Development of cation exchange resin-polymer

Development of cation exchange resinpolymer electrolyte membranes for microbial fuel cell application Prabhu Narayanaswamy Venkatesan & Sangeetha Dharmalingam

Journal of Materials Science Full Set - Includes `Journal of Materials Science Letters' ISSN 0022-2461 Volume 50 Number 19 J Mater Sci (2015) 50:6302-6312 DOI 10.1007/s10853-015-9167-x

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Author's personal copy J Mater Sci (2015) 50:6302–6312 DOI 10.1007/s10853-015-9167-x

Development of cation exchange resin-polymer electrolyte membranes for microbial fuel cell application Prabhu Narayanaswamy Venkatesan1 • Sangeetha Dharmalingam1

Received: 12 March 2015 / Accepted: 8 June 2015 / Published online: 30 June 2015 Ó Springer Science+Business Media New York 2015

Abstract A new class of composite membranes was made based on sulfonated poly ether ether ketone (SPEEK) incorporated with micron-sized sulfonate styrene-crosslinked divinyl benzene-based cation exchange resin particles as fillers with desired properties of higher ion exchange capacity, lower oxygen crossover, lesser mono, and divalent alkali cation transport for microbial fuel cell (MFC) applications. Such cation exchange resin-based composite membranes showed good membrane homogeneity as revealed from SEM images. XRD patterns showed better amorphous nature for the composite membranes with increase in resin loading. FT-IR spectra of composite membranes showed the presence of hydrogen bonding between the sulfonated PEEK and resin. The effects of existence of hydrogen bonding in the properties of membranes such as water uptake, transport of cations other than proton, oxygen crossover, and proton conductivity were discussed. The composite membranes showed one order lesser oxygen mass transfer coefficient (Ko) in the range of 10-6 cm/s when compared to Nafion membranes. The composite membranes were tested in a single chamber Pt/C-coated air cathode MFC with Escherichia coli as anodic microbial inoculum. With resin, the SPEEK composite membranes showed higher power density value of 410 mW/m2 for 7.5 % IER ? SPEEK composite membrane compared to that of Nafion (47 mW/m2) and SPEEK (77 mW/m2) membranes with same configuration.

& Sangeetha Dharmalingam [email protected] 1

Department of Mechanical Engineering, Anna University, Chennai 600 025, Tamil Nadu, India

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Introduction Microbial fuel cell (MFC) is a bio electrochemical device that has gained much attention among researchers as a promising technology for environmental friendly green energy generation from waste biomass using microorganisms. In general, MFC consists of anode, cathode chamber separated by a separator [1–3]. A single chamber MFC consists of anode chamber, separator, and air facing cathode, while a dual chamber MFC consists of anode chamber, separator, and cathode chamber with or without oxidizing agents such as oxygen-, permanganate-, and ferricyanide-based compounds [4]. The efficiency of MFC depends upon various factors such as type of microorganisms, electrodes, electrode spacing, electrode size, shape and the type of separator [5– 7]. Among all, separator is a very important component which can increase the power production of MFC due to its needed properties such as high proton conductivity to exchange protons produced in the anode chamber, prevent, or restrict oxygen crossover from cathode to anode to maintain anaerobic environment in anode chamber [8]. However, the separator may be micro or macro-sized, functionalized, or non-functionalized polymer. It should be capable of the above properties for its effective operation in MFC [9]. NafionÒ is one of the most widely used cation exchange membrane in fuel cells due to its high proton conductivity. Apart from its high cost and fluorinated polymer backbone, Nafion possess several drawbacks for is application in MFC such as high oxygen crossover, substrate loss, and transport of cations other than protons, which are present in microbial anode chamber media [10, 11]. In the past few years, intensive research has been focused on the development of membranes such as nylon,

