pressure of at least 10 kPa, more preferably at a temperature of at least 50 kPa, at least 75 kPa or at least 100 kPa and most preferably at a temperature of at least 500 kPa, at least 1,000 kPa or at least 20,000 kPa. Preferably, the metal or its alloy is contacted with steam at a pressure of less than 500,000 kPa, more preferably at a pressure of less than 300,000 kPa, less than 200,000 kPa or less than 100,000 kPa and most preferably at a temperature of less than 50,000 kPa, less than 40,000 kPa or less than 30,000 kPa. Preferably, the metal or alloy thereof is contacted with steam at a pressure between 10 and 500,000 kPa, more preferably between 50 and 300,000 kPa, between 75 and 200,000 kPa or between 100 and 100,000 kPa and most preferably between 500 and 50,000 kPa, between 1,000 and 40,000 kPa or between 2,000 and 30,000 kPa.

[0038] The metal or its alloy may comprise a powder, pellets or flakes.

[0039] The method may include placing the metal or its alloy in a thermochemical reactor before contacting the metal or its alloy with steam. The method may include continuously feeding the metal or its alloy into the thermochemical reactor while the thermochemical reaction is being carried out. Methods for continuously feeding the metal or its alloy into the thermochemical reactor will be known to the skilled person. For example, the thermochemical reactor may include a first rotary valve configured to feed the metal or its alloy into the thermochemical reactor. The first rotary valve may be a motorized rotary valve.

[0040] The method may include removing the metal oxide and / or metal hydroxide from the thermochemical reactor at the end of the thermochemical reaction. Alternatively, the method may include removing the metal oxide and / or metal hydroxide from the thermochemical reactor while the thermochemical reaction is being carried out. Methods for continuously removing metal oxides and / or metal hydroxides will be known to the skilled person. For example, the thermochemical reactor may include a second rotary valve configured to remove the metal oxide and / or metal hydroxide therefrom. The second rotary valve may be a motorized rotary valve.

[0041] The method may include stirring the metal or alloy thereof when it is in contact with steam. Thus, the method may include carrying out the thermochemical reaction in a self-stirring thermochemical reactor. The self-stirring reactor may be a spouted bed reactor, a fluidized bed reactor or a pneumatically transported bed reactor. Advantageously, stirring the metal or alloy thereof increases the surface area in contact with steam and improves the efficiency of the thermochemical reaction.

[0042] It will be appreciated that the hydrogen produced in the thermochemical reaction will be present in a gaseous mixture further comprising unreacted steam. Thus, the method may comprise condensing the unreacted steam from the gaseous mixture obtained from the thermochemical reaction. Advantageously, if no carrier gas is used in the reaction, the condensation step will allow the user to obtain the hydrogen.

[0043] In some embodiments, the vapor for contacting the metal or its alloy may be provided with a carrier gas. The carrier gas may be an inert gas, such as nitrogen or argon. Thus, the gaseous mixture may further include a carrier gas. Thus, the method may include separating the hydrogen from the inert gas. The method may include using a pressure swing absorption unit or a cryogenic system to separate the hydrogen from the inert gas.

[0044] The method may include:

[0045] - contacting a metal oxide and / or a metal hydroxide with water or an alkaline aqueous solution in a first container to produce a solution comprising metal ions; and

[0046] - placing said solution comprising said metal ions in an electrochemical cell comprising an anode and a cathode such that at least a portion of said cathode contacts said solution comprising said metal ions,

[0047] Wherein the first container is separate from the electrochemical cell.

[0048] Alternatively, the method may include contacting the metal oxide and / or metal hydroxide produced in the thermochemical reaction with water or an alkaline aqueous solution to produce a solution including metal ions in the electrochemical cell, such that at least a portion of the cathode contacts the resulting solution including metal ions.

[0049] In some embodiments, the method comprises contacting the metal oxide with an alkaline aqueous solution. In some embodiments, the method comprises contacting the metal hydroxide with an alkaline aqueous solution. In some embodiments, the method comprises contacting the metal oxide with water. In some embodiments, the method comprises contacting the metal hydroxide with water.

[0050] It will be appreciated that the alkaline aqueous solution comprises a base. The base may be an organic base or an inorganic base. The base may be an Arrhenius base, a Lewis base and / or a Bronsted-Lowry base, more preferably a strong Arrhenius base and / or a Lewis superbase. The Arrhenius base may comprise an alkali metal or alkaline earth metal hydroxide. The Arrhenius base may comprise potassium hydroxide, sodium hydroxide, barium hydroxide, cesium hydroxide, strontium hydroxide, calcium hydroxide, lithium hydroxide and / or rubidium hydroxide. Thus, the alkaline aqueous solution may comprise an aqueous alkaline solution.

[0051] The Lewis base may include ammonia (NH3), butyllithium (n-BuLi), lithium diisopropylamide (LDA), lithium diethylamide (LDEA), sodium amide, sodium hydride (NaH), and / or lithium bis(trimethylsilyl)amide.

[0052] The Bronsted-Lowry base may include ammonium hydroxide, an aliphatic amine, or an aromatic amine. The aliphatic amine may include methylamine, ethylamine, or dimethylamine. The aromatic amine may include aniline, phenylenediamine, or o-toluidine.

[0053] In a preferred embodiment, the alkaline aqueous solution comprises arene base.

[0054] The alkaline aqueous solution may include a base in a concentration of at least 0.5M, at least 1M or at least 1.5M, more preferably at least 2M, at least 2.5M or at least 3M and most preferably at least 3.5M or at least 4M. The alkaline aqueous solution may include a base in a concentration of less than 8.5M, less than 8M or less than 7.5M, more preferably less than 7M, less than 6.5M or less than 6M and most preferably less than 5.5M or less than 5M. The alkaline aqueous solution may include a base in a concentration of between 0.5 and 8.5M, between 1 and 8M or between 1.5 and 7.5M, more preferably between 2 and 7M, between 2.5 and 6.5M or between 3 and 6M and most preferably between 3.5 and 5.5M or between 4 and 5M. Advantageously, the inventors have found that a solution comprising about 4.5M sodium hydroxide exhibits the greatest conductivity.

[0055] The metal oxide and / or metal hydroxide may be contacted with a sufficient amount of water or an alkaline aqueous solution to produce a solution comprising metal ions, wherein the metal ions are present at a concentration of at least 0.001 M or at least 0.005 M, more preferably at least 0.01 M, at least 0.02 M, or at least 0.06 M, and most preferably at least 0.08 M or at least 0.1 M. In some embodiments, the metal ions are present at a concentration of at least 0.2 M or at least 0.6 M, and most preferably at least 0.8 M or at least 1 M. The metal oxide and / or metal hydroxide may be contacted with a sufficient amount of water or an alkaline aqueous solution to produce a solution comprising metal ions, wherein the metal ions are present at a concentration of less than 5 M, less than 4 M, less than 3 M, less than 2 M, less than 1.5 M, less than 1 M, or less than 0.5 M, more preferably less than 0.3 M, less than 0.25 M, or less than 0.2 M, and most preferably less than 0.17 M or less than 0.14 M. The metal oxide and / or metal hydroxide may be contacted with a sufficient amount of water or alkaline aqueous solution to produce a solution comprising metal ions, wherein the metal ions are present in a concentration of between 0.001 and 5 M or between 0.005 and 4 M, more preferably between 0.02 and 3 M, between 0.06 and 2 M or between 0.1 and 1.5 M.

[0056] In one embodiment, the metal oxide and / or metal hydroxide is contacted with a sufficient amount of water or an alkaline aqueous solution to produce a solution comprising metal ions, wherein the metal ions are present in a concentration of between 0.001 and 1 M or between 0.005 and 0.5 M, more preferably between 0.01 and 0.3 M, between 0.02 and 0.25 M or between 0.06 and 0.2 M and most preferably between 0.08 and 1.7 M or between 0.1 and 0.14 M. Preferably, in this embodiment, the metal oxide and / or metal hydroxide is contacted with an alkaline aqueous solution.

