Hydrogen production and battery storage

Abstract

The disclosure describes an apparatus for hydrogen production. The apparatus comprises (a) an electrochemical cell comprising an anode and a cathode, (b) a battery comprising a positive current collector and an electrolyte compartment configured to hold an electrolyte therein and (c) a thermochemical reactor. The electrochemical cell is configured to receive a basic aqueous solution comprising zinc hydroxide and / or zincate, such that at least a portion of the cathode contacts the solution comprising the zinc hydroxide and / or zincate when it is disposed in the electrochemical cell. The apparatus further comprises a battery comprising a positive current collector and an electrolyte compartment configured to hold an electrolyte therein. The battery is configured to receive a gas comprising oxygen on the positive current collector and to receive at least a portion of the zinc produced in the electrochemical cell, such that the zinc forms an anode of the battery. The apparatus further comprises a thermochemical reactor. The thermochemical cell comprises a reaction chamber configured to receive at least a portion of the zinc metal produced in the electrochemical cell. The thermochemical cell is configured to enable the zinc metal to contact water in the reaction chamber and thereby cause a thermochemical reaction to proceed and thereby produce zinc oxide and a gas stream comprising hydrogen.

Description

[0001]Hydrogen Production and Battery Storage The invention relates to an apparatus and method of producing hydrogen gas. In particular embodiments of the invention, the apparatus and method may use renewable energy sources to continuously produce hydrogen gas. Hydrogen is an important energy carrier and has the potential to replace hydrocarbon based fuels for sustainable development. The current energy related problems with hydrocarbon fuels, such as air pollution, climate change and scarcity of the resource, 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 is convenient for efficient energy storage. Hydrogen can be used directly as a transportation fuel yielding a higher energy efficiency which is receiving much favourable attention as a technical and political issue. Currently, several industrial methods of hydrogen production exist, and among these are reforming, photoconversion and electrolysis, which have gained prominence. Water electrolysis provides the cleanest solution for hydrogen production. Its advantages are (i) it gives zero carbon emissions; (ii) it produces pure hydrogen, influencing fuel cell technology which is heavily affected by impurities in the hydrogen feed; (iii) it is independent of hydrocarbon resources; (iv) it can be operated in small scale plants; and (v) renewable energy sources (such as photovoltaic solar power, wind power, hydroelectric power, etc.) could be easily associated with water electrolysis cells to produce hydrogen. US 2019 / 0296410 A1 is concerned with a dynamic metal-anode flow battery energy- storage system. However, US 2019 / 0296410 A1 is not concerned with the production of hydrogen or suggest how it could be produced. US 2016 / 0261012 A1 describes a zinc-air cell and an apparatus for recharging the cell. Similarly, US 2014 / 0370401 A1 describes an air cathode battery. Both of these documents focus on the zinc-air battery per se. They do not suggest how such a battery could be used as a component in a system configured to produce hydrogen continuously. US 5,378,329 describes a process for the preparation of an alkaline-zinc slurry for use in batteries. This is the primary focus of US 5,378,329. US 5,378,329 specifically teaches that the production of hydrogen gas is undesirable. Accordingly, none of the prior art documents disclose a system which may be capable of producing hydrogen continuously and incorporate a battery to provide energy on demand. None of the prior art documents suggest how such a system may be designed and the provision of such a system would not have been obvious to the skilled person. The present invention arose from the inventors’ work in attempting to overcome the problems associated with the prior art. In accordance with a first aspect of the invention, there is provided an apparatus for hydrogen production, the apparatus comprising: an electrochemical cell comprising an anode and a cathode, and configured to receive a basic aqueous solution comprising zinc hydroxide and / or zincate, such that at least a portion of the cathode contacts the solution comprising the zinc hydroxide and / or zincate when it is disposed in the electrochemical cell; and a battery comprising a positive current collector and an electrolyte compartment configured to hold an electrolyte therein, wherein the battery is configured to receive a gas comprising oxygen on the positive current collector and to receive at least a portion of the zinc produced in the electrochemical cell, such that the zinc forms an anode of the battery. Advantageously, the electrochemical cell produces hydrogen. The battery can be used to store energy and used in a required application. The term “positive current collector” may be used interchangeably with “cathode plate”, “cathode pole” and “positive electrode”. The battery may be configured to receive zinc such that the zinc defines a plate, which forms the anode. However, in a preferred embodiment, the battery is preferably configured to receive a suspension or slurry comprising zinc particles. Accordingly, preferably the electrolyte compartment of the battery is configured to receive a suspension or slurry comprising zinc particles. Accordingly, the zinc may be viewed as a moving electrode. The battery may therefore be viewed as being a dynamic battery. Preferably, the apparatus comprises a zinc injector, configured to inject a suspension or slurry comprising zinc particles into the battery, and preferably into the electrolyte compartment of the battery. The apparatus may comprise a zinc store. Preferably, the zinc store is configured to store zinc, and more preferably a suspension or slurry comprising zinc particles. Preferably, the suspension or slurry comprises a basic aqueous solution. The zinc store may comprise an agitator configured to agitate a liquid in the zinc store. Accordingly, the agitator may be configured to mix the zinc particles in the suspension or slurry, i.e. the agitator may prevent the zinc particles from settling. The zinc injector may comprise a first zinc conduit extending between the zinc store and the battery, and being configured to transport a slurry or suspension comprising zinc particles from the zinc store to the battery. Preferably, the first zinc conduit extends between the zinc store and the electrolyte compartment of the battery, and is configured to transport a slurry or suspension comprising zinc particles from the zinc store to the electrolyte compartment of the battery. Alternatively, the zinc injector may comprise a zinc conduit which extends between the electrochemical cell and the battery and is configured to transport zinc from the electrochemical cell to the battery. The apparatus may comprise a pump configured to cause the slurry or suspension comprising zinc particles to flow from the zinc store, along the first zinc conduit and into the battery, preferably into the electrolyte compartment of the battery. Alternatively, the apparatus may comprise a pump configured to cause the slurry or suspension comprising zinc particles to flow from the electrochemical cell, along the first zinc conduit and into the battery, preferably into the electrolyte compartment of the battery. The pump may be a peristaltic pump and / or a slurry pump. The apparatus may comprise an electrolyte remover, configured to remove a solution from the electrolyte compartment. It may be understood that the solution may comprise zinc hydroxide and / or zincate. The apparatus may comprise a reservoir configured to store the solution comprising zinc hydroxide and / or zincate. The electrolyte remover may comprise a first hydroxide conduit extending between the electrolyte compartment of the battery and the reservoir, and being configured to transport a solution from the electrolyte compartment to the reservoir. Alternatively, the electrolyte remover may comprise a hydroxide conduit extending between the electrolyte compartment of the battery and the electrochemical cell, and being configured to transport a solution from the electrolyte compartment to the electrochemical cell. The apparatus may comprise a pump configured to cause a solution to flow from the electrolyte compartment, along the first hydroxide conduit and into the reservoir. Alternatively, the apparatus may comprise a pump configured to cause a solution to flow from the electrolyte compartment, along the hydroxide conduit and into the electrochemical cell. The pump may be the same pump as the pump described above. Alternatively, the apparatus may comprise a separate pump. The pump may be a peristaltic pump and / or a slurry pump. The apparatus may comprise a controller. Preferably, the controller and / or the pump(s) are configured to cause the slurry or suspension comprising zinc particles to flow from the zinc store, through the battery and into the reservoir. The controller and / or the pump(s) may be configured to cause the slurry or suspension comprising zinc particles to flow through the electrolyte compartment at a desired rate. The desired flow rate may be determined by a skilled person based on the size of the oxygen electrode surface area and / or based on a desired voltage and / or current output. It may be appreciated that unreacted Zn particles may remain suspended in the solution, and may thereby return back to electrolyte compartment in due course. Preferably the battery comprises a negative current collector, wherein the electrolyte compartment is disposed between the negative current collector and positive current collector. Preferably, the negative current collector is configured to carry a charge. Preferably, the negative current collector is electrically connected to the positive current collector to create an electrical circuit. It may be appreciated that the term “negative current collector” may be used interchangeably with “anode plate”, “anode pole” and “negative electrode”. Preferably, the positive current collector it porous. The positive current collector is preferably porous, and may be macro-porous or micro-porous. The positive current collector may comprise a carbon material or a metal. The metal is preferably chemically stable. For instance, the positive current collector may be or comprise a carbon felt, graphite, glassy carbon, carbon fibre, lead (Pb), tin (Sn), titanium (Ti), gold (Au), palladium (Pd), and / or iridium (Ir). Preferably, the negative current collector is porous. The negative current collector is preferably porous, and may be macro-porous or micro-porous. Advantageously, the porous structure helps to provide a high surface are for the zinc particles to be electrochemically converted. The negative current collector may comprise a carbon material or a metal. The metal is preferably chemically stable. For instance, the negative current collector may be or comprise a carbon felt, graphite, glassy carbon, carbon fibre, lead (Pb), tin (Sn), titanium (Ti), gold (Au), palladium (Pd), and / or iridium (Ir). The battery may comprise an undivided cell. Accordingly, in this embodiment, the battery may comprise an undivided electrolyte chamber, and it may be the undivided electrolyte chamber which is configured to receive the suspension or slurry comprising zinc particles. The battery may be configured such that at least a portion of the negative current collector contacts the solution comprising the suspension or slurry comprising zinc particles when it is disposed in the electrolyte chamber. In an alternative embodiment, the battery comprises a divided cell. Accordingly, the cell may comprise an electrolyte chamber and a separator disposed across the electrolyte chamber, thereby dividing the electrolyte chamber into a cathode portion and an anode portion. The separator may be disposed between the positive current collector and the negative current collector. The anode portion of the electrolyte chamber may be configured to receive the suspension or slurry comprising zinc particles. The cathode portion of the electrolyte chamber may be configured to receive a further electrolyte. The further electrolyte may be a basic aqueous solution. The basic aqueous solution may be as defined below. The separator preferably has a low ionic resistance and preferably has high electrical conductivity. The separator is preferably chemically resistant to corrosion and oxidation. The separator preferably has a high adsorption capacity of the electrolyte. The separator may be or comprise a hydroxide ion-conducting membrane. Suitable separators will be known to the skilled person. The separator may be or comprise polyethlyene (PE), polypropylene (PP), polyvinlylcohol (PVA), polyamide, polysufonium and / or polybenximidazole (PBI). The separator may be a laminated nonwoven separator. Preferably, the battery comprises an air distribution layer, wherein the air distribution layer is disposed between the positive current collector and the electrolyte compartment and the air distribution layer is configured to transport a gas to the electrolyte compartment. Preferably, the air distribution layer is disposed between the positive current collector and the separator. The air distribution layer may be understood to be porous, and preferably is nanoporous. The air distribution layer is preferably conductive. The air distribution layer may comprise a carbon material or a polymer, such as polytetrafluoroethylene (PTFE). Preferably, the battery comprises a semi-permeable membrane, wherein the positive current collector is disposed between the semi-permeable membrane and the electrolyte compartment. Preferably, the positive current collector is disposed between the semi-permeable membrane and the separator. Preferably, the positive current collector is disposed between the semi-permeable membrane and the air distribution layer. The semi-permeable membrane is preferably configured to transfer oxygen from air or an oxygen source to the positive current collector. Preferably, the semi- permeable membrane is non-porous. The semi-permeable membrane may be a gas permeable membrane. The semi-permeable membrane may comprise or consist of a polymer. The semi-permeable membrane may comprise or consist of silicone, polydimethylsiloxane (PDMS) and / or polysiloxane. Preferably, the apparatus comprises an oxygen injector, configured to inject oxygen into the battery. Preferably, the oxygen injector is configured to feed oxygen to the positive current collector. Preferably, the oxygen injector is configured to feed oxygen through the semi-permeable membrane to the positive current collector. The apparatus may comprise an oxygen store. Preferably, the apparatus comprises a first oxygen conduit which extends between the oxygen store and the battery, and is configured to transport a gas comprising oxygen from the oxygen store to the battery. Preferably, the first oxygen conduit extends between the oxygen store and the oxygen injector. Alternatively, the apparatus may comprise an oxygen conduit which extends between the electrochemical cell and the battery and is configured to transport a gas comprising oxygen from the electrochemical cell to the battery. It may be understood that the electrochemical cell is configured to conduct an electrochemical reaction to form zinc and hydrogen gas at the cathode and oxygen at the anode. The anode and cathode may each independently comprise a carbon based electrode or a metal based electrode. The or each carbon based electrode may comprise graphite. The 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 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 electrodes comprise graphite or steel. In an alternative preferred embodiment, the or each metal based electrode comprises zinc. Preferably, the cathode comprises a substantially non-porous material. Advantageously, when the cathode is non-porous the zinc would be electrodeposited on the surface of the structure and would not become trapped within pores thereof. The electrochemical cell may comprise an electrolyte chamber, wherein at least a portion of the electrolyte chamber is configured to receive the solution comprising zinc hydroxide and / or zincate. The electrochemical cell may be an undivided cell. Accordingly, in this embodiment, the electrochemical cell may comprise an undivided electrolyte chamber, and it may be the undivided electrolyte chamber which is configured to receive the solution comprising zinc hydroxide and / or zincate. The electrochemical cell may be configured such that at least a portion of the anode contacts the solution comprising the zinc hydroxide and / or zincate when it is disposed in the electrochemical cell. In an alternative embodiment, the electrochemical cell comprises a divided cell. Accordingly, the electrochemical cell may comprise a membrane disposed between the anode and the cathode dividing the cell into two portions. 