PES nanocomposite membranes in microbial fuel cell

Electrochimica Acta 85 (2012) 700–706

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Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta

Synthesis, characterization and application studies of self-made Fe3 O4 /PES nanocomposite membranes in microbial fuel cell Mostafa Rahimnejad a,∗∗ , Mostafa Ghasemi b,c , G.D. Najafpour a , Manal Ismail b,c , A.W. Mohammad c , A.A. Ghoreyshi a , Sedky H.A. Hassan d,∗ a

Biotechnology Research Lab., Faculty of Chemical Engineering, Noshirvani University, Babol, Iran Fuel cell Institute, Universiti Kebangsaan Malaysia (UKM), Malaysia c Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia (UKM), Malaysia d Department of Biological Environment, Kangwon National University, 192-1, Hyoja 2-dong, Chuncheon, Kangwon-do 200-701, South Korea b

a r t i c l e

i n f o

Article history: Received 1 June 2011 Received in revised form 2 August 2011 Accepted 8 August 2011 Available online 3 September 2011 Keywords: Microbial fuel cell Bioelectricity Saccharomyces cerevisiae Neutral red Nanocomposite membranes

a b s t r a c t Nanocomposite membranes are a promising alternative for proton exchange membrane (PEM) because it has the capability of transferring protons, is inexpensive, and also have higher resistance against fouling compared to other membranes in microbial fuel cells (MFCs). In this study, Saccharomyces cerevisiae was used as an active biocatalyst and neutral red with low concentration (200 ␮mol l−1 ) was selected as electron shuttle in anode chamber. Moreover, four different concentrations of Fe3 O4 /PES have been tested as new generation of nanocomposite membrane and its efficiencies were compared with Nafion 117 in dual chamber MFC. To improve the performance of PEM, several nanoparticle (5%, 10%, 15% and 20% of Fe3 O4 nanoparticle) concentrations were used. Maximum generated power and current with new synthesized membrane and 15% Fe3 O4 nanoparticle were 20 mW m−2 and 148 mA m−2 , while it was 15.4 mW m−2 and 112 mA m−2 , respectively by using Nafion 117 at the same experimental condition. The highest obtained voltage was 656 mV and it was stable for 72 h of operation time. © 2011 Elsevier Ltd. All rights reserved.

1. Introduction It is a common viewpoint that global fossil fuel resources are depleting. Moreover, fossil fuels have a lot of disadvantages and cause environmental problems. Power generation from renewable sources has been growing rapidly in recent years and scientists in the world have started to find new alternatives of renewable energies to overcome energy crisis in the near future [1,2]. Among renewable alternatives, MFCs are interesting for many researchers in the world because they provide the possibility of directly harvesting electricity from different substrates such as organic waste and renewable biomass. Furthermore, they operate under very mild conditions and wide variable ranges of biodegradable materials can be used as fuel [3]. MFC is a bioreactor that can generate electricity from waste or organic matter by using microorganisms as active biocatalyst [4,5]. MFC is a reliable system that may produce limited power or biohydrogen from different kinds of electron donors [6–8]. In fact, simultaneous bioelectricity genera-

∗ Corresponding author. Tel.: +82 33 243 6449; fax: +82 33 241 6640. ∗∗ Corresponding author. Tel.: +98 111 3234 204; fax: +98 111 3234 204. E-mail addresses: [email protected], Rahimnejad [email protected] (M. Rahimnejad), [email protected] (S.H.A. Hassan). 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.08.036

tion and waste water treatment is considered as one of the most important applications of MFC [8,9]. Traditional MFC consists of two separate chambers named cathode and anode ones. Oxidation of substrate by microorganisms leads to the generation of electrons and protons in anaerobic anode compartment. Produced electrons are transported to anode surfaces and then reach cathode from external circuit. Protons are moved through proton exchange membrane (PEM) toward cathode chamber and at the cathode surface react with oxygen and electrons. Water is produced from this reaction on cathode surface. Adding different mediators [10–12] and oxidizers can improve the performance of MFC [13,14]. PEMs have important role in two chambers of MFCs. The action of PEMs is one of the most critical parameters on MFC performances. It should have good ability to transport protons from anode to cathode compartment in MFCs. Moreover, PEMs must be able to prevent the transfer of other materials such as substrate or oxygen from anode and cathode chambers [15–19]. Different kinds of materials were used as PEM in MFCs such as ultrex, Nafion, bipolar membranes, dialyzed membrane, polystyrene and divinylbenzene with sulfuric acid group, glass wool, nano-porous filters and microfiltration membranes [20–22]. Among the aforementioned membranes, Nafion is one of the most common PEMs in MFCs [23].

