Graphene nanosheets were produced in large quantity via a soft chemistry synthetic route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. X-ray diffraction and transmission electron microscopy (TEM) observations show that graphene nanosheets were produced with sizes in the range of tens to hundreds of square nanometers and ripple-like corrugations. High resolution TEM (HRTEM) and selected area electron diffraction (SAED) analysis confirmed the ordered graphite crystal structure of graphene nanosheets. The optical properties of graphene nanosheets were characterized by Raman spectroscopy.
Although some strategies have been triggered to address the intrinsic drawbacks of zinc (Zn) anodes in aqueous Zn‐ion batteries (ZIBs), the larger issue of Zn anodes unable to cycle at a high current density with large areal capacity is neglected. Herein, the zinc phosphorus solid solution alloy (ZnP) coated on Zn foil (Zn@ZnP) prepared via a high‐efficiency electrodeposition method as a novel strategy is proposed. The phosphorus (P) atoms in the coating layer are beneficial to fast ion transfer and reducing the electrochemical activation energy during Zn stripping/plating processes. Besides, a lower energy barrier of Zn2+ transferring into the coating can be attained due to the additional P. The results show that the as‐prepared Zn@ZnP anode in the symmetric cell can be cycled at a current density of 15 mA cm−2 with an areal capacity of 48 mAh cm−2 (depth of discharge, DOD ≈ 82%) and even at an ultrahigh current density of 20 mA cm−2 and DOD ≈ 51%. Importantly, a discharge capacity of 154.4 mAh g−1 in the Zn/MnO2 full cell can be attained after 1000 cycles at 1 A g−1. The remarkable effect achieved by the developed strategy confirms its prospect in the large‐scale application of ZIBs for high‐power devices.
Single crystalline copper oxide nanoribbons were synthesized via a surfactant-assisted hydrothermal route. The resulting CuO nanoribbons contain substantial amounts of nanorings and nanoloops. High resolution TEM analysis identified CuO nanoribbons growing along the [010] direction. CuO nanoribbons exhibited excellent sensing performance towards formaldehyde and ethanol vapours with rapid response and high sensitivity at low operating temperatures. We found that the loading of a small amount of Au or Pt nanoparticles on the surface of CuO nanoribbons can effectively enhance and functionalize the gas sensing performance of CuO nanoribbons.
First-order solid–solid phase transition of crystalline solids at the nanoscale has attracted an increasing interest in solid-state physics and chemistry, which can be used to alter the properties of materials without changing chemical compositions. Herein, we report the results of our comparative studies on phase transitions between tetragonal (t), orthorhombic (β), and cubic (α) polymorphs in Ag2Se nanocrystals. A significant discrepancy in stability and phase transition behavior is determined for t-Ag2Se nanocrystals, which were prepared separately by two different methods. Differential scanning calorimetry (DSC) and variable-temperature XRD studies reveal that the t-Ag2Se nanocrystals prepared by the oleylamine (OLA)-mediated method show a highly temperature- and time-sensitive metastability and undergo a t → β → α → β phase transition during the thermal cycling, in which the t → β transition is exothermic and irreversible, whereas the β → α transition is reversible. Similarly, the reversible β → α structure transition is detected in the β-Ag2Se nanocrystals, which were also prepared using the OLA-mediated method with different post-treatment manners and stabilized conditions. In contrast, the t-Ag2Se nanocrystals prepared by the PVP-assisted solvothermal method are more stable and exhibit a direct, reversible t → α phase transition without undergoing the β phase; however, when heated to a high temperature, for example, ≥250 °C, the stability of the t phase and the reversibility of the t → α transition will be destroyed due to the sintering and size increase of the sample, which is confirmed by the determination of the t → α → β phase transition in the DSC cycle. The formation of the t phase is attributed to the α → t structure transformation with the temperature cooled from synthetic temperatures (160–220 °C) to room temperature. Moreover, the reasons for the difference in the stabilities and phase transitions of t-Ag2Se nanocrystals prepared in our two methods are discussed based on the influences of size, surface (or shape), and defects on the thermodynamics and kinetics of a solid–solid structure transformation.
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