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 could include a polymer anion exchange base membrane of a chloromethylated polysulfone, or a copolymer of chloromethylstyrene and divinylvenzene with polyethylene fabric. In this embodiment, the method may comprise disposing the solution comprising the comprising zinc hydroxide and / or zincate in a cathode portion of the cell, such that at least a portion of the cathode contacts the solution comprising the metal alloy. The method may also comprise disposing a further electrolyte in an anode portion of the cell, such that at least a portion of the anode contacts the further electrolyte. The further electrolyte preferably comprises an aqueous solution, and more preferably a basic aqueous solution. The basic aqueous solution may be as defined below. The apparatus may comprise a second hydroxide conduit extending between the reservoir and the electrochemical cell. The second hydroxide may extend between the reservoir and the electrolyte chamber or the cathode portion of the electrolyte chamber. The apparatus may comprise a pump configured to cause the solution comprising the zinc hydroxide and / or zincate to flow from the reservoir, along the second hydroxide conduit and into the electrochemical cell, preferably into the electrolyte chamber or the cathode portion of the electrolyte chamber. The pump may be the same pump as either or both of the pumps defined above. Alternatively, the apparatus may comprise a separate pump. The pump may be a peristaltic pump and / or a slurry pump. The apparatus may comprise a pH meter configured to monitor the pH of the solution comprising the zinc hydroxide and / or zincate. The pH meter may be disposed in the reservoir or the electrochemical cell. In embodiments where the electrochemical cell comprises a divided cell, the pH meter may be disposed in the reservoir or the cathode portion of the electrolyte chamber. Preferably, the pH meter is disposed in the reservoir. The apparatus may comprise a second water injector configured to feed water into the reservoir or the electrochemical cell. Preferably, the second water injector is configured to feed water into the reservoir. The apparatus may be configured to feed water into the reservoir or the electrochemical cell when the pH meter senses a pH which is above a predetermined maximum pH. The apparatus may comprise a zinc transporter configured to remove the zinc from the electrochemical cell. The zinc transporter may comprise a remover for removing the zinc from the cathode. The remover may comprise a blade configured to remove the zinc from the cathode. The blade may be configured to move across the cathode and thereby remove the zinc from a surface of the cathode. The apparatus may be configured to move the blade using a magnetic force or an electromotor. However, the inventors have found that simply pumping a solution in and out of the electrochemical cell can be sufficient to remove the zinc from the cathode. Accordingly, in some embodiment the apparatus may not need to comprise a blade. The remover may comprise a collection vessel configured to receive the zinc once it has been removed from the cathode and to remove it from the cell. In embodiments where the cell is a divided cell, the collection vessel may be disposed in the cathode portion of the cell. The collection vessel may comprise a first zinc valve configured to receive the zinc once it has been removed from the cathode and to remove it from the cell. The first zinc valve may be a rotary valve. The rotary valve may be motorised. The apparatus may comprise a second zinc conduit configured to transport zinc from the electrochemical cell to the zinc store. Preferably, the second zinc conduit extends between the first zinc valve and the zinc store. The apparatus may comprise a pump configured to cause a slurry or suspension comprising zinc to flow from the electrochemical cell, along the second zinc conduit and into the zinc store. The pump may be the same pump as any or all of the pumps defined above. Alternatively, the apparatus may comprise a separate pump to cause the slurry or suspension comprising zinc to flow from the electrochemical cell, along the second conduit and into the zinc store. The pump may be a peristaltic pump and / or a slurry pump. The apparatus may comprise a second oxygen conduit extending between the electrochemical cell and the oxygen store, and configured to transport oxygen from the electrochemical cell to the oxygen store. In some embodiments, the second oxygen conduit extends between the electrolyte chamber or the anode portion of the electrolyte chamber and the oxygen store. The apparatus may comprise a hydrogen store configured to store hydrogen produced in the electrochemical cell. The apparatus may comprise a first hydrogen conduit extending between the electrochemical cell and the hydrogen store, and configured to transport hydrogen from the electrochemical cell to the hydrogen store. In some embodiments, the first hydrogen conduit extends between the electrolyte chamber or the cathode portion of the electrolyte chamber and the hydrogen store. In a preferred embodiment, the apparatus further comprises: a thermochemical reactor, comprising: a reaction chamber configured to receive at least a portion of the zinc metal produced in the electrochemical cell; and configured to enable the zinc metal to contact water in the reaction chamber and thereby cause a thermochemical reaction to proceed and thereby produce zinc oxide or zinc hydroxide and a gas stream comprising hydrogen. In some embodiments, the thermochemical reactor is configured to cause the zinc metal to contact steam in the reaction chamber and thereby cause the thermochemical reaction to proceed. Accordingly, the thermochemical reactor may comprise a steam injector configured to feed steam into the reaction chamber and to cause the steam to contact zinc disposed in the reaction chamber. Preferably, the apparatus is configured to prevent the zinc, zinc hydroxide and / or zinc oxide from escaping from the thermochemical reactor while a thermochemical reaction is being conducted therein. Accordingly, the apparatus may comprise a container configured to hold the zinc, zinc hydroxide and / or zinc oxide therein and to be placed in the reaction chamber. The steam injector may be configured to feed steam directly into the container. The container may comprise a mesh configured to allow gases to flow out of the container while being further configured to prevent the zinc from being removed from the container. The mesh may comprise a pore size of 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 mesh may be sandwiched between two or more further meshes. The further meshes may comprise a pore size of 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 meshes ensure that the resultant mesh structure has enough strength to hold the weight of the zinc, zinc hydroxide and / or the zinc oxide. Alternatively, the thermochemical reactor may be configured to hold a basic aqueous solution and the zinc metal therein, such that the zinc metal contacts the basic aqueous solution and thereby causes the thermochemical reaction to proceed. Accordingly, the term “thermochemical reactor” may be used interchangeably with “hydrolyser”, “hydrolysis reactor” or “hydrothermal reactor”. The thermochemical reactor may comprise an agitator configured to agitate the zinc in the reaction chamber. In embodiments where the thermochemical reactor is configured to hold a basic aqueous solution, the agitator may be configured to agitate the basic aqueous solution. Accordingly, the thermochemical reactor may comprise a self-agitated thermochemical reactor. The self-agitated thermochemical reactor may be a spouted-bed reactor, a fluidized-bed reactor or a pneumatic conveying-bed reactor. In one embodiment, the thermochemical reactor is configured to hold the reaction chamber 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. In some embodiments, the thermochemical reactor is configured to hold the reaction chamber at a temperature of at least 400°C, at least 450°C, at least 500°C, at least 550°C, at least 600°C, at least 650°C, at least 700°C, at least 750°C, at least 800°C at least 850°C or at least 900°C. In an embodiment, the thermochemical reactor is configured to hold the reaction chamber at a temperature of less than 1,000°C, least than 950°C, less than 900°C, less than 800°C or less than 850°C. The thermochemical reactor may be configured to hold the reaction chamber at a temperature of less than 700°C, less than 650°C, less than 600°C or less than 550°C. In an embodiment, the thermochemical reactor is configured to hold the reaction chamber at a temperature of less than 500°C or less than 450°C. In some embodiments, the thermochemical reaction is conducted at a temperature of between 0 and 1,000°C, between 5 and 950°C, between 10 and 900°C, between 15 and 850°C, between 20 and 800 or between 25 and 750°C. In an embodiment, the thermochemical reactor is configured to hold the reaction chamber at a temperature of between 100°C and 700°C, more preferably at a temperature of 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 of between 300°C and 500°C or between 350°C and 450°C. In an alternative embodiment, the thermochemical reactor is configured to hold the reaction chamber at a temperature of at least 0°C, at least 5°C, at least 10°C, at least 15°C or at least 20°C. In some embodiments, the thermochemical reactor is configured to hold the reaction chamber at a temperature of at least 30°C, at least 40°C, at least 50°C or at least 60°C, more preferably at a temperature of at least 70°C, at least 80°C, at least 90°C or at least 100°C, and most preferably at a temperature of at least 110°C, at least 120°C, at least 130°C or at least 135°C. Preferably, the thermochemical reactor is configured to hold the reaction chamber 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, less than 450°C, less than 400°C, less than 300°C, less than 250°C, less than 200°C, less than 175°C, less than 160°C or less than 150°C. In some embodiments, the thermochemical reactor is configured to hold the reaction chamber at a temperature of less than 130°C, less than 100°C, less than 80°C, less than 60°C or less than 40°C. Preferably, the thermochemical reactor is configured to hold the reaction chamber at a temperature of between 30 and 600°C, between 40 and 500°C, between 60°C and 400°C, between 80 and 300°C or between 100 and 250°C, and most preferably at a temperature of between 110 and 200°C, between 120 and 175°C, between 130 and 160°C or between 135 and 150°C. In alternative embodiments, the thermochemical reactor is configured to hold the reaction chamber at a temperature of between 0 and 130°C, between 5 and 100°C, between 10 and 80°C, between 15 and 60°C or between 20 and 40°C. In some embodiments, the thermochemical reactor is configured to hold the reaction chamber at a temperature of between 350 and 1,000°C, between 400 and 950°C, between 500 and 900°C, between 600 and 850°C or between 700 and 800°C. Advantageously, increasing the temperature increases the rate of the reaction. Preferably, the apparatus comprises a temperature controller configured to control the temperature in the thermochemical reactor. The temperature controller may comprise a heater configured to heat the basic aqueous solution in the thermochemical reactor to an elevated temperature. Alternatively, or additionally, the temperature controller may comprise a heat exchanger, disposed adjacent to the thermochemical reactor, wherein the heat exchanger is configured to allow a first fluid to flow therethrough, such that heat may be exchanged between the first fluid and the thermochemical reactor. The heat exchanger may be a jacket disposed around the thermochemical reactor. Preferably, the heat exchanger is configured to maintain the thermochemical reactor at an elevated temperature. The elevated temperature may be as defined above. The apparatus may comprise a further heat exchanger configured to cool the first fluid. The further heat exchanger may be configured to transfer heat from the first fluid to a further fluid. The further fluid may be the basic aqueous solution or water. Accordingly, the further heat exchanger may be configured to pre-heat the basic aqueous solution or water prior to feeding it into the thermochemical reactor. It may be appreciated that the pressure that the thermochemical reactor is configured to hold the reaction chamber at may be selected depending upon the temperature which the thermochemical reactor is configured to hold the reaction chamber. The pressure may be selected to be high to ensure basic aqueous solution does not boil at the temperature at which the thermochemical reactor is configured to hold the reaction chamber. The thermochemical reactor may be configured to hold the reaction chamber at a pressure of at least 10 kPa or at least 20 kPa, more preferably at a pressure of at least 40 kPa, at least 60 kPa or at least 80 kPa, and most preferably at a pressure of at least 90 kPa, at least 95 kPa or at least 100 kPa. In an embodiment, the thermochemical reactor may be configured to hold the reaction chamber at a pressure of at least 200 kPa, at least 400 kPa, at least 600 kPa, at least 800 kPa or at least 1 MPa. In an embodiment, the thermochemical reactor may be configured to hold the reaction chamber at a pressure of at least 5 MPa, at least 10 MPa or at least 15 MPa. In an embodiment, the thermochemical reactor may be configured to hold the reaction chamber at a pressure of less than 5,000 kPa. In an embodiment, the thermochemical reactor may be configured to hold the reaction chamber at a pressure of less than 1,000 kPa, less than 500 kPa or less than 250 kPa, and most preferably at a pressure of less than 200 kPa, less than 150 kPa or less than 110 KPa. In an embodiment, the thermochemical reactor may be configured to hold the reaction chamber at a pressure of between 20 and 5,000 kPa, more preferably at a pressure of between 40 and 1,000 kPa, between 60 and 500 kPa or between 80 and 250 kPa, and most preferably at a pressure of between 90 and 200 kPa, between 95 and 150 kPa or between 100 and 110 kPa. In an alternative embodiment, the thermochemical reactor may be configured to hold the reaction chamber at a pressure of between 100 kPa and 75 MPa, between 200 kPa and 50 MPa, between 400 kPa and 40 MPa, between 600 kPa and 30 MPa, between 800 kPa and 25 MPa, between 1 and 20 MPa, between 5 and 17.5 MPa or between 7 MPa and 15 MPa. The apparatus may be configured to conduct the electrochemical reaction at the same or a different pressure to the thermochemical reaction. In some embodiments, the apparatus is configured to conduct the electrochemical reaction at the same or a different pressure to the thermochemical reaction. In this embodiment, the thermochemical reactor and the electrochemical cell may be configured to operate at the same pressure, which may be as defined above. Any conduits extending between the thermochemical reactor and the electrochemical cell may also be configured to operate at the same pressure. The steam injector is preferably configured to feed steam into the reaction chamber. Apparatuses capable of feeding steam into the reaction chamber will be well known to the skilled person. For instance, the steam injector may be configured to cause water disposed therein to evaporate, and thereby form steam. Accordingly, the steam injector may comprise a conduit, at least a portion of which is disposed in the thermochemical reactor. The conduit may comprise a coiled portion which is disposed in the thermochemical reactor. Advantageously, the heat from the reaction chamber may cause water disposed in the conduit to evaporate. Preferably, the steam injector comprises an outlet configured to inject the steam into the reaction chamber. Preferably, the outlet is disposed downstream of the conduit. The apparatus may comprise a pump configured to pump water into the conduit. The pump may comprise a syringe pump. The apparatus may comprise zinc feeder configured to feed the zinc into the reaction chamber. The zinc feeder may comprise a second zinc valve. The second zinc valve may be a rotary valve. The rotary valve may be a motorised rotary valve. The apparatus may comprise a third zinc conduit extending between the electrochemical cell and the reaction chamber. The third zinc conduit may extend between the first zinc valve and the second zinc valve. In embodiments where the electrochemical cell is a divided cell, the third zinc conduit may extend between the cathode portion of the electrochemical cell and the reaction chamber. The apparatus may comprise a pump configured to cause a slurry or suspension comprising zinc to flow from the electrochemical cell, along the third zinc conduit and into the reaction chamber. The pump may be the same pump as any or all of the pumps defined above. Alternatively, the apparatus may comprise a separate pump to cause the slurry or suspension