Author's personal copy J Mater Sci (2015) 50:6302–6312

cellulose, polycarbonate, J-cloths, and Teflon coated layers as effective separators in MFCs replacing Nafion [12]. Especially, J-cloth and PTFE layer coating on the cathode offers a high electrode performance. Even though these separators are cost effective alternatives for Nafion, their shortcoming is that they favor oxygen crossover [13] which will affect the power production since high power density is achieved only in highly anaerobic anodic conditions. In addition, these separators do not have ion exchangeable functional groups that will facilitate proton transport between anode and cathode [14]. The profound researches in the development of many novel eco-friendly hydrocarbon-based membranes such as SPEEK, sulfonated polystyrene ethylene butylene polystyrene, and sulfonated polyether sulfone with desired properties were investigated and reported. In our previous reports, development of novel hybrid hydrocarbon-based proton exchange membranes was synthesized and studied for their suitability in MFC. Such membranes with desired properties were found to be promising in terms of with higher power production compared to that of commercial Nafion [15–18]. Even though the sulfonation of polymers showed proton conductivity, it was limited. At higher degrees of sulfonation, they have high proton conductivity but results in unstable water soluble material [19]. By blending polymers and by adding fillers to polymer matrix, properties such as ion exchange capacity and proton conductivity that influenced the overall performance of fuel cell were improved [20]. However, the fillers used were mostly non-conductive ceramic materials, which were capable of holding water molecules that facilitate the transport of protons through various mechanisms. Other researchers have impregnated the membranes with low molecular weight strong acids (e.g., phosphoric acid, sulfuric acid, and CFSO3H) and sulfonated metal oxides such as Sulfonated-TiO2, Sulfonated-SiO2 showed higher power density but the increased water uptake by the fillers might affect the mechanical and dimensional stabilities. The conductivity of acid-doped membranes can be as high as that of NafionÒ. Unfortunately, these low molecular weight acids leached out of the membranes over tens to hundreds of hours [21–23]. Further, in order to improve the performance of polymer electrolyte, functionalized resins were added to improve the property of polymer electrolyte membranes. Resins are functionalized, crosslinked polymeric materials used for ion exchangeable properties. A conventional ion exchange resin (IER) consists of a cross-linked polymer matrix with a relatively uniform distribution of ion-active sites throughout the structure. The highly cross-linked polymer matrices have lesser water absorption and showed selectivity among metal ions in hydrated and unhydrated forms [24, 25]. Depending upon the type of functional group, the

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resins are classified as cation and anion exchange resin. A cation exchange resin consists of negatively charged matrix and exchangeable positive ions (cations). For example, a conventional gel type, styrenic ion exchanger is built on a matrix prepared by co-polymerizing styrene and DVB. Gel resins exhibit microporosity with pore volumes typically ˚ [25]. In the present work, the resin/sulup to 10 or 15 A fonated poly ether ether ketone (SPEEK) composite membranes were prepared by solvent-casting method, and the effects of resin in enhancing the properties of membranes such as oxygen crossover, cation transport, ion exchange capacity, proton conductivity, and water uptake were studied. Composite membranes were also evaluated in a single chamber microbial fuel cell (SCMFC).

Materials and methods The materials that were used in the study were procured commercially from different sources. PEEK (Mol. Wt. 1,00,000) (Victrex), Conc. H2SO4, (Merck) D-glucose (Sigma Aldrich), Ethanol (Sigma Aldrich), Nutrient medium (SRL), N-methylpyrrolidone (NMP) (SRL) and Seralite (cation exchange resin—H? form, 20–50 mesh standard grade) (SRL), and all other chemicals were used without any further purification. Sulfonation of PEEK and composite membrane preparation PEEK polymer was sulfonated using sulfuric acid as sulfonating agent. The weighed amount of PEEK was dissolved in concentrated sulfuric acid and magnetically stirred for 5 h. After 5 h, the reaction mixture was poured into cold water and the SPEEK was obtained in the form of white precipitate. The SPEEK was washed with deionized water for several times until the pH becomes neutral. The SPEEK obtained from the above process was dried in a vacuum oven at 80 °C overnight. It was then dissolved in a suitable quantity of NMP and cast onto a clean, dry petri dish [26]. The membrane was obtained by evaporating the solvent in vacuum oven at 80 °C for 24 h. The obtained membranes were pale brown in color and were peeled off from the dish and stored for further analysis. The reaction scheme is given in Fig. 1. For the preparation of composite membranes, SPEEK ionomer was dissolved in the NMP solvent and different proportions of IER was added to the solution and stirred for 24 h, and then ultrasonicated for about 15 min, followed by casting into a clean dried petri dish to obtain membrane of the required thickness. The cast membrane was dried at 80 oC for 24 h.

