To explore the process kinetics of hydrogen evolution reaction (HER) on carbon-based Ni/NiO nanocomposite in the microbial electrolysis cells (MECs), the performance was systematically studied by different time-course sampling of five parallel single-chamber MECs operated under identical operating conditions, which included the electrochemical performance of anodes and cathodes, and the mechanism and kinetics of HER. It was hypothesized that the decreased performance of the nickel cathodes was due to corrosion and Ni dissolution. These results provide valuable insights into the effects of long-term operation on MEC performance. (C) 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.