The Pt and Nafion free air-cathode is urgently needed for large scale membrane-less single chambered microbial fuel cells (MFCs). The activated carbon air-cathode (ACAC) consisted of a sintered catalyst layer (CL) and a gas diffusion layer (GDL) made by rolling method is such a promising cathode with a high performance. However, the microstructure of the CL in terms of three phase interface (TPI) needs to be further investigated. The maximum power density increases by 35% from 802 +/- 20 mW m(-2) (3.40 +/- 0.03 A m(-2)) to 1086 +/- 8 mW m(-2) (2.80 +/- 0.04 A m(-2)) when the CL is not sintered. The maximum Coulombic efficiency (CE) also increases from 34% to 40%, possibly due to the decrease of hydrophobicity and the total volume/area of the CL The total pore area and the porosity of the CL decrease by 87% and 42% after sintering, indicating that sintering reduced those pores among activated carbon aggregates so that TPIs are reduced. However, the available gas channel is produced when the GDL abundant of polytetrafluoroethylene (PTFE) is sintered. (C) 2013 Elsevier B.V. All rights reserved.