comprising zinc to flow from the electrochemical cell, along the third zinc conduit and into the reaction chamber. The pump may be a peristaltic pump and / or a slurry pump. The second zinc conduit may extend between the electrochemical cell and the zinc store. Alternatively, the second zinc conduit may extend between the third zinc conduit and the zinc store. In embodiments where the thermochemical reactor is configured to cause the zinc metal to contact steam in the reaction chamber. In this embodiment, the zinc may react with the steam to produce zinc oxide and hydrogen. The apparatus may comprise a zinc oxide feeder configured to feed the zinc oxide out of the reaction chamber. The zinc oxide feeder may comprise a zinc oxide valve. The zinc oxide valve may be a rotary valve. The rotary valve may be a motorised rotary valve. The zinc oxide feeder may comprise a zinc oxide conduit extending between the reaction chamber and the reservoir, and is configured to transport zinc oxide from the reaction chamber to the reservoir. Preferably, the zinc oxide conduit extends between the zinc oxide valve and the reservoir, and is configured to transport zinc oxide from the zinc oxide valve to the reservoir. Alternatively, in embodiments where the thermochemical reactor is configured to hold a basic aqueous solution and the zinc metal therein, it may be appreciated that the zinc oxide as it is produced may react with the basic aqueous solution to produce zinc hydroxide and / or zincate. Alternatively, the method may directly produce zinc hydroxide. The zinc hydroxide may react with the basic aqueous solution to produce zincate. The apparatus may comprise a further conduit extending between the reaction chamber and the electrochemical cell. The further conduit may be configured to transport zinc oxide and / or the basic aqueous solution from the reaction chamber to the electrochemical cell. The basic aqueous solution may be understood to have the zinc hydroxide and / or zincate dissolved therein. In embodiments where the electrochemical cell is a divided cell, the further conduit may extend between the reaction chamber and the cathode portion of the electrochemical cell. The second hydroxide conduit may extend between the reservoir and the further conduit. The apparatus may comprise a pump configured to cause the basic aqueous solution to flow from the reaction chamber along the further conduit into the electrochemical cell. The pump may be the same pump as any or all of the pumps defined above. Alternatively, the apparatus may comprise a separate pump. The pump may be a peristaltic pump and / or a slurry pump. The apparatus may comprise a heat exchanger, and the third zinc conduit and further conduit may extend therethrough, wherein the heat exchanger is configured to transfer heat between the third zinc conduit and further conduit. The heat exchanger is preferably configured to transfer heat from the further conduit to the third zinc conduit. Advantageously, the heat exchanger is configured to decrease the temperature of the basic aqueous solution after it exits the thermochemical reactor and prior to it entering the electrochemical reactor. The heat exchanger is simultaneously configured to increase the temperature of the basic aqueous solution after it exits the electrochemical reactor and prior to it entering the thermochemical reactor. The apparatus may comprise a condenser configured to cool the gas stream produced in the thermochemical reactor, and thereby cause water in the gas stream to condense. Advantageously, this will allow concentrated hydrogen gas to be obtained. The apparatus may be configured to return the condensed water to the thermochemical reactor. The condenser may be configured to transfer heat from the gas stream to a cooling fluid. The cooling fluid may be the basic aqueous solution or water. Preferably, the condenser is preferably configured to pre-heat the basic aqueous solution and / or water prior to it being fed it into the thermochemical reactor. The apparatus may comprise a gas separator configured to separate hydrogen gas from other gases. The gas separator may be or comprise a pressure swing absorption unit or a cryogenic system. Accordingly, the gas separator may be configured to process the output gas or the dehydrated output gas to obtain a gas with a high concentration of hydrogen. The apparatus may comprise a hydrogen store configured to store hydrogen gas produced in the thermochemical reactor. The hydrogen store configured to store hydrogen gas produced in the thermochemical reactor may be the same as the hydrogen store configured to store hydrogen gas produced in the electrochemical cell. Alternatively, the apparatus may comprise a separate hydrogen store to store hydrogen gas produced in the thermochemical reactor. The apparatus may comprise a second hydrogen conduit extending between the reaction chamber, the condenser and / or the gas separator and the hydrogen store. In addition to the battery, the apparatus may comprise a further power supply configured to supply electrical power to the apparatus. Accordingly, the further power supply may be configured to apply a voltage across the anode and cathode. Alternatively, or additionally, the further power supply may be configured to supply power to the thermochemical reactor. The further power supply may comprise a battery, a generator, a renewable power source or it could comprise the national grid. The renewable power source may comprise a solar power generator, wind power generator or a hydropower generator. The power supply may be configured to supply a direct current to the anode and cathode. Additionally, the battery may also be configured to apply a voltage across the anode and cathode. Advantageously, the battery could be used to apply a voltage across the anode and cathode when the renewable power source is unable to apply a voltage across the anode and cathode. For instance, if the further power supply was a renewable power source the battery could be used to apply a voltage across the anode and cathode at times when the renewable power source was either not producing power or was not producing adequate power. The further power supply and / or the battery may be configured to apply a voltage of at least 1 V or at least 2 V across the anode and cathode, more preferably a voltage of at least 2.5 V, at least 3 V or at least 3.5 V across the anode and cathode, and most preferably a voltage of at least 4 V or at least 4.5 V across the anode and cathode. The further power supply and / or the battery may be configured to apply a voltage of less than 8 V or less than 7.5 V across the anode and cathode, more preferably a voltage of less than 7 V, less than 6.5 V or less than 6 V across the anode and cathode, and most preferably a voltage of less than 5.5 V or less than 5 V across the anode and cathode. The further power supply and / or the battery may be configured to apply a voltage of between 1 and 8 V or between 2 and 7.5 V across the anode and cathode, more preferably a voltage of 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 a voltage of between 4 and 5.5 V or between 4.5 and 5 V across the anode and cathode. The further power supply and / or the battery may be configured to cause a current of at least 0.5 A, at least 1 A or at least 1.5 A to flow through the anode, cathode and the solution comprising the metal ion, more preferably to cause a current of at least 2 A, at least 2.5 A or at least 3 A to flow through the anode, cathode and the solution comprising the metal ion and most preferably to cause a current of at least 3.5 A to flow through the anode, cathode and the solution comprising the metal ion. The further power supply and / or the battery may be configured to cause a current of less than 10 A, less than 8 A or less than 6 A to flow through the anode, cathode and the solution comprising the metal ion, more preferably to cause a current of less than 5.5 A, less than 5 A or less than 4.5 A to flow through the anode, cathode and the solution comprising the metal ion and most preferably to cause a current of less than 4 A to flow through the anode, cathode and the solution comprising the metal ion. The further power supply and / or the battery may be configured to cause a current of between 0.5 and 10 A, between 1 and 8 A or between 1.5 and 6 A to flow through the anode, cathode and the solution comprising the metal ion, more preferably to cause a current of between 2 and 5.5 A, between 2.5 and 5 A or between 3 and 4.5 A to flow through the anode, cathode and the solution comprising the metal ion and most preferably to cause a current of between 3.5 and 4 A to flow through the anode, cathode and the solution comprising the metal ion. The apparatus may comprise a flow meter configured to measure the flow of the basic aqueous solution. The apparatus may comprise a flow meter disposed in the thermochemical reactor, the electrolysis cell and / or in any of the conduits defined herein. The apparatus may be configured to continuously conduct the electrochemical reaction in the electrochemical cell. The apparatus may be configured to continuously conduct the thermochemical reaction in the thermochemical reactor. Accordingly, the apparatus may be configured to continuously feed zinc produced in the electrochemical cell to the thermochemical reactor. The apparatus may also be configured to continuously feed the basic aqueous solution comprising zincate and / or zinc hydroxide from the thermochemical reactor to the electrochemical cell. The apparatus may be configured to divert a portion of the zinc produced in the electrochemical cell from the electrochemical cell to the battery or zinc store for a discrete time period. The apparatus may be configured to simultaneously feed the rest of the zinc produced in the electrochemical cell to the thermochemical reactor. In particular, the apparatus may be configured to divert a portion of the zinc produced in the electrochemical cell from the electrochemical cell to the battery or zinc store when power output from the further power source increases above a predetermined first power output. Accordingly, when the further power supply is outputting power at an output which exceeds the predetermined first power output a store of zinc may be built up. The apparatus may be configured to transport the solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell for a discrete time period. In particular, the apparatus may be configured to transport the solution comprising zinc hydroxide and / or zincate from the reservoir along the second hydroxide conduit and to the electrochemical cell for a discrete time period. The apparatus may be configured to transport the solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell at the same time as diverting a portion of the zinc produced in the electrochemical cell from the electrochemical cell to the battery or zinc store. Accordingly, the apparatus may be configured to transport the solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell when power output from the further power source increases above a predetermined first power output. Accordingly, when the apparatus is diverting a portion of the zinc produced in the electrochemical cell from the electrochemical cell to the battery or zinc store the electrochemical cell may receive zinc hydroxide and / or zincate at a higher rate so it will produce a hydrogen gas and zinc at a higher rate compared to when the power output from the further power source is below the predetermined first power output. The apparatus may be configured to stop diverting a portion of the zinc produced in the electrochemical cell from the electrochemical cell to the battery or zinc store when a predetermined amount of zinc has been diverted to the battery or zinc store and / or when the further power supply is outputting power at an output which is less than a predetermined second power output. The predetermined second power output may be the same or different to the predetermined first power output. The apparatus may be configured to stop transporting the solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell at the same time as it stops diverting a portion of the zinc produced in the electrochemical cell from the electrochemical cell to the battery or zinc store. The apparatus may be configured to stop transporting the solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell when a predetermined amount of zinc has been diverted to the battery or zinc store and / or when the further power supply is outputting power at an output which is less than a predetermined second power output. The apparatus may be configured to run the battery, and thereby generate power therefrom, for a discrete time period. In particular, the apparatus may be configured to run the battery when power output from the further power source decreases below a predetermined third power output. Accordingly, when the further power supply is outputting power at an output which is below the predetermined third power output the battery will be generating power which can be used to power the apparatus. The predetermined first, second and third power outputs would vary depending upon a number of factors, including the further power source which is used and the average power output from that source. The predetermined first, second and third power outputs could be set by the skilled person. The predetermined third power output may be less that the predetermined first and second power outputs. In accordance with a second aspect, there is provided a method of producing hydrogen, the method comprising: disposing a basic aqueous solution comprising zinc hydroxide and / or zincate in an electrochemical cell comprising an anode and a cathode, such that at least a portion of the cathode contacts the basic aqueous solution; conducting an electrochemical reaction by applying a voltage across the anode and the cathode, to thereby produce hydrogen, oxygen and zinc; disposing at least a portion of the zinc produced in the electrochemical reaction in a battery, such that the zinc defines an anode; and contacting a positive current collector in the battery with a gas comprising oxygen to thereby cause a chemical reaction to occur to produce zinc oxide, zinc hydroxide and / or zincate and generate a current. The method of the second aspect may be conducted on the apparatus of the first aspect. The battery is preferably as defined in the first aspect. The method may comprise conducting the chemical reaction in the battery continuously or repeatedly. Preferably, the method comprises conducted the chemical reaction in the battery repeatedly. The method may comprise conducting the chemical reaction in the battery for a discrete time interval. The method preferably comprises disposing an electrolyte in an electrolyte compartment of the battery. Preferably, the electrolyte comprises a basic aqueous solution. The method may comprise transporting a portion of the zinc produced in the electrochemical reaction to the battery or a zinc store. The method may comprise transporting a portion of the zinc produced in the electrochemical reaction to the zinc store for a discrete time interval. The method may comprise transporting a portion of the zinc produced in the electrochemical reaction to the zinc store when power output from the further power source increases above a predetermined first power output. The method may comprise no longer transporting a portion of the zinc produced in the electrochemical cell from the electrochemical cell to the battery or zinc store when a predetermined amount of zinc has been diverted to the battery or zinc store and / or when the further power supply is outputting power at an output which is less than a predetermined second power output. While the chemical reaction in the battery is being conducted, the method may comprise transporting zinc from the zinc store and disposing it in the battery, such that the zinc defines an anode. Disposing at least a portion of the zinc produced in the electrochemical reaction in the battery may comprise disposing zinc in the form of a plate in the battery, such that the plate of zinc defines an anode. However, in a preferred embodiment, disposing at least a portion of the zinc produced in the electrochemical reaction in the battery comprises disposing a suspension or slurry comprising zinc particles in the battery. Preferably, the slurry or suspension is disposed in an electrolyte compartment of the battery. Preferably, the method comprises causing the suspension or slurry comprising zinc particles to flow through the battery and preferably to flow through the electrolyte compartment of the battery. The method may comprise causing the suspension or slurry comprising zinc particles to flow through the battery at a desired flow rate. The method may comprise causing the suspension or slurry comprising zinc particles to flow from the zinc store, through the battery and into the reservoir. The suspension or slurry may comprise at least 0.1 wt% or at least 0.5 wt% zinc, more preferably at least 1 wt%, at least 2 wt%, at least 3 wt%, at