Ion-conducting membrane

1. A catalyst-coated ion-conducting membrane comprising an ion-conducting membrane and an electrocatalyst layer deposited on at least one side of the ion conducting membrane, wherein the ion-conducting membrane comprises:

(i) a first ion-conducting layer comprising one or more first ion-conducting polymers; and

(ii) a barrier layer consisting of graphene-based platelets, and,

(iii) a second ion-conducting layer comprising one or more second ion-conducting polymers, wherein the second ion-conducting layer is applied to a face of the barrier layer not in contact with the first ion-conducting layer,

and wherein

the ion-conducting membrane has a total thickness of 5 to 50 μm and the barrier layer has a thickness of from 1 nm to 1 μm.

2. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the graphene-based platelets have an x:y aspect ratio of 0.1 to 10, a x:z aspect ratio of at least 10 and a y:z aspect ratio of at least 10.

3. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the graphene-based platelets are selected from the group consisting of graphene oxide, sulphonated graphene oxide, graphene sulphide, graphene hydroxide, graphene carbonate and graphene nitride.

4. The catalyst-coated ion-conducting membrane according to claim 3 , wherein the graphene-based platelets are graphene oxide.

5. The catalyst-coated ion-conducting membrane according to claim 1 , wherein an electrocatalyst layer is deposited on both sides of the ion-conducting membrane.

6. A membrane electrode assembly comprising a catalyst-coated ion-conducting membrane according to claim 1 .

7. A membrane electrode assembly comprising a catalyst-coated ion-conducting membrane according to claim 5 .

8. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the graphene-based platelets have an x:y aspect ratio of 0.1 to 10, a x:z aspect ratio of at least 10 and a y:z aspect ratio of at least 10.

9. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the graphene-based platelets are selected from the group consisting of graphene oxide, sulphonated graphene oxide, graphene sulphide, graphene hydroxide, graphene carbonate and graphene nitride.

10. The catalyst-coated ion-conducting membrane according to claim 1 , which further comprises a second ion-conducting layer comprising one or more second ion-conducting polymers, wherein the second ion-conducting layer is applied to a face of the barrier layer not in contact with the first ion-conducting layer.

11. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the barrier layer has a thickness of from 5 nm to 500 nm.

12. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the ion-conducting membrane has a total thickness of 10 to 30 μm and the barrier layer has a thickness of from 10 nm to 250 nm.

13. The catalyst-coated ion-conducting membrane according to claim 1 , wherein barrier layer has a thickness of from 1 nm to 250 nm.

14. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the first ion-conducting layer consists of one or more first ion-conducting polymers, and, optionally, one or both of (i) a polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), poly ether ether ketone (PEEK), or polyethylene (PE) reinforcing material, and (ii) a hydrogen peroxide decomposition catalyst, a radical scavenger, or both.

15. The catalyst-coated ion-conducting membrane according to claim 1 , wherein the first and second ion-conducting layers do not include graphene-based platelets.