Simple synthesis of ironIII sulfophenyl phosphate

Simple synthesis of ironIII sulfophenyl phosphate nanosheets as a high temperature inorganic–organic proton conductor Guohong Liu, Zhongfang Li, Lei Jin & Suwen Wang

Ionics International Journal of Ionics The Science and Technology of Ionic Motion ISSN 0947-7047 Volume 20 Number 10 Ionics (2014) 20:1399-1406 DOI 10.1007/s11581-014-1109-0

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Author's personal copy Ionics (2014) 20:1399–1406 DOI 10.1007/s11581-014-1109-0

ORIGINAL PAPER

Simple synthesis of ironIII sulfophenyl phosphate nanosheets as a high temperature inorganic–organic proton conductor Guohong Liu & Zhongfang Li & Lei Jin & Suwen Wang

Received: 4 January 2014 / Revised: 25 February 2014 / Accepted: 9 March 2014 / Published online: 28 March 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract IronIII sulfophenyl phosphate (FeSPP) is successfully synthesized by an optimized process from the reaction of ironIII chloride and m-sulfophenyl phosphonic acid (msPPA) by a simple and environmentally friendly method. Experimental results show FeSPP has a kind of layered structure, and multilayer sheet is about 2 nm thick. FeSPP exhibits good thermal stability and does not decompose under 200 °C. Protons transfer through vehicle and Grotthuss mechanisms at different relative humidities (RH). The conductivity of FeSPP can reach to 0.115 S/cm at 180 °C and RH=100 %. Under this condition, vehicle mechanism plays the leading role, and the Grotthuss mechanism plays the minor role. At low RH, Grotthuss plays the leading role, and vehicle plays the minor role. In a drying oven at 180 °C, the proton conductivity remains 2.15×10−3 S/cm. Good conductivities at different RH and thermal stabilities clearly demonstrate that FeSPP is a highly effective conductor. It can be used as catalysts, chemical sensors, and in the preparation of composite membrane. Keywords Proton conductor . IronIIIsulfophenyl phosphate . Nanostructure powder . Proton conductivity . Relative humidity

Introduction Many kinds of solid proton acids are extensively used for chemical sensors [1] and solid acid catalysts [2-5] because of their advantages, such as, high acid strength, nonG. Liu : Z. Li (*) : L. Jin : S. Wang School of Chemical Engineering, Shandong University of Technology, 12# Zhangzhou Road, Zibo City 255049, Shandong Province, People’s Republic of China e-mail: [email protected]

corrosiveness in reactors, ease of handing, easy recovery, and reusability, compared with traditional liquid acids [6]. However, few solid proton acids can be used as a proton conductor [7-9], which is an important solid electrolyte with proton conductivity. Solid proton acids, such as, heteropolyacid (HPA) [10-13] and metalIV phosphates [14], are used as proton conductors in the fabrication of composite membranes due to their high proton conductivity. HPA can increase both the water uptake and concentration of acid sites [15]. However, HPA tends to be lost by dissolution in water at a high temperature and high relative humidity (RH). MetalIV phosphates are of great interest because of their practical applications in areas, such as, ion exchange, catalysis, intercalation chemistry, and proton conduction [16]. The most important is that these inorganic materials are not highly compatible with organic aromatic thermoplastics. ZirconiumIV sulfophenyl phosphate (ZrSPP), which has been reported as a good proton conductor, is synthesized by zirconium phenyl phosphate and concentrated sulfuric acid [17]. MetalIV sulfophenyl phosphate is an inorganic–organic material that organic moieties are bridged by phosphorus atoms to form an inorganic two-dimensional matrix [18]. This material exhibits good compatibility with organic polymer [17]. ZrSPP with a high degree of sulfonation (DS), i.e., DS≥95 % cannot be separated from the reaction solution due to its dissolution in sulfuric acid (H2SO4). Thus, this process cannot be used to prepare ZrSPP with high DS that is what we really need. CeriumIV sulfophenyl phosphate (CeSPP) (DS = 100 %) has been synthesized with msulfophenyl phosphonic acid (msPPA) as a precursor instead of phenyl phosphate in our previous work, meanwhile, msPPA is prepared by using SO3 to sulfonate phenyl phosphonic acid [19]. CeSPP exhibits high proton conductivity and good themostability. During the preparation of CeSPP, msPPA must be purified to remove SO 42− formed by

