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Single-atom catalysts with precise structure and tunable coordination nature provide opportunities for developing novel catalytic centers and understanding reaction mechanisms. Herein, hollow Co9S8 polyhedrons with lattice-confined Ru single atoms (Ru-Co9S8) are fabricated. Aberration-corrected scanning transmission electron microscopy and X-ray absorption spectroscopy verify the isolated Ru atoms are confined in Co9S8 to form Co-S-Ru catalytic centers. Theoretical calculations indicate that the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) energy barriers are extensively reduced, and the d-band center of Co9S8 downshifts from the Fermi level, therefore boosting the desorption of O-containing intermediates. Consequently, the Ru-Co9S8 exhibits an ultralow overpotential of 163 mV at 10 mA·cm−2 for OER and could catalyze a rechargeable Zn-air battery with a high-power density of 92.0 mW·cm−2. This work provides a promising approach for designing novel bifunctional catalytic active centers for energy conversion. [ABSTRACT FROM AUTHOR]

Designing a highly efficient non-precious based oxygen reduction reaction (ORR) electrocatalyst is critical for the commercialization of various sustainable energy storage and conversion devices such as metal-air batteries and fuel cells. Herein, we report a convenient strategy to synthesis Fe3O4 embedded in N doped hollow carbon sphere (NHCS) for ORR. What's interesting is that the carbon microsphere is composed of two-dimensional (2D) nanoplate that could provide more exposed active sites. The usage of solid ZnO nanowires as zinc source is crucial to obtain this structure. The Fe3O4@NHCS-2 exhibits better catalytic activity and durability than the commercial Pt/C catalyst. Moreover, it further displays high-performance of Zn-air batteries as a cathode electrocatalyst with a high-power density of 133 mW·cm−2 and high specific capacity of 701 mA·h·g−1. The special hollow structure composed 2D nanoplate, high surface area, as well as synergistic effect between the high active Fe3O4 nanoparticles and N-doped matrix endows this outstanding catalytic activity. The work presented here can be easily extended to prepare metal compounds decorated carbon nanomaterials with special structure for a broad range of energy storage and conversion devices. [ABSTRACT FROM AUTHOR]