Optimum spacing between electrodes in an air-cathode single chamber microbial fuel cell with a low-cost polypropylene separator

The performance of a single chamber microbial fuel cell (MFC) with a low-cost polypropylene separator was investigated at various electrode interspaces in a separator electrode assembly (SEA). The lag period was shortened (3.74–0.17 days) and voltage generation was enhanced (0.2–0.5 V) as electrode spacing was increased from 0 to 9 mm. Power density was increased from 220 to 370 mW/m² with increased spacing. The highest power density of 488 mW/m² was obtained in polarization analysis with 6 mm. The oxygen mass transfer coefficients with 0 mm (K_o = 3.69 × 10⁻⁵ cm/s) electrode spacing were 3.8 times higher than with 9 mm (K_o = 0.96 × 10⁻⁵ cm/s) spacing. Columbic efficiency (CE) was increased from 5 to 32% due to less oxygen diffusion with increase in electrode spacing, but on contrary the ohmic resistance (R_oh) was increased from 2 to 4 Ω. In a long-term operation (200 days), a gradual decrease in cathode potentials was observed in all electrode spacing as the main limiting factor of stable MFC performance.