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excessive unreacted SO3 through a complex process due to the insoluble of CeSO4. The purification process reduces the productivity of msPPA, and eventually reduces the productivity of CeSPP. Several metalIII sulfates dissolve in water, such as Al2(SO4)3, Fe2(SO4)3, and Cr2(SO4)3. Thus, SO42− need not be removed when fabricating metalIII sulfophenyl phosphate. We can only to remove the unreacted phenyl phosphonic acid. Thus, BaCl2 addition for precipitation, centrifugation, cation exchange, and filtering to remove SO42− are also not required. Consequently, materials, time, efforts, and wastewater discharges are reduced. IronIII sulfophenyl phosphate can be synthesized from the reaction of iron(III) chloride with msulfophenyl phosphonic acid without removing SO42−. However, Al3+ and Cr3+ cannot generate sulfophenyl phosphate precipitate. MetalIII sulfophenyl phosphates prepared by this sample process have not yet been reported. In this study, novel ironIII sulfophenyl phosphate (FeSPP) using msPPA as a precursor by a simple and environmentally friendly process is prepared. FeSPP has a regular layered structure that contributes to proton conduction. FeSPP is characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetry (TG)-differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscope (TEM), and energy-dispersive X-ray spectroscopy (EDS). Proton conductivity is examined by AC impedance measurements at different values of RH. This material is a potential proton conductor for many applications, for example, composite proton exchange membrane, acid catalyst, and chemical sensors.

Experimental Materials 1,2-dichloroethane, phosphorus pentoxide, diethyl ether, iron chloride (FeCl 3 . 6H 2 O), and phenylphosphonic acid (C6H5O3P) was purchased from Qingdao Fusilin chemical Science & Technology Co. Ltd., China.. All chemicals were of analytical grade, obtained commercially, and used without further purification. Synthesis and coarse purification of msPPA msPPA was synthesized using the method reported in [20]. SO3 gas was slowly absorbed into a round-bottom flask containing phenylphosphonic acid (PPA) (20 g, 127 mmol) and 1,2-dichloroethane (100 mL). The flask was refluxed at 70 °C for 12 h. The viscous liquid was then dissolved in distilled water. The unreacted PPA acid that remained in the solution was extracted using diethyl ether and the extracted

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msPPA solution (coarse purified msPPA) was concentrated at 70 °C . Synthesis of FeSPP The coarse purified msPPA and ironIII chloride were separately dissolved in distilled water and dilute hydrochloric acid (0.01 mol/L), and then mixed together. The resulting mixture was heated at 80 °C by a magnetic stirrer to produce a light yellow emulsion. The emulsion was centrifuged and the upper layer (supernate) was eliminated. The lower layer (white precipitate) was washed and centrifuged times until Cl− and SO42− could not be detected in supernate. The resulting light yellow precipitate was dried in an oven at 60 °C. Characterizations FT-IR spectra were recorded between 4,000 and 400 cm−1 by a Nicolet 5700 Fourier transform infrared spectrometer (Thermo Electron). UV-Vis spectra were analyzed by UV-3600 (Shimadzu) from 200 to 800 nm. The morphology of the FeSPP powder was investigated using a scanning electron microscope (FEI Sirion 200). TEM images were recorded on a Tecnai G2 F20 transmission electron microscope operating at 200 kV. Elemental composition of FeSPP was analyzed by energy-dispersive X-ray, which was an auxiliary equipment of SEM. X-ray diffraction was employed to identify the crystal structure and determine the d space value that indicates the average interlayer distance of FeSPP and IronIII phenyl phosphate (FePP), with a diffractometer (Bruker D8 Advance) using a solid detector and Cu Kα radiation at 40 kV and 40 mA. The 2θ ranges were from 2 to 60°. TGA was used to analyze the thermal stability. Thermo gravimetric analysis was carried out using a thermogravimetric analyzer (Netzsch STA 409) from 30 to 900 °C at a rate of 10 °C/min under normal atmospheric pressure (flow rate 30 mL/min). Proton conductivity Proton conductivities of FeSPP slice were calculated from AC impedance spectroscopy data using a Potentiostat Model 263A workstation (PerkinElmer Instruments) with a lock-in amplifier (Model 5210, 1 Hz–10 kHz) (PerkinElmer Instruments). The software Powersuite was used to collect the data and plot the figures. The samples were humidified by water vapor at all temperatures. Conductivities of different temperature and different humidities were calculated as Eq. (1). σ¼

