Bioelectrochemistry 92 (2013) 22–26
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Air-cathode preparation with activated carbon as catalyst, PTFE as binder and nickel foam as current collector for microbial fuel cells Shaoan Cheng ⁎, Jiancheng Wu State Key Laboratory of Clean Energy, Department of Energy Engineering, Zhejiang University, Hangzhou 310027, PR China
a r t i c l e
i n f o
Article history: Received 8 December 2012 Received in revised form 5 March 2013 Accepted 6 March 2013 Available online 13 March 2013 Keywords: Microbial fuel cell Nickel foam Activated carbon Air cathode Bioenergy
a b s t r a c t
A cathode is a critical factor that limits the practical application of microbial fuel cells (MFCs) in terms of cost and power generation. To develop a cost-effective cathode, we investigate a cathode preparation technique using nickel foam as a current collector, activated carbon as a catalyst and PTFE as a binder. The effects of the type and loading of conductive carbon, the type and loading of activated carbon, and PTFE loading on cathode catho de performance performance are system systematica atically lly studied by linea linearr sweep voltammetry voltammetry (LSV). The nickel foam catho cathode de MFC produces a power density of 1190 ± 50 mW m − 2, comparable with 1320 mW m− 2 from a typical carbon cloth Pt cathode MFC. However, the cost of a nickel foam activated carbon cathode is 1/30 of that of carbon cloth Pt cathode. The results indicate that a nickel foam cathode could be used in scaling up the MFC system. © 2013 Elsevier B.V. All rights reserved.
1. Introduction
As a poten potential tialtech technolog nology y for rene renewabl wable e ener energy gy produ production ction,, mic microbi robial al fuel ce fuel cells(MFC lls(MFC)) ha have ve rec receiv eived ed gre great at att attent entionin ionin re recen centt yea years rs [1–3] 3].. MF MFCs Cs could cou ld pro produc duce e a cer certai tain n am amoun ountt of ele electr ctric icity ity wh while ile tre treati ating ng was wastew tewate ater. r. It could be considered a major technology for energy recovery from wastewater in the future. High cost and low power output are two major hurdles of MFC development on a large scale. The cathode accounts for the main part of these problems due to the high cost of its components and slow kinetics of oxygen reduction at neutral medium. In order to overcome these bottlenecks researchers have investigated alternative catalysts to Pt [4,5] Pt [4,5],, different oxidants as electron acceptors [6 acceptors [6–8] 8],, different pHs [9],, different binders [10] [9] [10] and and the structure of the diffusion layer [6] [6].. cobaltt tetram cobal tetramethoxy ethoxypheny phenyll porphy porphyrin rin (CoTMP (CoTMPP), P), iron phthal phthalocyani ocyanin n (FePC) and manganese dioxide (MnO2) can serve as alternative catalysts to Pt [10 Pt [10–13] 13].. Inexpensive PTFE solutions can be used in place of a Na�on solution as a catalyst binder. Recently, a non-metal cathode made with activated carbon and PTFE showed a comparable performance with a Pt cathode, but with a much lower cost [14] cost [14].. There are also a few works presented on using a hydrophilic ionomer and an anion ani on exc exchan hange ge ion ionome omerr as the bin binder der for for an oxy oxygen gen redu reducti ction on cata catalys lystt in an MFC, showing an improved activity for catalysts than using PTFE [15,16].. The cathode contributes a high percentage of internal resis[15,16] tance of MFC [17] MFC [17].. In addition to the catalyst and binder, the cathode current curre nt collector also plays an import important ant role in catho cathode de performance performance and cost. The most common current collector material is carbon cloth, ⁎
Corresponding author. Tel.: +86 571 87952038; fax: +86 571 87951616. E-mail address:
[email protected] [email protected] (S. (S. Cheng).
