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Safe and green modified ostrich eggshell membranes as dual functional fuel cell membranes Mohammad Reza Molavian, Amir Abdolmaleki, Hamidreza Gharibi, Koorosh Firouz Tadavani, and Mohammad Zhiani Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 20 Jan 2017 Downloaded from http://pubs.acs.org on January 20, 2017

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Safe and green modified ostrich eggshell membranes as dual functional fuel cell membranes Mohammad Reza Molavian a, Amir Abdolmaleki

a,b,1

, Hamidreza Gharibia, Koorosh Firouz

Tadavani a, Mohammad Zhiani a

a

Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran

b

Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71467-13565, Iran

1

Corresponding author: Tel.: +98 3133913249; Fax: +98 3133912350 E-mail address: [email protected], [email protected] (A. Abdolmaleki)

1 ACS Paragon Plus Environment

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Abstract Two new natural based membranes were prepared based on modification of hierarchical interwoven (OESMs).

ostrich The

eggshell

modified

membranes

OESMs

were

employed for both proton and anion exchange applications. For proton exchange, the surface of OESM was grafted by in-situ polymerization of allyl sulfate in aqueous media. The modified membrane shows good proton conductivity value of around 48 mS.cm-1 in acidic solution. Also, OESM was quaternized and hydroxide showed an acceptable conductivity in 1M NaOH (about 40 mS.cm-1).


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1. Introduction Ostrich eggshell membrane (OESM) is a thin layer between calcified layer and albumen of ostrich eggs 1, 2. This natural waste has valuable applications in nanocrystal growth as a template, heavy metal absorption and separation of dyes, biosensor devices and medicines

3-9

. This

structure is a natural semi-interpenetrated polymer network that shows excellent mechanical properties compared with other avian eggshells and also, exhibits porous morphology with nonwoven textures

2, 10-13

. Due to some special features such as good mechanical properties,

hydrophilic functional groups and porous structure, OESMs are considered as a good candidate for fuel cell applications. Anion exchange membrane (AEM) and proton exchange membrane (PEM) are two most common types of polymeric electrolyte that play a critical role in fuel cell performance 14-18. OESMs are made from two C-type lectin-like proteins, namely struthiocalcin1 (SCA-1) and struthiocalcin-2 (SCA-2). The nitrogen abundance in these natural membranes is about 15%, which could provide sufficient amount of the quaternary ammonium salts for anion exchange 19-23. Also, OESMs are capable to perform proton transfer by introducing acidic groups such as SO3H group. Synthesis of porous membranes is an important strategy for preparation of membranes with high conductivity both in proton and anion exchange membranes. In a PEM, increased porosity enhances the amount of acid doping in the membrane and also, increases proton conductivity 24-27. Shen et al. and Li et al. reported different phosphoric acid doped porous polybenzimidazole membranes for PEMFC applications

24, 25

. Also in AEMs, hydroxide

conductivity occurs based on vehicle mechanism, and presence of pores in the membrane facilitates ion transfer across the membrane based on an increase in electrolyte attraction and ion solvation. In this regard, Zarrin et al. and Zeng et al. reported a porous polybenzimidazole


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membrane for alkaline fuel cells

