An aluminum can. I use a soda can.
A piece of sandpaper. I happen to have some sticky sandpaper for a sanding block. Very convenient. This is used to remove the surface treatments from the can. This actually may be optional. I will experiment and update the instructable appropriately.
A sponge. This will be cut to fit inside the battery. I used a cellulose sponge from a 6 pack my wife had under the sink. A natural sponge may be more conductive.
A charcoal briquet.
Several readers have suggested alternative, readily available carbon sources. The most scientific sites I've visited have recommended activated charcoal for the carbon electrode.
- Britta disposable filters
1 gallon plastic garbage bag
Rolling pin or short piece of pipe for crushing charcoal
Duck Tape - That's right its called Duck Tape, not Duct Tape.
Some copper wire or copper mesh. The effectiveness of this device is directly linked to connectivity between the copper drain and the carbon cathode. Also it is not possible to solder a lead to the aluminum.
I am using copper mesh and foil from K&S Metals to obtain connectivity. In the first release I tried a simple copper mesh/carbon combination that generates power but I am working on second generation and will update the instructable when it's available.