Impact of external resistance acclimation on charge transfer and diffusion resistance in bench-scale microbial fuel cells

Reducing the external resistance (Rext) for microbial fuel cell (MFC) acclimation can substantially alter the anode performance in terms of charge transfer (RCT), diffusion (Rd) and total anode resistance (RAn). Electrochemical impedance spectroscopy (EIS) was used to quantify anode impedance at different set potentials. Reducing Rext from 50 Ω to 20 Ω during acclimation reduced RCT by 31% (from 6.12 ± 0.09 mΩ m2 to 4.21 ± 0.03 mΩ m2) and Rd by 18% (from 3.4 ± 0.2 mΩ m2 to 2.8 ± 0.1 mΩ m2) at a set anode potential of -115 mV during EIS. Overall RAn decreased by 27%, to 5.13 ± 0.02 mΩ m2 for acclimation at 20 Ω, enabling the anode to achieve 38% higher current densities of 29 ± 1 A m-2. The results show a clear dependence of acclimation procedures and external resistance on kinetic and diffusion components of anode impedance that can impact overall bioelectrochemical performance.