Preparation of a Cross-linked Sulfonated Poly(arylene ether ketone

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Preparation of a Cross-linked Sulfonated Poly(arylene ether ketone) PEM with Enhanced Proton Conductivity and Methanol Resistance by Introducing Ionic Liquid Impregnated MOF Chunyu Ru, Yiyang Gu, Hui Na, Haolong Li, and Chengji Zhao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b09183 • Publication Date (Web): 13 Aug 2019 Downloaded from pubs.acs.org on August 13, 2019

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ACS Applied Materials & Interfaces

Preparation of a Cross-linked Sulfonated Poly(arylene ether ketone) PEM with Enhanced Proton Conductivity and Methanol Resistance by Introducing Ionic Liquid Impregnated MOF Chunyu Rua, Yiyang Gua, Hui Na a,b, Haolong Lic, Chengji Zhao*a,b, aAlan

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

bKey

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

University, Changchun 130012, PR China cState

Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun

130012, PR China * Corresponding

author: Tel.: +86 431 85168870;

Fax: +86 431 85168870; [email protected];

Abstract A novel ionic liquid impregnated metal-organic-framework (IL@NH2-MIL-101) was prepared and introduced into sulfonated poly(arylene ether ketone) with pendent carboxyl groups (SPAEK) as the nano-filler for achieving hybrid proton exchange membranes. The nano-filler was anchored in polymeric matrix by the formation of amido linkage between pendent carboxyl group attached to molecule chain of SPAEK and amino group belonging to inorganic framework, thus leading to the enhancement in mechanical properties and dimensional stability. Besides, hybrid membrane (IL@MOF-1) exhibits enhanced proton conductivity up to 0.184 S·cm-1 due to the incorporation of ionic liquid in the nano-cages of NH2-MIL-101. Moreover, the special structure of NH2-MIL-101 contributes to a low leakage of ionic liquid so as to remain stable proton conductivity of hybrid membranes under fully hydrated condition. Furthermore, as a result of cross-linked structure formed by inorganic nano-filler, IL@MOF-1 hybrid membrane 1 ACS Paragon Plus Environment

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

shows a lower methanol permeability (7.53×10-7 cm2 s−1) and superior selectivity (2.44×105 S s cm-3) than pristine SPAEK membrane. Especially, IL@MOF-1 performs high single cell efficiency with a peak power density of 37.5 mW cm-2, almost 2.3-fold to SPAEK. Electrochemical impedance spectroscopy and scanning electron microscope indicated that the nano-filler not only contributed to faster proton transfer but also resulted in tighter bond between membrane and catalyst. Therefore, the incorporation of IL@NH2-MIL-101 to prepare hybrid membrane is proven to be suitable for application in direct methanol fuel cells. Key words: sulfonated poly (arylene ether ketone), metal-organic framework, ionic liquid, polymer electrolyte membranes, direct methanol fuel cells

1. Introduction Recent years, in-depth studies about direct methanol fuel cells (DMFCs) have been done for producing renewable and eco-friendly energy resources, so as to resolve the exhaustion of petroleum and air pollution problem.1-3 Efficient proton exchange membrane (PEM) is one of the key components contributing to high performance DMFCs, and a commercial perfluorosulfonic acid resin named Nafion is used as the most common PEM.4 However, high cost and methanol crossover of Nafion have drastically limited its application in DMFCs. Therefore, varies of alternative polymeric electrolyte materials have been developed in past decades.5-9 Among of them, sulfonated poly (arylene ether)s (SPAEs) seem to be the most promising candidates because of high proton conductivity, low methanol crossover, satisfactory chemical stability, as well as low cost7-9. But even so, inferior dimensional stability is the most severe defect of SPAEs which restricts their application as PEMs. As is well known, proton conductivity of SPAEs is mainly connected with the concentration of sulfonic acid group. The high degree of sulfonation (DS) not only leads to high proton conductivity, but also results in a sharp increase of methanol liquor uptake and swelling ratio.10-12 High proton conductivity 2 ACS Paragon Plus Environment

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facilitates proton transfer and then enhances DMFCs performance, while high swelling ratio impairs the adhesion of PEMs and catalyst layers and then causes the performance degradation. Hence, a number of efforts such as hybrid, blending, grafting, and cross-linking have been made to develop SPAEs with high proton conductivity and satisfactory dimensional stability.13-16 Inorganic nano-fillers includes carbon nanotubes (CNTs), graphene oxides (GOs), and metal organic frameworks (MOFs) have been utilized as the addictives for preparing hybrid PEMs.17-22 For example, Gong and his coworkers designed high-performance polymer electrolyte membranes by incorporating functionalized carbon nanotubes.17 Lee’s group prepared composite membranes with antioxidant grafted GOs, which exhibited enhanced physical stability.20 Wu et al. incorporated MOFs into polyelectrolyte for achieving high proton conductivity up to 0.25 S cm-1.22 Our group also synthesized an amino-sulfo bifunctionalized MOF as the modifier for SPAEs based PEMs.23 Besides, many groups attempted to use chemical cross-linking to restrict the swelling ratio of SPAEs with high DS, though it might cause a decline on proton conductivity. For instance, Na’s group prepared the cross-linked PEM by incorporating with molecular cross-link agent, which significantly reduced the swelling ratio and methanol permeability of pristine membrane.10 Lee and coworkers developed a kind of terminally cross-linked aromatic polymeric electrolytes for DMFCs.11 Anahidzade utilized MOF as the cross-linking agent to anchor sulfonated poly(ether sulfone) for high temperature fuel cells.24 In general, cross-linking usually restricts the molecular segment movement and then leads to the decrease in proton conductivity. Therefore, introducing extra proton conductors into cross-linked membranes could efficiently compensate the decrease of proton conductivity. Due to its excellent ionic conductivity and chemical stability, ionic liquid (IL) seems to be a sensible choice as the extra proton conductor. Many researchers 3 ACS Paragon Plus Environment


have put forward preparing high ionic conducting polyelectrolyte by incorporating ILs into polymeric matrix.5-6,

