HYDROGEN GENERATION

This invention relates generally to the generation of hydrogen, and specifically to the generation of hydrogen gas by reaction of silicon with water.

For years it has been the aim of many to reduce the world’s reliance on fossil fuels. This is, at least in part, driven by the deleterious effects that the production and combustion of fossil fuels has on the environment. Hydrogen has been shown to be a clean and renewable energy carrier with a high calorific value. This allows hydrogen to find application as a viable alternative to non-renewable energy sources such as fossil fuels that additionally produce harmful waste products. However, whilst hydrogen is energy rich compared to, say, petroleum on a per weight basis, it is comparatively poor on a per volume basis. Furthermore, the portability of hydrogen gas as a fuel is problematic, requiring the transportation of significant volumes under high pressure. These issues have combined to arrest progress of the‘hydrogen economy’ as a viable alternative (and/or replacement) for the‘fossil fuel economy’.

To seek to address the issues concerning hydrogen, alternative methods for storing and transporting hydrogen have been proposed. One such method entails the use of an energy carrier which can react to form hydrogen. It has been proposed that silicon can provide an energy carrier and that it can be utilised to produce hydrogen gas by reaction with water.

The hydrolysis of silicon is known to produce hydrogen in the following reaction:

It will be appreciated from reaction (I) that solid silicon reacts with water to generate gaseous hydrogen and silica (sand). Accordingly, the co-reactant is plentiful and the reaction products of the process are the usable hydrogen and silica, which is a benign solid co-product.

It will be appreciated that the reaction between a solid and a liquid is rate limited by the surface area of solid that is available for contact with the liquid. Accordingly, in reaction (I) the greater surface area of silicon the higher the rate of reaction. It is also known that silicon reacts with air to form silica. The formation of silica on the surface of silicon‘passivates’ the silicon thereby inhibiting the progress of reaction (I). WO2011/058317 teaches the wet milling of silicon to generate a powder, with a preferable D90 of less than 800nm. The silicon powder was reacted with water at 90°C. The reaction had a yield of 60% and was complete in 2.75 hours.

As will be appreciated, the milling of silicon generates a powder with a very large surface area. Indeed, as the D90 decreases, so the surface area increases. The most preferable D90 is less than 250nm. Accordingly, this patent application teaches to maximise the surface area available for reaction with water.

WO2014/053799 teaches that the performance of the material described in WO2011/058317 can be improved by inclusion of a dispersing agent, a dispersant or a colloidal stabilizer. The teaching of this patent application is that aggregation of silicon particles and the aggregation of silica in solution limits the yield, this is improved by addition of dispersing agent and synergistically improved with the addition of a dispersing agent and a colloidal stabilizer. The examples of this application use very small amounts of silicon (150 mg).

It is known that fine powders can be difficult to handle, especially when it is required to use large amounts of reactant. Typically, fine powders are difficult to handle because of the build-up of electrostatic charges and/or the generation of dust when dispensing. However in reaction (I), both the rate of production of hydrogen, and the overall yield of hydrogen, are limited by the surface area of silicon that is available to react with water. WO2014/053799 refers to the use of pellets comprising silicon, which may be encapsulated within an organic coating. The organic coating is described as being a dissolvable substance, typically gelatine. However, no method or examples are provided for the fabrication of an encapsulated pellet, and no experimental details or results are provided for the use of an encapsulated pellet to generate hydrogen.

Brack et. al. (Journal of Alloys and Compounds, 704 (2017) pp 146-151) describes pelletisation of silicon for use in hydrogen generation. However, the silicon powder used in the pellets is passivated, i.e. is coated in a thin layer of silicon dioxide. It is taught that the silicon powder is mixed with sodium chloride before compression of the mixture into pellets. The pellets are contacted with 2 wt% sodium hydroxide solution at 50 °C to generate hydrogen.

It is therefore a first non-exclusive object of the invention to provide a silicon composition for the production of hydrogen by reaction with water with improved handleability and/or with a simplified production process. It is a further non-exclusive object of the invention to provide a silicon composition that exhibits an at least comparative rate of reaction and/or hydrogen yield to that of a powdered composition comprising the same amount of reactant. Accordingly, a first aspect of the invention provides an uncoated pellet, the uncoated pellet comprising silicon present, for example, in an amount greater than or equal to 70, 75 or 80 w/w% and a dispersant preferably present in an amount of less than or equal to 30, 25 or 20 w/w%. A further aspect of the invention provides an uncoated pellet, the uncoated pellet comprising silicon and a dispersant and wherein a) the dispersant has a heat of solution of less than -20 kJ mol ¹ and/or b) the solubility of the dispersant is greater than 40 g /100 ml in water (20°C). In this specification‘uncoated’ means that the pellet does not have a protective coating to inhibit contact of the surface of the pellet with oxygen in the air. By not providing a coating (i.e. by providing an uncoated pellet) the processing time to produce a pellet is reduced and/or the cost of producing a pellet is reduced. Typically, the silicon in the uncoated pellet of the present invention is non-passivated. The term‘passivated’ is defined as the formation of a non-reactive film or layer on the surface of the material. In WO2014/053799, it is described that silicon is normally unreactive towards water due to highly efficient passivation of the silicon surface by S1O2 upon exposure to air or moisture; the S1O2 layer formed can have a thickness of well below 1 nm. Such passivated silicon is not capable of reacting with water to produce hydrogen.

