Proton-Exchange-Induced Configuration Rearrangement in a Poly

Subscriber access provided by University of Florida | Smathers Libraries

Letter

Proton Exchange Induced Configuration Rearrangement In a Poly(ionic liquid) Solution: a NMR Study Haijin Zhu, Hengrui Yang, Jiaye Li, Kristine J. Barlow, Lingxue Kong, David Mecerreyes, Douglas R. Macfarlane, and Maria Forsyth J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.7b02439 • Publication Date (Web): 17 Oct 2017 Downloaded from http://pubs.acs.org on October 19, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Proton Exchange Induced Configuration Rearrangement In a Poly(ionic liquid) Solution: a NMR Study Haijin Zhu,a,b,* Hengrui Yang,a,b Jiaye Li,c Kristine J. Barlow,d Lingxue Kong,a David Mecerreyes,e Douglas R. MacFarlane,c and Maria Forsytha,b a

Institute for Frontier Materials, Deakin University, Geelong, VIC 3216, Australia. b

ARC Centre of Excellence for Electromaterials Science, Deakin University, 221 Burwood HWY, Burwood, VIC 3125, Australia. c

d

e

School of Chemistry, Monash University, Clayton, VIC 3800, Australia.

CSIRO Manufacturing Flagship, Bag 10, Clayton South, VIC 3169, Australia.

Polymat, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, Avda, Tolosa 72, 20018 Donostia-San Sebastian, Spain.

* Corresponding author: H. Zhu. Tel: +61 3 5227 3696; E-mail: [email protected].

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 16

ABSTRACT: Polymeric ionic liquids have emerged recently as a promising alternative to traditional polymers as the polymer electrolyte membrane materials of choice because of their strongly decoupled dynamics between the polymer backbone and the counter ions. Knowledge of proton exchange and transport mechanism in such materials is critical to the design and development of new poly(ionic liquid) materials with improved electrochemical properties. Our NMR results show that the proton exchange between the labile proton of the diethylmethylammonium (NH122) cation and H2O molecules is accompanied by a concerted configuration rearrangement of the ammonium. Through a combination of PFG-NMR and proton relaxation (linewidth) analysis, we demonstrate that at lower temperatures the labile proton diffuses along with the NH122 ammonium as an integral unit, whereas at higher temperatures the NH/H2O proton exchange sets in gradually, and the PFG-NMR measured diffusion coefficient is a population averaged value between the two exchanging sites.

TOC GRAPHICS

KEYWORDS: diffusion, proton-exchange membrane (PEM), protic ammonium cation, PFGNMR


2

Page 3 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Proton exchange is an essential process for many electrochemical devices such as fuel cells, chloralkali cells, and redox-flow batteries, etc.1-3 Understanding the proton exchange processes at a molecular level will allow for a more rational design of chemistry and functionality of the materials, and thereby is critical to improving the electrochemical device performance. A wellknown example of proton exchange is found in bulk water, where each molecule can form a high number of labile hydrogen bonds. Proton exchange is accomplished via breaking, rearrangement and reforming of hydrogen bonds.4 The average time for rearrangement of hydrogen bonds is about 1.12 ps as calculated using MD simulations by Tay et al.5 Eigen and Demaeyer calculated the rate coefficient for the proton association reaction in water using a rapid electrical pulse technique and found ݇௔ = ሺ1.4 ± 0.2ሻ × 10ଵଵ Hz/mol at 25 oC.6 While both rearrangement and formation of hydrogen bonds are rapid, breaking hydrogen bonds is an extremely slow process and requires substantial energy. The rate constant for the dissociation reaction of water molecules is 2.5 × 10ିହ Hz at 25 oC.4 This implies that ‘a given intact water molecule will on

average take about 11 hours to dissociate spontaneously’.4 Therefore, proton exchange is a

hydrogen bond-breaking controlled process. A recent ab initio molecular dynamics study by Parrinello et al. also showed that the proton exchange occurs through periods of intense activity involving concerted proton hopping and structural rearrangement, followed by periods of rest that are longer than expected, similar to a jump-like diffusion mechanism.3 Although computer simulations have yielded various interesting insights into the proton exchange kinetics, these theories often lack experimental support due to i) the extremely short time scale as opposed to that required for observations, and ii) the only subtly different environments between the exchange sites. In this work, we investigate various proton exchange processes between the diethylmethylammonium (NH122) cations of a polymerized ionic liquid and the residual H2O


