Composite Anion Exchange Membrane from Quaternized Polymer

Article pubs.acs.org/IECR

Composite Anion Exchange Membrane from Quaternized Polymer Spheres with Tunable and Enhanced Hydroxide Conduction Property Haoqin Zhang, Benbing Shi, Rui Ding, Huiling Chen, Jingtao Wang,* and Jindun Liu School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001, P. R. China S Supporting Information *

ABSTRACT: In this research, novel quaternized polymer spheres (QPSs) with a high quaternary ammonium (QA) group loading amount and a controllable structure are synthesized and incorporated into a chitosan (CS) matrix to fabricate a composite membrane. Systematic characterizations and molecular simulation are adopted to elaborate the relationship between the QA structure of QPSs and physical-chemical as well as ion conduction properties of composite membranes. The welldispersed QPSs generate repulsive interaction to CS chains, endowing the composite membrane with promoted chain mobility and water uptake and thereby enhanced hydroxide conductivity. The QPSs work as hydroxide conductors within the membranes, affording a hydroxide conductivity increase over 80%. As the hopping sites in the membrane, the QA group with moderate OH− combination/dissociation capability exhibits higher OH− conductivity. By comparison, the QA group with the highest or lowest potential displays slightly lower OH− conductivity. Besides, extending the chain length of the QA ligand generates obvious steric hindrance and then impedes OH− combination. Menshutkin reaction.19,20 In this process, strongly carcinogenic chloromethyl methyl ether is an essential raw material.21,22 Besides, the disordered distribution of ionic side chains induces insufficient microphase separation between the backbones and side chains during membrane fabrication. This leads to numerous “dead ends” of ionic clusters in AEM and thus limits its OH− conductivity. For AEM, the ammonium loading amount (reflected by the value of ion exchange capacity (IEC)) governs OH− conductivity.23 It is found that the conductivity is elevated by 330% from 10 to 43 mS cm−1 when increasing the IEC of the membrane from 1.31 to 2.75 mmol g−1.24 Adequate conductivity is readily obtained by a high ammonium loading amount; however, it inevitably causes excessive water swelling due to the hydration of ammonium groups. The membrane would lose its structural stability and display serious fuel crossover, unable to be used in practical application.25,26 For instance, some of the aromatic-based membranes dissolve in

1. INTRODUCTION Like proton exchange membrane fuel cells (PEMFCs), alkaline anion exchange membrane fuel cells (AAEMFCs) have attracted a burgeoning interest as promising renewable power devices.1−6 The distinct advantages of facile electrochemical kinetics, lower fuel crossover, and the usage of nonpreciousmetal catalysts render AAEMFCs more attractive and easier to be commercially applied.7−11 Similarly, as the core component in fuel cells, the anion exchange membrane (AEM) must highly conduct OH− from anode to cathode for completing energy conversion, and the OH− conductivity determines fuel cell performance, including operational fuel cell voltage and current output. Generally, AEMs are composed of aromatic polymers (such as poly(ether ether ketone), 12 polysulfones, 13 poly(phthalazinon ether sulfone ketone),14 poly(2,6-dimethyl-1,4phenylene oxide),15 and poly(arylene ether sulfone)s16,17) bearing conducting groups as side chains. Different from the conducting groups of quaternary phosphonium and tertiary sulfonium, ammonium is more attractive due to the features of easy synthesis together with its adequate chemical and thermal stability.18 Currently, ammonium groups are mainly grafted onto the polymer chains by chloromethylation and then the © 2016 American Chemical Society

Received: Revised: Accepted: Published: 9064

May 5, 2016 June 28, 2016 August 3, 2016 August 3, 2016 DOI: 10.1021/acs.iecr.6b01741 Ind. Eng. Chem. Res. 2016, 55, 9064−9076

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Industrial & Engineering Chemistry Research water (milder than the alkaline aqueous solution) at 80 °C (operation temperature) with the IEC of only 2.10 mmol g−1.27 Different from the direct grafting on polymer chains, introducing ammonium on inorganic fillers and then preparing the organic−inorganic hybrid membrane is an attractive approach to offer a high loading amount and meanwhile maintain or even enhances the structural stability. In this manner, the ammonium groups can create long-range hopping pathways along the filler surface to provide efficient OH− conduction. The pathways and the conductivity of this kind of membrane can be facilely tuned by altering the structure and content of fillers. To date, quaternized HNTs,28 CNTs,29 GO,30,31 and silica32 have been utilized to prepare AEMs, which all achieved enhanced OH− conductivity. In spite of these advances, polymer fillers are ideal alternatives as they possess a high ammonium loading amount throughout the fillers, considering the low grafting degree and natural nonconductive feature of inorganic materials. OH− can transport through both the surface and inside of polymer fillers, ensuring facile OH− migration. Besides, the addition of polymer fillers allows the membrane to sorb more water molecules, which is favorable for the OH− transfer via the Grotthuss mechanism. Polymer fillers have been rarely used as active conductors in AEM at present. Furthermore, although previous studies have demonstrated that the chemical structure of ammonium plays an important role in OH− hopping, more efforts remain to be made in this aspect, especially theoretical stimulation and calculation. Herein, cross-linked quaternized imidazole spheres with a high QA loading amount and various QA chemical structures were facilely synthesized for the first time. Vinyl imidazole (VI) was chosen as the monomer due to its good reactive activity and the relatively high N content (21.2 mmol g−1). The fivemembered heterocyclic ring and the π conjugated structure donate good stability to the imidazolium cation in alkaline condition.33 The resultant imidazole spheres were quaternized by five kinds of chlorinated reagents (chlorobutane, chlorodecane, benzyl chloride, allyl chloride, and ethyl chloroformate) to generate different ligand structures on the QA group. Chitosan (CS) was chosen as the membrane matrix due to its good film forming and mechanical properties as well as low cost.34 To better investigate the function and transfer feature of QA groups on polymer spheres, CS was not quaternized to minimize its influence on ionic conduction of the composite membrane. The microstructures and physicochemical properties of membranes were investigated in detail. Additionally, the hydroxide conductivities and transfer mechanism of the membranes at different humidity were systematically evaluated.

(0.018 g) were dispersed into acetonitrile (80 mL) in a roundbottom flask (100 mL) with ultrasonic treatment for 30 min to form a homogeneous solution. The mixture was subsequently stirred and kept at 82 °C for 30 min. Afterward, the prepared poly(vinyl imidazole) spheres (PSs) were purified by centrifugation with washing by acetonitrile and then dried in vacuum oven. To obtain QPSs, PSs (0.6 g) and the quantitative quaternary aminating reagent (CB, CD, AC EC, BC) were dispersed into absolute alcohol (100 mL), and the solution was refluxed under 70 °C for 20 h. The resultant QPSs were purified and dried in a vacuum oven until a constant weight. Subsequently, the QPSs were immersed into KOH (0.5 M) solution for 24 h to convert to OH− form, then washed thoroughly, and dried in vacuum oven. The as-synthesized QPSs are designated as C4-QPSs, C10-QPSs, A-QPSs, B-QPSs, and E-QPSs, correspondingly. The functional groups are named as C4-QVI, C10-QVI, A-QVI, B-QVI, and E-QVI, accordingly. PSs with diverse diameter and degree of cross-linking are prepared by the same process as mentioned above, and the detailed synthesis parameters are presented in Table 1. Table 1. Polymer Spheres Prepared in This Study sample

VI (mL)

EGDMA (mL)

time (min)

size (d) (μm)

QAa

PSs(3:1) PSs(1:3) PSs-15 PSs-30 PSs-45 E-QPSs C4-QPSs C10-QPSs A-QPSs B-QPSs

0.9 0.3 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

0.3 0.9 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

30 30 15 15 45 30 30 30 30 30

1.10 0.90 0.48 0.98 1.50 0.98 0.98 0.98 0.98 0.98

E C4 C10 A B

“E” represents ethyl chloroformate; “C4” represents n-chlorobutane; “C10” represents chlorodecane; “A” represents allyl chloride; “B” represents benzyl chloride.