The pellet comprises greater than or equal to 70 w/w% silicon, i.e. the pellet may comprise between 75 to 100 w/w% silicon. The pellet may comprise 75, 76, 77, 78, 79, 80, 81 , 82, 83, 84, 85, 86, 87, 88, 89, 90, 91 , 92, 93, 94, 95, 96, 97, 98, 99 or 100 w/w% silicon. In embodiments, the pellet comprises between 85 to 100 w/w% silicon, for example, 90 to 100 w/w% silicon, e.g. 90 w/w% silicon, or 95 w/w% silicon.

The silicon in the pellet may comprise silicon powder. The silicon powder may comprise particles of a sub-micron size, for example, the silicon powder may comprise particles with a largest dimension, e.g. a length or a maximum transverse dimension (l.e. a diameter in a spherical particle) of between 50 nm to 500 nm, for example, between 100 nm to 400 nm, or 200 nm to 300 nm.

The silicon in the pellet may comprise a polydisperse powder. The polydisperse powder may comprise particle sizes with a mean diameter and/or a D50 of between 50 nm and 500 nm, e.g. 100 to 400 nm, or 200 to 300 nm. For example, a D50 of 200 nm, or 250 nm, or 300 nm.

Alternatively, the silicon powder may comprise particles in two or more particles size ranges. For example, the silicon powder may comprise particles in a first size range, e.g. between 50 nm to 300 nm (D90<300nm), and particles in a second size range, e.g. between 150 nm and 600 nm (D90<600nm).

The pellet may further comprise a dispersant in less than or equal to 25 w/w%. In embodiments the pellet comprises less than or equal to 22.5 w/w% of a dispersant, for example, the pellet may comprise less than 20 w/w% of a dispersant, or less than 15 w/w% of a dispersant, or less than 10 w/w% of a dispersant, or less than 5 w/w% of a dispersant. In embodiments, the pellet comprises no dispersant, i.e. 0 w/w%.

The pellet may comprise more than one dispersant. The dispersant(s) may be any water- soluble ionic compound. In embodiments, the dispersant has a heat of solution in water of less than, i.e. more negative than, -20 kJ mol ¹ . The dispersant may comprise a metal hydroxide, e.g. lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and/or caesium hydroxide. Other salts may be used. The weight of the salt may also be important. For example, a lighter salt may have a higher relative heat of solution per unit mass and so may be beneficial from an overall system weight perspective. For example KOH has a heat of solution of -57.61 kJ mol ¹ and a MW of 56 g mol ¹ , providing a heat of solution of -1.03 kJ g ¹ , whereas NaOH has a heat of solution of -1.1 1 kJ g ^-1 and LiOH a heat of solution of -0.98kJ g ¹ . Although the heat of solution per mole is more negative for KOH than it is for NaOH and LiOH, the lower molecular weights of NaOH and LiOH result in comparable values for the heat of solution per gram. From an overall system weight perspective, it may therefore be beneficial to use a dispersant with a less negative heat of solution per mole, if the value per gram is more negative.

The dispersant may have a solubility in water of greater than 40 g /100 ml at 20°C, for example greater than 50, 60, 70 or 80 g / 100 ml at 20°C.

It should be noted that some dispersants are sold in purities of less than 100%. For example, potassium hydroxide may be sold in a purity of 85%, the remainder being water and/or potassium carbonate. Therefore, by less than or equal to, say, 15 w/w% of a dispersant, we mean less than or equal to 15 w/w% of the pure dispersant, i.e. if 1 g of KOH as sold (85% purity) is used as part of a 10 g pellet, then the w/w% is equal to 8.5 w/w% of dispersant (rather than 10 w/w%).

The density of the pellet may be between 0.5 g/cm ³ and 2.2 g/cm ³ , for example, between 1.0 g/cm ³ to 1.8 g/cm ³ , or between 1.0 g/cm ³ to 1.6 g/cm ³ , for example, between 1.2 g/cm ³ to 1.4 g/cm ³ . For example, the silicon powder may be compressed into pellets with a density of 1.0, 1.1 , 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1 , or 2.2 g/cm ³ . Preferably, the density of the pellet is between 1.0 g/cm ³ to 1.6 g/cm ³ . The density of the pellet may be from 20 to 95 % of the theoretical value, for example from 30, 40, 50, 60 % theoretical to 90, 80 or 70 % theoretical.

The mass of the pellet may be between 0.05 g and 20, 15, 10 or 5.0 g, for example, between 0.10 g and 18, 13, 8 or 4.0 g. In embodiments the pellet may be between 0.15 g and 3.0 g, or between 0.20 g and 2.0 g, or between 0.25 g and 1.0 g. In embodiments, the mass of the pellet is between 0.10 g and 0.50 g, for example, 0.10 g, 0.20 g, 0.30 g, 0.40 g, or 0.50 g. For example, the mass of the pellet may be 0.24 g. The volume of the pellet may be between 0.02 cm ³ and 5.0 cm ³ , for example, between 0.05 cm ³ and 3.0 cm ³ , or between 0.10 cm ³ to 1.0 cm ³ , for example, between 0.15 cm ³ and 0.24 cm ³ .

