Facilitating Anion Transport in Polyolefin-Based Anion Exchange

Subscriber access provided by Northern Illinois University

Article

Facilitating Anion Transport in Polyolefin-based Anion Exchange Membranes via Bulky Side Chains Min Zhang, Chunrong Shan, Lei Liu, Jiayou Liao, Quan Chen, Meng Zhu, Yiguang Wang, Linan An, and Nanwen Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b06426 • Publication Date (Web): 16 Aug 2016 Downloaded from http://pubs.acs.org on August 20, 2016

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.

ACS Applied Materials & Interfaces 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 30

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

ACS Applied Materials & Interfaces

Facilitating Anion Transport in Polyolefin-based Anion Exchange Membranes via Bulky Side Chains Min Zhang§, Chunrong Shan§, Lei Liu∥, Jiayou Liao∥, Quan Chen†, Meng Zhu⊥,Yiguang Wang⊥, Linan An‡ and Nanwen Li∥,* §

College of Materials Science and Engineering, Beijing Institute of Petrochemical Technology, Beijing, 102617, China.

∥

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, China. †

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, China.

‡

Department of Materials Science and Engineering, Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, FL 32816, USA. ⊥

State Key Laboratory of Solidiﬁcation Processing, Northwestern Polytechnical University, Xi’an, 710072, China.

ABSTRACT

Highly anion-conductive polymer electrolyte membranes with excellent alkaline stabilities for fuel cell applications were prepared. Thus, a series of polyolefin copolymers with poly(4-methyl1-pentene) (PMP) moieties containing bulky side-chains and side-chain quaternary ammonium (QA) groups were prepared through copolymerization with Ziegler–Natta catalyst and subsequent quaternization. The separation of hydrophilic micro-phase and hydrophobic microphase was induced by PMP bulky side chains and then well-connected ionic domains were formed. This result was confirmed by AFM (atomic force microscopy) and SAXS (small-angle X-ray scattering) analyses. It was discovered that well-defined ionic domains of the PMP-TMAx membranes depended on the content of PMP moieties. The well-defined ionic domains enhanced the hydroxide conductivity of the PMP-TMA-x membranes despite their lower water uptake (WU) as compared to polypropylene (PP)-containing membranes (PP-TMA-x). The

ACS Paragon Plus Environment


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

PMP-TMA-41 membrane showed the highest ionic conductivity value (43 mS/cm) while maintaining low WU (29.2 wt%) at room temperature. The membranes mostly preserved (> 93.0%) their initial hydroxide conductivity after alkaline treatment (10 M aqueous NaOH, 80 ºC, 700 h), thereby revealing desirable alkali stability characteristics. Presumably, the nucleophilic attack from hydroxide or water in the cationic center is inhibited by long alkyl spacers (-CH2-)n (n = 9) which are located between the cation groups and the polymer backbone.

Graphic abstract

KEYWORDS: poly(4-methyl-1-pentene); anion exchange membranes; phase separation; anion conductivity; alkaline stability.

Introduction

Anion-exchange membrane fuel cells (AEMFC) which have broken the restrictions of conventional proton-exchange membrane fuel cells (PEMFC) in expenses, the size of system,


Page 2 of 30

Page 3 of 30

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


efficiency and catalytic stability have been regarded as the epoch-making progress in the area of fuel cell technology. With the help of anion-exchange membrane (AEM) which is the critical constituent part of AEMFC, fuel is isolated from oxidant and anions are transferred from cathode to anode. It is the primary barrier in AEMFC development to improve the alkali stability, mechanical capacity and oxyhydrate anion conductivity in order to accommodate alkaline, humid, and elevated temperature operating conditions of fuel cell.1,2

Particularly, high ionic conductivity and stability are crucial properties for achieving suitable current values and further applying AEM in fuel cells.3 Thus large quantity of investigations have been conducted to develop more satisfactory polymeric AEM materials such as polyolefins,4

polystyrenes,5

polyphenylene

oxides

(PPO),6–8

polyphenylenes,9

polybenzimidazolium,10 polyarylene ethers,11 and polysulfone12,13 with tethered organic or inorganic cations. Among all these polymeric materials, polyolefins have been demonstrated to be capable of existing stably in electrochemical and alkali conditions for the example of lithiumion charge batteries,14–16 and research has been conducted on AEM materials based on quaternized polyolefins displaying improved performance. Hickner et al.17 systematically demonstrated that the stability of para-substituted styrenic AEM was notably increased in contrast to those of

quaternary ammonium-functionalized polyphenylene oxide and ortho-

substituted polyarylene ether sulfone materials. Thus it was clearly revealed that the quaternary ammonium group was stabilized by the olefinic hydrocarbon backbone type. Chung et al.18 reported the preparation of polyethylene (PE)-based AEM which had ‘side chain-type’ quaternary ammonium groups and the ionic conductivity of which in 2 mol/L HCl solution was 119.6 mS/cm.



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 ring-open metathesis polymerization (ROMP) method on functional monomers followed by hydrogenation was applied in the research of Coats et al.19 to make a solution processable uncrosslinked PE-based AEM which exhibited a high hydroxide conductivity of 65 mS/cm at the temperature of 323.15K. Subsequently, this synthetic method was modified to produce crosslinking AEM materials through copolymerizing cycloolefins and the quaternary derivatives.20Although the alkali stability of unsaturated double bonds in crosslinking unsaturated ROMP polymer was potentially not desirable, the polymer did not tend to be hydrogenated. More recently, Coats et al. prepared AEM containing tetrakis(dialkylamino) phosphonium cations with high alkaline stability (i.e., no loss in conductivity under the condition of 1 mol/L KOH solution for 22 days at the temperature of 353.15K).21 However, the synthetic technique employed was multistep, low yield, or noble metal-catalyzed which increases the process complexity and reduce controllability. Guiver et al. developed a PE grafting method with poly(vinylbenzyltrimethylammonium hydroxide) via a radiation grafting technique.22 The asobtained AEM showed high alkaline stability and moderate conductivity. While these systems displayed a wide range of ionic conductivities and demonstrated reasonable alkaline stabilities as AEM, these key parameters are still limiting the performance of AEMFC.

