METHOD AND APPARATUS FOR PRODUCING HYDROGEN FROM WATER

Abstract

A method of producing hydrogen comprises electrolysing water to produce a mixture of hydrogen and oxygen gases. passing the mixture into a chamber containing a hydrogen storage medium to store the hydrogen by adsorption therein, venting the oxygen from the chamber, and subsequently treating the hydrogen storage medium to release the hydrogen stored therein. Apparatus for producing hydrogen from water comprises an electrolyser unit (1, 2) having mounted thereon a chamber (5) in communication with a gas outlet (3) from the electrolyser. the chamber containing a hydrogen storage medium (4) and being provided with means (8) for venting oxygen from the chamber.

Claims

1. A method of producing hydrogen, comprising: electrolysing water to produce a mixture of hydrogen and oxygen gases; and separating the hydrogen from the oxygen, wherein the separation stage comprises passing the mixture into a chamber containing a hydrogen storage medium whereby to separate the hydrogen by adsorption into the storage medium; venting the oxygen from the chamber; and subsequently treating the hydrogen storage medium to release the hydrogen stored therein.

2. The method according to claim 1, further comprising electrolysing water using a membrane free electrolyser.

3. The method according to claim, further comprising storing the vented oxygen for use.

4. The method according to claim 1, further comprising using a metal hydride as the hydrogen storage medium.

5. The method according to claim 1, wherein the chamber is in the form of a detachable cartridge.

6. The method according to claim 1, further comprising heating the hydrogen storage medium to release the hydrogen.

7. The method according to claim 1, further comprising exposing the hydrogen storage medium to light to release the hydrogen.

8. An apparatus for producing hydrogen from water, comprising an electrolyser unit having mounted thereon a chamber in communication with a gas outlet from the electrolyser, the chamber containing a hydrogen storage medium and being provided with means for venting oxygen from the chamber.

9. The apparatus according to claim 8, wherein the chamber is connected to the gas outlet of the electrolyser via a releasable coupling.

10. The apparatus according to claim 8, wherein the electrolyser is a membrane free electrolyser.

11. The apparatus according to claim 8, wherein the vented oxygen is stored for use.

12. The apparatus according to claim 8, wherein the chamber contains a metal hydride as the hydrogen storage medium.

13. The apparatus according to claim 8, wherein the chamber is in the form of a detachable cartridge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In the drawings, which illustrate an exemplary embodiment of the invention:

[0026] FIG. 1 is a diagrammatic view representing apparatus for the production of hydrogen from water according to an embodiment of the invention; and

[0027] FIG. 2 is a diagram illustrating the use of the apparatus in the fuelling of a hydrogen-powered vehicle.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

[0028] Referring to FIG. 1, a water electrolyser system for the provision of pure hydrogen and oxygen gases comprises an electrolyte reservoir/separating cylinder 2, a reactor stack 1 in which the water is decomposed into its component parts of hydrogen and oxygen gases, a heat rejection system 7 which maintains the temperature of the electrolyte, a water replenishment system, an electrolyte recirculation pump 6, an electrolyte monitoring and maintenance system, a fluid control system, a one way pressure-actuated non-return valve 3, a metal hydride or other adsorption medium filter purifier 4 in a pressure capable vessel 5, oxygen vent valve 8, hydrogen vent valve 9 and a control system.

[0029] The reactor stack 1 and associated electrolyte circulation 6 and cooling (heat rejection) system 7 are generally as disclosed in WO 2014/170337 A1 and will therefore not be described in detail here. In a typical stack of this design, electrolyte (e.g. KOH) concentrations can vary widely from a low of 0.5% to a high of 30% (w/w). However, in order to reduce reactivity and the potential for personal and environmental damage, a concentration of around 2% is preferred.

[0030] There are numerous metal hydrides (e.g. nickel metal hydrides, lithium hydride, and lithium 6 deuteride) and compounds (e.g. lithium aluminium hydride, ammonia borane and sodium borohydride) which have strong hydrogen adsorption capacities. These may be produced in bead or granular form, deposited as a thin coating on film substrates or housed in lattices within appropriately-designed, typically cylindrical, vessels. Other materials capable of adsorbing and releasing hydrogen selectively are currently under development, for example based on carbon nano-tubes or graphene.

[0031] Venting the oxygen may be done in batch releases on attainment of pressures in excess of those required for hydrogen adsorption, with a substantial release at reduced pressure at the end of each charge cycle to eliminate the last of the oxygen.

[0032] In the embodiment shown in FIG. 2, the reactor stack 20 is a membrane-free electrolytic cell arrangement supplied with electricity from, for example, photovoltaic panels and with aqueous electrolyte by a pump 21. The stack produces a mixed-gas stream of hydrogen and oxygen, the gases being separated from excess electrolyte in a separator 22, from which the electrolyte is returned to the reactor 20 via an electrolyte line 23 by the pump 21. The mixed gases pass through a heat exchanger 24 to maintain the elevated temperature of the electrolyte, and then into a gas dryer 25. The gas dryer 25 may comprise a pre-drying stage and then a desiccant stage. The pre-drying stage, whose purpose is to reduce the workload on the desiccant stage, suitably consists of one or more of: a cooled water cylinder through which the moist gas is bubbled; a vortex generator where differential masses are separated out by velocity; and a dash-pot in which different diameters are used to create different velocities.

[0033] A mixed gas supply line 26 can direct the output of the gas dryer 25 to a hydride separation and storage tank installed in a vehicle 27. The separation and storage tank 27 is essentially a pressure capable vessel as described with reference to FIG. 1, containing a metal hydride or other adsorption medium filter purifier, and having an oxygen vent valve which vents oxygen to the atmosphere. Alternative configurations may be employed in which the oxygen is captured for storage and subsequent use.

[0034] The separation and storage tank may be configured to apply heat to the storage medium to release hydrogen from it for use in the drive system of the vehicle, for example a fuel cell providing electricity to an electric drive motor.