Depending on the energy loss due to the cathode reaction and bacterial metabolism, a voltage of typically 0.3–0.5 V can be obtained from organic substrates such as glucose or acetic acid . Anodes in these systems are usually small, generally in the range of cm2, but projected power densities are reported on the scale of mW per m2. Scaling in a MFC does not seem to be as easy as increasing the surface area of the anode and cathode. Problems associated with internal resistance, diffusion of substrate and protons are encountered.