Since, most microbial cells are electrochemically inactive; electron transfer from microbial cells to the electrode is facilitated by the help of mediators such as thionine, methyl viologen, humic acid, etc. Enzyme catalyzed generation of NADH (dihydro-nicotinamide adenine dinucleotide) from alcohol, lactic acid, amino acids, formate or other abundant substrates could provide the bio-transformations that activate the anodic compartment of the fuel cell. Theoretically, any organic or inorganic compound or a mixture can serve as a fuel, provided it is oxidized by the appropriate organism, e.g.,