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Although Nafion is a common PEM, several problems associated with Nafion membranes still exist, including high cost, oxygen leakage from cathode to anode, substrate loss, cation transport and accumulation rather than protons and biofouling [24]. Due to these disadvantages, researchers in the world are working to fabricate a new kind of PEM to overcome these disadvantages and induce better performance than Nafion membrane as well [14]. Nowadays, due to the huge and potential applications of polymer/inorganic nanoparticle membranes in energy, environment and biomedical materials, much attention has been paid to membrane science and technology. Nanoparticles improve separation performance by generating preferential permeation paths while they prevent from permeation of undesired species as well as they increase thermal, and mechanical properties [25–27]. This means that distribution of nanoparticles into the polymer matrix modifies chemical and physical properties of polymeric membranes [28]. Recently, due to unique and promising properties of Fe3 O4 nanoparticles (magnetic, conductive, easy to be synthesized, ecofriendly, and catalytic), intensive attention has been paid to them [29,30]. The objective of this research paper was to demonstrate the power production from glucose as sole electron donors in dual chamber MFC, and to fabricate the new PEM for improving MFC performances. Four new nanocomposite PEMs were fabricated and compared to traditional proton exchange membrane. 2. Materials and methods 2.1. Chemicals for preparation of nanoparticle Ferrous chloride (FeCl2 , MW = 198.81 g/mol), ferric chloride (FeCl3 , MW = 270.3 g/mol), sodium hydroxide, 1-methyle 2 pyrrolidone (NMP), ethanol (95%, MW = 46.07 g/mol) and polyethersulfone (PES) were purchased from Merck (Darmstadt, Germany); they were of analytical grade and used as received. 2.2. Ferric oxide (Fe3 O4 ) nanoparticle synthesis For production of Fe3 O4 nanoparticles, FeCl2 , FeCl3 and sodium hydroxide solutions were prepared by dissolving certain amount of pure reagent in deionized water in 1, 2 and 8 molar ratios, respectively at 70 ◦ C. Then, iron solutions were added to the sodium hydroxide solution. When the solutions were mixed properly, centrifuge was used for separation of ferric oxide nanoparticles. The ferric oxide nanoparticles were washed three times with ethanol and then dried at 80 ◦ C before use [29–32]. 2.3. PEM membranes 2.3.1. Fabrication of PEM Phase inversion method has been used for fabrication of membranes. At first step, PES was dissolved in NMP at 70 ◦ C by using mechanical stirrer. Different membranes with different concentrations of produced ferric oxide nanoparticles were prepared (membrane 1: 5 wt%, membrane 2: 10 wt%, membrane 3: 15 wt% and membrane 4: 20 wt% of PES). Then, it was added to solution and dispersed uniformly by mechanical stirrer. Due to adsorption of nanoparticles on magnet surface, the magnet cannot be used for dispersion of magnetic nanoparticles. After that, the solution was left overnight to release the dissolved bubbles. In the next step, the solution was cast in a glass plate by using casting knife and was put into the water immediately. The fabricated membrane was separated from the glass plate. Then, the membranes were left in distilled water for at least one day for separation of residual solvent.

