The present invention relates to an apparatus for generating hydrogen gas for use inter alia in powering an internal combustion engine or a fuel cell.

With the development of fuel cell technology there has grown a need to develop methods of economically and efficiently delivering the hydrogen gas fuel on which they rely. One method of achieving this is to use a storage vessel in which the gas is stored under pressure. However such vessels tend to be large and heavy making them unsuitable for many duties; especially those in which the power source needs to be easily moveable or energy efficiency is a principal concern. In addition, complications can arise when the vessels themselves need to be refilled as a consequence of a need to manipulate this highly inflammable gas at high pressure.

As an alternative, solid hydride fuels which release hydrogen gas on heating have been proposed. Examples of such materials include the Group IA and MA metal hydrides and borohydrides and boranes and adducts thereof. On account of its atmospheric stability and the amount of hydrogen gas it is able to release per unit mass one material which has shown considerable promise is ammonia borane. Recently in our patent application WO 2014/096866 we have disclosed improved solid hydride fuels based on this approach comprising mixtures of ammonia borane and a polyethylene oxide which, on heating, release hydrogen gas without the detrimental foaming encountered with pure ammonia borane. This problem has in the past proven to be a significant obstacle to using ammonia borane on a commercial scale.

Various designs for a hydrogen generation apparatus employing a hydride fuel have been proposed in the art. For example, US 7267148 and 7682411 disclose designs based on a static array of small pellets each of which comprise the hydride fuel and a second exothermic initiation material which is used to heat the fuel indirectly. Once the hydrogen release reaction has begun its own exothermic nature sustains further gas release. In these designs, heat release from the exothermic material is typically initiated by an electrical heater embedded in the pellets or incorporated into a platform on which they are mounted. In an alternative approach, US 8137627 teaches the use of a static arrangement of hydride fuel sticks comprised of ammonia borane each of which can be caused to release its hydrogen in turn by means of an electrical controller. However all these designs suffer from the disadvantage that it is difficult to manage the heat produced in the hydrogen generator as a consequence of the exothermic nature of the chemical reactions used to generate the hydrogen gas. This means that there is a considerable risk that multiple pellets or fuel sticks will be caused to release hydrogen gas at the same time leading to a run-away situation. Furthermore, in these designs replacing the pellets and fuel sticks when they are spent is not easy; especially where the fuel cell is being used in a remote location far from specialist equipment.

In a recent co-pending application we have taught the use of elongate cartridges containing hydride fuel as an alternative to fuel sticks. Typically such hydride fuels are metal hydrides or boranes; for example ammonia borane and those mixtures disclosed in WO 2014/096866. Such cartridges have the advantage that evolution of hydrogen gas therefrom can be achieved by a heating method characterised by the steps of (1) directly heating the fuel at one or more location(s) along the major axis of the cartridge to cause hydrogen gas to be evolved at the location(s); (2) causing hydrogen gas evolved at the location(s) to flow along the axis towards the exit-point and (3) causing a heat front generated at the location(s) to propagate along the axis of the cartridge to heat any remaining fuel indirectly. By containing the hydride fuel the cartridges are also easily replaceable.

We have now developed a hydrogen generator suitable for use with these cartridges which overcomes the various problems mentioned above. Thus, according to the present invention there is provided a hydrogen generator characterised by comprising:

• a magazine (1) adapted to store a plurality of hydride fuel cartridges (2);

• a hydrogen-releasing location (3) adapted to receive the hydride fuel cartridges at which the cartridge is supported and hydrogen can be released;

· a transmission means (4), (5), (6) for moving unused hydride fuel cartridges to the hydrogen- releasing location;

• a cartridge sealing means for forming a hydrogen gas-tight seal between the hydride fuel cartridge and hydrogen gas-handling pipework (11) and

• an ejection means for removing the spent hydride fuel cartridges from the hydrogen releasing location (5), (8) (19) and (20).

The hydrogen generator and its various embodiments will now be described with reference to the attached Figures in which:

Figure 1 is an outline view of a hydrogen generator according to the invention;

Figure 2 is a transverse section across the magazine 1;

Figure 3 is a longitudinal section of the generator and

Figure 4 is an expanded view of part of Figure 3.

