Micro Single Crystals of Hematite with Nearly 100%
Exposed {104} Facets: Preferred Etching and Lithium Storage
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Abstract
The controlled synthesis of inorganic
single crystals with a large
percentage of exposed high-index facets has attracted much attention.
However, high-index facets usually disappear during the early stage
of crystal growth due to the minimization of surface energy and typically
facet-controlling agents are employed. Here a facile fast hydrothermal
method for the preparation of microsize α-Fe<sub>2</sub>O<sub>3</sub> rhombohedra with nearly 100% exposed {104} facets was developed
in a simple formulated solvent without any additives. The hydrothermal
reaction time could be as short as 75 min, in contrast to typical
hydrothermal reactions over days. The preferred etching edges along
the diagonal axis of microsize rhombohedra by the self-generated ions
was observed, which could be potentially extended to synthesize and
tailor other transition metal oxides. The formation mechanism was
revealed by ex situ FESEM observations of the samples prepared at
different reaction times. Improved electrochemical performances in
terms of cyclability, specific capacity, and high rate were achieved.
The specific capacity was maintained at 550 mAh/g after 120 cycles
at a rate of 200 mA/g. Experimental evidence clearly shows that the
as-designed solid microsize α-Fe<sub>2</sub>O<sub>3</sub> can
effectively and reversibly store lithium ions with performance comparable
to nanosize α-Fe<sub>2</sub>O<sub>3</sub>, suggesting electrode
materials with particle size at the microscale will be worth further
exploration