Using cathode spacers to minimize reactor size in air cathode microbial fuel cells

► Spacers were successfully used in MFCs to minimize cathode spacing. ► Power generation was not affected when using a 1.5 mm spacer. ► Using spacers slightly increased coulombic efficiencies. ► Cathode plates could be removed from the reactor when spacers were used. ► An airflow of 4.7 L h−1 m−2 cathode area would be needed to support 1 W m−2 of power.