Influence of the preparation method of MnO2-based cathodes on the performance of single-chamber MFCs using wastewater

Microbial Fuel Cells (MFCs) are a promising technology that offers new opportunities for bioenergy generation with simultaneous wastewater treatment. The search for new and inexpensive catalysts that replace precious metal-based materials for their application in air-cathode single-chamber MFCs is crucial for improving the efficiency of this technology and, thus, for its commercialization and scaling-up in the field of wastewater treatment. In this work, several types of cathodes consisting of a mixture of MnO2 as catalyst material and two different additive conductor supports, carbon nanotubes (CNTs) and acetylene black (AB), respectively, are investigated in single-chamber MFCs, in the presence and in the absence of a polymer binder, polytetrafluoroethylene (PTFE), both in terms of power performance and wastewater treatment (COD and heavy metal removal). Furthermore, the influence of two preparation methods to fix the above mixtures onto carbon cloth electrodes, spraying and mechanical pressure techniques, are compared to optimize cathode construction. Maximum values of current and power densities were observed for the cathode based on MnO2/CNT/PTFE prepared by mechanical pressure, 1.536 mA dm−3 and 511.11 mW m−3, respectively. This cathode configuration achieved the maximum chemical oxygen demand (COD) removal with a value of 77% after 240 h of MFC operation using wastewater as fuel. The analysis of the removal of heavy metals (63Cu, 66Zn, 111Cd, 121Sb, 208Pb, 55Mn and 56Fe) from wastewater in the different MFC types offered removal efficiencies within the interval 60-97% for most of the metals studied.