28, 29

. The presence of holes in OESMs and also, existence of

different protogenic groups leads to great ion conductivity. Herein we report the first modification of OESM as a natural waste to use for both proton and anion exchange membrane in fuel cells. The anion exchange functionality is introduced to the membrane through quaternization of nitrogen with methyl iodide. Also, the membrane is grafted by poly(allyl sulfate) through the radical polymerization of sodium allyl sulfate on the activated membrane. 2. Experimental procedure 2.1. Materials and method 2.1.1. Materials Methyl iodide, chloroform, N,N-dimethylformamide (DMF), sodium allyl sulfate, ammonium persulfate, sodium bisulfite, NaOH and HCl were purchased from Merck and Sigma-Aldrich Chemical Co. 2.1.2. Method FT-IR spectra were recorded using a Jasco-680 FT-IR spectrophotometer (Japan) with KBr pellet. Vibration bands were reported as wavenumber (cm-1). The band intensities were classified as weak (w), medium (m), strong (s), broad (br) and shoulder (sh). Elemental analysis was performed with a CHNS-932, Leco. Thermal gravimetric analysis (TGA) was performed with a STA503 win TA (Bahr-Thermoanalyse GmbH, Hüllhorst, Germany) at a heating rate of 10 °C/min from 25 °C to 800 °C under nitrogen atmosphere. Tensile measurements were determined with Testometric Universal Testing Machine M350/500 (UK), according to ASTM D882 (standards) at room temperature. The dimensions of the test 4 ACS Paragon Plus Environment

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specimens were 35 mm × 2 mm × 0.06 mm at cross-head speed of 10.0 mm min−1. The morphology of membranes was studied by a scanning electron microscope (SEM, Philips, XL30) at an accelerating voltage of 10 kV, after sputter coating with gold. Moreover, the average fiber diameter, surface area porosity and total surface pore area of membranes were analyzed from the SEM images using an image analysis software package (Image J, National Institutes of Health, USA). 2.2. Membrane preparation 2.2.1. Preparation of q-OESM The membrane was immersed in 15 mL chloroform in a petri dish. Then 3 mL (excess amount) methyl iodide was added to the solution and the petri dish was sealed at 30 ˚C for 48 h. The resultant membrane was immersed in 1M NaOH solution for 24 h to exchange iodide with hydroxide. Finally, the membrane was washed with DI water to remove excess amount of sodium hydroxide (Scheme 1) 30, 31. FT-IR (KBr, cm-1): 4000-3000 (ammonium salt, s, br), 1681 (C=O amide, s). 2.2.2. Preparation of s-OESM The membrane was dipped in solution of ammonium persulfate and sodium bisulfite (0.06 g in 10 mL DI water) as an initiator and heated at 60 ˚C for 6 h. After activation of the membrane surface, 3 g of sodium allyl sulfate was added to the solution and polymerization was performed at 60 ˚C for 24 h. Then the membrane was immersed in 1M HCl solution to exchange sodium ion with proton. Subsequently, the membrane was washed with water to remove sodium allyl sulfate and immersed in DMF to wash not bonded poly(allyl sulfate)


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and dried under vacuum at 100 ˚C for 24 h (Scheme 1)

32, 33

. FT-IR (KBr, cm-1): 4000-3000

N+ OH -

NH

NH+ N OH

(SO3H group, s, br), 1681 (C=O amide, s), 1217, 1040 (S=O).

NH

N+ OH -

NH

NH

N+ O H-

NH

NH

N+ O H-

HNH

NH

N+ O H-

NH

NH

te lfi su bi um di so d an h te fa , 6 ul rs o C te pe 60 l fa su m iu yl l h on al m h 24 um , 24 am di o C l, 0 1) C So 6 H 1M 3)

NH

NH

NH N+ OH

NH

NH

N+ O

N+ O

H-

NH

NH

NH

SO 3H

2)

NH

N

SO 3H

H

3

N

SO

N NH

H 3 SO

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N

NH

NH

Scheme 1. Schematic procedure for preparation of q-OESM and s-OESM 2.3. Membrane characterization 2.3.1. Ion exchange capacity (IEC) For s-OESM, the membranes in the acidic form were immersed in 100 mL of 1 M NaCl solution for 24 h. The resultant solutions were then titrated with 0.01 N NaOH. Moreover, q-OESM was


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soaked in 0.01 M HCl solution for 24 h and titrated with 0.01 N NaOH. The ion exchange capacity of the membranes was calculated as follows (Eq. 1): Eq. 1. IEC =

