Graphene has a promising role in electrode fabrication/modification for microbial fuel cell (MFC) applications but there is a lack of research on graphene in MFCs. This study has systematically investigated two types of graphene materials with very different morphologies, namely regular graphene (like flat sheets of paper) and crumpled particles (like crumpled paper balls), respectively, to modify anode and cathode electrodes in MFCs. The higher electricity generation with the crumpled graphene particles is attributed to their higher electrical conductivity in the thickness direction, their larger surface area, catalytic activities of oxygen reduction, and the open structure they pack into that facilitates mass transfer of the fuels and ions. The crumpled graphene-modified anode electrode produces the highest maximum power density (3.6W m(-3)), twice that of the activated carbon-modified anode electrode (1.7 W m(-3)). The maximum power densities with the crumpled graphene- and flat graphene-modified cathode electrodes are 3.3W m(-3) and 2.5W m(-3), significantly higher than 0.3W m(-3) with the unmodified carbon cloth, although still lower than a platinum cathode electrode. These results have demonstrated that graphene-based materials, especially the crumpled graphene particles, can be effective electrode modifying materials for improving electricity generation in MFCs. (C) 2012 Elsevier B.V. All rights reserved.