The uncoated pellet may be manufactured in a process comprising compressing a volume and/or mass of a silicon composition to create a pellet, the silicon composition comprising silicon preferably in an amount greater than or equal to 70 or 75 w/w% and a dispersant in an amount less than or equal to 20 or 25 w/w%. The compressed volume of the silicon composition within the resulting uncoated pellet may be between 0.02 cm ³ and 20, 15, 10 or 5.0 cm ³ . In embodiments the pellet may have a volume for example, between 0.05 cm ³ and 3.0 cm ³ , or between 0.10 cm ³ to 1.0 cm ³ , for example, between 0.15 cm ³ and 0.24 cm ³ .

The mass of the silicon composition used to manufacture the uncoated pellet in the process may be between 0.05 g and 20, 15, 10 or 5.0 g, for example, between 0.10 g and 4.0 g, or between 0.15 g and 3 g, or between 0.20 g and 2.0 g, or between 0.25 g and 1.0 g. In embodiments, the mass of the silicon composition used to manufacture the uncoated pellet in the process is between 0.10 g and 0.50 g, for example, 0.10 g, 0.20 g, 0.30 g, 0.40 g, or 0.50 g. For example, the mass of the silicon composition used to manufacture the uncoated pellet may be between 0.20 g and 0.25 g, for example, 0.21 g, 0.22 g, 0.23 g, 0.24 g or 0.25 g.

The compression of a volume and/or mass of the silicon composition may comprise compression with a compressive force of between 10 kN to 30 kN, for example, 15 kN, or 20 kN, or 25 kN.

The process may further comprise milling the silicon with the dispersant, e.g. potassium hydroxide, to provide the composition.

The density of the pellet of the process may be between 0.5 g/cm ³ and 2.2 g/cm ³ , for example, between 1.0 g/cm ³ to 1.8 g/cm ³ , or between 1.0 g/cm ³ to 1.6 g/cm ³ , for example, between 1.2 g/cm ³ to 1.4 g/cm ³ . For example, the density of the pellet of the process may be 1.0, 1.1 , 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1 , or 2.2 g/cm ³ . Preferably, the density of the pellet is between 1.0 g/cm ³ to 1.6 g/cm ³ .

The process may be performed in an inert atmosphere, for example, argon and/or nitrogen.

The pellet may be any suitable geometry or shape. For example, the pellet may be spherical, cylindrical, toroidal, ellipsoidal, cuboid, or any other three-dimensional shape. In embodiments, the pellets are cylindrical. The pellet may have a length, width, and/or height, of between of between 2 mm and 20 mm, for example, between 5 mm and 15 mm, or between 8 mm and 12 mm, for example, 10 mm. In embodiments, the pellet is a cylinder with a diameter of approximately 8 mm. In an embodiment, a pellet has a diameter of less than 30mm, for example less than 25, 20, 15, 10 mm and a height of less than 15 mm, for example less than 12.5, 10, 7.5, 5 mm. In an embodiment the pellet has a diameter of 8.0 mm and a height of 4.5 mm.

A further aspect of the invention provides a method of reacting silicon and water, the method comprising: (i) providing an uncoated pellet comprising silicon in greater than or equal to, say, 70 or 75 w/w% and a dispersant in less than or equal to, say, 30 or 25 w/w%; (ii) contacting the uncoated pellet with water.

A yet further aspect of the invention provides a method of reacting silicon and water, the method comprising: (i) providing an uncoated pellet comprising silicon and a dispersant wherein a) the dispersant has a heat of solution of less than -20 kJ mol ¹ and/or b) the solubility of the dispersant is greater than 40 g /100 ml in water (20°C) and (ii) contacting the uncoated pellet with water. The silicon may be non-passivated.

The water of Step (ii) may be provided to the silicon within the uncoated pellet in a range of ratios of between 1 :100 moles of silicon to water to 1 :1 moles of silicon to water, for example, 1 :50 moles, or 1 :25 moles, or 1 : 10 moles, or 1 :2 moles of silicon to water to 1 : 1 moles of silicon to water. In embodiments, the reactants are provided in a ratio of approximately 1 :6 moles of silicon to water.

The water of Step (ii) may comprise sea water. It has been surprisingly found that sea water may be used in a method for the production of hydrogen from silicon. In particular, the use of sea water in the method is advantageous because the supply is virtually limitless and may be obtained from any location near the coast or at sea. This is particularly advantageous for situations in which the hydrogen fuel will be used in freight transport applications, e.g. to fuel ships and/or haulage lorries. Therefore, the need to transport large volumes of purified water for use in the reaction to generate hydrogen is removed, and the Net Energy Gain (NEG) of hydrogen as a fuel is increased.

In general, the salinity of sea water is approximately 3.5% or 35 parts per thousand (although the salinity in different locations ranges from approximately 3.4% to 3.7% depending on the evaporation or addition of water locally). Therefore, for every litre of water there is approximately 35 g of salts. The major component of these salts is sodium chloride. The most abundant ions in sea water are chloride, sodium, sulphate, magnesium, calcium, and potassium. These six ions represent 99% of the salt present in sea water. The remaining 1 % of the salt comprises inorganic carbon, bromide, boron, strontium, and fluoride. Other substances may also be present at low concentrations, in addition to the salts, for example, inorganic and organic materials, particulates, and atmospheric gases.