least 4 wt% or at least 5 wt%, and most preferably at least 10 wt%, at least 20 wt%, at least 30 wt% or at least 40 wt%. Preferably, the slurry or suspension comprises a basic aqueous solution. It may be appreciated that, disposing a suspension or slurry comprising zinc particles and a basic aqueous solution in the electrolyte compartment of the battery comprises both disposing at least a portion of the zinc produced in the electrochemical reaction in the battery and disposing an electrolyte in an electrolyte compartment of the battery. The basic aqueous solution may be understood to comprise a base. The base may be an organic 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. Accordingly, the base may comprise a hydroxide. The Arrhenius base may comprise an alkali metal hydroxide or alkaline earth metal hydroxide. The Arrhenius base may comprise potassium hydroxide, sodium hydroxide, barium hydroxide, caesium hydroxide, strontium hydroxide, calcium hydroxide, lithium hydroxide and / or rubidium hydroxide. Accordingly, the basic aqueous solution may be an aqueous alkaline solution. The Lewis base may comprise ammonia (NH3), butyllithium (n-BuLi), lithium diisopropylamide (LDA), lithium diethylamide (LDEA), sodium amide, sodium hydride (NaH) and / or lithium bis(trimethylsilyl)amide. The Bronsted-Lowry base may comprise ammonium hydroxide, an aliphatic amine, or an aromatic amine. The aliphatic amine may comprise methylamine, ethylamine or dimethylamine. The aromatic amine may comprise aniline, phenylenediamine or o- toludine. In a preferred embodiment, the basic aqueous solution comprises an Arrhenius base. The basic aqueous solution may comprise a concentration of at least 0.5 M, at least 1 M or at least 1.5 M of the base or the hydroxide, more preferably at least 2 M, at least 2.5 M or at least 3 M of the base or the hydroxide, and most preferably at least 3.5 M or at least 4 M of the base or the hydroxide. The basic aqueous solution may comprise a concentration of less than 8.5 M, less than 8 M or less than 7.5 M of the base or the hydroxide, more preferably less than 7 M, less than 6.5 M or less than 6 M of the base or the hydroxide, and most preferably less than 5.5 M or less than 5 M of the base or the hydroxide. The basic aqueous solution may comprise a concentration of between 0.5 and 8.5 M, between 1 and 8 M or between 1.5 and 7.5 M of the base or the hydroxide, more preferably between 2 and 7 M, between 2.5 and 6.5 M or between 3 and 6 M of the base or the hydroxide, and most preferably between 3.5 and 5.5 M or between 4 and 5 M of the base or the hydroxide. Alternatively, the basic aqueous solution may comprise a concentration of at least 0.5 M, at least 1 M or at least 2 M of the base or the hydroxide, more preferably at least 4 M, at least 6 M or at least 8 M of the base or the hydroxide, and most preferably at least 10 M, at least 12M, at least 14 M or at least 15 M of the base or the hydroxide. The basic aqueous solution may comprise a concentration of less than 8.5 M, less than 8 M or less than 7.5 M of the base or the hydroxide , more preferably less than 7 M, less than 40 M or less than 30 M of the base or the hydroxide, and most preferably less than 25 M or less than 20 M of the base or the hydroxide. In some embodiments, the basic aqueous solution may comprise a concentration of between 0.5 and 50 M, between 1 and 45 M or between 2 and 40 M of the base or the hydroxide, more preferably between 4 and 35 M, between 6 and 30 M or between 8 and 28 M of the base or the hydroxide, and most preferably between 10 and 26 M, between 12 and 24 M, between 14 and 22 M or between 15 and 20 M of the base or the hydroxide. In alternative embodiments, the basic aqueous solution may comprise a concentration of between 6 and 20 M, between 8 and 15 M or between 10 and 12 M base or the hydroxide. It may be appreciated that zinc oxide would be produced in the battery. However, if the zinc oxide is in contact with the basic aqueous solution it will react to produce a solution comprising zinc hydroxide. Furthermore, it may be appreciated that zincate and zinc hydroxide equilibrate in a basic aqueous solution. Accordingly, contacting the positive current collector in the battery with oxygen would produce a solution comprising zinc hydroxide and / or zincate. It may be appreciated that zincate has the formula Zn(OH)2-4. The zincate may be provided with a counterion, and have formula (Mn+)xZn(OH)4, where M is a counterion, n+ is the charge of the counterion and x is the number of counterions required to balance the charge of the zincate. For instance, if the basic aqueous solution comprises sodium hydroxide and / or potassium hydroxide, then the zinc oxide produced in the battery would react with the sodium hydroxide or potassium hydroxide to produce a solution comprising zinc hydroxide in equilibrium with sodium zincate or potassium zincate. The method may comprise transporting the solution comprising zinc hydroxide and / or zincate produced in the battery to a reservoir, and thereby storing the zinc hydroxide and / or zincate produced in the battery. The gas comprising oxygen may comprise at least 20 vol% oxygen, more preferably at least 40 vol% oxygen, at least 60 vol% oxygen or at least 80 vol% oxygen, and most preferably at least 90 vol%, at least 95 vol%, at least 99 vol% or at least 99.9 vol% oxygen. In a preferred embodiment, the gas comprising oxygen substantially consists of oxygen. The method may comprise feeding the gas comprising oxygen through an air distribution layer to the positive current collector. The method may comprise feeding the gas comprising oxygen through a semi-permeable membrane to the positive current collector. In a preferred embodiment, the method comprises feeding the gas comprising oxygen through a semi-permeable membrane and subsequently through an air distribution layer to the positive current collector. The gas comprising oxygen may be gas which has been produced in the electrochemical reaction. Accordingly, the method may comprise transporting oxygen produced in the electrochemical reaction to the positive current collector of the battery. Alternatively, the method comprises transporting oxygen produced in the electrochemical reaction to an oxygen store and transporting oxygen from the oxygen store to the positive current collector of the battery. The method may comprise operating the battery at a desired temperature range. The desired temperature range may be between -50 and 150°C, between -30 and 100°C, between -20 and 70°C, between 0 and 50°C or between 10 and 30°C. The method may comprise cooling the battery if it reaches a temperature above the desired temperature range. The electrochemical reaction may be conducted continuously or repeatedly. In a preferred embodiment, the electrochemical reaction is conducted continuously. The electrochemical cell may be as defined in relation to the first aspect. Providing a basic aqueous solution comprising zinc hydroxide and / or zincate may comprise transporting a basic aqueous solution comprising zinc hydroxide and / or zincate from the thermochemical reactor to the electrochemical cell. Preferably, the method comprises continuously transporting a basic aqueous solution comprising zinc hydroxide and / or zincate from the thermochemical reactor to the electrochemical cell. Alternatively, or additionally, providing a basic aqueous solution comprising zinc hydroxide and / or zincate may comprise transporting a basic aqueous solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell. Preferably, the method comprises transporting a basic aqueous solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell for a discrete time period. The method may comprise transporting a portion of the zinc produced in the electrochemical reaction to the zinc store for a discrete time interval. The method may comprise transporting a basic aqueous solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell at the same time as transporting a portion of the zinc produced in the electrochemical reaction to the zinc store. The method may comprise transporting a basic aqueous solution comprising zinc hydroxide and / or zincate from the reservoir to the electrochemical cell when power output from the further power source increases above a predetermined first power output. Preferably, the basic aqueous solution comprising zinc hydroxide and / or zincate comprises a zinc ion (Zn2+) 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 zinc ion is 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. In some embodiments, the zinc ion is present 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 zinc ion may be present at 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. In one embodiment, the zinc ion is present at 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. In an alternative embodiment, the zinc ion is present at 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. In embodiments where the electrochemical cell is an undivided cell, disposing the basic aqueous solution comprising zinc hydroxide and / or zincate in the electrochemical cell may cause at least a portion of the anode to contact the basic aqueous solution comprising zinc hydroxide and / or zincate. In embodiments where the electrochemical cell is a divided cell, the method may comprise disposing the basic aqueous solution comprising zinc hydroxide and / or zincate in a cathode portion of the cell, such that at least a portion of the cathode contacts the solution comprising the metal alloy. The method may also comprise disposing a further electrolyte in an anode portion of the cell, such that at least a portion of the anode contacts the further electrolyte. The further electrolyte preferably comprises an aqueous solution, and more preferably a basic aqueous solution. The basic aqueous solution may be understood to comprise a base, and preferably comprises a hydroxide. The base and / or the hydroxide and the concentration thereof may be as defined above. The method may comprise continuously feeding the basic aqueous solution comprising zinc hydroxide and / or zincate into the electrochemical cell while the electrochemical reaction is being conducted. The method may further comprise removing the solution from the cell as the electrochemical reaction is being conducted. Advantageously, this step continuously refreshes the solution. In embodiments where the cell is a divided cell, the method may comprise feeding the basic aqueous solution comprising zinc hydroxide and / or zincate into the cathode portion of the electrochemical cell while the electrochemical reaction is being conducted. The method may further comprise removing the solution from the cathode portion of the cell as the electrochemical reaction is being conducted. The method may comprise feeding the further electrolyte into the anode portion of the electrochemical cell while the electrochemical reaction is being conducted and / or removing the further electrolyte from the cathode portion of the cell as the electrochemical reaction is being conducted. The method may comprise applying a voltage of at least 1 V, at least 1.5 V, at least 1.75 V or at least 2 V across the anode and cathode, more preferably the method comprises applying a voltage of at least 2.5 V, at least 3 V or at least 3.5 V across the anode and cathode, and most preferably the method comprises applying a voltage of at least 4 V or at least 4.5 V across the anode and cathode. The method may comprise applying a voltage of less than 8 V or less than 7.5 V across the anode and cathode, more preferably the method comprises applying a voltage of less than 7 V, less than 6.5 V or less than 6 V across the anode and cathode, and most preferably the method comprises applying a voltage of less than 5.5 V or less than 5 V across the anode and cathode. In some embodiments, the method comprises applying a voltage of less than 4 V, less than 3 V or less than 2.5 V. The method may comprise applying a voltage of between 1 and 8 V or between 2 and 7.5 V across the anode and cathode. In some embodiments, the method comprises applying a voltage of 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 of between 4 and 5.5 V or between 4.5 and 5 V across the anode and cathode. In alternative embodiment, the method comprises applying a voltage of between 1 and 4 V, between 1.5 and 3 V or between 1.75 and 2.5 V across the anode and cathode. The method may comprise causing a current of at least 0.5 A, at least 1 A or at least 1.5 A to flow through the anode, cathode and the solution comprising the metal ion, more preferably causing a current of at least 2 A, at least 2.5 A or at least 3 A to flow through the anode, cathode and the solution comprising the metal ion and most preferably causing a current of at least 3.5 A to flow through the anode, cathode and the solution comprising the metal ion. The method may comprise causing a current of less than 10 A, less than 8 A or less than 6 A to flow through the anode, cathode and the solution comprising the metal ion, more preferably causing a current of less than 5.5 A, less than 5 A or less than 4.5 A to flow through the anode, cathode and the solution comprising the metal ion and most preferably causing a current of less than 4 A to flow through the anode, cathode and the solution comprising the metal ion. The method may comprise causing a current of between 0.5 and 10 A, between 1 and 8 A or between 1.5 and 6 A to flow through the anode, cathode and the solution comprising the metal ion, more preferably causing a current of between 2 and 5.5 A, between 2.5 and 5 A or between 3 and 4.5 A to flow through the anode, cathode and the solution comprising the metal ion and most preferably causing a current of between 3.5 and 4 A to flow through the anode, cathode and the solution comprising the metal ion. Applying the voltage across the anode and the cathode may comprise using power from a further power supply. The further power supply may be as defined above. In a preferred embodiment, applying the voltage across the anode and the cathode comprises using power from a further power supply. The method may comprise conducting the chemical reaction in the battery at discrete intervals. The chemical reaction in the battery may be conducted when there is a need for electrical power to drive the electrochemical reaction. Accordingly, the method may comprise conducting the chemical reaction in the battery when power output from the further power source decreases below a predetermined third power output. When the chemical reaction is being conducted in the battery, the method may comprise using power generated by the battery to apply the voltage across the anode and the cathode. The power generated by the battery may be used instead of or in addition to power from the further power supply. Advantageously, the battery can supply power at times when power from the further power supply may be unavailable or too low to provide the required power. Preferably, the electrochemical reaction is conducted 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 conducted 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 conducted 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 conducted at a temperature of less than 50°C, less than 40°C, less than 30°C or less than 25°C. Preferably, electrochemical reaction is conducted at a temperature of between 0°C and 95°C, more preferably at a temperature of between 10°C and 90°C. In some embodiments, the electrochemical reaction is conducted at a temperature between 20°C and 85°C or between 25°C and 80°C, and most preferably at a temperature of between 30°C and 70°C or between 55°C and 65°C. Advantageously, at higher temperatures, hydrogen is produced more quickly. In some embodiments, the electrochemical reaction is conducted 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. The electrochemical reaction may be conducted at the same or a different pressure to the thermochemical reaction. In some embodiments, the electrochemical reaction is conducted at the same pressure as the thermochemical reaction. In this embodiment the electrochemical cell and the thermochemical reactor may be maintained at the same pressure, which may be an elevated pressure. Any conduits extending between the electrochemical cell and the thermochemical reactor may also be maintained at the same pressure. The pressure may be as defined above. In some embodiments, the pressure may be between 100 kPa and 7 MPa, between 1 and 6 MPa, between 2 and 4 MPa or between 3 and 4 MPa. In alternative embodiments, the electrochemical reaction is conducted at a lower pressure than the thermochemical reaction. In this embodiment, the thermochemical reaction may be conducted at a first pressure (e.g. an elevated pressure) and the electrochemical reaction may be conducted at a second pressure (e.g. at or around atmospheric pressure). The electrochemical reaction may be conducted at a pressure of at least 10 kPa or at least 20 kPa, more preferably at a pressure of at least 40 kPa, at least 60 kPa or at least 80 kPa, and most preferably at a pressure of at least 90 kPa, at least 95 kPa