Ceramic cation exchange materials
Cation exchange membranes and materials including silica-based ceramics, and associated methods, are provided. In some aspects, cation exchange membranes that include a silica-based ceramic that forms a coating on and/or within a porous support membrane are described. The cation exchange membranes and materials may have certain structural or chemical attributes (e.g., pore size/distribution, chemical functionalization) that, alone or in combination, can result in advantageous performance characteristics in any of a variety of applications for which selective transport of positively charged ions through membranes/materials is desired. In some embodiments, the silica-based ceramic contains relatively small pores (e.g., substantially spherical nanopores) that may contribute to some such advantageous properties. In some embodiments, the cation exchange membrane or material includes sulfonate and/or sulfonic acid groups covalently bound to the silica-based ceramic.
1. A cation exchange membrane, comprising:
a porous support membrane comprising an outer surface and having a volumetric porosity of greater than or equal to 10%, wherein the porous support membrane is in the form of a non-woven fabric or mesh, veil, knit fabric, woven fabric or mesh, open-cell structure, fibril and node structure, or open-cell foam; and
a layer comprising a silica-based ceramic that forms a coating on at least a portion of the outer surface of the porous support membrane, wherein the silica-based ceramic comprises sulfonate and/or sulfonic acid groups covalently bound to the silica-based ceramic, wherein the cation exchange membrane has a sodium ion (Na + ) conductivity of greater than or equal to 0.00001 S/cm, and wherein the weight ratio of the silica-based ceramic to the porous support membrane in the cation exchange membrane is greater than or equal to 1:10.
2. A cation exchange membrane, comprising:
a porous support membrane comprising an outer surface and having a volumetric porosity of greater than or equal to 10%, wherein the porous support membrane is in the form of a non-woven fabric or mesh, veil, knit fabric, woven fabric or mesh, open-cell structure, fibril and node structure, or open-cell foam; and
a layer comprising a silica-based ceramic that forms a coating on at least a portion of the outer surface of the porous support membrane, wherein the silica-based ceramic comprises sulfonate and/or sulfonic acid groups covalently bound to the silica-based ceramic, wherein the silica-based ceramic has an average pore diameter of less than or equal to 10 nm, wherein the weight ratio of the silica-based ceramic to the porous support membrane in the cation exchange membrane is greater than or equal to 1:10.
3. A method for using the cation exchange membrane of claim 1 in an electrochemical application, comprising:
contacting the cation exchange membrane with an electrolyte; and
passing current through an electrode in electrical communication with the electrolyte.
4. The cation exchange membrane of claim 1 , wherein the sulfonate and/or sulfonic acid groups are present in the cation exchange membrane in an amount of greater than or equal to 0.01 mmol per gram of the cation exchange membrane.
5. The cation exchange membrane of claim 1 , wherein the cation exchange membrane has a cation exchange capacity of greater than or equal to 0.1 meq/g.
6. The cation exchange membrane of claim 1 , wherein the silica-based ceramic comprises Si in an amount greater than or equal to 6 wt % of the silica-based ceramic.
7. The cation exchange membrane of claim 1 , wherein the cation exchange membrane has a linear expansion of less than or equal to 5%.
8. The cation exchange membrane of claim 1 , wherein the cation exchange membrane has a cation permselectivity of greater than or equal to 65%.
9. The cation exchange membrane of claim 1 , wherein the silica-based ceramic comprises pores, and wherein an average diameter of the pores of the silica-based ceramic is larger when the cation exchange membrane is in a hydrated state than when the cation exchange membrane is in a dry state by a factor, wherein the factor is greater than or equal to 1.1.
10. The cation exchange membrane of claim 9 , wherein the factor is less than or equal to 5.
11. The cation exchange membrane of claim 1 , wherein the silica-based ceramic comprises pores, and wherein:
when the cation exchange membrane is in a dry state, the pores of the silica-based ceramic fit a model of small angle scattering spectra with intensity (I) as a function of a scattering vector, q, as follows:
I
(
q
)
=
1
a
+
c
1
q
2
+
c
2
q
4
+
bck
,
wherein a, c 1 , and c 2 are adjustable parameters and bck is background scattering; and
when the cation exchange membrane is in a hydrated state the pores of the silica-based ceramic fit a core-shell model of small angle scattering spectra with intensity (I) as a function of a scattering vector, q, as follows:
I
(
q
)
=
P
(
q
)
S
(
q
)
+
bck
,
S
(
q
)
=
1
+
D
f
Γ
(
D
f
-
1
)
[
1
+
1
/
q
ξ
)
2
]
(
D
f
-
1
)
/
2
sin
[
(
D
f
-
1
)
tan
-
1
(
q
ξ
)
]
(
qR
0
)
D
f
,
P
(
q
)
=
scale
V
s
[
3
V
c
(
ρ
c
-
ρ
s
)
[
sin
(
qr
c
)
-
qr
c
cos
(
qr
c
)
]
(
qr
c
)
3
+
3
V
s
(
ρ
s
-
ρ
block
)
[
sin
(
qr
s
)
-
qr
cos
(
qr
s
)
]
(
qr
s
)
3
]
2
+
bck
,
wherein R O is a radius of the building blocks (pores), ρ solvent is a scattering length density of the silica-based ceramic, D f is a fractal dimension, ξ is a correlation length, Γ is a standard mathematical gamma function, scale is a volume fraction of building blocks of the measured silica-based ceramic, V c is a volume of the core, V s is a volume of the shell, ρ c is a scattering length density of the core, ρ s is a scattering length density of the shell, P block is a scattering length density of the pores, r c is a radius of the core, r s is a radius of the shell, and bck is background scattering.
12. The cation exchange membrane of claim 1 , wherein the silica-based ceramic is derived from a mixture comprising (3-mercaptopropyl)triethoxysilane.
13. The cation exchange membrane of claim 1 , wherein the silica-based ceramic has an average pore diameter of less than or equal to 2 nm.
14. The cation exchange membrane of claim 1 , wherein the porous support membrane has a volumetric porosity of less than or equal to 99%.
15. The cation exchange membrane of claim 1 , wherein the porous support membrane has a mechanical burst pressure of greater than or equal to 2.0 pounds per square inch (PSI).
16. The cation exchange membrane of claim 1 , wherein the porous support membrane comprises an interior, and wherein the cation exchange membrane further comprises the silica-based ceramic present within at least a portion of the interior of the porous support membrane.
17. The cation exchange membrane of claim 2 , wherein the porous support membrane comprises an interior, and wherein the cation exchange membrane further comprises the silica-based ceramic present within at least a portion of the interior of the porous support membrane.
18. The cation exchange membrane of claim 1 , wherein the porous support membrane is in the form of a non-woven fabric or mesh.
19. The cation exchange membrane of claim 2 , wherein the porous support membrane is in the form of a non-woven fabric or mesh.