Hydrogen generation

Abstract

An apparatus 1 for generating hydrogen includes a housing 10 containing a cylindrical first electrode 11 surrounding a part-conical or frusto-conical second electrode 12. Each of the first and second

Description

TECHNICAL FIELD The present disclosure relates generally to hydrogen generation. In particular, but not exclusively, it relates to an apparatus and a method for generating hydrogen from water for use as an energy source. Aspects of the invention relate to an apparatus for generating hydrogen, a plant for generating hydrogen, and a method of generating hydrogen from water. BACKGROUND It is recognised that the increase in atmospheric carbon dioxide, at least in part, is caused by the use of fossil fuels as an energy source. In order to meet legal obligations on the emission of carbon dioxide it is essential that we reduce our reliance on this type of nonrenewable fuels, which produce pollutants and greenhouse gases when combusted. A promising alternative to the use of fossil fuels is hydrogen fuel. This is because hydrogen is considered to be a clean fuel which, when consumed in a fuel cell or engine, produces only water as a byproduct. Consequently, this makes hydrogen fuel an attractive option for transportation, as well as for producing electricity and thermal energy to power our homes, in addition to many other applications. The most common methods for generating hydrogen include steam-methane reforming and electrolysis. In steam-methane reforming, high temperature steam under pressure is reacted with methane in the presence of a catalyst to produce hydrogen, carbon monoxide, and a small amount of carbon dioxide. In contrast, electrolysis of water splits water into its constituents using an electric current. Therefore, if the electricity used in the process is from a renewable source, then electrolysis of water to produce hydrogen is considered to be a clean and green process, because it does not produce carbon-containing emissions. Several different types of electrolysers for producing hydrogen are known. These include polymer electrolyte membrane (PEM) electrolysers, alkaline electrolysers, and solid oxide electrolysers. There is a need to increase the rate of hydrogen production from the electrolysis of water. There is also a need to reduce the complexity and expense of the components used in electrolysers of the prior art. There is also a need to provide electrolysers which can be used on different water sources, including, but not limited to, potable water, rainwater, and sea water. It is therefore a first non-exclusive object of the invention to provide an apparatus and method for generating hydrogen from water, which is at least one of more efficient, green, universally applicable to many water sources and cost effective. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide an apparatus for generating hydrogen, a plant for generating hydrogen, and a method of generating hydrogen from water, as claimed in the appended claims. According to an aspect of the invention there is provided an apparatus for generating hydrogen, the apparatus comprising a housing containing a first electrode and a second electrode for submersion within water located within the housing, the first electrode surrounding the second electrode, wherein the first electrode is of cylindrical form and the second electrode is of at least part conical or frusto-conical form. The first electrode may be an anode and the second electrode may be a cathode. The housing may be formed of, fabricated from, or comprise, glass. The housing may be formed of, fabricated from, or comprise metal. If the housing is formed of, fabricated from, or comprises metal, the electrodes may be electrically insulated from the housing. A glass body may be provided within the housing. The second electrode may be proximate to, for example may be in physical contact with, a glass body, for example a glass cylinder. It will be appreciated that the second electrode may be conical or frusto-conical, or at least a part of the second electrode may be conical or frusto-conical. In this regard, the walls of the second electrode may taper inwardly from a base portion of the second electrode towards a top portion of the second electrode, the degree of taper may be constant or may vary between the base portion of the second electrode and the top portion of the second electrode. The housing may have a base portion and a top portion. The second electrode may taper outwardly from the base portion of the housing towards the top portion of the housing. That is, such that the top portion of the second electrode is proximate the base portion of the housing and the base portion of the electrode is located towards the top portion of the housing. The glass cylinder may be located between the housing {e.g. the top portion of the housing) and the second electrode {e.g. the base portion of the second electrode). The top portion of the housing may comprise a glass body receiving portion. The glass body may be secured to the top portion of the housing. In embodiments, the water may be fresh or pure or deionised water. Advantageously, the apparatus does not require the use of an electrolyte to generate hydrogen. However, a small amount of electrolyte (up to 1 w / w%) may be utilised to increase the efficiency of the reaction. In alternative