Enhanced Proton Conductivity of Sulfonated ... - ACS Publications

Subscriber access provided by UNIVERSITY OF CONNECTICUT

Article

Enhanced Proton Conductivity of Sulfonated Hybrid Poly(arylene ether ketone) Membranes by Incorporating an Amino-Sulfo Bifunctionalized Metal-Organic-Framework for Direct Methanol Fuel Cells Chunyu Ru, Zhenhua Li, Chengji Zhao, Yuting Duan, Zhuang Zhuang, Fanzhe Bu, and Hui Na ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17299 • Publication Date (Web): 14 Feb 2018 Downloaded from http://pubs.acs.org on February 14, 2018

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 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 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 31 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

Enhanced Proton Conductivity of Sulfonated Hybrid Poly(arylene ether ketone) Membranes by Incorporating an Amino-Sulfo Bifunctionalized Metal-Organic-Framework for Direct Methanol Fuel Cells Chunyu Rua, Zhenhua Lib, Chengji Zhaoa,c, Yuting Duana, Zhuang Zhuanga, Fanzhe Bua, Hui Na*a,c a

Alan G. MacDiarmid Institute, College of Chemistry, Jilin University, Changchun 130012, PR China

b

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin

University, Changchun, 130012, PR China c

Key Laboratory of Advanced Batteries Physics and Technology (Ministry of Education), Jilin

University, Changchun 130012, PR China. *

Corresponding author. E-mail: [email protected] . Tel.: +86-431-85168870; Fax:

+86-431-85168870

Key words: sulfonated poly (arylene ether ketone), bifunctionalized metal-organic framework, polymer electrolyte membranes, proton conductivity, direct methanol fuel cells

Abstract Novel side-chain-type sulfonated poly (arylene ether ketone) (SNF-PAEK) containing naphthalene and fluorine moieties on the main chain was prepared in this work, and a new

amino-sulfo-bifunctionalized

MIL-101-NH2-SO3H)

was

metal-organic

synthesized

via

a

framework

(MNS,

hydrothermal

short

for

technology

and

post-modification. Then MNS was incorporated into SNF-PAEK matrix as an inorganic nano-filler

to

prepare

(MNS@SNF-PAEK-XX).

a

series

The

of

organic-inorganic

mechanical

property,

1 ACS Paragon Plus Environment

hybrid

membranes

methanol

resistance,

ACS Applied Materials & Interfaces 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

electrochemistry and other properties of MNS@SNF-PAEK-XX hybrid membranes were detailed characterized. We found the mechanical strength and methanol resistances of these hybrid membranes were improved by the formation of ionic cross-linking structure between -NH2 of MNS and -SO3H on the side-chain of SNF-PAEK. Particularly, the proton conductivity of these hybrid membranes increased obviously after the addition of MNS. MNS@SNF-PAEK-3% exhibited the proton conductivity of 0.192 S·cm-1, which was much higher than pristine membrane (0.145 S·cm-1) and recast Nafion (0.134 S·cm-1) at 80°C. The result indicated that bifunctionalized MNS rearranged the microstructure of hybrid membranes, which could accelerate the transfer of protons. The hybrid membrane (MNS@SNF-PAEK-3%) showed a better direct methanol fuel cell performance with a higher peak power density of 125.7 mW/cm2 at 80°C and a higher OCV (0.839V) than pristine membrane.

1. Introduction Proton exchange membrane fuel cells (PEMFCs) have attracted much attention in recent years for high energy density, good conversion efficiency, and environmentally friendly property. Advanced proton exchange membrane (PEM), as the heart of PEMFCs, has been widely and extensively researched by several research groups.1-3 In past decades, numerous PEMs have been developed to meet the following requirements: high proton conductivity, low methanol crossover, high chemical and mechanical stability as well as low cost.4-6 Among these PEMs, materials based on sulfonated aromatic polymers, such as sulfonated poly (arylene ether ketone) (SPAEK), sulfonated poly (ether sulfone) (SPES) and sulfonated polyimide (SPI), have attracted increasing attention as alternatives to Nafion.7-9 Since proton conductivity is the determinant factor to evaluate the performance of PEMs, many studies have been done to pursue the proton conductivity as high as possible. For SPAEKs, the proton conductivity is related to the concentration of sulfonic acid group, so the common way to enhance conductivity is increasing the degree of 2 ACS Paragon Plus Environment

Page 2 of 31

Page 3 of 31 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


sulfonation (DS).9 However, for most reported SPAEKs, the sulfonic acid group is directly attached to the backbone of the polymer; high DS usually sacrifices other properties of SPAEKs-based PEMs, such as dimensional stability, mechanical strength, and chemical resistance. Hence, significant research efforts have been devoted to the design of side-chain-type SPAKEs by chemical grafting the pendants onto polymer backbone, which can improve the mechanical properties of the polymer while maintaining sufficient proton conductivity.10-11 Besides, methods such as chemical, ionic and

physical

cross-linking,12-14

especially

fabricating

organic-inorganic

hybrid

membranes by incorporation with inorganic nano-fillers have been adopted to reduce methanol crossover and further improve mechanical strength.15-16 Inorganic additives such as polyhedraloligomeric silsesquioxanes (POSSs), graphene oxide (GO), and metal-organic frameworks (MOFs) have been utilized for preparing high performance PEMs.17-19 Subianto et al. incorporated sulfonated POSS into Nafion® to promote the conductivity of the membrane.17 Choi et al. found that functionalized GO can manipulate ion channels in nanoscale.19 Particularly, MOFs have attracted much attention due to the variety of architectures with significant functional groups and easy to modify.20-22 Fedin’s group imparted high proton conductivity to a MOF material by controlled acid impregnation.22-23 Phang et al. synthesized sulfonated UiO-66 by a facile post-synthetic oxidation, which performs super-protonic conductivity.21 However, the application of MOFs as the filler to prepare composite membranes is far away from extensive studies. Zhu et al. prepared a MOF–polymer composite membrane to enhance proton conductivity at low humidity.

24

Our group also synthesized a MOF by the ionothermal method for

addressing the ionic liquid (IL) leaching problem of IL–polymer composite membranes.25-26 In this paper, novel SPAEK containing naphthalene and fluorine moieties on the backbone and sulfonic acid groups on the pendent side chains was firstly synthesized as the polymer electrolytes matrix. As reported, the naphthalene moieties on the main chain 3 ACS Paragon Plus Environment


can enhance the rigidity of polymer chains and restrain the membrane’s swelling.27 Meanwhile the structure containing fluorine on the main chain and sulfonic acid groups on the pendant is similar to Nafion, which can be attributed to the formation of typical Nafion-like ionic clusters in the microstructure. Then we synthesized a bifunctionalized MOF base on MIL-101 (Cr), by incorporating sulfonic acid groups on the bones of MIL-101 while attaching ethylenediamine to the coordinatively unsaturated metal sites of MIL-101, named as MIL-101-NH2-SO3H (MNS). Next, we fabricated a series of organic-inorganic hybrid membranes by incorporating various amounts of MNS into polymer matrix. MNS can not only play a role as ionic cross-linking agent, but also promote the conductivity of hybrid membranes, for both amidogen and sulfonic acid groups were added onto the nanocage of MIL-101. Finally, the microstructure and properties of hybrid membranes were investigated, including conductivity, dimensional stability, thermal stability, methanol permeability. In addition, the membrane electrode assembly (MEA) of hybrid membranes was fabricated to test their performance in single direct methanol fuel cell (DMFC).