A representative composition of sea water comprises sodium chloride (66.1 %), magnesium sulphate heptahydrate (16.3%), magnesium chloride (12.7%), calcium chloride (3.30%), and potassium chloride (1.60%).

The water of Step (ii) may have a salinity of between 0.1 % to 4.0%, say from 2.5% or 3.4% to 3.7%. The water may comprise 34 to 37 parts per thousand salt to water, the salt comprising sodium chloride as the major component. Step (ii) of the method may comprise contacting the uncoated pellet with water at a temperature of between 2 °C to 40 °C. For example, if the water is obtained from the environment, e.g. from the sea or from a fresh water source, the water is provided at its temperature at source, and is not artificially heated.

The water may be treated prior to use, for example to reduce the salinity, turbidity, solids content and so on.

Additionally or alternatively, the water in Step (ii) may further comprise water obtained from a fresh water source, e.g. a fresh water lake, river or other body of water found in the environment.

Additionally or alternatively, the water of Step (ii) may further comprise potable or tap water. The tap water may contain ions, for example, one or more of calcium ions, sulphate ions, magnesium ions, sodium ions, potassium ions, manganese ions, iron ions, aluminium ions, nitrates, phosphates, copper ions, zinc ions, lead ions, chloride, and/or fluoride.

The water of Step (ii) may be provided at any temperature of between 0 °C and 100 °C at standard pressure. Preferably, the temperature of the water is at ambient temperature, i.e. the water is not heated to a temperature above that of its source. The temperature of the water may be between 0 °C to 50 °C, for example, between 0 °C to 40 °C, or between 0 °C to 35 °C. For example, the temperature of the water may be provided at 1 , 2, 3, 4, 5, 6, 7,

8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, 35, 36, 37, 38, 39 or 40 °C. Surprisingly, the inventors have found that yields are not impaired by using water which has not been heated (e.g. heated to above 50 °C) prior to contact with the silicon. This is advantageous from a system, energy-balance perspective. A yet further aspect of the invention provides a cartridge containing an uncoated pellet, the uncoated pellet comprising silicon in greater than or equal to say 70 or 75 w/w% and a dispersant in less than or equal to, say 30 or 25 w/w%. The cartridge may comprise a port or opening for injection or delivery of water to contact the uncoated pellet.

The hydrogen generated in the cartridge may be directly fed into a fuel cell. The fuel cell may be used to provide electricity, for example to power electronic devices.

The inventors have surprisingly found that silicon in the form of a pellet according to the invention provides a comparable rate of reaction with water to produce hydrogen, to that exhibited by silicon in a powder form. Surprisingly, this is despite the available total surface area of the pellet being much smaller than that of silicon powder. This is advantageous because pellets exhibit improved handleability in comparison with the powdered form of silicon without detrimentally impacting the rate of reaction or yield of hydrogen.

It has been surprisingly found that the density of the compressed composition within the pellet can restrict oxygen permeation. This limits passivation of the bulk material within the pellet. Therefore, a coating, i.e. a coating that is chemically distinct from the silicon or its reaction products, that encapsulates the pellet is not provided. This is advantageous because the processing and cost of the pellet is reduced in the method of manufacture, i.e. a coating step is not required. Moreover, the pellet does not require warm water or any other energy source to dissolve or melt the coating from the pellet to initiate the reaction of silicon with water. Advantageously, this allows the reaction to be conducted in cold, i.e. unheated, water. Also, we have found that it is not necessary to change the composition of the water to initiate reaction, for example by using an etchant such as sodium hydroxide. This is advantageous because the weight of the water is not increased and the complexity of the system is reduced.

Additionally, the compressed composition within the pellet of the present invention imparts an advantageous density and structure for the thermal control of the reaction of silicon with water. In use, cold water is added to the system and is able to make contact with the silicon on the outer surface of the pellet immediately, without removal of a coating, to initiate the reaction. The reaction of silicon with water is highly exothermic, and therefore the environment around the outer surface of the pellet experiences rapid local heating. The heat energy surrounding the pellet is then transferred via convection to the bulk water in the reaction mixture of the system. Advantageously, the high specific heat capacity of water allows the temperature of the reaction to be controlled to prevent overheating and/or thermal runaway of the reaction.

A further aspect of the invention provides an apparatus for reacting water and silicon, the apparatus comprising a container in which is located a reactor, a first conduit for introducing water in to the reactor for contacting silicon with water within the reactor, a second conduit for receiving hydrogen from the reactor, a third conduit for receiving silica from the reactor.

The apparatus may further comprise a treatment zone, for treating water before or after it enters the first conduit. The treatment zone may comprise a filter. The filter may comprise a filter medium.

