Cobalt sulfide/N,S-codoped defect-rich carbon nanotubes hybrid as an excellent bi-functional oxygen electrocatalyst

The design of high-efficient and durable bi-functional oxygen electrocatalysts is still a great challenge. In this work, novel Co9S8 nanoparticles/N,S-codoped defect-rich carbon nanotubes (Co9S8/N,S-CNTs) were fabricated by an ingenious template method. CdS nanowires, as a sacrificial template, can be removed simultaneously during the carbonization process without additional post-treatments. The large BET surface area (661.2 m2 g−1) and pore volume (1.49 cm3 g−1) of Co9S8/N,S-CNTs could largely enhance the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities by facilitating the mass transportation and exposing more active sites. The abundant defects produced by the evaporation of Cd and S doping could provide more active sites for ORR and OER. Coupling with Co9S8, Co9S8/N,S-CNTs possesses more defects in the carbon skeleton, better electron conductivity, and larger effective electrochemical area. Co9S8/N,S-CNTs not only performs excellent ORR activity with a half-wave potential of 0.821 V but also owns RuO2-like OER activity in alkaline solution. The potential difference (ΔE) between ORR and OER is as low as 0.78 V in 0.10 M KOH. The excellent bi-functional performance enables the potential to be utilized in fuel cells and metal-air batteries.