2. Experimental Section 2.1 Materials. 1,5-Bis(4-fluorobenzoyl)-2,6-dimethoxynaphthalene (DMNF) was prepared according to our previous work.11 4,4'-(Hexafluoroisopropylidene)diphenol (98%), 1,4-butane sultone (99%), trifluoroacetic acid (TFA), and chlorosulfonic acid were purchased from Energy Chemical (Chaoyang, China) Ltd. 1 M BBr3 dichloromethane solution was obtained from Sigma-Aldrich. N-boc-ethylenediamine was purchased from Aladdin Chemical (Shanghai, China). Nafion D-520 dispersion solution was obtained from DuPont Fluoroproducts Co. (Wilmington, DE, USA). N, N-dimethylformamide (DMF; 99%) and toluene received from Sigma-Aldrich were dehydrated and distilled before used. All other chemicals and solvents were at least analytical grade and used without additional purification. 4 ACS Paragon Plus Environment

Page 4 of 31

Page 5 of 31 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


2.2 Preparation of poly(arylene ether ketone) polymer containing naphthalene and fluorine moieties on main chain and flexible pendent sulfobutyl groupsy. Firstly, DMNF(12.97 g, 30.0 mmol), 4,4'-(hexafluoroisopropylidene) diphenol (10.08 g， 30.0 mmol), K2CO3(4.56 g，33.0 mmol), 50 mL tetramethylene sulfone, and 10 mL toluene were added into a 250 mL three-neckedflask. Then the mixture was heated up to 140°C and stirred for 3 h under nitrogen atmosphere to remove water. After removing toluene, the mixture was kept at 200°C for 12 h to complete the polymer chain growth. Then, the viscous solution was poured into deionized water, washed by deionized water for several times, and then dried in oven at 60°C for 24 h. The polymer was nominated as NF-PAEK. Secondly, NF-PAEK (6.0 g, 8.5 mmol) was dissolved in 120 mL dichloromethane in ice-salt baths, and 1 M BBr3 dichloromethane solution (30 mL) was added dropwise into the solution system. Then the system was stirred for 24 h at room temperature. After that, 500 mL water was added into the system to quench the reaction. The product was collected by filtration, washed with refluxing water, and labeled as HO-NF-PAEK. Finally, HO-NF-PAEK (5 g, 7.1 mmol) was dissolved in 50 mL dimethyl sulfoxide. Next, 0.7 g NaH (0.7 g, 24 mmol) and 1, 4-butane sultone (6 g, 44 mmol) were quickly added into the solution. The sulfobutyl grafting reaction was carried out under nitrogen atmosphere and kept at 90°C for 12 h. The mixture was poured into acetone (500 mL) to precipitate the production, and the solid was collected by filtration, washed several times with acetone, and washed with 1000 mL of 1 M hydrochloric acid. After drying in an oven for 24 h, naphthalene-based PAEK with pendent sulfobutyl groups was obtained and named as SNF-PAEK. The synthesis procedure of SNF-PAEK is shown in Scheme 1.



Scheme1. The synthesis procedure of SNF-PAEK


Page 6 of 31

Page 7 of 31 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


2.3 Synthesis and Purification of MIL-101-NH2-SO3H MIL-101 was synthesized according to a traditional hydrothermal reaction method as reported.28 1,4-Dicarboxybenzene (H2BDC) (1.66 g, 10 mmol), Cr(NO3)3.9H2O(4 g, 10mmol), hydrofluoric acid (2 mL, 1mmol), and 48 mL H2O were added into a Teflon-lined steel autoclave, then heated up to 220°C and hold for 8 h. Then a mixture of MIL-101 and H2BDC was filtered off, and washed with boiling DMF and ethanol, each for three times to remove H2BDC. Finally the green powder of pure MIL-101 was centrifuged and dried in a vacuum oven at 60°C for 12 h. After that, 2 g MIL-101 was dehydrated in a vacuum oven at 150°C for 12 h, and then added into anhydrous toluene (30 mL). N-boc-ethylenediamine (0.48 g, 3 mmol) was also added into the system. Then the mixture was stirred under N2 for 12 h at 80ºC. The product, named as MIL-101-NHBOC, was recovered by filtration, washed with toluene for five times to remove spare N-boc-ethylenediamine, and then dried at 60ºC. Next, MIL-101-NHBOC was degassed under vacuum at 120ºC for 5 h. After stirring the activated

MIL-101-NHBOC (2.0 g) in 20 mL CHCl3 in an ice bath for 10 min, ClSO3H

(0.66 g, 5.6 mmol) in 10 mL CHCl3 was dropwise added to the mixture, and then stirred for another 10 min at room temperature. The solid was collected by centrifugation, washed several times with ClSO3H and H2O, and dried to give MIL-101-NHBOC-SO3H. Finally, MIL-101-NHBOC (2.0 g) was dispersed in 50 ml CHCl3. 1 M TFA (10 ml) was dropwise added into the system, and the dispersion was stirred under atmosphere until no gas came out from the dispersion. The target product, MIL-101-NH2-SO3H, was collected by filtration, washed several times with CHCl3 and followed by drying in vacuum. The schematic preparation of MIL-101-NH2-SO3H (MNS) is shown in Scheme 2.



Scheme 2. The schematic preparation and the nanostructure of MIL-101-NH2-SO3H

2.4 Preparation of Hybrid Membranes SNF-PAEK was dissolved in dimethylacetamide to form a homogeneous solution, and various amounts of MNS (0, 1%，2%, 3%, 4% and 5% by weight of SNF-PAEK) were added into the solution. To achieve a homogeneous dispersion of inorganic fillers, the solution was ultrasonic treated for 1 h and then stirred 48 h till a uniform solution was obtained. Then the solution was casted onto a flat glass plate. After evaporating the solvent at 60°C for 24 h, the hybrid membrane was annealed at 140°C for 4 h. The obtained membranes were represented as MNS@SNF-PAEK-XX (XX represents the content of MNS). For a comparison, recast Nafion membrane was prepared in the same way.


