Electric field-regulated extracellular polymeric substances enhance extracellular electron transfer at the biofilm-electrode interface.

To address the bottleneck imposed by low rates of extracellular electron transfer (EET), which limits the efficiency of bioelectrochemical systems (BESs), an electric field-coupled microbial fuel cell was developed using an auxiliary electrode. The electric field was employed as an intervention factor targeting extracellular polymeric substances (EPS), which are a key component of biofilms, to propose a strategy of enhancing EET by modulating EPS properties. Focusing on biofilms, this study investigated their formation and EET behavior. By integrating the electric field response characteristics of EPS, the intrinsic relationships among biofilm performance, EPS, and electric field were examined. The results demonstrated that the electric field promoted microbial accumulation on the electrode and enhanced metabolic activity, thereby increasing biofilm density and electron transfer system activity. Furthermore, the electric field improved the electronic conduction environment within the biofilm, reduced resistance to EET, and generated highly active EET functional microzones on the biofilm surface. Consequently, the maximum reaction rate and EET rate constant increased by 60.3% and 53.9%, respectively. The transformation of EPS properties under electric field intervention was identified as the primary mechanism underlying improved biofilm formation and EET performance. The electric field promoted biofilm development by increasing the ratio of protein components within the EPS and reducing the electrostatic repulsion between EPS particles. Furthermore, it enhanced EET by upregulating electrochemically active components. These findings indicate that modulation of EPS characteristics is a key strategy for promoting biofilm formation and EET in BESs, offering new opportunities for improving EET efficiency.