or at least 100 kPa. In an embodiment, the electrochemical reaction is conducted at a pressure of at least 200 kPa, at least 400 kPa, at least 600 kPa, at least 800 kPa or at least 1 MPa. In an embodiment, electrochemical reaction is conducted at a pressure of at least 5 MPa, at least 10 MPa or at least 15 MPa. In an embodiment, the electrochemical reaction is conducted at a pressure of less than 5,000 kPa. In an embodiment, the electrochemical reaction is conducted at a pressure of less than 1,000 kPa, less than 500 kPa or less than 250 kPa, and most preferably at a pressure of less than 200 kPa, less than 150 kPa or less than 110 KPa. In an embodiment, the electrochemical reaction is conducted at a pressure of between 20 and 5,000 kPa, more preferably at a pressure of between 40 and 1,000 kPa, between 60 and 500 kPa or between 80 and 250 kPa, and most preferably at a pressure of between 90 and 200 kPa, between 95 and 150 kPa or between 100 and 110 kPa. In an alternative embodiment, the electrochemical reaction is conducted at a pressure of between 100 kPa and 75 MPa, between 200 kPa and 50 MPa, between 400 kPa and 40 MPa, between 600 kPa and 30 MPa, between 800 kPa and 25 MPa, between 1 and 20 MPa, between 5 and 17.5 MPa or between 7 MPa and 15 MPa. In a further alternative embodiment, the electrochemical reaction is conducted at a pressure of between 100 kPa and 7 MPa, between 1 and 6 MPa, between 2 and 4 MPa or between 3 and 4 MPa. Preferably, the method comprises recovering the zinc produced in the electrochemical reaction. Recovering the zinc produced in the electrochemical reaction may comprise removing the zinc produced in the electrochemical reaction from the cathode. The zinc may be removed after the electrochemical reaction has been completed. However, in a preferred embodiment, the electrochemical reaction is conducted continuously. Accordingly, the zinc may be removed continuously as the electrochemical reaction is conducted. The method may comprise causing the basic aqueous solution to flow through the electrochemical cell, and thereby removing zinc therefrom. Alternatively, or additionally, the electrochemical cell may comprise a blade configured to remove the zinc from the cathode. The blade may be configured to move across the cathode and thereby remove the zinc from a surface of the cathode. The blade may be moved using a magnetic force or an electromotor. The method may comprise transporting hydrogen produced in the electrochemical reaction to a hydrogen store. In a preferred embodiment, the method further comprises: conducting a thermochemical reaction by contacting at least a portion of the zinc produced in the electrochemical reaction with water to produce zinc oxide or zinc hydroxide and hydrogen. The thermochemical reaction may be conducted repeatedly or continuously, and is preferably conducted continuously. The method may comprise contacting the active reagent and the basic aqueous solution in the presence of a catalyst. The catalyst may be or comprise an iron-based catalyst, a nickel-based catalyst, a stannous-based catalyst and / or a copper-based catalyst. The catalyst may be a metal oxide or a metal hydroxide. Accordingly, the catalyst may comprise or be iron(III) oxide (Fe2O3), nickel hydroxide (Ni(OH)2), potassium stannate (K2SnO3), copper hydroxide (Cu(OH)2), or combinations thereof. In some embodiments, the catalyst is iron(III) oxide. The catalyst may be in the form of a powder. The molar ratio of active reagent to the catalyst may be between 1:0.001 and 1:1, between 1:0.005 and 1:0.75, between 1:0.01 and 1:0.5, between 1:0.02 and 1:0.3, between 1:0.04 and 1:0.2, between 1:0.06 and 1:0.15, between 1:0.08 and 1:0.12 or between 1:0.09 and 1:0.11. The concentration of the catalyst may be at least 0.01 mmol, at least 0.02 mmol, at least 0.04 mmol, at least 0.06 mmol, at least 0.08 mmol, at leas 0.1 mmol, at least 0.3 mmol or at least 0.4 mmol. The concentration of the catalyst may be between 0.01 and 50 mmol, between 0.02 and 10 mmol, between 0.04 and 5 mmol, between 0.06 and 2 mmol, between 0.08 and 1.5 mmol, between 0.1 and 1 mmol, between 0.3 and 0.8 mmol or between 0.4 and 0.6 mmol. If the catalyst is insoluble or substantially insoluble, the concentration may be understood to be calculated as the number of moles of catalyst present as a suspension in the solution. Accordingly, the concentration may be calculated using the standard formula: Concentration of catalyst = Number of moles of catalyst * 1000 volume of basic aqueous solution (ml) In some embodiments, the catalyst may be magnetic. The method may comprise separating the catalyst from the basic aqueous solution and the catalyst prior to feeding the basic aqueous solution to the electrochemical cell. The method may comprise holding the catalyst in the thermochemical reactor. The method may comprise using one or more magnets to separate the catalyst from the basic aqueous solution and / or hold the catalyst in the thermochemical reactor. Contacting at least a portion of the zinc produced in the electrochemical reaction with water may comprise contacting at least a portion of the zinc produced in the electrochemical reaction with steam. The portion of the zinc produced in the electrochemical reaction, may be contacted with steam, wherein the steam flows over the zinc at a rate of at least 0.01 standard cubic meters per hour, more preferably wherein the steam flows over the zinc 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 over the zinc at a rate of at least 0.3 or at least 0.31 standard cubic meters per hour. The zinc may be contacted with steam, wherein the steam flows over the zinc at a rate of less than 5 standard cubic meters per hour, more preferably wherein the steam flows over the zinc 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 over the zinc at a rate of less than 0.8 or less than 0.78 standard cubic meters per hour. The zinc may be contacted with steam, wherein the steam flows over the zinc at a rate of between 0.01 and 5 standard cubic meters per hour, more preferably wherein the steam flows over the zinc at a rate of between 0.05 and 2, between 0.1 and 1.75, between 0.15 and 1.5, between 0.2 and 1.25 or between 0.25 and 1 standard cubic meters per hour, and most preferably wherein the steam flows over the zinc at a rate of between 0.3 and 0.8 or between 0.31 and 0,78 standard cubic meters per hour. Preferably, the zinc is contacted with water (optionally 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. In some embodiments, the zinc is contacted with water (optionally steam) at a temperature of at least 400°C, at least 450°C, at least 500°C, at least 550°C, at least 600°C, at least 650°C, at least 700°C, at least 750°C, at least 800°C at least 850°C or at least 900°C. In an embodiment, the zinc is contacted with water (optionally steam) at a temperature of less than 1,000°C, least than 950°C, less than 900°C, less than 800°C or less than 850°C. Preferably, the zinc is contacted with water (optionally 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. In some embodiments, the thermochemical reaction is conducted at a temperature of between 0 and 1,000°C, between 5 and 950°C, between 10 and 900°C, between 15 and 850°C, between 20 and 800 or between 25 and 750°C. In some embodiments, the zinc is contacted with water (optionally steam) at a temperature of between 100°C and 700°C, more preferably at a temperature of 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 of between 300°C and 500°C or between 350°C and 450°C. Advantageously, at higher temperatures, hydrogen is produced more quickly. In some embodiments, the zinc is contacted with water (optionally steam) at a temperature of at least 0°C, at least 5°C, at least 10°C, at least 15°C or at least 20°C. In some embodiments, the zinc is contacted with water (optionally steam) at a temperature of at least 30°C, at least 40°C, at least 50°C or at least 60°C, more preferably at a temperature of at least 70°C, at least 80°C, at least 90°C or at least 100°C, and most preferably at a temperature of at least 110°C, at least 120°C, at least 130°C or at least 135°C. Preferably, the zinc is contacted with water (optionally steam) 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, less than 450°C, less than 400°C, less than 300°C, less than 250°C, less than 200°C, less than 175°C, less than 160°C or less than 150°C. In some embodiments, the zinc is contacted with water (optionally steam) at a temperature of less than 130°C, less than 100°C, less than 80°C, less than 60°C or less than 40°C. Preferably, the zinc is contacted with water (optionally steam) at a temperature of between 30 and 600°C, between 40 and 500°C, between 60°C and 400°C, between 80 and 300°C or between 100 and 250°C, and most preferably at a temperature of between 110 and 200°C, between 120 and 175°C, between 130 and 160°C or between 135 and 150°C. In alternative embodiments, the zinc is contacted with water (optionally steam) at a temperature of between 0 and 130°C, between 5 and 100°C, between 10 and 80°C, between 15 and 60°C or between 20 and 40°C. In some embodiments, the zinc is contacted with water (optionally steam) at a temperature of between 350 and 1,000°C, between 400 and 950°C, between 500 and 900°C, between 600 and 850°C or between 700 and 800°C. In an embodiment, the zinc is contacted with water (optionally 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. In an embodiment, the zinc is contacted with water (optionally steam) at a pressure of at least 10 kPa or at least 20 kPa, more preferably at a pressure of at least 40 kPa, at least 60 kPa or at least 80 kPa, and most preferably at a pressure of at least 90 kPa, at least 95 kPa or at least 100 kPa. In an embodiment, the zinc is contacted with water (optionally steam) at a pressure of at least 200 kPa, at least 400 kPa, at least 600 kPa, at least 800 kPa or at least 1 MPa. In an embodiment, the zinc is contacted with water (optionally steam) at a pressure of at least 5 Mpa, at least 10 Mpa or at least 15 Mpa. Preferably, the zinc is contacted with water (optionally 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. In an embodiment, the zinc is contacted with water (optionally steam) at a pressure of less than 5,000 kPa. In an embodiment, the zinc is contacted with water (optionally steam) at a pressure of less than 1,000 kPa, less than 500 kPa or less than 250 kPa, and most preferably at a pressure of less than 200 kPa, less than 150 kPa or less than 110 Kpa. Preferably, the zinc is contacted with water (optionally steam) at a pressure of between 10 and 500,000 kPa, more preferably at a pressure of between 50 and 300,000 kPa, between 75 and 200,000 kPa or between 100 and 100,000 kPa, and most preferably at a pressure of between 500 and 50,000 kPa, between 1,000 and 40,000 kPa or between 2,000 and 30,000 kPa. In an embodiment, the zinc is contacted with water (optionally steam) at a pressure of between 20 and 5,000 kPa, more preferably at a pressure of between 40 and 1,000 kPa, between 60 and 500 kPa or between 80 and 250 kPa, and most preferably at a pressure of between 90 and 200 kPa, between 95 and 150 kPa or between 100 and 110 kPa. In an embodiment, the zinc is contacted with water (optionally steam) at a pressure of between 100 kPa and 75 Mpa, between 200 kPa and 50 Mpa, between 400 kPa and 40 Mpa, between 600 kPa and 30 Mpa, between 800 kPa and 25 Mpa, between 1 and 20 Mpa, between 5 and 17.5 Mpa or between 7 Mpa and 15 Mpa. The zinc may comprise a powder, pellets or flakes. The method may comprise placing the zinc in a thermochemical reactor prior to contacting the zinc with the water. The method may comprise continuously feeding the zinc into the thermochemical reactor while the thermochemical reaction is being conducted. Methods of continuously feeding the zinc into the thermochemical reactor will be known to the skilled person. For instance, the thermochemical reactor may comprise a first rotary valve configured to feed the metal, or the alloy thereof, into the thermochemical reactor. The first rotary valve may be a motorised rotary valve. However, in a preferred embodiment, the method comprises contacting at least a portion of the zinc produced in the electrochemical reaction with a basic aqueous solution. The basic aqueous solution may be as defined above. The zinc may be suspended in the basic aqueous solution or form a slurry with the basic aqueous solution. Accordingly, the basic aqueous solution comprising the zinc as a suspension or a slurry may be fed straight from the electrochemical cell to the thermochemical reactor without the need for further processing. The basic aqueous solution may be as defined above. The amount of the zinc in the basic aqueous solution may be as defined above. The method may comprise continuously feeding the basic aqueous solution and the zinc into the thermochemical reactor. The thermochemical reaction may be conducted at a temperature of at least 0°C, at least 5°C, at least 10°C, at least 15°C or at least 20°C. In some embodiments, the thermochemical reaction may be conducted at a temperature of at least 30°C, at least 40°C, at least 50°C or at least 60°C, more preferably at a temperature of at least 70°C, at least 80°C, at least 90°C or at least 100°C, and most preferably at a temperature of at least 110°C, at least 120°C, at least 130°C or at least 135°C. Preferably, the thermochemical reaction is conducted 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, less than 450°C, less than 400°C, less than 300°C, less than 250°C, less than 200°C, less than 175°C, less than 160°C or less than 150°C. In some embodiments, the thermochemical reaction may be conducted at a temperature of less than 130°C, less than 100°C, less than 80°C, less than 60°C or less than 40°C. The thermochemical reaction is conducted at a temperature of between 0 and 1,000°C or between 5°C and 700°C. In some embodiment, the thermochemical reaction is conducted at a temperature of between 30 and 600°C, between 40 and 500°C, between 60°C and 400°C, between 80 and 300°C or between 100 and 250°C, and most preferably at a temperature of between 110 and 200°C, between 120 and 175°C, between 130 and 160°C or between 135 and 150°C. In alternative embodiments, the thermochemical reaction is conducted at a temperature of between 0 and 130°C, between 5 and 100°C, between 10 and 80°C, between 15 and 60°C or between 20 and 40°C. Advantageously, a catalyst enables the reaction to proceed at a lower temperature. The method may comprise conducting the thermochemical reaction In a thermochemical reactor. The method may comprise controlling the temperature in the thermochemical reactor. The method may comprise causing the temperature in the thermochemical reactor to be as defined above. Controlling the temperature in the thermochemical reactor may comprise causing a first fluid to flow through a heat exchanger disposed adjacent the thermochemical reactor such that heat may be transferred between the thermochemical reactor to the first fluid and thereby maintaining the temperature in the thermochemical reactor. The method may comprise transferring heat from the thermochemical reactor to the first fluid. The first fluid may be or comprise water. The first fluid may be a liquid when it is fed into the heat exchanger. Transferring heat to the first fluid from the thermochemical reactor may cause the first fluid to evaporate and form a gas (e.g. steam). The method may subsequently comprise recovering heat from the first fluid. Recovering heat from the fluid may cause the first fluid to condense. Recovering heat from the fluid may comprise transferring heat from the gas stream to a cooling fluid. The cooling fluid may be or comprise water. Advantageously, recovering heat from the first fluid may heat the cooling fluid. In embodiments where the cooling fluid is or comprises water, the water may subsequently be used in the thermochemical reaction. Accordingly, cooling the gas stream may preheat water which is used in the thermochemical reaction. It may be appreciated that the thermochemical reaction may conducted at a higher temperature than the electrochemical reaction. Accordingly, subsequent to conducting the thermochemical reaction and prior to conducting the electrochemical reaction, the method may comprise cooling the basic aqueous solution. Similarly, subsequent to conducting the electrochemical reaction and prior to conducting the thermochemical reaction, the method may comprise heating the basic aqueous solution. It may be appreciated that in a preferred embodiment, where both the thermochemical reaction and the electrochemical reaction are conducted continuously, the method may comprise continuously circulating the basic aqueous solution between the thermochemical reactor and the electrochemical cell. Accordingly, the method may comprise transferring heat from a portion of the basic aqueous solution at a location upstream of the electrochemical reactor and downstream of the thermochemical cell to a further portion of the basic aqueous solution at a location upstream of the thermochemical cell and downstream of the electrochemical