Running an MFC Experiment

This page is intended as a comprehensive guide to completing a microbial fuel cell setup and running an experiment from start to finish.

Creating a Testing Environment

Begin 1-2 weeks prior to experiment

Constructing Fuel Cell Components

Materials (per fuel cell)

• 4" Polycarbonate Square Tube, 2" Outer Diameter
• 6" x 6" Polycarbonate Sheet, 1/4" Thick
• 4 Steel Fully Threaded Stud, 1/4"-20 Thread, 6" Length
• 8 Zinc Alloy Wing Flange Nut, 1/4"-20 Screw Size, 1" Wing Spread
• 1" x 1" Nafion® membrane, 0.180mm thick
• 1" x 1" Carbon felt, 0.25" thick
• 1.5" x 1.5" E-TEK ELAT™ GDE (platinum on carbon)
• 2' Titanium Grade 2 Wire .046" Diameter
• Teflon Tape, 1/4" Width
• 5" x 2.5" Silicone Sheet
• Silicone Glue
• Spiral Point Tap 1/4"-28
• 8 Plastic Luer Lock Coupling Nylon, Female to Male Thread, 1/4"-28
• 8 Luer Lock Injection Ports

Procedure

1. Mill Polycarbonate
   • Cut polycarbonate sheet into 4 equal 3" x 3" pieces
   • Drill four 3/8" holes through each piece, 1 per corner, indented 5mm from both sides

1. • Cut polycarbonate tube into two equal 2" halves
   • Drill four 1/4" holes through each half in configuration shown

1. • Tap each hole with 1/4" -28 spiral tap

1. Glue Chambers (repeat for each half)
   • Center tube on endplate by marking plate with 'X' from corner to corner
   • Squirt 2mm thick line of silicone on edge of tube (edge furthest from holes)
   • Press tube firmly against marked location on endplate
   • Quickly spread excess silicone along edge
   • Let stand 24h to harden

1. Construct Gaskets
   • Cut silicone sheet into two equal 2.25" x 2.25" pieces
   • Cut out centered inner squares in each piece, 1.75" x 1.75"
   • Using inner squares, cut two 'O' rings, inner diameter 1/4", outer diameter 1/2"

1. Construct Electrodes
   • Cut titanium wire into one 8" piece and one 16" piece
   • Using pliers, shape anode and cathode as shown

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1. • Spear carbon felt with tip of anode titanium wire and wedge into frame
   • Weave platinum carbon cloth through cathode titanium wire

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1. Seal Injection Ports
   • Wrap threads of all eight Luer Lock screws with 1' of teflon tape in opposite direction of screwing
   • Screw Luer Locks into all tapped holes in both chambers

Setup of Measurement Device

Materials

• Keithley 2700 Digital Multimeter
• Keithley 7700 Multiplexer
• Small Breadboard
• Supply of insulted thin copper wire
• 470 Ohm resistors (one/fuel cell)

Procedure

1. Wire Multiplexer
   • Open multiplexer, note channels
   • Cut two wire 18" wire leads per fuel cell
   • Strip ends, place one wire in each screw terminal, screw tight
   • Tape paired wires (two are attached to each channel) near non-attached ends and label
   • Clamp wire bundles near back of device with provided plastic latch clamps
   • Close Multiplexer and slide into 2700 DMM

1. Create Resistor Array
   • Connect resistors across middle of breadboard (one per fuel cell)
   • Connect leads from multiplexer across resistors (one pair across each resistor)

Controlling the DMM with LabVIEW™

1. Initialize Multimeter
   • Attach 2700 to COM1 port of desktop computer w/ LabVIEW™
   • Download our LabVIEW™ source code MFCs.vi
   • Open Program in LabVIEW™, adjust block diagram as necessary

Experiment Preparation

Begin 1 day prior to experiment

Assembling Chambers

Procedure

1. Prepare Electrodes
   • Attach Luer Lock injection ports to all chamber screws
   • Poke tip of electrodes through designated ports from the inside

1. Align Chambers
   • Lay one chamber on a flat surface
   • Place silicone square ring on top edge of tube
   • Place polycarbonate square on silicone
   • Place silicone 'O' ring around central pore
   • Place Nafion membrane on top of 'O' ring
   • Sandwich membrane between second 'O' ring
   • Align second polycarbonate square on top of 'O' ring
   • Center second silicone square ring on polycarbonate square
   • Set second chamber on top of silicone, ensuring ports facing same direction as first chamber

1. Clamp Chambers
   • Move assembly into vice or clamp
   • Insert rods through holes in end plates and screw on wing nuts
   • Tighten evenly

Solutions Prep

1. Chamber media
   • 5.844 g/L 100mM NaCl
   • 15.1185 g/L 50mM PIPES (hydrogen)
   • 7.0 pH

1. Phosphate buffer
   • 2.918 g/L Monosodium phosphate, monohydrate
   • 4.095 g/L Disodium phosphate, anhydrous
   • 5.844 g/L 100mM NaCl
   • 7.0 pH

Gas Tubing Assembly

Materials

• 25' Silicone Soft Rubber Tubing, 3/32" ID, 7/32" OD, 1/16" Wall
• Tank of Compressed Nitrogen
• Gas Regulator
• Lab Supply of Air
• 4 Plastic Luer Lock Coupling Nylon, Male X Barb, for 3/32" Tube
• 4 Plastic Luer Lock Coupling Nylon, Female X Barb, for 3/32" Tube
• 3 Plastic Luer Lock Coupling Nylon, T junctions, for 3/32" Tube
• 2 Aspirator Flasks
• 2 Rubber Stoppers

Procedure

1. Make Flow Regulators
   • Insert nozzle of female Luer Lock into rubber stoppers (poke hole if necessary)
   • Cap aspirator flasks with rubber stoppers
   • Attach tubing from gas sources to each glass nozzle of aspirator flask

1. Make Manifolds

Growing Strains

Runtime

Begin 2 hours prior to experiment

Bacteria

Fuel Cells

Injections/Variables

Clean Up