∆௏ಿೌೀಹ ×஼ಿೌೀಹ ௐ೏

(meq.g-1)

where ∆ܸ is the volume of NaOH, C is the concentration of NaOH and Wd is the weight of dry membrane 34, 35. 2.3.2. Water uptake The membranes were placed at 100 ºC for 15 h until their weight remained constant to dry materials. Then, the membranes were immersed in distilled water for 24 h and taken out. Next, their surfaces were cleaned with tissue paper and then, they were quickly weighed on a microbalance. Water uptake was measured at different temperatures related to time. The water uptakes of the membranes were calculated as follows (Eq. 2): Eq. 2. Water uptake (%) =

ௐೢ ିௐ೏ ௐ೏

× 100

where Ww is the weight of wet membrane and Wd is the weight of dry membrane 34. 2.3.3. Conductivity The resistance of the membranes was measured at different conditions and ion conductivities were calculated according to the following equation (Eq. 3): ௟

Eq.3. σ =ோ஺ where R (Ω) is the resistance of the membrane, A (cm2) is the area of the membrane and l (cm) is the distance between the reference electrodes 36.


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2.3.4. Methanol crossover The methanol crossover was measured employing a drive mode cell. A membrane electrode assembly (MEA, 5 cm2) was made at 4 MPa for 5 min. The Pt catalyst for both cathode and anode were 3 mg.cm-2. The cathode side of MEA was fed by 0.5M MeOH and potential applied on anode at range 0-0.9 V and scan rate 5 mV.s. The current density obtained for membranes explore methanol crossover through the membranes. 3. Results and discussion 3.1. Synthesis and characterization The OESMs have made from fibrous proteins with a large variety of amino acids. Presence of different amino acids including Glutamine, Asparagine, Alanine, Serine, Leucine, Alanine, Arginine, Phenylalanine and etc. provide futilities and made this membrane as potential for many further modifications

37

. To synthesize the quaternized ostrich eggshell membrane (q-OESM),

methyl iodide was added to the membrane immersed in chloroform at 30 ˚C for 48 h. The sulfonated ostrich eggshell membrane (s-OESM) was prepared by in-situ polymerization of sodium allyl sulfate on the OESM. The membrane was dipped in solution of ammonium persulfate and sodium bisulfite as the initiator and heated at 60 ˚C for 6 h. After activation of the membrane surface, the sodium allyl sulfate was added to the solution and polymerization was performed at 60 ˚C for 24 h. The q-OESM and s-OESM were characterized by elemental analysis and FT-IR spectroscopy. Fig. 1 shows the FT-IR related to the neat OESM and modified OESM. For both q-OESM and s-OESM, a peak broadening occurred in 3000-4000 cm-1, which was attributed to formation of ammonium salt and presence of the sulfonate group. The carbonyl bond in the q-OESM was shifted from 1631 to 1681 cm-1, indicating diminishing of nitrogen lone-pair by quaternization. Also, s-OESM showed a similar shift in carbonyl bond due to 8 ACS Paragon Plus Environment

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grafting of allyl bond to nitrogen. Other significant signals that prove existence of the sulfonate group in s-OESM are peaks at 1040 and 1217 cm-1 related to symmetric and asymmetric stretching of the SO3H group, respectively 8. In addition, the result of elemental analysis in Table 1 confirms that modification occurs on the OESMs. The sulfur content in s-OESM is 8.26%, which is more than two-fold of that for the neat OESM (3.86%). Also for q-OESM, enhancement in oxygen content and decrease in carbon and nitrogen content prove that quaternization occurs successfully.