reactor. Zinc produced in the electrochemical reaction may be continuously fed into the thermochemical reactor. During time intervals when a portion of the zinc produced in the electrochemical reaction is being fed to the zinc store or the battery, the remainder of the zinc produced in the electrochemical reaction may be being continuously fed into the thermochemical reactor. During time intervals when zinc produced in the electrochemical reaction is not being fed to the zinc store or the battery, all of the zinc produced in the electrochemical reaction may be being continuously fed into the thermochemical reactor. The zinc oxide or zinc hydroxide produced in the thermochemical reaction may be collected as the thermochemical reaction is being conducted. The method may comprise contacting the zinc oxide produced in the thermochemical reaction with a basic aqueous solution to produce the basic aqueous solution comprising zinc hydroxide and / or zincate. The method may comprise contacting the zinc oxide produced in the thermochemical reaction with a basic aqueous solution continuously or repeatedly. The method may comprise contacting the zinc oxide produced in the thermochemical reaction with a basic aqueous solution in the reservoir. Alternatively, the method may comprise contacting the zinc oxide produced in the thermochemical reaction with a basic aqueous solution to obtain the basic aqueous solution comprising zinc hydroxide and / or zincate and subsequently feeding the basic aqueous solution comprising zinc hydroxide and / or zincate into the reservoir. The method may comprise removing the zinc oxide or zinc hydroxide from a thermochemical reactor at the end of the thermochemical reaction. Alternatively, the method may comprise removing the zinc oxide or zinc hydroxide from a thermochemical reactor while the thermochemical reaction is being conducted. Methods of continuously removing the zinc oxide or zinc hydroxide will be known to the skilled person. For instance, the thermochemical reactor may comprise a second rotary valve configured to remove the zinc oxide therefrom. The second rotary valve may be a motorised rotary valve. Alternatively, in embodiments where the method comprises contacting at least a portion of the zinc produced in the electrochemical reaction with a basic aqueous solution, it may be appreciated that the zinc oxide may further react with the basic aqueous solution to form zincate and / or zinc hydroxide. The method may therefore comprise removing the basic aqueous solution comprising the zincate and / or zinc hydroxide from the thermochemical reactor. The method may comprise continuously moving the basic aqueous solution comprising the zincate and / or zinc hydroxide from the thermochemical reactor. The method may comprise continuously transporting the basic aqueous solution comprising the zincate and / or zinc hydroxide from the thermochemical reactor to the electrochemical cell. The method may comprise agitating the zinc while it is being contacted with the water. In embodiments where the method comprises feeding the basic aqueous solution into the thermochemical reactor, the method may comprise agitating the basic aqueous solution in the thermochemical reactor. It may be appreciated that hydrogen produced in the thermochemical reaction will be present in a gaseous mixture. The gaseous mixture may further comprise steam. Accordingly, the method may comprise condensing steam from a gaseous mixture obtained from the thermochemical reaction. Advantageously, if no carrier gas is used in the reaction, the condensation step will allow a user to obtain hydrogen gas. Accordingly, the thermochemical reaction may be conducted under reflux conditions. Condensing the steam may comprise transferring heat from the gaseous mixture to another fluid. The other fluid may be a liquid and is preferably water of the basic aqueous solution. The water or the basic aqueous solution may subsequently be fed into the thermochemical reactor. Advantageously, this enables the water or the basic aqueous solution to be pre-heated. In some embodiments, the steam which is used to contact the metal, or the alloy thereof, may be provided together with a carrier gas. The carrier gas may be an inert gas, such as nitrogen or argon. Accordingly, the gaseous mixture may further comprise the carrier gas. Accordingly, the method may comprise separating the hydrogen from a carrier gas. The method may comprise using a gas separator. The gas separator may be as defined in relation to the first aspect. The method may comprise transporting hydrogen produced in the thermochemical reaction to a hydrogen store. The hydrogen store may be the same or different to the hydrogen store where hydrogen produced in the electrochemical reaction is stored. It may be appreciated that as the electrochemical reaction proceeds the water will react to produce hydrogen and oxygen. Similarly, as the thermochemical reaction proceeds, water will react to produce hydrogen. Accordingly, the concentration of the base in the basic aqueous solution will increase. Similarly, in embodiments where the cell comprises a divided cell, the concentration of a base in the further electrolyte will also increase. Accordingly, the method may comprise contacting the basic aqueous solution with a sufficient quantity of water to cause the basic aqueous solution to have a desired concentration of the base. The method may comprise monitoring the pH of the basic aqueous solution, and contacting the solution with a sufficient quantity of water to cause the solution to have a desired concentration of the base and / or the hydroxide when the pH rises above a predetermined maximum. The method may comprise monitoring the pH in the thermochemical reactor, the electrochemical cell, the battery and / or any conduit defined above. The method may comprise injecting a quantity of water into the thermochemical reactor, the electrochemical cell, the battery and / or any conduit defined above to maintain the basic aqueous solution at a desired pH. In embodiments where the method comprises pre-heating water, the pre-heated water may be injected into the thermochemical reactor or a conduit upstream of the thermochemical reactor. In embodiments where the cell comprises a divided cell, the method may comprise contacting the further electrolyte with a sufficient quantity of water to cause the further electrolyte to have a desired concentration of a base and / or a hydroxide. The method may comprise monitoring the pH of the further electrolyte, and contacting the further electrolyte with a sufficient quantity of water to cause the further electrolyte to have a desired concentration of a base and / or a hydroxide when the pH rises above a predetermined maximum. The desired concentration of the base and / or the hydroxide may be as defined above. The predetermined maximum pH may correspond to a concentration of the base and / or the hydroxide as defined above. In some embodiments, the predetermined maximum pH may correspond to a concentration of the base and / or the hydroxide of at least 8.5 M, at least 8 M or at least 7.5 M of the base and / or the hydroxide, more preferably at least 7 M, at least 6.5 M or at least 6 M the base and / or the hydroxide, and most preferably at least 5.5 M or at least 5 M of the base and / or the hydroxide. All features described herein (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a schematic showing a hydrogen production cycle comprising a hydrolyser and an electrolyser; Figure 2 provides the reaction mechanisms for the chemical reactions which occur in the electrolyser of Figure 1; Figure 3 provides an energy storage system with an electrolyser – Zn / air battery couple; Figure 4 is a simple representation of Zn / air battery integration to the hydrogen production cycle of Figure 1; Figure 5 is a lab-scale hydrolysis reactor setup; Figure 6 (a) shows hydrogen generation from zinc powder hydrolysis in alkaline solution KOH (8M) at 130°C; and (b) shows the kinetics of zinc hydrolysis at 130°C; Figure 7 (a) shows hydrogen generation from zinc hydrolysis in alkaline solution where Fe2O3was present at a molar ratio of Fe2O3 / zinc from 0.06 to 0.5; and (b) shows the kinetics of zinc hydrolysis in the presence of Fe2O3, wherein the molar ratio of Fe2O3 / zinc was 0.1; Figure 8 (a) shows hydrogen generation with different Fe2O3loading; and (b) shows the kinetics of zinc hydrolysis with different Fe2O3loading; Figure 9(a) shows hydrogen generation at different temperatures; and (b) shows the kinetics of zinc hydrolysis at different temperatures; Figure 10 (a) shows hydrogen generation at different KOH concentrations; and (b) shows the kinetics of zinc hydrolysis at different KOH concentrations; and Figure 11 demonstrates the zinc conversion in the thermochemical reaction using (a) Gibbs minimization method, (b) conversion rates at various activation energy values based on experimental reaction rates where the reaction pressure is kept above the corresponding saturation temperature of water to prevent evaporation through passing the reactor cooling jacket and (c) effect of boosting the pressure at the reactor on conversion rate at E_a=35 kJ / mol. Example 1 – Integration of zinc-air battery into hydrogen production cycle WO 2020 / 016580 A2, the contents of which is incorporated herein by reference, describes a highly efficient and low-cost hybrid thermochemical cycle for hydrogen production, represented in Figure 1. In particular, zinc metal (Zn) is disposed in a thermal reactor or hydrolyser and contacted with water at an elevated temperature to produce zinc oxide (ZnO) and hydrogen gas (H2). The water may be in the form of steam, as taught by WO 2020 / 016580 A2. Alternatively, as discussed below, the zinc may be disposed of in a basic aqueous solution. When the zinc is contacted with steam, the zinc oxide which is produced is then added to a basic aqueous solution, e.g. sodium hydroxide (NaOH) solution, to provide zinc hydroxide (Zn(OH)2). Conversely, when the zinc is disposed of in a basic aqueous solution, the zinc oxide will react with the solution as it is produced. As shown in Figure 2, in a sodium hydroxide solution, zinc hydroxide will equilibrate with sodium zincate (Na2Zn(OH)4). The zinc hydroxide / sodium zincate solution may be disposed of in an electrolyser and electrolyse carried out. As shown in Figure 2, the electrolysis step of the cycle reduces zinc from the zincate produced in the thermal reactor and produces hydrogen concurrently as shown in Figure 2 [2]. The inventors’ continuous electrochemical cell experiments have shown that the pressure forces of a flowing solution can easily remove the zinc particles from the cathodic surface. The reaction which occurs in the thermal reactor or hydrolyser may be conducted at a higher temperature than the reaction which occurs in the electrolyser. Accordingly, a recuperator may be configured to transfer heat from the solution after it exits the thermal reactor or hydrolyser and prior to it entering the electrolyser and to simultaneously preheat the solution after it exits the electrolyser and prior to it entering the thermal reactor or hydrolyser. It was noted that the reaction mechanism of Zn reduction in the electrolyser works reversely like those of stagnant cell Zn-Air batteries. In particular, the reactions occurring in a Zn-air battery are mainly based on oxidation of Zn in an alkali media (KOH or NaOH) to generate voltage, as shown below. Anode: Zn + 4OH- ^ Zn(OH)2-4+ 2e- Zn(OH)2-4⇌ ZnO + H2O +2OH- Cathode: O2+ 4e- + 2H2O ^ 4OH- Overall reaction: Zn + ½O2^ ZnO Accordingly, as shown in Figure 3, a zinc-air battery could be coupled with an electrolyser. In particular, the zinc produced in the electrolyser could be used to provide power in a zinc-air battery. Additionally, oxygen in the electrolyser could also be used in the battery. This has the advantage that damage in oxygen electrode due to CO2presence in air is prevented. Alternatively, the Zn-air battery can be integrated with the complete system of Figure 1, as shown in Figure 4. It will be noted that when Zn produced in the electrolyser is stored for later use in the battery, some part of the hydrogen to be generated in the thermal reactor is sacrificed for the sake of energy storage. As shown in Figure 4, power from the battery can be used to power the electrolyser when there is no external source of energy. This potentially increase the capacity of the cycle especially particularly if it is power by intermittent renewable energy sources, such as wind and solar energy. Meanwhile, it is noted that Zn-air batteries can be classified into two different forms, stagnant and dynamic. Stagnant cell batteries can either be provided in a primary (non-rechargeable) or secondary (rechargeable) cell configuration. In theory Zn-air batteries have a standard cell potential of 1.65 V. However, their practical working voltages are below 1.2 V. In secondary cell configurations recharging requires over 2 V to revert the reactions, meaning that their cyclic efficiency is around 60%. Furthermore, rechargeable batteries show the disadvantage of dendrite formation [3]. Mechanically rechargeable Zn-air batteries are also an option where the spent Zn and electrolyte are removed from a stagnant cell and replaced by the new electrode and electrolyte. A flow cell Zn-air battery is a dynamic battery where the Zn electrode is stagnant in the cell in metallic form while an electrolyte flows between two electrodes and removes oxidised Zn from the cell. This concept is more advantageous than stagnant cell operations to prevent disadvantages due to dendrite formation, hydrogen evolution reaction, passivation layer occurrence and low cyclic efficiency [5-7]. It is also possible to directly feed the battery with Zn in alkali media in slurry form to continuously produce power (moving electrode). In the present system, Zn in KOH media can be stored in a tank and used in the battery when needed, while reduced Zn may be stored in another tank to be used in the electrolyser. The Zn-air battery shown in Figure 3 comprises an electrolyte chamber configured to house an electrolyte. The electrolyte will comprise an alkaline solution (e.g. NaOH or KOH) with particles of zinc suspended therein. The zinc particles in the solution will define the anode and a negative current collector is provided adjacent to the electrolyte chamber. The battery further comprises a positive current collector, which is porous such that oxygen may pass therethrough, and may be made from a carbon based material. Adjacent the positive current collector is a semi-permeable membrane, such that the positive current collector is disposed between the semi-permeable membrane and the air distribution layer. The semi-permeable membrane is configured to feed oxygen to the positive current collector. Between the positive current collector and the electrolyte chamber is an air distribution layer configured to distribute oxygen which has passed through the positive current collector to the electrolyte, where it will react with water as discussed above. The air distribution layer comprises a porous conductive material. In the embodiment shown in Figure 3, the electrolyte chamber is divided by a separator disposed between the air distribution layer and the negative current collector. During operation, an electrical connection will be in place between the negative current collector and the positive current collector, and the anode and cathode reactions described above will drive a current therethrough. Example 2 – Size of a 1 kWh battery system Based on a 95% efficient battery, for a 1 kWh system, 1.05 kWh worth of Zn is required. Zn energy density is 1.37 kWh / kg. So for a 1 kWh system the amount of Zn required is 1.05 / 1.37=0.76 kg. The energy efficiency of the electrolysis step can be calculated like so: Energy Efficiency = Amount Zn * Zn energy density + Amount H2* H2energy density Energy Consumption When the electrolyser produces 0.76 kg zinc, it also produces 0.024 kg hydrogen and H2energy density is 39.4 kWh / kg. The energy efficiency of the electrolysis step has been determined as being 89.6%. Rearranging the equation provided above, it is possible to calculate the energy consumption required to produce 0.76 kg zinc , and this will be 2.22 kWh. The electrical efficiency and hydrogen efficiency of the cyclic process for the battery and electrochemical cell may be calculated like so: Electrical efficiency = (0.76 kg Zinc * 1.37 kWh / kg*0.95) / 2.22 kWh = 44.9% Hydrogen efficiency = (0.024 kg H2* 39.4 kWh / kg) / 2.22 kWh = 42.6% The total efficiency is 86.6%. Size of the battery is 1.97 kg and 0.68 litre based on 1470 Wh / liter and 385 Wh / kg energy densities. Table 1, below, summarizes some key values at higher capacity of the battery system. Table 1: Summary of some key figures for Zn-air batteries with different powers Battery Needed Electrolyser Produced Battery Battery Power Zn (kg) Energy hydrogen size in size in (kWh) (kWh) (kg) mass volume (kg) (litre) 1 0.76 2.22 0.024 2.6 0.68 10 7.68 22.1 0.24 25.6 6.75 50 38.4 111.1 1.17 128 