Assembly of a Microbial Fuel Cell

Assembly of a Microbial Fuel Cell November 2005 Laboratory of Professor Derek Lovely, University of Massachusetts, Amherst, USA by Dr. Hanno Richter

The material described here is used for the construction of one fuel cell as shown in the picture on the front page. This type of fuel cell is generally used for investigations in our laboratory. Additional material is required to fill the fuel cell with media and for maintenance, and for monitoring the Voltage or Current, but it is not listed under Materials. The costs for one fuel cell can only roughly be estimated by the author. Most expensive are the glass chambers, because they are manufactured by the University glass shop. The total costs for one fuel cell of this type may be located around $ 2000. Fig. 1: Shematic drawing of our microbial Fuel Cell:

1) Materials needed: Fig 2: All components in one picture 1) Two glass vessels (Fig. 3) for the anode and the cathode chamber, manufactured by the glass shop of UMASS, Massachusetts. Each with a screw thread aperture, OD (Outside Diameter) = 50 mm, made of a PYREX glass bottle (Fisher scientific), a glass joint (tubing OD = 28 mm, ID (Inside Diameter) = 25 mm, ACE Glass Incorporated, Order no. 7646-12, and 3 apertures located sideways, OD of tubing = 15 mm, to be sealed by blue butyl stoppers and Aluminum seal. Fig. 3

2 ) One pinch clamp (Fig. 4) size 35, with screw lock, ACE Glass Incorporated, cat. no. 7669-14. Fig. 4 3) Two glass chimneys (Fig. 5), manufactured by the UMASS glass shop from anaerobic culture tubes (18 mm x150 mm, Belco). Fig. 5 4) Two orange rubber stoppers (Fig. 6), 29 mm diameter, Wheaton with 18 mm hole for the glass chimneys. Fig. 6

5) Six blue butyl stoppers (Fig. 7), Belco, Catalogue no. 2048-11800 for sealing the chambers sideways. Fig. 7 6) Six Aluminium seals (Fig. 8), Belco, no. 2048-11020. Fig. 8 7) Two Graphite electrodes (Fig. 9): 1 x 3 x 0.5 inches sticks of unpolished graphite grade g10, Graphite Engineering and sales, Greenville, Mich. And 2 threaded watertight connectors, type XSA-BC, Impulse, San Diego, Calif. In the picture they are already assembled to the electrode. Fig. 9

8) Two wires (Fig. 10), type RMA-FS, Impulse, San Diego, Calif. Fig. 10 9) One O-ring (Fig. 11), D = 35 mm, KALREZ, size -217, Ace Glass, cat. no. 7855-640 (provided together with glass joints). Fig. 11 10) Epoxy, type 730, and silver Epoxy (Epoxy Technology, Billerica, Mass.). 11) One Proton exchange membrane (PEM), 5 x 5 cm, Nafion 117, Electrosynthesis, Lancaster, N.Y. 12) Two small magnetic stir bars, which fit into the chambers.

Further laboratory equipment: 13) Magnetic stirrer(s) to stir both chambers. 14) Nitrogen gas, or N 2 /CO 2 mixture (80:20) when anode medium is carbonate buffered. 15) Sterile Filters or rubber-stoppered Syringes with glass wool and needles. 16) Gas-proof tubing. 17) Vacuum pump. 18) Sterile filters, 200 µm pore size. 19) Sterile needles and syringes.

2) How to assemble the Microbial Fuel Cell: 1) Preparation of the electrodes: - A hole (2 mm diameter, depth 2 cm) was drilled into the top of each graphite block. - Into the same spot a second hole was drilled with a 5 mm drill, but only 1 cm deep. - Silver epoxy was inserted into the hole, and the XSA-BC connector was screwed into the hole, until the silver-epoxy oozed out. - The surface around the connector-insertion was covered with the 730-type epoxy, to prevent watercontact with the metal and corrosion of the electrode which sticks in the graphite. - The electrodes were air dried for at least one day, better two. - The electrodes were then connected to the wires - Each chimney was inserted into an orange rubber stopper. - A hole was drilled into a blue butyl stopper, just big enough to let the wire through, but small enough to seal it very tightly against oxygen diffusion. If neccessary, Epoxy was used finally to seal the hole, after the wire was threaded through. The wires were lead through the chimney and the blue butyl stoppers. After making sure, that the position of the graphite electrode was at the level of the membrane, but high enough to allow the stir bar to rotate, the butyl stoppers could be sealed with Epoxy. 2) Preparation of the membrane: - A piece of 5 x 5 cm was cut out of the Nafion 117-membrane - The membrane-piece was put into a glass beaker filled with double destilled water. Care was taken to cover the piece completely with water. Once the membrane had contact with water, it should always stay in direct contact with water all over the surface, at least on one side! Otherwise it would dry and be destroyed. - The water was heated until boiling. - After boiling it was allowed to cool down to room temperature. 3) Assembling the Fuel Cell - The glass chambers were sealed with the blue butyl stoppers and crimped with the Aluminium seals. - One chamber was filled with double distilled water. - The O-ring was put on the joint of this chamber. - The membrane was taken out of the water-filled beaker and layed onto the O-ring. Care was taken not to loose contact with water.

- The other chamber was held with its junction against the membrane, and the both chambers were assembled by clamping them with the pinch clamp. - Each chamber was filled with approx. 150 ml double distilled water until the membrane was totally covered. - A stir bar was put into each chamber - Now both electrode/wire/rubberstopper/chimney constructions from step 1) were inserted into the fuel cell chambers and fixed with the red screw caps. - Into the top sideways aperture of each chamber a needle was inserted and covered with Aluminium foil, to allow pressure equilibration in the autoclave. - The Fuel cell was autoclaved for 20 min. - After cooling the fuel cell was ready for use. 4) Filling the Fuel Cell (additional material required) - One of the cambers was chosen as Anode chamber, the other one as cathode chamber. - The water was pumped out of the anode chamber with a vacuum pump. The pump was connected to the chamber by a tubing and a sterile needle, which was injected into the bottom sideways aperture. Simultaneously the chamber was flushed with filtersterilized anaerobic gas. The needle in the top sideways aperture allowed pressure equilibration and prevented bursting of the membrane. - After emptying, the anode chamber was filled with anaerobic medium. The anaerobic medium was stored in a PYREX bottle, which was sealed by a chimney/ruberstopper/screw cap construction identical to the construction of step 1), fig. 2, just without the electrode and the hole in the butyl stopper. The bottle was pressurized with sterile anaerobic gas, and connected to the top sideways aperture by a Brand Blood Collection Needle. The anode chamber was filled until the medium completely covered the graphite electrode (total volume 200-250 ml). - While still bubbling the anode chamber with sterile anaerobic gas, the cathode chamber was emptied using the vacuum pump. - Then the cathode chamber was filled with sterile aerobic medium or buffer, using the same method as for the anode chamber. Both chambers use the same medium and ph-value, with the exceptions that the cathode chamber can never be carbonate buffered, because of the constant bubbling with air, which removes CO 2 and causes a rise of the ph value. Instead, TRIS buffer at the same molarity as the anode buffer was used. If the anode chamber was carbonate buffered, it was bubbled with a sterile gas mixture of 80 % N 2 and 20 % CO 2. No carbon source or electron donor was added to the cathode chamber. - During operation, the cathode chamber was constantly bubbled with sterile air, and the anode chamber with sterile anaerobic gas. To avoid contamination, the gas outlets, too were provided with sterile filters or rubber stoppered syringes filled with glass wool (see fig. 1).