Iron-oxide nanoparticles and the Tween 80 have previously been shown to improve power generation in microbial fuel cells (MFCs), presumably by improving electron transfer from the bacteria to the anode. We examined whether several chemicals would affect current production in single-chamber microbial electrolysis cells (MECs), where hydrogen gas is produced at the cathode, using mixed cultures and Geobacter sulfurreducens. Tween 80 did not increase the current. Fe(OH) 3 addition increased the maximum current density of both the mixed cultures (from 6.1 ± 0.9 A/m 2 to 8.8 ± 0.3 A/m 2) and pure cultures (from 4.8 ± 0.5 A/m 2 to 7.4 ± 1.1 A/m 2). Improved current production was sustained even after iron was no longer added to the medium. It was demonstrated that increased current resulted from improved cathode performance. Analysis using electrochemical impedance spectroscopy (EIS) showed that the iron primarily reduced the diffusion resistances of the cathodes, and scanning electron microscopy (SEM) images showed the formation of highly porous structures on the cathode. The addition of DNA also did not improve MEC or MFC performance. These results demonstrated that among these treatments only Fe(OH) 3 addition was a viable method for enhancing current densities in MECs, primarily by improving cathode performance. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.