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Water uptake Water uptake of the composite membranes was studied by change in weight of the composite membranes before and after hydration. The percentage of water absorption was calculated using the relation given below. % water absorption wt:of wet polymer wt:of dry polymer 100 ¼ wt:of dry polymer Fig. 1 Schematic representation of sulfonation of PEEK

SPEEK membrane with 2.5, 5, 7.5, and 10 % of IER was fabricated and characterized using the following techniques: Instrumental characterization Characterization of polymer electrolyte membrane The prepared polymer electrolyte membranes were characterized by FT-IR (Alpha T Bruker Optics) to study the presence of functional groups, XRD (Xpert Pro, Pan Analytical) to study the crystallinity, while SEM (VEGA3 TECSCAN) and non-contact profilometer (Taylor Hobson hardness tester) were used to study the morphology of the membranes. Cations transport (such as Na?, K?, Ca2?, and Mg2?) through prepared membranes was measured [27] and determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES; Perkin-Elmer Optima 3000XL), and ammonium ion concentrations were determined by Phenate method using UV–Visible spectrophotometer at 640 nm. All the characterizations were performed as per our previous study [18]. Proton conductivity Proton conductivity of all the prepared membranes was measured at room temperature and was studied using electrochemical impedance spectrometer (Biologics VSP, France). The 1 cm 9 1 cm sized membranes were sandwiched between two brass rods, which were supported on an acrylic plate. A signal amplitude of 10 mV in the frequency range of 1 MHz to 100 Hz was applied. The twoelectrode method was used to study the proton conductivity of the composite membrane using Z fit software. Conductivity (S/cm) =

L ; ðR AÞ

where, R = sample resistance (X), L = wet sample thickness (cm), and A = sample area (cm2).

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Ion exchange capacity (IEC) Ion exchange capacity is a measure of the ability of an insoluble material to undergo displacement of ions previously attached and loosely incorporated into its structure by oppositely charged ions present in the surrounding solution. IEC is generally found out by volumetric method. The greater the ion exchange capacity better will be the proton conductivity of the membrane. Ion exchange capacity is directly dependent on the number of sulfonic acid groups present in the sulfonated polymer. The sulfonated membranes and composite membranes were soaked in 2 M KCl solution for 24 h to saturate the membranes and the protons released by the membranes were neutralized by sodium carbonate solution of known concentration with phenolphthalein as indicator. IEC was calculated by using the formula given below IEC =

Titre valueðin mlÞ Normality of Na2 CO3 meq/g weight of dry polymer membrane (in g)

Dissolved oxygen cross over The oxygen mass transfer coefficient (Ko) of fabricated composite membranes was studied using a portable dissolved oxygen (DO) probe (Extech 407510A, Taiwan). For Ko determination study, a two chambered bottle MFC was used as described earlier [28] to find out the oxygen mass transfer for each membrane using uninoculated bottle-MFC reactors and nutrient medium. The cathode chamber was continuously aerated to maintain saturated DO conditions. A DO probe was placed in the nitrogen saturated completely sealed anode chamber. The Ko was calculated [28] from DO concentration over a period of 10 h. The study showed the resistance of PEM separator to oxygen permeability, which in turn affects the anaerobic atmosphere of anodic chamber. MFC construction and operation The fabricated MFC consisting of an acrylic cylindrical chamber 4 cm long and 3 cm in diameter (empty bed volume of 28 mL) was separated by a proton exchange


membrane and Escherichia coli was used as bacterium in the anodic chamber. The anode and cathode electrodes were prepared as per our previous studies [18, 29]. Escherichia coli strains (DH5-a) from our pre adapted laboratory culture collection were used, and the bacterial culture was enriched by purging nitrogen gas and kept in shaker for 48 h. The anode chamber was filled with the enriched E. coli nutrient medium, and the chamber was continuously flushed with N2/CO2 (80:20) to maintain anaerobic conditions as well as the pH of the growth medium at 7. The bacterium containing inoculum in anodic chamber was changed 3–5 times (i.e., over 72–120 h) to allow a biofilm to form on the anode surface. The chamber was refilled each time when the voltage reached a minimum value. Fuel cell analysis The coulombic efficiency (CE) was calculated using the following equation. CE =

CP 100; CT

where, CP is the total Coulombs calculated by integrating the current over time. CT is the theoretical amount of coulombs that can be produced from glucose and is calculated as CT =

FbSv ; M

where, F is Faraday’s constant (98485 C/mol of electrons), b is the number of mol of electrons produced per mol of substrate (glucose) (b = 24), S (g/L) is the substrate (glucose) concentration, v (mL) the liquid volume, and M the molecular weight of the substrate (glucose) (M = 180). Cell voltage and current were observed and recorded using a precision digital multimeter (Model 702, Metravi, India). The circuit was completed with a resistor of 1 kX except when different resistors (100–1000 X) were used to determine the power generation as a function of load. The power density values were obtained after stable voltage was obtained. The current was calculated as I = V/R Using Ohm’s law where, I (mA) is the current, V (mV) is the voltage, and R is the external resistance (X). Power (P) was calculated as, P = IV.