[0057] In alternative embodiments, the metal oxide and / or metal hydroxide is contacted with a sufficient amount of water or alkaline aqueous solution to produce a solution comprising metal ions, wherein the metal ions are present in a concentration of between 0.2 and 5 M, or between 0.4 and 4 M, more preferably between 0.6 and 3 M, or between 1 and 1.5 M. Preferably, in this embodiment, the metal oxide and / or metal hydroxide is contacted with water.

[0058] The anode and cathode can be disposed in an electrochemical cell. The electrochemical cell can be an undivided cell. Thus, in this embodiment, disposing a solution comprising metal ions in an electrochemical cell will contact at least a portion of the anode with the solution comprising metal ions. In embodiments where the metal oxide and / or metal hydroxide is in contact with water, an undivided cell can be used.

[0059] In alternative embodiments, the electrochemical cell comprises a separator cell. Thus, the cell may comprise a membrane disposed between the anode and cathode that divides the cell into two parts. Preferably, the membrane is an anion exchange membrane, more preferably an alkaline anion exchange membrane (AAEM). Suitable AAEMs will be known to the skilled person, but may comprise a polymer anion exchange base membrane of chloromethylated polysulfone, or a copolymer of chloromethylstyrene and divinylvenzene with a polyethylene fabric. In embodiments where the metal oxide and / or metal hydroxide is contacted with an alkaline aqueous solution, an unseparated cell may be used.

[0060] In this embodiment, the method may include placing a solution comprising metal ions in a cathode portion of the battery such that at least a portion of the cathode contacts the solution comprising the metal alloy. The method may also include placing an additional electrolyte in an anode portion of the battery such that at least a portion of the anode contacts the additional electrolyte. The additional electrolyte preferably comprises an aqueous solution, and more preferably an alkaline aqueous solution. The alkaline aqueous solution may be as defined above.

[0061] It will be appreciated that as the electrochemical reaction proceeds, water will react to produce hydrogen and oxygen. Therefore, the concentration of alkali in the solution comprising the metal alloy will increase. Similarly, in embodiments where the battery comprises a separator cell, the concentration of alkali in the additional electrolyte will also increase.

[0062] Thus, the method may include contacting the solution comprising the metal alloy with a sufficient amount of water so that the solution comprising the metal alloy has a desired concentration of base. The method may include monitoring the pH of the solution comprising the metal alloy and contacting the solution comprising the metal alloy with a sufficient amount of water so that the solution comprising the metal alloy has a desired concentration of base when the pH rises above a predetermined maximum value.

[0063] In embodiments where the battery comprises a separator cell, the method may include contacting the additional electrolyte with a sufficient amount of water so that the additional electrolyte has a desired base concentration. The method may include monitoring the pH of the additional electrolyte and contacting the additional electrolyte with a sufficient amount of water so that the additional electrolyte has a desired base concentration when the pH rises above a predetermined maximum value.

[0064] The desired concentration of base may be at least 0.5M, at least 1M or at least 1.5M of base, more preferably at least 2M, at least 2.5M or at least 3M of base and most preferably at least 3.5M or at least 4M of base. The desired concentration of base may be less than 8.5M, less than 8M or less than 7.5M of base, more preferably less than 7M, less than 6.5M or less than 6M of base and most preferably less than 5.5M or less than 5M of base. The desired concentration of base may be 0.5 and 8.5M, between 1 and 8M or between 1.5 and 7.5M of base, more preferably between 2 and 7M, between 2.5 and 6.5M or between 3 and 6M of base and most preferably between 3.5 and 5.5M or between 4 and 5M of base.

[0065] The predetermined maximum pH may correspond to a base concentration of at least 8.5M, at least 8M or at least 7.5M, more preferably at least 7M, at least 6.5M or at least 6M and most preferably at least 5.5M or at least 5M.

[0066] The method may include continuously feeding a solution comprising metal ions into an electrochemical cell while the electrochemical reaction is being carried out. The method may further include removing the solution comprising metal ions from the cell while the electrochemical reaction is being carried out. Advantageously, this step continuously renews the solution comprising metal ions.

[0067] In embodiments where the cell is a separator cell, the method may include feeding a solution comprising metal ions into a cathode portion of the electrochemical cell while the electrochemical reaction is being conducted. The method may further include removing the solution comprising metal ions from the cathode portion of the cell while the electrochemical reaction is being conducted. The method may include feeding additional electrolyte into an anode portion of the electrochemical cell while the electrochemical reaction is being conducted and / or removing additional electrolyte from the cathode portion of the cell while the electrochemical reaction is being conducted.

[0068] The anode and cathode may independently comprise a carbon-based electrode or a metal-based electrode. The carbon-based electrode or each carbon-based electrode may comprise graphite. The metal-based electrode or each metal-based electrode may comprise chromium, nickel, zinc, cadmium, copper, tin, lead, rhodium, platinum, gold, palladium, iridium, osmium, rhenium, ruthenium, germanium, beryllium and / or silver. Alternatively, the metal-based electrode or each metal-based electrode may comprise an alloy such as brass, bronze or steel. The steel may be stainless steel. In a preferred embodiment, the electrode comprises graphite or steel. In an alternative preferred embodiment, the electrode comprises the same metal as the metal or its alloy. For example, if the electrochemical reaction produces zinc, the electrode may comprise zinc.

[0069] The method may include applying a voltage of at least 1V, at least 1.5V, at least 1.75V or at least 2V across the anode and cathode, more preferably the method includes applying a voltage of at least 2.5V, at least 3V or at least 3.5V across the anode and cathode and most preferably the method includes applying a voltage of at least 4V or at least 4.5V across the anode and cathode. The method may include applying a voltage of less than 8V or less than 7.5V across the anode and cathode, more preferably the method includes applying a voltage of less than 7V, less than 6.5V or less than 6V across the anode and cathode and most preferably the method includes applying a voltage of less than 5.5V or less than 5V across the anode and cathode. In some embodiments, the method includes applying a voltage of less than 4V, less than 3V or less than 2.5V. The method may include applying a voltage between 1 and 8V or between 2 and 7.5V across the anode and cathode. In some embodiments, the method comprises applying a voltage between 2.5 and 7 V, between 3 and 6.5 V or between 3.5 and 6 V across the anode and cathode and most preferably the method comprises applying a voltage between 4 and 5.5 V or between 4.5 and 5 V across the anode and cathode. In alternative embodiments, the method comprises applying a voltage between 1 and 4 V, between 1.5 and 3 V or between 1.75 and 2.5 V across the anode and cathode.

[0070] The method may include passing a current of at least 0.5 A, at least 1 A, or at least 1.5 A through the anode, cathode, and the solution comprising metal ions, more preferably passing a current of at least 2 A, at least 2.5 A, or at least 3 A through the anode, cathode, and the solution comprising metal ions, and most preferably passing a current of at least 3.5 A through the anode, cathode, and the solution comprising metal ions. The method may include passing a current of less than 10 A, less than 8 A, or less than 6 A through the anode, cathode, and the solution comprising metal ions, more preferably passing a current of less than 5.5 A, less than 5 A, or less than 4.5 A through the anode, cathode, and the solution comprising metal ions, and most preferably passing a current of less than 4 A through the anode, cathode, and the solution comprising metal ions. The method may comprise passing a current of between 0.5 and 10 A, between 1 and 8 A or between 1.5 and 6 A through the anode, cathode and the solution comprising metal ions, more preferably passing a current of between 2 and 5.5 A, between 2.5 and 5 A or between 3 and 4.5 A through the anode, cathode and the solution comprising metal ions and most preferably passing a current of between 3.5 and 4 A through the anode, cathode and the solution comprising metal ions.

