Cobalt, manganese zeolitic-imidazolate-framework-derived Co3O4/Mn3O4/CNx embedded in carbon nanofibers as an efficient bifunctional electrocatalyst for flexible Zn-air batteries

Efficient bifunctional oxygen catalysts are required for practical applications in fuel cells and metal-air batteries due to their core electrode reactions: oxygen reduction (ORR) and oxygen evolution (OER). Rational design of nanostructured metal oxides supported by carbon is urgently required to improve the electrochemical properties of Zn-air batteries. Here it is reported that 1D bimetal (Co,Mn) zeolite-imidazole-framework pyrolysis method is used for the low-cost and easy preparation of Co3O4, Mn3O4 nanoparticles and CNx active sites embedded in 1D carbon nanofibers (Co3O4/Mn3O4/CNx@CNFs). The optimized Co3O4/Mn3O4/CNx@CNFs reveals the excellent ORR performance with the diffusion current of −6.96 mA/cm2, along with excellent electrocatalytic activity towards OER (1.63 V at a current density of 10 mA/cm2), which are better than that previously reported bifunctional catalysts dirved from Co, Mn bimetal-oxides. Besides, we assembled the Co3O4/Mn3O4/CNx@CNFs into the air electrode of the Zn-air battery (and flexible Zn-air battery), indicating that the maximum power density is 265 mW/cm2 (and 191 mW/cm2), the latter power density is better than previously reported MOF-derived bifuctional catalysts. The excellent electrocatalytic performance is attributed to the support of 1D highly conductive CNFs and the synergistic effect of active sites such as Co3O4, Mn3O4 and CNx. [Display omitted] •A method of MOF synthesis and pyrolysis for prepare bifunctional electrocatalyst.•Co3O4, Mn3O4 nanoparticles and CNx active sites embedded in 1D carbon nanofibers.•Co3O4/Mn3O4/CNx@CNFs reveals the excellent ORR and OER performances.•The power density of flexible Zn-air battery was 191 mW/cm−2.