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2.3.2. Traditional PEM Nafion 117 (Dupont Co., USA) was selected as traditional PEM to compare the efficiency of the new synthesized membrane with that of traditional membrane. The Nafion surface area was 9 cm2 . Nafion-PEM was subjected to a course of pretreatment to take off any impurities that was boiling the film for 1 h in 3% H2 O2 , washed with deionized water, 0.5 M H2 SO4 , and finally washed with deionized water. In order to maintain the membrane for good conductivity, the cell anode and cathode compartments were filled with deionized water when the MFC was not in use. 2.4. Microorganism and cultivation Saccharomyces cerevisiae PTCC 5269 was supplied by Iranian Research Organization for Science and Technology (Tehran, Iran). The microorganism was grown under anaerobic condition in an anaerobic jar vessel. The prepared medium for seed culture consisted of glucose, yeast extract, NH4 Cl, NaH2 PO4 , MgSO4 and MnSO4 : 10, 3, 0.2, 0.6, 0.2 and 0.05 g l−1 , respectively. The medium was sterilized, by autoclaving at 121 ◦ C and 15 psig for 20 min. The medium pH was initially adjusted to 6.5 and the inoculums were introduced into sterilized media at ambient temperature. The inoculated cultures were incubated at 30 ◦ C. The yeast was fully grown in a 100 ml flask without any agitation for the duration of 24 h. Growth was monitored by measuring the optical density (OD at 600 nm). The pH meter, HANA 211 (Romania) model glasselectrode was employed to measure pH values of the aqueous phase. The initial pH of the working solution was adjusted by the addition of diluted HNO3 or 0.1 M NaOH solutions. 2.5. MFC construction and operation The fabricated cells made of Plexiglas material were used as MFC in the laboratory scale. The volume of each chamber (anode and cathode chambers) was 850 ml with a working volume of 760 ml. The sample port was provided for the anode chamber, wire point inputs and inlet port. The selected electrodes in MFC were graphite plates, size of 40 mm × 50 mm × 2 mm. Anode and cathode were separated with a tube which contains Nafion 117 (Sigma–Aldrich) or new fabricated membrane of Fe3 O4 nanoparticles, was used to separate two compartments as PEM (surface area of these membranes was 9 cm2 ). The anode chamber was inoculated with fresh cells of yeast S. cerevisiae suspension, glucose was used as the sole carbon source, cathode and anode compartment were filled with 50 mM of phosphate buffer (pH 7.0). Nitrogen was purged through anode to maintain anaerobic conditions for 10 min, while air was continuously purged through cathode compartments to maintain aerobic condition. Neutral red (NR) was used as an electron mediator in anode chamber of MFCs, at 200 ␮mol l−1 . The schematic diagram, photographic images and auxiliary equipments of the fabricated MFC cell are shown in Fig. 1. 2.6. Electrochemical measurements and calculations The performance of the MFC system was evaluated by polarization curve. Polarization curves were obtained by an external resistance. Power and current were calculated based on the following equations: P =I×E

(1)

E I= Rext

(2)

where P is the generated power; E is the measured cell voltage; Rext is the external resistance and I is the produced current. The produced current and power normalized by the surface area of the

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Fig. 1. Fabricated MFC (a) schematic drawing and (b) MFC picture with the auxiliary equipments.

The morphologies of the ferric oxide nanoparticles were observed by transmission electron microscopy (TEM) (Philips, class CM12; Netherlands). Scanning electron microscopy (SEM) (FESEM, supra 55vp-Zeiss, Germany) technique was also used for characterization of synthesized membrane. The resolution was set to 15,000. The tilt of the sample plate was adjusted to 20◦ . Furthermore, Atomic Force Microscopy (AFM) (NIEGRA PRIMA, Russian) images were used to demonstrate the physical characteristics of the fabricated membrane surface. Surface profiles were generated from AFM raw data by the NOVA (1.0.26.1443) software.

3.2. New synthesized PEM 3.2.1. Characterization of self made ferric oxide nanoparticles (Fe3 O4 ) The nanoparticle size and dispersion of ferric oxide nanoparticles were investigated by TEM and the results are shown in Fig. 3.

16

600

14 500

12

400

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300

8

3. Results and discussion

200

3.1. Nafion as PEM in MFC

100

Protons and electrons were generated via biochemical reactions in an anaerobic anode chamber of MFC. Protons must travel to cathode chamber via one PEM or salt bridge. These days, due to the good reputation of Nafion, it is commonly used as PEM in MFC by the researchers. At the first step of this research, Nafion 117 was used

18

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6 Voltage Power

4 2

0 0

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Current (mA.m ) Fig. 2. Polarization curve with Nafion 117 as PEM.

