Commercial activated carbon (AC) was subjected to various kinds of acid treatment, which were employed as air-breathing cathodes for Microbial fuel cells (MFCs). Obviously, both the acid species and the concentration of acidic solution have an effect on the catalytic activity of AC, and the electrochemical performance of AC was increased after acid treatment. Cathodes used 1 M H3PO4 treated AC (AC-H3PO4-1) showed the maximum power density of 1546 +/- 43 mW m (2), which was 115% higher than the pristine AC. The electrochemical studies showed that AC-H3PO4-1 exhibited the least resistance and highest kinetic activity. In addition, Nitrogen adsorption-desorption demonstrated that the acid treatment could increase the total surface area and pore volume, especially the exposure of mesopore to the reactants. Raman, X-ray photoelectron spectroscopy and temperature programmed desorption with ammonia revealed that the degree of graphitization, surface oxygenic functional groups and the acid sites of AC were enhanced after acid treatment. However, too much strong acidic functional groups were detrimental to the oxygen reduction reaction. In general, the treatment of activated carbon with 1 M H3PO4 will be a promising way to improve the performance of microbial fuel cells. (C) 2017 Elsevier Ltd. All rights reserved.