Dandelion-type Mn-promoted Co 3 O 4 /CNTs composite as an efficient bifunctional electrocatalyst for rechargeable zinc – air batteries

In the present work, dandelion-type composites of manganese-promoted Co 3 O 4 on carbon nanotube films (Mn x -Co 3 O 4 /CNTs) were successfully synthesized using a facile hydrothermal route and a subsequent calcination process. The composition and morphology of Mn x -Co 3 O 4 /CNTs were thoroughly analyzed by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The as-prepared dandelion-type Mn x -Co 3 O 4 has nano-needles with a diameter of 75 ± 10 nm. The numbers of active sites and oxygen vacancies for the catalytic process were increased by the incorporation of Mn in Co 3 O 4 , thereby enhancing electrochemical performance of Co 3 O 4 /CNTs. Twenty-five percent (w/w) Mn doping in Co 3 O 4 (Mn 0.25 -Co 3 O 4 /CNTs) exhibited the best electrocatalytic performance in the oxygen reduction/evolution reaction (ORR/OER) among all as-prepared Mn x -Co 3 O 4 /CNTs, which is even superior to the Pt/C based electrode in the Zn–air battery tests, including higher open-circuit voltage (1.43 V), greater discharge peak power density (56.7 mW/cm 2 ), and a larger specific capacity (707.3 mAh/g -Zn at 10 mA/cm 2 ). Owing to its high efficiency, stability and low-cost, Mn 0.25 -Co 3 O 4 /CNTs, is a promising alternative to prepare ORR/OER bifunctional catalysts for the rechargeable Zn–air battery industry. Graphical abstract The dandelion structure of Mn x -Co 3 O 4 /CNT over CNT films increases active catalytic sites and oxygen vacancy concentrations on its nano-needle surfaces to endow the bifunctional catalyst with a high efficiency.