Strategic regulation of barrier characteristics of biofilms to enhance the extracellular electrogenic performance in MFCs: an electrochemical dynamic evaluation study

Abstract

The electron transfer (ET) characteristics of an exoelectrogenic biofilm in the bacterial community are the rate limiting factor that decisively determines the efficiency of a microbial fuel cell (MFC). However, the heterogeneities of exoelectrogenic biofilms differentially contribute in the energy conversion system, which cannot be evaluated by any conventional techniques available. Thus in the present study, we put forward the important strategic role of electrochemical impedance spectroscopic characteristics for comprehensive assessment of heterogeneities in the electron transfer characteristics of the biofilm. In contrast to previous reports, the present study reveals that free bacterial cells produce more charge than surface attached cells. This, in the present case, is attributed to the fact that free cells augment the mobility of ions and electrons by electron hopping, leading to a decrease in R_ct from 1.13 × 10³ Ω cm² to 2.71 × 10¹ Ω cm². This could lead to achieving the highest current output of 1.97 × 10¹ mA. Meanwhile, the biofilm enables aggregation of bacterial cells, which alters the cell surface characteristics and masks the active sites of the free cells. This further restricts the mass transfer of ionic species leading to about 50% of the total internal resistance in the MFC. Based on these studies, we present a strategic correction to regulate the biofilm of Gram-positive bacteria from the bacterial community to mitigate the extracellular energy loss for achieving enhanced performance in the MFC system. We hope that this key strategic regulation of barrier characteristics of biofilms should be adopted for achieving high performance in similar MFC systems.