Huiteng Tan

Controlled soft-template synthesis of ultrathin C@FeS nanosheets with high-Li-storage performance

We report a facile approach to prepare carbon-coated troilite FeS (C@FeS) nanosheets via surfactant-assisted solution-based synthesis. 1-Dodecanethiol is used as both the sulfur source and the surfactant, which may form different-shaped micelles to direct the growth of nanostructures. Under appropriate growth conditions, the iron and sulfur atoms react to form thin layers of FeS while the hydrocarbon tails of 1-dodecanethiol separate the thin FeS layers, which turn to carbon after annealing in Ar. Such an approach can be extended to grow C@FeS nanospheres and nanoplates by modifying the synthesis parameters. The C@FeS nanosheets display excellent Li storage properties with high specific capacities and stable charge/discharge cyclability, especially at fast charge/discharge rates.

Ultrathin S-doped MoSe2 nanosheets for efficient hydrogen evolution

We report the synthesis of ultrathin S-doped MoSe2 nanosheets demonstrating enhanced HER catalysis with a low onset overpotential of 90 mV and a Tafel slope of 58 mV per decade. We attribute the improved catalytic effects to the proliferation of unsaturated HER active sites in MoSe2 resulting from S-doping.

Olivine-Type Nanosheets for Lithium Ion Battery Cathodes

Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 μs for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets).

One‐Pot Synthesis of Tunable Crystalline Ni3S4@Amorphous MoS2 Core/Shell Nanospheres for High‐Performance Supercapacitors

Transition metal sulfides gain much attention as electrode materials for supercapacitors due to their rich redox chemistry and high electrical conductivity. Designing hierarchical nanostructures is an efficient approach to fully utilize merits of each component. In this work, amorphous MoS(2) is firstly demonstrated to show specific capacitance 1.6 times as that of the crystalline counterpart. Then, crystalline core@amorphous shell (Ni(3)S(4)@MoS(2)) is prepared by a facile one-pot process. The diameter of the core and the thickness of the shell can be independently tuned. Taking advantages of flexible protection of amorphous shell and high capacitance of the conductive core, Ni(3)S(4) @amorphous MoS(2) nanospheres are tested as supercapacitor electrodes, which exhibit high specific capacitance of 1440.9 F g(-1) at 2 A g(-1) and a good capacitance retention of 90.7% after 3000 cycles at 10 A g(-1). This design of crystalline core@amorphous shell architecture may open up new strategies for synthesizing promising electrode materials for supercapacitors.

Oxidation-Etching Preparation of MnO2 Tubular Nanostructures for High-Performance Supercapacitors

1D hierarchical tubular MnO(2) nanostructures have been prepared through a facile hydrothermal method using carbon nanofibres (CNFs) as sacrificial template. The morphology of MnO(2) nanostructures can be adjusted by changing the reaction time or annealing process. Polycrystalline MnO(2) nanotubes are formed with a short reaction time (e.g., 10 min) while hierarchical tubular MnO(2) nanostructures composed of assembled nanosheets are obtained at longer reaction times (>45 min). The polycrystalline MnO(2) nanotubes can be further converted to porous nanobelts and sponge-like nanowires by annealing in air. Among all the types of MnO(2) nanostructures prepared, tubular MnO(2) nanostructures composed of assembled nanosheets show optimized charge storage performance when tested as supercapacitor electrodes, for example, delivering an power density of 13.33 kW·kg(-1) and a energy density of 21.1 Wh·kg(-1) with a long cycling life over 3000 cycles, which is mainly related to their features of large specific surface area and optimized charge transfer pathway.

Synthesis of cobalt phosphides and their application as anodes for lithium ion batteries

A facile thermal decomposing method has been developed for the fabrication of Co(x)P nanostructures with controlled size, phase, and shape (e.g., Co(2)P rod and spheres, CoP hollow and solid particles). An amorphous carbon layer could be introduced by the carbonization of organic surfactants from the precursors. The electrochemical performance of typical CoP and Co(2)P samples as anode materials has been investigated and the CoP hollow nanoparticle with carbon coating layer depicts good capacity retention and high rate capability (e.g., specific capacity of 630 mA h g(-1) at 0.2 C after 100 cycles, and a reversible capacity of 256 mA h g(-1) can be achieved at a high current rate of 5 C).