[0071] Preferably, the electrochemical reaction is carried out at a temperature of at least 0°C, more preferably at a temperature of at least 10°C, at least 12.5°C, at least 15°C, at least 17.5°C or at least 20°C. In some embodiments, the electrochemical reaction is carried out at a temperature of at least 25°C and most preferably at a temperature of at least 30°C or at least 55°C. Preferably, the electrochemical reaction is carried out at a temperature of less than 95°C, more preferably at a temperature of less than 90°C, less than 85°C or less than 80°C and most preferably at a temperature of less than 70°C or less than 65°C. In some embodiments, the electrochemical reaction is carried out at a temperature of less than 50°C, less than 40°C, less than 30°C or less than 25°C. Preferably, the electrochemical reaction is carried out at a temperature between 0°C and 95°C, more preferably at a temperature between 10°C and 90°C. In some embodiments, the electrochemical reaction is carried out at a temperature between 20°C and 85°C or between 25°C and 80°C and most preferably at a temperature between 30°C and 70°C or between 55°C and 65°C. Advantageously, at higher temperatures, hydrogen is produced faster.In some embodiments, the electrochemical reaction is performed at a temperature between 10°C and 50°C, between 12.5 and 40°C, between 15°C and 30°C, or between 17.5°C and 25°C.

[0072] Preferably, the method includes recovering the metal or alloy thereof produced in the electrochemical reaction. Recovering the metal or alloy thereof produced in the electrochemical reaction may include removing the metal or alloy thereof produced in the electrochemical reaction from the cathode. The metal or alloy thereof may be removed after the electrochemical reaction has been completed. Alternatively, the metal or alloy thereof may be removed continuously while the electrochemical reaction is being performed. For example, the electrochemical cell may include a blade configured to remove the metal or alloy thereof from the cathode. The blade may be configured to move across the cathode and thereby remove the metal or alloy thereof from the surface of the cathode. A magnetic force or an electric motor may be used to move the blade. The electrochemical cell may include a collection vessel configured to receive the metal or alloy thereof once it has been removed from the cathode and remove the metal or alloy thereof from the battery. In an embodiment in which the battery is a separated battery, the collection vessel may be placed in the cathode portion of the battery. The collection vessel may include a rotary valve configured to receive the metal or alloy thereof once it has been removed from the cathode and remove the metal or alloy thereof from the battery. The rotary valve may be motorized.

[0073] The inventors believe that apparatus for carrying out the methods of the first and second aspects are novel and inventive in their own right.

[0074] Therefore, according to a third aspect, there is provided an apparatus for producing hydrogen, the apparatus comprising:

[0075] a thermochemical reactor configured to contain a metal or an alloy thereof therein, the thermochemical reactor comprising a feeding device configured to feed steam into the thermochemical reactor and thereby convert the metal or the alloy thereof into a metal oxide and / or a metal hydroxide; and

[0076] - an electrochemical cell comprising an anode and a cathode and configured to receive a solution comprising metal ions such that at least a portion of the cathode contacts the solution comprising the metal ions.

[0077] Preferably, the device is configured to prevent the metal, the alloy thereof, the metal oxide and / or the metal hydroxide from escaping from the thermochemical reactor when a thermochemical reaction is carried out in the thermochemical reactor. Therefore, the device may include a container configured to contain the metal or the alloy thereof and placed in the thermochemical reactor. The feeding device may be configured to feed steam directly into the container. The container may include a grid configured to allow gas to flow out of the container while being further configured to prevent the metal, the alloy thereof, the metal oxide and / or the metal hydroxide from being removed from the container. The pore size of the grid may be between 0.1 and 1000 μm, more preferably between 1 and 750 μm, between 2 and 500 μm or between 3 and 250 μm and most preferably between 5 and 100 μm, between 10 and 50 μm, between 15 and 40 μm or between 20 and 30 μm. The grid may be sandwiched between two or more additional grids. The pore size of the further mesh may be between 0.1 and 1000 μm, more preferably between 10 and 900 μm, between 25 and 850 μm or between 50 and 800 μm and most preferably between 75 and 750 μm, between 100 and 700 μm, between 125 and 650 μm or between 150 and 600 μm. Advantageously, the further mesh ensures that the resulting mesh structure has sufficient strength to accommodate the weight of the metal, its alloy and / or metal oxide and / or metal hydroxide.

[0078] The apparatus may include a stirring device configured to stir the metal or its alloy in the thermochemical reactor. Thus, the thermochemical reactor may include a self-stirring thermochemical reactor. The self-stirring thermochemical reactor may be a spouted bed reactor, a fluidized bed reactor or a pneumatically transported bed reactor.

[0079] Preferably, the thermochemical reactor is configured to contain the metal or its alloy at a temperature of at least 100°C, more preferably at a temperature of at least 150°C, at least 200°C or at least 250°C and most preferably at a temperature of at least 300°C or at least 350°C. Preferably, the thermochemical reactor is configured to contain the metal or its alloy at a temperature of less than 700°C, more preferably at a temperature of less than 650°C, less than 600°C or less than 550°C and most preferably at a temperature of less than 500°C or less than 450°C. Preferably, the thermochemical reactor is configured to contain the metal or its alloy at a temperature between 100°C and 700°C, more preferably at a temperature between 150°C and 650°C, between 200°C and 600°C or between 250°C and 550°C and most preferably at a temperature between 300°C and 500°C or between 350°C and 450°C.

[0080] Devices capable of feeding steam into a thermochemical reactor are well known to the skilled person. For example, the feed device may be configured to evaporate water disposed therein and thereby form steam. Thus, the feed device may comprise a coiled section disposed in the thermochemical reactor. The device may comprise a pump configured to pump water or steam, preferably water, into the feed device. The pump may comprise a syringe pump.

[0081] The apparatus may include a feed device configured to feed the metal or its alloy into the thermochemical reactor. The feed device may include a first rotary valve. The first rotary valve may be a motorized rotary valve.

[0082] The apparatus may comprise a feed device configured to feed the metal oxide and / or metal hydroxide out of the reactor. The feed device may comprise a second rotary valve. The second rotary valve may be a motorised rotary valve.

[0083] The apparatus may include a condenser configured to remove steam from the gaseous mixture. Preferably, the apparatus includes a conduit extending between the thermochemical reactor and the condenser. Thus, the condenser may condense unreacted steam to obtain hydrogen.

[0084] The apparatus may include a pressure swing absorption unit or a cryogenic system configured to separate the hydrogen from the carrier gas.

[0085] The apparatus may include a hydrogen collection vessel configured to contain hydrogen produced in the thermochemical reactor. The apparatus may include a conduit extending between the condenser and the hydrogen collection vessel.

[0086] The electrochemical cell may be an undivided cell.

[0087] Alternatively, the electrochemical cell may comprise a separator cell. Thus, the cell may comprise a membrane disposed between the anode and cathode dividing the cell into two parts. Preferably, the membrane is as defined in relation to the first and second aspects.

[0088] In this embodiment, the cathode portion of the battery can be configured to accommodate a solution comprising metal ions, such that at least a portion of the cathode contacts the solution comprising metal ions. The anode portion of the battery can be configured to accommodate an additional electrolyte, such that at least a portion of the anode contacts the electrolyte. The additional electrolyte can be as defined in relation to the first and second aspects.

[0089] The apparatus may include a reservoir configured to hold a solution comprising metal ions. The apparatus may include a first conduit extending between the reservoir and the electrochemical cell, and a pump configured to cause the solution comprising metal ions to flow from the reservoir along the first conduit and into the first electrochemical cell. The apparatus may include a second conduit extending between the electrochemical cell and the reservoir, and a pump configured to cause the solution comprising metal ions to flow from the electrochemical cell along the second conduit and into the reservoir. The same pump may be configured to cause the solution comprising metal ions to flow from the reservoir along the first conduit and into the electrochemical cell, and also cause the solution comprising metal ions to flow from the electrochemical cell along the second conduit and into the reservoir. The pump or each pump may be a peristaltic pump.

