Changchang Xu

Novel three-dimensional NiCo2O4 hierarchitectures: solvothermal synthesis and electrochemical properties

Three-dimensional flower-like NiCo2O4 hierarchitectures have been successfully prepared on a large scale via a facile solvothermal method followed by an annealing process. The as-synthesized NiCo2O4 flower-like architectures have uniform diameters of about 500 nm assembled by numerous nanosheets radially grown from the center. The possible growth mechanism of the unique structures has been investigated. Both the poly(vinylpyrrolidone) (PVP) surfactant and the formation of metal glycolate play important roles in the formation of these novel three-dimensional flower-like hierarchitectures. With a large surface specific area of 212.6 m2 g−1, this novel NiCo2O4 material exhibited a superior specific capacitance of 1191.2 F g−1 and 755.2 F g−1 at current densities of 1 and 10 A g−1, respectively, which suggests that 63.4% of the capacitance is still retained when the charge–discharge rate is increased from 1 A g−1 to 10 A g−1. This superior electrochemical performance of NiCo2O4 as an electrode material for supercapacitors can be ascribed to the synergetic effect of the porous structure and the small diffusion lengths in the nanosheet building blocks. The simple, versatile and cost-effective route reported here may provide a general methodology for the high-yield synthesis of metal cobaltite nanostructures featuring improved properties and structures.

Synthesis of triple-layered Ag@Co@Ni core-shell nanoparticles for the catalytic dehydrogenation of ammonia borane.

Triple-layered Ag@Co@Ni core-shell nanoparticles (NPs) containing a silver core, a cobalt inner shell, and a nickel outer shell were formed by an in situ chemical reduction method. The thickness of the double shells varied with different cobalt and nickel contents. Ag0.04 @Co0.48 @Ni0.48 showed the most distinct core-shell structure. Compared with its bimetallic core-shell counterparts, this catalyst showed higher catalytic activity for the hydrolysis of NH3 BH3 (AB). The synergetic interaction between Co and Ni in Ag0.04 @Co0.48 @Ni0.48 NPs may play a critical role in the enhanced catalytic activity. Furthermore, cobalt-nickel double shells surrounding the silver core in the special triple-layered core-shell structure provided increasing amounts of active sites on the surface to facilitate the catalytic reaction. These promising catalysts may lead to applications for AB in the field of fuel cells.

Porous nickel cobaltite nanorods: desired morphology inherited from coordination precursors and improved supercapacitive properties

A facile and general method for the synthesis of porous complex oxides is highly desirable owing to their significant applications for energy storage. In this contribution, the porous nickel cobaltite nanorods have been successfully prepared by thermal decomposition of organometallic compounds, using nitrilotriacetic acid (NTA) as a chelating agent to coordinate with the Ni and Co ions. The obtained precursors were demonstrated to be one-dimensional nanorods. The resultant porous nickel cobaltite nanorods basically preserved the morphology of the precursors. In addition, these nanoparticles show good crystallinity. The as-prepared nickel cobaltite displays nanorod-like morphology with about 1 μm length and about 100 nm diameter. With a large surface area of 103.4 m2 g−1, this novel material exhibited high specific capacitance of 1078 F g−1 and 704 F g−1 at current densities of 1 and 20 A g−1, respectively. This suggests that about 65% of the capacitance is still retained when the charge–discharge rate is increased from 1 A g−1 to 20 A g−1. The specific capacitance retention is 94.4% after 2500 cycles, suggesting its excellent cycling stability. In addition, these porous nickel cobaltite nanorods may be useful in other fields such as Li-ion batteries and Li-O2 batteries.

Synthesis of size-controlled Ag@Co@Ni/graphene core-shell nanoparticles for the catalytic hydrolysis of ammonia borane.

Size-controlled Ag0.04@Co0.48@Ni0.48 core-shell nanoparticles (NPs) were synthesized by employing graphene (rGO) with different reduction degrees as supports. The number of C=O and C=O functional groups on the surface of rGO might play a major role in controlling the particle size. The strong steric-hindrance effect of C=O resulted in the growth of large particles, whereas C=O contributed to the formation of small particles. The particle size of Ag0.04@Co0.48@Ni0.48 NPs supported on rGO with different reduction degrees decreased as the number of C=O functional groups decreased. The decrease in the particle size probably led to the increase in the catalytic activity towards the hydrolysis of ammonia borane (AB). The enhanced catalytic activity largely stemmed from the increasing active sites on the surface of catalysts owing to the decreasing particle size.

Graphene oxide assisted facile hydrothermal synthesis of LiMn0.6Fe0.4PO4 nanoparticles as cathode material for lithium ion battery

Abstract Assisted by graphene oxide (GO), nano-sized LiMn0.6Fe0.4PO4 with excellent electrochemical performance was prepared by a facile hydrothermal method as cathode material for lithium ion battery. SEM and TEM images indicate that the particle size of LiMn0.6Fe0.4PO4 (S2) was about 80 nm in diameter. The discharge capacity of LiMn0.6Fe0.4PO4 nanoparticles was 140.3 mAh·g−1 in the first cycle. It showed that graphene oxide was able to restrict the growth of LiMn0.6Fe0.4PO4 and it in situ reduction of GO could improve the electrical conductivity of LiMn0.6Feo.4PO4 material.