The magazine 1 employed as part of the hydrogen generator is one which is adapted to hold both unused and spent hydride fuel cartridges. In one embodiment therefore the magazine comprises first and second chambers for respectively storing them. In a preferred form of this embodiment, the first chamber comprises a hopper which enables each unused fuel cartridge to be fed to the transmission means; for example either mechanically or under the influence of gravity. In another embodiment, where the fuel cartridges are generally elongate cylinders containing the hydride fuel or sticks thereof, this hopper is adapted to deliver them so that the major axis of each cartridge is aligned with the direction in which the transmission means works.

Turning to the transmission means, its function is to allow fresh fuel cartridges to be delivered to the hydrogen-release location in a sequential fashion. In one embodiment, this sequential delivery is achieved by the transmission means comprising a moveable belt, bandolier or carousel arrangement into which the cartridges (fresh and/or spent) can be introduced and/or stored. In another embodiment, the transmission means includes a rotor 5 comprising a block, for example an aluminium block, provided with an arrangement of longitudinal cavities which are a snug-fit for the cartridges. In all these embodiments, the transmission means may be moveable relative to the hydrogen-release location and/or to the magazine. In one preferred embodiment, the rotor is moveable about an axis or shaft relative to both the magazine and hydrogen-release location whose positions are fixed. Where the rotor comprises a cylindrical block it is preferred that the cavities are arranged radially about the axis of rotation and/or that the transmission means is further provided with a means for rotating the rotor stepwise about an axis or shaft so that cartridges can be introduced and ejected one-at-a-time from the cavities into the hydrogen- release location or vice versa.

In one embodiment, the transmission means and/or the ejection means may further include a ram-like arrangement, e.g. a piston, which can be actuated, for example, hydraulically or electromagnetically, to introduce the cartridges into the transmission means 4. Suitably, such arrangements further comprise a bias (e.g. a spring 19) so that the piston can return automatically to their un-actuated position(s) once they have acted upon the cartridge. In an embodiment of the invention, the ejection means operates in two steps; a first step to remove the spent cartridge from the hydrogen release location back to the rotor means or to another intermediate position 9 where it is allowed to cool and a second step where the cooled spent cartridge is returned to the magazine; for example by employing a second transmission means. These two steps can be performed either by the same ram or separate ones if so desired. In a preferred embodiment the spent cartridge is allowed to cool under conditions where the absolute or partial pressure of hydrogen gas is lower than that of the hydrogen gas being emitted at the hydrogen-release location. As regards the hydrogen-release location, this suitably comprises in one embodiment a hollow tubular furnace into which the hydride fuel cartridge 10 is inserted, an outlet 11 for removing the hydrogen gas from the hydrogen generator and delivering it to a fuel cell via gas handling pipework and optionally an intermediate buffer vessel. The cartridge within the hydrogen-release location is suitably heated, for example by electrically heating an element 12 arranged within or on the outside of the furnace and may consist of conductive or inductive heating.

Whilst the hydrogen gas released from the hydride fuel cartridge can be allowed to fill the whole of the generator and allowed to escape naturally from the outlet as a consequence of a pressure gradient, suitably the generator includes a means of forming a hydrogen gas-tight seal between the cartridge and the hydrogen gas handling pipework 11. In one embodiment thereof, the hydride fuel cartridge therefore includes a cartridge sealing means forming a gas-tight seal at or inside the hydrogen-release location. For example, the transmission means may act to push the cartridge against the sealing means enabling the hydrogen gas to flow directly to the outlet, preventing or limiting the escape of hydrogen gas from the system. In one embodiment, this sealing means comprises an O-ring 7 on, in or adjacent the cartridge and an outlet with a corresponding seat 18 at the hydrogen release location, or vice-versa. In another embodiment, the sealing means comprises two or more seals (e.g. O rings) between the cartridge on the one hand and the hydrogen-release location on the other so that when hydrogen gas is released it passes through one or more orifices in the cartridge, positioned between the seals. In yet another embodiment, the cartridge sealing means comprises an O-ring and seating arrangement which are protected from condensate contamination by actively or passively heating the seal and/ or seating or by intentionally cooling the gas flow elsewhere to encourage condensation at an alternative location which is less sensitive to condensate contamination.