The third conduit may communicate with the filter, for example to allow the or to cause the silica to become or join the filter medium. Advantageously, the recirculating of the waste silica (which may be present as small sized particles) to the filter medium provides a use for the waste product and also would allow for the reclamation of any unreacted silicon and/or any dispersant present in the silica.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. For the avoidance of doubt, the terms“may”,“and/or”,“e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

To further exemplify the invention, reference is also made to the following non-limiting Examples with reference to the accompanying drawings in which:

Figure 1 is a graph showing the pressure and temperature change over time of the hydrolysis of pellets according to Example 1 ;

Figure 2 is a graph showing the pressure and temperature change over time of the hydrolysis of powder according to Comparative Example 1 ;

Figure 3 is a graph showing the pressure and temperature change over time of the hydrolysis of pellets according to Example 2;

Figure 4 is a graph showing the pressure and temperature change over time of the hydrolysis of powder according to Comparative Example 2;

Figure 5A is a graph showing the pressure and temperature change over time of the hydrolysis of a coated pellet after 15 minutes, according to Comparative Example 3; Figure 5B is a graph showing the pressure and temperature change over time of the hydrolysis of a coated pellet after 2 hours, according to Comparative Example 3 Figure 6 is a graph showing the pressure and temperature change over time of the hydrolysis of pellets with tap water, according to Example 3;

Figure 7 is a graph showing the pressure and temperature change over time of the hydrolysis of pellets with tap water, according to Example 4;

Figure 8 is a graph showing the pressure and temperature change over time of the hydrolysis of pellets with simulated sea water according to Example 5;

Figure 9 is a graph showing the pressure and temperature change over time of the hydrolysis of pellets with simulated sea water according to Example 6; and

Figure 10 is an apparatus for the generation of hydrogen from silicon and water, according to a further embodiment of the invention.

Reference is made to the following non-limiting examples. In the examples set out below, the following milling process was utilised:

Milling Process

The milling process was performed using a ball mill (Retsch PM 100) and a zirconium oxide milling jar (125 ml capacity) with zirconium oxide balls under inert (non-oxidising) conditions. A maximum available speed of 650 rpm was used in the active milling steps. A dry milling step (performed using 5 mm diameter balls) was performed comprising 20 minutes of active milling in two 10 minute steps, separated by a cooling period of 10 minutes (total time 30 minutes). A wet milling step was performed thereafter. The wet milling step (using 0.5 mm diameter balls and anhydrous acetonitrile as the solvent) was conducted under inert conditions and comprised 30 minutes of active milling in three 10 minute periods, separated by cooling periods of 10 minutes (total time 50 minutes).

Example 1

Silicon pieces (1 1.7 g, CAS number 7440-21-3) were crushed into a coarse powder by hand with a pestle and mortar. The resulting powder was milled using the milling process (described above) with potassium hydroxide (1.3 g, 85% purity, CAS number 1310-58-3) to produce a silicon composition in 90 w/w% silicon and 8.5 w/w% potassium hydroxide. The remaining 1.5 w/w% comprised impurities present in the potassium hydroxide as purchased.

A portion of the resulting silicon composition (between 0.20 g to 0.30 g) was used to fabricate a pellet by compression using a tablet press (VICE (RTM) handheld pill press, available from LFA Tablet Presses, Bicester, UK) with a compressive force of approximately 20 kN. The resulting pellets had average dimensions of 8 mm in diameter and 4.5 mm in height, with an average mass of 0.24 g.

A reactor was charged with 3 g of pellets. A background of hydrogen gas at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 10 ml_ of deionised water (T = 24°C) was injected into the reactor.

The results of Example 1 are shown in Figure 1. The graph 1 shows the pressure change over time 1 1 and the temperature change over time 12 of the reaction of 3 g of pellets with 10 mL of water. The hydrogen generation was complete within three minutes of injection. The temperature increased to a peak of 133 °C within three minutes. A final pressure of 256 kPa (2.56 bar) above starting pressure was recorded. The hydrogen yield was 66%.

Comparative Example 1

Silicon pieces (1 1.7 g, CAS number 7440-21-3) were crushed into a coarse powder by hand with a pestle and mortar. The resulting powder was milled using the milling process (described above) with potassium hydroxide (1.3 g, 85% purity, CAS number 1310-58-3) to produce a silicon composition in 90 w/w% silicon and 8.5 w/w% potassium hydroxide. The remaining 1.5 w/w% comprised impurities present in the potassium hydroxide as purchased.

A reactor was charged with 3 g of the powder. A background of hydrogen gas at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 10 ml_ of deionised water (T = 23°C) was injected into the reactor.

The results of Comparative Example 1 are shown in Figure 2. The graph 2 shows the pressure change over time 21 and the temperature change over time 22 of the reaction of 3 g powder with 10 mL of water. The hydrogen generation was complete within three minutes of injection. The temperature increased to a peak of 133 °C within two minutes. A final pressure of 242 kPa (2.42 bar) above starting pressure was recorded. The hydrogen yield was 62%.

Example 2

Silicon pieces (1 1.7 g, CAS number 7440-21-3) were crushed into a coarse powder by hand with a pestle and mortar. The resulting powder was milled using the milling process (described above) with potassium hydroxide (1.3 g, 85% purity, CAS number 1310-58-3) to produce a silicon composition in 90 w/w% silicon and 8.5 w/w% potassium hydroxide. The remaining 1.5 w/w% comprised impurities present in the potassium hydroxide as purchased.

A portion of the resulting silicon composition (between 0.20 g to 0.30 g) was used to fabricate a pellet by compression using a tablet press (VICE handheld Pill Press) with a compressive force of approximately 20 kN. The resulting pellets had average dimensions of 8 mm in diameter and 4.5 mm in height, with an average mass of 0.24 g.

