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

Scaling up microbial fuel cells (MFCs) will require more compact reactor designs. Spacers can be used to minimize the reactor size without adversely affecting performance. A single 1.5 mm expanded plastic spacer (S1.5) produced a maximum power density (973 ± 26 mW m−2) that was similar to that of an MFC with the cathode exposed directly to air (no spacer). However, a very thin spacer (1.3 mm) reduced power by 33%. Completely covering the air cathode with a solid plate did not eliminate power generation, indicating oxygen leakage into the reactor. The S1.5 spacer slightly increased columbic efficiencies (from 20% to 24%) as a result of reduced oxygen transfer into the system. Based on operating conditions (1000 Ω, CE = 20%), it was estimated that 0.9 L h−1 of air would be needed for 1 m2 of cathode area suggesting active air flow may be needed for larger scale MFCs.