Conduction-band edge dependence of carbon-coated hematite stimulated extracellular electron transfer of Shewanella oneidensis in bioelectrochemical systems

•A C/Hematite coated CC electrode was developed using ferrocene as precursor.•Current density of 0.22 ± 0.01 mA/cm2 was attained with the C/Hematite electrode.•The C/Hematite electrode achieved 6-fold higher current density over CC.•Low charge transfer resistance (14 Ω) confirmed fast EET on C/Hematite electrode.•The optimized electrical properties of hematite contributed to the enhanced EET.

Bacteria-based bioelectrochemical systems (BESs) are promising technologies used for alternative energy generation, wastewater treatment, and environmental monitoring. However, their practical application is limited by the bioelectrode performance, mainly resulting from low extracellular electron transfer (EET) efficiency. In this study, a carbon-coated hematite (C/Hematite) electrode was successfully obtained by a green and solvent-free route, that is, heat treatment in an oxygen-rich environment using solid ferrocene as the precursor. The as-prepared C/Hematite electrode was evaluated as a high-performance electrode material in a Shewanella oneidensis-inoculated BES. The maximum biocurrent density of the Shewanella-attached C/Hematite electrode reached 0.22 ± 0.01 mA cm− 2, which is nearly 6-times higher than that of a bare carbon cloth (CC) electrode (0.036 ± 0.005 mA cm− 2). Electrochemical measurements revealed that the enhanced conductivity and better energy matching between the outer membrane c-type cytochromes of S. oneidensis and the electrode contributed to the improved EET efficiency. The results of this study demonstrated that the semiconductive properties of iron oxides play important roles for the involved bacterial extracellular respiration activities.