Page 8 of 31

Page 9 of 31 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


2.5 Measurements 1

H NMR spectra of the monomer and polymers were conducted on a Bruker 500 MHz

NMR spectroscopy. Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements of MIL-101, MIL-101-NHBOC, MIL-101-NHBOC-SO3H and MIL-101-NH2-SO3H were performed on Rigaku D/max 2550 powder X-ray diffractometer, Bruker Vector 22 spectrometer, and ESCALAB 250 X-ray photoelectron spectroscopy, respectively. The morphology of MOF and hybrid membranes were investigated by scanning electron microscope (SEM, Hitachi SU8020), transmission electron microscope (TEM, JEM-3100F) and small angle X-ray scattering (SAXS, Anton Paar SAXSees). Besides, all the thermogravimetric analysis (TGA) was carried out by TA 2050. Proton Conductivity. The proton conductivity (σ) of hybrid membranes (1 cm ×4 cm) was obtained by a Princeton Applied Research 2273 potentiostat, under the AC impedance condition over the frequency between 0.1 Hz and 1 MHz. σ (S cm-1) was calculated by the following equation:

σ=

(1)

×

where L is the distance between the electrodes (cm), R is the membrane resistance, and S is the cross-sectional area of the membrane (cm2). Water Sorption Properties. Water sorption properties include swelling ratio and water uptake, and they were calculated respectively by equations mentioned below:

swelling ratio in area =

water uptake in weight =

× 100%

" " "

× 100%

(2)

(3)

where S and W are the area and weight of each membrane samples, respectively, and the subscript is on behalf of the wet or dry condition of samples. Ionic Exchange Capacity (IEC) of Membranes 9 ACS Paragon Plus Environment


Page 10 of 31

The IECs of the pristine membrane, hybrid membranes and recast Nafion membrane were determined via acid-base titration. All membranes were firstly immersed in 1 mol·L−1 NaCl for 48 h to release the protons completely and then the liquid was titrated with 0.01 mol·L−1 NaOH solution. The IEC titration experiment was repeated three times and IEC was calculated by following formula:

IEC =

&'()* +'()*

(4)

"

Membrane Electrode Assembly and Single Cell Test. MEA was fabricated by a hot-pressing technique, and the performance of single cell using 1 M methanol as fuel was operated on an Arbin FCTS system. Pt/Ru black and 50% Pt/C were chosen as the anode and the cathode catalysts each with 4 mg·cm−2 loading, respectively. The anode was circulated with 1 M methanol at a flow rate of 5 mL·min−1, while the cathode was supplied with oxygen at a flow rate of 0.5 L·min−1. Before the test, all MEAs were activated in single cell for 4 h.

3. Result and Discussion 3.1 Characterization of SNF-PAEK Matrix and MNS Filler. As shown in Fig. 1，the 1H NMR spectra confirmed the successful synthesis and purification of DMNF,

NF-PAEK , HO-NF-PAEK, and SNF-PAEK ， where the

chemical shift of different protons corresponding to the structure of target compounds were labeled. The characteristic peaks at 7.87−7.14 ppm were assigned to the phenyl protons that are adjacent to the carbonyl group, and the characteristic peak at 3.76 ppm was assigned to the methoxyl groups (Fig. 1a). 1H NMR spectra in Fig. 1c referring to HO-NF-PAEK was similar to NF-PAEK in Fig. 1b, except for the absence of the characteristic peak of methoxyl groups at 3.76 ppm and the appearance of the characteristic peak of hydroxyl groups at 9.86 ppm. The result indicated the demethylation reaction of NF-PAEK was completed. Lastly, the grafting reaction with 1, 10 ACS Paragon Plus Environment

Page 11 of 31 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


4-butane sultone was proved by the characteristic peak of protons on -CH2- groups at 4.02, 2.36, 1.55, and 1.46 ppm, and the disappearance of the characteristic peak of hydroxyl groups at 9.86 ppm. According to XRD patterns in Fig. 2a, we found that almost all peaks maintained after the post-synthetic modification, thus clearly indicating that MNS retained the same structure as MIL-101 during the functionalization process, only with some slight variations in the Bragg intensities.

Fig.1

1

H NMR spectra of DMNF (a), NF-PAEK (b), HO-NF-PAEK (c), and SNF-PAEK (d).

FT-IR was used to further confirm the successful synthesis of MNS and the spectra was displayed in Fig. 2b. Compared to pristine MIL-101, all intermediates and target MNS showed the characteristic peaks at 2934cm-1 and 3263cm-1, ascribing to the absorption 11 ACS Paragon Plus Environment


peaks

for

v(CH)

and

v(NH),

which

indicated

the

Page 12 of 31

successful

grafting

of

N-boc-ethylenediamine and the remain of ethylenediamine after sulfonation. In addition, the IR adsorption band at 1207 cm-1 for MIL-101-SO3H-NHBOC and MNS was assigned to the asymmetric vibration mode of –SO3H. Besides, the post-synthetic modification was also proved via XPS analysis (Supporting Information), where the sulfur XPS signal appeared at a binding energy of 168.97 eV corresponding to the S6+ of sulfonic acid group, while the nitrogen XPS signal appeared at a binding energy of 402.06 eV corresponding to the N1s of ethylenediamine that was attached to metal-oxygen clusters. Then we drew a conclusion that MIL-101 was converted into MNS successfully by the post-synthetic modification. Besides, SEM image in Fig. 3a shows the octahedral structure of MNS, as same as MIL-101, which has been reported by previous work.29 The result confirmed that MNS still retained its framework structure after modification. The thermodynamic stability of MOFs was measured by TGA (Supporting Information). The result showed that the decomposition temperature at 5% weight loss (T5%) of MIL-101 and MIL-101-NH2-SO3H was 200°C and 280°C, respectively. This indicated that they had good thermal stability to be used in DMFCs.

