posted on 2021-01-18, 14:33authored byKévin Lemoine, Zahra Gohari-Bajestani, Romain Moury, Alexandre Terry, Amandine Guiet, Jean-Marc Grenèche, Annie Hémon-Ribaud, Nina Heidary, Vincent Maisonneuve, Nikolay Kornienko, Jérôme Lhoste
The
development of earth-abundant catalysts for the oxygen evolution
reaction (OER) in acidic media represents a significant challenge
in the context of polymer electrolyte membrane (PEM)-based electrolysis.
In this scope, transition metal oxides constitute an emerging alternative
to Ir and Ru oxides. Notably, Mn oxides are among the few that have
sufficient stability in acidic electrolytes, but their performance
still lacks behind Ir/Ru oxides. To this end, the modification of
Mn oxides’ structure, crystallinity (or amorphous structure),
and/or composition may work to enhance their catalytic activity. In
this report, we focused our attention on the development of mixed-metal
Mn–Fe-based catalysts containing highly electronegative fluorine
ions as acid-stable OER catalysts. Inspired by our recent work on the preparation Mn-Fe-based fluorinated
materials MnFe2F8(H2O)2 and MnFe2F5.8O1.1, a new hydrated
fluoride, MnFeF5(H2O)2, was prepared
by microwave-assisted solvothermal synthesis and its subsequent thermal
treatment under air yielded the corresponding oxyfluoride MnFeF4.6O0.2. The resultant composition and structure
of the materials were determined from powder X-ray diffraction (XRD),
Mössbauer spectrometry, thermal analyses, and electronic microscopies.
The crystalline-hydrated fluorides (MnFeF5(H2O)2 and MnFe2F8(H2O)2) and the corresponding amorphous oxyfluorides (MnFeF4.6O0.2 and MnFe2F5.8O1.1) were subsequently evaluated for the first time as OER
electrocatalysts in highly acidic (0.5 M H2SO4) media. Notably, the oxyfluorides featured sustained OER activity
at 10 mA/cm2 for more than 10 h and, thus, present an important
addition to the growing library of earth-abundant alternatives to
Ir and Ru oxides.