Synthesis of mixed-​metal transition metal oxido cubanes (MMn_3O_4) and their potential as prescursors for water oxidation electrocatalysts

Abstract

The study of mixed transition metal oxido cubane complexes is crucial to the development of materials for oxygen evolution reaction, oxygen redn. reaction, and energy storage. A discreet series of heterometallic trimanganese-tetraoxido cubanes (MMn_3O_4 ; M = Fe, Co, Ni, Cu) supported by a trisalkoxy-hexapyridyl ligand with a 1, 3,5-triarylbenzene spacer were synthesized and characterized by single crystal X-ray diffraction, dispersive difference diffraction anal., cyclic voltammetry, Mossbauer spectroscopy, and X-ray absorption spectroscopy. To det. their potential as precursors for heterogeneous water oxidn. electrocatalysts, these well-defined complexes were drop-casted on electrodes, and electrolysis of the material was performed in basic aq. media. Oxygen evolution was obsd., and the activity was compared to a few other mixed metal oxide electrocatalysts reported in literature. Electrolysis of MMn_3O_4 resulted in the different ratio of M to Mn in the final material depending on the metal M (M = Co, Ni) as characterized by XPS and energy dispersive X-ray spectroscopy. X-ray absorption spectroscopy shows the retention of the cubane moiety in the post-electrolysis NiMn_3O_4 materials.