Moreover, most functionalized polyolefins cannot be directly prepared by the classic and low cost Ziegler–Natta mediated polymerization process since the polar monomers deactivate the catalysts commonly used for the polymerization of olefinic hydrocarbons. In this sense, it was revealed by Bacskai et al.23 that 8-bromo-1-octene was capable of being integrated with PP through a copolymerization process which was promoted by Ziegler–Natta catalyst, although copolymers showing up to ca. 7 mol% functional content could be achieved. In this study, longer spacer (i.e., nine carbon atoms) such as 11-bromo-1-undecene was selected as the co-monomer


Page 4 of 30

Page 5 of 30

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


for a PP copolymer instead of 8-bromo-1-octene which had a six carbon atom spacer.24 High concentration (up to 20.8 mol%) of bromoalkyl-functionalized PP was achieved owing to the higher flexibility of long alkyl chains. They effectively vied with PP which had smaller volume and exhibited lower reactivity in the process of copolymerizing. Thus, a series of cationic polyolefins containing PP moieties and trimethylalkylammonium cations attached by a nonylmethylene spacer were obtained as AEM materials. The as-obtained AEM showed considerable alkaline stability and the results of computational calculations on model compounds sustained this finding. It was proposed in these studies that the alkyl spacers between the quaternary ammonium groups and the polymer backbone which had more than three carbon atoms were capable of improving cation alkali stability.25 Although the PP-based AEM showed promising properties, particularly the alkaline stability, lower anion conductivities were observed probably originated from a poor defined micro morphological structure. We therefore tuned the chemical structure of the polymer backbone to develop a new system with well-defined microphase separation which consequently improved the hydroxide conductivity and meanwhile remained advantageous characters such as alkaline stability.

Isotactic poly(4-methyl-1-pentene) (PMP) containing a bulky side chain combines excellent chemical resistance and high thermal stability characteristics, thereby being widely used in film and coating for gas permeable packaging. The bulky side chain is expected to induce welldefined microphase separation6, 26–29 allowing the incorporation of bromoalkyl moieties in PMPbased polyolefin copolymers at high molar ratios, and resulting in improved AEM anion conductivity. A detailed investigation on the properties of PMP-based polyolefin AEM was performed herein. The conductivity, alkali stability as well as morphological construction were explored and comparative analysis was conducted on these characters of this material and PP-



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

based polyolefin counterparts.

Experimental Section

Materials. 4-Methyl-1-pentene (Tokyo Chemical Industry) was distilled through calcium hydride (CaH2) in vacuum before utilizing. TiCl3·AA, AlEt2Cl (10 wt% dissolved with toluene), trimethylamine (TMA) were obtained from Sigma-Aldrich without further purification. Methanol, sodium hydroxide, tetrahydrofuran (THF), n-heptane, 11-bromo-1-undecene as well as hydrochloric acid were bought from J&K Scientific Ltd. n-heptane and 11-Bromo-1-undecene were purified in accordance of published literature.24

Synthesis of Bromoalkylated Poly(4-methyl-1-pentene) (PMP). The polymerization procedure was carried out according to our previous report24. Herein, the comonomer 4-methyl-1-pentene was used. As an example, an autoclave with mechanical stirrer containing the heptanes, 4methyl-1-pentene, and a given mass of 11-bromo-1-undecene was heated to 343.15K and the temperature was maintained. Subsequently, the prepared TiCl3·AA and Et2AlCl (10 wt% in toluene) mixture was added into the reactor. The reactant liquid was quenched with methanol after reacting for a given period at 343.15K. Subsequently, the bromo-alkylated copolymer was then obtained by precipetation the mixture into acidic methanol solution.

Preparing ion-exchange membranes. The membranes were fabricated from bromoalkylated copolymer by a typical hot press method at a high temperature of 240 oC. The detailed procedure has been described in our previous report.24 Subsequently, the membranes were treated by trimethylamine solution at 35–40 oC for 36 h to obtained quaternized PMP-based anion exchange membranes. After washing by DI water and drying, the membranes were then further hot pressed


Page 6 of 30

Page 7 of 30

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


in vacuum at 373.15K for 1 h. Subsequently, the membranes were treated with 1 mol/L sodium hydroxide of ambient temperature for 48 hours to obtain AEMs of hydroxide form. Membrane characterization. High temperature 1H NMR (Bruker AM-300, 300 MHz) was employed to confirm the polymer composition. A high temperature gelatin permeation chromatography of PL-220 series which had four PLgel Mixed-A (20µm) columns and used polystyrene (PS) as the calibration standard was applied to record the average molecular weight (Mw). A Perkin-Elmer Differential scanning calorimetry DSC-7 was used to conduct measurements and the heating rated was set to 20 °C/min to the membranes in bromide form. Thermogravimetric analysis (TGA) curve was obtained from TA instrument model TA SDT Q600 from 30 to 700 °C and the heating rate was set to 20 °C/min in air atmosphere. A PE-1710 spectrometer was used to measure Fourier transform infrared spectroscopy (FTIR). A universal tester of Instron 5866 was used to evaluate mechanical capacity and the speed was set as 1mm/min. A Rigaku instrument was used to measure small angle X-ray scattering (SAXS) data and a tapping-mode bio-atomic force microscope was used to conduct atomic force microscopy measurements.

The membranes were immersed into 10 mol/L sodium hydroxide at 353.15K for 700h to investigate the alkali stability of AEMs. The variation of hydroxide conductivity and the IEC value of tested membranes were recorded. The standard back-titation methods were used according to previous report24 for determining the IEC values of these membranes which were calculated from the equation (1):

IEC =

n1 • HCl − n2 • HCl (mequiv/ g) M dry


(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 8 of 30

Where n1 ⋅ HCl is the amount (mmol) of hydrogen chloride which was required to titrate the NaOH solution before equilibrium while n2 ⋅ HCl is that after equilibrium. M dry is the dry weight.