25-26

However, the leaching problem of ILs from composite

membranes has not yet been resolved, which restricts its potential application in DMFC. MOFs, as the representative three-dimensional nano-fillers, possess a huge specific surface area and multifunctional framework architectures, which help to form more continuous proton-transport channels in composite membranes.27 More intriguingly, some kinds of MOFs can be served as “nano-cages” that can impregnate ILs with a low leakage ratio.28 Therefore, introducing IL impregnated MOF in to composite membrane has been proven to be an effective strategy for addressing the leaching problem of ILs. Wherein, a high conductive polymer electrolyte based on IL impregnated MOFs (ILs@MOF) has been synthesized and characterized by Wan’s groups, which exhibits a long-term durability.29 Nonetheless, developing an ILs@MOF additive, which serves as both chemical cross-linking agent and proton transfer promoter, is rarely reported. In the present work, polymer electrolyte matrix based on sulfonated poly(arylene ether ketone) with carboxyl pendant group (SPAEK) was prepared via traditional condensation polymerization,30 while MOF (NH2-MIL-101) was synthesized by hydrothermal reaction as reported previously.22 Then, sulfonic acid-functionalized IL was encapsulated in MOF and inorganic nano-filler (IL@NH2-MIL-101) was obtained. Next, a series of hybrid membranes were fabricated by adjusting the content of nano-filler in polymeric matrix. The microstructure and properties of these hybrid membranes were investigated, including proton conductivity, dimensional stability and methanol resistance. More importantly, single cell performance of each membrane was evaluated to assess its potential to be applied in DMFCs. Besides, we put forward further study into the improvement mechanism by scanning electron microscope and electrochemical impedance spectroscopy.

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2. Experimental Section 2.1 Materials. Monomers phenolphthalin (PPL), sodium 5,5′-carbonylbis(2-fluobenzene-sulfonate) (SDFBP), 4,4′-difluorobenzophenone (DFBP) and 3,3′,5,5′-tetramethyl-4,4′-biphenyl (TMBP) were chemically pure grade and purchased from Yanjin Technology (Tianjin, China). Ligand 2-aminoterephthalic acid (HN2-H2BDC) was obtained from Energy Chemical Ltd. Ionic liquid 1-sulfobutyl-3-methylimidazolium trifluoromethansulfonate (IL) was received from Watson International Ltd. All chemical reagents and solvents were at least analytical pure grade and used without further purification. The preparation of sulfonated poly(arylene ether ketone) (SPAEK) copolymers with carboxylic acid groups was according to our previous work.30 NH2-MIL-101 was synthesized via a hydrothermal reaction as reported in literature.22 The synthesis procedures of SPAEK and NH2-MIL-101 are shown in Scheme 1 and their synthetic procedure are present in Supporting Information.

Scheme 1.

The synthesis procedure of SPAEK and NH2-MIL-101

2.2 Preparation of IL@NH2-MIL-101 inorganic filler. 5 ACS Paragon Plus Environment


The size of IL was simulated by Materials Studio in advance (Figure S1), and the 1-sulfobutyl-3-methylimidazolium possesses the longest extent of 7.428 Å, which is smaller than the diameter of NH2-MIL-101. Hence, it is viable for impregnating IL into the nano-cages of NH2-MIL-101. The schematic diagram of IL@NH2-MIL-101 preparation is shown in Scheme 2. First, 3.0 g NH2-MIL-101 was degassed in a vacuum oven at 150°C for 12 h, followed by dispersion in 15 mL ethanol. Then 3.0 g IL was dropwise added into dispersion as-prepared. After that, the mixture was kept stirring for 24 h, and then ethanol was evaporated off. The precipitated powder was recovered and then washed with ethanol to remove IL attached to the surface of NH2-MIL-101. Finally, the inorganic filler IL@NH2-MIL-101 was obtained by filtration and dried in vacuum oven at 80ºC. By comparing the weight of IL@NH2-MIL-101 and pristine NH2-MIL-101, there is almost 0.93 g IL impregnated into 1 g NH2-MIL-101, and the images of the powder are shown in Figure S2.

Scheme 2.

Preparation of IL@NH2-MIL-101 inorganic filler

2.3 Preparation of hybrid membranes SPAEK was dissolved in dimethylsulfoxide (DMSO) to prepare homogeneous cast solution, and different content of IL@NH2-MIL-101 (0, 0.5%，1%, and 2%, by weight 6 ACS Paragon Plus Environment

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of SPAEK) was introduced into cast solution. After that, the mixture was ultrasonic treated every 2 h, and then rotated with stirring, and this procedure keeping for 48 h until a uniform dispersion was received. The dispersion was casted onto a flat glass plate, followed by solvent evaporation at 60°C for 24 h. The IL@MOF-X hybrid membrane was peeled off by immersing in deionized water and then processed in vacuum oven at 175°C for 3 h to form cross-links between organic and inorganic components. All hybrid membranes were labeled as IL@MOF-X (X represents the content of inorganic filler). In addition, pristine SPAEK membrane (SPAEK) and hybrid membrane with pure NH2-MIL-101(MOF-2) were prepared via the same procedure for comparison. 2.4 Fabrication of direct methanol fuel cells (DMFCs) First, all membranes in this work were pre-activated by 1 M H2SO4 and washed with deionized water. For catalyst coating, Pt-Ru/C (HISPEC 9000, 60 wt.% Pt-Ru) was used as the catalyst on the anode with a dosage of 3.0 mg cm-2, meanwhile 2.0 mg cm-2 Pt/C catalyst (HISPEC 6000, 60 wt.% Pt) was loaded on the cathode. The pictures of catalyst-coated-membrane and the ionomer used in catalyst coating are shown in Figure S3. Then, membrane electrode assembly (MEA) was prepared by clamping catalyst-coated-membranes between two carbon papers (SGL, 29BC). Afterwards, the sandwich component was fabricated into DMFC by cold-pressed method under a certain pressure of 8 N·m. The working electrode area prepared was 5 cm2. 2.5 Measurements 2.5.1 Primary measurement 1H

