Ion Mobility in Anion Exchange Membranes

Ion Mobility in Anion Exchange Membranes

Ion Mobility in Anion Exchange Membranes
Michael A. Hickner, Associate Professor
Department of Materials Science and Engineering
The Pennsylvania State University
310 Steidle Building
[email protected]
Acknowledgements
Dr. Guang Chen – Ph.D. Chemistry Chinese Academy of Sciences, Changchun  Dr. Shudipto Dishari – Ph.D. CHE Singapore
National University  Dr. Dongyang Chen – Ph.D. CHE Sun Yat-sen University, China  Dr. Brandon Calitree – Ph.D. Chemistry
SUNY Buffalo  Dr. Ian Sines – Ph.D. Chemistry Penn State  Dr. Min Zhang – Ph.D. Chemistry Chinese Academy of Sciences,
Changchun  Dr. Nanwen Li – Ph.D. Chemistry Chinese Academy of Sciences, Changchun  Dr. Geoff Geise – Ph.D CHE UT
Austin  He Xie – B.S. MATSE Tsinghua U.  Stephanie Petrina – B.S. MATSE Virginia Tech  David Jones – B.S. Engineering
Physics CWRU  Alfonso Mendoza – B.S. Ceramic Engineering Rutgers, M.S. MATSE PSU  Sarah Black – B. S. Chemistry Virginia
Tech  Brian Chaloux (NRL) – B.S. Chemistry CWRU  Melanie Disabb-Miller - B. S. MATSE Florida, M.S. MATSE Northwestern 
Lizhu Wang – B. S. Chemistry Jilin U., China, M.S. Chemistry Marquette U.  Zhaoyan Ai – B.S. Chemistry Hong Kong Polytech 
Sean Nunez – B.S. Chemistry SUNY Buffalo, M.S. Chemistry PSU  Changwoo Nam – B.S. CHE Pukyong National University, M.S.
CHE Seoul National University  Douglas Kushner – B.S. MATSE PSU  John Nese – PSU MATSE  Will Salem – PSU MATSE
DOE ARPA-E Award # DE-AR0000121a
Greg Tew – UMass Amherst
- Ru cation and polymer synthesis
Andy Herring/Rob Mantz - ARO
- travel support
Conductivity Comparison of AEMs and PEMs
2
10
1
10
(mS·cm-1)
0
10
-1
10
-2
P-1.2-H
P-1.5-H
P-2.3-H
A-1.1-HCO3
A-1.2-Cl
A-1.7-Cl
A-2.0-Cl
10
-3
10
-4
10
0
5
10
15
20

Disabb-Miller, Johnson and Hickner Macromolecules 2013.
Ion Conductivity With OH-, HCO3-…Cl- and BrMobility
(rel. to K+)
Hydration
number
H+
4.76
3
OH-
2.69
3
Na+
0.68
5
K+
1.00
4
Cl-
1.04
1
I-
1.05
0
Conductivity
λ
47/12
dilute
solution
3.9
OH
HCO
3
4.4
Yan and Hickner Macromolecules 2010.
Chen and Hickner ACS Appl Mater 2012.
(mS cm-1)
OH- HCO3- OH- HCO3QA-FEKS
18.2
11.1
22.3
5.1
IM-PFEKS
14.8
9.9
17.1
3.9
Normalized Conductivity as a Metric
Since ion mobilities are different, we need to compare normalized conductivity.
 i  qmi n
mH+/mK+ =
mOH-/mK+ =
mCl-/mK+ =
mHCO3-/mK+ =
4.76
2.69
1.04
0.61
Want to understand
conductivity behavior
independent of ion mobility
PEM
AEM
AEM
AEM
2
AEMs and PEMs have similar σn
10
(a)
1
1
10
-1
(mS·cm ))
nn (mS·cm
• Ionic mobilities derived from
conductivity measurements of
dilute solutions
• Mobility is a function of the
charge density of the ion and
how it is solvated
• Approximation for membranes
that are ~1 M ionic
concentration
0
0
10
-1
-1
10
-2
-2
10
P-1.2-H
P-1.2-H
P-1.5-H
P-1.5-H
P-2.3-H
P-2.3-H
A-1.1-HCO3
A-1.1-HCO3
A-1.2-Cl
A-1.2-Cl
A-1.7-Cl
A-1.7-Cl
A-2.0-Cl
A-2.0-Cl
-3
10
-4
10
0
1
52
3 10 4
515
6
7
20


Dean, J.A.. (1999). Lange’s Handbook of Chemistry, 15th Edition, McGraw-Hill, New York.
Vanysek, P. (2002). Ionic conductivity and diffusion at infinite dilution. In: CRC Handbook of Chemistry and Physics), CRC Press, Boca Raton.
TEM Images Suggest Same AEM and PEM Morphology
2
10
PEM
AEM
1
10
n (mS·cm-1)
PEM
0
10
-1
10
-2
10
-3
10
200 nm
P-1.2-H
A-1.2-Cl
200 nm
-4
10
0
5
10
15
20