Fig. 1. FT-IR spectra related to a) OESM, b) q-OESM and c) s-OESM Table 1. Elemental analysis for neat OESM, q-OESM and s-OESM membrane

%C

%N

%S

%O

%H

neat OESM

47.03

15.25

3.86

27.12

6.74

q-OESM

44.03

13.51

1.82

33.95

6.69


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s-OESM

41.10

11.54

8.26

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32.69

6.41

3.2.Membranes morphology The camera images were shown in Fig. 2a–c. Also, the morphology of the membranes was studied by SEM (Fig. 2d-f) images and analyzed by the ImageJ software (Fig. 2g-i). Pure OESM (Fig. 2d) fibers have messy arrangement and construct a porous structure that is ideal for ion exchange application. When the membrane is quaternized with methyl iodide, protein structure is denatured and changes the polymer morphology (Fig. 2e). Two main factors are responsible for denaturation of proteins: increased temperature enhances chain mobility and facilitates reordering of chains. In addition, when quaternization occurs, some dense positive charge centers are formed in protein and also, the hydrogen bond between chains is reduced due to diminishing of amine and amide hydrogens. Therefore, introducing these positively charged centers causes electrostatic repulsion and reduces protein chains entanglement. For sulfonated membrane (Fig. 2c), an opposite behavior was observed and also, addition of the sulfonate group increased polar interactions (hydrogen bonding) between the chains. Furthermore, increase of temperature during the polymerization rearranged the protein chains and a more regular morphology was obtained for the sulfonated OESM. To confirm the observations, the SEM images were studied by the ImageJ software. The obtained fiber dimeters of neat-OESM by imageJ is about 1.92 µm and is similar to fiber diameters reported previously 38. According to these results (Table 2), the fiber diameters in the s-OESM is increase compare to the neat membrane that indicated the introducing of sulfonate groups increase hydrogen bond interaction and helps to order of fibers.


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Also, decreased pore surface area of s-OESM, as compared to that of neat-OESM, confirms that fiber density increased and thus, decreased the surface porosity percentage. Table 2. Average of fiber diameters, surface area porosity and total pore area for all membranes Average of fiber

Surface area

Total surface pore area

diameter(µm)

porosity(%)

(µm2)

Neat-OESM

1.92

21.23

303.51

q-OESM

-

0.92

13.21

s-OESM

2.80

6.59

95.42

Membrane

All data were obtained by image J software.


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Fig. 2. Membranes images: a-c are camera images for a) pure OESM, b) q-OESM and c) sOESM; d-f are SEM images for d) pure OESM, e) q-OESM and f) s-OESM; g-i are graphs obtained from the ImageJ software for g) pure OESM, h) q-OESM and i) s-OESM. 3.3.Thermal analysis Thermal properties are very important in fuel cell membranes. Accordingly, the thermal stability of OESMs was investigated by thermogravimetric analysis (TGA). The results indicated that all the membranes had good thermal stability (Fig. 3 and Table 3). Moreover, thermal degradation for neat OESM was observed to occur between 310 to 460 ˚C that related to degradation of collagen and glycan chains. Second weight loss between 500 to 800 ˚C attributed to degradation of final membrane matrix

39

. Both the modified OESMs showed thermal degradation with a


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milder slope than that of the neat OESM, which was due to loss of the alkyl group on the nitrogen prior to degradation of the main chain. According to the table 5, T5 for s-OESM and qOESM are 187 ˚C and 237 ˚C, respectively that is higher than neat membrane (152 ˚C). These data demonstrate that thermal properties of both modified membranes improved compared to the neat membrane. Furthermore, thermogram data shows that these membranes have comparable thermal stability (starting decomposition temperature is 272 ºC and 21-24% char yield at 800 ºC) with Nafion117 and treated Nafion membranes (starting decomposition temperature is about 330 ºC and approximately zero percent char yield at 800 ºC) 40, 41.