1567-5394/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bioelechem.2013.03.001
which is expensive ($1000 m − 2). A stainless steel mesh or a nickel mesh have been studied as current collector in MFC, showing high power density and low cost [14,18] cost [14,18].. However, in these studies, the current collector had a two-dimensional structure, on which the catalyst layer was coated or pressed. The formed cathode structure could cause increased ohmic resistance, especially for a cathode made of PTFE and activated carbon (AC), because they have no or low conductivity [14] [14].. Thus, Thu s, the ca catho thode de pe perfo rform rmanc ance e is sti still ll thelimi thelimiti ting ng fa fact ctor or of MF MFC C dev devel elopopment [17,19] ment [17,19].. Nickel foam has a three-dimensional structure with high porosity and high conductivity. The porous framework of nickel foam is � lled with catalyst paste such as the mixture of activated carbon and PTFE binder, resulting in a decrease in ohmic resistance and an increase in cataly cat alyst st util utiliza ization tion.. Nic Nickel kel foam has a good corr corrosi osion on res resist istanc ance e in alk alkaaline and neutral medium, but corrodes in acid media. Nickel foam is widely used as a current collector in alkaline batteries [20] [20].. Recently, Liu et al. reported an air-cathode made of nickel foam, Pt catalyst and Na�on bin binder der [21] [21].. In th thei eirr st stud udy, y, Na�on so solut lutio ion n wa wass us used ed as a ca cata taly lyst st binder, which exposed the nickel foam to an acidic environment and caused it to corrode. In order to prevent corrosion of nickel foam in theacid env enviro ironme nment nt (Na�on sol solutio ution n as thecataly thecatalyst st bin binder der), ), the nic nicke kell foam was coated with with PTFE (30 wt.% solution) [21] [21].. However, the PTFE coated coa ted on the sur surfac face e of thenicke thenickell foamincre foamincrease ased d the ele electr ctric ic res resis istanc tance e betwee bet ween n the met metal al mat matrix rix cur curren rentt col collec lector tor and the cata catalys lystt lay layer er due to the electrically non-conductive property of PTFE. The power density with PTFE-coated nickel foam cathode was not improved compared with the carbon cloth cathode [21] cathode [21].. In this study, we report a new air-cathode made of nickel foam as a cur curre rent nt col collec lector tor,, act activa ivated ted car carbon bon as cat cataly alyst st and PTF PTFE E as a dif diffus fusion ion layer and catalyst binder. The preparation technology was optimized
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through the study of catalyst type and loading, conductive addition material and PTFE loading. The performance of nickel foam air-cathode was evaluated using linear sweep voltammetry (LSV). 2. Materials and methods 2.1. Preparation of cathode
The nickel foam cathodes were composed of the nickel foam current collector, the conductive carbon base diffusion layer, the PTFE diffusion layer and the catalyst layer. Nickel foam was used as supplied (Changle New Technology Electronics Co., Ltd, China). The conductive carbon diffusion layers were made by applying a mixture of carbon powder (6 mg cm − 2) and PTFE (15 mg cm − 2) onto one side of the nickel foam. The PTFE diffusion layer was formed by coating 60% the PTFE solution (Yilida Power Source Co., Ltd, China) on the surface of the carbon base layer, which was subsequently heated for 30 min at 370 °C as previously described [22]. The conductive carbon diffusion layer and the PTFE diffusion layer together play a part in preventing water leakage, salting-out and controlling oxygen diffusion. Unless otherwise stated, the carbon base diffusion layer was made of a mixture of F900-CC (Tianjin Yiborui Carbon Co. Ltd, China) 6 mg cm− 2, PTFE 15 mg cm− 2 and Isopropyl alcohol 84 μ L cm− 2, and four PTFE diffusion layers were applied onto one side of the nickel foam as previously described [23]. The catalyst layer was prepared by pasting a mixture of activated carbon, conductive carbon, PTFE and isopropyl alcohol onto the other side of the nickel foam, which was subsequently heated at 370 °C for 30 min. Unless otherwise stated, the catalyst layer was prepared with activated carbon 20 mg cm− 2, and conductive carbon, PTFE, isopropyl alcohol (per cm2 of nickel foam) 0.8 mg, 6 mg, 40 μ L, respectively. Finally, the formed cathode was rolled to a thickness of 1 mm using a roller (DYG-703, Dali Electric Co., Ltd, China). Two kinds of activated carbon (having a high porous structure, but a low conductivity), supercapacitor activated carbon (S-AC, Shanghai Heda Carbon Materials Co., Ltd, China) and Nano activated carbon (Nano-AC, Shanghai Hainuo Carbon Co., Ltd, China), were used as catalysts in the study. S-AC was used to investigate the effect of catalyst loadingon theperformance of cathode,and its loadings were varied at 10, 15 and 20 mg cm −2. Conductive carbon (having a high conductivity, but a low porous structure) was mixed with a catalyst to improve the conductivity of the catalyst layer. The conductive carbons tested are Nano conductive carbon (Nano-CC, Shanghai Hainuo Carbon Co., Ltd, China), 3000 mesh conductive carbon (3000-CC, Shanghai Hainuo Carbon Co., Ltd, China), XC-72 (XC-72, Wuxi Sophie Roland International Trading Co. Ltd, China), and F900 carbon (F900-CC). For the comparison study, air-cathodes using carbon cloth (30% wet-proofed, E-TEK) or stainless steel (#30 mesh, 0.30 mm wire diameter)as current collector were prepared with thesame preparation method as described above. 2.2. MFC setup and operation