Fig.2 PXRD (a) and FT-IR (b) of the bifunctionalized MNS filler and all intermediates (all samples were dehydrated at 120°C under vacuum for 48 h before test) 12 ACS Paragon Plus Environment

Page 13 of 31 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


3.2 Microstructure of MNS@SNF-PAEK-XX Membranes. The morphology of hybrid membranes was observed by probing cross sections of MNS@SNF-PAEK-3% by SEM. As shown in Fig. 3b, octahedral structure of MNS was clearly observed from the sectional view. Moreover, MNS was uniformly dispersed in hybrid membranes without agglomeration. 3.3 Thermal, Oxidative Stability and Mechanical Properties of Membranes. TGA measurements of pristine and hybrid membranes were performed to evaluate whether the membranes were thermally stable within the temperature range for application in direct methanol fuel cells. As shown in Fig. 4, all membranes displayed two decomposition stages. The first stage starting from 220 to 330°C belonged to the decomposition of the grafted flexible sulfoalkyl groups on the side chain, and the second stage in the range from 400 to 650°C was assigned to the degradation of polymer backbone. According to the data in Table 1, all the decomposition temperatures at 5% weight loss (Td5%) of samples were higher than 230°C. After the addition of MNS, the Td5% increased from 244.93 to 266.51°C. It is because of the cross-linked structure formed by MNS, restraining the decomposition of polymer matrix. Therefore, the composite membranes have good thermal stabilities to be used for DMFCs. The oxidative stability of membranes was investigated via exposing the membranes to Fenton’s reagent at 80°C, and measuring the remained weight percentage (%) of membranes each 30 min. The detail of the characterization and result were shown in Fig. S3 (Supporting Information). The time of 80% remained weight of pristine and hybrid membranes were more than 1 h, except for MNS@SNF-PAEK-5%. It might because the extra MNS in MNS@SNF-PAEK-5% damaged the compactness of the polymer matrix surface, which made it easier for molecule chain to be attacked by the HOO· or HO· of Fenton’s reagent.



Fig.3

SEM image of MNS (a) and cross-section SEM image of MNS@SNF-PAEK-3% hybrid membrane (b).

As summarized in Table 1, all these MNS@SNF-PAEK-XX and SNF-PAEK membranes showed higher strength properties of tensile strength (33.38−36.97 MPa) and Young’s modulus (0.90−1.06 GPa) than those of tensile strength and Young’s modulus of recast Nafion of 13.7 MPa and 0.24 GPa, respectively. With the amount of MNS addition increasing, the Young’s modulus increased from 0.90 GPa to 1.06 GPa while the tensile strength increased from 33.38 MPa to 36.97 MPa. However, the elongation at break decreased sharply from 118% to 10% as the content of MNS varied from 1%−5%. Besides, the stress-strain curves of MNS@ SNF-PAEK-XX membranes were shown in Fig. S4 (Supporting Information). It is because MNS at an increasing content exists as an ionic cross-linker in the composite membranes. Since the amino groups of ethylenediamine were immobilized onto the metal-oxygen clusters of MIL-101, they could be cross-linked with the polymer matrix of SNF-PAEK by the formation of electrostatic forces between sulfonic groups and amino groups. Furthermore, all inorganic fillers act as a physical cross-linker which blocks the movement of molecular chain. Hence, the tensile strength of hybrid membranes increases due to the formation of cross-linked structure, while the toughness decreases at a higher density of cross-linking.


Page 14 of 31

Page 15 of 31 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


Table 1 The decomposition temperature and the mechanical properties of hybrid membranes. MNS

Young’s

Maximum

Tensile

Modulus

Elongation

Strength

(GPa)

(%)

(MPa)

Td5% Sample name

content (°C) ( in weight )

SNF-PAEK

0

244.93

0.90±0.14

118±26

33.38±1.30

MNS@SNF-PAEK-1%

1%

247.72

0.91±0.17

123±19

35.46±1.53

MNS@SNF-PAEK-2%

2%

250.60

0.95±0.29

89±23

35.81±2.28

MNS@SNF-PAEK-3%

3%

250.82

0.97±0.05

60±13

35.47±1.88

MNS@SNF-PAEK-4%

4%

257.64

0.97±0.29

37±15

35.73±1.90

MNS@SNF-PAEK-5%

5%

266.51

1.06±0.20

10±5

36.97±1.60

recast Nafion†

--

--

0.24±0.02

154±5

13.7±0.30

†Data of recast Nafion were adapted from our previous work 27.

Fig. 4 TGA curves of SNF-PAEK and MNS@SNF-PAEK-XX 15 ACS Paragon Plus Environment


Page 16 of 31

3.4 IEC, Water Uptake and Swelling Ratio of membranes. As shown in Table 2, IEC increased with the content of MNS increasing. There were large amount of sulfonic acid groups on the framework of MNS, so the addition of MNS led to extra more ionic exchange groups into the matrix, thus resulting in a higher IEC. Fig.5 shows the water uptake and swelling ratio of membranes as a function of temperature. MNS@SNF-PAEK-1%, MNS@SNF-PAEK-2%, and MNS@SNF-PAEK-3% displayed higher water uptake (45.71%-47.32%) than pristine membrane (45.44%) at 30°C. This was because extra more hydrophilic groups, such as sulfonic acid groups and amino groups in the inorganic fillers could absorb more water. However the water uptake of MNS@SNF-PAEK-4% and MNS@SNF-PAEK-5% (45.03% and 43.08%, respectively) was lower than SNF-PAEK due to higher density of cross-linking structure formed between MNS and polymer matrix, which restricted the water absorption. Meanwhile, all hybrid membranes exhibited lower water uptake (75.55% — 62.46%) than pristine membrane (75.66%) at 80°C. This could be attributed to the interaction between the polymer matrix and MNS, which suppressed the absorption of water in the membranes. As for dimensional stability, MNS reduced the swelling ratio of the membranes, especially

at

high

temperature

(49.65%

and

32.10%

for

SNF-PAEK

MNS@SNF-PAEK-3%, respectively).

Fig. 5

Water Uptake (a) and Swelling Ratio (b) of membranes


and

Page 17 of 31 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


Table 2

IEC, Water Uptake and Swelling Ratio of membranes. Water Uptake in

Swelling Ratio in area

weight( % )

(%)

IEC Sample

( mequiv.g-1) 30°C

80°C

30°C

80°C

SNF-PAEK

1.70

45.44±1.96

75.66±3.01

21.73±1.56

49.65±3.82

MNS@SNF-PAEK-1%

1.73

45.71±1.44

75.55±3.11

22.10±1.83

35.85±3.72

MNS@SNF-PAEK-2%

1.79

46.33±1.63

75.33±3.66

19.17±2.47

33.90±2.32

MNS@SNF-PAEK-3%

1.85

47.21±1.62

73.34±3.47

18.08±3.71

32.10±3.98

MNS@SNF-PAEK-4%

1.91

45.03±1.54

68.17±2.67

16.63±1.37

31.10±4.02

MNS@SNF-PAEK-5%

1.90

43.08±1.33

62.46±3.07

14.84±1.04

28.44±3.27

There are two aspects to the MNS effect: (i) a hygroscopic effect due to the porous structure of the framework and hydrophilic groups including sulfonic acid groups and amino groups, which would increase the content of bound water; (ii) a cross-linking effect due to electrostatic force between amino groups on the MNS and sulfonic acid groups on the polymer matrix, which would reduce the mobility and the free-volume of polymer chains. Hence, hygroscopic effect plays a leading role at low temperature, while cross-linking effect becomes more dominant when temperature rises. 3.5 Proton conductivity, Methanol permeability, and Selectivity of membranes. The performance of a fuel cell is usually based on the proton conductivity of the PEM materials. The proton conductivities of all membranes were measured at 100% RH and plotted as a function of temperature (Fig. 6). As expected, the proton conductivities increased with the temperature increasing. All the membranes showed comparable proton conductivity to the recast Nafion. It was interesting to observe that the proton conductivities increased first and then decreased with increasing the addition amount of MNS. The proton conductivities increased from 0.055 S·cm-1 to 0.080 S·cm-1 at 25°C and from 0.145 S·cm-1 to 0.192 S·cm-1 at 80°C as the content of MNS increased from 0 to 3%. Then the conductivities decreased from 0.080 S·cm-1 to 0.070 S·cm-1 at 25°C and 0.192 17 ACS Paragon Plus Environment