Water and methanol uptake. Water uptake (WU) and methanol uptake (MU) are obtained by the following equation:

W (%) =

(Ww − Wd ) × 100% Wd

(2)

where Wd is the weight of dried membranes and Ww is that of completely hydrated membranes. The literature method24 was used to calculate the swelling ratio (SR) and the following equation was the basis of calculation:

Swelling(%)=

X wet − X dry X dry

× 100%

(3)

where X dry and X wet are lengths of dry and wet membranes respectively. The quantity of bound water molecules of each ammonium group (λ) was calculated based on obtained WU and IEC values by equation 4:

λ=

WU 1000 × 18 IEC

(4)

Methanol permeability measurements. Methanol permeability (P, cm2/s) was tested at 30 ºC using a two-chamber diffusion cell method.24


Page 9 of 30

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 two-chamber diffusion cell method

24

was applied to test the permeability of methanol (P,

cm2/s) at 303.15K and a Shimadzu GC-1020A gas chromatograph was used to determine methanol permeance. The permeability was calculated according to the equation as follows:

CB (t) =

A DK × × C A × (t − t 0 ) VB L

(5)

Where C A is the methanol concentration at feed side and CB is that at permeate side. VB , L, A refer to the volume, thickness as well as area of membrane of the permeating compartment separately. t 0 refers to the time lag and DK to the permeability of methanol.

Hydroxide conductivity measurements. The conductivity was measured with AC impedance spectroscopy by the Solartron SI 1260A impedance/gain-phase analyzer.24 The impedance was measured in water under certain temperature and the conductivity (σ, mS/cm) was calculated according to equation 6:

σ OH (mS⋅ cm −1 ) = –

L RA

(6)

where R refers to the ohmic resistance (Ω). L (cm) refers to the space between reference electrodes. A (cm2) refers to the electrode area of the membrane. The hydroxide conductivity was tested in completely hydrated environment where gas was eliminated from tested water and Argon was used to remove CO2 gas.

Fuel Cell Performance. The H2/O2 fuel cell performance testing was carried out.24 Herein, a catalyst-coated membrane (CCM) for membrane electrode assembly was employed. The



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 30

catalyst ink was prepared with deionized water and Pt/C catalysts (TKK, Japan, 46.4 wt%), AS-4 ionomer (Tokuyama Corporation, Japan) (5 wt% in 1-propanol) as well as 1-propanol and then sprayed onto the surface of membrane. The Pt and ionomer loading were designed to be ~0.50 mg/cm2 and ~20 wt.% separately. Subsequently, the assembly of carbon paper (SGL 25BC, Germany) and CCM were used to obtain membrane electrode assembly (MEA) and the area of which was f 2.25 cm × 2.25 cm (about 5 cm2). The H2/O2 fuel cell performance testing at 60 oC under full humidification (RH = 100%) was carried out by a commercialized detecting system for fuel cell (Smart Two, WonATech, Korea). The hydrogen and oxygen were supplied at 200 SCCM to the anode and cathode, respectively. Firstly, high current density of 100 mV was used to activate the MEA for about 1 h. Then, the polarization curve was obtained under galvanostatic mode.

Results and Discussions Synthesis of PMP-based Polyolefin Copolymers bearing Bromoalkyl Groups Scheme 1 depicts the straightforward route used for the synthesis of polyolefins containing PMP moieties. The PMP-based bromoalkyl-functionalized polyolefins (PMP-Br-x) were synthesized via copolymerization of 4-methyl-1-pentene with 11-bromo-1-undecene using Ziegler-Natta catalyst. The 11-bromo-1-undecene was found to efficiently compete with the 4methyl-1-pentene comonomer during copolymerization thereby resulting in high incorporated comonomer contents. The optimal way to monitor the copolymerization involves measuring 4methyl-1-pentene (r1) and 11-bromo-1-undecene (r2) reactivity ratio evaluated by the Fineman– Ross equation (Table S1 and Figure S1). Thus, r1 = 1.23 and r2 = 0.84, with r1 ×r2 = 1.03 (equal to unity) values were obtained, indicating a tendency of alternated copolymerization reaction. Bromoalkyl moieties were thus incorporated into PMP at high contents. As shown in Figure 1,


Page 11 of 30

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 appearance of proton peak at 3.49 ppm can be assigned to the protons adjacent to bromine. Thus, according to the 1H NMR results, the incorporation ratio of bromoalkyl in the PMP-Br-x product was determined to be in the range of 4.2–41.4 mol% (Table 1). Remarkably, higher degrees of Br functionalization (up to 41.4 mol%) were achieved as compared to PP-based polyolefin copolymers (20.8 mol%, reactivity ratio of propylene r1 = 1.98, 11-bromo-1-undecene r2 = 0.47, Table S2 and Figure S2 in Supporting Information).24 Though the catalytic activity reduced in a systematic manner in the wake of the feed ratio of 11-bromo-1-undecene to PMP, the molecule weight of PMP-Br was considerably high (Mw > 113 kg/mol) with the typical PDI in the range of 5.6–7.1, as shown in Table 1 and Figure S3.

Scheme 1. Synthesis of PMP-Br-x and PMP-TMA-x copolymers.