l AR

ð1Þ

σ (S.cm−1) is the conductivity, A (cm2) is the area, R (Ω) is the resistance, and l (cm) is the thickness. The formula is used

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Fig. 1 Schematic of membrane conductivity measurement equipment

to measure the vertical conductivity. The test device in Fig. 1 is for transverse conductivity; therefore, the above formula is ought to do the corresponding transformation. σ¼

1:22 m⋅n⋅R

ð2Þ

As is shown in Eq. (2), l is corresponding to the distance between two electrodes; in this device, the value is 1.22 cm. m·n is surface contact area between electrodes and proton conductor slice. The proton conductor is pressed into thin slice. The width is constant and the value is 0.8129 cm. The formula is as Eq. (3). σ¼

1:22 0:8129⋅n⋅R

ð3Þ

n is the thickness, and R is the resistance. In this paper, FeSPP was pressed into thin slice and the thickness is about 0.7 mm.

Results and discussion (FT-IR) spectroscopy The FT-IR spectra of FeSPP and msSPPA are presented in Fig. 2. In the spectra of FeSPP, the band at 1,683 cm−1 results from the P=O vibration [21]. Several shoulder peaks at 1,010 and 1,150 cm−1 correspond to S=O stretching and O=S=O symmetric vibration [22], respectively. The P-O and/or S-O stretching band positions range from 900 to 1,010 cm−1. Peaks at 765 and 703 cm−1 are assigned to C-S symmetric stretching [23]. In addition, the out-of-plane bands at 725 and 800 cm−1 of phenyl ring indicate that the ring is meta-substituted. The peak at 3,060 cm−1 corresponds to C-H stretching vibrations of the phenyl ring. The sharp medium intensity band at 1,435 cm−1 is probably the C=C stretching of the phenyl ring. In the spectra of msPPA, a very broad band appears in the hydroxyl stretching region (3,100 cm−1) ascribed to the presence of SO-H, PO-H, and water stretching vibrations. During FeSPP generation, Fe displaces the H of PO-H, and weakens the role of hydrogen bonds.

160 140

3.0

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120 1435 3060

100

2.0

Absorbance

%transmittance

FeSPP

FeSPP

80 60

msPPA

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765

20

800 703

3410

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0.0

1010 937 1150

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2000

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wavenumbers(cm )

Fig. 2 FT-IR spectra of msPPA and FeSPP

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Fig. 3 The UV spectra of FeSPP

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Fig. 4 SEM (a) and EDS (b) of FeSPP

b

a

UV-Vis Spectra

SEM and EDS

UV-Vis spectra of FeSPP are shown in Fig. 3. It is used to observe the structure of FeSPP. The wavelength at 217–218 and 266 nm is the ultraviolet absorption of benzene ring. The strong absorption peak at 200–204 nm (E2) is the characteristic absorption band of three conjugate double bonds in the benzene ring. In Fig. 3, the data is 217–218 nm. It is due to the red shift. It can be explained that sulfur oxygen double bond conjugates with benzene ring, and the absorption band of K is strong. Absorption band (E2) in the benzene ring merges with the absorption band (K). This phenomenon leads to the change of wavelength. Absorption band (B) in the benzene ring occurs at 230–270 nm. In Fig. 3, it is 266 nm which is consistent with the theoretical value. The addition of substituent can simplify the fine structure of absorption band (B). In the structure of FeSPP, there exists −SO3H group. The UV spectra can further confirm the structure of FeSPP.

