Opening size optimization of metal matrix in rolling-pressed activated carbon air–cathode for microbial fuel cells

Stainless steel mesh (SSM) with four opening sizes (20–80 M) were investigated as matrixes of activated carbon air–cathodes in microbial fuel cells (MFCs). The highest power density of 2151 ± 109 mW m−2 (at 5.54 ± 0.14 A m−2) was obtained using 40 M, with a value 45% higher than 1485 ± 18 mW m−2 of 80 M. The trend of linear sweep voltammetries were in accordant with power output over a cathodic potential range from −0.2 to 0 V. The differences in performance were attributed to the internal resistances. Charge transfer resistance (Rct) was the dominant internal resistance in most of air–cathodes, with the lowest value of 2 Ω in 40 M. Density of metal mesh exhibited a more significant correlationship with maximum power densities (R2 = 0.9222) compared to opening size (R2 = 0.7068), demonstrated that the density of metal current collector was vital to the performance of cathodes.