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characteristic OH peak at 3406 cm-1, C=O peak at 1645 cm-1 and S=O peak at 1080 cm-1 these showed the sulfonation of PEEK polymer. Hydrogen bonding between sulfonyl groups in IER and polar groups (C=O) in SPEEK was evidenced from the broadened—OH band at 3400 cm-1, shifted C=O from 1082 to 1046 cm-1, shifted –SO3H band at 1284 toward 1277 cm-1. The shifting of hydrogen bonding site confirmed the interaction due to hydrogen bond. The remaining O–H group bands at 1413 and 3440 cm-1 in SPEEK membrane were shifted due to the hydrogen bonding interaction between O–H groups of –SO3H and C=O. The C=O groups in SPEEK membrane shifted from 1082 to 1046 cm-1. The sulfonic groups (–SO3H) in SPEEK membrane are also shifted from 1284 to 1277 cm-1. These results clearly indicate the existence of hydrogen bond between SPEEK and resin [30, 31]. XRD The crystalline structures of the PEEK, SPEEK, and IER ? SPEEK composite membranes were characterized by wide-angle X-ray diffraction. Figure 3a, b show the XRD patterns of PEEK, SPEEK polymers, and IER ? SPEEK composite membranes, respectively. PEEK is semi crystalline in nature. The four main peaks of the pure PEEK are found at a 2h of 19°, 22°, 23°, and 38° which correspond to the diffractions of the (110), (111), (200), and (211) crystalline planes, respectively. All these peaks of PEEK were absent in the XRD pattern of SPEEK. The

Results and discussion FT-IR Figure 2 shows the FT-IR spectra of SPEEK and its composite membranes. SPEEK membrane showed the

Fig. 2 FT-IR Spectra of SPEEK and IER ? SPEEK composite membranes

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SPEEK matrix enhanced the amorphous nature of the composite membranes with an increase up to 7.5 % IER ? SPEEK composite membrane. This kind of observation disclosed the amorphous nature of the membrane with uniform distribution of inorganic fillers in the membrane surface which in turn was useful for the enhancement of ionic conductivity [34, 35]. However, beyond 7.5 wt% of IER, crystalline nature of the polymer increased due to the decreased polymeric chain mobility [31], which was inferred from the Fig. 3d. From Table 1, it was observed that the composite membranes had nearly constant proton conductivity with resin content, independent of the water absorption, and ion exchange capacity. Since the composite membrane consists of resin particles embedded in a continuous phase of SPEEK, it suggests that the proton conductivity in both phases was nearly the same. The lower water uptake of crosslinked resin results in smaller hydrophilic domains or channels for protons mobility, and therefore, lower conductivity was observed. However, higher IEC of the resin increases its conductivity. These two opposite factors compensate each other, resulting in the conductivity of the composite being almost the same as that of SPEEK [23]. SEM

Fig. 3 XRD spectra of a PEEK and SPEEK, b IER ? SPEEK composite membranes

XRD pattern of SPEEK showed an amorphous structure with only a board peak at a 2h equal to 20°. This was observed due to the presence of sulfonic acid group (SO3H) which obstructs the polymer chain packing, thus bringing about a loss of crystallinity. From this, it has been confirmed that the sulfonation of PEEK decreased its crystallinity, as shown by the loss of the crystalline reflections in the XRD in Fig. 3a [32]. As shown in Fig. 3b, the XRD patterns of all the composite membranes showed amorphous phases with broad bands at 20° 2h. Reference [33] showed that the polymeric resin particles exhibit only a broad amorphous peak at 20° 2h [33] and the addition of resin particles did not show any additional patterns with SPEEK membranes as observed in Fig. 3b. It was also observed that the presence of IER in