Page 18 of 31

S·cm-1 to 0.174 S·cm-1 at 80°C when the content of MNS up to 5%. This indicated that too much MNS led the polymer matrix to a high density of cross-linking, which might hinder the motion of molecular chain. As listed in Table 3, MNS@SNF-PAEK-3% exhibited the highest proton conductivity (0.080 S cm-1 at 25°C and 0.198 S cm-1 at 80°C) among these hybrid membranes, even higher than that of recast Nafion (0.073 S·cm-1 at 25°C and 0.134 S·cm-1 at 80°C). The results indicated that the hybrid membranes have the potential to be used as the practical PEM for applications in fuel cells. Methanol permeability of membranes was obtained according to method mentioned in our previous work,30 and the data are showed in Table 3. It could be found that hybrid membranes

displayed

a

lower

methanol

permeability

of

4.92×10-7 cm2·s-1

(MNS@SNF-PAEK-4%) compared with pristine membrane of 6.44×10-7 cm2·s-1 and recast Nafion (2.18×10-6 cm2·s-1). In general acknowledged, proton and methanol utilize the same pathway for transport, thus high conductivity leading to high methanol crossover. Selectivity (φ, S·s·cm-3) is another factor to evaluate methanol resistance property of PEMs, which shows the relationship between proton conductivity and methanol permeability. MNS makes the polymer chain be cross-linked as the hybrid membranes become more compact, and the compact structure improves the methanol resistance of hybrid membranes. For instance, MNS@SNF-PAEK-4% exhibited the highest selectivity of 15.24×104 S·s·cm-3, which implied the hybrid membrane maintained its low methanol permeability even at a high conductivity. However, the extra free MNS destroys the compact structure of polymer matrix, then the methanol permeability increases while selectivity declined when the content of MNS increases up to 5%. However, both pristine membrane and hybrid membranes performed much better than recast Nafion in methanol resistance (21.87×10-7 cm2·s-1) and selectivity (3.34×104 S·s·cm-3).


Page 19 of 31 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


Fig. 6 Proton conductivity of the membranes under 100% relative humidity

Table 3. Proton Conductivity, Methanol Permeability (P) and Selectivity (φ) of membranes. σ ( S cm-1 ) sample 25°C

40°C

60°C

P (10-7

φ(104

cm2·s-1)

S·s·cm-3)

†

†

80°C

SNF-PAEK

0.055±0.006

0.069±0.004

0.103±0.007

0.145±0.004

6.44

8.54

MNS@SNF-PAEK-1%

0.060±0.004

0.075±0.005

0.109±0.003

0.149±0.006

6.20

9.68

MNS@SNF-PAEK-2%

0.066±0.004

0.087±0.004

0.130±0.005

0.188±0.008

5.92

11.15

MNS@SNF-PAEK-3%

0.080±0.004

0.098±0.005

0.143±0.007

0.198±0.009

5.28

15.15

MNS@SNF-PAEK-4%

0.075±0.003

0.095±0.006

0.136±0.006

0.190±0.009

4.92

15.24

MNS@SNF-PAEK-5%

0.070±0.004

0.089±0.003

0.122±0.005

0.174±0.008

7.76

9.02

recast Nafion

0.073±0.003

0.093±0.004

0.115±0.005

0.134±0.007

21.87

3.34

† P and φ referred to the methanol permeability and selectivity, respectively (Supporting Information). 19 ACS Paragon Plus Environment


Fig. 7 shows the schematic diagram of proton conduction mechanism for hybrid membranes. Generally, there are two main mechanisms for the proton diffusion in PEMs: Vehicle mechanism and Grotthuss mechanism.31-32 As for Vehicle mechanism, H+ combines with water molecules to form ions such as H3O+, H5O2+,and H9O4+ , and these ions transport between the hydrophilic clusters, sulfonic acid groups for instance. In Grotthuss mechanism, H+ jumps to the neighboring groups which can bind and dissociate protons. For these hybrid membranes, the sulfonated MNS fillers provide lots of additional sulfonic acid groups, thus forming more clusters to transport H3O+ and other ions in aqueous phase, which follows the Vehicle mechanism. Furthermore, a huge amount of dense and sequential sulfonic acid groups in the framework of MNS could build high-speed channels for proton conducting, like a short-range transmission. According to the Grotthuss mechanism, the orderly series of sulfonic acid groups make it easier for H+ to jump through the membrane, which can promote the proton transfer. Furthermore, some researches hypothesized that the metal (CrIII) increases the acidity of the water molecule, enabling it to donate such protons as H3O+ to enhance the proton conductivity.33

Fig. 7 Proton conduction schematic diagram of MNS@SNF-PAEK-XX 20 ACS Paragon Plus Environment

Page 20 of 31

Page 21 of 31 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


Fig. 8

SAXS of pristine membrane (SNF-PAEK) and hybrid membranes (MNS@SNF-PAEK-XX)

Meanwhile, we suggested that the ethylenediamine attaching on the surface of MNS attracted more hydrophilic side chain around itself by the electrostatic interaction between amino group and sulfonic group on the end of the pendent chain (blue dotted line in Fig.7). In another word, MNS might cause a rearrangement of the polymer conformation.34 A microstructure analysis was performed by small-angle X-ray scattering (SAXS) to prove our hypothesis, and the curves are shown in Fig. 8. All hydrated membranes revealed a clear ionomer peak in SAXS due to the existence of the self-organized ionic cluster networks formed by hydrophilic groups. The location of the SAXS peak is related to the intercluster distance according to the two-phase model or to the short-range order distance according to the core−shell model.35 We found the scattering vector (q) of hybrid membranes was shifted to a larger value compared to 21 ACS Paragon Plus Environment


pristine SNF-PAEK with the incorporation of MNS. And the calculated Bragg spacing (d, d=2π/q), ascribing to the average distance of the ionic clusters decreased from 2.79 nm (SNF-PAEK) to 2.34 nm (MNS@SNF-PAEK-3%). Therefore, the changes in distance of ionic clusters reflected the shrinkage of ionic clusters through rearrangement of the polymer microstructure, which was caused by specific interactions with the functionalized MOF.

