4 research outputs found
Solid-Solutioned Homojunction Nanoplates with Disordered Lattice: A Promising Approach toward “Phonon Glass Electron Crystal” Thermoelectric Materials
The concept of “phonon glass electron crystal”
(PGEC)
was proposed in the mid-1990s to maximize the <i>ZT</i> value
for thermoelectric materials, based on its combined advantages of
low thermal conductivity as in a glass but high electricity as in
a well-ordered crystal. Although a great amount of research in complex
materials systems for achieving this concept has been done, a perfect
“PGEC” material has not been acquired yet. Herein, we
first put forward a solid-solutioned homojunction in high temperature
phase with disordered lattice, which possesses both high electrical
conductivity and low thermal conductivity, as an effective way to
optimize the low/mid-temperature thermoelectric property. As an example,
nonambient cubic phase AgBiSe<sub>2</sub> was successfully stabilized
to room temperature through the formation of a solid solution by Sb
incorporation for the first time, and furthermore, in situ formed
homojunctions on the surface of solid-solutioned nanoplates were also
first achieved through a simple colloidal method. A significant enhancement
of thermoelectric performance at low/mid-temperature was realized
through synergistical regulation on electronic and thermal transport.
As a result, compared to that of original AgBiSe<sub>2</sub> (<i>ZT</i> = 0.03 at 550 K), the <i>ZT</i> value of AgBi<sub>0.5</sub>Sb<sub>0.5</sub>Se<sub>2</sub> was increased to 0.51 at
550 K by the formation of a solid solution, and then further increased
to 1.07 at 550 K by the formation of solid-solutioned homojunction
Half-Metallic Ferromagnetism in Synthetic Co<sub>9</sub>Se<sub>8</sub> Nanosheets with Atomic Thickness
Controlling the synthesis of atomic-thick nanosheets
of nonlayered
materials is extremely challenging because of the lack of an intrinsic
driving force for anisotropic growth of two-dimensional (2D) structures.
In that case, control of the anisotropy such as oriented attachment
of small building blocks during the reaction process will be an effective
way to achieve 2D nanosheets. Those atomic-thick nanosheets possess
novel electronic structures and physical properties compared with
the corresponding bulk samples. Here we report Co<sub>9</sub>Se<sub>8</sub> single-crystalline nanosheets with atomic thickness and unique
lamellar stacking formed by 2D oriented attachment. The atomic-thick
Co<sub>9</sub>Se<sub>8</sub> nanosheets were found to exhibit intrinsic
half-metallic ferromagnetism, as supported by both our experimental
measurements and theoretical calculations. This work will not only
open a new door in the search for new half-metallic ferromagnetic
systems but also pave a practical way to design ultrathin, transparent,
and flexible paperlike spintronic devices
Synthesis of Nitrogen-Doped Porous Carbon Nanofibers as an Efficient Electrode Material for Supercapacitors
Supercapacitors (also known as ultracapacitors) are considered to be the most promising approach to meet the pressing requirements of energy storage. Supercapacitive electrode materials, which are closely related to the high-efficiency storage of energy, have provoked more interest. Herein, we present a high-capacity supercapacitor material based on the nitrogen-doped porous carbon nanofibers synthesized by carbonization of macroscopic-scale carbonaceous nanofibers (CNFs) coated with polypyrrole (CNFs@polypyrrole) at an appropriate temperature. The composite nanofibers exhibit a reversible specific capacitance of 202.0 F g<sup>–1</sup> at the current density of 1.0 A g<sup>–1</sup> in 6.0 mol L<sup>–1</sup> aqueous KOH electrolyte, meanwhile maintaining a high-class capacitance retention capability and a maximum power density of 89.57 kW kg<sup>–1</sup>. This kind of nitrogen-doped carbon nanofiber represents an alternative promising candidate for an efficient electrode material for supercapacitors
Ag Nanoparticle Decorated Nanoporous ZnO Microrods and Their Enhanced Photocatalytic Activities
Nanostructured Ag nanoparticles (Ag-NPs)/nanoporous ZnO
micrometer-rods
(n-ZnO MRs) have been synthesized by a two-step method. The n-ZnO
MRs was initially prepared by solvothermal-assisted heat treatment.
The rods had the diameter ranged from 90 to 150 nm and length between
0.5 and 3 ÎĽm. They were found to be porous and were composited
of ZnO nanopartiles with size of about 20 nm. In the second stage,
Ag-NPs with a diameter of 20–50 nm were anchored onto the surface
of the as-prepared n-ZnO MRs by a photoreduction method. The Ag-NPs/n-ZnO
MRs were evaluated for their ability to degrade methylene blue (MB)
solution under visible to ultraviolet (UV) light irradiation. The
rate of degradation of the as-prepared Ag-NPs/n-ZnO MRs was more than
twice and nearly 5.6 times faster than that of using bare n-ZnO MRs
under the UV and solar light irradiation, respectively. The formation
of Schottky barriers in the regions between the Ag-NPs and n-ZnO MRs
had improved the charge separation and consequently enhanced the efficiency
of the degradation process. Moreover, the as-prepared hybrid structure
exhibited high photostability, and 98% of degradation efficiency could
be maintained even after being used five times. This endurance was
attributed to the retardation of photocorrosion of ZnO as a result
of the low concentration of surface defects in the as-prepared n-ZnO
MRs. It also minimized the surface defects of the as-prepared n-ZnO
MRs and consequently further inhibited the photocorrosion of ZnO when
the deposited Ag-NPs were much more inclined to combine with the chemisorbed
oxygen