CATALYST COATED MEMBRANES FOR WATER ELECTROLYSERS

1 . A catalyst coated membrane for a water electrolyser, the catalyst coated membrane comprising:

an ionomer membrane having a first surface and a second surface;

an anode catalyst layer on the first surface of the ionomer membrane; and

a cathode catalyst layer on the second surface of the ionomer membrane,

wherein the ionomer membrane comprises reinforcement material, and

wherein the reinforcement material is distributed asymmetrically relative to a central plane of the ionomer membrane such that its average location is closer to the anode catalyst layer than the cathode catalyst layer.

2 . The catalyst coated membrane according claim 1 , wherein the ionomer membrane is a multilayer structure formed by: at least 3 ionomer layers and wherein at least one of the ionomer layers comprise a reinforcement material in addition to the ionomer.

3 . The catalyst coated membrane according to claim 2 , wherein only one of the ionomer layers comprises reinforcement material and said layer is closer to the anode catalyst layer than the cathode catalyst layer.

4 . The catalyst coated membrane according to claim 2 , wherein two of the ionomer layers comprise reinforcement material and a mid-point between the two ionomer layers is closer to the anode catalyst layer than the cathode catalyst layer.

5 . The catalyst coated membrane according to claim 1 , wherein the reinforcement material comprises a porous polymer layer which is impregnated with ionomer.

6 . The catalyst coated membrane according to claim 1 , wherein the ionomer membrane further comprises a radical reducing additive.

7 . The catalyst coated membrane according to claim 1 , wherein the anode catalyst layer comprises an iridium containing catalyst material.

8 . The catalyst coated membrane according to claim 1 , wherein the cathode catalyst layer comprises a platinum-on-carbon catalyst material.

9 . The catalyst coated membrane according to claim 1 , wherein one or both of the anode catalyst layer and the cathode catalyst layer comprise both catalyst material and ionomer material.

10 . The catalyst coated membrane according to claim 9 , wherein the ionomer in one or both of the anode catalyst layer and the cathode catalyst layer is different to the ionomer in the ionomer membrane.

11 . The catalyst coated membrane according to claim 1 , wherein the first surface of the ionomer membrane has fewer defects than the second surface of the ionomer membrane.

12 . The catalyst coated membrane according to claim 1 , wherein the anode catalyst layer comprises an iridium containing catalyst material disposed in ionomer, and wherein the ionomer in the anode catalyst layer differs from the ionomer in the membrane in that it has longer side chains than the membrane ionomer.

13 . The catalyst coated membrane according to claim 1 , wherein the anode catalyst layer comprises an iridium containing catalyst material disposed in ionomer, and wherein the ionomer in the anode catalyst layer has an equivalent weight of: no less than 900EW.

14 . The catalyst coated membrane according to claim 1 , wherein the membrane ionomer has an equivalent weight greater than 750EW and less than 850EW.

15 . The catalyst coated membrane according to claim 1 , wherein the cathode catalyst layer comprises a platinum-on-carbon catalyst material disposed in ionomer, and wherein the cathode catalyst layer has a platinum loading, provided by the platinum-on-carbon catalyst material, of less than 0.5 mg Pt cm −2 and more than 0.01 mg Pt cm −2 .

16 . The catalyst coated membrane according to claim 1 , wherein the cathode catalyst layer comprises a platinum-on-carbon catalyst material disposed in ionomer and the cathode catalyst layer has an ionomer/carbon weight ratio of between 0.6 and 1.0.

17 . A method of manufacturing the catalyst coated membrane for a water electrolyser according to claim 1 , the method comprising:

forming an ionomer membrane having a first surface and a second surface, the ionomer membrane comprising reinforcement material;

forming an anode catalyst layer on the first surface of the ionomer membrane; and

forming a cathode catalyst layer on the second surface of the ionomer membrane,

wherein the reinforcement material is distributed asymmetrically relative to a central plane of the ionomer membrane such that its average location is closer to the anode catalyst layer than the cathode catalyst layer.

18 . The method according to claim 17 , wherein the ionomer membrane is formed by depositing a dispersion of ionomer in liquid carrier onto a solid backing layer and at least partially drying to form a first ionomer layer;

depositing a dispersion of ionomer in liquid carrier onto the first ionomer layer and at least partially drying to form a second ionomer layer over the first ionomer layer; and

optionally sequentially depositing and drying one or more further layers of ionomer over the first and second ionomer layers to build up the ionomer membrane structure on the solid backing layer,

wherein at least one of the ionomer layers comprises the reinforcement material.

19 . The method according to claim 18 , wherein the anode catalyst layer is formed on an outer surface of the first ionomer layer after removal of the ionomer membrane from the solid backing layer.

20 . A water electrolyser comprising the catalyst coated membrane according to claim 1 .