Fig. 3

Nyquist plots of MFCs (a), the inset is the enlarged curves of the low current density region. The internal resistances of MFCs (b) analyzed by fitting to the equivalent circuit: R_s (R_ct1Q₁) (R_ct2Q₂), where R_s, R_ct1, and R_ct2 represent ohmic resistance, charge transfer resistance, and finite diffusion resistance, respectively