NMR spectra were used to verify the successful synthesis of SPAEK polymer matrix,

which was carried out by a Bruker 500 MHz NMR spectroscopy. Measurements for IL@NH2-MIL-101 such as Powder X-ray diffraction (PXRD), scanning electron microscope (SEM) and N2 adsorption-desorption were performed on Rigaku D/max 2550 powder X-ray diffractometer, Hitachi SU8020, and 3H-2000PS2, respectively. Fourier transform infrared spectroscopy (FT-IR) test for inorganic filler and hybrid membranes 7 ACS Paragon Plus Environment


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was done via Bruker Vector 22 spectrometer. Transmission electron microscope (TEM, JEM-3100F) was used to investigate the microstructure of proton exchange membranes prepared. The thermogravimetric analysis (TGA) was carried out by TA 2050, and mechanical properties were obtained by universal testing machine (AG-I-20KN, Shimadzu). 2.5.2 Ionic Exchange Capacity (IEC) of Membranes The IECs of SPAEK and IL@MOF-X membranes were determined via acid-base titration. All membranes were dried and weighted (Wdry, g) before immersing them into 1 M NaCl for 24 h to release the protons completely and then the liquid was titrated with 0.01 M NaOH (CNaOH) solution. The IEC titration experiment was repeated three times and IEC was calculated by following equation:

IEC =

VNaOHCNaOH

(1)

Wdry

where VNaOH is the volume of NaOH solution consumed. 2.5.3 Proton conductivity (σ) and electrochemical impedance spectroscopy (EIS) The surface resistance (R, ohm) of all PEMs was measured by Princeton Applied Research 2273 potentiostat (0.1 Hz~1M Hz, four-probe method), and proton conductivity (σ) was calculated by the following equation: (2)

σ = L/(R × A)

Particularly, L is the membrane thickness (cm) and A is cross section area of membrane samples (cm2). Besides, electrochemical impedance of DMFC fabricated in this work was also obtained by the instrument aforementioned, at a frequency of 1 Hz~1M Hz, with a discharge voltage of 300mV using three-probe method. 2.5.4 Methanol solution uptake (MU), swelling ratio (SR) in area and gel fraction The weight and size of SPAEK based membranes were recorded after dehydration in vacuum before test, named as Wdry (g) and Adry (g) respectively. Then, all samples were immersed into 2 M methanol solution, which is the same concentration of fuel to be applied for DMFC. Next, they were kept at 80°C, the optimum operating temperature of 8 ACS Paragon Plus Environment

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DMFC, for 24 h. Finally, the extra liquid on the surface of samples was wiped off slightly, and their weight (Wwet, g) and size (Awet, g) were remeasured. The MU (%) and SR (%) are calculated by the following equations: MU = SR =

Wwet ― Wdry Wdry Awet ― Adry Adry

(3)

× 100%

(4)

× 100%

The pristine SPAEK membrane can be easily dissolved in DMSO, while the IL@MOF-X membranes are partial soluble. The gel fraction was obtained from the ratio of the remnant weight of the IL@MOF-X membranes after extraction from DMSO, calculated via the equation: Wafter

(5)

Gel fraction = Winitial × 100%

where Wafter is the remnant weight after extraction from DMSO and Winitial is the initial weight of membrane sample. 2.5.5 Oxidative stability The oxidative stability of the membranes was determined by their durability in Fenton’s reagent (3% H2O2, 2 ppm FeSO4). All membranes were kept in Fenton’s reagent at 80°C, and the oxidative stability was characterized by recording the time when the membranes began to break into pieces. 2.5.6 Methanol resistance measurements The methanol crossover of membranes was measured via a linear sweep voltammetry (LSV) method, where electrochemical oxidation occurred when methanol permeated through PEM to cathode. For the measurement, the anode of DMFC was delivered by 2 M methanol, while the cathode was protected by pre-humidified nitrogen. Under such conditions, cathode served as the working electrode and anode acted as the reference electrode. Thus the electrochemical oxidation current density reflected the quantity of methanol crossover from anode to cathode, because higher methanol crossover resulted in larger current density. Moreover, according to a previous literature,31 the redox current 9 ACS Paragon Plus Environment


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could be translated into methanol permeability via following equation: L × CDmax

(6)

P = 6F × k × Cfuel

where P refers to methanol permeability of the PEM (cm2 s−1), L is the thickness of membrane (cm), CDmax (mA cm-2) is the peak current density obtained by LSV test, F is the Faraday constant, Cfuel is the concentration of methanol solution as the fuel, and k is the drag correction factor of 0.739 when fed with 2 M methanol. Selectivity (φ, S·s·cm-3) is another key factor to evaluate methanol resistance property of PEMs, which reflects the balance between proton conductivity and methanol permeability. It can be calculated via the following equation: (7)

φ = σ/P 2.5.5

Single cell performance evaluation

Single cell performance evaluation was operated on an Arbin instrument. In detail, the anode was fed up with 2 M methanol at a flow rate of 2 mL min-1, while the cathode was supplied by O2 at a constant flow rate of 30 mL min-1. All DMFCs were pre-activated for 4 h and tested at 80°C.

3. Result and Discussion 3.1 Characterization of IL@NH2-MIL-101 inorganic filler As shown in Figure 1a, it could be observed the SEM image that IL@NH2-MIL-101 exhibited the similar octahedral structure to MIL-101 as reported in previous work.32 However, IL@NH2-MIL-101 monocrystal has a rough surface, which is different from MIL-101, and it might be caused by the impregnation of IL. Besides, Figure 1b shows the comparison between their XRD patterns. It could be found that after impregnation of acidic IL, IL@NH2-MIL-101 remains the similar XRD pattern, only with a slight variation in the Bragg intensity. The result indicated that NH2-MIL-101 could coexist with the acidic IL. Furthermore, the stability of NH2-MIL-101and IL@NH2-MIL-101 in acidic aqueous solution (pH=1) was also investigated. The XRD spectra in Figure S4 10 ACS Paragon Plus Environment