The micro-morphology of the FeSPP and elemental analysis results are presented in Fig. 4. The SEM images (Fig. 4a) reveal that FeSPP particles are piled up by scaly shaped sheet (about 32 nm thick). EDS results (Fig. 4b) show that FeSPP consists of elements in theory. The molecular structure of FeSPP is illustrated in Fig. 5. The theoretical composition is C, 23.20 %; H, 1.62 %; Fe, 23.97 %; O, 30.91 %; P, 9.97 %; and S, 10.32 %. Experimental results of EDS are shown atom composition Fe:S:P:O is about 1:1:1:3, agreement with theoretical composition.

TEM images (Fig. 6a) show that the scaly shaped sheet in Fig. 6a is made up of multilayer sheets about 2 nm thick. The interlayer distance is about 2 nm. The diffractograms (Fig. 6b)

HO3S

HO3S

HO3S

XRD and TEM

2500

O

O

Fe O P

Fe

O O

O

O

Fe

Fe

Fe O

O

Fe

Fe

Fe

O

O O

P

SO3H

Fig. 5 The molecular structure of FeSPP

Lin(Cps)

O

P O O O

a

FeSPP FePP

2000

P P

b

1500

1000

O O P

500

SO3H

SO3H

0 10

20

30

40

2-Theta-Scale Fig. 6 a TEM of FeSPP. b XRD of FeSPP and FePP

50

60


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15.35649 5.750 100.0 4.81249 18.421 35.3 3.33433 26.714 45.2

9.86528 8.957 25.6 4.36830 20.313 50.7 3.18781 27.967 44.9

of FeSPP and FePP both show a pattern typical for layered compounds with well-pronounced reflections. Two distinct reflections of the layered structure are found. Data of X-ray powder diffraction of FeSPP and FePP are shown in Tables 1 and 2. The interplanar distance is the first d value. The interlayer distance (d) of FeSPP is about 15.36 Å which matches the value measured by TEM analysis, that of FePP is about 12.77 Å. Combined with the FT-IR and EDS data, the results indicate that sulfonic acid groups are introduced into the structure of FePP; the groups do not destroy the layered structure, but increases the interlayer distance. TG-DTA The thermal stability of FeSPP is determined by TG-DTA in air (Fig. 7). No weight loss is observed at 30–100 °C. This indicates the sample is completely dry. The first weight loss starts from 100 °C. An endothermic peak exists between 100 and 290 °C on DTA curve. This is due to the loss of crystal water and interlayer water. The weight loss is 6.64 %. It indicates that Fe (PO3C6H5SO3), as one unit of FeSPP, contains 3.3 crystal water. An endothermic peak exists between 290 and 350 °C on DTA, and a corresponding weight loss attributed to the degradation of sulfonic groups is observed. The last two weight loss stages occur between 400–650 °C and 650–760 °C. Three exothermic peaks appear on the DTA curve. This finding is due to the rupture and burning of the aromatic ring. The exothermic peak at 650–760 °C is much higher than the other two peaks. This is due to the degraded phosphoric acid group which forms a retardant film that prevents carbon burning. This phenomenon shows that FeSPP has excellent thermal stability and flame-resistant effect.