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 16

molecules in a DMSO solution, as well as the concerted configuration rearrangement in the NH122 cations. We show that through dissolution, the proton exchange between H2O and ammonium cations has been reduced to a modest rate thereby allowing us to probe by NMR T2 relaxation analysis.

Figure 1. The 1H-NMR spectrum of the poly([STFSI][NH122]) sample measured at 20 oC. The molecular structure of the poly(ionic liquid) is shown as an inset on the top left of the figure.

The

poly(ionic

liquid)

sample,

poly([diethylmethylammonium]

[4-styrenesulfonyl-

trifluoromethylsulfonylimide]), poly([NH122][STFSI]) was synthesized using the procedures described elsewhere.7-8 The molecular structure and 1H-NMR spectrum are shown in Figure 1. The proton peaks were assigned with the help of 13C-DEPT 135 spectrum and the 1H-13C HSQC spectrum (Figures S1 and S2). All the protons on the ammonium cation (peaks 8, 9, 10) exhibit


4

Page 5 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


an extreme narrowed peak width suggesting fast isotropic motions of the cation, whereas the protons on the poly[STFSI] chain show much broader peak widths. This sharp contrast in peak widths indicates a strongly decoupled mobility between the cation and polymeric anion in the solution. It is worth mentioning that this decoupled mobility is seen not only in solution but also in bulk state,7 making the material an attractive candidate for electrolyte membrane applications because the ‘free’ cation can give an enhanced ionic conductivity while the ‘immobile’ polymer chain can provide superior mechanical strength without sacrificing conductivity. Interestingly, it is seen that the methylene group (peak 9) splits into a doublet, with each peak further splits into a quartet. Note that the methylene carbon is prochiral, and the two methylene protons should be magnetically equivalent with two exceptions: i) the positions of protons are locked by steric effects, and ii) the neighboring atom to the carbon can be rapidly turned chiral which renders the two enantiotopic protons diastereotopic.9 In the case of NH122 cation, the magnetic inequivalence of the two protons suggests that the rotation of the ethyl group is hindered by steric effects. Figure 2a shows the two stereoisomers which result in a different electron-shielding environment for the two methylene protons. To avoid ambiguity, in the following discussion the proton close to the ethyl group and methyl group will be referred as H1, and the proton close to the labile proton and methyl group will be referred as H2. Figure 2c shows that with increasing temperature, the two peaks became broadened first, then gradually merged into a single peak. In order to visualize the peak change more clearly, the 1H spectra at each temperature were deconvoluted and the results are shown in Figure 2d. It is clearly seen that from 20 to 60 oC, the peak broadened significantly. Upon further increase in temperature from 60 to 70 oC, the two peaks merged into a single peak. This is a typical NMR phenomenon for exchange induced peak broadening followed by chemical shift averaging.10


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 16

From a molecular perspective, the exchange process between the two enantiotopic protons H1 and H2 can be induced by the proton exchange between the labile proton and the H2O molecules in the solvent. As shown in Figure 2b, the labile proton (indicated by an arrow) may ‘leave’ the cation, and in the meantime, the H2O molecules may approach from the other side and ‘donate’ a proton to the cation. As a result of this process, the configuration of the whole cation is inversed, and an exchange cycle between H1 and H2 is accomplished.