Single-chambered air cathode cubic-shaped MFCs (26 mL liquid volume, 4 cm anode chamber) were constructed as previously reported [24] and were used to investigate the power density at various cathodes using carbon � ber brush anodes (25 mm diameter, 25 mm length). The anodes were taken from the MFC reactors that were inoculated with the primary clari �er over�ow of the local wastewater treatment plant and operated using acetate (1.0 g L − 1) as fuel for over half a year. The MFCs were operated using 1.0 g L − 1 sodium acetate as fuel in 50 mM phosphate buffer solution (PBS, pH 7.0) containing (per liter deionized water): KCl, 0.13 g L − 1; NaH2PO4 · 2H2O, 2.75 g L − 1; Na2HPO4 · 12H 2O, 11.466 g L − 1; NH4Cl, 0.31 g L − 1, and metal (12.5 mL L − 1) and vitamins (5 mL L − 1) [25]. The chamber was re�lled when the voltage decreased to less than 50 mV. The polarization curves and the power densities are measured after MFCs were
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operated with 1000 Ω resistor for 40 re�lled times (around 60 days). Each MFC test was conducted in triplicate. 2.3. Analysis
Cathode performance was evaluated with LSV conducted by a potentiostat (CHI660D, Shanghai Chenhua Instrument Co. Ltd) in a three-electrode-setup electrochemical cell. The electrochemical cell was built as a 2 cm-cubic single-chamber reactor [15]. A Pt plate (6 cm2 projected surface area) was used as counter electrode (anode). The studied cathode (7 cm2 projected surface area) was used as working electrode(set up inthe sameway as that ina MFC). AnAg/AgCl electrode (0.201 vs SHE) was used as reference electrode located close to the working electrode.All potentials refer to theAg/AgCl referenceelectrode in the paper. LSV was typically conducted in 50 mM PBS with a potential range from 0.2 to − 0.2 V at the scan rate of 1 mV s − 1. Because the working potential of an air cathode in the MFC was mostly in the region from 0.05 to − 0.2 V, the currents that responded in this cathodepotentialregion in LSVwere typically used to evaluate thecathode performance in this paper. Every designed cathode was tested in triplicate. Each LSV test of cathode was conducted in three scans. The data of current, potential and power density are reported in average. All experiments were conducted in a 30 °C temperature controlled room. Voltage (V) across an external resistance (1000 Ω , unless otherwise noted) was measured using a multimeter with a data acquisition system (2700, Keithley, U.S.) and used to calculate thepower (P) according to P = I V. Power density was then calculated usingthe power normalized by the projected surface area of the cathode. A polarization curve was measured by varying the external resistance from 1000 to 50 Ω . 3. Results and discussion 3.1. The effect of preparation conditions on the performance of nickel foam cathode
The current of a cathode with Nano-AC (Nano activated carbon) is signi�cantly lower than that of a cathode with S-AC (supercapacitor activated carbon) in the potential region from 0.0 to − 0.2 V (Fig. 1-A). The Nano-AC cathode has − 7.7 ± 0.2 mA at − 0.2 V, while the S-AC has − 8.9 ± 0.5 mA, which is 13% higher. Nano-AC has a particle size of 200 nm and a speci�c surface area of 1350 m 2 g − 1, while S-AC has a particle size of 5 μ m and a speci�c surface area of 2000 ± 100 m 2 g − 1. These results indicate that the high surface area of activated carbon is the critical factor in cathode performance, not the particle size. Increasing catalyst loading has a signi �cant effect on the cathode performance in the studied potential region ( Fig. 1-B). For example, the reduction current increases from − 0.4 ± 0.2 to − 1.1 ± 0.2 mA at 0.1 V, and from − 6.6 ± 0.2 to − 7.3 ± 0.3 mA at − 0.2 V when the catalyst loading increases from 10 to 15 mg cm − 2. Further increasing catalyst loading from 15 to 20 increases reduction current in the low potential region below 0.05 V, but has no signi�cant effect on reduction current in the high potential region over 0.05 V. The highest reduction current with the catalyst loading of 20 mg cm − 2 at − 0.2 V is − 8.0 ± 0.4 mA, which is 24% higher than a cathode with a catalyst load of 10 mg cm − 2. These results indicate that a high catalyst loading has more contribution to performance improvement in the low potential region (high reduction current). 3000-CC(3000 mesh conductive carbon)and F900-CC (F900 carbon) show a slightly better performance, with a current of − 8.0 ± 0.2 mA and − 7.8 ± 0.1 mA at − 0.2 V, respectively (Fig. 1-C). Nano-CC (Nano conductive carbon) shows a lower performance with current of − 7.5 ± 0.2 mA, while XC-72 (XC-72 carbon)shows the lowest current of − 6.8 ± 0.1 mA. F900-CC should be the best choice of conductive carbon because it costs far less than the others.
