Heterometallic Ludwigite M 2.5 T 0.5 (O 2 BO 3 ) and (M 2 T)(O 2 BO 3 ); (M = Co, Ni, Cu; T = Ti, Sn, Fe) Compounds as Electrocatalysts

Abstract

New compounds, M2.5T0.5(O2BO3) and (M2T)(O2BO3); (M = Co, Ni, Cu; T = Ti, Sn, Fe) stabilised with the ludwigite structure, were prepared employing conventional solid-state methods and the structures determined by powder X-ray diffraction (PXRD) studies. Room temperature Raman spectroscopic studies were consistent with the various polyhedral building units in the structure. Some of the prepared compounds exhibited colors that are different from the normally expected colors for the transition metal ions having octahedral coordination. The observed colors were explained with the help of allowed d-d transitions and metal-to-metal charge transfer (MMCT) transitions. Magnetic studies were carried out on Co5Ti(O2BO3)2, (Co2.5Ni2.5)Ti(O2BO3)2, (Co2.5Ni2.5)Sn(O2BO3)2, (CoNi)Fe(O2BO3) compounds which indicated that the compounds exhibit antiferromagnetic behavior. The compounds, M2.5T0.5(O2BO3) and (M2T)(O2BO3); (M = Co, Ni, Cu; T = Ti, Sn, Fe) were evaluated for the oxygen evolution reaction (OER). The compounds behave as good electrocatalyst that were comparable to RuO2. XPS studies confirmed the presence and oxidation state of the different transition elements in the compounds. Electronic structure calculations using density functional theory support the finding of the experimental observations. The present study suggests that the mineral structures provide a rich platform to investigate and study many material properties.