DIY Microbial Fuel Cell
"Non-catalyzed cathodic oxygen reduction at graphite granules in microbial fuel cells"
There are both one-cell and two-cell MFCs; the two-cell MFCs require some sort of salt bridge. The salt bridge can be as simple as a rope or fabric soaked in salt, or composed of a gel like agar or gelatin. In a one-cell MFC, the anode is placed deep in the anaerobic mud and the cathode is placed at the very surface.
Electrocatalytic reduction of oxygen and H+ occur at the cathode, generating water. Under acidic aqueous conditions, this occurs at a standard potential of 1.229V. The literature says that oxygen requires a large 'cathodic activation overpotential':
"While ambiguous, "activation overpotential" often refers exclusively to the activation energy necessary to transfer an electron from an electrode to an analyte. This sort of overpotential can also be called "electron transfer overpotential""
Ideally, a carbon electrode is used for both the cathode and the anode. You can acquire one!: http://www.instructables.com/id/Easy-Carbon-Electrode/ Instead of replacement power tool motor brushes, you can also use carbon cloth, carbon mesh, etc etc.
Buy carbon electrode material:
Salvage from a carbon-zinc lantern battery:
where to get dead lantern batteries?
What Can It Run?
- LEDs: ultrabrite versus low-current
The voltages generated by an MFC appear to be quite low, in the range of 200-300mV. A typical LED forward voltage is 1.7-3.3V (color-dependent; red is the lowest), with current typically in the 2-20mA range. Super-bright LEDs, however, can be run at vanishingly low currents — as low as 100 μA — when acting as low-output indicators. The joule thief boost converter will certainly run an LED on this fuel cell!