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; and
a silica-based ceramic that coats at least a portion 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 sulfonate and/or sulfonic acid groups are present in the cation exchange membrane in an amount of 0.01 mmol per gram of the cation exchange membrane,
the silica-based ceramic comprises Si in an amount greater than or equal to 6 wt % of the silica-based ceramic,
the silica-based ceramic has an average pore diameter of less than or equal to 10 nm,
the cation exchange membrane has a sodium ion (Na + ) conductivity of greater than or equal to 0.00001 S/cm,
the cation exchange membrane has a water uptake of greater than or equal to 1 wt %, and
the cation exchange membrane has a linear expansion along at least one dimension of less than or equal to 10%.
2. The cation exchange membrane of claim 1 , wherein the silica-based ceramic forms a coating, and wherein the sulfonate and/or sulfonic acid groups are substantially homogeneously distributed within the silica-based ceramic based on the average amount of sulfonate and sulfonic acid groups measured across a thickness of the coating.
3. The cation exchange membrane of claim 1 , wherein the silica-based ceramic forms a coating, and wherein the sulfonate and/or sulfonic acid groups are substantially homogeneously distributed within the silica-based ceramic based on the maximum amount of sulfonate and sulfonic acid groups measured across a thickness of the coating.
4. The cation exchange membrane of claim 1 , wherein the cation exchange membrane has a cation exchange capacity of greater than or equal to 0.01 meq/g.
5. The cation exchange membrane of claim 1 , wherein the cation exchange membrane has a cation permselectivity of greater than or equal to 65%.
6. The cation exchange membrane of claim 1 , wherein no intervening layers are present between the silica-based ceramic comprising the sulfonate and/or sulfonic acid groups and the porous support membrane.
7. 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 of greater than or equal to 1.1.
8. 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
+
b
c
k
,
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
)
+
b
c
k
,
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
)
]
(
q
R
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
b
l
o
c
k
)
[
sin
(
qr
s
)
-
qr
cos
(
qr
s
)
]
(
qr
s
)
3
]
2
+
b
c
k
,
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, is a correlation length, Γ is the 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, ρ 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.
9. The cation exchange membrane of claim 1 , wherein the silica-based ceramic has a silicon to sulfur molar ratio of less than or equal to 120:1.
10. The cation exchange membrane of claim 1 , wherein the silica-based ceramic has a silicon to carbon molar ratio of less than or equal to 3,000:1.
11. The cation exchange membrane of claim 1 , wherein the silica-based ceramic has an average pore diameter of less than or equal to 5 nm.
12. The cation exchange membrane of claim 1 , wherein the silica-based ceramic has an average pore diameter of greater than or equal to 0.25 nm.
13. The cation exchange membrane of claim 1 , wherein the silica-based ceramic comprises pores, and wherein the pores of the silica-based ceramic have an aspect ratio of less than or equal to 40:1.
14. The cation exchange membrane of claim 1 , wherein the silica-based ceramic comprises pores, and wherein the pores of the silica-based ceramic have an ordered structure.
15. The cation exchange membrane of claim 1 , wherein the silica-based ceramic comprises pores, and wherein the pores of the silica-based ceramic fit a spherical model of small angle scattering spectra with a chi 2 /N value of less than or equal to 10, where N is the number of points small-angle scattering data points over the spherical model fitting range.
16. The cation exchange membrane of claim 1 , wherein the silica-based ceramic has a fractal porous structure.
17. The cation exchange membrane of claim 1 , wherein the pores of the silica-based ceramic have a log-normal polydispersity index of pore radius of less than or equal to 0.8.
18. The cation exchange membrane of claim 1 , wherein greater than or equal to 50% of a pore volume of the porous support membrane is filled by the silica-based ceramic.
19. The cation exchange membrane of claim 1 , wherein the cation exchange membrane comprises an edging material comprising a polymeric material.
20. 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).