Zhengbing Qi

CrN thin films prepared by reactive DC magnetron sputtering for symmetric supercapacitors

Supercapacitors have been becoming indispensable energy storage devices in micro-electromechanical systems and have been widely studied over the past few decades. Transition metal nitrides with excellent electrical conductivity and superior cycling stability are promising candidates as supercapacitor electrode materials. In this work, we report the fabrication of CrN thin films using reactive DC magnetron sputtering and further their applications for symmetric supercapacitors for the first time. The CrN thin film electrodes fabricated under the deposition pressure of 3.5 Pa show an areal specific capacitance of 12.8 mF cm−2 at 1.0 mA cm−2 and high cycling stability with 92.1% capacitance retention after 20 000 cycles in a 0.5 M H2SO4 electrolyte. Furthermore, our developed CrN//CrN symmetric supercapacitor can deliver a high energy density of 8.2 mW h cm−3 at the power density of 0.7 W cm−3 along with outstanding cycling stability. Thus, the CrN thin films have great potential for application in supercapacitors and other energy storage systems.

Electroless nickel-boron plating to improve the corrosion resistance of magnesium (Mg) alloys

Abstract: This chapter briefly reviews current electroless plating techniques for Mg alloys. Among them, a recently developed Ni-B plating is particularly selected for further discussion. Following that, the Ni-B plating methodology is presented and its electroless plating mechanism is proposed. The deposited Ni-B layer on AZ91D is then systematically characterized for its microstructure, porosity, thickness, adhesion and corrosion resistance. Based on the plating performance and characteristics, some possible applications and future developments of this new plating are predicted.

Microstructure and corrosion behavior of hafnium coatings on AZ91D magnesium alloys by magnetron sputtering

Hf coatings are fabricated on the AZ91D Mg alloys by magnetron sputtering with bias voltage ranges from 0 to −125 V. Both potentiodynamic polarization test and neutral salt spray test reveal that the Hf coating deposited at −100 V exhibits the best protective performance. It possesses the lowest corrosion current density of 1.032 μA cm−2 and the highest protection rate of 6, respectively. This perfect anticorrosion property is due to the dense structure and low porosity induced by applying the appropriate bias voltage. Various types of corrosion sites after corrosion tests are examined in detail. The results indicate that the coating failure is strongly dependent on the coating defects and the random phase distribution in the substrate.