0 120

Power (mW.m-2)

2.7. Nanoparticles and physical characterization of the new membrane

as PEM in dual chamber of MFC and the performances of cells were considered by polarization curve. The polarization curve and power density versus current density are shown in Fig. 2. The maximum power and current density with this traditional membrane were 15.4 mW m−2 and 112 mA m−2 , respectively. Production of bioelectricity from MFC has not been developed up to now, and this may be due to some expensive components such as mediators, oxidizer, PEM and the highest power generation is still less than other fuel cells. Most of the researchers who were interested to MFC work are searching for new membranes and mediators which improve the efficiency of MFC and have low price and are eco-friendly [33,34].

Voltage (mV)

used membrane were recorded online every 4 min using analog digital data acquisition system. The system had measurements for variable resistances (65,535–1 ) which were imposed to the MFC. The current in MFC was recorded, dividing the obtained voltage by the defined resistance. Then, the system provides power calculation by multiplication of voltage and current. Moreover, the online system demonstrates polarization graphs for power generation and MFC voltage with respect to the current. The online system had the ability to operate automatically or manually. While it operates in auto-mode, the assembled relays were able to regulate automatically the resistances. Voltage of MFC was amplified and then data were transmitted to a microcontroller by an accurate analog to digital converter. The microcontroller was also able to send the primary data to a computer by serial connection. In addition, a special function of MATLAB software (7.4, 2007a) was used to store and synchronically display the obtained data.

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As the results show, the produced nanoparticles have more than 98% purity with a little sodium and chloride particle as impurity.

Fig. 3. TEM images of produced Fe3 O4 nanoparticles.

Table 1 EDX pattern of self assembled Fe3 O4 nanoparticles. Element

Weight%

Atomic%

Fe O Na Cl

72.81 26.43 0.27 0.49

43.73 55.41 0.4 0.46

The Fe3 O4 particles have black spot forms and their sizes are different from 10 to 30 nm. Moreover, the purity of nanoparticles has been measured by using Energy-dispersive X-ray spectroscopy (EDX, INCA, Oxford). The results are shown in Table 1.

3.2.2. Characterization of membranes For understanding the influence of PES/Fe3 O4 composition on the membrane surface structure, the surface of membranes was observed by using field emission SEM. After drying of membranes, the SEM images of nanocomposite membranes were obtained. As Fig. 4 shows, when the amount of ferric oxide nanoparticles increases from 5 wt% to 15 wt%, the nodular structure (white color) in membrane surface also increases. Moreover, the average pore size and roughness also increase in the membranes. However, when the amount of ferric oxide passes from 15 to 20 wt%, the surface of membrane shows some aggregation (red circle). So, the roughness of 20 wt% ferric oxide nanoparticles in membrane increases more than other membranes. AFM has also been used for complementing the morphological characterization of fabricated membranes. Fig. 5 demonstrates two and three dimensional AFM images of membranes with different Fe3 O4 /PES compositions in the casting solution. The bright color represents the high points of membrane surface. However, valley and pores of membranes are indicated by dark color. Definitely, by changing the content of ferric oxide nanoparticles in casting solution, the morphologies of the surfaces change. As Fig. 4 shows, the pore sizes increase with ferric oxide nanoparticle increments up to 15%; however, at 20% ferric oxide nanoparticles, the pore sizes are irregular and the roughness of this membrane is also very high. One of the most important factors for determining the fouling tendency of membranes is surface topology. Rough surface fouls more easily than smooth surface because surface area will be increased with roughness. The roughness also influences other parameters that are important for fouling. Table 2 shows the

Fig. 4. SEM images from outer surface of different kinds of synthesized PEM: (a) membrane 1 (5 wt% Fe3 O4 /PES), (b) membrane 2 (10 wt% Fe3 O4 /PES), (c) membrane 3 (15 wt% Fe3 O4 /PES) and (d) membrane 4 (20 wt% Fe3 O4 /PES).

