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MnCo2O4 (MCO) spinel powders have been synthesized by a sol-gel process with glucose as pore-former. The samples are characterized by XRD, SEM, BET. SEM and BET results show that MCO-700 has a porous structure and a high specific surface area of 11.1 m² g-1. Catalytic activities of these oxides for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in 0.1 M KOH solution have been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that MCO-700 exhibits better catalytic activity for the ORR. The ORR mainly favors a direct four electron pathway, and a maximum cathodic current density of 6.69 mA cm-2 at 2500 rpm has been obtained, which is close to that of commercial Pt/C electrocatalyst under the same testing conditions. Anodic linear scanning voltammograms results show that MCO-700 is more active for the OER. Although MCO-700 shows a stable catalytic activity for the ORR, a serious attenuation exists for the OER due to the oxidization of carbon under high potential. [ABSTRACT FROM AUTHOR]

It is highly challenging to explore high–performance bi-functional oxygen electrode catalysts for their practical application in next-generation energy storage and conversion devices. In this work, we synthesize hierarchical N–doped carbon microspheres with porous yolk–shell structure (NCYS) as a metal-free electrocatalyst toward efficient oxygen reduction through a template-free route. The enhanced oxygen reduction performances in both alkaline and acid media profit well from the porous yolk–shell structure as well as abundant nitrogen functional groups. Furthermore, such yolk–shell microspheres can be used as precursor materials to motivate the oxygen reduction activity of oxygen evolution oriented materials to obtain a desirable bi-functional electrocatalyst. To verify its practical utility, Zn–air battery tests are conducted and exhibit satisfactory performance, indicating that this constructed concept for preparation of bi-functional catalyst will afford a promising strategy for exploring novel metal–air battery electrocatalysts. [ABSTRACT FROM AUTHOR]