Electrochemical impedance spectroscopy (EIS) is an efficient and non-destructive test for analyzing the bioelectrochemical processes of microbial fuel cells (MFCs). The key factors limiting the output performance of an MFC can be identified by quantifying the contribution of its various internal parts to the total impedance. However, little attention has been paid to the measurement conditions and diagrammatic processes of the EIS for MFC. This review, starting with the analysis of admittance of bioelectrode, introduces conditions for the EIS measurement and summarizes the representative equivalent circuit plots for MFC. Despite the impedance from electron transfer and diffusion process, the effect of unnoticeable capacitance obtained from the Nyquist plot on MFCs performance is evaluated. Furthermore, given that distribution of relaxation times (DRT) is an emerging method for deconvoluting EIS data in the field of fuel cell, the application of DRT-analysis to MFC is reviewed here to get insight into bioelectrode reactions and monitor the biofilm formation. Generally, EIS measurement is expected to optimize the construction and compositions of MFCs to overcome the low power generation.

Microbial fuel cells (MFCs) were embedded into constructed wetlands to form microbial fuel cell coupled constructed wetlands (CW-MFCs) and were used for simultaneous azo dye wastewater treatment and bioelectricity generation. For the first time, the effects of different substrate biomass on the performance of CW-MFCs were studied. Group A had the highest substrate biomass of 0.453 g VSS per L, followed in order by group D, group B and group C. CW-MFCs with more substrate biomass showed higher decolorization efficiencies but lower electrode performance. The decolorization efficiency and the maximal power density of group A were 92.7% and 0.117 W m⁻³, respectively, while the decolorization efficiency and the maximal power density of group C were 76.26% and 0.256 W m⁻³, respectively. The cathode performance had the greatest impact on the CW-MFC performance. This may be due to the high cathode activation resistance which may be caused by the lack of cathode microbes. The substrate biomass exerted significant effects on the electrode microbes. The CW-MFCs with more substrate biomass had fewer electrode microbes, which may reduce the electrode performance. This study highlights the applications of CW-MFCs and other MFCs that were built in a natural environment.