Fig. 9 TEM images of SNF-PAEK and hybrid MNS@SNF-PAEK-3%: TEM of SNF-PAEK (a), TEM of MNS@SNF-PAEK-3% (b), enlarged view of red circle area (c). All membranes were dyed by 1M AgNO3 before test.

TEM was carried out to further prove the hypothesis fore-mentioned. Fig. 9a-b show the TEM images of pristine and hybrid membranes. Nafion-like hydrophilic/hydrophobic phase separation morphology could be found in TEM images, where the dark region referred to the hydrophilic phase formed by sulfonic acid groups while the light region corresponded to the hydrophobic phase of the polymer main-chain. Besides, we found that the hydrophilic/hydrophobic phase separation became more obviously with the incorporation of MNS, compared Fig. 9a with Fig. 9b. It might be attributed to the extra sulfonic acid groups and electrostatic interaction formed by amino groups of MNS. In addition, the enlarged view showed in Fig. 9c exhibited the micrograph of MNS in the hybrid membrane. The octahedron covered by dark region was the crystal of MNS, which was surrounded by the hydrophilic phase of SNF-PAEK matrix. It was attributed to the electrostatic interaction between amino groups of MNS and sulfonic groups on the end of the pendent chain. The electrostatic interaction between polymer matrix and MNS 22 ACS Paragon Plus Environment

Page 22 of 31

Page 23 of 31 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


nano-filler caused the rearrangement of polymer and formed bigger ionic clusters just as fast channel, which accelerated the proton conduct and demonstrated our hypothesis.

Fig. 10 Polarization and power density curves of SNF-PAEK (a), MNS@SNF-PAEK-3% (b), and recast Nafion (c); the peak power density of SNF-PAEK, MNS@SNF-PAEK-3%, and recast Nafion at different temperature (d).

3.6 Single Cell Performance To further investigate the practical application of the hybrid membranes in DMFC, a single cell measurement was carried out at 25, 40, 60 and 80°C. As shown in Fig. 10a-c, the power density of membranes increased obviously with the operating temperature increasing, which is similar to the tendency of proton conductivity. Fig. 10d shows the peak power density of SNF-PAEK, MNS@SNF-PAEK-3%, and recast Nafion at different temperatures. The hybrid membrane (MNS@SNF-PAEK-3%) demonstrated a higher power density than that of pristine SNF-PAEK membrane, especially at low operating temperature. For instance, MNS@SNF-PAEK-3% gave a peak power density of 23.5 23 ACS Paragon Plus Environment


Page 24 of 31

mW/cm2 at 25°C and 40.2 mW/cm2 at 40°C, much higher than that of SNF-PAEK(14.9 mW/cm2 at 25°C and 28.6 mW/cm2 at 40°C) and recast Nafion (9.1 mW/cm2 at 25°C and 10.9 mW/cm2 at 40°C). Furthermore, MNS@SNF-PAEK-3% reached high levels of peak power density at high temperature, 79.5 mW/cm2 at 60°C and 125.7 mW/cm2 at 80°C. In short, higher power density is attributed to higher proton conductivity of hybrid membrane. In addition, owing to a superior methanol resistance, MNS@SNF-PAEK-3% showed a better open circuit voltages (OCVs), 0.839V in average, compared with that of SNF-PAEK of 0.816V and recast Nafion of 0.634V. The maximum peak power densities of different membranes at different temperatures can be found in Table S2 (Supporting Information). Compared with other hybrid sulfonated polymeric PEMs listed in Table 4, MNS@SNF-PAEK-3% showed a higher proton conductivity, good methanol resistance, and much better single cell performance. All these results indicated the hybrid membrane based on SNF-PAEK matrix and MNS nano-filler have great potential to be used as alternative PEMs for DMFCs.

Table 4. Proton conductivity (σ), Methanol Permeability (P), and peak Power Density (PDMax) of different types of hybrid PEMs studied in previous works. σ P PDMax Hybrid PEMs References -1 -7 2 -1 ( S cm ) (10 cm ·s ) (mW/cm2) MNS@SNF-PAEK-3% SPEEK/SHGO SPSf/ZrP-42 SPEEK/SHGO/SPEEK SPEEK/SSi-GO SPEEK/sSrZrO3@TiO2 S40-N3 SPEEK/CC2.5/TAP5.0

0.198 0.136 0.156 0.156 0.160 0.121 0.142 0.066

5.28 30.83 -41.5 8.30 9.03 3.80 0.03

125.7 80.3 119.0 50.1 72.2 140.0 66.0 54.9

This work 36 37 38 39 40 41 42

4. Conclusions In this study, novel sulfonated poly(arylene ether ketone) with flexible pendent sulfonic 24 ACS Paragon Plus Environment

Page 25 of 31 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


acid groups, consisting of naphthalene and fluorine on the main chain, was successfully prepared. Then bifunctionalized MIL-101-NH2-SO3H was used as a functional nano-filler to SNF-PAEK matrix for preparing a series of hybrid membranes. The remarkable enhancement on dimensional stability, mechanical properties, and methanol resistance property of hybrid membranes was attributed to the incorporation of MNS that acted as an ionic physical crosslinking agent. In addition, MNS provided extra dense and sequential sulfonic acid groups, and rearranged the polymer microstructure by electrostatic interactions formed by the amino groups, helping hybrid membranes display the highest proton conductivity of 0.198 S cm-1 at 80°C. Moreover, MNS@SNF-PAEK-3% showed an excellent single cell performance of 125.7 mW/cm2 at 80°C, thus proving its great potential for application in DMFCs.

5. Acknowledgements We acknowledge the financial support from the Natural Science Foundation of China (No. 21474036 and 21374034) and the Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences.

References 1.

Jia, W.; Tang, B.; Wu, P., Novel Composite Proton Exchange Membrane with

Connected Long-Range Ionic Nanochannels Constructed via Exfoliated Nafion-Boron Nitride Nanocomposite. ACS Appl Mater Interfaces 2017, 9 (17), 14791-14800. 2.

Tanaka, M.; Takeda, Y.; Wakiya, T.; Wakamoto, Y.; Harigaya, K.; Ito, T.; Tarao, T.;

Kawakami, H., Acid-doped Polymer Nanofiber Framework: Three-dimensional Proton Conductive Network for High-performance Fuel Cells. Journal of Power Sources 2017, 342, 125-134. 3.

