Green-Synthesized Nitrogen-Doped Carbon-Based Aerogels as Environmentally Friendly Catalysts for Oxygen Reduction in Microbial Fuel Cells

A green approach to the synthesis of nitrogen-doped, carbon-based aerogels with good conductivity and catalytic properties is presented. With the aim to design an easily sustainable process, the starting precursors are selected from abundant waste-related organic materials. The naturally derived polysaccharide agar acts as the carbon source in a water solution and an amino acid, glycine or lysine, is used as the nitrogen source. Using this synthesis approach, nitrogen defects are created in a 3D porous aerogel. They are shown to act as active catalytic sites for the reaction of oxygen reduction to water as demonstrated by electrochemical measurements. The best performing materials are tested as cathodes in microbial fuel cells for 50 days, in conditions close to those the device would face in a real environment. The glycine-derived carbon aerogels with the higher content of pyridinic nitrogen exhibit the best performance, as confirmed by several morphological characterizations.