Fig. 3. Thermograms related to the neat and modified OESMs Table 3. Thermal Properties of the neat and modified OESMs Polymer

Decomposition Temperature (ºC)


Char Yieldb (%)

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T5a

T10a

OESM

152

282

21

q-OESM

187

282

24

s-OESM

237

283

22

a

Temperature at which 5% and 10% weight loss were recorded by TGA at heating rate of 10 ºC min−1

in a N2 atmosphere b

Weight percent of the material left undecomposed after TGA at maximum temperature 800 °C in a N2

atmosphere

3.4. Mechanical properties Fig. 4 shows the representative tensile stress–strain (σ–Ɛ) plots of the neat OESM, resultant sOESM and q-OESM. Further, the σmax and Ɛmax are listed in Table 3. It was observed that the σmax and Ɛmax values of the neat OESM were 2.40 MPa and 65.35%, respectively, as compared with 1.40 MPa and 52.92% of the q-OESM and 2.08 MPa and 54.80% of the s-OESM. Although the young moduli of these membranes are lower than Nafion117, but also strain values are about two times greater than Nafion117

40, 42

. The introduction of positively charged centers by

quaternization on backbone of the protein chains led to the reduction of hydrogen bond and caused electrostatic repulsion between the chains. Thus, disruption of the interwoven structure by denaturation (as shown in SEM) can decrease the mechanical properties of the q-OESM. In contrast, the s-OESM showed a higher σmax, Ɛmax and Young’s modulus than the q-OESM that is attributed to the presence of the sulfonate groups. The side chains containing the sulfonate 14 ACS Paragon Plus Environment

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groups enhance polar interactions through bonding of hydrogen to amine, amide and carboxylic acid groups in the protein chains. As shown in Table 4, in both the s-OESM and q-OESM, the σmax and Ɛmax values decreased, as compared with native OESM, which may be due to change of the balance between hydrophobic and hydrophilic regions (enthalpic deformation) and some alteration in levels of hierarchical organization of fibrous proteins (entropic deformation) 43.

Fig. 4. Tensile stress–strain (σ–Ɛ) plots of the neat and modified OESMs Table 4. Mechanical properties neat OESM, q-OSEM and s-OESM Membrane

σmax (MPa)

Ɛmax (%)

E-Modulus

OESM

2.4

65.35

5.04

q-OESM

1.4

52.92

3.41

s-OESM

2.08

54.08

6.58


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3.5. Ion exchange capacity, water uptake, ion conductivity and methanol crossover Ion exchange capacity of the modified membranes was determined and also, ion conductivity of the membranes was measured in both the acidic and alkaline solutions to obtain proton and anion conductivity of the membranes. Table 5 shows the IEC, proton conductivity and anion conductivity of the membranes. As seen in Table 5, the q-OESM shows the IEC value to be about 0.99 meq.g-1, demonstrating a considerable hydroxide conductivity. According to the obtained results, this membrane could be considered as good potential for anion exchange membranes. As mentioned in Table 5, the modified ostrich eggshell membrane s-OESM showed comparable proton conductivity in acidic solution that had good agreement with the IEC value for this membrane (2.05 meq.g-1). In comparison with the neat membrane, both s-OESM and qOESM showed greater conductivity values and confirmed that modifications effectively improved the conductivity of OESM. Also, water uptake was measured for all the membranes. Accordingly, the water uptake at 25 ˚C was 274 % and at 80 ˚C was 286 %, which showed great potential of saving water content at high temperature. These data could herald production of membranes based on natural polymers as an alternative for synthetic membranes. The s-OESM shows higher IEC than Nafion117 (0.96 meq.g-1) and also water uptake is 10-fold compared with Nafion membranes (about 19-25% at 25 ˚C); regarding that increase in IEC and water uptake usually enhances fuel crossover, but these modified membranes due to intrinsic structure and morphology, exhibit appropriate fuel crossover. The proton conductivity for s-OESM is about 48 mS.cm-1 that reveal appropriate proton conductivity. Based on literatures, Nafion117 and recasted Nafion membranes have 54 to 75 mS.cm-1 proton conductivity at 25-30 ˚C 40, 41, 44. The q-OESM shows suitable anion conductivity compared with previously synthetic membranes. The anion conductivity for this membrane is 16 ACS Paragon Plus Environment