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The surface morphologies of the prepared membranes were examined under SEM. Figure 4a–d shows the SEM images of different weight percentages of IER composite membranes. Figure 4a shows the solvent cast SPEEK membrane with uniform surface without any pores. Figure 4e of the composite membrane confirmed the presence of micro-sized resin particles on the surface of polymer electrolyte membrane. All the SEM images of the composite membranes showed non-porous, relatively uniform membrane surface and good homogeneity of polymer matrix with resin. The uniform distribution of resins, i.e., functional groups, can provide a more conducting region in membrane surface and, therefore, improve the electrochemical properties of the prepared membranes [36]. Above the optimum addition (i.e., 7.5 wt%) further increase in filler particle concentration (i.e., 10 wt%), led to particle agglomeration which was observed on the surface of polymer matrix. Surface roughness One of the important roles of the fillers in the composite membranes of the MFCs is to block oxygen migration and substrate loss through the membrane. The membrane surface roughness is also an important parameter that decides the performance of the separator since it provides more


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Table 1 Properties of composite membranes Oxygen mass transfer coefficient (Ko) (cm/s)

Membrane

Thickness (cm)

% Water uptake

IEC (milli equiv/g)

Proton conductivity 9 10-2 S/cm)

Nafion 117

0.019

22

1.28

2.0

8 9 10-5

SPEEK

0.017 ±0.003

16.46

1.52

0.15

4 9 10-6

2.5 % IER ? SPEEK

0.018±0.002

16.16

1.66

0.153

3.8 9 10-6

5 % IER ? SPEEK

0.017 ±0.003

15.84

1.75

0.155

3.4 9 10-6

7.5 % IER ?SPEEK

0.019 ±0.001

15.12

1.88

0.162

3.0 9 10-6

10 % IER ? SPEEK

0.018 ±0.002

15.08

1.80

0.156

3.2 9 10-6

Fig. 4 SEM images of a SPEEK, b 2.5 %, c 5 %, d 7.5 %, e 10 % IER ? SPEEK and f resin particles on SPEEK surface

surface area for the bacterial biofilm growth [8] that reduce oxygen crossover in long-term MFC run. Figure 5 shows the surface roughness of the prepared membranes and these figures clearly witnessed that the images exhibit a major change on the surface upon the addition of IER. Table 2 depicts the surface roughness values of the composite membranes. The surface roughness (Ra) of SPEEK was found to be 0.106 lm, which was increased upon the addition of IER and found to be 0.178 lm (Ra) for SPEEK with 10 % IER membrane. The increase in the surface roughness of the IER ? SPEEK was due to the presence of

the IERs. The higher roughness will provide more membrane surface area for the biofilm growth and bacterial adhesion over a period, which will reduce the oxygen crossover from cathode to anode [13]. However, much higher bacterial adhesion on the surface will have an adverse effect of substrate loss and membrane fouling [20]. Dissolved oxygen crossover Maintaining anaerobic condition in anode chamber is important for the effective generation of protons and

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Fig. 5 Surface roughness images of a SPEEK, b 2.5 %, c 5 %, d 7.5 %, and e 10 % IER ? SPEEK

Table 2 Average surface roughness of the membranes Membrane

Average surface roughness (lm)

Nafion 117

0.097

SPEEK

0.106

2.5 % IER ? SPEEK

0.135

5 % IER ? SPEEK

0.142

7.5 % IER ? SPEEK

0.158

10 % IER ? SPEEK

0.178

electrons due to bacterial metabolic activities to run MFC. The addition of fillers into the polymeric matrix influenced the gas barrier property of the composite membranes. The addition of fillers on polymer matrix showed a significant improvement of one order lesser oxygen mass transfer

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coefficient (Ko) than Nafion while 7.5 % IER ? SPEEK showed the least Ko of 3.0 9 10-6 cm s-1 amongst all the composite membranes, which were evidenced from the values, listed in Table 1. It shows that gas can diffuses easily through the polymer matrix than through filler incorporated polymer matrix because the solid particle has much higher density than the polymer matrix [37]. Thus, the larger amount of filler added, the higher resistance to the gas diffusion was achieved. The oxygen mass transfer coefficient of the membranes is an important factor in designing hybrid membranes for MFC. From the values, it was observed that SPEEK-based membranes showed better oxygen mass transfer coefficient than Nafion 117Ò. It was observed that the increase in amount of IER content in SPEEK decreased the oxygen mass transfer coefficient rate of the composite membranes one order lesser than that of


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Fig. 6 Development of the cation concentrations (Na?, K?, NH4?, Ca2?, and Mg2?) in cathode chamber of a microbial fuel cell