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A
by the decrease in ohmic resistance of the catalyst layer as the PTFE loading decreases. However, PTFE loading cannot be further decreased below 0.3 mg PTFE per mg S-AC, at which point the catalyst powder drops off the cathode surface after it dries.
2 0 -2
A m -4 / I
3.2. A comparison of nickel foam cathode with carbon cloth cathode and stainless steel cathode
-6 Nano-AC
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10 15 20
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LSV (linear sweep voltammetry) studies show that a nickel foam activated carbon cathode has a signi�cantly higher current than a carbon cloth activated carbon cathode and a stainless steel activated carbon cathode (Fig. 2A). The current of nickel foam cathode at − 0.2 V is − 8.4 ± 0.4 mA, which is 11% higher than that of carbon cloth cathode (− 7.5 ± 0.2 mA) and 28% higher than that of stainless steel cathode ( − 6.59 ± 0.2 mA). In the MFC studies, the nickel foam cathode MFC (NF) produces a maximum power density of 1190 ± 50 mW m − 2, while a MFC with a carbon cloth cathode (CC) has a 22% lower power density with 928 ± 37 mW m − 2 (Fig. 2B).
2 0 0.2
E/V (vs. Ag/AgCl)
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0.7 0.3 -0.2
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E/V (vs. Ag/AgCl) Fig. 1. The LSV of cathodes with: (A) Nano activated carbon (Nano-AC) and super capacitor activated carbon (S-AC); (B) different loading of activated carbon catalyst, numbers stand for the loading of 10 mg cm− 2, 15 mg cm − 2 and 20 mg cm − 2, respectively; (C) different conductive carbons in the catalyst layer: 3000 mesh conductive carbon; nano conductive carbon; XC-72; F900 carbon; (D) different PTFE loadings, the numbers show the PTFE loading of 0.3, 0.5 and 0.7 mg PTFE per mg-AC.
Decreasing PTFE (polytetra�uoroethylene) in the catalyst layer results in an increase in reduction current at − 0.2 V (Fig. 1-D). The current is − 7.8 ± 0.2 mA at the PTFE loading of 0.7 mg PTFE per mg-AC. When the PTFE loading decreases to 0.3 mg PTFE per mg S-AC, the current increases by 12% to − 8.8 ± 0.3 mA. This increase is caused
Fig. 2. A comparison of the nickel foam cathode, carbon cloth cathode and stainless steel cathode. (A) LSV. (B) Power density. (C) Electrode polarization. NF: nickel foam cathode; CC: carbon cloth cathode; SS: stainless steel cathode; Ea: anode potential; Ec: cathode potential.