a

2.3. Membrane Preparation. CS (1.2 g) and 0−10 wt % QPSs were mixed in an acetic acid (2 wt %) solution and then heated at 80 °C for 5 h under a continuous agitation. To obtain a close cross-linking degree, the same dosage of the cross-linker and reaction procedure was applied to prepare a casting solution based on the literature reported,3,35 and the detailed procedure was that 5 mL of glutaraldehyde (2%, v/v) aqueous solution was added to the mixture and stirred vigorously at room temperature for 3 h. The resulting solution was cast onto a glass plate until the solvent evaporated completely at room temperature. Afterward, the obtained membrane was immersed in 0.5 mol L−1 KOH solution for 24 h to obtain the OH− form membrane. Finally, the membranes were washed thoroughly with deionized water to remove the residual KOH and dried in vacuum oven. All the membranes were kept in a ziplock bag before testing to avoid accessing to CO2. The thickness of dry membranes falls in the range of 60−65 μm. The membranes are designated as CS, CS/C4-QPSs-X, CS/C10-QPSs-X, CS/AQPSs-X, CS/B-QPSs-X, and CS/E-QPSs-X, where X (X = 2, 4, 6, 8, and 10) represents the weight percentage of QPSs to the CS matrix. 2.4. Characterization of the QPSs and Membranes. The morphology of QPSs and membranes was observed by a scanning electron microscope (SEM, Nanosem430). Fourier

2. EXPERIMENTAL SECTION 2.1. Materials and Chemicals. Vinyl imidazole (VI), chlorobutane (CB), chlorodecane (CD), benzyl chloride (BC), allyl chloride (AC), and ethyl chloroformate (EC) were purchased from Xiya reagent and used as received. 2,2Azobis(isobutyronitrile), ethylene glycol dimethyl acrylate (EGDMA), and acetonitrile were obtained from Kewei Chemistry Co. Ltd. CS with the deacetylation degree of 95% was obtained from Golden-Shell Biochemical Co. Deionized water was used throughout the experiments. 2.2. Synthesis of Quaternized Polymer Spheres (QPSs). The five kinds of QPSs are prepared through dispersion polymerization and the quaternization method. Detailed synthetic procedures are described as follows. VI (0.6 mL), EGDMA (0.6 mL), and 2,2-azobis(isobutyronitrile) 9065

DOI: 10.1021/acs.iecr.6b01741 Ind. Eng. Chem. Res. 2016, 55, 9064−9076

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Industrial & Engineering Chemistry Research Scheme 1. Preparation Process and the Structures of (a) QPSs and (b) the Composite Membrane

transform infrared (FTIR) spectra were recorded on a Nicolet MAGNAIR560 with the range of 4000−400 cm−1 at room temperature. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were carried out to analyze the thermal properties of QPSs and the composite membranes. TGA was carried out on a TGA-50SHIMADZU by heating the sample from room temperature to 800 °C with a heating rate of 10 °C min−1 under nitrogen atmosphere. The DSC curve was obtained on a 204 F1 NETZSCH, and the sample was first preheated from room temperature to 130 °C with a heating rate of 10 °C min−1 under nitrogen atmosphere, then cooled down to 90 °C, and reheated to 260 °C. Mechanical properties of the membranes were measured with an Instron mechanical tester (Testometric 350 AX) at room temperature with the elongation rate of 5 mm min−1. The nanostructures of QPSs and membranes were probed by an X-ray diffractometer (XRD) using a RigakuD/max2500v/Pc (CuK 40 Kv, 200 mv) in the range of 5−60°. 2.5. Determination of IEC, Water Uptake, and Area Swelling. The IEC values of QPSs and the membranes are determined by Mohr titrations.36 The dry sample (about 0.4 g) was soaked in an HCl solution (0.1 mol L−1, 20 mL) for 24 h. Subsequently, the solutions were titrated with standard NaOH solution (0.1 mol L−1). The value of IEC was calculated from the consumption of hydrochloric acid and the weight of the dry sample as follows −1

IEC (mmol g ) =

Area swelling (%) =

Wwet − Wdry Wdry

× 100 (3)

where Wwet (g) and Awet (cm ) are the mass and area of the wet sample, respectively, whereas Wdry (g) and Adry (cm2) are values in a dry state. 2.6. Hydroxide Conductivities of QPSs and Membranes. Hydroxide conductivities of QPSs and membranes in through-plane direction are measured by an alternating current (AC) over the frequency range from 100 to 107 Hz at 20 mV. The ionic conductivity of the membrane was calculated from the resistance of the membrane obtained from the Nyquist plot (Figure S1), and the resistance value was obtained from the intercept of impedance at high frequency. The QPSs powder in OH− form was pressed into a 300 μm disk under the same pressure using a sheeter (769YP-15A), and the OH − conductivities were measured under the relative humidity (RH) of 0%. The OH− conductivities of membranes were measured under both anhydrous and hydrated conditions. For anhydrous testing, the samples were dried at 80 °C to eliminate the residual moisture. The conductivities under hydrous condition were obtained by measuring the hydrated membranes, and the RH was kept at 100% by using water vapor. The hydroxide conductivities of the membranes were calculated by the following equation

σ=

l R×A

(4) 2

where l (cm), A (cm ), and R (Ω) represent sample thickness, contact area, and resistance, respectively. 2.7. Alkaline Stability of Membranes. The alkaline stability of membranes was evaluated by immersing the membranes into a 1.0 M KOH aqueous solution at 80 °C for 240 h. The changes in IEC, hydroxide conductivity, and mechanical property were monitored. The hydroxide conductivity of membranes was determined under a fully hydrated condition at 80 °C. Prior to measurement, the membranes were completely washed with water and kept in water at room temperature for 24 h. The mechanical property of the membrane was tested in a dry state at room temperature.

(1)

where M1,HCl and M2,HCl are the moles of HCl before and after equilibrium, respectively, and Wdry is the weight of the dry sample. Water uptake and area swelling of the sample are determined by evaluating the alteration of mass and area before and after immersing in water. The sample was dried at 60 °C under vacuum until a constant weight was obtained. Afterward, the dry sample was immersed in water at room temperature and periodically tested until constant wet weight and area were recorded. The water uptake and area swelling were calculated by the following equations Water uptake (%) =

Adry 2

M1,HCl − M 2,HCl Wdry

A wet − Adry

3. RESULTS AND DISCUSSION 3.1. Synthesis of QPSs. As illustrated in Scheme 1a, PSs are synthesized by dispersion polymerization in a mixture of VI (functional monomer), acetonitrile (solvent), EGDMA (crosslinker), and AIBN (radical initiator). Afterward, the PSs are

× 100 (2) 9066


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Figure 1. SEM images of (a) QPSs-15, (b) QPSs-30, (c) QPSs-45, (d) QPSs (1:3), and (e) QPSs (3:1) and (f) FTIR of the QPSs.

