Zhuyi Wang

The sol?gel template synthesis of porous TiO2 for a high performance humidity sensor

This research develops a simple template assisted sol-gel process for preparing porous TiO2 for a high performance humidity sensor. Tetraethyl orthosilicate (TEOS) as a template was directly introduced into TiO2 sol formed by the hydrolysis and condensation of titanium alkoxide; the following calcination led to the formation of TiO2-SiO2 composite, and the selective removal of SiO2 by dilute HF solution led to the formation of porous structure in TiO2. The resulting porous TiO2-based sensor exhibits high sensitivity and linear response in the wide relative humidity (RH) range of 11%-95%, with an impedance variation of four orders of magnitude to humidity change. Moreover, it exhibits a rapid and highly reversible response characterized by a very small hysteresis of <1% RH and a short response-recovery time (5 s for adsorption and 8 s for desorption), and a 30-day stability test also confirms its long-term stability. Compared with pure TiO2 prepared by the conventional sol-gel method, our product shows remarkably improved performance and good prospect for a high performance humidity sensor. The complex impedance spectra were used to elucidate its humidity sensing mechanism in detail.

Solvothermal Synthesis of Crystalline Phase and Shape Controlled Sn4+-Doped TiO2 Nanocrystals: Effects of Reaction Solvent

The Sn(4+)-doped TiO(2) nanocrystals with controlled crystalline phase and morphology had been successfully prepared through easily adjusting the solvent system from the peroxo-metal-complex precursor by solvothermal method. The Sn(4+)-doped TiO(2) nanocrystals were characterized by XRD, Raman, TEM, HRTEM, XPS, ICP-AES, BET, and UV-vis. The experimental results indicated that the Sn(4+)-doped TiO(2) nanocrystals prepared in the pure water or predominant water system trend to form rodlike rutile, whereas the cubic-shaped anatase Sn(4+)-doped TiO(2) nanocrystals can be obtained in the alcohol system. The growth mechanism and microstructure evolution of the Sn(4+)-doped TiO(2) nanocrystals prepared in the different solvent systems are discussed. The liquid-phase photocatalytic degradation of phenol was used as a model reaction to test the photocatalytic activity of the synthesized materials. It was found that sample Sn(4+)-doped TiO(2) prepared in 1-butanol showed the maximum photoactivity, which attributed to higher band gap, optimal crystalline phase and surface state modifications.

Layer-by-Layer Deposition of Organic–Inorganic Hybrid Multilayer on Microporous Polyethylene Separator to Enhance the Electrochemical Performance of Lithium-Ion Battery

A simple layer-by-layer (LbL) self-assembly process of poly(acrylic acid) (PAA) and ZrO2 was applied to construct functional ultrathin multilayers on polyethylene (PE) separators without sacrificing the excellent porous structure of separators. Such PAA/ZrO2 LbL-modified PE separators possess good electrolyte wettability, excellent electrolyte uptake, high ionic conductivity and large Li(+) transference number. More importantly, the top layer of LbL self-assembly would affect the dissociation of electrolyte and the formation of solid electrolyte interphase (SEI) layer in half-cells. Compared with the pristine and (PAA/ZrO2)1PAA-modified PE separators, (PAA/ZrO2)3-modified PE separator shows a larger Li(+) transference number (0.6) and a faster tendency to form a stable SEI layer, endowing half-cells with excellent capacity retention at high C-rates and superior cycling performance. These fascinating characteristics will provide the LbL self-assembly with a promising method to improve the surface property of PE separators for high performance lithium-ion batteries.

Self-Assembly of PEI/SiO2 on Polyethylene Separators for Li-Ion Batteries with Enhanced Rate Capability

A simple and environmentally friendly self-assembly process of oppositely charged polymer PEI and inorganic oxide SiO2 was demonstrated for the construction of an ultrathin layer on the surface of PE separator. The XPS, FT-IR, SEM, and EDS characterizations give clear evidence of the successful self-assembly of PEI and SiO2 without significantly increasing the thickness and sacrificing the pristine porous structure of PE separator. This process improves a variety of crucial properties of PE separator such as the electrolyte wetting, the electrolyte uptake, the thermal stability, the ionic conductivity, Li+ transference number, the electrochemical stability and the compatibility with lithium electrode, endowing lithium-ion battery (Li as anode and LiCoO2 as cathode) with excellent capacity retention at high C-rates and superior cycling performance. At the current density of 5 C, the cell with PE separator almost loses all the capacity. In contrast, the cell with (PEI/SiO2)-modified PE separator still holds 45.2% of the discharge capacity at 0.2 C. The stabilized SEI formation and high Li+ transference number of (PEI/SiO2)-modified PE separator were interpreted to be the substantial reasons leading to the remarkably enhanced battery performance, rendering some new insights into the role of the separator in lithium-ion batteries.

Hydrothermal synthesis and humidity sensing properties of size-controlled Zirconium Oxide (ZrO2) nanorods

Size-controlled ZrO2 nanorods were prepared via a facile hydrothermal treatment approach in the presence of NH4F as mineralizer. The effects of the type and concentration of mineralizers on the particle size and dispersibility of ZrO2 nanorods were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption measurements (BET), and X-ray photoelectron spectroscopy (XPS), confirming the essential role of F(-) in tuning the particle size. Humidity sensors based on ZrO2 nanorods with different sizes exhibit different sensitivity depending on their proportion of surface adsorbed oxygen. High sensitivity, linear response, small hysteresis, and rapid response-recovery behavior (5s for adsorption and 38s for desorption) make ZrO2 prepared by our method a good candidate for application in humidity sensor. The complex impedance spectra were used to elucidate its humidity sensing mechanism in detail.

