A self-recirculation electrolyte system driven by air bubble buoyancy force is proposed for unbuffered microbial fuel cells (MFC) in this study. It was demonstrated that the electrolyte recirculation rate increased with the aeration rate in a certain range. Compared with buffer condition, buffer-less condition resulted in a 10% similar to 20% lower voltage (14.2% lower maximum power density) but a 9.1% higher Coulombic efficiency (CE) at an aeration rate of 92.0 ml/min. Under buffer-less condition, increasing the aeration rate resulted in a higher voltage output, a higher COD removal, and a higher CE due to the enhanced proton transfer and increased oxygen for cathode reaction. However, an extra high aeration rate induced a rapid deterioration of anode performance due to the excessive oxygen transfer into anode. This study demonstrates that the self-recirculation electrolyte system could be helpful for future unbuffered MFC designs. (C) 2017 Elsevier Ltd. All rights reserved.