Facile synthesis of cobalt oxide as electrocatalyst for the oxygen reduction reaction in microbial fuel cells

Cost-effective cobalt oxides were synthesized at mild condition as alternatives to platinum catalyst for oxygen reduction in microbial fuel cells (MFCs). The catalysts were prepared by heating Co(NO₃)₂ above its decomposition temperature together with carbon black (CB). At a catalyst loading of 5 mg/cm², cobalt oxide cathodes with a Co(NO₃)₂ to CB ratio of 0.732:1 produced a maximum power density of 1220 mW/m², which was slightly lower than that of Pt/C cathodes (1360 mW/m²). Further increase in the loading of cobalt oxides resulted in an increase in performance. The maximum power densities produced by cobalt oxide cathodes increased to 1400 mW/m² at a catalyst loading of 20 mg/cm² and 1540 mW/m² at 30 mg/cm², which outperformed the Pt/C control. The durability of cobalt oxide catalysts was comparable to that of Pt/C in single-chamber MFCs with biological contamination. The costs of cobalt oxide catalysts were much lower than that of Pt/C catalyst, even when the loading of cobalt oxides was several times higher than Pt/C catalyst. These findings show that the facilely synthesized cobalt oxides were cost-effective catalysts for oxygen reduction in air-cathode MFCs.