Many of these embodiments have the advantages that the hydrogen gas is confined to a smaller volume thereby saving weight and space; the other parts of the hydrogen generator are prevented from becoming contaminated with any impurities which may be released by the hydride fuel, and the other parts of the hydrogen generator are kept separate from the hydrogen gas. It is particularly advantageous to be able to keep the hydrogen-release location's associated electrical components (not shown in the Figures) separate from the hydrogen gas in order to improve the safety of the system. Where the hydride fuel cartridge has no internal filtration, or filtration in the cartridge is not sufficiently effective, compounds may condense upon the seal or surfaces in the locality of the cartridge sealing means. These compounds may cause damage to the seal or to seals on subsequent cartridges. Methods to ensure adequate sealing on a repetitive basis may include, for example, heating the areas in which sealing is required by active or passive means or cooling areas away from the seal to encourage condensation away from the seal. Mechanical methods 13 for shielding the seal 7 and sealing surfaces from direct gas flow may also be used to preserve sealing functionality.

In one embodiment, the hydrogen-release location bears upon the hydride fuel cartridge walls 15, allowing the former to withstand pressures elevated above the surroundings. This has the advantage that the hydride fuel cartridge need not be pressure resistant and so may be constructed from a lightweight and/or low-cost material, thereby allowing the construction of cheaper, lighter cartridges with higher hydrogen content per unit weight. Another advantage is that there need only be one area of the hydrogen generator system (the hydrogen-release location) that has to be capable of withstanding elevated pressures (if elevated pressures are required or desired). Also, the more cartridges that can be loaded into the magazine(s), the more weight can be saved with a single generator.

As regards the hydride fuel cartridges for use in the hydrogen generator of the present invention, these can in principle take any shape or form including for example, spherical, cubic, cuboid or any other regular geometric shape. However, in one preferred embodiment, the cartridges comprise an elongate tubular sheath, fabricated, for example, from a tube of a high- temperature engineering polymer such as PEEK. These sheaths then contain one or more hydride fuels such as those metal hydrides, metal borohydrides or boranes described above in solid form 16 (e.g. powder, pellets or a stick). Preferably, the sheath is made from a material or materials having a softening or melting point substantially higher than the temperature at which most of the hydrogen gas is released from the fuel, for example a polyketone, a polyether hydrocarbyl ketone, a polysulfone, or a polyimide. The sheath itself can be manufactured using any conventional technique including inter alia machining, injection moulding, drawing and spiral- winding. Thereafter end caps 17 can, if required, be attached to the sheath by gluing, welding or the use of pressure-tight fittings. In one preferred embodiment, the hydride fuel comprises ammonia borane; for example a mixture of ammonia and a polyethylene oxide having a molecular weight in the range 1 to 9 M Da; see, for example, WO 2014/096866 the subject-matter of which is incorporated herein by reference. Suitably, the hydride fuel cartridges are additionally provided with an outlet and optionally a filter, included near its outlet end, to capture any small particles of fuel and chemical by-products liberated during the hydrogen-release reaction. Alternatively, if filtration is required it can be located in the hot cell at or within the gas-handling pipework. The hydride fuel cartridges may also include thermal breaks within them (e.g. zones along the major axis of the cartridge which are fuel-free) and/or heat conducting or insulating elements contained therein or arranged around the outside. The hydride fuel cartridges may also contain an exothermic chemical initiator mixed with the hydride if so desired and/or an initiator material which heats the fuel when excited by electromagnetic induction.

The hydrogen generators of the present invention are especially suitable for use in applications where a portable source of hydrogen gas is required. Such applications include, inter alia, transportation power sources such as internal combustion engines and fuel cells. Thus in an embodiment of the invention there is provided a power source comprising at least one hydrogen generator of the type described above and at least one fuel cell or internal combustion engine. Such power sources are especially useful where weight is a premium and are therefore applicable in vehicles (e.g. automobiles, trucks etc.), trains, aircraft, spacecraft and boats; as well as in association with portable devices consuming electrical power such as laptop computers, tablets, mobile phones and the like.