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MnxOy/NC and CoxOy/NC Nanoparticles Embedded in a Nitrogen-Doped Carbon Matrix for High-Performance Bifunctional Oxygen Electrodes

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  • Financial support from the DFG (Deutsche Forschungsgemeinschaft) in the framework of the Cluster of Excellence RESOLV (EXC 1069) and in the framework of Helmholtz-Energie-Allianz “Stationäre elektrochemische Speicher und Wandler” (HA-E-0002) is gratefully acknowledged. A.Z. is grateful to the China Scholarship Council for a Ph.D. Scholarship. We thank Dr. Dennis König of the Department of Mechanical Engineering, Institute for Materials, Ruhr-University Bochum for the TEM measurements and Sandra Schmidt for the SEM measurements. The XAFS measurements were performed at CLÆSS beamline at ALBA Synchrotron Light Facility with the collaboration of ALBA staff.

Abstract

Reversible interconversion of water into H2 and O2, and the recombination of H2 and O2 to H2O thereby harnessing the energy of the reaction provides a completely green cycle for sustainable energy conversion and storage. The realization of this goal is however hampered by the lack of efficient catalysts for water splitting and oxygen reduction. We report exceptionally active bifunctional catalysts for oxygen electrodes comprising Mn3O4 and Co3O4 nanoparticles embedded in nitrogen-doped carbon, obtained by selective pyrolysis and subsequent mild calcination of manganese and cobalt N4 macrocyclic complexes. Intimate interaction was observed between the metals and nitrogen suggesting residual M–Nx coordination in the catalysts. The catalysts afford remarkably lower reversible overpotentials in KOH (0.1 M) than those for RuO2, IrO2, Pt, NiO, Mn3O4, and Co3O4, thus placing them among the best non-precious-metal catalysts for reversible oxygen electrodes reported to date.

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