6

Page 7 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

(b)

(c)

(d)

Figure 2. (a) Molecular view of the stereoisomers of the [NH122] cation which give different electron-shielding environment to the two enantiotopic protons, H1 and H2. The labile proton in both stereoisomers is indicated by an arrow. (b) Schematic illustration of the exchange process between the labile proton NH and H2O and the concerted configuration inversion. (c) Variabletemperature 1H NMR spectra of the two enantiotopic protons. (d) Deconvoluted peaks of the two enantiotopic protons H1 and H2.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 16

(a)

(b)

Figure 3. (a) Variable-temperature 1H NMR spectra evolution of the labile proton of the [NH122] and water molecules. (b) Arrhenius plot of the exchange rates of both H1/H2 and


8

Page 9 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


NH/H2O processes against temperature. The points are experimental values, and the solid lines are drawn as guides to the eyes.

To confirm this hypothesis, the proton exchange between the labile proton and the H2O molecules is studied, and the exchange rate is quantified and compared. Figure 3a shows the 1H NMR spectra of the labile proton and the water molecules at different temperatures. It is evident that exchange line-broadening is present in both proton peaks. The spatial proximity between the labile proton NH and the H2O has been verified by a NOESY spectrum shown in Figure S3. The off-diagonal cross peaks between NH and H2O resonances can be clearly seen in this figure. The exchange effects on the NMR peak widths can be described using McConnell’s Modification of the Bloch Equation:11 ୢ

ୢ௧

‫ܯ‬ ‫ܯ‬ ൬ ஺ ൰ = −ሺ࣓݅ + ࡾ + ࡷሻ ൬ ஺ ൰. ‫ܯ‬஻ ‫ܯ‬஻

where ࣓ is the frequency matrix given by ࣓ = ൬ ૚

ࢀ૛,࡭

ࡾ=ቌ

૙

૙ ૚

ࢀ૛,࡮

Eq. (1) ߱஺ 0

0 ൰, ࡾ is the relaxation matrix given by ߱஻

ቍ , ࡷ is the exchange matrix defined by ࡷ = ቀ

݇ −݇

−݇ ቁ , where ݇ is the ݇

exchange rate constant in Hz for a single molecule. The eigenvalues of Eq. (1) are the (complex) frequencies of the NMR spectrum: the imaginary part gives the frequency (chemical shift) of the peak and the real part gives the peak width.12-13 The solution to Eq. (1) is quite complex and has been discussed in various literature and text books,10, 14 however, in the case of equal population of exchange sites, the expression can be significantly simplified at two extreme conditions: slow exchange limit (݇ ≪ ሺ߱஺ − ߱஻ )) and fast exchange limit (݇ ≫ ሺ߱஺ − ߱஻ )). At slow exchange limit,


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 16

ࡹሺ‫ݐ‬ሻ = ‫ܯ‬஺ ሺ0ሻ݁ ሺିோಲ ି௞భ ା௜ఠಲ ሻ௧ + ‫ܯ‬஻ ሺ0ሻ݁ ሺିோಳ ି௞షభ ା௜ఠಳ ሻ௧

Eq. (2)

݇௦௟௢௪ = ߨሺ‫ܯܪܹܨ‬௘ − ‫ܯܪܹܨ‬଴ ሻ

Eq. (3)

where ܴ஺ is the relaxation rate defined by ܴ஺ = 1/ܶଶ,஺ . Thus the exchange rate can be written as: where FWHM is the peak-width at half-height, and the subscripts e denote exchange, 0 denote no exchange. At fast exchange limit, ࡹሺ‫ݐ‬ሻ = ሺ‫ܯ‬஺ ሺ0ሻ + ‫ܯ‬஻ ሺ0ሻሻ݁

మ

೛ ೛ ൫ഘ షഘ ൯ ഥ ାோത ା ಲ ಳ ಲ ಳ ቉௧ ିቈ௜ఠ ೖభ శೖషభ

Eq. (4)