Figure 2. SEM images ((a) and (b)), DSC curves (c), and strain−stress curves (d) of the membranes.

quaternized using five kinds of chlorinated reagents to prepare QPSs. SEM images in Figure 1a−c suggest that the QPSs are monodisperse spheres with tunable diameters from 0.48 to 1.5 μm when altering the polymerization time from 15 to 45 min. The short transition time from homogeneous to heterogeneous affords QPSs narrow size distribution. A high-magnification SEM image (Figure S2b) demonstrates that the cross-linked QPSs possess a slightly rough surface, different from the inorganic silica with a smooth surface. The VI:EGDMA ratio is utilized to regulate the structure of PSs (size and density), and it is found that altering the ratio from 1:3, 1:1, and 3:1 increases the size of PSs from 0.90, 0.98, and 1.10 μm (polymerization time, 30 min) (Figure 1d, b, and e). In addition, PSs cannot be obtained within 30 min when the ratio exceeds 6:1, and further prolonging the polymerization time to 60 min only gives rise to 0.55 μm PSs (Figure S2a). These findings suggest that the cross-linker plays a critical role in the balling of the polymer chain, and a certain amount of the cross-linker is required for PSs formation. As expected, the PSs become compact with the increase of polymerization time or cross-linker dosage as confirmed by XRD patterns in Figure S3. PSs exhibit bands of

cross-linked structure at 2θ = 11.6° and 18.9°, the intensities of which become stronger with polymerization time and the EGDMA:VI ratio. The quaternization mainly occurs on N atoms in imidazole of the PSs, and the morphology of PSs almost remains unchanged upon the reaction (Figure S3c). The introduction of QA groups is probed by FTIR spectra of PSs and QPSs in Figure 1f. The presence of imidazole groups gives PSs two bands at 1640 (CN) and 1453 cm−1 (C−N).37 Upon quaternization, QPSs give rise to the characteristic bands at 721 cm−1 for the bending vibration of the imidazolium ring.38,39 AQPSs (Figure S4) and B-QPSs (Figure 1f) give rise to several additional characteristic bands in the range of 1590−1520 cm−1, which are assigned to the typical vibration of CC and phenyl groups. Since there is no special chemical group, the characteristic bands of C4-QPSs, C10-QPSs, and E-QPSs are close to that of PSs. Furthermore, the enhancement of hydrophilic nature by quaternization slightly increases the characteristic band for adsorbed water of QPSs at 3423 cm−1. 3.2. Preparation of the Membranes. QPSs are incorporated into the CS matrix to prepare composite 9067


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Figure 3. TGA (a) and DTG (b) curves of QPSs and the TGA (c) and DTG (d) curves of membranes.

the CS chain is partially protonated to −NH3+ during the membrane preparation process due to the presence of acetic acid, electrostatic repulsion would emerge among CS chains and QPSs. Together with the spatial interference effect, these factors lead to the destruction of hydrogen bonds among CS chains near interfacial domain, resulting in promoted chain motion.43 Generally, CS displays a gentle degradation process without an obvious endothermic peak in the range of 190−250 °C. However, a measurable endothermic peak at around 200 °C appears for all composite membranes. Also, this should be ascribed to the promoted chain mobility, which allows more side chains of CS to degrade under this temperature. For QA with an electron-withdrawing ligand (allyl, ester group), the strengthened electropositivity generates stronger interference with CS chains, offering lower thermal degradation temperature to CS/A-QPSs and CS/E-QPSs. In contrast, the electrondonating ligand (n-butyl, decyl) gives higher thermal degradation temperature to other composite membranes. With the increase of QPSs content, the chain mobility of CS is further enhanced. For instance, the transition temperature of CS/E-QPSs decreases from 142.2 to 134.4 °C as the filler content increases from 2% to 8% (Figure S6). Mechanical properties of the membranes in term of stress− strain curves are presented in Figure 2d, which reveals that the CS control membrane exhibits acceptable mechanical stability with Young’s modulus of 810.2 MPa, along with the tensile strength of 29.5 MPa and the elongation at a break of 11.7%. By comparison, the spatial interference effect from QPSs and well compatibility afford composite membranes enhanced mechanical stabilities. For instance, incorporating 6% C4-QPSs, C10QPSs, A-QPSs, B-QPSs, and E-QPSs will elevate the tensile strengths of the composite membranes to 45.4, 44.1, 41.1, 42.7, and 42.3 MPa, along with the Young’s modulus of 974.3,

membranes through a solution casting method as shown in Scheme 1b. The cross-sectional SEM images in Figure 2 indicate that the CS control membrane (Figure 2a) is dense and smooth without obvious cracks or pinholes. The addition of QPSs makes the cross-section of the composite membrane rough with wrinkles, and QPSs retain their pristine structure and disperse evenly throughout the whole cross-section (Figure 2b). Different from the weak compatibility between polymer and inorganic filler, QPSs display well compatibility with CS bulk, and no obvious interface can be observed. FTIR spectra of the membranes in Figure S5a reveal that the characteristic bands for CS chains at 3380 (hydroxyl), 1647 (amide I), and 1579 (amide II) cm−1 are observed for all the membranes.40 The well compatibility gives a full coverage of QPSs by the CS matrix, bringing almost the same FTIR spectra to composite membranes as that of the CS control membrane. This finding also indicates that QPSs are physically mixed with the CS matrix without forming chemical bonds. Nevertheless compared with the CS control membrane, the band for water near 3380 cm−1 of composite membranes becomes stronger (especially with high QPSs content (Figure S5b)) due to the strong water adsorption ability of QPSs. 3.3. Chain Mobility, Mechanical Properties, and Crystal Structure of the Membranes. The chain mobility of the membrane is performed on DSC (Figure 2c), which suggests that the incorporation of QPSs alters CS chain mobility. The CS control membrane displays an endothermic peak at 146.8 °C, resulting from the dissociation process of interchain hydrogen bonds among CS chains.41,42 By comparison, this peak for the composite membrane shifts to a lower temperature. For example, CS/E-QPSs-6 exhibits an endothermic peak at 138.2 °C, inferring an elevated chain mobility of CS in the composite membrane. Since the −NH2 in 9068


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Figure 4. Molecular surfaces of QVI: (a) MEP and (b) total density. (c) IEC values of the QPSs and membranes and (d) water uptake and swelling ratio of CS control and composite membranes.

strengthens the bond energy of the functional group. In contrast, the electron-withdrawing property of allyl, benzyl, and ester groups reduces the degradation temperature of A-QVI, BQVI, and E-QVI to about 246 °C. The DTG curves in Figure 3b reveal the degradation rate of QPSs at different temperatures. The peak at 274 °C clearly reveals that C4-QPSs and C10-QPSs exhibit higher thermal stability than that of A-QVI, B-QVI, and E-QVI. The TGA and DTG curves of membranes are shown in Figure 3c and d. TGA curves reveal that the decomposition process of the as-prepared membranes can be divided into three stages: the first stage of water evaporation from the membrane (30−200 °C), the second stage of degradation of side chains of CS and QPSs (200−340 °C), and the third stage of degradation of their backbones (340−800 °C). In agreement with FTIR results, CS/QPSs exhibit higher weight loss (9.6− 10.4%) than the CS control membrane (8.9%) during the first stage. Beyond that, the physical mixture and close component of CS and QPSs offer similar thermal degradation behavior to the composite membrane when compared with that of the CS control membrane. All the as-prepared membranes show similar thermal degradation behaviors, which can be clearly seen from their DTG curves (Figure 3d), where two stages (two peaks) of fast thermal degradation can be observed. The peak at 82 °C should be attributed to the rapid evaporation of moisture. The peak at 274 °C is owing to the fast thermal degradation of the CS side chain. 3.5. Molecular Electrostatic Potential (MEP), IEC, Water Uptake, and Swelling Ratio. As the OH− hopping site, the MEP of the QA group strongly influences its energy barrier for OH− conduction. The MEP values of QA groups in QPSs are calculated in the GAUSSIAN 09W package at the DFT/B3LYP level, and the MEP maps are shown in Figure 4a

