Ternary metal oxides with spinel structures have garnered substantial interest due to their promising electrochemical properties. NiMn 2O 4, a representative example, is used as an electrocatalyst for electrochemical oxidation reactions. While NiMn 2O 4 offers the advantage of low toxicity, its intrinsic conductivity poses a limitation. However, sulfurization can effectively enhance its electrical conductivity by transforming the oxide into nickel and manganese sulfides and their hybrid structure.[ 1] Sulfides of both metals, nickel and manganese have been extensively studied for their superior performance in various applications, including electrochemical reactions, photocatalysis, and supercapacitors.[ 2] This study sheds light on the design and development of low-cost and efficient transition metal hybrid chalcogenide electrocatalysts through sulfurization for electrochemical energy conversion devices.
Herein, NiMn 2O 4 flowers were synthesized using a hydrothermal method, which was then vacuum-annealed for 2 hours as shown in Figure 1(a). Using distinct sulfur precursors, thiourea and sodium sulfide, the mixed metal oxide NiMn 2O 4 was selectively sulfurized to NiS 2 and MnS, respectively. The phase purity and crystallinity of the synthesized products were confirmed by powder X-ray diffraction (PXRD) and selected area electron diffraction (SAD) patterns. While MnS maintains its flower morphology, the resultant NiS 2 forms intergrown nanocubes, as shown in Figure 1(b,c). A hybrid structure of NiS 2/MnS with a comparable flower morphology was formed when equimolar amounts of precursors were used. The elemental composition of these synthesized materials was analyzed using scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDS). The BET analysis showed a slight increase in the surface area of MnS, whereas due to the formation of cubes, the surface area of NiS 2 decreased significantly.
Figure 1:
SEM micrographs of (a) NiMn 2O 4 flowers; thiourea leads to the formation of (b) NiS 2 cubes; while sodium sulfide results in the formation of (c) MnS flowers.
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