ഥ is the where ‫݌‬஺ and ‫݌‬஻ are the population percentage of species A and B, respectively. ߱

population weighted frequency (chemical shift) ߱ ഥ = ‫݌‬஺ ߱஺ + ‫݌‬஻ ߱஻ , ܴത is the population weighted relaxation rate ܴത = ‫݌‬஺ ܴ஺ + ‫݌‬஻ ܴ஻ . Thus the exchange rate can be written as:

ಳ ݇௙௔௦௧ = ଶሺிௐுெಲ ିிௐுெ

గሺఠ ିఠ ሻమ ೐

బሻ

Eq. (5)

For the calculation of exchange rate of H1/H2 (Figure 2c), the coalescence temperature for the two peaks is determined by first plotting the chemical shift difference ߱஺ − ߱஻ against

temperature T, and then extrapolate the line to ߱஺ − ߱஻ = 0. In the case of H1/H2 exchange, the coalescence temperature is determined to be around 70

o

C. Thus the slow exchange

approximation (Eq. (3)) was used for the temperature of 60 oC and below, and fast exchange approximation (Eq. (5)) was used for temperatures of 70 oC and above. The coFor the calculation of exchange rate of NH/H2O (Figure 3a), the slow exchange approximation is used for all the temperatures. The calculated exchange rates for both exchange processes are presented as an Arrhenius plot in Figure 3b (All the numbers are summarized in Table S1 in the Supporting Information). Interestingly, at lower temperatures (60 oC and below), both the H1/H2 and NH/H2O exchange processes exhibit very similar rates within experimental error. This is an indication of a


10

Page 11 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


concerted proton hopping (NH/H2O exchange) and structural rearrangement (H1/H2) of the NH122 cation. In other words, at lower temperatures the exchange between the two enantiotopic protons is accomplished mostly by the cation configuration inversion induced by the proton exchange between NH/H2O. At 70 oC and above, however, the H1/H2 exchange shows a much faster rate constant than that of the NH/H2O exchange. This means that, besides the configuration inversion, there must be a second mechanism that could give rise to the H1/H2 exchange. We attribute this to the axial rotation of the ethyl group around the N-C bond. It is worth mentioning that, although the peak areas of H1 and H2 seem to be equal in the spectra, they are not necessarily equal because there are three possible configurations (two of them have the same chemical shifts). The peak area ratio between H1/H2 depends on the dwell time (therefore population ratio) of the adopted configurations. As a brief summary, the exchange study shows that below 60 oC, the rotation of whole ethyl group is negligible on the time scale of about 10 ms (NMR T2 relaxation time), and the H1/H2 exchange is mainly caused by the concerted cation configuration rearrangement induced by NH/H2O proton exchange. At temperatures higher than 70 oC, the axial rotation of the ethyl group sets in and this becomes much faster than the NH/H2O exchange, and thereby dominates the H1/H2 exchange.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 16

Figure 4. Arrhenius plot of the diffusion coefficients of various proton species in the solution. The solid lines for H2O, NH122 and PSTFSI represents the best fit to the Arrhenius equation, whereas the solid line for NH is drawn as a guide to the eyes only.

To further understand the proton transport behavior of the labile proton, the entire cation itself, and the polymeric anion in the solution, the diffusion coefficients of various species have been measured at various temperatures and the results are shown in Figure 4. The diffusion coefficient of H2O molecules is slightly lower than that of the bulk water. For example, at 20 oC the observed diffusion coefficient for H2O is 5.8×10-10 m2/s, lower than that of the bulk water of 2.03 × 10-9 m2/s at this temperature.15-16 The NH122 cation diffusion coefficients were obtained from the attenuation of the NMR signal of the methyl group and shows apparently