Han, H.; Li, H. Q.; Liu, M.; Xu, L.; Xu, J.; Wang, S.; Ni, H.; Wang, Z., Effect of

“Bridge” on the Performance of Organic-Inorganic Crosslinked Hybrid Proton Exchange 25 ACS Paragon Plus Environment


Membranes via KH550. Journal of Power Sources 2017, 340, 126-138. 4. Li, H.; Cui, Z.; Zhao, C.; Wu, J.; Fu, T.; Zhang, Y.; Shao, K.; Zhang, H.; Na, H.; Xing, W., Synthesis and Property of a Novel Sulfonated Poly(ether ether ketone) with High Selectivity for Direct Methanol Fuel Cell Applications. Journal of Membrane Science 2009, 343 (1-2), 164-170. 5.

Lin, H.; Zhao, C.; Jiang, Y.; Ma, W.; Na, H., Novel Hybrid Polymer Electrolyte

Membranes with High Proton Conductivity Prepared by a Silane-crosslinking Technique for Direct Methanol Fuel Cells. Journal of Power Sources 2011, 196 (4), 1744-1749. 6.

Zhang, Y.; Shao, K.; Zhao, C.; Zhang, G.; Li, H.; Fu, T.; Na, H., Novel Sulfonated

Poly(ether ether ketone) with Pendant Benzimidazole Groups as a Proton Exchange Membrane for Direct Methanol Fuel Cells. Journal of Power Sources 2009, 194 (1), 175-181. 7.

Li, X.; Wang, Z.; Lu, H.; Zhao, C.; Na, H.; Zhao, C., Electrochemical Properties of

Sulfonated PEEK Used for Ion Exchange Membranes. Journal of Membrane Science 2005, 254 (1-2), 147-155. 8.

Wang, Z.; Li, X.; Zhao, C.; Ni, H.; Na, H., Synthesis and Characterization of

Sulfonated Poly(arylene ether ketone ketone sulfone) Membranes for Application in Proton Exchange Membrane Fuel Cells. Journal of Power Sources 2006, 160 (2), 969-976. 9.

Gil, M.; Ji, X.; Li, X.; Na, H.; Eric Hampsey, J.; Lu, Y., Direct Synthesis of

Sulfonated Aromatic Poly(ether ether ketone) Proton Exchange Membranes for Fuel Cell Applications. Journal of Membrane Science 2004, 234 (1-2), 75-81. 10. Zhang, Y.; Wan, Y.; Zhao, C.; Shao, K.; Zhang, G.; Li, H.; Lin, H.; Na, H., Novel Side-chain-type Sulfonated Poly(arylene ether ketone) with Pendant Sulfoalkyl Groups for Direct Methanol Fuel Cells. Polymer 2009, 50 (19), 4471-4478. 11. Shao, K.; Zhu, J.; Zhao, C.; Li, X.; Cui, Z.; Zhang, Y.; Li, H.; Xu, D.; Zhang, G.; Fu, T.; Wu, J.; Na, H.; Xing, W., Naphthalene-based Poly(arylene ether ketone) Copolymers 26 ACS Paragon Plus Environment

Page 26 of 31

Page 27 of 31 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


Containing Sulfobutyl Pendant Groups for Proton Exchange Membranes. Journal of Polymer Science Part A: Polymer Chemistry 2009, 47 (21), 5772-5783. 12. Wang, J.; Zhao, C.; Lin, H.; Zhang, G.; Zhang, Y.; Ni, J.; Ma, W.; Na, H., Design of a Stable and Methanol Resistant Membrane with Cross-linked Multilayered Polyelectrolyte Complexes for Direct Methanol Fuel Cells. Journal of Power Sources 2011, 196 (13), 5432-5437. 13. Zhang, G.; Li, H.; Ma, W.; Zhang, L.; Lew, C. M.; Xu, D.; Han, M.; Zhang, Y.; Wu, J.; Na, H., Cross-linked Membranes with a Macromolecular Cross-linker for Direct Methanol Fuel Cells. Journal of Materials Chemistry 2011, 21 (14), 5511-5518. 14. Zhu, J.; Zhang, G.; Shao, K.; Zhao, C.; Li, H.; Zhang, Y.; Han, M.; Lin, H.; Li, M.; Na, H., Hybrid Proton Conducting Membranes Based on Sulfonated Cross-linked Polysiloxane Network for Direct Methanol Fuel Cell. Journal of Power Sources 2011, 196 (14), 5803-5810. 15. Wu, Y.; Wu, C.; Xu, T.; Yu, F.; Fu, Y., Novel Anion-exchange Organic–inorganic Hybrid Membranes: Preparation and Characterizations for Potential Use in Fuel Cells. Journal of Membrane Science 2008, 321 (2), 299-308. 16. Xiong, Y.; Liu, Q. L.; Zhu, A. M.; Huang, S. M.; Zeng, Q. H., Performance of Organic–Inorganic Hybrid Anion-exchange Membranes for Alkaline Direct Methanol Fuel Cells. Journal of Power Sources 2009, 186 (2), 328-333. 17. Subianto, S.; Mistry, M. K.; Choudhury, N. R.; Dutta, N. K.; Knott, R., Composite Polymer Electrolyte Containing Ionic Liquid and Functionalized Polyhedral Oligomeric Silsesquioxanes for Anhydrous PEM Applications. ACS Appl Mater Interfaces 2009, 1 (6), 1173-1182. 18. Yang, L.; Tang, B.; Wu, P., Metal–organic Framework–graphene Oxide Composites: a Facile Method to Highly Improve the Proton Conductivity of PEMs Operated under Low Humidity. J. Mater. Chem. A 2015, 3 (31), 15838-15842. 19. Choi, B. G.; Hong, J.; Park, Y. C.; Jung, D. H.; Hong, W. H.; Hammond, P. T.; Park, 27 ACS Paragon Plus Environment