Nafion 117Ò. A strict anaerobic environment was maintained at the anode chamber due to the lesser oxygen crossover through membrane from cathode to anode, which in turn improved the performance of MFC in terms of power density generation [38]. Cations transport through membrane The other cation transport was studied in order to maintain membrane performance in MFC. The transport of cations (Na?, K?, NH4?, Ca2?, and Mg2?) present in anode media with concentration of 105 than that of proton can reduce the membrane performance by blocking ion exchange sites and by developing pH gradient across the membrane. The concentration development of cation species (Na?, K?, NH4?, Ca2?, and Mg2?) in cathode chamber was observed as shown in Fig. 6. The competing behavior between the

ions in solution was due to the ion mobility and hydration of metal ions in aqueous solution. In aqueous solution, depending on metal ions charge, the metal ions get hydrated by water molecules. Depending upon the charge on metal ion, the size of hydrated metal ions gets altered [39]. The nature of ionic channels in the SPEEK membrane which are dead end channels [40]. Hence, the passage or movement of hydrated metal ions through these channels was restricted and in addition to that the crosslinked divinyl benzene resin matrix have high selectivity toward smaller hydrated metal ion than that of larger ones [41]. This was reflected in this study, which showed lesser cation transport through the SPEEK composite membranes than that of Nafion and SPEEK. The hydrated metal ions showed lesser cationic (Na?, K?, NH4?, Ca2?, and Mg2?) transport through the membrane [42]. Hence, the addition of fillers acts as barrier to hydrated metal cations transport that

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Fig. 7 Polarization curves of prepared composite membranes

resulted in significant reduction of crossover of other cations in SPEEK composite membranes than in Nafion.

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(77 mW/m2), and Nafion (47 mW/m2). This was highly due to the better membrane properties and less other cation transport due to the presence of highly cross-linked resin particles, which restrict the movement of huge hydrated cations through them [41]. These results well correlated with ion exchange capacity and proton conductivity properties of the composite membranes. Table 1 clearly showed that the ionic and proton conductivity of the composite membrane with IER always exhibited higher values [31] than those of Nafion and SPEEK, which reflected on the power density values. The increase in the amorphous nature of the polymer composite membranes (Fig. 3) showed uniform mixing of nano fillers with that of polymer matrix, which helped for the improved ionic conductivity [34, 35]. However, 10 wt% of IER composite membrane showed lesser performance which was due to the increased oxygen cross over and decreased proton conductivity of the membranes. This kind of decreased proton conductivity was due to the addition of excess filler particles and its aggregation that blocked the ionic channel (‘‘blocking effect’’) movement of the polymeric membrane [14]. With respect to the cost analysis also, it is worth noting that the cost involved in the preparation of SPEEK composite polymer (approximately 4$/cm2) was much lower when compared to the commercial membrane, Nafion (10$/cm2) [1].

MFC performance

Conclusion The performance of the prepared composite membranes in single chamber MFC is shown in Fig. 7. The main objective of this present study is to determine the significant impact of resin particles in the betterment of properties of SPEEK membrane such as ion exchange capacity, proton conductivity, oxygen crossover, and transport of other cations that are essential to be an efficient electrolyte in MFCs operation. The prepared composite membranes showed higher percentage of columbic efficiency of 73, 75, 79, and 74 % for composites with 2.5, 5, 7.5, and 10 wt% of IER, respectively, compared to that of Nafion (47 %) and SPEEK (65 %). It was also observed that the polarization curves of the prepared composite membranes exhibited better power density values than that of Nafion and SPEEK membranes. The increased performance of MFC with better ion exchange capacity, proton conductivity, and oxygen crossover properties of composite membranes was due to the presence of number of sulfonyl groups (SO3–H) in resin particles, which forms denser ion transport network in SPEEK matrix. 7.5 % IER ? SPEEK showed the highest power density of 410 mW/m2 compared to that of other IER composite membranes, SPEEK

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In this paper, the IER added SPEEK composite membranes were prepared, characterized physically, electrochemically, and evaluated in MFC. It was found that varying the compositions effectively controlled the properties of the SPEEK/IER composite membranes. The water absorption of the prepared composite membranes showed decreased absorption property with the increasing content of IER due to the highly crosslinked structure which has less level of expansion. Although the proton conductivities of the membranes were found to be in the same range as that of SPEEK, addition of IER reduced the DO coefficients and improved the selectivity toward protons than other cations leading to better performance. Therefore, SPEEK/IER hybrid composite membranes were found to be promising for the usage in MFCs. Acknowledgements The authors thank the Department of Science and Technology (DST) India, for their financial support to carry out this work vide letter No. DST/TSG/AF/2010/09, dt. 01-10-2010. Conflict of interest of interest.

The authors declare that they have no conflict


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