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Rational design of non-noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for rechargeable metal-air batteries. A new route involving S was developed to achieve atomic dispersion of Fe-N x species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe-N x species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn-air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co4Nporous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co4N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257 mV at a current density of 10 mAcm-2, and a low Tafel slope of 44 mVdec-1 in an alkaline medium, which is the best OER performance among reported Co-based electrocatalysts to date. Moreover, in-depth mechanistic investigations demonstrate the active phases are the metallic Co4N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of highefficiency OER electrocatalysts. [ABSTRACT FROM AUTHOR]