H., Innovative Polymer Nanocomposite Electrolytes: Nanoscale Manipulation of Ion Channels by Functionalized Graphenes. Acs Nano 2011, 5 (6), 5167-5174. 20. Li, B.; Zhang, Y.; Ma, D.; Li, L.; Li, G.; Li, G.; Shi, Z.; Feng, S., A Strategy toward Constructing a Bifunctionalized MOF Catalyst: Post-synthetic Modification of MOFs on Organic Ligands and Coordinatively Unsaturated Metal Sites. Chem Commun (Camb) 2012, 48 (49), 6151-6153. 21. Phang, W. J.; Jo, H.; Lee, W. R.; Song, J. H.; Yoo, K.; Kim, B.; Hong, C. S., Superprotonic Conductivity of a UiO-66 Framework Functionalized with Sulfonic Acid Groups by Facile Postsynthetic Oxidation. Angew Chem Int Ed Engl 2015, 54 (17), 5142-5146. 22. Ponomareva, V. G.; Kovalenko, K. A.; Chupakhin, A. P.; Dybtsev, D. N.; Shutova, E. S.; Fedin, V. P., Imparting High Proton Conductivity to a Metal-Organic Framework Material by Controlled Acid Impregnation. J Am Chem Soc 2012, 134 (38), 15640-15643. 23. Dybtsev, D. N.; Ponomareva, V. G.; Aliev, S. B.; Chupakhin, A. P.; Gallyamov, M. R.; Moroz, N. K.; Kolesov, B. A.; Kovalenko, K. A.; Shutova, E. S.; Fedin, V. P., High Proton Conductivity and Spectroscopic Investigations of Metal-Organic Framework Materials Impregnated by Strong Acids. ACS Appl Mater Interfaces 2014, 6 (7), 5161-5167. 24. Liang, X.; Zhang, F.; Feng, W.; Zou, X.; Zhao, C.; Na, H.; Liu, C.; Sun, F.; Zhu, G., From Metal–Organic Framework (MOF) to MOF–Polymer Composite Membrane: Enhancement of Low-Humidity Proton Conductivity. Chem. Sci. 2013, 4 (3), 983-992. 25. Liu, C.; Zhang, G.; Zhao, C.; Li, X.; Li, M.; Na, H., MOFs Synthesized by the Ionothermal Method Addressing the Leaching Problem of IL-Polymer Composite Membranes. Chem Commun (Camb) 2014, 50 (91), 14121-14124. 26. Liu, C.; Feng, S.; Zhuang, Z.; Qi, D.; Li, G.; Zhao, C.; Li, X.; Na, H., Towards Basic Ionic Liquid-Based Hybrid Membranes as Hydroxide-Conducting Electrolytes under Low Humidity Conditions. Chem Commun (Camb) 2015, 51 (63), 12629-12632. 28 ACS Paragon Plus Environment

Page 28 of 31

Page 29 of 31 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


27. Wang, B.; Hong, L.; Li, Y.; Zhao, L.; Wei, Y.; Zhao, C.; Na, H., Considerations of the Effects of Naphthalene Moieties on the Design of Proton-Conductive Poly(arylene ether ketone) Membranes for Direct Methanol Fuel Cells. ACS Appl Mater Interfaces 2016, 8 (36), 24079-24088. 28. Ferey, G., A Chromium Terephthalate-Based Solid with Unusually Large Pore Volumes and Surface Area. Science 2005, 310 (5751), 1119-1119. 29. Zhang, J.; Sun, L.; Chen, C.; Liu, M.; Dong, W.; Guo, W.; Ruan, S., High Performance Humidity Sensor Based on Metal Organic Framework MIL-101(Cr) Nanoparticles. Journal of Alloys and Compounds 2017, 695, 520-525. 30. Wang, B.; Cai, Z.; Zhang, N.; Zhang, B.; Qi, D.; Zhao, C.; Na, H., Fully Aromatic Naphthalene-Based Sulfonated Poly(arylene ether ketone)s with Flexible Sulfoalkyl Groups as Polymer Electrolyte Membranes. RSC Adv. 2015, 5 (1), 536-544. 31. Hickner, M. A.; Ghassemi, H.; Kim, Y. S.; Einsla, B. R.; McGrath, J. E., Alternative Polymer Systems for Proton Exchange Membranes (PEMs). Chemical Reviews 2004, 104 (10), 4587-4611. 32. Winter, M.; Brodd, R. J., What Are Batteries, Fuel Cells, and Supercapacitors? Chemical Reviews 2004, 104 (10), 4245-4269. 33. Jeong, N. C.; Samanta, B.; Lee, C. Y.; Farha, O. K.; Hupp, J. T., Coordination-Chemistry Control of Proton Conductivity in the Iconic Metal-Organic Framework Material HKUST-1. J Am Chem Soc 2012, 134 (1), 51-54. 34. Ansari, S.; Kelarakis, A.; Estevez, L.; Giannelis, E. P., Oriented Arrays of Graphene in a Polymer Matrix by in Situ Reduction of Graphite Oxide Nanosheets. Small 2010, 6 (2), 205-209. 35. Mauritz, K. A.; Moore, R. B., State of Understanding of Nafion. Chemical Reviews 2004, 104 (10), 4535-4585. 36. Jiang, Z. J.; Jiang, Z.; Tian, X.; Luo, L.; Liu, M., Sulfonated Holey Graphene Oxide (SHGO) Filled Sulfonated Poly(ether ether ketone) Membrane: The Role of Holes in the 29 ACS Paragon Plus Environment


SHGO in Improving its Performance as Proton Exchange Membrane for Direct Methanol Fuel Cells. ACS Appl Mater Interfaces 2017, 9 (23), 20046-20056. 37. Ozden, A.; Ercelik, M.; Devrim, Y.; Colpan, C. O.; Hamdullahpur, F., Evaluation of Sulfonated Polysulfone/Zirconium Hydrogen Phosphate Composite Membranes for Direct Methanol Fuel Cells. Electrochimica Acta 2017, 256, 196-210. 38. Li, C.; Huang, N.; Jiang, Z.; Tian, X.; Zhao, X.; Xu, Z.-L.; Yang, H.; Jiang, Z.-J., Sulfonated Holey Graphene Oxide Paper with SPEEK Membranes on its Both Sides: a Sandwiched Membrane with High Performance for Semi-Passive Direct Methanol Fuel Cells. Electrochimica Acta 2017, 250, 68-76. 39. Jiang, Z.; Zhao, X.; Manthiram, A., Sulfonated Poly(ether ether ketone) Membranes with Sulfonated Graphene Oxide Fillers for Direct Methanol Fuel Cells. International Journal of Hydrogen Energy 2013, 38 (14), 5875-5884. 40. Gnana kumar, G.; Manthiram, A., Sulfonated Polyether Ether Ketone/Strontium Zirconite@TiO2 Nanocomposite Membranes for Direct Methanol Fuel Cells. Journal of Materials Chemistry A 2017, 5 (38), 20497-20504. 41. Liu, K.-l.; Lee, H.-C.; Wang, B.-Y.; Lue, S. J.; Lu, C.-Y.; Tsai, L.-D.; Fang, J.; Chao, C.-Y.,

Sulfonated

Poly(styrene-block-(ethylene-ran-butylene)-block-styrene

(SSEBS)-Zirconium Phosphate (ZrP) Composite Membranes for Direct Methanol Fuel Cells. Journal of Membrane Science 2015, 495, 110-120. 42. Ilbeygi, H.; Ismail, A. F.; Mayahi, A.; Nasef, M. M.; Jaafar, J.; Jalalvandi, E., Transport Properties and Direct Methanol Fuel Cell Performance of Sulfonated Poly (ether ether ketone)/Cloisite/Triaminopyrimidine Nanocomposite Polymer Electrolyte Membrane at Moderate Temperature. Separation and Purification Technology 2013, 118, 567-575.


Page 30 of 31

Page 31 of 31 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


TOC


Enhanced Proton Conductivity of Sulfonated ... - ACS Publications

Recommend Documents