S. Cheng, J. Wu / Bioelectrochemistry 92 (2013) 22– 26
The MFC with a stainless steel cathode (SS) has the lowest power density with 814 ± 38 mW m − 2. The polarization curves show that all the anode potentials are similar for all three MFCs, but the cathode performances are much different with an increasing order: the nickel foam cathode > carbon cloth cathode > stainless steel cathode (Fig. 2C), which is consistent with the results of the LSV studies. The thicknesses of nickel foam, carbon cloth and stainless steel are 1, 0.6 and 0.3 mm, respectively. Nickel foam has a three-dimensional and porous structure which allows the catalyst to � ll and distribute into its porous frame, resulting in a low ohmic resistance and high performance of the cathode. The internal resistance of the nickel foam cathode measured from polarization curves is 85 Ω , which is 22% lower than that of the carbon cloth cathode (109 Ω ) and 26% lower than that of the stainless steel cathode (115 Ω ). Although the high conductivity of nickel foam may partially contribute to increasing the cathode performance, the result that the carbon cloth with low conductivity performs better than the stainless steel with high conductivity indicates that the structure (the thickness of porous material) of the current collector is more important for increasing the cathode performance, and thus the power density of the MFC. The power density achieved here with nickel foam is comparable with that produced with the Pt-carbon cloth cathode under the same condition (1320 mW m − 2) [26]. However, the cost of a nickel foam activated carbon cathode is only $50 m − 2, which is 1/30 of that of a Pt carbon cloth cathode ($1500 m− 2). These results are comparable to that reported with the cathode made with activated carbon as a catalyst, PTFE as a binder and nickel mesh as a current collector [14]. The nickel mesh has a two-dimensional structure which could result in a high ohmic resistance of cathode when the electrode was scaled up, while the nickel foam activated carbon cathode could keep a low resistance. The performance of the nickel foam activated carbon cathode is � in uenced by the type and amount of activated carbon, the type of conductive carbon, and PTFE loading. The best performance is achieved with the cathode that contained (1) the catalyst layer prepared with 20 mg cm− 2 S-AC, 6 mg cm− 2 PTFE, 0.8 mg cm− 2 F900-CC and 40 μ L cm − 2 isopropyl alcohol; (2) the carbon base diffusion layer prepared with F900-CC 6 mg cm− 2, PTFE 15 mg cm− 2 and isopropyl alcohol 84 μ L cm − 2; (3) the diffusion layer prepared with 4 PTFE coatings. The most important factors for improving cathode performance are the structure of the current collector and the surface characteristic of the catalyst. The activated carbons used here are commercial products that are mostly used as the active materials in battery and capacitor. Their surface characteristics well match the requirement of a battery or a capacitor, but may not well match the requirement of the MFC cathode to the oxygen reduction reaction. The surface characteristics of activated carbon could be changed by treating activated carbon at a high temperature [27] or in acid solution [28]. A further increase in performance of thenickel foam activated carboncathode could be achieved by modifying the surfacecharacteristics of activated carbon withspecial treatment technology. The nickel foam corrodes in acid environments, but has good corrosion resistance in neutral and alkaline media. Liu et al. [21] have reported that a nickel foam cathode is seriously corroded during the operation of a MFC when a bare nickel foam is used as a cathode current collector with a Na �on solution as a catalyst binder. However, the corrosion of nickel foam is signi�cantly decreased by coating PTFE on the surface of the nickel foam. The corrosion is likely due to the use of Na�on as a catalyst binder resulting in nickel foam being in an acid environment. We do not measure corrosion of our PTFE bonded nickel foam cathode during the operation of MFC, but it is likely to be very minor, based on the very stable performance of the MFC during 6 months of operation. Increasing PTFE loading in the catalyst layer can prevent the corrosion of nickel foam, but increasing PTFE loading resulted in a decrease in cathode performance (Fig. 1-D). However, we recently found that the performance of a cathode with a high PTFE
