Sediment microbial fuel cells (SMFCs) have a proven potential for energy harvesting from marine sediment. This study examines a simple thermo-treatment method on flat carbon cloth electrodes in an SMFC. For this purpose, the electricity generation behavior in the SMFC systems is evaluated when the carbon cloth electrodes are heated to 300, 400, 450, and 500 degrees C. The higher heat-treated carbon fibers show clearer, deeper slits and striations on the main fiber surface direction. XPS analysis shows the O1s/C1s and C1s/N1s atom ratio decrease when the thermal treatment changes from 0 to 500 degrees C; it may be due to the removal of oxygen-containing groups and the introduction of nitrogen-containing groups. Maximum power density Pmax increases as the O1s/C1s and C1s/N1s ratio decrease. The highest power density of 23.43 mW m(-2) occurs with a thermo-treated carbon cloth electrode at 500 degrees C, which is approximately 23-fold higher than that in the SMFC with untreated electrodes. Polarization curves show steady decreases in voltage at low current densities in higher heat-treated SMFCs, suggesting that activation losses are reduced. These results demonstrate that carbon fiber surface roughness, morphology, and functionalities are greatly improved by increasing heat-treated temperature, which subsequently enhances the power production of SMFC systems. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.