DEVICE FOR THE PRODUCTION OF HYDROGEN

Abstract

This invention relates to a device for the electrolytic production of hydrogen and oxygen from a water-containing liquid, the device comprising: an anodic half-cell (3) and a cathodic half-cell (4), with an anion exchange membrane (9) situated between the two half-cells. The electrodes (7, 8) of the half-cells (3, 4) and the anion exchange membrane (9) form a membrane/electrode assembly (MEA). There is also provided means (2) for feeding the water-containing liquid to only one of the anodic half-cell (3) and the cathodic half-cell (4), wherein the electrode in the other, substantially dry, half-cell is ionomer-free and/or binder-free.

Claims

1. A device for the electrolytic production of hydrogen and oxygen from a water-containing liquid, the device comprising: an anodic half-cell which includes an anodic electrode, and a cathodic half-cell which includes a cathodic electrode, an anion exchange membrane (AEM) situated between the two half-cells, wherein: the anodic electrode, the cathodic electrode, and the anion exchange membrane form an MEA, means for feeding the water-containing liquid to only one of the anodic half-cell and the cathodic half-cell are provided, wherein: at least the electrode in the other, substantially dry, half-cell is ionomer-free and/or binder-free.

2. A device as claimed in claim 1 wherein during use the water-containing liquid has a pH of 7 or higher.

3. A device as claimed in claim 1 wherein during use the water-containing liquid has a pH between 12 and 14.

4. A device as claimed in claim 1 wherein the water containing liquid also comprises between 0.1% and 10% KOH.

5. A device as claimed in claim 1 wherein the temperature of the system is in the range of 40° C. to 80° C.

6. A device as claimed in claim 1 wherein the electrodes are connected to a power supply which is a source of renewable energy.

7. A device as claimed in claim 1 wherein the MEA is stabilised by one or more of: crosslinking of the polymeric backbone, spacer or ion-exchange groups of the membrane, improving the intermolecular binding forces between the polymer and the catalyst, a thicker membrane, or a combination of any of the above.

8. A device as claimed in claim 1 wherein the device is adapted to produce hydrogen at elevated pressures above 1 bar.

9. A device as claimed in claim 1 wherein any of the anodic, or cathodic electrodes is: A catalyst coated membrane, A catalyst coated substrate, or A direct membrane deposition.

10. A device as claimed in claim 9 wherein the catalyst coated substrate may be any one of: Carbon based cloth Carbon based paper Carbon based felt Stainless steel foam, and Nickel based foam.

11. A device as claimed in claim 1 wherein at least one catalyst is made of platinum group free metals.

12. A device as claimed in claim 1 wherein a catalyst at the anode, for oxygen evolution reaction, includes non-stoichiometric transition metal oxides.

13. A device as claimed in claim 1 wherein a catalyst at the cathode, for hydrogen evolution reaction, includes: chalcogenides, pnictogenides, transition metal sulphides, transition metal phosphides, transition metals dispersed in an electrically conductive substrate, or other non-stoichiometric transition metal oxides having spinel or perovskitic structures or transition metal complexes.

14. A device as claimed in claim 1 wherein the AEM is formed of a polymer backbone coupled with a functional group suitable for transporting anions, the polymer being any one of: polystyrene, polysulfone, polybenzimidazole, polyphenylene oxide, styrene-butadiene block copolymer, polyethylene.

15. A device as claimed in claim 14 wherein there is a spacer between the polymer backbone and functional group.

16. A device as claimed in claim 1 wherein the functional group can be any one or more of: ammonium, sulfonium or phosphonium salts.

Description

[0038] To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

[0039] FIG. 1A shows an AEM system with a dry cathode; and

[0040] FIG. 1E3 shows an AEM system with a dry anode.

[0041] FIG. 1A and FIG. 1E3 pertain to embodiments of the invention utilising AEM. FIG. 1A shows an embodiment of the present invention wherein the substantially aqueous solution is introduced on the anode side. Typical operation of this embodiment is described herein.