A reactor was charged with 6 g of the pellets. A background of hydrogen gas at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 20 mL of deionised water (T = 22°C) was injected into the reactor.

The results of Example 2 are shown in Figure 3. The graph 3 shows the pressure change over time 31 and the temperature change over time 32 of the reaction of 6 g of pellets with 20 mL of water. The hydrogen generation was complete within two minutes of injection. The temperature increased to a peak of 162 °C. A final pressure of 547 kPa (5.47 bar) above starting pressure was recorded. The hydrogen yield was 67%.

Comparative Example 2

Silicon pieces (1 1.7 g, CAS number 7440-21-3) were crushed into a coarse powder by hand with a pestle and mortar. The resulting powder was milled using the milling process (described above) with potassium hydroxide (1.3 g, 85% purity, CAS number 1310-58-3) to produce a silicon composition in 90 w/w% silicon and 8.5 w/w% potassium hydroxide. The remaining 1.5 w/w% comprised impurities present in the potassium hydroxide as purchased.

A reactor was charged with 6 g of the powder. A background of hydrogen gas at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 20 mL of deionised water (T = 24°C) was injected into the reactor.

The results of Comparative Example 2 are shown in Figure 4. The graph 4 shows the pressure change over time 41 and the temperature change over time 42 of the reaction of 6 g powder with 20 mL of water. The hydrogen generation was complete within two minutes of injection. The temperature increased to a peak of 167 °C within two minutes of injection. A final pressure of 544 kPa (5.44 bar) above starting pressure was recorded. The hydrogen yield was 67%.

Advantageously, the reaction of the silicon composition with water provides a favourable yield of hydrogen gas in a short timescale of several minutes, regardless of whether the silicon composition is provided in a powder form or a pellet form with evidence of a slight improvement of yield when using the pellets. The similarity in performance, i.e. the similar rate of reaction and overall yield of hydrogen, is surprising because it would be expected that the reaction is limited by the surface area of the silicon available to water.

The advantage of using pellets in preference to powder is that pellets are much easier to handle and do not have the associated hazards of powder, such as the creation of a dust atmosphere. Comparative Example 3

An encapsulated pellet was prepared by placing pellets of Example 1 or Example 2 into an empty gelatine capsule. This was performed to compare the experimental results of an encapsulated pellet as suggested in WO2014/053799 with an uncoated pellet, of the present invention. In the absence of experimental details for the fabrication of an encapsulated pellet in WO2014/053799, the following protocol was devised.

A silicon composition was provided in the form of pellets, which were prepared in an identical manner to that described in Example 1 or Example 2.

In an inert atmosphere glovebox, 3 g of pellets were loaded into gelatine capsules (two pellets per capsule, 7 capsules at 0.1 1g/capsule, size 00 from Bulk Powders of Colchester, UK) to fabricate encapsulated pellets. The gelatine capsules each consisted of two parts; a body and a cap, which were pushed together to secure the pellets within the capsule.

A reactor was charged with the encapsulated pellets (3 g of pellets, 0.8 g of gelatine). A background of hydrogen gas at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 10 mL of deionised water (T = 23 ^C C) was injected into the reactor.

The results of Comparative Example 3 are shown in Figures 5A and 5B. The graph 5A shows the pressure change over time 51 and the temperature change over time 52 of the reaction of the encapsulated pellet with 10 mL of water over the first 15 minutes of the experiment. The graph 5B shows the pressure change over time 53 and the temperature change over time 54 of the reaction of the encapsulated pellet with 10 mL of water over the first 2 hours of the experiment.

The temperature increased to a peak of 45 °C at approximately 12 minutes after injection. The pressure increased to 23 kPa (0.23 bar) above starting pressure at 10 minutes after injection to provide a hydrogen yield of 6%, and then further increased to 76 kPa (0.76 bar) above starting pressure two hours after injection, to provide a hydrogen yield of 19%.

Therefore, both the hydrogen yield and the rate of release are too low to be useful. The examples of WO2014/053799 (for powder compositions) use heated water. However, the water used in this example was unheated (the water was provided at room temperature) to duplicate the conditions of the earlier examples. Without wishing to be bound by any theory, it is thought that although some water was available to penetrate the capsule to contact the silicon, the temperature of the water was too low to dissolve the gelatine coating to release the pellets. Therefore, the water would need to be heated to a higher temperature to achieve better results. In addition, it is thought that a higher volume of water may be required to effectively dissolve the gelatine and to react with the silicon, to achieve better results. It is thought that swelling within the gelatine coating upon contacting the water further limits the rate of reaction, and also limits the quantity of water available for reaction with silicon.

As will be appreciated, heating of the water is disadvantageous from an energy perspective.

Comparative Example 4

Comparative Example 4 is taken from the results reported in Brack et. al. (supra). In this publication, a powder composition was prepared by mixing passivated silicon powder and an additive (sodium chloride or sodium polyacrylate). The powder composition was compressed into a pellet using a 13 mm diameter anvil inserted into a die set (Specac).

