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Nano-Enhanced
Microbial Electrochemical Cells
Xing Xie, Craig S. Criddle, Yi Cui
Stanford University
Nov. 5, 2013
SNO Conference 2013
Microbial Electrochemical Cells (MECs)
• Energy: organic matter electricity
• Electrons: microorganisms electrode
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Three pathways for extracellular electron transfer
1. Direct membrane contact
2. Electron mediators
3. Microbial nanowires
(Logan, Nat Rev Microbiol, 2009; Lovley, Nat Rev Microbiol, 2006)
More efficient
electron transfer
Microbial Bio-Electrodes
• Conductive
• Stable (chemical & bio)
• Biocompatible
• Macroscale porous structure
• Affinitive electrode surface
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More microbes for
electron transfer
Carbon Nanotube (CNT)-Textile Synthesis
• A simple and scalable process
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+ water + surfactantsonication
CNT inkCNT powder
dry
Hierarchical Structure of CNT-Textile
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Macroscale
porous
textile
Microscale
porous
CNT
coating
~200 nm
• Conductive
– CNTs: 2000~4000 S/cm
– CNT-textile fiber (as a homogeneous solid material): ~50 S/cm
• Diameter of CNT-textile fiber: ~20 μm
• Thickness of CNT coating: 200 nm
– CNT-textile sheet (2 mm thick): ~1 Ω/sq
• Stable
– Mechanical force
– Wash
– Heat
– Acid
– Base
Physical and Mechanical Properties of CNT-Textile
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(Hu, Nano Lett, 2010)
MFC Experimental Setup
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• H-shaped classic reactor
• Anode
– Carbon cloth vs. CNT-textile
• Cathode
– Pt on Carbon cloth
• Separator
– Anion exchange membrane
• Feeding
– Glucose (1 g/L)
• Inoculum (bacteria source)
– Wastewater from Palo Alto Regional Water Quality Control Plant
500 μm
Carbon cloth
Biocompatibility
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Evidence of colonization on CNT surface in MFCs
• Scanning Electron Microscope (SEM)
Macroscale Porous for Internal Colonization
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• Cross-section of the anodes after 50 days of operation
Carbon cloth vs. CNT-textile
Biofilm-electrode interfacial area increased by ~10 times
Biofilm
Graphite fibers
Affinitive Electrode Surface
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• Rough and soft
1 Direct membrane contact
• Microscale porous
2 Electron mediators
3 Microbial nanowires
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Carbon cloth vs. CNT-textile
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Affinitive Surface for Microbial Attachment
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• Mechanical binding test
Carbon cloth vs. CNT-textile
Original:
After 5 mins
sonication and
10 s vortex
agitation:
Affinitive Surface for Electron Transfer
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• Electrochemical impedance spectroscopy (EIS)
Carbon cloth
~30 ΩCNT-textile
~300 Ω
vs.
Diameter of the semicircle Electron transfer resistance
Resistance Efficiency
• Linear staircase voltammetry (LSV)
Maximum Current Output
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2.6 times
CNT-textile (7.2 A/m2)
Carbon cloth (2.8 A/m2)
vs.
Internal colonization
Affinitive electrode surface
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Modification 1
CNT-textile CNT-sponge
Random pore size Uniform &Tunable
Individual fibers 3D frameworkvs.
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Modification 2
CNT-sponge Graphene-sponge
Cost:
100 vs. 1
More efficient
electron transfer
Summary
• Conductive
• Stable (chemical & bio)
• Biocompatible
• Macroscale porous structure
• Affinitive electrode surface
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More microbes for
electron transfer
Acknowledgement
• Collaborators
– Prof. Zhenan Bao
– Liangbing, Mauro, George, Guihua, Yuan, James, Meng, Nian, Desheng
• Funding
– Stanford SOE/CEE Fellowship - Larry C. K. Yung Fellowship
– Stanford Graduate Fellowship - David and Lucile Packard Foundation Fellowship
– Stanford Interdisciplinary Graduate Fellowship - Fan Fellowship (A/P Scholars)
• SNO Student Award
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Thank you!
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