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showed that all characteristic peaks of framework were maintained. This indicated that both NH2-MIL-101 and IL@NH2-MIL-101 had good acid resistance and stability. FT-IR (Figure.1c) was used to prove that IL was successfully impregnated into the pores of NH2-MIL-101. Compared to pristine MOF, the new adsorption bands appeared at 1165 cm-1 and 1030 cm-1 contributing to the asymmetric vibration modes of -SO3H units of IL@NH2-MIL-101. In order to further confirm the IL was successfully loaded inside the pores of NH2-MIL-101, N2 adsorption-desorption test of inorganic fillers was carried out. As displayed in Figure 1d, the N2 quantity absorbed sharply decreased after impregnation of

IL

into

the

pore

of

NH2-MIL-101,

with

a

significant

decline

in

Brunauer-Emmett-Teller (BET) surface area (from 1056.3 m2 g-1 to 200.8 m2 g-1). Additionally, the adsorption bands belonging to -SO3H units remained after immersing in 2 M methanol for 7 days, and N2 adsorption isotherm was barely changed. These evidences suggested that IL exhibit a very low leaching when it was impregnated into nano-pores of NH2-MIL-101. For NH2-MIL-101cages have pores about 1.21 nm and 1.47 nm, we suggest that this nano-pores restrict the loss of IL. Moreover, an ionic linkage was formed between NH2-MIL-101 nano-cages and IL, where the –NH2 on the framework of MOF has a strong electrostatic interaction with –SO3H belonging to IL (Scheme 2). Hence, the ionic linkage help IL possess superior retention rate after impregnation into NH2-MIL-101.



Figure 1. Characterizations including SEM (a), XRD (b), FT-IR (c) and BET (d) of NH2-MIL-101 and IL@NH2-MIL-101 inorganic filler (†: tested after immersing in 2 M methanol for 7 days)

3.2 Fundamental characteristics of IL@MOF-X hybrid Membranes Since carboxyl group could react with amino group at high temperature under anhydrous condition, the as-prepared hybrid membranes were processed in vacuum oven at 175°C in order to form amido linkage. FT-IR was performed to demonstrate the formation of crosslinking structure between IL@NH2-MIL-101 modifier and SPAEK matrix. As shown in Figure 2, the characteristic peak of ƲC=O (1680 cm−1) belonging to amido bond appeared, together with the characteristic peak of δN-H at 1385 cm−1, proving the successful reaction between carboxyl group and amino. At the same time, the peaks at wave number 1707 cm−1 corresponding to absorption vibration ƲC=O of carboxyl group existed, for there were still carboxyl group of SPAEK remained. In addition, the formation of amido bond was proved via XPS of nitrogen in the hybrid membrane. The 12 ACS Paragon Plus Environment

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binding energy of N1s belong to NH2- is about 400.7 eV before the high temperature treatment. However, the N1s split into two binding energy of 400.2 and 401.8 eV after the cross-linking reaction, where the formation of -CONH- results in the differences.

Figure 2. FT-IR (a) and XPS (b) spectra of SPAEK and IL@MOF-2 membranes Table 1 Properties of pristine SPAEK and S@N/fEO composite membranes Tensile

Young’s

Maximum

Oxidative Gel Fraction

Sample

Strength

Modulus

Elongation

MU (%)

SR (%)

Stability† (%)

(MPa)

(MPa)

(%)

SPAEK

42.2±6.9

561.2±73.9

25.8±2.1

100.8±13.2

69.0±11.3

--

49

[email protected]

48.0±3.1

705.8.9±60.3

19.2±3.4

85.4±10.9

58.7±12.1

42.3±6.7

95

IL@MOF-1

50.8±6.3

1111.5±92.4

14.2±3.2

79.2±7.5

50.6±10.8

47.7±3.2

107

IL@MOF-2

58.3±3.9

1388.1±70.7

11.3±4.7

76.2±8.2

41.2±8.7

55.9±2.8

140

(min)

†: The time when the membranes broke into pieces in Fenton’s reagent.

Except from evidence of FT-IR, the test results derived from mechanical properties and TGA also suggested the successful formation of amido linkage between SPAEK and IL@NH2-MIL-101. All membranes were kept in 2 M methanol before tensile testing, and the results are summarized in Table 1. Tensile strength and Young’s modulus of IL@MOF-X were significantly enhanced with the addition of IL@NH2-MIL-101, but the elongation was sharply decreased. Specifically, tensile strength increased from 42.2 MPa to 58.3 MPa and Young’s modulus was enhanced almost 2.5-fold, compared between 13 ACS Paragon Plus Environment


pristine SPAEK membrane and IL@MOF-2. However, the enhanced rigidity dramatically reduced the maximum elongation of hybrid membranes, from 25.8% to 11.3% (Figure 3a). Since the amido linkage served as cross-link section of polyelectrolyte matrix, the cross-linking degree increased with the addition amount of IL@NH2-MIL-101. Therefore, a cross-linking structure caused by amido bond between SPAEK and IL@NH2-MIL-101 leads to this enhancement in tensile strength and Young’s modulus but reduction in maximum elongation at break. To confirm both inorganic filler and polymer matrix have good thermal stability to be applied in DMFC, TGA under atmosphere was carried out. It can be observed from Figure 3b that all samples possessed of 5% weight loss temperature (Td5%) higher than 250°C, which proved that the chosen materials completely satisfied the requirement of membrane to be applied in DMFC. In addition, IL@NH2-MIL-101 has one more thermal weight loss than NH2-MIL-101 due to the degradation of IL impregnated in MOF pores. It is noteworthy that the degradation temperature of hybrid membrane IL@MOF-2 is almost 30°C higher than that of pristine SPAEK in the range of 100~400°C, which is because of the cross-linked structure induced by amido bone between polymer chain and inorganic nano-filler. As is well known, cross-linked structure makes molecules more compact to resist oxidative degradation. However, IL@MOF-2 degraded more quickly when the temperature is over 400°C. It might be due to the existence of Fe(III) facilitating the degradation progress after the polymer chain has been degraded.