embodiments, the water may be rainwater. Rainwater may be easily harvested and may have a generally neutral pH value. In embodiments, the glass may be borosilicate glass and may comprise or be heat tempered glass. Advantageously, the use of a housing fabricated from glass absorbs less, or reflects more, of the generated vibrational energy than housings made of other materials, such as plastics. Therefore, the use of a glass housing may increase the effectiveness of hydrogen production. In embodiments, one or both of the electrodes, e.g. both the anode and / or the cathode, are fabricated from materials that are conductive and resistant to oxidation. In embodiments, the anode comprises or is fabricated from metal. The metal may have a low carbon content. The anode may comprise or be fabricated from stainless steel. One example of a metal for the anode is 316L stainless steel. The anode may be coated with a protective coating. The protective coating may provide corrosion protection. In embodiments, the cathode may comprise or be fabricated from or coated with a metal. The metal may be a noble metal, selected from rhenium, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, copper and gold, preferably selected from copper, silver, gold or platinum. The cathode may be formed of stainless steel and coated with a second metal. The second metal may be provided as a corrosion inhibitor. In embodiments, the anode may comprise or be fabricated from a mesh material. In embodiments, the mesh material may be an unwelded mesh. Such an unwelded mesh may have a grid spacing from 841 pm to 149 pm (20 to 100 US Mesh), preferably from 400 pm to 250 pm (40 to 60 US Mesh). The mesh material may be welded at the base to provide increased structural integrity. It will be understood that the grid spacing of the mesh material may vary depending on the size of the apparatus, and therefore be higher or lower than the above defined ranges in other embodiments. In embodiments, the cathode, may comprise or be fabricated from a solid sheet material into its frusto-conical form. The solid sheet material may be an unperforated sheet material. In embodiments the surface of the cathode may be patterned or textured. The surface of the cathode may be patterned or textured for example by sandblasting. The surface of the cathode may be provided with indentations or fins to increase the surface area of the cathode. Advantageously, the patterned or textured surface of the cathode may increase the surface area for reaction. Advantageously, increasing the surface area for reaction increases the hydrogen production efficiency of the cathode. The anode and the cathode may be retained away from the walls of the housing. The apparatus may comprise leads to connect the anode and cathode to a source of electricity, wherein said leads may extend through the housing. In embodiments, the frusto-conical cathode has a thickness : lower inner diameter: upper inner diameter ratio of 1 : 24 : 48, for example 1 mm : 24 mm : 48 mm. In some embodiments, the cathode may have a length from the top portion to the base portion of the frusto-conical shape. The length may be between 4 to 10cm, e.g. 5 to 7cm, e.g. 5.7cm. In embodiments, the opening of the base portion of the frusto-conical cathode may be from 2 to 10cm in diameter, e.g. 5cm. In embodiments, the top portion of the frusto-conical cathode may be from 1 to 5cm in diameter, e.g. 2.5cm. The uppermost inner diameter of the second electrode may be from 35 to 65 mm, say from 40 to 50 mm, for example 48mm. The lowermost inner diameter of the second electrode may be from 15 to 35, say from 20 to 30 mm, for example 24mm. The thickness of the second electrode may be from 0.5 to 2mm thick, for example 1mm. However, it will be understood that the dimensions of the electrodes are dependent on the mesh size, and it will therefore be understood that a change in mesh size may require a change in electrode size and vice versa. The lowermost part of the second electrode may be fitted with a conductive member, for example a washer, for example a stainless steel washer. The conductive member may be mounted in place by a bolt and nut (or other conductive connection means), e.g. a 6mm threaded bolt and nut. The nut may provide the connection point for the power source. The housing may be defined to have a lowermost portion and an uppermost portion. The distance between the lowermost portion and uppermost portion may be at least three times greater than the height of the first electrode, where the first electrode may be the anode. In embodiments, the housing may have a height from the upper edge to the base, in use. The height of the housing may be at least three times the height of the first electrode. Advantageously, this allows precipitation of any steam residue so that there is less moisture in the gas phase. Furthermore, this height provides for a sufficient sized reservoir to provide for an on-demand store of hydrogen in the apparatus. In embodiments, the housing may be cylindrical or cuboidal (including of rectangular cross section). In embodiments, the housing may comprise an opening for extracting the hydrogen gas. In embodiments, the opening may be circular. The opening may have a maximum transverse dimension, e.g. a diameter, of from 5 mm to 10 mm, e.g. 7.0 mm. In embodiments, the housing may have a