Abstract
We have successfully demonstrated a passive scheme that employs interfacial tensions to discharge a CO 2 by-product out of portable microbial fuel cells (MFCs). The MFCs consume glucose to generate electricity and CO 2 gas in a reaction catalyzed by encapsulated microorganisms. The bio-catalysts, fuels and electrolytes are sealed inside two liquid-impermeable compartments, which are separated by a proton exchange membrane. The discharge of unwanted CO 2 bubbles from a closed anode compartment could result in desired agitation, which significantly facilitates the electron transport to the anode electrode. In our experiment, a MFC with a projected electrode area of 1 cm 2 and an overall size of 30 × 15 × 5 mm 3 was built. It was demonstrated that an open-circuit voltage of roughly 0.37 V per unit and a 1 h average power output up to 32 μW cm -2 , which is five times a regular-sized MFC, were achieved by the proposed discharge and agitation mechanism. With 40 mg of glucose fuels, the miniature MFC continuously operated for up to 4 h. Furthermore, a fuel-cell plate of six units, which had an overall open-circuit voltage over 2 V, was built and successfully powered a light-emitting diode. As such, the proposed discharge and agitation mechanism could self-regulate the electricity harvesting inside a MFC and produce steady voltage and current outputs for portable applications. © 2007 IOP Publishing Ltd.