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Figure 3. Stress-strain curves of prepared membranes (a); TGA curves of inorganic fillers, polymer matrix, and hybrid membrane (b)

Good dimensional stability is essential requirement of PEM when fabricated in DMFC, which is beneficial for good electrical contact and mass transfer. The test results are shown in Figure 4. It can be found that MU and SR decrease with a higher content of IL@NH2-MIL-101. Due to the existence of cross-linked structure caused by NH2-MIL-101, the polymer chain motion and the liquid absorption of SPAEK matrix are hindered. Consequently, MU decreased from 100.8% to 76.2%, meanwhile SR decreased from 69.0% to 41.2% with the cross-link agent of IL@NH2-MIL-101 rises to 2% weight content. In addition, the gel fraction was a factor used to indirectly measure the cross-linking density of membrane. The gel fractions of IL@MOF-X membranes are shown in Table 1, which increased with higher addition of IL@NH2-MIL-101. This result also indicated that the cross-linking density increased when more cross-link agent was introduced into SPAEK matrix, which can contribute to a better dimensional stability of hybrid membranes.

Figure 4. Methanol solution uptake and swelling ratio of prepared membranes 15 ACS Paragon Plus Environment


The oxidative stability is also an important property of PEMs for utilization in DMFCs, and Fenton’s reagent is usually used to evaluate the oxidative durability of membranes in fuel cells. As shown in Table 1, the time when IL@MOF-X membranes broke into pieces was much longer than pristine SPAEK membrane, where SPAEK started to break after 49 min while IL@MOF-2 hold for 140 min. It is because that the cross-linked structure induced by IL@NH2-MIL-101 enhanced oxidative stability of the hybrid membranes. 3.3 Proton conductivity and IEC of IL@MOF-X membranes Proton conduction is the most primary property for polyelectrolyte materials. Hereof, proton conductivity of SPAEK and IL@MOF-X is investigated in aqua phase, which is same to DMFC operating condition. According to proton conductivity curves shown in Figure 5a, all membranes exhibited an upward trend of conductivity with the temperature increasing as expected. Since the movement of molecular segment will be facilitated at high temperature, which results in higher proton conductivity. As for hybrid membranes, it is interesting to observe that [email protected] and IL@MOF-1 shows higher proton conductivity (0.172 S·cm-1 and 0.184 S·cm-1 at 80°C, respectively) than SPAEK membrane (0.168 S·cm-1), but the IEC of them is lower than pristine SPAEK. Though the addition of IL with sulfonic acid groups could compensate the IEC decline of polyelectrolyte caused by cross-linked structure, which is not effective enough since the CF3SO3¯ can only serve as proton conductor but not ionic exchanger. However, owing to the abundant −SO3¯ in IL, the incorporation of IL@NH2-MIL-101 provided another proton transport pathway in membranes, whose schematic diagram is shown in Figure 6a. For SPAEK matrix, the −SO3H and −COOH get together and form the ionic clusters via polymer chain movement and rearrangement, and proton can transfer among these ionic clusters.1 Basically, IL impregnated in pores of MOFs constructs new high-speed channels for proton conducting, distinguished from that of molecular segment movement. According to the Grotthuss mechanism,33 the dense and sequential −SO3¯, especially CF3SO3¯ in inorganic filler make it easier for H+ to jump through the proton conductor, 16 ACS Paragon Plus Environment

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serving as a short-range transmission which can promote the proton transfer. Therefore, the proton conductivity of IL@MOF-1 increased when more IL@NH2-MIL-101 was added into SPAEK matrix, though with a low IEC. Besides, the activation energy (Ea) of proton conductivity of each membrane was calculated by Arrhenius equation and the results are listed in Table 2. It could be found that the Ea of membranes decreased when incorporated with more IL@NH2-MIL-101, corresponding to the easier proton conduction aforementioned. TEM of hybrid membranes was carried out in order to represent more visual effect deduced by IL@NH2-MIL-101, and the image is shown in Figure 6b-c. The sample were dyed by 1 M (CH3COO)2Pb, so that the hydrophilic organic phase (ionic clusters) stained by Pb2+ formed the dark region; meanwhile the hydrophobic phase consisting of polymer backbone formed the light regions. It is easy to distinguish the monocrystal of IL@NH2-MIL-101 (marked by red rhombus) in Figure 6b, and the dark region corresponding to ionic clusters of IL is also easily observed. Besides, an obvious phase separation of SPAEK matrix could be found, the enlarged image shown in Figure 6c, and the dark region refers to the ionic clusters of polymer matrix. Herein, the proton can not only transfer in the channel formed by ionic clusters in polymer matrix, but also use the “high-way” formed by IL@NH2-MIL-101. However, introducing too much inorganic filler (IL@MOF-2) makes SPAEK polyelectrolyte over cross-linked, due to an excess of amido bonds attached on nano-filler frameworks. This over cross-linked structure produces a great limitation on molecular segment movement, thus impeding the proton transport. A hybrid membrane with pristine NH2-MIL-101 (MOF-2) was prepared and tested in the same way to verify this point, and we found it showed much inferior proton conductivity compared with SPAEK matrix. Moreover, proton conductivity stability is an important factor for hybrid membranes to be applied in DMFC. The results of long-term conductivity test are shown in Figure 5b. Taking IL@MOF-1 for instance, proton conductivity decreased from 0.184 S·cm-1 to 17 ACS Paragon Plus Environment


0.174 S·cm-1, which was 94.5% remaining after 30 days immersion and still higher than that of pristine SPAEK. In addition, the IEC was remeasured after immersing all samples in 2 M methanol for 15 days, whose result is shown in Table 2. The IEC of IL@MOF-X marginally declined as well, and these results corresponded to low leakage ratio of IL in NH2-MIL-101 as aforementioned. Thus, it could be concluded that hybrid membranes have the potential to be used as PEMs.