[0042] In FIG. 1A an electrolyser cell 1a can be seen, the cell comprising an anodic half-cell 3 and a cathodic half-cell 4 as well as an MEA 10. There is an inlet 2 for introducing an aqueous solution to the anodic half-cell. This may be a dilute aqueous solution of KOH, but it is envisaged that alternative alkaline salts can be used, or, potentially, pure water. The means for supplying power to the cell are well known, and as such are not shown; this is the case for all embodiments.

[0043] The MEA 10 comprises the anodic electrode (or anode) 7, the cathodic electrode (or cathode) 8 and the anion exchange membrane 9. In this embodiment of the invention, as the inlet 2 is to the compartment containing the anodic half-cell 3, it is the cathode 8 which is ionomer and/or binder free.

[0044] The oxygen generated on the anode side of the cell leaves the cell by outlet 5. Whilst the oxygen may be processed for use elsewhere, normally it is vented. The hydrogen produced at the cathode leaves the cell via outlet 6. The hydrogen stream may comprise trace amounts of water as a result of osmotic drag, so this stream may be passed through a drier prior to compression for storage. In the embodiment with a dry cathode, altering the current density will impact the purity of the hydrogen produced. Increasing the current density increases the rate of hydrogen production, meaning less water is present at the cathode. Water is further removed from the cathode due to the migration of hydroxyl ions back to the anode, simultaneously bringing solvated water by electroosmotic drag.

[0045] The reaction in each half-cell is as follows:

Anode:4OH.sup.−.fwdarw.2H.sub.2O+4e.sup.−+O.sub.2

Cathode:4H.sub.2O+4e.sup.−.fwdarw.2H.sub.2+4OH.sup.−

[0046] The hydrogen produced is substantially dry due to the fact that there is no electrolyte/water on the cathode side. It is acknowledged that some water may cross the membrane due to osmotic drag, however this is understood to be minimal, and is not considered to render the cathode not dry.

[0047] Now referring to FIG. 1B, it can be seen that the embodiment of FIG. 1B largely resembles that of FIG. 1A. The difference is that the inlet 2 is to the compartment containing the cathodic half-cell 4 as opposed to the anodic half-cell 3. The reaction in each half-cell is the same as above. It can be seen that water is consumed at the cathode 8, so this embodiment is therefore not limited by the movement of water from the anode 7 to the cathode 8. However, this mode of operation results in moist hydrogen being generated whereas dry hydrogen is generally preferred. As such, a drier (not shown) would be used to purify the hydrogen. Such a stage would normally be done before compression of the produced hydrogen (not shown).

[0048] In FIG. 1A, as the cathode 8 is dry and at least the cathode 8 is ionomer and/or binder free. In FIG. 1B as the anode 7 is dry at least the anode 7 is ionomer and/or binder free.

[0049] In the preferred embodiment, both the anode and cathode are ionomer and/or binder free. This meaning that there is no ionomer in the anode, or cathode and/or there is no binder in the anode, or cathode, or a combination thereof.

[0050] The present invention is not intended to be limited to any particular membrane beyond being an AEM. Any membrane exhibiting the required characteristics may be used, that being one which allows for the transport of ions from one half-cell to the other.

[0051] Furthermore, both the functionalised group and the polymeric backbone are not intended to be limited to any named example, and any suitable polymer backbone comprising any ion exchange group may be used, or any inorganic or organic fillers or acting as a reinforcement to be added to its composition.

[0052] The present invention is not intended to be limited to the catalysts used. Any suitable catalyst or membrane may be used as long as the appropriate characteristics are displayed.

[0053] Additionally, the construction and or composition of the MEA may be varied to enable the utilisation of de-ionised water or another solution with a substantially neutral pH. Buffer solutions may also be used. In either case, the adaptations are not intended to extend beyond the scope of the invention.