[0090] The device may include a pH meter configured to monitor the pH of a solution including metal ions. The pH meter may be placed in a reservoir or an electrochemical cell. Preferably, the pH meter is placed in the reservoir. The device may include a feed device configured to feed water into the reservoir or the electrochemical cell. Preferably, the feed device is configured to feed water into the reservoir. The device may be configured to feed water into the reservoir or the electrochemical cell when the pH meter senses a pH above a predetermined maximum pH.

[0091] The apparatus may include a feed device configured to feed the metal oxide and / or metal hydroxide into the reservoir or the electrochemical cell. Preferably, the feed device is configured to feed the metal oxide and / or metal hydroxide into the reservoir. The feed device may include a rotary valve. The rotary valve may be a motorized rotary valve.

[0092] In embodiments where the battery is a divided battery, the apparatus may include a first reservoir configured to contain a solution comprising metal ions. The apparatus may include: a first conduit extending between the reservoir and the cathode portion of the electrochemical cell, and a pump configured to cause the solution comprising metal ions to flow from the first reservoir along the first conduit and into the cathode portion of the electrochemical cell. The apparatus may include a second conduit extending between the cathode portion of the electrochemical cell and the first reservoir, and a pump configured to cause the solution comprising metal ions to flow from the cathode portion of the electrochemical cell along the second conduit and into the first reservoir. The same pump may be configured to cause the solution comprising metal ions to flow from the first reservoir along the first conduit and into the anode portion of the electrochemical cell, and also cause the solution comprising metal ions to flow from the anode portion of the electrochemical cell along the second conduit and into the first reservoir. The pump or each pump may be a peristaltic pump.

[0093] The apparatus may include a second reservoir configured to hold additional electrolyte. The apparatus may include: a third conduit extending between the second reservoir and the anode portion of the electrochemical cell, and a pump configured to cause additional electrolyte to flow from the second reservoir along the third conduit and into the anode portion of the electrochemical cell. The apparatus may include a fourth conduit extending between the anode portion of the electrochemical cell and the second reservoir, and a pump configured to cause additional electrolyte to flow from the anode portion of the electrochemical cell along the fourth conduit and into the second reservoir. The same pump may be configured to cause additional electrolyte to flow from the second reservoir along the third conduit and into the anode portion of the electrochemical cell, and also cause additional electrolyte to flow from the anode portion of the electrochemical cell along the fourth conduit and into the second reservoir. The pump or each pump may be a peristaltic pump.

[0094] The device may include a first pH meter configured to monitor the pH of a solution including metal ions. The first pH meter may be placed in the first reservoir or the cathode portion of the electrochemical cell. Preferably, the first pH meter is placed in the first reservoir. The device may include a feeding device configured to feed water into the first reservoir or the cathode portion of the electrochemical cell. Preferably, the feeding device is configured to feed water into the first reservoir. The device may be configured to feed water into the cathode portion of the first reservoir or the electrochemical cell when the first pH meter senses a pH above a predetermined maximum pH.

[0095] The device may include a second pH meter configured to monitor the pH of another analyte. The second pH meter may be placed in the second reservoir or the anode portion of the electrochemical cell. Preferably, the second pH meter is placed in the second reservoir. The device may include a feed device configured to feed water into the second reservoir or the anode portion of the electrochemical cell. Preferably, the feed device is configured to feed water into the second reservoir. The device may be configured to feed water into the anode portion of the second reservoir or the electrochemical cell when the second pH meter senses a pH above a predetermined maximum pH.

[0096] The apparatus may include a feed device configured to feed the metal oxide and / or metal hydroxide into the first reservoir or the cathode portion of the electrochemical cell. Preferably, the feed device is configured to feed the metal oxide and / or metal hydroxide into the first reservoir. The feed device may include a rotary valve. The rotary valve may be a motorized rotary valve.

[0097] The anode and cathode may be as defined in relation to the first and second aspects.

[0098] The device may include a removal device configured to remove the metal or its alloy from the electrochemical cell. The removal device may include a device for removing the metal or its alloy from the cathode. The removal device may include a blade configured to remove the metal or its alloy from the cathode. The blade may be configured to move across the cathode and thereby remove the metal or its alloy from the surface of the cathode. The device may be configured to move the blade using magnetic force or an electric motor. The removal device may include a collection vessel configured to receive the metal or its alloy once it has been removed from the cathode and remove the metal or its alloy from the battery. In an embodiment in which the battery is a separated battery, the collection vessel may be placed in the cathode portion of the battery. The collection vessel may include a rotary valve configured to receive the metal or its alloy once it has been removed from the cathode and remove the metal or its alloy from the battery. The rotary valve may be motorized.

[0099] The apparatus may include a power source configured to apply a voltage across the anode and cathode. The power source may include a battery, a generator, a renewable power source, or the power source may include a national grid. The renewable power source may include a solar generator, a wind generator, or a hydroelectric generator. The power source may be configured to supply direct current to the anode and cathode.

[0100] The power supply may be configured to apply a voltage of at least 1V or at least 2V across the anode and cathode, more preferably at least 2.5V, at least 3V or at least 3.5V across the anode and cathode and most preferably at least 4V or at least 4.5V across the anode and cathode. The power supply may be configured to apply a voltage of less than 8V or less than 7.5V across the anode and cathode, more preferably less than 7V, less than 6.5V or less than 6V across the anode and cathode and most preferably less than 5.5V or less than 5V across the anode and cathode. The power supply may be configured to apply a voltage between 1 and 8V or between 2 and 7.5V across the anode and cathode, more preferably between 2.5 and 7V, between 3 and 6.5V or between 3.5 and 6V across the anode and cathode and most preferably between 4 and 5.5V or between 4.5 and 5V across the anode and cathode.

[0101] The power supply can be configured to cause a current of at least 0.5A, at least 1A or at least 1.5A to flow through the anode, cathode and the solution comprising metal ions, more preferably at least 2A, at least 2.5A or at least 3A to flow through the anode, cathode and the solution comprising metal ions, and most preferably at least 3.5A to flow through the anode, cathode and the solution comprising metal ions. The power supply can be configured to cause a current of less than 10A, less than 8A or less than 6A to flow through the anode, cathode and the solution comprising metal ions, more preferably less than 5.5A, less than 5A or less than 4.5A to flow through the anode, cathode and the solution comprising metal ions, and most preferably less than 4A to flow through the anode, cathode and the solution comprising metal ions. The power supply can be configured to pass a current of between 0.5 and 10 A, between 1 and 8 A, or between 1.5 and 6 A through the anode, cathode, and the solution comprising metal ions, more preferably between 2 and 5.5 A, between 2.5 and 5 A, or between 3 and 4.5 A through the anode, cathode, and the solution comprising metal ions, and most preferably between 3.5 and 4 A through the anode, cathode, and the solution comprising metal ions.

[0102] The apparatus may include a hydrogen collection vessel configured to contain hydrogen generated in the electrochemical cell. The apparatus may include a conduit extending between the electrochemical cell and the hydrogen collection vessel. In embodiments where the cell is a split cell, the conduit may extend between a cathode portion of the electrochemical cell and the hydrogen collection vessel.

[0103] The hydrogen collection vessel configured to contain hydrogen produced in a thermochemical reactor may also be a hydrogen collection vessel configured to contain hydrogen produced in an electrochemical cell. Alternatively, the apparatus may include two separate hydrogen collection vessels.