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 30

Figure 1. 1H NMR spectra of: (a) PMP, and (b) PMP-Br-41 in 1,1,2,2-tetrachloroethane-d2 at 110 ºC. Table 1. Collected results of Ziegler–Natta catalyzed copolymerized reaction between 4methyl-1-pentene (M1) and 11-bromo-1-undecene (M2) Polymerization Conditions Copolymerization results b b e a M1 M2 Time Yield [M2]c Mwd ∆He Samples PDId To m (M) (M) (min) (g) (mol%) (Kg/mol) ( C) (J/g) PMP PMP-Br-4 PMP-Br-20 PMP-Br-32 PMP-Br-41 PP-Br-2024

1.8 1.8 1.8 1.8 1.8 0.2

0 0.1 0.6 1.2 1.8 1.2

30 30 60 60 60 60

6.5 5.4 2.7 2.1 1.6 2.3

0 4.2 20.1 32.3 41.4 20.8

287 239 141 126 113 148

5.6 6.0 6.2 6.8 7.1 6.6

243.9 221.4 114.5 115.3

59.9 50.8 32.8 31.6

a

General conditions: TiCl3 AA:0.4g, Et2AlCl:5ml, n-heptane:100ml, T=343.15K. M1: 4-methyl-1-pentene; M2: 11-bromo-undecene. c Comonomer content ([M2] mol%) determined by 1H NMR at 383.15K in 1,1,2,2-tetrachloroethane-d2. d Mw and PDI were tested with GPC at the temperature of 423.15K in 1,2,4-trichlorobenzene. versus narrowed polystyrene standards. e Tm and ∆H were measured with DSC. b

Quaternization and Membrane Preparation The PMP-based AEM were fabricated by hot pressing of PMP-Br-x copolymers. Subsequently, the PMP-Br membranes were quaternized by trimethylamine (ca. 45wt.%% in H2O) via the Menshutkin reaction to obtain the quaternized PMP-based membranes with anion conductivity.30 Then aqueous sodium hydroxide solution of 1mol/L was used to treat the bromide form membranes at normal temperature for 24h in order to generate AEM in hydroxide form. The 1H NMR spectrum of the hydroxide form of PMP-TMA-4 was shown in Fig.2. After the quaternization process, the signals at 3.49 ppm attributed to non-quaternized methylene groups in PMP-Br-4 became significantly lower while the signal corresponding to the backbone protons remained constant. Simultaneously, a new signal, which could be attributed to the protons of methyl and methylene in quaternary ammonium groups was shown at 3.35 ppm. There was still signal trace at 3.49 ppm after quaternization, thereby suggesting incompleted bromoalkyl to


Page 13 of 30

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


quaternary ammonium conversion. The PMP-TMA-y membranes with the higher –N+(Me)3OH– content (y>4 mol%) becomes insoluble in commonly used organic solvents due to strong polar group interactions. Similar result was also found in polyethylene-based AEMs containing high content of ammonium chloride (–NR3+Cl–) groups.18 The IEC value of PMP-TMA-4 was characterized as 0.40 mequiv/g compared with integrated area ratios of respective peaks and this value was slightly lower than its theoretical value (0.46 mequiv/g). The 1H NMR spectra of PMP-TMA-20, PMP-TMA-32, and PMP-TMA-41 were not obtained because of their poor solubility (Table S2), although the IEC values of these membranes which ranged from 1.47 to 1.92 mequiv/g were obtained by titration. These values are still lower than their theoretical values (1.76–2.84 mequiv/g) calculated from the chemical composition (on the basis of function degree and the quaternization efficiency was assumed to be 100%), thereby suggesting that bromoalkyl was conversed to quaternary ammonium incompletely. It was discovered that such imperfect conversion also occurred in chloromethylated poly(arylene ether sulfone)31 as well as polyolefins bearing PP moieties.24



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 30

Figure 2. 1H NMR spectra of: (a) PMP-Br-4, and (b) PMP-TMA-4 in 1,1,2,2-tetrachloroethaned2 at 110 ºC.

FTIR analysis was used to analyze the chemical construction of AEM. As is seen in Figure 3, the absorption bands of 550 cm–1 was due to the C–Br stretching, and 1472 and 1463 cm–1 were the C–H bending of the PMP-based polymer. After quaternization, the absorption band at 550 cm–1 disappeared while new bands at 1100 and 1126 cm–1 which was due to C–N stretching appeared for PMP-TMA-41 membrane, revealing the formation of quaternary ammonium groups. The broad absorption band (3400–3200 cm–1) in PMP-TMA-41 membrane was probably due to the O–H stretching. Thus it was confirmed by these features that the anion membranes was generated by incorporating high density of –Br group into PMP-TMA-x membrane and then quaternizing it with TMA.


Page 15 of 30

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


Figure 3. FTIR spectra of: (a) PMP, (b) PMP-Br-41, (c) PMP-TMA-41 membranes in their hydroxide form.

Thermal and Mechanical Properties DSC was employed to characterize the Tm and ∆H values for the obtained polymers. As shown in Figure 4, the PMP-Br-20 copolymer displayed an endothermic peak at Tm = 114.5 ºC. Tm, which is a function of the crystalline structure, remained nearly unchanged after the quaternization, thereby revealing that the original crystalline structure in the PMP-TMA-20 membranes remained intact. However, the quaternization reaction and following ion-exchange produced a dilution effect on the copolymer crystallinity, thereby resulting in a significant decrease at the endothermic peak area (i.e., ∆H values) for the PMP-TMA-20 membrane.



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 30

Figure 4. DSC thermogram of: a) PMP (Tm=243.9 ºC, ∆H = 59.9 J/g), b) PMP-Br-20 (Tm = 114.5 ºC, ∆H = 32.8 J/g), and c) PMP-TMA-20 membranes (Tm = 113.7 °C, ∆H = 23.6 J/g).

The hydroxide form of PMP-TMA-41 membrane was tested by TGA in air atmosphere to figure out its thermal stability. The thermal stabilities of PMP and PMP-Br-41 were also investigated as control experiments. According to TGA curves, two weight loss stages are observed for membrane PMP-Br-41. The first weight loss occurs after 165 °C and corresponds to the process of quaternary ammonium groups (QA groups) degrading which had overlap with degraded alkyl side chains. The temperature of degrading exceeds those found for quaternized PPO (ca. 145 oC),32 which suggests the QA groups as attachment of pendent alkyl chain are considerably stable under high temperature. The second stage (360–480 ºC) results from the decomposition of polymer backbone,which is similar to PMP and PMP-Br-41 and implies that the process of degrading in backbone of polymer was not triggered by QA groups which was also confirmed by aromatic poly(aryl ether) AEMs.33

Figure 5. TGA curves of: (a) PMP, (b) PMP-Br-41, and (c) PMP-TMA-41 membranes in their hydroxide form. It is well known that PMP films have excellent mechanical properties. As discussed above, the introduction of bromoalkyl groups decreased the molecular weight of PMP (Table 1) and


Page 17 of 30

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


gradually decreased the entire crystallinity. Thus, poorer mechanical properties were observed for PMP-Br-32 and PMP-Br-41 (Table 2). Additionally, it was observed that the elongation at break, Young's modulus as well as tensile strength of quaternized PMP AEM were all decreased a little compared with those of their precursor polymers. Thus Young's moduli of PMP-TMA-32 and PMP-TMA-41 membranes were 0.17 and 0.11 GPa while the tensile strength values of both were 3.6 and 3.0 MPa, respectively (Table 2). Ion groups in aromatic AEMs could absorb water and decrease Young's modulus and tensile strength values on the basis of plasticizing effect. Consequently, the process of quaternizing causes decreased mechanical properties.

