As
a matter of synthetic novelty, Fe3O4 (magnetite)
nanorods (NRs) have been successfully generated by using a reproducible
four-step protocol, wherein goethite is initially produced, morphologically
tuned, chemically treated with a passivating agent to reduce aggregation,
and ultimately converted to magnetite by thermal annealing within
a reductive atmosphere. Our equally important objective was in correlating
electrochemical behavior with the unique morphology of these Fe3O4 anode materials. As such, both conventionally
coated and binder-free electrodes were tested using as-prepared magnetite
NRs and nanoparticles (NPs) with controlled crystallite size as the
active materials. Our study revealed that both the NR and NP Fe3O4 materials were amenable to effective binder-free
electrode design. For the conventionally coated electrodes, the NR
electrodes demonstrated an improved rate capability using a sequential
discharge/charge current density profile as compared with that for
corresponding NP electrodes. Most significantly, within the cycling
stability test, the NR electrode delivered a high and stable capacity
with a superior capacity retention relative to that of the NP for
more than 50 cycles in half cells and 100 cycles in full cells. These
data in particular showcase the undeniable benefits of the anisotropic
structure of the material.
Synchrotron-based scanning hard X-ray microscopy (SHXM) was used to extract localized chemical and structural information within a system of model alkaline earth-metal tungstate nanorods, characterized by multiple chemical configurations. Specifically, we have highlighted the practical ability of SHXM to probe chemically distinctive nanoscale species, consisting of (i) chemically doped versus (ii) solid solution-state nanorods of comparable dimension, synthesized using a template-directed method under ambient conditions. Indeed, we show that SHXM can be used to map out elemental distributions within individual anisotropic nanorods with nanoscale resolution, coupled with chemical sensitivity and specificity. Complementary electrochemical results suggest the possibility of using these nanorods as support materials for electro-oxidation reactions within an acidic electrolyte medium. Our structural and chemical composition results have been corroborated using parallel lines of inquiry involving scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. These measurements confirmed the relatively even and uniform distribution of the expected, individual elements within all of the nanorod samples tested.
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