[0104] According to a further aspect, there is provided a method of producing hydrogen, the method comprising:

[0105] - thermochemical reaction of a metal or its alloy in contact with steam to produce metal oxides and hydrogen;

[0106] - contacting the metal oxide produced in the thermochemical reaction with an alkaline aqueous solution to produce a solution comprising metal ions; and

[0107] - performing an electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of the cathode contacts the solution comprising the metal ions, to produce hydrogen, oxygen and the metal or the alloy thereof.

[0108] According to still further aspects, there is provided a method of producing hydrogen, the method comprising:

[0109] - contacting the metal oxide with an alkaline aqueous solution to produce a solution comprising metal ions;

[0110] - performing an electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of said cathode contacts said solution comprising said metal ions, to produce hydrogen, oxygen and a metal or an alloy thereof; and

[0111] - A thermochemical reaction is carried out by bringing the metal or the alloy thereof produced in the electrochemical reaction into contact with steam to produce the metal oxide and hydrogen.

[0112] According to a final aspect, there is provided an apparatus for producing hydrogen, the apparatus comprising:

[0113] a thermochemical reactor configured to contain a metal or an alloy thereof therein, the thermochemical reactor comprising a feeding device configured to feed steam into the thermochemical reactor and thereby convert the metal or the alloy thereof into a metal oxide; and

[0114] - an electrochemical cell comprising an anode and a cathode and configured to receive a solution comprising metal ions such that at least a portion of the cathode contacts the solution comprising the metal ions.

[0115] The apparatus may include an oxygen collection vessel configured to contain oxygen generated in the electrochemical cell. The apparatus may include a conduit extending between the electrochemical cell and the oxygen collection vessel. In embodiments where the cell is a split cell, the conduit may extend between the anode portion of the electrochemical cell and the oxygen collection vessel.

[0116] All features described herein (including any accompanying claims, abstract, and drawings) and / or all steps of any method or process so disclosed may be combined with any of the above-described aspects in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive.

[0117] For a better understanding of the invention and to show how embodiments of the invention may be implemented, reference will now be made, by way of example, to the accompanying drawings, in which:

[0118] Figure 1 is a schematic diagram of an apparatus for carrying out a thermochemical reaction;

[0119] Figure 2 is a graph showing the effect of temperature on the volume of hydrogen produced in a thermochemical reaction;

[0120] Figure 3 is a graph showing the effect of steam flow rate on the volume of hydrogen produced in a thermochemical reaction;

[0121] Figure 4 is a graph showing the effect of the form of zinc on the volume of hydrogen produced in a thermochemical reaction;

[0122] Figure 5 is a graph showing the effect of mixing zinc on the volume of hydrogen gas produced in a thermochemical reaction;

[0123] Figure 6 is a graph showing experimental hydrogen production in an experiment carried out to completion;

[0124] Figure 7 is a schematic diagram of the experimental setup used for the electrolysis reaction;

[0125] Figure 8 Shown in Figure 7 The electrolytic cell used in the experimental setup;

[0126] Fig. 9 is a graph showing the maximum solubility of zinc oxide (ZnO) in aqueous solutions including different concentrations of sodium hydroxide (NaOH);

[0127] Fig.10 is a graph showing the conductivity of a sodium zincate solution as a function of the concentrations of sodium zincate and sodium hydroxide;

[0128] Fig.11 is a graph showing how the conductivity of a sodium hydroxide solution varies with the concentration of sodium hydroxide;

[0129] Fig.12is a graph showing how the voltage applied across the electrodes affects the volume of hydrogen gas produced;

[0130] Fig.13 is a graph showing how voltage applied across electrodes affects current;

[0131] Fig.14 is a schematic diagram showing the cyclic nature of the entire process;

[0132] Fig.15 is a graph showing how the conductivity and resistance of a sodium stannate trihydrate solution vary with the concentration of sodium stannate trihydrate;

[0133] Fig.16 is a graph showing hydrogen generation versus time for different concentrations of sodium stannate trihydrate at an applied voltage of 2V; and

[0134] Fig.17 is a graph showing hydrogen gas generation versus time for a 1.2 M electrolyte as the applied voltage is varied.

[0135] Example 1—Thermochemical Reaction of Zinc

[0136] The first experiment conducted involved reacting zinc with steam to form zinc oxide and hydrogen gas.

[0137] method

[0138] use Figure 1 The apparatus 1 shown carries out thermochemical experiments. The apparatus 1 comprises a tube furnace 2 with a crucible 4 and a temperature sensor 5 arranged therein. The crucible 4 comprises a mesh cover 6.

[0139] The syringe pump 8 is arranged outside the tube furnace 2, and the conduit 10 extends between the syringe pump 8 and the crucible 4. The conduit 10 includes a coiled section 12 arranged inside the tube furnace 2.

[0140] The condenser 16, the measuring cylinder 18, the water bath 20 and the vacuum pump 22 are also arranged outside the tube furnace 2. The cylinder 18 is inverted in the water bath 20, and the conduit 24 extends between the base 26 of the cylinder 18 and the vacuum pump 22. The conduit 28 extends between the tube furnace 2 and the condenser 16, and a further conduit 30 extends between the condenser and the cylinder 18.

[0141] When a user wishes to conduct an experiment, the user places a pre-weighed amount of zinc 32 in the crucible 4. In the experiments described below, 10 g of zinc was used in each experiment.

[0142] The user fills the syringe pump 8 with deionized water 34. The user also fills the water bath 20 with water 36 and starts the vacuum pump 22. The vacuum pump 22 removes the gas from the cylinder 18 and replaces it with water 36. The user then flushes the system with nitrogen and then starts the tube furnace 2 and waits for it to reach the desired temperature.

[0143] Before conducting the experiment, the user will start the vacuum pump 22 again to remove any gas that has entered the cylinder 18 due to the expansion of the gas caused by the heating of the tube furnace 2. The user will then start the syringe pump 8. This will feed deionized water 34 along the conduit 10. As the deionized water 34 passes through the coiled section 12, it will evaporate, ensuring that the vapor is fed to the crucible 4 and contacts the zinc powder 32. The vapor will react with the zinc 32 according to the following formula:

[0144] Zn (s) +H2O (l) →ZnO (s) +H 2(g) 1a

[0145] The net will prevent zinc 32 and zinc oxide from escaping from the crucible, while allowing gas to flow out of the crucible. The gas will then flow along conduit 28 and through condenser 16, which condenses the steam into water and removes it. Hydrogen 38 will continue to flow along conduit 30 and into cylinder 18, displacing water 36. The user can thus measure the volume of hydrogen 38 produced. In the experiments described below, readings were taken every five minutes.

[0146] result

[0147] The effect of temperature was studied by measuring the generation of hydrogen at four different temperatures, namely, 250°C, 300°C, 350°C and 400°C. All experiments were performed using zinc powder at a steam flow rate of 150 ml / min. The results from the temperature experiments showed that an increase in the reaction temperature resulted in an increase in the volume of hydrogen generated in the reaction, see Figure 2 All different temperatures followed a similar shape of an initial rapid increase in hydrogen followed by a decrease in production rate. The production rates followed a general pattern: the higher the temperature, the greater the rate of hydrogen production. It was further observed that the higher the temperature, the smaller the delay in hydrogen production after water was injected into the system.

[0148] The effect of the steam volume flow rate was studied by measuring the hydrogen production at three different rates: 50 ml / min, 100 ml / min and 150 ml / min. All experiments were performed at a constant temperature of 350 °C using zinc powder. The results show that an increase in the steam volume flow rate leads to an increase in the volume of hydrogen produced, see Figure 3The results follow a pattern of a rapid increase in the rate of hydrogen production followed by a gradual decrease. The differences in the rate and volume produced are minor when compared to the effect of temperature. After water was injected into the system, there was a consistent delay of 10 minutes before the reaction began.