Figure 5. Proton conductivity of the membranes in aqua phase (a) and long-term stability of proton conductivity (b)

Figure 6. Proton conduction schematic diagram of IL@MOF-X hybrid membranes (a); TEM imgaes of image of IL@MOF-1 membrane (b) and its partial enlarged detail (c) 18 ACS Paragon Plus Environment

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Page 19 of 29 1 2 3 4 5 6 7 Sample 8 9 10 SPAEK 11 12 [email protected] 13 14 IL@MOF-1 15 16 IL@MOF-2 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 The proton conductive properties and DMFC performances of membranes IECa

IECb

σ (S cm-1)

Ea

P

φ

PDmax

(meq g-1)

(meq g-1)

at 80°C

(kJ mol-1)

(×10-7 cm2 s-1)

(×105 S s cm-3)

(mW·cm-2)

1.51

1.51

0.168

18.45

10.25

1.64

16.3

1.35

1.33

0.172

13.15

9.34

1.84

29.6

1.32

1.30

0.184

13.29

7.53

2.44

37.5

1.16

1.12

0.136

10.42

6.77

2.00

26.8

a: Titration was carried out as soon as the membranes were prepared; b: Titration was carried out after the membranes were immersed in 2 M methanol after 15 days.

3.4 Methanol crossover of membranes. Methanol crossover is a major factor affecting the output power and efficiency of DMFC, which causes polarization loss as well as wastes fuel.3 Hence, developing PEMs with low methanol permeability is essential to heighten power density and fuel utilization of DMFC. An in-situ methanol crossover measurement was carried out via LSV test on a single cell, and the results are shown in Figure 7a. The electrochemical oxidation current increased with an increasing voltage applied on cathode, meanwhile a maximum current density (CDmax) appeared at around 1.1V, reflecting the amount of methanol crossover to cathode. The cross-linked structure induced by IL@NH2-MIL-101 makes polyelectrolyte matrix compact, which enhances the methanol resistance as a consequence. The CDmax of membranes is in order of SPAEK>[email protected]>IL@MOF-1>IL@MOF-2, and it can be converted into methanol permeability (P) according to eq. 6. As shown in Figure 7b, the methanol permeability decreases from 10.25×10-7 cm2 s−1 to 6.77×10-7 cm2 s−1 when the inorganic filler addition increases from 0 to 2% weight content. Besides, IL@MOF-1 exhibits a best selectivity of 2.44×105 S s cm-3, due to its highest proton conductivity and acceptable methanol permeability. In short, IL@MOF-1 possesses an appropriate cross-linking between nano-filler and matrix, which enhances the methanol resistance of 19 ACS Paragon Plus Environment


PEM but without obviously sacrificing proton conductivity.

Figure 7. LSV curves (a), methanol permeability and selectivity of membranes (b)

Figure 8. The polarization and power density curves of DMFCs fabricated by membranes prepared (a); Electrochemical impedance spectroscopy of DMFCs corresponding to respective membranes (b)

3.6 Single Cell Performance To further verify the application potential of as-prepared hybrid membranes in DMFC, a single cell performance evaluation was carried out at 80°C and fed with 2 M methanol, the optimized operating condition of DMFC. As shown in Figure 8a, pristine SPAEK membrane shows a power density of 16.3 mW/cm2, and the power density increases 20 ACS Paragon Plus Environment

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obviously when modified by IL@NH2-MIL-101. It was noted that IL@MOF-1 performs the highest power density (37.5 mW/cm2) among all hybrid membranes, which is account for its highest proton conductivity and selectivity. Furthermore, EIS of respective DMFCs was applied at a constant discharge voltage of 300 mV to investigate the mechanism of single cell performance improvement. As seen in Figure 8b, the Ohm resistance (in high frequency region) of each sample is basically the same, which depended on resistance of components.34-35 However, the fabricated single cells show very different mass transfer resistance in low frequency region. More specifically, pristine SPAEK possesses the highest mass transfer resistance of 0.49 Ω, while the hybrid membranes’ fall by nearly half. Obviously, IL@MOF-1 shows the lowest resistance (0.22Ω), which helps itself output highest power density. In general, mass transfer resistance is determined by many factors, such as proton conductivity, components assembly, especially contact status of PEM and catalyst et al. Herein, we supposed that enhanced dimensional stability of hybrid membranes is beneficial to reduce the mass transfer resistance, because PEM and catalyst layer connect more integrated so that proton, fuel, and gas could transport fluently. Furthermore, the -NH2 of nano-filler produces electrostatic interaction with –SO3H belonging to catalyst ionomer, which can also help to form exquisite catalyst coated layer. SEM investigation of catalyst coated membranes was carried out to prove our hypothesis, and images are shown in Figure 9. By contrast, IL@MOF-1 tightly attached to catalyst layer (Figure 9a), while the peeling between catalyst layer and pristine SPEAK could be easily found (marked by red ellipse). A comparison between this work and other recent study about SPAEs based PEMs for DMFCs was made. As listed in Table 3, IL@MOF-1 exhibited a high proton conductivity, superior relative selectivity and good DMFC performance. All these results indicated that hybrid membranes with IL@NH2-MIL-101 nano-filler have a great potential to be used as alternative PEMs for DMFCs.



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Figure 9 Microstructure of catalyst coated membranes of IL@MOF-1 (a) and SPAEK (b)

retrieved from single cells.

Table 3 Comparison with recent researches about developing SPEs based PEMs for DMFCs P

φ

PDmax

(×10-7 cm2 s-1)

(×105 S s cm-3)

(mW·cm-2)

σ (S cm-1)

Sample

Reference

IL@MOF-1

0.184

7.53

2.44

37.5

This work

semi-SPEK-18

0.157

6.30

2.50

16.0

Ref 8

SP/Cr-fa-SPA-40

0.110

4.6

2.39

7.7

Ref 36

SPEEK/GO-his-4

0.069

1.35

5.14

43.0

Ref 37

SP-B-20

0.064

1.39

1.20

23.9

Ref 38

4. Conclusions In this study, novel hybrid proton exchange membranes (IL@MOF-X) based on SPAEK with pendent carboxyl groups were prepared by incorporating an IL impregnated MOF inorganic

nano-filler

(IL@NH2-MIL-101).