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Fig. 5. AFM images from outer surface of two types of synthesized PEM: (a) two and three dimensional images of membrane 1 and (b) two and three dimensional images of membrane 4.

Table 2 Pore size and roughness of the membranes. Membrane

Pore size (nm)

Roughness (nm)

PES–5% Fe3 O4 PES–10% Fe3 O4 PES–15% Fe3 O4 PES–20% Fe3 O4

3.9 5.8 20 39.1

31 47.6 71.9 129.23

roughness and pore size information of nanocomposite membranes. Generally, the roughness increases with nanoparticle increments. The roughness of the membranes with 5 wt%, 10 wt% and 15 wt% Fe3 O4 nanoparticles is nearly in the same range but for 20 wt% Fe3 O4 the roughness was very high (see Table 2). Also, all membranes have smaller pore size than bacteria (0.5–2 ␮m) diameter and 1–10 ␮m in length so they cannot pass through the membranes and migrate from anode to cathode and disturb the MFC performance. 3.2.3. Comparison between synthesized and traditional PEM Nafion membranes have good ability to transfer produced protons in anode to cathode chamber but this good PEM is expensive. The price of PEM must be reduced without decreasing the MFC

performance. The nanocomposite membranes have been tested as PEM in MFC to examine their performance and compare to Nafion 117 membrane. At first, ferric oxide (Fe3 O4 ) semi conductive nanoparticle with 5% was used to improve the produced power in MFC. The generated power and current were very low. It was 0.79 mW m−2 and 7 mA m−2 , respectively (see Fig. 6a and b). In order to improve the produced power and current, while the other factors were kept constant in the MFC, other synthesized membranes with different coated Fe nanoparticles (10, 15 and 20%) were analyzed and the data are presented in Fig. 6. By increasing the nanoparticle up to 15%, the produced power and current increased up to 20 mW m−2 and 148 mA m−2 , respectively. At any percentages of Fe nanoparticle more than 15%, there was negative impact for additional current and power (see Fig. 6a and b). Moreover, the maximum current and power with 20% Fe nanoparticle was less than that of 10 wt% Fe3 O4 . Due to high percentage of roughness, some biofilm may be developed on the outer surface of this membrane (see Table 2). Open circuit potential (OCP) of fabricated MFC was investigated with both synthesized membranes and Nafion 117 PEM for 72 h of operation time (see Fig. 7). Online data acquisition system was used to record produced potential every 30 min. Fig. 7 shows that

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a

Table 3 Optimum condition obtained from this study at different membranes.

800

Membrane1 Membrane2 Membrane3 Membrane 4

Voltage (mV)

600

400

0 0

20

40

60

80

100

120

140

160

Current (mA.m-2) 25

Power (mW.m-2)

20

15

Nanoparticle %

Pmax (mW m−2 )

Imax in Pmax (mA m−2 )

OCV at SSa condition (mV)

Membrane 1 Membrane 2 Membrane 3 Membrane 4 Nafion 117

5 10 15 20 –

0.79 12.8 20 5 15.4

2.9 45 75 17 52

481 566 656 568 610

SS (steady state condition).

In any power supply, the main goal is to increase the output power and then to acquire the highest current density under maximum produced power density [35]. The maximum power density, maximum current density at the highest power density and also obtained OCV at the steady state condition at different used PEM are summarized in Table 3. The presented data indicated that the PEM has essential roles on performances of MFC. Moreover, this table showed that membrane with 15% Fe nanoparticles had the best ability for transferring the generated protons from anode to cathode compartment. Coating the indicated concentration of Fe nanoparticle on synthesized membrane increases the maximum power more than 29% in comparison with Nafion 117 as PEM in fabricated MFC. 4. Conclusions

10 Membrane 1 Membrane 2 Membrane 3 Membrane 4

5

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160

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Current (mA.m ) Fig. 6. Generated voltage (a) and power density (b) as function of current density at various synthesized membranes.

the initial voltage for all studied PEM was nearly the same value. The initial voltage gradually increased and reached the steady state condition for each PEM. Membrane 4 reached at steady state condition before the other PEMs, but membrane 3 had the highest OCP. At steady state condition, the maximum potential was obtained with membrane 3 and it was 628 mV.