Fluorine-Doped Tin Oxide Nanocrystal/Reduced Graphene Oxide Composites as Lithium Ion Battery Anode Material with High Capacity and Cycling Stability

Tin oxide (SnO2) is a kind of anode material with high theoretical capacity. However, the volume expansion and fast capability fading during cycling have prevented its practical application in lithium ion batteries. Herein, we report that the nanocomposite of fluorine-doped tin oxide (FTO) and reduced graphene oxide (RGO) is an ideal anode material with high capacity, high rate capability, and high stability. The FTO conductive nanocrystals were successfully anchored on RGO nanosheets from an FTO nanocrystals colloid and RGO suspension by hydrothermal treatment. As the anode material, the FTO/RGO composite showed high structural stability during the lithiation and delithiation processes. The conductive FTO nanocrystals favor the formation of stable and thin solid electrolyte interface films. Significantly, the FTO/RGO composite retains a discharge capacity as high as 1439 mAhg(-1) after 200 cycles at a current density of 100 mAg(-1). Moreover, its rate capacity displays 1148 mAhg(-1) at a current density of 1000 mAg(-1).

Microwave-hydrothermal synthesis and humidity sensing behavior of ZrO2 nanorods

ZrO2 nanorods with different dispersibility were prepared via a facile microwave-hydrothermal approach in the absence of any organic modifier. XRD, TEM, HRTEM, N2 adsorption–desorption measurements (BET) and XPS were used to characterize the microstructure of as-prepared ZrO2 nanorods, and a possible mechanism was proposed to explain the formation and evolution of ZrO2 nanorods under microwave irradiation. The concentration of zirconium precursor was found to significantly affect the dispersion of ZrO2 nanorods, and the lower concentration of zirconium precursor favors the formation of ZrO2 nanorods with higher dispersibility under microwave irradiation. The as-prepared ZrO2 nanorods were further used to estimate their potential application as a humidity sensor. The sample with a higher concentration of surface oxygen vacancies exhibits a higher humidity sensor response due to more active sites for water adsorption, and the humidity sensing mechanism of ZrO2 nanorods was also discussed by complex impedance spectra in detail.

Porous cellulose diacetate-SiO2 composite coating on polyethylene separator for high-performance lithium-ion battery

The developments of high-performance lithium ion battery are eager to the separators with high ionic conductivity and thermal stability. In this work, a new way to adjust the comprehensive properties of inorganic-organic composite separator was investigated. The cellulose diacetate (CDA)-SiO2 composite coating is beneficial for improving the electrolyte wettability and the thermal stability of separators. Interestingly, the pore structure of composite coating can be regulated by the weight ratio of SiO2 precursor tetraethoxysilane (TEOS) in the coating solution. The electronic performance of lithium ion batteries assembled with modified separators are improved compared with the pristine PE separator. When weight ratio of TEOS in the coating solution was 9.4%, the composite separator shows the best comprehensive performance. Compared with the pristine PE separator, its meltdown temperature and the break-elongation at elevated temperature increased. More importantly, the discharge capacity and the capacity retention improved significantly.

Influence of interface properties on charge density, band edge shifts and kinetics of the photoelectrochemical process in p-type NiO photocathodes

Nickel oxide as one of the few p-type semiconductors has great potential applications in the construction of photovoltaics and solar fuel production devices. The present work focuses on understanding the surface structure of NiO by controlling the surface Ni3+ species (e.g. NiO(OH)) that influence the electrochemical process at the NiO/liquid electrolyte interface. With the aid of the Mott–Schottky method, electrochemical impedance spectroscopy and photocurrent–voltage correlation testing, various NiO surface structures were correlated with observed changes in the band energies, energetic distributions of the trap states densities, charge interface transfer, charge transport, and as a result the p-type DSSC device performances. The primary results demonstrate that the NiO(OH) species act as recombination centers and cause worse interface recombination. Furthermore, we also report an effective way of reducing the surface NiO(OH) structures by a Ni(CH3COOH)2 post-treatment method, resulting in a 31.3% increase in the photovoltaic performance. Our work provides good guidance for the design and fabrication of solar energy-related devices employing NiO electrodes.

In Situ Synthesis of Tungsten-Doped SnO2 and Graphene Nanocomposites for High-Performance Anode Materials of Lithium-Ion Batteries

The composite of tungsten-doped SnO2 and reduced graphene oxide was synthesized through a simple one-pot hydrothermal method. According to the structural characterization of the composite, tungsten ions were doped in the unit cells of tin dioxide rather than simply attaching to the surface. Tungsten-doped SnO2 was in situ grown on the surface of graphene sheet to form a three-dimensional conductive network that enhanced the electron transportation and lithium-ion diffusion effectively. The issues of SnO2 agglomeration and volume expansion could be also avoided because the tungsten-doped SnO2 nanoparticles were homogeneously distributed on a graphene sheet. As a result, the nanocomposite electrodes of tungsten-doped SnO2 and reduced graphene oxide exhibited an excellent long-term cycling performance. The residual capacity was still as high as 1100 mA h g-1 at 0.1 A g-1 after 100 cycles. It still remained at 776 mA h g-1 after 2000 cycles at the current density of 1A g-1.