Fast polysulfide catalytic conversion and self-repairing ability for high loading lithium-sulfur batteries using a permselective coating layer modified separator.

Li-S batteries are considered as one of the most promising battery systems because of their large theoretical capacity and high energy density. However, the "shuttle effect" of soluble polysulfides and sluggish electrochemical redox kinetics of Li-S batteries could cause a broken electrode structure and poor electrochemical performance. Herein, a high-performance and stable Li-S battery has been demonstrated by employing organo-polysulfide chain modified acetylene black (ABPS) as the coating layer on the separator. In addition to the traditional advantages of fast electron transport and polysulfide-interception ability of the carbon coating layer, the grafted organo-polysulfide chain endows the ABPS coating layer with permselectivity for lithium ion against polysulfides, electrocatalytic ability for the sluggish redox kinetics and self-repairing ability for the broken electrode. Hence, the battery prepared using an ABPS-coated separator delivers the best cycling performance (970 mA h g-1 at 0.2 C after 100 cycles) and rate performance (805 mA h g-1 at 2 C) as compared to the cells using acetylene black (AB)-coated or Celgard separators. Moreover, the Li-S battery prepared using an ABPS-coated separator exhibits a stable cycling performance at 1 C over 500 cycles with a low degradation of 0.04% per cycle, and a high coulombic efficiency (near 100%). Furthermore, as the sulfur loading was increased to 6.8 mg cm-2, the Li-S battery using the ABPS-coated separator still could deliver a high areal capacity of 6.03 mA h cm-2 with a low electrolyte/sulfur ratio (E/S = 4, µLelectrolyte mgS-1) after 170 cycles. Significantly, ABPS is an effective coating layer material for improving and stabilizing Li-S batteries.

Photovoltaic Effect in BiFeO3 Film Deposited by RF Magnetron Sputtering.

A polycrystalline BiFeO3 film was deposited on ITO substrate by RF magnetron sputtering method. Small crystallite size and compact structure are obtained for BiFeO3 film which has the excellent ferroelectric properties. The measured photovoltaic response reveals an open-circuit voltage of ~0.52 V and a short-circuit current density of ~10 µA/cm² under the illumination of 100 mW/cm² irradiance. Moreover, a tunable photovoltaic effect with light illumination is observed under different voltage sweep mode. High initial sweep voltage can enhance the photovoltaic effect largely, however, the photovoltaic response decreases with the increase of voltage sweep interval. The results indicate the ferroelectric polarization plays an important role in the photovoltaic effect.

Improved Photovoltaic Effect of p-i-n Structured BiFeO3 Film Deposited by Radio-Frequency Magnetron Sputtering.

Pure phase polycrystalline BiFeO3 film was deposited onto FTO substrate by RF magnetron sputtering method. SEM result shows that BiFeO3 film has the obvious porosity and large clusters which lead to the poor ferroelectric and photovoltaic properties in FTO/BiFeO3/Ag device. However, these properties are improved in p-i-n structured FTO/TiO2/BiFeO3/HTM/Ag device by incorporating the electron and hole transport materials. The hysteresis loop measurement demonstrates the excellent ferroelectric property with large remnant polarization (2Pr = 180 µC/cm²) and low leakage current. The J-V curve shows the short-circuit current density is dozens of times larger than that of FTO/BiFeO3/Ag device. Moreover, the photovoltaic output depends on the poling field where the positive poling improves the short-circuit current density to -85 µA/cm2 and the negative poling reduces both the photocurrent and photovoltage. It is believed that the ferroelectric polarization plays a dominant role in the photovoltaic effect.

Raman enhancement by graphene-Ga2O3 2D bilayer film.

2D ß-Ga2O3 flakes on a continuous 2D graphene film were prepared by a one-step chemical vapor deposition on liquid gallium surface. The composite was characterized by optical microscopy, scanning electron microscopy, Raman spectroscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy (XPS). The experimental results indicate that Ga2O3 flakes grew on the surface of graphene film during the cooling process. In particular, tenfold enhancement of graphene Raman scattering signal was detected on Ga2O3 flakes, and XPS indicates the C-O bonding between graphene and Ga2O3. The mechanism of Raman enhancement was discussed. The 2D Ga2O3-2D graphene structure may possess potential applications.

Geometry and stability of Cu(n)N (n=1-6) and Cu(3n)N(n) (n=1-5) clusters.

The gradient-corrected density functional calculation is applied to search the lowest-energy configurations of Cu(n)N (n=1-6) clusters and the calculation indicated that Cu(3)N cluster is the most stable one. Based on the result, we further investigate the equilibrium geometries and stabilities of the Cu(3n)N(n) (n=2-5) clusters. We found that in Cu(6)N(2) cluster, N atoms formed a separate N(2) molecule away from the other part of the cluster. Furthermore, it was shown that the lowest-energy configurations of Cu(3n)N(n) (n=3-5) are stable with the nitrogen atoms well separated by the copper atoms. Therefore, it can be concluded that the Cu(3)N cluster can be used as a building block for the construction of the cluster-assembled compounds.