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Voltage (mV)

Type of membrane

a

200

b

705

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400 Membrane 1 Membrane 2 Membrane 3 Membrane 4 Nafion 117

200

0

20

40

60

80

Time (h) Fig. 7. Open circuit voltage produced in a dual chamber MFC using different kinds of PEM.

Renewable source of energy and new method for production of bioelectricity has been evaluated. S. cerevisiae had good ability for growing under anaerobic condition and production of bioelectricity in MFC. In this study, Fe3 O4 nanoparticles were prepared by co precipitation of iron chloride salts with sodium hydroxide. Four different Fe3 O4 /PES membranes with different percentages of Fe3 O4 nanoparticles (5 wt%, 10 wt%, 15 wt%, and 20 wt%) were prepared by phase inversion method. These fabricated PEM and Nafion 117 were tested in MFC. Membrane 3 with 15 wt% of Fe3 O4 nanoparticles produced maximum current and power. The highest power and current density obtained were 20 mW m−2 and 148 mA m−2 , respectively. This amount of power was 29% more than what has been achieved with Nafion as PEM in MFC. References [1] D. Lovley, Curr. Opin. Biotechnol. 17 (2006) 327. [2] D. Strik, H. Terlouw, H. Hamelers, C. Buisman, Appl. Microbiol. Biotechnol. 81 (2008) 659. [3] C. Picioreanu, K. Katuri, M. van Loosdrecht, I. Head, K. Scott, J. Appl. Electrochem. 40 (2010) 151. [4] H. Liu, R. Ramnarayanan, B. Logan, Environ. Sci. Technol. 38 (2004) 2281. [5] L. Huang, J. Chen, X. Quan, F. Yang, Bioprocess. Biosystems Eng. 33 (2010) 937. [6] D. Pant, G. Van Bogaert, M. De Smet, L. Diels, K. Vanbroekhoven, Electrochim. Acta 55 (2010) 7710. [7] F. Zhang, T. Saito, S. Cheng, M. Hickner, B. Logan, Environ. Sci. Technol. 44 (2010) 1490. [8] X. Zhang, S. Cheng, X. Huang, B. Logan, Biosens. Bioelectron. 15 (2010) 1825. [9] L. Zhuang, C. Feng, S. Zhou, Y. Li, Y. Wang, Process Biochem. 45 (2010) 929. [10] B. Logan, B. Hamelers, R. Rozendal, U. Schröder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Environ. Sci. Technol. 40 (2006) 5181. [11] Z. He, L. Angenent, Electroanalysis 18 (2006) 2009. [12] Y. Feng, Q. Yang, X. Wang, B. Logan, J. Power Sources 195 (2010) 1841. [13] Z. Liu, J. Liu, S. Zhang, Z. Su, Biochem. Eng. J. 45 (2009) 185. [14] H. Liu, B. Logan, Environ. Sci. Technol. 38 (2004) 4040. [15] B. Min, S. Cheng, B. Logan, Water Res. 39 (2005) 1675. [16] Q. Deng, X. Li, J. Zuo, A. Ling, B. Logan, J. Power Sources 195 (2010) 1130. [17] H. Liu, S. Cheng, B. Logan, Environ. Sci. Technol. 39 (2005) 658. [18] S. Oh, B. Logan, Appl. Microbiol. Biotechnol. 70 (2006) 162. [19] C. Sund, S. McMasters, S. Crittenden, L. Harrell, J. Sumner, Appl. Microbiol. Biotechnol. 76 (2007) 561. [20] R. Rozendal, T. Sleutels, H. Hamelers, C. Buisman, Water Sci. Technol. 57 (2008) 1757. [21] Y. Zuo, S. Cheng, B. Logan, Environ. Sci. Technol. 42 (2008) 6967. [22] J. Sun, Y. Hu, Z. Bi, Y. Cao, J. Power Sources 187 (2009) 471. [23] P. Jana, M. Behera, M. Ghangrekar, Int. J. Hydrogen Energy 35 (2010) 5681.

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