18 research outputs found
Image steganography based on digital holography and saliency map
International audienc
Tunable Pseudocapacitance in 3D TiO<sub>2−δ</sub> Nanomembranes Enabling Superior Lithium Storage Performance
Nanostructured TiO<sub>2</sub> of different polymorphs, mostly
prepared by hydro/solvothermal methods, have been extensively studied
for more than a decade as anode materials in lithium ion batteries.
Enormous efforts have been devoted to improving the electrical conductivity
and lithium ion diffusivity in chemically synthesized TiO<sub>2</sub> nanostructures. In this work we demonstrate that 3D Ti<sup>3+</sup>-self-doped TiO<sub>2</sub> (TiO<sub>2−δ</sub>) nanomembranes,
which are prepared by physical vapor deposition combined with strain-released
rolled-up technology, have a great potential to address several of
the long-standing challenges associated with TiO<sub>2</sub> anodes.
The intrinsic electrical conductivity of the TiO<sub>2</sub> layer
can be significantly improved by the <i>in situ</i> generated
Ti<sup>3+</sup>, and the amorphous, thin TiO<sub>2</sub> nanomembrane
provides a shortened Li<sup>+</sup> diffusion pathway. The fabricated
material shows a favorable electrochemical reaction mechanism for
lithium storage. Further, post-treatments are employed to adjust the
Ti<sup>3+</sup> concentration and crystallinity degree in TiO<sub>2</sub> nanomembranes, providing an opportunity to investigate the
important influences of Ti<sup>3+</sup> self-doping and amorphous
structures on the electrochemical processes. With these experiments,
the pseudocapacitance contributions in TiO<sub>2</sub> nanomembranes
with different crystallinity degree are quantified and verified by
an in-depth kinetics analysis. Additionally, an ultrathin metallic
Ti layer can be included, which further improves the lithium storage
properties of the TiO<sub>2</sub>, giving rise to the state-of-the-art
capacity (200 mAh g<sup>–1</sup> at 1 C), excellent rate capability
(up to 50 C), and ultralong lifetime (for 5000 cycles at 10 C, with
an extraordinary retention of 100%) of TiO<sub>2</sub> anodes
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A hydrated crystalline calcium carbonate phase: Calcium carbonate hemihydrate.
As one of the most abundant materials in the world, calcium carbonate, CaCO3, is the main constituent of the skeletons and shells of various marine organisms. It is used in the cement industry and plays a crucial role in the global carbon cycle and formation of sedimentary rocks. For more than a century, only three polymorphs of pure CaCO3-calcite, aragonite, and vaterite-were known to exist at ambient conditions, as well as two hydrated crystal phases, monohydrocalcite (CaCO3·1H2O) and ikaite (CaCO3·6H2O). While investigating the role of magnesium ions in crystallization pathways of amorphous calcium carbonate, we unexpectedly discovered an unknown crystalline phase, hemihydrate CaCO3·½H2O, with monoclinic structure. This discovery may have important implications in biomineralization, geology, and industrial processes based on hydration of CaCO3