thickness. In embodiments, the thickness of the housing may be from 1.0 mm to 5.0 mm, e.g. 3.0 mm. In embodiments, the operating temperature of the apparatus may be from 30°C to 70°C, preferably 40°C to 60°C, preferably still 45°C to 55°C. Advantageously this operating temperature range is optimal for maximum hydrogen gas production. Advantageously, the specific geometry provided by the configuration and shape of the first and second electrodes contained within the housing of the apparatus provides the conditions for more efficient hydrogen generation from water. The combination of the first electrode (the mesh electode) surrounding the frusto-conical shape of the second electrode provides an advantageous acoustical output, leading to more efficient hydrogen generation via sonolysis through the cavitation effect resulting from the ultrasonic vibration production of the electrode arrangement. In embodiments, one or both of the electrodes may be suspended within the housing. In embodiments, one or both of the electrodes may be suspended within and / or secured to the housing. In embodiments, the apparatus may comprise a means to suspend and / or secure one or both electrodes to the housing. In embodiments, the means may be or comprise a bolt. In embodiments, a first bolt may secure the first electrode to the housing. In embodiments, a second bolt may secure the second electrode to the housing. In embodiments, the housing may comprise one or more opening(s) for receiving means to suspend and / or secure the first and / or second electrode to the housing, e.g. using one or more bolts. In embodiments, the opening(s) may be located at the base of the housing, in use. In embodiments, the housing may comprise a first opening for securing the first electrode to the housing. In embodiments, the housing may comprise a second opening for securing the second electrode to the housing. In embodiments, the one or more opening(s) may have a diameter from 0.5 cm to 1.5 cm, e.g. 0.6 cm. In embodiments, the electrodes, e.g. the anode and / or cathode, of the housing may be electrically connected to a source of electricity, wherein the electrical connection is configured to energise the electrodes and thereby generate hydrogen. In embodiments, the electrical connection may be provided by the means to suspend and / or secure one or both electrodes to the housing, e.g. one or more bolts. In some embodiments, AC power may be provided to the apparatus. In some embodiments, DC power may be provided to the apparatus. The apparatus functions using DC but when AC power is supplied, it can be rectified to DC. The apparatus may also be provided with a pulsed DC input, which may increase efficiency of hydrogen production. According to an aspect of the invention there is provided a plant for generating hydrogen, the plant comprising one or more apparatus according to any preceding paragraph. In embodiments, the plant may comprise plural housings wherein each housing contains a first electrode and a second electrode for submersion within water located within the housing, the first electrode surrounding the second electrode, wherein the first electrode is of cylindrical form and the second electrode is of frusto-conical form. In each of the housings, the first electrode may be an anode and the second electrode may be a cathode, and the housing may be fabricated from glass. In embodiments, the plant may further comprise a tank. In embodiments, one or more apparatus may be located within the tank. In embodiments, the tank may comprise means to introduce water into the tank, such as an inlet for receipt of water, e.g. pure or deionised water and / or potable water. In embodiments, the tank may comprise means for extracting hydrogen from the tank, such as an outlet for generated hydrogen. The plant may comprise a source of electrical power and means to connect the anode and cathode of the or each of said one or more apparatus to the source of electrical power. In embodiments, the apparatus may comprise a means for desalinating sea water, e.g. via reverse osmosis or evaporation, to produce fresh or pure or deionised water for use generating hydrogen. In embodiments, the apparatus may comprise a means for irradiating water, with a magnetic field prior to the water, contacting the electrodes. Advantageously, irradiating water with a magnetic field prior to the water contacting the electrodes improves the efficiency of dissociation of the water molecules into hydrogen and oxygen, as less energy is required to overcome the activation energy. In embodiments, the apparatus may alternatively or additionally comprise a means for providing ultrasonic energy to the water located within the housing, e.g. an ultrasonic generator. In embodiments, the means for providing ultrasonic energy may be or comprise an ultrasonic horn, an ultrasonic probe, and / or one or more piezoelectric transducers. However, in some embodiments, a separate means for providing ultrasonic energy may not be required as ultrasonic energy may be generated by energising the electrodes, thereby causing vibrations within one or other of the electrodes to generate ultrasonic vibration. Advantageously, ultrasonic energy provides acoustic vibrations to the water, which may increase the conversion efficiency of water to hydrogen. In particular, the ultrasonic vibrations cause microbubbles