[0149] The effect of the form of the zinc was investigated by comparing the volume of hydrogen produced when the zinc was provided in pellet form with the volume of hydrogen produced when the zinc was provided in powder form. All experiments were conducted using a constant temperature of 350°C and a steam volume flow rate of 150 ml / min. The results showed that zinc in powder form produced more hydrogen than zinc in pellet form, see Figure 4 At the end of the experiment, the zinc sample was removed from the crucible. When removed, the pellets were found to be slightly broken up and there were lumps of zinc surrounded by zinc powder that had broken off.

[0150] During the above experiments, channelling was observed in the crucible, whereby the steam would flow out of the crucible, bypassing large amounts of zinc in specific areas. As a result, certain areas of the zinc sample were exposed to the steam, while other areas were not. In order to evaluate how this channelling affects the reaction rate, an experiment was conducted involving removing the zinc sample and mixing it midway through the experiment. The experiments were conducted using zinc powder at a constant temperature of 400°C and a steam volume flow rate of 150 ml / min. As would be expected, the initial reactions for both experiments were similar, but the volume of hydrogen produced jumped at the point where the zinc was mixed, see Figure 2. Figure 5 .

[0151] In order to determine how long the reaction takes to complete, two experiments were performed until hydrogen production ceased. The first experiment was performed using zinc powder at 350°C and a steam volume flow rate of 100 ml / min and was performed until production stabilized, which occurred after approximately 8 hours, see Figure 6 The second experiment was conducted using zinc powder at 400 °C and a steam volume flow rate of 150 ml / min. Similar to the first experiment, it took about 8 hours for the hydrogen production to start to level off, see Figure 6 .

[0152] Example 2—Electrochemical reaction of zinc oxide

[0153] method

[0154] The second experiment was to use Figure 7 The electrochemical reaction is performed by the device 100 shown. The device 100 includes an electrolytic cell 102 manufactured by the University of Surrey workshop. Figure 8 As shown, the pool 102 includes Perspex disposed in two separate sections 106, 108. TMHousing 104. A cathode 110 is disposed in a first portion 106 of housing 104, and an anode 112 is disposed in a second portion 108 of housing 104. Both cathode 110 and anode 112 include graphite plates.

[0155] A rubber O-ring 114 is disposed in the first portion 106 of the housing 104 and surrounds the cathode. Prior to use, an anion exchange membrane 116 is placed over the cathode 110 and the O-ring 114 so that the edge of the membrane 116 extends over the O-ring 114. The second portion 108 of the housing 104 is then placed over the membrane 116, and the first and second portions 106, 108 of the housing are secured together by screwing bolts into corresponding bolt holes 118 disposed in the first and second portions 106, 108 of the housing.

[0156] Throughout the experiment, sodium zincate 120 was circulated through the cathode 110 side of the cell 102, and sodium hydroxide 122 was circulated through the anode 112 side of the cell 102 using a peristaltic pump (not shown). Details describing the preparation of sodium zincate 120 are provided below.

[0157] Power is applied to the electrodes 110 , 112 using a conventional DC power supply 124 .

[0158] Two measuring cylinders 126a, 126b are inverted in a bath 128 comprising water 130. Nylon tubes 132 are connected to the tops of the cylinders 126, allowing the cylinders to be filled with waste 130 using a vacuum pump 134 before the experiment begins. Then, valve 136 can be closed. Nylon tubes 138 extending between the cathode 110 side of the cell 102 and one of the measuring cylinders 126a are configured to deliver hydrogen 140 produced in the experiment to the measuring cylinders 126a. Similarly, nylon tubes 142 extending between the anode 112 side of the cell 102 and one of the measuring cylinders 126b are configured to deliver oxygen 144 produced in the experiment to the measuring cylinders 126b.

[0159] result

[0160] Solubility test results

[0161] Before any electrolytic cell experiments can be performed, the best electrolyte solution to use must be determined.

[0162] Zinc oxide is insoluble in water. However, zinc oxide will react with sodium hydroxide according to the following formula:

[0163] ZnO (s) +2NaOH (aq) →Zn(OH) 2(aq) +Na2O (aq) 1

[0164] The sodium oxide then reacts with water as follows:

[0165] Na2O (aq) +H2O (l) →2NaOH (aq) 2

[0166] The excess NaOH available in the solution is used to dissolve Zn(OH)2 to form a pseudo compound which can be labeled as sodium zincate Na2Zn(OH)4 as shown below:

[0167] Zn(OH) 2(aq) +2NaOH (aq) →Na2Zn(OH) 4(aq) 3

[0168] In order to find the range of molar concentrations of the sodium zincate solution that can be prepared, the solubility of sodium hydroxide (NaOH) in water must first be determined. An experiment was conducted to find the maximum solubility of sodium hydroxide in water at room temperature. This was achieved by periodically adding sodium hydroxide to 100 ml of deionized water that was continuously mixed by a magnetic stirrer. When the solution began to become turbid, it was noted that dissolution had ceased.

[0169] Since the dissolution of sodium hydroxide in water is exothermic, an ice bath is used to keep the solution cool. Initially, sodium hydroxide pellets are added to the water in 10 g intervals, allowing the solution to cool between additions. Once the range of maximum solubility is found (in the range of 80 g–90 g), the solution can be re-prepared and smaller increments of sodium hydroxide added closer to the saturation point at room temperature.

[0170] It was found that a maximum mass of 82 g NaOH could be dissolved in 100 ml water. The maximum value found is less than the maximum value in the literature (O'Neil, 2006), which states that 109 g can be dissolved in 100 ml water at 20° C. In order to keep the solution contained and prevent any water vapor from escaping, Parafilm was used to cover the top of the beaker between the additions of the sodium hydroxide pellets. However, some water droplets did form on the underside of the film, which may have contributed to this difference from the literature because sodium hydroxide dissolves less water.

[0171] To find the maximum solubility of zinc oxide in sodium hydroxide solution, first 100 ml of water and 4 g of NaOH were used to create a 1 M NaOH solution. Then 0.5 g of ZnO was added and allowed to mix for about 5 minutes. If it dissolved, another 0.5 g of ZnO was added, if it did not, another 4 grams of NaOH was added to the solution. This process was carried out until no more ZnO dissolved, despite adding more NaOH to the solution, and the results are shown in Fig. 9The maximum solubility of zinc oxide in a solution containing 100 ml of water and 64 g of NaOH was found to be 14 g (to produce a 1.78 M sodium zincate solution). The graph shows that as more NaOH is added to the solution, more zinc oxide can react and sodium zincate can dissolve in the solution. However, as Fig. 9 As shown, as the solution reaches 30 wt% NaOH, the percentage of reacted and dissolved zinc oxide increases more slowly and then levels off just below 8 w% ZnO.

[0172] Conductivity test results

[0173] Sodium zincate solutions were prepared by adding 12 g, 16 g, 20 g or 24 g of NaOH and the required amount of ZnO to 100 ml of deionized water. The solution was dissolved for between 5-10 minutes until clear, and then the conductivity was measured by using a Mettler Toledo conductivity probe. All readings were calibrated to 20°C to keep the results consistent and directly comparable. After the readings were completed, the conductivity probe was rinsed with deionized water to remove any sodium zincate solution and left in deionized water between readings to avoid contamination.

[0174] like Fig.10 As shown, as the molar concentration of sodium zincate decreases, the conductivity increases. In addition, increasing the concentration of NaOH increases the conductivity of the solution. Based on these results, a solution containing 100 ml of water, 16 g of NaOH and 1 g of ZnO (0.12 M) was selected to be scaled up to a litre solution for use as the electrolyte on the cathode side of the cell. It will be appreciated that a higher concentration of NaOH can be used if a solution with a higher conductivity is desired.

