Jingcheng Zhang

N-Doped hierarchically porous carbon derived from heterogeneous core–shell ZIF-L(Zn)@ZIF-67 for supercapacitor application

Heterogeneous core–shell ZIF-L(Zn)@ZIF-67 nanoleaves are controllably synthesized in aqueous media at room temperature in the light of our previously reported strategy. After direct carbonization under a nitrogen atmosphere, hierarchically porous amorphous carbon@graphite carbon core–shell nanoleaves with high nitrogen-doping content and carbon nanotubes (N-C@GC/CNTs) are obtained. The morphology, microstructure and the evolution process of N-C@GC/CNTs are systematically investigated by scanning electron microscopy, transmission electron microscopy, adsorption/desorption isotherms etc. All obtained N-C@GC/CNTs are employed to construct supercapacitors, and the results indicate that the optimized N-C@GC/CNTs exhibit a distinguished capacitance (252.1 F g−1) and excellent stability (about 91.2% capacitance retention after 10 000 cycles) as supercapacitor electrodes due to their hierarchical pore structure, high nitrogen content and superior electrical conductivity resulting from graphitic structure and carbon nanotubes. This work not only extends our previously proposed strategy to synthesize heterogeneous core–shell of zeolitic imidazolate frameworks, but also provides a new avenue for preparing novel core–shell N-C@GC/CNTs with superior electrochemical performance.

High-speed electrical sliding wear behaviors of Cu-WS2-graphite-WS2 nanotubes composite

Abstract Cu-WS2-graphite-WS2 nanotubes composite was fabricated by the powder metallurgy hot-pressed method. The effects of electrical current (5–15 A/cm2) and sliding velocity (5–15 m/s) on the electrical wear behaviors of the composite were investigated using a block-on-slip ring wear tester rubbing against Cu-5 wt% Ag alloy ring under 2.5 N/cm2 of applied load. The lubricating effect of WS2 nanotubes and composition of tribo-film were analyzed. The results demonstrated that the contact resistance decreases but the wear rate increases as electrical current increases, because the adverse effects of electrical current soften the materials at “a-spots” and damage the tribo-film. Due to the adsorption of gaseous molecule film on the tangential direction of slip ring surface, with the rise of sliding velocity, the contact resistance increases while the wear rate reaches the minimum at a sliding velocity of 10 m/s. The reasonable addition of WS2 nanotubes into the Cu-WS2-graphite composite to replace WS2 powder can result in a reduction of both contact resistance and wear rate. X-ray photoelectron spectroscopy (XPS) analyses revealed that copper oxides, graphite, WS2 and WS2 nanotubes in the tribo-film play the main lubrication action at the tribo-interface.

Physical, mechanical, and ablation properties of Cu–Ti3AlC2 composites with various Ti3AlC2 contents

ABSTRACT The effects of Ti3AlC2 content on the physical, mechanical, and arc ablation resistance properties of a fabricated Cu–Ti3AlC2 composite are investigated in detail. Composite samples containing 10, 15, 20, 25, 30, and 35 vol.-% Ti3AlC2 are sintered at 800°C without decomposition of Ti3AlC2. It is demonstrated that with increasing Ti3AlC2 content, the relative density, electrical conductivity, and flexural strength of Cu–Ti3AlC2 decrease but the Brinell hardness first increases and then decreases. After eroded by an electric arc, Cu–Ti3AlC2 oxidises to CuO, TiO2, and Al2O3. Meanwhile, field emission-SEM observations reveal that the dimensions of protrusions and the percentage of TiO2 increase with increasing Ti3AlC2 content. Remarkably, the electric arc mainly occurs at the Ti3AlC2 particles, and the Cu matrix remains well protected.