33.8 200 153.7 444.6 4.69 512 135.1 1000 768.3 2223 23.5 2564 675.7 50000 38417 111146 1175 128205 33784 Example 3 – 1 kg / h H2production system efficiency and size For an electrolyser producing 1 kg of hydrogen per hour, the energy consumption can be calculated as explained above and is 94.6 kWh per hour. For every kilogram of hydrogen produced 32.7 kg Zn is also produced. Therefore, the energy content of Zn produced in an hour is 44.8 kWh based on 1.37 kWh / kg energy content. Stored energy with Zn is used in the battery cell with a high discharge efficiency of 95%. Overall cyclic efficiency of the system is 85.1%. Size of the system is based on the practical mass and volumetric energy density. Mass of the battery system to store 44.8 kWh of Zn energy corresponds to 83.8 kg and 30 litres. Example 4 – Size comparison with Li-ion and Pb-acid batteries Li-ion and Pb-acid batteries are two common battery types used in short- and long- term electrical energy storage. Li-ion battery mass and volumetric energy density are 250 Wh / kg and 650 Wh / l, respectively. Pb-acid battery mass and volumetric density are 40 Wh / kg and 90 Wh / l, respectively. Table 2, below, summarises size comparisons at different rated battery power. Table 2: Size comparison for Zn-air, Li-ion and Pb-acid batteries with different powers Rated Zn-air Li-Ion Pb-Acid Power Mass Volume Mass Volume Mass Volume (kWh) (kg) (l) (kg) (l) (kg) (l) 1 2.56 0.68 4 1.54 25 11.1 10 25.6 6.75 40 15.4 250 110.1 100 256 67.5 400 154 2500 1111 1000 2560 675 4000 1540 25000 11111 It is noted that Zn-air batteries have a significantly lower mass and volume than Li-ion or Pb-acid batteries with the same power. Example 5 – A 25 MW wind-based hydrogen and energy storage plant For a wind farm that provides 25 MWe power for the system shown in Figure 1 with 5 m / s average wind speed at a capacity of 50%, at high wind speed times (average 7 m / s), 46 MWe extra electricity can be produced and at low speed (average 4 m / s) 12 MWe extra electricity will be required for power management. Storing the surplus energy produced at high wind speed times in Zn-air battery would produce 30 tons of Zn, with a capacity of 4.2 m3. This battery can provide 11.8 Mwe, which can be used when the wind speeds are low. Using this system, the capacity of the capacity of the plant can be increased from 50% to 95%. Cost of battery system (100 $ / kWh [8]) in this case is 11 million USD and adds 0.07 $ / kg H2to CapEx. This is calculated as ratio of increase in CapEx (in USD) to total hydrogen produced through operational life (in kg). At 50% capacity (wind driven with no storage) H2cost from 25 MWe hydrogen plant is 2.58 $ / kg, while with increased capacity cost is 2.32 $ / kg + 0.07 $ / kg, where 2.32 $ / kg is the decrease in cyclic hydrogen production cost with increased daily capacity of wind energy with battery storage. This shows that a 7% cost saving is possible in a system which uses a Zn-air battery to store power. Example 6 – Conducting the Thermochemical Reaction Using Liquid Water The inventors set up the lab-scale hydrolysis reactor shown in Figure 5. In brief, a round bottom flask 2 was disposed on a hot plate 1. A thermocouple 3 was provided and configured to measure the temperature in the flask 2. The apparatus further comprised a condenser 4 disposed on top of the round bottom flask and configured to cool any gas produced in the round bottom flask 2. A chiller 5 was provided to ensure a constant stream of chilled fluid would flow through the condenser 4. A rotameter 6 was provided downstream of the condenser to measure the flow of the gas which was produced in the reaction, and downstream of the rotameter a 1 Litre capacity syringe 7 was provided to capture the evolved gas. The round bottom flask was fitted with a nitrogen line (a stainless steel tube connected to the side of the round bottom flask), configured to allow nitrogen to be fed into the round bottom flask. The round bottom flask was also fitted with an input tube and an output tube configured to feed liquids into and remove liquids from the round bottom flask 2. A carbonate-free, clear solution of 180 g of NaOH in 250 ml of H2O was prepared and added to the round-bottom flask. Pure nitrogen gas was supplied (at the rate of 100 ml / min for 30 minutes) to purge the reactor before starting the reaction. 1.37 g of Zn was separately suspended in 50 ml of water and added to the reactor through the input tube. Inlet valves were then closed, and the hot plate heated the mixture while it was vigorously stirred using a magnetic stirrer. All the hydrogen gas product was collected in the syringe. The reaction system was refluxed for 4 hours at 135°C and atmospheric pressure to complete the reaction, producing 504 ml of hydrogen, equivalent to 96.8 % hydrolysis conversion percentage for the zinc powder initially added to the apparatus. Stoichiometric calculations show that the reaction yielded 3.68 g of Na2Zn(OH)4. Table 1: Quantity of reactants provided and products obtained Reaction systemP, atm T, °C Na2Zn(OH)4, Zn Conv. Zn, g H2O, g NaOH, g H2 (ml) g % 1 135 1.37 300 180 3.68 504 96.8 Example 7 – Conducting the Thermochemical Reaction Using Liquid Water The hydrolysis reactor described above in example 6 and shown in Fig 5 was also used for the present example. A carbonate-free, clear solution of 337 g of KOH in 350 ml of H2O was prepared and added to the hydrolysis reactor. Pure nitrogen gas was supplied (at the rate of 100 ml / min for 30 minutes) to purge the reactor before starting the reaction. 1.93 g of Zn was separately suspended in 50 ml of water and added to the reactor. The reactor mixture was refluxed for 4 hours (at 150°C and atmospheric pressure) while stirring to complete the reaction.715 ml of hydrogen was collected by the end of the reaction, equivalent to 97.5 % hydrolysis conversion percentage for the zinc powder initially loaded to the reactor. Stoichiometric calculations showed the reaction yielded 6.08g of K2Zn(OH)4. Table 2: Quantity of reactants provided and products obtained Reaction system P, atm T, °C Zn Conv. Zn, g H2O, g KOH, g K2Zn(OH)4, g H2(ml) % 1 150 1.93 400 337 6.08 715 97.5 The reaction was repeated at 130°C for 30 minutes using an 8M concentration of KOH, and the results are shown in Figure 6. In Figure 6b the results were fitted to the Avrami-Eroveef model was applied to fit the data: α(t) = 1 – exp(k.t-m) where α=is the fraction of reacted particles, t is the time for fraction of reacted particles, k is a specific rate constant and m is a parameter which depends on geometry. Example 8 – Improving Hydrolysis Reaction Efficiency The inventors wished to increase the rate of the hydrolysis reaction at lower temperatures. Accordingly, they looked into the use of a catalyst, hematite (Fe2O3). Without wishing to be bound by theory, the inventors believe that Fe2O3can catalyse the reaction as discussed below. Firstly, the inventors note that Fe2O3can form iron(III) oxide-hydroxide or ferric oxyhydroxide followed by iron(III) hydroxide in the presence of water and KOH solution, as follows: Fe2O3+ 3H2O + KOH ⇌ 2FeO.OH +2H2O + KOH ⇌ 2Fe(OH)3+ KOH There is then reduction of the iron(III) oxide, as follows: 3Zn + 2Fe(OH)3+KOH.xH2O ^ 3Zn(OH)2+ 2Fe + KOH.xH2O Finally, there is oxidation of the iron and production of hydrogen: 2Fe + 6H2O + KOH.xH2O ^ 2Fe(OH)3+ 3H2+ KOH.xH2O The inventors investigated how various factors effected the catalysed reaction, as discussed below. Effect of molar ratio of Fe2O3 / Zinc A series of tests were carried out with a constant amount of Fe2O3(0.0005 mole) and different amount of zinc from 0.001 to 0.0125 mole. Accordingly, the molar ratio of zinc to Fe2O3varied from 1:0.5 to 1:0.06. In these experiments, the concentration of potassium hydroxide was 8M. The volume of the solution was 15 ml. The results are provided in Figure 7 and show two moles of zinc can generate one mole hydrogen when the mole ratio of Fe2O3 / Zn decreased from 0.5 to 0.1. Further decreasing the ratio to 0.06 decreased the hydrogen which was generated. Accordingly, the optimum molar ratio of F2O3 / zinc appears to be 0.5. Effect of concentration of Fe2O3The inventors then conducted a series of tests where the Fe2O3dosage varied from 0.0625 mmol to 0.5 mmol. It will be appreciated that Fe2O3is relatively insoluble in aqueous solutions. Accordingly, the Fe2O3was provided as a powder suspended in the KOH solution. The “concentrations” given may be understood to confirm the amount of the Fe2O3in the solution, as opposed to a true concentration. In these experiments, the amount of zinc present was 0.1 mole and the concentration of potassium hydroxide was 8M. The volume of the solution was 15 ml. As shown in Figure 8, an increase in Fe2O3dosage from 0.0625 mmol to 0.5 mmol cause the volume of hydrogen produced in 30 min to increase. This indicates an increase in the catalyst amount results in much chance for the reactant to contact the catalst. However, the hydrogen production yield decreased from 0.985 to 0.529 when the concentration of Fe2O3increased from 0.5 mmol to 1.25 mmol. This is likely due to the increased concentration causing an observed increase in pH in the solution. The increase in pH may be due to converting Fe ions into Fe(OH)3. Effect of temperature The inventors then investigated how temperature affected the rate of the reaction. The inventors conducted a series of tests where the temperature varied from 4 to 36°C. In these experiments, the amount of zinc present was 0.1 mole, the concentration of Fe2O3was 0.5 mmol and the concentration of potassium hydroxide was 8M. The volume of the solution was 15 ml. As shown in Figure 9, an increase in temperature has a significant effect in zinc hydrolysis because of the increase in the speed of molecular movement. Accordingly, molecular collisions appear to be the most important factor in increasing the hydrogen generation rate. However, it should be noted that even at 4°C, a significant amount of hydrogen was produced. Effect of concentration of KOH The inventors then investigated how the concentration of KOH affected the rate of the reaction. The inventors conducted a series of tests where the concentration of KOH varied from 4 to 12 M. In these experiments, the amount of zinc present was 0.1 mole, the concentration of Fe2O3was 0.5 mmol and the volume of the solution was 15 ml. As shown in Figure 10, the generated hydrogen increased with increasing the KOH concentration from 4 to 12 M. However, only a slight enhancement was observed for the 12M solution compared to the 10M solution. It is thought that this is due to increasing viscosity of the solution. Analysis of experimental design using a general full factorial (Minitab) The study of the effect of individual factors and the influence of possible interactions between three factors in the experiments were conducted in the Minitab® software. A full factorial experimental design (DoE) in three levels was carried out to determine the relative contribution of three factors KOH concentration (8, 10 and 12 M), catalyst dosage (0.06, 0.08 and 0.12 g) and temperature (4, 21 and 36 °C) to find the most significant parameters that influence hydrogen production. The statistical significance of each factor was evaluated using P-values at a 95% confidence interval. The results are provided in table 3. Table 3: Results of analysis of experimental design L1 L2 L3 P-value KOH (M) 8 10 12 0.005 Catalyst (mmol) 0.37 0.5 0.75 0.004 Temo (°C) 4 21 36 0.000 The temperature had the lowest P-value (0.000) indicating the most influential parameter on hydrogen production. Besides, the low p-value of 0.000 indicates the high significance of the regression model. The KOH concentration had the highest P- value of (0.005) providing the least influential factor on the hydrogen production. In conclusion, the addition of a catalyst is highly advantageous as it allows the hydrolysis reaction to proceed at low temperatures. The catalyst can also easily be separated from the electrolyte. In particular, both iron and its oxides, including hematite (Fe2O3), have very good magnetic properties. The inventors noted that a magnet could easily separate all the catalyst particles very effectively. In the above described experiments, the inventors used a magnetic stirrer, and the catalyst only dispersed when a rigorous spinning rate above 150 rpm was used. At lower speeds, the iron catalyst particles were attached to the magnet. Example 9 – Effect of temperature on the thermochemical reaction The inventors calculated the conversion rate of zinc to zinc oxide at various temperatures and pressures, and the results are shown in Figure 11. As shown in Figure 11a, low temperature is desired for good conversion. However, as shown in Figure 11b, at low temperatures the rate of reaction is low, resulting in a low yield. However, as shown in Figure 11c, if higher temperature are used along with higher pressures, thereby keeping the media in liquid form then a high conversion may be achieved. It is noted that the conversion rate was calculated on the basis that the catalyst was not present. It may be appreciated that lower temperatures and / or pressures could be used if the catalyst was present. Conclusion There are a significant number of advantages associated with zinc-air batteries. In particular: ^ They have high energy density, which means they can store a lot of energy in a small space. This makes them a great option for applications where size and weight are important, such as in hearing aids and electric vehicles; ^ Zinc is an abundant and low-cost material, which makes zinc-air batteries a cost-effective option for energy storage; ^ Zinc-air batteries are non-toxic and non-flammable, making them a safer alternative to traditional lithium-ion batteries; ^ They have a long shelf life and can be stored for several years without losing their charge. This makes them a great option for emergency backup power; ^ They can be recharged by replacing the zinc electrode (mechanical charging), which makes them a more sustainable option compared to disposable batteries, in different configurations; and ^ Zinc is a naturally occurring material, and is 3rd most abundant non-ferrous metal on earth, which means that a Zn-air battery is cost effective compared to its alternatives (around 100 $ / kWh). At higher storage times above 8 hours, cost decreases further; ^ Zn-air batteries are half the cost of Li-ion batteries and four times cheaper than Pb-acid batteries, which is the most common battery used in renewable energy storage [8]; and ^ Zinc-air batteries can be recycled, making them a more environmentally friendly option compared to other battery chemistries. In addition to the advantages associated with the use of zinc-air batteries per se, there are also some specific advantages associated with the incorporation of a zinc-air battery into the hydrogen production cycle, as described above. In particular: ^ Zinc-air batteries are a perfect match with the thermal reactor / electrolyser for energy storage that allows recovery of chemicals used in the process while producing power; ^ The battery may be electrically recharged outside the battery cell while hydrogen is produced in the electrolyser. Total efficiency of the electrolysis for Zn(OH)4reduction is 89%. Overall cyclic efficiency is above 85% which is higher than stagnant rechargeable Zn-air batteries; ^ The system can use a dynamic battery where the flow carries both the electrolyte and Zn particles in slurry form (moving electrode), unlike present Zn-air flow batteries that are in hybrid form which are not decoupled from the battery size; ^ The system prevents low cyclic efficiency, dendrite formation and passivation issues as in stagnant rechargeable Zn-air batteries; and ^ The system allows the use of pure oxygen from the electrolyser in the oxygen electrode. This means that air does not need to be used, which might otherwise clog the porous electrode and poison the electrolyte and decrease the battery life due to the presence of carbon dioxide. References [1] Horri, Bahman Amini, and Sai Gu. "A continuous process for sustainable production of hydrogen." U.S. Patent Application No.17 / 260,991. [2] HORRI, Bahman, and G. U. Sai. "Hydrogen generator." [3] Li, Yanguang, and Hongjie Dai. "Recent advances in zinc–air batteries." Chemical Society Reviews 43.15 (2014): 5257-5275. [4] Leong, Kee Wah, et al. "Rechargeable Zn-air batteries: Recent trends and future perspectives." Renewable and Sustainable Energy Reviews 154 (2022): 111771. [5] Gilligan, G. E., and D. Qu. "Zinc-air and other types of metal-air batteries." Advances in Batteries for Medium and Large-Scale Energy Storage. Woodhead Publishing, 2015.441-461. [6] Pei, Pucheng, Keliang Wang, and Ze Ma. "Technologies for extending zinc–air battery’s cyclelife: A review." Applied Energy 128 (2014): 315-324. [7] Lao-Atiman, Woranunt, et al. "Model-based analysis of an integrated zinc-air flow battery / zinc electrolyzer system." Frontiers in Energy Research 7 (2019): 15. [8] Service, Robert F. "Zinc aims to beat lithium batteries at storing energy." (2021): 890-891.