to grow and rapidly collapse, causing shock and extremely high bubble temperatures. The energy caused by the cavitation may be sufficient to break the bonds between the hydrogen and oxygen molecules in the water. This increases the rate of reaction. According to an aspect of the invention there is provided a combination of an internal combustion engine and an apparatus as set out above. The internal combustion engine and the apparatus may be in fluid communication. At least a portion of the gaseous output from the apparatus may be fed to the internal combustion engine. According to an aspect of the invention there is provided a method for generating hydrogen from water, which may be, for example fresh or pure or deionised water, the method comprising providing an apparatus according to any of the above paragraphs, submerging the first electrode and the second electrode in water, and connecting the first electrode and second electrode to a source of electricity to generate hydrogen. Therefore, the first electrode and second electrode may be energised in order to generate hydrogen. In embodiments, the method may comprise irradiating water, with a magnetic field prior to the water contacting the electrodes. Advantageously, irradiating water with a magnetic field prior to the water contacting the electrodes improves the efficiency of dissociation of the water molecules into hydrogen and oxygen, as less energy is required to overcome the activation energy. Advantageously, the method does not require the use of an electrolyte to generate hydrogen, although a small amount of electrolyte (e.g. up to 1 w / w%) may be added to the water. The method may comprise one or more of operating the apparatus within a temperature range of 30°C to 70°C, preferably 40°C to 60°C, and more preferably 45°C to 55°C, and ensuring the water is at neutral, or near neutral, pH. In embodiments, the method may be performed at neutral, or near neutral, pH, such as a pH of 6 to 8 (e.g. pH 7). Advantageously, the apparatus is able to produce hydrogen from water without addition of an electrolyte and / or without the use of a catalyst. Advantageously, the apparatus and method according to the invention provide for an increased rate of hydrogen generation, as well as improved efficiency, through sonolysis and optionally through some additional electrolysis. This provides a clean and green process for generating hydrogen. More advantageously, the electrodes may be fabricated from inexpensive materials, e.g. stainless steel, which are more cost effective than other electrode materials that have been previously used. 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. It will be further appreciated that the terms top, bottom, right, left and so on are intended to provide indications of relative spatial positions and are not intended to provide a strict limitation with respect to spatial orientation. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is diagram of an apparatus comprising a housing according to the invention; Figure 2 is an apparatus comprising plural housings according to the invention; Figure 3A is a diagram of a second apparatus according to the invention; Figure 3B is a diagram of the internal components of the second apparatus; Figure 3C is a sectional view of Figure 3B; and Figure 3D provides further details of some of the components of the second apparatus. In the drawings, like parts are denoted by like reference numerals. DETAILED DESCRIPTION Examples of the present disclosure relate to apparatus and methods for generating hydrogen. In particular, examples of the present disclosure relate to an apparatus for generating hydrogen, a plant for generating hydrogen, and a method of generating hydrogen from water. Non-limiting examples will now be described with reference to the accompanying drawings. Referring now to Figure 1, there is shown an apparatus 1 for generating hydrogen, according to the invention. The apparatus 1 comprises a housing 10, a first electrode 11, and a second electrode 12. The apparatus 1 comprises a first electrical connection 13, and a second electrical connection 14. The housing 11 further comprises a first opening 15 and a second opening 16 for receiving the first electrical connection 13 and the second electrical connection 14 respectively. In this embodiment, the first electrode 11 is the anode and the second electrode 12 is the cathode. The first electrical connection 13 is connected to the first electrode 11 and the second electrical connection 14 is connected to the second electrode 12. The first electrode 11 and the second electrode 12 are located within the housing 10. In use, the housing 10 contains water, e.g. fresh or pure or deionised water, and the electrodes 11,12 are submerged within the water. The first and second electrical connection 13, 14 are each provided as a bolt, though other means of connection would be apparent to the skilled person. The bolts 13, 14 enable the first and second electrodes 11, 12 to be suspended within, and secured to, the housing 11 respectively. The first electrode 11 is in cylindrical form and the second electrode 12 is of frusto-conical form. It is shown that the first electrode 11 surrounds the second electrode 12. In other words, the frusto-conical shape of the second electrode 12 is located within the cylindrical form of the first