1250.9, 1167.5, 1531.2, and 1163.5 MPa, respectively. The promoted chain motion leads to a break of the composite matrix, resulting in the lower elongation at a break of 6.2%, 11.3%, 7.4%, 7.5%, and 9.2%, correspondingly. Increasing the QPSs content generates stronger interference with CS bulk, and the Young’s modulus of composite membranes elevates while elongations at a break reduce (Figure S7). For the composite membrane, different strengths of interfacial interaction result in diverse mechanical properties. Generally, strong or more interfacial interaction leads to high chain motion and hence low elongation at a break, whereas weak interfacial interaction affords high elongation at a break. The morphology regulation also affects the crystalline structure of membranes. For the CS-based membrane, the hydrogen-bonding interactions provide semicrystalline character, as confirmed by the scattering bands of 11.3° and 22.5° in XRD (Figure S8). For composite membranes, the interference from QPSs with CS chain motion inhibits the ordered stacking near interface, slightly reducing the band intensity (i.e., crystalline). 3.4. Thermal Properties of the QPSs and Membranes. The thermal stability of as-prepared QPSs is examined by TGA and DTG, as shown in Figure 3a and b. TGA curves in Figure 3a reveal that PSs display a two-stage weight loss: the evaporation of adsorbed water (30−140 °C) and the decomposition of the functional group and polymer skeleton (286−436 °C). QPSs display a similar degradation behavior to PSs due to that the quaternization only introduces small organic ligands without altering their pristine structure. However, the degradation temperatures for the second stage can be divided into two classes. C4-QPSs and C10-QPSs possess high thermal stability as PSs due to the electron-donating property of n-butyl and decyl. The electron-donating effect enhances the electron density of the imidazole ring and then 9069


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Industrial & Engineering Chemistry Research Table 2. IEC Values, Ea Values, and Ionic Conductivities of the Membranes in This Work and the Literature membrane CS/GA GPPO-0.05 CS/K-4 QPVA/5 wt %GA Mi-GOH CS/C4-QPSs-6 CS/A-QPSs-6 CS/E-QPSs-6 PES-MeIm/OH PSGOH-0.4 QPAE QPSF/5%MMT-1 PEEK-Q-60 quaternized poly(ether-imide) QAPVA/GA FPAEO-1.0MIM CPAES-Q80 PVA/TiO2-2% PVDF-QVBC 5

IEC (mmol g−1)

temp (°C)

σ (mS cm−1)

RT RT RT 30 30 20 20 20 25 20 20 25 20 RT RT 20 25 30 25

1 11 12 1.2 5.5−5.7 3.78 3.14 4.22 1.8 5.0 5.6 10 12 2.3 2.8−7.3 4.5 30.1 5.6 36

0.37 0.39 0.41 0.22−0.41 0.53 0.52 0.51 0.56 0.79 0.87 0.90 0.98 1.14 1.43 2.38

Ea (kJ mol−1)

16−21 17.4 18.0 16.5

24.07 16.1

6.5−12.3 19.7 10.4 11.0

ref 47 48 49 44 50 this study this study this study 51 52 53 54 55 56 57 58 59 60 61

membranes obey the same order of the QPSs. Due to the high value (above 1.8 mmol g−1) of QPSs, the composite membranes display higher IEC values (above 0.48 mmol g−1) than the CS control membrane (0.4 mmol g−1). Compared with the IEC values in the literature (Table 2), the IEC values of the as-prepared membranes are comparable to those of other membranes. Additionally, the tested IEC values for composite membranes are a little higher than their theoretical values. This indicates that the promoted mobility of CS chains and decreased crystallinity allow more available functional groups to exchange with OH−. It should be noted that IEC is related to the amount of available exchangeable groups, which, actually, are carrier sites for OH−. The IEC values of QPSs and membranes have a strong influence on hydroxide conductivity. Figure 4d depicts the water uptake and swelling ratio of membranes at 20 °C. The CS control membrane attains a water uptake of 90%, close to the values in the literature.28,37 As QPSs possess high water absorbing capacity (Figure S10), the incorporation of QPSs obviously elevates the water uptake of the composite membrane by over 12.2%. Again, the values of water uptake for composite membranes are higher than theoretical values. Considering the highly cross-linked structure of QPSs, this result is probably due to the enhanced motion of CS chains and the decreased crystallinity, which promote water adsorption and storage. The adsorbed water and enhanced chain mobility directly yields a high swelling ratio to the composite membrane. For the five kinds of composite membranes, their water uptakes and swelling ratios vary with electrostatic potentials of the filled QPSs, roughly following the order of CS/E-QPSs-6 > CS/C4-QPSs-6 > CS/A-QPSs-6 > CS/C10-QPSs-6 > CS/B-QPSs-6. This indicates that the high electrostatic potential of QA groups generates strong electrostatic repulsion to CS chains, conferring high CS chain motion and hence high water uptake and swelling ratio and vice versa. To further verify this conjecture, Table S1 lists the comparison of the enhancements of water uptake and the swelling ratio, which suggest that the enhancements of the swelling ratio of composite membranes are higher than those of water uptake. The result suggests that the enhanced chain motion is an important contribution for the increase of membrane uptaking

and b. Note that colors in the map represent the values of the electrostatic potential at the surface, and the potential enhances in the order of red < orange < yellow < green < blue. The color code of these maps falls in the range from −0.179 a.u. (deepest red) to 0.179 a.u. (deepest blue) in the compound, where red and blue correspond repulsion and attraction to electron, respectively. The electrostatic potential of QA groups in Figure 4a is obtained without setting the total charge (+1), from which it can be found that the electron-donating ligand displays positive potential whereas the electron-withdrawing ligand exhibits negative potential. Figure 4b illustrates the total density by setting one charge to QA groups. As expected, E-QVI displays the highest electrostatic potential (0.179 a.u.) due to the strong electron-withdrawing ability of the ester group. In contrast, the electron-donating ability of n-butyl and decyl results in low electrostatic potential for C4-QVI and C10-QVI, and the longer alkyl chain makes C10-QVI lower electrostatic potential (0.172 a.u.) than C4-QVI (0.173 a.u.). Different from the general electron-withdrawing group, the π-electron delocalization of benzyl donates a partial electron cloud to the imidazole ring, affording the lowest electrostatic potential (0.171 a.u.) to B-QVI. IEC values for QPSs and membranes are shown in Figure 4c. The QPSs attain relatively close IEC values in the range of 1.80−2.24 mmol g−1 which should result from the similar chemical structure and component of QPSs. The IEC value of QPSs is higher than those of QA modified inorganic fillers and is one of the highest values in the literature at present.44−46 For QPSs, the IEC value varies with the QA ligand in the order of C4-QPSs > A-QPSs > C10-QPSs > E-QPSs > B-QPSs. For the electron-withdrawing ligand (e.g., A- and E-), the decreased electron cloud of the imidazole group endows the QA with higher potential, which generates a strong electrostatic attraction to Cl− and thus impedes the exchange of Cl− with OH− during the measurement. B-QPSs display the lowest IEC value due to the lowest potential caused by benzyl. As for an electron-donating group (such as C4- and C10-), prolonging the length of the alkyl chain produces an additional shielding effect to QA and then suppresses the ion exchange process, giving a lower IEC value to C10-QPSs. The IEC values of composite 9070


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Figure 5. (a) Hydroxide conductivities of QPSs at 20 °C under 0% RH. Hydroxide conductivities of the membranes at 20 °C under 0% RH (b) and 100% RH (c). Temperature-dependent conductivities of the membranes (d). Arrhenius plots (e and f) of hydroxide conductivity of the membranes under 100% RH.

