Bias voltage enhances extracellular polymeric substances-mediated extracellular electron transport

Low extracellular electron transfer (EET) efficiency remains the primary bottleneck limiting the performance of bioelectrochemical systems (BES). In BES, extracellular polymeric substances (EPS) serve as the critical interface between microorganisms and the electrode, and their electrochemical properties directly influence the rate of EET. Here, we demonstrate that bias voltage (BV) can significantly enhance EPS-mediated EET by regulating its composition and structure. Examining EPS by employing multi-scale characterization methods, we found that BV induced a shift in the dominant secondary structure of EPS proteins from β-sheets to β-turns and enriched key redox mediators. The relative contents of humic acid substances rich in redox mediators and cytochrome c both increased substantially, with maximum increases of 21.4% and 110.6%, respectively. Ultimately, a mediator system dominated by cytochrome c, quinones, and indole compounds was established within EPS, thereby enhancing its electrochemical activity. At a BV of 0.4 V, the contribution of each component to EET reached an optimal balance, optimizing the redox state of EPS and significantly enhancing its electron exchange capacity. This facilitated a 24.6% increase in the EPS-mediated EET rate. The findings elucidate the mechanism by which BV enhances EPS-mediated EET and provide novel insights into the key role of EPS in EET.