A facile synthesis of CoFe2O4/biocarbon nanocomposites as efficient bi-functional electrocatalysts for the oxygen reduction and oxygen evolution reaction

Efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for improving the performance of metal-air batteries. In this study, CoFe2O4/biocarbon (CFO/BC) nanocomposites have been synthesized via a facile biosynthesis method by using yeast cells as carbon sources and structural templates. The as-prepared CFO/BC nanocomposites possess a hierarchical structure with a high surface area (79.84 m(2) g(-1)). The rotating ring-disk electrode (RRDE) and rotating disk electrode (RDE) measurements revealed that CFO/BC nanocomposites exhibit excellent catalytic activity for both the ORR and OER. The onset potential of CFO/BC for the ORR is -0.14 V (vs. Ag/AgCl), which is higher than that of CoFe2O4 (-0.29 V) and that of biocarbon (-0.25 V), respectively. Meanwhile, the CFO/BC nanocomposites show much higher activity for the OER as compared to CoFe2O4 and biocarbon. The chronoamperometric tests show that the CFO/BC catalyst shows high durability for both the ORR and OER, outperforming the commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey). The high electrocatalytic activity and durability of the CFO/BC nanocomposite are mainly attributed to the strong coupling between CoFe2O4 nanoparticles and biocarbon as well as the hierarchical structure of CFO/BC.