OH− transfer mainly adopts a hopping manner under anhydrous conditions, in which OH− first combines with the carrier site (i.e., QA group) and then dissociates from it to complete one “jump”. Like the protonation and deprotonation for proton hopping, the interaction between OH− and carrier site should be moderate, that is the acceptor and donor capability of carrier site should be moderate. This can be understood by the facts that (i) high electrostatic potential can endow the QA group with strong acceptor capability to OH−, whereas the subsequent OH− dissociation might be “trapped”; (ii) low electrostatic potential makes the OH− dissociation easy from the QA group, while the next combination with another OH− is laborsome. The highest OH− conductivity of C4-QPSs implies that the C4-ligand endows the QA group with moderate acceptor/donor capability. Slightly different from the C4-ligand, the long hydrocarbon chain acts as transfer barrier for OH− and makes the OH− combination and dissociation of the QA group

and swelling. As the temperature elevates, all membranes exhibit promoted water uptakes and swelling ratios due to the enhanced chain mobility, yet all the membranes maintain acceptable swelling ratios at 80 °C (Figure S11). 3.6. Hydroxide Conductivity. As the key parameter, high hydroxide conductivity of AEM, that is efficient hydroxide transfer, can yield high fuel cell performance. For better investigating the hydroxide conduction property of membranes, the hydroxide conductivities of QPSs at a dry state are tested by pressing the powder into a disk. Figure 5a exhibits their conductivities at 20 °C and anhydrous condition. As expected, the hydroxide conductivities of the composite membranes are influenced by their IEC values and follow the same order of C4QPSs (4.02 × 10−2 mS cm−1) > A-QPSs (3.79 × 10−2 mS cm−1) > E-QPSs (3.56 × 10−2 mS cm−1) > C10-QPSs (3.27 × 10−2 mS cm−1) > B-QPSs (2.85 × 10−2 mS cm−1), close but different from the order of the electrostatic potential. In fact, 9071


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The conductivities of composite membranes follow the order of CS/E-QPSs-6 (4.92 mS cm−1) > CS/C4-QPSs-6 (3.78 mS cm−1) > CS/A-QPSs-6 (3.14 mS cm−1) > CS/C10-QPSs-6 (2.88 mS cm−1) > CS/B-QPSs-6 (2.63 mS cm−1). This order is close to that of the conduction ability of QPSs, except for CS/ E-QPSs-6, which acquires the highest OH− conductivity. This finding should be attributed to the electronegative O atom in an ester group as testified by MEP, which can form additional hydrogen bonds with water for OH− hopping through QA groups. For composite membranes, increasing QPSs content further elevate OH− conductivity by generating more efficient hopping sites. It should be noted that a comparison of OH− conductivity and conductivity improvement of the as-prepared membranes with those reported in the literature is conducted and listed in Table S2. Although the achieved conductivities of QPSs-filled membranes are a little lower than the results reported in the literature as the membrane matrix of CS is not quaternized, the improvement degree upon QPSs incorporation is higher than most of the other fillers. This corroborates the distinct promotion ability of QPSs on OH− conduction property of AEMs by providing a larger amount of QA groups. The temperature-dependent conductivities of membranes from 20 to 90 °C are shown in Figure 5d and Figure S12. The promoted motion of polymer chains and activated water molecules at elevated temperature result in the positive correlation between OH− conductivity and temperature, indicating that the OH− conduction under hydrated condition is a thermally activated process. For instance, the conductivity of the CS control membrane increases from 1.0 to 8.0 mS cm−1 within this temperature range. The composite membranes possess higher conductivities than that of the CS control membrane at every temperature, and the maximum conductivity is obtained by CS/E-QPSs-8 of 17.7 mS cm−1 at 90 °C. To obtain the activation energy (Ea), these conductivity data are shown as Arrhenius plots in Figure 5e and f, from which the energy needed for hydroxide transfer is calculated using the Arrhenius equation. The CS control membrane attains the Ea of 21.9 kJ mol−1, and this value decreases to the range of 18.9−16.5 kJ mol−1 for the composite membranes, which is close to the range (16−21 kJ mol−1) in the literature for OH− conduction with water molecules.50 The reduced Ea infers easy hydroxide transfer within the composite membrane driven by the incorporation of QPSs. Increasing QPSs content gives more hopping sites to the composite membrane and then results in a gradual reduction of Ea values. For instance, the Ea values of CS/E-QPSs decrease from 17.8 to 16.1 kJ mol−1 as filler content increases from 2% to 8%. The Ea values of composite membranes vary with QPSs and follow the order of CS/E-QPSs-6 < CS/C4-QPSs-6 < CS/A-QPSs-6 < CS/C10QPSs-6 < CS/B-QPSs-6. As expected, this is in agreement with the tendency of their OH− conduction ability. Collectively, these results suggest that the QPSs with the high QA group loading amount possess obvious promotion ability for OH− migration of AEM, and the structure of the QA group has a great influence on the conduction ability of QPSs and QPSfilled membranes. 3.7. The Influence of Physical Structure of QPSs on Membrane Properties. As the structure of QA groups obviously affects the conduction ability of the QPSs-filled membrane, another two series of QPSs with different particle size and cross-linking degree are synthesized by controlling the reaction time and cross-linker dosage, respectively. Considering the highest promotion ability of E-QPSs for OH− conduction,

in C10-QPSs difficult when compared with that in C4-QPSs. By comparison, E-QPSs or B-QPSs with the highest or lowest electrostatic potential displays a little lower OH− conductivity due to the unoptimized OH− acceptor/donor capability. Although the relevant phenomenon is seldom reported for OH− conductivity, similar observation has been found for proton conduction.62−64 The OH− conductivities of membranes under both anhydrous and hydrous conditions are tested to well investigate the functions of QPSs on the prepared AEM. Although it has little significance to practical application, OH− conductivity under 0% RH is probed to avoid the influence of water on OH− transfer. Figure 5b reveals that the CS control membrane displays a conductivity of 2.87 × 10−3 mS cm−1 at 20 °C achieved by the existence of hopping sites (−NH3+) in the CS chain, close to the value in the literature.35 In comparison, composite membranes exhibit obviously enhanced OH− conductivities (over 54%) resulting from the increased IEC values and the excellent conduction capability of QPSs as well as additional transfer pathway. At the CS-QPSs interface, the OH− hops along the cambered transfer pathway. Besides, the OH− also transports through the agminated hopping sites within QPSs. As expected, the conductivities of composite membranes display the similar order to that of QPSs: CS/C4QPSs-6 > CS/A-QPSs-6 > CS/E-QPSs-6 > CS/C10-QPSs-6 > CS/B-QPSs-6, which also confirms that the QPSs own the capability to enhance the OH− conduction ability of AEMs. In addition, the test values of the composite membranes are close but slightly higher than their theoretical values, a similar observation found in IEC values. This phenomenon should be attributed to the promoted motion of CS chains and the decreased crystallinity, which results in letting more functional groups in the CS matrix transport OH−. OH− conductivities of membranes under hydrated condition (20 °C), the key parameter for evaluating one AEM for practical application, are depicted in Figure 5c. The CS control membrane obtains a conductivity of 1.46 mS cm−1, which is close to the value reported in the literature.47 Since the Grotthuss mechanism (OH− hopping from one cationic group to a neighboring one through a hydrogen-bond network), diffusion, and migration (OH− diffusing with water molecule) are regarded as the predominant mechanisms for OH− transfer under hydrated condition, a water molecule plays a critical role for AEM to achieve high OH− conduction, and the relationship between water content and hydroxide conductivity has been demonstrated by Kreuer et al.65 On one hand, water molecules provide sufficient carriers for OH− diffusion; on the other hand, they can form continuous hydrogen-bond networks to support the OH− hopping. In such a way, the conduction efficiency of QA groups is obviously activated. Similar to that found in the CS control membrane, the hydrated conductivities of composite membranes are much higher than those under anhydrous condition by about 550−850 times. Compared with the CS control membrane, the enhanced conductivities of composite membranes are probably due to the more effective QA groups and higher water uptake. Besides, the addition of QPSs significantly elevates the conduction ability of the composite membrane. The hydroxide conductivities of composite membranes fall in the range of 2.63−4.92 mS cm−1. Compared with commercial AEM of Tokyuyama A-201 (38 mS cm−1, 20 °C, 100% RH), the low conduction property of the as-prepared membrane is reasonably due to the low QA loading amount and nonexistence of continuous ionic clusters. 9072