In a series of experiments, various silicon compositions and additives were contacted with 2 wt% NaOH solution (10 ml_) at 50 °C in separate experiments

The results of Comparative Example 4 are shown in Figures 7 and 8 of Brack et. al. The graphs show the hydrogen generation over time for various compositions (0 to 0.2g NaCI or 0 to 0.2g NaPAA). The results show that for zero additives (i.e. 0 g NaCI or 0 g NaPAA) hydrogen generation was complete within 10 minutes, when using 10 mL of 2 wt.% NaOH at 50 °C. We estimate that the yield was a maximum of 59%.

In contrast, the results of Example 1 or Example 2 show that the hydrogen generation was complete within two minutes (Example 2) or three minutes (Example 1) of injection, when using neutral water and at room temperature.

Further, a comparison of the results of Brack et al relating to the pellet and the crushed pellet (as shown in the graph of Figure 1 of Brack et al) imply that the reaction is indeed surface area limited or controlled. This comparative result further demonstrates the surprising reactivity of Examples of the invention. Example 3

A silicon composition was provided in the form of pellets, which were prepared in an identical manner to that described in Example 1 or Example 2. Tap water was taken from the mains supply in building R79 at the Rutherford Appleton Laboratory, Didcot, Oxfordshire UK and used without any treatment or further modification.

A reactor was charged with 3 g of pellets. A background gas of hydrogen at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 10 mL of tap water (T = 22 C) was injected into the stainless-steel pressure vessel.

The results of Example 3 are shown in Figure 6. The graph 6 shows the pressure change over time 61 and the temperature change over time 62. The temperature had increased to a peak of 135 °C within three minutes of injection. The hydrogen generation was complete within three minutes of injection. A final pressure of 260 kPa (2.60 bar) above starting pressure was recorded, with a hydrogen yield of 66%.

Therefore, the performance of the pellets of the present invention with tap water is very similar to the performance of the pellets with deionised water, as demonstrated in Examples 1 and 2.

Example 4

A silicon composition was provided in the form of pellets, which were prepared in an identical manner to that described in Example 1 or Example 2.

Tap water was taken from the mains supply in building R79 at the Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK and used without any treatment or further modification.

A reactor was charged with 6 g of pellets. A background gas of hydrogen at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 20 mL of tap water (T = 22°C) was injected into the stainless-steel pressure vessel.

The results of Example 4 are shown in Figure 7. The graph 7 shows the pressure change over time 71 and the temperature change within the reactor over time 72. The temperature had increased to a peak of 214 °C within three minutes of injection. A final pressure of 564 kPa (5.64 bar) above starting pressure was recorded, with a hydrogen yield of 69%.

Therefore, the performance of the pellets of the present invention with tap water is very similar to the performance of the pellets with deionised water, as demonstrated in Examples 1 and 2.

This provides clear evidence that pellets of the invention can be used with potable, and/or mains water.

Example 5

A silicon composition was provided in the form of pellets, which were prepared in an identical manner to that described in Example 1 or Example 2.

Simulated sea water was prepared by dissolving Peacock Seamix in tap water. A watersalt weight ratio of 24: 1 was used, giving an estimated salinity of 35 parts per thousand. This represents the highest expected salinity for natural sea water.

A reactor was charged with 3 g of pellets. A background gas of hydrogen at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 10 ml_ of simulated sea water (T = 25 °C) was injected into the stainless-steel pressure vessel.

The results of Example 5 are shown in Figure 8. The graph 8 shows the pressure change over time 81 and the temperature change over time 82. The temperature had increased to a peak of 115 °C within three minutes of injection. The hydrogen generation was complete within four minutes of injection. A final pressure of 151 kPa (1.51 bar) above starting pressure was recorded, with a hydrogen yield of 39%.

Therefore, the use of simulated sea water results in reduced hydrogen yield in comparison with deionised water.

Example 6

A silicon composition was provided in the form of pellets, which were prepared in an identical manner to that described in Example 1 or Example 2. Simulated sea water was prepared by dissolving Peacock Seamix in tap water. A watersalt weight ratio of 24: 1 was used, giving an estimated salinity of 35 parts per thousand. This represents the highest expected salinity for natural sea water.

A reactor was charged with 6 g of pellets. A background gas of hydrogen at a pressure of 120 kPa (1.2 bar) absolute was provided within the reactor. After one minute, 20 ml_ of simulated sea water (T = 22 °C) was injected into the stainless-steel pressure vessel.

The results of Example 6 are shown in Figure 9. The graph 9 shows the pressure change over time 91 and the temperature change over time 92. The temperature increased to a peak of 131 °C within two minutes of injection. A final pressure of 313 kPa (3.13 bar) above starting pressure was recorded, with a hydrogen yield of 39%. Therefore, the use of simulated sea water results in reduced hydrogen yield in comparison with deionised water.

Therefore, although the yield of hydrogen obtained from the reaction of the pelletised silicon composition with simulated sea water is lower than when deionised (or tap) water is used, the difference is more than compensated in the lifecycle of hydrogen as a fuel because water may be obtained at the point of use, removing the energy requirement for purification and transportation.

Additionally, the abundance of sea water in a virtually limitless supply means that the partially reacted pellets may be contacted with sea water for a second time to generate hydrogen from any unreacted silicon within the pellets. Also, sea water may be purified, for example by filtration, ultrafiltration, ion exchange, chemical treatment (e.g. desalination), evaporation/condensation or other means to reduce the salinity prior to use.