8.33050 10.611 25.4 3.76579 23.607 40.9 2.87157 31.120 47.4

7.52867 11.745 26.0 2.71769 32.931 46.1 2.49963 35.897 46.5

6.93813 12.749 29.0 2.37073 37.922 45.4 6.35969 13.914 29.9

5.08919 17.412 38.7 2.31712 38.834 45.2

Proton conductivity Conductivity is an important parameter, and proton conductivities of FeSPP at RH=100 % and RH=50 % in a drying oven are presented in Fig. 8a–c). Proton conductivities of FeSPP slice increase with the increasing temperature. At 100 % RH, the conductivity of FeSPP (Fig. 8a) is 0.01 S/cm at 30 °C, which is two orders higher than ZrSPP (6.0397× 10−4 S/cm at 30 °C). Although the conductivity of ZrSPP can reach 0.22661 S/cm at 180 °C, the conductivity is low at room temperature. The conductivity of FeSPP is 0.0966 S/cm at 150 °C. It is a little lower than CeSPP (0.13 S/cm at 150 °C) [19]. The conductivity of FeSPP can reach 0.115 S/cm at 180 °C; however, the conductivity of CeSPP can only be measured under 150 °C due to the rupture of CeSPP slice at high temperature. The thermal durability of FeSPP is better than CeSPP. The dependence of conductivity on temperature can be expressed by the Arrhenius relationship: Eact σ ¼ Aexp − RT σ, A, Eact, R, and T denote proton conductivity, frequency factor, activation energy for proton conduction, gas constant, and absolute temperature, respectively. At RH=100 %, the 100

0.8 6.64%

95

0.6

90

0.4

85

0.2

80

0.0 30%

75

-0.2

Table 2 Data of X-ray powder diffraction of FePP d 2θ I/I0 d 2θ I/I0

12.76649 5.771 100.0 3.03265 29.429 26.0

7.47151 11.835 27.5 2.21027 40.792 19.5

6.99681 12.641 30.6 3.37102 26.418 27.2

5.75451 15.385 25.7 3.26442 27.297 27.7

5.11901 17.309 28.8 6.59341 13.418 28.4

4.32734 20.507 33.7

70

-0.4

65

-0.6

60

-0.8 56.7%

55 100

200

300

400

500

600 o

temperature/ C

Fig. 7 TG-DTA of FeSPP

700

DTA/uv/mg%

d 2θ I/I0 d 2θ I/I0 d 2θ I/I0

TG/%

Table 1 Data of X-ray powder diffraction of FeSPP

-1.0 800

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a

0.12

0.055

RH 100%

b

RH 50%

0.050

0.10

conductivity/S/cm

Fig. 8 Conductivities of FeSPP. a Conductivities of FeSPP at 100 % RH. b Conductivities of FeSPP at 50 % RH. c Conductivities of FeSPP in a drying oven

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0.08

0.06

0.04

0.045 0.040 0.035 0.030 0.025

0.02

0.020 0.015

0.00 2.2

180 0.01

2.4

2.6

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140

c

3.0

3.2

120

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2.2

2.3

2.4

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2.7

2.8

2.9

100

in drying oven

1E-3

1E-4

1E-5

2.2

2.4

temperature ranges from 30 to 180 °C, Eact =18.06 kJ/mol which is much higher than Nafion 117 (6.81 kJ/mol) [19]. At RH = 50 %, the proton conductivity of FeSPP is 0.0261 S/cm at 100 °C, which is higher than Zr (O3POH)2·H2O (in the range 10−6 to 10−5 S/cm at 100 °C) [18]. The proton conductivity is 1.88×10−2 S/cm at 80 °C and can reach 5.41×10−2 S/cm at 180 °C. The temperature ranges from 80 to 180 °C, Eact =13.3 kJ/mol. In a drying oven, the