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Figure 6. Water uptake and swelling ratio (a) and hydroxide conductivity (b) of the membranes containing QPSs with different particle size; water uptake and swelling ratio (c) and hydroxide conductivity (d) of the membranes containing QPSs with different cross-linking degrees. The testing condition is 20 °C under 100% RH.

weak water adsorption and storage capability. The OH− conductivities of the composite membrane are shown in Figure 6d, which implies that the OH− conductivity displays a similar trend to that of water uptake of the membrane. The conductivity reduces from 4.73 to 3.86 mS cm−1 as the ratio increases from 1/3 to 3/1. It should be noted that further decreasing the ratio of the cross-linker (i.e., lower cross-linking degree) will make the pelletizing difficult, and therefore the cross-linker/functional monomer ratio is kept above 1/3. 3.8. Alkaline Stability of Membranes. Sufficient alkaline stability of AAEM is crucial to the stable performance of a fuel cell.66 The alkaline stability of the membrane is investigated in a 1.0 M KOH aqueous solution at 80 °C for 240 h, and the alterations in IEC, conductivity, and mechanical property with time are recorded. As shown in Figure 7a and b, the IEC and conductivity of all the membranes display acceptable stability with the reduction below 10%. This also suggests that the asprepared membranes maintain structural and component stabilities, resulting from the cross-linked structure and adequate alkali stability of imidazolium cation. This can be further proven by the mechanical stability of membranes as depicted in Figure 7c, which reveals only a slight reduction in tensile strength after being immersed in KOH solution for 240 h.

E-QVI is selected as the functional group to synthesize the QPSs. By altering the reaction time from 15 to 45 min, three EQPSs with particle size of about 0.48, 0.98, and 1.5 μm are obtained, and the water uptake, swelling ratio, and OH− conductivity of CS/E-QPSs are shown in Figure 6a and b. The composite membranes display higher water uptake and swelling ratio than the CS control membrane. Increasing the particle size of E-QPSs reduces the water uptake of the composite membrane due to the decreased specific surface area. E-QPSs with large dimension might generate stronger interference with CS chains and then offer a slight increase of the swelling ratio. The OH− conductivity at 20 °C under RH 100% in Figure 6b clearly reveals that the OH− conduction ability of the composite membrane becomes weak with the size of QPSs increases, as the OH− conductivity reduces from 5.02 to 3.74 mS cm−1. The reduced specific surface area and water uptake should be responsible for the conductivity reduction. During the polymerization of QPSs, their internal structure can be facilely regulated by the dosage of the cross-linker to give different water uptake and OH− conducting ability. Similarly, three kinds of E-QPSs with diverse cross-linking degrees are synthesized by changing the cross-linker/functional monomer ratios to 1/3, 1/1, and 3/1, respectively. The change in internal structure can be reflected by their XRD patterns in Figure S4. Figure 6c indicates that although water uptake and the swelling ratio of the composite membranes are higher than those of the CS control membrane, both reduce with the increase of the cross-linking degree. This is reasonably due to the dense chain stacking and reduced interfacial interaction under an elevated cross-linker ratio, which cocontributes the

4. CONCLUSION In summary, quaternized polymer spheres with the high QA group loading amount and controllable structure are synthesized to enhance the OH− conductivity of AEM. The QPSs display well compatibility with the CS matrix and uniform 9073


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Figure 7. Time-dependent IEC (a) and conductivity (b) of membranes in 1.0 M KOH solution at 80 °C. (c) Tensile strength of membranes before and after being immersed in KOH solution for 240 h.

dispersion within the membrane, slightly elevating the thermal and mechanical stabilities. Repulsive interactions emerge in CSQPSs interface, promoting CS chain motion and then slightly reducing the crystallinity of the CS matrix. As a result, the composite membranes exhibit high water uptake and swelling ratio. The data of MEP and OH− conductivity suggest the QPSs give significant promotion to OH− conduction of the composite membrane by over 80%, and both the chemical and physical structures govern the OH− conductivity of QPSs and the QPS-filled membrane. The QA groups with moderate electrostatic potential endow QPSs with both easy OH− combination and dissociation ability, affording fast OH− hopping. Unoptimized OH− donor or acceptor capability and a long ligand increase the energy barrier for OH− hopping, resulting in lower OH− conductivities of QPSs and the QPSfilled membrane. In addition, reducing the particle size or crosslinking degree of QPSs can elevate the OH− conduction ability of the composite membrane by providing a large surface area and a loose chain network.

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and hydroxide conductivities (Figure S12) as a function of temperature of the membranes; enhancement of swelling ratio and water uptake of the composite membranes and their comparison (Table S1); hydroxide conductivities of the membranes prepared in the literature and this study (Table S2) (PDF)

AUTHOR INFORMATION

Corresponding Author

*Phone (Fax): +86-371-63887135. E-mail: jingtaowang@zzu. edu.cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (21576244, 21476215, and U1407121).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b01741. Nyquist plot of the sample (Figure S1); SEM images (Figure S2), FTIR spectra (Figure S3), XRD patterns (Figure S4), and water uptake (Figure S10) of the polymer sphere; FTIR spectra (Figure S5), DSC curves (Figure S6), stress−strain curves (Figure S7), and XRD patterns (Figure S8) of the membranes; TGA curves (Figure S9), water uptake, swelling ratio (Figure S11),

REFERENCES

(1) Chen, C.; Tse, Y. L. S.; Lindberg, G. E.; Knight, C.; Voth, G. A. Hydroxide solvation and transport in anion exchange membranes. J. Am. Chem. Soc. 2016, 138, 991. (2) Zeng, L.; Zhao, T. S. An effective strategy to increase hydroxideion conductivity through microphase separation induced by hydrophobic-side chains. J. Power Sources 2016, 303, 354. (3) Tanaka, M.; Fukasawa, K.; Nishino, E.; Yamaguchi, S.; Yamada, K.; Tanaka, H.; Bae, B.; Miyatake, K.; Watanabe, M. Anion conductive block poly(arylene ether)s: synthesis, properties, and application in alkaline fuel cells. J. Am. Chem. Soc. 2011, 133, 10646.