Monodispersed Ag nanoparticles loaded on the PVP-assisted synthetic Bi2O2CO3 microspheres with enhanced photocatalytic and supercapacitive performances

Uniform 1 μm-sized Bi2O2CO3 microspheres constructed by nanoplates with a thickness of about 12 nm have been obtained through a facile hydrothermal method. Ag is deposited on the surface of Bi2O2CO3via a subsequent facile photoreduction process. In the synthesis process, polyvinylpyrrolidone (PVP) is used as a reactant that not only provides C and O sources but also serves as a template to induce the nanoplate-assembly to form microspheres. With the addition of KCl in the synthesis, the size of the Bi2O2CO3 microspheres can be reduced from ∼6 μm to ∼1 μm. It is demonstrated that PVP and KCl play key roles in the formation of such hierarchical microspheres. The obtained Bi2O2CO3 and novel Ag/Bi2O2CO3 composites are evaluated for photocatalytic and supercapacitive applications. The test result of the photocatalytic activity demonstrates that 0.6 wt% loading of Ag on the Bi2O2CO3 microspheres exhibits significantly enhanced activity for the photodegradation of methyl orange (MO) dye, compared with Bi2O2CO3. The enhanced photocatalytic activity can be attributed to the Ag deposits acting as electron traps and the high surface area of Bi2O2CO3. Furthermore, the Ag/Bi2O2CO3 composites are primarily evaluated as supercapacitor electrodes, which deliver specific capacities of 620 and 361 F g−1 at current densities of 1 and 5 A g−1, respectively.

Facile preparation of hydrated vanadium pentoxide nanobelts based bulky paper as flexible binder-free cathodes for high-performance lithium ion batteries

Hydrated vanadium pentoxide (V2O5·0.44H2O, HVO) nanobelts were synthesized by a simply high-yield (e.g. up to ∼99%) hydrothermal approach. The length of these nanobelts was up to several hundred micrometers while the diameter was only ∼20 nm and the thickness was ∼10 nm. Binder-free bulky papers were prepared by using these HVO nanobelts and were tested as Li ion battery cathodes. The unique architecture of the HVO bulky paper provides hierarchical porous channels and large specific surface area, which facilitate fast ion diffusion and effectively strain relaxation upon charge-discharge cycling. The electrochemical tests revealed that the flexible HVO cathode could deliver high reversible specific capacities with ∼100% Coulombic efficiency, especially at high C rates. For example, it achieved a reversible capacity of 163 mAh g−1 at 6.8 C.

Direct growth of FeVO4 nanosheet arrays on stainless steel foil as high-performance binder-free Li ion battery anode

Amorphous FeVO4 nanosheet arrays have been grown directly from a flexible stainless steel (SS) substrate by a facile template-free and catalyst-free chemical vapour deposition (CVD) method. These FeVO4 nanosheets showed superior Li storage properties, especially at high current densities.

General Approach for MOF-Derived Porous Spinel AFe2O4 Hollow Structures and Their Superior Lithium Storage Properties

A general and simple approach for large-scale synthesis of porous hollow spinel AFe2O4 nanoarchitectures via metal organic framework self-sacrificial template strategy is proposed. By employing this method, we can successfully synthesize uniform NiFe2O4, ZnFe2O4, and CoFe2O4 hollow architectures that are hierarchically assembled by nanoparticles. When these hollow microcubes were tested as anode for lithium ion batteries, good rate capability and long-term cycling stability can be achieved. For example, high specific capacities of 636, 449, and 380 mA h g(-1) were depicted by NiFe2O4, ZnFe2O4, and CoFe2O4, respectively, at a high current density of 8.0 A g(-1). NiFe2O4 exhibits high specific capacities of 841 and 447 mA h g(-1) during the 100th cycle when it was tested at current densities of 1.0 and 5.0 A g(-1), respectively. Discharge capacities of 390 and 290 mA h g(-1) were delivered by the ZnFe2O4 and CoFe2O4, respectively, during the 100th cycle at 5.0 A g(-1).