Abstract
We report a simple one-pot synthesis of uniform transition metal difluoride MF2 (M = Fe, Mn, Co) nanorods based on transition metal trifluoroacetates (TMTFAs) as single-source precursors. The synthesis of metal fluorides is based on the thermolysis of TMTFAs at 250–320 °C in trioctylphosphine/trioctylphosphine oxide solvent mixtures. The FeF2 nanorods were converted into FeF3 nanorods by reaction with gaseous fluorine. The TMTFA precursors are also found to be suitable for the synthesis of colloidal transition metal phosphides. Specifically, we report that the thermolysis of a cobalt trifluoroacetate complex in trioctylphosphine as both the solvent and the phosphorus source can yield 20 nm long cobalt phosphide nanorods or, 3 nm large cobalt phosphide nanoparticles. We also assess electrochemical lithiation/de-lithiation of the obtained FeF2 and FeF3 nanomaterials.
Highlights
Synthesis of nanoscale inorganic materials remains an active research area in inorganic chemistry, owing to the unique and improved material properties that emerge with respect to their bulk counterparts[1,2,3,4,5,6,7]
Co) NRs were obtained by thermolysis of corresponding transition metal trifluoroacetates (TMTFAs) [“Fe3OTFA”, “Mn(TFA)2”, and “Co(TFA)2”] at temperatures of 250–320 °C with the use of TOP or trioctylphosphine oxide (TOPO) as solvents (Fig. 1, see methods and Tables S1–S3 for reaction conditions)
We show that the use of TOP or TOPO solvents is essential for synthesizing monodisperse MF2 NRs, which act as neutral L-type ligands that coordinate to Lewis acidic surfaces leading to the preferred rod morphology
Summary
Synthesis of transition metal (Fe, Co, Mn) difluoride NPs. Monodisperse MF2 TEM analysis and EDX mapping (Fig. 3) point to the following formation mechanism (Fig. 3g): First, “Co(TFA)2” starts to decompose at 250 °C forming CoF2 NRs (Figs 3a–c and S10), which react with TOP at 300 °C At this point, we observed a mixture of both cobalt fluoride and cobalt phosphide (Figure S11a,b), followed by the formation of phase-pure 20 nm long cobalt phosphide NRs after 90 min (Fig. 3d–f). The thermolysis of “Co(TFA)2” in TOP with OA for a short reaction time of 0–10 min yielded the mixture of cobalt fluoride and phosphide NRs/NPs (Figure S11c,d). Www.nature.com/scientificreports relatively sharp with a low polarization compared with previously reported data on FeF3 cathodes[13,92,93] These results point to an intermittent mechanism of lithiation/de-lithiation of the FeF3 NRs through the formation of intermediate Li0.5FeF3 and Li0.25FeF3 phases. The galvanostatic measurements of FeF2 and FeF3 NRs are presented in Figures S14 and S15, respectively
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