9074


Article


and charge density for molecular/ionic separation. J. Membr. Sci. 2015, 496, 250. (24) Li, N. W.; Leng, Y. J.; Hickner, M. A.; Wang, C. Y. Highly stable, anion conductive, comb-shaped copolymers for alkaline fuel cells. J. Am. Chem. Soc. 2013, 135, 10124. (25) Liu, H.; Yang, S. L.; Wang, S. L.; Fang, J.; Jiang, L. H.; Sun, G. Q. Preparation and characterization of radiation-grafted poly (tetrafluoroethylene-co- perfluoropropyl vinyl ether) membranes for alkaline anion-exchange membrane fuel cells. J. Membr. Sci. 2011, 369, 277. (26) Merle, G.; Wessling, M.; Nijmeijer, K. Anion exchange membranes for alkaline fuel cells: a review. J. Membr. Sci. 2011, 377, 1. (27) Yang, Y. Q.; Wang, J.; Zheng, J. F.; Li, S. H.; Zhang, S. B. A stable anion exchange membrane based on imidazolium salt for alkaline fuel cell. J. Membr. Sci. 2014, 467, 48. (28) Shi, B. B.; Li, Y. F.; Zhang, H. Q.; Wu, W. J.; Ding, R.; Dang, J. C.; Wang, J. T. Tuning the performance of anion exchange membranes by embedding multifunctional nanotubes into a polymer matrix. J. Membr. Sci. 2016, 498, 242. (29) Li, Q.; Liu, L.; Liang, S. E.; Dong, Q. B.; Jin, B. K.; Bai, R. K. Preparation and characterization of composite membranes with ionic liquid polymer-functionalized multiwalled carbon nanotubes for alkaline fuel cells. RSC Adv. 2013, 3, 13477. (30) Ye, Y. S.; Cheng, M. Y.; Xie, X. L.; Rick, J.; Huang, Y. J.; Chang, F. C.; Hwang, B. J. Alkali doped polyvinyl alcohol/graphene electrolyte for direct methanol alkaline fuel cells. J. Power Sources 2013, 239, 424. (31) Zarrin, H.; Fu, J.; Jiang, G.; Yoo, S.; Lenos, J.; Fowler, M.; Chen, Z. Quaternized graphene oxide nanocomposites as fast hydroxide conductors. ACS Nano 2015, 9, 2028. (32) Wang, E. D.; Zhao, T. S.; Yang, W. W. Poly (vinyl alcohol)/3(trimethy lammonium) propyl-functionalized silica hybrid membranes for alkaline direct ethanol fuel cells. Int. J. Hydrogen Energy 2010, 35, 2183. (33) Hossain, M. A.; Lim, Y.; Lee, S.; Jang, H.; Choi, S.; Jeon, Y.; Lee, S.; Ju, H.; Kim, W. G. Anion conductive aromatic membrane of poly(tetra phenyl ether sulfone) containing hexa-imidazolium hydroxides for alkaline fuel cell application. Solid State Ionics 2014, 262, 754. (34) Ramalingam, B.; Khan, M. M. R.; Mondal, B.; Mandal, A. B.; Das, S. K. Facile Synthesis of silver nanoparticles decorated magneticchitosan microsphere for efficient removal of dyes and microbial contaminants. ACS Sustainable Chem. Eng. 2015, 3, 2291. (35) Wan, Y.; Creber, K. A. M.; Peppley, B.; Bui, V. T. Chitosanbased electrolyte composite membranes II. Mechanical properties and ionic conductivity. J. Membr. Sci. 2006, 284, 331. (36) Poynton, S. D.; Varcoe, J. R. Reduction of the monomer quantities required for the preparation of radiation-grafted alkaline anion-exchange membranes. Solid State Ionics 2015, 277, 38. (37) Sabaa, M. W.; Mohamed, N. A.; Mohamed, R. R.; Khalil, N. M.; Abd El Latif, S. M. Synthesis, characterization and antimicrobial activity of poly (N-vinyl imidazole) grafted carboxymethyl chitosan. Carbohydr. Polym. 2010, 79, 998. (38) Hu, J.; Wan, D. L.; Zhu, W. G.; Huang, L. H.; Tan, S. Z.; Cai, X.; Zhang, X. J. Fabrication of a high-stability cross-linked quaternized poly (epichlorolydrin) /PTFE composite membrane via a facile route. ACS Appl. Mater. Interfaces 2014, 6, 4720. (39) Lin, B. C.; Qiu, L. H.; Qiu, B.; Peng, Y.; Yan, F. A soluble and conductive polyfluorene ionomer with pendant imidazolium groups for alkaline fuel cell applications. Macromolecules 2011, 44, 9642. (40) Kanti, P.; Srigowri, K.; Madhuri, J.; Smitha, B.; Sridhar, S. Dehydration of ethanol through blend membranes of chitosan and sodium alginate by pervaporation. Sep. Purif. Technol. 2004, 40, 259. (41) Chuang, W. Y.; Young, T. H.; Yao, C. H.; Chiu, W. Y. Properties of the poly(vinyl alcohol)/chitosan blend and its effect on the culture of fibroblast in vitro. Biomaterials 1999, 20, 1479. (42) Yang, J. M.; Su, W. Y.; Leu, T. L.; Yang, M. C. Evaluation of chitosan/PVA blended hydrogel membranes. J. Membr. Sci. 2004, 236, 39.

(4) Pan, J.; Chen, C.; Zhuang, L.; Lu, J. T. Designing advanced alkaline polymer electrolytes for fuel cell applications. Acc. Chem. Res. 2012, 45, 473. (5) Zarrin, H.; Jiang, G.; Lam, G. Y. Y.; Fowler, M.; Chen, Z. High performance porous polybenzimidazole membrane for alkaline fuel cells. Int. J. Hydrogen Energy 2014, 39, 18405. (6) Wright, A. G.; Holdcroft, S. Hydroxide-stable ionenes. ACS Macro Lett. 2014, 3, 444. (7) Si, Z. L.; Qiu, L. H.; Dong, H. L.; Gu, F. L.; Li, Y. Y.; Yan, F. Effects of substituents and substitution positions on alkaline stability of imidazolium cations and their corresponding anion exchange membranes. ACS Appl. Mater. Interfaces 2014, 6, 4346. (8) Si, Z.; Sun, Z.; Gu, F. L.; Qiu, L. H.; Yan, F. Alkaline stable imidazolium-based ionomers containing poly(arylene ether sulfone) side chains for alkaline anion exchange membranes. J. Mater. Chem. A 2014, 2, 4413. (9) Pan, J.; Lu, S. F.; Li, Y.; Huang, A. B.; Zhuang, L.; Lu, L. T. Highperformance alkaline polymer electrolyte for fuel cell applications. Adv. Funct. Mater. 2010, 20, 312. (10) Vandiver, M. A.; Caire, B. R.; Pandey, T. P.; Li, Y. F.; Seifert, S.; Kusoglu, A.; Knauss, D. M.; Herring, A. M.; Liberatore, M. W. Effect of hydration on the mechanical properties and ion conduction in a polyethylene-b-poly(vinylbenzyl trimethylammonium) anion exchange membrane. J. Membr. Sci. 2016, 497, 67. (11) Bayer, T.; Cunning, B. V.; Selyanchyn, R.; Daio, T.; Nishihara, M.; Fujikawa, S.; Sasaki, K.; Lyth, S. M. Alkaline anion exchange membranes based on KOH-treated multilayer graphene oxide. J. Membr. Sci. 2016, 508, 51. (12) Si, J. J.; Lu, S. F.; Xu, X.; Peng, S. K.; Xiu, R. J.; Xiang, Y. A gemini quaternary ammonium poly (ether ether ketone) anionexchange membrane for alkaline fuel cell: design, synthesis, and properties. ChemSusChem 2014, 7, 3389. (13) Park, J. S.; Park, S. H.; Yim, S. D.; Yoon, Y. G.; Lee, W. Y.; Kim, C. S. Performance of solid alkaline fuel cells employing anion-exchange membranes. J. Power Sources 2008, 178, 620. (14) Fang, J.; Shen, P. K. Quaternized poly (phthalazinon ether sulfone ketone) membrane for anion exchange membrane fuel cells. J. Membr. Sci. 2006, 285, 317. (15) Xu, T.; Liu, Z.; Li, Y.; Yang, W. Preparation and characterization of type II anion exchange membrane from poly(2,6 dimethyl-1,4phenylene oxide) (PPO). J. Membr. Sci. 2008, 320, 232. (16) Wang, C. Y.; Shen, B.; Xu, C.; Zhao, X. Y.; Li, J. Side-chain-type poly(arylene ether sulfone)s containing multiple quaternary ammonium groups as anion exchange membranes. J. Membr. Sci. 2015, 492, 281. (17) Varcoe, J. R.; Atanassov, P.; Dekel, D. R.; Herring, A. M.; Hickner, M. A.; Kohl, P. A.; Kucernak, A. R.; Mustain, W. E.; Nijmeijer, K.; Scott, K.; Xu, T.; Zhuang, L. Anion-exchange membranes in electrochemical energy systems. Energy Environ. Sci. 2014, 7, 3135. (18) Wang, Y. J.; Qiao, J. L.; Baker, R.; Zhang, J. J. Alkaline polymer electrolyte membranes for fuel cell applications. Chem. Soc. Rev. 2013, 42, 5768. (19) Singh, S.; Jasti, A.; Kumar, M.; Shahi, V. K. A green method for the preparation of highly stable organic-inorganic hybrid anionexchange membranes in aqueous media for electrochemical process. Polym. Chem. 2010, 1, 1302. (20) Yan, J. L.; Hickner, M. A. Anion-exchange membranes by bromination of benzylmethyl containing poly(sulfone)s. Macromolecules 2010, 43, 2349. (21) Mohanty, A. D.; Lee, Y. B.; Zhu, L.; Hickner, M. A.; Bae, C. Anion exchange fuel cell membranes prepared from C−H borylation and Suzuki coupling reactions. Macromolecules 2014, 47, 1973. (22) Xu, T. W.; Liu, Z. M.; Yang, W. H. Fundamental studies of a new series anion exchange membranes: membrane prepared from poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) and trimethylamine. J. Membr. Sci. 2005, 249, 183. (23) Manohar, M.; Thakur, A. K.; Pandey, R. P.; Shahi, V. K. Efficient and stable anion exchange membrane: Tuned membrane permeability 9075