Claims

Claims 1. An apparatus for hydrogen production, the apparatus comprising: an electrochemical cell comprising an anode and a cathode, and configured to receive a basic aqueous solution comprising zinc hydroxide and / or zincate, such that at least a portion of the cathode contacts the solution comprising the zinc hydroxide and / or zincate when it is disposed in the electrochemical cell; a battery comprising a positive current collector and an electrolyte compartment configured to hold an electrolyte therein, wherein the battery is configured to receive a gas comprising oxygen on the positive current collector and to receive at least a portion of the zinc produced in the electrochemical cell, such that the zinc forms an anode of the battery; and a thermochemical reactor, comprising a reaction chamber configured to receive at least a portion of the zinc metal produced in the electrochemical cell; and configured to enable the zinc metal to contact water in the reaction chamber and thereby cause a thermochemical reaction to proceed and thereby produce zinc oxide and a gas stream comprising hydrogen.

2. The apparatus according to claim 1, wherein the battery comprises a negative current collector, wherein the electrolyte compartment is disposed between the negative current collector and positive current collector and the battery is configured to receive a suspension or slurry comprising zinc particles.

3. The apparatus according to claim 1 or claim 2, wherein the apparatus comprises a zinc store configured to store a suspension or slurry comprising zinc particles and a basic aqueous solution and a reservoir configured to store a solution comprising zinc hydroxide and / or zincate, and the apparatus comprises one or more pumps configured to cause the slurry or suspension comprising zinc particles to flow from the zinc store, through the battery and into the reservoir.

4. The apparatus according to any preceding claim, wherein the apparatus further comprises: an oxygen store, a first oxygen conduit which extends between the oxygen store and the battery, and is configured to transport a gas comprising oxygen from the oxygen store to the battery, anda second oxygen conduit extending between the electrochemical cell and the oxygen store, and configured to transport oxygen from the electrochemical cell to the oxygen store.

5. The apparatus according to any preceding claim, wherein the apparatus comprises a further power supply configured to supply electrical power to the apparatus.

6. A method of producing hydrogen, the method comprising: disposing a basic aqueous solution comprising zinc hydroxide and / or zincate in an electrochemical cell comprising an anode and a cathode, such that at least a portion of the cathode contacts the basic aqueous solution; conducting an electrochemical reaction by applying a voltage across the anode and the cathode, to thereby produce hydrogen, oxygen and zinc; disposing a first portion of the zinc produced in the electrochemical reaction in a battery, such that the zinc defines an anode; contacting a positive current collector in the battery with a gas comprising oxygen to thereby cause a chemical reaction to occur to produce zinc oxide, zinc hydroxide and / or zincate and generate a current; and conducting a thermochemical reaction by contacting a second portion of the zinc produced in the electrochemical reaction with water to produce zinc oxide or zinc hydroxide and hydrogen.

7. The method according to claim 6, wherein the method comprises conducting the chemical reaction in the battery for a discrete time interval.

8. The method according to claim 7, wherein the method comprises conducting the chemical reaction in the battery when power output from a further power source decreases below a predetermined third power output, wherein the further power source is used to power the electrochemical reaction and using power generated by the battery to power the electrochemical reaction.

9. The method according to any one of claims 6 to 8, wherein the method comprises transporting a portion of the zinc produced in the electrochemical reaction to a zinc store when power output from a further power source increases above apredetermined first power output, wherein the further power source is used to power the electrochemical reaction.

10. The method according to any one of claims 6 to 9, wherein disposing at least a portion of the zinc produced in the electrochemical reaction in the battery comprises disposing a suspension or slurry comprising zinc particles and a basic aqueous solution in the battery.

11. The method according to claim 10, wherein disposing a suspension or slurry comprising zinc particles and a solution in the battery comprises causing the suspension or slurry comprising zinc particles to flow through the battery.

12. The method according to any one of claims 6 to 11, wherein the electrochemical reaction is conducted continuously.

13. The method according to any one of claims 6 to 12, wherein the method comprises continuously feeding the basic aqueous solution comprising zinc hydroxide and / or zincate into the electrochemical cell while the electrochemical reaction is being conducted and further comprises continuously removing the solution from the cell as the electrochemical reaction is being conducted.

14. The method according to any one of claims 6 to 13, wherein the thermochemical reaction is conducted continuously.

15. The method according to any one of claims 6 or 14, wherein the method comprises conducting a thermochemical reaction by contacting at least a portion of the zinc produced in the electrochemical reaction with a basic aqueous solution.

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