•
Transmission electron microscope (TEM) images suggest membranes have spherical
morphology
– Domains ~ 20 nm
•
Membranes are kinetically trapped due to high MW and ion content
•
PEMs, AEMs have similar morphology → explains similar σn values
6
Charge Carrier Concentration
Charge carrier concentration can be determined by:
0.001  IEC  ρ
c
1  0.01  v-H2O
c = moles ion per cm3 of polymer IEC = millimoles of ion per gram polymer
ρ = polymer density (for a monovalent ion, mmol/g = meq/g)
Xv-H2O = the volume-based water uptake
Conductivity can be used in a form of the Nernst-Einstein equation to determine
the ion diffusivity:
RT
D 2 2
cz F
σ = measured conductivity R = ideal gas constant T = temperature
c = concentration of ions
z = charge
F = Faraday’s constant
(1) Kim, Y.; Einsla, B.; Sankir, M.; Harrison, W.; Pivovar, B. Polymer 2006, 47, 4026–4035.
(2) Peckham, Schmeisser, Rodgers, Holdcroft J. Mater. Chem. 2007, 17, 3255–3268.
Diffusion Coefficients of Triblock Copolymers
-8
10
2 -1
D (cm ·s )
-9
10
-10
10
-11
10
-12
10
-13
10
0
Sample
A-1.2-Cl
A-1.7-Cl
A-2.0-Cl
P-1.2-H
P-1.6-H
P-2.3-H
DF
IEC
(%)
(meq·g-1)
28
42
53
27
38
61
1.2
1.7
2.0
1.2
1.6
2.3
5
10
15
20

The diffusion coefficient as a function of
hydration number of P-1.2-H (), P-1.6-H
(), P-2.3-H (), A-1.2-Cl (), A-1.7-Cl
(), and A-2.0-Cl () at all hydration
numbers.
Dilute Solution Diffusivity (D/D0)
0
10
We can compare the diffusion
coefficients to the dilute solution
diffusivity of the mobile ions
-2
10
D/D0
mk B T
D0 
z
-1
10
-3
10
-4
10
-5
10
μ = dilute ion mobility
kB = Boltzmann constant
T = temperature
z = ion charge
μH+ = 362.4 x 10-5 cm2/V·s
μCl- = 76.3 x 10-5 cm2/V·s
-6
10
0
5
10
15
20

Ratio of the diffusion coefficient, D, to the dilute solution
diffusivity, D0 as a function of hydration number for P1.2-H (), P-1.6-H (), P-2.3-H (),
A-1.2-Cl (), A-1.7-Cl (), and A-2.0-Cl ().
Diffusion coefficients of both mobile, solvated ions are suppressed by the
same amount in membranes compared to dilute solution
Bis(terpyridine) Ruthenium-Based AEMs
Volume = 187 Å3
Volume - 187 Å3
•
•
•
•
•
•
3
Volume
=
496
Å
Volume - 187 Å
3
Volume - 496 Å3
Volume - 496 Å3
Tew, Hickner, et al JACS 2012.
Ru 101 g/mol = $ 82 USD/oz = $ 2.90/g
Triphenyl phosphine 262 g/mol = $ 1/g
Tris(2,4,6-trimethoxyphenyl)phosphine 533 g/mol= $ 12.30/g
Anhydrous trimethyl amine 59 g/mol= $ 0.81/g
N,N-Dimethyldecylamine 185g/mol = $12/g
3/4-vinylbenzyl chloride 153 g/mol = $2/g
D/D0 versus  for Ru AEMs
Chloride form Ru AEMs
Bicarbonate form Ru AEMs
0
0
10
10
1.6 IEC
1.0 IEC
1.6 IEC 1.8 IEC
1.6 IEC
1.8 IEC
1.4 IEC
-1
10
1.6 IEC
1.4 IEC
D/D0
D/D0
1.0 IEC
1.4 IEC
-1
10
1.4 IEC
1.0 IEC
1.0 IEC
-2
-2
10
10
0
20
40
60
80
100 120 140 160 180

Conduction in the polymer
is about a 5-10 x penalty (in
the best case) to conduction
in solution.
0
20
40
60
80
100 120 140 160 180

Increased water uptake in
bicarbonate form increases
the D/D0.
D/D0 for a series of AEMs
Bicarbonate conductivity
Bicarbonate D/D0
2
0
10
10
1.6 IEC
1.8 IEC
1.4 IEC
1
10
1.8 IEC
1.4 IEC
1.6 IEC
D/D0
 (mS·cm-1)
1.0 IEC
-1
1.4 IEC
10
1.6 IEC
1.0 IEC
1.6 IEC
1.4 IEC
1.0 IEC
1.0 IEC
-2
0
10
10
0
20
40
60
80
100 120 140 160 180

0
20
40
60
80
100 120 140 160 180

Ru AEMs [DCPD]:[M+COD] ratios of () 1:1, () 2:1, and () 5:1
trimethyl ammonium-based TMBA with () 100, () 80, () 60, and () 40 mol % DF
imidazolium poly(fluorenyl ether ketone sulfone) () 67 % DF
phosphonium PPO AEM () 20%, () 34%, () 57%, and () 90% DF
Where Does the Water Go With Larger Cations?
101
57
150
123
97
• Arrows indicate value of charge density on benzyl trimethyl
ammonium and bis(terpyridine) Ru cations.
• Distributed charge in Ru cation may not be effective in
recruiting water for ion conductivity.