Simultaneous Cr(VI) reduction and electricity generation in Plant-Sediment Microbial Fuel Cells (P-SMFCs): Synthesis of non-bonding Co3O4 nanowires onto cathodes.

Development of low-cost cathode materials for Plant-Sediment Microbial Fuel Cells (P-SMFCs) has gained increasing interest, due to improved performance levels in terms of power and pollutant removal. A novel low cost three-dimensional cathode prepared by simple three-step strategy with growth of Co3O4 in-situ biofilm was successfully prepared. Different cathodes were applied to the six parallel P-SMFCs systems (reactor: R1-R6), such as graphite felt (GF), Pt/C, GF@Co3O4 (non-bonding Co3O4 nanowires on GF), GF@SG-Co3O4 (using argon as shielding gas (SG)). Its performances (R1, R2: control groups) were evaluated by electricity generation and Cr(VI) reduction at initial cadmium concentrations (4.97, 10.29 and 21.16 mg L-1). A significant Cr(VI) removal efficiency of 99.76%, maximum power density of 75.12 ± 2.90 mW m-2 and Cr(VI) adsorption capacity of 1.67 mg g-1 were obtained at initial Cr(VI) concentration of 21.16 mg L-1 with non-bonding GF@Co3O4 and bio-GF@SG-Co3O4 as cathodes. This indicated that these two materials were better than others (GF, Pt/C and GF@Co3O4) as cathodes. Characterization analysis including scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Polarization curve, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) showed that high current generation Cr(VI) removal mainly attributed to transportation of plants, adsorption of bio-cathode, formation of a relatively high concentration region and abundant oxygen vacancies of GF@SG-Co3O4. The results show that P-SMFCs with GF@SG-Co3O4 cathode may be a potentially novel approach for remediating Cr(VI) contaminated waster or soil.