Yongming Zhu

Improvement of wear resistance for carburised steel by Ti depositing and plasma nitriding

ABSTRACT In order to improve the wear resistance of carburised M50NiL steel, the surface layer was deposited with Ti coating by magnetron sputtering and then plasma nitrided for 2 h with hollow cathode equipment. The influence of nitriding temperature (750, 800 and 850°C) on microstructure and mechanical properties of the coating were investigated. Results show that the coating of specimen 750 containing Ti-based-nitrides possesses higher nanohardness (13.769 ± 0.738 GPa) than the carburised layer (7.695 ± 0.338 GPa) and the load bearing capacity reaches 18 N due to the supporting carburised layer. The friction coefficient and wear rate of the specimen 750 decrease 23.1 and 72.2%, respectively, compared with the carburised specimen. The hardness and wear performance of the specimen 800 and 850 were underestimated by traditional test criterion because a loose and porous a′C(N) layer was formed on the surface due to sputtering effect of steel hollow cathode.

Preparation of a novel carbon nanofiber as a high capacity air electrode for nonaqueous Li-O2 batteries

A new carbon nanofiber codoped with nitrogen and phosphorus (NPCNF) that has a high specific surface area and good electrocatalytic properties for the oxygen reduction reaction (ORR) was synthesized using a template‐free method. The fabrication process involves the pyrolysis of phytic acid doped polyaniline aerogel. A nonaqueous Li‐O2 battery with a specific capacity as high as 12 607 mA h g−1 was constructed by using an oxygen electrode based on NPCNFs supported by Ni foam. The NPCNF electrode showed a lower overpotential than pure carbon. The observed excellent electrochemical performance could be because of the unique foamlike N‐ and P‐codoped carbon microstructure, which had a high ORR catalytic activity. These results indicate that the use of NPCNF as a cathode material could be a feasible approach to obtain a high‐capacity Li–O2 battery.

Establishment and practical application of the electron transfer model in lithium-air batteries

The electron transfer failure model is proposed to analyze the effects of discharge products on the air electrode performance in lithium-air batteries. In order to understand how the air electrode products are obtained during the discharge cycle, three kinds of carbon-based air electrode are constructed, and discharged products are analyzed by powder XRD and SEM techniques. It can be concluded that the air electrode is covered with the products, indicating that the discharge products closely depended on the surface states of carbon materials. EIS studies show that the value of Rct value changes due to the deposition of discharge products on carbon materials. Finally, all present studies show that the air electrode failure is mainly caused by the difficulty of charge transfer.

Hierarchical carbon-free NiCo2O4 cathode for Li–O2 batteries

Li–oxygen battery provides much higher specific energy density compared to conventional Li–ion batteries, but there is a lack of desired cathodes which show lower over-potential during the charging cycle. Here, we report the effect of surface morphology of carbon-free spinel-like NiCo2O4 nanowires and nanosheets on Ni foam on cathode performance in Li–O2 battery. Two hierarchical structured NiCo2O4 cathodes were synthesized by using a hydrothermal method. Physical, chemical, and electrochemical properties of NiCo2O4 were characterized using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, BET surface area, electrochemical AC impedance spectroscopy, and linear sweep voltammetry. Scale-like NiCo2O4 electrode showed the highest specific capacity, compared to that of rod-like morphology, which seems due to a superior catalytic activity for oxygen reduction reaction, with lower charging over-potential, high discharge capacity, and excellent cycle performance.