Table 2. The mechanical capacities of PMP-based membranes under 30% RH and ambient temperature Young’s modulus Elongation at Tensile strength values Samples values break (MPa) (MPa) (%) PMP 25±5 1155±105 28±6 PMP-Br-32 4.0±0.6 185±45 46±9 PMP-TMA-32 3.6±1.0 175±35 44±7 PMP-Br-41 3.4±0.5 148±45 52±9 PMP-TMA-41 3.0±0.7 111±35 46±8 Morphology of the Membranes SAXS and AFM were used to characterize the morphological construction of prepared AEM. Figure 6 shows that the SAXS analysis of PMP-TMA-32 and PMP-TMA-41 membranes yielded clear ionomer peaks thereby implying the process of generating a nanophase separation with ion domains. qmax values of 2.9 nm–1

and 2.6 nm–1 were obtained, which corresponded to

construction of periodicity which had length scale d values (d=2π/q) of 2.1 and 2.4 nm for PMPTMA-32 and PMP-TMA-41 membranes, respectively. The q values slightly decreased and the ionomer peaks became narrower with the concentration of quaternary ammonium in the PMPbased copolymers, which may indicate that the ionic clustering was facilitated by the increasing



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 18 of 30

IEC value. The narrow peak profiles of the PMP-TMA-41 membrane indicated that a significant phase which exhibited desirable separation was generated by ion domains.

Figure 6. SAXS of PMP-TMA-32 and PMP-TMA-41 membranes. Respective datasets are moved towards Y axis. Tapping mode AFM was applied in order to demonstrate the construction revealed by the data which were generated from SAXS. As shown in Figure 7, a significant separation of hydrophilic phase and hydrophobic phase was found for all the membranes. Moreover, the hydrophilic domains were well-connected to form hydrophilic micro-channels and the diameter range of which was 10–150 nm. Increasing the concentration of hydrophilic chain would promote the separation of hydrophilic and hydrophobic separation and thus accelerate the formation of ion cluster and the separation of phases. An ion cluster of up to ca. 150 nm was observed for the PMP-TMA-41 membrane showing the highest concentration of quaternary ammonium groups. It was suggested by results of AFM and SAXS that hydrophilic phase and hydrophobic phase separated and well-connected and well-defined ionic domains were generated. This process is facilitated by the introduction of the bulky side-chain containing PMP moieties and side chaintype quaternary ammonium groups. As will be shown below, this well-defined morphological structure has a strong influence on the WU and ionic transport properties.


Page 19 of 30

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


Figure 7. AFM images of PMP-based: (a) PMP-TMA-4, (b) PMP-TMA-20, and (c) PMP-TMA41 polyolefins membranes. Water and Methanol Uptake Behaviors The IEC, WU as well as swelling ratio were compared in the in-plane orientation of PMPbased AEM in Table 3. PMP-TMA-x membranes of which the IEC values ranged from 0.41– 1.92 mequiv/g had WU percentages ranged from 4.7 to 29.2 % at 20 ºC in water. The highest WU value was observed for PMP-TMA-41 (IEC = 1.92 mequiv/g, WU = 29.2 wt%). The WU values of aroma copolymers34 and quaternized polyethylene (WU = 97 wt%, IEC = 1.29 mequiv/g)4 are significantly higher than above mentioned value. However, all membranes had similar numbers of H2O molecules per quaternary ammonium group (Table 3). Thus about 8 H2O molecules solvate one quaternary ammonium group and this ratio is much lower than that in PP-based polyolefin AEM (λ≈12)24 having similar side chaintype QA groups and quaternized polyethylene (λ = 41.8).3 It is assumed that the bulky side chain of the PMP moieties provides strong hydrophobicity thereby preventing water absorption on the PMP-TMA-x membranes. Moreover, decreased WU values could also be attributed to the ‘side chain-type’ construction. Thus it was observed that the swelling ratios or all the PMP-TMA-x membranes in water (Table 3) were lower and that of in-plane water at 293.15K was inferior to 8.9%. Unlike previously reported copolymers in which excessive swelling was induced by high



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 20 of 30

temperatures, the WU and the dimensional swelling of PMP-based AEM remained nearly unchanged with temperature (WU: 29.2 versus 35.4%; swelling ratio: 8.9 versus 12.7%, at 20 and 80 ºC, respectively, Figure 8). It was demonstrated by these results that redundant water swelling ratio was prevented effectively by bulky side-chain and side chain-type architectures even under higher temperatures.

Table 3. Characteristics of PMP-based AEM under ambient temperature (20 ºC) WU Swelling MUc PMeOH σ Samples IECa IECb λ –7 2 (wt %) (%) (wt %) (×10 cm /s) (mS/cm) PMP-TMA-4 0.41 0.44 4.7 1.7 6.4 4.0 0.12 5.1 PMP-TMA-20 1.47 1.76 21.8 6.9 8.6 20.5 1.21 20.3 PMP-TMA-32 1.66 2.44 25.5 7.8 8.5 23.7 1.92 36.9 PMP-TMA-41 1.92 2.84 29.2 8.9 8.4 27.9 2.08 43.2 24 PP-TMA-20 1.56 2.57 34.0 8.1 12.1 31.2 2.19 17.4 QA-PE4 1.2 97.0 -41.8 --40.0 1.82 20.0 11 5.7 --22.0 QA-PAES31 6 QA-PPOs 1.39 25.9 7 10.4 --4.0 a

tested by titrating (mequiv/g); b IEC values in theory (mequiv/g); c methanol was uptaken at 20 oC.