electrode 11. In this embodiment, the first electrode 11 is fabricated from a metal mesh. The metal mesh may be made from stainless steel, e.g. 316L stainless steel. In this embodiment, the second electrode 12 is fabricated from metal. The metal of the second electrode 12 may be a sheet of stainless steel, e.g. 316L stainless steel. The mesh may have a mesh size of 250 pm (60 US mesh size). The housing 10 may be fabricated from glass. In some embodiments, the glass is heat tempered glass and may be Borosilicate glass. When using Borosilicate glass for the housing 10, the composition may comprise 80% silica and 13% boric oxide. Such glass has particularly good resistance to temperature variations. In some embodiments, the glass may have a thickness of between 0.2 mm and 1 mm. The glass housing 10 is an efficient reflector of ultrasonic vibrations which are formed due to the vibration of the mesh (which is formed of unwelded strands). The ultrasonic vibrations causing dissociation of the hydrogen from the oxygen in the water, thereby producing hydrogen in the process. It will be understood that, rather than glass, another material could be used which is efficient in the reflection of ultrasonic vibrations. Therefore, the housing may be formed of any material which efficiently reflects ultrasonic vibrations. In particular the housing may be formed of a material which efficiently reflects vibrations above 20 kHz. In some embodiments, the housing 10 has a height H of 18.5 cm and a diameter D of 7.5 cm, though it will be understood that other sizes of housing may be provided depending on the particular application. In some embodiments, the second electrode 12 has a length L of 5.7 cm. The diameter D1 of the top portion B of the second electrode 12 is 2.5 cm, and the diameter D2 of the base portion O of the second electrode 12 is 5 cm. In this way the second electrode 12 may be conical or frusto-conical, and may have a linearly tapered form or may have a curved or varied taper form, for example in the shape of a trumpet cone. In some embodiments the angle of taper is between 10 degrees and 45 degrees measured from an axis of the second electrode 12 running parallel to the central axis of the second electrode, the central axis of the second electrode 12 being an axis through, and perpendicular to, the base portion of the second electrode 12 and the top portion of the second electrode 12. The openings 15, 16 may each have a diameter of 0.6 cm. In use, the housing 10 is filled with water, e.g. fresh or pure or deionised water. The first electrical connection 13 and second electrical connection 14 are connected to a source of electricity to energise the electrodes 11, 12. The water, is split to produce hydrogen gas (not shown), primarily by the energy caused by cavitation and secondarily by electrochemical splitting. Advantageously, the use of fresh or pure or deionised water means that an electrolyte is not required for the generation of hydrogen. More advantageously, the specific geometry provided by the configuration and shape of the first and second electrodes contained within the housing of the apparatus provides the conditions for more efficient hydrogen generation from water. The combination of the first, e.g. mesh, electrode surrounding the frusto-conical shape of the second electrode means that when the electrodes are energised, ultrasonic vibrations may be generated. This causes microbubbles to grow and rapidly collapse, causing shock and extremely high bubble temperatures. The energy caused by the cavitation breaks the bonds between the hydrogen and oxygen molecules in the water to produce hydrogen gas. Referring now to Figure 2, there is shown an apparatus 2 in the form of a plant 2 according to a second embodiment of the invention. The plant 2 comprises a tank 21, a water inlet 22, and a hydrogen gas outlet 23. In this embodiment, plural housings 10 are located within the tank 21. Each housing 10 contains a first electrode 11, a second electrode 12, a first electrical connection 13, and a second electrical connection 14, according to the housing 10 of the apparatus 1 shown in Figure 1. In this embodiment, the first electrode 11 is the anode and the second electrode 12 is the cathode. In the plant 2, eight housings 10 are shown, but more or less housings 10 may be present. In use, water, e.g. fresh or pure or deionised water, is supplied to the tank 21 via the water inlet 22. The first electrical connection 13 and second electrical connection 14 of each housing 10 are connected to a source of electricity to energise the electrodes 11, 12. The electrochemical splitting of the water occurs to produce hydrogen gas (not shown). The hydrogen is removed from the apparatus 2 via the hydrogen outlet 23. The hydrogen may be piped to a scrubber (not shown) to remove contaminants. Referring now to Figure 3A, there is shown a diagram of a second apparatus 3 according to a third embodiment of the invention. The apparatus 3 comprises a tank 30 with a lid 31 and a base 32. The tank 30, including the lid 31 and the base 32, are fabricated from stainless steel. In a non-limiting example embodiment, the tank 30 has a height H of 24 cm extending between the base 32 and the lid 31. The lid 31 has a length L of 36 cm and a width W of 18 cm. The base 32 has a length L’ of 30 cm and a width W which is less than the width