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about 40 mS.cm-1 whit 0.99 meq.g-1 IEC value, while some previous studies reported similar anion conductivity (about 39.5 and 43.0) with higher IEC (1.31 and 2.37) values

45, 46

. Beside

appropriate anion conductivity, high water uptake and very low methanol permeability improved performance of this membrane. Table 5. Ion exchange capacity (IEC), proton and hydroxide conductivity of membranes in different conditions Proton Conductivity

Hydroxide Conductivity

(mS.cm-1)

(mS.cm-1)

Ion Exchange membrane Capacity (meq.g-1)

DI

0.1M

0.5M

2M

2M DI Water

Water Neat-OESM

HCl

HCl

HCl

NaOH

1.1

1.7

3.8

5.2

2.1

3.5

s-OESM

2.05

8.1

16.0

32.2

47.9

-

-

q-OESM

0.99

-

-

-

-

18.2

40.1

The methanol crossover was measured for all membrane by the voltammetric method. As shown in Fig. 5, methanol crossover is in agreement with SEM results. The neat membrane shows higher current density (about 2.35 mA.cm-2) than modified membranes. In the case of modified membranes, the q-OESM showed very low methanol oxidation and current density (0.18 mA.cm2

) which lead to a lower methanol crossover compared to the neat-OESM and s-OESM. Obtained

current density for s-OESM decreased greatly compare to the neat membrane, however, its


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methanol crossover is higher than q-OESM. These results indicate that the membrane modifications by quaternization (q-OESM) and also grafting with poly(allyl sulfate) (s-OESM) successfully decreased fuel crossover and improved its performance for fuel cell.

Fig. 5. Methanol crossover current densities for neat and modified OESMs measured by drive mode cell at 25 ˚C. 4. Conclusion In summary, two new ion conductive membranes were prepared based on a natural polymer with a hierarchical interwoven structure. These membranes had suitable morphology and composition for ion conduction (porosity and protogenic groups). The membranes were easily modified for both proton and anion conduction. The s-OESM showed reasonable proton conductivity in different acidic solutions (0.48 mS.cm-1). Moreover, anion conductivity obtained for q-OESMs was about 0.40 mS.cm-1, introducing this membrane as a promising candidate for use in alkaline fuel cells. The water uptake values indicated that the membranes were able to preserve their water content at 80 ˚C and maintain their performance. Also, methanol crossover measurement 18 ACS Paragon Plus Environment

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illustrates that the performance of modified membranes improved compare to the neat membrane and methanol crossover of membrane reduced after modifications. The results obtained in this research notify that synthetic membranes could be replaced by natural membranes in future. 5. References 1.

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Tan, Y. H.; Abdullah, M. O.; Nolasco-Hipolito, C.; Taufiq-Yap, Y. H., Waste ostrich-

and chicken-eggshells as heterogeneous base catalyst for biodiesel production from used cooking oil: Catalyst characterization and biodiesel yield performance. Appl. Energy 2015, 160, 58-70. 4.

Ruiz-Arellano, R. R.; Moreno, A., Obtainment of Spherical-Shaped Calcite Crystals

Induced by Intramineral Proteins Isolated from Eggshells of Ostrich and Emu. Cryst. Growth Des. 2014, 14, (10), 5137-5143. 5.

Balaz, M., Eggshell membrane biomaterial as a platform for applications in materials

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Fink, D.; Rojas-Chapana, J.; Petrov, A.; Tributsch, H.; Friedrich, D.; Küppers, U.;

Wilhelm, M.; Apel, P. Y.; Zrineh, A., The “artificial ostrich eggshell” project: Sterilizing polymer foils for food industry and medicine. Sol. energ. mat. sol. cells 2006, 90, (10), 14581470. 7.

MM Cordeiro, C.; T Hincke, M., Recent patents on eggshell: shell and membrane

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