Article

Industrial & Engineering Chemistry Research (43) Rachipudi, P. S.; Kittur, A. A.; Sajjan, A. M.; Kariduraganavar, M. Y. Synthesis and characterization of hybrid membranes using chitosan and 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane for pervaporation dehydration of isopropanol. J. Membr. Sci. 2013, 441, 83. (44) Yang, C. C.; Chiu, S. S.; Kuo, S. C.; Liou, T. H. Fabrication of anion-exchange composite membranes for alkaline direct methanol fuel cells. J. Power Sources 2012, 199, 37. (45) Liu, L.; Tong, C.; He, Y.; Zhao, Y.; Hu, B.; Lü, C. Novel quaternized mesoporous silica nanoparticle modified polysulfonebased composite anion exchange membranes for alkaline fuel cells. RSC Adv. 2015, 5, 43381. (46) Zhu, Y.; Chen, C.; Zuo, D.; Zhang, H. Hybrid anion-exchange membranes derived from quaternized polysulfone and functionalized titanium dioxide. Electrochim. Acta 2015, 177, 128. (47) Wan, Y.; Creber, K. A. M.; Peppley, B.; Bui, V. T. Ionic conductivity and related properties of crosslinked chitosan membranes. J. Appl. Polym. Sci. 2003, 89, 306. (48) Lin, X.; Wu, L.; Liu, Y.; Ong, A. L.; Poynton, S. D.; Varcoe, J. R.; Xu, T. Alkali resistant and conductive guanidinium-based anionexchange membranes for alkaline polymer electrolyte fuel cells. J. Power Sources 2012, 217, 373. (49) Wan, Y.; Peppley, B.; Creber, K. A. M.; Bui, V. T.; Halliop, E. Preliminary evaluation of an alkaline chitosan-based membrane fuel cell. J. Power Sources 2006, 162, 105. (50) Sherazi, T. A.; Zahoor, S.; Raza, r.; Shaikh, A. J.; Naqvi, A. A. R.; Abbas, G.; Khan, Y.; Li, S. Guanidine functionalized radiation induced grafted anion-exchange membranes for solid alkaline fuel cells. Int. J. Hydrogen Energy 2015, 40, 786. (51) Lu, W.; Shao, Z.; Zhang, G.; Zhao, Y.; Li, J.; Yi, B. Preparation and characterization of imidazolium functionalized poly(ether sulfone) as anion exchange membrane and ionomer for fuel cell application. Int. J. Hydrogen Energy 2013, 38, 9285. (52) Wang, J.; Li, S.; Zhang, S. Novel hydroxide-conducting polyelectrolyte composed of a poly (arylene ether sulfone) containing pendant quaternary guanidinium groups for alkaline fuel cell applications. Macromolecules 2010, 43, 3890. (53) Li, X.; Liu, Q.; Yu, Y.; Meng, Y. Quaternized poly(arylene ether) ionomers containing triphenyl methane groups for alkaline anion exchange membranes. J. Mater. Chem. A 2013, 1, 4324. (54) Liao, X.; Ren, L.; Chen, D.; Liu, X.; Zhang, H. Nanocomposite membranes based on quaternized polysulfone and functionalized montmorillonite for anion-exchange membranes. J. Power Sources 2015, 286, 258. (55) Xu, S.; Zhang, G.; Zhang, Y.; Zhao, C.; Zhang, L.; Li, M.; Wang, J.; Zhang, N.; Na, H. Cross-linked hydroxide conductive membranes with side chains for direct methanol fuel cell applications. J. Mater. Chem. 2012, 22, 13295. (56) Wang, G.; Weng, Y.; Chu, D.; Xie, D.; Chen, R. Preparation of alkaline anion exchange membranes based on functional poly (etherimide) polymers for potential fuel cell applications. J. Membr. Sci. 2009, 326, 4. (57) Xiong, Y.; Fang, J.; Zeng, Q.; Liu, Q. Preparation and characterization of cross-linked quaternized poly(vinyl alcohol) membranes for anion exchange membrane fuel cells. J. Membr. Sci. 2008, 311, 319. (58) Hu, Q.; Shang, Y.; Wang, Y.; Xu, M.; Wang, S.; Xie, X.; Liu, Y.; Zhang, H.; Wang, J.; Mao, Z. Preparation and characterization of fluorinated poly(aryl ether oxadiazole)s anion exchange membranes based on imidazolium salts. Int. J. Hydrogen Energy 2012, 37, 12659. (59) Nie, G.; Li, X.; Tao, J.; Wu, W.; Liao, S. Alkali resistant crosslinked poly(arylene ether sulfone)s membranes containing aromatic side-chain quaternary ammonium groups. J. Membr. Sci. 2015, 474, 187. (60) Yang, C. C. Synthesis and characterization of the cross-linked PVA/TiO2 composite polymer membrane for alkaline DMFC. J. Membr. Sci. 2007, 288, 51. (61) Ran, J.; Wu, L.; Lin, X.; Jiang, L.; Xu, T. Synthesis of soluble copolymers bearing ionic graft for alkaline anion exchange membrane. RSC Adv. 2012, 2, 4250.

(62) Wang, J. T.; Bai, H. J.; Zhang, H. Q.; Zhao, L. P.; Chen, H. L.; Li, Y. F. Anhydrous proton exchange membrane of sulfonated poly(ether ether ketone) enabled by polydopamine-modified silica nanoparticles. Electrochim. Acta 2015, 152, 443. (63) He, Y. K.; Wang, J.; Zhang, H. Q.; Zhang, T.; Zhang, B.; Cao, S. K.; Liu, J. D. Polydopamine-modified graphene oxide nanocomposite membrane for proton exchange membrane fuel cell under anhydrous conditions. J. Mater. Chem. A 2014, 2, 9548. (64) Wu, W. J.; Li, Y. F.; Chen, P. P.; Liu, J. D.; Wang, J. T.; Zhang, H. Q. Constructing ionic liquid-filled proton transfer channels within nanocomposite membrane by using functionalized graphene oxide. ACS Appl. Mater. Interfaces 2016, 8, 588. (65) Marino, M. G.; Melchior, J. P.; Wohlfarth, A.; Kreuer, K. D. Hydroxide, halide and water transport in a model anion exchange membrane. J. Membr. Sci. 2014, 464, 61. (66) Wright, A. G.; Weissbach, T.; Holdcroft, S. Poly(phenylene) and m-terphenyl as powerful protecting groups for the preparation of stable organic hydroxides. Angew. Chem., Int. Ed. 2016, 55, 4818.

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