Xianbao Wang

Hierarchical architectured MnCO3 microdumbbells: facile synthesis and enhanced performance for lithium ion batteries

Hierarchical architectured MnCO3 microdumbbells and lamellar structured MnCO3 nanosheets were selectively synthesized by a facile reflux route. Hierarchical architectured MnCO3 microdumbbells (approximately 0.5–1.5 μm in length and 0.3–0.9 μm in width) were composed of nanoparticles, while the lamellar structured MnCO3 nanosheets had uniform length of approximately 400 nm. Both structures were employed as anode active materials in lithium ion batteries. Experimental results showed that the hierarchical architectured MnCO3 microdumbbells exhibited superior electrochemical performances compared with the lamellar structured MnCO3 nanosheets. At a current rate of 0.5 C, the reversible capacity of the hierarchical architectured MnCO3 microdumbbell electrode after 100 cycles was 775 mA h g−1, while the lamellar structured MnCO3 nanosheets electrode was only 50 mA h g−1 after 100 cycles. The superior electrochemical behavior of hierarchical architectured MnCO3 microdumbbell materials could be ascribed to the unique micro-nano assembly structure, simultaneously cushioning the volume change, maintaining the electrode integrity, and offering a short diffusion distance.

Low-temperature and one-pot synthesis of sulfurized graphene nanosheets via in situ doping and their superior electrocatalytic activity for oxygen reduction reaction

The chemical doping of foreign atoms and functional moieties is a significant strategy for tailoring the electronic properties and enhancing the catalytic ability of graphene. However, the general approaches to the synthesis of heteroatom-doped graphene often involve chemical vapor deposition (CVD) and/or thermal annealing performed at high temperature under gas phases, which require special instruments and tedious process. In this study, we have developed a low temperature, economical, and facile one-pot hydrothermal method to synthesise sulfur-doped reduced graphene oxide (S-RGO) nanosheets, in which the sodium sulfide (Na2S) was employed not only as a sulfur source but also as a reductant to reduce the graphene oxide (GO) simultaneously with sulfur (S) being in situ doped into graphene frameworks. The as-prepared S-RGO has a high S content (4.19 at%), as well as high-quality sulfurated species (mainly as C–S–C–), and possesses numerous open edge sites and defects on its surface, which are beneficial for the improved ORR catalytic activity. Electrochemical characterizations clearly demonstrated the excellent electrical conductivity and superior electrocatalytic activity of S-RGO for oxygen reduction reaction (ORR), coupled with considerably enhanced stability and methanol tolerance compared to the commercial Pt/C catalyst. The present low temperature and one-pot approach provides the possibility for the synthesis of S-RGO at the Gram-scale for its application in electronic nanodevices and electrode materials for fuel cells.

Thermal Stability-Enhanced and High-Efficiency Planar Perovskite Solar Cells with Interface Passivation

As the electron transport layer (ETL) of perovskite solar cells, oxide semiconductor zinc oxide (ZnO) has been attracting great attention due to its relatively high mobility, optical transparency, low-temperature fabrication, and good environment stability. However, the nature of ZnO will react with the patron on methylamine, which would deteriorate the performance of cells. Although many methods, including high-temperature annealing, doping, and surface modification, have been studied to improve the efficiency and stability of perovskite solar cells with ZnO ETL, devices remain relatively low in efficiency and stability. Herein, we adopted a novel multistep annealing method to deposit a porous PbI2 film and improved the quality and uniformity of perovskite films. The cells with ZnO ETL were fabricated at the temperature of <150 °C by solution processing. The power conversion efficiency (PCE) of the device fabricated by the novel annealing method increased from 15.5 to 17.5%. To enhance the thermal stability of CH3NH3PbI3 (MAPbI3) on the ZnO surface, a thin layer of small molecule [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was inserted between the ZnO layer and perovskite film. Interestingly, the PCE of PCBM-passivated cells could reach nearly 19.1%. To our best knowledge, this is the highest PCE value of ZnO-based perovskite solar cells until now. More importantly, PCBM modification could effectively suppress the decomposition of MAPbI3 and improve the thermal stability of cells. Therefore, the ZnO is a promising candidate of electron transport material for perovskite solar cells in future applications.

One-pot synthesis of carbon nanoribbons and their enhanced lithium storage performance

Carbon nanoribbons are obtained on a large scale by an easy one-pot pathway. The nanoribbons, which have thicknesses of ∼5 nm, widths of ∼500 nm and lengths exceeding 15 μm, are prepared from ferrocene and Mg(CH3COO)2·4H2O at 600 °C for 10 h. The Raman spectrum of the as-obtained sample indicates that it possesses a mass of disorder and defects. X-ray photoelectron spectroscopy (XPS) results show that the nanoribbons are doped by nitrogen at an atomic percentage of 2.09%. The specific surface area of the sample is measured to be as large as 1240 m2 g−1. In the charge–discharge experiments of secondary lithium ion batteries, the carbon nanoribbons demonstrate a stable reversible capacity of 750 mA h g−1 after 300 cycles at 0.5 A g−1, suggesting that the as-prepared carbon nanoribbons have potential applications as electrode materials in electronic devices.

Low-Temperature and Solution-Processable Zinc Oxide Transistors for Transparent Electronics

Zinc oxide (ZnO) thin-film transistors (TFTs) have many promising applications in the areas of logic circuits, displays, ultraviolet detectors, and biosensors due to their high performances, facile fabrication processing, and low cost. The solution method is an important technique for low-cost and large fabrication of oxide semiconductor TFTs. However, a key challenge of solution-processable ZnO TFTs is the relatively high processing temperature (≥500 °C) for achieving high carrier mobility. Here, facile, low-cost, and solution-processable ZnO TFTs were fabricated under the annealing temperature of ≤300 °C. Dense and polycrystalline ZnO films were deposited by the spin-coating method. The ZnO TFTs showed the maximum electron mobility of 11 cm2/V s and a high on/off ratio of >107 when the ZnO thin films were annealed at 300 °C. The mobility was extremely high among solution-processable undoped ZnO TFTs reported previously, even better than some high-cost indium-doped ZnO TFTs fabricated at low temperature. Furthermore, it is found that the mechanism of oxygen vacancies dominates the electron transport in ZnO thin film and interface behaviors of ZnO thin film and SiO2 gate insulator, and then dominates the performances of devices.