The

successfully

impregnation

and

satisfactory retention of IL in MOF nano-cages were verified by FT-IR and BET, which promoted proton transfer durability in hybrid electrolyte. Besides, IL@NH2-MIL-101 served as cross-linked anchors to restrict the liquid uptake and swelling ratio, as well as 22 ACS Paragon Plus Environment

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to form dense structure for enhancing methanol resistance of hybrid membranes. Due to the modification by IL@NH2-MIL-101 aforementioned, IL@MOF-1 possessed of high proton conductivity of 0.184 S·cm-1, low methanol permeability of 7.53×10-7 cm2 s−1, and outstanding selectivity of 2.44×105 S s cm-3. Thus their synergistic effect contributed IL@MOF-1 to have a much higher single cell performance (37.5 mW/cm2) and lower mass transfer resistance (0.22Ω) than those of pristine SPAEK. In addition, the microstructure of hybrid membranes and catalyst coated membranes was investigated via TEM and SEM respectively to show most visible change of them. In brief, introducing IL impregnated MOF into SPAEK polyelectrolyte as cross-link agent and proton conductor for hybrid membrane proved its great potential for application in DMFCs.

5. Acknowledgements We acknowledge the financial support from the Natural Science Foundation of China (No. 21875088 and No. 21622403).

References 1.

Zhang, H.; Shen, P. K. Recent Development of Polymer Electrolyte Membranes for

Fuel Cells. Chem. Rev, 2012, 112 (5), 2780-832. 2.

He, G.; Li, Z.; Zhao, J.; Wang, S.; Wu, H.; Guiver, M. D.; Jiang, Z. Nanostructured

Ion-Exchange Membranes for Fuel Cells: Recent Advances and Perspectives. Adv. Mater, 2015, 27 (36), 5280-95. 3.

Zakil, F. A.; Kamarudin, S. K.; Basri, S. Modified Nafion Membranes for Direct

Alcohol Fuel Cells: An Overview. Renew. Sustain. Energy Rev, 2016, 65, 841-852. 4.

Mauritz, K. A.; Moore, R. B. State of Understanding of Nafion. Chem. Rev, 2004,

104 (10), 4535-4585. 5.

Kim, S. Y.; Kim, S.; Park, M. J. Enhanced Proton Transport in Nanostructured

Polymer Electrolyte/ionic Liquid Membranes under Water-free Conditions. Nat. Commun, 23 ACS Paragon Plus Environment


2010, 1, 88. 6.

Lin, B.; Cheng, S.; Qiu, L.; Yan, F.; Shang, S.; Lu, J. Protic Ionic Liquid-Based

Hybrid Proton-Conducting Membranes for Anhydrous Proton Exchange Membrane Application. Chem. Mater, 2010, 22 (5), 1807-1813. 7.

Dong, T.; Hu, J.; Ueda, M.; Wu, Y.; Zhang, X.; Wang, L. Enhanced Proton

Conductivity of Multiblock Poly(phenylene ether ketone)s via Pendant Sulfoalkoxyl Side Chains with Excellent H2/air Fuel Cell Performance. J. Mater. Chem. A, 2016, 4 (6), 2321-2331. 8.

Feng, S.; Pang, J.; Yu, X.; Wang, G.; Manthiram, A. High-Performance

Semicrystalline Poly(ether ketone)-Based Proton Exchange Membrane. ACS. Appl. Mater. Interfaces, 2017, 9 (29), 24527-24537. 9.

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), 24079-88. 10. 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. J. Mater. Chem, 2011, 21 (14), 5511. 11. Lee, K.-S.; Jeong, M.-H.; Lee, J.-P.; Kim, Y.-J.; Lee, J.-S. Synthesis and Characterization of Highly Fluorinated Cross-linked Aromatic Polyethers for Polymer Electrolytes. Chem. Mater, 2010, 22 (19), 5500-5511. 12. Wang, J.; Zhao, C.; Zhang, G.; Zhang, Y.; Ni, J.; Ma, W.; Na, H. Novel Covalent-ionically Cross-linked Membranes with Extremely Low Water Swelling and Methanol Crossover for Direct Methanol Fuel Cell Applications. J. Membr. Sci, 2010, 363 (1-2), 112-119. 13. 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 24 ACS Paragon Plus Environment

Page 24 of 29

Page 25 of 29 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. J. Polym. Sci. Polym. Chem, 2009, 47 (21), 5772-5783. 14. Wang, H.; Li, X.; Zhuang, X.; Cheng, B.; Wang, W.; Kang, W.; Shi, L.; Li, H. Modification of Nafion Membrane with Biofunctional SiO2 Nanofiber for Proton Exchange Membrane Fuel Cells. J. Power Sources, 2017, 340, 201-209. 15. Titvinidze, G.; Kreuer, K.-D.; Schuster, M.; de Araujo, C. C.; Melchior, J. P.; Meyer, W. H. Proton Conducting Phase-Separated Multiblock Copolymers with Sulfonated Poly(phenylene sulfone) Blocks for Electrochemical Applications: Preparation, Morphology, Hydration Behavior, and Transport. Adv. Funct. Mater, 2012, 22 (21), 4456-4470. 16. Li, H. Q.; Liu, X. J.; Yang, H.; Wang, Z.; He, J. Enhanced Proton Conductivity and Relative Selectivity of Sulfonated Poly(arylene ether ketone sulfone) Proton Exchange Membranes

by

Using

Triazole-grafted

3-Glycidyloxypropyltrimethoxysilane.

Electrochim. Acta, 2018, 291, 49-63. 17. Gong, C.; Zheng, X.; Liu, H.; Wang, G.; Cheng, F.; Zheng, G.; Wen, S.; Law, W.-C.; Tsui, C.-P.; Tang, C.-Y. A New Strategy for Designing High-performance Sulfonated Poly(ether ether ketone) Polymer Electrolyte Membranes Using Inorganic Proton Conductor-functionalized Carbon Nanotubes. J. Power Sources, 2016, 325, 453-464. 18. Yin, C.; Li, J.; Zhou, Y.; Zhang, H.; Fang, P.; He, C. Enhancement in Proton Conductivity and Thermal Stability in Nafion Membranes Induced by Incorporation of Sulfonated Carbon Nanotubes. ACS. Appl. Mater. Interfaces, 2018, 10 (16), 14026-14035. 19. Yan, X. H.; Wu, R.; Xu, J. B.; Luo, Z.; Zhao, T. S. A Monolayer Graphene – Nafion Sandwich Membrane for Direct Methanol Fuel Cells. J. Power Sources, 2016, 311, 188-194. 20. Kim, K.; Bae, J.; Lim, M.-Y.; Heo, P.; Choi, S.-W.; Kwon, H.-H.; Lee, J.-C. Enhanced Physical Stability and Chemical Durability of Sulfonated Poly(arylene ether 25 ACS Paragon Plus Environment


