Graphitic biochar as a cathode electrocatalyst support for microbial fuel cells

•Abundant and low-cost municipally wood waste was used as graphitic carbon precursor.•Manganese oxide catalyst was successfully functionalized onto biochar carbon surface.•Base wash removed divalent citations (Ca2+) and increased overall catalyst loading.•Manganese oxide biochar composites serves as an effective oxygen reduction catalyst.•Manganese oxide biochar composites could serve as a low-cost electrode material.

Graphitic biochar (BC) was generated using high temperature gasification and alkaline post-treatment (BCw) of wood-based biomass. The BCw was evaluated as a manganese oxide electrocatalytic support (MnO/BCw) and microbial fuel cell (MFC) air cathode. Nano-structured MnO2 crystals were successfully immobilized on biomass-based graphitic sheets and characterized using physical, chemical, and electrochemical analyses. Cyclic voltammetry of MnO/BCw/Nafion inks showed electrochemical features typical of β-MnO2 with a current density of 0.9 mA cm−2. BC showed satisfactory maximum power densities of 146.7 mW m−2 (BCw) and 187.8 W m−2 (MnO/BCw), compared with Vulcan Carbon (VC) (156.8 mW m−2) and manganese oxide VC composites (MnO/VC) (606.1 mW m−2). These materials were also tested as oxygen reduction reaction (ORR) catalysts for single chamber MFCs inoculated with anaerobic sludge. Our results demonstrate that BC can serve as an effective, low cost, and scalable material for MFC application.