Enhanced Cathodic Oxygen Reduction and Power Production of Microbial Fuel Cell Based on Noble-Metal-Free Electrocatalyst Derived from Metal-Organic Frameworks

Microbial fuel cell (MFC) can generate electricity from organic substances based on anodic electrochemically active microorganisms and cathodic oxygen reduction reaction (ORR), thus exhibiting promising potential for harvesting electric energy from organic wastewater. The ORR performance is crucial to both power production efficiency and overall cost of MFC. A new type of metal-organic-framework-derived electrocatalysts containing cobalt and nitrogen-doped carbon (CoNC) is developed, which is effective to enhance activity, selectivity, and stability toward four-electron ORR in pH-neutral electrolyte. When glucose is used as the substrate, the maximum power density of 1665 mW m^-2 is achieved for the optimized CoNC pyrolyzed at 900 °C, which is 39.8% higher than that of 1191 mW m^-2 for commercial Pt/C catalyst in the single-chamber MFC. The improved performance of CoNC catalyst can be attributed to large surface area, microporous nature, and the involvement of nitrogen-coordinated cobalt species. These properties enable the efficient ORR by increasing the active sites and enhancing mass transfer of oxygen and protons at "water-flooding" three-phase boundary where ORR occurs. This work provides a proof-of-concept demonstration of a noble-metal-free high-efficiency and cost-effective ORR electrocatalyst for effective recovery of electricity from biomass materials and organic wastewater in MFC.