Low-cost biochar derived from corncob was prepared by a facile pyrolysis method at controlled temperatures (250-750 degrees C) and the biochar was employed as oxygen reduction reaction (ORR) catalyst in air cathode microbial fuel cells (MFCs). The obtained biochar at 650 degrees C (CC-650) showed an excellent electrochemical active area up to 655.89 m(2) g(-1), and various forms of nitrogen were introduced to the carbon molecular skeleton successfully. The electrochemical measurements indicated that the CC-650 with the highest contents of graphitic and pyridinic nitrogen can accelerate the electron transfer to participate in ORR by a four-electron pathway. In MFCs tests, the maximum output voltage and power density with CC-650 cathode was 0.221 V and 458.85 mW m(-3) respectively, which was significantly higher than those of the other biochar. Our results demonstrated a potential route based on sustainable and economical biochar as promising oxygen reduction catalyst for MFCs. (C) 2018 Elsevier Ltd. All rights reserved.