Figure 8. In PMP-TMA-x membranes, WU and swelling ratio is a function of temperature.


Page 21 of 30

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 methanol uptake of PMP-based AEM was in the range of 4.0–27.9%, which is noticeably lower than that of Nafion 212 (103%) at 20 ºC (Table 3). Thus, lower methanol permeability values (0.12–2.08 × 10–7 cm2/s) were observed for the PMP-TMA-x membranes. These values were nearly one order of magnitude inferior to that of Nafion (1.67×10–6 cm2/s).

Hydroxide Conductivity As in the case of the WU, the hydroxide conductivity of PMP-TMA-x membranes raised along with IEC value since local mobility of water which was enhanced by elevated moisture contents subsequently induced long range percolation of ion domain. The hydroxide conductivity of PMP-TMA-x membranes significantly exceeded that of PP-TMA-x membranes in equal conditions. Thus the hydroxide conductivity of PMP-TMA-41 membrane (IEC = 1.92 mequiv/g; WU = 29.2 wt%) was the highest one (43.2 mS/cm) at 20 ºC. The hydroxide conductivity of PMP-TMA-32 (IEC = 1.66 mequiv/g) was almost twice as much as that of PP-AEM-20 (IEC = 1.56 mequiv/g) (36 versus 17 mS/cm). The bulky side chains in PMP moieties and side chaintype QA groups favored the phase separation, thereby leading to the formation of well-defined ion domains which facilitated hydroxide transporting, as corroborated by SAXS and AFM measurements. It was previously confirmed in our investigations that sustainable ion domains were essential for transporting anion efficiently in quaternized poly(pheneylene oxide) membranes. Moreover, the PMP-TMA-x membranes displayed lower WU values and considerably higher hydroxide conductivity than their PP-based counterparts. After the hydroxide conductivity of the membrane was normalized according to WU, a λ-normalized hydroxide conductivity was obtained. The PMP-TAM-x membranes exhibited extremely high normalized hydroxide conductivity (> 2.4 mS/cm) except for the PMP-TMA-4 membrane which showed a value of 0.8 mS/cm (Figure 9b). The values of PP-TMA-20 (1.96 mS/cm), QA-PPO



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 22 of 30

(0.38 mS/cm),6 and QA-PE (0.96 mS/cm)4 membranes were significantly lower than above mentioned values. It was accepted that the efficiency of PMP-based AEM using H2O molecules in the process of transporting hydroxide was promoted by well-defined ionic domains. It was suggested by these results that our theory of applying the bulky side chain and 'side chain-type' function groups in AEM was effective on alleviating water swelling as well as increasing conductivity. Particularly, it was observed that PMP-TAM-32 and PMP-TAM-41 membranes exhibited exceedingly high values of normalized hydroxide conductivity (> 4.2 mS/cm, higher than those of QA-PAES AEM)35 with few exceptions36 despite having similar IEC values. These results could be interpreted in view of PMP-TMA-2 and PMP-TMA-41 membranes being prepared by quaternization and subsequent hot press processes. Well-defined ionic domains were achieved for hydroxide transport, as confirmed by SAXS and AFM results. It was demonstrated in Fig.10 that the hydroxide conductivity of PMP-based AEM was dependent on temperature. Due to the improved H2O mobility, the conductivity smoothly raised along with the temperature thereby hydroxide ions could be transported. High hydroxide conductivity values (equivalent to 75.2 mS/cm at 80 oC for the PMP-TMA-41 membrane) were achieved comparable to those of polysulfone-based AEM with high IEC values (IEC > 2 mequiv/g).34


Page 23 of 30

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


Figure 9. (a) Conductivity of PMP-based AEM, QA-PAES, QA-PPO, QA-PE, and QA-PP membranes at 20 ºC as a function of IEC values. (b) WU-normalized conductivity versus the quantity of H2O molecules which were absorbed in every quaternary ammonium (QA) group (λ) for several membranes.

Figure 10. Hydroxide conductivity of PMP-based AEM as a function of temperature.

Alkali stability It is widely accepted that tetraalkylammonium ions could be degraded through numerous pathways in alkaline environment such as Hofmann elimination, β- hydrogen, nitrogen ylide formation or direct nucleophilic substitution at an alpha-carbon. 37–40 thus the long time stability



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

of AEM is exceptionally important. The long-term stability of AEM under alkaline solution conditions was explored by testing the IEC and hydroxide conductivity before, during, and after the membranes were immersed in a 10 mol/L sodium hydroxide aqueous solution at the temperature of 353.15 K for 700 h. Since the backbone of polyolefin was exceptionally stable in alkaline environment, all tested membranes were flexible and tough during the whole examination process. The IEC and hydroxide conductivity values of all tested membranes exhibited a tendency of continuous and slow decreasing (Fig.11) except a fast drop of conductivity in the first 100h. All the PMP-TMA-x membranes showed excellent alkaline stabilities (see FTIR results before and after testing, Fig.S4 in Supporting Information). The IEC values and hydroxide conductivities decreased less than 10 and 8 %, respectively. This result accords well with our previously published work on PP-TMA-x AEM, and it was further supported by the computational study which revealed that attaching quaternary ammonium groups to polymer backbones which had an alkyl spacer could improve the alkali stability of cations.25


Page 24 of 30

Page 25 of 30

Figure 11. Hydroxide conductivity (a), and (b) IEC of PMP-based AEM membranes as a function of the immersion time in a 10 M aqueous NaOH solution at 80 ºC.

The Properties of Fuel Cell Fig.12 shows the polarization curves of an H2/O2 AEMFC which has electrolyte membranes made of PMP-TMA-41. It is seen that the open circuit voltages (OCVs) approximated the theoretical value of 1.07 V which indicated that the catalysing activity of Pt was not affected notably by PMP-TMA-41 membranes. It is important to state out that the capacities of fuel cell could be improved by the optimization of the MEA fabrication.

