Microbial Fuel Cell Construction
Clear 70 mL polystyrene sample bottles (pottles) with opaque polyethylene caps (Labserv, New Zealand, part number LBS32002NX) were used for the construction of the pMFC’s (Fig. 1A) similar to those described by Zou and colleagues (Zou et al. 2009). Carbon fibre threads (approximately 2 mm in width) were extracted from a carbon fibre cloth (200 g plain woven cloth containing 3000 carbon filaments per tow (thread), part number CC200P-1250, New Zealand Composites Ltd) and were used as electrical leads. A hole was melted at the bottom of the pottle with a needle that had been heated in a flame and a single 23 cm thread inserted through the hole and looped around the inner edge of the pottle. The bottom of the anode chamber was coated with a carbon paint using a variety of methods. These were assessed for smoothness and resilency, resulting in the following easy method utilising a cheap commercially available carbon powder in a non-toxic binder. Polypyrrole (90 mg, undoped 20% wt on carbon black, Sigma #577065) and ethanol (2.7 ml of 100%) were added to 9 ml of Wire GlueTM (Anders Products Division of Idolon Technologies, purchased from Jaycar electronics supply store) and mixed with a 1 ml pipette tip with the end 2 mm removed from the end, to aliquot 650 µl of the solution per anode chamber (surface area of 14 cm2 ). The mixture was spread across the bottom ensuring that the carbon fibre lead was pushed to the edges of the pottle. The chambers were air dried at room temperature for 48 h. The hole where the carbon fibre leads enters the pottle were then glued with super glue and the chambers washed three times for 30 mins with deionised water followed by a 30 min wash with MLA media on a rocking table.
Cathode assembly insert and reference electrode
The cathode assembly insert (CAI, Fig. 1) was fabricated from a 29 mm outside diameter tube of polycarbonate that had a recess machined on one end to fit a titanium ring (29 mm outside diameter, 27.5 mm internal diameter, 1 mm thick; Artifact.co.nz Dunedin, New Zealand). A 2 mm carbon fibre lead (as described above) was wrapped around the titanium ring as a charge collector. A stack of cathode exchange membrane (Ultrex CMI-7000S, Membranes International Inc., Ringwood, New Jersey, USA) and carbon fibre cloth containing 10% platinum (Part# EC1019, Fuel Cell Earth, LLC, Stoneham, Massachusetts, USA) were held in place by a plastic cap machined out of ABS plastic or polyethylene that was pressed over the end of the polycarbonate tube. A hole was cut in the lid of the anode chamber to match the size of the cathode assembly insert, and for a Ag/AgCl reference electrode (part# MF-2052, BASi, West Lafayette, USA) used in some experiments, allowing the cathode to be placed at a set distance above the anode surface.
Zou Y, Pisciotta J, Billmyre RB, Baskakov IV (2009) Photosynthetic microbial fuel cells with positive light response. Biotechnol Bioeng 104:939-946