Strengthening CoCo bond by copper doping in Co9S8 coupled with nitrogen-doped carbon sphere for enhancing the catalytic activity of oxygen reaction

Oxygen reaction plays a vital role in energy storage such as zinc-air battery and microbial fuel cell (MFC). Thus, it is necessary to search and develop non-precious metal electrocatalysts with remarkable activity. In this work, copper is cleverly doped into the octahedral sites of Co9S8 to strengthen the CoCo bond and then combined with nitrogen-doped hollow carbon spheres to achieve high catalytic activity and durability for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The prepared Cu-Co9S8-NHCS-1 exhibits the potential gap of 0.788 V between Ej=10 of OER and E1/2 of ORR. Moreover, the zinc-air battery with Cu-Co9S8-NHCS-1 cathode possesses a power density of 91.0 mW cm-2 and long-term stability over 120 h. The MFC using Cu-Co9S8-NHCS-1 cathode exhibits a power density of 924 ± 18 mW m-2, higher than that of 862 ± 20 mW m-2 with Pt/C. These results indicate that the Cu-Co9S8-NHCS-1 is an excellent bifunctional electrocatalyst for ORR and OER, and has promising applications in energy conversion.