W of the lid 31. It will be understood that other sizes of tank may be provided depending on the particular application. In some embodiments a plurality of apertures A may be provided which extend through the lid 31. The apertures A are positioned around the periphery of the lid, overhanging the tank 30. Three threaded bolts TB extend through the lid 31 into the tank 30. Referring now to Figure 3B, there is shown a diagram of some of the internal components of the second apparatus 3. Like components are denotated by the same references as in Figure 3A. Each threaded bolt TB extending through the lid 31 of the tank 30, secures an internally-threaded circular lid 33 to the internal surface of the lid 31 ( / .e. the surface facing the base 32). The lids 33 may also be secured in place by a layer of silicon adhesive between the base of each lid 33 and the internal surface of the lid 31 of the tank 30. Positioned directly opposite each lid 33 and bolted to the base of the tank 32 are three electrodes 112. The electrodes 112 are of conical form. In this embodiment, these three electrodes 112 are cathodes. Figure 3C, shows a sectional view of Figure 3B with more of the internal components of the second apparatus 3 shown. Figure 3D shows details of some of the components of the second apparatus. Referring to Figures 3C and 3D, the second apparatus 3 comprises three first electrodes 111 of cylindrical form. Each of the first electrodes 111 surround one of the conical electrodes 112, to form three working electrode pairs, positioned within the tank 30. In this embodiment, each first electrode 111 is an anode and each second electrode 112 is a cathode. Each individual electrode is electrically connected to an electrical connection (not shown) which extend through openings in the tank 30. These electrical connections are provided via bolts, such as stainless steel bolts, which extend through the base 32 of the tank 30, allowing the first 111 and second electrodes 112 to be suspended within, and secured to, the tank 30 respectively. In use, the tank 30 contains water e.g. fresh or pure or deionised water and the electrodes 111, 112 are submerged within the water. This water is introduced into the tank 30 via an inlet (not shown). The first electrodes 111 are in cylindrical form and the second electrodes 112 are in frusto-conical form. It is shown that a first electrode 111 surrounds each of the second electrodes 112. In other words, the frusto-conical shape of each of the second electrodes 112 is located within the cylindrical form of one of the first electrodes 111. In some embodiments, a glass cylinder 35 is received in each of the circular threaded lids 33, secured to the tank lid 31. Each glass cylinder 35 partially surrounds each of the second electrodes 112, and is partially surrounded by one of the first electrodes 111, such that the distance between the lid 33 and the top of the second electrode 112 is 18 cm. In some embodiments, the glass is heat tempered glass. In some embodiments, each glass cylinder 35 may be proximate to a respective second electrode 112. The glass cylinders 35 and respective second electrodes 112 may be separated from each other through a rubber or other non-conductive component or material. In this embodiment, the first electrodes 111 are fabricated from a mesh made from stainless steel, e.g. 216L stainless steel. In this embodiment, the second electrodes 112 are fabricated from a sheet of stainless steel, e.g. 316L stainless steel. The mesh may have a mesh size of 250 pm (60 US mesh size). In some embodiments, the first electrodes 111 have a length L1 of 7 cm. The second electrodes 112 have a length L2 of 5.7 cm. The diameter D1’ of the top portion B’ of the second electrodes 112 is 2.5 cm, and the diameter D2’ of the base portion O’ of the second electrodes 112 is 5 cm. The openings in the stainless steel bolts which extend through the base of the 32 of the tank 30 each have a diameter of 0.6 cm. It will be understood that other sizes of electrodes and openings in the bolts may be provided depending on the particular application. The above described electrode configuration together with a DC energy source induces a simultaneous phenomenon of cavitation and ultrasound beginning at the anode. The effect is then amplified at the cathode which results in hydrogen extraction being enhanced at the cathode. The output from the apparatus 10, also known as reactors, of the invention ( / .e. the generated gas) can be added to an internal combustion engine. The gaseous output of the reactor can be used to reduce fuel consumption of an internal combustion engine (ICE). Advantageously the gas can be added to the engine without further treatment. Advantageously, the apparatus and method according to the invention provide for an increased rate of hydrogen generation by the use of sonolysis over purely electrolysis driven hydrogen generation, as well as improved efficiency. This provides a clean and green process for generating hydrogen. More advantageously, the electrodes may be fabricated from inexpensive materials, e.g. stainless steel, which are more cost effective than other electrode materials that have been used in the prior art. Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not particular emphasis 5 has been placed thereon.

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