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Surprisingly low reactivity of manganese oxide toward  water oxidation in an ultra-pure electrolyte under  alkaline conditions

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journal contribution
posted on 2023-05-25, 14:27 authored by Mahya Salmanion, Ivan Kondov, Matthias VandichelMatthias Vandichel, Pavlo Aleshkevych, Mohammad Mahdi Najafpour

So far, many studies on the oxygen-evolution reaction (OER) by Mn oxides have been focused on activity; however, the identification of the best performing active site and corresponding catalytic cycles is also of critical importance. Herein, the real intrinsic activity of layered Mn oxide toward OER in Fe/Ni-free KOH is studied for the first time. At pH ≈ 14, the onset of OER for layered Mn oxide in the presence of Fe/Ni-free KOH happens at 1.72 V (vs reversible hydrogen electrode (RHE)). In the presence of Fe ions, a 190 mV decrease in the overpotential of OER was recorded for layered Mn oxide as well as a significant decrease (from 172.8 to 49 mV/decade) in the Tafel slope. Furthermore, we find that both Ni and Fe ions increase OER remarkably in the presence of layered Mn oxide, but that pure layered Mn oxide is not an efficient catalyst for OER without Ni and Fe under alkaline conditions. Thus, pure layered Mn oxide and electrolytes are critical factors in finding the real intrinsic activity of layered Mn oxide for OER. Our results call into question the high efficiency of layered Mn oxides toward OER under alkaline conditions and also elucidate the significant role of Ni and Fe impurities in the electrolyte in the presence of layered Mn oxide toward OER under alkaline conditions. Overall, a computational model supports the conclusions from the experimental structural and electrochemical characterizations. In particular, substitutional doping with Fe decreases the thermodynamic OER overpotential up to 310 mV. Besides, the thermodynamic OER onset potential calculated for the Fe-free structures is higher than 1.7 V (vs RHE) and, thus, not in the stability range of Mn oxides.



Inorganic Chemistry, 2022, 61 (4) pp. 2292–2306


American Chemical Society

Other Funding information

M.S. and M.M.N. acknowledge support from the Institute for Advanced Studies in Basic Sciences and the National Elite Foundation for their financial support. The computational modeling was performed on the supercomputer ForHLR funded by the Ministry of Science, Research, the Arts Baden-Württemberg and by the Federal Ministry of Education and Research.


© 2022 ACS This document is the author version of a Published Work that appeared in final form in Organic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx..doi.

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