It is possible to use the pellets in apparatus for the local generation of hydrogen. For example, a container, e.g. an ISO container, could be provided incorporating a reactor and a conduit for supply of water to the reactor. If the apparatus was located on a sea-going vessel the conduit could supply water (e.g. sea water) to the reactor, or for example, water, which comprises sea water (e.g. sea water diluted with waste or other water).

Referring now to Figure 10, there is shown an apparatus 10 for generating hydrogen from silicon and water, according to an embodiment of the invention. The apparatus 10 comprises a reaction vessel 11 1 and an optional treatment chamber 1 12. The reaction vessel 111 comprises a water inlet 113, an optional silicon inlet 114, a hydrogen outlet 115, and an optional silica outlet 116. The optional treatment chamber 112, where provided, is arranged so that the water inlet 113 passes therethrough upstream of the reaction vessel 111.

In one embodiment the silicon may be provided in cartridges which are loaded into (or may provide at least a part of) the reaction vessel. In embodiments, the silicon inlet may feed silicon pellets or silicon in a cartridge into the reaction vessel. The reaction vessel will be pressure rated to be able to withstand the pressure generated during the reaction.

The optional treatment chamber 112, where provided, may be used to treat, e.g. filter, water, e.g. sea water, or water containing entrained matter, flowing through the water inlet 113 to the reaction chamber 111. The purpose of the optional treatment chamber 112 is to remove any entrained matter contained within the reactant water before it enters the reaction vessel 111. The optional treatment chamber 112 may preferably contain silica, which may be used to filter and/or purify impure water flowing thereinto and/or therethrough. Purified water, i.e. water that has had entrained matter removed, may enter the reaction vessel 111 by flowing along the water inlet 113. In this way, water, e.g. sea water, may be purified before it undergoes reaction with silicon, and advantageously, the yield of hydrogen may be increased.

The optional silica outlet 116 comprises a first end 116A in communication with the reaction vessel 111. In an embodiment, a second end 116B of the silica outlet 116 may communicate with the optional treatment chamber 112 (via the optional flow path indicated by dotted line 116C). Alternatively, the second end 116B may transport the silica product to waste.

The water outlet 118 comprises a first end 118A in communication with the reaction vessel 111. In an embodiment, a second end 118B of the water outlet 118 may communicate with the water inlet 113 (via the optional flow path indicated by dotted line 118C). Alternatively, the second end 118B may transport waste water from the reaction chamber 111 to waste.

The apparatus 10 is formed from any suitable materials that are capable of withstanding the pressure generated from hydrogen gas generated within the reaction vessel 111 , for example, stainless-steel. The pressure rating is selected depending on the scale of the reaction.

In use, the reaction between silicon and water takes place within the reaction vessel 1 11. Silicon is added to the reaction vessel 1 11 of the apparatus 10 through the silicon inlet 1 14, and water is added to the reaction vessel 11 1 of the apparatus 10 through the water inlet 1 13. Upon reaction of silicon and water, hydrogen gas is generated. The resulting hydrogen gas is harvested at the hydrogen outlet 115. The hydrogen outlet 1 15 may, for example, feed the hydrogen gas into a fuel cell for conversion into electricity. Waste silica generated in the reaction of silicon and water is removed from the reaction vessel 11 1 by flowing out of the silica outlet 116. In embodiments, the reaction vessel 1 11 may contain silicon prior to the introduction of water thereto.

Where the silica outlet 1 16 is in communication with the optional treatment chamber 1 12, the silica outlet 1 16 and/or flow path 1 16C may comprise a shut off valve or gateway (not shown). The shut off valve or gateway may be configured to open and close to selectively prevent fluid communication between the silica outlet 116 and the optional treatment chamber 1 12 when a reaction is occurring within the reaction chamber 1 11 and to allow fluid communication between the silica outlet 1 16 and the optional treatment chamber 1 12 when a reaction is not occurring in the reaction chamber 1 1 1. Where the water outlet 1 18 is in communication with the water inlet 1 13 the water outlet 1 18 and/or flow path 118C may comprise a further shut off valve or gateway (not shown). The further shut off valve or gateway may be configured to open and close to selectively prevent fluid communication between the water outlet 1 18 and the water inlet 1 13 when a reaction is occurring within the reaction chamber 11 1 and to allow fluid communication between the water outlet 118 and the water inlet 1 13 when a reaction is not occurring in the reaction chamber 1 11.

In embodiments, where the silica outlet 1 16 is in communication with the optional treatment chamber 112, any unreacted silicon within the waste silica within the purification chamber 1 12 may react with water flowing thereinto, and the hydrogen thereby generated may be harvested from this step, in addition to that generated in the reaction vessel 1 11.

The hydrogen provided by the reaction of silicon with water can be used in a fuel cell, in a combustion additive as a fuel or fuel additive, as a buoyancy aid or otherwise. For example, it is possible to continually supply hydrogen at a suitable pressure of e.g. 1.5 bar, which is a pressure at which it may be used by a device, for example a fuel cell. Alternatively, the hydrogen may be provided to an accumulator at a pressure of up to 1000 bar (e.g. at 700 or 350 bar or 10 bar) for use. It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention.

It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.