12

Page 13 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lower diffusion coefficients than H2O molecules at all temperatures, as well as a slightly higher activation energy as indicated by the larger slope. It is also seen that the PSTFSI anion shows an order of magnitude lower diffusion than the ammonium cation, which agrees well with the decoupled mobility between cation and anion as suggested by the difference linewidths in Figure 1. To the best of our knowledge, this is the first time the decoupled motion of such poly(ionic liquid) material in solution has been identified and quantified. Interestingly, the labile proton (NH) shows the same diffusion coefficients as the whole cation at lower temperatures of 20 and 30 oC. With increasing temperature, the diffusion coefficient of the labile proton gradually deviates from the straight line of the cation, and eventually reaches an equilibrium line in-between the H2O and NH122 cation lines. This behavior can be explained by the proton exchange between the labile proton and the H2O. At low temperatures (T ≤ 30 oC), the exchange rate is slow and negligible on the time scale of diffusion (∆ = 15 ms). The labile proton diffuses with the cation as a whole, whereas increasing temperature leads to a gradual increase in the proton exchange rate. When the exchange time becomes comparable with the diffusion time, the chemical exchange severely affects the echo decay and thereby the measured diffusion coefficients.17-18 For this case Kärger derived a double exponential decay model to describe the effect of chemical exchange.19-20 The NMR signal attenuation (against the gradient strength) is a function of the diffusion coefficients (of both species), the maximum gradient strength, and the exchange rate. In this work, the diffusion coefficient of the NH labile proton at 40 oC was obtained by fitting the attenuation curve with a single component Stejskal-Tanner equation (Eq. (S1) in the supporting information), just like the rest of the temperatures. Therefore, the physical meaning of this diffusion coefficient is vague, as it is a function of both the diffusion coefficients of NH and H2O, as well as the exchange range between them. A complete analysis using


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 16

Kärger’s model would need input parameters of exchange rates, populations and the diffusion coefficient of one species. At the extremely fast exchange limit, the double exponential decay model can be simplified to a mono-exponential decay,18, 20 and the observed (apparent) diffusion coefficient is a population-weighted average of the two diffusion coefficients. This is the case for the diffusion coefficients obtained at 50 oC and above. As a brief summary, the PFG-NMR results have nicely demonstrated that, on the diffusion time scale of 15 ms, the proton exchange between NH/H2O is negligible at 20 and 30 oC, but becomes increasingly important at 40 oC, and eventually reaches the fast-exchange limit at 50 oC.

In this work we have studied the proton exchange and transport behavior of a protic poly(ionic liquid) solution.

The results revealed a concerted labile proton hopping and structural

rearrangement of the ammonium cation. The axial rotation of the ethyl group around the N-C bond is hindered at T < 60 oC. However, this rotation motion is activated at about 70 oC and increases rapidly with temperature. We have also shown that the labile proton on the cation diffuses with the cation as a whole at low temperatures, whereas this proton exchanges with H2O more significantly at T > 50 oC where the measured diffusion coefficient is a populationweighted value. We believe that these results are important for a better understanding of the molecular-level mechanisms of the charge (proton) transport processes in the ammonium based poly(ionic liquid) solution, and allows for a more rational design of next-generation polymer electrolyte materials.

ASSOCIATED CONTENT The Supporting Information is available free of charge on the ACS Publications website.


14

Page 15 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Experimental details, HSQC spectra, NOESY NMR spectra, a table of the H1/H2 proton exchange rate.

ACKNOWLEDGMENT HZ thanks the financial support from the Central Research Grants Scheme (CRGS) of Deakin University and the Australia Awards-Endeavour Research Fellowship funded by the Australian Government. MF wishes to thank the ARC for fellowship support under the Australian Laureate program funding FL110100013. Deakin University’s Advanced Characterisation Facility is acknowledged for use of the NMR instruments.

