The rolling catalyst layers in air cathode microbial fuel cells (MFCs) are prepared by introducing NH4HCO3 as pore former (PF) with four PF/activated carbon mass ratios of 0.1, 0.2, 0.3 and 1.0. The maximum power density of 892 +/- 8 mW M-2 is obtained by cathodes with the mass ratio of 0.2, which is 33% higher than that of the control reactor (without PF, 671 +/- 22 mW m(-2)). Pore analysis indicates the porosity increases by 38% and the major pore range concentrates between 0.5 mu m-0.8 mu m which likely facilitates to enrich the active reaction sites compared to 0.8 mu m-3.0 mu m in the control and other PF-cathodes. In addition, pore structure endows the cathode improved exchange current density by 2.4 times and decreased charge transfer resistance by 44%, which are the essential reasons to enhance the oxygen reduction. These results show that addition of NH4HCO3 proves an effective way to change the porosity and pore distribution of catalyst layers and then enhance the MFC performance. (C) 2014 Elsevier B.V. All rights reserved.