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loading in the catalyst layer can be signi �cantly improved by treating the cathode with a solution, such as isopropyl alcohol. Details about this treatment technology for treating cathode with chemicals will be reported in the near future. 4. Conclusion
In this paper, a nickel foam cathode is prepared with nickel foam as a current collector, activated carbon as a catalyst and PTFE as a binder. The optimal conditions for the preparation of a nickel foam cathode are: the catalyst layer prepared with 20 mg cm− 2 S-AC, 6 mg cm− 2 PTFE, 0.8 mg cm − 2 F900-CC and 40 μ L cm− 2 isopropyl alcohol; the carbon base diffusion layer prepared with F900-CC 6 mg cm − 2, PTFE 15 mg cm − 2 and isopropyl alcohol 84 μ L cm − 2; and the PTFE diffusion layer prepared with 4 PTFE coatings. Compared to the carbon cloth cathode and stainless steel cathode, the nickel foam cathode shows a higher performance and lower cost. Power production is 1190 ± 50 mW m− 2 with nickel foam activated carbon cathode, comparable to 1320 mW m− 2 with typical carbon cloth Pt cathode. However, the cost of nickel foam activated carbon cathode is 1/30 of that of carbon cloth Pt cathode. These results show that the nickel foam cathode is feasible for the MFC scale-up. Acknowledgments
This research was supported by the National Natural Science Foundation of China (no. 21073163), the National High Technology Research and Development Program of China (863 Program) (no. 2011AA060907), and the Zhejiang Provincial Natural Science Foundation, China (no. Z4110186). References [1] H. Liu, R. Ramnarayanan, B.E. Logan, Production of electricity during wastewater treatment using a single chamber microbial fuel cell, Environ. Sci. Technol. 38 (2004) 2281 –2285. [2] B.E. Logan, Simultaneous wastewater treatment and biological electricity generation, Water Sci. Technol. 52 (2005) 31 –37. [3] F. Zhao, N. Rahunen, J.R. Varcoe, A.J. Roberts, C. Avignone-Rossa, A.E. Thumser, R.C.T. Slade, Factors affecting the performance of microbial fuel cells for sulfur pollutants removal, Biosens. Bioelectron. 24 (2009) 1931 –1936. [4] B.E. Logan, B. Hamelers, R. Rozendal, U. Schroder, J. Keller, S. Freguia, P. Aelterman, W.Verstraete,K. Rabaey, Microbial fuelcells:methodology andtechnology, Environ. Sci. Technol. 40 (2006) 5181 –5192. [5] S. Cheng, B.E. Logan, Ammonia treatment of carbon cloth anodes to enhance power generation of microbial fuel cells, Electrochem. Commun. 9 (2007) 492–496. [6] U. Schröder, J. Nießen, F. Scholz, A generation of microbial fuel cells with current outputs boosted by more than one order of magnitude, Angew. Chem. Int. Ed. 42 (2003) 2880 –2883. [7] K. Rabaey, N. Boon, S.D. Siciliano, M. Verhaege, W. Verstraete, Biofuel cells select for microbial consortia that self-mediate electron transfer, Appl. Environ. Microbiol. 70 (2004) 5373–5382. [8] S.E. Oh, B. Min, B.E. Logan, Cathode performance as a factor in electricity generation in microbial fuel cells, Environ. Sci. Technol. 38 (2004) 4900–4904. [9] L.Zhuang,S. Zhou, Y. Li,Y. Yuan, Enhancedperformanceof air-cathode two-chamber microbial fuel cells with high pH-anode and low-pH cathode, Bioresour. Technol. 101 (2010) 3514 –3519. [10] S. Cheng, H. Liu, B.E. Logan, Power densities using different cathode catalysts (Pt and CoTMMP) and polymer binders (Na �on and PTFE) in single chamber microbial fuel cells, Environ. Sci. Technol. 40 (2006) 364–369. [11] F. Zhao, F. Harnisch, U. Schröder, F. Scholz, P. Bogdanoff, I. Herrmann, Application of pyrolysed iron(II) phthalocyanine and CoTMPP basedoxygen reduction catalystsas cathode materialsin microbialfuel cells,Electrochem.Commun.7 (2005) 1405–1410. [12] H. Yu, S. Cheng, K. Scott, B.E. Logan, Microbial fuel cell performance with non-Pt cathode catalysts, J. Power Sources 171 (2007) 275 –281. [13] L. Zhang, C. Liu, L. Zhuang, W. Li, S. Zhou, J. Zhang, Manganese dioxide as an alternative cathodic catalyst to platinum in microbial fuel cells, Biosens. Bioelectron. 24 (2009) 2825 –2829. [14] F. Zhang, S. Cheng, D. Pant, G.V. Bogaert, B.E. Logan, Power generation using an activated carbon and metal mesh cathode in a microbial fuel cell, Electrochem. Commun. 11 (2009) 2177 –2179. [15] T. Saito, T.H.Roberts,T.E. Long, B.E.Logan,M.A. Hickner, Neutralhydrophilic cathode catalyst binders for microbial fuel cells, Energy Environ. Sci. 4 (2011) 928–934. [16] E.H. Yu, R. Burkitt, X. Wang, K. Scott, Application of anion exchange ionomer for oxygen reduction catalysts in microbial fuel cells, Electrochem. Commun. 21 (2012) 30–35.
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