REFERENCES 1. Zhu, H.; Rana, U. A.; Ranganathan, V.; Jin, L.; O'Dell, L. A.; MacFarlane, D. R.; Forsyth, M. Proton transport behaviour and molecular dynamics in the guanidinium triflate solid and its mixtures with triflic acid. J. Mater. Chem. A 2014, 2, 681-691. 2. Zhu, H.; MacFarlane, D.; Forsyth, M. Probing ion exchange in the triflic acid– guanidinium triflate system: A solid-state nuclear magnetic resonance study. J. Phys. Chem. C 2014, 118, 28520-28526. 3. Hassanali, A.; Giberti, F.; Cuny, J.; Kühne, T. D.; Parrinello, M. Proton transfer through the water gossamer. Proc. Natl. Acad. Sci. 2013, 110, 13723-13728. 4. Stillinger, F. H. Proton transfer reactions and kinetics in water. In Theoretical Chemistry, Advances and Perspectives, Eyring, H.; Henderson, D., Eds. Academic Press: New York, 1978; Vol. 3, pp 177-234. 5. Tay, K. A.; Bresme, F. Kinetics of hydrogen-bond rearrangements in bulk water. Phys. Chem. Chem. Phys. 2009, 11, 409-415. 6. Eigen, M.; de Maeyer, L. Self-dissociation and protonic charge transport in water and ice. Proc. Royal Soc. London. Series A. Math. Phys. Sci. 1958, 247, 505-533. 7. Shah, A. H.; Li, J.; Yang, H.; Rana, U. A.; Ranganathan, V.; Siddigi, H. M.; MacFarlane, D. R.; Forsyth, M.; Zhu, H. Enhancement of 'dry' proton conductivity by self-assembled nanochannels in all-solid polyelectrolytes. J. Mater. Chem. A 2016, 4, 7615-7623. 8. Li, J.; Zhu, H.; Wang, X.; Armand, M.; MacFarlane, D. R.; Forsyth, M. Synthesis of sodium poly[4-styrenesulfonyl(trifluoromethylsulfonyl)imide]-co-ethylacrylate] solid polymer electrolytes. Electrochim. Acta 2015, 175, 232-239.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 16

9. Jennings, W. B. Chemical shift nonequivalence in prochiral groups. Chem. Rev. 1975, 75, 307-322. 10. Bain, A. D. Chemical exchange in NMR. Progr. Nuclear Magnetic Resonance Spectroscopy 2003, 43, 63-103. 11. McConnell, H. M. Reaction rates by nuclear magnetic resonance. J. Chem. Phys. 1958, 28, 430-431. 12. Lian, L. Y.; Roberts, G. C. K. Effects of chemical exchange on NMR Spectra. In NMR of Macromolecules, Roberts, G. C. K., Ed. IRL Press: New York, 1993. 13. Cavanagh, J.; Fairbrother, W. J.; Palmer III, A. G.; Rance, M.; Skelton, N. J. Chapter 5 Relaxation and dynamic processes. In Protein NMR Spectroscopy (Second Edition), Academic Press: Burlington, 2007; pp 333-404. 14. Freeman, R. Chemical exchange. In A Handbook of Nuclear Magnetic Resonance, 2 ed.; Pearson Education Limited: Harlow, United Kingdom, 1997. 15. Mills, R. Self-diffusion in normal and heavy water in the range 1-45.deg. J. Phys. Chem. 1973, 77, 685-688. 16. Yang, H.; Zhang, J.; Li, J.; Jiang, S. P.; Forsyth, M.; Zhu, H. Proton transport in hierarchical-structured nafion membranes: A NMR study. J. Phys. Chem. Lett. 2017, 8, 36243629. 17. Kärger, J. NMR self-diffusion studies in heterogeneous systems. Adv. Colloid Interface Sci. 1985, 23, 129-148. 18. Melchior, J.-P. A multiscale study of transport in model systems for proton conducting polybenzimidazole phosphoric acid fuel cell membranes. Max Planck Institute for Solid State Research, 2015. 19. Kärger, J. Transport phenomena in nanoporous materials. ChemPhysChem 2015, 16, 2451. 20. Mehlhorn, D.; Valiullin, R.; Kärger, J.; Cho, K.; Ryoo, R. Exploring the hierarchy of transport phenomena in hierarchical pore systems by NMR diffusion measurement. Microporous Mesoporous Mater. 2012, 164, 273-279.


16

Proton-Exchange-Induced Configuration Rearrangement in a Poly

Recommend Documents