Publications

Enhancing the water splitting performance of cryptomelane-type α-(K)MnO2

Antoni, H. and Morales, D.M. and Bitzer, J. and Fu, Q. and Chen, Y.-T. and Masa, J. and Kleist, W. and Schuhmann, W. and Muhler, M.

JOURNAL OF CATALYSIS
Volume: 374 Pages: 335-344
DOI: 10.1016/j.jcat.2019.05.010
Published: 2019

Abstract
Sustainable energy storage systems require the development of non-precious metal catalysts for water splitting. Cryptomelane-type α-(K)MnO2 is one of the few oxides of manganese with promising electrocatalytic activity for the oxygen evolution reaction (OER). We report a strategy to boost the performance of cryptomelane-type α-(K)MnO2 in OER electrocatalysis in alkaline electrolyte by thermal treatments in specific gas atmospheres. The thermal treatment of α-(K)MnO2 at 300 °C in He, H2O/He and air can lower the potential required to reach a current density of 10 mA cm−2 for the OER by up to 60 mV. We discuss the structural changes on the atomic level, by combining X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, transmission electron microscopy and electrochemical impedance spectroscopy. The simultaneous presence of three structural features for MnOx-based water oxidation catalysts is considered essential: (i) Mn3+ sites, (ii) structural defects, and (iii) mono- and di-µ-oxo bridges, which can be tailored on the surface and in the bulk. Notably, extended X-ray absorption fine structure measurements suggest that more Mn3+ sites are detected in the corner-sharing positions, which are suggested to be the favorable sites for the electrocatalytic water oxidation. © 2019

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