Page 26 of 29

sulfone) Composite Membranes Having Antioxidant Grafted Graphene Oxide for Polymer Electrolyte Membrane Fuel Cell Applications. J. Membr. Sci, 2017, 525, 125-134. 21. Wu, B.; Liang, G.; Lin, X.; Wu, L.; Luo, J.; Xu, T. Immobilization of N-(3-aminopropyl)-imidazole through MOFs in Proton Conductive Membrane for Elevated Temperature Anhydrous Applications. J. Membr. Sci, 2014, 458, 86-95. 22. Wu, B.; Lin, X.; Ge, L.; Wu, L.; Xu, T. A Novel Route for Preparing Highly Proton Conductive Membrane Materials with Metal-organic Frameworks. Chem. Commun (Camb), 2013, 49 (2), 143-145. 23. Ru, C.; Li, Z.; Zhao, C.; Duan, Y.; Zhuang, Z.; Bu, F.; Na, H. 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. ACS. Appl. Mater. Interfaces, 2018, 10 (9), 7963-7973. 24. Dinari, N. Metal-organic Framework Anchored Sulfonated Poly(ether sulfone) as a High Temperature Proton Exchange Membrane for Fuel Cells. J. Membr. Sci, 2018, 565 (565), 281-292. 25. Gohil, J. M.; Karamanev, D. G. Novel Approach for the Preparation of Ionic liquid/imidazoledicarboxylic

Acid

Modified

Poly(vinyl

alcohol)

Polyelectrolyte

Membranes. J. Membr. Sci, 2016, 513, 33-39. 26. Rogalsky, S.; Bardeau, J.-F.; Makhno, S.; Babkina, N.; Tarasyuk, O.; Cherniavska, T.; Orlovska, I.; Kozyrovska, N.; Brovko, O. New Proton Conducting Membrane Based on

Bacterial

Cellulose/polyaniline

Nanocomposite

Film

Impregnated

with

Guanidinium-based Ionic Liquid. Polymer, 2018, 142, 183-195. 27. Dong, X.-Y.; Li, J.-J.; Han, Z.; Duan, P.-G.; Li, L.-K.; Zang, S.-Q. Tuning the Functional Substituent Group and Guest of Metal–organic Frameworks in Hybrid Membranes for Improved Interface Compatibility and Proton Conduction. J. Mater. Chem. A, 2017, 5 (7), 3464-3474. 26 ACS Paragon Plus Environment

Page 27 of 29 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


28. Li, Z.; Wang, W.; Chen, Y.; Xiong, C.; He, G.; Cao, Y.; Wu, H.; Guiver, M. D.; Jiang, Z. Constructing Efficient Ion Nanochannels in Alkaline Anion Exchange Membranes by the In Situ Assembly of a Poly(ionic liquid) in Metal–organic Frameworks. J. Mater. Chem. A, 2016, 4 (6), 2340-2348. 29. Chen, H.; Han, S.-Y.; Liu, R.-H.; Chen, T.-F.; Bi, K.-L.; Liang, J.-B.; Deng, Y.-H.; Wan, C.-Q. High Conductive, Long-term Durable, Anhydrous Proton Conductive Solid-state Electrolyte Based on a Metal-organic Framework Impregnated with Binary Ionic Liquids: Synthesis, Characteristic and Effect of Anion. J. Power Sources, 2018, 376, 168-176. 30. Lin, H.; Zhao, C.; Cui, Z.; Ma, W.; Fu, T.; Na, H.; Xing, W. Novel Sulfonated Poly(arylene ether ketone) Copolymers Bearing Carboxylic or Benzimidazole Pendant Groups for Proton Exchange Membranes. J. Power Sources, 2009, 193 (2), 507-514. 31. Ren, X. Methanol Transport through Nafion Membranes. Electro-osmotic Drag Effects on Potential Step Measurements. J. Electrochem. Soc, 2000, 147 (147), 466-474. 32. 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. J. Alloy. Compd, 2017, 695, 520-525. 33. Hickner, M. A.; Hossein, G.; Seung, K. Y.; Einsla, B. R.; Mcgrath, J. E. Alternative Polymer Systems for Proton Exchange Membranes (PEMs). Chem. Rev, 2004, 104 (10), 4587-611. 34. Chen, R.; Zhao, T. S. A Novel Electrode Architecture for Passive Direct Methanol Fuel Cells. Electrochem. Commun, 2007, 9 (4), 718-724. 35. Mueller, J. T.; Urban, P. M. Characterization of Direct Methanol Fuel Cells by AC Impedance Spectroscopy. J. Power Sources, 1998, 75 (1), 139-143. 36. Cuicui, L.; Yunfeng, Z.; Zehui, Y. Cross-linked Fully Aromatic Sulfonated Polyamide as a Highly Efficiency Polymeric Filler in SPEEK Membrane for High Methanol Concentration Direct Methanol Fuel Cells, J. Mater. Sci., 2018, 53,5501–5510 27 ACS Paragon Plus Environment


37. Yongheng, Y.; Hong, W. Sulfonated Poly(ether ether ketone)-based Hybrid Membranes containing Graphene Oxide with Acid-base Pairs for Direct Methanol Fuel Cells. Electrochim. Acta, 2016, 203, 178-188. 38. Xupo, L.; Yunfeng, Z.; Zehui, Y. A Superhydrophobic Bromomethylated Poly(phenylene oxide) as a Multifunctional Polymer Filler in SPEEK Membrane towards Neat Methanol Operation of Direct Methanol Fuel Cells. J. Power Sources, 2017, 544, 58-67.


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Graphical Abstract 467x197mm (72 x 72 DPI)

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Preparation of a Cross-linked Sulfonated Poly(arylene ether ketone

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