Ion-conducting membrane

Abstract

An ion-conducting membrane includes: (i) a first ion-conducting layer including one or more first ion-conducting polymers; and (ii) a barrier layer including graphene-based platelets.

Claims

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 m and the barrier layer has a thickness of from 1 nm to 1 m.

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 m 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.

Description

(1) The invention is described further with reference to the FIGURE and following example, all of which are illustrative and not intended to be limiting.

(2) FIG. 1 is a schematic diagram showing an example of an ion-conducting membrane of the invention. The diagram depicts an ion-conducting membrane (1) having an anode side supplied with hydrogen and a cathode side supplied with oxygen. Ion-conducting membrane (1) comprises a first ion-conducing layer (2), a barrier layer (3) and a second ion-conducting layer (4). First ion-conducting layer (2) and second ion-conducting layer (4) are formed from one or more proton conducting polymers as hereinbefore described and may, or may not, be reinforced. Barrier layer (3) comprises graphene-based platelets and optionally a second component as hereinbefore described.

(3) Although FIG. 1 shows a membrane having a first ion-conducting layer (2) and second ion-conducting layer (4), it will be clear to one skilled in the art that the membrane may comprise only the first ion-conducting layer (2) and barrier layer (3); in this case, the barrier layer (3) could be adjacent to the cathode side or alternatively could be adjacent to the anode side. Furthermore, FIG. 1 shows first ion-conducting layer (2) and second ion-conducting layer (4) to be of similar thickness; it will be clear to one skilled in the art that this is not essential and one of the first and second ion-conducting layers may be considerably thinner than the other.

(4) Although not depicted in FIG. 1, all other embodiments which would be clear to one skilled in the art are within the scope of the present invention.

EXAMPLE

(5) Graphene oxide was prepared by following the method of Tour et al disclosed in ACS Nano, 2010, 4 (8), pp 4806-4814.

(6) A dispersion of the graphene oxide in water was prepared by ultra-sonicating a 1.3 wt % dispersion for 30 minutes at room temperature. The dispersion was then further diluted by adding 3 volumes of water to one volume of dispersion.

(7) 15 g of a 2 wt % dispersion of Aquivion PFSA ionomer (Solvay) in 50/50 wt % water/isopropanol was spray-coated onto a heated polytetrafluoroethylene sheet held in place on a vacuum bed. A quantity of the graphene oxide dispersion sufficient to form an approximately 1 m thick layer was spray-coated onto the ionomer layer. Finally, a further 15 g of the Aquivion PFSA ionomer dispersion described above was spray-coated onto the graphene oxide layer to form an ion-conducting membrane of the invention (Example 1)

(8) A reference ion-conducting membrane (Comparative Example 1) was prepared by spray-coating onto a heated PTFE sheet 30 g of the Aquivion PFSA dispersion described above.

(9) The two ion-conducting membranes (Example 1 and Comparative Example 1) were hot-pressed at elevated temperature and pressure for 10 minutes.

(10) Membrane electrode assemblies were prepared by hot pressing the membrane to Pt black electrodes, with a Pt loading of 3-3.85 mg/cm.sup.2, at elevated temperature and pressure for 2 minutes. The membrane thickness in both cases was approximately 40 m.

(11) Electrochemical testing was carried out in a 6 cm.sup.2 active area fuel cell at 80 C. using ambient and 7 psig pressures. Gases were humidified at 75 C. Hydrogen crossover was measured by recording the current passed when applying 0.35 to 0.45V to the cell with 200 ml/min H.sub.2 fed to one electrode and 400 ml/min N.sub.2 to the other. The number of moles of hydrogen that crossed the membrane were calculated from the current. Membrane resistance was measured by the current interrupt technique at 0.5 A/cm.sup.2 on H.sub.2/air at ambient pressure. The results of the current, calculated H.sub.2 cross-over and membrane resistance are given in Table 1:

(12) TABLE-US-00001 TABLE 1 H.sub.2 per cm.sup.2 per Current second crossed to (mA/cm.sup.2) cathode (nano-moles) Membrane Ambient 7 psig Ambient 7 psig Resistance pressure pressure pressure pressure (ohm .Math. cm.sup.2) Example 1 4.12 2.89 10.7 15.0 0.067 Compara- 2.93 2.07 15.2 21.4 0.058 tive Example 1

(13) Example 1 (with a barrier layer) clearly demonstrates a reduction in the cross-over of H.sub.2 from the anode to the cathode when compared with Comparative Example 1 (without the barrier layer) with only a small increase in the resistance of the membrane of Example 1 compared to Comparative Example 1.