A low cost, naturally abundant, and highly active oxygen reduction reaction (ORR) electrocatalyst is essential for the commercialization of microbial fuel cells (MFCs). In this study, a promising strategy was proposed to prepare catalyst CoO nanosheets supported by nitrogendoped activated carbon (CoO@N-AC) to achieve a synergetic effect between metallic oxide and heteroatomdoped carbon. The nanocomposites possess a large Brunauer-Emmett-Teller surface area (1577.2 m(2) g (1)), low total resistance (9.26 Omega), and fourelectron ORR pathway. These nanocomposites are utilized as the aircathode catalysts in MFCs. CoO@N-AC remarkably increases the maximum power density by 122.5% from 741.5 +/- 8.5 mW m (2) to 1650.1 +/- 36.2 mW m +/- 2, which is higher than that of Pt/C (1201.4 +/- 13.5 mW m (2)). The excellent catalytic activity makes CoO@N-AC a promising cathodic electrocatalyst for practical application of MFCs. (C) 2017 Published by Elsevier Ltd.