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

•A power density of 2151mWm−2 was achieved using an optimized matrix of 40 mesh.•Power exhibited the same trend as that of linear sweep voltammetry at −0.2 to 0V.•An optimized matrix can significantly decrease the charge transfer resistance.•Mesh density had a better correlationship with power density than opening size. Stainless steel mesh (SSM) with four opening sizes (20–80M) were investigated as matrixes of activated carbon air–cathodes in microbial fuel cells (MFCs). The highest power density of 2151±109mWm−2 (at 5.54±0.14Am−2) was obtained using 40M, with a value 45% higher than 1485±18mWm−2 of 80M. The trend of linear sweep voltammetries were in accordant with power output over a cathodic potential range from −0.2 to 0V. 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 2Ω in 40M. 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.