40

1.2

35 1.0

Voltage (V)

30 0.8

25 20

0.6

15 0.4 10 0.2

5

2

Power density (mW/cm )

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


0

0.0

-5 0

20

40

60

80

100

2

Current density (mA/cm )

Fig. 12. Polarization curves as well as power density curves of PMP-TMA-41 membrane which



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 26 of 30

was incorporated in AEMFC.

CONCLUSIONS The use of bulky side-chain and side chain-type functional groups during the preparation of quaternized polyolefins allowed the improvement of the hydrophilic-hydrophobic separation and alkaline stability characteristics. This provided an excellent and systematic control over the concentration of functional groups in polyolefins. Thus, the PMP-based polyolefin copolymer showed an unprecedented high content of bromoalkyl functional group of 41 mol%. The asobtained PMP-TMA-x membranes exhibited well-defined ionic domains (which depended on the content of PMP moieties) resulted in enhanced hydroxide conductivities despite their lower WU as compared to their PP-TMA-x counterparts. It was assumed that the bulky side chain of PMP moieties induced the hydrophilic-hydrophobic separation and thus the micro-phase separation to form well-connected ionic domains, as confirmed by SAXS and AFM analyses. Moreover, excellent alkaline stability was observed for the PMP-based AEM up to 700 h in 10 mol/L sodium hydroxide at the temperature of 353.15K. The ‘side chain-type’ framework which surrounds the QA core is believed to be the cause of the excellent alkaline stability of these materials. PMP-based polymers which exhibit great chemical and thermal stability, exceptional mechanical performance and perfect balance between swelling ration and hydroxide conductivity is considered as promising AEM materials for alkali fuel cells.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].


Page 27 of 30

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


Notes

The authors declare that they have no competing financial interests.

ACKNOWLEDGEMENTS

This work was supported by the National Natural Science Foundation of China under Grant 21404084 and 51532003, the Fundamental Research Funds for the Central Universities under Grant B040307. Dr. Nanwen Li would like to acknowledge the financial support from the National Natural Science Foundation of China (No. 21474126 and 21504101) and The Hundred Talents Program of the Chinese Academy of Sciences.

REFERENCES

(1) Jacobson, M. Z.; Colella, W. G.; Golden, D. M. Cleaning the Air and Improving Health with Hydrogen Fuel-Cell Vehicles. Science, 2005, 308, 1901–1905. (2) Zhang, H.; Shen, P. Recent Development of Polymer Electrolyte Membranes for Fuel Cells. Chem. Rev. 2012, 112, 2780–2832. (3) Steele, B. C. H.; Heinzel, A. Materials for Fuel-cell Technologies. Nature, 2001, 414, 345– 352. (4) Kostalik, H. A.; Clark, T. J.; Robertson, N. J.; Mutolo, P. F.; Longo, J. M.; Abruña, H. C. D.; Coates, G. W. Solvent Processable Tetraalkylammonium-Functionalized Polyethylene for Use as an Alkaline Anion Exchange Membrane. Macromolecules 2010, 43, 7147–7150. (5) Stokes, K. K.; Orlicki, J. A.; Beyer, F. L. RAFT Polymerization and Thermal Behavior of Trimethylphosphonium Polystyrenes for Anion Exchange Membranes. Polym. Chem. 2011, 2, 80–82. (6) Li, N.; Yan, T.; Li, Z.; Thurn-Albrecht, T.; Binder, W. H. Comb-shaped Polymers to Enhance Hydroxide Transport in Anion Exchange Membranes. Energy Environ. Sci. 2012, 5, 7888–7892.



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 28 of 30

(7) Liu, L.; He, S.; Zhang, S.; Zhang, M.; Guiver, M. D.; Li, N. 1,2,3-Triazolium-Based Poly(2,6-Dimethyl Phenylene Oxide) Copolymers as Anion Exchange Membranes. ACS Appl. Mater. Interfaces. 2016, 8, 4651–4660. (8) Ge, Q.; Ran, J.; Miao, J.; Yang, Z.; Xu, T. Click Chemistry Finds Its Way in Constructing an Ionic Highway in Anion-Exchange Membrane. ACS Appl. Mater. Interfaces. 2015, 7, 28545–28553. (9) Hibbs, M. R.; Fujimoto, C. H.; Cornelius, C. J. Synthesis and Characterization of Poly(phenylene)-Based

Anion

Exchange

Membranes

for

Alkaline

Fuel

Cells.

Macromolecules 2009, 42, 8316–8321. (10) 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, 1973–1980. (11) Pan, J.; Lu, S.; Li, Y.; Huang, A.; Zhuang, L.; Lu, J. High Performance Alkaline Polymer Electrolyte for Fuel Cell Applications. Adv. Funct. Mater. 2010, 20, 312–319. (12) Arges, C. G.; Ramani, V. Two-dimensional NMR Spectroscopy Reveals Cation-triggered Backbone Degradation in Polysulfone-based Anion Exchange Membranes. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 2490−2495. (13) Li, X.; Nie, G.; Tao, J.; Wu, W.; Wang, L.; Liao, S. Assessing the Influence of Side-Chain and Main-Chain Aromatic Benzyltrimethyl Ammonium on Anion Exchange Membranes. ACS Appl. Mater. Interfaces 2014, 6, 7585−7595. (14) Bae, B.; Chun, B. H.; Kim, D. Surface Characterization of Microporous Polypropylene Membranes Modified by Plasma Treatment. Polymer, 2001, 42, 7879–7885. (15) Venugopal, G.; Moore, J.; Howard J.; Pendawar, S. Characterization of Microporous Separators for Lithium-ion Batteries. J. Power Sources, 1999, 77, 34–41. (16) Matsuyama, H.; Yuasa, M.; Kitamura, Y.; Teramoto, M. Lloyd, D. R. Structure Control of Anisotropic and Asymmetric Polypropylene Membrane Prepared by Thermally Induced Phase Separation. J. Membr. Sci., 2000, 179, 91–100. 1

(17) Nuñez, S. A.; Hickner, M. A. Quantitative H NMR Analysis of Chemical Stabilities

in AnionExchange Membranes. ACS Macro Lett., 2013, 2, 49–52.


