Electrochemical membrane
This disclosure relates to polymer electrolyte membranes, and in particular, to a composite membrane having at least two reinforcing layers comprising a microporous polymer structure and a surprisingly high resistance to piercing. This disclosure also relates to composite membrane-assemblies and electrochemical devices comprising the composite membranes of the disclosure, and to methods of manufacture of the composite membranes.
1 . A composite membrane for an electrochemical device, comprising:
a) at least two reinforcing layers, each of said at least two reinforcing layers comprising a microporous polymer structure; and
b) an ion exchange material (IEM) at least partially imbibed within the microporous polymer structure of the at least two reinforcing layers and rendering the microporous polymer structure occlusive;
wherein the composite membrane has a thickness at 0% RH of at least 10 μm; and
wherein the microporous polymer structure is present in a total content of at least 15 vol % based on the total volume of the composite membrane, wherein the normalized total content of microporous polymer structure within the composite membrane is at least 3.5 μm based on the total area of the composite membrane,
wherein the normalized total content of the microporous polymer structure within the composite membrane is calculated with the following formula:
[
∑
M
mps
1
in
each
reinforcing
layer
/
A
composite
membrane
(
g
·
m
-
2
)
matrix
skeletal
density
mps
1
(
g
·
cm
-
3
)
+
∑
M
mps
2
in
each
reinforcing
layer
/
A
composite
membrane
(
g
·
m
-
2
)
matrix
skeletal
density
mps
2
(
g
·
cm
-
3
)
+
…
+
∑
M
mps
N
in
each
reinforcing
layer
/
A
composite
membrane
(
g
·
m
-
2
)
matrix
skeletal
density
mps
N
(
g
·
cm
-
3
)
]
·
10
-
6
m
3
cm
3
wherein mps 1 is microporous polymer structure 1 , mps 2 is microporous polymer structure 2 , mpsN is microporous polymer structure N (if there are N different types of microporous polymer structures within the composite membrane).
2 . The composite membrane according to claim 1 , wherein a composition of the at least two reinforcing layers is the same or wherein a composition of the at least two reinforcing layers is different.
3 . A composite membrane according to claim 1 , wherein the microporous polymer structure comprises at least one fluorinated polymer.
4 . A composite membrane according to claim 3 , wherein
the composite membrane has a total content of microporous polymer structure of at least 8 g·m −2 based on the sum of the mass per area of all the reinforcing layers present in the composite membrane.
5 . A composite membrane according to claim 1 , wherein the microporous polymer structure comprises a hydrocarbon polymer.
6 . A composite membrane according to claim 1 , wherein one of:
the at least two reinforcing layers are in direct contact; or
the composite membrane comprises at least one internal layer of ion exchange material between the at least two reinforcing layers.
7 . A composite membrane according to claim 1 , wherein the at least two reinforcing layers are separated by a distance d.
8 . A composite membrane according to claim 7 , wherein
the distance d is from 0.1 μm to 20 μm at 0% RH.
9 . A composite membrane according to claim 1 , wherein one of:
the composite membrane comprises more than one layer of ion exchange material,
wherein the layers of ion exchange material are formed of the same ion exchange material; or the ion exchange material comprises more than one layer of ion exchange material.
10 . A composite membrane according to claim 1 , wherein at least one of:
the microporous polymer structure is fully imbibed with the ion exchange material;
the microporous polymer structure of each of the at least two reinforcing layers has a first surface and a second surface, and wherein the ion exchange material forms a layer on at least one of the first surface or the second surface of each of the at least two reinforcing layers.
11 . The composite membrane as in claim 1 , wherein the microporous polymer structure of each of the at least two reinforcing layers has a first surface and a second surface, and
wherein the microporous polymer structure is mostly imbibed with the ion exchange material, but comprises a region of un-imbibed or non-occlusive region of the microporous polymer structure closest to the first surface of at least one of the at least two reinforcing layers.
12 . The composite membrane as in claim 11 , wherein the microporous polymer structure of the at least two reinforcing layers is 90% occluded with the ion exchange material.
13 . A composite membrane according to claim 1 , wherein the average equivalent volume of the ion exchange material is from 240 cc/mole eq to 870 cc/mole eq.
14 . A composite membrane according to claim 1 , wherein the ion exchange material comprises at least one ionomer, or wherein the ion exchange material comprises at least one ionomer and wherein
the at least one ionomer comprises a proton conducting polymer.
15 . A composite membrane according to claim 1 , wherein
the composite membrane has a thickness at 0% RH of from 10 μm to 115 μm.
16 . A composite membrane according to claim 1 , wherein the composite membrane has an average failure pressure from 150 psi to 500 psi.
17 . A composite membrane according to claim 1 , further comprising at least one backer layer removably attached to one or more external surfaces of the composite membrane.
18 . A membrane electrode assembly for an electrochemical device, comprising:
at least one electrode; and
the composite membrane according to claim 1 in contact with the at least one electrode.
19 . A membrane electrode assembly according to claim 18 , wherein at least one of:
the composite membrane is attached to the at least one electrode;
the at least one electrode comprises a porous layer;
the at least one electrode comprises carbon fibers.
20 . A membrane electrode assembly according to claim 18 , wherein the membrane electrode assembly is a redox flow battery membrane-electrode assembly comprising:
a first electrode with a first surface and a second surface;
a second electrode with a first surface and a second surface; and
a composite membrane with a first surface and a second surface according to claim 1 ,
wherein the second surface of the first electrode is in contact with the first surface of the composite membrane and the first surface of the second electrode is in contact with the second surface of the composite membrane.
21 . The membrane electrode assembly according to claim 20 , wherein the first electrode layer and/or the second electrode layer is a porous layer having a pore size from 1 to 200 μm.
22 . A membrane electrode assembly according to claim 20 , wherein
the first and/or second electrode is a carbon/platinum electrode with ionomer or wherein the electrode comprises an alloy with ionomer.
23 . A membrane electrode assembly according to claim 18 , wherein the at least one electrode is selected from a felt, a paper or a woven material.
24 . A membrane electrode assembly according to claim 18 , wherein the membrane electrode assembly is a fuel cell membrane electrode assembly comprising:
a composite membrane as described according to claim 1 , wherein the composite membrane has a first surface and a second surface;
a first layer of electrode catalyst adhered to the first surface of the composite membrane; and
a second layer of electrode catalyst adhered to the second surface of the composite membrane.
25 . A membrane electrode assembly according to claim 24 , wherein
the first and second layers of electrode catalyst are nanoporous layers having a pore size of up to 100 nm.
26 . A membrane electrode assembly according to claim 24 , wherein a layer of platinum or ruthenium catalyst is adhered to the composite membrane.
27 . A membrane electrode assembly according to claim 18 , wherein the membrane electrode assembly is an electrolyzer electrode assembly comprising:
the composite membrane of claim 1 , wherein the composite membrane has a first surface and a second surface,
a first layer of electrode catalyst adhered to the first surface of the composite membrane; and
a second layer of electrode catalyst adhered to the second surface of the composite membrane.
28 . A fuel cell comprising the composite membrane according to claim 1 .
29 . A redox flow battery comprising the composite membrane according to claim 1 .
30 . An electrolyzer comprising the composite membrane according to claim 1 .