Fig. 9 Proton conduct mechanisms in FeSPP

2.6

proton conductivity is 1.827×10−6 at 100 °C and can reach 2.15×10−3 S/cm at 180 °C, which is three orders higher than α-Zr (O3POH)2 (1×10−6 S/cm at 180 °C) [24]. In a drying oven, the temperature ranges from 30 to 180 °C, Eact = 106.55 kJ/mol. Two principal mechanisms underlie proton transfer, namely, the vehicle (① in Fig. 9) and Grotthuss mechanisms (② in Fig. 9) [25]. At high RH, vehicle mechanism plays the leading


role, and the Grotthuss mechanism plays the minor role. Water-connected protons (H (H2O)×)+ resulting from electroosmotic drag carry one or more molecules of water through FeSPP slice. A high Eact suggests that the temperature significantly influences the ion mobility (u), which increases with the increasing temperature. Consequently, proton conductivity increases with the increasing temperature. At low RH, Grotthuss plays the leading role, and vehicle plays the minor role. Given the exceptional ability of FeSPP which can combine with water, protons hop from one hydrolyzed ionic site (SO3H3O+) to another. In a drying oven, the external environment does not provide an aqueous medium, and protons hop through hydrogen bonds between sulfonic acids arranged between FeSPP layers. Under this condition, proton transfer occurs almost entirely by the Grotthuss mechanism. Excellent thermal stability, exceptional ability to combine with water, and hydrogen bonding between sulfonic acids and regular layered structure together make FeSPP a good proton conductor at high temperatures and different RH values.

Conclusions IronIII sulfophenyl phosphate (FeSPP) nanosheets are successfully synthesized by a simple and environmentally friendly process. FeSPP shows an obvious layered structure, and good thermal stability. The conductivity of FeSPP can reach 0.115 S/ cm at 180 °C and RH=100 %. Under this condition, the vehicle mechanism plays the leading role. At 180 °C and RH=50 %, the Grotthuss mechanism plays the leading role, and the proton conductivity is 5.41×10−2 S/cm. In a drying oven at 180 °C, proton transfer almost entirely occurs by the Grotthuss mechanism, and the proton conductivity remains 2.15×10−3 S/cm. This material is a potential proton conductor for many applications. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (grant nos. 21276148, 21076119, and 20776081), the State Key Laboratory of Chemical Engineering (Tianjin University) (Grant no. SKL-ChE-14B01), and the Natural Science Foundation of Shandong Province, China (grant no. ZR2010BM004)

References 1. Shi D, Wei L, Wang J, Zhao J, Chen C, Xu D, Geng H, Zhang Y (2013) Solid organic acid tetrafluorohydroquinone functionalized single-walled carbon nanotube chemiresistive sensors for highly sensitive and selective formaldehyde detection. Sens Actuators, B 177:370 2. Hu Y, Fu X, Barry BD, Bi X, Dong D (2012) Regiospecific β-lactam ring-opening/recyclization reactions of N-aryl-3-spirocyclic-βlactams catalyzed by a Lewis-Brønsted acids combined superacid catalyst system: a new entry to 3-spirocyclicquinolin-4(1H)-ones. Chem Commun 48:690