Page 29 of 30

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


(18) Zhang, M.; Kim, H. K.; Chalkova, E.; Mark, F.; Lvov, S. N.; Chung, T. C. New Polyethylene Based Anion Exchange Membranes (PE-AEMs) with High Ionic Conductivity. Macromolecules, 2011, 44, 5937–5946. (19) Clark, T. J.; Robertson, N. J.; Kostalik, H.; Lobkovsky,A. E. B.; Mutolo, P. F.; Abruña, H. D.; Coats, G. W. A Ring-Opening Metathesis Polymerization Route to Alkaline Anion Exchange Membranes: Development of Hydroxide-Conducting Thin Films from an Ammonium-Functionalized Monomer. J. Am. Chem. Soc., 2009, 131, 12888–12889. (20) Robertson, N. J.; Kostalik, H. A.; Clark, T. J.; Mutolo, P. F.; Abruña, H. D.; Coats, G. W. Tunable High Performance Cross-Linked Alkaline Anion Exchange Membranes for Fuel Cell Applications. J. Am. Chem. Soc., 2010, 132, 3400–3404. (21) Noonan, K. J. T.; Hugar, K. M.; Kostalik, H. A.; Lobkovsky, E. B.; Abruña, H. D.; Coats, G. W. Phosphonium-Functionalized Polyethylene: A New Class of Base-Stable Alkaline Anion Exchange Membranes. J. Am. Chem. Soc., 2012, 134, 18161–18164. (22) Sherazi, T. A.; Sohn, Y.; Lee, Y. M.; Guiver, M. D. Polyethylene-based Radiation Grafted Anion-exchange Membranes for Alkaline Fuel cCells. J. Membr. Sci., 2013, 441, 148–157. (23) Bacskai, R. Copolymerization of α-Olefins with ω-Halo-α-Olefins by Use of Ziegler Catalysts. J. Polym. Sci., Part A: Gen. Pap., 1965, 3, 2491–2510. (24) Zhang, M., Liu, J., Wang, Y., An, L., Guiver, M. D.; Li, N. Highly stable anion exchange membranes based on quaternized polypropylene. J. Mater. Chem. A, 2015, 3, 12284–12296. (25) Hibbs, M. R. Alkaline Stability of Poly(phenylene)-Based Anion Exchange Membranes With Various Cations. J. Polym. Sci. B Polym. Phys., 2013, 51, 1736–1742. (26) Li, N.; Leng, Y.; Hickner, M. A.; Wang, C.-Y. Highly Stable, Anion Conductive, CombShaped Copolymers for Alkaline Fuel Cells. J. Am. Chem. Soc., 2013, 135 (27), 10124– 10133. (27) Tanaka, M.; Koike, M.; Miyatake, K.; Watanabe, M. Anion Conductive Aromatic Ionomers Containing Fluorenyl Groups. Macromolecules, 2010, 43, 2657–2659. (28) 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– 10654.



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 30 of 30

(29) Yang, Z.; Liu, Y.; Guo, R.; Hou, J.; Wu, L.; Xu, T. Highly Hydroxide Conductive Ionomers with Fullerene Functionalities. Chem. Commun., 2016, 52, 2788–2791. (30) Wang, L.; Hickner, M. A. Low-temperature Crosslinking of Anion Exchange Membranes. Polym. Chem., 2014, 5, 2928–2935. (31) Hibbs, M. R.; Hickner, M. A.; Alam, T. M.; McIntyre, S. K.; Fujimoto, C.; Cornelius. Transport Properties of Hydroxide and Proton Conducting Membranes. Chem. Mater., 2008, 20, 2566–2573. (32) Li, N.; Wang, L.; Hickner, M. A. Cross-linked Comb-shaped Anion Exchange Membranes with High Base Stability. Chem. Commun., 2014, 50, 4092–4095. (33) Tanaka, M.; Koike, M.; Miyatake, K.; Watanabe, M. Synthesis and Properties of Anion Conductive Ionomers Containing Fluorenyl Groups for Alkaline Fuel Cell Applications. Polym. Chem., 2011, 2, 99–106. (34) Wang, J.; Wang, J.; Li, S.; Zhang, S. Poly(arylene ether sulfone)s Ionomers with Pendant Quaternary Ammonium Groups for Alkaline Anion Exchange Membranes: Preparation and Stability Issues. J. Membr. Sci., 2011, 368, 246–253. (35) Chempath, S.; Boncella, J. M.; Pratt, L. R.; Henson, N.; Pivovar, B. S. Density Functional Theory Study of Degradation of Tetraalkylammonium Hydroxides. J. Phys. Chem. C, 2010, 114, 11977–11983. (36) Li, N.; Zhang, Q.; Wang, C.; Lee, Y. M.; Guiver, M. D. Phenyltrimethylammonium Functionalized Polysulfone Anion Exchange Membranes. Macromolecules 2012, 45, 2411– 2419. (37) Merle, G.; Wessling, M.; Nijmeijer, K. Anion Exchange Membranes for Alkaline Fuel Cells: A Review. J. Membr. Sci., 2011, 377, 1–35. (38) 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. W.; Zhuang L. AnionExchange Membranes in Electrochemical Energy Systems. Energy Environ. Sci., 2014, 7, 3135–3191. (39) Li, N.; Guiver, M. D. Ion Transport by Nanochannels in Ion-Containing Aromatic Copolymers. Macromolecules 2014, 47, 2175–2198. (40) Mohanty, A. D.; Bae, C. Mechanistic Analysis of Ammonium Cation Stability for Alkaline

Exchange Membrane Fuel Cells. J. Mater. Chem. A, 2014, 2, 17314–17320.


Facilitating Anion Transport in Polyolefin-Based Anion Exchange

Recommend Documents