Showing papers by "Yong Wang published in 2015"

Multilayer CuO@NiO Hollow Spheres: Microwave-Assisted Metal–Organic-Framework Derivation and Highly Reversible Structure-Matched Stepwise Lithium Storage

Abstract: A unique CuO@NiO microsphere with three-layer ball-in-ball hollow morphology is successfully synthesized by Cu–Ni bimetallic organic frameworks. The beforehand facile microwave-assisted production of the Ni organic framework sphere is used as the template to induce the morphology control of bimetallic oxides. Designed by the controlled surface cationic exchange reactions between Cu and Ni ions, there is an elemental gradient (decreased amount of CuO but increased amount of NiO) from the shell to the core of the microsphere product. This ternary metal oxide hollow structure is found to be very suitable for solving the critical volume expansion problem, which is critical for all high-capacity metal oxide electrodes for lithium ion batteries. A reversible larger-than-theoretical capacity of 1061 mAh·g–1 can be retained after a repetitive 200 cycles without capacity fading compared to the initial cycle. These excellent electrochemical properties are ascribed to the step-by-step lithium insertion reactions ind...

Microwave Hydrothermal Synthesis of Ni-based Metal–Organic Frameworks and Their Derived Yolk–Shell NiO for Li-Ion Storage and Supported Ammonia Borane for Hydrogen Desorption

Abstract: This paper reports fast microwave hydrothermal synthesis of Ni-based metal–organic frameworks (Ni-MOFs) and their derived yolk–shell NiO structures by direct calcination in air. The molar ratio of the Ni ion to the benzene-1,3,5-tricarboxylic acid (H3BTC) ligand has important influence on the NiO morphologies and their electrochemical performances. The obtained yolk–shell NiO microsphere displays a large reversible capacity of 1060 mAh g–1 at a small current density of 0.2 A g–1 and a good high-rate capability when evaluated as an anode for rechargeable lithium-ion batteries. Moreover, the facilitated hydrogen release from ammonia borane (AB) at a lower temperature and the depressed release of undesired volatile byproducts are also observed in the Ni-MOFs supported AB.

Standing carbon-coated molybdenum dioxide nanosheets on graphene: morphology evolution and lithium ion storage properties

Abstract: Transitional metal oxides are a class of high-capacity anodes for lithium ion batteries. Drastic volume changes during cycling and intrinsically poor electronic conductivity diminish their electrochemical performances such as cycliability and high-rate capabilities. This study reports an unprecedented MoO2/carbon network, consisting of the standing carbon-coated MoO2 nanosheets on graphene nanosheets to solve these problems. The obtained MoO2 products can be tuned to have particle-like, rod-like, or sheet-like morphologies (standing MoO2@C core–shell nanosheets or flat-lying MoO2 nanosheets) on graphene by adjusting the experimental parameters. Due to the unique three dimensional porous MoO2@C/graphene hierarchical structure, the composite manifests excellent electrochemical properties including high capacity, long cycle life and stable high-rate performances. A large reversible capacity of above 500 mA h g−1 can be achieved after 200 cycles at a large current of 5 A g−1.

Self-assembly and template-free synthesis of ZnO hierarchical nanostructures and their photocatalytic properties.

Abstract: Despite significant progress in the field of semiconductor photocatalysis has been made, it is still a great challenge to prepare low-cost photocatalysts with high activities. In our work, three dimensional (3D) flower-like ZnO hierarchical nanostructures assembled with numerous nanosheets were fabricated by a simple, template-free and one-step hydrothermal route. The products were characterized by XRD, UV–Vis, PL, SEM, TEM, HRTEM techniques. In the process, NH4F played a crucial role for the formation of ZnO hierarchical nanostructures, which was acted both as the alkali source and morphology director. Furthermore, the growth of ZnO involved a phase transformation from intermediate compound ZnF(OH) to ZnO. To further improve the photocatalytic activity, Ag-doped ZnO photocatalyst was also prepared. The photocatalytic results indicated that the Ag/ZnO exhibited higher photocatalytic activity than the pure ZnO. The great enhancement was mainly ascribed to their unique hierarchical nanostructures as well as the modification of Ag nanoparticles. Additionally, both ZnO and Ag/ZnO microspheres showed good recycling stabilities over several separation cycles in photodegradation.

Topotactical conversion of carbon coated Fe-based electrodes on graphene aerogels for lithium ion storage

Abstract: Iron oxides and iron sulfides have attracted significant research concerns for lithium-ion batteries (LIBs) due to their higher theoretical capacity than the commercial electrode. However, they both suffer from large volume expansion during cycling and poor electrical conductivity. Iron sulfides have another problem of the dissolution of polysulfides into organic electrolytes. This work reports a sulfur-doped graphene aerogel (GA) supported FeS2@carbon composite with better lithium ion storage properties than its intermediate precursors (GA supported Fe–Fe3O4@C and Fe2O3). It exhibits a high reversible capacity of ∼1000 mA h g−1 at 0.1 C during cycling with good rate capability. These enhanced electrochemical properties are mainly attributed to the synergetic effect of the GA support, carbon coating and sulfur doping.

New Cr2Mo3O12-based anodes: morphology tuning and Li-storage properties

Abstract: A new ternary metal oxide (Cr2Mo3O12) anode for Li-ion batteries is reported in this work. Experimental conditions such as reaction temperature, reaction time, and reactant concentration have all been investigated. The product can be obtained with sheet-like or rod-like morphology with/without the presence of a graphene support. The Cr2Mo3O12/graphene rod-on-sheet composite is found to be more suitable for Li-storage compared to the Cr2Mo3O12/graphene sheet-on-sheet composite and pristine Cr2Mo3O12 nanosheets/nanorods. The rod-on-sheet composite delivers a large reversible capacity of 988 mA h g−1 after 50 cycles at a current density of 100 mA g−1 and a good rate capability. Moreover, a preliminary Li-storage mechanism is also explored and suggested.