1405 3. Williams LA, Marks TJ (2011) Synthesis, characterization, and heterogeneous catalytic implementation of sulfated alumina nanoparticles. Arene hydrogenation and olefin polymerization properties of supported organozirconium complexes. ACS Catal 1:238 4. Zheng A, Huang SJ, Liu SB, Deng F (2011) Acid properties of solid acid catalysts characterized by solid-state 31P NMR of adsorbed phosphorous probe molecules. Phys Chem Chem Phys 13:14889 5. Vasireddy S, Ganguly S, Sauer J, Cook W, Spivey JJ (2011) Direct conversion of methane to higher hydrocarbons using AlBr3-HBr superacid catalyst. Chem Commun 47:785 6. Dingwall LD, Lee AF, Lynam JM, Wilson K, Olivi L, Deeley JMS, Gaemers S, Sunley GJ (2012) Bifunctional organorhodium solid acid catalysts for methanol carbonylation. ACS Catal 2: 1368 7. Tang Q, Yuan S, Cai H (2013) High-temperature proton exchange membranes from microporous polyacrylamide caged phosphoric acid. J Mater Chem A 1:630 8. Luo J, Conrad O, Vankelecom IFJ (2013) Imidazolium methanesulfonate as a high temperature proton conductor. J Mater Chem A 1:2238 9. Wang J, Zhang Z, Yue X, Nie L, He G, Wu H, Jiang Z (2013) Independent control of water retention and acid–base pairing through double-shelled microcapsules to confer membranes with enhanced proton conduction under low humidity. J Mater Chem A 1:2267 10. Thanganathan U, Bobba R (2012) Enhanced conductivity and electrochemical properties for class of hybrid systems via sol–gel techniques. J Alloy Compd 540:184–186 11. Yang M, Lu S, Lu J, Jiang SP, Xiang Y (2010) Layer-by-layer selfassembly of PDDA/PWA–Nafion composite membranes for direct methanol fuel cells. Chem Commun 46:1434 12. Duan XX, Liu Y, Zhao Q, Zhang X, Wang XH, Li SW (2013) Watertolerant heteropolyacid on magnetic nanoparticles as efficient catalysts for esterification of free fatty acid. RSC Adv 3:13748 13. Thanganathan U (2011) Structural study on inorganic/organic hybrid composite membranes. J Mater Chem 21:456 14. Dong FL, Li ZF, Wang SW, Xu LJ, Yu XJ (2011) Preparation and properties of sulfonated poly(phthalazinone ether sulfone ketone)/ zirconium sulfophenylphosphate/PTFE composite membranes. Int J Hydrogen Energy 36:3681 15. Mosa J, Larramona G, Durán A, Aparicio M (2008) Synthesis and characterization of P 2 O 5 -ZrO 2 -SiO 2 membranes doped with tungstophosphoric acid (PWA) for applications in PEMFC. J Membr Sci 307:21 16. Hogarth WHJ, Diniz Da Costa JC, Lu GQM (2005) Solid acid membranes for high temperature (>140°C) proton exchange membrane fuel cells. J Power Sources 142:229–235 17. Li ZF, Dong FL, Xu LJ, Wang SW, Yu XJ (2010) Preparation and properties of medium temperature membranes based on zirconium sulfophenylphosphate/sulfonated poly(phthalazinone ether sulfone ketone) for direct methanol fuel cells. J Membr Sci 351:50 18. Alberti G, Casciola M (1997) Layered metalIV phosphonates, a large class of inorgano-organic proton conductors. Solid State Ionics 97: 177–181 19. Dong FL, Li ZF, Wang SW, Wang ZH (2011) A novel inorganoorganic solid proton conductor material. Mater Lett 65:1431 20. Kim YT, Song MK, Kim KH, Park SB, Min SK, Rhee HW (2004) Nafion/ZrSPP composite membrane for high temperature operation of PEMFCs. Electrochim Acta 50:645 21. Kim YT, Kim KH, Song MK, Rhee HW (2006) Nafion/ ZrSPP composite membrane for high temperature operation of proton exchange membrane fuel cells. Curr Appl Phys 6: 612–615

Author's personal copy 1406 22. Jin L, Li ZF, Wang SW, Wang ZH, Dong FL, Yin XY (2012) Highly conductive proton exchange membranes based on sulfonated poly(phthalazinone ether sulfone) and cerium sulfophenyl phosphate. React Funct Polym 72:549 23. Hwang M, Ha HY, Kim D (2008) Zirconium meta-sulfophenyl phosphonic acid-incorporated Nafion® membranes for reduction of methanol permeability. J Membr Sci 325:647

Ionics (2014) 20:1399–1406 24. Jerus P, Clearfield A (1982) Ionic conductivity of anhydrous zirconium bis (monohydrogen orthophosphate) and its sodium ion forms. Solid state ionics 6:79–83 25. Park CH, Lee CH, Guiver MD, Lee YM (2011) Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs). Prog Polym Sci 36: 1443