[0175] The conductivity of the sodium hydroxide also needs to be measured to decide which sodium hydroxide solution has the best conductivity and will therefore provide the best performance for the cell. Sodium hydroxide solutions between 0.5M and 7M were prepared and the conductivity measured. Fig.11 As shown, the inventors observed that the conductivity increased with increasing molar concentration until reaching a peak at 4.5 M when the conductivity began to decrease. Therefore, the concentration of sodium hydroxide in the electrolyte for the anode side was chosen to be 4.5 M as it gave the highest conductivity.

[0176] Pool Experiment Results

[0177] A sodium zincate (Na2Zn(OH)4) solution electrolytically decomposes in the cell by evolving hydrogen gas along with simultaneous electrodeposition of zinc particles on the cathode surface and evolving oxygen gas at the anode, as described in the following overall anode-cathode reaction:

[0178] Na2Zn(OH)4(aq) →2NaOH+Zn+H2+O2 3a

[0179] The effect of voltage on hydrogen generation was studied using voltages of 2.5 V, 3.0 V, and 3.5 V. Fig.12 As shown, as the voltage increases, the amount of hydrogen produced also increases. From 2.5V to 3V, only a small increase in hydrogen production occurs.

[0180] The effect of voltage on the current in the cell was studied for three different voltages: 2.5V, 3.0V and 3.5V, and the results are shown in Fig.13 The results show that as the voltage increases, the current also increases. The pattern for the 2.5V experiment shows an initial decrease in current over time, which then stabilizes, resulting in an average current of 0.25A. The current in the 3V experiment initially remains level but then slowly increases to nearly 1.5A, with the average current for the experiment recorded as 1.22A. The 3.5V experiment initially has a rapid rise, then continues to rise slowly over time, resulting in an average current of 3.51A.

[0181] The zinc produced in the above experiments was recovered from the electrode surface. Additional experiments were performed varying various experimental parameters and the results are shown in Table 1.

[0182] Table 1: Mass of zinc recovered from various electrolysis experiments

[0183]

[0184] As shown in Table 1, the higher the voltage, and therefore the greater the current, the greater the amount of zinc recovered. Comparing Experiments 8 and 9, it is noted that increasing the concentration of the sodium zincate solution increases the mass of zinc recovered. It is noted that the current increases at a faster rate in Experiment 9 and reaches a higher overall current than in Experiment 8. It is believed that this is due to the increase in the conductivity of the electrolyte and the resulting increase in the mass of zinc.

[0185] The cell efficiencies for Experiments 1 to 3 were calculated so that the performance of the cells could be compared, and the results are shown in Table 2.

[0186] Table 2: Pool efficiency for experiments 1 to 3

[0187]

[0188] The trend shows that the cell efficiency increases as the voltage increases and more hydrogen is produced.

[0189] Example 3—Electrochemical reaction of sodium stannate

[0190] To show that the method is suitable for use with metals other than zinc, the inventors also studied the electrochemical reaction of sodium stannate.

[0191] method

[0192] equipment

[0193] An undivided electrolytic cell was used to perform batch experiments. The cell consisted of a rectangular open-top plexiglass acrylic vessel with two cylindrical graphite electrodes arranged 6 cm apart and connected to the bottom of the vessel. The vessel was 25 cm high, 20 cm long, and 12 cm wide. The length of the electrode portion retained inside the vessel was 3 cm and 1 cm in diameter. Wires connected the electrodes to a power source. The power source set the voltage (and current) before each experiment. Each electrode had a cylinder (500 ml) on which a fitting valve was placed. A tube was used to connect one cylinder to a vacuum pump, which was used to fill the cylinder with an electrolyte solution before the experiment began. The valve was then closed before the experiment began.

[0194] Conductivity

[0195] The electrolyte was prepared by dissolving 55.4 g of sodium stannate (based on 42-45% SnO2) in 200 ml of distilled water. The resulting solution had a concentration of 1.3 M. This concentration was determined based on the solubility limit of sodium stannate in water. The reaction that occurred was exothermic:

[0196]

[0197] A conductivity measuring device was used to measure the conductivity of the electrolyte. The solution was then diluted to the desired concentration by adding distilled water. These concentrations ranged from 1.3-0.1M with a decrease of 0.1M at each interval. The conductivity was measured at each concentration. Using the conductivity, the resistance was calculated using the following equation:

[0198] R=L / σ.S 5

[0199] where R is the resistance (Ω), σ is the conductivity (mS / cm), L is the distance between the electrodes (cm), and S is the electrode surface area (cm 2 ). In this experiment, the electrode surface area is fixed at 11 cm 2 .

[0200] Hydrogen production

[0201] Once the electrolyte with the desired concentration as described above is produced, it is mixed thoroughly to ensure a constant concentration gradient. It is then carefully poured into the reaction vessel and the power supply is turned on. The current is fixed at 1A for all experiments.

[0202] Two different experimental procedures were performed. The first experimental procedure involved measuring the hydrogen generation rate over time at three different electrolyte concentrations around the optimal concentration value. The optimal concentration was determined based on the conductivity measurements. The second experimental procedure involved measuring the hydrogen generation rate over time at three different voltages: 2, 2.5 and 3V. Each experiment lasted three hours, with the hydrogen generation rate measured at five-minute intervals.

[0203] The desired electrolysis is that of sodium stannate trihydrate. However, it can exist in equilibrium with tin (IV) hydroxide and NaOH as shown below:

[0204]

[0205] The process is carried out at room temperature, which is advantageous because it tends to favor the formation of sodium stannate trihydrate at equilibrium. Even though the dissociation of water is relatively small in this process, it is still possible. This will lead to the production of hydrogen at the cathode. However, the more prominent reaction occurring at the same time is the reduction of tin (IV) hydroxide to tin. The metal is deposited on the surface of the cathode. These reactions can be considered respectively:

[0206]

[0207] The reaction at the anode involves the generation of oxygen:

[0208]

[0209] The sum of equations 6 to 9 simplifies to:

[0210]

[0211] The tin deposited on the cathode can then be oxidized to produce tin (IV) hydroxide and hydrogen. It should be understood that this method can be performed using the apparatus described in Example 1. The equation for this reaction is:

[0212]

[0213] The generated tin (IV) hydroxide can be used to replace the sodium stannate trihydrate that has been reacted according to Equation 6. By summing Equations 10 and 11, the overall equation for the process can be simplified to:

[0214]

[0215] Pool efficiency

[0216] The cell efficiency is calculated based on a combination of the measurements obtained from the experiment and the parameters used to conduct the experiment. The equation used to determine the cell efficiency is:

[0217] n=q / (UIt)13

[0218] where n is the cell efficiency based on the hydrogen production rate [m 3 m -3 h -1 (kWh) -1 ], q is the hydrogen production rate per unit volume of electrolyte in the electrolytic cell (m 3 m -3 h -1 ), U is the battery voltage (V), I is the battery current (A) and t is the time (hours).

[0219] Item(kWh) -1 is the combination of the terms in the denominator of equation 10. It represents the amount of electricity consumed by electrolysis.

[0220] During these experiments, the voltage was varied (2, 2.5 and 3 V) with fixed electrolyte concentration, current and specified time.

[0221] Results and Discussion

[0222] Concentration and conductivity

[0223] As explained above, the conductivity of the electrolyte was measured at various concentrations. Fig.15 As shown, a decrease in electrolyte concentration leads to a decrease in conductivity. This is because the number of ions per unit volume decreases as the concentration decreases. Therefore, there are fewer ions carrying a charge per unit volume, which leads to a decrease in conductivity. Based on this fact, it was expected that the electrolyte concentration of 1.3 M (maximum concentration) used in the experiment would have the highest conductivity. However, this was not the case. The optimum conductivity was the conductivity at a concentration of 1.2 M. The unexpected result can be explained by the electrolyte being at its solubility limit.

[0224] Additionally, the relationship between resistance and conductivity is inverse.

[0225] Concentration and hydrogen production

[0226] Based on these electrolytes having the highest conductivity, concentrations of 1.1 M, 1.2 M, and 1.3 M sodium stannate trihydrate were selected. The hydrogen production of these electrolytes was then measured.

[0227] The maximum hydrogen production was measured for 1.2M electrolyte, see Fig.16 Therefore, the electrolyte with the highest conductivity produces the most hydrogen in a given time.

[0228] Voltage and Hydrogen Production

[0229] Fig.17The three voltages considered in were selected based on the minimum cell voltage for hydrogen production in water electrolysis, which is 2 V. The hydrogen production was then measured.

[0230] The greatest amount of hydrogen gas accumulated was when the voltage was at its highest (i.e., 3V). This is expected because a greater voltage speeds up the rate at which electrolysis occurs, which causes more ions to flow to the electrodes. Therefore, more hydrogen gas accumulates over time. Compare this to Fig.16 By comparison, it can be seen that voltage has a more significant effect on hydrogen production than concentration. The difference in hydrogen production rate between 2V and 2.5V is about 150m 3 This is a significant change in the amount of hydrogen accumulated based on the scale of production relative to the change in voltage.

[0231] Pool efficiency

[0232] The cell efficiency was calculated based on 1.2 M electrolyte solution and the results are provided in Table 3.

[0233] Table 3: Cell efficiency of 1.2M electrolyte solution

[0234] Voltage (V) <![CDATA[Pool efficiency [m 3 m -3 h -1 (kWh) -1 > 2 10.68 2.5 4.35 3 2.03

[0235] The first observation made is that an increase in voltage results in a decrease in cell efficiency. Even though it produces a greater amount of hydrogen, the cell efficiency is lower, which is not desirable. Based on these results, the cell using sodium zincate (discussed in Example 2) is considered to be more efficient. However, due to the different amounts of electrical power consumed during the electrolysis experiments, a direct comparison is difficult to make. Therefore, this will result in some differences in the results.

[0236] There appears to be a significant drop in efficiency in the 2-2.5 V range compared to 2.5-3 V. For this reason, it would be more efficient to use a smaller voltage since this is when the battery is most efficient. However, at lower voltages (i.e., 2 V), it is clear that the battery is more efficient than the water electrolyzer, which may be a result of the ionic activators in the electrolyte solution.

[0237] in conclusion

[0238] The inventors have shown that hydrogen can be generated by converting zinc to zinc oxide in a thermochemical reaction, and additional hydrogen can be generated by converting zinc oxide to zinc in an electrochemical reaction. Thus, once an initial amount of zinc / zinc oxide is provided, these reactions can be performed in a cycle, such as Fig.14 As shown, a large amount of hydrogen is produced, wherein the only raw material required is water.

[0239] The inventors have shown that this system can also be applied to other metals, such as tin. Specifically, the inventors have produced tin from sodium stannate in an electrolytic reaction.

Claims

1. A method for producing hydrogen, the method comprising: - thermochemical reaction of zinc or tin or their alloys by contacting them with steam to produce zinc oxide and / or zinc hydroxide or tin oxide and / or tin hydroxide and hydrogen; - contacting the zinc oxide and / or the zinc hydroxide or the tin oxide and / or the tin hydroxide produced in the thermochemical reaction with water or an alkaline aqueous solution to produce a solution comprising zinc ions or tin ions; as well as - performing an electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of the cathode contacts the solution comprising the zinc ions or tin ions, to produce hydrogen, oxygen and the zinc or tin or an alloy thereof.

2. A method for producing hydrogen, the method comprising: - contacting zinc oxide and / or zinc hydroxide or tin oxide and / or tin hydroxide with water or an alkaline aqueous solution to produce a solution comprising zinc ions or tin ions; - performing an electrochemical reaction by applying a voltage across an anode and a cathode, whereby at least a portion of said cathode contacts said solution comprising said zinc ions or tin ions, to produce hydrogen, oxygen and zinc or tin or an alloy thereof; as well as - a thermochemical reaction is carried out by contacting the zinc or tin or alloy thereof produced in the electrochemical reaction with steam to produce zinc oxide and / or zinc hydroxide or tin oxide and / or tin hydroxide and hydrogen.

3. The method according to claim 1 or claim 2, wherein the electrochemical reaction is repeated.

4. The method according to claim 1 or claim 2, wherein the electrochemical reaction is performed continuously.

5. The method according to claim 1 or claim 2, wherein the thermochemical reaction is carried out continuously.

6. The method according to claim 1 or claim 2, wherein the thermochemical reaction is repeated.

7. A method according to claim 1 or claim 2, wherein the zinc or tin or alloys thereof are contacted with steam at a temperature between 100°C and 700°C.

8. A method according to claim 1 or claim 2, wherein the method comprises agitating the zinc or tin or alloy thereof while it is in contact with the steam.

9. A method according to claim 1 or claim 2, wherein the method comprises condensing unreacted steam from a gaseous mixture obtained from the thermochemical reaction.

10. The method according to claim 1 or claim 2, wherein the method comprises contacting the zinc oxide and / or the zinc hydroxide or the tin oxide and / or the tin hydroxide with the alkaline aqueous solution, and the alkaline aqueous solution comprises a base, and the base is an Arrhenius base, a Lewis base or a Bronsted-Lowry base.

11. The method of claim 10, wherein the base is an arene base and comprises an alkali metal or alkaline earth metal hydroxide.

12. The method of claim 1 or claim 2, wherein the method comprises contacting the zinc oxide and / or the zinc hydroxide or the tin oxide and / or the tin hydroxide with the alkaline aqueous solution, and the alkaline aqueous solution comprises a base at a concentration between 0.5M and 8.5M.

13. The method of claim 1 or claim 2, wherein the method comprises contacting the zinc oxide and / or the zinc hydroxide or the tin oxide and / or the tin hydroxide with the alkaline aqueous solution, and the zinc oxide and / or the zinc hydroxide or the tin oxide and / or the tin hydroxide are contacted with a sufficient amount of the alkaline aqueous solution to produce the solution comprising the zinc ions or the tin ions, wherein the zinc ions or the tin ions are present in a concentration between 0.001M and 1M.

14. The method of claim 1 or claim 2, wherein the method comprises contacting the zinc oxide and / or the zinc hydroxide or the tin oxide and / or the tin hydroxide with water, and the zinc oxide and / or the zinc hydroxide or the tin oxide and / or the tin hydroxide is contacted with a sufficient amount of water to produce the solution comprising the zinc ions or the tin ions, wherein the zinc ions or the tin ions are present in a concentration between 0.2M and 5M.

15. The method of claim 1 or claim 2, wherein the anode and the cathode are disposed in an undivided electrochemical cell.

16. The method of claim 1 or claim 2, wherein the anode and cathode are disposed in an electrochemical cell, and the electrochemical cell includes a membrane disposed between the anode and cathode that divides the cell into two parts.

17. The method of claim 16, wherein the method comprises placing the solution comprising the zinc ions or the tin ions in a cathode portion of the battery such that at least a portion of the cathode contacts the solution comprising the zinc ions or the tin ions, and the method further comprises placing an additional electrolyte in an anode portion of the battery such that at least a portion of the anode contacts the additional electrolyte.

18. The method of claim 17, wherein the additional electrolyte comprises an alkaline aqueous solution.

19. The method of claim 1 or claim 2, wherein the method comprises applying a voltage of between 1 V and 8 V across the anode and the cathode.

20. The method of claim 1 or claim 2, wherein the method comprises passing a current of between 0.5 A and 10 A through the anode, the cathode, and the solution comprising the zinc ions or the tin ions.

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